Palladium(Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics.However,the synthesis of large-scale uniform Pd...Palladium(Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics.However,the synthesis of large-scale uniform PdS and PdS_(2)nanofilms(NFs)remains an enormous challenge.In this work,2-inch wafer-scale PdS and PdS_(2) NFs with excellent stability can be controllably prepared via chemical vapor deposition combined with electron beam evaporation technique.The thickness of the pre-deposited Pd film and the sulfurization temperature are critical for the precise synthesis of PdS and PdS_(2) NFs.A corresponding growth mechanism has been proposed based on our experimental results and Gibbs free energy calculations.The electrical transport properties of PdS and PdS_(2) NFs were explored by conductive atomic force microscopy.Our findings have achieved the controllable growth of PdS and PdS_(2) NFs,which may provide a pathway to facilitate PdS and PdS_(2) based applications for next-generation high performance optoelectronic devices.展开更多
The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics(MD)method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures.It is demonstrat...The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics(MD)method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures.It is demonstrated that the thermal conductivity of GaN nanofilm increases with the increase of nanofilm thickness,while decreases with the increase of temperature.Meanwhile,the thermal conductivity of strained GaN nanofilms is weakened with increasing the tensile strain.The film thickness and environment temperature can affect the strain effect on the thermal conductivity of GaN nanofilms.In addition,the analysis of phonon properties of GaN nanofilm shows that the phonon dispersion and density of states of GaN nanofilms can be significantly modified by the film thickness and strain.The results in this work can provide the theoretical supports for regulating the thermal properties of GaN nanofilm through tailoring the geometric size and strain engineering.展开更多
Cu/W multilayer nanofilms are prepared in pure Ar and He/At mixing atmosphere by the rf magnetron sputtering method. The cross-sectional morphology and the defect distribution of the Cu/W multilayer nanofilms are char...Cu/W multilayer nanofilms are prepared in pure Ar and He/At mixing atmosphere by the rf magnetron sputtering method. The cross-sectional morphology and the defect distribution of the Cu/W multilayer nanofilms are characterized by scanning electron microscopy and Doppler broadening positron annihilation spectroscopy. The results show that plenty of point defects can be produced by introducing He during the growth of the multilayer nanofilms. With the increasing natural storage time, He located in the near surface of the Cu//W multilayer nanofilm at room temperature could be released gradually and induce the segregation of He-related defects due to the diffusion of He and defects. However, more He in the deep region spread along the interface of the Cu/W multilayer nanofilm. Meanwhile, the layer interfaces can still maintain their stability.展开更多
The amorphous I/Au composite nanofilms were prepared by low vacuum direct current sputtering(LVDCS) method. The optimized preparation technologies contain growth pressure, time, gaseous environment and annealing condi...The amorphous I/Au composite nanofilms were prepared by low vacuum direct current sputtering(LVDCS) method. The optimized preparation technologies contain growth pressure, time, gaseous environment and annealing conditions. The maximum fluorescence emission(λmax^em) of I/Au nanofilms was observed at wavelength of 375 nm, and the intensity of fluorescence emission peak of annealed I/Au films was smaller than that of unannealed one due to fewer amorphous Au nanoparticles, caused by annealing treatment. In the UV-Vis absorption spectra, the intensity of UV-Vis absorption peak of annealed I/Au nanofilms is larger than that of the unannealed one. This work also developed a new way to grow I/Au composite fluorescent thin films.展开更多
Terahertz radiation (THzR) consists of electromagnetic waves within the band of frequencies from 0.3 to 3 terahertz with the wavelengths of radiation in the range from 0.1 mm to 1 mm, respectively. The technology for ...Terahertz radiation (THzR) consists of electromagnetic waves within the band of frequencies from 0.3 to 3 terahertz with the wavelengths of radiation in the range from 0.1 mm to 1 mm, respectively. The technology for generating and manipulating THzR is still in its initial stage. Herein, we demonstrate that the wrinkled Si1–xGex/Si1–yGey films can be used as radiation sources, which emit electromagnetic waves (EMW) in a very wide range of the frequencies including the terahertz band from 0.3 to 3 THz and far IR from 3 THz to 20 THz. These findings provide the theoretical foundation for the wrinkled nanofilm radiation emission and may allow, to some extent, to fill the terahertz gap.展开更多
Surface charges can modify the elastic modulus of nanostructure,leading to the change of the phonon and thermal properties in semiconductor nanostructure.In this work,the influence of surface charges on the phonon pro...Surface charges can modify the elastic modulus of nanostructure,leading to the change of the phonon and thermal properties in semiconductor nanostructure.In this work,the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated.In the framework of continuum mechanics,the modified elastic modulus can be derived for the nanofilm with surface charges.The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation,phonon group velocity,density of states of phonons in nanofilm with the surface charges.The phonon thermal conductivity of nanofilm can be obtained by considering surface charges.The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm.Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons.The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm.Based on these theoretical results,one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.展开更多
The effect of piezoelectricity on phonon properties and thermal conductivity of gallium nitride (GaN) nanofilms is theoretically investigated. The elasticity model is utilized to derive the phonon properties in spat...The effect of piezoelectricity on phonon properties and thermal conductivity of gallium nitride (GaN) nanofilms is theoretically investigated. The elasticity model is utilized to derive the phonon properties in spatially confined GaN nanofilms. The piezoelectric constitutive relation in GaN nanofilms is taken into account in calculating the phonon dispersion relation. The modified phonon group velocity and phonon density of state as well as the phonon thermal conductivity are also obtained due to the contribution of piezoelectricity. Theoretical results show that the piezoelectricity in GaN nanofilms can change significantly the phonon properties such as the phonon group velocity and density of states, resulting in the variation of the phonon thermal conductivity of GaN nanofilms remarkably. Moreover, the piezoelectricity of GaN can modify the dependence of thermal conductivity on the geometrical size and temperature. These results can be useful in modeling the thermal performance in the active region of GaN-based electronic devices.展开更多
The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen (...The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen (77K) and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann-Franz law. We build an electron relaxation model based on Matthiessen's rule to analyse the thermal conductivity and employ the Mayadas & Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann-Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.展开更多
We investigate the formations of wurtzite (WZ) SiC nano polytypes in zinc blende (ZB) SiC nanofilms hetero-grown on Si-(100) substrates via low pressure chemical vapor deposition (LPCVD) by adjusting the Si/C ...We investigate the formations of wurtzite (WZ) SiC nano polytypes in zinc blende (ZB) SiC nanofilms hetero-grown on Si-(100) substrates via low pressure chemical vapor deposition (LPCVD) by adjusting the Si/C ratio of the introduced precursors. Through SEM, TEM, and Raman characterizations, we find that the nanofilms consist of discrete WZ SiC nano polytypes and ZB SiC polytypes composed of WZ polytypes (WZ + ZB) and disordered ZB SiC polytypes, respectively, according to Si/C ratios of 0.5, 1.5, and 3. We attribute the WZ polytype formation to being due to a kinetic mechanism based on the Si/C surface saturation control.展开更多
In this work, the prerequisite and mode of electromagnetic response of Al nanof ilms to electromagnetic wave field was suggested. Reflectance, transmittance in infrared region and carrier density of the films was meas...In this work, the prerequisite and mode of electromagnetic response of Al nanof ilms to electromagnetic wave field was suggested. Reflectance, transmittance in infrared region and carrier density of the films was measured. With the carrier density of the films, the dependence of their plasma frequencies on the film thickness was obtained. On the other hand, the dependence of absorptance on the frequency of electromagnetic wave field was set up by using the measured reflectance and transmittance, which provided plasma frequency-film thickness relation as well. Similarity of both plasma frequency-film thickness relations proved plasma resonance as a mode of electromagnetic response in Al nanofilms.展开更多
The electrocatalytic reduction of CO_(2)is a promising pathway to generate renewable fuels and chemicals.However,its advancement is impeded by the absence of electrocatalysts with both high selectivity and stability.H...The electrocatalytic reduction of CO_(2)is a promising pathway to generate renewable fuels and chemicals.However,its advancement is impeded by the absence of electrocatalysts with both high selectivity and stability.Here,we present a scalable in-situ thermal evaporation technique for synthesizing series of Bi,In,and Sn nanofilms on carbon felt(CF)substrates with a high-aspect-ratio structure.The resulting main-group metal nanofilms exhibit a homogeneously distributed and highly exposed catalyst surface with ample active sites,thereby promoting mass transport and ad-/desorption of reaction intermediates.Benefiting from the unique fractal morphology,the Bi nanofilms deposited on CF exhibit optimal catalytic activities for CO_(2)electroreduction among the designed metal nanofilms electrodes,with the highest Faradaic efficiency of 96.9%for formate production at−1.3 V vs.reversible hydrogen electrode(RHE)in H-cell.Under an industrially relevant current density of 221.4 mA·cm−2 in flow cells,the Bi nanofilms retain a high Faradaic efficiency of 81.7%at−1.1 V(vs.RHE)and a good long-term stability for formate production.Furthermore,a techno-economic analysis(TEA)model shows the potential commercial viability of electrocatalytic CO_(2)conversion into formate using the Bi nanofilms catalyst.Our results offer a green and convenient approach for in-situ fabrication of stable and inexpensive thin-film catalysts with a fractal structure applicable to various industrial settings.展开更多
Nature provides diverse models for manufacturing complex and hierarchical materials by controlling molecular assembly at scales ranging from sub-nano to macroscale. However, developing artificial strategies for manufa...Nature provides diverse models for manufacturing complex and hierarchical materials by controlling molecular assembly at scales ranging from sub-nano to macroscale. However, developing artificial strategies for manufacturing hierarchical materials with comparable machining capabilities to nature is extremely challenging. Here, a templated freezing assembly strategy is reported, enabling simultaneously regulating molecular assembly spatiotemporally to obtain hierarchical materials with structure control from sub-nano to macroscale. In this way, unique centimeter-scale freestanding nanofilms are assembled from diverse molecules, e.g., proteins and conjugated polymers. A generated silk fibroin(SF) nanofilm presents a tunable β-sheet fraction from 5% to 47%, fiber width from 30 to 3,000 nm, and micro-textures with desired shapes. Such a strategy will lay the foundation for customizing hierarchical functional materials from single or multi-component molecules, e.g., desired bioscaffolds with controlled cell adhesion.展开更多
Recently,Livingston and his colleagues published two articles in Nature and Science,respectively,to tackle the challenges of accurate molecular sieving and crude oil separation in the field of membrane separation by p...Recently,Livingston and his colleagues published two articles in Nature and Science,respectively,to tackle the challenges of accurate molecular sieving and crude oil separation in the field of membrane separation by preparing ultrathin nanofilms through interfacial polymerization.One is that the nanofilms with ordered sub-nanopores achieve accurate molecular sieving atångström precision,and the other is that the permeability of hydrophobic polyamide nanofilms to hydrophobic liquid is significantly enhanced by an order of magnitude.The thoughtful design and excellent performance provide a feasible strategy for the development of membrane separation,and show great potential in industrial applications(drug separation and crude oil fractionation).展开更多
Single-phase multiferroic BiFeO3 and rare-earth metal of holmium (Ho) doped BiFeO3 nanofilms were prepared on Pt (100)/Ti/SiO2/Si wafer via solution-gelation technique. It was suggested that the lattice distortion...Single-phase multiferroic BiFeO3 and rare-earth metal of holmium (Ho) doped BiFeO3 nanofilms were prepared on Pt (100)/Ti/SiO2/Si wafer via solution-gelation technique. It was suggested that the lattice distortion happened with the lattice parameter of d decreasing after doping rare-earth metal of Ho. Meanwhile, the structure of nanofilms transformed from hexahedron phase to tetragonal phase after doping Ho. The analysis on X-ray photoelectron spectroscopy (XPS) indicated that the ratio of Fe3~ cations to Fe2+ cations increased with the increase of binding energy between Fe and O and decrease of that between Bi and O after doping Ho. The present work provided an available way on enhancing multiferroic of BiFeO3 nanofilms.展开更多
Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption o...Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption owing to the low impedance matching between the absorbers and air. Carbon nanostructures are very promising candidates for high-efficiency absorption because of their attractive features including low density, high surface area, and good stability. Herein, a new strategy is proposed to improve the impedance matching of dielectric loss materials using electrospun carbon nanofibers as an example. The carbon nanofibers are coated with specifically designed gradient multilayer nanofilms with gradually increasing electroconductibility synthesized by doping ZnO with different A1203 content (AZO) by atomic layer deposition. The gradient nanofilms are composed of five layers of dielectric films, namely, pure A1203, AZO (5:1, the pulse cycle ratio of ZnO to A1203), pure ZnO, AZO (10:1), and AZO (20:1). The versatile gradient films serve as intermediate layers to tune the impedance matching between air and the carbon nanofiber surfaces. Therefore, the carbon nanofibers coated with gradient films of rationally selected thicknesses exhibit remarkably enhanced microwave absorption performance, and the optimal reflection loss reaches -58.5 dB at 16.2 GHz with a thickness of only 1.8 mm. This work can help further understand the contribution of impedance matching to microwave absorption. Our strategy is general and can be applied to improve the absorption properties of other dielectric loss materials and even for applications in other fields.展开更多
Fabrication of large-area and uniform semiconducting thin films of two-dimensional(2D)materials is paramount for the full exploitation of their atomic thicknesses and smooth surfaces in integrated circuits.In addition...Fabrication of large-area and uniform semiconducting thin films of two-dimensional(2D)materials is paramount for the full exploitation of their atomic thicknesses and smooth surfaces in integrated circuits.In addition to elaborate vapor-based synthesis techniques for the wafer-scale growth of 2D films,solution-based approaches for high-quality thin films from the liquid dispersions of 2D flakes,despite underdeveloped,are alternative cost-effective tactics.Here,we present layer-by-layer(LbL)assembly as an effective approach to obtaining scalable semiconducting films of molybdenum disulfide(MoS_(2))for field-effect transistors(FETs).LbL assembly is achieved by coordinating electrochemically exfoliated MoS_(2) with cationic poly(diallyldimethylammonium chloride)(PDDA)through electrostatic interactions.The PDDA/MoS_(2) percolating nanofilms show controlled and self-limited growth on a variety of substrates,and are easily patterned through lift-off processes.Ion gel gated FETs are fabricated on these MoS_(2) nanofilms,and they show mobilities of 9.8 cm^(2)·V^(−1)·s^(−1),on/off ratios of 2.1×10^(5) with operating voltages less than 2 V.The annealing temperature in the fabrication process can be as low as 200℃,thereby permitting the fabrication of flexible FETs on polyethylene terephthalate substrates.The LbL assembly technique holds great promise for the large-scale fabrication of flexible electronics based on solution-processed 2D semiconductors.展开更多
The interaction between mechanics and chemistry plays an essential and critical role in the behaviors and properties of materials,especially in nanoscale alloys. Based on the classical Gibbs and Mc Lean adsorption iso...The interaction between mechanics and chemistry plays an essential and critical role in the behaviors and properties of materials,especially in nanoscale alloys. Based on the classical Gibbs and Mc Lean adsorption isotherms, the present study takes the freestanding nanometer thick films of Pd-H solid solutions as a typic example to investigate surface segregation of hydrogen. The surface eigenstress model is further developed here to give analytic formulas, which have the capability to quantitatively predict the size-dependent surface segregation. Molecular dynamics(MD) simulations are conducted on free-standing Pd-H nanofilms.The MD simulations verify the theoretical analytic results and determine the values of parameters involved in the theoretical analysis. The integrated theoretical and numerical study exhibits that both surface excess H concentration and apparent biaxial Young’s modulus of Pd-H thin films depend on the nominal H concentration and the film thickness. The MD simulations determine the values of three parameters involved in the theoretical analysis. Especially, the parameter of the differentiation in reference chemical potential behaves like the molar free energy of segregation in the Mc Lean adsorption isotherm.展开更多
Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range.However,the limited absorption and serious backscattering of hot-e...Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range.However,the limited absorption and serious backscattering of hot-electrons result in inadequate quantum yields,especially in the mid-infrared range.Here,we report a macroscopic assembled graphene(nMAG)nanofilm/silicon heterojunction for ultrafast mid-infrared photodetection.The assembled Schottky diode works in 1.5-4.0μm at room temperature with fast response(20-30 ns,rising time,4 mm2 window)and high detectivity(1.61011 to 1.9109 Jones from 1.5 to 4.0μm)under the pulsed laser,outperforming single-layer-graphene/silicon photodetectors by 2-8 orders.These performances are attributed to the greatly enhanced photo-thermionic effect of electrons in nMAG due to its high light absorption(~40%),long carrier relaxation time(~20 ps),low work function(4.52 eV),and suppressed carrier number fluctuation.The nMAG provides a long-range platform to understand the hot-carrier dynamics in bulk 2D materials,leading to broadband and ultrafast MIR active imaging devices at room temperature.展开更多
1 Results Homogeneity of fibroin thin films by pulsed laser deposition (PLD) was significantly improved by introducing autogenous binders to consolidate and homogenize the irradiation targets.Homogenization includes a...1 Results Homogeneity of fibroin thin films by pulsed laser deposition (PLD) was significantly improved by introducing autogenous binders to consolidate and homogenize the irradiation targets.Homogenization includes among others,decreases in the size of nanostructural units and the fractional debris.Simultaneously,the deposition rate was substantially increased.Autogenous binders are prepared via degumming and liquefaction of fibroin by using Na2CO3 and LiBr,respectively.We also found that optically hom...展开更多
1 Results Protein thin films gather increasing interests in various biomedical-related materials including surface treatment of implants and bio-tips.Processes via colloid chemical routes such as simple adsorption,dip...1 Results Protein thin films gather increasing interests in various biomedical-related materials including surface treatment of implants and bio-tips.Processes via colloid chemical routes such as simple adsorption,dip-or spin coating enable formation of protein thin films on various substrates.Related methods are facile andconvenient without sophisticated instrumentation but not without restriction.Typical drawbacks are limited solubility of the film-forming species and wettability determined by the com...展开更多
基金supported by National Natural Science Foundation of China (No.11974301)Key Research and Development Program of Hunan Province (No.2022GK2007)+2 种基金Key Project from Department Education of Hunan Province (No.22A0123)Scientific Research Fund of Hunan Provincial Education Department (No.21B0136)National college students innovation and entrepreneurship training program (No.S202310530016)。
文摘Palladium(Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics.However,the synthesis of large-scale uniform PdS and PdS_(2)nanofilms(NFs)remains an enormous challenge.In this work,2-inch wafer-scale PdS and PdS_(2) NFs with excellent stability can be controllably prepared via chemical vapor deposition combined with electron beam evaporation technique.The thickness of the pre-deposited Pd film and the sulfurization temperature are critical for the precise synthesis of PdS and PdS_(2) NFs.A corresponding growth mechanism has been proposed based on our experimental results and Gibbs free energy calculations.The electrical transport properties of PdS and PdS_(2) NFs were explored by conductive atomic force microscopy.Our findings have achieved the controllable growth of PdS and PdS_(2) NFs,which may provide a pathway to facilitate PdS and PdS_(2) based applications for next-generation high performance optoelectronic devices.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11772294 and 11621062)the Fundamental Research Funds for the Central Universities(Grant No.2017QNA4031)。
文摘The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics(MD)method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures.It is demonstrated that the thermal conductivity of GaN nanofilm increases with the increase of nanofilm thickness,while decreases with the increase of temperature.Meanwhile,the thermal conductivity of strained GaN nanofilms is weakened with increasing the tensile strain.The film thickness and environment temperature can affect the strain effect on the thermal conductivity of GaN nanofilms.In addition,the analysis of phonon properties of GaN nanofilm shows that the phonon dispersion and density of states of GaN nanofilms can be significantly modified by the film thickness and strain.The results in this work can provide the theoretical supports for regulating the thermal properties of GaN nanofilm through tailoring the geometric size and strain engineering.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11275132,51171124 and 11505121the International Science and Technology Cooperation Program of China under Grant No 2014DFR50710the Scientific and Technical Supporting Programs Funded by the Science and Technology Department of Sichuan Province under Grant No 2014GZ0004
文摘Cu/W multilayer nanofilms are prepared in pure Ar and He/At mixing atmosphere by the rf magnetron sputtering method. The cross-sectional morphology and the defect distribution of the Cu/W multilayer nanofilms are characterized by scanning electron microscopy and Doppler broadening positron annihilation spectroscopy. The results show that plenty of point defects can be produced by introducing He during the growth of the multilayer nanofilms. With the increasing natural storage time, He located in the near surface of the Cu//W multilayer nanofilm at room temperature could be released gradually and induce the segregation of He-related defects due to the diffusion of He and defects. However, more He in the deep region spread along the interface of the Cu/W multilayer nanofilm. Meanwhile, the layer interfaces can still maintain their stability.
基金Funded by the National Natural Science Foundation of China(No.21676015)
文摘The amorphous I/Au composite nanofilms were prepared by low vacuum direct current sputtering(LVDCS) method. The optimized preparation technologies contain growth pressure, time, gaseous environment and annealing conditions. The maximum fluorescence emission(λmax^em) of I/Au nanofilms was observed at wavelength of 375 nm, and the intensity of fluorescence emission peak of annealed I/Au films was smaller than that of unannealed one due to fewer amorphous Au nanoparticles, caused by annealing treatment. In the UV-Vis absorption spectra, the intensity of UV-Vis absorption peak of annealed I/Au nanofilms is larger than that of the unannealed one. This work also developed a new way to grow I/Au composite fluorescent thin films.
文摘Terahertz radiation (THzR) consists of electromagnetic waves within the band of frequencies from 0.3 to 3 terahertz with the wavelengths of radiation in the range from 0.1 mm to 1 mm, respectively. The technology for generating and manipulating THzR is still in its initial stage. Herein, we demonstrate that the wrinkled Si1–xGex/Si1–yGey films can be used as radiation sources, which emit electromagnetic waves (EMW) in a very wide range of the frequencies including the terahertz band from 0.3 to 3 THz and far IR from 3 THz to 20 THz. These findings provide the theoretical foundation for the wrinkled nanofilm radiation emission and may allow, to some extent, to fill the terahertz gap.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11772294,11621062,and 11302189)the Fundamental Research Funds for the Central Universities,China(Grant No.2017QNA4031)
文摘Surface charges can modify the elastic modulus of nanostructure,leading to the change of the phonon and thermal properties in semiconductor nanostructure.In this work,the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated.In the framework of continuum mechanics,the modified elastic modulus can be derived for the nanofilm with surface charges.The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation,phonon group velocity,density of states of phonons in nanofilm with the surface charges.The phonon thermal conductivity of nanofilm can be obtained by considering surface charges.The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm.Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons.The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm.Based on these theoretical results,one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.
基金support received from the National Natural Science Foundation of China (11472243, 11302189, 11321202)the Doctoral Fund of Ministry of Education of China (20130101120175)
文摘The effect of piezoelectricity on phonon properties and thermal conductivity of gallium nitride (GaN) nanofilms is theoretically investigated. The elasticity model is utilized to derive the phonon properties in spatially confined GaN nanofilms. The piezoelectric constitutive relation in GaN nanofilms is taken into account in calculating the phonon dispersion relation. The modified phonon group velocity and phonon density of state as well as the phonon thermal conductivity are also obtained due to the contribution of piezoelectricity. Theoretical results show that the piezoelectricity in GaN nanofilms can change significantly the phonon properties such as the phonon group velocity and density of states, resulting in the variation of the phonon thermal conductivity of GaN nanofilms remarkably. Moreover, the piezoelectricity of GaN can modify the dependence of thermal conductivity on the geometrical size and temperature. These results can be useful in modeling the thermal performance in the active region of GaN-based electronic devices.
基金supported by the National Natural Science Foundation of China(Grant Nos 50676046 and 50730006)
文摘The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen (77K) and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann-Franz law. We build an electron relaxation model based on Matthiessen's rule to analyse the thermal conductivity and employ the Mayadas & Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann-Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.
基金supported by the National Natural Science Foundation of China(Grant No.61274007)the Beijing Natural Science Foundation,China(GrantNo.4132074)
文摘We investigate the formations of wurtzite (WZ) SiC nano polytypes in zinc blende (ZB) SiC nanofilms hetero-grown on Si-(100) substrates via low pressure chemical vapor deposition (LPCVD) by adjusting the Si/C ratio of the introduced precursors. Through SEM, TEM, and Raman characterizations, we find that the nanofilms consist of discrete WZ SiC nano polytypes and ZB SiC polytypes composed of WZ polytypes (WZ + ZB) and disordered ZB SiC polytypes, respectively, according to Si/C ratios of 0.5, 1.5, and 3. We attribute the WZ polytype formation to being due to a kinetic mechanism based on the Si/C surface saturation control.
文摘In this work, the prerequisite and mode of electromagnetic response of Al nanof ilms to electromagnetic wave field was suggested. Reflectance, transmittance in infrared region and carrier density of the films was measured. With the carrier density of the films, the dependence of their plasma frequencies on the film thickness was obtained. On the other hand, the dependence of absorptance on the frequency of electromagnetic wave field was set up by using the measured reflectance and transmittance, which provided plasma frequency-film thickness relation as well. Similarity of both plasma frequency-film thickness relations proved plasma resonance as a mode of electromagnetic response in Al nanofilms.
基金the National Key Research and Development Program of China(No.2017YFA0208200)the National Natural Science Foundation of China(Nos.22022505 and 21872069)+5 种基金the Fundamental Research Funds for the Central Universities of China(Nos.020514380266,020514380272,and 020514380274)the General Project of the Joint Fund of Equipment Pre-research and the Ministry of Education(No.8091B02052407)the Scientific and Technological Achievements Transformation Special Fund of Jiangsu Province(No.BA2023037)the Scientific and Technological Innovation Special Fund for Carbon Peak and Carbon Neutrality of Jiangsu Province(No.BK20220008)the Nanjing International Collaboration Research Program(Nos.202201007 and 2022SX00000955)the Suzhou Gusu Leading Talent Program of Science and Technology Innovation and Entrepreneurship in Wujiang District(No.ZXL2021273).
文摘The electrocatalytic reduction of CO_(2)is a promising pathway to generate renewable fuels and chemicals.However,its advancement is impeded by the absence of electrocatalysts with both high selectivity and stability.Here,we present a scalable in-situ thermal evaporation technique for synthesizing series of Bi,In,and Sn nanofilms on carbon felt(CF)substrates with a high-aspect-ratio structure.The resulting main-group metal nanofilms exhibit a homogeneously distributed and highly exposed catalyst surface with ample active sites,thereby promoting mass transport and ad-/desorption of reaction intermediates.Benefiting from the unique fractal morphology,the Bi nanofilms deposited on CF exhibit optimal catalytic activities for CO_(2)electroreduction among the designed metal nanofilms electrodes,with the highest Faradaic efficiency of 96.9%for formate production at−1.3 V vs.reversible hydrogen electrode(RHE)in H-cell.Under an industrially relevant current density of 221.4 mA·cm−2 in flow cells,the Bi nanofilms retain a high Faradaic efficiency of 81.7%at−1.1 V(vs.RHE)and a good long-term stability for formate production.Furthermore,a techno-economic analysis(TEA)model shows the potential commercial viability of electrocatalytic CO_(2)conversion into formate using the Bi nanofilms catalyst.Our results offer a green and convenient approach for in-situ fabrication of stable and inexpensive thin-film catalysts with a fractal structure applicable to various industrial settings.
基金supported by the National Key Research and Development Program of China(2020YFE0100300,2018YFA0208502)the National Natural Science Foundation of China(51925307,21733010,32001083,22105210)+2 种基金the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(ZDBS-LY-SLH031)the Beijing National Laboratory for Molecular Sciences(BNLMS-CXXM2020BMS20025).the Strategic Priority Research Program,Chinese Academy of Sciences(XDB28000000)the National Natural Science Foundation of China(12174388).
文摘Nature provides diverse models for manufacturing complex and hierarchical materials by controlling molecular assembly at scales ranging from sub-nano to macroscale. However, developing artificial strategies for manufacturing hierarchical materials with comparable machining capabilities to nature is extremely challenging. Here, a templated freezing assembly strategy is reported, enabling simultaneously regulating molecular assembly spatiotemporally to obtain hierarchical materials with structure control from sub-nano to macroscale. In this way, unique centimeter-scale freestanding nanofilms are assembled from diverse molecules, e.g., proteins and conjugated polymers. A generated silk fibroin(SF) nanofilm presents a tunable β-sheet fraction from 5% to 47%, fiber width from 30 to 3,000 nm, and micro-textures with desired shapes. Such a strategy will lay the foundation for customizing hierarchical functional materials from single or multi-component molecules, e.g., desired bioscaffolds with controlled cell adhesion.
基金supported by the Key R&D and Promotion Projects in Henan Province,China(Nos.212102310081,232102320125).
文摘Recently,Livingston and his colleagues published two articles in Nature and Science,respectively,to tackle the challenges of accurate molecular sieving and crude oil separation in the field of membrane separation by preparing ultrathin nanofilms through interfacial polymerization.One is that the nanofilms with ordered sub-nanopores achieve accurate molecular sieving atångström precision,and the other is that the permeability of hydrophobic polyamide nanofilms to hydrophobic liquid is significantly enhanced by an order of magnitude.The thoughtful design and excellent performance provide a feasible strategy for the development of membrane separation,and show great potential in industrial applications(drug separation and crude oil fractionation).
基金Project supported by National Key Projects for Basic Research of China(2012CB626815)the National Natural Science Foundation of China(11264026,10904065)+1 种基金Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region(NJYT-12-B05)Inner Mongolia Science Foundation for Distinguished Young Scholars(2014JQ01)
文摘Single-phase multiferroic BiFeO3 and rare-earth metal of holmium (Ho) doped BiFeO3 nanofilms were prepared on Pt (100)/Ti/SiO2/Si wafer via solution-gelation technique. It was suggested that the lattice distortion happened with the lattice parameter of d decreasing after doping rare-earth metal of Ho. Meanwhile, the structure of nanofilms transformed from hexahedron phase to tetragonal phase after doping Ho. The analysis on X-ray photoelectron spectroscopy (XPS) indicated that the ratio of Fe3~ cations to Fe2+ cations increased with the increase of binding energy between Fe and O and decrease of that between Bi and O after doping Ho. The present work provided an available way on enhancing multiferroic of BiFeO3 nanofilms.
文摘Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption owing to the low impedance matching between the absorbers and air. Carbon nanostructures are very promising candidates for high-efficiency absorption because of their attractive features including low density, high surface area, and good stability. Herein, a new strategy is proposed to improve the impedance matching of dielectric loss materials using electrospun carbon nanofibers as an example. The carbon nanofibers are coated with specifically designed gradient multilayer nanofilms with gradually increasing electroconductibility synthesized by doping ZnO with different A1203 content (AZO) by atomic layer deposition. The gradient nanofilms are composed of five layers of dielectric films, namely, pure A1203, AZO (5:1, the pulse cycle ratio of ZnO to A1203), pure ZnO, AZO (10:1), and AZO (20:1). The versatile gradient films serve as intermediate layers to tune the impedance matching between air and the carbon nanofiber surfaces. Therefore, the carbon nanofibers coated with gradient films of rationally selected thicknesses exhibit remarkably enhanced microwave absorption performance, and the optimal reflection loss reaches -58.5 dB at 16.2 GHz with a thickness of only 1.8 mm. This work can help further understand the contribution of impedance matching to microwave absorption. Our strategy is general and can be applied to improve the absorption properties of other dielectric loss materials and even for applications in other fields.
基金The work was supported by the National Natural Science Foundation of China(No.51873088)Tianjin Municipal Science and Technology Commission(No.18JCZDJC38400)111 Project(B18030)in China.
文摘Fabrication of large-area and uniform semiconducting thin films of two-dimensional(2D)materials is paramount for the full exploitation of their atomic thicknesses and smooth surfaces in integrated circuits.In addition to elaborate vapor-based synthesis techniques for the wafer-scale growth of 2D films,solution-based approaches for high-quality thin films from the liquid dispersions of 2D flakes,despite underdeveloped,are alternative cost-effective tactics.Here,we present layer-by-layer(LbL)assembly as an effective approach to obtaining scalable semiconducting films of molybdenum disulfide(MoS_(2))for field-effect transistors(FETs).LbL assembly is achieved by coordinating electrochemically exfoliated MoS_(2) with cationic poly(diallyldimethylammonium chloride)(PDDA)through electrostatic interactions.The PDDA/MoS_(2) percolating nanofilms show controlled and self-limited growth on a variety of substrates,and are easily patterned through lift-off processes.Ion gel gated FETs are fabricated on these MoS_(2) nanofilms,and they show mobilities of 9.8 cm^(2)·V^(−1)·s^(−1),on/off ratios of 2.1×10^(5) with operating voltages less than 2 V.The annealing temperature in the fabrication process can be as low as 200℃,thereby permitting the fabrication of flexible FETs on polyethylene terephthalate substrates.The LbL assembly technique holds great promise for the large-scale fabrication of flexible electronics based on solution-processed 2D semiconductors.
基金supported by the National Key R&D Program of China(Grant No.2017YFB0701604)support by the National Natural Science Foundation of China(Grant No.11672168)
文摘The interaction between mechanics and chemistry plays an essential and critical role in the behaviors and properties of materials,especially in nanoscale alloys. Based on the classical Gibbs and Mc Lean adsorption isotherms, the present study takes the freestanding nanometer thick films of Pd-H solid solutions as a typic example to investigate surface segregation of hydrogen. The surface eigenstress model is further developed here to give analytic formulas, which have the capability to quantitatively predict the size-dependent surface segregation. Molecular dynamics(MD) simulations are conducted on free-standing Pd-H nanofilms.The MD simulations verify the theoretical analytic results and determine the values of parameters involved in the theoretical analysis. The integrated theoretical and numerical study exhibits that both surface excess H concentration and apparent biaxial Young’s modulus of Pd-H thin films depend on the nominal H concentration and the film thickness. The MD simulations determine the values of three parameters involved in the theoretical analysis. Especially, the parameter of the differentiation in reference chemical potential behaves like the molar free energy of segregation in the Mc Lean adsorption isotherm.
基金National Natural Science Foundation of China,Grant/Award Numbers:52090030,51973191,92164106,61874094China Postdoctoral Science Foundation,Grant/Award Number:2020M681819+2 种基金Fundamental Research Funds for the Central Universities,Grant/Award Numbers:K20200060,2021FZZX001-17Key Laboratory of Novel Adsorption and Separation Materials and Application Technology of Zhejiang Province,Grant/Award Number:512301-I21502Hundred Talents Program of Zhejiang University,Grant/Award Number:188020*194231701/113。
文摘Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range.However,the limited absorption and serious backscattering of hot-electrons result in inadequate quantum yields,especially in the mid-infrared range.Here,we report a macroscopic assembled graphene(nMAG)nanofilm/silicon heterojunction for ultrafast mid-infrared photodetection.The assembled Schottky diode works in 1.5-4.0μm at room temperature with fast response(20-30 ns,rising time,4 mm2 window)and high detectivity(1.61011 to 1.9109 Jones from 1.5 to 4.0μm)under the pulsed laser,outperforming single-layer-graphene/silicon photodetectors by 2-8 orders.These performances are attributed to the greatly enhanced photo-thermionic effect of electrons in nMAG due to its high light absorption(~40%),long carrier relaxation time(~20 ps),low work function(4.52 eV),and suppressed carrier number fluctuation.The nMAG provides a long-range platform to understand the hot-carrier dynamics in bulk 2D materials,leading to broadband and ultrafast MIR active imaging devices at room temperature.
文摘1 Results Homogeneity of fibroin thin films by pulsed laser deposition (PLD) was significantly improved by introducing autogenous binders to consolidate and homogenize the irradiation targets.Homogenization includes among others,decreases in the size of nanostructural units and the fractional debris.Simultaneously,the deposition rate was substantially increased.Autogenous binders are prepared via degumming and liquefaction of fibroin by using Na2CO3 and LiBr,respectively.We also found that optically hom...
文摘1 Results Protein thin films gather increasing interests in various biomedical-related materials including surface treatment of implants and bio-tips.Processes via colloid chemical routes such as simple adsorption,dip-or spin coating enable formation of protein thin films on various substrates.Related methods are facile andconvenient without sophisticated instrumentation but not without restriction.Typical drawbacks are limited solubility of the film-forming species and wettability determined by the com...