Direct writing of carbon nanotube patterns by laser-induced chemical vapor deposition on a transparent substrate

Dot array and line patterns of multi-walled carbon nanotubes (MWCNTs) were successfully grown by laser-induced chemical vapor deposition (LCVD) on a transparent substrate at room temperature. In the proposed technique, a Nd:YVO₄ laser with a wavelength of 532 nm irradiates the backside of multiple catalyst layers (Ni/Al/Cr) through a transparent substrate to induce a local temperature rise, thereby allowing the direct writing of dense dot and line patterns of MWCNTs below 10 μm in size to be produced with uniform density on the controlled positions. In this LCVD method, a multiple-catalyst-layer with a Cr thermal layer is the central component for enabling the growth of dense MWCNTs with good spatial resolution.     

Modeling the process of chemical regeneration of air in airtight habitable facilities

Physical experiments and mathematical modeling are used to study the kinetics of the reactions of carbon dioxide and water with potassium superoxide accompanied by oxygen release at various values of the temperature and humidity of the breathing gas mixture. The kinetics of the chemisorption is demonstrated to be limited by the rate of air regeneration in an airtight habitable facility. Experimental and analytical approaches are applied to determine the kinetic coefficients of the chemical reactions using the experimental data and a mathematical model of chemisorption kinetics. To perform the above chemical reactions, an original-design chemisorption reactor was developed, which contains plates with potassium superoxide nanocrystalline fixed on the fibers and pore surface of a fibrous polymer matrix. A mathematical model of chemical air regeneration is developed to calculate the guaranteed values of the parameters of the reactor and the protective effect time of the chemisorbent during which, at a given load, the reactor provides the appropriate concentrations of oxygen and carbon dioxide in the breathing gas mixture in an airtight habitable.     

Computational modeling of forced flow laser chemical vapor deposition

Laser chemical vapor deposition (LCVD) utilizes a laser to localize a CVD reaction. The process involves complex physical interactions within a very small spatial region. Experimental investigations into the dynamics of the LCVD process are limited by spatial and resolution capabilities of instrumentation. Models are developed herein using the computational fluid dynamics (CFD) code, FLUENT, that incorporate heat transfer, fluid flow, and species transport in a single integrated modeling environment. The models are used to study the carbon deposition process. Insight is gained into the relationships among the process parameters and the deposition rates and deposition rate profiles. Phenomena such as thermal diffusion and the relative importance of mass convection and mass diffusion are explored. A designed set of model cases is executed and the results are used to develop a simple polynomial expression for relating experiment conditions to deposit attributes. PACS 81.10.Bk; 81.05.Uw; 81.15.Gh; 47.50.Cd; 81.16.Mk     

CFETR水冷包层第一壁模块中等离子体注入氚输运有限单元分析

采用多物理场计算程序COMSOL Multiphysics,构建了一维氚输运有限单元模型,并与文献中氢同位素在钨中的滞留实验数据进行模拟验证。基于经过校验的一维模型,并考虑Soret效应,对中国聚变工程实验堆(CFETR)水冷包层第一壁进行了二维氚分析计算。模拟结果表明,氚在单个典型包层第一壁中的总滞留量为0.12mg,进入冷却剂中的总渗透量为0.12mg•yr^-1。若不考虑Soret效应,氚在RAFM钢中的滞留量将增加8.80%,渗透到冷却剂的量增加65.97%。由此可见,Soret效应对于氚的渗透和滞留具有显著的意义。     

Gas-phase photolysis of tungsten hexachloride

The laser-induced decomposition of WCl₆ in the gas-phase is investigated by means of absorption, Raman and laser-induced fluorescence spectroscopy. With visible Ar⁺-laser radiation dissociation of WCl₆ into WCl₄ and Cl₂ has been observed. Further decomposition can be achieved in the presence of H₂ employing ultraviolet Ar⁺-laser radiation at 360 nm. A complete reduction to W requires even shorter wavelengths. The experimental results are analyzed on the basis of model calculations. Implications on the Laser-induced Chemical Vapor Deposition (LCVD) of W are discussed.     

Synthesis of carbon nitride films by low-power inductively coupled plasma-activated transport reactions from a solid carbon source

Thin films of carbon nitride were prepared by low-power inductively coupled plasma chemical vapor deposition from a solid carbon source by utilizing transport reactions. The maximum deposition rate achieved was 10 nm/min and depended mainly on the substrate position in the reactor. The nitrogen fraction in the films was not so sensitive to the process parameters and was at about 0.5 for all experiments as measured by Auger electron spectroscopy (AES) and elastic recoil detection (ERD) analysis. The chemical bonding structure studied by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the presence of triple, double and single bonds between carbon and nitrogen atoms. Received: 12 May 1999 / Accepted: 12 May 1999 / Published online: 24 June 1999     

Temperature effect on photolytic deposition of platinum ohmic contacts and schottky diodes

An argon laser is used to induce Laser Chemical Vapor Deposition (LCVD) of platinum using platinum bihexafluoroacetyl-acetonate as precursor. The process can be photolytic or pyrolytic depending on the laser power used. These processes are studied by recording the laser light transmitted through of deposit and substrate. Photolytic deposition takes place either in the adsorbed phase or in the gaseous phase depending on the temperature induced by radiation absorption. The induced-temperature calculation using a model developed by us confirms the experimental results obtained. The influence of the substrate base temperature and the precursor product vapour pressure confirms photolytic deposition from the adsorbed phase for low powers and from the vapour phase onwards for high powers. The deposits obtained present a typical 96% Pt composition and its use in Schottky diode manufacture permit obtaining devices with good characteristics in spite of experimental limitations.     

新型可燃性气体报警仪的研制

介绍新型可燃性气体报警仪的设计,可用于对丙烷、丁烷、氢气及其他可燃性气体的检测,用于检测可燃气体爆炸性;采用C8051F020单片机,通过2M007型电阻式气敏传感器采集信号,经过放大电路放大,传入单片机,进行模数转换,采用算术平均滤波对数据过滤,再通过一系列的数据处理,显示可燃性气体浓度,通讯方式采用以sim300通讯模块的GPRS通讯的新型可燃性气体报警系统;软件设计采用C语言编程,灵活方便、具有强大的移植性;如空气中可燃性气体浓度超标,开始报警,显示屏上显示出大于阀值的可燃性气体浓度,且通过无线通讯使手机也正常收到了报警短信;该系统功能齐全,操作简便,具有很高的应用价值。     

Heat and mass-transfer modeling of an angled gas-jet LCVD system

Laser chemical vapor deposition (LCVD) is a new manufacturing process that holds great potential for the production of small and complex metallic, ceramic and composite parts. Since LCVD is a thermally activated process, the most important process variable is temperature. Therefore, a thermal model was developed for a gas-jet LCVD system, accounting for Gaussian-beam laser heating and gas-jet convection cooling. The forced convection cooling imposed by the gas-jet reagent delivery system was significant, accounting for a 15 to 20% change in the substrate temperature. The deposition rate for a given material is not only affected by temperature, but also by the mass transport of reagent gases. An angled gas-jet reagent supply was designed to aid mass transport, but the need and impact of such a system has been debated. Therefore, a two-dimensional mass-transport model was developed to estimate the effects of a gas jet with respect to local reagent concentration variations and reaction rates. Across all deposition regimes, the gas jet was found to be an effective tool for increasing the concentration of reagent gases at the surface of the substrate. The gas jet also generated higher deposition rates and increased deposit resolution for those processes severely limited by diffusion. PACS 05.60.-k; 44.27+g; 44.05+e     

Modelling and Optimization for Deposition of SiOxNy Films by Radio-Frequency Reactive Sputtering

SiOxNy films are deposited by reactive sputtering from a Si target in Ar/O2/N2 atmospheres. In order to achieve the control of film composition and to keep a high deposition rate at the same time, a new sputtering model based on Berg＇s work is provided for the condition of double reactive gases. Analysis based on this model shows that the deposition process can easily enter the target-poisoning mode when the preset gas flow （N2 in this work） is too high, and the film composition will change from nitrogen-rich to SiO2-like with the increase of oxygen supply while keeping the N2 supply constant. The modelling results are confirmed in the deposition process of SiOxNy. Target self-bias voltages during sputtering are measured to characterize the different sputtering modes. FTIR-spectra and dielectric measurements are used to testify the model prediction of composition. Finally, an optimized sputtering condition is selected with the O2/N2 flow ratio varying from 0 to I and N2 supply fixed at I sccm. Average deposition rate of 17nm/min is obtained under this selected condition, which has suggested the model validity and potential for industry applications.     

On the reaction kinetics in laser-induced pyrolytic chemical processing

Reaction rates, particle densities, and temperature distribution in pyrolytic (photothermal) laser-induced microchemical processing are investigated with respect to temperature and concentration-dependent transport coefficients, and with respect to the effect of thermal diffusion. While the model employed is particularly suitable for laser-induced chemical vapor deposition (LCVD), it can also be applied to many cases of laser-induced surface modification and dry-etching.On leave from: General Physics Institute, Academy of Sciences, SU-117942 Moscow, USSR     

LCVD of tungsten microstructures on quartz

The pyrolytic laser-induced chemical vapor deposition (LCVD) of tungsten microstructures in the form of spots has been investigated. Fused quartz substrates and a mixture of WF₆ and H₂ have been employed in the experiments. Different shapes of spots related to different partial pressures of WF₆ and H₂ have been revealed. The results can qualitatively be described by a combination of surface reactions and gas-phase reactions resulting in tungsten deposition and surface etching.On leave from: Reserch Group on Laser Physics of the Hungarian Academy of Sciences, H-6720 Szeged, Dòm tér 9, Hungary     

Growth regimes in pulsed laser deposition of aluminum oxide films

Alumina is technologically exploited in several forms, ranging from compact hard films as protective coatings to open microstructures of high specific area as supports for catalysts. Currently, various production processes are used to deposit the different forms. PLD has the potential of obtaining not only the different forms, but also a continuous modulation of properties, by tuning of the process parameters. This work investigates the relationship between the process parameters and the resulting film morphology, structure and properties for PLD performed with an alumina target in a background oxygen atmosphere. Three distinct growth regimes are found, leading, respectively, to compact homogeneous films, columnar structures and open microstructures. These structures are quantitatively characterized, and the ranges of the process parameters corresponding to the three regimes are identified. An empirical scaling law is proposed, which can be exploited as a guide for the design of growth processes aimed at obtaining specific film properties.     

Growth of AlGaN Epitaxial Film with Chemical Vapour High A1 Content by Metalorganic Deposition

A high-Al-content AlGaN epilayer is grown on a low-temperature-deposited AlN buffer on （0001） sapphire by low pressure metalorganic chemical vapour deposition. The dependence of surface roughness, tilted mosaicity, and twisted mosaicity on the conditions of the AlGaN epilayer deposition is evaluated. An AlGaN epilayer with favourable surface morphology and crystal quality is deposited on a 2Onto low-temperature-deposited AlN buffer at a low V/Ⅲ flow ratio of 783 and at a low reactor pressure of 100 Torr, and the adduct reaction between trimethylaluminium and NH3 is considered.     

Processing of micro-particles by UV laser irradiation in a field cage

An electric cage-laser micro-turning lathe was realised and applied to contact-free handling and mechanical processing of micro particles. Since particles with diameters of several micrometers cannot be fixed in mechanical chucks, an octode field cage was used to trap and rotate a single particle in a fluid without any mechanical surface contact. A pulsed nitrogen laser of high beam quality focused to about 1 μm in diameter could be adjusted independently of the cage position. The trapping forces (negative dielectrophoresis) acting on a bead of 5 to 15 μm are up to several hundred pN. This and the surrounding fluid damp down the effect of the laser pulses during bead processing. Examples demonstrating the possibilities of this technique are shown. Microsystems with high optical quality were fabricated photolithographically or by laser direct-write chemical vapor deposition (LCVD). Technical and biotechnological applications are discussed. Received: 20 October 1999 / Accepted: 27 October 1999 / Published online: 10 November 1999     

管式等离子体化学气相沉积质量转换动力过程的研究

本文对管式装置中等离子体化学气相沉积过程提出了一种数学描述方式,具体讨论了沉积过程中活性粒子产生频率、沉积速率和沉积效率等与电子密度、气体流速、气体压强等的相互关系,并对部分结果进行了理论解释。 关键词：     

The importance of non-local shadowing for the topography evolution of a-C:H films grown by toluene based plasma enhanced chemical vapor deposition

The topography evolution of hydrogenated diamond-like carbon coatings deposited through toluene based capacitively coupled plasma enhanced chemical vapor deposition has been studied experimentally and with continuum growth models. The experimentally observed mound formation and surprisingly large growth exponents (β≈ 0.9±0.1) cannot be reproduced by familiar local stochastic differential equations that are successfully used for other thin film deposition techniques. Here we introduce a novel numerical approach to simulate a continuum growth model that takes into account non-local shadowing effects. We show that the major characteristics of the experimentally observed topography evolution can be accurately represented by this model.     

Nonmean-Field Model for Ostwald Ripening of Two-Dimensional Islands

A nonmean-field model for the ripening of two-dimensional islands is presented. In this model, the adatom sea is divided into many small cells that are the polygons of a Voronoi network. The chemical potentials of adatom seas surrounding different islands are different. Strain generated by lattice mismatch is introduced into the model.Computer simulation under periodic boundary conditions is carried out to describe the island ripening in two cases (with and without strain), and demonstrates that small islands may grow faster than large islands, which cannot occur in the mean-field model. The simulated results also show that including strain will slow down the evolution of average island size, and an explanation for this is given.     

Micropatterned vertically aligned carbon-nanotube growth on a Si surface or inside trenches

The good field-emission properties of carbon nanotubes coupled with their high mechanical strength, chemical stability, and high aspect ratio, make them ideal candidates for the construction of efficient and inexpensive field-emission electronic devices. The fabrication process reported here has considerable potential for use in the development of integrated radio-frequency amplifiers or field-emission-controllable cold-electron guns for field-emission displays. This fabrication process is compatible with currently used semiconductor-processing technologies. Micropatterned vertically aligned carbon nanotubes were grown on a planar Si surface or inside trenches, using chemical vapor deposition, photolithography, pulsed-laser deposition, reactive ion etching, and the lift-off method. This carbon-nanotube fabrication process can be widely applied for the development of electronic devices using carbon-nanotube field emitters as cold cathodes and could revolutionize the area of field-emitting electronic devices. Received: 30 August 2001 / Accepted: 3 September 2001 / Published online: 20 December 2001     

A point source analytical model of inverse pulsed laser deposition

A simple analytical model for inverse pulsed laser deposition is proposed. In the model the motion of the evaporated material is assumed to emerge as from a point source located above the surface of evaporation at some distance. The obtained thickness profiles of inverse deposited films agree well with those calculated by the test particle Monte Carlo method. The proposed approach has been applied for analysis of experimental data on inverse pulsed laser deposition of graphite in nitrogen atmosphere with nanosecond pulses of laser fluences between 1 and 7 J/cm². The model describes well the thickness profiles and pressure dependence of film growth rate for inverse deposition.