Laser-enhanced chemical vapor deposition

On a metal surface, silicide layers can be formed by two methods. In the first, Si atoms are vapor deposited by heating either a well degassed silicon wafer or a silicon rod to near its melting point. In the second method the metal is heated in 10 to 50 mTorr of silane for a desired length of time, usually about 10 to 60 s at a desired temperature, usually about 300 to 700°C. The first method is better suited for studying very early stages of silicide formation, the second more convenient for growing thick layers of silicides. Chemical vapor deposition or laser enhanced chemical vapor deposition may probably be used also, but have not yet been explored. 

DEC coating was first prepared by Aisenberg and Chabot using ion beam deposition in 1971 [2]. At present, PVD, such as ion beam deposition, sputtering deposition, cathodic vacuum arc deposition, pulsed laser deposition, and CVD, like plasma enhanced chemical vapor deposition are the most popular methods to be selected to fabricate DEC coatings. 

The first MWNTs have been obtained as early as 1976 by iron-catalyzed pyrolysis of benzene. Apart from that, there is a number of methods to produce MWNT, which all of them differ in the way of generating small carbon clusters or atoms from the respective starting materials. They include arc discharge, laser ablation, chemical vapor deposition with and without plasma enhancement or the catalytic decomposition of various precursor compounds. It turned out that MWNTs from low-temperature syntheses bear more defects and, as a whole, are less ordered than those generated at high temperatures. However, these drawbacks can still be compensated by subsequent recuperation of defective samples at elevated temperatures. 

Nanoparticles can be produced by several methods including mechanical, electric arc discharge, laser ablation, chemical vapor deposition (CVD), plasma-enhanced CVD (PECVD) and wet chemical reactions. 

Costa J, Roura P, Morante JR, Bertran E (1998) Blackbody emission under laser excitation of silicon nanopowder produced by plasma-enhanced chemical-vapor deposition. J Appl Phys 83 7879-7885... 

The VLS synthesis requires only the presence of a metaUic catalyst and nanowire material in the vapor. Consequently, a broad spectrum of VLS-based techniques has been developed for synthesizing nanowires. Here, only the three primary techniques will be described, namely, flow reaction, laser ablation and CVD, which indudes plasma-enhanced chemical vapor deposition (PECVD). However, the primary focus will be on CVD-based techniques utUized in the authors laboratory. 

The preparation of CNTs is a prerequisite step for the further study and application of CNTs. Considerable efforts have been made to synthesize high quality CNTs since then-discovery in 1991. Numerous methods have been developed for the preparation of CNTs such as arc discharge, laser vaporization, pyrolysis, and plasma-enhanced or thermal chemical vapor deposition (CVD). Among these methods, arc discharge, laser vaporization, and chemical vapor deposition are the main techniques used to produce CNTs. 

These specialized forms of CVD, referred to as nontraditional techniques for the purpose of this review, include laser (LCVD), aerosol (ACVD), hot filament (HFCVD), and ion beam (IBGVD) chemical vapor deposition. In such enhanced CVD technologies, a thermal CVD reaction occurs simultaneously with another driving force, which results... 

In the Chemical Vapor Deposition (CVD) methods, the starting material undergoes specific chemical reactions at the hot surface of the substrate to form thin layers of the desired material. The reaction can be stimulated by various energy sources, e.g. plasma, giving plasma enhanced CVD (PECVD), or a laser, giving laser CVD. 

J. Krishnaswamy, A. Rengan, A. R. Srivatsa, G. Matera, and J. Narayan, Laser and plasma enhanced deposition of diamond and diamondlike films by physical and chemical vapor deposition techniques, in Proc. SPIE, 1190 109-117 (1989)... 

Several techniques have been developed to deposit alumina films on different surfaces such as those of semiconductors or metals. These films find apphcation in various areas. In most cases, amorphous alumina films are desired. Depending on the deposition techniques, various precursors may be used the following combinations have been reported plasma-enhanced atomic layer deposition using trimethylaluminum (112), metal-organic chemical vapor deposition using aluminum tri-iso-propoxide (113), and condensation from the gas phase using laser-evaporated alumina (114). Similar evaporation techniques can also be apphed to prepare Y-AI2O3 powders (115,116). 

Many modern semiconductor devices comprise alternating layers of different materials forming superlattices and multiple quantum wells. One well-known example of such structures is the diode laser, a mass-produced device. This device depends on confinement of charges in the two-dimensional structures for enhanced laser output at lowered current thresholds. Such alternating semiconductor layers are usually manufactured either by chemical vapor deposition or by molecular beam epitaxy. The thickness of the layers can be closely controlled in both techniques. As mentioned earlier, electrodeposition also allows good control of thickness. 

The technology of growing carbon nanotubes from the vapor phase dates back to 1991 when they were first found [11] in arc discharge experiments. Nanotubes can be obtained by chemical vapor deposition, laser evaporation, arc discharge, and carbon ion bombardment [62], Addition of particulate metal catalysts creates a more controlled growth habitat and helps growth of whiskers with greatly enhanced dimensional uniformity. 

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