Lely method

Thermal oxidation of the two most common forms of single-crystal silicon carbide with potential for semiconductor electronics applications is discussed 3C-SiC formed by heteroepitaxial growth by chemical vapour deposition on silicon, and 6H-SiC wafers grown in bulk by vacuum sublimation or the Lely method. SiC is also an important ceramic ana abrasive that exists in many different forms. Its oxidation has been studied under a wide variety of conditions. Thermal oxidation of SiC for semiconductor electronic applications is discussed in the following section. Insulating layers on SiC, other than thermal oxide, are discussed in Section C, and the electrical properties of the thermal oxide and metal-oxide-semiconductor capacitors formed on SiC are discussed in Section D. 

The modified Lely process. Despite the high crystalline quality that may be obtained with the Lely method, it has never been considered an important technique for future commercial exploitation on account of the low yield and irregular sizes. In the modified Lely process, which is a seeded sublimation growth process, these problems are overcome, though at the price of a considerably lower crystalline quality. In the modified Lely technique, SiC powder or lumps of SiC are placed inside a cylindrical graphite crucible. The crucible is closed with... 

Growth from the vapor is the preferred phase transition for the production of thin epitaxial layers, while growth of bulk crystals from the vapor is rather the exception, only applied if unavoidable. An example is the growth of semiconductor-grade Sic by the so-called modified Lely method (MLM), a sublimation technique. The physical reason for the avoidance of vapor growth techniques for bulk crystals is the huge difference in the particle densities between the two states of aggregation. 

On the other hand, bulk crystals of 4H-SiC and 6H-SiC are made by a physical vapor transport (seeded sublimation growth) technique known as the modified-Lely method [32]. High-quality bulk materials (threading dislocation... 

Bulk SiC substrates made by the Acheson method or the Lely method have been used as the substrates for growth of a-SiC. Recently, SiC wafers sliced from an SiC ingot grown by the modified Lely method have been used. Usually, ((X)01) Si or ((X)01) C surfaces are used. Here, homoepitaxial growth of SiC by CVD using an SiH4-C3Hg-H2 reaction gas system is illustrated... 

Relatively sharp luminescence lines observed near the band edge arise from the recombination of electron-hole pairs that form bound excitons (BEs) at impurity sites or free-to-bound (FB) transitions that involve the recombination of free electrons (holes) with holes (electrons) bound at neutral acceptors (donors). Figure 12 shows the PL spectrum at 1.96 K for an undoped 3C-SiC epilayer grown on Si by CVD (63). In the energy range 2.4-2.2 eV, five sharp lines are seen. Choyke et al. (64) have observed five similar sharp luminescence peaks for a 3C-S1C crystal grown by the Lely method. These peaks have been assigned as the zero phonon line (ZPL, 2.379 eV) and its phonon replicas TA, LA, TO, and LO. They attributed these lines to... 

Maye, Mathew M., Dmytro Nykypanchuk, Daniel van der Lelie, and Oleg Gang. A Simple Method for Kinetic Control of DNA-Induced Nanoparticle Assembly. Journal of the American Chemical Society 128 (2006) 14,020-14,021. The researchers created nanoparticles by attaching the components to complementary strands of DNA. 

AG Burm, F Flaak-van der Lely, JW van Kleef, CJ Jacobs, JG Bovill, AA Vletter, RP van den Heuvel, W Onkenhout. Pharmacokinetics of alfentanil after epidural administration. Investigation of systemic absorption kinetics with stable isotope method. Anesthesiology 81 308—315, 1994. 

The 4H polytype has a wider gap compared to 6H and a much higher electron mobility, making the growth of the 4H polytype of significant practical interest. Favourable properties of this polytype could not be employed in the early studies since the abundance of the 4H polytype in crystals grown by the Lely process is below 1 %. Currently methods of governing the polytype structure permit the intentional growth of this polytype. 

Many microorganisms and plants are capable of transforming toxic chemical species into less toxic forms (e.g., Lytle et al. 1996, 1998 Hunter et al. 1997). Some plants are particularly useful for remediation of contaminants in soils and natural waters because they hyperaccumulate specific toxins (e.g., Van der Lelie et al. 2001 Fuhrmann et al. 2002). In most cases, however, the molecular-scale mechanisms of these transformations or of hyperaccumulation are not known. This is a fertile research field for geochemists and mineralogists that will require multidisciplinary studies and will benefit from SR-based microspectroscopy methods. 

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