Paper IS+AS+MC+SS-TuA11
In Situ Energy Loss Spectroscopy, A Novel Approach to the Characterization of Surfaces during MBE Growth

Tuesday, November 11, 2014, 5:40 pm, Room 313

A new energy analyzer for Auger Electron Spectroscopy (AES), the Auger Probe, is able to operate in growth vacuum chambers to measure in-situ during growth the composition of the surface [1,2,3]. The primary beam is provided by the RHEED electron gun at a very grazing incidence angle (2 to 3 degrees). The analyzer is also used in EELS mode to measure Characteristic Energy Losses (CEL). The use of a grazing incidence angle strongly enhances the strength of the energy losses peaks, which become more prominent than the elastic line

EELS data from the Auger Probe are presented showing the evolution of the CEL distributions during oxidation (ZnO), during thermal de-oxidation of GaSb, and during growth of binary and ternary materials ( GaAsSb ). Surprisingly, even during deposition of homoepitaxial layer, the CEL distribu tions show a marked dependence upon the flux of material to the sample which can reflect the formation of physi- rather than chemisorbed layers and the smoothness of the surface [4].

The CEL spectra cannot be interpreted simply, due to the strong overlapping of multiple excitations of single energy losses. A model is presented that takes into account the probability distribution for multiple losses, and allows extraction of the el ementary energy loss lines from the distribution. Using this model, ac curate energy loss values can be measured and an effective electron density can be calculated. The intensity of the extracted energy losses versus the intensity of the elastic peak is a measure of the ratio d/ l between the electron path length d and mean inelastic free path l of the specific loss. The inelastic mean free path for each loss line can be deducted using d values from monte-carlo simulation of the electron trajectories and the intensity ratio of the loss peak vs. elastic peak.

Special thanks to S. Svensson and W. Sarney of ARL for their collaboration during measurements used in this work.

This work is funded in part by ARO (STTR Phase I - W911NF-13-P-0021A13A-011-0305).

[1] P. Staib, J. Vac. Sci. Technol. B 29(3), (2011).

[2] W.L. Calley, et al. J. Vac. Sci. Technol. B, (2013).

[3] P. Staib in "In situ Characterization of Thin Film Growth", Edited by G. Koster and G. Rijnders, Woodhead Publishing In Materials, (2011)

[4] Strawbridge B., Shinh RK.,Beach C.,Mahajan S., Newman N., J. Vac. Sci. Technol. A 24 (5) 1776 (2006) .