We demonstrate the essential principles for performing a novel form of metastable-atom microscopy, namely focusing and scanning of a He 2(3)S beam. A magneto-optical lens, in conjunction with time-varying magnetic field components, has been used to scan a beam of He 2(3)S atoms across a sample surface in a manner analogous to other scanning probe techniques. The instrument developed is the first to apply methods in the laser manipulation of atoms specifically to the study of surfaces. With the lens in its current arrangement, a beam of He 2(3)S atoms with an intensity of similar to 6 x 10(12) atoms s(-1) cm(-2) may be directed anywhere within a sample area of similar to 64 mm(2) at a focal distance of 1.4 m and with a focal spot full-width at half-maximum of < 2 mm. Such control over the intensity and position of the He 2(3)S beam greatly benefits the surface analysis technique of metastable de-excitation spectroscopy, as demonstrated with example spectra from a clean Si( 1 1 1) 7 x 7 surface.

This article discusses an electron energy analyzer with a cylindrically symmetrical electrostatic field, designed for rapid Auger analysis. The device was designed and built. The best parameters of the analyzer were estimated and then experimentally verified.

This paper discusses an electron energy analyzer with a cyli ndrically symmetrical electrostatic field, designed for rapid Auger analysis. The device was designed and built. The best parameters of the analyzer were estimated and then experimentally verified.

Details of a new approach for performing metastable de-excitation spectroscopy are given. A beam of metastable (2S3) helium atoms, produced in a hollow cathode dc discharge, is collimated and subsequently focused using Doppler cooling of the 2S13–2P23 transition at 1083nm, forming an intense probe of up to 1×1012atomss−1cm−2. The large distance (2.5m) between source and sample means that the beam is relatively free of UV photons and 2S1 metastable atoms, removing the need for quench lamps and chopper wheels. As well as providing a clean high intensity source, the well defined nature of the beam is a necessary step towards using more sophisticated laser-cooling techniques with the ultimate aim of producing a metastable helium microscope. MDS and UPS spectra from Si(111) are shown.

The adsorption of methylsilane on Cu(111) has been investigated by metastable deexcitation spectroscopy. The deexcitation process for the clean copper and silicide surfaces was demonstrated to occur via resonance ionization followed by Auger neutralization, while upon the adsorption of methylsilane at 295K it changes to Auger deexcitation. Accompanied by ultraviolet photoelectron spectroscopy, the MD spectrum at 295K reveals the presence of a methyl group on the surface, supporting the assertion that the majority of the surface is covered with methylsilane fragments. Annealing the surface above 420K reveals the presence of clean copper sites on a partially silicide surface.

A new design of secondary electron (SE) detector is described for use in low-vacuum scanning electron microscopes. Its distinguishing feature is a separate detector chamber, which can be maintained at a pressure independent of the pressure in the specimen chamber. The two chambers are separated by a perforated membrane or mesh across which an electric field is applied, making it relatively transparent to low-energy electrons but considerably less so to the gas molecules. The benefits of this arrangement are discussed. The final means of detecting the electrons can be a conventional scintillator and photomultiplier arrangement or any of the methods using the ambient gas as an amplifying medium. Images obtained with the detector show good SE contrast and low backscattered electron contribution.

Second order focusing is a desirable property of dispersion type electron energy analyzers because it allows a greater angular acceptance or, alternatively, higher energy resolution. We derive the second order focusing conditions for the hyperbolic field analyzer, which also allows a large range of energies to be collected in parallel, making it suitable for surface analysis techniques such as Auger spectroscopy.

Using a parallel acquisition electron energy analyser (the HFA), the presence of sub-monolayer coverage of chlorine on in vacuo cleaved (110) surfaces of InP and GaAs has been observed. From the time evolution of the Auger features, together with sample absorption current images and residual gas analysis, it is apparent that both electron stimulated desorption and surface diffusion take place, and that these are influenced by the presence of two adsorption sites of differing strengths. In particular, the sample absorption current images provide a rapid means of measuring the spatial distribution of the chlorine thereby distinguishing the effects of desorption and diffusion.

Recent developments in scanning Auger microscopy (SAM) are described. Emphasis is given to a method of parallel acquisition of the electron energy spectra and the benefits of spectrum-imaging for which it is capable of performing. In view of the maturity of the field of SAM, motivations and prospects for further developments are discussed.

The analysis of Auger and other excited electrons in the energy range from about 50eV to 2500eV provides a nearly non-destructive means to determine the surface composition of materials. It is both highly surface sensitive (a few atomic monolayers) and capable of high spatial resolution. This makes it an attractive alternative to energy dispersive x-ray analysis for the examination of ever smaller structures such as in semiconductor devices. For many applications however one important drawback has been the relatively long time required to make useful measurements - usually many seconds or minutes. Spectrum-imaging, in which an entire spectrum is acquired for each pixel in a digital scanned image, is one example for which Auger, spectroscopy becomes a prohibitively lengthy process. Similarly, the study of electron beam sensitive materials is difficult because the measurement time is often longer than the damage time. One method of reducing the measurement time is by acquiring the whole energy spectrum of interest in parallel. This is achieved with the Hyperbolic Field Analyser. (In electron energy loss spectroscopy this approach has lead to the highly successful Gatan energy filter.)

The formation and decay of the two lowest-lying, triply excited resonances in the autoionizing region of the helium spectrum (57-60 eV) have been studied by measuring electron-impact excitation functions for the n = 2 singly excited states of helium as a function of electron scattering angle. These results offer unambiguous confirmation of the classification of these states as and , respectively. Furthermore, the observation of the relative strengths of the decay of these features into the various final states enables some speculation as to the structure of the three excited electrons.

A new type of electrostatic electron energy analyzer is described that can acquire an electron energy spectrum in 'one shot.' It uses a hyperbolic field to focus electrons emitted from a solid in the energy range 50 eV to 2500 eV into a dispersive plane of about 50 mm length. An expression for the energy resolution is given and the effect of side and base plates on the behavior of the device is discussed. The main intended area of application for this type of analyzer is parallel data acquisition in Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The potential to acquire a spectrum is just a few seconds is possible with this device.

This article describes a new kind of electrostatic charged particle analyzer capable of the parallel detection of a large kinetic energy range. The main purpose envisaged is for the simultaneous detection of electrons scattered from surfaces and having energies between a few tens of eV to greater than 2000 eV. A prototype has been constructed that approximates a hyperbolic deflection field for the electrons entering an entrance slit. It exhibits an energy resolution of a few eV and a collection efficiency of 0.05% of 2π sr. Useful Auger spectra can be acquired in a time of less than 2 s. The significant improvement in spectrum acquisition time that this represents offers many possibilities to further Auger and photoelectron spectroscopy.

We report the construction of a low pressure (∼0.5 Torr) helium direct current discharge cell to lock a 1083 nm InGaAs diode laser to the 2 3S–2 3P transition in helium using saturated absorption spectroscopy. The direct current discharge cell has the advantage of being radio frequency noise free.

The angular dependence of electrons superelastically scattered from metastable (23S) helium has been measured for the first time at incident electron energies of 10 and 30 eV. For comparison purposes these distributions, which cover the angular range from 35 degrees to 125 degrees , have been normalized to the convergent close coupling calculation of Bray et al. (1994). We also compare the normalized angular distributions to first-order many-body theory and R-matrix calculations.

An experimental investigation of mode-2 (’lump-Like’) Solitary waves propagaling on a thin interface between two deep layers of different densities is presented. Small-and large-amplitude waves behaved differently: small waves carried energy and momentum, whereas sufficiently large waves also carried mass. Weakly nonlinear theory anticipated the result for amplitudes a/h [les ] 0.5 but did not provide even a qualitative description of the large-amplitude waves. In particular, the prediction that for waves to maintain permanent form their wavelength must decrease with increasing amplitude failed; instead the wavelength of large waves was observed to increase with increasing amplitude. Furthermore, whilst the waves were expected to emerge from interactions along their precollision trajectories, the large waves actually suffered a backward shift.