Sheet electron concentration

FIGURE 3 Sheet electron concentration versus dose for 100 keV Si-implanted GaN annealed at 1100°C (after [7]). 

What happens if one sprinkles electrons onto the surface of liquid helium Surprisingly the electrons are not absorbed into the bulk of the fluid, but form a quasi-two-dimensional sheet of electrons concentrated at some distance above the helium sm-face. In general, electrons hovering above the surface of a dielectric are called surface state electrons. An excellent review of surface state electrons is that by Cole (1974). 

Electron diffraction studies [3] have revealed that hexagons within the sheets are helically wrapped along the axis of the nanotubes. The interlayer spacing between sheets is 0.34 nm which is slightly larger than that of graphite (0.3354 nm). It was dso reported [2] that the helicity aspect may vary from one nanotube to another. Ijima et al. [2] also reported that in addition to nanotubes, polyhedral particles consisting of concentric carbon sheets were also observed. 

The optimised interlayer distance of a concentric bilayered CNT by density-functional theory treatment was calculated to be 3.39 A [23] compared with the experimental value of 3.4 A [24]. Modification of the electronic structure (especially metallic state) due to the inner tube has been examined for two kinds of models of concentric bilayered CNT, (5, 5)-(10, 10) and (9, 0)-(18, 0), in the framework of the Huckel-type treatment [25]. The stacked layer patterns considered are illustrated in Fig. 8. It has been predicted that metallic property would not change within this stacking mode due to symmetry reason, which is almost similar to the case in the interlayer interaction of two graphene sheets [26]. Moreover, in the three-dimensional graphite, the interlayer distance of which is 3.35 A [27], there is only a slight overlapping (0.03-0.04 eV) of the HO and the LU bands at the Fermi level of a sheet of graphite plane [28,29],... 

A problem with the two correlations is that they are highly correlated with each other. Changing carrier concentration is changing the number of electrons in the Cu3dx2 y2-02p d band. Thus, we expect that the Cu-O distance in the Cu02 sheets will increase as the number of electrons increases regardless of whether the copper oxide is n-type or p-type. 

The TOP principle is based on generating a thin sheet of electron-hole pairs near the surface of the sample—usually a high-resistivity semiconductor with negligible thermal equihbrium-carrier concentration, sandwiched between two electrodes, one of which is semitransparent, as shown in Fig. 4.1. 

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