M.P. Nadesalingam

Stability of Se passivation layers on Si(001) surfaces characterized by time-of-flight positron annihilation induced Auger electron spectroscopy

The stability of the selenium passivation layer on the Si(001) surface was investigated using a nondestructive surface-sensitive technique: time-of-flight positron annihilation induced Auger electron spectroscopy. After 10days of exposure in the air, the Se passivation layer was observed to incorporate some oxygen but to remain largely intact. Part of the adsorbed oxygen was desorbed during annealing up to 400°C in the ultrahigh-vacuum environment. However, some oxygen remained on the surface until high-temperature annealing at 1030°C. We posit that the oxygen that remained after the low-temperature anneals was chemisorbed on the Si surface at defects in the Se passivation layer. The Se passivation layer was stable up to an annealing temperature of ∼800°C before desorbing from the surface. The stability of the Se-passivated Si(001) surface is attributed to the saturation of the Si dangling bonds on the surface and to the strong Se–Si bonds.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The PAES intensity then decreases monotonically as the annealing temperature is increased to ∼550 °C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M2,3VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface‐trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost...

Studies of Positrons Trapped at Quantum‐Dot Like Particles Embedded in Metal Surfaces

Experimental studies of the positron annihilation induced Auger electron (PAES) spectra from the Fe‐Cu alloy surfaces with quantum‐dot like Cu nanoparticles embedded in Fe show that the PAES signal from Cu increase rapidly as the concentration of Cu is enhanced by vacuum annealing. These measurements indicate that almost 75% of positrons that annihilate with core electrons due so with Cu even though the surface concentration of Cu as measured by EAES is only 6%. This result suggests that positrons become localized at sites at the surface containing high concentration of Cu atoms before annihilation. These experimental results are investigated theoretically by performing calculations of the “image‐potential” positron surface states and annihilation characteristics of the surface trapped positrons with relevant Fe and Cu core‐level electrons for the clean Fe(100) and Cu(100) surfaces and for the Fe(100) surface with quantum‐dot like Cu nanoparticles embedded in the top atomic layers of the host substrate. E...

Studies of oxidation of the Cu(100) surface using low energy positrons

Changes in the surface of an oxidized Cu(100) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the positron annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300° C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600° C. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface‐trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron‐positron correlations effects. Possible explanation for the observed behavior of the intensity of positron annihilation induced Cu M2,3VV Auger peak with changes of the annealing temperature is proposed.