Boron surface phase on Si(111): atomic structure and Si overgrowth studied by scanning tunneling microscopy and work function measurement

Surface reconstructions of boron (B) on silicon (Si) have been well known for several years. One reconstruction of special interest to us is the so called R30° boron surface phase (BSP) on Si(111). This reconstruction can occur in two different forms, one with B located on T₄ lattice sites (B-T₄), the second one with B residing in S₅ sites (B-S₅) directly underneath a Si adatom in a T₄ site. The two forms of the R30° reconstruction are expected to exhibit completely different properties due to their different chemical binding. In this paper we present work function measurements of these surface phases which clearly show their distinctively different behaviour and allow the determination of the temperature at which the boron atoms migrate from the T₄ sites to the S₅ sites. Furthermore, STM results concerning the overgrowth of BSPs with Si films of variable thicknesses and its effect on the BSP itself are shown.     

Interface structure at the large misfit, still common epitaxy β-FeSi2(101) or (110)//Si(111)

In this paper we compare the elastic energies obtained by tight-binding molecular dynamics simulations for several strained structures of β-FeSi₂, corresponding to the most frequent epitaxial relationships ‘on’ and ‘in’ silicon. Our results confirm that, for coherent interfaces, the very common β-FeSi₂(101) or (110)//Si(111) orientation generates a very large contribution to the elastic energy, due to the large misfit. Therefore, we suggest that the frequent nucleation of such epitaxial relationships in precipitates is provided by the correspondence of the two-dimensional crystal structure for the Si sites between Si(111) and β-FeSi₂(101) or (110). We show it to be maintained even after misfit relaxation in the silicon matrix, as simulated by a large-scale molecular dynamics run.     

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).     

Perspectives of the concept of van der Waals epitaxy: growth of lattice mismatched GaSe(0001) films on Si(111), Si(110) and Si(100)

The preparation of high quality epitaxial heterointerfaces of lattice mismatched dissimilar materials is one of the challenging tasks for advanced semiconductor devices. We have used the concept of van der Waals epitaxy, namely the deposition of two-dimensional layered materials like GaSe onto properly terminated three-dimensional substrates to prepare new heterointerfaces on Si of different surface orientation. Film growth and properties were investigated in situ by low-energy electron diffraction (LEED) and soft X-ray photoemission (SXPS) using integrated UHV preparation and analysis chambers. On Si(111) a hexagonal GaSe epitaxial layer grows on top of a preformed Si–Ga–Se van der Waals-like termination layer. A distorted Si–Ga–Se layer is also formed on Si(110), which evidently leads to an hexagonal surface mesh as substrate for further growth of crystalline GaSe. On Si(100), two domains of azimuthally aligned GaSe(0001) films are deposited. The usually given constraints in lattice mismatch, and even of different surface symmetry, can evidently be overcome by the use of van der Waals-like surface termination layers of the substrates. Thus, novel device structures combining compound semiconductors with Si seem to be feasible.     

The epitaxial growth of Ag on Si(111)-(7 x 7) surface and its (√3x√3)-R30 surface phase transformation

Ag is adsorbed in ultra-high vacuum on to the (7x7) reconstructed Si(111) surface with submonolayer coverage control with a deposition rate of 3-3 x 10¹² atoms/cm²/sec. The initial stages of growth and intermediate equilibrium phase formation are determined by using low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) for structural information, and auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) for composition and interaction analyses. Room temperature (RT) adsorption results in the nearly epitaxial (1 x 1) surface phase growth in the simultaneous multi-layer growth mode. The quenching of the dangling bond states during adsorption is observed by monitoring thep-character of the Si LVV auger peak. For depositions carried out at high temperatures (HT), several plateaus in the auger uptake curve with the (√3 x √3)-R30° LEED structures are formed. It is observed that a minimum coverage of 0–33 monolayer (ML) is required for the formation of the (√3 x √3) phase and this phase causes the reappearance of thep-electron-related states that were quenched by 1.0 ML adsorption at RT. However the (√3 x √3) is observed for higher coverages (0.66 and 1.0 ML) also. The polar angle anisotropy of Si(2p) emission in XPD indicates the rearrangement of substrate Si atoms for the formation of the (√3 x √3) phase. The EELS data also shows relevant changes due to adsorption of Ag at RT and upon annealing. The results suggest the importance of controlled deposition parameters, the lack of which may have kept the determination of the nature and coverage of the (√3 x √3) surface phase unresolved in literature.     

3D ES势垒对Cu(111)和Cu(OO1)晶面同质外延生长的影响

三维3D ES势垒直接影响着层间扩散,在Cu(111)和Cu(100)面2D ES势垒和3D ES势垒是不同的.本文主要研究了基于(1+1)维KMC模型,在这两个特殊的晶面上Cu薄膜的同质外延生长.观察两个面的生长情况,发现随着温度的增加薄膜的粗糙度逐渐减小,由于Cu(111)表面2D ES势垒较小,所以Cu(111)面粗糙度的下降的速度比Cu(100)要快,Cu(111)表面更有利于薄膜的生长.对于纳米棒的应用,在生长时间较短时两个面的生长速率逐渐减小,但是Cu(100)面的生长速度比Cu(111)面更快,随着生长时间的增加,这两个面会出现多层台阶,Cu(111)面的生长速度会逐渐增加,最终会超过了Cu(100)面.多层台阶出现后对两个面的影响是不同的.由于Cu(111)表面3D ES势垒较大,在Cu(111)表面会形成较多的多层台阶,Cu(111)面上多层台阶数有利于纳米棒的生长,然而在Cu(100)表面3D ES势垒较小,Cu(100)表面很难形成多层台阶,所以Cu(100)面上纳米棒的生长速度并没有增加.正是因为3D ES势垒的存在才会导致多层台阶的出现,较大的3D ES势垒有利于纳米棒的生长.     

Fe3Si nanodots epitaxially grown on Si(111) substrates using ultrathin SiO2 film technique

Ultrahigh density (> 10¹² cm⁻²) Fe₃Si nanodots (NDs) are epitaxially grown on Si(111) substrates by codeposition of Fe and Si on the ultrathin SiO₂ films with ultrahigh density nanovoids. We used two kinds of methods for epitaxial growth: molecular beam epitaxy (MBE) and solid phase epitaxy. For MBE, low temperature (< 300 °C) growth of the Fe₃Si NDs is needed to suppress the interdiffusion between Fe atoms deposited on the surfaces and Si atoms in the substrate. These epitaxial NDs exhibited the ferromagnetism at low temperatures, which were expected in terms of the application to the magnetic memory device materials.     

Dissolution of the γ′ phase in a nickel base superalloy at equilibrium and under rapid heating

Dissolution of the γ′ phase in a PM superalloy Astroloy was studied at equilibrium and under rapid heating. The ‘solvus’ temperature of primary and secondary γ′ precipitates was determined experimentally. The most prominent feature concerns the large departure from equilibrium for the dissolution of the γ′ precipitates during rapid heating and this departure depends on the initial size of the precipitates. A model for γ′ dissolution during fast thermal cycling is proposed.     

Composite detector for mixed radiations based on CsI(Tl) and dispersions of small ZnSe(Te) crystals

A new large area detector of high-energy X-ray and β-radiation has been designed and studied. A composite material based on small-crystalline ZnSe(Te) was applied onto the wide surface of a light guide. An experimental specimen has been prepared, which showed β-sensitivity . The spectrograms of a ⁹⁰Sr+⁹⁰Y β-source obtained with the specimen under study make it possible to evaluate the age of the source by the ratio of low- and high-energy regions of the spectrum.

The combined detector (CD) comprises a single crystalline plate of ZnSe(Te) placed onto the output window of a scintillating transparent light guide made of CsI(Tl) in the shape of a truncated pyramid. The CsI(Tl) light guide is used to create an additional channel for detection of γ-radiation, as well as for protecting the photodiode from the penetrating radiation. It is shown that introduction of the light guide does not worsen the energy resolution characteristics of ZnSe(Te). Separate detection of - and γ-radiation has been achieved under simultaneous excitation by ²³⁹Pu (ZnSe(Te), R=6%) and ²⁴¹Am (CsI(Tl), R_γ=20%). The use of selective optical filters allows separation of the peaks of total absorption (p.t.a.) in the case of their superposition.     

锰及其硅化物在Si(100)表面的反应外延生长

采用超高真空分子束外延-扫描隧道显微镜(UHVMBE-STM)系统研究了不同温度下锰及其硅化物在Si(100)-2 ×1重构表面上的外延生长情况.实验结果表明当生长过程中衬底温度控制在室温到135℃时,生成大小基本一致的锰纳米团簇;当衬底温度达到210℃时锰与硅开始发生反应,形成硅化物,并有纳米线结构出现;当衬底温度达到330℃时,纳米线完全被棒状物或不规则的三维岛状硅化物取代.随着沉积时衬底温度升高,生成物的成核密度与生长温度的关系与经典的二维岛成核理论相符合.     

Magnetocrystalline anisotropy energy and spin polarization of Fe3Si in bulk and on Si(001) and Si(111) substrates

In order to achieve highly efficient spin polarized transport, first of all magnetocrystalline anisotropy energy, which determines the magnetic easy axis, must be understood. The highly precise full-potential linearized augmented plane-wave method is employed to investigate the magnetism and magnetocrystalline anisotropy energy of a ferromagnetic Heusler alloy Fe₃Si on Si(001) and Si(111) substrates. The calculated magnetocrystalline anisotropy energy of bulk D0₃ Fe₃Si was found to depend sensitively on a tetragonal distortion: The magnetization is along the z-axis at c/a < 1 and on the xy plane at c/a > 1. The out-of-plane magnetic easy axis of both Fe₃Si/Si(001) and (111) was calculated to be quite stable with enhanced magnetocrystalline anisotropy energy compared with bulk value. The magnetic easy axis of Fe₃Si/Si(001) and (111) is discussed in detail with single particle energy spectra. The degree of spin polarization is also presented at the interfaces between Fe₃Si and Si. The calculated spin polarizations of Fe₃Si/Si(111) tend to retain the spin polarization of the bulk, whereas they are reduced for the (001) interfaces.     

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.     

两种势下的Si(100)表面重构及二聚体形成过程的分子动力学模拟

分别采用Tersoff势与S-W势对不同温度下Si(100)面重构情况进行分子动力学模拟,找出了这两种势函数下发生重构的温度范围,进而采用S-W势对几种典型情况进行模拟研究.结果发现,二聚体形成前后的温度、内能会出现明显变化,高温时重构速度快但效果较差且不稳定,会形成吸附单体.原子间距为0.33nm左右是二聚体形成的关键距离.     

在(111)Si基底上直接溅射合成PbTiO3薄膜以及Pb损失的抑制

利用射频磁控溅射系统，采用Ｔｉ、Ｐｂ组合靶，以Ｏ２为反应气体，在（１１１）Ｓｉ基板上直接沉积ＰｂＴｉＯ３薄膜，通过对不同基底温度以及沉积后的薄膜在不同的氧气氛中采用不同的降温速率降温制备。通过对所得的薄膜的结构和组成以及光学和电学特性的测试１分析得出：在５３５℃时沉积、溅射后直接充入１０７Ｐａ的氧气并且以３℃／ｍｉｎ的速率降至室温，制备出了性能较好的具有钙钛矿结构的ＰｂＴｉＯ３薄膜，并对薄膜的形成     

Characterization and body distribution of beta-elemene solid lipid nanoparticles (SLN)

Solid lipid nanoparticles (SLN) containing β-elemene, a volatile oil used for the treatment of cancer, were prepared by the method combining probe sonication and membrane extrusion. Effects of the formulations and procedures on the characteristics of SLN were investigated. Body distribution of β-elemene SLN in rats after intravenous administration was compared with that of the commercial emulsion. The results showed that dispersing the surfactant in the melted lipid matrix could obtain smaller particles than that dispersing in the water phase. Increasing the ratio of monostearin in the lipid matrix or the concentration of surfactant reduced the mean volume size of the SLN. Optimized formulation was composed of monostearin and precirol ATO 5 at a mass ratio of 3:7, which was quite stable for 8 months at room temperature. In vitro release of β-elemene from the SLN was slow and stable without obvious burst release and was found to follow the Higuich equation. After intravenous administration, the β-elemene levels after 5 min injection of SLN formulation were 1.5, 2.9, and 1.4 times higher than those of β-elemene emulsion in liver, spleen, and kidney, respectively, while the concentrations of β-elemene were decreased 30% in heart and lung. Therefore, the SLN containing β-elemene might be an attractive candidate for the treatment of liver cancer.     

Gas phase particle formation and elimination on Si (100) in low temperature reduced pressure chemical vapor deposition silicon-based epitaxial layers

Gas phase particle formation and elimination in silicon epitaxial layers grown on Si (100) substrates using reduced pressure chemical vapor deposition at low temperatures (< 600 °C) are investigated. High-order silane precursors (Si_nH_2n + 2; n = 3, n > 3) are useful for high growth rate epitaxy at low temperature. However, particulates are observed on the surface of the epitaxial layers grown with high-order silanes. These particulates are attributed to gas phase particles. As atomically smooth epitaxial films are desired, the elimination of gas phase particles is required. Cyclical deposition and etch process and/or low pressure deposition enables atomically smooth SiCP epitaxial films with a high-order silane.     

氮化硅纳米复合陶瓷的抗氧化性与耐蚀性研究

采用极性分散剂和超声分散技术，在氮化硅微米粉中加入碳化硅纳米粉真空热压制备出氮化硅／碳化硅（n)纳米复合陶瓷，研究了纳米增强相对纳米复合陶瓷抗氧化性与耐蚀性的影响。结果表明：随着SiC纳米粉的含量的增加，纳米复合陶瓷在空气中加热时抗氧化性增强，其中含15％SiC纳米粉的纳米复合陶瓷抗氧化性最好；纳米复合陶瓷的耐碱性也非常好，适于在酸、碱性环境中使用。     

氨化Si基Ga2O3/In制备GaN薄膜

研究了Ga2O3/In 膜反应自组装制备GaN薄膜,再将Ga2O3/In膜在高纯氨气气氛中氨化反应得到GaN薄膜,用X射线衍射(XRD),傅里叶红外吸收(FTIR),扫描电镜(SEM),原子力显微镜(AFM),透射电镜(TEM)对样品进行结构,形貌的分析.测试结果表明:用此方法得到了六方纤锌矿结构的GaN多晶膜,且900℃时成膜的质量最好.     

Al、O含量对SiAlCO纤维高温转化为Si(Al)C纤维过程的影响

采用不同Al含量的聚铝碳硅烷(PACS)为先驱体, 通过不同的PACS纤维不熔化方法调节O引入量, 制备了具有不同Al和O含量的连续SiAlCO纤维。研究了SiAlCO纤维经高温处理转变为Si(Al)C纤维过程中, Al、O含量对SiC_xO_y相分解、β-SiC结晶生长和微观形貌的影响。结果表明: 纤维中SiC_xO_y相的分解温度区间为1300~1700℃, 与Al、O含量基本无关; 提高Al含量可减少纤维在高温下表面形成粗大SiC结晶颗粒和相互连通的气孔, 并且对1700℃以上β-SiC结晶生长的抑制作用增强, 有利于烧结致密化; 利用纤维中O元素, 以放出CO或CO₂方式脱除富余C, 但O含量过高导致气体逸出时产生较大孔洞, 不利于烧结致密化。当Al和O含量分别约为0.6wt%和9wt%时, SiAlCO纤维经高温处理后能得到具有较大β-SiC晶粒尺寸的致密化Si(Al)C纤维。