Tunneling doped

The 3(X) — 4.2 K relaxation rate data for the PSS-doped complex were fitted to two different theoretical models. According to the model by Hopfield [172], electron tunneling between two molecular states is considered which are only very weakly interacting. The rate of tunneling between the two states a and b,... 

Nanomaterials can also be tuned for specific purposes through doping. Specifically, the effect of the presence of manganese oxides on photocatalysis involving primarily titanium dioxide will be considered in this section. Titanium dioxide is a well-known photocatalyst and will be considered separately. K-OMS-2, which has a cryptomelane structure, is illustrated in Figure 8.4. Not all the literature discussed in this section, however, involves OMS tunnel structure materials. For example, amorphous manganese oxide (AMO) is also discussed as a photocatalyst. Manganite (MnOOH) is also included in battery applications. 

When Es > FB, region (b), a depletion layer forms in the semiconductor due to the bending of the bands under the influence of the electric field. Increasing the potential increases this band bending and so increases the effective barrier to tunnelling it represents. However, the high doping level... 

The electrical contact with the bulk of the doped crystal is made through a very heavily doped layer, to reduce the height of the Schottky barrier between the bulk and the metal of the external contact (Au). The charge carriers cross this layer by tunnel effect. 

When the semiconductor is highly doped, the space-charge region is thin, and electrons can tunnel through the barrier formed at a depletion layer. 

For moderately doped substrates the crossover from tunneling to avalanche breakdown occurs at pore diameters of about 500 nm, corresponding to a bias in excess of 10 V. Above doping densities of 1017 cm-3 breakdown is always dominated by tunneling. Tunneling is therefore expected to dominate all pore formation in the mesoporous regime and extends well into the lower macropore regime, while avalanche breakdown is expected to produce structures of macropor-ous size. 

The formation of pores during anodization of an initially flat silicon electrode in HF affects the I-V characteristics. While this effect is small for p-type and highly doped n-type samples, it becomes dramatic for moderate and low doped n-type substrates anodized in the dark. In the latter case a reproducible I-V curve in the common sense does not exist. If, for example, a constant potential is applied to the electrode the current density usually increases monotonically with anodization time (Thl, Th2]. Therefore the I-V characteristic, as shown in Fig. 8.9, is sensitive to scan speed. The reverse is true for application of a certain current density. In this case the potential jumps to values close to the breakdown bias for the flat electrode and decreases to much lower values for prolonged anodization. These transient effects are caused by formation of pores in the initially flat surface. The lowering of the breakdown bias at the pore tips leads to local breakdown either by tunneling or by avalanche multiplication. The prior case will be discussed in this section while the next section focuses on the latter. 

Monsma DJ, Parkin SSP (2000) Spin polarization of tunneling current from ferromagnet/ AI2O3 interfaces using copper-doped aluminum superconducting films. Appl Phys Lett 77 720-722... 

Wu, X. L., and Lieber, C. (1990). Direct characterization of charge-density-wave defects in titanium-doped TaScj by scanning tunneling microscopy. Phys. Rev. B 41, 1239-1242. 

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