Showing papers on "Scanning tunneling spectroscopy published in 1980"

The temperature dependence of rotational tunneling

Abstract: In the last few years tunneling transitions have been observed for the highly symmetric groups CH4, CD4, NH4+, and CH3 rotating in various environments. Typically the tunneling lines shift to lower energies with increasing temperatures. In this paper the shift of the tunneling energy is calculated in a microscopic approach to the problem. The coupling of the rotating groups to the lattice modes is studied in two stages. First the rotating group is coupled to a single oscillator, then to the modes of a Debye crystal. The first calculation leads to a set of discrete tunneling lines with an energy that diminishes as the oscillator is excited into higher levels. The second approach yields a single tunneling line shifted down-wards with increasing phonon population. The shiftΔ ω is proportional toT4. The calculation explains the energy shift of the tunneling lines with reasonable values for the coupling parameters. In some cases also a broadening has been observed which does not follow from our calculations.

Rotational tunneling in methane (CD4): Isotope effect

Abstract: Well‐defined tunneling lines in the μeV range have been observed in CD4 at T=4 K by high resolution neutron scattering. The observed change of tunneling energies by about a factor 50 upon deuteration is in good accord with a theoretical estimate. The symmetry of the neutron scattering operator implies a selection rule.

Resonant tunneling spectroscopy in Schottky diodes

Abstract: A new method to detect deep centers close to the interface in metal‐semiconductor contacts is reported The presence of humps in the logIF‐ VF characteristics attributed to resonant tunneling contributions to the total forward current is investigated via the slope changes in the logIF‐ VF plots Although the relation between the voltage VFm at which the minimum of d2 logIF/ dV2F occurs, and the energy position of the levels causing the resonant tunneling current is not easy to calculate, this new method represents a powerful means to detect traps lying near the interface

Observation of spin-polarized tunneling in thin proximity-effect sandwiches

Abstract: Use of a tunneling Hamiltonian model for thin proximity-effect sandwiches in high parallel fields has indicated the possibility of spin splitting the quasiparticle density of states past the point where the up- and down-spin densities of states will cross. This crossing is signified by a large zero-bias peak in the tunneling conductance. In this paper we review the theory leading to this prediction and present the results of spin-polarized tunneling experiments in Al-oxide-Mg-Al junctions. Measurements at 0.4 K on a sandwich with 40 A of Al over 25 A of Mg at fields from zero to 3.4 tesla (where the sandwich went into the normal state) were in qualitative agreement with the theoretical predictions, including the peak at zero bias at the higher field values.

DC Tunneling Spectroscopy to Determine the Distribution of Interface States

Abstract: A method to determine the interface state distribution in an MOS structure with degenerate p-type semiconductor from the dc tunneling current is proposed and applied to metal/SiO2/p++-Si structure. The main feature of the present method is the use of the theory of tunneling developed by Freeman and Dahlke with some modification. The (Au/Ti)/SiO2/p++-Si was prepared by thermal oxidation in wet O2 at 800°C. It has been found that σtNss (σt is the tunneling capture cross-section and Nss the density of states per unit energy and unit area) varies concavely against the energy over the whole band gap of p++-Si and the interface state distribution obtained by the present method is consistent with that obtained for an MOS structure with thick SiO2 film provided σt is independent of energy. These features are found for both annealed and unannealed samples.