Boron ions B interaction with Si(100) and Ge(100) surfaces

The goal of this work is simulation of possible structures, formed by boron ions (B⁺) during adsorption on Si(100) and Ge(100) surfaces. Calculations were carried out using a semi-empirical method, known as the Modified Neglect of Differential Overlap method (MNDO). The surface was simulated using of Si₄₉(Ge₄₉) and Si₆₃(Ge₆₃) clusters. Results of quantum-chemical calculations the boron ion (B⁺) interaction with Si(100) − 2 × 1 and Ge(100) − 2 × 1 surfaces are presented and show adsorption barriers for boron ions and migration barriers of adsorbed boron ion (during migration along surface dimer row and along surface dimer).     

First-principles study of near surface point defects stability in Si (100) and SiGe(100)

Calculations based on Density Functional Theory are carried out to study interstitial generation close to the Si(100) surface with further consideration of effects related to the presence of substitutional Ge atoms on the surface. Defect structures, vacancy and Si interstitial, and associated energies are calculated. We observe that germanium atoms tend to increase the stability of created defects, promote the generation of interstitials through drastic structural changes and blocks the climb of Si interstitials towards the surface.     

水蒸气二氧化碳共活化制备聚苯胺基活性碳在离子液体超级电容器中的应用

通过水蒸气二氧化碳(H2 O(gas)-CO2)共活化的物理活化方法制备聚苯胺基活性碳被广泛应用于商业活性碳的规模化生产,相比于化学活化方法,该方法制备的活化产物无活化剂残留、 清洗简单且工艺过程环保.以聚苯胺为原料,探究了H2 O(gas)的量和CO2分压对活化产物的影响.采用氮气吸/脱附、 扫描电镜(SEM)、 透...     

Au8 cluster adsorption on Si(100):2 × 1 asymmetric surface studied by a first principles calculation

In this work, we investigate the adsorption of Au₈ cluster onto H-terminated Si(100):2 × 1 asymmetric surface by density functional theory within local density and generalized gradient approximations. We study the site-dependent shape of Au₈ cluster, adsorption energies, band structures and the corresponding charge distribution. We show that the electronic properties of the cluster and substrate complex change with the location of the cluster on the surface.     

N2 O-C2 H4预混气体火焰的传播特性

运用标准k-ε模型,对N₂O-C₂H₄预混气体在水平半封闭管道内火焰传播过程进行了数值模拟,得到了火焰锋面结构、传播速度、出口压力和燃烧区的气流速度随时间的变化规律。研究结果表明,管道内预混火焰传播过程分为3个阶段:点火初期的平面火焰传播阶段、Tulip火焰传播阶段和指形火焰传播阶段;火焰传播速度呈指数增长,管道出口处压力和气流速度均呈现出先增大后减小的趋势。同时,采用高速摄影系统、压力传感器、有机玻璃管等装置对预混气体的火焰加速进程和压力演变过程进行了验证,实验结果与数值模拟结果一致。     

Effects of deposition parameters on the crystallinity of CeO2 thin films deposited on Si(100) substrates by r.f.-magnetron sputtering

Deposition temperature, r.f.-power and seed layer deposition time were important parameters effecting the crystallinity of CeO₂ thin films deposited by r.f.-magnetron sputtering on Si(100) substrates. The CeO₂ (200) peak was notable for a deposition temperature above 600°C. With decreased r.f.-power and thus lower deposition rate, the intensity of the CeO₂(200) peak increased. When the seed layer deposition time was less than 20 s, the CeO₂(200) peak dominated. Transmission electron microscopy (TEM) diffraction revealed that the deposited CeO₂ thin film had a polycrystalline structure. Annealing at 950°C in O₂ atmosphere for 30 min increased and sharpened the CeO₂(200) peak.     

A study on thermal emission of charges at Si3N4—GaAs interfaces after annealing in N2 and N2 + H2 mixtures

Si₃N₄—GaAs interfaces subjected to annealing in N₂ + H₂ mixture or pure N₂ atmosphere were investigated by a small-signal charge deep-level transient spectroscopy (Q-DLTS) method. The method measures the physical parameters of selective populations of the interface traps continuum. A dependence of the capture cross-section on activation energy was constructed for the continuum of interface states at the Si₃N₄—GaAs interface. The dependence shows an exponential character in the part of the gap ranging from 0.3 to 1.0 eV below the conduction band minimum. It was found that annealing in the temperature interval 400–450 °C reduces the zero-bias band bending by about 0.1 eV. At temperatures of 500 °C and more, degradation of the interface started; compared with annealing in pure N₂ ambient, annealing in an N₂ + H₂ mixture degraded the interface slightly more.     

Infrared reflection absorption study of water interaction with H-terminated Si(100) surfaces

Water adsorption on clean and hydrogenated Si(100) surfaces was studied under ultra high vacuum conditions using surface infrared spectroscopy. The study shows that H-Si-Si-OH and SiH₂ species are formed on Si(100)-(2 × 1) and Si(100)-(2 × 1)-H surfaces, respectively. The reactivity behaviour of Si(100)-(3 × 1)-H and Si(100)-(1 × 1)-H is similar, both stabilizing oxygen inserted silicon dihydrides.     

Electrical properties of ultra-thin oxynitrided layer using N2O plasma in inductively coupled plasma chemical vapor deposition for non-volatile memory on glass

In this work, the silicon oxynitride layer was studied as a tunneling layer for non-volatile memory application by fabricating low temperature polysilicon thin film transistors on glass. Silicon wafers were oxynitrided by only nitrous oxide plasma under different radio frequency powers and plasma treatment times. Plasma oxynitridation was performed in RF plasma using inductively coupled plasma chemical vapor deposition. The X-ray energy dispersive spectroscopy was employed to analyze the atomic concentration ratio of nitrogen/oxygen in oxynitride layer. The oxynitrided layer formed under radio frequency power of 150 W and substrate temperature of 623 K was found to contain the atomic concentration ratio of nitrogen/oxygen as high as 1.57. The advantage of high nitrogen concentration in silicon oxide layer formed by using nitrous oxide plasma was investigated by capacitance-voltage measurement. The analysis of capacitance-voltage characteristics demonstrated that the ultra-thin oxynitride layers of 2 nm thickness formed by only nitrous oxide plasma have good properties as tunneling layer for non-volatile memory device.     

原位无压烧结制备Si2 N2O-Si3 N4复相陶瓷

以Y2O3和Al2O3陶瓷粉体作为烧结助剂,原位无压液相烧结制备Si3N4-Si2N2O复相陶瓷,Si2N2O相通过SiO2 Si3N4 2Si2N2O反应生成.生坯采用注凝成型制备,然后在1780℃保温2h烧结,烧结体基本由板条状的Si2N2O及长柱状的β-Si3N4晶粒构成.Si2N2O陶瓷相对于Si3N4陶瓷而言,具有优异的抗氧化性能,低的弹性模量,以及低的热膨胀系数,因此,Si2N2O-Si3N4复相陶瓷结合了两者的优异性能,并大大提高了材料的热冲击性,材料的热冲击温差即使达到1200℃,其残余强度基本上没有变化.     

ZrO2 (Y2O3) 增韧的氮化硅烧结体的性能及相关系

在高温(1400℃) 超高压(4. 2GPa) 下制备Y₂O₃ 部分稳定的ZrO₂ 增韧的氮化硅烧结体, 通过XRD 及机械性能测试等方法分析ZrO₂ 的相结构, 研究氮化硅烧结体的增韧机理。结果表明, 烧结体中加入少量的铝粉, 可提高t2ZrO₂ 的相变能力, 达到利用部分稳定的ZrO₂ 增韧氮化硅烧结体的目的。稳定剂Y₂O₃ 在ZrO₂ 中含量小于2. 5mol% 时, t→m 相变量及断裂韧性随Y₂O₃ 含量增加而逐渐提高, 韧性提高来源于相变增韧和微裂纹增韧; Y₂O₃含量大于2. 5mol% 时, t 相接近100% , 韧性主要来源于相变增韧, 增韧效果随Y₂O₃ 含量增加而逐渐减弱。Y₂O₃ 作为良好的烧结助剂, 促进氮化硅烧结体在超高压下致密化, 烧结体的硬度随Y₂O₃ 含量增加逐渐提高。      

In situ detection of F2 laser-induced oxidation on hydrogen-terminated Si(111) and Si(110) surfaces by Fourier transform infrared transmission spectroscopy

Although oxidation of silicon has been intensively investigated experimentally and theoretically, the composition and structure of the interface region between the bulk oxide and silicon are not very well known. In this work, we report on the vacuum UV laser-induced oxidation of well-defined atomically flat Si(111)-(1×1):H and Si(110)-(1×1):H surfaces, prepared by wet-chemical processing, using an F₂ laser (157 nm). The silicon samples were irradiated under ultra high vacuum conditions in water and oxygen atmospheres. The photo-induced partial oxidation of the first monolayer, controlled by the oxidant pressure, was monitored by in situ Fourier transform infrared transmission spectroscopy with different photon detectors. The chemical reactions occurring at the surface were monitored by the shift and decreasing strength of the stretching vibration of Si---H surface bonds. The IR absorption spectra recorded during surface processing yield detailed information on the rearrangement of chemical bonds with a sensitivity reaching monolayer resolution.     

Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites

The C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si_0.75Al_0.25)₂/0–20 vol.% Al₂O₃ materials, showing micron and submicron composite structure, possess a hardness of 13.9–14.6 GPa but a poor toughness of 1.78–1.80 MPa m^1/2. The addition of 30 vol.% Al₂O₃ leads to the formation of the micron C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composite with an intergranular distribution of Al₂O₃, that results in a drop of the hardness to 10.2 GPa and an improvement of the toughness to 3.67 MPa m^1/2. The transition of the cleavage facets to the intergranular fracture with the addition of Al₂O₃ is assumed as the main toughening mechanism.     

SiO2/Si(111)表面Ge量子点的生长研究

Si衬底用化学方法清洗后,表面大约残余1.0 nm厚SiO2薄膜.利用原子力显微镜(AFM)和反射高能电子衍射(RHEED)来研究温度和Ge蒸发厚度对在SiO2薄膜表面生长的Ge量子点的影响.实验结果表明,当衬底温度超过500 ℃时,SiO2开始与Ge原子发生化学反应,并形成与Si(111)表面直接外延的Ge量子点.在650 ℃时,只有Ge的厚度达到0.5nm时,Ge量子点才开始形成.     

Metal-induced negative oxide charge detected by an alternating current surface photovoltage in thermally oxidized Fe-contaminated n-type Si (001) wafers

The atomic-bridging type negative oxide charge in SiO₂ is investigated using the Fe-contaminated (001) surface of n-type Si wafers. The investigation is done on the basis of a chemical analysis and a method in which the frequency-dependent alternating current (AC) surface photovoltage (SPV) is measured. At room temperature, an AC SPV appears and gradually increases, saturating after approximately one day (with an Fe concentration on the Si surface of 4.0 × 10¹³ atoms/cm²). The AC SPV eventually becomes inversely proportional to frequency except at very low frequencies (< 10 Hz) corresponding to weak or strong inversion, indicating that the negative Fe induced oxide charge appears in the form of a (FeOSi)⁻ network. Also, in Fe-contaminated n-type Si(001) surfaces thermally oxidized at between 550 and 650 °C for 60 min, strong inversion is unquestionably observed, proving that the (FeOSi)⁻ network survives and that most of the added Fe has segregated into the region closest to the surface of the thin SiO₂ film. At 850 °C and/or for long oxidation times, the AC SPV decreases and ultimately disappears, implying that the (FeOSi)⁻ network has collapsed and may have changed into Fe₂O₃. A model for the metal-induced negative oxide charge in the conventional oxide charge diagram is proposed.     

Si（100）-（2×1）表面上Si薄膜生长的模拟

本文在分析表面扩散各向异性、二聚体和二聚体列影响的基础上,建立了Si（100）-（2×1） 表面上Si薄膜生长的Kinetic Monte Carlo（KMC）模型,利用该模型对薄膜生长的初始阶段进行了研究.结果表明：吸附原子的扩散距离随温度的变化满足指数函数L=L0Ae^T/C.在一定的入射率下存在一最佳成岛温度,该温度随入射率的增大而升高.随入射率的减小,薄膜逐渐从离散生长向紧致生长转变,表面扩散的各向异性越显著.     

Electronic conduction in SiO2:N thin films grown by thermal oxidation of silicon in N2O

Silicon oxynitride [SiO₂:N] thin films have been grown by oxidizing silicon in N₂O at 900, 1000 and 1100 °C and at 760 and 1520 torr. It is shown that the dominant electrical conduction mechanism, for high electric fields, is the field assisted thermionic emission from the traps (Poole-Frenkel effect), and is not direct or Fowler-Nordheim tunneling, as typically occurs in thermal silicon oxide with similar thickness. Electrical conduction in these films occurs by field assisted electron emission from donor traps with energy levels varying in the range from 0.5 to 1 eV from the conduction band. The results shown here indicate that the best quality films are those grown at low temperature and pressure, since they give films with a higher critical electric field, a higher energy barrier depth at the traps and less donors compensated by acceptors than those grown at high temperatures and pressures.     

硅基HA/Al2O3复合生物涂层的制备与表征

通过磁控溅射沉积、阳极氧化与溶胶-凝胶结合的多步技术在Si(100)表面制备了HA/Al2O3复合生物涂层材料.采用TG-DSC测定了复合涂层中HA外层的烧成温度,采用XRD、FT-IR以及EDS分析了Si(100)基HA/Al2O3复合生物涂层的组成,并借助SEM研究了复合涂层的表面与截面的微观形貌.研究表明,凝胶完全转变为HA外层的最低温度约为550℃,凝胶经600℃处理30min后可在Si(100)-Al2O3基上形成具有一定数量纳米细孔且含有少量CO3的HA外层;A外层嵌入Si(100)基阳极氧化Al2O3多孔层的孔洞中构成HA/Al2O3复合生物涂层.     

Highly oriented metallic SmS films on Si(100) grown by pulsed laser deposition

Stoichiometric and highly oriented in (100) direction SmS films in the metallic phase have been grown on Si(100) substrate at room temperature by pulsed laser deposition (PLD) as revealed from lattice parameter, reflectivity and electrical resistivity measurements. Above-critical compressive stress P = 0.9 GPa in as grown film was determined from sample curvature measurements and attributed to stress building up in PLD process further accompanied by stress due to SmS versus Si lattice parameter mismatch. Stress relaxation and subsequent metal-to-semiconductor phase transition occurred following annealing at T = 900 K as evident from consistent changes of SmS/Si sample curvature, structural, optical and electrical properties.     

Si2ON2 /LAS纳米复合材料的制备与性能研究

研究了Si2ON2/LAS纳米复合材料的制备和性能。结果表明,纳米β－Si3N4可在较低温度下与玻璃热压烧结制备出Si2ON/LASX纳米复合材料,材料的力学性能与生成的纳米Si2ON2含量有关,Si2ON2的含量在20％时材料的抗弯强度和断裂韧性达量高值,分别比未加Si2ON2的材料提高31％和88％。纳米Si2ON2的含量超过20％时,材料的力学性能急剧下降,其原因是材料的致密度迅速降低。