离子束溅射制备Si/Ge多层膜的结晶研究

采用离子束溅射制备Si/Ge多层膜,通过X射线小角衍射计算其周期厚度及各子层的厚度,用Raman光谱对Si/Ge多层膜的微观结构及Si子层的结构进行表征.结果表明,所制备的Si/Ge多层膜中,当Ge子层的厚度为6.2nm时,Si子层的结晶质量较好,表明适量的Ge含量有诱导Si结晶的作用.     

退火温度对镶嵌于SiO2膜中的Ge纳米晶结构的影响

采用磁控溅射及退火的方法制备了含Ge纳米晶的SiO2复合膜,应用拉曼散射和X射线衍射技术研究不同退火温度下的Ge纳米晶结构.结果表明:Ge纳米晶的结晶温度约为750 ℃.运用声子限域模型(RWL model)对样品的拉曼散射光谱进行拟合,确定出样品中Ge纳米晶的尺寸.通过XRD谱计算复合膜的内部压应力,得出由其引起的拉曼峰位的蓝移量,得出结论:压应力是造成拉曼模拟曲线与实验曲线峰位偏离的主要原因.     

离子束溅射制备Si/Ge多层膜及红外吸收性能研究

采用离子束溅射方法在Si衬底上制备Si/Ge多层膜.通过改变生长温度、溅射速率等因素得到一系列Si/Ge多层膜样品.通过X射线衍射、拉曼散射、原子力显微分析(AFM)等表征方法研究薄膜结构与生长条件的关系.在小束流(10mA)、室温条件下制备出界面清晰、周期完整的Si/Ge多层膜.通过红外吸收谱的测量发现薄膜样品具有较好的红外吸收性能.     

温度对SiO2表面上磁控溅射制备Ge纳米点的生长模式和尺寸的影响

采用磁控溅射技术在SiO2/Si(100)表面上制备了一系列不同生长温度的Ge纳米点样品.原子力显微镜(AFM)的实验结果表明:不同衬底温度下Ge纳米点在SiO2薄膜上的生长模式和尺寸分布有所不同.当衬底生长温度达到500 ℃时,SiO2开始与Ge原子发生化学反应,并形成"Ge纳米点的Si窗口".在此温度条件下,外延生长实验可获得尺寸均匀且密度高达3.2×1010 cm-2的Ge纳米点.     

不同衬底表面上大晶粒多晶Si薄膜的制备

利用高频感应加热化学气相沉积(HFCVD)工艺,以H2稀释的SiH4作为反应气体源,分别在n-(111)Si衬底上常规热生长的SiO2层、织构的SiO2层和纳米晶粒多晶Si薄膜表面上,制备了具有均匀分布的大晶粒多晶Si膜.采用扫描电子显微镜(SEM)和X射线衍射(XRD)等检测手段,测量和分析了沉积膜层的表面形貌、晶粒尺寸、密度分布与择优取向等结构特征.结果表明,多晶Si膜中Si晶粒的尺寸大小和密度分布不仅与衬底温度、SiH4浓度与反应气压等工艺参数有关,而且强烈依赖于衬底的表面状态.本实验获得的最好的薄膜中,Si晶粒平均尺寸约为2.3 μm,密度分布约为3.8×107/cm2.对薄膜的沉积机理分析表明,衬底表面上Si原子基团的吸附、迁移、成核与融合等热力学过程支配着大晶粒多晶Si膜的生长.     

SiO2-BaTiO3异质双尺寸超材料结构的制备

采用垂直沉积法自组装制备了SiO2胶体晶体模板,并结合Pechini溶胶-凝胶法实现多种SiO2-BaTiO3异质双尺寸超材料结构的制备.通过X射线衍射分析仪(XRD)和场发射扫描电子显微镜(FE-SEM)对所得粉体和光子晶体的晶型、形貌及排列方式进行测试分析.对比钛酸钡粉体,对SiO2-BaTiO3异质超材料的结构进行探讨,研究不同pH值对钛酸钡粉体的形貌和粒径的影响,进而研究不同凝胶对异质超材料结构的影响.研究结果表明异质结构中胶体晶体模板的排列更加紧密有序,缺陷减少,纳米颗粒的粒径与原钛酸钡粉体的粒径基本一致,利用不同凝胶可获得LS2、LS4、LS6型结构及层-层复合结构.     

Ge覆盖层诱导晶化多晶Si薄膜的晶化特性研究

采用电子束蒸发技术在衬底温度为180℃条件下生长具有Ge覆盖层的非晶Si薄膜,并于500℃、600℃、700℃真空退火5h.采用Raman散射、X射线衍射(XRD)、全自动数字式显微镜等对所制备薄膜的晶化特性进行研究.结果表明,Ge覆盖层具有诱导非晶Si薄膜晶化的作用,且随着退火温度的升高a-Si薄膜晶化越显著.具有Ge覆盖层非晶薄膜经500℃退火5h沿Si(400)方向开始晶化,对应晶粒尺寸约为4.9 nm.将退火温度升高到700℃时,非晶硅薄膜几乎全部晶化,晶化多晶Si薄膜在Si(400)方向表现出很强的择优取向特性,晶粒尺寸高达23.3μm.与相同条件下制备的无Ge覆盖层的非晶Si薄膜相比,晶化温度降低了300℃.     

提高掺铒硅基纳米材料发光效率的探索

本文中,我们以SiO2介质镶嵌的纳米晶Si薄膜(nc-Si/SiO2)作为基质,将稀土离子Er掺入其中所形成的nc-Si:Er3+/SiO2薄膜材料为主,介绍了nc-Si→Er3+之间的能量转移过程,探讨了实现各类掺Er的Si基纳米材料高效率发光的可能途径.这些方法主要包括:增强nc-Si→Er3+的能转移效率,提高有效Er的掺杂浓度,选择最佳的退火温度,增加Er-O发光复合体的浓度和制备新的Er掺杂Si基纳米结构等.这些方法对制备具有高发光效率的掺铒硅基纳米材料具有重要的实际意义.     

大范围ReS2纳米带的化学气相沉积制备及特性表征

采用化学气相沉积方法,在整个SiO2(300 nm)/Si衬底上制备出了大面积、高质量的单层及多层ReS2纳米带,纳米带的长度可达150μm.利用光镜、原子力显微镜(AFM)、荧光(PL),拉曼(Raman)以及X射线光电子能谱分析(XPS)等手段对所得不同层数的ReS2样品进行了表征.结果表明:所制备的ReS2纳米带的拉曼信号与化学气相沉积方法制备的(CVD)单层及多层的薄膜材料差别不大,而其荧光峰出现了明显的展宽,且峰位出现了明显的蓝移.化学气相沉积法(CVD)制备ReS2纳米带操作简单,可控性与可重复性高,对其基础研究和未来潜在应用有着比较重要的现实意义.     

声化学法可控合成硅酸钇纳米晶

以硝酸钇、硅酸钠和氢氧化钠为主要原料,通过调节起始溶液配比,采用声化学法可控合成硅酸钇纳米晶.借助X射线衍射仪(XRD)和场发射扫描电镜(FESEM)分析粉体的晶相结构和显微形貌,并探讨了硅酸钇纳米晶的声化学合成机理.结果表明:选不同配比的溶液体系,经超声波200W功率作用60min后,得到的沉淀于900℃下保温2h,最终可获得颗粒尺寸分别为40～55 nm、50～65 nm和25～40 nm的Y2SiO5、Y4.67(SiO4)3O和Y2Si2O7三种硅酸钇纳米晶.     

SiO_2中包埋纳米晶Si光电性质的计算

采用第一性原理平面波赝势方法计算了SiO_2基质包埋不同尺寸纳米晶粒Si_3和Si_5的电子结构及光学性质.结果表明,随着包埋纳米晶粒尺寸的减小,包埋Si_3结构的带隙比包埋Si_5结构宽,但包埋Si_5结构对可见光区的吸收优于包埋Si_3结构.Si_3结构的第一个吸收峰在约3.9 eV处,Si_5结构的第一个吸收峰在约4.6 eV处.计算表明,Si纳米颗粒中Si原子数与包埋基质的分子数之比为45.46;是一种较好的结构参数,对可见光区吸收效果好.     

Composition of Ge+ and Si+ implanted SiO2/Si layers: Role of oxides in nanocluster formation

X-ray photoelectron spectroscopy (XPS) has been used to examine the atomic content of implanted SiO₂/Si layers. In particular, an XPS analysis permits to identify elemental Ge and Si, as well as GeO₂ precipitations in SiO₂ matrices. The XPS results reveal valuable information not only about the formation mechanism of Ge and Si nanoclusters but also on the annealing kinetics of SiO₂ whose properties are known to be significantly altered during the process of ion implantation and subsequent annealing. The composition of ion beam-modified SiO₂ layers strongly depends on the annealing temperature. With respect to germanium implanted samples a possibility of Ge nanocrystals formation appears at high (above 1000 °C) annealing temperatures. It has been shown that an intermediate step in the Ge oxide formation is necessary for the creation of Ge nanoclusters. Additionally, the presence of a subsurface zone GeO_x (about 100 nm thick) predicted in kinetic three-dimensional lattice simulations has been confirmed. In the case of Si⁺ implanted samples substoichiometric silicon oxide lines in the XPS spectra of a SiO₂ layer for all samples have been observed. No evidence of a line connected to the Si–Si bonding has been observed even at the highest annealing temperatures, at which only stoichiometric SiO₂ has been detected.     

An interface clusters mixture model for the structure of amorphous silicon monoxide (SiO)

The present state of research on the structure of amorphous silicon monoxide (SiO) is reviewed. The black, coal-like modification of bulk SiO is studied by a combination of diffraction, microscopy, spectroscopy, and magnetometry methods. Partial radial distribution functions of SiO are obtained by X-ray, neutron and electron diffraction. Disproportionation of SiO into Si and SiO₂ is verified. High resolution TEM gives an upper limit of less than 2 nm for the typical Si cluster size. The Si K-edge electron energy-loss near-edge structure (ELNES) data of SiO are interpreted in terms of the oxidation states Si⁴⁺ and Si⁰. X-ray photoelectron spectroscopy gives first details about possible stoichiometric inhomogeneities related to internal interfaces. The wipe-out effect in the ²⁹Si MAS NMR signal of SiO is confirmed experimentally. The new estimation of the wipe-out radius is about 1.1 nm. First-time W-band, Q-band, and X-band ESR and SQUID measurements indicate an interfacial defect structure. Frequency distributions of atomic nearest-neighbours are derived. The interface clusters mixture model (ICM model) suggested here describes the SiO structure as a disproportionation in the initial state. The model implies clusters of silicon dioxide and clusters of silicon surrounded by a sub-oxide matrix that is comparable to the well-known thin Si/SiO₂ interface and significant in the volume because of small cluster sizes.     

The thermal study of oxyfluoride glass with strontium fluoride

A thulium (Tm 3+) doped oxyfluoride glass ceramic containing SrF2 nanocrystals has been presented. Transparent glass ceramic was obtained by heat treating the glass from the SiO2-Al2O3-ZnO-SrF2 system at the first crystallization temperature. Cerammization of glass was studied by DTA/DSC, XRD and SEM methods. It has been found that nanocrystallization of SrF2 strongly depends on the ratio between the components and amount of SrF2. Moreover the rare earth dopant Tm3+ influenced on the thermal properties of glass. The formation of SrF2 nanocrystals in glass ceramic was confirmed by X-ray diffraction. X-ray diffraction analysis of the transparent glass ceramic revealed that the SrF2 nanocrystals are precipitated in the glass matrix. Analysis of the local atomic interactions in the structure of oxyfluoride glass has been used to explain the course of the crystallization.     

MEMS用Si台面及SiO2/Si衬底上3C-SiC的LPCVD生长

本文报道用在Si台面及热氧化SiO2衬底上3C-SiC薄膜的LPCVD生长,反应生长使用的气体为SiH4和C2H4,载气为H2,采用光学显微镜、X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电镜（SEM）、以及室温Hall测试对所生长的3C—SiC材料进行了测试与分析,结果表明在3C-SiC和SiO2之间没有明显的坑洞形成。     

Systematic studies of Si and Ge hemispherical concave wafers prepared by plastic deformation

Si and Ge hemispherical concave wafers can be prepared by plastic deformation using Si and Ge single- and polycrystal wafers. Deformation regions in which such Si and Ge hemispherical wafers can be obtained by high-temperature plastic deformation were systematically studied. The deformation regions in which well-shaped Si concave wafers can be obtained were studied for (1 0 0), (1 1 1), and polycrystal Si. It was found that Si (1 1 1) crystal wafers can be more easily deformed to a perfect hemispherical shape than (1 0 0) wafers because of the crystallographic symmetry. Si hemispherical wafers with a small radius of 25 mm can be perfectly deformed when 0.5-mm-thick Si (1 1 1) crystal wafers are used. Ge hemispherical wafers with a radius of 100 mm can be perfectly deformed when 0.5-mm-thick Ge crystal wafers are used. Ge hemispherical concave wafers with a perfect shape can be more easily obtained using Ge (1 1 1) wafers than (1 0 0) wafers. According to these results, the deformation behavior of Ge wafers is very similar to that of Si wafers at a normalized pressing temperature. As both the radius and the load on Si and Ge hemispherical wafers increase, thicker Si and Ge wafers can be used to obtain hemispherical wafers with a perfect shape. The dislocation density in the shaped wafers markedly decreases as the pressing temperature and hemisphere radius increase. Thus, it is suggested that Si and Ge shaped wafers are of sufficient quality and have the high potential for use as several types of lens such as those in Si and Ge X-ray monochromators.     

Aluminum induced formation of SiGe alloy in Ge/Si/Al thin film structure

In this work, a study of aluminum induced crystallization (AIC) of thin film germanium/silicon/aluminum (Ge/Si/Al) structure on oxidized silicon is presented. The Ge/Si/Al trilayer structure was prepared in three consecutive thin film deposition processes. The AIC was performed in nitrogen at 500 °C within time duration between 1 and 9 h. The progress of crystallization was monitored by optical microscopy, Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). It was found that in Ge/Si/Al structure the AIC can lead to formation of SiGe alloy at temperature of 500 °C. This presents an alternative low-temperature formation method of SiGe which is suitable for integration with the conventional Si technology in electronic device fabrication.     

Structural properties of liquid Au–Si and Au–Ge alloys with deep eutectic region

Au–Si and Au–Ge alloys have a deep eutectic region around 19 at.% Si and 28 at.% Ge, respectively. The metallic glass was prepared by quenching around 25 at.% Si near the eutectic composition for the Au–Si alloys [2] which has stimulated many researchers to study on the structural properties of such liquid alloys. However their results were different from each other, which seems due to the experimental difficulties from heavy absorption of both X-ray and neutron beams by Au atom in diffraction experiments. X-ray diffraction measurements have been carried out for liquid Au–Si and Au–Ge alloys around the eutectic region by the transmission method using high-energy X-rays to investigate the atomic arrangements in the liquid state. From the temperature dependence of the observed structure factors, the partial pair correlation and the detailed atomic arrangements will be discussed by Reverse Monte Carlo analysis. The produced atomic arrangements around the eutectic region suggest a substitutional structure and also an increase in liquid density with decreasing temperature.