Metal-insulator boundary

The band diagram of the metal-insulator contact is shown in Fig. 3.7(a) in thermal equilibrium and in Fig. 3.7(b) under an applied bias. The charge carrier density N0 at the boundary (i.e. at the contact) in the insulator is given by [36],... 

The orientational ordering has also been found in other TMTSF compounds having asymmetric anions, such as Re04, NO, FSO, [76]. In these materials the one-dimensional axis, a-axis is doubled by the orientational ordering. Therefore the anion ordering causes a metal-insulator transition because the band gap at the Brillouin zone boundary opens just at the Fermi level. 

Due to the technological importance of metal-insulator-semiconductor (MIS) devices, understanding of the nature of their electrical characteristics such as current-voltage (1-V) and tunnel magnetoresistance (TMR) is of great interest. Unless intentionally fabricated, a silicon Schottky diode possesses a thin interfacial oxide layer between the metal and the semiconductor. Additionally, a density of interface states is always generated at the boundary between the semiconductor and insulator. 

Some Cu NMR studies have been carried out for the organic conductors (DMe-DCNQIjaCu, (DMeO-DCNQI)2Cu, (DBr-DCNQI)2Cu and partiaUy deuterated (DMe-DCNQI-d2[l, l 0])2Cu. The results show that the metallic and insulating states each possess similar electronic and magnetic properties. A systematic measurement of (l/Ti) for Cu failed to identify any specific effect of d-electron correlations near the metal-insulator (Cu-I) boundary. 

A metal/insulator interface plays a significant role in tunneling processes. There are several factors which influence the electron spin-dependent transfer through the potential barrier. Such factors are image potential, presence of different impurities, heterogeneity and boundary roughness. 

As a general rale the plot of W(T) for the metallic, critical and insulator regimes show positive, zero and ne tive slope respectively. It can be observed that at low temperatures the PAni-ES/AMPSA fibre exhibits a metallic profile (i.e. the temperature below which metallic transport is present) less than 10 K. Addition of Cbes shifts the metallic-insulator boundary towards higher temperatures ( 50 K). In addition, the neat PAni-ES/ AMPSA fibre compared with those fibres containing SWNT sustain a... 

Reghu, M., Y. Cao, D. Moses, and A.J. Heeger. 1993. Counterion-induced processibility of polyaniline—transport at metal-insulator boundary. Phys Rev B 47 1758. 

Bowman and Mattes [65] also showed that the low-temperature (<30 K) transport properties indicate that the reduced activation energy had a positive temperature coefficient, which is indicative of this material lying on the metallic side of a disorder-induced metal-insulator phase boundary. The reduced activation energy for these stretched polyaniline fibers is shown in Figure 2.26. Since the slope is negative for all of the godet-stretched fibers, this indicates that these fibers are on the insulating side of the disorder-induced metal-insulator transition. This is in contrast to that observed for the unstretched polyaniline fiber, which lies on the metal side of the disorder-induced metal-insulator transition. 

The data obtained allows us to conclude that highly doped PANI-SA and PANI-HCA are Fermi glasses with electronic states locahzes at the Fermi energy due to disorder, whereas PANI-TPSA and PANI-CSA are disordered metals on the metal-insulator boundary, so that the metallic quality of the emeraldine form of RANI grows in the series PANI-HCA —> PANI-SA —> PANI-PTSA —> PANI-CSA. 

Q.p = 9970 cm-1 (1.17 eV), 1/t = 4340 cm- (0.51 eV), and fcf A = 1.6 with an assumption of C = 1. These parameters are reasonable. The plasma frequency is close to that obtained from the reflectance minimum ( 1.4 eV) and the peak in the loss function ( 1.1 eV). The value of fcf A (= 1.6) indicates that PANI-CSA is not a good metal [1160]. Instead, this fact supports that PANI-CSA is on the metal-insulator boundary and approaching the loffe-Regel limit. Moreover, the deviations from simple Drude behavior in the far-IR are quantitatively consistent with the LMD model [1160, 1161]. As indicated by Eq. (4.18), localization depresses o(w) below the Drude curve in the far-IR. 

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