Laser assisted chemical vapor

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

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... 

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. 

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... 

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

Three-dimensional periodic photonic band-gap microstructures (PBG s) of aluminum oxide represent a new class of materials capable of uniquely controlling radiation since they are able to entirely reflect electromagnetic radiation in a band of frequencies propagating in any direction [10]. The successful construction of 3-dimensional PBG materials by laser assisted chemical vapor deposition (see Chapter 3.1.1(d) and Figure 5) showed transition minima around 4 tetrahertz (75 pm) and 2 tetrahertz (150 pm) required for the precise control of the optical properties of materials, including lasers without threshold [10]. 

H, Westberg, Thermal laser assisted chemical vapor deposition, Acta Universitatis Upsaliensis, Comprehensive summary of dissertations, No. 375, Faculty of Science, University of Uppsala, Sweden (1992). 

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). 

F. T. Wallenberger, Inorganic fibers and microfabricated parts by laser assisted chemical vapor deposition a new rapid prototyping tool. Journal of Materials Processing and Manufacturing Science, 3,196-213 (1994). 

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