Chlorination of Si surfaces with gaseous hydrogen chloride at elevated temperatures

Silicon wafers of different orientations were treated with gaseous hydrogen chloride at elevated temperatures in a chemical vapor deposition (CVD) reactor to generate chlorinated surfaces. After the chlorination process, a smooth surface morphology with single layer steps was observed on Si(1 1 1) surfaces. X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering (RBS) measurements showed that the chlorine coverage is directly affected by the Si surface orientation. The surface chlorine is highly reactive with moisture and alcoholic compounds, which provides a new route for organic molecular functionalization of silicon surfaces.     

Structural characteristics and connection mechanism of gold-catalyzed bridging silicon nanowires

Lateral, single-crystalline silicon nanowires were synthesized using chemical vapor deposition catalyzed by gold nanoparticles deposited on one of the vertical {1 1 1} sidewalls of trenches etched in Si(0 1 1) substrates. Upon encountering the opposing sidewalls of the trenches, the lateral nanowires formed a mechanically strong connection. The bridging connection at the opposing sidewall was observed using high-resolution transmission electron microscopy (TEM) to be epitaxial and unstrained silicon-to-silicon. Using energy-dispersive X-ray spectroscopy in TEM, gold could not be detected at the interface region where the nanowires formed a connection with the opposing sidewall silicon deposit but was detected on the surface adjacent to the impingement region. We postulate that a silicon-to-silicon connection is formed as the gold–silicon liquid eutectic is forced out of the region between the growing nanowire and the opposing sidewall.     

Silicon nanowires for sequence-specific DNA sensing: device fabrication and simulation

Highly sensitive, sequence-specific and label-free DNA sensors were demonstrated by monitoring the electronic conductance of silicon nanowires (SiNWs) with chemically bonded single-stranded (ss) DNA or peptide nucleic acid (PNA) probe molecules. For a 12-mer oligonucleotide, tens of pM of target ss-DNA in solution was recognized when the complementary DNA oligonucleotide probe was attached to the SiNW surfaces. In contrast, ss-DNA samples of ×1000 concentration with a single-base mismatch produce only a weak signal due to nonspecific binding. In order to gain a physical understanding of the change in conductance of the SiNWs with the attachment of the DNA targets and the probes, process and device simulations of the two-dimensional cross sections of the SiNWs were performed. The simulations explained the width dependence of the SiNW conductance and provided understanding to improve the sensor performance. PACS 85.35.-p; 87.83.+a; 07.07.Df     

Effect of self-assembled Ge nanostructures on Si surface electronic properties

Incorporating self-assembled Ge islands on Si surfaces into electronic devices has been suggested as a means of forming small features without fine-scale litho- graphy. For use in electronic devices, the electrical properties of the deposited Ge and their relation to the underlying Si substrate must be known. This report presents the results of a surface photovoltage investigation of the surface energy barrier as increasing amounts of Ge are added to a Si surface by chemical vapor deposition. The results are interpreted in terms of band discontinuities and surface states. The surface barrier increases as a wetting layer is deposited and continues to increase as defect-free islands form. It saturates as the islands grow. As the amount of Ge continues increasing, defects form, and the surface barrier decreases because of the resulting allowed states at the Ge/Si interface. Qualitatively similar behavior is found for Si(001) and Si(111). Covering the Ge with Si reduces the surface-state density and possibly modifies the wetting layer, decreasing the barrier to one more characteristic of Si. Initial hydrogen termination of the surface decreases the active surface-state density. As the H desorbs, the surface barrier increases until it stabilizes as the surface oxidizes. The behavior is briefly correlated with scanning-tunneling spectroscopy data. Received: 13 November 2000 / Accepted: 14 November 2000 / Published online: 23 May 2001     

Silicon–germanium interdiffusion and interfaces in self-assembled quantum dots

A scanning transmission electron microscope (STEM) study of silicon–germanium alloying using annular dark field (ADF) or Z-contrast imaging and electron energy loss spectroscopy (EELS) is presented. Results and techniques are discussed. Growth of 11 equivalent monolayers of germanium on silicon at 650 °C results in dome-shaped islands or quantum dots that contain up to ∼40% silicon. The interface between the as-grown island and substrate shows a highly disordered or amorphous zone ∼1.5-nm wide directly under the island. Annealing for 60 min at 650 °C gives larger pyramidal islands with diffuse crystalline interfaces and an equilibrium distribution of up to ∼70% silicon in the islands. PACS 61.16.Bg; 68.35.Dv; 68.35.Rh     

综放极限平衡区顶煤渗透性的计算模型

基于放顶煤开采中顶煤渗透率对工作面安全生产的重要性, 对煤壁前方极限平衡区内顶煤渗透率的变化规律进行了研究. 应用损伤力学和数理统计方法对顶煤垂直和水平应变进行了研究分析, 并建立了数学模型. 以甲烷气体为渗流体, 应用自制三轴实验机对煤样体积应变与渗透率的关系进行了试验研究, 并利用多项式拟合方法对试验结果进行了分段拟合. 结果表明：根据所建立的顶煤应变计算模型, 可以求出综放顶煤内任意点的体积应变, 且顶煤的水平应变与其距底板的高度无关. 依据试验及拟合所得到的煤体体积应变与渗透率的函数关系, 可以求得顶煤内任意点渗透率. 最后对计算模型进行了实践检验.