Substrates and Growth Conditions

Two types of pseudosubstrates are currently used for the heteroepitaxial growth of a-plane GaN or AlN layers (1-102) r-plane sapphire [10-16] and 

Further, it should be emphasized that the nature of the active N itself, that is, ammonia or N plasma, drastically influences growth kinetics. Actually, the above considerations on the growth diagram as well as all experimental results reported in this chapter refer to plasma-assisted molecular-beam epitaxy (MBE), active N being obtained by radio frequency cracking of N2 in a plasma cell. 

This suggests that surface diffusion barriers are lower in N-rich conditions than in Ga-rich conditions for (11-20) GaN, which again is the opposite of what is theoretically predicted [25] and experimentally observed [26] in the case of (0001) GaN growth. 

These results are consistent with those reported by Onojima et al. [27]- Two possible causes may account for the anisotropy of the a-plane nitride layers, namely (i) an anisotropy of the strain relaxation in the buffer coming from an in-plane anisotropy of the lattice mismatch between AlN and SiC (-1-1.0% along [1-100] and —1.2% along [0001]) and (ii) the presence of c-plane stacking faults propagating through the nitride layer and emerging at the surface of the buffer, which results in the observed ripples [20, 27]. 

It should be noted that anisotropic growth resulting from anisotropic lattice mismatch has been invoked to account for the spontaneous growth of silicide nanowires on Si [28] and of Ge islands on high-index Si substrates [29]. It is then expected that growth proceeds preferentially along the direction of lesser lattice mismatch, as observed for AlN growth on (11-20) SiC. 

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Allard A-S, M Remberger, AH Neilson (1985) Bacterial O-methylation of chloroguaiacols effect of substrate concentration, cell density and growth conditions. Appl Environ Microbiol 49 279-288. 

A methodology for OUR measurements in wastewater systems was originally developed for the characterization of activated sludge in terms of COD components and process parameters (Ekama and Marais, 1978 Dold et al 1980). It included OUR measurements of the activated sludge under substrate-limited and substrate-nonlimited growth conditions, typically performed by discontinuous addition of wastewater. Development of respirometry principles and techniques has taken place, e.g., motivated for the control of the activated sludge processes (Spanjers et al., 1998). 

As well as the lattice mismatch between the layer and the substrate, other factors influence the FWHM of the RC, including thickness of the buffer layer, miscut of the substrate, substrate quality, growth conditions etc. For example, Warren Weeks et al [16] reported 00.2 FWHMs of 58 and 151 arc sec for 1.4 pm GaN layers grown on on-axis and off-axis (3 - 4° toward the <11.0>) SiC substrates, respectively. The corresponding FWHMs for the 0.1 pm AIN buffer layers were approximately 200 and 400 arc sec. For a thicker GaN layer of 2.7 pm, the off-axis sample also exhibited an FWHM of 66 arc sec. 

An HOD film growth was carried out on 1-inch Si(l 10) substrates [269] using the three-step process. The pretreatment and growth conditions are listed in Table H.3. In this work, (i) there was no apparent grain boundaries in the central area of a diamond film, (ii) an array of misfit dislocations were seen in the periodicity of four D 111 on every three Si 111, and the spacing between the misfit dislocations was... 

Table H.l. Biasing and growth conditions using Si substrates. 

Table H.3. Biasing and growth conditions for HOD film growth on Si(lOO) substrate using the three-step process. 

Transition metals generally have the highest surface free energy, whereas noble metals and semiconductors have substantially lower surface energies. This implies that even if growing of material A on material B works fine, the opposite will not work—a common problem in the fabrication of multilayers with their inherently symmetric structure. Another frequently encountered problem is that of the possibility of interdiffusion at the interface and/or chemical reactions between the deposit and the substrate. It is well known that, especially with the very reactive materials Si and Ge, both can happen, depending on temperature and growth conditions. 

Morphological properties, although crucial in identification, depend (as was the case with yeast) on substrate and other conditions of growth. For example, some molds may appear yeastlike when growing under mi-croaerophilic conditions as would be found in bottled juice. The color of the mold colony is frequently used for preliminary field identification of molds. 

Since CVD-based techniques are free of carbonaceous particles they allow the direct growth of CNTs on substrates. In the work of K.B.K. Teo et ah, carbon nanotube growth was performed by adding acetylene to the NH3 gas flow (at a ratio of typically 20%) for 15 min [62]. If exactly the same catalyst and growth conditions are used in the presence of a plasma discharge (i.e., PECVD), vertically... 

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