Effects of high temperature rapid thermal annealing on Ge films grown on Si（001） substrate

Tensile strain,crystal quality,and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 C for a short period(20 s).The films were grown on Si(001)substrates by ultra-high vacuum chemical vapor deposition.These improvements are attributed to relaxation and defect annihilation in the Ge films.However,after prolonged(20 s)rapid thermal annealing,tensile strain and crystal quality degenerated.This phenomenon results from intensive Si–Ge mixing at high temperature.     

Effect of CoSi2 buffer layer on structure and magnetic properties of Co films grown on Si（001） substrate

Buffer layer provides an opportunity to enhance the quality of ultrathin magnetic films.In this paper,Co films with different thickness of Co Si2buffer layers were grown on Si(001)substrates.In order to investigate morphology,structure,and magnetic properties of films,scanning tunneling microscope(STM),low energy electron diffraction(LEED),high resolution transmission electron microscopy(HRTEM),and surface magneto-optical Kerr effect(SMOKE)were used.The results show that the crystal quality and magnetic anisotropies of the Co films are strongly affected by the thickness of Co Si2buffer layers.Few Co Si2monolayers can prevent the interdiffusion of Si substrate and Co film and enhance the Co film quality.Furthermore,the in-plane magnetic anisotropy of Co film with optimal buffer layer shows four-fold symmetry and exhibits the two-jumps of magnetization reversal process,which is the typical phenomenon in cubic(001)films.     

First-principle study of Mg adsorption on Si（111） surfaces

We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface.     

Atomic-Scale Study of Ge-Induced Incommensurate Phases on Si（111）

Two Ge-induced incommensurate phases, γ and β, on Si（111） are observed and studied by {／it in situ} scanning tunneling microscopy. The γ phase consists of aligned triangular domains whose stacking sequence is faulted with respect to the Si（111）-1×1 surface. The β phase consists of two kinds of triangular domains whose stacking sequences are faulted and unfaulted with respect to the Si（111）-1×1 surface, respectively. In the β phase, two types of domain walls, zigzag＇＇ and face-to-face＇＇, form to release the strain. The triangular domains all exhibit a quasi-1×1 hexagonal close-packed structure. By studying the structural evolution from magic clusters to incommensurate structures, the structure models for γ and β phases are proposed.     

Room-Temperature Ferromagnetism of Co-Doped CeO2 Thin Films on Si（111） substrates

Using Co2O3 as the Co source, doped cerium oxide thin films with the composition of Ce0.97C00.03O2-δ （CCO） are deposited on Si（111） and glass substrates by pulse laser deposition technique. X-ray diffraction reveals that CCO films with （111） preferential orientation are grown on Si, while the fihn on glass is polycrystalline with nanocrystal. X-ray photoelectron spectroscopy shows that the （Jo displaces the （;e atom and exists in high spin state rather than low spin state, which contributes to the room-temperature ferromagnetism confirmed by vibration sample magnetometer. I~ilms on Si and glass are different in ferromagnetism, which is believed to be induced by different film microstructures. Based on these results, the possible ferromagnetism in this insulating film is discussed. Anyway, successful fabrication of CCO films with room-temperature ferromagnetism on Si substrates is of great importance in both technological and theoretical aspects.     

Effect of 6H-SiC （1120） substrate on epitaxial graphene revealed by Raman scattering

A nonpolar SiC(1120) substrate has been used to fabricate epitaxial graphene (EG). Two EGs with layer numbers of 8-10 (referred to as MLG) and 2-3 (referred to as FLG) were used as representative to study the substrate effect on EG through temperature dependent Raman scattering. It is found that Raman lineshifts of G and 2D peaks of the MLG with temperature are consistent with that of a free graphene predicted by theory calculation, indicating that the substrate influence on the MLG is undetectable. While Raman G peak lineshifts of the FLG to that of the free graphene are obvious, however, its lineshift rate (-0.016 cm^-1/K) is almost one third of that (-0.043 cm^-1/K) of a EG on 6H-SiC (0001) in the temperature range from 300 K to 400 K, indicating a weak substrate effect from SiC (1120) on the FLG. This renders the FLG a high mobility around 1812 cm²- ·V^-1-·s^-1 at room temperature even with a very high carrier concentration about 2.95× 10¹³ cm^-2 (p-type). These suggest SiC (1120) is more suitable for fabricating EG with high performance.     

Effects of AlGaN/AlN Stacked Interlayers on GaN Growth on Si （111）

We report the growth of high quality and crack-free GaN film on Si （111） substrate using Al0.2Ga0.8N/AlN stacked interlayers. Compared with the previously used single AlN interlayer, the AlGaN/AlN stacked interlayers can more effectively reduce the tensile stress inside the GaN layer. The cross-sectional TEM image reveals the bending and annihilation of threading dislocations （TDs） in the overgrown GaN film which leads to a decrease of TD density.     

Anomalous Magneto-Transport Properties of Epitaxial Single-Crystal Bi Films on Si（111）

Anomalous transport properties of 40-nm-thick single-crystal Bi（111） films grown on Si（111）-7 × 7 substrates is investigated. The magnetoresistance （MR） of the films in perpendicular magnetic field shows a regular positive behavior in the temperature range 2–300K, the MR in parallel field （B｜｜） displays a series of interesting features. Specifically, we observe a change of the MR （B｜｜） behavior from positive to negative when the temperature is below 10K. In the range 10–170 K, the MR （B｜｜） is negative in the investigated field of 9T. When T 〉 170 K, a positive MR appears in the high field regime. The low temperature MR（B｜｜） behavior in the parallel field can be understood by the competition between weak localization and weak anti-localization （WAL）. Furthermore, our results suggest that the WAL is dominated by the interface carriers.     

Density functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clustersDensity functional theory study of Mg2Nin （n = 1-8） clusters

The density functional theory B3PW91 with LANL2DZ basis sets has been used to study the possible geometries of Mg2Nin （n - 1-8） clusters. For the lowest energy structures of the clusters, stabilities, electronic properties, and natural bond orbital （NBO） are calculated and discussed. The results show that the doped Mg atoms reduce the stabilities of pure Ni clusters. The Mg2Ni2, Mg2Ni4, and Mg2Ni6 clusters are more stable than neighboring clusters. The system appears magic number characteristics. In addition, the hybridization phenomenon occurs, owing to the interaction of Mg and Ni. The result of charge transfer is that Ni atom is negative and the Mg atom is positive. We also conclude that the 3p and 4d orbitals of the Ni atom have an effect on the stabilities of the clusters.     

The influence of an SixNy interlayer on a GaN film grown on an Si（lll） substrate

<正>A method to drastically reduce dislocation density in a GaN film grown on an Si(111) substrate is newly developed. In this method,the Si_xN_y interlayer which is deposited on an A1N buffer layer in situ is introduced to grow the GaN film laterally.The crack-free GaN film with thickness over 1.7 micron is successfully grown on an Si(111) substrate. A synthesized GaN epilayer is characterized by X-ray diffraction(XRD),atomic force microscope(AFM),and Raman spectrum.The test results show that the GaN crystal reveals a wurtzite structure with the(0001) crystal orientation and the full width at half maximum of the X-ray diffraction curve in the(0002) plane is as low as 403 arcsec for the GaN film grown on the Si substrate with an Si_xN_y interlayer.In addition,Raman scattering is used to study the stress in the sample.The results indicate that the Si_xN_y interlayer can more effectively accommodate the strain energy.So the dislocation density can be reduced drastically,and the crystal quality of GaN film can be greatly improved by introducing an Si_xN_y interlayer.     

The electronic structures of epitaxial CrSi2 film prepared on Si(111) substrate

The valence band (VB) electronic structures of CrSi₂ were studied by synchrotron radiation photoemission. Overall features of the VB photoemission spectra measured at room temperature (RT) and 20 K by using synchrotron radiation (photon energy, hν=20–120 eV) were similar. Two characteristic emissions were observed corresponding to the bonding and the nonbonding Cr-d partial density of states (PDOS) in the CrSi₂. The onset of the VB photoemission measured at 20 K was located at about 0.32 eV below Fermi level, due to the energy band gap of CrSi₂ more than 0.32 eV.     

第一性原理计算Mg2Ni氢化物的电子结构及其稳定性分析

对Mg₂Ni及其氢化物的能量和电子结构进行了第一性原理计算,并对Mg₂Ni低温氢化物和高温氢化物的稳定性进行了分析.结果发现:在Mg₂Ni中,Mg与Ni存在较强的相互作用.H原子的加入使得Mg的价电子向Ni的3d轨道转移,并在Ni-3d轨道和Ni-4p轨道间形成了带隙.Ni-4s和H-1s电子之间的成键作用,使得Mg和Ni间相互作用减弱了;从LT-Mg₂NiH₄中去掉一个H原子比HT-Mg_{关键词： 第一性原理 2}Ni')" href="#">Mg₂Ni 2NiH₄')" href="#">Mg₂NiH₄ 结构稳定性     

Li嵌入Mg2Ge的反应次序和电子结构变化

Mg₂Ge有望成为新的锂离子电池负极材料.使用基于平面波展开的第一性原理赝势法,计算并得到了Li嵌入Mg₂Ge负极材料时的反应次序.Li首先占据其中的间隙位置,占满间隙位置后随着嵌Li量的进一步增加,Li将逐步替位Mg₂Ge中一半的Mg位置,直到生成Li₂MgGe.计算结果表明,在整个嵌Li过程中主体材料的体积先膨胀后收缩,体积胀缩量很大,这是导致Mg₂Ge作为锂离子电池电极材料循环性能较差的重要 关键词： 锂离子电池 2Ge')" href="#">Mg₂Ge 反应次序 电子结构     

石英玻璃衬底上纤锌矿Mg0.25Zn0.75O薄膜的结构及光学性能

Mg_xZn_1-xO材料是一种新型光电功能材料.采用溶胶凝胶法在石英玻璃上制备了Mg_0.25Zn_0.75O薄膜,理论结合实验研究了Mg_0.25Zn_0.75O薄膜的结构和光学性能.研究表明,石英玻璃衬底上Mg_0.25Zn_0.75O薄膜呈六方纤锌矿结构,薄膜均匀,平均粒径约为20nm.吸收光谱表明吸收带边始于3 关键词： 0.25Zn_0.75O薄膜')" href="#">Mg_0.25Zn_0.75O薄膜 溶胶凝胶法 石英玻璃衬底 紫外发光     

氮掺杂Ge2Sb2Te5相变存储器的多态存储功能

通过反应溅射的方法，制备了N掺杂的Ge₂Sb₂Te₅(N-GST)薄膜，用作相变存储器的存储介质.研究表明，掺杂的N以GeN的形式存在，不仅束缚了Ge₂Sb₂Te₅ (GST)晶粒的长大也提高了GST的晶化温度和相变温度.利用N-GST薄膜的非晶态、晶态面心立方相和晶态六方相的电阻率差异，能够在同一存储单元中存储三个状态，实现相变存储器的多态存储功能. 关键词： 相变存储器 多态存储 N掺杂 2Sb₂Te₅')" href="#">Ge₂Sb₂Te₅     

衬底温度对PLD法生长的Mg0.05Zn0.95O薄膜结构和发光特性的影响

用脉冲激光沉积(PLD)法在不同温度的Si(111)衬底上成功制备了c轴择优取向的Mg_005Zn_095O薄膜.通过X射线衍射(XRD)和光致发光谱(PL)研究了衬底温度对Mg_005Zn_095O薄膜结构和发光特性的影响,探讨了薄膜的结晶质量与发光特性之间的关系.结果表明,在衬底温度为450℃时生长的Mg_005Zn_095O薄膜具有很好的c轴取向和较强的光致发光峰.室温下分别用激发波长为240,300和325nm的氙灯作为激发光源得到不同样品的PL谱,分析表明紫外发光峰和紫峰来源于自由激子的复合辐射且发光强度与薄膜的结晶质量密切相关,蓝绿发光峰与氧空位有关.此外,探讨了衬底温度影响紫外光致发光峰红移和蓝移的可能机理. 关键词： 005Zn_095O薄膜')" href="#">Mg_005Zn_095O薄膜 PLD 衬底温度 光致发光     

SiO2/Si衬底上石墨烯的制备与结构表征

在分子束外延(MBE)设备中,利用直接沉积C原子的方法在覆盖有SiO₂的Si衬底(SiO₂/Si)上生长石墨烯,并通过Raman光谱和近边X射线吸收精细结构谱等实验技术对不同衬底温度(500℃,600℃,700℃,900℃,1100℃,1200℃)生长的薄膜进行结构表征.实验结果表明,在衬底温度较低时生长的薄膜是无定形碳,在衬底温度高于700℃时薄膜具有石墨烯的特征,而且石墨烯的结晶质量随着衬底温度的升高而改善,但过高的衬底温度会使石墨烯质量降低.衬底温度为1100℃时结晶质量最好.衬底温度较低时C原子活性较低,难以形成有序的C-sp²六方环.而衬底温度过高时(1200℃),衬底表面部分SiO₂分解,C原子与表面的Si原子或者O原子结合而阻止石墨烯的形成,并产生表面缺陷导致石墨烯结晶变差.     

Effects of interface between SnO2 thin film and Si substrate on growth time

SnO₂ thin film was grown on Si substrate using the low pressure chemical vapor deposition (LPCVD) method. The SnO₂ thin film was grown in the direction of (110) as deposition time increased. The atomic ratio of O decreased by 62.4, 57.6, and 45.6%, and the thickness of the thin film increased to 0.2, 0.3, and 0.7 ? as the deposition time increased to 10, 20, and 30 min, respectively. The interface of the thin film was examined using high-resolution transmission electron microscope (HRTEM) and energy dispersive spectroscopy (EDS) analysis. The SiO₂ layer was observed at between the SnO₂ thin film and the Si substrate. This layer decreased in thickness as the deposition time increased, which indicates that the deposition time affected the interface of the thin film.     

Mo(CO)6在清洁的和氧化的Si(111)表面上吸附的对比

采用高分辨电子能量损失谱对比研究Mo(CO)₆在清洁的、预吸附氧的和深度氧化的Si(111)表面上的吸附行为. 吸附Mo(CO)₆的C-O伸缩振动模式向低频方向移动,说明Mo(CO)₆与清洁Si(111)和SiO₂/Si(111)表面发生了不同的相互作用,前者较弱而后者较强. 与SiO₂/Si(111)表面的强相互作用可能引起Mo(CO)₆部分解离,形成部分分解的羰基钼物种.     

Green emitting long lasting phosphorescence (LLP) properties of Mg2SnO4:Mn phosphor

A novel long-lasting phosphorescence phosphor, Mn²⁺-activated Mg₂SnO₄, has been synthesized and its optical properties have been investigated. The Mg₂SnO₄:Mn²⁺ emits green light with high luminance, upon UV irradiation, centered at 499 nm from the spin forbidden transitions of the d-electrons in Mn²⁺ ions. The CIE chromaticity coordinates of the Mg₂SnO₄:Mn²⁺ phosphor are x=0.0875 and y=0.6083 under 254 nm UV excitation. The phosphorescence can be observed by the naked eyes (0.32 mcd/m²) in the dark clearly for over 5 h after the 5 min UV irradiation. Thermoluminescence has been studied and the mechanism of the long-lasting phosphorescence has been discussed.