Formation of self-assembly and the mechanism of Si nanoquantum dots prepared by low pressure chemical vapor deposition

Si nanoquantum dots have been formed by self-assembled growth on the both Si-O-Si and Si-OH bonds terminated SiO2 surfaces using the low-pressure chemical vapor deposition (LPCVD) and surface thermal decomposition of pure SiH4 gas. We have experimentally studied the variation of Si. dot density with Si-OH bonds density, deposition temperature and SiH4 pressure, and analyzed qualitatively the formation mechanism of the Si nanoquantum dots based on LPCVD surface thermal dynamics principle. The results are very. important for the control of the density and size of Si nanoquantum dots, and have potential applications in the new quantum devices.

Electron transport through hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots

The transmission of electrons through a hierarchical self-assembly of GaAs/AlxGa(1-)xAs quantum dots (QDs) is calculated using the coupled-channel recursion method. Our results reveal that the number of conductance peaks does not change when the barrier widths change, but the intensities decrease as the barrier widths increase. The conductance peaks will shift towards low Fermi energies as the transverse width of GaAs QD increases, as the thickness of GaAs quantum well increases, or as the height of GaAs QDs decreases. Our calculated results may be useful in the application of QDs to photoelectric devices. (c) 2005 American Institute of Physics.

Asymmetric quantum-confined Stark effects of hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots

Quantum-confined Stark effects in GaAs/AlxGa1-xAs self-assembled quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. In our calculation, the effect of finite offset, valence-band mixing, the effects due to the different effective masses of electrons and holes in different regions, and the real quantum dot structures are all taken into account. The results show that the electron and hole energy levels and the optical transition energies can cause blueshifts when the electric field is applied along the opposite to the growth direction. Our calculated results are useful for the application of hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots to photoelectric devices. (c) 2005 American Institute of Physics.

Effective-mass theory for hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots

The electronic structures in the hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated. In our calculation, the effect of finite offset, valence-band mixing, the effects due to the different effective masses of electrons and holes in different regions, and the real quantum dot structures are all taken into account. The results show that (1) electronic energy levels decrease monotonically, and the energy difference between the energy levels increases as the GaAs quantum dot (QD) height increases; (2) strong state mixing is found between the different energy levels as the GaAs QD width changes; (3) the hole energy levels decrease more quickly than those of the electrons as the GaAs QD size increases; (4) in excited states, the hole energy levels are closer to each other than the electron ones; (5) the first heavy- and light-hole transition energies are very close. Our theoretical results agree well with the available experimental data. Our calculated results are useful for the application of the hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots to photoelectric devices.

Porous InP array-directed assembly of InAs nanostructure

Fascinating features of porous InP array-directed assembly of InAs nanostructures are presented. Strained InAs nanostructures are grown by molecular-beam epitaxy on electrochemical etched porous InP substrate. Identical porous substrate with different pore depths defines different growth modes. Shallow pores direct the formation of closely spaced InAs dots at the bottom. Deep pores lead to progressive covering of the internal surface of pores by epitaxial material followed by pore mouth shrinking. For any depth an obvious dot depletion feature occurs on top of the pore framework. This growth method presages a pathway to engineer quantum-dot molecules and other nanoelements for fancy physical phenomena. (c) 2006 American Institute of Physics.

Experiments and their analysis for self-assembly growth of GaN quantum dots via MOCVD

In recent years, growth of GaN-based materials-related quantum dots has become a hot topic in semiconductor materials research. Considerable efforts have been devoted to growth of self-assembled quantum dots of GaN-based materials via MOCVD (Metal Organic Chemical Vapor Deposition) and there are a lot of relevant literatures. There is, however, few review papers for the topic. In this paper, different experimental methods for fabrication of quantum dots of GaN-based materials via MOCVD are critically reviewed and the experimental conditions and parameters, which may affect growth of the quantum dots, are analyzed, with an aim at providing some critical reference for the related future experiment research.

Assembly of side-functional monomers with inorganic nanometer particles

Monomers of methacrylate with various pi -conjugated pendants were designed and prepared in our laboratory, The monomer with suitable end-group was successfully assembled with nano-scale inorganic particles to form an orderly-aligned structure that showed special optical properties, both absorption and emission band were much red-shifted compared with the monomer, A new type of organic/inorganic hybrid materials was obtained by in situ polymerization of the assembly, The hybrid materials could also show special optical properties as the assembly, This might open a new route to tune the emission color.

One-pot synthesis and self-assembly of colloidal copper(I) sulfide nanocrystals

A simple one-pot method is developed to prepare size-and shape-controlled copper(I) sulfide (Cu2S) nanocrystals by thermolysis of a mixed solution of copper acetylacetonate, dodecanethiol and oleylamine at a relatively high temperature. The crystal structure, chemical composition and morphology of the as-obtained products are characterized by powder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The morphology and size of the Cu2S nanocrystals can be easily controlled by adjusting the reaction parameters. The Cu2S nanocrystals evolve from spherical to disk-like with increasing reaction temperature. The spherical Cu2S nanocrystals have a high tendency to self-assemble into close-packed superlattice structures. The shape of the Cu2S nanodisks changes from cylinder to hexagonal prism with prolonged reaction time, accompanied by the diameter and thickness increasing. More interestingly, the nanodisks are inclined to self-assemble into face-to-face stacking chains with different lengths and orientations. This one-pot approach may extend to synthesis of other metal sulfide nanocrystals with different shapes and sizes.

construction of feature-matching perception in virtual assembly

An important characteristic of virtual assembly is interaction. Traditional di-rect manipulation in virtual assembly relies on dynamic collision detection, which is very time-consuming and even impossible in desktop virtual assembly environment. Feature-matching isa critical process in harmonious virtual assembly, and is the premise of assembly constraint sens-ing. This paper puts forward an active object-based feature-matching perception mechanism and afeature-matching interactive computing process, both of which make the direct manipulation in vir-tual assembly break away from collision detection. They also help to enhance virtual environmentunderstandability of user intention and promote interaction performance. Experimental resultsshow that this perception mechanism can ensure that users achieve real-time direct manipulationin desktop virtual environment.

核仁蛋白基因组的原核起源与核仁蛋白网络进化组装分析

核仁是真核细胞间期核中最明显的结构，其主要功能是作为rDNA 的转录加 工和核糖体亚基合成、组装的场所。这一重要功能是包括原核生物和真核生物在 内的所有细胞生物都具有的，但核仁这一结构却只存在于真核细胞中。那么在从 原核到真核的进化过程中，核仁是如何进化而来，核仁的蛋白成分又是通过怎样 的方式从简单到复杂地组装起来，这些问题到目前为止都还没有得到深入的了 解。随着 “组学”的发展，核仁蛋白基因组的研究逐渐开展起来。越来越多的 核仁蛋白基因组数据为我们从“组学”的角度来探讨核仁的起源及其蛋白网络的 进化组装等问题奠定了基础。 1）本文首先通过比较目前仅有的三种真核生物（人，拟南芥，芽殖酵母） 的核仁蛋白基因组数据库，将三个核仁蛋白基因组共享的直系同源蛋白簇提取出 来构建出真核生物基本核仁蛋白基因组I (EBNP I)。由于拟南芥和芽殖酵母核仁 蛋白数据库明显偏小，为避免它们可能不全而带来的影响，进一步将人的核仁蛋 白基因组与拟南芥和芽殖酵母的全蛋白基因组共享的直系同源蛋白簇提取出来 构建出真核生物基本核仁蛋白基因组II（EBNP II）。EBNP 中的人核仁蛋白质序 列用作搜索序列去BLASTP 原核基因组，并构建同源关系矩阵进行聚类分析。 结果发现核仁蛋白基因组原核起源部分具有复合起源的特性，一部分来源于古细 菌，一部分来源于真细菌。并对EBNP II 中人核仁蛋白进行功能划分和对不同的 功能类群进行了起源分析，结果发现‘与核糖体有关’这一功能类群起源于古细 菌，‘与mRNA 有关’和‘与翻译有关’功能类群可能起源于古细菌，并在真核 阶段招募了大量蛋白成分，‘与染色质有关’这一功能类群可能起源于真细菌， 随后在真核阶段此功能类群招募了大量蛋白成分。 2）本文利用芽殖酵母的蛋白质相互作用数据，通过在原核生物基因组和原 生生物基因组的同源搜索，将芽殖酵母核仁蛋白分成不同进化时期产生的三个部 分：原核起源蛋白，原生生物起源蛋白，酵母特异蛋白。通过分析各部分蛋白质 的GO 注释，结果发现，原核起源蛋白主要行使与核糖体亚基合成与组装等核仁最基本的功能。通过比较各个部分之间以及各部分内蛋白质相互连接情况，结果 发现，芽殖酵母核仁蛋白网络按照不对称原则将招募的新蛋白组装入网络，整个 芽殖酵母核仁蛋白网络以原核起源蛋白所构建的框架为基础，原核起源蛋白起着 核心的作用。

Electroluminescence and photoluminescence of Si/SiGe self-assembly quantum dot structures

Comparative electroluminescence (EL) and photoluminescence (PL) measurements were performed on Si/Si0.6Ge0.4 self-assembly quantum dots (QDs) structures. The samples were grown pseudomorphically by molecular beam epitaxy, and PIN diodes for electroluminescence were fabricated. Assisted TEM pictures shows the SiGe self-assembly QDs are platelike. And it showed that the diameters of QDs are in range from 40nm to 140nm with the most in 120nm. Both EL and PL has a wide luminescence peak due to wide distribution of QDs dimensions. At low temperature (T=14K), EL peak has a red shift compared to the corresponding PL peak. Its full-width at half-maximum (FWHM) is about 97meV, a little smaller than that of corresponding PL peak. The reasons of position and FWHM changes of EL peak from QDs have been discussed.