Crystal Quality Improvement

Figure 11 shows the DSD density of GaAs grown on Si substrate revealed by electron beam-induced current (EBIC) measurement for various TCA temperature. The DSD density decreases with increasing the TCA temperature gradually and is on the order of 10 cm at 1000 C. The crystal quality improvement by the relatively high TCA temperature... 

In samples prepared later on with better optical quality W. Schmid observed a different behaviour [120]. The damping became stronger with lower repetition rates, i.e. higher peak intensity. No thermo-optic effect was observed. This can be well explained by the advances in crystal preparation solvent inclusions were reduced and the crystal quality improved, resulting in a lower absorption coefficient at the same, near-resonant wavelength (e.g. 720 nm). So, the absorbed heat load and the thermo-optical coefficients were reduced concurrently. 

The crystal quality of the InGaN QWs becomes poor mainly due to the lattice-constant mismatch and the difference of the thermal expansion coefficient between InN and GaN with increasing the In composition [4,5]. Therefore, in order to improve the external quantum efficiency (i/ext) of the InGaN-based LEDs and LDs, it is important to elucidate and optimize the effects of the various growth conditions for the InGaN active layer on the structural and optical properties. Recently, we reported a fabrication of efficient blue LEDs with InGaN/GaN triangular shaped QWs and obtained a substantial improvement of electrical and optical properties of the devices [6,7]. 

In the early days of silicon device manufacturing the need for surfaces with a low defect density led to the development of CP solutions. Defect etchants were developed at the same time in order to study the crystal quality for different crystal growth processes. The improvement of the growth methods and the introduction of chemo-mechanical polishing methods led to defect-free single crystals with optically flat surfaces of superior electronic properties. This reduced the interest in CP and defect delineation. 

Saridakis, E. and Chayen, N. E. (2000). Improving protein crystal quality by decoupling nucleation and growth in vapor diffusion. Protein Sci. 9, 755-757. 

Initial screens can be distinguished between methods that are used to determine what factors are most important, and follow-up screens that allow optimization and improvement of crystal quality (Table 14.1). In experimental design, this is known as the Box-Wilson strategy (Box et al., 1978). The first group of screens is generally based on a so-called factorial plan which determines the polynomial coefficients of a function with k variables (factors) fitted to the response surface. It can be shown that the number of necessary experiments n increases with 2 if all interactions are taken into account. Instead of running an unrealistic, large number of initial experiments, the full factorial matrix can... 

Since we had to irradiate crystals within their growth solution in their original orientation, and at the same time to avoid other crystals in close proximity, we were strongly dependent not only on the intensity and the stability, but also on the size and shape of the incident beam. As a consequence, improvements in the quality of the data collection facilities were needed, alongside our efforts to improve the crystal quality. 

Improving Crystal Quality Through Postcrystal Analysis 127... 

Improving Crystal Quality Through [/ Postcrystal Analysis... 

Crystallization additives are a common method to improve crystal quality in proteins (McPherson and Cudney, 2006). With RNA, it is common to screen a series of different cations, as their role in RNA structure and catalysis is well documented for many RNA and RNA-protein systems (Pyle, 2002). Since various cations will interact with the RNA differently, our lab uses a cation screen comprised simple metal cations and polyamines (Table 6.1). Each solution in this table is a lOx stock that is added to an optimized condition (or one found in a sparse matrix) and the set of 24 conditions assessed for potential improvement in crystal quality. 

Alternatively, use the warm air from a hair dryer to dry the matrix from a distance of about 30 cm. Thus, the sample dries faster forming smaller more homogeneous crystals. This improves the quality of the spectra on some instruments. 

The economy of melt crystallization processes depends on the product purity, which is normally increased by an additional cleaning step. The application of gases under pressure is investigated to show possibilities of product quality improvement. Experimental devices for the determination of the freezing curve under gas pressure and for a solid layer crystallization process are shown. The influence of gas and pressure in respect to the freezing curve are explained on the basis of two binary mixtures (trioxane/water and para-/meta-dichlorobenzene) under CO2- and N2- pressure are presented. Furthermore the results of solid layer crystallization experiments with naphthalene/biphenyl and para-/meta-dichlorobenzene mixtures are shown. 

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