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Geometric characterization of 50 mm diameter, 50 µm thick single-crystal Si(1 1 1) wafers has been performed using complementary methods: industry-standard capacitance measurements of warp and total thickness variation (TTV), and a technique we term scanned chromatic confocal profilometry (SCCP). We compare the measurements made by the two techniques and demonstrate the limitations of capacitance measurements when applied to ultrathin wafers. The two-dimensional SCCP measurements are shown to enhance the description of wafer thickness variations beyond that generated by the standard test method. We discuss a Fourier transform-based analysis and show it to be useful in wafer quality assessment. Adding a summary of spatial frequencies in a wafer's thickness map to the conventional measures of warp and TTV provides a more complete summary of the salient features of a wafer's geometry.

The growth of thin platinum films on a nickel (100) substrate is investigated by helium atom scattering. Growth is shown to be disordered for all temperatures between 150 and 600 K, resulting in continual surface roughening and an absence of atomically flat terraces. We separate growth into three main regimes. First, at temperatures below 250 K, growth is three-dimensional and is described using a 'hit and stick' regime of limited adatom mobility. Between 250 and 370 K, deposited films remain three-dimensionally rough but involve intermixing of Pt and Ni. At temperatures above 370 K, large three-dimensional structures are absent and alloying is extensive, occurring via a sequence of thermally activated and well-defined alloy phases. Complete alloying occurs above 650 K.

The growth of Ni thin film on the Cu(100) surface at 280 K has been studied by means of thermal-energy helium atom scattering. A near layer-by-layer growth is observed below ~7 ML followed by a multilayer structure at higher coverages. Spot profile analysis shows Ni islands transfer from irregular shape to square with increasing Ni coverage. The mean island separation is measured as a function of coverage. The 0.5 ML Ni/Cu(100) surface turns out to be an ideal prototype, nano-structured surface for future interference measurements.

Electron energy loss spectroscopy has been used to probe the coverage-dependent electronic excitations from a C60 covered graphite surface. In the energy region corresponding to the optical band-gap of the bulk C60 solid, the dipole-scattering contribution to the loss features is simulated by a double dielectric layer model. We find that a good agreement between the simulated spectra and the experimental results can be achieved for a C60 multilayer. However, an additional energy loss channel is required in order to describe the electronic excitations for a C60 monolayer. The possible significances of this finding are discussed.

Electrically deformed single crystal mirrors will be a vital part of a first generation of scanning helium microscope (SHeM). Optimized mirrors will be used to focus thermal energy helium atoms into a surface-sensitive, low-energy probe, with a resolution that depends upon the precise mirror shape. Here, we present surface profilometry measurements of a prototype atom mirror. A temporal phase-stepping Mach-Zender fibre interferometer is used to profile the mirror surface with an accuracy of a few tens of nanometres. Results are compared with the theory of small deflections of an elastic thin plate. Our experiments suggest that relatively simple apparatus can induce the mirror profiles required to demagnify a conventional helium source into a microprobe suitable for a SHeM. Use of elliptical boundary conditions in the clamping mechanism afford biaxial bending in the crystal whilst a simple double-electrode design is demonstrated to be capable of asymmetric control of the mirror deformation.

A generalized methodology to analyse lattice-rod scans from helium atom scattering (HAS) has been developed, allowing in situ measurement of interlayer spacing during thin film growth. A Lomb periodogram technique is used to analyse the interference fringes observed in a lattice-rod scan of a stepped crystal surface. The algorithm is ideally suited to the small, unevenly sampled HAS data sets typically collected and has the advantage that the significance of peaks in the resulting frequency distribution can be calculated. We show how the method can be used to assess the significance of each interlayer spacing quantitatively. Using the growth of cobalt on copper(111) as an example, the statistical significance of the surface step height distribution is calculated directly. This paper represents a considerable improvement over existing fast Fourier transform-based methodologies.

Diffusion of an adsorbate is affected both by the adiabatic potential energy surface in which the adsorbate moves and by the rate of thermal coupling between the adsorbate and substrate. In principle both factors are amenable to investigation through quasi-elastic broadening in the energy spread of a probing beam of helium atoms. This review provides a topical summary of both the quasi-elastic helium-atom scattering technique and the available data in relation to the determination of diffusion parameters. In particular, we discuss the activation barriers deduced from experiment and their relation to the adiabatic potential and the central role played by the friction parameter, using the CO/Cu(001) system as a case study. The main issues to emerge are the need for detailed molecular dynamics simulations in the interpretation of data and the desirability of significantly greater energy resolution in the experiments themselves.

Measurements of the mechanical properties of ultra-thin Au(001) and Si(001) crystals are presented. The results for samples with thickness between 2000 A and 4000 A are discussed from the perspective of potential applications as optical elements for atomic beams of helium. The membranes were subject to uniform electrostatic pressure and deformation profiles were obtained using phase stepping interferometry. All samples showed mechanical properties dominated by internal stress, which we ascribe to processes in the sample manufacture. Simulations of the focusing properties, using the measured deformation profiles, show that the Si samples give better focal properties, but due to their internal stress they can only provide focal lengths above about 1 m for readily available fields. Imperfections in the Au samples limit their utility to applications requiring short focal lengths of less than approximately 100 mm.

A novel two-dimensional multichannel scaler is described, providing an inexpensive method for recording double modulated time-of-flight spectra generated by a 16-element multi-detector array. The design uses a hardware first stage implemented with programmable logic and a software second stage, running on a digital signal processing board. The hardware stage can count at a peak event rate of 20 MHz with a time resolution (minimum bin width) of 50 ns. The maximum sustained event rate is determined by the speed of the software processing. The flexibility of the design makes it suitable for a wide range of applications in which counts are recorded as a function of two variables.

A simple nozzle design for a free-jet atomic beam source is described. The design is compact (< 20 mm) and uses commercially available parts with only minor modification. Characterization of the source with a helium beam and time-of-flight detector showed that a velocity spread of less than 1% is readily obtained.

Field ionization from sharp tips is attracting increased attention for use in detectors for neutral atomic/molecular species. However, the direct detection of the ionized species typically results in low sensitivities due to the small acceptance angle of the receiving ion-sensitive measurement device (usually a channel electron multiplier) and can result in sputtering damage due to the relatively high mass and energy of the incident ion species. Here we present a design for a field-ionization-based neutral atom detector incorporating a simple secondary electron generating stage. The use of such a stage decouples the field-ionized species from the detected electron signal, thus eliminating any sputtering damage to the channel electron multiplier. The detector armature discussed is shown to exhibit a linear response to neutral gas pressure and a sensitivity that is improved by more than two orders of magnitude over a previous field ionization detector design.

We present finite element analysis of the deflections of clamped, ultrathin single crystals under electrostatic pressure. The crystals form concave mirrors that are suitable for low-aberration reflective focusing of inert atom beams, such as those required for the construction of a scanning helium microscope. The electrostatic and elastic aspects of the problem are coupled in the simulation. Additionally, realistic inhomogeneities in the crystal thickness are considered and it is shown that adaptive optic protocols using a minimal number of optimized electrodes can correct the resultant mirror aberrations.

International audience; Manipulation of atomic and molecular beams is essential to atom optics applications including atom lasers, atom lithography, atom interferometry and neutral atom microscopy. The manipulation of charge-neutral beams of limited polarisability, spin or excitation states remains problematic, but may be overcome by the development of novel diffractive or reflective optical elements. In this paper we present the first experimental demonstration of atom focusing using an ellipsoidal mirror. The ellipsoidal mirror enables stigmatic off-axis focusing for the first time and we demonstrate focusing of a beam of neutral, ground state helium atoms down to an approximately circular spot, (31.4 ± 0.8) μm x (26.8 ± 0.5) μm in size. This spot size is two orders of magnitude smaller than previous reflective focusing of atomic beams and is a critical milestone towards the construction of a high intensity scanning Helium microscope.

The papers collected here arise from the Workshop on Dynamical Phenomena at Surfaces, held in Cambridge, UK, in July 2008. The meeting has grown from the, SURPHON workshops [1], which traditionally had an emphasis on surface lattice dynamics. Over time the range of scientific interest has broadened and the recent meeting covered a wide range of topics including diffusion of adsorbates and clusters, growth, wetting, nanotribology, surface reactions and molecule–surface interactions as well as adsorbate vibrations and phonons. The contributions that appear here offer some sense of the breadth of the meeting. The motion of adsorbates on a surface serves as a particularly sensitive way to study the various interactions that take place on a surface and is therefore of fundamental importance. Theoretical work, of the type presented in the meeting, supplies us with important tools to analyze diffusion studies. For example, theoretical investigations of particularly complex surface dynamics exhibited by clusters [2] or due to internal degrees of freedom [3] are presented in this issue. The use of ab-initio calculations [4], to understand the relationship of electron motion to the underlying nuclear motion, is another illustration of the role theoretical methods have in the interpretation of experimental surface dynamics data. A wide variety of experimental probes, can be used to study complimentary aspects of surface interactions, the contributions in this issue reflect this variety. The helium spin echo technique is used to study gas–surface interactions with a silicone surface [5], metastable de-excitation spectra provides insight into the complex growth dynamics of a self assembled monolayer [6] and the role co-adsorption has on surface bonds is studied using high resolution electron energy loss spectroscopy [7]. The field of nanotechnology has driven a growing interest in atomic scale friction and dissipation mechanisms on a surface. This topic, which provides an interface between tribology and surface science was the subject of various contributions presented in the meeting. Theoretical assessment of the dissipation due to electron-hole excitation [8] and the role of phononic dissipation [9] provide two complimentary examples of studies in this field. Recent experimental data showing a discontinuity in sliding friction near a superconducting transition [10], supplies additional motivation for understanding the interaction of weakly bounded mono-layers, a topic studied in detail by Bruch et al [11]. The goal of understanding, and eventually designing surface assisted reactions from first principles has been a strong motivator for studying interactions on surfaces for decades. The increased ability to measure surfaces made possible with modern technology, provides critical tests for validating and developing the predictive capabilities of first principle methods. Combining surface dynamics data with a better understanding of the different dissipation mechanisms which take place on a surface, will provide the much needed perspective for reaction studies of the type presented in this issue [12]. Finally, we believe the level of synergy and close interaction between theory and experiment suggests a bright future for the field and for the next meeting in the series, provisionally scheduled for 2010 with a return to Schloss Ringberg. References [1] Toennies J P 2004 J. Phys.: Condens. Matter 16 264001 [2] Ferrando R and Fortunelli A 2009 J. Phys.: Condens. Matter 21 264001 [3] de Wijn A S and Fasolino A 2009 J. Phys.: Condens. Matter 21 264002 [4] Trioni M I, Fratesi G, Achilli S and Brivio G P 2009 J. Phys.: Condens. Matter 21 264003 [5] Tuddenham F E, Hedgeland H, Knowling J, Jardine A P, MacLaren D, Alexandrowicz G, Ellis J and Allison W 2009 J. Phys.: Condens. Matter 21 264004 [6] Canepa M, Lavagnino L, Pasquali L, Moroni R, Bisio F, De Renzi V, Terreni S and Mattera L 2009 J. Phys.: Condens. Matter 21 264005 [7] Politano A, Formoso V and Chiarello G 2009 J. Phys.: Condens. Matter 21 264006 [8] Goikoetxea I, Juaristi J I, Alducin M and Diez Muino R 2009 J. Phys.: Condens. Matter 21 264007 [9] Franchini A, Bortolani V, Santoro G and Brigazzi M 2009 J. Phys.: Condens. Matter 21 264008 [10] Highland M and Krim J 2006 Phys. Rev. Lett. 96 226107 [11] Bruch L W, Nabar R P and Mavrikakis M 2009 J. Phys.: Condens. Matter 21 264009 [12] Fink C and Jenkins S J 2009 J. Phys.: Condens. Matter 21 264010

Helium-3 spin-echo measurements of resonant scattering from the Si(111)-(1 × 1)H surface, in the energy range 4-14 meV, are presented. The measurements have high energy resolution yet they reveal bound state resonance features with uniformly broad linewidths. We show that exact quantum mechanical calculations of the elastic scattering, using the existing potential for the helium/Si(111)-(1 × 1)H interaction, cannot reproduce the linewidths seen in the experiment. Further calculations rule out inelastic and other mechanisms that might give rise to losses from the elastic scattering channels. We show that corrugation in the attractive part of the atom-surface potential is the most likely origin of the experimental lineshapes.

For pt. II see abstr. A6932 of 1972. Measurements have been made of the angular and energy distributions of electrons ejected from contaminated metal surfaces due to thermal energy metastable rate gas atom impact. Mechanisms are proposed to explain these observations and also the high values of secondary emission coefficients previously measured. The secondary electron yield was found to be approximately independent of the angle of incidence of the metastable atoms. Reflection coefficients for metastable atoms at contaminated metal and glass surfaces were found to be very small and no ion emission was observed.

Between 247 and 327 K cobalt grows epitaxially on Cu(100), with a smaller diffusion coefficient for cobalt on copper than for cobalt on cobalt. It is possible to grow ten monolayers of cobalt on Cu(100) before strain in the layers causes the defect density to rise. Above 347 K growth is perturbed-probably by interdiffusion.