Role of surface and interface science in chemical vapor deposition diamond technology

Diamond is well known as the hardest material in nature. It also has other unique bulk physical and mechanical properties, such as very high thermal conductivity and broad optical transparency, which enable a number of new applications now that large areas of diamond can be fabricated by the new diamond plasma chemical vapor deposition (CVD) technologies. However, some of the most interesting properties of diamond, including the ability to be grown over large areas by CVD processes, result not from its bulk properties but from its special and unique surface chemistry. The surface chemistry derived properties are as remarkable as the bulk properties, and in the end may enable the development of new applications, technologies, and industries which are at least as important as those based on the bulk properties. Some of these surface properties are extreme chemical inertness, low surface energy, low friction coefficients, negative electron affinity, biological inertness, and high over-voltage electrode behavior. The surface science and some of the interesting ongoing research in these areas are explored and illustrated, and unresolved questions are highlighted.     

Use of molecular beams for kinetic measurements of chemical reactions on solid surfaces

In this review we survey the contributions that molecular beam experiments have provided to our understanding of the dynamics and kinetics of chemical interactions of gas molecules with solid surfaces. First, we describe the experimental details of the different instrumental setups and approaches available for the study of these systems under the ultrahigh vacuum conditions and with the model planar surfaces often used in modern surface-science experiments. Next, a discussion is provided of the most important fundamental aspects of the dynamics of chemical adsorption that have been elucidated with the help of molecular beam experiments, which include the development of potential energy surfaces, the determination of the different channels for energy exchange between the incoming molecules and the surface, the identification of adsorption precursor states, the understanding of dissociative chemisorption, the determination of the contributions of corrugation, steps, and other structural details of the surface to the adsorption process, the effect to molecular steering, the identification of avenues for assisting adsorption, and the molecular details associated with the kinetics of the uptake of adsorbates as a function of coverage. We follow with a summary of the work directed at the determination of kinetic parameters and mechanistic details of surface reactions associated with catalysis, mostly those promoted by late transition metals. This discussion we initiate with an overview of what has been learned about simple bimolecular reactions such as the oxidation of CO and H₂ with O₂ and the reaction of CO with NO, and continue with the review of the studies of more complex systems such as the oxidation of alcohols, the conversion of organic acids, the hydrogenation and isomerization of olefins, and the oxidative activation of alkanes under conditions of short contact times. 6 Reactions on supported nanoparticles: Materials gap, 7 Low-probability reactions: Pressure gap of this review deal with the advances made in the use of molecular beams with more realistic models for catalysis, using surfaces comprised of metal nanoparticles dispersed on the oxide surfaces used as catalyst support and high-flux beams to approach the pressures used in catalysis. The next section deals with the study of systems associated with fields other than catalysis, mainly with the etching and oxidation of semiconductor surfaces and with the chemistry used to grow thin solid films by chemical means (chemical vapor deposition, CVD, or atomic layer deposition, ALD). We end with a personal assessment of the past accomplishments, present state, and future promise of the use of molecular beams for the study of the kinetics of surface reactions relevant to practical applications.     

Chemical vapor deposition growth of two-dimensional heterojunctions

The properties of two-dimensional (2D) layered materials with atom-smooth surface and special interlayer van der Waals coupling are different from those of traditional materials. Due to the absence of dangling bonds from the clean surface of 2D layered materials, the lattice mismatch influences slightly on the growth of 2D heterojunctions, thus providing a flexible design strategy. 2D heterojunctions have attracted extensive attention because of their excellent performance in optoelectronics, spintronics, and valleytronics. The transfer method was utilized for the fabrication of 2D heterojunctions during the early stage of fundamental research on these materials. This method, however, has limited practical applications. Therefore, chemical vapor deposition (CVD) method was recently developed and applied for the preparation of 2D heterojunctions. The CVD method is a naturally down-top growth strategy that yields 2D heterojunctions with sharp interfaces. Moreover, this method effectively reduces the introduction of contaminants to the fabricated heterojunctions. Nevertheless, the CVD-growth method is sensitive to variations in growth conditions. In this review article, we attempt to provide a comprehensive overview of the influence of growth conditions on the fabrication of 2D heterojunctions through the direct CVD method. We believe that elucidating the effects of growth conditions on the CVD method is necessary to help control and improve the efficiency of the large-scale fabrication of 2D heterojunctions for future applications in integrated circuits.     

Plasma deposition of hydrogenated amorphous silicon: Studies of the growth surface

This review focusses on the plasma-surface interactions and surface processes involved in a-Si: H thin film growth. We restrict our discussion of growth fluxes to a summary, and do not address plasma kinetics. In recent years, powerful in situ experiments have been carried out on the growing film surface, which reveal the adsorption, penetration, reaction, and elimination of precursor species, as well as the atomic-scale morphology and composition of the growth zone. Good data sets are available both for PACVD and reactive magnetron sputter deposition. These form an interesting comparison, since the former process is dominated by the hydrogen-rich radical SiH₃ at low energy, and the latter by energetic atomic Si and H. We review the key experiments and conclusions, underlining those aspects which are well established and those which remain qualitative; and we discuss the transition from amorphous to fine-grained polycrystalline film growth at high hydrogen pressures in terms of the surface mechanisms. This field is now entering a scientific stage where a detailed theory of low-temperature, plasma-assisted growth can be developed.     

锗硅/硅异质结材料的化学气相淀积生长动力学模型

基于化学气相淀积(CVD)的Grove理论和Fick第一定律,提出并建立了锗硅(SiGe)/硅(Si)异质结材料减压化学气相淀积(RPCVD)生长动力学模型.与以前锗硅/硅异质结材料生长动力学模型仅考虑表面反应控制不同,本模型同时考虑了表面反应和气相传输两种控制机理,并给出了两种控制机理极限情况下的模型.本模型不仅适用于低温锗硅/硅应变异质结材料生长的表征,也适用于表征高温锗硅/硅弛豫异质结材料生长的表征.将模型计算值与实验结果进行了对比,无论是625℃低温下的应变SiGe的生长,还是900℃高温下的弛豫 关键词： SiGe/Si异质结材料 化学气相淀积生长动力学模型 Grove理论 Fick第一定律     

Kinetics of water-assisted single-walled carbon nanotube synthesis revealed by a time-evolution analysis

Here we investigate the kinetics of water-assisted CVD (henceforth denoted as supergrowth CVD) by a quantitative time-evolution analysis based on a simple growth model. We found that the supergrowth can be well described by a model where the dynamics of the catalyst activity is treated similar to radioactive decay. An in-depth analysis based on this growth model revealed the kinetics of the supergrowth CVD, showing a scale relationship between the carbon source and water, and elucidated the role of water as a catalyst activity enhancer and preserver.     

核科学百年讲座第五讲辐射化学与辐射加工

介绍辐射化学和辐射加工的发展与应用，以及基本原理，侧重介绍辐射加工在高分子辐射交联改性、食品的辐照处理和医疗用品消毒等方面的应用．     

Combustion chemistry probed by synchrotron VUV photoionization mass spectrometry

Combustion is directly related to energy conversion and the environment. Gas-phase chemical reactions such as thermal decomposition, oxidation and recombination play a critical role in combustion processes. Here we review six applications of synchrotron vacuum-ultraviolet (VUV) photoionization mass spectrometry (PIMS) in fundamental studies of combustion chemistry. These applications range from the use of flow reactors to probe elementary reaction kinetics, studies of pyrolysis in plug-flow reactors and oxidation in jet-stirred reactors, studies of spatial evolution of species concentrations in premixed and non-premixed flames, product distributions in pyrolysis of biomass, and analysis of polycyclic aromatic hydrocarbon (PAH) formation. These experiments provide valuable data for the development and validation of detailed chemical kinetic models. Furthermore, some additional potential applications are proposed.     

Diagnostic studies of molecular plasmas using mid-infrared semiconductor lasers

Within the last decade mid-infrared absorption spectroscopy between 3 and 20 μm, known as infrared laser absorption spectroscopy (IRLAS) and based on tuneable semiconductor lasers, namely lead salt diode lasers, often called tuneable diode lasers (TDL), and quantum cascade lasers (QCL) has progressed considerably as a powerful diagnostic technique for in situ studies of the fundamental physics and chemistry of molecular plasmas. The increasing interest in processing plasmas containing hydrocarbons, fluorocarbons, organo-silicon and boron compounds has lead to further applications of IRLAS because most of these compounds and their decomposition products are infrared active. IRLAS provides a means of determining the absolute concentrations of the ground states of stable and transient molecular species, which is of particular importance for the investigation of reaction kinetics. Since plasmas with molecular feed gases are used in many applications such as thin film deposition, semiconductor processing, surface activation and cleaning, and materials and waste treatment, this has stimulated the adaptation of infrared spectroscopic techniques to industrial requirements. The recent development of QCLs offers an attractive new option for the monitoring and control of industrial plasma processes as well as for highly time-resolved studies on the kinetics of plasma processes. The aim of the present article is twofold: (i) to review recent achievements in our understanding of molecular phenomena in plasmas using TDLs and (ii) to report on selected new applications of QCLs in the mid-infrared. PACS  07.57.Ty; 52.70.Kz; 52.80.-s     

尘埃表面化学理论模拟研究进展

近年来天体化学在解释星际分子的形成过程中起重要作用的尘埃表面化学取得了长足的发展,本文综述了在天体化学模拟中用到的各种数值计算方法,以及尘埃冰幔的化学模型. 同时也介绍在实验室天体化学方面获得的结果,及其对尘埃表面化学所起到的促进作用.     

Adsorption and thermal decomposition of diethylaluminum hydride on Si(1 0 0)-2 × 1

Chemistry of organoaluminum compounds on silicon surfaces forms a foundation of chemical vapor deposition (CVD) for the formation of metal-semiconductor interconnects. We have applied multiple internal reflection Fourier-transform infrared spectroscopy and thermal desorption mass spectrometry to analyze the chemistry of one of the promising Al-CVD precursors, diethylaluminum hydride, on a Si(1 0 0)-2 × 1 surface. Diethylaluminum hydride adsorbs molecularly on this surface both at room temperature and at 100 K. Thermally induced surface reaction consumes the monolayer of adsorbed organoaluminum molecule. The only hydrocarbon product is ethylene desorbing from the silicon surface around 600 K. Despite a clean reaction that removes carbon from the surface, aluminum deposition is not significant because of the formation of alane products.     

物理学与化学交叉——有机分子固体与聚合物的物理问题

简略地回顾了有机固体领域中物理学与化学的交叉问题，从孤子、极化子、分数电荷理论到有机材料的光电应用，物理学与化学是紧密结合并且是互相促进的，交叉也会带来分歧，但科学的争论可提出更多，更深入的问题，更加促进学科的发展。     

A growth kinetics model of rate decomposition for Si1-xGex alloy based on dimer theory

According to the dimer theory on semiconductor surface and chemical vapor deposition(CVD) growth characteristics of Si1-xGex, two mechanisms of rate decomposition and discrete flow density are proposed. Based on these two mechanisms, the Grove theory and Fick’s first law, a CVD growth kinetics model of Si1-xGex alloy is established. In order to make the model more accurate, two growth control mechanisms of vapor transport and surface reaction are taken into account. The paper also considers the influence of the dimer structure on the growth rate. The results show that the model calculated value is consistent with the experimental values at different temperatures.     

Nanoparticle decoration with surfactants: Molecular interactions,assembly, and applications

Nanostructures of diverse chemical nature are used as biomarkers, therapeutics, catalysts, and structural reinforcements. The decoration with surfactants has a long history and is essential to introduce specific functions. The definition of surfactants in this review is very broad, following its lexical meaning “surface active agents”, and therefore includes traditional alkyl modifiers, biological ligands, polymers, and other surface active molecules. The review systematically covers covalent and non-covalent interactions of such surfactants with various types of nanomaterials, including metals, oxides, layered materials, and polymers as well as their applications. The major themes are (i) molecular recognition and noncovalent assembly mechanisms of surfactants on the nanoparticle and nanocrystal surfaces, (ii) covalent grafting techniques and multi-step surface modification, (iii) dispersion properties and surface reactions, (iv) the use of surfactants to influence crystal growth, as well as (v) the incorporation of biorecognition and other material-targeting functionality. For the diverse materials classes, similarities and differences in surfactant assembly, function, as well as materials performance in specific applications are described in a comparative way. Major factors that lead to differentiation are the surface energy, surface chemistry and pH sensitivity, as well as the degree of surface regularity and defects in the nanoparticle cores and in the surfactant shell. The review covers a broad range of surface modifications and applications in biological recognition and therapeutics, sensors, nanomaterials for catalysis, energy conversion and storage, the dispersion properties of nanoparticles in structural composites and cement, as well as purification systems and classical detergents. Design principles for surfactants to optimize the performance of specific nanostructures are discussed. The review concludes with challenges and opportunities.     

Free-electron lasers and their applications

We review the classical theory of the free-electron laser and discuss possible applications in laser fusion, laser-induced chemistry, biochemistry, and solid-state physics. The possibility of using optical wigglers to reach the VUV and soft X-ray regimes is also analysed.     

Ultrasonic approach for surface nanostructuring

The review is about solid surface modifications by cavitation induced in strong ultrasonic fields. The topic is worth to be discussed in a special issue of surface cleaning by cavitation induced processes since it is important question if we always find surface cleaning when surface modifications occur, or vice versa. While these aspects are extremely interesting it is important for applications to follow possible pathways during ultrasonic treatment of the surface: (i) solely cleaning; (ii) cleaning with following surface nanostructuring; and (iii) topic of this particular review, surface modification with controllably changing its characteristics for advanced applications. It is important to know what can happen and which parameters should be taking into account in the case of surface modification when actually the aim is solely cleaning or aim is surface nanostructuring. Nanostructuring should be taking into account since is often accidentally applied in cleaning. Surface hydrophilicity, stability to Red/Ox reactions, adhesion of surface layers to substrate, stiffness and melting temperature are important to predict the ultrasonic influence on a surface and discussed from these points for various materials and intermetallics, silicon, hybrid materials. Important solid surface characteristics which determine resistivity and kinetics of surface response to ultrasonic treatment are discussed. It is also discussed treatment in different solvents and presents in solution of metal ions.     

Computational Science and Engineering On-line: an integrated web-based environment for multi-scale modelling of complex reaction systems

We present a development of an integrated extendable web-based environment called Computational Science and Engineering On-line (CSEO) to include different fields of computational science. Our initial efforts are focusing on an integrated environment for multi-scale modelling of complex reacting systems from fundamental quantum chemistry with different entry points. CSEO provides an information management system that allows data flow from one application to another in a transparent manner. In addition, it provides a set of web-based graphic-user interfaces (GUIs) to different scientific applications. Current available GUIs are for quantum chemistry, thermodynamics and kinetics. Work is in progress to allow CSEO accessing resources from the computing grids using the Globus technology. CSEO can be accessed at http://cseo.net. It can also be hosted at different mirror sites.     

Cross-Sections,Rate Constants and Transport Coefficients in Silane Plasma Chemistry

This paper presents a critical review of the basic data concerning the physics and chemistry of low pressure SiH₄ glow discharges used to deposit hydrogenated amorphous silicon films (a-Si:H). Starting with an updated table of thermochemical data, we analyze the gas-phase elementary processes consisting of i) electron-molecule collisions, ii) ion-molecule collisions, iii) neutral-neutral collisions, iv) other electron and ion collisions involving electron-ion and ion-ion recombination, electron attachment on radicals and detachment of anions, and v) cluster growth kinetics in dusty plasmas. Experimental data or theoretical estimates are given and discussed in terms of cross-sections, collision and reaction rate constants, and transport coefficients. We also analyze the surface processes and reaction probabilities of ions, radicals and molecules.     

Aligned carbon nanotube from catalytic chemical vapor deposition technique for energy storage device: a review

Carbon nanomaterial especially carbon nanotube (CNT) possesses remarkably significant achievements towards the development of sustainable energy storage applications. This article reviews aligned CNTs grown from chemical vapor deposition (CVD) technique as electrode material in batteries and electrochemical capacitors. As compared to the entangled CNTs, aligned or well-organized CNTs have advantages in specific surface area and ion accessibility in which more electrolyte ions can access to CNT surfaces for better charge storage performance. CVD known as the most popular technique to produce CNTs enables the use of various substrates and CNT can grow in a variety of forms, such as powder, films, aligned or entangled. Also, CVD is a simple and economic technique, and has good controllability of direction and CNT dimension. High purity of as-grown CNTs is also another beauty of the CVD technique. The current trend and performance of devices utilizing CNTs as electrode material is also extensively discussed.