Surface enhancement of oxygen exchange and diffusion in the ionic conductor La2Mo2O9

Isotopic surface oxygen exchange and its subsequent diffusion have been measured using secondary ion mass spectrometry in the fast ionic conductor La2Mo2O9. A silver coating was applied to the sample surface to enhance the surface exchange process for dry oxygen. Contrary to previous studies performed using a wet atmosphere, no grain boundary diffusion tail was observed under these optimized dry exchange conditions. The activation energy for oxygen diffusion was found to be 0.66(+/- 0.09) eV at high temperature (>570 degrees C), and 1.25(+/- 0.01)eV at low temperature (<570 degrees C). Time-of-Flight secondary ion mass spectrometry was employed to investigate the correlation between the silver coating and the O-18 concentration on the sample surface. A close correlation between the presence of silver and oxygen incorporation on the surface was observed. (C) 2010 Elsevier B.V. All rights reserved

Optimisation studies on strain-engineered Germanium heterostructures

The physical gate lengths of state-of-the-art CMOS devices are 45 nm and are anticipated to reach just 20 nm by 2007. Due to the prohibitive capital expenditure required for next-generation CMOS technologies, leading device manufacturers are now exploring exotic device architectures and novel substrates in which significant device performance enhancements may by obtained using the existing device fabrication infrastructure. This thesis reports studies made on an initial evaluation of hole transport properties in strained Ge channels and comprises physical and electrical characterisation of these heterostructures as well as the analysis of SiGe layers using secondary ion mass spectrometry. The initial work of thesis describes the growth, characterisation and optimisation of a novel strained Ge substrate. The substrate technology was developed using a hybrid-epitaxy technique in which a SiGe strain-relaxed buffer layer, so called "virtual substrate", was grown using a ultra-high vacuum chemical-vapour deposition growth technique and the active strained Ge layer was grown using a solid-source molecular-beam epitaxy growth technology. An advanced chemical cleaning procedure has been developed which includes a modified Piranha etch. The novel cleaning procedure enables the successful integration of the two growth techniques. Significant hole carrier transport enhancements were observed for holes contained within the strained Ge channel. Optimisation of the hole mobility was achieved by the reduction of carrier scattering such as interface roughness scattering and point defect scattering. The optimisation methods employed included growth temperature iterations to reduce Ge channel roughening via elastic relaxation and, channel thickness iterations were also employed in order to minimize channel roughening and defect nucleation. Post-growth annealing procedures were used to combat defects arising from low temperature growth. The Ge heterostructures were grown on strain relaxed buffer layers, terminating with a Ge content of 60%. The optimised strained Ge channel thickness was found to be 20 nm and the growth temperature of the active layers was reduced to 350°C so as to minimise surface roughening. As grown point defects were eliminated at an optimised post-growth anneal temperature of 650°C for 30 minutes under dry N2• Hall mobilities reached 1910 cm2Ns at room temperature rising to 26,900 cm2Ns at 10K. A magneto-conductivity transfonnation measurement and maximum entropy mobility spectrum analysis revealed a room temperature drift mobility of 2700 cm2Ns at a carrier density of l.Ox1012 cm-2 . This result represents a 15-fo1d increase in hole mobility compared to conventional Si substrates at comparable effective fields. The second and important part of this thesis addresses charging effects observed when profiling undoped SiGe layers and the quantification of Ge fraction within SiGe layers using secondary ion mass spectrometry. Due to the highly resistive spreading resistance found for undoped SiGe layers when profiled using an O2+ incident beam, charging effects were found to mask the true layer profile. In order to overcome this problem a new approach is discussed for the first time. By illuminating the sample with a red laser light (wavelength 635mn) electron-hole pairs were created via photon absorption. The excess charge carriers were sufficient to overcome localised charging effects induced by the primary ion beam during SIMS analysis. In this manner, total charge suppression was achieved, thereby enabling a true determination of the SiGe sample profile to be obtained via SIMS. Finally, an analytical method enabling the accurate determination of Ge content of SiGe layers is discussed. The method employs a comparative ion yield methodology and enables both the spatial distribution and Ge concentration of SiGe layers to be accurately determined from a single SIMS measurement

Si1-x Ge x /Si interface profiles measured to sub-nanometer precision using uleSIMS energy sequencing

The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O2 + over an energy range of 0.25–2.5 keV were used to probe the interface between Si0.73Ge0.27/Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS

An origin behind Rashba spin splitting within inverted doped sGe heterostructures

In this paper, we demonstrate why cubic Rashba spin splitting is observed within inverted doped strained germanium (sGe) hetrostructures. Magnetotransport measurements showed beating within the SdH oscillation, with fast Fourier analysis revealing cubic Rashba spin splitting to be present. A cubic Rashba coefficient of β=7.97×10−29 eVm3β=7.97×10−29 eVm3 and a spin-splitting energy of Δ=1.17 meVΔ=1.17 meV were determined. The source of the cubic Rashba spin splitting was identified from a combination of ultra low energy secondary ion mass spectrometry analysis and subsequent band structure modelling using Nextnano3. Ultra-low eneIn this paper we demonstrate an origin for cubic Rashba spin splitting observed within inverted doped strained germanium (sGe) hetrostructures. Magnetotransport measurements showed beating within the SdH data, with ensuing Fast Fourier analysis revealing cubic Rashba spin splitting to be present. A spin orbit interaction value of and spin splitting energy were determined. The source of the cubic Rashba spin splitting was identified from a combination of ultra low energy secondary ion mass spectrometry analysis and subsequent band structure modelling using Nextnao3. Ultra low energy secondary ion mass spectrometry revealed an unintentional, highly B doped near surface region to be present. By incorporating this information into the Nextnano3 modelling, two single subband triangular QWs were predicted, one at the upper and the other at the lower interface of the sGe QW. Moreover, these triangular wells are expected to be asymmetric due to the difference in B doping levels and spacer layer thicknesses, and it is this asymmetry which induces the cubic Rashba spin splitting observed

Translocator protein in late stage Alzheimer\u27s disease and Dementia with Lewy bodies brains

OBJECTIVE: Increased translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), in glial cells of the brain has been used as a neuroinflammation marker in the early and middle stages of neurodegenerative diseases, such as Alzheimer\u27s disease (AD) and Dementia with Lewy Bodies (DLB). In this study, we investigated the changes in TSPO density with respect to late stage AD and DLB. METHODS: TSPO density was measured in multiple regions of postmortem human brains in 20 different cases: seven late stage AD cases (Braak amyloid average: C; Braak tangle average: VI; Aged 74-88, mean: 83 ± 5 years), five DLB cases (Braak amyloid average: C; Braak tangle average: V; Aged 79-91, mean: 84 ± 4 years), and eight age-matched normal control cases (3 males, 5 females: aged 77-92 years; mean: 87 ± 6 years). Measurements were taken by quantitative autoradiography using [ RESULTS: No significant changes were found in TSPO density of the frontal cortex, striatum, thalamus, or red nucleus of the AD and DLB brains. A significant reduction in TSPO density was found in the substantia nigra (SN) of the AD and DLB brains compared to that of age-matched healthy controls. INTERPRETATION: This distinct pattern of TSPO density change in late stage AD and DLB cases may imply the occurrence of microglia dystrophy in late stage neurodegeneration. Furthermore, TSPO may not only be a microglia activation marker in early stage AD and DLB, but TSPO may also be used to monitor microglia dysfunction in the late stage of these diseases

Dynamical description of vesicle growth and shape change

We systematize and extend the description of vesicle growth and shape change using linear nonequilibrium thermodynamics. By restricting the study to shape changes from spheres to axisymmetric ellipsoids, we are able to give a consistent formulation which includes the lateral tension of the vesicle membrane. This allows us to generalize and correct a previous calculation. Our present calculations suggest that, for small growing vesicles, a prolate ellipsoidal shape should be favored over oblate ellipsoids, whereas for large growing vesicles oblates should be favored over prolates. The validity of this prediction is examined in the light of the various assumptions made in its derivation.Comment: 6 page

A Markov Chain based method for generating long-range dependence

This paper describes a model for generating time series which exhibit the statistical phenomenon known as long-range dependence (LRD). A Markov Modulated Process based upon an infinite Markov chain is described. The work described is motivated by applications in telecommunications where LRD is a known property of time-series measured on the internet. The process can generate a time series exhibiting LRD with known parameters and is particularly suitable for modelling internet traffic since the time series is in terms of ones and zeros which can be interpreted as data packets and inter-packet gaps. The method is extremely simple computationally and analytically and could prove more tractable than other methods described in the literatureComment: 8 pages, 2 figure

Natural Wormholes as Gravitational Lenses

Visser has suggested traversable 3-dimensional wormholes that could plausibly form naturally during Big Bang inflation. A wormhole mouth embedded in high mass density might accrete mass, giving the other mouth a net *negative* mass of unusual gravitational properties. The lensing of such a gravitationally negative anomalous compact halo object (GNACHO) will enhance background stars with a time profile that is observable and qualitatively different from that recently observed for massive compact halo objects (MACHOs) of positive mass. We recommend that MACHO search data be analyzed for GNACHOs.Comment: 4 pages; plus 4 figures; ReV_TeX 3.0; DOE/ER/40537-001/NPL94-07-01

Stability of palm oil-based emulsion liquid membrane for succinic acid extraction from aqueous solution

Emulsion liquid membrane (ELM) process has high potential in the separation of succinic from the fermentation broth. However, the major drawback of this technology is the stability of emulsion globules during the extraction process and the chemical involve d in the liquid membrane formulation. This study investigate the stability of ELM using a greener formulation containing Amberlite LA - 2 as a carrier, Span 80 and Tween 80 as a surfactant, palm oil as a diluent and sodium carbonate (Na 2 CO 3 ) as an aqueous st ripping agent. The emulsion stability was evaluated by observing the water - oil separation of the emulsion and microscopic image of emulsion droplets count and size. Several operating parameters including the organic to internal ratio, homogenizer speed, ho mogenizing time, and surfactant concentration, and surfactant blend were investigated. The results show the most stable water - in - oil emulsion was observed at 3:1 organic to internal ratio; 7000rpm homogenizer speed; 5 minute emulsification time; 3% (w/v) s urfactant at HLB 8. Besides, the extraction study shows 70% of the succinic acid was extracted at 0.01M Na 2 CO 3 , 1:3 treat ratio, and 0.7M Amberlite in palm oil at optimum primary emulsion stability conditions. This indicates the potential of using palm oil based ELM for the extraction of succinic acid

To Act and Learn: A Bakhtinian Exploration of Action Learning

This paper considers the work of the Russian social philosopher and cultural theorist, Mikhail Mikhailovich Bakhtin as a source of understanding for those involved in action learning. Drawing upon data gathered over two years during the evaluation of 20 action learning sets in the north of England, we will seek to work with the ideas of Bakhtin to consider their value for those involved in action learning. We consider key Bakhtin features such as Making Meaning, Participative Thinking, Theoreticism and Presence, Others and Outsideness, Voices and Carnival to highlight how Bakhtin's can enhance our understanding of the nature of action and learning