Barrier height systematics

A systematic study was conducted on clean Si(lll) surface with a clean W tip (Chen and Hamers, 1991). The entire curve of the dependence of the measured apparent barrier height, Eq. (8.27), with z-piezo displacement, was recorded. The experiment was performed under the condition that a clear 7X7 pattern was observed, which indicated that both the tip (near the apex atom) and the sample were clean. By carefully moving the tip back and forth, so as not to press into the sample surface too deeply, the entire process is completely reversible. The experimental barrier height measurements were performed using an ac modulation method, by applying a small 0.05 A modu-... 

Experimental determinations of barrier heights on oxide semiconductor interfaces using photoelectron spectroscopy are rarely found in literature and no systematic data on interface chemistry and barrier formation on any oxide are available. So far, most of the semiconductor interface studies by photoelectron spectroscopy deal with interfaces with well-defined substrate surfaces and film structures. Mostly single crystal substrates and, in the case of semiconductor heterojunctions, lattice matched interfaces are investigated. Furthermore, highly controllable deposition techniques (typically molecular beam epitaxy) are applied, which lead to films and interfaces with well-known structure and composition. The results described in the following therefore, for the first time, provide information about interfaces with oxide semiconductors and about interfaces with sputter-deposited materials. Despite the rather complex situation, photoelectron spectroscopy studies of sputter-deposited... 

Finally, semiempirical MR-CI calculations based on analytic gradients are sufficiently fast for on-the-fiy determinations of excited-state trajectories, which are essential for more detailed information on the mechanisms of organic photoreactions. Because the results of such studies depend on barrier heights, semiempirical methods will not reproduce quantitative aspects correctly, but studies based on suitable model potentials as well as systematic studies of structural variations and substituent effects might be very valuable in getting deeper insight into the details of organic photoreactions. 

In summary, DFT-calculated barrier heights and spectroscopic constants using model complexes give good reproducibihty of experimental data. Generally, the deviation from experiment is systematic rather than random. 

The calculations are CASSCF/multireference single and double excitation Cl (MRCI). The use of the MRCI method for computing potential energy surfaces is supported by full Cl studies as discussed by Bauschlicher, Langhoff, and Taylor in another article in this volume. The accuracy of this approach has also been demonstrated for reaction (2) by Walch [2], who showed that by systematically expanding the active space and basis set, the computed barrier height converged to the currently accepted value [14]. 

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