Silicon nanowires of high purity and regular morphology are of prime importance to ensure high specific capacities of lithium-ion batteries and reproducible electrode assembly process.Using nickel formate as a metal c...Silicon nanowires of high purity and regular morphology are of prime importance to ensure high specific capacities of lithium-ion batteries and reproducible electrode assembly process.Using nickel formate as a metal catalyst precursor,straight silicon nanowires(65–150 nm in diameter)were directly prepared by electrolysis from the Ni/SiO2 porous pellets with 0.8 wt%nickel content in molten CaCl2 at 900℃.Benefiting from their straight appearance and high purity,the silicon nanowires therefore offered an initial coulombic efficiency of 90.53% and specific capacity of 3377 m Ah/g.In addition,the silicon nanowire/carbon composite exhibited excellent cycle performance,retaining 90.38%of the initial capacity after 100 cycles.Whilst further study on the charge storage performance is still ongoing,these preliminary results demonstrate that nickel formate is an efficient and effective metal catalyst precursor for catalytic preparation of high purity straight silicon nanowires via the molten salt electrolysis,which is suitable for large-scale production.展开更多
Large-scale amorphous silicon nanowires (SiNWs) with a diameter about 100 nm and a length of dozens of micrometers on silicon wafers were synthesized by thermal evaporation of silicon monoxide (SiO). Scanning electron...Large-scale amorphous silicon nanowires (SiNWs) with a diameter about 100 nm and a length of dozens of micrometers on silicon wafers were synthesized by thermal evaporation of silicon monoxide (SiO). Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show that the silicon nanowires are smooth. Selected area electron diffraction (SAED) shows that the silicon nanowires are amorphous and en-ergy-dispersive X-ray spectroscopy (EDS) indicates that the nanowires have the composition of Si and O elements in an atomic ratio of 1:2,their composition approximates that of SiO2. SiO is considered to be used as a Si sources to produce SiNWs. We conclude that the growth mechanism is closely related to the defect structure and silicon monoxide followed by growth through an oxide-assisted vapor-solid reaction.展开更多
The influence of vacancy defect on the doping of silicon nanowires is systematically studied by the first-principles calculations. The atomic structures and electronic properties of vacancies and vacancy-boron （vacan...The influence of vacancy defect on the doping of silicon nanowires is systematically studied by the first-principles calculations. The atomic structures and electronic properties of vacancies and vacancy-boron （vacancy-phosphor） com- plexes in H-passivated silicon nanowire with a diameter of 2.3 nm are explored. The results of geometry optimization indicate that a central vacancy can exist stably, while the vacancy at the edge of the nanowire undergoes a local surface reconstruction, which results in the extradition of the vacancy out of the nanowire. Total-energy calculations indicate that the central vacancy tends to form a vacancy-dopant defect pair. Further analysis shows that n-type doping efficiency is strongly inhibited by the unintentional vacancy defect. In contrast, the vacancy defect has little effect on p-type doping. Our results suggest that the vacancy defect should be avoided during the growth and the fabrication of devices.展开更多
Using the Stillinger Weber （SW） potential model,we investigate the thermal stability of pristine silicon nanowires based on classical molecular dynamics （MD） simulations.We explore the structural evolutions and th...Using the Stillinger Weber （SW） potential model,we investigate the thermal stability of pristine silicon nanowires based on classical molecular dynamics （MD） simulations.We explore the structural evolutions and the Lindemann indices of silicon nanowires at different temperatures in order to unveil atomic-level melting behaviour of silicon nanowires.The simulation results show that silicon nanowires with surface reconstructions have higher thermal stability than those without surface reconstructions,and that silicon nanowires with perpendicular dimmer rows on the two （100） surfaces have somewhat higher thermal stability than nanowires with parallel dimmer rows on the two （100） surfaces.Futher-more,the melting temperature of silicon nanowires increases as their diameter increases and reaches a saturation value close to the melting temperature of bulk silicon. The value of the Lindemann index for melting silicon nanowires is 0.037.展开更多
We report on the fabrication and performance of a room-temperature NO2 gas sensor based on a WO3 nanowires/porous silicon hybrid structure. The W18O49 nanowires are synthesized directly from a sputtered tungsten film ...We report on the fabrication and performance of a room-temperature NO2 gas sensor based on a WO3 nanowires/porous silicon hybrid structure. The W18O49 nanowires are synthesized directly from a sputtered tungsten film on a porous silicon （PS） layer under heating in an argon atmosphere. After a carefully controlled annealing treatment, WO3 nanowires are obtained on the PS layer without losing the morphology. The morphology, phase structure, and crystallinity of the nanowires are investigated by using field emission scanning electron microscopy （FESEM）, X-ray diffractometer （XRD）, and high-resolution transmission electron microscopy （HRTEM）. Comparative gas sensing results indicate that the sensor based on the WO3 nanowires exhibits a much higher sensitivity than that based on the PS and pure WO3 nanowires in detecting NO2 gas at room temperature. The mechanism of the WO3 nanowires/PS hybrid structure in the NO2 sensing is explained in detail.展开更多
Large-scale uniform nanostructured surface with superwettability is crucial in both fundamental research and engineering applications.A facile and controllable approach was employed to fabricate a superwetting tilted ...Large-scale uniform nanostructured surface with superwettability is crucial in both fundamental research and engineering applications.A facile and controllable approach was employed to fabricate a superwetting tilted silicon nanowires(TSNWs) surface through metal-assisted chemical etching and modification with low-surface-energy material.The contact angle(CA) measurements of the nanostructured surface show a large range from the superhydrophilicity(the CA approximate to 0°) to superhydrophobicity(the CA up to 160°).The surface becomes antiadhesion to water upon nanostructuring with a measured sliding angle(a) close to 0°.Moreover,the fluorinated TSNWs surface exhibits excellent stability and durability because strong chemical bonding has been formed on the surface.展开更多
Classic field ionization requires extremely high positive electric fields, of the order of a few million volts per centimeter. Here we show that field ionization can occur at dramatically lower fields on the electrode...Classic field ionization requires extremely high positive electric fields, of the order of a few million volts per centimeter. Here we show that field ionization can occur at dramatically lower fields on the electrode of silicon nanowires （SiNWs） with dense surface states and large field enhancement factor. A field ionization structure using SiNWs as the anode has been investigated, in which the SiNWs were fabricated by improved chemical etching process. At room temperature and atmospheric pressure, breakdown of the air is reproducible with a fixed anode-to-cathode distance of 0.5 μm. The breakdown voltage is -38 V, low enough to be achieved by a batterypowered unit. Two reasons can be given for the low breakdown voltage. First, the gas discharge departs from the Paschen＇s law and the breakdown voltage decreases sharply as the gap distance falls in μm range. The other reason is the large electric field enhancement factor （β） and the high density of surface defects, which cause a highly non-uniform electric field for field emission to occur.展开更多
Liquid junction solar cell(LJSC) with vertically silicon nanowires(SiNWs) as the primary photosensitizer,co-sensitized with luminescent and narrow gap CdTe nanoparticles,and cuboidal microstructures of zinc tetrapheny...Liquid junction solar cell(LJSC) with vertically silicon nanowires(SiNWs) as the primary photosensitizer,co-sensitized with luminescent and narrow gap CdTe nanoparticles,and cuboidal microstructures of zinc tetraphenyl porphyrin(ZnTPP) dye offers broad and intense visible light absorption that translates into a maximum power conversion efficiency(PCE) of 9.09%,when combined with a polymeric gel of a I_(2)/I^(-)redox couple as the hole transport material and a counter electrode(CE) of poly(3,4-ethyelenedioxythio phene) doped with imide ions(PEDOT-N(CF_(3) SO_(2))_(2)),under 1 sun irradiance.The p-type CdTe efficiently scavenges holes from SiNWs and simultaneously allows the passage of photoexcited electrons from ZnTPP to SiNWs via electrical conduction thus imparting an enhanced solar cell performance.Cosensitization also supresses back electron transfer effectively,as is inferred from a ~68% enhancement in PCE compared to SiNWs alone.Optimization of the CE entailed the evaluation of the effect of dopant anion:imide versus dicyanamide in PEDOT,and revealed that the presence of macro-cracks in the polymer surface,a deeper work function,and a lower electrical conductance are the shortcomings of the dicyanamide doped PEDOT and reduce the overall PCE,compared to imide.This study brings out how by judicious choice of photoanode and CE components,efficient,stable and easy-to-assemble LJSCs can be developed.展开更多
Thermal transport in silicon nanowires(SiNWs)has recently attracted considerable attention due to their potential applications in energy harvesting and generation and thermal management.The adjustment of the thermal c...Thermal transport in silicon nanowires(SiNWs)has recently attracted considerable attention due to their potential applications in energy harvesting and generation and thermal management.The adjustment of the thermal conductivity of SiNWs through surface effects is a topic worthy of focus.In this paper,we briefly review the recent progress made in this field through theoretical calculations and experiments.We come to the conclusion that surface engineering methods are feasible and effective methods for adjusting nanoscale thermal transport and may foster further advancements in this field.展开更多
The ultra-low thermal conductivity of roughened silicon nanowires(SiNWs)can not be explained by the classical phonon-surface scattering mechanism.Although there have been several efforts at developing theories of phon...The ultra-low thermal conductivity of roughened silicon nanowires(SiNWs)can not be explained by the classical phonon-surface scattering mechanism.Although there have been several efforts at developing theories of phonon-surface scattering to interpret it,but the underlying reason is still debatable.We consider that the bond order loss and correlative bond hardening on the surface of roughened SiNWs will deeply influence the thermal transport because of their ultra-high surface-to-volume ratio.By combining this mechanism with the phonon Boltzmann transport equation,we explicate that the suppression of high-frequency phonons results in the obvious reduction of thermal conductivity of roughened SiNWs.Moreover,we verify that the roughness amplitude has more remarkable influence on thermal conductivity of SiNWs than the roughness correlation length,and the surface-to-volume ratio is a nearly universal gauge for thermal conductivity of roughened SiNWs.展开更多
MACE (Metal-Assisted Chemical Etching) approach has drawn a lot of attentions due to its ability to create highly light-absorptive silicon surface. This method can generate numerous cylindrical shape microstructure on...MACE (Metal-Assisted Chemical Etching) approach has drawn a lot of attentions due to its ability to create highly light-absorptive silicon surface. This method can generate numerous cylindrical shape microstructure on the surface of silicon like a forest, which is called “silicon nanowires arrays”. This structure can dramatically suppress both reflection and transmission at the wavelength range from 400 nm to near-infrared 1800 nm by increasing the propagation path of light. In this paper, ordered silicon nanowires arrays with a large area are prepared by wet chemical etching. It is demonstrated that the SiNWs (Silicon nanowires) arrays with different morphologies can be fabricated from monocrystalline silicon of a given orientation by changing silver-plating time. Excellent anti-reflection performance in broadband wavelengths and incident angle is obtained. The fabrication method and potential application of such SiNWs in the field of photoelectric detection have great value and can provide reference for further research in this field.展开更多
This computational research study analyzes the increase of the specific charge capacity that comes with the reduction of the anisotropic volume expansion during lithium ion insertion within silicon nanowires. This res...This computational research study analyzes the increase of the specific charge capacity that comes with the reduction of the anisotropic volume expansion during lithium ion insertion within silicon nanowires. This research paper is a continuation from previous work that studied the expansion rate and volume increase. It has been determined that when the lithium ion concentration is decreased by regulating the amount of Li ion flux, the lithium ions to silicon atoms ratio, represented by x, decreases within the amorphous lithiated silicon (a-LixSi) material. This results in a decrease in the volumetric strain of the lithiated silicon nanowire as well as a reduction in Maxwell stress that was calculated and Young’s elastic module that was measured experimentally using nanoindentation. The conclusion as will be seen is that as there is a decrease in lithium ion concentration there is a corresponding decrease in anisotropic volume and a resulting increase in specific charge capacity. In fact the amplification of the electromagnetic field due to the electron flux that created detrimental effects for a fully lithiated silicon nanowire at x = 3.75 which resulted in over a 300% volume expansion becomes beneficial with the decrease in lithium ion flux as x approaches 0.75, which leads to a marginal volume increase of ~25 percent. This could lead to the use of crystalline silicon, c-Si, as an anode material that has been demonstrated in many previous research works to be ten times greater charge capacity than carbon base anode material for lithium ion batteries.展开更多
In this paper, we simulate the propagation of chirped pulses in silicon nanowires by solving the nonlinear Schrodinger equation (NLSE) using the split-step Fourier (SSF) method. The simulations are performed both for ...In this paper, we simulate the propagation of chirped pulses in silicon nanowires by solving the nonlinear Schrodinger equation (NLSE) using the split-step Fourier (SSF) method. The simulations are performed both for the pulse shape (time domain) and for the pulse spectrum (frequency domain), and various linear and nonlinear effects changing the shape and the spectrum of the pulse are analyzed. Owing to the high nonlinear coefficient and a very small effective-mode area, the required length for observing nonlinear effects in nanowires is much shorter than that of conventional optical fibers. The impacts of loss, nonlinear effects, second- and third-order dispersion coefficients and the chirp parameter on pulse propagation along the nanowire are investigated. The results show that the sign and the value of the chirp parameter have important role in pulse propagation so that in the anomalous dispersion regime, the compression occurs for the up- chirped pulses, whereas the broadening takes place for the down-chirped pulses. The opposite situation happens for up- and down-chirped pulses propagating in the normal dispersion regime.展开更多
3C-SiC又称β-SiC,有着优异的耐高温、耐腐蚀、耐辐照性能,是反应堆这类复杂环境中的理想材料。近年来,一维碳化硅纳米线材料成为碳化硅材料研究领域的热门研究方向,同时也面临加工手段匮乏、加工难度大的问题。我们通过化学气相沉积法...3C-SiC又称β-SiC,有着优异的耐高温、耐腐蚀、耐辐照性能,是反应堆这类复杂环境中的理想材料。近年来,一维碳化硅纳米线材料成为碳化硅材料研究领域的热门研究方向,同时也面临加工手段匮乏、加工难度大的问题。我们通过化学气相沉积法成功制备了含有高密度堆叠层错的3C-SiC纳米线,并采用扫描电子显微镜(Scanning Electron Microscope,SEM)、透射电子显微镜(Transmission Electron Microscope,TEM)、X射线衍射(X-Ray Diffraction,XRD)以及拉曼光谱(Raman spectrum)等多种手段对制备出来的碳化硅纳米线进行了微观结构表征,揭示了其独特的微观形态和晶体结构特征;进一步研究了超声裁剪碳化硅纳米线,利用“气泡-射流”模型结合碳化硅纳米线的形态解释了碳化硅纳米线的超声裁剪过程,探索了碳化硅纳米线的直径、强度、缺陷等对其在超声过程中断裂行为的影响。本研究为碳化硅纳米线的超声裁剪加工和纳米线的强度研究提供了新的视角,对于未来碳化硅纳米线在核能领域的应用具有重要的意义。展开更多
Mimicking the structure of natural bone collagen fibers/hydroxyapatite(HA)to synthesize large size of HA for accelerated bone repair remains a challenge.Herein,silicon nitride nanowires(SN)-graphene(GE)was designed by...Mimicking the structure of natural bone collagen fibers/hydroxyapatite(HA)to synthesize large size of HA for accelerated bone repair remains a challenge.Herein,silicon nitride nanowires(SN)-graphene(GE)was designed by the chemical vapor deposition,forming SN-GE(SG)similar to collagen fibers.Then,the large size HA was assembled onto SG by pulsed electrochemical deposition,the SG/HA(SGH)mimics the collagen fibers/HA structure of bone.The introduction of SG induces HA to large size grow in the form of coral-like.HA can be grown on a large size inextricably with the existence of GE modified layers.On the one hand,the upright GE sheets effectively increases the surface roughness which enhances the nucleation site of HA.On the other hand,the C=O provides chemical bonding and induces HA nucle-ation.Compared with SN/HA(SH),the porosity of SGH decreased by 71%.The average diameter of the SGH is(9.76±0.25)mm.Compared with SH,the diameter of SGH is 22 times larger than the diameter of SH.Indicating that SG induces large size growth of HA.Our work can provide a general strategy for the efficient preparation of biological scaffolds with large size HA that can be used in bone tissue engineering.展开更多
基金financially supported by the National Key R&D Program of China (No. 2016YFB0100400)the National Natural Science Foundation of China (No. 51604032)
文摘Silicon nanowires of high purity and regular morphology are of prime importance to ensure high specific capacities of lithium-ion batteries and reproducible electrode assembly process.Using nickel formate as a metal catalyst precursor,straight silicon nanowires(65–150 nm in diameter)were directly prepared by electrolysis from the Ni/SiO2 porous pellets with 0.8 wt%nickel content in molten CaCl2 at 900℃.Benefiting from their straight appearance and high purity,the silicon nanowires therefore offered an initial coulombic efficiency of 90.53% and specific capacity of 3377 m Ah/g.In addition,the silicon nanowire/carbon composite exhibited excellent cycle performance,retaining 90.38%of the initial capacity after 100 cycles.Whilst further study on the charge storage performance is still ongoing,these preliminary results demonstrate that nickel formate is an efficient and effective metal catalyst precursor for catalytic preparation of high purity straight silicon nanowires via the molten salt electrolysis,which is suitable for large-scale production.
文摘Large-scale amorphous silicon nanowires (SiNWs) with a diameter about 100 nm and a length of dozens of micrometers on silicon wafers were synthesized by thermal evaporation of silicon monoxide (SiO). Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show that the silicon nanowires are smooth. Selected area electron diffraction (SAED) shows that the silicon nanowires are amorphous and en-ergy-dispersive X-ray spectroscopy (EDS) indicates that the nanowires have the composition of Si and O elements in an atomic ratio of 1:2,their composition approximates that of SiO2. SiO is considered to be used as a Si sources to produce SiNWs. We conclude that the growth mechanism is closely related to the defect structure and silicon monoxide followed by growth through an oxide-assisted vapor-solid reaction.
基金supported by the National Natural Science Foundation of China(Grant Nos.61006051 and 61177050)the Zhejiang Provincial Natural Science Foundation,China(Grant No.Y1110777)
文摘The influence of vacancy defect on the doping of silicon nanowires is systematically studied by the first-principles calculations. The atomic structures and electronic properties of vacancies and vacancy-boron （vacancy-phosphor） com- plexes in H-passivated silicon nanowire with a diameter of 2.3 nm are explored. The results of geometry optimization indicate that a central vacancy can exist stably, while the vacancy at the edge of the nanowire undergoes a local surface reconstruction, which results in the extradition of the vacancy out of the nanowire. Total-energy calculations indicate that the central vacancy tends to form a vacancy-dopant defect pair. Further analysis shows that n-type doping efficiency is strongly inhibited by the unintentional vacancy defect. In contrast, the vacancy defect has little effect on p-type doping. Our results suggest that the vacancy defect should be avoided during the growth and the fabrication of devices.
基金Project supported by the National Natural Science Foundation of China (Grant No 10774127)
文摘Using the Stillinger Weber （SW） potential model,we investigate the thermal stability of pristine silicon nanowires based on classical molecular dynamics （MD） simulations.We explore the structural evolutions and the Lindemann indices of silicon nanowires at different temperatures in order to unveil atomic-level melting behaviour of silicon nanowires.The simulation results show that silicon nanowires with surface reconstructions have higher thermal stability than those without surface reconstructions,and that silicon nanowires with perpendicular dimmer rows on the two （100） surfaces have somewhat higher thermal stability than nanowires with parallel dimmer rows on the two （100） surfaces.Futher-more,the melting temperature of silicon nanowires increases as their diameter increases and reaches a saturation value close to the melting temperature of bulk silicon. The value of the Lindemann index for melting silicon nanowires is 0.037.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61271070,61274074,and 60771019)the Key Research Program of Application Foundation and Advanced Technology of Tianjin,China(Grant No.11JCZDJC15300)
文摘We report on the fabrication and performance of a room-temperature NO2 gas sensor based on a WO3 nanowires/porous silicon hybrid structure. The W18O49 nanowires are synthesized directly from a sputtered tungsten film on a porous silicon （PS） layer under heating in an argon atmosphere. After a carefully controlled annealing treatment, WO3 nanowires are obtained on the PS layer without losing the morphology. The morphology, phase structure, and crystallinity of the nanowires are investigated by using field emission scanning electron microscopy （FESEM）, X-ray diffractometer （XRD）, and high-resolution transmission electron microscopy （HRTEM）. Comparative gas sensing results indicate that the sensor based on the WO3 nanowires exhibits a much higher sensitivity than that based on the PS and pure WO3 nanowires in detecting NO2 gas at room temperature. The mechanism of the WO3 nanowires/PS hybrid structure in the NO2 sensing is explained in detail.
文摘Large-scale uniform nanostructured surface with superwettability is crucial in both fundamental research and engineering applications.A facile and controllable approach was employed to fabricate a superwetting tilted silicon nanowires(TSNWs) surface through metal-assisted chemical etching and modification with low-surface-energy material.The contact angle(CA) measurements of the nanostructured surface show a large range from the superhydrophilicity(the CA approximate to 0°) to superhydrophobicity(the CA up to 160°).The surface becomes antiadhesion to water upon nanostructuring with a measured sliding angle(a) close to 0°.Moreover,the fluorinated TSNWs surface exhibits excellent stability and durability because strong chemical bonding has been formed on the surface.
基金supported by National Natural Science Foundation of China(Nos.61076070,61204018)Education Committee of Jiangsu Province of China(No.11KJB510023)+1 种基金The Science and Technology Project of Nantong,Jiangsu Province of China(No.BK2012039)The Natural Science Foundation of Nantong University(No.10Z025)
文摘Classic field ionization requires extremely high positive electric fields, of the order of a few million volts per centimeter. Here we show that field ionization can occur at dramatically lower fields on the electrode of silicon nanowires （SiNWs） with dense surface states and large field enhancement factor. A field ionization structure using SiNWs as the anode has been investigated, in which the SiNWs were fabricated by improved chemical etching process. At room temperature and atmospheric pressure, breakdown of the air is reproducible with a fixed anode-to-cathode distance of 0.5 μm. The breakdown voltage is -38 V, low enough to be achieved by a batterypowered unit. Two reasons can be given for the low breakdown voltage. First, the gas discharge departs from the Paschen＇s law and the breakdown voltage decreases sharply as the gap distance falls in μm range. The other reason is the large electric field enhancement factor （β） and the high density of surface defects, which cause a highly non-uniform electric field for field emission to occur.
基金Financial support from the Ministry of Education-Scheme for Transformational and Advanced Research in Sciences (Mo ESTARS, Grant number:STARS/APR2019/CS/375) India。
文摘Liquid junction solar cell(LJSC) with vertically silicon nanowires(SiNWs) as the primary photosensitizer,co-sensitized with luminescent and narrow gap CdTe nanoparticles,and cuboidal microstructures of zinc tetraphenyl porphyrin(ZnTPP) dye offers broad and intense visible light absorption that translates into a maximum power conversion efficiency(PCE) of 9.09%,when combined with a polymeric gel of a I_(2)/I^(-)redox couple as the hole transport material and a counter electrode(CE) of poly(3,4-ethyelenedioxythio phene) doped with imide ions(PEDOT-N(CF_(3) SO_(2))_(2)),under 1 sun irradiance.The p-type CdTe efficiently scavenges holes from SiNWs and simultaneously allows the passage of photoexcited electrons from ZnTPP to SiNWs via electrical conduction thus imparting an enhanced solar cell performance.Cosensitization also supresses back electron transfer effectively,as is inferred from a ~68% enhancement in PCE compared to SiNWs alone.Optimization of the CE entailed the evaluation of the effect of dopant anion:imide versus dicyanamide in PEDOT,and revealed that the presence of macro-cracks in the polymer surface,a deeper work function,and a lower electrical conductance are the shortcomings of the dicyanamide doped PEDOT and reduce the overall PCE,compared to imide.This study brings out how by judicious choice of photoanode and CE components,efficient,stable and easy-to-assemble LJSCs can be developed.
基金Project supported by the National Natural Science Foundation of China(Grant No.11504418)China Scholarship Council(Grant No.201706425053)+1 种基金Basic Research Program in Shenzhen,China(Grant No.JCYJ20160229165210666)the Fundamental Research Funds for the Central Universities of China(Grant No.2015XKMS075)
文摘Thermal transport in silicon nanowires(SiNWs)has recently attracted considerable attention due to their potential applications in energy harvesting and generation and thermal management.The adjustment of the thermal conductivity of SiNWs through surface effects is a topic worthy of focus.In this paper,we briefly review the recent progress made in this field through theoretical calculations and experiments.We come to the conclusion that surface engineering methods are feasible and effective methods for adjusting nanoscale thermal transport and may foster further advancements in this field.
基金the National Natural Science Foundation of China(Grant No.11874145).
文摘The ultra-low thermal conductivity of roughened silicon nanowires(SiNWs)can not be explained by the classical phonon-surface scattering mechanism.Although there have been several efforts at developing theories of phonon-surface scattering to interpret it,but the underlying reason is still debatable.We consider that the bond order loss and correlative bond hardening on the surface of roughened SiNWs will deeply influence the thermal transport because of their ultra-high surface-to-volume ratio.By combining this mechanism with the phonon Boltzmann transport equation,we explicate that the suppression of high-frequency phonons results in the obvious reduction of thermal conductivity of roughened SiNWs.Moreover,we verify that the roughness amplitude has more remarkable influence on thermal conductivity of SiNWs than the roughness correlation length,and the surface-to-volume ratio is a nearly universal gauge for thermal conductivity of roughened SiNWs.
文摘MACE (Metal-Assisted Chemical Etching) approach has drawn a lot of attentions due to its ability to create highly light-absorptive silicon surface. This method can generate numerous cylindrical shape microstructure on the surface of silicon like a forest, which is called “silicon nanowires arrays”. This structure can dramatically suppress both reflection and transmission at the wavelength range from 400 nm to near-infrared 1800 nm by increasing the propagation path of light. In this paper, ordered silicon nanowires arrays with a large area are prepared by wet chemical etching. It is demonstrated that the SiNWs (Silicon nanowires) arrays with different morphologies can be fabricated from monocrystalline silicon of a given orientation by changing silver-plating time. Excellent anti-reflection performance in broadband wavelengths and incident angle is obtained. The fabrication method and potential application of such SiNWs in the field of photoelectric detection have great value and can provide reference for further research in this field.
文摘This computational research study analyzes the increase of the specific charge capacity that comes with the reduction of the anisotropic volume expansion during lithium ion insertion within silicon nanowires. This research paper is a continuation from previous work that studied the expansion rate and volume increase. It has been determined that when the lithium ion concentration is decreased by regulating the amount of Li ion flux, the lithium ions to silicon atoms ratio, represented by x, decreases within the amorphous lithiated silicon (a-LixSi) material. This results in a decrease in the volumetric strain of the lithiated silicon nanowire as well as a reduction in Maxwell stress that was calculated and Young’s elastic module that was measured experimentally using nanoindentation. The conclusion as will be seen is that as there is a decrease in lithium ion concentration there is a corresponding decrease in anisotropic volume and a resulting increase in specific charge capacity. In fact the amplification of the electromagnetic field due to the electron flux that created detrimental effects for a fully lithiated silicon nanowire at x = 3.75 which resulted in over a 300% volume expansion becomes beneficial with the decrease in lithium ion flux as x approaches 0.75, which leads to a marginal volume increase of ~25 percent. This could lead to the use of crystalline silicon, c-Si, as an anode material that has been demonstrated in many previous research works to be ten times greater charge capacity than carbon base anode material for lithium ion batteries.
文摘In this paper, we simulate the propagation of chirped pulses in silicon nanowires by solving the nonlinear Schrodinger equation (NLSE) using the split-step Fourier (SSF) method. The simulations are performed both for the pulse shape (time domain) and for the pulse spectrum (frequency domain), and various linear and nonlinear effects changing the shape and the spectrum of the pulse are analyzed. Owing to the high nonlinear coefficient and a very small effective-mode area, the required length for observing nonlinear effects in nanowires is much shorter than that of conventional optical fibers. The impacts of loss, nonlinear effects, second- and third-order dispersion coefficients and the chirp parameter on pulse propagation along the nanowire are investigated. The results show that the sign and the value of the chirp parameter have important role in pulse propagation so that in the anomalous dispersion regime, the compression occurs for the up- chirped pulses, whereas the broadening takes place for the down-chirped pulses. The opposite situation happens for up- and down-chirped pulses propagating in the normal dispersion regime.
文摘3C-SiC又称β-SiC,有着优异的耐高温、耐腐蚀、耐辐照性能,是反应堆这类复杂环境中的理想材料。近年来,一维碳化硅纳米线材料成为碳化硅材料研究领域的热门研究方向,同时也面临加工手段匮乏、加工难度大的问题。我们通过化学气相沉积法成功制备了含有高密度堆叠层错的3C-SiC纳米线,并采用扫描电子显微镜(Scanning Electron Microscope,SEM)、透射电子显微镜(Transmission Electron Microscope,TEM)、X射线衍射(X-Ray Diffraction,XRD)以及拉曼光谱(Raman spectrum)等多种手段对制备出来的碳化硅纳米线进行了微观结构表征,揭示了其独特的微观形态和晶体结构特征;进一步研究了超声裁剪碳化硅纳米线,利用“气泡-射流”模型结合碳化硅纳米线的形态解释了碳化硅纳米线的超声裁剪过程,探索了碳化硅纳米线的直径、强度、缺陷等对其在超声过程中断裂行为的影响。本研究为碳化硅纳米线的超声裁剪加工和纳米线的强度研究提供了新的视角,对于未来碳化硅纳米线在核能领域的应用具有重要的意义。
基金supported by the National Natural Science Foundation of China under Grant Nos.51872232the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),China(Grant No.136-QP-2015)and“111”project of China(B08040)+2 种基金The Key Scientific and Technological Innovation Research Team of Shaanxi Province(2022TD-31)Project supported by the Joint Funds of the National Natural Science Foundation of China(Grant No.U21B2067)The Key R&D Program of Shaanxi Province(2021ZDLGY14-04).
文摘Mimicking the structure of natural bone collagen fibers/hydroxyapatite(HA)to synthesize large size of HA for accelerated bone repair remains a challenge.Herein,silicon nitride nanowires(SN)-graphene(GE)was designed by the chemical vapor deposition,forming SN-GE(SG)similar to collagen fibers.Then,the large size HA was assembled onto SG by pulsed electrochemical deposition,the SG/HA(SGH)mimics the collagen fibers/HA structure of bone.The introduction of SG induces HA to large size grow in the form of coral-like.HA can be grown on a large size inextricably with the existence of GE modified layers.On the one hand,the upright GE sheets effectively increases the surface roughness which enhances the nucleation site of HA.On the other hand,the C=O provides chemical bonding and induces HA nucle-ation.Compared with SN/HA(SH),the porosity of SGH decreased by 71%.The average diameter of the SGH is(9.76±0.25)mm.Compared with SH,the diameter of SGH is 22 times larger than the diameter of SH.Indicating that SG induces large size growth of HA.Our work can provide a general strategy for the efficient preparation of biological scaffolds with large size HA that can be used in bone tissue engineering.
