In this study,we employed molecular dynamics simulations to investigate the interfacial thermal conductance(ITC)and phonon transport of heterostructures composed of graphene(GE)and quasi-hexagonal phase fullerene(qHPC...In this study,we employed molecular dynamics simulations to investigate the interfacial thermal conductance(ITC)and phonon transport of heterostructures composed of graphene(GE)and quasi-hexagonal phase fullerene(qHPC60).We examined the effects of size,interface interaction coefficients,and thermal equilibrium time on the ITC of the GE/qHPC60 heterostructure.展开更多
The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission fr...The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission from multilayer to bulk crystal,relax the stringent fabrication requirements of nanodevices.However,detailed knowledge on the optical properties of Ga Te varies as layer thickness is still missing.Here we perform thickness-dependent PL and Raman spectra,as well as temperature-dependent PL spectra of Ga Te nanoflakes.Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in Ga Te nanoflakes.To understand the experimental results,we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes.On the basis of temperature-dependent PL spectra,the optical gap of the hexagonal phase is determined to be 1.849 eV,which can only survive under temperature higher than 200 K with the increasing phonon population.Furthermore,the strength of exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 me V/K.Our results prove the coexistence of dual crystalline phases in multilayer Ga Te nanoflakes,which may provoke further exploration of phase transformation in Ga Te materials,as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.展开更多
Deposition and structural characteristics of cadmium sulfide (CdS) thin films by chemical bath deposition (CBD) technique from a bath containing thiourea,cadmium acetate,ammonium acetate and ammonia in an aqueous solu...Deposition and structural characteristics of cadmium sulfide (CdS) thin films by chemical bath deposition (CBD) technique from a bath containing thiourea,cadmium acetate,ammonium acetate and ammonia in an aqueous solution are reported.Researches are made on the influence of the fundamental parameters including pH,temperature,and concentrations of the solution involved in the chemical bath deposition of CdS and titration or dumping of the thiourea solution on the structure characteristic of CdS thin films.The pH of the solution plays a vital role on the characteristic of the CdS thin films.The XRD patterns show that the change in the pH of the solution results in the change in crystal phase from predominant hexagonal phase to predominant cubic phase.The CdS thin films with the two different crystal phases have different influences on CIGS thin film solar cells.The crystal mismatch and the interface state density of the c-CdS(cubic phase CdS) and CIGS are about 1 419% and 8 507×10 12cm -2 respectively,and those of the h-CdS(hexagonal phase CdS) and CIGS are about 32 297% and 2 792×10 12cm -2 respectively.It is necessary for high efficiency CIGS thin film solar cells to deposit the cubic phase CdS thin films.展开更多
The energy band-gap and related factors of tantalum pentoxide with hexagonal phase were investigated using hybrid functional B3LYP and sX-LDA methods. The results showed that both sX-LDA and B3LYP techniques reveal th...The energy band-gap and related factors of tantalum pentoxide with hexagonal phase were investigated using hybrid functional B3LYP and sX-LDA methods. The results showed that both sX-LDA and B3LYP techniques reveal the indirect semiconductor nature of δ-Ta2O5, whereas the obtained value of energy band-gap is much higher than previous theoretical reports but closer to the experimental data. The optical band- gap of δ-Ta2O5 is expected to originate from the O 2p→Ta 5d transition which may benefit from the d-s-p hybridization.展开更多
Synthesis and separation of asymmetrically octa-substituted phthalocyanines （Pcs） derivatives obtained by cyclotetramerization of two different phthalonitriles （Pns） precursors is described. The phthalonitriles we...Synthesis and separation of asymmetrically octa-substituted phthalocyanines （Pcs） derivatives obtained by cyclotetramerization of two different phthalonitriles （Pns） precursors is described. The phthalonitriles were designed to have different polarity to enable successful chromatographic isolation. The side-chains was designed to lie perpendicular to the plane of the macrocycle via ketal link. It was hoped that the obtained materials would exhibit enhanced solubility and less columnar aggregation both in solution and in the solid state. The preparation of the ketal compounds （2,2-didodecyl- 1,3-benzodioxoles ） with was performed according to Cole method in which catechol and the didodecyl ketone were refluxed in toluene solution in the presence of a catalytic amount of p-toluene sulphonic acid （PTSA）. The resultant water was removed by azeotropic distillation using a Dean-Stark trap. 2,2-didodecyl-l,3-benzodioxoles was brominated then cyanated as described in literature to give the desired phthalonitrile. The other phthalonitrile （4,5-bis（1＇,4＇,7＇,10＇-tetraoxaundecyl） phthalonitrile was obtained also as described in literature. The structures of the obtained isomers were confirmed by spectroscopic methods. Optical microscopy and differential scanning calorimetry （DSC） measurements revealed that two of the obtained derivatives display hexagonal and rectangular columnar liquid crystalline phases （Dhd＆Drd） over a wide temperature range.展开更多
A series of poly{2,5-bis[(4-butoxyphenyl)-oxycarbonyl]styrenes}(PBPCS)with low mo-lecular weight distribution was synthesized by atom transfer radical polymerization(ATRP).The me-somorphic properties were investigated...A series of poly{2,5-bis[(4-butoxyphenyl)-oxycarbonyl]styrenes}(PBPCS)with low mo-lecular weight distribution was synthesized by atom transfer radical polymerization(ATRP).The me-somorphic properties were investigated by differential scanning calorimetry(DSC),polarizing optical microscopy(POM)and rheometer.PBPCS showed the phase transition from isotropic into liquid crystal(LC)phase,and the LC phase formed at high temperature and disappeared in the subsequent cooling procedure.Using the WAXD fiber pattern,the phase structure of the PBPCS at higher tem-perature showed hexagonal columnar nematic phase.Experimental results demonstrated that the driving force of the entropy is an important factor during the unusual LC phase formation of PBPCS.展开更多
The inherent uncertainty of chain length in synthetic polymers casts doubt on the explicit understanding of fundamental principles.This study quantitatively assesses the critical role of chain-length distribution in t...The inherent uncertainty of chain length in synthetic polymers casts doubt on the explicit understanding of fundamental principles.This study quantitatively assesses the critical role of chain-length distribution in the self-assembly process,aiming to identify the point at which discernible discrepancies begin to emerge.By blending discrete diblock copolymers of varying sizes,chain-length nonuniformity can be precisely regulated while the average composition remains constant.Introducing a minor heterogeneity leads to an expansion of lattice dimension,while a phase transition occurs as the difference exceeds a threshold.Interestingly,a transition from the Frank–Kasperσphase to the body-centered cubic phase was triggered by enlarging the size difference of the corona block,while introducing heterogeneity in the core block stabilized the hexagonally close-packed spheres.A self-consistent field theory calculation reveals that the synergy between the long and short chains effectively releases packing frustration,leading to substantial changes in the free-energy landscape and stabilizing unconventional phases otherwise inaccessible.This work calls particular attention to the importance of chain-length heterogeneity and provides a robust approach to finely tuning the phase behavior and physical properties of block copolymers without altering their chemical composition.展开更多
The importance of this research is to study the effect of changing the temperature at the same time on each of the prepared samples and during the gas sensing processes,the effects of substrate temperature T_(s) were ...The importance of this research is to study the effect of changing the temperature at the same time on each of the prepared samples and during the gas sensing processes,the effects of substrate temperature T_(s) were investigated after precipitation by the microstructural and optical characteristics of cadmium sulfide using thermal spraying method with different temperatures of(300,400,and 500)℃.The structural investigations of these films were studied,showing that the increases in substrate temperature were shown cubic and hexagonal phases according to ICDD card no.(21-0929)and(43-0989).The dramatic change occurred at 500℃in changing the phase from hexagonal to a cubic structure.XRD exhibits a dominant plane at(200)for different substrate temperatures.Optical transmittance,absorption coefficient,and energy gap values were calculated by UV/VIS spectrophotometer.These results showed that the band gap values decreased with increasing substrate temperature.The gas sensitivity was tested for NO_(2)gas at several working temperatures from 175℃to 250℃,and various gas concentrations from 150 ppm to 200 ppm and found that the sensitivity increase with increasing both the operating temperature and gas concentration for a T_(s) at 500℃which offer also the best crystallization the best sensitivity at an operating temperature of 175℃is 75%at a gas concentration of 150 ppm.展开更多
A new method for growing silicon nanowires is presented. They were grown in an aqueous solution at a temperature of 85℃ under atmospheric pressure by using sodium methylsiliconate as a water-soluble silicon precursor...A new method for growing silicon nanowires is presented. They were grown in an aqueous solution at a temperature of 85℃ under atmospheric pressure by using sodium methylsiliconate as a water-soluble silicon precursor. The structure, morphology, and composition of the as-grown nanowires were characterized by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectrometry. It was also confirmed by X-ray powder diffraction and Raman spectroscopy that the silicon nanowire has a hexagonal structure. It was possible to grow the crystalline silicon nanowires at low temperature under atmospheric pressure because potassium iodide, which was used as a gold etchant, sufficiently increased the surface energy and reactivity of gold as a metal catalyst for the reaction of the Si precursor even at low temperature.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12204130)the Fundamental Research Funds for the Central University of China(Grant No.2019ZDPY16)+2 种基金the Basic Research Project of Xuzhou City(Grant No.KC22043)the support funded by the Graduate Innovation Program of China University of Mining and Technology(Grant Nos.2024WLJCRCZL266 and 2024WLJCRCZL294)the Postgraduate Research Practice Innovation Program of Jiangsu Province(Grant No.KYCX24_2692)。
文摘In this study,we employed molecular dynamics simulations to investigate the interfacial thermal conductance(ITC)and phonon transport of heterostructures composed of graphene(GE)and quasi-hexagonal phase fullerene(qHPC60).We examined the effects of size,interface interaction coefficients,and thermal equilibrium time on the ITC of the GE/qHPC60 heterostructure.
基金supported by the National Natural Science Foundation of China(No.91950109 and 61875109)the Natural Science Foundation of Shanxi Province(No.201901D111010(ZD))Postgraduate Education Innovation Project of Shanxi Province(No.2019SY052 and No.2020BY022)。
文摘The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission from multilayer to bulk crystal,relax the stringent fabrication requirements of nanodevices.However,detailed knowledge on the optical properties of Ga Te varies as layer thickness is still missing.Here we perform thickness-dependent PL and Raman spectra,as well as temperature-dependent PL spectra of Ga Te nanoflakes.Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in Ga Te nanoflakes.To understand the experimental results,we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes.On the basis of temperature-dependent PL spectra,the optical gap of the hexagonal phase is determined to be 1.849 eV,which can only survive under temperature higher than 200 K with the increasing phonon population.Furthermore,the strength of exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 me V/K.Our results prove the coexistence of dual crystalline phases in multilayer Ga Te nanoflakes,which may provoke further exploration of phase transformation in Ga Te materials,as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.
文摘Deposition and structural characteristics of cadmium sulfide (CdS) thin films by chemical bath deposition (CBD) technique from a bath containing thiourea,cadmium acetate,ammonium acetate and ammonia in an aqueous solution are reported.Researches are made on the influence of the fundamental parameters including pH,temperature,and concentrations of the solution involved in the chemical bath deposition of CdS and titration or dumping of the thiourea solution on the structure characteristic of CdS thin films.The pH of the solution plays a vital role on the characteristic of the CdS thin films.The XRD patterns show that the change in the pH of the solution results in the change in crystal phase from predominant hexagonal phase to predominant cubic phase.The CdS thin films with the two different crystal phases have different influences on CIGS thin film solar cells.The crystal mismatch and the interface state density of the c-CdS(cubic phase CdS) and CIGS are about 1 419% and 8 507×10 12cm -2 respectively,and those of the h-CdS(hexagonal phase CdS) and CIGS are about 32 297% and 2 792×10 12cm -2 respectively.It is necessary for high efficiency CIGS thin film solar cells to deposit the cubic phase CdS thin films.
基金Funded by the National Natural Science Foundation of China(No.51102172)Hebei Natural Science Foundation(No.E2013210038)+1 种基金Colleges and Universities in Hebei Province Science and Technology Research Project(No.YQ2014033)Hebei Key Discipline Construction Project
文摘The energy band-gap and related factors of tantalum pentoxide with hexagonal phase were investigated using hybrid functional B3LYP and sX-LDA methods. The results showed that both sX-LDA and B3LYP techniques reveal the indirect semiconductor nature of δ-Ta2O5, whereas the obtained value of energy band-gap is much higher than previous theoretical reports but closer to the experimental data. The optical band- gap of δ-Ta2O5 is expected to originate from the O 2p→Ta 5d transition which may benefit from the d-s-p hybridization.
文摘Synthesis and separation of asymmetrically octa-substituted phthalocyanines （Pcs） derivatives obtained by cyclotetramerization of two different phthalonitriles （Pns） precursors is described. The phthalonitriles were designed to have different polarity to enable successful chromatographic isolation. The side-chains was designed to lie perpendicular to the plane of the macrocycle via ketal link. It was hoped that the obtained materials would exhibit enhanced solubility and less columnar aggregation both in solution and in the solid state. The preparation of the ketal compounds （2,2-didodecyl- 1,3-benzodioxoles ） with was performed according to Cole method in which catechol and the didodecyl ketone were refluxed in toluene solution in the presence of a catalytic amount of p-toluene sulphonic acid （PTSA）. The resultant water was removed by azeotropic distillation using a Dean-Stark trap. 2,2-didodecyl-l,3-benzodioxoles was brominated then cyanated as described in literature to give the desired phthalonitrile. The other phthalonitrile （4,5-bis（1＇,4＇,7＇,10＇-tetraoxaundecyl） phthalonitrile was obtained also as described in literature. The structures of the obtained isomers were confirmed by spectroscopic methods. Optical microscopy and differential scanning calorimetry （DSC） measurements revealed that two of the obtained derivatives display hexagonal and rectangular columnar liquid crystalline phases （Dhd＆Drd） over a wide temperature range.
基金This work was supported by the National Natural Science Foundation of China(Grant No.20134010)the Ministry of Education of China(Key Project No.104005).
文摘A series of poly{2,5-bis[(4-butoxyphenyl)-oxycarbonyl]styrenes}(PBPCS)with low mo-lecular weight distribution was synthesized by atom transfer radical polymerization(ATRP).The me-somorphic properties were investigated by differential scanning calorimetry(DSC),polarizing optical microscopy(POM)and rheometer.PBPCS showed the phase transition from isotropic into liquid crystal(LC)phase,and the LC phase formed at high temperature and disappeared in the subsequent cooling procedure.Using the WAXD fiber pattern,the phase structure of the PBPCS at higher tem-perature showed hexagonal columnar nematic phase.Experimental results demonstrated that the driving force of the entropy is an important factor during the unusual LC phase formation of PBPCS.
基金supported by the National Natural Science Foundation of China(grant no.22273026)the Recruitment Program of Guangdong(grant no.2016ZT06C322)+1 种基金the Research Funds from State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials,Soochow University(grant no.SDGC2109)the 111 Project(grant no.B18023).
文摘The inherent uncertainty of chain length in synthetic polymers casts doubt on the explicit understanding of fundamental principles.This study quantitatively assesses the critical role of chain-length distribution in the self-assembly process,aiming to identify the point at which discernible discrepancies begin to emerge.By blending discrete diblock copolymers of varying sizes,chain-length nonuniformity can be precisely regulated while the average composition remains constant.Introducing a minor heterogeneity leads to an expansion of lattice dimension,while a phase transition occurs as the difference exceeds a threshold.Interestingly,a transition from the Frank–Kasperσphase to the body-centered cubic phase was triggered by enlarging the size difference of the corona block,while introducing heterogeneity in the core block stabilized the hexagonally close-packed spheres.A self-consistent field theory calculation reveals that the synergy between the long and short chains effectively releases packing frustration,leading to substantial changes in the free-energy landscape and stabilizing unconventional phases otherwise inaccessible.This work calls particular attention to the importance of chain-length heterogeneity and provides a robust approach to finely tuning the phase behavior and physical properties of block copolymers without altering their chemical composition.
文摘The importance of this research is to study the effect of changing the temperature at the same time on each of the prepared samples and during the gas sensing processes,the effects of substrate temperature T_(s) were investigated after precipitation by the microstructural and optical characteristics of cadmium sulfide using thermal spraying method with different temperatures of(300,400,and 500)℃.The structural investigations of these films were studied,showing that the increases in substrate temperature were shown cubic and hexagonal phases according to ICDD card no.(21-0929)and(43-0989).The dramatic change occurred at 500℃in changing the phase from hexagonal to a cubic structure.XRD exhibits a dominant plane at(200)for different substrate temperatures.Optical transmittance,absorption coefficient,and energy gap values were calculated by UV/VIS spectrophotometer.These results showed that the band gap values decreased with increasing substrate temperature.The gas sensitivity was tested for NO_(2)gas at several working temperatures from 175℃to 250℃,and various gas concentrations from 150 ppm to 200 ppm and found that the sensitivity increase with increasing both the operating temperature and gas concentration for a T_(s) at 500℃which offer also the best crystallization the best sensitivity at an operating temperature of 175℃is 75%at a gas concentration of 150 ppm.
文摘A new method for growing silicon nanowires is presented. They were grown in an aqueous solution at a temperature of 85℃ under atmospheric pressure by using sodium methylsiliconate as a water-soluble silicon precursor. The structure, morphology, and composition of the as-grown nanowires were characterized by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectrometry. It was also confirmed by X-ray powder diffraction and Raman spectroscopy that the silicon nanowire has a hexagonal structure. It was possible to grow the crystalline silicon nanowires at low temperature under atmospheric pressure because potassium iodide, which was used as a gold etchant, sufficiently increased the surface energy and reactivity of gold as a metal catalyst for the reaction of the Si precursor even at low temperature.
