Field sensitive temperature dependence

However, great care must be taken in choosing an appropriate sample holder and a suitable sample geometry.9 Cylindrical capsules machined from high-purity PTFE, enclosed in long polyethylene straws, allow the measurement of compressed polycrystalline samples or even solutions. Polycrystalline samples need to be pulverized so that preferential orientation can be avoided. The sample should be placed into a cylindrically shaped sample holder. Air-sensitive compounds can be sealed in small tubes from synthetic quartz glass. The field- and temperature-dependent contribution of the sample holder must be known precisely. 

Special attention is paid to transport properties (resistance and Hall effect) because they are very sensitive to external parameters being the base for working mechanisms in many types of sensors and devices. The magnetic field and temperature dependences of resistance and Hall effect are considered in the framework of the percolation theory. Various types of magnetoresistances such as giant and anisotropic ones as well as their mechanisms are under discussion. 

The temperature sensitivity of the saturation velocity, Vsat, used in Eq. (4.5) to describe the effect of the lateral field, is additionally considered. The saturation velocity is moderately affected by temperature changes however, when the temperature largely deviates from Tnom. there is a strong effect on the saturation region characteristics of the transistor. The temperature dependence of the saturation velocity is taken into account using the temperature coefficient, AT, [BSIM 3.v3,129] ... 

Figure 27 presents values of W(T) calculated by Dietl et al. (2001a) in comparison to the experimental data of Shono et al. (2000). Furthermore, in order to establish the sensitivity of the theoretical results to the parameter values, the results calculated for a value of Xc that is 1.8 times larger are included as well. The computed value for low temperatures, W = 1.1 /xm, compares favorably with the experimental finding, W = 1.5 fim. However, the model predicts a much weaker temperature dependence of IV than observed experimentally, which Dietl et al. (2001a) link to critical fluctuations, disregarded in the mean-field approach. 

The theory predicts a strong dependence of photogeneration efficiencies on the field and it approaches unity at high field. The temperature sensitivity decreases with the increase in field. The theory has found satisfactory explanations in the photogeneration process in many organic disordered systems, such as PVK (Scheme la) [25], and triphenylamine doped in polycarbonate [26], Figure 4 shows an example of the field dependence of c() calculated from Eq. (22) (the solid lines) to fit the quantum efficiency data at room temperature for hole and electron generation in an amorphous material. The material consists of a sexithiophene covalently linked with a methine dye molecule (compound 1) (Scheme 2). 

---