D.C. Peacock

Scatter diagrams in energy analysed digital imaging: application to scanning Auger microscopy

In order to improve methods for the systematic characterization of inhomogeneous materials the procedures of multi‐spectral imaging and scatter diagram construction have been deployed. Although the techniques described are relevant to all instruments which detect signals on several different information channels (e.g. wavelength or energy analysed optical, X‐ray or electron imaging), they are illustrated with scanning Auger microscopy (SAM). The construction and use of bivariate correlation diagrams is described by reference to simple samples consisting of patterns of Al film upon Si substrates. The method is then applied to LaNi5 and GaInAs samples each with different signal/noise ratios and chemical characteristics. The software windowing of scatter diagrams by computer combined with presentation of false colour images is demonstrated. The multi‐spectral Auger mapping (MUSLAM) procedure thus evolved is demonstrated to be a powerful, general analytical technique for characterizing the number, abundance and chemistry of each type of region in the surface of an inhomogeneous solid.

Scanning auger electron microscopy with high spatial or high energy resolution

Abstract An all-electrostatic, computer controlled, high spatial and high energy resolution, scanning Auger electron microscope incorporating a RHEED camera is described. The electron column has a 50 nm spatial resolution at 55 mm working distance. The energy analyser allows high energy resolution of up to 630 or constant energy windows of down to 1 eV over the energy range of 20 eV to 1000 eV. A system software allowing flexibility of the computer control is described. 128 × 128 pixel Auger images of Al and SiO 2 , with frame scan times of the order of 8 min, are presented.

Instrumental effects in quantitative Auger electron spectroscopy

Abstract Experiments used to determine the energy resolution, field of view, depth of field and instrumental response of a concentric hemispherical analyser (CHA) are described. The effect of analysis energy on the size and shape of the field of view is investigated using a procedure which employs the imaging facilities of a scanning Auger electron microscope. The transmission of the CHA, for different input lens retardation ratios, is found, firstly, in an experiment using a thermionic electron source and, secondly, using the departure from linearity of spectra plotted in a log N ( E ) vs log E form. Such a plot is found to provide a convenient and sensitive method of detecting possible sources of error, such as mispositioning of the sample surface or electrostatic charging of material in the specimen region. These findings indicate the need for careful mechanical alignment of the spectrometer and for the sample surface to be positioned reproducibly within ±200 μm of the centre of the CHA field of view to ensure an accuracy of better than ±10% in estimates of Auger current. A procedure for repositioning the specimen to give a reproducibility of ca +2% in signal measurement is deduced. Computer techniques, to correct for effects of both spectrometer transmission and detector efficiency, are described.

An AES, SAM and RHEED study of InP(110) subjected to ion bombardment and annealing treatments

Abstract It has been found that preferential sputtering of P from InP(110) is pronounced at low Ar ion energies (500 eV) but that for higher ion energies (ca 3 keV) no departure from the stoichiometric surface composition is observed. Annealing of the disordered surface produced by bombardment causes agglomeration of In atoms into microdroplets accompanied by a reordering of the remaining surface regions which, after the loss of In to the droplets, have a near stoichiometric composition. Reordering involves the formation of randomly oriented crystallites which at higher temperatures align with the underlying InP crystal structure to form flat ordered surface regions. These regions give rise to LEED and RHEED patterns essentially similar to those from the (110) cleavage surface despite the non-stoichiometric large-area composition.

On the role of rare earth additives in the oxidation of superalloys

Abstract The surface segregation of zirconium in a NiCrAlZr(0.5% Zr by weight) is reported for the first time. After in situ annealing of the alloy in a Scanning Auger Microscope (SAM) to above 690 K for 16 h, zirconium has segregated over the two surface phases. An AES estimate of the segregated zirconium shows it to be in a film of about 1 nm thick. The surface of the unheated alloy showed no zirconium using SAM, despite the presence of zirconium-rich precipitates (1–2 μm) observed on the alloy surface using EPMA.

Some strategies for quantitative scanning Auger electron microscopy

The general applicability of power law forms of the background in electron spectra is pointed out and exploited for background removal from under Auger peaks. This form of B(E) is found to be extremely sensitive to instrumental alignment and to fault-free construction - an observation which can be used to set up analyser configurations in an accurate way. Also, differences between N(E) and B(E) can be used to derive a spectrometer transmission function T(E). The questions of information density in an energy-analysing spatially-resolving instrument are addressed after reliable instrumental characterization has been established. Strategies involving ratio histograms, showing the population distribution of the ratio of a pair of Auger peak heights, composition scatter diagrams and windowed imaging are discussed and illustrated.