Predicting Relaxation in Strained Epitaxial Layers

Strained epitaxial semiconductor layers, much thicker than the critical thickness, have been used as strain-relief buffer layers for many years. The most successful structure developed so far dates back to the 1960\u27s, and consists of a very thick ( ~30 μm) layer in which the misfit is gradually and continuously increased. These structures relax completely and have a sufficiently low threading dislocation density to allow a device structure to be grown on top. This process requires a very high growth rate to produce the buffer layer in a reasonable time, which is only provided by hydride vapourphase epitaxy. Recently, there has been interest in developing thinner structures using both graded and constant composition buffer layers, which, if successful, would resolve this problem. Here, we consider the mechanisms of strain relaxation, paying special attention to the changes in threading dislocation density and surface roughness that occur during misfit relief. An extensive series of experiments shows that the relaxation of constant composition layers, although not following current theoretical models, does appear to follow a simple empirical law. This result suggests an approach which can be used to predict the state of strain in any epitaxial structure, allowing more efficient strain-relief buffer layers to be designed

The perceived barriers to the inclusion of rainwater harvesting systems by UK house building companies

This work investigates the barriers that exist to deter the implementation of rainwater harvesting into new UK housing. A postal questionnaire was sent to a selection of large, medium and small house-builders distributed across the UK. Questions were asked concerning potential barriers to the inclusion of rainwater harvesting in homes separated into five sections; (1) institutional and regulatory gaps, (2) economic and financial constraints, (3) absence of incentives, (4) lack of information and technical knowledge, and (5) house-builder attitudes. The study concludes that although the knowledge of rainwater systems has increased these barriers are deterring house-builders from installing rainwater harvesting systems in new homes. It is further acknowledged that the implementation of rainwater harvesting will continue to be limited whilst these barriers remain and unless resolved, rainwater harvesting's potential to reduce the consumption of potable water in houses will continue to be limited

Engaging People with Energy Efficiency: A Randomised Controlled Trial Testing the Effects of Thermal Imaging Visuals in a Letter Communication

The study tested the effect of adding visualisations to a communication to engage householders with an energy efficiency programme. External wall insulation is an appropriate way of insulating homes, yet take-up is low. Householders may be unaware of the heat loss from uninsulated walls. In earlier research, seeing thermal images prompted the uptake of simple energy efficiency actions amongst householders. Thermal images were added to a standard letter to visualise heat transfer from a home before and after external wall insulation had been installed. A randomised controlled trial tested three types of letter (standard, standard plus thermal image showing problem, standard plus thermal images showing problem and solution) in 5483 UK households. The target outcome was the rate of telephone enquiries after exposure to the letters. Enquiry rates were low (1.6%) and did not differ between letter type. We discuss the null effect in relation to the target action (external wall insulation), the manner of presentation of the visuals (mass communication, letter through the door) and the ingredients of a persuasive intervention. Findings suggest that taking a key ingredient from an intervention and applying it in a different context may result in the loss of its impact.</jats:p

Exploring backscattered imaging in low voltage FE-SEM

Contrast levels in backscattered SEM images were investigated, utilising stage deceleration for low voltage imaging and also electron energy filtering. Image contrast variations are explained via use of Monte Carlo simulations which can predict the optimum accelerating and filter voltages for imaging complex sample mixtures

Formation and annihilation of nanocavities during keV ion irradiation of Ge

Nanocavities in Ge(111) created by 5 keV Xe ion irradiation are characterized by ex situ transmission electron microscopy and Rutherford backscattering spectrometry. Nanocavities nucleate near the surface and then undergo thermal migration. Nanocavities with average diameter of 10 nm and areal density of 5.1 x 10-3 nm-2 are observed at 773 K, while nanocavities with average diameter of 2.9 nm and areal density of 3.1 x 10-3 nm-2 are observed at 673 K. The estimated Xe gas pressure inside the nanocavities is 0.035 GPa at 773 K, much smaller than the estimated equilibrium pressure 0.38 GPa. This result suggests that the nanocavities grow beyond equilibrium size at 773 K. The nanocavities are annihilated at the surface to form surface pits by the interaction of displacement cascades of keV Xe ions with the nanocavities. These pits are characterized by in situ scanning tunneling microscopy. Pits are created on Ge(111) and Ge(001) at temperatures ~ 523-578 K by keV Xe ions even when less than a bilayer (monolayer) of surface material is removed.Comment: 26 pages, 7 figures, to be published in Physical Review