Search Results for vapor-phase growth

This article describes the vapor-phase growth techniques applied to the epitaxial deposition of semiconductor films and discusses the fundamental processes involved in metal-organic chemical vapor deposition (MOCVD). It reviews the thermodynamics that determine the driving force behind the overall growth process and the kinetics that define the rates at which the various processes occur. The article provides information on the reactor systems and hardware, MOCVD starting materials, engineering considerations that optimize growth, and the growth parameters for a variety of Group III-V, II-VI, and IV semiconductors.

This article begins with the one-component, or unary, diagram for magnesium. The diagram shows what phases are present as a function of the temperature and pressure. When two metals are mixed in the liquid state to produce a solution, the resulting alloy is called a binary alloy. The article describes the various types of solid solutions such as interstitial solid solutions and substitutional solid solutions. Free energy is important because it determines whether or not a phase transformation is thermodynamically possible. The article discusses the thermodynamics of phase transformations and free energy, as well as kinetics of phase transformations. It concludes with a description of solid-state phase transformations that occur when one or more parent phases, usually on cooling, produces a phase or phases.

This article describes eight stages of the atomistic film growth: vaporization of the material, transport of the material to the substrate, condensation and nucleation of the atoms, nuclei growth, interface formation, film growth, changes in structure during the deposition, and postdeposition changes. It also discusses the effects and causes of growth-related properties of films deposited by physical vapor deposition processes, including residual film stress, density, and adhesion.

This article presents a general description of pulsed-laser deposition. It describes the components of pulsed-laser deposition equipment. The article also discusses the effects of angular distribution of materials. Finally, the article reviews the characteristics of high-temperature superconductors and ferroelectric materials.

This article focuses on transport phenomena and modeling approaches that are specific to vapor-phase processes (VPP). It discusses the VPP for the synthesis of materials. The article reviews the basic notions of molecular collisions and gas flows, and presents transport equations. It describes the modeling of vapor-surface interactions and kinetics of hetereogeneous processes as well as the modeling and kinetics of homogenous reactions in chemical vapor deposition (CVD). The article provides information on the various stages of developing models for numerical simulation of the transport phenomena in continuous media and transition regime flows of VPP. It explains the methods used for molecular modeling in computational materials science. The article also presents examples that illustrate multiscale simulations of CVD or PVD processes and examples that focus on sputtering deposition and reactive or ion beam etching.

Furnace soldering (FS) encompasses a group of reflow soldering techniques in which the parts to be joined and preplaced filler metal are put in a furnace and then heated to the soldering temperature. This article describes three reflow soldering techniques in surface-mount technology, namely, vapor-phase reflow, area conduction, and infrared heating. These three techniques are considered as mass reflow techniques, because all of the solderable interconnections on the surface of a printed wiring board (PWB) assembly are brought through the reflow heating cycle simultaneously. The article explains four regions of reflow profile, namely, preheat (prebake), preflow (soak), reflow, and cooldown. It concludes with a description on the bare copper assembly process, which is carried out in the inert atmosphere.

Sintering provides the interparticle bonding that generates the attractive forces needed to hold together the otherwise loose ceramic powder mass. It also improves hardness, strength, transparency, toughness, electrical conductivity, thermal expansion, magnetic saturation, corrosion resistance, and other properties. This article discusses the fundamentals of sintering and its effects on pore structures and particle density. It addresses some of the more common sintering methods, including solid-state, liquid-phase, and gas pressure sintering, and presents alternative processes such as reaction sintering and self-propagating, high-temperature synthesis. It also describes several pressure densification methods, including hot isostatic pressing, gas pressure sintering, molten particle deposition, and sol-gel processing. The article concludes with a section on grain growth that discusses the underlying mechanisms and kinetics and the relationship between grain growth and densification.

Sintering is a thermal treatment process in which a powder or a porous material, already formed into the required shape, is converted into a useful article with the requisite microstructure. Sintering can be classified as solid-state, viscous, liquid-phase, and pressure-assisted (or pressure) sintering. This article provides information on the mechanisms and theoretical analysis of sintering and focuses on the types, mechanisms, process and microstructural variables, computer simulation, stages, and fundamentals of densification and grain growth of solid-state sintering and liquid-phase sintering. It describes the models for viscous sintering and the methods used in pressure-assisted sintering, namely, uniaxial hot pressing, hot isostatic pressing, sinter forging, and spark plasma sintering.

Corrosion fatigue refers to the phenomenon of cracking in materials under the combined actions of fatigue loading and a corrosive environment. This article focuses on the various mechanisms of corrosion fatigue, namely, hydrogen-assisted cracking, anodic dissolution, and surface energy reduction. It discusses the variables affecting corrosion fatigue. The effect of fatigue load frequency, environment, grain size, stress ratio, waveform, and temperature fatigue crack growth are also discussed.

This article provides an overview of how thermal spray technology has adapted to meet the needs of the orthopaedic industry. It includes the challenges facing the development of artificial joints, substrate material selection criteria, thermal spray solutions, and clinical outcomes of thermal spray coatings. The article focuses on plasma thermal spray, which is the technique most often used to make porous titanium and hydroxyapatite (HA) coatings, such as thermal spray titanium, thermal spray HA, solution-precipitated HA, thermal spray chromium oxide, and thermal spray chromium carbide cermet coatings.

This article discusses two major sintering methods: pressureless and pressure-assisted sintering. Pressureless sintering techniques include vacuum and partial-pressure, hydrogen, and microwave sintering. Pressure-assisted consolidation techniques include overpressure sintering, sintering followed by postsinter hot isostatic pressing, hot pressing, and several rapid hot consolidation techniques. The article describes nitrogen sintering and the sintering of cermets. It reviews the furnaces used for sintering and presents the lubrication removal techniques. The article also outlines the need to control carbon and oxygen to obtain optimal properties and explains microstructure development and grain size control.

This article presents the principles of chemical vapor deposition (CVD) with illustrations. It discusses the types of CVD processes, namely, thermal CVD, plasma CVD, laser CVD, closed-reactor CVD, chemical vapor infiltration, and metal-organic CVD. The article reviews the CVD reactions of materials related to hard, tribological, and high-temperature coatings and to free-standing structures. It concludes by reviewing the advantages, disadvantages, and applications of CVD.

This article focuses on different thin-film deposition techniques used to make superconducting films and discusses the properties and advantages of high-critical-temperature and low-critical-temperature materials in a number of applications, including signal processing and analog electronic devices. The article gives a brief introduction on superconducting materials, substrates and buffer layers and discusses the major deposition techniques such as, electron-beam co-evaporation, sputtering from either a composite target or multiple sources and laser ablation. The article also describes the in-situ film growth techniques for producing atomic oxygen by radio frequency excitation or microwave discharge or with ozone.

This article discusses the fundamentals of thermal vaporization and condensation and provides information on the various vaporization sources and methods of vacuum deposition. It offers an overview of reactive evaporation and its deposition techniques. The article also explains the advantages, limitations, and applications of vacuum deposition processes. Finally, it provides information on the gas evaporation process, its processing chamber, and related systems.

This article describes the structure of coatings produced by plasma spraying, vapor deposition, and electrodeposition processes. The main techniques used for microstructure assessment are introduced. The relationship between the microstructure and property is also discussed. The experimental techniques for microstructural characterization include metallographic technique, X-ray diffraction, electron, microscopies, and porosimetry.

This article begins with a list of the factors that influence the properties of physical vapor deposited films. It describes the steps involved in ion plating, namely, surface preparation, nucleation, interface formation, and film growth. The article discusses the factors influencing the properties of ion-plated films. The sources of potential applied on substrate surface, bombarding species, and depositing species are addressed. The article also provides information on the parameters that influence bombardment. It concludes with a discussion on the advantages, limitations, and applications of ion plating.

This article discusses the array of fiber products, manufacturing approaches, and production suppliers. It also discusses carbon fibers, their range of uses, and their performance capabilities, which are unique and separate from oxide and non-oxide fibers. The article reviews the history of developing silicon carbide (SiC) fibers and SiC-base ceramic-matrix composites. CMCs provide a roadmap and timeline for the technologies developed and refined over the last 50 years of effort to make SiC-SiC composites a reality. The article also describes the use of fiber in composite applications.

Zirconium and hafnium surfaces require cleaning and finishing for reasons such as preparation for joining, heat treatment, plating, forming, and producing final surface finishes. This article provides information on various surface treatment processes, surface soil removal, blast cleaning, chemical descaling, pickling or etching, anodizing, autoclaving, polishing, buffing, vapor phase nitriding, and electroplating. Applications of these surface treatment processes are also reviewed.

This article reviews general corrosion of uranium and its alloys under atmospheric and aqueous exposure as well as with gaseous environments. It describes the dependence of uranium and uranium alloy corrosion on microstructure, alloying, solution chemistry, and temperature as well as galvanic interactions between uranium, its alloys, and other metals. The article provides information on the atmospheric corrosion of uranium based on oxidation in dry air or oxygen, water vapor, and oxygen-water vapor mixtures depending upon particular storage conditions. The mechanism and morphology of hydride corrosion of uranium are discussed. The article provides information on environmentally assisted cracking, protective coatings, and surface modification of uranium and its alloys. It also summarizes the environmental, safety, and health considerations for their use.

Spray quenching refers to a wide variety of quenching processes that involve heat removal facilitated by the impingement of a quenchant medium on a hot metal surface. This article provides information on the basic concepts of spray quenching, and discusses the most commonly used techniques in quench tank agitation to establish uniformity of the quenched part. Common techniques include quenchant stirring, quenchant circulation, and submerged jet/spray mixing. The article also describes the effect of quenching agitation and reviews heat-transfer characteristics of immersion quenching and spray quenching with water.