Rapid thermal processing of CuAISe2

CuAl thin film metallic precursors were selenised using a tube furnace or a rapid thermal processor (RTP). A comparison is made between the two processes for slightly Cu rich films and best crystallographic and elemental properties are obtained for films selenised by RTP: it was found that ternary compound could only be formed using the RTP. In both cases a large amount of CuxSey grains are found to develop at the surface of the films. Only samples processed in the RTP showed cathodoluminscence excitation at 2.68 eV characteristics of the electronic bandgap. Al rich samples were used to study the effect of etching the CuxSey phases from the surface in order to reveal the underlying CuAlSe2 material

Investigating rate enhancements in alpha-keto esters using cinchona and non-cinchona alkaloids

The products of the hydrogenation of alpha-ketoesters like ethyl pyruvate (EtPy), methyl benzoylformate (MBF) and ethyl benzoylformate (EBF) are used in many industries including pharmaceuticals, fragrances, solvent synthesis, and organic chemical intermediates. The rate of hydrogenation of EtPy increases substantially using cinchona alkaloid modifiers such as cinchonidine (CD) but the mechanism of rate enhancement is poorly understood, despite having been investigated extensively over the last few decades. The objective of this thesis is to investigate the mechanism of modifier-induced rate enhancement for the hydrogenation reactions of the alpha-keto esters EtPy, MBF and EBF. Rate enhancements were observed for the reactions of all three substrates (MBF, EBF and EtPy) using the different modifiers (CD, quinuclidine (QD) 3-quinuclidinol (QL), 1,4- diazabicyclo[2.2.2]octane (DABCO), and 4-aminoquinoline (AQ)). QD, QL, DABCO and AQ are modifiers that represent parts of the CD molecule, the aim of studying them being to deduce which parts of the CD molecule were involved in the rate enhancements. The concentrations of the modifiers were optimised, and the reaction data was kinetically fitted. Theoretical calculations were also completed to see if the rate enhancement mechanism could be understood computationally. The reaction mechanism when using CD may involve the 1:1 modifier: reactant model which stabilizes the half-hydrogenated state. This is suggested especially because of the rate enhancements observed for EBF and MBF which made the alternative theory for the mechanism of action via a ‘cleaning’ the catalyst model unlikely. The EtPy reaction mechanism may be a combination of the CD stabilizing the half-hydrogenated state and the cleaning effect. Concerning the achiral tertiary amines, the mechanism of action is unclear but the previous literature suggestion, supported by results from this project point to the modifier-surface complex being stabilized by the half-hydrogenated substrate. The cleaning effect and competitive adsorption may also be involved. Different substrates that were similar in structure to either EtPy, EBF and MBF were tested also to see if other rate enhancements could be found but none of these reactions gave significant rate enhancement. Theoretical computational results provided evidence for the existence of a solution-dimer intermediate

Square Patterns and Quasi-patterns in Weakly Damped Faraday Waves

Pattern formation in parametric surface waves is studied in the limit of weak viscous dissipation. A set of quasi-potential equations (QPEs) is introduced that admits a closed representation in terms of surface variables alone. A multiscale expansion of the QPEs reveals the importance of triad resonant interactions, and the saturating effect of the driving force leading to a gradient amplitude equation. Minimization of the associated Lyapunov function yields standing wave patterns of square symmetry for capillary waves, and hexagonal patterns and a sequence of quasi-patterns for mixed capillary-gravity waves. Numerical integration of the QPEs reveals a quasi-pattern of eight-fold symmetry in the range of parameters predicted by the multiscale expansion.Comment: RevTeX, 11 pages, 8 figure

An adaptive non-raster scanning method in atomic force microscopy for simple sample shapes

It is a significant challenge to reduce the scanning time in atomic force microscopy while retaining imaging quality. In this paper, a novel non-raster scanning method for high-speed imaging is presented. The method proposed here is developed for a specimen with the simple shape of a cell. The image is obtained by scanning the boundary of the specimen at successively increasing heights, creating a set of contours. The scanning speed is increased by employing a combined prediction algorithm, using a weighted prediction from the contours scanned earlier, and from the currently scanned contour. In addition, an adaptive change in the height step after each contour scan is suggested. A rigorous simulation test bed recreates the x-y specimen stage dynamics and the cantilever height control dynamics, so that a detailed parametric comparison of the scanning algorithms is possible. The data from different scanning algorithms are compared after the application of an image interpolation algorithm (the Delaunay interpolation algorithm), which can also run on-line.We would like to acknowledge the support of the Engineering and Physical Sciences Research Council (EPSRC) (grant nos. EP/I034882/1 & EP/I034831/1)

Nonlinear Competition Between Small and Large Hexagonal Patterns

Recent experiments by Kudrolli, Pier and Gollub on surface waves, parametrically excited by two-frequency forcing, show a transition from a small hexagonal standing wave pattern to a triangular ``superlattice'' pattern. We show that generically the hexagons and the superlattice wave patterns bifurcate simultaneously from the flat surface state as the forcing amplitude is increased, and that the experimentally-observed transition can be described by considering a low-dimensional bifurcation problem. A number of predictions come out of this general analysis.Comment: 4 pages, RevTex, revised, to appear in Phys. Rev. Let

Amplitude equations and pattern selection in Faraday waves

We present a systematic nonlinear theory of pattern selection for parametric surface waves (Faraday waves), not restricted to fluids of low viscosity. A standing wave amplitude equation is derived from the Navier-Stokes equations that is of gradient form. The associated Lyapunov function is calculated for different regular patterns to determine the selected pattern near threshold. For fluids of large viscosity, the selected wave pattern consists of parallel stripes. At lower viscosity, patterns of square symmetry are obtained in the capillary regime (large frequencies). At lower frequencies (the mixed gravity-capillary regime), a sequence of six-fold (hexagonal), eight-fold, ... patterns are predicted. The regions of stability of the various patterns are in quantitative agreement with recent experiments conducted in large aspect ratio systems.Comment: 12 pages, 1 figure, Revte

Energy eigenfunctions of the 1D Gross-Pitaevskii equation

We developed a new and powerful algorithm by which numerical solutions for excited states in a gravito optical surface trap have been obtained. They represent solutions in the regime of strong nonlinearities of the Gross--Pitaevskii equation. In this context we also shortly review several approaches which allow, in principle, for calculating excited state solutions. It turns out that without modifications these are not applicable to strongly nonlinear Gross-Pitaevskii equations. The importance of studying excited states of Bose-Einstein condensates is also underlined by a recent experiment of B\"ucker et al in which vibrational state inversion of a Bose-Einstein condensate has been achieved by transferring the entire population of the condensate to the first excited state. Here, we focus on demonstrating the applicability of our algorithm for three different potentials by means of numerical results for the energy eigenstates and eigenvalues of the 1D Grosss-Pitaevskii-equation. We compare the numerically found solutions and find out that they completely agree with the case of known analytical solutions.Comment: 18 pages, 11 figure

A Multi-mode Transverse Dynamic Force Microscope - Design, Identification and Control

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this record.The transverse dynamic force microscope (TDFM) and its shear force sensing principle permit true non-contact force detection in contrast to typical atomic force microscopes. The two TDFM measurement signals for the cantilever allow, in principle, two different scanning modes of which, in particular, the second presented here permits a full-scale non-contact scan. Previous research mainly focused on developing the sensing mechanism, whereas this work investigates the vertical axis dynamics for advanced robust closed-loop control. This paper presents a new TDFM digital control solution, built on field-programmable gate array (FPGA) equipment running at high implementation frequencies. The integrated control system allows the implementation of online customizable controllers, and raster-scans in two modes at very high detection bandwidth and nano-precision. Robust control algorithms are designed, implemented, and practically assessed. The two realized scanning modes are experimentally evaluated by imaging nano-spheres with known dimensions in wet conditions.Engineering and Physical Sciences Research Council (EPSRC