Here we report the structures of the nucleosome containing the mouse genomic CX3CR1 enhancer DNA and its complexes with PU.1 alone and with both PU.1 and the C/EBPα DNA binding domain. Our structures reveal that PU.1 binds the DNA motif at the exit linker, shifting 17 bp of DNA into the core region through interactions with H2A, unwrapping ~20 bp of nucleosomal DNA. C/EBPα binding, aided by PU.1’s repositioning, unwraps ~25 bp entry DNA. The PU.1 Q218H mutation, linked to acute myeloid leukemia, disrupts PU.1-H2A interactions. PU.1 and C/EBPα jointly displace linker histone H1 and open the H1-condensed nucleosome array. Our study unveils how two pioneer factors can work cooperatively to open closed chromatin by altering DNA positioning in the nucleosome.Pioneer transcription factors are vital for cell fate changes. PU.1 and C/EBPα work together to regulate hematopoietic stem cell differentiation. However, how they recognize  Pioneering transcription factors constitute a distinctive category of proteins capable of identifying closed chromatin regions, which are resistant to DNase I.6 These factors exhibit the ability to locally open chromatin, facilitating subsequent recruitment of other transcription factors. This coordination contributes to the regulation of gene expression, often assuming indispensable roles in processes such as cellular differentiation and development.Gene expression and its regulation hold pivotal significance in governing cell fate and reprogramming processes.12 The DNA motifs for binding the transcription factors are incorporated into them by either design or in vitro selection from a DNA library, leading to various transcription factor binding modes. The structural basis of how transcription factors bind to the nucleosomes containing the in vivo DNA targets has only been investigated recently, but no structures of nucleosome-pioneer factor complexes have been determined.15 This is because the nucleosomes containing genomic DNA are often more fragile and tend to dissociate during sample preparation for structural studies using the single-particle cryo-EM method.Although the structural basis of a transcription factor recognition of its cognitive motif in free DNA is well understood, how it targets the nucleosomal DNA in chromatin remains elusive. Current structural studies primarily use nucleosomes containing non-genomic DNA to form stable structures.spi1 gene) is a master regulator for hematopoietic stem cell differentiation and is essential for the terminal differentiation of macrophages.16 PU.1 mutation and reduced expression have been associated with acute myeloid leukemia (AML) and agammaglobulinemia.19 PU.1 binds to its DNA motif alone or co-binds with other factors, such as the C/EBPa family nearby at the enhancers of cell type-specific genes, and regulates their expression.21 It can target compact chromatin and enhance chromatin accessibility.22 In contrast, C/EBPα binding to nucleosome-enriched regions in chromatin is more dependent on PU.1, and knockdown of PU.1 results in a decreased C/EBPα binding to de novo enhancers during B cell transdifferentiation.23 Genomic and chromatin state analyses of PU.1 and C/EBPα targeting in B cells and macrophages have revealed that they bind nucleosome-enriched chromatin.24 Comparison of fibroblast nucleosome occupancy by MNase-seq signals and transcription factor binding by ChIP-seq in macrophages shows that the CX3 chemokine receptor 1 (CX3CR1) locus consists of a nucleosome targeted by both PU.1 and C/EBPα.25 In addition, previous in vitro biochemical studies have confirmed the binding of the nucleosome consisting of the 162 bp CX3CR1 DNA by the pioneer factors.25PU.1  that contains three acidic regions and a glutamate-rich region, and the N-terminal region of C/EBPα contains two TAD domains. Both the N-terminal regions of PU.1 and C/EBPα interact with basal transcription factors such as TFIID, TFIIB, and TBP,29 and histone acetyltransferases CREB-binding protein (CBP)31 as well as SWI/SNF chromatin remodelers.32PU.1 is a member of the erythroblast transformation-specific transcription factor family with the DNA binding domain (DBD or ETS) at its C-terminal region . In compCX3CR1 enhancer DNA,25 the in vivo target of the transcription factors. Our study shows that PU.1 and C/EBPα each can unwrap the nucleosomal DNA at the exit and entry sides, respectively. However, PU.1 binds the nucleosome with higher affinity by interacting with the core histone, leading to nucleosome repositioning, which shifts the binding site of C/EBPα from the inner region of the nucleosome to the end region, facilitating the binding of C/EBPα. Our results reveal how two pioneer factors can synergistically bind to the nucleosome, unwrap nucleosomal DNA, evict linker histone H1, and open the H1-condensed nucleosome array.In this study, we used cryo-EM and biochemical methods to investigate how PU.1 and C/EBPα recognize the nucleosome containing the genomic CX3CR1 nucleosome, we reconstituted the nucleosome consisting of human core histones and the 162 bp DNA from the CX3CR1 enhancer loci.25 We expressed and purified the recombinant full-length PU.1 and the DNA binding domain of C/EBPα fused to maltose binding protein at the N-terminus to increase its solubility (dapp of ~0.65 μM obtained by fitting the data to the Hill equation (MBP-DBDC/EBPα binds the nucleosome with a lower affinity (Kdapp of ~1.7μM). Using the single-chain antibody (scFv)-assisted cryoEM method,33 we obtained the density map of the nucleosome-scFv2 complex at an overall resolution of 2.6 Å  and measured the apparent binding affinity changes. We performed EMSA experiments by titrating the nucleosome with PU.1. Fitting the binding data to the Hill equation showed that the mutations of PU.1 Q218H and 3AH2A reduced the binding affinity by ~2- and 3-fold, respectively  PU.1 and H2A  binds the DNA motif and core histones, leading to the repositioning of the nucleosome, which in turn shifts the DNA motif of the other transcription factor (C/EBPα) from the inner nucleosome core region to the location near the entry site  cells. All mutations were generated using QuikChange kit (Agilent). E. coli cells harboring each histone expression plasmid were grown at 37 °C in 2 × YTB Broth. When OD600 reached around 0.6–0.8, 0.5 mM IPTG was added to induce recombinant protein expression for 5 h at 37 °C. The cells were harvested and resuspended in 50 ml of buffer A , followed by sonication on ice for 360s with a pulse of 15s on and 30s off. The cell lysates were centrifuged at 40,000 × g for 20 min at 4 °C. The pellet containing histones was resuspended in 50 ml of buffer B . The samples were rotated for 12 h at 4 °C, and the supernatant was recovered by centrifugation at 96,000 × g for 60 min at 4 °C. The supernatant was loaded to Hitrap S column chromatography . The column was washed with buffer B, and histone protein was eluted by a linear gradient of 100 to 800 mM NaCl in buffer B. The purified histones were dialyzed against water three times and freeze-dried.Recombinant human histones and their mutants were expressed individually in ETSPU.1, residue 165–272) with N-terminal his tag and DBD of C/EBPα (residues 214–359) with C-terminal His-tag were directly synthesized in Genscript. Q218H and G220C mutations were introduced into both full-length PU.1 and ETSPU.1 using QuikChange kit (Extended Data Table 2). The plasmids were transformed into BL21(DE3) cells and grown in LB medium. When OD600 reached 0.8, 0.5 mM IPTG was added at 37 °C for 2 hrs. Expression and purification procedures was finished within 1 day for the full-length protein to avoid degradation. Cells were harvested and resuspended in the buffer containing 20 mM HEPES, pH 7.1, 1 M NaCl, 0.5 mM TCEP, and a protease inhibitor cocktail (Roche). After sonification and ultracentrifuge, the supernatant went through the column containing nickel affinity beads . The column was washed with the buffer containing 20 mM HEPES, pH 7.1, 1 M NaCl, 0.5 mM TCEP, 80 mM imidazole, then eluted by the buffer containing 20 mM HEPES, pH 7.1, 1 M NaCl, 0.5 mM TCEP, 250 mM imidazole. The solution was concentrated to ~1 ml and went through gel filtration on Superdex 75 10/300 increase column  equilibrated with a buffer containing 20 mM HEPES, pH 7.1, 200 mM NaCl, 0.5 mM TCEP. C/EBPα DNA binding domain containing residues 214–359 (DBDC/EBPα) was coned both into pET28a with C-terminal His-tag and pET30a with an N-terminal MBP tag (MBP-DBDC/EBPα). I295C/C357A was introduced into DBDC/EBPα for the labeling of fluorescence dye. All C/EBPα proteins were expressed and purified the same way as PU.1.The plasmids (pET28a) containing the mouse full-length PU.1 and PU.1 ETS (DNA fragments (Supplementary Data Table 1) were prepared by PCR amplification, followed by ethanol precipitation and purification using the POROS column. Briefly, The PCR products were pelleted by 75% ethanol containing 0.3 M NaAc at pH 5.2. The sample was incubated for 120 min at −20 °C, followed by centrifugation. The pellet was resuspended by TE buffer, loaded to POROS column chromatography , and washed with buffer containing 20 mM Tris-HCl, pH 7.4, 5 mM 2-mercaptoethanol. The DNA was eluted by a linear gradient of 0 to 2 M NaCl and stored at 4 °C.Purified recombinant histones in the equal stoichiometric ratio were dissolved in ~6 ml unfolding buffer  and were dialyzed against refolding buffer  for about 12 hours. The mixture was centrifuged at 20,000 × g to remove any insoluble material. Soluble octamers were purified by size fractionation on a Superdex 200 10/300 increase gel filtration column. Purified histone octamers and DNA were mixed with a 1.3:1 ratio in high-salt buffer . 1 ml mixture in a dialysis bag was placed in 600 mL of the high-salt buffer and dialyzed for 30 min followed by salt gradient dialysis. 3 L of a low-salt buffer  were gradually pumped into dialysis buffer with a flow rate of 2 ml/min for 18 h. It was then dialyzed against a low-salt buffer for 30 min in the cold room. The sample was then incubated at 37 °C for 3–5 h. The mixture was centrifuged at 20,000 × g to remove any insoluble material. The nucleosomes were further purified by ion-exchange chromatography  to remove free DNA and histones. The purified nucleosomes were dialyzed against the buffer containing 20 mM HEPES, pH 7.1, 0.5 mM TCEP.CX3CR1 nucleosome in the middle, a pUC-18 plasmid was reconstructed with the incorporation of sequentially ligated fragments of 5 × 197 bp W601 DNA, 1 × 197bp CX3CR1 DNA, and 6 × 197 bp W601 DNA  and purified by stepwise PEG 6000 precipitation. The fractions containing the 12 × 197 bp DNA was used for nucleosome array reconstitution according to early methods.45 Saturation of nucleosome in the reconstituted nucleosome array was verified by SmaI digestion, which showed a predominant mono-nucleosome band on a 1.2% agarose gel. Linker histone H1.4-bound nucleosome array was made by mixing 1.3-fold of H1.4 (relative to the molar concentration of nucleosomes in the array) with the nucleosome array in 10 mM Tris-HCl, pH 8.0, 1 mM EDTA, 1 mM DTT and 0.6 M NaCl buffer, followed by dialysis using the same buffer without NaCl.To reconstitute a 12×197 bp nucleosome array with the W601 DNA . The resCX3CR1 DNA (162 bp), 6 μM (50 μL) ScFv, and 40 μM (20 μL) PU.1 were mixed in the buffer of 20 mM HEPES, pH 7.1, 150 mM NaCl, 0.5 mM TCEP. The sample was incubated on ice for 0.5 h and then concentrated to 200 ng/ul (measured by OD260), which was loaded onto the glow-discharged holey carbon grid (Quantifoil 300 mesh Cu R1.2/1.3). For the disulfide bond mutation complex, nucleosomes containing T77CH2A and G220CPU.1 were used at the same concentration instead of wild-type nucleosomes and wild-type PU.1. DNA was elongated to 167 bp with 5 additional base pairs ‘TTCTA’ at the exit site for better PU.1 binding, and 2 mM oxidized glutathione was added to the complex solution to accelerate disulfide bond formation. For nucleosome-ScFv-PU.1-C/EBPα quaternary complex, 2 μM (50 μL) nucleosome containing mouse CX3CR1 DNA (167 bp) and T77CH2A, 6 μM (50 μL) ScFv, and 40 μM (20 μL) G220CPU.1 and 40 μM (40 μL) dimeric MBP-DBDC/EBPα were mixed in the buffer of 20 mM HEPES, pH 7.1, 200 mM NaCl, 0.5 mM TCEP. The sample was then concentrated to 100 ng/ul (measured by OD260). Holey Lacey carbon grids  were used. The grids were blotted for 3 s at 14 °C and 100% relative humidity using an FEI Vitrobot Mark IV plunger before being plunge-frozen. For the free 162bp CX3CR1 nucleosome sample, an equal volume (25 μL) for each 4 μM nucleosome was mixed with 12 μM scFv and the grids were prepared using the same parameter for the nucleosome-PU.1 complex.2 μM (50 μL) nucleosome containing mouse −/pixel/s. The total exposure time of each micrograph was 4 s fractionated into 50 frames with 0.08 s exposure time for each frame. The data collection was automated using the SerialEM software package.46 A total of 2,986 micrographs were collected for free CX3CR1 nucleosome sample, and 4,503 micrographs were collected for the wild-type nucleosome-PU.1 complex sample. 7,014 micrographs were collected for the disulfide bond mutated nucleosome- G220CPU.1 sample and 5,204 micrographs were collected for the nucleosome- G220CPU.1-MBP-DBDC/EBPα complex sample.Cryo-EM data were collected using a Titan Krios G3 electron microscope (Thermo-Fisher) operated at 300kV. Micrographs were acquired in super-resolution mode at the nominal magnification of 81,000x with 0.528 Å image pixel size using a 20-eV slit post-GIF Gatan K3 camera. The dose rate on the camera was set to 15 e48 The beam-induced image drift was corrected using MotionCor2.49 The averaged images without dose weighting were used for defocus determination using CTFFIND4.150, and images with dose weighting were used for particle picking and extraction. Particles were automatically picked using Gautomatch (https://www.mrc-lmb.cam.ac.uk/kzhang/Gautomatch/).All datasets were processed in RELION/3.1.3 and cryoSPARC v3.2 following the standard procedures.CX3CR1 nucleosome dataset. Bad particles were removed by 2D classification and 3D classification in RELION using 4x binned particles. 674,406 particles were selected and re-extracted without binning, followed by two more rounds of 3D classification using 7.5° and 3.7° angular sampling rate. 1 class containing 143,068 particles with good density of DNA was selected for auto-refine. Bayesian Polishing, followed by importing to CryoSPARC for CTF-refinement and nonuniform refinement, further improved the resolution to 2.6 Å.1,274,643 particles were picked for the free For Nuc-ScFv-PU.1 complex dataset, 2,506,660 particles were picked from 4,503 micrographs. Bad particles and free nucleosome particles were removed from 2D classification and 3D classification using 2x binned particles. 581,016 particles with one blurry DNA end were selected and re-extracted without binning. Two more rounds of 3D classification with angular sampling rate 7.5° and 3.7° were performed. one class with good density of unwrapped DNA end was selected for focused 3D classification without alignment and with a small mask only covering the unwrapped DNA part. Another two classes with blurry DNA end density were also selected for focused 3D classification without alignment. The two focused 3D classification jobs generate two classes with clearly unwrapped DNA and also the extra bulb density on the unwrapped DNA. The two classes were combined and submitted for Bayesian Polishing. After CTF-refinement and 3D-auto refinement in RELION, a 2.9 Å map was generated for model building. The PU.1 ETS domain (PDB: 1PUE) can fit into the extra density on the unwrapped DNA well.T77CH2A), scFv, G220CPU.1 complex, 3,243,708 particles were picked and submitted for 2D classification using 4x binned particles. 2,000,352 particles were selected for 3D classification using the above wild type nucleosome-scFv-PU.1 map lowpass filtered into 60 Å as the initial model. 622,795 particles with both good nucleosome density (contained one side unwrapped DNA) and also good ETSPU.1 density were selected. Particles were then re-extracted without binning and submitted to 2 more rounds of 3D classification. One class with high-resolution feature and good ETSPU.1 density were selected. Bayesian Polishing was performed, followed by importing into CryoSPARC. CTF refinement and non-uniform refinement were used to further improve the resolution to 2.7 Å.For the complex containing nucleosome (T77CH2A)-scFv- G220CPU.1-MBP-DBDC/EBPα complex dataset, 2,888,287 particles were picked, and 1,411,125 particles were selected after 2D classification using 4x binned particles. 3D classification using the above nucleosome (T77CH2A)-scFv- G220CPU.1 lowpass filtered to 60 Å as the initial model generated a class with good nucleosome and PU.1 density. 468,250 particles in this class were then re-extracted without binning, and two more rounds of 3D classification were performed. 1 class with good PU.1 density and clearly unwrapped entry site DNA density was selected for 3D auto-refine, generating a 3.9 Å map with 116,597 particles. Focused refinement with mask only covering the nucleosome core and PU.1, excluding the unwrapped entry site DNA, generated a 2.8 Å map. The focused 3D classification without alignment and with mask only covering the unwrapped entry site DNA generated three classes all around 4.1 Å. For these 3 classes, the entry site DNA was all unwrapped.For the nucleosome . The model was fitted into the cryo-EM density map of the CX3CR1 nucleosome-scFv complex. The DNA sequence was built into the map from scratch in COOT51 and the histone octamer and scFv were optimized by manual rebuilding. The whole complex was refined using real-space refinement in PHENIX.52 For the nucleosome-scFv-PU.1 complex, the free CX3CR1 nucleosome-scFv was used as the initial model. Histone octamer and scFv were fitted into the map and manually rebuilt in COOT, and DNA was built in COOT. The model was refined using real-space refinement in PHENIX. ETSPU.1 from the crystal structure (PDB: 1PUE) was rigid-body fitted into the density on the unwrapped DNA. The side chains including I217 and Q218 were adjusted based on the interaction with H2A. For the nucleosome (T77CH2A)-scFv- G220CPU.1 complex, the nucleosome-scFv-PU.1 was used as the initial model. The whole model was rigid-body fitted into the map, and both proteins and DNA were manual rebuilt in COOT. The model was further optimized using real space refinement in PHENIX. For the nucleosome (T77CH2A)-scFv- G220CPU.1-MBP-DBDC/EBPα complex, the nucleosome-scFv-PU.1 structure was used as the initial model. Histone octamer, PU.1 and scFv were fitted into the map, and DNA was built in COOT. The structure was optimized by manually rebuilding in COOT, followed by further refinement using real-space refinement in PHENIX. C/EBPα model from the structure (PDB 1NWQ) was rigid-body fitted into the extra density on the unwrapped entry site DNA. All the figures and movies were made using UCSF Chimera53 and PyMOL .For the free n/(Kdapp + [L]n). Here, θ is the fraction of total nucleosome bound to PU.1 or C/EBPα . [L] is the total concentration of corresponding pioneer factors. Kdapp is the apparent binding constant. n is the Hill coefficient.Nucleosomes or free DNA at a final concentration of 0.5 μM were mixed with purified proteins at different concentrations. Typical binding reactions were carried out for 30 min at room temperature in buffer containing 20 mM HEPES, pH 7.3, 150 mM NaCl, and 0.5 mM TCEP. Six μl of the binding reactions were analyzed on 4% or 5 % acrylamide gels in 0.2 x TBE at 120 V for 60 minutes at 4 °C. After electrophoresis, gels were stained with ethidium bromide (EtBr) and quantified using ImageJ. For the apparent binding affinity measurements, we quantified band intensities using ImageJ, subtracted against the background and normalized to the signal of the input free nucleosome. We used Prism (GraphPad) to fit the binding data with the Hill equation: θ = [L]CX3CR1 nucleosome (Table S2) was used in this assay. 1000 ng nucleosome was mixed with PU.1 at different concentrations in 18.5 μl reaction system in buffer 20 mM HEPES, pH 7.1, 100 mM NaCl and 0.5 mM TCEP. After 20 min incubation at room temperature, 1 μl Cutsmart buffer and 1 U Sau96I (New England Biolabs) were added into the system. The mixture was placed into 37 °C incubator for 20 min. Purple gel loading dye (New England Biolabs) was added to stop the enzyme digestion reaction. Then 1 μl proteinase K (New England Biolabs) was used at 50 °C for 1 hour to digest PU.1 and histones. 4 μl of the digestion products were analyzed on 5 % acrylamide gels in 0.2 × TBE at 120 V for 60 minutes at 4 °C. After electrophoresis, gels were stained with ethidium bromide (EtBr) and quantified using ImageJ. Three independent experiments were performed. Microsoft Excel and Prism were used to generate the figures.180bp native G220CPU.1, MBP-DBDC/EBPα containing I295C and K26CH1.4 was labeled with Cy5 following the manufacture’s protocol (Cytiva). 1 mg target protein was dissolved in 1 mL degassed buffer containing 20 mM HEPES, pH 7.1, 400 mM NaCl and 1 mM TCEP. One vial of Cy5 maleimide was dissolved in dimethylformamide (DMF) and mixed with target protein. The mixture was agitated overnight at cold room. Size-exclusive chromatography was used to separate the free Cy5 dye. L116CH2A was labeled with Cy3 according to the previous publication.54 1 mg L116CH2A was dissolved in 1 mL degassed buffer containing 800 mM HEPES, pH 7.1, 1.5 mM Guanidine HCl, 1 mM TCEP. 1vial Cy3 maleimide  in DMF was mixed with L116CH2A and incubated at room temperature for 5 hours. A Sephadex G-25 column was used to separate the free Cy5 dye. Labeled L116CH2A was refolded to octamer following the same protocol with unlabeled histones.MBP-DBDC/EBPα was titrated into 200 nM nucleosome in buffer 20 mM HEPES, pH 7.1, 100mM NaCl, 0.5mM TCEP. For the DNA repositioning assay, PU.1 was titrated into 200 nM nucleosome in buffer 20 mM HEPES, pH 7.1, 150mM NaCl or 20 mM HEPES, pH 7.1, 140mM KCl at both room temperature (20 °C) and low temperature (4 °C). For the binding of C/EBPα to 162bp CX3CR1 nucleosome, Cy5 labeled C/EBPα was titrated into 200 nM Cy3 labeled nucleosome (Cy3 on nucleotide 19) in buffer 20 mM HEPES, pH 7.1, 100mM NaCl, 0.5mM TCEP without or with 800 nM unlabeled PU.1. For the binding of PU.1 to 162bp nucleosome, Cy5 labelled PU.1 was titrated into 200 nM Cy3 labeled nucleosome (Cy3 on nucleotide 162) without or with 2 μM C/EBPα. In H1 eviction FRET assay, Cy5 labeled K26CH1.4 was mixed with nucleosome containing Cy3 labeled H2A at a ratio of 1.3:1 before adding PU.1, Q218HPU.1 and MBP-DBDC/EBPα. The fluorescence intensity was recorded using QuantaMaster from Photon Technology International. The excitation wavelength was set to 510 nm, and emission spectra were collected between 530nm ~ 730nm. Three independent experiments were performed.Fluorescent DNA fragments were produced using PCR by the Cy3 or Cy5 labeled primers (IDT). For the unwrapping assay, PU.1 or DBDC/EBPα with a molar ratio to the nucleosome array ranging from 0:1 to 16:1, respectively, in digestion buffer  at room temperature. 10 units of restriction enzyme XhoI (NEB) were added to the nucleosome array with and without PU.1. 5 units of restriction enzyme EcoRI (NEB) were added to the nucleosome array in the absence and presence of DBDC/EBPα. Samples were incubated at 37 °C for 30 min, and the enzyme was inactivated by NEB purple loading dye. Samples were then incubated with proteinase K at 50 °C for 60 min. After centrifugation, the top solution was harvested and loaded into a 1 % agarose gel stained with SYBR Safe dye (Invitrogen). Electrophoresis was performed at 130 V in 1 × TBE buffer for 25 min. Band intensities for the digestion product and input were measured using ImageJ. The relative digestion efficiency was calculated using the intensity of the product in the presence of transcription factors divided by the product intensity without transcription factors.3 mg wild-type CX3CR1 nucleosome array or mutated nucleosome array or 601 nucleosome array in 20 μL was mixed with PU.1 or


The characterization of nanocomposites included their morphological, structural, and thermal properties, achieved using SEM, XRD, and TGA, respectively. The shielding properties for all synthesized samples including pristine PMMA were measured with gamma spectrometry using a NaI (Tl) scintillator detector spanning a wide range of energies and using different radioisotopes, namely Am-241 (59.6 keV), Co-57 (122.2 keV), Ra-226 (242.0), Ba-133 (80.99 and 356.02 keV), Cs-137 (661.6 keV), and Co-60 (1173.2 and 1332.5 keV). A substantial increase in the mass attenuation coefficients was obtained at low and medium energies as the filler weight percentage increased, with minor variations at higher gamma energies (1173 and 1332 keV). The mass attenuation coefficient decreased with increasing energy except under 122 keV gamma rays due to the K-absorption edge of bismuth (90.5 keV). At 40% loading of Bi2O3, the mass attenuation coefficient for the cesium 137Cs gamma line at 662 keV reached the corresponding value for the toxic heavy element lead. The synthesized PMMA-Bi2O3 nanocomposites proved to be highly effective, lead-free, safe, and lightweight shielding materials for X- and gamma rays within a wide energy range (<59 keV to 1332 keV), making them of interest for healthcare applications.Polymer composites were synthesized via melt mixing for radiation shielding in the healthcare sector. A polymethyl-methacrylate (PMMA) matrix was filled with Bi The contribution to the attenuation is mainly from photoelectric effect, Compton scattering, and pair production at energies greater than the threshold energy of 1.022 MeV. The cross section of each interaction and its contribution to the total attenuation coefficient depends on the photon energies, the atomic numbers (Z) (of constituents of mixtures or compounds), and the density of the material. The linear attenuation coefficient decreases with increasing photon energy except at K-edges where an abrupt increase occurs in the photoelectric cross section. It is worth noting that the K-absorption edge of bismuth (at 90.5 keV with Z = 83) is slightly above that of lead (at 88.0 keV with Z = 82). The photoelectric effect has an absorption cross section that strongly depends on E and Z number (of the absorbing medium) as σpe~Z4/E3.5 [2. Therefore, it is insignificant in our current study of 60 keV–1332 keV energy range.In terms of μ~Z4/E3.5 . Therefo241Am (59 keV), 57Co (122.2 keV), 226Ra (242.0 keV), 133Ba (80.99 and 356.02 keV), 137Cs (661.6 keV), and 60Co . The distance between the detector entrance and radioactive source was ~40 cm. In the narrow beam transmission experiment, the incident and transmitted intensities were determined by the net area under relevant photo peaks, i.e., region of interest (ROI). The obtained results were then fitted to Beer–Lambert’s law to extract the linear and mass attenuation coefficients. The measurement of mass attenuation coefficients was performed using a complete gamma-ray spectrometry system with personal computer (PC)-based multichannel analyzer (MCA). A 2.5″ × 2.5″ NaI (Tl) scintillation detector with 7.2% resolution at the Cesium-137 line (662 keV) was used in a narrow beam (good) geometry set up with a lead collimator around the source and a lead shield around the detector entrance to eliminate backscattered radiation as shown in 2O3 nanocomposites for 0%, 10%, 20%, 30%, and 40% filler loadings. A good dispersion of the Bi2O3 nanofiller within the PMMA matrix with increasing concentrations by increasing the filler weight percentage was achieved. A close look at the SEM images shows that the claimed particle size 90 to 210 nm of the purchased nanopowder is indeed verified overall with the exception of a few agglomerations (with diameters ~400 to 600 nm). There was no contamination in all samples, as shown in the Energy-Dispersive Spectroscopy (EDS) images provided in the 2O3 nanocomposites for 0%, 10%, 20%, 30%, and 40% filler loadings. The XRD pattern of the used matrix, i.e., PMMA sample (0% Bi2O3 blue plot), indicates its amorphous nature with a broad hump diffraction peak centered at 2θ = 18.84°. A similar value of 2θ = 19.12° was reported by Abasi et al. [2O3 nanoparticles at different loading % led to XRD patterns with well-defined peaks with the prominent ones at 25.35°, 26.82°, 28.02°, 30.41°, 31.33°, 31.87°, 32.76°, 44.27°, 44.8°, 46.30°, 46.4°, 46.99°, 46.99°, 51.9°, 53.02°, 54.5°, and 55.54°, and others with less intensity at higher diffraction angles. As loading with the Bi2O3 filler increased, the broad hump attributed to pristine PMMA diminished considerably. At 40% loading, the PMMA hump almost disappeared completely.i et al. . Filling2O3 and monoclinic α-Bi2O3 with some interferences. Different crystallographic cards were assigned to Bi2O3 by different authors [2O3 that is well defined at 2θ = 28.02° in this study is in agreement with reported values of 27.94°, 27.80°, and 27.92°, respectively, by [2O3 crystal structure [2O3 is well defined at 2θ = 26.83° in this study and is assigned to the (111) reflection plane. It is in agreement with the reported value of 26.92 by Hou et al., who synthesized α-β phase heterojunction on Bi2O3 nanowires and therefore obtained XRD spectra comprising both phases [The obtained complex spectra may indicate the presence of two phases: tetragonal β-Bi authors ,24,37,38vely, by ,37,38. Itructure . In addi2O3 (PDF NO. 4-294) dominated over the tetragonal β-Bi2O3 phase (PDF NO. 18-244). It is worth mentioning that there are six polymorphic forms of Bi2O3 reported by researchers, which include monoclinic (α-Bi2O3), tetragonal (β-Bi2O3), cubic body-centered (γ-Bi2O3), cubic face-centered (δ-Bi2O3), orthorhombic (ε-Bi2O3), and triclinic (ω-Bi2O3) phases [2O3 loadings. The average crystallite size derived from the two strongest peaks (with “similar” intensities) was 26 nm, ranging from 24 nm to 27 nm.They reported that when the hydrothermal temperature was increased above 150°, the α-phase appeared in addition to the β-phase. At higher temperatures, 180–240°, the monoclinic α-Bi) phases . Table 12O3 and monoclinic α-Bi2O3 phases and their interferences may have affected the computed values to some extent. The separated XRD spectra for different loadings are given in the The presence of both tetragonal β-Bi2O3 nanocomposites for different filler loadings. 2O3 loadings, respectively, within experimental errors. This may indicate a good uniform dispersion of Bi2O3 nanoparticles into the polymer matrix. In addition, a gradual shift in the extrapolated onset temperature toward lower temperature values is noticed, as shown in 2O3 in our case) is increased, as reported by other authors [Thermogravimetric analysis was performed between 25 and 600 °C to investigate the thermal stability of synthesized nanocomposites.  authors ,24. High2O3) into the PMMA polymer matrix considerably enhanced the shielding properties of the composite. Shielding properties are best described by the mass attenuation coefficient of the absorbing material. The incorporation of a high-Z element . At high energy (~1 MeV), the Compton effect dominates with μm becoming almost constant for all elements independent of the atomic number Z of the absorbing material, except hydrogen (Z/A = 1). Pair production is insignificant in our measured energy range of interest, 60 to 1332 keV. At 40% loading of Bi2O3 nanocomposites, the mass attenuation coefficient is found to decrease with increasing photon energy except near the K-absorption edge of bismuth at 90.5 keV, where an abrupt increase occurs due to the photoelectric cross section. This is well demonstrated by the increase in the mass attenuation coefficient at 122 keV energy above that of the nearby 81 keV measured energy. For the sake of clarity, we deliberately performed the XCOM simulation based on the NIST database for the PMMA-Bi2O3 mixture for 0%, 10%, 20%, 30%, and 40% filler loadings [It is worth mentioning that our measured values for pristine PMMA are similar to those obtained by Manjunatha, within the evaluated error of 2–3% using Equation (12) in his paper . He usedloadings . The ploloadings . The rea2O3 nanocomposites for the energy range (81–662 keV) are compared to their corresponding ones (XCOM-derived) for lead, steel, and baryte as shown in 2O3, the mass attenuation coefficient for the cesium gamma line at 662 keV has reached the corresponding value for the toxic heavy element lead (0.104 g/cm2) and has surpassed it at 40% loading by 10%.However, at higher energies (1173 and 1332 keV), the Compton effect is dominant and the variations in the mass attenuation coefficient become minor. Finally, the mass attenuation coefficients obtained for synthesized PMMA-Bi2/g compared to lead, steel, and PMMA-Bi2O3 at 40% loading, with values of 4.738, 1.164, and 2.603 cm2/g, respectively.For the lowest measured energy at 59 keV, the mass attenuation coefficient is highest for barite with a value of 5.171 cm2O3 nanocomposites to be a very effective and efficient alternative for radiation shielding in the health sector for the whole studied energy range (<59 keV to 1332 keV). It is worth noting that theoretical XCOM-based simulations for computing the mass absorption coefficient for different mixtures and compounds do not take into account the filler size, density, and dispersion uniformity in the matrix. MNCPX simulations performed by Tekin et al. on concrete filled with WO3 nanoparticles showed that they have better shielding properties than their micro counterparts for the same fillers and same loadings [2O3 loadings, for all measured energies, are shown in In view of the toxicity and heaviness of lead, we consider PMMA-Biloadings . The exppe~Z4/E3.5 [2O3 polymeric composites are very efficient at lower energies as reported elsewhere [HVL is defined as the thickness of shielding material required to attenuate the incident photon intensity by half . ~Z4/E3.5 . In addilsewhere ,27.To gain more insight on the importance of the acquired results, the thickness required for an attenuation of 75% or 90% of the incident photons is computed for the low-energy portion due its wide use in shielding as derived from Equation (2) :(5)x=−1μThe results are plotted in Furthermore, let us consider, for example, the Co-57 gamma line at 122 keV, which corresponds approximately to the effective energy of a computed tomography (CT) X-ray tube at 150 kV. Thicknesses of 6.8 mm or 11.3 mm are required for 75% or 90% attenuations, respectively. Again, this is a very good result for such a relatively high X-ray tube voltage and attenuation percentage. It is worth noting that usually sheets of shielding barriers are manufactured with specified thicknesses. They can be superposed to fulfill higher thickness requirements for different diagnostic and therapeutic facilities.Finally, the previous analysis can be carried out equivalently in terms of the radiation protection efficiency (RPE) defined as follows :(6)RPE=(Using Equation (2), we obtain RPE as a function of thickness x and linear attenuation coefficient, which is energy- and shielding-material-dependent:2O3 nanocomposites, for the same photon energies at 59, 81, 122, and 242 keV, as before. The pure PMMA showed clearly low shielding abilities. RPE is less than 9% and 17% for 5 mm and 10 mm thicknesses, respectively, in all cases. At 40% loading and a thickness of 5 mm, RPE reached 86% and 64% for 59 keV and 122 keV photons. At a thickness of 10 mm (two superposed sheets of 5 mm for example), RPE jumped to 98% and 87%, respectively. Both results for the 5 mm and 10 mm thicknesses are very promising.2O3 nanocomposites were synthesized by the melt-mixing method and characterized by SEM, XRD, and TGA to study their morphological, structural, and thermal properties. SEM analysis showed a good homogeneity in the dispersion of Bi2O3 nanoparticles in the PMMA matrix with increased concentrations as filler loadings increased. This was supported by TGA analysis, which showed very smooth thermograms for all synthesized composites ending up with a residual weight at 600 °C in accordance with the initial loadings within experimental errors. Structural analysis with XRD showed the presence of both tetragonal (β-Bi2O3) and monoclinic (α-Bi2O3) phases in all nanocomposites synthesized by the melt-mixing method at 220 °C. Gamma spectrometry measurements showed that the mass absorption coefficient (at low and medium energies) increased with filler loadings (and density) and decreased with energy, except near the K-absorption edge of bismuth, where an abrupt increase occurs. At 30% loading of Bi2O3, the mass attenuation coefficient for the cesium gamma line at 662 keV reached the corresponding value for the toxic heavy element lead and surpassed it at 40% by 10%. Finally, the main objective of the study was achieved successfully. The synthesized PMMA- Bi2O3 nanocomposites have proven to be very effective, safe, and lightweight shielding materials for a wide range of photon energies from <60 keV to 1332 keV as applied to the medical field  and to other radiation fields as well.This study aimed at synthesizing a convenient safe polymeric nanocomposite for gamma radiation shielding in the medical sector principally. PMMA-Bi


Its surface morphology and composition were characterized by scanning electron microscopy (SEM) and X-ray photo spectroscopy (XPS), and its H2O2 sensing performances include catalytic reduction and quantitative detection were studied with electrochemical methods. Our sensor had a high sensitivity of 174.5 μA mM−1 cm−2 (R2 = 0.9978) in an extremely wide range of concentrations from 10 μM to 100 mM, a fast response (about 5 s) and a low limit of detection (S/N = 3) of 2.13 μM. The sensor exhibits outstanding selectivity in the presence of various biological interference, such as dopamine, ascorbic acid, uric acid, citric acid, etc. In addition, the constructed sensor continued 95% current responsiveness after 1 month of storage further points to its long-term stability. Last but not least, it has a good recovery rate (90.12–102.00%) in milk sold on the open market, indicating that it has broad application possibilities in the food industry and biological medicine.In this paper, a novel composite is constructed as a non-enzymatic hydrogen peroxide (H H2O2 is not only one of the by-products of many classical enzymatic reactions, such as glucose oxidation, uric acid oxidation, oxalic acid oxidation, amino acid oxidation, glutamic acid, lysine oxidation, etc.2, but also plays a significant role as the primary messenger molecule in the cellular and redox metabolism3. It is worth noting that H2O2 has strong oxidizability, ingesting residual H2O2 in food will consume antioxidant substances in the body, accelerate the aging process of the human body, and reduce the resistance after ingestion. Excessive H2O2 in the body will produce a large number of OH·, which participates electron transfer and hydroxylation reaction in biochemical process, damage cells, induce gene mutation and various diseases, even cause human cell canceration4. In 2017, the list of carcinogens was announced by International Agency for Research on Cancer of the World Health Organization, and H2O2 appeared in the list of Class III carcinogens5. At present, it has been detected in the market that excessive amounts of H2O2 residues exist in prepackaged milk, beverages, soy products, aquatic products, chicken feet, etc., posing a serious threat to human health. Therefore, the newly revised National Food Safety Standard in China (GB 2760-2014) stipulates that H2O2 can be used as a food processing aid in various food processing processes, and the residual amount does not need to be limited, but it needs to be removed from the finished product. The Food and Drug Administration (FDA) requires H2O2 to be used as an antimicrobial agent in milk, with a residual amount not exceeding 0.05 wt% in 21 CFR 184.1366. In addition, it is also stipulated that H2O2 solution should be used in the sterilization of food packaging materials, and the residual amount of H2O2 in distilled water after packaging should be less than 0.5 parts per million (testing should be conducted immediately after packaging) in 21 CFR 178.1005. Therefore, sensitive detection of H2O2 is crucial for monitoring the quality of food and for applications of clinical, and biomedical.H2O2 include titration, spectroscopy, chromatography, chemiluminescence and electrochemical methods6. The Chinese national standard GB 5009. 226-2016 stipulates that the determination methods for H2O2 in food residues are iodometry and titanium salt colorimetry. The quantitative limit of the above two methods is 3 mg kg−1. These two methods are cumbersome, time-consuming, poor selectivity, and low accuracy, making it difficult to achieve trace detection. However, electrochemical method has the advantages of rapid response, rapid response, high-cost efficiency, simple operation, high selectivity and high sensitivity7. The first generation electrochemical H2O2 detector relies on the reaction of enzyme with hydrogen peroxide. This enzyme-based technology has been mature and can now provide high sensitivity, high selectivity and low background noise8. Nevertheless, the complex process of immobilizing the enzyme on the electrode, strict conditions to maintain the enzyme activity, and the lack of long-term stability and reproducibility limit the application of this technology. More importantly, almost all enzymes are made of proteins, which will hinder the electrochemical reaction on the surface of electrode9. Therefore, non-enzymatic electrochemical H2O2 detection have been developed to eliminate these shortcomings due to its faster and more effective electron transport10.Nowadays, the methods used in the detection of H2O2 sensors generally prepared by precious metal nanoparticles (NPs) include Au, Ag, Pt and Pd NPs11, As a precious metal, Ag NPs have large specific surface area, good stability, good biocompatibility, excellent conductivity and electrocatalytic activity12. It is reported that Tran et al. have successfully developed a series of electrochemical sensors based on AgNPs for sensitive detection for glucose and H2O215. But expensive cost, poor tolerance immensely limits their mercantile application. Consequently, it is urgent to develop low-cost, reliable and sensitive H2O2 electrochemical sensing materials. So far, Co3O4, Fe3O4, Cu2O, MnO2 have been successfully applied in H2O2 electrochemical sensors16. CuO and Cu2O have also been developed to prepare H2O2 sensors, which are inexpensive and strong stability, but with low sensitivity and narrow linear detection range. However, metal NPs have limited catalytic ability, because they are easily oxidized, and aggregative owing to the existence of van der Waals force between NPs17. In order to improve this problem, a suitable carrier is needed. At present, the substrates that have been widely studied are usually carbon materials, including ordered mesoporous carbon, carbon nanotubes, carbon nanofibers and graphene18. Among them, graphene has high specific surface area, good thermal stability, good conductivity, stability and high electron transfer ability, and its surface defects can anchor metal NPs, so it is an excellent carrier material19. Most of the existing related studies use graphene oxide prepared by Hummer’s method as carbon substrate to prepare metal nanoparticle composites. The preparation process is complex, and the distribution position and size of metal particles are uneven, which affects the sensing performance of the composites20. The liquid phase exfoliated method is low-cost, simple and controllable, green and environmentally friendly, and easy to large-scale production. It has been studied for use in Cd2+ and Pb2+ sensors, as well as flavomycin sensors21.Enzyme-free HxO/Ag@FLG composite by a simple ultrasonic exfoliation method for the first time. After a series of characterization, the morphology and structure of the composite were studied and modified on a glassy carbon electrode (GCE) to explore the detection of H2O2 performance. Compared with the reported Ag, CuO or Cu2O NPs for H2O2 sensors, the CuxO/Ag@FLG/GCE H2O2 electrochemical sensor has the advantages of simple preparation, low cost and stable physicochemical properties. Our electrochemical experiments show the prepared sensor displays wide linear range, high sensitivity and selectivity toward the reduction of H2O2 with a low detection, and we also demonstrate it is successfully used to detect the concentration of H2O2 in milk. This study would offer a new routine for developing graphene-based electrochemical sensors for detecting H2O2.In this work, we have used water-in-oil emulsion as a stabilizing system to synthesis Cu3·H2O purchased from Shanghai Yien Chemical Technology Co., Ltd , cyclohexane were purchased from Guangzhou Chemical Reagent Factory , Span 80 was purchased from Shanghai yuanye Bio-Technology Co., Ltd , ethanol, CuSO4·5H2O, AgNO3, NaBH4, NaCl, FeCl3, glucose (Glu) and CaCl2 were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd , MgCl2 were purchased from Damao Chemical Reagent Factory , hydrogen peroxide(H2O2) was purchased from Jiangsu Qiangsheng functional Chemistry Co., Ltd , Ltd , glycine (Gly), lysine (Lys) were purchased from Nine-Dinn Chemistry Co., Ltd. , dopamine (DA), uric acid (UA), citric acid (CA), lactic acid (LA), arginine (Arg), valine were purchased from Shanghai McLean Biochemical Technology Co., Ltd , polyvinylpyrrolidone k30 (PVP k30) was purchased from Shanghai bide Pharmaceutical Technology Co., Ltd .Graphite was purchased from Sinopharm Chemical Reagent Co.,Ltd , Tween 80, NH4 in 2 wt% PVP solution, 3 g Tween 80, 4 g Span 80, 5 mL anhydrous ethanol are added into 30 mL cyclohexane, stable emulsion can be formed through vortex mixing. Then, ultrasonic unit is used to exfoliate the above solution for 2 h, with 40 kHz ultrasonic power. After that, 0.057 g NaBH4 is added into the emulsion above and exfoliate the above solution for 2 h. Finally, the solid were carefully collected by filter to obtain CuxO@FLG.0.4 g graphite powder, 5 mL 3 wt% CuSOxO@FLG, 5 ml 3 wt% AgNO3 in 2 wt% PVP and 20% NH3·H2O mixing solution, 3 g Tween 80, 4 g Span 80, 5 mL anhydrous ethanol are added into 30 mL cyclohexane, stable emulsion can be formed through vortex mixing. Then, ultrasonic cleaner is used to exfoliate the above solution for 2 h. At the end, the solid were carefully collected by filter to obtain CuxO/Ag@FLG.0.4 g Cu−1 of well-dispersed CuxO/Ag@FLG solution (include 0.05 wt% Chitosan and 0.5% acetic acid) was dropped to the washed GCE and dried under an infrared drying lamp for 10 min to prepare CuxO/Ag@FLG/GCE. For comparison, we prepared CuxO@FLG/GCE and Ag@FLG/GCE using the same method.Before modification, bare GCE was polished with 0.05 μm alumina powder and ultrasonically cleaned with ethanol and water for 5 min. 5 μL of 1 mg mL2O2 within a time interval of 40 s.JSM-7610F PLUS scanning electron microscope , H-7650 transmission electron microscope , D/max-2200/PC X-ray diffractometer  and ESCALAB 250 X-ray Photoelectron Spectroscopy  were used to characterize the surface morphology and structure. Cyclic Voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Chronoamperometry (i–t) were determined by the CHI660E electrochemical workstation . Electrolyte was consisting of phosphoric acid buffer solution, the working electrode was modified GCE, the counter electrode was platinum sheet, the reference electrode was saturated calomel electrode (SCE). The i–t test was performed by adding HxO/Ag@FLG/GCE sensor are summarized in Fig. xO nanosheet supported on the surface of crumble layers of exfoliated graphene. Furthermore, EDS images shown in Fig. xO/Ag@FLG, which is conducive to the rapid transfer and conduction of electrons, so as to detect target analytes sensitively.The construction and detection principles of the CuxO/Ag@FLG investigated by TEM. As shown in Fig. 2O (JCPDS no. 74-1230). The lattice spacing of 0.254 nm corresponds to the (111) crystal plane of Ag0 (JCPDS no. 04-0783) . Other peaks at 42.33° and 53.54° respectively arise from (200) plane of Cu2O and (020) plane of CuO (JCPDS no. 74-1230 and JCPDS no. 45-0937).As a supplement, the micromorphologies and microstructures of synthetic CuxO/Ag@FLG nanocomposites were analyzed by XPS. The full scan XPS spectra of CuxO/Ag@FLG showed signals corresponding to C 1s, O 1s, Cu 2p and Ag 3d , which illustrates its excellent electron transport ability owing to the large surface area and the potential synergism of the nanocomposites. Figure p) of GCE, CuxO@FLG/GCE, Ag@FLG/GCE and CuxO/Ag@FLG/GCE are 265, 332, 429 and 221 mV respectively, indicating CuxO/Ag@FLG can promote the electron transfer on the electrode surface to the most extent. The peak current of CuxO/Ag@FLG/GCE is the largest, which is 3.98 times of GCE, 2.58 times of CuxO@FLG/GCE and 1.55 times of Ag@FLG/GCE. It is clear that Ag@FLG/GCE has a larger peak current of redox peaks of [Fe(CN)6]3−/4− couple, suggesting that the electrochemical probe of [Fe(CN)6]3−/4− has good electron transfer at Ag@FLG/GCE due to its excellent electronic conductivity. However, on CuxO@FLG/GCE, the redox peaks current of [Fe(CN)6]3−/4− are much smaller, suggesting that the material of CuxO@FLG is less effective for the electron transfer of the [Fe(CN)6]3−/4− because of its inferior conductivity. It is interesting that when the CuxO/Ag@FLG/GCE electrode was applied, the redox peak current was enhanced much more comparison with Ag@FLG, showing that the CuxO/Ag@FLG/GCE nanocomposite has better performance for electron transfer of electrochemical probe than the single-component of Ag@FLG or CuxO@FLG. Comparison histograms of Rct, ΔEp and peak current (Ip) of different electrodes are shown in Fig. As depicted in Fig. 2O2 by the synthesized composite was studied using CV method. Therefore, the CV curves are shown in Fig. 2-saturated 0.01 M PBS contained 4 mM H2O2 at a scan rate of 50 mV s–1. The reduction peak current enhancement of CuxO@FLG/GCE is extremely weak  in 0.01 M PBS (pH 7.4) contained 4 mM H2O2 were investigated  was fitted as 0.9803, which indicates that the diffusion-controlled electrochemical process   2O2 elec2O2 were optimized which include volume of catalyst ink, pH of supporting electrolyte and applied potential. The response current is the largest when the volume of ink was 5 µL , i–t curve was plotted for CuxO/Ag@FLG/GCE as H2O2 was added every 40 s  − 13.963, R2 = 0.9978, the detection limit is 2.13 μM (S/N = 3), and the sensitivity is 174.5 μA mM−1 cm−2. These are attributed to the large specific surface area of graphene sheet and the synergistic effect of graphene, CuxO and Ag NPs in reducing H2O2 and amplifying signal.Under the best conditions  of current response in the same concentration of H2O2 was 3.69%, which presents a good repeatability , low detection limit (2.13 μM), high sensitivity (174.5 μA mM−1 cm−2) and long-term stability. In addition, the prepared sensor can detect H2O2 in milk samples, which makes it possible for quality control in food industry, suggesting that as-synthetic CuxO/Ag@FLG has a broad application prospect in electrochemical sensors.To summaries, CuSupplementary Information.


The bulk of the tert-butyl substituentsand the smaller radii of gadolinium, terbium, and dysprosium precludeformation of the side-on dinitrogen bonding mode on steric grounds.Elongation of the nitrogen-nitrogen bond relative to N2 is observed in M1, and their Raman spectrashow a major absorption consistent with N=N double bonds. Computationalanalysis of Gd1 identifies that the localsymmetry of the metallocene units lifts the degeneracy of two 5dπ orbitals, leading to differing overlap with the π*orbitals of [N2]2–, a consequence ofwhich is that the dinitrogen ligand occupies a singlet ground state.Magnetic measurements reveal antiferromagnetic exchange in M1 and single-molecule magnet (SMM) behavior in Dy1. Ab initio calculations show that the magneticeasy axis in the ground doublets of Tb1 and Dy1 align with the {M–N=N–M}connectivity, in contrast to the usual scenario in dysprosium metalloceneSMMs, where the axis passes through the cyclopentadienyl ligands.The [N2]2– ligands in M1 allow these compounds to be regarded as two-electron reducingagents, serving as synthons for divalent gadolinium, terbium, anddysprosium. Proof of principle for this concept is obtained in thereactions of M1 with 2,2′-bipyridyl(bipy) to give [Cp2tttM(κ2-bipy)] , in which the lanthanide is ligated by a bipy radicalanion, with strong metal–ligand direct exchange coupling.High-yield syntheses of the lanthanide dinitrogen complexes[(Cp The delicate energeticbalance between the two coordination modes of [N2]2– was underscored by the neodymium congener, whichforms as [{(N″)2Nd}2]2– below −90 °C and convertsinto the side-on version [{(N″)2Nd}2(μ-η2:η2-N2)]2– inthe solid-state at higher temperatures.22To date, examples of pure end-on dinitrogen-bridgedrare-earthcomplexes are limited to the bulky amido-ligated anions [{(N″)2]2– and its S = 1/2 radical [N2]3– derivative.23 Wewere motivated to target end-on dinitrogen-bridged lanthanide metallocenesto gain insight into how {Cp2Ln} fragments influence theelectronic structure of the μ-1,2-N2 ligand and phenomenasuch as magnetic exchange interactions and slow magnetic relaxation.Furthermore, by regarding the [N2]2– ligandas a two-electron reservoir, the dinitrogen complexes themselves mightalso serve as surrogate divalent reducing agents for lanthanides thatdo not readily form the oxidation state +2, allowing them to be usedin the synthesis of lanthanide complexes of molecular magnets withradical ligands.The end-on bonding mode of dinitrogen has hitherto not beenobservedin lanthanide metallocene chemistry, whereas lanthanide metalloceneswith side-on bridging dinitrogen are known with [N2tttM)2]  by reduction of [Cp2tttM(κ2-BH4)] withan excess of potassium graphite under an atmosphere of dinitrogenat room temperature. Combined with the relatively small radii of thelanthanide M3+ cations, the bulky cyclopentadienyl ligandCpttt was selected assuming that the tert-butyl substituents would hinder close approach of the two metalloceneunits, discouraging formation of the side-on dinitrogen coordinationmode and encouraging formation of the end-on mode. The target compounds Gd1, Tb1, and Dy1 were isolated in yields of 87, 83, and 84%, respectively,based on the lanthanide according to Our strategy focused on synthesizing  to divalent [Cp2tttM], which then rapidly activates N2 by electron transfer. The formation of divalent lanthanide intermediatesis reasonable given the similarities between our reaction conditionsand those used to prepare other, related divalent lanthanide metallocenes.25 Attempts at isolating the putative[Cp2tttM] complexeswere made by conducting the KC8 reductions under an atmosphereof argon; however, the dinitrogen complexes M1 still form even under these conditions, implying that the divalentmetallocenes are sufficiently reactive to scavenge trace N2 from the high-purity argon.In synthesizing M1 were determinedby single-crystal X-ray diffraction measurements . The three complexes are isostructural,forming as centrosymmetric molecules with two {Cp2tttM} units bridged by an end-ondinitrogen ligand, and with the inversion center coinciding with themidpoint of the N=N bond. The resulting {M–N=N}connectivities are essentially linear at 179.0(3)°, 179.6(3)°,and 179.3(5)° for Gd1, Tb1, and Dy1, respectively. Consistentwith the gradual decrease in ionic radius of the M3+ cations,the M–N distances decrease from 2.325(4) Å in Gd1 to 2.296(4) Å in Tb1 and 2.268(7) Å in Dy1. Concomitantly,the N=N distances increase across the series, being 1.130(8),1.175(8), and 1.215(13) Å for Gd1, Tb1, and Dy1, respectively.The trend in M–N distances, combined with the apparent flexibilityof the N=N bond, produces similar M···M separationsof 5.7791(9), 5.7659(9), and 5.7500(9) Å for Gd1, Tb1, and Dy1, respectively. Other pertinent geometric parameters include M–Cpttt distances of 2.4370(16) and 2.4399(17) Å for Gd1, 2.4146(19) and 2.419(2) Å for Tb1, and 2.405(3) and 2.406(3) Å for Dy1, with associated Cpttt–M–Cpttt angles of 144.63(8)°, 143.96(9)°, and 143.86(13)°,respectively.The molecular structures of 2 to give M1. The extent to which the N2 bond lengthensis, evidently, dependent on the lanthanide, although the supportingCpttt ligands may also influence this aspect given thatthe analogous distances in the series [{(N″)2M}2]2– are typicallylonger almost regardless of the metal.22 However, it has beenpointed out that the nitrogen–nitrogen distance is an imperfectmeasure of the extent of activation1 andthat greater insight can be obtained from vibrational spectroscopy.The Raman spectra of M1 were therefore recordedand found to be very similar  calculations, whichwere performed on the coordinates obtained from the X-ray structurewithout optimization, except for the hydrogen atoms. Full computationaldetails are provided in the Supporting Information. The calculations show that the highest occupied molecular orbital(HOMO) corresponds to gadolinium-N2 interactions and isdoubly occupied, indicating transfer of two electrons from two putative[Cp2tttGd] complexesto dinitrogen  involves an interactionbetween the other N2 π* orbital and a gadolinium5d orbital, but this is weaker due to the relatively poor spatialoverlap. An important consequence of this orbital scenario is theHOMO–LUMO gap of 2.03 eV (approximately 196 kJ mol–1), which results in a well-isolated singlet ground state for thebridging [N2]2– ligand. The HOMO–LUMOgap calculated for Gd1 agrees well with theobservation of a major absorption in the UV-vis spectrum of Gd1 at λmax = 619 nm 2M}2]2–, which is a consequenceof the degeneracy of the π* orbitals being preserved.20 In addition, negligible spin density .Furthermore, the natural electronic configuration of the gadoliniumatoms assigned by the calculations is 4f6.995 5d0.45, which equates to the expected 4f7 5d0 configurationof Gd3+ and agrees with the formal dianionic charge ofthe dinitrogen ligand. The X-band EPR spectrum of polycrystalline Gd1 at 298 K shows extensive fine structure , and a fit of the experimental spectrumwas possible with the inclusion of a small rhombic term with the parameters g = 2.001, D = −0.014 cm–1, and E = −0.0013 cm–1 (E/D = 0.09). The EPR data are consistentwith previously reported Gd3+ complexes of diamagneticligands.27The singlet character of the end-on dinitrogenligand in 2]2– has considerablepotential to allow M1 to be developed forbespoke electron-transfer reactivity. For example, adding the two-electronreducing agents M1 to N-heterocyclicligands with an odd number of binding sites should result in electrontransfer and elimination of N2, accompanied by the formationof paramagnetic lanthanide metallocene complexes by heterocyclic radicalanions. Achieving reactivity of this nature would provide a new methodfor the synthesis of molecular magnets such as SMMs, going beyondearly studies examining the reactivity of diamagnetic side-on dinitrogencomplexes of lanthanum and lutetium.29 Indeed, itis noteworthy that bimetallic lanthanidocene complexes of radical N-donor ligands are a well-known type of SMM,35 with some examples displaying remarkable magnetic hysteresis propertiesarising from direct magnetic exchange with the radical ligand.37 To the best of our knowledge,monometallic lanthanide metallocene SMMs containing radical ligandsare unknown. We therefore undertook to synthesize such species byreacting M1 with 2,2′-bipyridyl (bipy),resulting in the formation of [Cp2tttM(κ2-bipy)]  according to The stronglyreducing nature of − orbitalmanifold.In contrast to ion form S6. TheUN-heterocyclic ligands are an established class of compounds,yetexamples containing metals other than ytterbium or samarium are rare.39 The popularity of ytterbium stems from the ready availability ofytterbium(II) metallocenes,45 especially [(C5Me5)2Yb], whichhas been used to reduce N-heterocycles to give complexessuch as [(C5Me5)2Yb(κ2-bipy)], which has an unusual electronic ground state with intermediatevalence and multiconfigurational character. The rich redox chemistryof bipy-type ligands has also been showcased with trivalent and tetravalentactinide complexes typified by [Cp2tttAn(κ2-bipy)] , which were synthesized by in situreduction of bipy with KC8 in the presence of [Cp2tttAnCl2].48 Actinide metallocenes such as these are notable fortheir reactivity as one- or two-electron reducing agents in a rangeof small-molecule activation processes. Similar synthetic routes werealso developed for the potassium salt of a radical diazafluorenylidene-substitutedphospha-alkene and a boryl-substituted bipy radical, which were usedin salt metathesis reactions to give complexes with the radical ligandbound to gadolinium, terbium, and dysprosium.50Lanthanide complexes of reduced bipyridyl and related M1 as bespokereducingagents offers numerous synthetic advantages. For example, complexesof M1 allow an extension of lanthanide-basedreduction chemistry beyond the classical divalent lanthanides samarium,europium, and ytterbium. In place of large excesses of KC8 as the reductant, the dinitrogen ligand in M1 is a well-defined two-electron source that converts into N2 as a traceless leaving group following reduction, avoiding formationof salt-like bimetallic products. The high-yielding synthesis of M1 is also noteworthy.The availability of M) in fields of0–70 kOe were measured for all compounds. Additionally, theAC susceptibility and magnetic hysteresis properties of Tb1, Dy1, Tb2, and Dy2 were investigated to checkfor SMM behavior.The magnetic properties of lanthanidecomplexes with end-on bridging dinitrogen ligands have, hitherto,not been subjected to detailed investigations by DC and AC susceptometry.To address this gap in understanding, the temperature dependence ofthe molar magnetic susceptibility  plot for Gd1 at 2 K shows thatthe magnetization increases in a near-linear manner up to a valueof 6.10 Nβ at the maximum field of 70 kOe attainable with themagnetometer, well below the saturation magnetization value of 14Nβ expected for two Gd3+ ions  plots in the temperature range 1.9–5.0 K showa gradual increase in magnetization up to 25 kOe before increasingmore rapidly toward 8 Nβ, but without reaching saturation at70 kOe .54 The axial crystal field parameters Bk0 and Ck0  were then included in the spin Hamiltonian in MT(T) and M(H) data with J= −0.65 cm–1  and χ″(T), respectively, were measured in an AC fieldof 3 Oe and a frequency of 1000 Hz. Slow magnetic relaxation was notobserved, and the M(H) magnetichysteresis measurements produced closed S-shaped traces at 1.9 K . Since complexes of the non-Kramersion Tb3+ normally show SMM behavior when occupying a high-symmetryenvironment or when bound to a radical ligand,55 the observations on Tb1 are in line withexpectations based on magneto-structural correlations developed forlanthanide metallocene SMMs.56The real and imaginary components of the AC susceptibilityof Dy1 produced aχMT value of 27.27 cm3 K mol–1 at 300 K, slightly lower than the expectedvalue of 28.34 cm3 K mol–1 expected fortwo non-interacting Dy3+ ions.51 A gradual decrease in the susceptibility on lowering the temperatureresults in a χMT value of 10.13cm3 K mol–1 at 2 K  in Table S11, resultingin an exchange coupling constant of J = –0.07 cm–1.TheDC susceptibility of 1 at 2 K 7, indicat70 kOe 7.A goodTb1, χ″(ν) for Dy1 in zero DC field above7 K shows maxima up to 23 K, with the maxima shifting to a higherfrequency with increasing temperature (S10). A Cole–Coleplot of χ″(χ′) wasfitted using α-parameters in the range 0.25–0.39, implyinga reasonably broad distribution of relaxation times, τ. Theplot of ln(τ/s) versus T–1  was fitted with Orbach and Raman termsaccording to 0 is the attempt time, Ueff is the effective energy barrier, C is the Ramancoefficient, and n is the Raman exponent.0 = 7.30 × 10–10 s, Ueff = 180(37) cm–1, C = 0.20(5) s–1 Kn–, and n = 3.3(3). The observationof SMM behavior in the AC susceptibility is complemented by a narrowopening of the M(H) hysteresis loopat 1.9 K .In contrast to perature 8 and S10Gd2, χMT at 300 K is 7.48 cm3 K mol–1, closeto the expected value of 7.50 cm3 K mol–1 for a Gd3+ ion coupled antiferromagnetically to a bipyradical anion with S = 1/2. The temperature-dependenceof χMT decreases steadily down to75 K before decreasing more rapidly to reach 1.68 cm3 Kmol–1 at 2 K . A gradual increase in the magnetization was observed for Gd2 at 2 K up to a field of approximately 30 kOe,before leveling off at higher fields and reaching 5.93 Nβ at70 kOe but not saturating .A fit of the susceptibility for Gd2 using grad and Srad refer to the g-tensor and total spin of the bipy radical anion, was obtainedusing g = 2.0 for Gd3+ and the bipy radicalanion, yielding an isotropic exchange coupling constant of J= −5.50 cm–1 . This value is comparable in magnitude to thosedetermined for other gadolinium complexes of radical N-heterocyclic ligands.50For Tb2 is similarto that of Tb1. From a value of 11.43 cm3 K mol–1 at 300 K, χMT decreases gradually down to 100 K before showing a muchsharper decrease at lower temperatures and reaching 1.29 cm3 K mol–1 at 2 K . The room-temperature value of the susceptibility is essentiallythe same as that of 11.46 cm3 K mol–1 expected for a Tb3+ ion coupled antiferromagneticallyto an S = 1/2 organic radical. The coupling is alsoreflected in the M(H) data at 1.9–5.0K, with a steady increase in magnetization occurring up to 35 kOe,followed by a sharp upturn at higher fields without approaching saturationat 70 kOe . A reasonable simulationof the χMT(T) datawas obtained for Tb2 using the spin Hamiltonianin grad = 2.0, gTb =1.51, and the crystal field parameters stated in Table S15, which produced a terbium-bipy exchange couplingconstant of J = – 4.65 cm–1.The DC susceptibilityof ″(ν) data for Tb2 do not display maxima , openings in the M(H) hysteresis loops were observed up to 6 K with a small remanentmagnetization in zero field . Bifurcation in the field-cooled/zero-field-cooled (FC/ZFC) susceptibilityalso occurred at 5.3 K, broadly consistent with SMM behavior . The absence of maxima in the ACsusceptibility likely indicates that fast quantum tunneling of themagnetization (QTM) is the dominant relaxation process in Tb2 in zero field, which is corroborated below with theaid of an ab initio theoretical study.While the χDy2 isconsistent with a Dy3+ ion coupled antiferromagneticallyto the bipy radical anion, the value of 13.96 cm3 K mol–1 for χMT at 300K being close to the expected value of 13.80 cm3 K mol–1. Lowering the temperature results in the susceptibilityreaching 1.51 cm3 K mol–1 at 2 K . The M(H) data for Dy2 show an increase in the magnetizationin low fields, followed by a plateau around 35 kOe, and then a secondrapid increase to reach 3.3 Nβ at 70 kOe, but without saturation. Since the magnetization isclearly still increasing at this field value, relatively strong directantiferromagnetic exchange should be occurring. A fit of the susceptibilityof Dy2 using grad = 2.0 and gDy = 1.36 and the crystal field parameters statedin Table S15 gave J =– 3.50 cm–1, which is comparable to the isotropic J-value determined for Gd2 and the J-value for Tb2. Since J-values for highly anisotropic lanthanide-radical pairs are rarelyreported, few systems are available for comparison. However, the couplingsin Tb2 and Dy2 areseemingly weaker than those found in the [Bi2]3– radical bridged dimetallic systems [{C5Me5)2M}2(μ-η2:η2-Bi2)]− ,57 most likely because of the relatively diffusespin density in the bipy radical anion in M2.The DC magnetic susceptibilityof Dy2 in zeroDC field, although this is less pronounced than for Dy1. Broad maxima in χ″(ν) occurfrom 1.9 to 4.0 K (S19), with the relaxationtimes allowing a fit of the Cole–Cole plot with α= 0.6–0.7,indicating a broad range of relaxation times . A fit ofthe relaxation times was possible using Orbach and Raman terms accordingto 0 = 1.40 × 10–8 s, Ueff = 24(5) cm–1, C = 19(4) s–1Kn–, and n = 5.2(3). The magnetic hysteresismeasurements showed open loops up to 9 K, with two distinct stepsaround 24 and 59 kOe due to QTM at the magnetic fields correspondingto level crossings . A slightbifurcation of the FC/ZFC data was observed at 7 K .SMM behavior was observed for to 4.0 K 8 and S19Dy1 can be interpreted in terms of howthe end-on dinitrogenligand impacts the crystal field at dysprosium relative to the influenceof the Cpttt ligands. It is well-known that large energybarriers and open hysteresis loops can occur in dysprosium metalloceneSMMs because the bis(cyclopentadienyl) frameworkprovides a dominant axial crystal field.63 In SMMs with competing equatorial crystal fields such as [{(η5-Cp*)2Dy}(μ-Fp)]2 (Fp = CpFe(CO)2),56 a large energy barrier of662 cm–1 and wide butterfly hysteresis loops canbe observed, albeit with the latter showing negligible coercivityand remnant magnetization. In contrast, the molecular structure of Dy1 reveals that the Dy–N distances to theequatorial anionic nitrogen donor atoms are shorter by almost 0.14Å than the Dy–Cp centroid distances, suggesting that theend-on bridging dinitrogen ligand should dominate the crystal field.This structural property of Dy1 also explainswhy the barrier of 180(37) cm–1 is much lower thanthose found in purely axial dysprosocenium SMMs, which can exceed1500 cm–1,65 and similar to the barriers of approximately 100–300 cm–1 found in SMMs of the type [{(η5-C5H4Me)2Dy}{μ-ERn}]3 (ERn = MesP(H),MesAs(H), MesSb(H), MesSe, Mes = mesityl).68 The same rationaleapplies to Tb1, with the added requirementfor strict axial symmetry for non-Kramers ions, hence the poorer SMMproperties.The energy barrier and hysteresis propertiesof Tb1 and Dy1, multireference abinitio calculationswere used to provide deeper insight into their electronic structure.To simplify the calculations, one of the Ln3+ ions in thedinitrogen complexes was replaced by diamagnetic Y3+ andthe resulting hypothetical heterobimetallic species subjected to theSINGLE_ANISO routine implemented in ORCA 5.0.2. A complete activespace (CAS) of CAS was used for Tb1 andCAS for Dy1, with the calculations yieldingthe g-tensors and crystal field parameters of thelow-lying excited states. Full computational details are providedin the Supporting Information (Tables S11–S14).To support the empirical observations on Tb1 and Dy1 doesindeeddominate the crystal field, with the easy axis of magnetization oneach lanthanide center coinciding with the {M–N=N–M}axis  cm–1, respectively,are comparable in magnitude, Orbach relaxation in Dy1 should proceed via the first-excited KD.The calculations show that the end-on dinitrogen ligandin –M}axis 9. Thisr2]2– invokedthe idea of steric bulk to preclude formation of the common side-onbonding mode. Since side-on N2-bridged di-lanthanide metalloceneswith Ln = Gd, Tb or Dy tend to be capped by relatively small C5Me5 or C5Me4H ligands,23 the bulk of Cpttt is evidently sufficientfor the end-on bridging to form exclusively in M1. The same dinitrogen bonding mode is therefore also likelyto be observed in analogous complexes of heavier, smaller lanthanidesbeyond dysprosium. For the lighter lanthanides with larger radii,it has been shown that the bonding mode of dinitrogen is finely balancedbetween the two possibilities by steric and other factors, with bothend-on and side-on occurring. It is, therefore, of interest to explorethe limits and applicability of the chemistry developed for M1 across the full range of the lanthanide seriesin future work.The original rationale for targeting metallocene-cappedlanthanidecomplexes of end-on bridging [Nbis(trimethylsilyl)amidoas the capping ligand in the dinitrogen-bridged di-lanthanide complexesstudied by Evans and co-workers22 to Cpttt in M1 has important consequences for the interactionsof the lanthanide valence 5d orbitals and [N2]2– and, hence, the spin configuration of the dinitrogen ligand. Thelocal symmetry of the lanthanide sites results in effective overlapof a 5dπ orbital with one of the dinitrogen π*orbitals, and poorer overlap of a second 5dπ orbitalwith the other dinitrogen π* orbital. The resulting HOMO–LUMOgap produces an energetically isolated singlet configuration for theend-on bridging [N2]2– ligand in M1, whereas a triplet configuration was proposedfor the end-on dinitrogen complexes capped by bis(trimethylsilyl)amido ligands. These contrasting scenarios pointtoward the possibility of engineering the singlet-triplet energy gapvia the capping ligand bound to the lanthanide, which could be usedto address magnetic and photophysical properties of lanthanide metallocenes.The switch from bulky M1 in yields reproducibly greater than 80% offers opportunities fornew lanthanide-based reduction chemistry without the need to use KC8 in the presence of the target substrate, i.e., 2,2′-bipyin the case of M2. This is especially valuablefor lanthanides that do not readily form a stable +2 oxidation state,such as gadolinium, terbium, and dysprosium. By regarding the [N2]2– ligand as a two-electron reservoir,compounds M1 have potential to act as ‘synthons’for [Cp2tttM]in bespoke reduction chemistry, potentially across the full 4f series(except promethium). Proof of principle has been achieved with thesynthesis of the radical-ligated complexes M2. Extension of the reactivity to, for example, tri-nucleating N-heterocycles would give access to strongly exchanged-coupledradical-bridged compounds, potentially with SMM properties. Furthermore,noting the recent demonstration of CO homologation by the isolabledivalent thulium metallocene [Cp2tttTm],24 applicationsof M1 in small-molecule activation with abroader range of lanthanides can be envisaged. This approach wouldcomplement existing methodologies involving stable divalent lanthanidemetallocenes and sterically induced reduction.The ability to synthesize and isolate 1:κ1-bridging mode has been achieved with M1. Formation of these compounds is aided by the bulk of the Cpttt ligand substituents in combination with the relativelysmall radii of gadolinium, terbium, and dysprosium. The high-yieldingsynthesis and stability at room temperature are noteworthy featuresof M1, as is the charge-neutral nature ofthe complexes, which eliminates considerations relating to alkalimetal counter ions and associated chelate ligands. Raman spectroscopyrevealed a major stretching vibration for each complex, located at1623, 1621, and 1618 cm–1 for Gd1, Tb1, and Dy1, respectively, consistent with N=N double bonds in the [N2]2– ligands. Analysis of the bonding in Gd1 shows that the singlet form of the dinitrogenligand is strongly preferred to the triplet form, which is a consequenceof different spatial overlap between gadolinium 5dπ orbitals and the two dinitrogen π* orbitals.The targeted synthesis of metallocene-cappedlanthanide dinitrogencomplexes exclusively with the end-on μ-κ2]2– mediates antiferromagneticexchange between the Ln3+ ions, with AC susceptibilityand magnetic hysteresis measurements also showing that Dy1 is an SMM. A striking theoretical result from a studyof Tb1 and Dy1 isthe dominance of the dinitrogen ligand in the lanthanide crystal field,with the easy axis of magnetization being oriented along the {Ln–N=N–Ln}axis as opposed to aligning with the cyclopentadienyl ligands, asis commonly found.DC magneticsusceptibility and magnetization measurements revealthat [N2]2– as a source oftwo electrons, compounds M1 have been shownto react as synthons for divalent gadolinium, terbium, and dysprosiummetallocenes. Proof-of-principle reactions led to the isolation ofthe radical-ligated complexes [Cp2tttM(κ2-bipy)] , which feature appreciable directexchange coupling between the lanthanide and the bipy radical anion.SMM behavior was also found in Dy2. The electron-transferreactivity of M1 introduces possibilitiesfor new directions in lanthanide small-molecule activation, the discoveryof molecular magnets, and, potentially, for stoichiometric organicsynthesis as alternatives to samarium(II) reductions.By regarding [N


We examined the effects of the processing parameters onthe composition, microstructure, and electrical transport propertiesof the SnS films. Deposition temperature dominates charge transport;the room temperature electrical conductivity increased from 0.003to 0.19 S·cm–1 as deposition temperature increasedfrom 375 to 445 °C. Similarly, the maximum power factor (PF)increased with deposition temperature, reaching ∼0.22 μW·cm–1·K–2 at 570 K. The power factorsfor SnS films deposited by AACVD are higher than values from earlierwork on SnS bulks and SnS/SnSe films at temperatures up to 520 K.The electronic structure and electrical transport properties of SnSwere investigated using density-functional theory to provide an improvedunderstanding of the materials performance. To the best of our knowledge,the thermal conductivity (κ) of SnS film was measured for thefirst time allowing the figure of merit (zT) forSnS film to be evaluated. A relatively low thermal conductivity of∼0.41 W·m–1·K–1 was obtained at 550 K for SnS films deposited at 445 °C; thecorresponding zT value was ∼0.026. The SnSfilms are good candidates for thermoelectric applications and AACVDis a promising technique for the preparation of high-performance thermoelectricfilms.Orthorhombic SnS exhibits excellent thermoelectric performanceas a consequence its relatively high Seebeck coefficient and low thermalconductivity. In the present work, polycrystalline orthorhombic SnSthin films were prepared by aerosol-assisted chemical vapor deposition(AACVD) using the single source precursor dibutyl- The product S2 σ is defined as the power factor (PF).2 In order to maximize zT, the focus isto increase PF by increasing the Seebeck coefficient and/or electricalconductivity, and to reduce thermal conductivity. This is problematicin bulk materials due to the entanglement of electronic and thermaltransport parameters embodied by the Wiedmann–Franz law. However,strategies to circumvent this limitation have been developed and includegrain boundary engineering,3 and compositionalcontrol .4 All of these strategies rely on optimizing thermoelectricperformance by tuning the carrier concentration and reaching the optimumbalance between Seebeck coefficient, electrical conductivity and electronicthermal conductivity to maximize zT. Band structureengineering, such as band convergence and resonant level incorporationnear the band edge has been also used to improve Seebeck coefficientswithout degrading electrical conductivity.5 Lattice thermal conductivity is relatively independent of the electricalconductivity, so reducing the lattice thermal conductivity is alsoan effective way to optimize zT.6 This can be achieved by enhancing phonon scattering throughnanostructuring, and control of point defects and dislocations.7As we seek to addressthe growing need for renewable energy sources,thermoelectric (TE) materials have attracted considerable interest.TE materials enable the conversion between thermal energy and electricalenergy and the opportunity to generate power from waste heat.Pnma/Pbnm phase) at room temperature, transforming into Cmcm/Bbmm phase around 878 K.8 SnS is an attractive TE material because it isan inexpensive, nontoxic, and earth-abundant semiconductor.9 Furthermore, it possesses a high Seebeck coefficientand low lattice thermal conductivity due to its layered structure.10 The electrical conductivity of pure SnS is toolow for device applications, but it can be enhanced by adjusting carrierconcentration.12 The thermoelectric propertiesof single crystal and ceramic SnS have been the subject of a numberof investigations. Wu et al.13 grew SnSand Na-doped SnS single crystals and showed thermoelectric performancewas enhanced by Na doping, increasing the maximum zT from ∼0.35 for pure SnS to 1.1 for Na0.02Sn0.98S at 870 K. Later, He et al.14 reported that thermoelectric properties of SnS crystal could alsobe enhanced by Se alloying; the maximum zT at 873K was increased to ∼1.6 for SnS0.91Se0.09. Polycrystalline SnS bulk ceramics were prepared by Tan et al.15 using mechanical alloying and spark plasma sintering(SPS); the highest zT was 0.16 at 823 K. SnS bulkceramics, containing rod-shaped nanocrystals, were synthesized byrapid annealing, achieving a maximum zT of 0.25 at773 K.16 Dopants have also been introducedinto polycrystalline SnS bulk ceramics to improve electrical transportproperties and reduce thermal conductivity. Zhou et al.12 doped polycrystalline SnS with Na to increasehole concentration, achieving a peak zT value of0.65 at 850 K. Han et al.17 prepared SnSx1–Sex (0< x < 1) solid solutions and obtained a maximum zT of 0.82 for SnS0.2Se0.8 at 823K; defects in the solid solutions acted as phonon scattering centers,reducing the lattice thermal conductivity. By using Ag doping (0.5%),Tan et al.11 reported an improved zT value of 0.6 at 873 K. Later, a maximum zT value of 1.1 at 877 K was achieved by Ag doping and vacancy engineeringfor polycrystalline Sn0.99Ag0.05S by Asfandiyaret al.18 A similar high zT of ∼1.1 was reported by Wu et al.19 for Na0.02Sn0.98S0.5Se0.5 at 820 K.Tin sulfide (SnS) is a IV–VI semiconductingcompound, whichcrystallizes in an orthorhombic structure , achieving a maximum PFvalue of 0.049 μW cm–1·K–2 at 450 K. However, the thermal conductivity and zT of the films were not measured, and to the best of our knowledge,to date there is no documented experimental research on these parameters.In recent work, SnS thin films were deposited for photovoltaic, supercapacitor,and solar cell applications by a variety of techniques including thermalevaporation,23 radio frequency magnetronsputtering,24 modified chemical vapor deposition(CVD),25 spray pyrolysis, spin coating,26 chemical bath deposition (CBD),27 and electrodeposition.28 Amongthe available deposition methods, aerosol-assisted chemical vapordeposition (AACVD), a variant of CVD, is a low-cost and simple techniquewhich can be conducted under ambient pressure for the preparationof uniform films with the extra advantage of high purity and reproducibility.29 AACVD also reduces the volatility requirementfor precursors and allows the deposition of films from single-sourceprecursors (SSPs), making it easier to control stoichiometry and morphologyby designing the precursors.30 Kevin etal.29 synthesized SnS thin films containingsheet-like grains by AACVD using tin(II) precursors with the formula[Sn(S2CNRR′)2] ; R = Me, R′ = n-Bu (2); R = R′ = Et (3)). Ramasamy et al.25 successfully depositedSnS thin films using a range of organotin dithiocarbamates by AACVD.To address the requirement for low power and portabledevices formicrogeneration, there is growing interest in thin film thermoelectrics.4H9)2S2CN(C2H5)2)2], as single-sourceprecursor and optimized the AACVD deposition parameters  to enhance chargetransport properties. For the first time, the effects of AACVD depositionparameters on the growth of SnS films are systematically investigated.We conclusively show that the deposition temperature has the mostinfluence on morphology and electrical conductivity. For films measuredbelow 540 K, we achieved the highest PF values reported for SnS thinfilms. The thermal conductivity of SnS films was measured for thefirst time, and the zT values were evaluated. Theelectronic structure and thermoelectric performance of bulk SnS werealso investigated using density functional theory calculations toprovide an improved understanding of the materials and processes.In this work, we prepared SnS films by AACVD using dibutylbis(diethyldithiocarbamato)tin(IV),[Sn((C22.12.1.1bis(diethyldithiocarbamato) tin(IV) [Sn(C4H9)2(S2CN(C2H5)2)2] was conducted under an inert atmosphereof dry nitrogen using a Schlenk line.All reagents and solvents (detailedin the synthesis and deposition sections below) were obtained fromSigma-Aldrich and used without further purification. The preparationof dibutyl-–1 under nitrogen.Elemental analysis,to confirm the purity of the precursors, was carried out by the microanalyticallaboratory of The University of Manchester. Analysis of C, H, N, andS analysis was carried out using a Thermo Flash 2000 and the Sn contentdetermined by inductively coupled plasma atomic emission spectroscopy(ICP-AES) analysis using a Thermo Scientific iCAP 6300 DUO. Thermogravimetricanalysis (TGA) and differential scanning calorimetry (DSC), were carriedout by a TGA/DSC analysis Mettler-Toledo from 10 to 600 °C witha heating rate of 10 °C·min18H38N2S4Sn: C, 40.83; H, 7.23; N, 5.29; S, 24.22; Sn, 22.42. Found: C, 40.86;H, 7.30; N, 5.28; S, 24.08; Sn, 22.43.First, 0.03mol (6.8 g) of sodium diethyldithiocarbamate trihydrate  and 0.015 mol (4.6 g) dibutyl dichloride tin(IV)(purity 96%) were dissolved separately in ethanol, and the solutionswere mixed and stirred for 1 h. The fine, white sodium chloride powdergenerated during stirring was removed by vacuum filtration and thepale-yellow filtrate distilled under vacuum until around 50 mL ofsolution was left. The solution was kept at 4 °C for 12 h forrecrystallization; colorless crystals were formed. The crystals wereisolated by vacuum filtration, washed three times in 30 mL of coldethanol and dried at room temperature under vacuum. Yield: 6.1 g (77%).Anal. Calcd for C2.1.24H9)2(S2CN(C2H5)2)2] was dissolved in10 mL of toluene in a two-neck flask and stirred for 30 min beforeuse. The reactor glass tube was placed in a preheated Carbolite tubefurnace connected to the flask. Aerosol droplets were generated bynebulizing the precursor solution using a digital ultrasonic humidifier.The precursor-infused aerosol was transferred into the reactor tubeusing argon (Ar) gas, delivered with a constant flow rate (150 to300 cm3·min–1). By evaporation ofthe solvent and thermal decomposition of the precursor, films weredeposited onto the substrates. The temperature profile for the Carbolitetube furnace  was measured usinga K-type thermocouple under Ar gas flowing at a rate of 150 cm3·min–1. With the ability to controlthe gas flow rate, precursor solution concentration, and depositiontemperature, it was possible to independently examine their effectson the composition, microstructure, and thermoelectric performanceof the SnS films.Prior to deposition, glass substrates (1.5 cm × 2.5 cm) werecleaned and sonicated in acetone for 30 min and were then loaded intoa reactor glass tube after drying by compressed air. The precursor precursor was examinedby TGA and DSC (4H9)2(S2CN(C2H5)2)2] complex is lower than the theoretical percentage forSnS (29%) possibly due to sublimation of SnS.29 The DSC data [Sn(C4H9)2(S2CN(C2H5)2)2] shows asharp endothermic peak near 50 °C, corresponding to melting ofthe complex. The two broad endothermic peaks between 180–350°C can be attributed to the decomposition steps, which is consistentwith the TGA data. There is no significant weight loss above 350 °Cbut the increasingly upward trend of the DSC curve suggests continuedcrystallization of SnS.48 Thus, a depositiontemperature above 350 °C is required to ensure complete decompositionof the precursor for SnS film preparation, and subsequent high qualitycrystal growth. The decomposition pathway and thermal analysis datafor [Sn(C4H9)2(S2CN(C2H5)2)2] are in good agreementwith earlier studies.50The thermal decompositionof the  is completed around 350 °C and there isno significant weight loss above 350 °C, suggesting that thedecomposition product is SnS above 350 °C without obvious furthersublimation of Sn or S. Thus, irrespective of deposition temperaturethere are only slight differences in composition and stoichiometry.SEM micrographs and cross sectional images of theSnS films depositedat 375 to 445 °C are presented in to ∼7 μm 6, while to ∼7 μm 1. The ob results 4 the deck 1) orientation, which indicates theplate-like grains are aligned in the ac plane andstack in the b axis direction. Such features arevisible in As XRD data 5 and the–1 to 0.19 S·cm–1 (more than 60× increase)as a result of the improvement in microstructure reflected in theimproved film coverage, denser structure . The SEM images , show that the grains in the annealed samples are wider and betterconnected to each other than in the as-prepared samples. The resultsin Table S8 indicate that the electricalconductivity of the annealed samples is ∼3 times larger thanthat of unannealed samples. Therefore, annealing provides a routefor enhancement of thermoelectric performance.To validate the quality of the films, we first determinedthe electricalconductivity from sheet resistance at room temperature 7, prior tructure 6, and retructure 7b. Thus,3.456 The smallwhite spots near the bright spots appear to belong to the other SnScrystals beneath the main crystal in area c of 57 The interplane spacings of (1 0 0), (0 1 0), and (0 0 1) are estimatedto be 0.42, 1.12, and 0.39 nm, agreeing with lattice parameters for a, b, and c from the XRDrefinement ; the twin boundaries are identified by yellow dash lines. Yu etal. demonstrated that twin-boundary scattering can lead to a reductionof lattice thermal conductivity, which is beneficial to thermoelectricperformance.58 In Parts a and b of finement 1. In SnSfinement S14; the 3.5–1and 219 cm–1 and a broad peak at 161.6 cm–1 agree well withthe Raman spectra reported for SnS films prepared by AACVD and spincoating.57 The Raman peaks at 92 and 219 cm–1 are attributed to the Ag phonon mode and the peak at162 cm–1 originates from the B3g mode.59 There is no significant movement of the Ramanpeaks with increasing deposition temperature.Raman spectra for SnS films deposited at different temperature arepresented in 60hν is the photo energy, A is a constant,and gE is the bandgap. In the presentwork, equation is satisfied for n = 2, implying adirect allowed transition in these SnS films. By plotting the curvesof (αhν)2 vs hν and extrapolating the linear region  are significantlyhigher than the reported value.22 The exceptionalperformance achieved here reflects the high quality of the films  is close to the predicted value ∼0.24 μW·cm–1·K–2 at 600 K. We thereforeconsider there to be sufficient agreement between the calculationsand experimental results to have confidence in the modeling. Thisbeing the case, we note that the highest predicted PF of 1.13 μW·cm–1·K–2 at 850 K is much higherthan the present data for films, albeit at lower temperatures, andwe take this as an indication of what could be possible with highquality SnS. Indeed, we found that the predicted PF values reportedin this work are remarkably close to the PFs reported for SnS bulkceramics ,63 which indicatesboth that the calculated results are reliable and that the experimentalresults on SnS films are highly encouraging.Comparing the experimentalresults in 3.7–1·K–1. The reductionof the thermal conductivity for the SnS film with increasing temperatureis consistent with the normal trends in the thermal conductivity ofSnS bulk ceramics reported in the literature  is calculated approximatelyvia the Wiedemann–Franz law63κe = LσT, where L is Lorenz number (2.45 × 10–8 W·Ω·K–2). The lattice thermalconductivity (κL) can then be calculated as κL = κ – κe.63 In our previouswork, the lattice thermal conductivity of SnS was calculated,44 and we showed that the lattice thermal conductivityreduced from ∼2.15 W·m–1·K–1 at 300 K to ∼1.2 W·m–1·K–1 at 550 K, both of which are larger thanthe results obtained for SnS thin films tin(IV)as the single source precursor. AACVD deposition parameters includingsolution concentration, flow rate and deposition temperature wereoptimized to maximize transport properties. SnS films deposited usinga solution concentration of 0.4 mol·LzT for SnS film,and provide a feasible method of measuring thermal conductivity forAACVD thin film samples by TFA system. The AACVD technique is a reliableand easy to use method for the preparation of thermoelectric films,allowing optimization of thermoelectric performance by adjustmentof the AACVD parameters.This work demonstrates that earth-abundant,low-cost and nontoxicSnS films are promising thermoelectrics. We for the first time reportthe thermal conductivity and the