Laser induced CVD

Current study in this area is prompted by laser-induced CVD of such volatile gold compounds, permitting direct laser writing in gold [155]. 

Zhang, G. Q., Krypton Laser Induced CVD of Tungsten, /. Appl. 

Tremendous fundamental research especially in the CVD technologies and precursor synthesis extends the applicability to some new area. These technologies include metal-organic CVD (MOCVD), plasma-enhanced CVD, photo CVD and laser induced CVD etc. The advancement of the synthesis technology provides new precursors to deposit a variety of materials with high purity. 

CVD can also be classified using its activation methods. Thermal activated CVD processes are initiated only with the thermal energy of resistance heating, RF heating or by infrared radiation. They are widely used to manufacture the materials for high-temperature and hard-to-wear applications. In some cases enhanced CVD methods are employed, which includes plasma-enhanced CVD (PECVD), laser-induced CVD (LCVD), photo CVD (PCVD), catalysis-assisted CVD and so on. In a plasma-enhanced CVD process the plasma is used to activate the precursor gas, which significantly decreases the deposition temperature. 

Transition metal carbonyl is important in laser chemistry as sources of metal atoms or as precursors for chemical vapor deposition (CVD) [104]. Ni(CO)4 shows a typical photofragmentation reaction initiated by the XeCl laser (308 nm, 4.03 eV), and the knowledge on the mechanism is valuable for the design and control of the laser-induced CVD. The SAC-Cl method was applied to the excitation spectrum and the potential energy curves relevant to the photofragmentation reaction [105]. 

An example of this process is laser-induced CVD, where the radiation frequency is tuned to the vibrational frequency of the precursor molecule, to enhance decomposition. This resonance absorption/excitation is the basis of laser-induced fluorescence, which may be used to determine species on a surface or in the gas phase. 

Another approach is to coat the cutting tool material with a carbide former, such as titanium or silicon or their respective carbides by CVD and deposit diamond on top of it. The carbide layer may serve as an interface between diamond and the cemented carbide, thus promoting good bonding. Yet another method to obtain adherent diamond coatings is laser-induced microwave CVD. By ablating the surface of the substrate with a laser (typically, ArF excimer laser) and coating this surface with diamond by microwave CVD, it is possible to improve the adhesion between the tool and the substrate. Partial success has been achieved in this direction by many of these techniques. 

Nanopowders have been of particular interest in recent years as they can be used to make high-performance products due to their superior properties. Manufacturing of these powders is therefore important. Such a system using a laser-induced cold-wall CVD reactor is shown in Figure 3.28. It mainly consists of five parts a reactor with two reaction zones, an oven for vaporising hexamethyl disilylamine (HMDS-... 

Figure 3.28. Schematic of laser-induced cold-wall CVD reactor [57] (1 C02 laser, 2 reflector, 3 laser beam, 4 GaAs lens, 5 cooling water, 6 reactor, 7 nozzle, 8 reaction flame, 9 particle plume, 10 board, 11 window, 12 throttling valve, 13 powder collector, 14 pump, 15 pressure gauge, 16 water-cooled Cu block, 17 temperature controller, 18 oven, 19 heater, 20 precursor vessel, 21 liquid HMDS, 22 needle valve, 23 flow meter, 24 preheating tube, 25 co-axial protection gas, 26 lens protective gas)...

Chapter 6 LASER INDUCED PHOTMIEACTIONS AND PHOTO-CVD ON SOLID SURFACES... 

T. Goto, High-Speed Deposition ofZirconia Films by Laser-Induced Plasma CVD, Solid State Ionics, 172, 225-229 (2004). 

Determination of reaction kinetics alone is not enough to get a reasonably complete picture of surface processes during deposition. Often the gaseous reactants and products are identified by mass spectroscopy and time-dependent concentrations are measured. Adsorbed species are identified by in situ spectroscopy (infrared, Raman, or laser-induced fluorescence). The morphology of the product as studied by electron microscopy also contributes to an understanding of CVD reaction mechanisms. 

Laser-assisted CVD of BN can originate from a gaseous reactant [58], or the plasma can be formed by irradiating a target consisting mainly of BN [59 to 63, 139]. The cluster distribution of boron nitride in a laser plasma and the structure of the BN phases in the case of laser-induced plasma deposition have been studied [64]. It is also reported that a combination of an electron cyclotron plasma with laser irradiation produces a coating which consists of p-BN and y-BN [65]. 

Maity techniques exist for examining the composition of the species (including radical species) generated in CVD reactors optical emission spectroscopy (OES) [80], FT-IR spectroscopy [81] laser induced fluorescence (LIE) spectroscopy [82], diode laser IR absorption spectroscopy [83], and MS [84-87]. Each has its own strengths and shortcomings. A major advantage of MS over other techniques is its... 

The complexes PdlTj -allyDlTj -cyclopentadienyl), " PdlTj -allylK/J-diketonate), and Pd(77 -allyl)(/ -ketiminate) are classical derivatives used to obtain Pd metal surfaces by CVD techniques, and have received some attention in recent years. Thermal or laser-induced decomposition of these complexes has been carried out by different modified techniques, and the resulting surface has been analyzed by spectroscopic techniques and microscopy. The finely dispersed surfaces of the metal have application in catalysis and other fields. 

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