Laser-assisted chemical vapor deposition

Stereolithography Selective Laser Sintering X-ray Lithography Mechanical Prepolymer Deposition Conventional Chemical Vapor Eteposition Laser Assisted Chemical Vapor Deposition... 

Chemical Vapor Deposition. In chemical vapor deposition (CVD), often referred to as vapor transport, the desired constituent(s) to be deposited are ia the form of a compound existing as a vapor at an appropriate temperature. This vapor decomposes with or without a reducing or oxidizing agent at the substrate— vapor interface for film growth. CVD has been used successfully for preparing garnet and ortho ferrite films (24,25). Laser-assisted CVD is also practiced. 

Shinn, G. B. Gillespie, P. M. Wilson, W. L., Jr. Duncan, W. M. 1989. Laser-assisted metalorganic chemical vapor deposition of zinc selenide epitaxial films. Appl. Phys. Lett. 54 2440-2442. 

Bondi, S. N., et al. (2006), Laser assisted chemical vapor deposition synthesis of carbon nanotubes and their characterization, Carbon, 44,1393-1403. 

Stephan was the first to attempted direct synthesis of the B and N multi walled carbon nanotubes (BCN-MWNTs) in 1994 [15-17]. Since then, considerable progress has been made in the synthesis of BCN-MWNTs by different means of arc-discharge [16-18], laser ablation [18-20], piyolysis methods [18,21], and chemical vapor deposition [18,20-24]. Aligned BNC nanotubes have been sueeessfully fabricated by bias assisted hot filament chemieal vapor deposition [27,28]. Up to now, the only existing BCN-SWNTs synthesis was achieved via an... 

Laser-assisted chemical vapor deposition a CVD in which the excitation is delivered from photons delivered from a laser Metal-organic chemical vapor deposition (MOCVD) the same as CVD, except that the precursor is a volatile organometallic or coordination compound with carbon-containing ligands... 

Chemical beam epitaxy a process in which one or more beams of volatile metal-organic precursors is directed to the substrate surface to effect film growth Chemical vapor deposition (CVD also termed vapor phase epitaxy) the deposition of a thin film of an element or compound using some form of excitation for the decomposition of a volatile precursor Laser-assisted chemical vapor deposition a CVD in which the excitation is delivered from photons delivered from a laser Metal-organic chemical vapor deposition (MOCVD) the same as CVD, except that the precursor is a volatile organometallic or coordination compound with carbon-containing ligands... 

MWCNT Chemical vapor deposition (CVD) Arc-discharge deposition Laser vaporization deposition Ion beam assisted deposition... 

Structural investigations in laser-assisted chemical vapor-deposited boron carbide thin films by Raman microspectroscopy and glancing incidence XRD, have provided... 

Laser assisted chemical vapor deposition (LCVD) yields continuous or discontinuous low diameter fibers directly from the vapor phase by tip growth. Chemical vapor deposition (CVD) on the surface of a small diameter, preferably sacrificial, precursor fiber yields a large diameter fiber or microtube. Chemical vapor infiltration (CVI) can change the chemistry of precursor fibers by infiltration of a chemically reactive vapor species. Finally, laser vaporization (LV) of carbon-metal mixtures yields highly entangled mats of nearly endless nanotube ropes. 

Laser assisted chemical vapor deposition (LCVD) is a relatively new process. It has already shown promise of becoming a major route for the fabrication of (1) potentially continuous small diameter fibers having premium structural, thermal or optical functionality, (2) complex fiber based microparts such as microsprings and solenoids, and (3) microdevices which operate by using coupled electrical, magnetic and thermal fields. Three excellent reviews should be consulted for details [1-3]. 

Laser assisted chemical vapor deposition is an evolutionary extension of the metal particle catalyzed chemical vapor deposition, wherein a hot laser focus takes the place of a hot solid or liquid metal particle catalyst (Figure 1). (Conventional chemical vapor deposition has no "hot spot" capable of preferentially focusing the vapor phase deposition. 

Figure Metal particle catalyzed and laser assisted chemical vapor deposition. Left Chemical vapor deposition causes the formation of a film or coating on a hot surface. Center and right Metal catalyzed and laser assisted chemical vapor deposition causes the formation of a potentially continuous fiber with a diameter corresponding to the hot metal catalyst particle or laser focus respectively. Redrawn from F. T. Wallenberger, P. C. Nordine and M. Boman, Inorganic fibers and microstructures directly from the vapor phase, Composites Science Technology, 5,193-222 (1994).

Short (or discontinuous) fibers are best prepared in a batch process, e.g., in a small cylindrical reaction chamber. The value of the technology, however, lies in its capability to facilitate the growth of continuous (potentially endless) fibers with a recently discovered automatic self-regulating growth mechanism [2], Finally, the diameter of the laser focus determines the diameter of fibers grown by laser assisted chemical vapor deposition, just as the diameter of the metal particles determines the diameter of the whiskers grown by metal catalyzed chemical vapor deposition. 

Figure 2. Growth of microstructures by laser assisted chemical vapor deposition (LCVD). Linear single laser system (A). Goniometer controlled single laser system (B) and complex dual laser system (C). Redrawn from F. T. Wallenberger, Rapid prototyping directly from the vapor phase, Science, 267,1274-1275 (1995).

Recently, a method was described for the real-time measurement of growth rates and feedback control of three-dimensional laser assisted chemical vapor deposition [11]. This method allows the accurate reproduction of high quality films, fibers, and three-dimensional structures. High aspect ratio axisymmetric forms of desired shape and microstructure were grown from vapor phase precursors by this method. Three-dimensional rods, cones, hyperboloids, and spheroids of pyrolytic graphite, nickel, iron, and nickel-iron superalloys were obtained from ethylene, nickel tetracarbonyl, iron pentacarbonyl, and mixtures of nickel and iron carbonyls, respectively. 

Mass transfer in metal catalyzed and in laser assisted CVD processes is driven by highly localized temperature gradients. The relatively small area of either a hot molten metal particle or of a hot laser focus affords whiskers [4] or continuous fibers, respectively [2] [18-19]. The transfer of an equal mass from the vapor to the solid phase in a conventional chemical vapor deposition results in a thin coating over the relatively large area of a hot surface, i.e., that of a flat complex shaped composites part. 

Figure 8. Boron fibers made by hot filament and by laser assisted CVD. This illustration compares the fiber diameter and surface character of a sheath/core boron/tungsten fiber (A,C) with that of a pure boron fiber (B,D). Reproduced from F. T. Wallenberger and P. C. Nordine, Strong, Small Diameter Boron Fibers by Laser Assisted Chemical Vapor Deposition, Materials Letters, 14 [4] 198-202 (1992). With permission from Elsevier Publishers (1992).

The relationships between process variables and structures and properties [2] [20-21] are best illustrated with examples from the extensive literature describing important commonalties and differences between the high pressure and the low pressure laser assisted chemical vapor deposition. 

Fiber growth by laser assisted chemical vapor deposition... 

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