Influence of Substrate Temperature

In the CVD process, the substrate temperature is a key parameter by heating the substrate, one supplies, directly to the growing surface, additional energy that favorably influences the specific chemical reactions that lead to ZnO growth. 

Lower growth rates around 5-15 A s 1 have been reported for a vertical reactor configuration (see Fig. 6.18b). In this case, the reactant mixture always reaches the substrate at the same location. The growth rate now depends on the quantity of film precursors created in the gas phase during the transfer of the reactants from the gas inlet down to the growing surface. 

LP-CVD ZnO In contrast to AP-CVD processes, LP-CVD processes are kinetically limited, i.e., the growth rate of the film depends mainly on the rate of reactions at the growing surface. These reactions become the limiting factor, because the transport time necessary to carry the reactant from the gas inlet to the growing surface is strongly reduced by choosing the low pressure regime. 

As the speed of the reactions at the growing surface is increased when the temperature is raised, a temperature-dependent growth rate should basically be observed for LP-CVD process. In Fig. 6.19, the deposition rate and the consumption of DEZ (defined as the percentage of DEZ effectively used for ZnO growth, the rest of DEZ being pumped out of the chamber) are shown as a function of the substrate temperature for the LP-CVD process developed at IMT Neuchatel, which operates at 0.5mbar and uses DEZ and water vapors as growth precursors. 

More DEZ is consumed by the growing surface at higher temperatures, leading to an increased growth rate, from less than 15 As-1 at 130°C to more than 40 As-1 at 180°C. Wenas et al. [4], who worked at higher pressures, at the limit between the AP-CVD and LP-CVD regimes (i.e., they worked at 

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When film growth occurs under an excess of zinc, the influence of substrate temperature becomes significant. The expected steady decrease in deposition rate with increasing reactive gas partial pressure is only observed at low substrate temperatures - an increase in rate can already be seen at Ts = 200°C when the reactive gas partial pressure is increased. As a first approximation, the deposition rate in this region is directly proportional to the reactive gas partial pressure, so that for p(O2) = OmPa, no coating would result. 

FIGURE 22. Influence of substrate temperature and oxygen flow rates on the stoichiometry of the films grown by AP-CVD (top) and DLI-CVD (bottom). M = monocUnic phase, B = metastable monocfinic phase appearing in nanocrystalUne form. Reproduced from Reference 325 by permission of Wiley-VCH... 

This work is devoted to study the influence of substrate temperature on CrSi2 island size distribution on Si substrate and the effect of Si layer thickness at MBE process on the formation of Si(l 1 l)/CrSi2 NCs/Si(l 11) heterostructures and CrSi2 NC moving in it. 

Figures 5 and 8 show the influence of substrate temperature on growth rates of diamond in CVD. Clearly, a small change in the substrate temperature can alter the growth rates markedly, especially at higher gas pressures. This is attributable to the Arrhenius behavior of the deposition reactions. Moreover, in both low-temperature and high-temperature regimes, the growth rates are lower.

Figure 1. Time evolution of nucleation density and influence of substrate temperature on nucleation. Gas pressure 30 torr CH4/H2 0.4 vol.% MW power 700 W and substrate temperature (a) 816°C, (b) 716°C and (c) 516°C.t l (Reproduced with permission.)...

Tin oxide films have been deposited onto soda-lime-silica glasses in a cold-wall reactor at substrate temperatures between 350°C and 490°C [108]. The mechanism of formation was carefully studied using four different tin alkyls as starting compounds namely dibutyl tin diacetate (DTD), tetrabutyl tin (TBT), tetraethyl tin (TET) and tetramethyl tin (TMT). The investigations showed for the mechanism a dependence on the molecular structure and reactivity of the initial tin compound to oxygen. The influence of substrate temperature on deposition rate (Arrhenius plots) showed three characteristic regions for which three processes were proposed [108] ... 

Finally, we should address the question of the influence of substrate temperature - thus kinetics - on the template-controlled growth on surfaces. It is quite obvious from the example of the particles in a box (Fig. 1) that temperature strongly influences the structures formed. On the one hand it has to be low enough to allow for the adsorption of the building blocks on the surface (Fig. lb), on the other hand it has to be high enough to provide a sufficient mobility of the entities on the surface in order to avoid a mere hit-and-stick (random) adsorption (Fig. Ic). In that sense the structures formed on surfaces by a template-controlled process will be subject to strong kinetic effects and temperature control will be an important factor (see Sects. 3 and 4). 

Fig. 1.13. The dependence of growth flux on vapor pressure p is illustrated schematically on the left, where pe is the equilibrium pressure of the for vapor, my is the atomic mass of the vapor, Ty is the temperature of the vapor, and k is the Boltzmann constant. The diagram on the right is a schematic microstructure map suggesting the influence of substrate temperature Ts and growth flux on film structure.

Figure 10 Influence of substrate temperature on critical load of TiN film deposited using HCD ion plating. Deposition rate 0.08 pm/min substrate bias voltage —20 V 2.1 pm thick micro Vickers hardness 1650 kg/mm under 10-g load. (From Oishi, 1990.)...

The influence of substrate bias on q and fx can be estimated from (2.10) using the linear region of the log (/ ) versus curve. From the dependence of the inclination on temperature, the values of Hfx are obtained. It is almost independent... 

Since the As antisite is anyway one of the most important defects acting as the compensating donor, the excess As influences substantially the magnetic and transport properties of (Ga,Mn)As. The increase of substrate temperature and the decrease of the As pressure reduces the density of excess As, which result in a decrease of the lattice constant and an increase in both the hole concentration and conductivity. Importantly, this generates a raise of 7c (Shimizu et al. 1999), confirming the critical role of band holes in the ferromagnetism of (Ga,Mn)As. The annealing of (Ga,Mn)As at relatively low temperatures ( 300 K) leads to similar results due to the evaporation of excess As (Hayashi et al. 2001 Potashnik et al. 2001). 

Wang, G, Mu, Y., and Yu, H. Q. 2005. Response surface analysis to evaluate the influence of pH, temperature, and substrate concentration on the acidogenesis of sucrose-rich wastewater. Biochem. Eng J., 23,175-184. 

From the definition of Ao.s, it follows that to.s is inversely proportional to the rate constant of the chemical reaction. The influence of substrate concentration, proton concentration pH), and temperature on the reaction rate can therefore be deduced simply from the variation in For example, the reaction order of the substrate can be determined as - logros/ logCo- Likewise, apparent activation energies, Fa, may be obtained from plots of to,5 against the inverse temperature (T ), since the slope is equal to —E /R [8], Kinetic isotope effects can also easily be... 

The carbon films obtained were diamond crystals (Figure 5.4(a)). The diamond crystals present predominantly a (111) facet. Raman spectrum of the film is shown in Figure 5.4(b). The sharp peaks due to diamond detected at 1335 cm showed the good quality of diamond. The average crystal size is about 10 pm. The influence of the ratio of acetylene to oxygen and of substrate temperature on the qualities and orientation of diamond have been discussed in a previous paper [33]. 

In order to perform a scale-up to the ton scale, optimal conditions for the activity were investigated with respect to the influence of pH, temperature, and substrate concentration. Optimal pH and temperature were established to be 6.9 and 30 °C, respectively. A concentration above 8% CHB had a negative effect on the activity, and methyl CHB (CHBM) was preferred to ethyl CHB. 

Figure 7. Evolution of surface radioactivity from tritiated pancreatic lipase (2 mg/l) after 2.5 min of adsorption. Influence of subphase temperature. Substrate concentration 0.5 mg/m2, pH8UbphQf8e = 8.2. Surface radioactivity is in cpm (counts/minute) (fraction C5).

Evaporation without contamination has today been solved by modem means such as new types of non-reactive boat material and inserts or electron beam guns for refractory metals most difficult to evaporate because of high evaporation temperatures. Condensation, problematic in a few cases, such as Zn, Cd, Ga, Sn, Sb, can be influenced by nucleation and the selection of evaporation speed (generally high) and substrate temperature (generally low). Reactions with the residual gas during condensation which cause undefined film products, difficult to reproduce, can be reduced by decreasing the residual gas pressure and the unwanted gas components, and by correct choice of substrate temperature and evaporation speed [292, 293]. 

In this paper, the Mlchaells-Menten reaction mechanism will be modified to eliminate these and other shortfalls. The modified reaction mechanism will then be used to explore the Influence of substrate concentration on the optimum temperature of blomass-productlon and metabolite-excretion rates. The Influence of dilution rate will also be examined. The scope of analysis will still be confined to processes whose rates saturate In substrate concentration. 

Figure 7. Predicted influence of substrate concentration on the rate of net biomass production, with temperature as a parameter. Parameter values correspond to Figures 3-6. Note shift of optimum temperature to higher values with increasing...

Figure 10. Predicted influence of substrate concentration and dilution rate on the temperature that maximizes the rates of net biomass production and metabolite excretion in batch (d = 0) and continuous (d > 0) culture.

Figure 39 Influence of substrate preheat temperature on the quasi-equilibrium droplet...

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