Mg2Si化合物在静水压下的电子输运性能研究

本文基于第一性原理采用全电势线性缀加平面波方法和波尔兹曼理论运算了在静水压下Mg₂Si的电子和热电性能. 研究发现, 对于n型载流子控制Mg₂Si输运性质, 应变达到0.02时, 室温情况下, 热电性能参数得到了明显提高, 其塞贝克系数增幅为26%, 功率因数增幅47%; 高温时, 功率因数增幅45%. 而对于主要载流子为空穴时, 其热电系数最值出现在应变为0.01时. 但其数值与未施加静水压的结构相比提高不多, 表明对于p型Mg₂Si半导体应变对其输运性能的影响不大. 并且结合电子能带结构图解释这些现象.     

High-performance self-organized Si nanocomposite anode for lithium-ion batteries

Silicon is being investigated extensively as an anodic material for next-generation lithium ion batteries for portable energy storage and electric vehicles.However,the large changes in volume during cycling lead to the breakdown of the conductive network in Si anodes and the formation of an unstable solid-electrolyte interface,resulting in capacity fading.Here,we demonstrate nanoparticles with a Si@Mn_(22.6)Si_(5.4)C_4@C double-shell structure and the formation of self-organized Si-Mn-C nanocomposite anodes during the lithiation/delithiation process.The anode consists of amorphous Si particles less than 10 nm in diameter and separated by an interconnected conductive/buffer network,which exhibits excellent charge transfer kinetics and charge/discharge performances.A stable specific capacity of 1100 mAh·g~(-1) at 100 mA·g~(-1) and a coulombic efficiency of 99.2%after 30 cycles are achieved.Additionally,a rate capacity of 343 mAh·g~(-1) and a coulombic efficiency of 99.4%at 12000 mA·g~(-1) are also attainable.Owing to its simplicity and applicability,this strategy for improving electrode performance paves a way for the development of high-performance Si-based anodic materials for lithium ion batteries.     

电感耦合等离子体原子发射光谱法测定镍基钎料中Cr,Si,B,Fe

建立了电感耦合等离子体原子发射光谱法测定镍基钎料中Cr,Si,B,Fe含量的新方法。以硝酸–氢氟酸溶解样品,分别选择267.716,288.158,249.677,259.940 nm作为分析谱线,不用进行基体匹配,可直接测定镍基钎料中Cr,Si,B,Fe含量。在优化的实验条件下,测定结果的相对标准偏差为0.71%~1.43%(n=11),加标回收率为97.0%~102.0%。该方法可满足日常分析对镍基钎料中Cr,Si,B,Fe含量的检测要求。     

Parametric simulation of the back-surface field effect in the silicon solar cell

Recombination of minority carriers in the solar cell is a major contributing factor in the loss of quantum efficiency and cell power. While the surface recombination is dealt with by depositing a passivation layer of SiO₂ or SiN_x, the bulk recombination is minimized by use of nearly defect-free monocrystalline substrate. In addition, the back-surface field (BSF) effect has been very useful in aiding the separation of free electrons and holes in the bulk. In this study, the key BSF parameters and their effect on the performance of a typical p-type front-lit Si solar cell are investigated by use of Medici, a 2-dimensional device simulator. Of the parameters, the doping concentration of the BSF layer is found to be most significant. That is, for a p-type substrate of 1 × 10¹⁴ cm⁻³ acceptor concentration, the optimum doping concentration of the BSF layer is 1 × 10¹⁸ cm⁻³ or more, and the maximum cell power can be increased by 24%, i.e., 25.4 mW cm⁻² vs. 20.5 mW cm⁻², by using a BSF layer with optimum doping. With regards to the BSF layer thickness, the impact is less. That is, the maximum cell power is about 11% higher at 100 μm than at 5 μm, which translates to an increase of 1.2% μm⁻¹. In practice, therefore, it would be better to rely on the control of the doping concentration than the thickness in maximizing the BSF effect in real Si solar cells.     

Raman spectroscopic study on boron-doped silicon nanoparticles

Raman analyses were performed on thin films prepared from B-doped Si nanoparticles with an average diameter of 15 nm using the spin-coating method. The resulting spectrum exhibited a broad band with a peak near 520 cm⁻¹. The band was decomposed into three bands corresponding to the crystalline, grain boundary (GB), and amorphous regions by the least-squares band-fitting method based on the three Voigt bands. The fractions of the crystalline, GB, and amorphous regions were 37%, 35%, and 28%, respectively. A spherical particle exhibited an ordered crystalline core surrounded by a disordered shell in a transmission electron microscope (TEM) image. The crystalline fraction of the 15-nm B-doped Si nanoparticle film was much lower than that of the 19-nm P-doped Si nanoparticle film. This result suggested that the B-doping mechanism was different from that of P-doping. The temperature of the sample was estimated from the ratio of the peak intensities of anti-Stokes to Stokes Raman bands (I^AS/I^S) observed near 520 cm⁻¹. The temperature of the B-doped Si nanoparticle film upon irradiation at a power density of 4.6 kW/cm² was 298 °C, whereas the temperature of the P-doped Si nanoparticle film was 92 °C. The B-doped Si nanoparticle films were capable of producing light-induced heat.     

单轴应变SiNMOSFET源漏电流特性模型

本文在建立单轴应变Si NMOSFET迁移率模型和阈值电压模型的基础上, 基于器件不同的工作区域, 从基本的漂移扩散方程出发, 分别建立了单轴应变Si NMOSFET源漏电流模型. 其中将应力的影响显式地体现在迁移率和阈值电压模型中, 使得所建立的模型能直观地反映出源漏电流特性与应力强度的关系. 并且对于亚阈区电流模型, 基于亚阈区反型电荷, 而不是采用常用的有效沟道厚度近似的概念, 从而提高了模型的精度. 同时将所建模型的仿真结果与实验结果进行了比较, 验证了模型的可行性. 该模型已经被嵌入进电路仿真器中, 实现了对单轴应变Si MOSFET 器件和电路的模拟仿真.     

A Convenient Synthesis of Protoanemonin

Abstract

A new convenient synthesis of protoanemonin (1) starting from 2-deoxy-d-ribose (3) is described. A key step in the sequence is the successive β- and δ-eliminations of 3,5-di-O-p-toluoyl-2-deoxy-d-ribono-1,4-lactone (6).     

Ab Initio molecular dynamics study of ethylene adsorption onto Si(001) surface: Short‐time fourier transform analysis of structural coordinate autocorrelation function

The reaction dynamics of ethylene adsorption onto the Si(001) surface have been studied by combining density functional theory‐based molecular dynamics simulations with molecular adsorption sampling scheme for investigating all kinds of reaction pathways and corresponding populations. Based on the calculated results, three possible reaction pathways—the indirect adsorption, the direct adsorption, and the repelling reaction—have been found. First, the indirect adsorption, in which the ethylene (C₂H_4(ads)) forms the π‐bonded C₂H_4(ads) with the buckled‐down Si atom to adsorb on the Si(001) surface and then turns into the di‐σ‐bonded C₂H_4(ads), is the major reaction pathway. The short‐time Fourier transform analysis of structural coordinate autocorrelation function is performed to further investigate the evolution of different vibrational modes along this indirect reaction pathway. This analysis illustrates that the Infrared (IR) inactive peak of the C?C stretching mode of the π‐bonded C₂H_4(ads) shifts to the IR inactive peak of the C? C stretching mode of di‐σ‐bonded C₂H_4(ads), which is in a good agreement with the IR inactive peak of the C?C stretching mode vanished in the vibrational spectrum at 150 K (Nagao et al., J. Am. Chem. Soc. 2004 , 126, 9922). Second, the direct adsorption, in which the di‐σ‐bonded C₂H_4(ads) is formed directly with the Si intradimer or the Si interdimer on the Si(001) surface, is the less significant reaction pathway. This reaction pathway leads to the C? C stretching mode and the C? H stretching mode of the di‐σ‐bonded C₂H_4(ads) appeared in the vibrational spectra at 48 and 150 K, respectively (Nagao et al., J. Am. Chem. Soc. 2004 , 126, 9922). Finally, the repelling reaction, in which the C₂H_4(g) first interacts with the Si dimer and then is repelled by Si atoms, is the least important reaction pathway. Consequently, neither the π‐bonded C₂H_4(ads) nor the di‐σ‐bonded C₂H_4(ads) is formed on the Si(001) surface. © 2013 Wiley Periodicals, Inc.     

2‐Aminobenzenethiol‐Functionalized Silver‐Decorated Nanoporous Silicon Photoelectrodes for Selective CO2 Reduction

A molecularly thin layer of 2‐aminobenzenethiol (2‐ABT) was adsorbed onto nanoporous p‐type silicon (b‐Si) photocathodes decorated with Ag nanoparticles (Ag NPs). The addition of 2‐ABT alters the balance of the CO₂ reduction and hydrogen evolution reactions, resulting in more selective and efficient reduction of CO₂ to CO. The 2‐ABT adsorbate layer was characterized by Fourier transform infrared (FTIR) spectroscopy and modeled by density functional theory calculations. Ex situ X‐ray photoelectron spectroscopy (XPS) of the 2‐ABT modified electrodes suggests that surface Ag atoms are in the +1 oxidation state and coordinated to 2‐ABT via Ag?S bonds. Under visible light illumination, the onset potential for CO₂ reduction was ?50 mV vs. RHE, an anodic shift of about 150 mV relative to a sample without 2‐ABT. The adsorption of 2‐ABT lowers the overpotentials for both CO₂ reduction and hydrogen evolution. A comparison of electrodes functionalized with different aromatic thiols and amines suggests that the primary role of the thiol group in 2‐ABT is to anchor the NH₂ group near the Ag surface, where it serves to bind CO₂ and also to assist in proton transfer.     

Correlation between morphological, electrical and optical properties of GaN at all stages of MOVPE Si/N treatment growth

GaN has been grown using Si/N treatment growth by MOVPE on sapphire (0001) in a home-made vertical reactor. The growth was monitored by in situ laser reflectometry. The morphological, electrical and optical properties of GaN are investigated at all the growth stages. To this aim, the growth was interrupted at different stages. The obtained samples are ex situ characterized by scanning electron microscopy (SEM), room temperature Van der Pauw–Hall electrical transport and low temperature (13 K) photoluminescence (PL) measurements. The SEM images show clearly the coalescence process. A smooth surface is obtained for a fully coalesced layer. During the coalescence process, the electron concentration (n) and mobility (μ) vary from 2×10¹⁹ cm⁻³ to 2×10¹⁷ cm⁻³ and 12 cm²/V s–440 cm²/V s, respectively. The PL maxima shift to higher energy and the FWHM decreases to about 4 meV. A correlation between PL spectra and Hall effect measurements is made. We show that the FWHM follows a n^2/3 power law for n above 10¹⁸ cm⁻³.