Nuclear Instruments and Methods in Physics Research. Section B; Microstructural Characterization of Semi-Interpenetrating Polymer Networks by Positron Lifetime Spectroscopy

The impact-induced deposition of Al13 clusters with icosahedral structure on Ni(0 0 1) surface was studied by molecular dynamics (MD) simulation using Finnis–Sinclair potentials. The incident kinetic energy (Ein) ranged from 0.01 to 30 eV per atom. The structural and dynamical properties of Al clusters on Ni surfaces were found to be strongly dependent on the impact energy. At much lower energy, the Al cluster deposited on the surface as a bulk molecule. However, the original icosahedral structure was transformed to the fcc-like one due to the interaction and the structure mismatch between the Al cluster and Ni surface. With increasing the impinging energy, the cluster was deformed severely when it contacted the substrate, and then broken up due to dense collision cascade. The cluster atoms spread on the surface at last. When the impact energy was higher than 11 eV, the defects, such as Al substitutions and Ni ejections, were observed. The simulation indicated that there exists an optimum energy range, which is suitable for Al epitaxial growth in layer by layer. In addition, at higher impinging energy, the atomic exchange between Al and Ni atoms will be favourable to surface alloying.

Nuclear instruments and methods in physics research section B : beam interactions with materials and atoms

A common problem in teaching students in science or engineering is the decreasing level of formal and practical knowledge of mathematics in recent generations of students. This problem seems to be quite international (although its severity may vary from country to country), and many physics degree courses are in the process of dealing with this problem. Usually the solution (or alleviation) of the problem consists of starting the maths teaching from a more elementary level, with more or less extended reviews of differentiation, integration and complex numbers, and of adopting a less rigorous, less mathematical approach in teaching the more advanced topics. The choice of a suitable textbook is, of course, crucial for the teaching strategy. This new book aims at covering the full range of mathematical topics necessary for physics and engineering degree courses. Therefore it starts with preliminary calculus, differentiation and integration, and proceeds to quite advanced material such as groups and representations, and tensor analysis. It also contains a chapter on numerical analysis. I have compared this book with two other well known texts, Mathematical Methods in the Physical Sciences by Mary L Boas (John Wiley, second edition, 1983, $42.95) and Mathematical Methods for Physicists by George B Arfken and Hans J Weber (Academic Press, fourth edition, 1995 $69.00) (these prices being found on the Internet pages of the respective publishers). All these books treat matrices and vectors, differential equations, special functions, complex analysis, variational calculus, probability theory, Fourier series analysis, vector calculus and integral equations. All three books present the mathematics for physicists and/or engineers rather than for mathematicians, who will, for example, look in vain for epsilon-delta proofs of continuity. The differences between the books are mainly in the level from which they start, in the choice of advanced topics and in the style of presentation. Boas starts off at a rather elementary level, though without reviewing ordinary differentiation and integration. There is nothing on group theory in this book, but it includes tensor analysis. Arfken and Weber's book starts off at a more advanced level: the first chapter deals with vector analysis, including the Gauss and Stokes theorems and the Dirac delta-function, and the second chapter deals already with curved coordinates and tensor analysis. This book contains a chapter on group theory and, interestingly, one on nonlinear methods and chaos. The three books show a difference in style of presentation. The explanations in Boas are clear and down to earth. The presentation of special functions is characteristic - it is not cast into the framework of self-adjoint (Hermitian) differential operators and Sturm-Liouville equations, as in the other two books. Personally I prefer the latter approach because it shows that special functions arise as eigenfunctions of self-adjoint operators, which ties in nicely with the variational formulation into which most physical theories can be cast. On the whole this book is therefore less formal than that by Riley et al, which is nevertheless not so formal as to put off physics students. Riley et al has clear, thorough and straightforward explanations of the subjects treated. It rigorously adopts a three-stage approach throughout the book: first a heuristic, intuitive introduction, then a formal treatment, and finally one or two examples. This consistent presentation, the layout, and the print quality make the book most attractive. Arfken and Weber's explanations are very much linked into physics, because this book is intended specifically for physicists, whereas the other two cater for a wider audience, though all are suitable for physics degree courses. Arfken and Weber's book treats the subjects in somewhat less detail than the other two, and it is the only book of the three which does not contain answers or hints to selected problems. Arfken and Weber is the most physical, but also the most advanced of the three. Making a choice between these books is not easy. If I had to recommend a maths book to a graduate student, I would probably choose Arfken and Weber because of its more in-depth discussion of advanced material directly related to physics. For an undergraduate university degree course, I would prefer Riley et al because of its clearness of presentation, comprehensiveness and value for money. It contains a thousand pages, there are plenty of exercises with each chapter, and as mentioned above, the layout and print quality are very good. This is a valuable book with great potential use in present-day university physics courses. Furthermore, the book will be useful for graduates too, and researchers will find it useful for looking up material which they have forgotten since their undergraduate days.

Mathematical Methods for Physics and Engineering: A Comprehensive Guide

PrefaceCh. 1Historical Introduction3Ch. 2Continuum Mechanics25Ch. 3Equations of Motion56Ch. 4Normal Modes109Ch. 5Seismic Source Representation146Ch. 6Anelasticity and Attenuation193Ch. 7Rayleigh-Ritz Method237Ch. 8Spheroidal and Toroidal Oscillations257Ch. 9Elastic and Anelastic Perturbations327Ch. 10Synthetic Seismograms363Ch. 11Love and Rayleigh Waves405Ch. 12Mode-Ray Duality451Ch. 13Perturbation Theory537Ch. 14Mode Splitting and Coupling596Ch. 15Body-Wave Ray Theory669Ch. 16Surface-Wave JWKB Theory737App. AVectors and Tensors811App. BSpherical Harmonics838App. CGeneralized Spherical Harmonics877App. DWhole Earth Catalogue932Bibliography967Index999

Theoretical global seismology

Scanning helium microscopy is an emerging form of microscopy using thermal energy neutral helium atoms as the probe particle. The very low energy combined with lack of charge gives the technique great potential for studying delicate systems, and the possibility of several new forms of contrast. To date, neutral helium images have been dominated by topographic contrast, relating to the height and angle of the surface. Here we present data showing contrast resulting from specular reflection and diffraction of helium atoms from an atomic lattice of lithium fluoride. The signature for diffraction is evident by varying the scattering angle and observing sharp features in the scattered distribution. The data indicates the viability of the approach for imaging with diffraction contrast and suggests application to a wide variety of other locally crystalline materials.

/pdf/observation-of-diffraction-contrast-in-scanning-helium-59tzjq58bg.pdf

Observation of diffraction contrast in scanning helium microscopy.

A ray tracing method for predicting contrast in neutral atom beam imaging.

Using atom beams to image the surface of samples in real space is an emerging technique that delivers unique contrast from delicate samples. Here, we explore the contrast that arises from multiple scattering of helium atoms, a specific process that plays an important role in forming topographic contrast in scanning helium microscopy (SHeM) images. A test sample consisting of a series of trenches of varying depths was prepared by ion beam milling. SHeM images of shallow trenches (depth/width   1) exhibited an enhanced intensity. The scattered helium signal was modeled analytically and simulated numerically using Monte Carlo ray tracing. Both approaches gave excellent agreement with the experimental data and confirmed that the enhancement was due to localization of scattered helium atoms due to multiple scattering. The results were used to interpret SHeM images of a bio-technologically relevant sample with a deep porous structure, highlighting the relevance of multiple scattering in SHeM image interpretation.

/pdf/multiple-scattering-in-scanning-helium-microscopy-30b3q8x4r6.pdf

Multiple scattering in scanning helium microscopy.

Complex optical elements for scanning helium microscopy through 3D printing

In understanding the nature of contrast in the emerging field of neutral helium microscopy, it is important to identify if there is an atom-surface scattering distribution that can be expected to apply broadly across a range of sample surfaces. Here we present results acquired in a scanning helium microscope (SHeM) under typical operating conditions, from a range of surfaces in their native state, i.e. without any specialist sample preparation. We observe diffuse scattering, with an approximately cosine distribution centred about the surface normal. The 'cosine-like' distribution is markedly different from those distributions observed from the well-prepared, atomically pristine, surfaces typically studied in helium atom scattering experiments. Knowledge of the typical scattering distribution in SHeM experiments provides a starting basis for interpretation of topographic contrast in images, as well as a reference against which more exotic contrast mechanisms can be compared. 

/pdf/observation-of-diffuse-scattering-in-scanning-helium-256qfpk4.pdf

Observation of diffuse scattering in scanning helium microscopy

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