C.R. Helms

Surface segregation in alloys: Existence of surface miscibility gaps within regular solution theory

Much attention has been paid to the relationship between the bulk phase diagram and the phenomena of surface segregation. There is no reason to believe, however, that the equilibrium phase boundaries for the surface region are identical to those of the bulk. In this paper, we have derived the surface phase boundaries within the regular solution approximation using pairwise interactions. We find that the concept of phase separation for the surface region is not important if the surface phase is in equilibrium with the bulk and the bulk is in a region of solid solubility. The experimental conditions employed in some studies, however, lead to nonequilibrium states (due to quenching). For these cases, surface phase separation may be expected under typical experimental conditions.

New studies of the Si-SiO2 interface using auger sputter profiling

Abstract We have made new measurements of the morphology and chemistry of “state of the art” thermally grown Si-SiO 2 interfaces using Auger sputter profiling. With improved experimental technique and theoretical treatment of electron escape depth and ion knock-on effects, we find the width of the interface to be about 2.0 nm. This width is probably due to an undulating interface, the period of which is less than 100 μm. Any SiO x present resides in a connective layer no greater than 0.8 nm thick at any point.

An elementary model of neutral and ion sputtering yields

Abstract We have recently developed a simple statistical model of sputtering which indicates that the magnitudes of elemental sputtering yields are consistent with a neutralization model of atom emission. In this model, displaced ion cores at the target surface have a finite probability of neutralization; unneutralized ions must surmount an additional coulombic barrier and therefore have a much reduced probability of escape. The neutral yield will be proportional to the probability of neutralization. The positive ion yield will be proportional to one minus this probability. These suppositions are supported by experimental data in the literature. We also suggest that oxidation enhancement of positive and negative ion yields may result from a reduction of the coulombic force.

A surface spectroscopic study of reactive ion bombardment of silicon

Abstract In this paper we report on a surface spectroscopy and etch yield study of the bombardment of Si by CF 3 + , SF 5 + and CH 4 + . The bombardment of Mo by CF 3 + is also discussed. Ion energies in the range of 0.5 to 3.0 keV were studied. Bombardment by SF 5 + yielded the lowest etchant surface concentrations and the smallest deviation from predicted etch yields. The highest surface concentration of etchant was found with CH 4 + bombardment. These observations are consistent with the conclusion that the etch yields are explained by physical sputtering perturbed by the formation of involatile surface layers.

The effect of surface composition on the surface electronic structure of the CuNi alloys: A study by UPS

Abstract We report a.u.v. photoemission study of the surface electronic structures of the well annealed and argon sputtered surface of Cuue5f8Ni alloys. The UPS results indicate substantial Cu enrichment on the annealed alloy surface, in agreement with previous AES measurements. Furthermore, individual peaks in the surface electronic structure can be associated with the Ni or Cu component of the alloy, in accord with the CPA theory and the more recent ATA theory.

Auger analysis of Si sputtered with Ar+ ions in an F2 ambient

Abstract Ar + ion sputtering of undoped polycrystalline Si films in an F 2 ambient has been studied using in-situ Auger electron spectroscopy. An enhancement to the physical sputtering yield was observed at all energies from 300 to 2000 eV with an Ar + ion beam current of 10 microA/cm 2 and F 2 pressure of 3.2 × 10 −5 Torr. The enhancement increased at higher energies, while the F surface coverage decreased. A second order mass balance model is proposed to explain the F coverage and sputter yield data. At a fixed ion energy, the chemical yield appears to be proportional to the square of the F surface coverage.

The Effect of Electrostatic Screening on Energy Positions of Spectra Near SiO2/Si Interfaces

XPS and Auger spectra of thin SiO2 films grown on Si substrates are shifted when compared with those from thick oxide films. The spectral features associated with the SiO2 films are shifted towards lower binding energies as the thickness of the film-decreases. Using an electrostatic image charge calculation it can be shown that a large part of these spectral shifts may simply be due to the proximity of the semiconducting substrate. This brings into question any model of the SiO2/Si interface based on these shifts.