In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six （x=0-0.2） electrode alloys were prep...In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six （x=0-0.2） electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of （La, Mg）2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in （La, Mg）2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.展开更多
The formation of periodic layered structure in Ni3Si/Zn diffusion couples with Zn in vapor or liquid state was investigated by SEM-EDS, FESEM and XRD. The results show that the diffusion path in solid-liquid reaction ...The formation of periodic layered structure in Ni3Si/Zn diffusion couples with Zn in vapor or liquid state was investigated by SEM-EDS, FESEM and XRD. The results show that the diffusion path in solid-liquid reaction is Ni3Si/（T＋γ）/γ/…T/γ/Ni4Zn12Si3/γ/…Ni4Zn12Si3/γ/Ni4Zn12Si3/δ…/Ni4Zn12Si3/δ/liquid-Zn, and the diffusion path in solid-vapor reaction is Ni3Si/θ/（T＋γ）/γ/…/T/γ/…T/γ/vapor-Zn. With increasing Zn diffusion flux, the diffusion reaction path moves toward the Zn-rich direction, and the distance from the Ni3Si substrate to the periodic layer pair nearest to the interface decreases. In the initial stage of both reactions,γphase nucleates and grows within T matrix phase at first, and then conjuncts together to form a band to reduce the surface energy. Based on the experimental results and diffusion kinetics analysis, the microstructure differences were compared and the formation mechanism of the periodic layered structure in Ni3Si/Zn system was discussed.展开更多
A porous coral-structured Si/C composite as an anode material was fabricated by coating Si nanoparticles with a carbon layer from polyvinyl alcohol（PVA）, erosion of hydrofluoric（HF） acid, and secondary coating wit...A porous coral-structured Si/C composite as an anode material was fabricated by coating Si nanoparticles with a carbon layer from polyvinyl alcohol（PVA）, erosion of hydrofluoric（HF） acid, and secondary coating with pitch. Three samples with different pitch contents of 30%, 40% and 50% were synthesized. The composition and morphology of the composites were characterized by X-ray diffractometry（XRD） and scanning electron microscopy（SEM）, respectively, and the properties were tested by electrochemical measurements. The results indicated that the composites showed obviously enhanced electrochemical performance compared with that without secondary carbon coating. The second discharge capacity of the composite was 773 m A·h/g at a current density of 100 m A/g, and still retained 669 m A·h/g after 60 cycles with a small capacity fade of less than 0.23%/cycle, while the content of secondary carbon source of pitch was set at 40%. Therefore, the cycle stability of the composite could be excellently improved by regulating carbon content of secondary coating.展开更多
In order to minimize the self-heating effect of the classic SOI devices,SOI structures with Si3 N4 film as a buried insulator （SOSN） are successfully formed using epitaxial layer transfer technology for the first ti...In order to minimize the self-heating effect of the classic SOI devices,SOI structures with Si3 N4 film as a buried insulator （SOSN） are successfully formed using epitaxial layer transfer technology for the first time. The new SOI structures are investigated with high-resolution cross-sectional transmission electron microscopy and spreading resistance profile. Experiment results show that the buried Si3 N4 layer is amorphous and the new SOI material has good structural and electrical properties. The output current characteristics and temperature distribution are simulated and compared to those of standard SOI MOSFETs. Furthermore, the channel temperature and negative differential resistance are reduced during high-temperature operation, suggesting that SOSN can effectively mitigate the selfheating penalty. The new SOI device has been verified in two-dimensional device simulation and indicated that the new structures can reduce device self-heating and increase drain current of the SOI MOSFET.展开更多
Au films with a thickness of about 300 nm were deposited on SiO_2/Si(100) andmica substrates by dc sputtering. X-ray diffraction spectroscopy and field emission scanningelectron microscopy were used to analyze the str...Au films with a thickness of about 300 nm were deposited on SiO_2/Si(100) andmica substrates by dc sputtering. X-ray diffraction spectroscopy and field emission scanningelectron microscopy were used to analyze the structure and internal stress of the Au films. Thefirms grown on SiO_2/Si(100) show a preferential orientation of [111] in the growth direction.However the films grown on mica have mixture crystalline orientations of [111], [200], [220] and[311] in the growth direction and the orientations of [200] and [311] are slightly more than thoseof [111] and [220]. An internal stress in the films grown on SiO_2/Si(100) is tensile. For Au filmsgrown on mica the internal stresses in the [111]- and [311]-orientation grains are compressive whilethose in the [200]- and [220]-orientation grains are tensile. Au films grown SiO_2/Si(100) havesome very large grains with a size of about 400 nm and have a wider grain size distribution comparedwith those grown on mica.展开更多
To mitigate the massive volume expansion of Si-based anode during the charge/discharge cycles,we synthesized a superstructure of Si@Co±NC composite via the carbonization of zeolite imidazolate frameworks incorpor...To mitigate the massive volume expansion of Si-based anode during the charge/discharge cycles,we synthesized a superstructure of Si@Co±NC composite via the carbonization of zeolite imidazolate frameworks incorporated with Si nanoparticles.The Si@Co±NC is comprised of Sinanoparticle core and N-doped/Co-incorporated carbon shell,and there is void space between the core and the shell.When using as anode material for LIBs,Si@Co±NC displayed a super performance with a charge/discharge capacity of 191.6/191.4 mA h g^(-1)and a coulombic efficiency of 100.1%at 1000 mA g^(-1)after 3000 cycles,and the capacity loss rate is 0.022%per cycle only.The excellent electrochemical property of Si@Co±NC is because its electronic conductivity is enhanced by doping the carbon shell with N atoms and by incorporating with Co particles,and the pathway of lithium ions transmission is shortened by the hollow structure and abundant mesopores in the carbon shell.Also,the volume expansion of Si nanoparticles is well accommodated in the void space and suppressed by the carbon host matrix.This work shows that,through designing a superstructure for the anode materials,we can synergistically reduce the work function and introduce the confinement effect,thus significantly enhancing the anode materials’electrochemical performance in LIBs.展开更多
In this work, the Nb-14Si 24Ti-10Cr-2Al-2Hf-0.1Y alloy （at.%） was processed by the liquid-metal-cooled directional solidification （DS） at 1750 ℃ with withdrawal rates of 1.2, 6, 18 mm/min and post heat treatment ...In this work, the Nb-14Si 24Ti-10Cr-2Al-2Hf-0.1Y alloy （at.%） was processed by the liquid-metal-cooled directional solidification （DS） at 1750 ℃ with withdrawal rates of 1.2, 6, 18 mm/min and post heat treatment （HT） at 1450 ℃ for 10 h. The microstructures of the direction- ally solidified and heat treated samples were investigated. The results show that the microstructure of directionally solidified alloy mainly consists of petaloid Nbss ＋ Nb5Si3 eutectics and Ti-rich Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics. With the increase of withdrawal rate, the primary NbsSi3 is eliminated, Nbss ＋ Nb5Si3 eutectic cells turn round and connected with the microstructure refine- ment and Nbss ＋ Nb5Si3 ＋ CrzNb eutectics turn to a river-like morphology. After heat treatment, Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics disappeared and petaloid Nbss ＋ Nb5Si3 eutectics turn to a spe- cific fiber-mesh structure gradually, which is promoted by higher withdrawal rates. Furthermore, both the volume fraction of Cr2Nb and the content of Cr in Nbss of Nbss ＋ Nb5Si3 eutectics change regularly with the increase of withdrawal rate and heat treatment at 1450 ℃ for 10 h.展开更多
Novel models （2× 1） of Si（001）-SiO2 interface structure have been established. The method of the first-principle General Gradient Approximation （GGA） is employed to structurally optimize the established the...Novel models （2× 1） of Si（001）-SiO2 interface structure have been established. The method of the first-principle General Gradient Approximation （GGA） is employed to structurally optimize the established theoretical models under the K-point space of periodic boundary condition. The structures after optimization have been analyzed, and the results show that the interfaces present in disordered state and both Si-O-Si and Si=O structures exist. Meanwhile, the bonding of surface structure is analyzed via the graphics of electron localization function（ELF）.展开更多
We study structural,mechanical,and electronic properties of C_（20）,Si_（20） and their alloys（C_（16）Si_4,C_（12）Si_8,C_8Si_（12）,and C_4Si_（16）） in C2/m structure by using density functional theory（DFT） ba...We study structural,mechanical,and electronic properties of C_（20）,Si_（20） and their alloys（C_（16）Si_4,C_（12）Si_8,C_8Si_（12）,and C_4Si_（16）） in C2/m structure by using density functional theory（DFT） based on first-principles calculations.The obtained elastic constants and the phonon spectra reveal mechanical and dynamic stability.The calculated formation enthalpy shows that the C-Si alloys might exist at a specified high temperature scale.The ratio of BIG and Poisson＇s ratio indicate that these C-Si alloys in C2/m-20 structure are all brittle.The elastic anisotropic properties derived by bulk modulus and shear modulus show slight anisotropy.In addition,the band structures and density of states are also depicted,which reveal that C_（20）,C_（16）Si_4,and Si_（20） are indirect band gap semiconductors,while C_8Si_（12） and C_4Si_（16） are semi-metallic alloys.Notably,a direct band gap semiconductor（C_（12）Si_8） is obtained by doping two indirect band gap semiconductors（C_（20） and Si_（20））.展开更多
Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devi...Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devices, such as Si-based solar cells and light emitting diodes. Here, we report the fabrication of periodically nano-patterned Si structures by using polystyrene nano-sphere lithography technique. By changing the diameter of nano-spheres and the dry etching parameters, such as etching time and etching power, the morphologies of formed Si nano-structures can be well controlled as revealed by atomic force microscopy.A good broadband antireflection property has been achieved for the formed periodically nano-patterned Si structures though they have the low aspect ratio(<0.53). The reflection can be significantly reduced compared with that of flat Si substrate in a wavelength range from 400 nm to 1200 nm. The weighted mean reflection under the AM1.5 solar spectrum irradiation can be as low as 3.92% and the corresponding optical absorption is significantly improved, which indicates that the present Si periodic nano-structures can be used in Si-based thin film solar cells.展开更多
To design a promising Al−Si filler alloy with a relatively low melting-point,good strength and plasticity for the Cu/Al joint,the Cu,Ni,Zr and Er elements were innovatively added to modify the traditional Al−Si eutect...To design a promising Al−Si filler alloy with a relatively low melting-point,good strength and plasticity for the Cu/Al joint,the Cu,Ni,Zr and Er elements were innovatively added to modify the traditional Al−Si eutectic filler.The microstructure and mechanical properties of filler alloys and Cu/Al joints were investigated.The result indicated that the Al−Si−Ni−Cu filler alloys mainly consisted of Al(s,s),Al_(2)(Cu,Ni)and Si(s,s).The Al−10Si−2Ni−6Cu filler alloy exhibited relatively low solidus(521℃)and liquidus(577℃)temperature,good tensile strength(305.8 MPa)and fracture elongation(8.5%).The corresponding Cu/Al joint brazed using Al−10Si−2Ni−6Cu filler was mainly composed of Al_(8)(Mn,Fe)_(2)Si,Al_(2)(Cu,Ni)3,Al(Cu,Ni),Al_(2)(Cu,Ni)and Al(s,s),yielding a shear strength of(90.3±10.7)MPa.The joint strength was further improved to(94.6±2.5)MPa when the joint was brazed using the Al−10Si−2Ni−6Cu−0.2Er−0.2Zr filler alloy.Consequently,the(Cu,Ni,Zr,Er)-modified Al−Si filler alloy was suitable for obtaining high-quality Cu/Al brazed joints.展开更多
The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = ...The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) and c = 3.4551(1) and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 and 4.01 in the ferromagnetic state to 2.61 and 3.96 in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 –2.73 below the Curie temperature and2.68 –2.75 above it.展开更多
The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and grow...The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and growth interruption on the electrical properties are investigated by changing the Si-cell temperature, doping time and growth process. It is found that the optimal Si ^-doping concentration （Nd） is about 5.0 x 1012 cm-2 and the use of growth interruption has a dramatic effect on the improvement of electrical properties. The material structure and crystal interface are analyzed by secondary ion mass spectroscopy and high resolution transmission elec- tron microscopy. An InGaAs/InAiAs/InP HEMT device with a gate length of lOOnm is fabricated. The device presents good pinch-off characteristics and the kink-effect of the device is trifling. In addition, the device exhibits fT = 249 GHa and fmax 〉 400 GHz.展开更多
The effect of electric pulse modifying on the solidification structure of an Al-15%Si alloy was investigated. The result shows that the primary silicon disappears sometimes and the eutectic phase is refined after the ...The effect of electric pulse modifying on the solidification structure of an Al-15%Si alloy was investigated. The result shows that the primary silicon disappears sometimes and the eutectic phase is refined after the treatrnent of EP （electric pulse） though there are different modalities in different treating durations. DSC （differential scanning calorimetry） analysis indicates that the super-cooling texture decreases and the freezing range narrows evidently after the electric pulse treatment.展开更多
This paper reported a novel synthetic route to Eu2＋ doped SrSiN2 deep red phosphors for white light-emitting diodes. A series of single-phased and high-efficiency SrSiN2：Eu2＋ red phosphors were synthesized based on...This paper reported a novel synthetic route to Eu2＋ doped SrSiN2 deep red phosphors for white light-emitting diodes. A series of single-phased and high-efficiency SrSiN2：Eu2＋ red phosphors were synthesized based on this method. Their structure, morphology, luminescence, quantum efficiency （QE） and thermal quenching properties were investigated and compared with those of SrSiN2： Eu2＋ prepared by the conventional route. It was found that the addition of a small amount of Si3N4 could promote the formation of SrSiN2 from Sr2SisN8 phase. A highly uniform rod-shaped morphology was obtained based on this method. The X-ray powder diffraction and the Rietveld refinement analysis identified the preferential crystalline orientation growth. Under the blue light excitation, Eu2＋ doped SrSiN2 phosphors showed excellent optical properties. Compared with those prepared by the conventional approaches, the external QE of SrSiN2：Eu2＋ phosphor was greatly improved, allowing it a promising phosphor for white LEDs.展开更多
基金Projects(50961009,51161015)supported by the National Natural Science Foundation of ChinaProject(2011AA03A408)supported by the High-tech Research and Development Program of ChinaProjects(2011ZD10,2010ZD05)supported by the Natural Science Foundation of Inner Mongolia,China
文摘In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six （x=0-0.2） electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of （La, Mg）2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in （La, Mg）2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.
基金Projects(51271040,51171031)supported by the National Natural Science Foundation of ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘The formation of periodic layered structure in Ni3Si/Zn diffusion couples with Zn in vapor or liquid state was investigated by SEM-EDS, FESEM and XRD. The results show that the diffusion path in solid-liquid reaction is Ni3Si/（T＋γ）/γ/…T/γ/Ni4Zn12Si3/γ/…Ni4Zn12Si3/γ/Ni4Zn12Si3/δ…/Ni4Zn12Si3/δ/liquid-Zn, and the diffusion path in solid-vapor reaction is Ni3Si/θ/（T＋γ）/γ/…/T/γ/…T/γ/vapor-Zn. With increasing Zn diffusion flux, the diffusion reaction path moves toward the Zn-rich direction, and the distance from the Ni3Si substrate to the periodic layer pair nearest to the interface decreases. In the initial stage of both reactions,γphase nucleates and grows within T matrix phase at first, and then conjuncts together to form a band to reduce the surface energy. Based on the experimental results and diffusion kinetics analysis, the microstructure differences were compared and the formation mechanism of the periodic layered structure in Ni3Si/Zn system was discussed.
基金Project(11204090)supported by the National Natural Science Foundation of ChinaProject(2013KJCX0050)supported by the Department of Education of Guangdong Province+6 种基金ChinaProjects(2014B0404040672014A0404010052015A0404040432015A090905003201508030033)supported by the Scientific and Technological Plan of Guangdong Province and Guangzhou CityChina
文摘A porous coral-structured Si/C composite as an anode material was fabricated by coating Si nanoparticles with a carbon layer from polyvinyl alcohol（PVA）, erosion of hydrofluoric（HF） acid, and secondary coating with pitch. Three samples with different pitch contents of 30%, 40% and 50% were synthesized. The composition and morphology of the composites were characterized by X-ray diffractometry（XRD） and scanning electron microscopy（SEM）, respectively, and the properties were tested by electrochemical measurements. The results indicated that the composites showed obviously enhanced electrochemical performance compared with that without secondary carbon coating. The second discharge capacity of the composite was 773 m A·h/g at a current density of 100 m A/g, and still retained 669 m A·h/g after 60 cycles with a small capacity fade of less than 0.23%/cycle, while the content of secondary carbon source of pitch was set at 40%. Therefore, the cycle stability of the composite could be excellently improved by regulating carbon content of secondary coating.
文摘In order to minimize the self-heating effect of the classic SOI devices,SOI structures with Si3 N4 film as a buried insulator （SOSN） are successfully formed using epitaxial layer transfer technology for the first time. The new SOI structures are investigated with high-resolution cross-sectional transmission electron microscopy and spreading resistance profile. Experiment results show that the buried Si3 N4 layer is amorphous and the new SOI material has good structural and electrical properties. The output current characteristics and temperature distribution are simulated and compared to those of standard SOI MOSFETs. Furthermore, the channel temperature and negative differential resistance are reduced during high-temperature operation, suggesting that SOSN can effectively mitigate the selfheating penalty. The new SOI device has been verified in two-dimensional device simulation and indicated that the new structures can reduce device self-heating and increase drain current of the SOI MOSFET.
文摘Au films with a thickness of about 300 nm were deposited on SiO_2/Si(100) andmica substrates by dc sputtering. X-ray diffraction spectroscopy and field emission scanningelectron microscopy were used to analyze the structure and internal stress of the Au films. Thefirms grown on SiO_2/Si(100) show a preferential orientation of [111] in the growth direction.However the films grown on mica have mixture crystalline orientations of [111], [200], [220] and[311] in the growth direction and the orientations of [200] and [311] are slightly more than thoseof [111] and [220]. An internal stress in the films grown on SiO_2/Si(100) is tensile. For Au filmsgrown on mica the internal stresses in the [111]- and [311]-orientation grains are compressive whilethose in the [200]- and [220]-orientation grains are tensile. Au films grown SiO_2/Si(100) havesome very large grains with a size of about 400 nm and have a wider grain size distribution comparedwith those grown on mica.
基金financial supports by the National Natural Science Foundation of China(No.51772295)support of GTIIT for the collaboration,and the start-up fund provided by GTIIT
文摘To mitigate the massive volume expansion of Si-based anode during the charge/discharge cycles,we synthesized a superstructure of Si@Co±NC composite via the carbonization of zeolite imidazolate frameworks incorporated with Si nanoparticles.The Si@Co±NC is comprised of Sinanoparticle core and N-doped/Co-incorporated carbon shell,and there is void space between the core and the shell.When using as anode material for LIBs,Si@Co±NC displayed a super performance with a charge/discharge capacity of 191.6/191.4 mA h g^(-1)and a coulombic efficiency of 100.1%at 1000 mA g^(-1)after 3000 cycles,and the capacity loss rate is 0.022%per cycle only.The excellent electrochemical property of Si@Co±NC is because its electronic conductivity is enhanced by doping the carbon shell with N atoms and by incorporating with Co particles,and the pathway of lithium ions transmission is shortened by the hollow structure and abundant mesopores in the carbon shell.Also,the volume expansion of Si nanoparticles is well accommodated in the void space and suppressed by the carbon host matrix.This work shows that,through designing a superstructure for the anode materials,we can synergistically reduce the work function and introduce the confinement effect,thus significantly enhancing the anode materials’electrochemical performance in LIBs.
基金supported by National Natural Science Foundation of China (No. 51101005)
文摘In this work, the Nb-14Si 24Ti-10Cr-2Al-2Hf-0.1Y alloy （at.%） was processed by the liquid-metal-cooled directional solidification （DS） at 1750 ℃ with withdrawal rates of 1.2, 6, 18 mm/min and post heat treatment （HT） at 1450 ℃ for 10 h. The microstructures of the direction- ally solidified and heat treated samples were investigated. The results show that the microstructure of directionally solidified alloy mainly consists of petaloid Nbss ＋ Nb5Si3 eutectics and Ti-rich Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics. With the increase of withdrawal rate, the primary NbsSi3 is eliminated, Nbss ＋ Nb5Si3 eutectic cells turn round and connected with the microstructure refine- ment and Nbss ＋ Nb5Si3 ＋ CrzNb eutectics turn to a river-like morphology. After heat treatment, Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics disappeared and petaloid Nbss ＋ Nb5Si3 eutectics turn to a spe- cific fiber-mesh structure gradually, which is promoted by higher withdrawal rates. Furthermore, both the volume fraction of Cr2Nb and the content of Cr in Nbss of Nbss ＋ Nb5Si3 eutectics change regularly with the increase of withdrawal rate and heat treatment at 1450 ℃ for 10 h.
基金Supported by the National Grand Fundamental Research 973 Program of China (No. 51310Z07-3) and the Research Program of Application of Sichuan Department of Science and Technology (No. 02GY029-006)
文摘Novel models （2× 1） of Si（001）-SiO2 interface structure have been established. The method of the first-principle General Gradient Approximation （GGA） is employed to structurally optimize the established theoretical models under the K-point space of periodic boundary condition. The structures after optimization have been analyzed, and the results show that the interfaces present in disordered state and both Si-O-Si and Si=O structures exist. Meanwhile, the bonding of surface structure is analyzed via the graphics of electron localization function（ELF）.
基金Project supported by the National Natural Science Foundation of China(Grant No.61474089)the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology,China Academy of Engineering Physics(Grant No.2015-0214.XY.K)
文摘We study structural,mechanical,and electronic properties of C_（20）,Si_（20） and their alloys（C_（16）Si_4,C_（12）Si_8,C_8Si_（12）,and C_4Si_（16）） in C2/m structure by using density functional theory（DFT） based on first-principles calculations.The obtained elastic constants and the phonon spectra reveal mechanical and dynamic stability.The calculated formation enthalpy shows that the C-Si alloys might exist at a specified high temperature scale.The ratio of BIG and Poisson＇s ratio indicate that these C-Si alloys in C2/m-20 structure are all brittle.The elastic anisotropic properties derived by bulk modulus and shear modulus show slight anisotropy.In addition,the band structures and density of states are also depicted,which reveal that C_（20）,C_（16）Si_4,and Si_（20） are indirect band gap semiconductors,while C_8Si_（12） and C_4Si_（16） are semi-metallic alloys.Notably,a direct band gap semiconductor（C_（12）Si_8） is obtained by doping two indirect band gap semiconductors（C_（20） and Si_（20））.
基金supported by NSFC(Nos.61036001and 11274155)"973"pro ject(2013CB632101)NSF of Jiangsu Province(BK2010010)and PAPD
文摘Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devices, such as Si-based solar cells and light emitting diodes. Here, we report the fabrication of periodically nano-patterned Si structures by using polystyrene nano-sphere lithography technique. By changing the diameter of nano-spheres and the dry etching parameters, such as etching time and etching power, the morphologies of formed Si nano-structures can be well controlled as revealed by atomic force microscopy.A good broadband antireflection property has been achieved for the formed periodically nano-patterned Si structures though they have the low aspect ratio(<0.53). The reflection can be significantly reduced compared with that of flat Si substrate in a wavelength range from 400 nm to 1200 nm. The weighted mean reflection under the AM1.5 solar spectrum irradiation can be as low as 3.92% and the corresponding optical absorption is significantly improved, which indicates that the present Si periodic nano-structures can be used in Si-based thin film solar cells.
基金the financial support from the Primary Research&Development Plan of Zhejiang Province,China(No.2021C01178)the National MCF Energy R&D Program,China(No.2019YFE03100400)+1 种基金the National Natural Science Foundation of China(Nos.51705457,51975530,52005445,52175368)the Natural Science Foundation of Zhejiang Province,China(Nos.LQ21E050015,LQ21E050018).
文摘To design a promising Al−Si filler alloy with a relatively low melting-point,good strength and plasticity for the Cu/Al joint,the Cu,Ni,Zr and Er elements were innovatively added to modify the traditional Al−Si eutectic filler.The microstructure and mechanical properties of filler alloys and Cu/Al joints were investigated.The result indicated that the Al−Si−Ni−Cu filler alloys mainly consisted of Al(s,s),Al_(2)(Cu,Ni)and Si(s,s).The Al−10Si−2Ni−6Cu filler alloy exhibited relatively low solidus(521℃)and liquidus(577℃)temperature,good tensile strength(305.8 MPa)and fracture elongation(8.5%).The corresponding Cu/Al joint brazed using Al−10Si−2Ni−6Cu filler was mainly composed of Al_(8)(Mn,Fe)_(2)Si,Al_(2)(Cu,Ni)3,Al(Cu,Ni),Al_(2)(Cu,Ni)and Al(s,s),yielding a shear strength of(90.3±10.7)MPa.The joint strength was further improved to(94.6±2.5)MPa when the joint was brazed using the Al−10Si−2Ni−6Cu−0.2Er−0.2Zr filler alloy.Consequently,the(Cu,Ni,Zr,Er)-modified Al−Si filler alloy was suitable for obtaining high-quality Cu/Al brazed joints.
基金supported by the National Natural Science Foundation of China(Grant Nos.51461035,51161017,and 11404176)the Scientific Research Projects of the Higher Educational Department of Inner Mongolian Autonomous Region,China(Grant No.NJZZ14033)The XAFS measurement was performed under the approval of Photon Factory Program Advisory Committee(Proposal Nos.2012G095 and 2014G047)
文摘The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) and c = 3.4551(1) and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 and 4.01 in the ferromagnetic state to 2.61 and 3.96 in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 –2.73 below the Curie temperature and2.68 –2.75 above it.
基金Supported by the National Natural Science Foundation of China under Grant No 61434006
文摘The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and growth interruption on the electrical properties are investigated by changing the Si-cell temperature, doping time and growth process. It is found that the optimal Si ^-doping concentration （Nd） is about 5.0 x 1012 cm-2 and the use of growth interruption has a dramatic effect on the improvement of electrical properties. The material structure and crystal interface are analyzed by secondary ion mass spectroscopy and high resolution transmission elec- tron microscopy. An InGaAs/InAiAs/InP HEMT device with a gate length of lOOnm is fabricated. The device presents good pinch-off characteristics and the kink-effect of the device is trifling. In addition, the device exhibits fT = 249 GHa and fmax 〉 400 GHz.
基金This work is financially supported by the National High Technology Research and Development Program of China (No.2001AA337040).
文摘The effect of electric pulse modifying on the solidification structure of an Al-15%Si alloy was investigated. The result shows that the primary silicon disappears sometimes and the eutectic phase is refined after the treatrnent of EP （electric pulse） though there are different modalities in different treating durations. DSC （differential scanning calorimetry） analysis indicates that the super-cooling texture decreases and the freezing range narrows evidently after the electric pulse treatment.
基金supported by the National Basic Research Program of China(9732014CB643801)+1 种基金the National Natural Science Foundation of China(5110202151302016)
文摘This paper reported a novel synthetic route to Eu2＋ doped SrSiN2 deep red phosphors for white light-emitting diodes. A series of single-phased and high-efficiency SrSiN2：Eu2＋ red phosphors were synthesized based on this method. Their structure, morphology, luminescence, quantum efficiency （QE） and thermal quenching properties were investigated and compared with those of SrSiN2： Eu2＋ prepared by the conventional route. It was found that the addition of a small amount of Si3N4 could promote the formation of SrSiN2 from Sr2SisN8 phase. A highly uniform rod-shaped morphology was obtained based on this method. The X-ray powder diffraction and the Rietveld refinement analysis identified the preferential crystalline orientation growth. Under the blue light excitation, Eu2＋ doped SrSiN2 phosphors showed excellent optical properties. Compared with those prepared by the conventional approaches, the external QE of SrSiN2：Eu2＋ phosphor was greatly improved, allowing it a promising phosphor for white LEDs.
