D. J. Bottomley

Determination of the crystallographic orientation of cubic media to high resolution using optical harmonic generation

Using the tensorial characteristic of optical harmonic generation it is shown that the crystallographic orientation of centrosymmetric and noncentrosymmetric cubic media can be determined to within ±0.1°. As an illustration of the technique the orientation of vicinal GaAs(001) and Si(111) single‐crystal wafers is obtained using second‐ and third‐harmonic generation, respectively, with a continuously mode‐locked Ti:sapphire laser operating at 775 nm. Intensity measurements were taken as a function of the wafer azimuthal angle and are fit to a truncated Fourier series derived from a phenomenological theory.

Kinetics of oxygen adsorption, absorption, and desorption on the Cu(111) surface

The interaction of oxygen with the Cu(111) surface in ultrahigh vacuum (UHV) has been studied in the temperature range 400<T<800 K using second‐harmonic generation (SHG) and x‐ray photoelectron spectroscopy (XPS). When the clean surface is exposed to oxygen at pressures between 5×10−8 and 10−5 Torr and for T<500 K, the SHG intensity decreases monotonically with exposure by more than one order of magnitude to a value which has no measurable temperature dependence. For T≳500 K, the SHG intensity passes through a minimum before achieving this constant value. The observation of this minimum is interpreted in terms of an outward relaxation of the Cu(111) surface as oxygen penetrates the subsurface region. When UHV conditions are restored for T≳600 K, the SHG intensity reverses its temporal dependence. These observations are consistent with initial incorporation of atomic oxygen into the subsurface region at a rate which is dependent on surface temperature and oxygen pressure and subsequent backdiffusion in UHV...

Second harmonic generation from SimGen superlattices

We report the observation of optical second harmonic generation (SHG) from SimGen short‐period superlattices grown on different substrates. For a 775 nm fundamental beam, the SHG signals from odd‐odd, even‐even, and even‐odd specimens are comparable, apart from substrate‐dependent strain enhancement. It is concluded that the lack of a large bulk dipole‐allowed signal in odd‐odd superlattices predicted by Ghahramani, Moss, and Sipe [Phys. Rev. Lett. 64, 2815 (1990)] is due to the inevitable presence of monatomic steps on the substrate which lead to antiphase domains; a possible circumvention of this limitation is outlined based on the use of a single domain vicinal Si(001) substrate.

Detection of subsurface oxygen on Cu(111): correlation of second-harmonic generation and Auger electron spectroscopy observations

The incorporation of atomic oxygen into the Cu(111) subsurface at pressures of 2.5 × 10−7 < P < 10−2 Torr and temperatures of 300 < T < 800 K is demonstrated using second-harmonic generation and Auger electron spectroscopy. We have also been able to use in situ second-harmonic generation to time-resolve the incorporation of oxygen into the surface as well as its evacuation when high vacuum conditions are restored. It is shown that the temperature at which subsurface to surface transfer becomes significant is around 600 K, below which it is possible to trap the oxygen.

Structural transformations in thin oxide layers on the (211) surface of an Al–Li alloy

Optical second harmonic generation is used in conjunction with Auger electron spectroscopy to study the evolution with temperature T of oxygen adsorbed at 320 K on the clean, annealed (211) surface of an Al–Li alloy with a bulk Li concentration of 6.5 at. %. The oxygen is chemically bonded to form an oxide. The presence of Li at the clean alloy surface increases the rate of oxygen adsorption by a factor of ∼60 relative to pure Al. The oxygen chemisorption rate is consistent with a sticking coefficient of 1 for O2 on the clean unoxidized surface. For all oxygen exposures, the surface oxide film that is formed undergoes two distinct transformations. A structural transformation occurs between T=450 K and T=860 K, depending on oxygen exposure. This transformation exposes bare Al. Between 860 and 905 K, Li diffuses rapidly to the surface, thus increasing the surface concentration of elemental Li, and the remaining surface oxide becomes predominantly Li2O.

On the detection of elemental Li on AlLi alloy surfaces using Auger electron spectroscopy

Abstract We confirm that the KVV transition of elemental Li produces a line at 52 eV in the Auger electron spectrum of Al-Li alloys. This eliminates confusion present hitherto on the labelling of Auger electron spectroscopy (AES) Li spectral lines from AlLi alloy surfaces. A simple procedure is presented for interpreting AES data in order to establish a lower limit on the surface Li concentration. The presence of the elemental Li line at 52 eV means that the Li concentration at the surface of these commercially important alloys can be studied using AES.

Addendum to ‘‘Determination of the crystallographic orientation of cubic media to high resolution using optical harmonic generation’’ [J. Appl. Phys. 74, 6072 (1993)]

Calculations of the optical harmonic response of cubic centrosymmetric and noncentrosymmetric media with arbitrary facial orientation are extended to the general case of s‐ or p‐polarized fun‐ damental beam radiation and s‐ or p‐polarized harmonic beam radiation.

Resonant surface second-harmonic generation on Cu(111) by a surface state to image-potential state transition

The authors present the first observations of resonant enhancement of /spl chi//sup (2)/ from a metal by a surface state-image potential state transition. This conclusion is reached from a systematic experimental investigation of second-harmonic (SH) generation from a clean Cu(111) surface as a function of photon energy, and crystal azimuthal orientation. The authors also suggest that earlier observations of the sensitivity of the SH resonance in Cu(111) to lattice temperature and bombardment of the surface by ions can be explained by a linewidth broadening associated with electrons in surface states scattering into bulk states, consistent with angle-resolved photoemission measurements.<<ETX>>