Assisted Techniques

In order to enhance the deposition process of the resultant product, several assisted techniques have been investigated. In general, these techniques are meant to enhance the chemistry and, to a lesser extent, the surface mobility or reactivity. The result may be an increased growth rate, improved crystallinity or purity, or reduced growth temperatures, each of which may significantly help the process, throughput, or both. 

A popular technique is that of light (or photon) assisted OMVPE. Typically, a mercury lamp may be used to provide light at 185 and 254 nm, or a laser tuned to a specific wavelength may be used. In the case of UV assist, either the UV is used to assist with reactant decomposition — at or above the deposition plane, or the light is focused onto the substrate to promote reactivity and surface mobility. A laser, selectively tuned to a specific molecular transition, may be employed to promote molecules to an excited 

Care must be present when involing a photo process in CVD. In particular, the absorption induced reaction of a vapor phase precursor molecule must be distinguished from temperature effects. Otherwise, the irreversible result is a combination of a photo-event and a pyro-event. Although substrate cooling will rule out surface mobility of atoms due to light-induced heating, care must be utilized when attributing all gas phase chemistries to purely photo events. 

The compound semiconductor equipment market, while small compared to the Si-equipment market, is extremely competitive and volatile. Several equipment manufacturing companies have explored and subsequently exited the market. Presently the 

The MBE system market for compound semiconductors has been equally turbulent, most notably with the demise of Perkin-Elmer and Varian MBE equipment vendors. At this time the predominant MBE manufacturers are EPI in the United States and Riber in Europe. 

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Plasma-jet diamond techniques yield growth rates of about 980 p.m/h (163,164). However, the rate of diamond deposition is still one to two orders of magnitude lower than the HP—HT technology, which is about 10,000 p.m/h (165). Diamond deposition rates of ca 1 p.m/s have been reported usiag laser-assisted techniques (166). This rate is comparable to the HP—HT synthesis. 

TABLE 3 Photocurent Observed in a System Using Porous Membranes Covered with BR Film Deposited by the Usual LB Technique and Electric Field-Assisted Technique... 

Downs GM, Willett P. Clustering of chemical structure databases for compound selection. In van de Waterbeemd H, editor, Advanced computer-assisted techniques in drug discovery. Weinheim VCH Verlag, 1994. p. 111-30. 

Computer-assisted techniques for optimizing HPTLC have been available for a number years and are well presented in the hterature [20,77-82]. The strategy of integrating these techniques is to solve each separation problem in the simplest way possible. 

P.J. Lewi, Spectral mapping of drug-test specificities. In Advanced Computer-Assisted Techniques in Drug-Discovery (H. van de Waterbeemd, Ed.). VCH, Weinheim, Germany, 1994, pp. 219-253. 

Micro-stirring and vibration technique (Ultrasonic-assisted technique) Au, Ag, Bi2Te3 [15, 16]... 

Castro-Garcia, S., Julien, C., Senaris-Rodriguez, M. A., Structural and electrochemical properties of Li-Ni-Co oxides synthesized by wet chemistry via a succinic-acid-assisted technique, Int. J. Inorg. Mat. 3, 323-329 (2001). 

Evaluation of the morphology of a pharmaceutical solid is of extreme importance, since this property exerts a significant influence over the bulk powder properties of the material. In addition to providing insights into the micromeritic properties of the solid, microscopy can also be used to develop preliminary estimations of the particle-size distribution. A determination can be easily made regarding the relative crystallinity of the material, and it is often possible to deduce crystallographic information as well. Unknown particulates can often be identified solely on the basis of their microscopic characteristics, although it is useful to obtain confirmatory support for these conclusions with the aid of microscopically assisted techniques. 

Yadav and Kapoor <2003TL8951> reported on a microwave-assisted ring closure leading to novel thiazolo[l,3,5]-triazines, as shown in Scheme 36. This three-component one-pot procedure started from the thiazolyl Schiff base 230, to which ammonium acetate and an aldehyde was added. In the first step, the azomethine moiety of the Schiff base reacted with ammonia to give the zwitterionic first intermediate 231, which underwent deprotonation to the amine 232, and, finally, reaction of this second intermediate with the aldehyde involving the ring-closure step afforded the product 233. It is important to emphasize that the MW-assisted technique ensured high yields (76-88%)... 

Gomputer-assisted techniques for the analysis of sleep EEG have been used to investigate the intensity and distribution of various frequency bands... 

H. van de Waterbeemd (1995). Advanced Computer Assisted Techniques in Drug Discovery. New York John Wiley. 

Advanced Computer-Assisted Techniques in Drug Discovery... 

The redox balance of the two inorganic Se species, Se(IV) and Se(VI), in the sample can be significantly affected. Therefore, acid hydrolysis is unfit for the analysis of Se inorganic species. Accordingly, if no independent analysis of the protein fraction of the sample under study is carried out, a substantial part of Se can only be identified as total inorganic Se fraction. Apart from this drawback, one of the most important advantages of acid hydrolysis is the short-term analysis provided by the introduction of MW-assisted techniques [65]. 

Nous tenons k remercier ici le Professeur J. O. Hirschfelder, pour nous avoir permis d utiliser le calculateur Bendix du Laboratoire de Chimie Thdorique de l Universit6 de Wisconsin. Nous remercions dgalement le Professeur S. E. Lovell qui a dtabli le programme des calculs, ainsi que Madame M. H. Taylor pour son assistance technique. 

One of the most serious limitations in the application of these powerful GC/MS and LC/MS systems is the accurate and efficient identification of this flood of unknown mass spectra. A variety of computer-assisted techniques have been proposed (2, 3, 4), which can be classified generally as "retrieval" or "interpretive programs (2). The former matches the unknown mass spectrum against a data base of reference spectra the ultimate limitation of this approach is the size of the data base, which currently contains the mass spectra of 33,000 different compounds (j>, 6), less than 1% of the number listed by Chemical Abstracts. If a satisfactorily-matching reference spectrum cannot be found by the retrieval program, an interpretive algorithm can be used to obtain partial or complete structure information, or to aid the human interpreter in this task (7-10). 

The capabilities of two plasma assisted techniques (laser ablation and electrical discharge in liquids) for fabrication of nanoscale composite (Al-Cu/oxide matrix), zinc oxide and doped gadolinium oxide have been piesented. 

In the present paper, the laser/plasma assisted techniques for fabrication of Al-Cu/oxide matrix particles, doped gadolinium oxide and zinc oxide are considered. They offer advantages eliminating the need in large-scale vacuum system since the laser ablation and discharges are performed at normal pressure and they offer a good control over the synthesis process. 

Compared with many other techniques, sensitivity factors for LA-ICP hyphenated to either MS or AES are relatively uniform across the periodic table [21,22]. Also, the spectra for LA-assisted techniques are relatively simple and interferences between elements are more easily identified and corrected. 

The chromatograms of natural polymers, such as proteins and polysaccharides, are so complex that they have been mostly used for general identification. The potential of Pyr-GC-MS has been greatly enhanced by the use of high-resolution capillary columns combined with computer-assisted techniques. 

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