Chemical vapors, challenges

Laser chemical vapor deposition has been used to prepare films with an unfocused beam (Kimura, 2006) and free-standing fibers with a focused beam. A continuing challenge in this area of chemical vapor deposition is the production of lines that remain on the substrate surface. This is the operational mode that would be useful for replacing lithography as the method for a patterned deposition. 

Maroudas, D., Modeling of radical-surface interactions in the plasma-enhanced chemical vapor deposition of silicon thin films, in (A.K. Chakraborty, Ed.), Molecular Modeling and Theory in Chemical Engineering , vol. 28, p. 252. Academic Press, New York (2001). Maroudas, D. Multiscale modeling, Challenges for the chemical sciences in the 21st century Information and communications report , National Academies, Washington, DC. p. 133. 

Superlattice and low-dimensional physics are some of the most interesting subjects in solid-state physics. A challenging problem in this field is the formation of quantum wire and quantum box structures by using ultra-high technology such as MBE, MOCVD (metallorganic chemical vapor deposition), and related frontier microprocessing. However, this problem has not yet been solved. Poly silane is probably a perfect quantum wire in itself The absorption spectrum of polysilane clearly shows the characteristics of a one-dimensional quantum wire. Even a quantum box or a one-dimensional superlattice can be formed by chemical polymerization, which may be the simplest way. 

Elemental boron is a light element with a density of 2.34 g/cm It has a high melting point (2080°C), is hard, brittle and is an electrical insulator (resistivity 1.8 x 10 pQcm at 20°C) [10]. The element is barely reactive at room temperature, however it reacts with almost every element at elevated temperature. Thus, the preparation of pure boron presents a challenge, since impurities are incorporated readily into the boron lattice [221]. Boron has been prepared by chemical vapor deposition as early as 1911, when Weintraub deposited elemental boron from a mixture of BCI3 and Hi onto a heated wire [222]. Today, the CVD of boron is used to prepare coatings (e.g., for the first wall in fusion reactors) as well as fibers. Boron can be prepared by the hydrogen... 

Microfabrication has been the topic of a recent review in which thin-film (<1 pm, based on vacuum evaporation, sputtering or chemical vapor deposition) and thick-film (>10pm, based on screen printing or lamination) technologies are described for the mass production of potentiometric sensors and sensor arrays [80]. Current challenges include the cost of fabrication, especially for thin-film devices, the control of physical dimensions of the sensing elements, the incorporation of liquid reservoirs, and the stability of the integrated reference electrodes. 

Some of the major forms of gas-solid chemical interactions are (1) catalytic reactions, (2) simple chemisorption, chemical vapor deposition (CVD), or crystal growth, (3) oxidation or reduction reactions, and (4) addition reactions, such as carbonate or sulfate formation. Each of these classes presents unique experimental challenges. The first two categories involve reactions at the surface and do not require bulk diffusion. The latter two types, however, need material transport through the product layer in order to continue. There are numerous examples where the film of product initially produced is essentially impervious and thus becomes protective, forming a barrier to further reaction. 

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