Electron-stimulated desorption: Principles and applications

Molecular beam experiments on model catalysts

Studies of the chemistry that occurs on the nanosurfaces of size-selected silicon clusters reveal a number of fascinating qualitative similarities to the behavior of bulk surfaces. However, silicon clusters containing up to 70 atoms appear to be much less reactive than bulk silicon surfaces. This unexpected result suggests that these large silicon clusters are not just small crystals of bulk silicon, but have much more compact geometric structures

https://science.sciencemag.org/content/sci/252/5009/1085.full.pdf

Nanosurface Chemistry on Size-Selected Silicon Clusters

The interaction of molecular and atomic oxygen with Si(100) and Si(111)

The theory of electronically non-adiabatic processes in atom scattering on surfaces of solids, in particular metals, is reviewed. It is assumed that resonant tunnelling of electrons between an electronic orbital of the adatom and the conduction band of the substrate is the dominant charge exchange mechanism. The kinetic energy of the adatom is assumed to be in the intermediate range (eV to keV), which makes it possible to treat the adatom trajectory classically and to obtain a time-dependent electronic Hamiltonian. The aim of the theory is to find the deviations from adiabaticity, i.e. the fraction of the minority charge states of the atom after scattering and the spectrum of the electron-hole pairs created in the substrate. Under some simplifying approximations, these quantities can be calculated explicitly. Their dependence upon the adatom velocity and other parameters of the model is analysed, with particular attention paid to features which are characteristic of an extended substrate, in contrast to atom-atom or atom-molecule scattering. The present understanding of more complete models, for example inclusion of the intra-atomic Coulomb correlation, is also reviewed.

https://iopscience.iop.org/article/10.1088/0034-4885/52/6/001/pdf

Theory of electronic processes in atom scattering from surfaces

Direct evidence has been obtained for electron tunneling between sputtered Cs/sup +/ ions and the solid surfaces from which they originate. Strong neutralization of the Cs/sup +/ ions is observed whenever the tunneling channel is opened by changing the surface work function so that a crossing of the Fermi level by the Cs 6s level occurs. A tunneling model which takes the spatial dependences of the position and the width of the atomic level into account explains the data successfully.

Direct Evidence of Electron Tunneling in the Ionization of Sputtered Atoms

The velocity dependence of the ionization probability of sputtered ${\mathrm{O}}^{\ensuremath{-}}$ from chemisorbed oxygen layers on V and Nb is studied. The ionization probability is found to depend on the normal component of the emission velocity, which suggests that the ionization process is an ion-surface interaction and not an ion-atom binary interaction. For ${v}_{\ensuremath{\perp}}g1\ifmmode\times\else\texttimes\fi{}{10}^{6}$ cm/sec, the ionization probability shows an exponential dependence on ${v}_{\ensuremath{\perp}}$. However, this velocity dependence fails at lower velocities.

Velocity Dependence of the Ionization Probability of Sputtered Atoms

We have studied the static-mode ion-beam sputtering of ${\mathrm{Si}}^{+}$ from a Si (100) surface during oxidation and nitridation. The data are consistent with the ionization of sputtered atoms resulting from the breaking of the local chemical bond during sputtering. A model is proposed to explain the dependences of the ionization probability of the ionization potential, emission energy, and isotopic mass.

Bond breaking and the ionization of sputtered atoms.

The reaction of oxygen on Si(100) surfaces from 700 to 950\ifmmode^\circ\else\textdegree\fi{}C has been studied in real time with about 10-\ensuremath{\mu}s resolution, by use of pulsed molecular-beam reactive scattering. The oxygen reaction probability is roughly proportional to the normal component of the incident ve- locity of the ${\mathrm{O}}_{2}$ molecule. An intermediate step between the initial adsorption of oxygen and the desorption of SiO was observed.

Real-time study of oxygen reaction on Si(100).

We have studied the surface reactions of WF6/SiH4 mixtures on Si(100) that are relevant to the chemical vapor deposition of tungsten using x‐ray photoemission and molecular‐beam reactive scattering. The overall reaction is found to be 3SiH4+2WF6→2W+3SiF4+6H2 with very little production of HF. The reaction proceeds by repeating the cycle of tungsten deposition by the reaction of WF6 with silicon, and the deposition of silicon by the reaction of SiH4 with the fluorinated tungsten surface.

Ming L. Yu

Papers

Direct Evidence of Electron Tunneling in the Ionization of Sputtered Atoms

Velocity Dependence of the Ionization Probability of Sputtered Atoms

Bond breaking and the ionization of sputtered atoms.

Real-time study of oxygen reaction on Si(100).

Gas/surface reactions in the chemical vapor deposition of tungsten using WF6/SiH4 mixtures