Thermodynamics of homogeneous and heterogeneous nucleation of clusters of catalysts for growing carbon nanotubes

A thermodynamical model of the homogeneous and heterogeneous formation of clusters of catalysts is developed. Parameters of cluster formation during ferrocene pyrolysis were studied experimentally and theoretically. It was shown that the surface tension and size of clusters strongly depend on the temperature. The coefficient of surface tension and characteristic sizes of the clusters were calculated. The obtained dependences and parameters allow us to reconstruct the size distribution function of the clusters by setting the temperatures in the working zone and in the zone of ferrocene sublimation. This makes it possible to predict the cluster size, depending on the synthesis parameters, especially, the temperature.     

The effect of misorientation of the GaAs substrate on the properties of InAs quantum dots grown by low-temperature molecular beam epitaxy

The structural and optical properties of arrays of InAs quantum dots grown on GaAs substrates at relatively low temperatures (250 and 350°C) and with various degrees of misorientation of the surface are studied. It is shown that low-temperature growth is accompanied by the formation of quantum dot clusters along the dislocation loops on the singular surface and along the steps caused by the surface vicinality on the misoriented surface. The formation of quantum dot clusters leads to the appearance of a new long-wavelength band in the exciton photoluminescence (PL) spectra. It is found that the degrees of polarization of the PL spectral band for clusters of various shapes are different.     

Reversible Cluster Formation of Colloidal Nanospheres by Interparticle Photodimerization

Crosslinked spherical nanoparticles based on trimethoxysilane monomers have been prepared by polycondensation in aqueous emulsion. These particles have been labeled chemically at their surface region with two different types of organic dye molecules (cinnamate, coumarin), which both are well known for their ability to undergo a reversible photodimerization if irradiated with light of a suitable wavelength. Upon irradiation of dilute solutions of these nanoparticles with UV light, the photodimerization of labels belonging to different colloidal nanoparticles caused the formation of large colloidal clusters consisting of chemically bound individual nanospheres. This process has been quantitatively investigated using light scattering and atomic force microscopy. Importantly, utilizing the reversibility of the photoreaction, the clusters could be broken up by irradiation of the sample with UV light of shorter wavelengths than the light used for their formation     

一个描述硅原子团簇退火行为的模型

在考虑硅原子团簇的尺寸对其俘获半径的影响的基础上提出了一个改进的模型,来描述团簇的退火行为,并给出了点缺陷的表面复合速率的表达式.为了验证此模型,给出了动力学蒙特卡洛方法的模拟结果,模拟结果与实验结果相吻合.通过表面复合速率的模拟结果和模型的对比,模型得到了验证.分析表明团簇尺寸对其退火行为有明显的影响     

A detailed physical model for ion implant induced damage in silicon

A unified physically based ion implantation damage model has been developed which successfully predicts both the impurity profiles and the damage profiles for a wide range of implant conditions for arsenic, phosphorus, BF₂, and boron implants into single-crystal silicon. In addition, the amorphous layer thicknesses predicted by this new damage model are also in excellent agreement with experimental measurements. This damage model is based on the physics of point defects in silicon, and explicitly simulates the defect production, diffusion, and their interactions which include interstitial-vacancy recombination, clustering of same type of defects, defect-impurity complex formation, emission of mobile defects from clusters, and surface effects for the first time. New computationally efficient algorithms have been developed to overcome the barrier of the excessive computational requirements. In addition, the new model has been incorporated in the UT-MARLOWE ion implantation simulator, and has been developed primarily for use in engineering workstations. This damage model is the most physical model in the literature to date within the framework of the binary collision approximation (BCA), and provides the required, accurate as-implanted impurity profiles and damage profiles for transient enhanced diffusion (TED) simulation     

银纳米团簇在HOPG表面上的控制生长

由于银与高定向热解石墨(highly oriented pyrolytic graphite,HOPG)面间的相互作用很小,银在HOPG表面上的生长通常采取三维的Volmer-Weber模式,得到空间分布不均匀的银团簇。本文分别采用加热氧化和氩离子轰击来改变HOPG衬底的表面结构,并用扫描隧道显微镜(STM)研究了银在它们上面的生长过程。实验结果表明：在氩离子轰击过的HOPG表面上,可以得到大小基本一致、空间分布均匀的银纳米团簇,实现了银团簇的控制生长．氩离子轰击导致了平整的HOPG表面产生缺陷,这些缺陷对银原子的扩散进行限制并成为优先成核中心,最终形成均匀的银纳米团簇。     

Dynamic modeling for resin self-alignment mechanism

A new self-alignment process using surface tension of resin material was developed to realize a low-temperature, fluxless, and cost-effective alternative alignment process for the future assembly of electronic and optoelectronic systems. In this new self-alignment process, we achieved self-alignment capability by using 3-dimensional pads to form the positioning boundary, and by mounting chips in the opposite direction. This process releases the force acted on liquid bumps, even when using resin material, which has been known not to possess self-alignment capability because of its low surface tension. As the viscosity of the resin material is considerably higher than that of the solders, the restoring force resulting from its low surface tension must be larger than the resistance force resulting from its high viscosity.In this paper, we propose a new passive alignment mechanism using the surface tension of a resin material and a comprehensive mathematical model in order to enhance understanding of the self-alignment behavior of resin. Moreover, we conducted a scaled-up experiment to calibrate and verify the model's accuracy. It has been proved that resin self-alignment behavior is totally different from the oscillatory motion of solder alignment. This shows that the motion is aperiodic, regardless of the initial conditions of the system, such as an overdamped system due to the low surface tension and high viscosity characteristics of resin material.     

Threshold behavior of the formation of nanometer islands in a Ge/Si(100) system in the presence of Sb

Atomic-force microscopy is used to study the behavior of an array of Ge islands formed by molecular-beam epitaxy on an Si (100) surface in the presence of an antimony flux incident on the surface. It is shown that, as the Sb flux increases to a certain critical level, the surface density of the islands increases; however, if this critical level is exceeded, nucleation of the islands is suppressed and mesoscopic small-height clusters are observed on the surface. This effect is explained qualitatively in the context of a kinetic model of the islands’ formation in heteroepitaxial systems mismatched with respect to their lattice parameters.     

Suppression of dome-shaped clusters during molecular beam epitaxy of Ge on Si(100)

Morphological properties of Ge nanoscale island arrays formed on the Si(100) surface during molecular beam epitaxy are studied using reflection high-energy electron diffraction and atomic-force microscopy. It is shown that codeposition of Sb and Ge significantly increases the density of final island arrays and suppresses the formation of dome-shaped clusters at substrate temperatures of 550–600°C. The results are discussed in the context of the kinetic model of formation of elastically strained islands in heteroepitaxial systems with a lattice mismatch.     

Modification of the surface of GaAs and observation of surface enhanced Raman scattering after the diffusion of indium

The results of studies of the surface of GaAs in the presence of indium and phosphorus surfactants are reported. It is shown that, as a result of their diffusion (annealing) at a temperature of 650–670°C, clusters enriched with indium are formed in the GaAs surface region. The clusters can be seen as bright spots in an image obtained by a scanning electron microscope with the use of an in-lens detector. At the same time, studies of the morphology of this surface with an atomic-force microscope show a decrease in the root-meansquare roughness of the surface after annealing (diffusion), which is indicative of the incorporation of In atoms into the GaAs crystal lattice. The clusters are responsible for changes in the Raman spectra. Specifically, an increase in the signal intensity due to surface-enhanced Raman scattering and a shift of the vibration frequency in the surface region are observed. It is found that cluster formation is defined by the crystallographic orientation of the surface and by the technological conditions of surface preparation.     

On the simulation of the formation and dissolution of silicon self-interstitial clusters and the corresponding inverse modeling problem

The formation and dissolution of silicon self-interstitial clusters is linked to the phenomenon of transient-enhanced diffusion (TED) which in turn has gained importance in the manufacturing of semiconductor devices. Based on theoretical considerations and measurements of the number of self-interstitial clusters during a thermal step, a model for the formation and dissolution of self-interstitial clusters is presented including the adjusted model parameters for two different technologies (i.e. material parameter sets). In order to automate the inverse modeling part, a general optimization framework was used. In addition to solving this problem, the same setup can solve a wide range of inverse modeling problems occurring in the domain of process simulation. Finally, the results are discussed and compared with a previous model.     

Nickel silicide encroachment formation and characterization

The stability of nickel-based silicides integrated in CMOS circuits has been studied. The evolution of transistor electrical failures is then reported, linked to Ni abnormal migration through different process steps. We have found in our studies that Ni encroachment is not only due to NiSi₂ clusters formation but also to NiSi precipitates formation. Silicon substrate doping, surface preparation, nickel film thickness and the thermal treatments were identified to modify occurrences of this randomly localized phenomenon. Ni-rich phase initial formation is preferable to prevent Ni encroachment even though other upstream process steps for CMOS integration are also key for Ni migration control.     

Control of the crystalline phase and morphology of CdS deposited on microstructured surfaces by chemical bath deposition

Chemical bath deposition (CBD) has been used extensively to deposit thin films of CdS for window layers in solar cells. The microtopography or roughness of the surface, however, can affect the quality of the film by influencing the morphology, uniformity, or crystal phase of the CdS film. Here, we have demonstrated that thin films of CdS can be successfully patterned on surfaces bearing micropillars as a model surface for roughness. The phase purity of CdS deposited on the micropillar surfaces is uniform and conformal with the formation of packed clusters on the micropillars at pH 10 that form flower-like structures at long deposition times. Smaller crystallites were observed on micropillar arrays at pH 8 with “network” like structures observed at long deposition times. Additionally, by controlling the pH of the chemical bath, the hexagonal and cubic crystal phases of CdS were both accessible in high purity at temperatures as low as 85 °C.     

五硼酸铵在高压铝阳极箔化成液中的作用机理

采用恒流恒压法化成制备高压铝阳极箔,研究了硼酸溶液中添加五硼酸铵对化成液的表面张力、电导率及化成铝箔耐电压和比电容的影响,探讨了五硼酸铵在铝箔高压化成液中的作用机理。结果表明:在硼酸化成液中添加的微量五硼酸铵提高了化成液的表面张力和电导率,改变了化成液的电离平衡,使化成铝箔的耐电压提高了约5%。     

Measurement of Surface Tension of Epoxy Resins Used in Dispensing Process for Manufacturing Thin Film Transistor-Liquid Crystal Displays

This paper presents an inverse method for measuring the surface tension of the epoxy resins used in the dispensing process for manufacturing TFT-LCD based on droplet images. A direct method, which is capable of predicting the profile of an axisymmetric liquid droplet, is developed, and then the direct method is incorporated with a droplet imaging system to build up a measurement system for determination of the surface tension of the epoxy resins. When applying the surface tension measurement method, one only needs to give the density of the liquid and identify the geometric parameters of the liquid droplet, such as the droplet volume and the contact angle, through the imaging system. This approach has been used to determine surface tension of various epoxy resins. Finally, for testing the accuracy of the approach, some commonly used fluids are tested. Results show that the approach leads to satisfactory accuracy.     

A New Method of Studying Surface Activity for Liquid Alloys

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有机酸促进大气气溶胶成核机理研究进展

大气中有机成分种类繁多，结构复杂，有机酸作为大气环境各相中含量最丰富的有机物种之一备受关注，最近的实验研究表明，部分芳香族有机酸能够促进硫酸-水团簇的成核及生长。理论计算也表明在有机酸的存在下，一些小分子有机酸与硫酸通过氢键的相互作用形成非均相的团簇降低了成核壁垒，从而促进团簇的形成，对新粒子的成核产生具有重要促进作用。鉴于有机酸对大气气溶胶成核机理研究具有重要的意义，文中对其近些年在实验和理论上的进展进行了回顾，并对未来前景作了展望。     

Structural and energy characteristics of native vacancy-type defects in the biaxially stressed GaN lattice

For biaxially stressed GaN clusters, the structure, charges, and energies of the formation of intrinsic Ga and N vacancies are calculated by the quantum-chemical method in the SCF MO LCAO approximation taking into account relaxation of the crystalline surroundings. It is established that the use of substrates introducing compressive or tensile stresses into the epitaxial layer affects the concentrations of intrinsic vacancy-type point defects. This effect most clearly manifests itself in the nitrogen sublattice in the GaN crystal lattice, especially in the case of its tension, i.e., during the epitaxial grown of GaN on the Si substrate. Redistribution of the electron density in the defect region in the case of lattice compression or tension can be the cause of variation in the location of electronic levels of defects in the band gap of the crystal.     

Silicon nanocrystal formation upon annealing of SiO2 layers implanted with Si ions

The formation of silicon nanocrystals in SiO₂ layers implanted with Si ions was investigated by Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence. The excess Si concentration was varied between 3 and 14 at. %. It was found that Si clusters are formed immediately after implantation. As the temperature of the subsequent annealing was raised, the segregation of Si accompanied by the formation of Si-Si₄ bonds was enhanced but the scattering by clusters was reduced. This effect is attributed to the transformation of loosely packed clusters into compact, separate-phase nanoscale Si precipitates, with the Raman peak observed at 490 cm^?1 being related to surface scattering. The process of Si segregation was completed at 1000°C. Nevertheless, characteristic nanocrystal photoluminescence was observed only after annealing at 1100°C. Simultaneously, scattering in the range 495–520 cm^?1, typical of nanocrystals, appeared; however, the “surface-related” peak at 490 cm^?1 persisted. It is argued that nanocrystals are composed of an inside region and a surface layer, which is responsible for their increased formation temperature.     

Features of defect formation under the thermal treatment of dislocation-free single-crystal large-diameter silicon wafers with the specified distribution of oxygen-containing gettering centers in the bulk

Possibilities of obtaining a defect-free layer in wafers of dislocation-free single-crystal silicon subjected to rapid thermal annealing (RTA) are analyzed. The application of RTA is based on the possibility of effectively affecting the distribution profile of the density of oxygen precipitates over the wafer thickness by means of controlling the distribution profiles of the vacancies and interstitial atoms. However, the solution of this important task encounters the problem of the appearance of large local stresses in the vicinity of the fastening supports of a large-diameter silicon wafer and its bending in the course of RTA, which are caused by its own weight. Using mathematical modeling of the three-dimensional stress-strain state and defect formation in large-diameter silicon wafers in the course of RTA, various methods of fastening the wafers are considered and the possibilities of lowering the stress-strain state of the silicon wafer are determined. A mathematical model taking into account the diffusion-recombination processes of vacancies and interstitial silicon atoms, as well as the formation of vacancy clusters is proposed to describe the defect formation in the course of RTA. Based on this model, temperature-temporal parameters of RTA, which correspond to the required (depleted near the surface) concentration profile of the vacancies and the density and size of the vacancy clusters over the wafer thickness, are determined (heating time, holding time at the highest temperature, the cooling rate of the wafer). The results of the calculations are verified for test samples using optical microscopy and transmission electron microscopy (OM and TEM).