镶嵌有纳米硅的氮化硅薄膜键合特性分析

采用螺旋波等离子体化学气相沉积(HWPCVD)技术制备了非化学计量比的氢化氮化硅薄膜,对所沉积样品及氮气环境中920 ℃退火样品的微观结构及键合特性进行了分析。Raman散射结果表明,薄膜中过量硅以非晶纳米粒子形式存在,退火样品呈现纳米晶硅和氮化硅的镶嵌结构。红外吸收和可见光吸收特性比较结果显示,薄膜样品的微观结构依赖于化学计量比以及退火过程,硅含量较低样品因高的键合氢含量而表现出低的纳米硅表面缺陷态密度;退火过程将引起Si—H和N—H键合密度的减少,因晶态纳米颗粒的形成,退火样品表现出更高的结构无序度。     

氮化硼纳米管阵列储氢的计算机模拟

采用巨正则蒙特卡罗方法模拟常温、中等压强下单壁氮化硼纳米管阵列的物理吸附储氢,重点研究压强、纳米管阵列的管径和管间距对单壁氮化硼纳米管阵列物理吸附储氢的影响.计算结果表明,氮化硼纳米管阵列的储氢性能明显优于碳纳米管阵列,在常温和中等压强下的物理吸附储氢量(质量百分数)可以达到和超过美国能源部提出的商业标准.并给出相应的理论解释.     

Carbon Nitride Thin Films Deposited by Plasma Assisted Nd:YAG Laser Ablation of Graphite in N2+H2 Atmosphere

Carbon nitride thin films are deposited on silicon wafers by 532 nm Nd:YAG laser ablation of graphite in the N2+H2 atmosphere assisted by a dc glow discharge plasma at a higher gas pressure of about 4.0 kPa. The properties of the thin films are investigated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray diffraction (XRD). The results show that the deposited films are composed of α-C3N4, β-C3N4 phase and have the N/C atomic ratio of 2.01. The optical emission spectroscopy (OES) studies indicate that the introduction of a dc glow discharge and the adoption of a higher gas pressure during the film deposition are favorable to the net generation of the atomic N, CN radicals and N+2 in B2Σ+u excited state in the plasma, which are considered to play a major role in the synthesis of carbon nitride.     

A density functional theory study on parameters fitting of ultra long armchair （n, n） single walled boron nitride nanotubes

Armchair(n,n) single walled boron nitride nanotubes with n = 2-17 are studied by the density functional theory at the B3LYP/3-21G(d) level combined with the periodic boundary conditions for simulating the ultra long model.The results show that the structure parameters and the formation energies bear a strong relationship to n.The fitted analytical equations are developed with correlation coefficients larger than 0.999.The energy gaps of(2,2) and(3,3) tubes are indirect gaps,and the larger tubes(n = 4-17) have direct energy gaps.Results show that the armchair boron nitride nanotubes(n = 2-17) are insulators with wide energy gaps of between 5.93 eV and 6.23 eV.     

Carbon nitride films by RF plasma assisted PLD: Spectroscopic and electronic analysis

Carbon nitride (CNx) thin films have been grown on Si 〈1 0 0〉 by 193 nm ArF ns pulsed laser ablation of a pure graphite target in a low pressure atmosphere of a RF generated N₂ plasma and compared with samples grown by PLD in pure nitrogen atmosphere. Composition, structure and bonding of the deposited materials have been evaluated by X-ray photoelectron spectroscopy (XPS), and Raman scattering. Significant chemical and micro-structural changes have been registered, associated to different nitrogen incorporation in the two types of films analyzed. The intensity of the reactive activated species is, indeed, increased by the presence of the bias confined RF plasma, as compared to the bare nitrogen atmosphere, thus resulting in a different nitrogen uptake in the growing films. The process has been also investigated by some preliminary optical emission studies of the carbon plume expanding in the nitrogen atmosphere. Optical emission spectroscopy reveals the presence of many excited species like C⁺ ions, C atoms, C₂, N₂; and CN radicals, and N₂⁺ molecular ions, whose relative intensity appears to be increased in the presence of the RF plasma. The films were also characterised for electrical properties by the “four-probe-test method” determining sheet resistivity and correlating surface conductivity with chemical composition.     

Surface plasmon enhanced light emission of silicon-rich silicon nitride: Dependence on metal island size

Surface plasmon coupled light emission of silicon-rich silicon nitride (SRSN) was investigated as a function of metal island size. It was found that the emission intensity was enhanced by surface plasmon (SP) and the enhancement factors increase greatly with the increase of metal island size. Moreover, SP coupled emission spectral shape was found also correlating with Ag island size. By calculating the extinction characteristics of the Ag islands, it was believed that SP scattering and absorption efficiency of the metal islands decide the photoluminescence (PL) changes including emission intensity enhancement and band position shift.     

Ⅲ族氮化物异质结构二维电子气研究进展

本文总结了近年来Ⅲ族氮化物半导体异质结构二维电子气的研究进展。从Ⅲ族氮化物材料晶格结构和特有的极化性质出发,重点讨论了AlGaN/GaN异质结构中二维电子气的性质,总结分析了异质结构中Al组分、势垒层厚度、应变弛豫度、掺杂等对二维电子气浓度和迁移率的影响,同时还涉及AlGaN/GaN/AlGaN,AlGaN/AlN/GaN和AlGaN/InGaN/GaN等异质结构二维电子气性质。     

Influence of Ga/(Ga + In) grading on deep‐defect states of Cu(In,Ga)Se2 solar cells

The benefits of gallium (Ga) grading on Cu(In,Ga)Se₂ (CIGS) solar cell performance are demonstrated by comparing with ungraded CIGS cells. Using drive‐level capacitance profiling (DLCP) and admittance spectroscopy (AS) analyses, we show the influence of Ga grading on the spatial variation of deep defects, free‐carrier densities in the CIGS absorber, and their impact on the cell's open‐circuit voltage V_oc. The parameter most constraining the cell's V_oc is found to be the deep‐defect density close to the space charge region (SCR). In ungraded devices, high deep‐defect concentrations (4.2 × 10¹⁶cm^–3) were observed near the SCR, offering a source for Shockley–Read–Hall recombination, reducing the cell's V_oc. In graded devices, the deep‐defect densities near the SCR decreased by one order of magnitude (2.5 × 10¹⁵ cm^–3) for back surface graded devices, and almost two orders of magnitude (8.6 × 10¹⁴ cm^–3) for double surface graded devices, enhancing the cell's V_oc. In compositionally graded devices, the free‐carrier density in the absorber's bulk decreased in tandem with the ratio of gallium to gallium plus indium ratio GGI = Ga/(Ga + In), increasing the activation energy, hindering the ionization of the defect states at room temperature and enhancing their role as recombination centers within the energy band. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Ultra fine carbon nitride nanocrystals synthesized by laser ablation in liquid solution

Crystalline carbon nitride nanopowders and nanorods have been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation of a graphite target in liquid ammonia solution. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FTIR) were used to systematically study the morphology, nanostructure and chemical bonding. The experimental composition and structure of the nanoparticles are consistent with the theoretical calculations for α-C₃N₄. After 2 h ablation the particles had a size distribution ∼8–12 nm, whereas after 5 h ablation the particles had grown into nanorod-like structures with a crystalline C₃N₄ tip. A formation mechanism for these nanorods is proposed whereby nanoparticles are first synthesized via rapid formation of an embryonic particle, followed by a slow growth, eventually leading to a one-dimensional nanorod structure.     

确定磁性体在绝热磁化过程中达到最高温度的方法

在磁性体磁化过程中, 决定其能够达到的最高温度, 对磁热材料的优化选取是重要的. 本文以钆镓石榴石(Gd₃Ga₅O₁₂) 为例, 根据高磁场下趋近饱和定律的思想, 给出了低温、超强磁场下, Gd₃Ga₅O₁₂晶体等效磁化率的定量形式. 在外磁场从0---40 T范围内, 计算了该晶体的磁熵变、声子熵变以及磁性体温度随外磁场的变化, 结果均与实验值符合较好. 利用声子熵变与饱和磁熵变曲线交点的唯一性, 给出了在磁性体磁化过程中, 确定其温度达到最大值的方法, 预言了Gd₃Ga₅O₁₂晶体在绝热磁化过程中达到的最高温度为64.7K. 该方法还可以对所加外磁场大小进行预言或估计.