The coupled interactions among the fundamental carriersof charge,heat, and electromagnetic fields at interfaces and boundaries giverise to energetic processes that enable a wide array of technologies.The energy transduction among these coupled carriers results in thermaldissipation at these surfaces, often quantified by the thermal boundaryresistance, thus driving the functionalities of the modern nanotechnologiesthat are continuing to provide transformational benefits in computing,communication, health care, clean energy, power recycling, sensing,and manufacturing, to name a few. It is the purpose of this Reviewto summarize recent works that have been reported on ultrafast andnanoscale energy transduction and heat transfer mechanisms acrossinterfaces when different thermal carriers couple near or across interfaces.We review coupled heat transfer mechanisms at interfaces of solids,liquids, gasses, and plasmas that drive the resulting interfacialheat transfer and temperature gradients due to energy and momentumcoupling among various combinations of electrons, vibrons, photons,polaritons (plasmon polaritons and phonon polaritons), and molecules.These interfacial thermal transport processes with coupled energycarriers involve relatively recent research, and thus, several opportunitiesexist to further develop these nascent fields, which we comment onthroughout the course of this Review. I4 catalysis can be greatly enhanced through non-equilibrium chargeinjection across interfaces before thermal equilibration with phonons,7 and the ability of photoexcited charges to efficiently couple acrossa semiconductor/metal interface dictates the efficiency of solar energyharvesting devices.14 In these applications, the interaction and transport among the variouscarriers across and around the interface between two materials giverise to increased energy density, which can result in deleterioustemperature rises that can impact the efficiency of the devices.17 Specifically, it is well known that the resulting thermal boundaryresistances (TBRs) that occur at interfaces of two different materialsor phases of matter are the limiting factor that dictate, for example,the scalability of transistors in CMOS architectures that drives thesemiconductor industry’s capability to keep pace with Moore’slaw;20 the ability of wide- and ultrawide-bandgap-basedpower devices from achieving their intrinsic material potentials inRF power converters for applications ranging from military radar systemsto wireless communication for 6G and beyond;17 and the efficiency of photothermal therapeutics to maintain localizedand controlled temperature rise to target selective treatment of cancerouscells while ensuring the healthy tissues are unperturbed.21The coupled interactionsbetween the fundamental carriers of charge,heat, and electromagnetic fields are critical processes that dictatethe functionality, efficiency, and design of a wide array of materialcomposites and devices. At interfaces and surfaces in nanomaterials,these intertwined mechanisms are the foundation of the modern technologiesthat are continuing to provide transformational benefits in computing,communication, health care, clean energy, power recycling, sensing,and manufacturing, to name a few. For example, transistors rely onthe interaction of field with carriers across metal/oxide/active regionboundaries,22 In this case, the temperaturedrop and resulting TBR were explained to be driven by acoustic waves transmitting from the solid Cu to theacoustic waves in the liquid He. This original work by Kapitza andseveral other works studying this low-temperature TBR effect wereoften focused on low-temperature heat transfer across solid/liquidor sold/gas interfaces, thus involving the transduction of energyfrom solid acoustic waves (dispersionless phonons) to pressure wavesin different phases of matter.30 The ensuing theories from these studies resulted in translatablemodels to describe phonon transmission across solid/solid interfacesdue to the similarities in acoustic wave reflection and transmissioninteractions at interfaces.31 From this,classic theories that are often used to predict the phonon thermalboundary conductance across solid/solid interfaces were born, suchas the acoustic mismatch model (AMM),33 the diffuse mismatch model (DMM),31 and the phonon radiation limit (PRL).25 These models have been routinely applied to describe TBRacross solid/solid interfaces.40 However, to capture the true dynamics of heat flow across theseinterfaces, several re-derivations of these theories have been proposedto account for more complex interface features and phonon scatteringevents.49Clearly, the energy coupling among thedifferent carriers at interfacescan be the critical heat transfer pathway, dictating the efficacyof various processes and applications. This finding of coupling betweendifferent types of energy carriers driving TBR across interfaces datesback to Kapitza’s original work in 1941 demonstrating thata temperature drop can exist at an interface between Cu and liquidhelium.52 as we discuss in 53 or phonons (phonon polaritons),56 which offer a potential interfacial process that could drive TBR,a currently bourgeoning area of research we overview in 59 where thisfourth phase of matter delivers a plethora of energy carriers to thesolid and can give rise to different energy transfer processes asa function of time during plasma exposure, including the recent demonstrationof “plasma cooling”, where a directed plasma jet canbe used to transiently cool a surface.The limitations of this historical understanding of heat flowacrossinterfaces , however, prevent a greater foundational and nanoscopicunderstanding of TBR across interfaces when different energy carriersare coupled near and across interfaces. For example, the creationof hybridized vibrational states around interfaces  is not accountedfor in continuum-based mismatch models, and a more accurate understandingof how these modes influence TBR must be approached with atomisticmodels and experimental probes, which we review in 62 However, the topic of ultrafastenergy transduction and coupled thermal carriers driving TBR has notbeen a major focus of any recent perspective or review, most likelydue to the relative infancy of many of these results reviewed herein.Thus, this manuscript serves to present the community with our perspectiveand perceived opportunities for further developing the field of ultrafastenergy transduction mechanisms and coupled thermal transport acrossinterfaces.It is the purpose ofthis Review to describe recent works thathave reported on the ultrafast energy transduction mechanisms acrossinterfaces when different thermal carriers couple near or across interfacesto drive the resulting TBR. Notably, as suggested in the paragraphabove, many of these interfacial thermal transport processes withcoupled energy carriers involve relatively recent research, and thus,several opportunities exist to further develop these nascent fields,which we comment on throughout the course of this Review. Our articleis separated into four main sections focusing on different coupledthermal transport processes across interfaces, as depicted in II64 controlling the metal–insulatortransition,65 strengthening the superconductingnature,66 and manipulating the overallheat conduction in various heterostructures.67 However, for the purposes of this Review, we will only focus onhybrid vibrational states that couple across heterostructures andinterfaces with broken symmetries and their influence on the overallheat transfer mechanisms. In particular, we highlight the recentdevelopments in characterization and computational tools that haveled to the realization of hybrid vibrational states that significantlyinfluence interfacial thermal transport, thus questioning the applicabilityof the often used phonon gas models that can only describe propagatingmodes in solids and the transmission of these modes across solid/solidinterfaces. Furthermore, we will also focus on nanophononic metamaterialsin which strategically placing nanoresonators on the surface of thinfilms or nanowires can lead to the coupling of low-frequency hybridizedmodes and phonon resonances across the boundaries, which are otherwiseunaffected by conventional nanostructuring strategies.Interfaces in heterostructures can give rise to hybridized vibrationalstates that result from changes in the atomic scale symmetry andare otherwise absent from the vibrational spectrum of either “bulk”material. The existence of these interfacial modes that are ascribedto the chemical and structural makeup of the interface has been demonstratedthrough various experimental and computational approaches with ampleevidence of their global response, such as influencing the magneticand ferroelectric properties,II.a72 inelastic X-ray and neutron scattering,74 and electron tunneling experiments with spatial resolutions thatare typically on the order of several micrometers.75 Due to the lack of spatial resolution, it has proven difficultto identify and visualize localized vibrational states at interfacesin heterostructures, which requires very high spatial resolutions capable of revealing the dynamicsof individual atoms. This capability was achieved in 2014 from thebreakthrough work of Krivanek et al.76 wherethey demonstrated that vibrational spectroscopy could be combinedwith sub-nanometer spatial resolution via spatially resolved electronenergy loss spectroscopy (EELS), thus allowing the measurement oflocal phonon spectra at the atomic scale. More recently, utilizingthis technique, the local vibrational spectra at a high-quality epitaxialSi/Ge interface68 and the interface phonondispersion relation for the cubic boron nitride/diamond heterointerface77 with features that appear ∼1 nm aroundthe interface have been studied. These breakthroughs have significantlycontributed to our understanding of localized and hybrid phonon statesthat are uncharacteristic of either “bulk” constituent,thus offering insight into the lattice dynamics of heterostructures.Moreover, these findings can also potentially impact applicationssuch as thermal management in electronics and topological phononics.The characterization ofvibrational states has generally relied on infrared and Raman spectroscopies,68 utilized a combination of Raman spectroscopy,scanning transmission electron microscope (STEM) with a probe sizeof 1.5 Å, and high-energy-resolution EELS to demonstrate theexistence of interfacial modes at ∼12 THz that are confinedat the interface. The schematic diagram of their experiment is shownin For the Si/Ge interface mentioned above, Cheng et al.85 An example of such a localized mode at 12.01 THz is depicted in 35Prior to this work, numerous theoretical and computationalstudieshave predicted the existence of interfacial modes that are otherwisenot present in the bulk of the constituent materials comprising theinterface.II.b90 Such a controlof the dual-wave-particle nature of phonon transport can be used forphonon engineering and controling the overall thermal conductivityof superlattices. For instance, in superlattices, the internal interfacescan diffusively scatter phonons in the classical size effect regime(or the Casimir regime), or the internal interfaces can cause interferenceof phonon waves, thus modifying the intrinsic phonon dispersion ofthe superlattice material.92 However, a clear experimental observation of the latter case requirespristine internal interfaces with minimal intermixing between thedifferent material layers of the periodic superlattice. This is becauseinterface roughness can diffusely scatter phonons and lead to thereduction in the experimentally measured thermal conductivities insuperlattices that are lower as compared to their bulk parent materials.96 In this regard, measurements of thermal conductivity on epitaxiallygrown calcium titanate/strontium titanate (CTO/STO) superlattices, the transport can be well-describedby diffuse (or incoherent) scattering in the classical Casimir regimethat leads to a reduction in thermal conductivity as interface densityis increased.97 In contrast, for the casewhen the phonon dispersion is modified by the formation of minibandsin the phonon dispersion  transport to a wave-like (coherent) transport regime thatis possible through the strategic choice of the period thickness insuperlattices.lattices) with prC is the heat capacity, v is the group velocity, and λ is the mean free pathof vibrational modes. In this picture, thermal conductivity is expectedto decrease with decreasing v due to the minibandformation in short-period superlattices. However, the increase inthermal conductivity with shorter periods is attributed to phononswith mean free paths that are longer than the period thickness ofthe superlattices, which can dictate the overall heat conduction.Therefore, this interplay between the particle and wave types of thermaltransport at and across interfaces in superlattices can be utilizedto minimize the thermal conductivity of superlattices well below thealloy limit .102 This has been demonstrated computationally for aperiodic Si/Ge superlatticeswhere increasing the system size not only leads to miniband formations(and folding of the Brillouin zone as observed for periodic superlattices)but also leads to further miniband formations and larger reductionsin the group velocities  calculations. With these techniques,they provide direct visualization of emergent interfacial vibrationalmodes in the oxide superlattices through changes in the atomic scalesymmetry of superlattices with period thicknesses comparable to thoseof the structurally diffuse interfaces. The observed octahedral coupling occurs at the individual layersand is uncharacteristic of either “bulk” constituentphonons rather than targeting nanoscale Bragg scattering as has beenthe usual strategy to manipulate heat conduction in nanostructuredmaterials.108 Stated differently, the hybridizationbetween resonant phonons and propagating modes of the underlying solidreduces the group velocities and phonon mean free paths of the low-frequencyphonons that are otherwise hard to scatter with some of the oftenutilized nanostructuring techniques such as defect engineering, alloying,or inclusion of quantum nanodots, and as such, it is highly efficientin blocking phonon transport.109 This techniquehas been thoroughly demonstrated for resonators that are strategicallyplaced on the surface of silicon thin films or nanowires,112 which introduces standing waves that hybridize with the underlyingpropagating modes giving rise to localized modes and avoided levelcrossings with greatly reduced group velocities . For the flat bands representedin the phonon dispersion, the mismatch in the vibrational amplitudesbetween the resonators and the underlying material causes only theatoms in the resonator to vibrate at that particular frequency. Sucha concept has also been applied to organic materials based on carbonnanotubes and graphene sheets functionalized with strategic placementof fullerene molecules 4c on the115The standing vibrations that couple across the boundarybetweenthe nanoscale resonators and the underlying structure can thereforeresult in (i) group velocity reductions, (ii) mode localizations,and (iii) reduction in lifetimes of vibrations across the entire broadbandspectrum. This could prove to be very useful for engineering extremethermal conductivity reductions in materials that are well suitedfor applications in thermoelectrics, which require uncompromised electronicand mechanical properties. In this regard, the general route to loweringthe thermal conductivity of nanostructures through interfaces, grainboundaries, nanoinclusions, and pores can result in severely reducedelectronic transport or mechanical integrity. Therefore, the mainadvantage of introducing nanoresonators on the surface to lower thethermal conductivity gives the opportunity to simultaneously adjustthe electronic and thermal properties, all the while not influencingtheir mechanical integrity. For example, DFT calculations show thatthe electronic properties of nanobuds are highly tunable by changingthe surface coverage of fullerenes on the sidewall of carbon nanotubes,while another work based on MD simulations shows that the surfacecoverage can tune the thermal conductivity through hybridization ofvibrational states between the fullerenes and the underlying carbonnanotube 4d.105,11Taken together, hybridized vibrational modes that couple acrossmaterial interfaces provide a platform to control the thermal transportproperties of nanocomposites and heterostructures without the needto intrusively modify their intrinsic microstructural architecture.These hybrid interfacial modes can also lead to emergent optical,electrical, magnetic, and thermal properties in superlattices, whichcan drive the pursuit of designer materials with unrivaled physicalproperties. However, these hybrid interfacial modes have only beenstudied in a handful of material systems, as mentioned in the abovediscussions. Therefore, although the aforementioned works have laidthe foundation for such designer materials, there is still room forimproving our understanding of hybrid vibrational modes in differenttypes of nanocomposites to ultimately harness the potential of designersolids with extreme and tailored physical properties.IIIThe electron–phonon heat transfer mechanismsat both metal/metaland metal/non-metal interfaces have been historically robust topicsof both theoretical and computational studies over the past severaldecades. Relatively few experimental works have studied these topics,presumably due to the rather well coordinated material systems andexperimental parameters needed to properly examine these processes.Several recent reviews have focused on this electron–phononenergy exchange at interfaces under “near-equilibrium”conditions, which we define here as when the electrons and phononsin a metal can be described at the same temperature. For the mostpart, we focus this section on the current state of understandingof electron–phonon energy exchange across interfaces when thetemperatures of these two subsystems are different. Often, this isdenoted as “electron–phonon non-equilibrium”,which refers to the condition when the electrons are in local equilibrium(and can be well described by a Fermi–Dirac distribution andelectron temperature) and the vibrations or phonons are in local equilibrium, but these two temperatures are not equal.For the purpose of this Review, we avoid this terminology of “electron–phononnon-equilibrium” since this can often be muddled to also inferstates of non-equilibrium in the electron subsystem , a topic that has been studied in depth, especially inthe context of short pulsed laser heating.Thus, we focus ourdiscussion in this section on electron–phononor electron–vibrational coupled energy transport processesacross interfaces when the electron and phonon/vibrational subsystemsare both well described by only slight perturbations from their respectiveequilibrium distributions, but each of their equilibrium distributionsare defined by statistically and significantly different temperatures.We refer to this state of a material as electron–phonon (EP)or electron–vibrational (EV) coupled local equilibria (CLE).Our discussion below begins by reviewing the current state of experimentalmeasurements of EP heat transfer processes at metal/metal interfacesfollowed by metal/non-metal interfaces during conditions of CLE. Weculminate the experimental section by reviewing a recent experimentalobservation of ballistic thermal injection (BTI) at metal/doped non-metalinterfaces that relies on EP CLE between the metal electrons and electronsand phonons in the doped non-metal. This BTI process was used to createlong-lived hot electrons in the non-metal to control plasmonic absorption,offering an approach to thermally modulate plasmon resonances andthus optical absorption in non-metals. Further, BTI can be used totransiently control the directionality of heat flow across metal/non-metalinterfaces, unlocking potential avenues for ultrafast thermal diodesthat rely on EP CLE.ab initio quantum dynamicssimulations.118 This approach provides a fundamental perspectiveon the evolution of hot carriers coupled to vibrational motions bycreating a time-domain atomistic description, most closely mimickingthe time-resolved experiments. We conclude this section with a reviewof recent advances in ab initio quantum dynamicssimulations that have focused on EP and EV CLE at metal/metal andmetal/non-metal interfaces, including the role of plasmon-like stateson interfacial energy exchange.True quantum mechanical insight into theenergy exchange mechanismsassociated with hot electrons in CLE with the phonons and vibrationsat interfaces comes from III.a120 This theory is rooted in thediffuse mismatch model for the electrons that has been confirmed experimentallyand follows the Wiedemann–Franz law at interfaces.122 However, we note that this has not been studied in metals with relativelyhigh phonon contributions to heat conduction, such as for tungsten.123Under near-equilibriumconditions, when the electrons and phonons in a metal can be describedby the same temperature, the thermal boundary conductance at metal/metalinterfaces can be well captured by the ratio of the electronic densityof states and Fermi velocities in the materials on either side ofthe interface.124 predicted that, in the absence ofelectron–phonon scattering, the electron–electron thermalboundary conductance is also driven by the differences in the electronicdensities of states of each material adjacent to the interface, similarto the near-equilibrium scenario discussed above. Under conditionsof strong EP CLE and high electron temperatures, the electron–electronthermal boundary conductance was predicted to deviate from the freeelectron predictions based on changes in the electron density of stateswithin a few kBTe of the Fermi level. At these extremely elevated electrontemperatures, electron–electron thermal boundary conductanceswere predicted that far exceed 10 GW m–2 K–1,124 values that are orders of magnitudehigher than typical phonon–phonon dominated thermal boundaryconductances. However, these model predictions of electron–electronthermal boundary conductance at metal/metal interfaces during strongEP CLE have never been experimentally validated. To do so would involvethe use of a short-pulsed pump–probe experiment that couldaccurately determine the metal/metal thermal boundary conductanceat electron temperatures of thousands of Kelvin before any electron–phononscattering occurs, so that the phononic subsystems of each metal atthe interface remain cold. This extremely high electron–electronthermal boundary conductance at metal/metal interfaces during electron–phononnon-equilibrium could have a tremendous impact on heat removal duringmetal 3D printing and short-pulsed manufacturing.Under conditions of EP CLE, Hopkins etal.125 Specifically, they theoretically examined theelectron and phonon heat transfer processes in laser irradiated Au,Au/Cr, and Au/Cr/Au films. The weak electron–phonon couplingin Au results in longer lived hot electrons in the excited Au thattraverse across the Au/Cr interface and couple their energy to theCr phonons before the Au phonons heat up. This results in subsurfaceheating, where, for a few picoseconds, the Au lattice remains cold,while the Cr lattice under the Au surface is hot. This indirect heatingwas described in an analogy by the late Professor Chang-Lin Tien asbeing akin to “staring at the sun and getting sunburned onthe back of your head”126 and hasbeen since observed in transient temperature rises monitored duringultrafast laser heating of metallic bilayers and metal thin filmswith adhesion layers on insulating substrates.128 The ultrafast interfacial heat transfer processes and subsurfaceheating of laser excited metallic bilayers under conditions of EPCLE were later experimentally studied in a series of works that usedthis geometry to accurately deconvolve ballistic heat transfer inself-assembled monolayers,130 thermally inducedspin current and torque,132 robust measurementsof the intrinsic electron–phonon coupling factor in Au andCu,133 subsurface melting in deeply undercooledsilver,135 and measurements of the ballistic electron–phononmean free path in metals136 and to assessthe role of oxygen defects and adhesion layer stoichiometry on theelectron–electron thermal boundary conductance across Au/TiOx interfaces.136At time scalesduring and after EP CLE at metal/metal interfaces,Qiu and Tien predicted that the interfaces can lead to subsurfaceand delocalized heat sinking depending on the thickness of the topmetal and strength of electron–phonon coupling.III.b138 which we describe in more detail later in thissection. Given this, the three assumed mechanisms for electron–phononcoupling heat transfer at metal/non-metal interfaces are (i) electronsin the metal coupling to phonons in the non-metal across the metal/non-metalinterface, (ii) electrons in the metal coupling to phonons in themetal on the metal side of the metal/non-metal interface, and (iii)subsequent phonon–phonon conductance across the interface.We focus our discussion here on mechanism (i), since this representsheat transfer across an interface. As originally derived by Majumdarand Reddy,50 mechanism (ii) involves electron–phononcoupling in the metal and heat transfer across the metal/non-metalinterface is still driven by phonon–phonon coupling (iii);thus, we do not focus our discussion on these mechanisms here. However,recent reviews have discussed this process in detail,62 and we refer the readers to these extensive bodies of work for anin-depth review of this process. We therefore focus our discussionon the current state of understanding of the mechanisms of metal electronto non-metal phonon coupling across a metal/non-metal interface, specificallyduring CLE.At metal/non-metalinterfaces, the processes that contribute to thermal boundary conductanceduring EP CLE are more obfuscated compared to the metal/metal interfacecase. Relative to metal/metal interfaces, the role of electron–phononcoupling on the thermal transport across metal/non-metal interfacesis less clear due to the lack of direct experimental evidence provingor disproving the influence of this coupling mechanism, regardlessof the degree of non-equilibrium. The pathway of electron–phononcoupling at metal/non-metal interfaces under near-equilibrium transportconditions  has been theorized to influencethermal boundary conductance via two pathways, depicted in 52 to be driven by electronic scatteringprocesses similar to electron-defect scattering. Additional analyticaltheories by Huberman and Overhauser139 andMahan140 suggest that this mechanism isdriven by metal electrons interacting with different types of interfacialstates at the metal/non-metal interfaces. Lu et al.141 have argued that surface state electrons from the metalside can couple with the phonons of the semiconductor or the insulatoron the other side, which should be considered in parallel with thephonon–phonon heat conduction channel across the metal/non-metalinterfaces. More recently, Sadasivam et al.137 used an ab initio approach to determine that theelectron–phonon coupling at the interface between a metal silicideand silicon can lead to electron–phonon thermal boundary conductancesthat can rival that of phonon–phonon thermal boundary conductances due to the vastly different energy carrier populations on eitherside  of the interface. This topic of thermal rectification was raisedas early as 1969 by Pollack143 in his seminalreview, and as shown by Li et al.,144 asymmetricthermal boundary conductance can be achieved when highly dissimilarmaterials come in contact . However, wewill not review this topic here but refer the interested readers torefs . Ballistic thermalinjection (BTI) is a recently discovered energy transduction mechanismthat arises from the CLE dynamics at metal/non-metal interfaces. Inshort, BTI is an interfacial energy injection mechanism (without concomitantcharge injection) that was observed at an interface between ultrafastlaser-excited Au- and Y-doped CdO. When electrons in the Au are excitedfrom the sub-picosecond laser pulse, they travel ballistically towardthe metal/non-metal interface; upon reaching the interface, thesehot electrons in the metal scatter with electrons in the non-metal,the heat transfer of which is facilitated by the high electron-mediatedthermal boundary conductances discussed in A CLE process between hot electrons in a metal and electrons andphonons in a doped non-metal was recently observed by Tomko et al.149 could be a candidate to observe BTI given hotmetal silicide electrons in CLE with the phonons. However, there couldalso be a material constraint on this BTI process being a significantcontributor to thermal boundary conductance. CdO and doped metal oxidesin general offer a distinct advantage for enhancing BTI due to theirability to maintain high electron mobilities at carrier concentrationsas high as 1019–1020 cm–3.155 However, this process has only begun tobe studied, and thus, additional investigations into different materialinterfaces and the role of CLE on enhancing this BTI process are warrantedand would result in hot-electron-based control over various materialfunctionalities. For example, in the work from Tomko et al.,138 they used this BTI process to control the infraredplasmonic response of CdO via ultrafast thermal modulation of CdO’sepsilon near zero mode.In principle, this BTI process can occur at anymetal/doped non-metalinterface with high enough carrier concentrations. For example, thepreviously studied metal/metal-silicide interface by Ye et al.Additionally, one can envision the abilityto create delocalizedthermalization and transient thermal diodes by embracing BTI at metal/semiconductorinterfaces. In this process, the non-metal electrons, after gainingenergy from the high energy density electrons from the metal, thenconduct heat away from the interface based on the electron mobilityin the non-metal. The electrons in the non-metal then thermalize withthe phonons in the non-metal, creating the hot-spot from this BTIprocess that is spatially removed from the metal interface, akin tothe metal/metal discussion in III.d156 Subsequently, usingthe proper framework, various excited energy and/or higher temperaturestates in the electronic systems can be modeled to capture the CLEbetween the electrons and vibrational states and resulting energyexchange and thermal boundary conductance across the metal/non-metalinterfaces. Sadasivan et al.156 suggested this couldbe accomplished with the non-equilibrium Green function (NEGF) formalism,a well-developed approach to model transport in electron and phononsystems with atomistic control and input.158 Here, we review a recently developed approach, rooted in ab initio quantum dynamics simulations, that captures theelectron–vibrational CLE dynamics at metal/semiconductor interfacesby combining non-adiabatic molecular dynamics and time-dependent DFT.This robust technique not only allows for the degree of CLE betweenelectronic and vibrational states to be controlled but also can beextended to capture plasmon dynamics and resulting energy exchangeat metal/non-metal interfaces, offering insight into the energy exchangeprocesses during CLE.As overviewedin III.d.1Ab initio quantumdynamics simulations118 provide a foundational perspective on theevolution of hot carriers coupled to vibrational motions, by creatinga time-domain atomistic description, most closely mimicking the time-resolvedexperiments. The state-of-the-art methodology, developed by the Prezhdogroup,160 combines real-time time-dependent DFT forthe evolution of the electrons with non-adiabatic molecular dynamicsfor the evolution of ionic cores and electron–vibrational interactions.The electrons are treated quantum mechanically by solving the time-dependentSchrodinger equation, which depends parametrically on the classicalvibrational coordinates. The vibrational motions are described classicallyby molecular dynamics with semiclassical corrections.161 The electron–vibrational coupling matrixelements are computed on-the-fly along the trajectories. Charge–chargescattering is described by screened Coulomb interactions.162 Quantum transitions between electronic states are modeled by surfacehopping,159 which can be viewed as a master equation with non-perturbative configuration-and time-dependent transition rates.164III.d.2165 Parts a and bof 166 since the coupling matrixelement depends on the sensitivity of the electronic states to atomicdisplacements.Metals support severaltypes of electronic excitations, including single particle, image-potential,and collective states.167 whose inversegives the homogeneous optical line width. Classic theories of surfaceplasmons consider plasmon–surface scattering to be the fastestcontribution to plasmon dephasing.168 Sinceplasmonic excitation is localized away from atoms, the electron–phononcoupling is much weaker for plasmons than bulk and surface states,as demonstrated for Ag clusters using ab initio moleculardynamics.166 Phonon-induced pure-dephasingof plasmons took 30–40 fs and showed modest size dependence,with electron–phonon coupling being stronger in smaller clusters.Both plasmon and non-plasmon states coupled mostly to low-frequencyacoustic phonons that modulated the size and shape of the nanoparticlesand were sensitive to temperature variations, because the frequenciesof acoustic phonons in metallic clusters are comparable to the thermalenergy, kBT. The inelasticscattering process in a Ag particle took picoseconds,169 2 orders of magnitude longer than the elasticscattering. Higher energy plasmon excitations were delocalized fartheraway from the cores and, hence, exhibited weaker coupling to phononsand decayed more slowly than lower energy plasmons. The picosecondlifetimes of hot electrons generated by plasmon excitations can besufficient to allow charge extraction or elementary photochemicalevents associated with bond breaking, formation, or rearrangement.Electron–vibrational interactions produceelastic and inelasticscattering. Inelastic scattering involves the exchange of electronicand vibrational energy, while elastic scattering induces the lossof phase information and coherence. The decoherence time can be quantifiedas the pure-dephasing time,170 rationalizingthe time-resolved thermo-reflectance measurement.128 Increasing temperature accelerated both processes and alloweda broader range of vibrations to couple to the electronic excitationsdue to increased anharmonicity. The inelastic scattering was strongestbetween states with small energy differences and the elastic scatteringwas fastest between pairs of states that were distant in energy, becauseit is determined by the magnitude of the phonon-induced energy gapfluctuation, which generally increases for larger gaps.167The elastic and inelastic electron–phonon scattering analyseswere performed on Au films,III.d.355 cluster showed a long-lived intermediate state0.8 eV above the Fermi level.171 The longlifetime of the intermediate state facilitated the charge transferto the TiO2 substrate. Interestingly, the Au55/TiO2 and Ru10/TiO2 systems showedpicosecond electron–vibrational relaxation,172 while the Au20/TiO2 exhibited sub-picosecondrelaxation.173 The difference could belinked to the cluster shape; both Ru10 and Au55 were spherical, while the Au20 particle was a pyramid.Metals exhibit a variety of structural motifs on the surface, andcertain structures can give rise to states that partly decouple fromthe continuum of bulk states and trap charges for relatively longtimes. This is particularly important for catalysis, which often occurson defects, single metal atoms, or metal clusters. Hot electron relaxationin the Au20 cluster adsorbedon the MoS2 substrate.174 Whilethe perfect Pt20 pyramid gave rapid electron–phononrelaxation, the top atom of the pyramid was oscillating between twoconfigurations on a hundred picosecond time scale, producing anotherstructure  mechanismrelies on a strong metal–semiconductor interaction due to whichthe charge density of the plasmonic excitation attains a strong tailextending into the acceptor  mechanism by which hot carriers are initially generatedin the metal by plasmon decay and then transfer to an acceptor. However,PHET is rather inefficient, since hot electrons in a metal have shortlifetimes. An alternative proposal was put forth theoreticallyacceptor 7c. Upon 173 and experimental182 work demonstrating PICT focused on interfacesof metallic particles with 3D semiconductors, the surfaces of whichcontain unsaturated chemical bonds that create strong interfacialcoupling. Interaction of metals with 2D materials is weaker because2D materials contain no dangling chemical bonds. Therefore, the traditionalPHET mechanism plays a more important role with 2D substrates.183 The two mechanisms, PHET and PICT, can coexisteven in weakly bound hybrids.184 The combinationof the two mechanisms leads to fast charge transfer, overcoming hot-carriercooling. Spatial polarization of the excited state in the metal influencesits coupling to the semiconductor and alters the contributions ofeach mechanism. The probabilities of PHET and PICT are also sensitiveto external stimuli, such as strain.185The initialtheoreticalIII.d.6118 and the ab initio simulationrequires consideration of ensembles of electrons.164 If the thickness of the metal layer is less than the lengthof electron scattering inside the metal, then the energy transferacross the metal/semiconductor interface becomes ballistic and extremelyfast. Such a process has been observed and modeled at the Au/CdO interfaces result in a net dipole moment, leading to the strong absorptionof IR light at the transverse optic (TO) phonon frequency. The correspondinglongitudinal optic (LO) phonon is shifted to higher frequencies dueto the breaking of the degeneracy of the optical phonons at the Γpoint. This spectral splitting gives rise to the so-called Restrahlenband where the real part of the permittivity tensor becomes negative.This is the critical requirement for stimulating surface phonon polaritons(SPhPs) at an interface between the polar crystal and a dielectric. SPhPs result in highly confined optical fields andsubstantially reduced resonance line widths due to the long lifetimeof the optical phonons (on the order of a few to tens of picoseconds)in comparison to their plasmon polariton counterparts.188 However, there is a large momentum mismatch between these SPhPsin the energy–momentum dispersion relationship with light;i.e., SPhPs cannot be stimulated directly from free-space photons.To overcome this mismatch, high-index prisms, gratings, nanostructures,and sub-wavelength scatterers such as the metallized atomic-forcemicroscope tip employed in scattering-type scanning near-field opticalmicroscopy (s-SNOM) can be employed to launch and probe SPhPs.56 While metals usually exhibit isotropic dielectricfunctions, low-symmetry polar crystals can possess strongly anisotropicpermittivity values along three optical axes. The anisotropic dielectricfunctions of a polar material can even go to the extreme such thatat least one of the principal components of the permittivity has theopposite sign with respect to the other principal components. Thisleads to only certain directions being allowed for SPhP propagationaccording to the hyperbolic isofrequency contours (IFCs),190 for example, out-of-plane hyperbolic phonon polariton propagationin hBN,191 in-plane hyperbolic phonon polaritonpropagation in α-MoO3192 and V2O5,193 ghostpolariton propagation in calcite (CaCO3),194 and hyperbolic shear polaritons in beta-phase Ga2O3 (bGO).196 The above optical propertiesfor polar crystals present opportunities to engineer the radiativeheat transfer (both in the far-field199 and near-field202) and potentially conductive thermal transportvia SPhP stimulation.204In this section, we summarize the recent research involving surfacephonon polaritons  for thermal radiation and thermal conductionat surfaces and interfaces. For polar materials, such as SiC, SiO206 and free-space optical communications.207 Kirchoff’s law states that the thermalemissivity is equivalent to optical absorption at the same frequency,direction, and polarization state in a reciprocal system,208 and thus, the far-field thermal emission signaturecan be altered through engineering the optical properties of the materials.While engineered nanostructures or metasurfaces have been extensivityexploited to tailor far-field thermal emission,210 polar materials supporting SPhPs are a particularly interestingplatform to control thermal radiation patterns. The seminal work byGreffet et al.197 demonstrated spatiallycoherent  thermal emission from a patterned one-dimensionalSiC grating with the frequency-specific emission angles diffractioninduced SPhP dispersion  phononcan emit electromagnetic radiation, called thermal radiation or thermalemission. Sunlight, light from incandescent bulbs, and infraredradiation from human bodies are all examples of such thermal emission.The emission patterns provided by such traditional blackbody thermalemitters are nearly isotropic, broadband, and unpolarized in the farfield, which are less useful for many IR applications such as nondispersiveIR sensorsspersion 8a, whilespersion 8b.53 In sonances 8c.198 Bu) phonon8d.199 Fu197 calculated the density of electromagnetic energyabove a phonon–polariton medium, SiC, at 300 K ,the energy density spectrum resembles that of a traditional blackbodyexcept within the Restrahlen band of SiC, where the material exhibitsa negative permittivity and is therefore highly reflective . However, in the near-field,i.e., for a distance z smaller than the thermal wavelength(10 μm), the energy density spectrum changes dramatically, anda strong peak emerges inside the Restrahlen band of SiC. At 100 nmabove the SiC surface, the thermal emission evolves to become nearlymonochromatic, with the energy density increasing by more than 4 ordersof magnitude at the SPhP frequency . Such near-field contributionsfrom evanescent fields of SPhPs are the basis of NFRHT enhancement.Far-field thermal emission follows Planck’slaw, which setsan upper limit for the radiative heat transfer between objects atdifferent temperatures. However, Planck’s law fails in a varietyof situations, specifically when the radiative heat transfer processoccurs between a source and sink spaced at a distance less than thethermal  wavelength, which is about 10 μm atroom temperature (∼300 K) according to Wien’s displacementlaw. Such situations are termed the near-field regime, where the fast-decayingevanescent component of the electromagnetic waves dominates the radiativeheat transfer process. As SPhPs possess well-known evanescent character,i.e., evanescent surface waves, the phonon–polariton mediumprovides an ideal platform to explore near-field radiative heat transfer(NFRHT), which can even suppress the far-field blackbody limit fromthe contribution of tunneling of evanescent surface waves. To illustratethe near-field contribution in NFRHT enhancement, Greffet et al.at 300 K 9a.212 In213 experimental verificationof the anticipated NFRHT enhancement from SPhPs is challenging becauseof the necessity of achieving small uniform vacuum gaps on the orderof a few nanometer separation. Initial efforts toward NFRHT were basedon the Derjaguin approximation; i.e., the radiative heat transferbetween a sphere and a plane is obtained by integrating the localcontributions for two parallel planes with a distance of d  propagationof SPhPs, with propagation lengths much larger than the typical meanfree path of the optical phonon at the same frequency and the surface-confinedfields associated with most SPhPs being of critical importance forthis effect in nanostructures featuring a very high surface-to-volumeratio.2 in this case  increases with decreasing polar film thicknessand can even exceed the heat flux carried by acoustic phonon modes. However, as the interatomic bondsweaken and the density of a single medium comprising the interfacereduces toward that of a liquid, there becomes a shift in the underlyingprocesses that dictate energy transfer. Indeed, the mathematical frameworkof phonons themselves begins to breakdown; the lack of a well-definedcrystalline symmetry imposes a difficulty in defining vibrationalwavevectors and group velocities in amorphous solids and other low-densityphases . This is not to suggestthat we simply have no theory of heat transfer in these systems. Infact, there have been a number of fairly successful frameworks thatcan be applied toward the modeling and understanding of thermal transportin amorphous media, such as the “model of the minimum thermalconductivity of solids”,220 in whichthe relaxation time of vibrational modes in a standard phonon gasmodel is taken to be half a period of vibrational oscillation . However, there existsa nearly equivalent number of works that exemplify the inadequaciesof such formalisms and approximations.223Thus far, this Review has focused on the energy transfermechanismsacross interfaces composed of solid density media , there are two regimes of pertinent cooling.The first is at low-to-moderate interfacial heat fluxes, where thelocal liquid temperature remains well below the boiling point. Thesecond is at increased heat fluxes, where the temperature rise issufficient such that the liquid media undergo a phase transition toa vapor phase. In both cases, conduction from the solid to the liquidphase remains as the primary heat transfer mechanism. This shouldcome as little surprise: the liquid-to-vapor phase transition, nucleatepool boiling, and other phenomena that increase the net heat transferrate of the macroscopic system can only occur after sufficient energyhas transferred across the solid–liquid interface itself. Indeed,such are the cases in which nucleate pool boiling arises, and theinterfacial heat transfer remains fundamentally dictated by the rateat which vibrations in the solid can transfer energy to impinginggas molecules, as discussed in the following section for solid–gasinterfaces. Thus, while a significant body of work has been understandablydevoted toward net-heat transfer rates, ranging from clever microscalegeometries and active systems231 In addition to this, fundamental theory, modeling, and simulationshave helped frame a basis to suggest that the strength of the bondat the solid/liquid interface, which can be determined via the equilibriumcontact angle, can be correlated to the efficacy of thermal transport.238 For instance, the Kapitza conductance, hK, across a Lennard-Jones-based solid–liquid interface increaseslinearly with the energy parameter , asshown in 239 has extended the Boltzmann transport equation to the conditionsthat arise at solid–liquid interfaces, providing predictiveinsight toward the interfacial temperature drop based on macroscopicparameters, such as liquid density, without the need for explicitcontact angle measurements.With respect to the nanoscopic mechanisms that drive interfacialenergy transport, a number of recent works have pushed the theoreticalunderstanding of vibrational scattering and energy exchange acrosssolid/liquid interfaces.241 For instance, as shown in hK across these interfaces.In these studies, the interfacial bond strength and resultant hydrophobicitywere manipulated via changes in constituents of self-assembled monolayers(SAMs) formed at the solid–liquid interface . In general, these results imply thata smaller contact angle, and hence better “wetting”,leads to greater TBC. However, experimental works studying energycoupling across planar solid/liquid interfaces in which the liquidis not water, and relating this energy coupling to wetting, are scarce.The strengths of the intermolecular forces in a liquid relative tothe interfacial bonding environment are the underlying mechanism thatdrives the manifestation of contact angles and wettability.242In general, various experimental works have resultedin similarconclusions, where greater hydrophobicity at solid/water interfaces,determined via contact angle measurements, leads to a reduction inthermal boundary conductance .42 the experimental insensitivity to the interfacialresistance posed by a solid–liquid interface, due to the largethermal resistance of liquids relative to that of the interface, makethis approach prone to large uncertainties; in some cases, such asthose that involve low-thermal-effusivity fluids, the TBC is simplyunmeasurable with these techniques. In a recent study by Tomko etal., the experimental sensitivity and resulting uncertainty in measuringsolid–liquid thermal boundary conductance via TDTR measurementswas surveyed.243 The relative sensitivityof the interfacial resistance is significantly lower compared to thatof the liquid thermal conductivity for both water (κ = 0.6 Wm–1 K–1) and the common refrigerant,a fluorocarbon-based liquid, FC70 (κ < 0.1 W m–1 K–1); these results suggest that only a lowerbound of TBC can be recovered in such solid/liquid systems with TDTR.Rather, the authors provide alternative laser-based methods, suchas picosecond acoustics245 and laser ablation,246 as a means of extracting the relative TBC acrossdifferent solid/liquid interfaces. However, in the case of extremelyhigh interfacial resistances, these methods are certainly applicable.For example, Yu et al.247 found throughthe introduction of nonane, a hydrocarbon ideally representative ofmolecules that would arise in oil immersion environments, an Au/waterTBC of 610 kW m–2 K–1—aresistance certainly large enough to overcome typical experimentaluncertainties.This experimental scarcity can be stronglyattributed to the errorsand limitations associated with state-of-the-art nanoscale thermalmetrology techniques, namely, laser-based thermoreflectance methodssuch as TDTR and FDTR. While these methods would be optimal for probingthe solid–liquid interactions on the nanoscale due to its routineuse in measurements of TBC mainly across solid–solid interfaces,248 In this limit, the thermalboundary conductance at the nanoparticle/liquid interface is givenby r is the particleradius, Cv is the particle’svolumetric heat capacity, and τ is the thermal decay time constant.This method has been widely applied to a number of colloidal particlesystems, providing, arguably, the largest breadth of experiments associatedwith nanoscale solid–liquid interfacial thermal transport;these studies include metal nanoparticles composed of various elements,248 nanorods and nanotubes,249 and suspended molecules.250 Theprimary limitation of this approach is the viability of suspendingsuch particles in the fluid of interest. For example, it is difficultto manufacture colloidal metal nanoparticles lacking an adhesion layerin an arbitrary liquid of choice, thus making this approach inapplicablefor the study of a “bare” metal/liquid interface.Even with experimental uncertainties in planargeometries, thesethermoreflectance methods remain well-suited for the measurement ofsolid–liquid TBCs in colloidal nanoparticle systems. Indeed,in the limit of which the nanoparticle radius is such that it canbe considered a point source with respect to the surrounding fluid,the thermal model for extracting TBC is simplified with respect tothe analysis required for thin films that undergo bidirectional heattransfer into both the supporting substrate and the overlying liquidof interest. Rather than requiring a multilayer thermal model, withnumerous thermophysical inputs associated with each layer, for colloidalsystems with sufficiently small particle diameters, the thermal relaxationfollowing pulsed excitation can be modeled as an exponential decayin time.251 on the role of interfacial hot-electron processes acrosssolid–liquid interfaces provides an in-depth survey of manyrecent works. Nonetheless, the heat flux of such processes remainsquite small relative to vibrational energy transport based on ourcurrent understanding; further interfacial engineering and excitationmay be likely to increase the contribution of electron-mediated heatfluxes across solid–liquid interfaces and thus deserves continuedexploration. Additionally, radiative processes, particularly thoseunder near-field conditions that are known to enhance solid–solidinterfacial energy transfer as reviewed in 252 are ill-equippedfor liquid-phase studies, and (ii) the potentially weak collectiveoscillations that exist in liquid phases. Nonetheless, recent workby Wang et al.253 has developed a liquid-phasepeak force infrared (LiPFIR) method capable of performing near-fieldmeasurements within liquids, providing in situ measurementsof h-BN PhPs, thus displaying accessibility toward overcoming theexperimental hurdle. Further, many liquids in theory should sustainphonon polaritons based solely on the fact that they are polar; thelack of crystalline order is by no means a requisite for polaritonexcitation, as exhibited even through enhanced heat transfer ratesin amorphous materials nearly two decades ago.254 Indeed, detailed analysis on the optical activity pairedwith molecular dynamic simulations performed by Elton and Fernández-Serra255 has shown that the network of hydrogen bondsin liquid water leads to dispersive optical modes, thus exhibiting optical mode splitting and vibrational propagation.The aforementioned advances in metrology methods capable of liquid-phasenear-field measurements paired with solid–liquid interfacialengineering and microfluidics should provide a test-bed for furtherexploration of true liquid-sustained SPhPs, potentially providinga means of overcoming the intrinsically low thermal conductivity ofmany liquids.It should be noted that the majority of the preceding discussionand works have focused on vibration-mediated heat transfer processesdue to the fact that they carry a large majority of the associatedenergy flux. However, this is not to suggest that electronic and photonicenergy transport does not arise across such interfaces; this shouldcome as no surprise due to the fact that application spaces such aselectrochemical and photochemical catalysis both rely on interfacialcharge transport and sustain large optical-mode activity for radiativetransport. Indeed, a recent review by Lee et al.V.b256 At a continuum level, this interfacial heat transfer is understoodthrough convection, as the coupled heat-mass transfer of a movingfluid is the dominant heat transfer process; this is similar to ourcase of solids, where the interfacial thermal resistance plays a negligiblerole until the dimensions of the system are greatly reduced. Indeed,non-continuum heat transfer effects arise when the characteristiclength scale of the system becomes comparable to the mean free pathof the gas. Thus, a detailed description of the nanoscopic energytransfer mechanisms across a solid–gas interface is necessaryin not only systems with reduced dimensionalities but also systems immersed in low-pressure gases due to the inverserelationship of gas pressure and the molecular mean free path. Togain insight into the rate of energy transfer across a solid–gasinterface, we can consider a flux of gas molecules impinging upona solid surface. If the incident gas molecules were to “stick”to the surface without any reflections, the entirety of the molecule’smomentum, and thus energy, would have been transferred to the solidbody. In this simple scenario, the rate of energy transfer is nothingmore than the incident energy flux . In a more physically relevantscenario, where the molecules only transfer a fraction of their energyand reflect upon interaction with a solid surface, it should not besurprising that the primary descriptor for this non-continuum rateof energy transfer at a solid–gas interface is given by Ei and Ef are the average molecularenergies of the incident and scattered gas particles, respectively,and Es is the energy flux that would beachieved if the reflected molecules were in thermal equilibrium withthe solid surface post-scattering. The descriptor, α, variesfrom zero  and unity (perfect accommodation)and is termed the accommodation coefficient. Not only is this formalismreliant upon the flux of gas molecules being well-described by a singletemperature (or average energy), but it should be noted that it typicallydoes not provide a priori prediction of heat fluxesunless a pre-existing, detailed knowledge of solid–gas interactionsis already known.The exchangeof energy between a solid surface and adjacent gas molecules is aprerequisite for a range of fundamental processes and applications,including thermal mitigation of electronic devices and nanostructuresvia convection, deposition methods accessed with vapor adsorption, and even for considerationof drag coefficients in moving bodies.260 These ultrahigh vacuum studies are typically performed on a “clean”metal surface, where the greatly reduced pressures facilitate ballisticpropagation of gas molecules from a source to the sample as well asthe sample to the detector. These studies have provided valuable insightinto gas–surface interactions; for example, these studies havedemonstrated that kinetic energy is more readily transferred whenthe mass of the incident atom is similar to the mass of the atomscomprising the solid surface.262 Despite such insight,it is critical that a similar understanding of gas–solid dynamicsis achieved at near-atmospheric pressures, due to both technologicalrelevance and the transfer to a diffusive nature of the interactions.To this end, there is an intrinsic difficulty in experimentally resolvingthe energy transfer rates at solid–gas interfaces under ambientconditions. First, the measurement must have spatial resolution onthe order of the characteristic length scale of energy transport (∼submicronfor atmospheric conditions); the experimental method must be capableof resolving both flux and temperature distributions at this scalewithout altering heat flow. Similarly, the temporal resolution mustbe adequate for resolving the proper mechanisms of heat transfer atthe solid–gas interface; at ultrafast  time scales,there is insufficient time for mass transport to occur, and the techniqueis only capable of resolving conductive heat transfer mechanisms.On the contrary, steady-state methods can measure a heat transfercoefficient that is dominated by convection, as it is the primaryheat transfer pathway in gases due to the phase’s intrinsicallylow thermal conductivity. Lastly, due to the comparatively low heattransfer coefficients associated with solid–gas interfaces(<1 MW m–2 K–1) relative tothose at solid–solid interfaces , or conduction in bulk solids,it is difficultto decouple the weak heat loss to the gas relative to that of thesupporting substrate, as similarly found in the case of solids.It is important to note the extensive volumeof literature that has investigated this specific exchange of kineticenergy at the solid–gas interface via beam scattering experiments.268 For example, Liang et al.263 investigatedthe effect of interfacial parameters on the thermal accommodationcoefficient (TAC) at the solid–gas interface, which revealedthat the TAC on a smooth and perfect interface is significantly lowerthan that on a disordered interface. This was attributed to the roughnessand defects on the disordered interface, which are more conduciveto diffuse scattering of gas molecules. However, these physical mechanismscan be drastically different when the gas molecules are confined inthe nanopores of a solid framework. In this regard, Feng et al.268 conducted non-equilibrium molecular dynamicssimulations on polymer surfaces exposed to various types of gasesand found that, when the gases are confined to 10 nm pores, the gasthermal conductivities can be as much as 3 orders of magnitude lowerthan their bulk values, providing important design criteria for thermalinsulation materials.Atomistic modeling of solid–gas TBC has also provided importantphysical insights into the heat transfer mechanisms at these interfaces.269 Generally,there is a trade-off between reducing the solid thermal conductivityby increasing porosity, but it also leads to enhanced contributionsfrom the gas and radiative heat transfer channels. More recently,the control of the relative contributions of the solid framework andthe infiltrated gases to the overall heat transfer has been demonstratedin two-dimensional (2D) covalent organic frameworks (COFs).271 Specifically, it has been shown that the solid–gas interactionsin the one-dimensional pore volumes of the COFs can lead to additionalconductive heat transfer channels associated with the gas moleculesthat facilitate heat transfer along the pores.271 Through increased collisions with the solid framework of the COFs,confined gas molecules have been shown to conduct heat along the 1Dpores (that resemble “chimneys”) of COFs to enhancetheir thermal conductivity. However, if the pores are smaller thanor comparable to ∼1.5 nm, the solid–gas interactionsare shown to lead to reduction in the overall thermal conductivityvia solid–gas scattering.270 Theseresults highlight the prowess of molecular dynamics simulations inproviding unparalleled atomistic insights into heat transfer mechanismsfor various solid/gas systems and can have major implications foradvancing some very important next-generation technologies such asthose based on 2D COFs for catalysis and gas storage applications.In porous materials, heat transfer ismainly contributed by conductionthrough the solid framework and the gas particles, and also partiallyvia radiation through the voids.V.cWithregard to the mechanisms that drive interfacial energy transport,plasmas lie at an intriguing intersection between that of metallicsolids and that of a free gas. Plasma is an ionized gas that containsapproximately equal numbers of positively and negatively charged species.Typically, these charged particles are in the form of positive ionsand free electrons, which are created by adding energy, either thermal,light, or electric, to a gas volume to ionize the gas. A distinctionthat separates this fourth state of matter from a gas is that, whilethe plasma volume is electrically neutral, there are enough chargedparticles to make the plasma conductive. The plasma state is the mostcommon form of matter in the universe, with stars and the accompanyinginterstellar medium comprising most of this matter. In contrast, plasmasrarely occur on earth; lightning and auroras are examples. Accordingly,the number density and energy of the ions and electrons, neutral gasdensity and temperature, and other properties of a plasma can varywidely.The properties of plasmas, however, make them a powerfultool in advancing technological applications that range from energyto the manufacture of commonplace materials and devices. Indeed, man-madeplasmas have found uses in, for example, fusion energy, lighting,and wide screen televisions. Plasma-based material processing, onthe other hand, is employed to synthesize and modify materials usedfor the production of hard, barrier, and multifunctional coatings,optical elements, and sensing platforms. Perhaps the most well-recognizedapplication for plasma processing is in the semiconductor industry,where plasma processing is an indispensable tool in the fabricationof computer chips.The most common types of plasmas used inmaterials processing arenon-equilibrium, low-temperature plasmas, which are typically producedby applying an electric field to a gas volume. The field acceleratesthe electrons to an energy sufficient to ionize a fraction of thegas and, thus, sustain the plasma. The resulting electron energy ismuch greater than the heavy ions, which like the neutral backgroundgas are at or near room temperature. When produced in a moleculargas background, the energetic electrons will also excite and dissociatea fraction of the gas molecules. As such, these plasmas can delivera rich flux of species to a material surface including positive ions,negative ions, and electrons; charged and neutral reactive radicals;excited ions and neutrals; and a flux of photons created when excitedspecies decay. These are depicted in the schematic of 272 Energy delivery is an essential component in driving physical andchemical processes either directly through particle and photon interactionsor indirectly via surface heating. In particular, the energy fluxserves to drive the surface out of thermal equilibrium with the bulkmaterial, thus enabling local physicochemical processes that can beexploited to remove (etch) substrate material, add (deposit) differentmaterials, or chemically modify the surface. This is distinct fromheating a material to enhance surface reactions, where the entirematerial and/or environment is elevated in temperature. It is alsoa cumulative result of numerous energy transfer events associatedwith the individual particles and photons. As such, there is a needto develop approaches that provide a direct measure of the localizedand transient energy transport mechanisms associated with the fluxof species at the solid surface.In order to preserve the neutrality of the plasma,an electricalpotential forms at the surfaces exposed to plasmas, which serves toaccelerate the positive ions toward the surface (and decelerate theelectrons) and thus equalize the flux of positive and negative chargesleaving the plasma. This potential scales with electron energy butwill typically cause ions to impact the walls with kinetic energiesabove their thermal values. The synergistic effects associated withthe simultaneous delivery of both chemically active species and energyto a material’s surface is an attribute that separates plasma-basedapproaches from other processing techniques.274 and atmospheric-pressure275 plasma systems. One can begin to understandthe response of a material immersed in a plasma by considering thepower balance at the surface,273 givenby Pin = Pheat + Pout. Here Pin is related to the energy flux (or power flux density) intothe material, Pout is related to the energyflux leaving the material, and Pheat isthe power that heats the material. Pin is determined by accounting for all collisional and radiative sourcesof energy from the mix of charged particles (electrons and ions),reactive gas molecules and atoms, and excited species generated inthe gas phase that will either impact the material surface or producephotons that reach the surface. Also included are exothermic chemicaland physical reactions at the materials’ surface and systemcontrols such as substrate heating and/or biasing. Similarly, Pout is determined by accounting for all theprocesses that remove energy from the surface including particlesthat leave the surface (or diffuse into the bulk), radiation, endothermicreactions, and system components that serve to cool the material.While it is a difficult task to properly account for all sources thatcontribute to Pin and Pout in even the simplest plasma processing environments,their difference (Pheat) is accessibleby monitoring the temperature of the materials exposed to the plasmausing ms is the mass, Cs is the specific heat capacity, and Ts is the temperature of the material exposed to theplasma. While of practical interest, it is important to note thattemperature is a macroscopic property that describes the statisticaldistribution of particle energies within the material. It is not adirect measure of the energy flux or transfer but rather the resultof the energy transfer from the plasma to the surface. To addressthis, devices and techniques have been developed278 to measure the thermal flux directly by measuring the change intemperature over some distance or time.A number of approaches havebeen aimed at understanding and quantifyingthe energy flux and associated energy transfer mechanisms at the solid–plasmainterface, for both low-pressure272 estimate that Ar+ ions with 200eV of kinetic energy release most of their energy within about 25Å of the surface in about 10–12 s. Anders279 argues that the potential (ionization) energyis released at (or very near) the point of contact during neutralizationof ions and absorbed locally within the same time scale. Similar scalingcan be expected for other particles possessing kinetic energy  or potential energy . Photons willtypically deliver their energy much deeper than low-energy particles,with a penetration depth that depends on wavelength. However, whenthey do lose their energy in the material, it is a nearly instantaneouslytransferred. Energy transport in a solid is largely mediated by electronsand lattice vibrations or phonons, which are typically characterizedby mean free paths on the order of several to hundreds of nanometersand relaxation times that range from several femtoseconds for electronsto picoseconds or even nanoseconds for phonons.280 In other words, the time required to propagate energy awayfrom a plasma-interaction zone near the surface, determined by theelectron and phonon diffusion times, can be much longer than the typicaltimes associated with Pin. Thus, the energydelivered by the plasma produces a well-localized “thermalspike” near the surface that exceeds the average temperatureof the material and will then dissipate in time and space. The spatiotemporalcharacteristics of this thermal spike and associated kinetics arenot easily accessible with conventional temperature measurements usingthermocouples or radiation. As such, an increasing body of work hasbegun investigating the surface heating and resulting energy transportprocesses of the thermal energy carriers in materials exposed to plasmas.Despite the advancesin technology, measuring the plasma’senergy flux to a surface remains challenging. To understand this,consider that most particle energy is delivered and adsorbed rapidlywithin a few nanometers of the surface. For example, Graves and Humbird57 applied afemtosecond pump–probe technique, TDTR, to measure the electronicresponse of a gold film exposed to an atmospheric pressure plasmajet . The results suggest a substantialincrease in the graphene temperature above the underlying substrate,which varies with plasma operating conditions. Importantly, the increasein the temperature with increasing applied power indicates a correlationbetween the fluence of energetic and reactive species and surfacetemperature.Berrospe-Rodriguez et al.While these studies are limited in their scope,the promise ofnoncontact methods such as the thermoreflectance technique is substantial.Indeed, the ability to characterize surface heating over physicaland temporal scales associated with the flux of energy carriers deliveredby the plasma, as well as the ability to monitor the response of electronsand phonons in the material, should provide valuable insight intothe physical and chemical processes that arise during plasma exposure.VIWe reviewed and providedour perspective on the topic of ultrafastenergy transduction mechanisms across various types of material interfaces.Specifically, we focused our discussions on the role of coupled energystates dictating interfacial energy transport. These include interfacialthermal transport mediated through hybridized and localized interfacialphonons, electron–phonon coupling at solid/solid interfaces,surface phonon polariton-driven heat transfer, and thermal transportacross different phases of matter including energy transfer processesat the solid–plasma interactions. For purely phonon-driventhermal boundary conductance, interfacial vibrational modes that donot exist on either “bulk” material have been shownto contribute substantially to interfacial heat flow. These emergentlocalized modes can dictate the vibrational physics and even the overallheat conduction in short-period superlattices. For example, the emergenceof hybridized phonon modes in superlattices with high interface densitiesleads to rich phonon physics such as the demonstration of Andersonlocalization of phonons in aperiodic superlattices and the crossoverfrom the incoherent to the coherent regime of phonon transport insuperlattices with systematically varying period thicknesses. Alongwith the significant role of interfacial modes in dictating heat transferacross solid interfaces, hybridized phonon modes across interfaceshave also been leveraged to tune the thermal conductivity of nanophononicmetamaterials and appear to be a robust strategy to manipulate theentire phonon spectrum in these materials.ab initio quantumdynamics simulations has also tremendously increased our understandingof coupled electron–phonon processes across material interfaces.For example, these first-principles-based calculations have shed lighton the direct plasmon-induced charge transfer mechanisms across metal/semiconductorinterfaces, a process that had been theorized previously but neverrigorously studied with first-principles. As charge–chargescattering is much faster than the energy transport by phonon–phononscattering, a sufficiently high concentration of charge carriers inthe semiconductor is required to transfer a significant amount ofenergy across the metal/semiconductor interface. It is also possiblethat the hot electrons generated in a semiconductor can transfer chargeor energy into a metal where participation of plasmon-like acceptorstates in the metal aids in the overall energy transport process.Studies have alsoshown the prospect of energy transduction fromhot electrons coupling across the interface with the phonons of thematerial on the other side. This process is highlighted by the experimentalobservation of ballistic thermal injection at metal/doped non-metalinterfaces, which was used to create long-lived hot electrons in thenon-metal to ultimately control the plasmonic absorption and offeran approach to thermally modulate plasmon resonances in the non-metals.Simultaneously, the development of Surface phonon polaritons, where photons are coupled to opticalphonons, are also rapidly gaining more attention for the purposesof thermal radiation and thermal conduction at surfaces and interfaces.For instance, near-field radiative heat transfer originating fromthe contribution of tunneling of evanescent surface waves and surfacephonon polaritons in periodic nanostructures has been proposed toenhance energy transport with a strong focus on SiC-based designs.Surface phonon polariton mediated conductive heat transfer has beendemonstrated as a viable route that occurs through the hybridizationof light with optical phonons that possess higher heat capacities.However, these optical phonon modes inherently have slower group velocitiesas compared to the dispersionless acoustic modes and, therefore, typicallydo not substantially contribute to heat conduction in typical crystallinesemiconductors. Thus, overcoming this limitation of the intrinsicallylocalized nature of the majority of optical modes and allowing thesehigh-energy modes the opportunity to participate in the conductiveheat transfer processes can lead to dramatic enhancements in surfacephonon polariton-driven heat transfer. In addition to the noted benefitsof the high heat capacities associated with optical phonons, suchsurface phonon polariton-driven thermal conduction could benefit significantlyfrom the fast  propagation of thesecoupled energy carriers with propagation lengths much larger thanthe typical mean free path of the optical phonons at the same frequency.This will be of critical importance for heat conduction in nanostructuresfeaturing a very high surface-to-volume ratio.We have alsoreviewed the energy transfer mechanisms across interfacescomposed of various phases of matter. Although thermal conductanceacross solid/liquid and solid/gas interfaces has been shown to besubstantially lower than that across solid/solid interfaces, physicalphenomena such as thermal accommodation in solid/gas interfaces andthe ability to tune thermal conductance across a wide range throughsolid–liquid interactions have led to a considerable amountof research for these interfaces. For example, in nanoporous materialssuch as covalent organic frameworks, heat transfer efficacy can besubstantially increased by inducing strong solid–gas interactionsalong the laminar pores; the gas adsorbates present additional heattransfer channels, where these gas molecules can conduct heat viafrequent and strong collisions with the pore walls. Likewise, theflux of energy carriers delivered to the surface of plasma-exposedmaterials has also recently been shown to drive the physical processesat the solid/plasma interface. For instance, the interaction of apulsed plasma jet with a metallic solid surface has been shown toinclude periods dominated by both heating and cooling processes. Takentogether, these intertwined mechanisms of coupling between differentenergy carriers at interfaces and surfaces in nanomaterials are thefoundation of modern technologies that are continuing to providetransformation benefits in a plethora of applications, and as such,further advancement in research in all of the aforementioned topicsis a prerequisite to realize the potential of manipulating these processesfor enhancing our current technology.Coupled local equilibria (CLE): When two populationsof carriers are both well described by only slight perturbations fromtheir respective equilibrium distributions, yet each of their equilibriumdistributions is defined by statistically and significantly differenttemperatures relative to each other.Interfacial hybridphonon modes: At the interfaceor atomic junction between two materials, the non-intrinsic and heterogeneousmasses and force constants do not intrinsically exist in the “bulk”of either homogeneous material. When degenerate with Bloch phononwaves in even one of the materials adjacent to the interface, thesehybrid and interfacially localized phonon modes are resonances thatshow localized behavior near the interface but are smoothly connectedto propagating phonon states in the material.Ab initioquantum dynamics simulations: This simulationapproach provides a foundational perspective on the evolution of hotcarriers coupled to vibrational motions by creating a time-domainatomistic description, most closely mimicking time-resolved experiments.This computational approach combines real-time time-dependent DFTfor the evolution of the electrons with non-adiabatic molecular dynamicsfor the evolution of ionic cores and electron– vibrationalinteractions.Ballistic thermal injection (BTI): A process forenergy transfer across metal/semiconductor interfaces during conditionsof CLE. This process begins with hot-electron generation in the metal,and prior to the electron–phonon coupling (less than a coupleof picoseconds), energy propagates ballistically toward the metal/semiconductorinterface. The electron energy front reaches the interface, wherebythe electrons transfer their energy, rather than charge, to the pre-existingfree electrons in the semiconductor’s conduction band, thusrelying on electron–electron thermal boundary conductance atthe metal/doped semiconductor interface. The pre-existing semiconductor’selectrons are now at an elevated temperature.Phononpolaritons: Quasiparticles comprised ofstrongly coupled photons and optical phonons.Reststrahlenband: Narrow energy band in a givenmedium where the real part of the permittivity tensor becomes negative,resulting in the inability for electromagnetic radiation to propagate.


Toxic cations, including heavy metals, pose significant environmental and health risks, necessitating the development of reliable detection methods. This review investigates the techniques and approaches used to strengthen the sensitivity and selectivity of Schiff base fluorescent chemosensors designed specifically to detect toxic and heavy metal cations. The paper explores a range of strategies, including functional group variations, structural modifications, and the integration of nanomaterials or auxiliary receptors, to amplify the efficiency of these chemosensors. By improving selectivity towards targeted cations and achieving heightened sensitivity and detection limits, consequently, these strategies contribute to the advancement of accurate and efficient detection methods while increasing the range of end-use applications. The findings discussed in this review offer valuable insights into the potential of leveraging Schiff base fluorescent chemosensors for the accurate and reliable detection and monitoring of heavy metal cations in various fields, including environmental monitoring, biomedical research, and industrial safety. Schiff bases are a class of organic compounds characterized by an imine (-C=N-) functional group formed by the reaction between the amine amino group and the aldehyde or ketone carbonyl group . This imThe synthesis of Schiff bases involves the condensation reaction between any combination of aliphatic or aromatic amines and aldehydes/ketones with a reactive carbonyl group. While the procedure is generally the same, the specific conditions, such as reactant ratio, solvent, temperature, and reaction time, may vary depending on the reactants and desired product. In general, the amine and the aldehyde/ketone are mixed in a suitable solvent, such as ethanol or methanol. The ratio of reactants is typically 1:1, but it can be slightly modified to obtain a larger yield of the desired product . Acidic 2+ chromene-3-carbaldehyde and carbazide by Wang et al. -phenol (probe-21), shown in 2+ -4-nitrophenol, as shown in 3+, Cr2+, and Cd2+ in a turn-off response. The NPs complemented the Schiff base, resulting in the fast electron transfer between the surface functional imine group and metal ions. NPs, particularly transition metal sulfide NPs, have been used to amplify the qualities of Schiff base chemosensors for sensing many other metal ions, as they have tailored surface properties, narrow size distribution, and wide band gap . Ayodhya2+ tracker (probe-51), synthesized from the reaction between rhodamine 6G hydrazide and 3,4,5-trimethoxybenzaldehyde, shown in 2+. When the probe was functionalized with (3-aminopropyl) triethoxysilane and gold nanoparticles, the color intensity increased 9-fold, with an LOD of 0.12 nM. For application, the probe was grafted onto paper strips and used to analyze Pb2+ in meat samples, with results consistent with those obtained from inductively coupled plasma-mass spectrometry method. While these results are impressive, investigating its stability over time and under different environmental conditions would provide a deeper understanding of its limitations. Its performance should be reproducible across multiple experiments.As previously mentioned, rhodamine dyes are used in fluorescent chemosensors because of their ability to exist in equilibrium between two forms. This allows the open and closed forms to emit optical changes that allow detection. When used in synergy with gold nanoparticles, it is conceivable that this signal could be amplified. Srisukjaroen et al. reported a calorimetric Schiff base PbQuantum dots are nanoscale semiconductor particles with unique optical and electronic properties. They are typically composed of inorganic materials, such as cadmium selenide (CdSe), lead sulfide (PbS), or indium phosphide (InP). One of the defining characteristics of quantum dots is their size-dependent bandgap. This means that the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which determines the electronic and optical properties of the material, changes as the size of the QDs changes. Due to their small size, QDs exhibit quantum mechanical behavior, leading to unique optical properties. They have a broad absorption spectrum, effectively capturing photons across various wavelengths. Additionally, they have a narrow and tunable emission spectrum, with the emission wavelength determined by the size of the QDs. QDs also possess a high quantum yield, efficiently converting absorbed photons into emitted photons, resulting in bright fluorescence. The emission color of QDs can be tuned by controlling their size, thus producing a wide range of colors. Integrating quantum dots with Schiff base chemosensors can synergistically improve the sensor system’s efficiency, sensitivity, selectivity, stability, and multiplexing capabilities, making it a promising approach for advanced sensing applications. Fan et al. prepared a luminescent fluorescent probe for the detection of picric acid by immobilizing a Schiff base chromophore on graphene quantum dots . The proNanoporous materials have attracted significant attention in developing chemosensors due to their high surface area, large pore volume, and tunable pore size . These mSchiff base ligands can be immobilized through covalent bonding, coordination with metal centers within the nanoporous material, or physical encapsulation . The nanprobe-52a and 52b) for the turn-on detection of Hg2+. The nanoparticles were unique because the particle size could be altered by adjusting the synthesis procedure, thus potentially allowing it to be tailor-made for different Schiff bases. Another highly useful but different class of nanoporous materials is graphite. Modified graphite tends to increase the stability of the chemosensor, limiting degradation and aggregation. An example is a study by Selvan et al., who modified graphite electrodes with asymmetrical N4 tetradentate Schiff base ligand N,N′-bis(pyrrole-2-ylmethylene)-2-amino benzylamine for the simultaneous detection and recovery of Pb2+ and Hg2+ ions in sea and lake water (probe-53) . . 2+ is a3+ detection in water (probe-56)  with a “triple-decker” structure for tracking Co2+, as shown in Cd–Ln nanoclusters possess both luminescent and magnetic properties. The luminescent property arises from the doped lanthanide ions, while the magnetic property is attributed to Cd and lanthanide elements. This dual functionality allows for the development of multifunctional sensors. Schiff base chemosensors can modify the luminescence properties of Cd–Ln nanoclusters. This alteration can lead to enhanced emission intensity, longer luminescence lifetime, or changes in emission wavelength upon interaction with the target analyte. Wang et al. synthesized Cd–Ln clusters from Schiff base ligands bearing a long methylene group skeleton for monitoring Ferobe-63) . The cluIn this review, we have explored a range of strategies to improve the selectivity and sensitivity of Schiff base fluorescent chemosensors for detecting toxic and heavy metal ions. The different mechanisms and the underlying photophysical phenomena behind them influences chemosensor design. For instance, PET relies on electron transfer, AIE-gen is based on the restriction of intramolecular motion and prevention of non-radiative decay pathways, while ESIPT is a photophysical process that occurs in certain fluorophores such as coumarin derivatives, where light-induced proton transfer leads to significant changes in fluorescence properties. By critically evaluating the literature of several Schiff base chemosensors, we have identified several key approaches, including functional group variations, structural modifications, and the integration of nanomaterials or auxiliary receptors. Functional group variations have been highlighted as an effective strategy to enhance selectivity and sensitivity of Schiff base sensors. The modulation of binding affinity towards target cations can be accomplished through meticulous design and incorporation of specific functional groups into the Schiff base structure. The inclusion of electron-donating or electron-withdrawing groups, along with chelating moieties, serves to greatly enhance the chemosensor’s performance. Rational design of the binding pocket to optimize interactions with the target cation is another approach. This can involve introducing specific binding sites, modifying the cavity size, or incorporating steric hindrance to exclude interfering cations.2+, simply incorporating thiol (-SH) or amine (-NH2) functionalities into the rhodamine dye structure may not be enough. Researchers can enhance the spacing and functionalization of the linker between the rhodamine dye and the receptor unit. The linker can be designed to provide an ideal distance and arrangement for efficient Hg2+ binding and signal output. The structure could also be modified to stabilize the spirolactam form of the rhodamine dye, which is non-fluorescent. In the presence of Hg2+, the spirolactam ring opens, resulting in a highly fluorescent merocyanine form. Enhancing the stability of the spirolactam form will improve the selectivity and sensitivity of the chemosensor. The probe could also be modified to increase its rigidity, as this can enhance selectivity by reducing non-specific interactions with other cations. Furthermore, novel selectivity filters could be introduced within the receptor unit to discriminate against other metal ions that may interfere with Hg2+ detection. Researchers can design these filters to favor Hg2+ binding over other competing ions, thereby enhancing the selectivity and accuracy of the chemosensor.As a practical example, in rhodamine-based Schiff base chemosensors that target HgSpacer length optimization: Researchers can find ways to adjust the length and flexibility of the spacer connecting the chelating unit and the reporter moiety. This modification helps Schiff base compounds achieve the optimum distance and orientation for efficient cation binding and signal transduction.Conformational control: Sensor design should consider incorporating conformational switches within the Schiff base structure. These switches can be responsive to the presence of the target cation, leading to conformational changes that amplify the signal output, thereby improving sensitivity.Signal amplification strategies: Introduce amplification mechanisms, such as signal amplification tags, to enhance the signal response generated by the Schiff base structure upon cation binding.Analyte-binding pocket modification: Rational design of the binding pocket to optimize interactions with the target cation. This can involve introducing specific binding sites, modifying the cavity size, or incorporating steric hindrance to exclude interfering cations.Since these modifications depend on the chemosensor design and experimental conditions, a combination of multiple strategies may also be necessary to achieve the desired improvements. Stabilizing Schiff base compounds on nanomaterials has also been shown to improve efficiency as they can be excellent signal amplifiers, enhancing fluorescence emission upon cation binding. Surface functionalization of nanomaterials with Schiff base structures can impart selectivity towards specific cations. Future research should consider the exploration of novel nanomaterials to incorporate these Schiff base compounds. Improving the biocompatibility of the Schiff base chemosensors is also important for their applications in biological and medical fields. Nanomaterial modifications can and should focus on reducing potential cytotoxicity and enhancing bioconjugation strategies. Integrating these strategies will ultimately pave the way for the creation of highly efficient chemosensors, enabling accurate detection and monitoring of toxic cations across various applications. In summary, future research should consider the following steps to improve performance of the Schiff base chemosensors:


The aging population in the developed world has implied increasing age diversity in the workforce of organizations. Consequently, mutual perceptions about one’s co-workers and age discrimination is becoming increasingly important.This study aims to explore how perceptions about older workers’ work (un)adaptability, work effectiveness and workplace age discrimination vary according to participants’ psychosocial factors, such as age group, gender, education level and work sector.This study included a sample of 453 workers in Portugal, diverse in terms of age, gender, education level and work sector. Four different instruments were used: (a) a sociodemographic questionnaire; (b) an older workers’ Work Adaptability scale; (c) an older workers’ Work Effectiveness Scale and; (d) the Workplace Age Discrimination Scale (WADS).Middle-aged and older participants perceive older workers as more adaptable than younger participants. The oldest group of participants perceives older workers to be more work-effective and experience the highest levels of age discrimination in the workplace, when compared to the other age groups. Also, participants with lower levels of education tend to perceive higher levels of workplace age discrimination, when compared to participants with high school and higher education.Generational perceptions in the workplace are perceived by workers differently, hence organizations should implement age management strategies to address age discrimination, particularly due to the increasing proportion of older workers.None Declared