Ab initio study of CsI and its surface

Prova tipográfica (In Press)Cesium iodide properties, both in the bulk and on (110) and (100) surfaces, are studied using Density Functional Theory. The bulk lattice constant, bulk modulus and elastic constants are in good agreement with the experimental values. The electronic band structure is also calculated, as well as the density of states. On the surfaces, relaxation of the atoms was performed, and the atomic geometry and electronic structure have been studied.Fundação para a Ciência e a Tecnologia (FCT) - Project nr. POCI/FP/63442/2005, Ref. BSAB/466/2004.Fundação Calouste Gulbenkian

Increasing the acceptability and rates of organ donation among minority ethnic groups: a programme of observational and evaluative research on Donation, Transplantation and Ethnicity (DonaTE)

Background: Black, Asian and minority ethnic (BAME) groups have a high need for organ transplantation but deceased donation is low. This restricts the availability of well-matched organs and results in relatively long waiting times for transplantation, with increased mortality risks. Objective: To identify barriers to organ donor registration and family consent among the BAME population, and to develop and evaluate a training intervention to enhance communication with ethnic minority families and identify impacts on family consent. Methods: Three-phase programme comprising (1) community-based research involving two systematic reviews examining attitudes and barriers to organ donation and effective interventions followed by 22 focus groups with minority ethnic groups; (2) hospital-based research examining staff practices and influences on family consent through ethics discussion groups (EDGs) with staff, a study on intensive care units (ICUs) and interviews with bereaved ethnic minority families; and (3) development and evaluation of a training package to enhance cultural competence among ICU staff. Setting: Community focus group study in eight London boroughs with high prevalence of ethnic minority populations. Hospital studies at five NHS hospital trusts (three in London and two in Midlands). Participants: (1) Community studies: 228 focus group participants; (2) hospital studies: 35 nurses, 28 clinicians, 19 hospital chaplains, 25 members of local Organ Donation Committees, 17 bereaved family members; and (3) evaluation: 66 health professionals. Data sources: Focus groups with community residents, systematic reviews, qualitative interviews and observation in ICUs, EDGs with ICU staff, bereaved family interviews and questionnaires for trial evaluation. Review methods: Systematic review and narrative synthesis. Results: (1) Community studies: Organ Donor Register – different ethnic/faith and age groups were at varying points on the ‘pathway’ to organ donor registration, with large numbers lacking knowledge and remaining at a pre-contemplation stage. Key attitudinal barriers were uncertainties regarding religious permissibility, bodily concerns, lack of trust in health professionals and little priority given to registration, with the varying significance of these factors varying by ethnicity/faith and age. National campaigns focusing on ethnic minorities have had limited impact, whereas characteristics of effective educational interventions are being conducted in a familiar environment; addressing the groups’ particular concerns; delivery by trained members of the lay community; and providing immediate access to registration. Interventions are also required to target those at specific stages of the donation pathway. (2) Hospital studies: family consent to donation – many ICU staff, especially junior nurses, described a lack of confidence in communication and supporting ethnic minority families, often reflecting differences in emotional expression, faith and cultural beliefs, and language difficulties. The continuing high proportion of family donation discussions that take place without the collaboration of a specialist nurse for organ donation (SNOD) reflected consultants’ views of their own role in family consent to donation, a lack of trust in SNODs and uncertainties surrounding controlled donations after circulatory (or cardiac) death. Hospital chaplains differed in their involvement in ICUs, reflecting their availability/employment status, personal interests and the practices of ICU staff. (3) Evaluation: professional development package – a digital versatile disk-based training package was developed to promote confidence and skills in cross-cultural communication (available at: www.youtube.com/watch?v=ueaR6XYkeVM&feature=youtu.be). Initial evaluation produced positive feedback and significant affirmative attitudinal change but no significant difference in consent rate over the short follow-up period with requirements for longer-term evaluation. Limitations: Participants in the focus group study were mainly first-generation migrants of manual socioeconomic groups. It was not permitted to identify non-consenting families for interview with data regarding the consent process were therefore limited to consenting families. Conclusions: The research presents guidance for the effective targeting of donation campaigns focusing on minority ethnic groups and provides the first training package in cultural competence in the NHS. Future work: Greater evaluation is required of community interventions in the UK to enhance knowledge of effective practice and analysis of the experiences of non-consenting ethnic minority families. Funding: The National Institute for Health Research Programme Grants for Applied Research programme

Atomic Hole Doping of Graphene

Graphene is an excellent candidate for the next generation of electronic materials due to the strict two-dimensionality of its electronic structure as well as the extremely high carrier mobility. A prerequisite for the development of graphene based electronics is the reliable control of the type and density of the charge carriers by external (gate) and internal (doping) means. While gating has been successfully demonstrated for graphene flakes and epitaxial graphene on silicon carbide, the development of reliable chemical doping methods turns out to be a real challenge. In particular hole doping is an unsolved issue. So far it has only been achieved with reactive molecular adsorbates, which are largely incompatible with any device technology. Here we show by angle-resolved photoemission spectroscopy that atomic doping of an epitaxial graphene layer on a silicon carbide substrate with bismuth, antimony or gold presents effective means of p-type doping. Not only is the atomic doping the method of choice for the internal control of the carrier density. In combination with the intrinsic n-type character of epitaxial graphene on SiC, the charge carriers can be tuned from electrons to holes, without affecting the conical band structure

Tuning the graphene work function by electric field effect

We report variation of the work function for single and bi-layer graphene devices measured by scanning Kelvin probe microscopy (SKPM). Using the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene.Comment: 11 pages and 8 figures including supplementary information, to appear in Nano Letter

Properties of Graphene: A Theoretical Perspective

In this review, we provide an in-depth description of the physics of monolayer and bilayer graphene from a theorist's perspective. We discuss the physical properties of graphene in an external magnetic field, reflecting the chiral nature of the quasiparticles near the Dirac point with a Landau level at zero energy. We address the unique integer quantum Hall effects, the role of electron correlations, and the recent observation of the fractional quantum Hall effect in the monolayer graphene. The quantum Hall effect in bilayer graphene is fundamentally different from that of a monolayer, reflecting the unique band structure of this system. The theory of transport in the absence of an external magnetic field is discussed in detail, along with the role of disorder studied in various theoretical models. We highlight the differences and similarities between monolayer and bilayer graphene, and focus on thermodynamic properties such as the compressibility, the plasmon spectra, the weak localization correction, quantum Hall effect, and optical properties. Confinement of electrons in graphene is nontrivial due to Klein tunneling. We review various theoretical and experimental studies of quantum confined structures made from graphene. The band structure of graphene nanoribbons and the role of the sublattice symmetry, edge geometry and the size of the nanoribbon on the electronic and magnetic properties are very active areas of research, and a detailed review of these topics is presented. Also, the effects of substrate interactions, adsorbed atoms, lattice defects and doping on the band structure of finite-sized graphene systems are discussed. We also include a brief description of graphane -- gapped material obtained from graphene by attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic

Understanding the consumption of folic acid during preconception, among Pakistani, Bangladeshi and white British mothers in Luton, UK: a qualitative study

Background To review the similarities and differences in Pakistani, Bangladeshi and White British mothers health beliefs (attitudes, knowledge and perceptions) and health behaviour regarding their consumption of folic acid pre-conception, to reduce the risk of neural tube defects. Methods Our study used a descriptive qualitative research approach, implementing face-to-face focus group discussions with Pakistani, Bangladeshi or White British mothers (normal birth outcomes and mothers with poor birth outcomes) and semi-structured interviews or focus groups with service providers using semi-structured topic guides. This method is well suited for under researched areas where in-depth information is sought. There were three sample groups: 1. Pakistani, Bangladeshi and White British mothers with normal birth outcomes (delivery after 37 weeks of gestation, in the preceding 6 to 24 months, weighing 2500 g and living within a specified postcode area in Luton, UK). 2. Pakistani Bangladeshi and white British bereaved mothers who had suffered a perinatal mortality (preceding 6 to 24 months, residing within a specificied postcode area). 3. Healthcare professionals working on the local maternity care pathway (i.e. services providing preconception, antenatal, antepartum and postpartum care). Transcribed discussions were analysed using the Framework Analysis approach. Results The majority of mothers in this sample did not understand the benefits or optimal time to take folic acid pre-conception. Conversely, healthcare professionals believed the majority of women did consume folic acid, prior to conception. Conclusions There is a need to increase public health awareness of the optimal time and subsequent benefits for taking folic acid, to prevent neural tube defects.</p

Gift of life or sacrifice?: Key discourses to understanding organ donor families' decision-making

Globally, there is a critical shortage of donor organs to meet the demands for human organ transplantation. An understanding of what motivates families to agree to donation is therefore essential to maximise organ availability. The “gift for life” is a popular discourse long associated with pro-donation and transplant activists, its use seemingly directed at heightening public awareness about the perceived benefits of organ donation. However the potential pressure and obligation implicit within such rhetoric could be detrimental to donor families. It has been suggested that the donation event is better represented as a “sacrifice” as this discourse acknowledges the suffering of the bereaved family and the possible difficulties encountered in their decision-making about organ donation. Drawing on data from three studies that explored the bereavement experiences of donor families, this paper examines the relative value of gift of life or sacrifice as discourses that contribute to a greater understanding of organ donor families’ decision-making. We propose that the compelling nature of sacrifice and the manner in which it impinges on families’ decision-making may help to explain the high refusal rates in populations that appear generally aware of the benefits of organ transplantation. Insights into the relative importance of gift of life or sacrifice to families when making decisions could potentially contribute to enhancing families’ satisfaction with their decisions, improve support to families and increase the incidence of donation

The dynamics of surface donor traps in AlGaN/GaN MISFETs using transient measurements and TCAD modelling

This paper presents a detailed and correlated (i) Id-Vg, (ii) Cgg-Vg, and (iii) transient analysis of donor traps in a SiN/GaN/AlGaN/GaN Metal-Insulator-Semiconductor Field-Effect Transistor (MISFET) fabricated on a silicon substrate. We explain for the first time that the long-time constants are due to the close coupling between the emission/capture processes on one hand and the transient transport of electrons across the GaN/AlGaN barrier on the other. Emission and capture time constants were extracted for several bias conditions and temperatures. Moreover, we have developed a TCAD model that consistently gives a good match to DC, AC, and transient experimental results

Investigation of surface charges and traps in gallium nitride/aluminium gallium nitride/gallium nitride high-voltage transistors via measurements and technology computer-aided design simulations of transfer characteristics of metal-insulator-semiconductor field-effect transistors and high-electron-mobility transistors

This study presents a detailed analysis of the Plasma-enhanced chemical vapour deposition (PECVD) silicon-nitride/semiconductor interface of gallium nitride (GaN) transistors through the study of the transfer characteristics of a large-gate-area metal-insulator-semiconductor field-effect transistor (MISFET). Id-Vg measurements were performed on several MISFETs across the wafer and for all of them the authors observed strong hysteresis between forward and reverse sweeps and a double kink. These features indicate the presence of traps beneath the gate electrode. Neither the hysteresis nor the kinks were seen in the measured high-electron-mobility transistor (HEMT) characteristics suggesting that the passivation/semiconductor interface is electrically responsible for them. The transfer characteristics of the MISFET have been reproduced using a technology computer-aided design (TCAD) deck that includes fixed charges and donor traps at the passivation/semiconductor interface. The impact of these charges on the Id-Vg and their influence on the formation of a surface-inversion layer is here explained through extensive TCAD simulations. This study has also been extended to different temperatures between 35 and 75°C to investigate the change in the transfer characteristics at elevated temperatures. It is shown that the hysteresis observed between forward and reverse sweeps and the transconductance decrease significantly with increasing temperature