A Si nano–micro-wire array on a Si(111) substrate and field emission device applications

A large number of Si wires on Si(111) can be fabricated selectively by the vapor–liquid–solid growth method with a high aspect ratio greater than 100. The diameter of the wire can be controlled from less than a micron to a few hundred microns. We propose a novel smart field electron emission device using silicon nano-wires fabricated by this vapor–liquid–solid growth method, and demonstrate field electron emission with a quite low operation voltage from a gated silicon nano-wire. The threshold voltage is about 13 V, and the value is similar to those for gated carbon-nanotube field emitters. The emission current reaches 10 nA at 15 V gate voltage.     

Preparation of silica nanowires using porous silicon as Si source

This very paper is focusing on the preparation of silica nano-wires via annealing porous silicon wafer at 1200 °C in H₂ atmosphere and without the assistant metal catalysts. X-ray diffraction, X-ray energy dispersion spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and selected area diffraction technology have been employed for characterizing the structures, the morphology and the chemical components of the nano-wires prepared, respectively. It is found that the diameter and the length of the nano-wires were about 100 nm and tens micron, respectively. Meanwhile, it is also necessary to be pointed out that silica NWs only formed in the cracks of porous wafers, where the stress induced both by the electro-chemical etching procedure for the porous silicon preparation and nanowires growth procedure is believed to be lower than that at the center of the island. Therefore, a stress-driven mechanism for the NWs growth model is proposed to explain these findings.     

一维纳米材料的拉曼光谱学研究

本文将报告对硅纳米线、多孔硅、Si C纳米棒和碳纳米管等一维纳米体系的本征拉曼光谱及其特征的研究结果 ,并讨论拉曼光谱在上述材料的几何和物理特性研究中的应用。     

Si_3N_4/Si表面Si生长过程的扫描隧道显微镜研究

利用原位扫描隧道显微镜和低能电子衍射分析了Si的纳米颗粒在Si3N4 /Si(111)和Si3N4 /Si(10 0 )表面生长过程的结构演变 .在生长早期T为 35 0— 10 75K范围内 ,Si在两种衬底表面上都形成高密度的三维纳米团簇 ,这些团簇的大小均在几个纳米范围内 ,并且在高温退火时保持相当稳定的形状而不相互融合 .当生长继续时 ,Si的晶体小面开始显现 .在晶态的Si3N4 (0 0 0 1) /Si(111)表面 ,Si的 (111)小面生长比其他方向优先 ,生长方向与衬底Si(111)方向一致 .最后在大范围内形成以 (111)为主的晶面 .相反 ,在非晶的Si3N4 表面 ,即Si3N4 /Si(10 0 ) ,Si晶体的生长呈现完全随机的方向性 ,低指数面如 (111)和 (10 0 )面共存 ,但它们并不占据主导地位 ,大部分暴露的小面是高指数面如 (113)面 .对表面生长过程进行了探讨并给出了合理的物理解释     

Growth of metallic nanowires on anisotropic Si substrates: Pb on vicinal Si(0 0 1), Si(7 5 5), Si(5 3 3), and Si(1 1 0)

The spontaneous formation of mesoscopic Pb-wires, on 4° off-cut Si(0 0 1) vicinal surface, Si(7 5 5), Si(5 3 3), and Si(1 1 0) substrates was studied by low-energy electron microscopy. Before the deposition of Pb the substrates were modified by predeposition of a submonolayer amount of Au followed by annealing. The Au-induced reconstruction creates quasi-one-dimensional facets and superstructures. Their width ranged from several hundred nm in the case of the vicinal Si(0 0 1) down to atomic scale size, for the Si(1 1 0) surface. The best-developed arrays of parallel aligned mesoscopic wires were obtained during the deposition of Pb on substrates cooled slightly below room temperature. Wires with length to width ratio reaching 130 were produced on the Si(7 5 5) and the Si(5 3 3) substrates. The width of these nanowires was uniform over the whole substrate and was about 60 nm. The driving forces for the formation of the mesoscopic wires are the anisotropic strain due to the large misfit between the Pb and the Si lattice and one-dimensional diffusion of Pb.     

Nucleation and growth of Si on Pb monolayer covered Si(111) surfaces

With a scanning tunneling microscope (STM), we study the initial stage of nucleation and growth of Si on Pb monolayer covered Si(111) surfaces. The Pb monolayer can work as a good surfactant for growth of smooth Si thin films on the Si(111) substrate. We have found that nucleation of two-dimensional (2D) Pb-covered Si islands occurs only when the substrate temperature is high enough and the Si deposition coverage is above a certain coverage. At low deposition coverages or low substrate temperatures, deposited Si atoms tend to self-assemble into a certain type of Si atomic wires, which are immobile and stable against annealing to ~ 200 °C. The Si atomic wires always appear as a double bright-line structure with a separation of ~ 9 Å between the two lines. After annealing to ~ 200 °C for a period of time, some sections of Si atomic wires may decompose, meanwhile the existing 2D Pb-covered Si islands grow laterally in size. The self-assembly of Si atomic wires indicate that single Si adatoms are mobile at the Pb-covered Si(111) surface even at room temperature. Further study of this system may reveal the detailed atomic mechanism in surfactant-mediated epitaxy.     

Si3N4/Si表面Si生长过程的扫描隧道显微镜研究

利用原位扫描隧道显微镜和低能电子衍射分析了Si的纳米颗粒在Si₃N₄/Si(111)和Si₃N₄/Si(100)表面生长过程的结构演变.在生长早期T为350—1075K范围内,Si在两种衬底表面上都形成高密度的三维纳米团簇,这些团簇的大小均在几个纳米范围内,并且在高温退火时保持相当稳定的形状而不相互融合.当生长继续时,Si的晶体小面开始显现.在晶态的Si₃N₄(0001)/S 关键词： 氮化硅 扫描隧道显微镜 纳米颗粒     

Strain-driven morphology of Si1-xGex islands grown on Si(100)

A study has been carried out on the morphology and structure of three-dimensional (3D) SiGe islands grown by molecular beam epitaxy (MBE) on Si(100) substrates. Samples of Si1-xGex alloys have been prepared to investigate the effects either of the alloy composition or of the growth temperature. Atomic force microscopy (AFM) evidenced the growth of 3D islands and transmission electron microscopy (TEM) demonstrated wetting layer growth on Si(100), independently on the deposition conditions. Energy dispersive spectroscopy (EDS) micro-analyses carried out on cross-sections of large Si1-xGex islands with defects allowed a measurement of the Ge distribution in the islands. To the best of our knowledge, these have been the first experimental evidences of a composition change inside SiGe islands. The interpretation of the experimental results has been done in terms of strain-enhanced diffusion mechanisms both of the growing species (Si and Ge) and of small islands.     

Photoluminescence in heavily doped Si: B and Si: As

We report the results of low-temperature photoluminescence measurements on a series of heavily-doped Si: As and Si: B samples. New spectra are obtained for very high doping levels (10¹⁹ 2- 10²⁰ cm^-3), and the results for the more lightly doped samples are found to be in good agreement with previously published data. By comparing the luminescence of a Si: As sample before and after partial compensation with B, we verify that minority carriers can be localized even in “metallic” samples.     

Si衬底上分子束外延Ge,Si时的反射式高能电子衍射强度振荡观察

本文观察了在Si(100)和Si(111)衬底上分子束外延Si,Ge时的反射式高能电子衍射(RHEED)强度振荡现象。其振荡特性表明,外延一定厚度的缓冲层可以改善表面的平整性,较慢的生长速率或中断生长一段时间有利于外延膜晶体质量的提高。Si(100)上外延Si或Ge时,沿[100]和[110]方位观测到的振荡特性均为单原子模式,起因于表面存在双畴(2×1)再构;而Si(111)上外延Ge时,[112]方位观测到的振荡为双原子层模式,但在[110]方位观察到不均匀周期的强度振荡行为。两种衬底上保持RHEED     

Surface diffusion of Pb on clean Si surfaces

Pb diffusion on clean Si(111), (100), and (110) surfaces was studied by Auger electron spectroscopy and low energy electron diffraction in the temperature range from 100 to 300°C. It is shown that lead transport along sillicon surfaces takes place via the mechanism of solid-phase spreading with a sharp moving boundary. The temperature dependence of the Pb diffusion coefficients on Si(111), (100) and (110) surfaces have been obtained. A Si(110)-4×2-Pb surface structure has been observed for the first time.     

碳硅链和氮铝链的电子输运特性的第一性原理研究

采用第一性原理非平衡格林函数方法研究了一维碳硅链 （SiC）_n和氮铝（Al-N）_n的电子输运特性,n为原子链所包含的Si,C（Al,N）原子数目.碳硅链（SiC）_n（或氮铝链（Al-N）_n）置于两个Al（100）电极中.计算了一维碳硅链和氮铝链体系的平衡电导随原子链的长度变化情况.结果发现,它们的平衡电导随原子链的长度增加而减小.对电荷转移分析发现, 关键词： 平衡电导 分子开关 转移电荷     

Photoluminescence of Si from Si nanocrystal-doped SiO2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO₂/Si (or Si-nc:SiO₂/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO₂ results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers (N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d_Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d_Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO₂ prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.     

MgO和Si上NbN超薄薄膜的生长研究

我们在单晶MgO(100)、Si(100)和SiOx/Si基片上成功生长了纳米厚度的超薄NbN薄膜,利用现代分析手段:X射线衍射(XRD)、透射电子显微镜(TEM)、原子力显微镜(AFM)等技术分析研究了所制备的超薄NbN薄膜的微观结构、厚度、表面界面情况等物理特性。研究表明,在MgO(100)基片上获得了外延生长的单晶NbN超薄薄膜,在Si(100)和SiOx/Si基片上获得的是多晶NbN超薄薄膜。厚度均约6nm左右。这些超薄薄膜的超导转变温度分别为:MgO上薄膜是14.46K,Si和SiOx上薄膜分别是8.74K和9.01K.     

Ordered Si/Si–O nanowire array and its optical properties

Glancing angle deposition (GLAD) has been employed to fabricate the Si/Si–O nanowires (NWs). The perpendicular NW on silicon substrate shows the amorphous nature. The visible light emission from the NWs was observed from the Si/Si–O nanoparticles. High light absorption inside the Si/Si–O NW structure was recorded.     

Eu掺杂Si纳米线的光致发光特性

利用Si(111)衬底, 以Au-Al为金属催化剂, 基于固-液-固生长机理, 在温度为1100℃, N₂气流量为1.5 L/min、生长时间为30–90 min等工艺条件下, 制备了直径约为100 nm、长度为数微米的高密度、均匀分布、大面积的Si纳米线(～10¹⁰ cm^-2). 对Si纳米线进行了Eu掺杂, 实验研究了不同长度的Si纳米线以及不同掺杂温度、掺杂时间等工艺参数对Eu离子红光发射的影响, 利用扫描电子显微镜和X射线衍射仪对Si纳米线表面形貌和Eu掺杂后Si纳米线的结晶取向进行了测量和表征; 室温下利用Hitachi F-4600型荧光分光光度计对样品的激发光谱和发射光谱进行了测试和分析. 结果表明: 在Si纳米线生长时间为30 min、掺杂温度为1000℃、 最佳激发波长为395 nm时, 样品最强荧光波长为619 nm (⁵D₀→⁷F₂); 同时, 还出现了576 nm (⁵D₀→⁷F₀), 596 nm (⁵D₀→⁷F₁), 658 nm (⁵D₀→⁷F₃)和708 nm (⁵D₀→⁷F₄)四条谱带.     

Low-temperature formation of nanocrystalline SiC particles and composite from three-layer Si/C/Si film for the novel enhanced white photoluminescence

In this article, nanocrystalline silicon carbide (nc-SiC) and composite have been synthesized at an annealing temperature as low as 750 °C through the thermal reaction of Si/C/Si multilayers deposited on the Si(100) substrate by ultra-high-vacuum ion beam sputtering (UHV IBS) compared with the conventional thermal formation of crystalline SiC (c-SiC) nanostructures above 1,000 °C. The evolution of microstructure and reaction between C and Si was examined by Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), high-resolution field emission scanning electron microscope (HR-FESEM), and high-resolution transmission electron microscopy. The c-SiC nanoparticles (np-SiC) of around 20–120 nm in diameter appeared on the top and bottom of the three-layer film with a particle density of around 2.63 × 10¹⁰ cm⁻² after 750 °C annealing. The composite of nc-SiC and Si nanocrystals (nc-Si) size below 5 nm embedded in an amorphous SiC (a-SiC) matrix appeared at the interface between the Si and C layers. Efficient thermal energy is the driving force for the formation of nc-SiC and composite through interdiffusion between C and Si. The broad visible photoluminescence (PL) spectrum of 350–750 nm can be obtained from the annealed composite Si/C/Si multilayer and deconvoluted into four bands of blue (~430 nm), green (~500 nm), green–yellow (~550 nm), and orange (~640 nm) emission, corresponding to the emission origins from nc-SiC, sp² carbon clusters, np-SiC, and nc-Si, respectively.     

Study of GaN adsorption on the Si surface

The adsorption energy, the band structures and DOS (density of states) of GaN on surface of Si(1 0 0) and Si(1 1 1) are calculated by the first-principle using plane-wave pseudo-potentials method based on the density functional theory in order to know the adsorption between the surface of Si and GaN. The calculation results show that GaN is easier adsorbed on the surface of Si(1 0 0) than the surface of Si(1 1 1) under the same experimental condition. There are strong charge distributions between N and Si atom. The bandgap of GaN on surface of Si(1 0 0) becomes a little narrower than that of pure GaN. On the other hand, GaN film is deposited on the surface of Si(1 0 0) by ECR-MOPECVD (electron cyclotron resonance-plasma enhanced chemical vapor deposition) at low temperature. For substrate of Si(1 1 1), no film is obtained under the same experimental condition.     

Thin-film formation of Si clathrates on Si wafers

In this study, we prepared Si clathrate films (Na₈Si₄₆ and Na_xSi₁₃₆) using a single-crystalline Si substrate. Highly oriented film growth of Zintl-phase sodium silicide, which is a precursor of Si clathrate, was achieved by exposing Na vapour to Si substrates under an Ar atmosphere. Subsequent heat treatment of the NaSi film at 400 °C (3 h) under vacuum (<10⁻² Pa) resulted in a film of Si clathrates having a thickness of several micrometres. Furthermore, this technique enabled the selective growth of Na₈Si₄₆ and Na_xSi₁₃₆ using the appropriate crystalline orientation of Si substrates.     

From Si nanowire to SiC nanotube

Si nanowires (NWs), with diameters of about 800 nm and lengths of about 10 ??m, previously synthesized by the VLS method with gold catalyst, were carburized at 1,100 °C under methane for conversion into SiC nanostructures. These experiments have shown that Si NWs have been transformed into SiC nanotubes (NTs) with approximately the same sizes. Nanotubes?? sidewall thickness varies from 20 to 150 nm depending on the NTs?? height. These SiC nanotubes are hexagonal in shape and polycrystalline. A model of growth based on the out-diffusion of Si through the SiC layer was proposed to explain the transformation from Si nanowires to SiC nanotubes. This model was completed with thermodynamic calculations on the Si?CH₂?CCH₄?CO₂ system and with results from complementary experiment using propane precursor. Routes for obtaining crystalline SiC NTs using this reaction are proposed.