Surface transfer doping of diamond using transition metal oxides

This thesis presents a body of work which advances the use of single crystal hydrogen terminated diamond as a semiconducting material. Surface transfer doping of intrinsic diamond is investigated, examining the current state of this technology and its limitations. New techniques for producing robust, thermally stable surface transfer doped diamond were achieved through use of transition metal oxides such as MoO3 and V2O5, as demonstrated experimentally by way of Hall measurement. Through use of these materials, thermal stability was greatly increased up to temperatures of at least 300oC. To achieve this higher temperature operation, encapsulation of MoO3 and V2O5 was found to be necessary in maintaining conductivity of the diamond surface due to suspected thermally-induced loss of hydrogen termination. Similarly, long term atmospheric stability is shown to necessitate annealing of the diamond surface prior to oxide deposition and for thinner layers of oxide, down to 10 nm, encapsulation of the oxide to isolate from atmosphere is shown to be required for increased stability. As well as the improvements in stability offered by these transition metal oxides, sheet resistance of the hydrogen terminated diamond surface was also greatly reduced. Carrier densities as high as ~7.5 ×1013 cm-2 were observed for MoO3-induced surface transfer doping, resulting in a low sheet resistance of ~ 3 kΩ/□. In parallel to the development of oxide acceptor materials, conditioning of the diamond surface was explored using Atomic Force Microscopy (AFM). Techniques for smoothing the surface after mechanical polishing were developed by way of RIE and ICP etching using both chlorine and oxygen mixtures. Surface roughness down to 2 angstroms was demonstrated, showing a significant improvement in roughness over mechanical polishing alone. Similarly, observed defects produced by polishing induced damage were removed through use of this etching strategy. The effects of varied plasma density during hydrogen termination was explored on etched surfaces, which produced higher quality hydrogen-terminated surfaces as verified by surface conductivity and AFM measurements. Finally, incorporation of MoO3 into a preliminary Field Effect Transistor (FET) device on diamond was attempted. Fabrication techniques to produce a FET device on hydrogen-terminated diamond is shown with preliminary results of MoO3 encapsulated devices. Insights into the fabrication of ohmic and gate contacts, incorporating MoO3, is also discussed

The direct hydrothermal deposition of cobalt-doped MoS2 onto fluorine-doped SnO2 substrates for catalysis of the electrochemical hydrogen evolution reaction

Metal chalcogenides, and doped molybdenum sulfides in particular, have considerable potential as earth-abundant electrocatalysts for the hydrogen evolution reaction. This is especially true in the case of solar-to-hydrogen devices, where an ability to deposit these materials on transparent substrates is therefore desirable. Hydrothermal methods are perhaps the most common route by which metal chalcogenide materials suitable for the hydrogen evolution reaction are produced. Such methods are simple and scalable, but the direct hydrothermal deposition of metal chalcogenides on transparent oxide electrodes has hitherto never been reported. Such an advance would greatly facilitate the expansion of the field by removing the requirement for separate hydrothermal-synthesis and catalyst-deposition steps. In this paper, we show that the ternary chalcogenide Co2Mo9S26 can be synthesised on a fluorine-doped tin oxide substrate by hydrothermal methods directly from solutions of the simple metal salts. These films display good activity for the hydrogen evolution reaction from acid solution, achieving current densities of 10 mA cm−2 at 260 mV overpotential with a Tafel slope of 64 mV per decade. Moreover, the resulting films can be made to be translucent, a very useful property which would allow light to be transmitted through the catalyst to an underlying light-harvesting array in any solar-to-hydrogen device employing this material at the cathode

Text messaging and brief phone calls for weight loss in overweight and obese English- and Spanish-speaking adults: A 1-year, parallel-group, randomized controlled trial.

BACKGROUND:Weight loss interventions based solely on text messaging (short message service [SMS]) have been shown to be modestly effective for short periods of time and in some populations, but limited evidence is available for positive longer-term outcomes and for efficacy in Hispanic populations. Also, little is known about the comparative efficacy of weight loss interventions that use SMS coupled with brief, technology-mediated contact with health coaches, an important issue when considering the scalability and cost of interventions. We examined the efficacy of a 1-year intervention designed to reduce weight among overweight and obese English- and Spanish-speaking adults via SMS alone (ConTxt) or in combination with brief, monthly health-coaching calls. ConTxt offered 2-4 SMS/day that were personalized, tailored, and interactive. Content was theory- and evidence-based and focused on reducing energy intake and increasing energy expenditure. Monthly health-coaching calls (5-10 minutes' duration) focused on goal-setting, identifying barriers to achieving goals, and self-monitoring. METHODS AND FINDINGS:English- and Spanish-speaking adults were recruited from October 2011 to March 2013. A total of 298 overweight (body mass index [BMI] 27.0 to 39.9 kg/m2) adults (aged 21-60 years; 77% female; 41% Hispanic; 21% primarily Spanish speaking; 44% college graduates or higher; 22% unemployed) were randomly assigned (1:1) to receive either ConTxt only (n = 101), ConTxt plus health-coaching calls (n = 96), or standard print materials on weight reduction (control group, n = 101). We used computer-based permuted-block randomization with block sizes of three or six, stratified by sex and Spanish-speaking status. Participants, study staff, and investigators were masked until the intervention was assigned. The primary outcome was objectively measured percent of weight loss from baseline at 12 months. Differences between groups were evaluated using linear mixed-effects regression within an intention-to-treat framework. A total of 261 (87.2%) and 253 (84.9%) participants completed 6- and 12-month visits, respectively. Loss to follow-up did not differ by study group. Mean (95% confidence intervals [CIs]) percent weight loss at 12 months was -0.61 (-1.99 to 0.77) in the control group, -1.68 (-3.08 to -0.27) in ConTxt only, and -3.63 (-5.05 to -2.81) in ConTxt plus health-coaching calls. At 12 months, mean (95% CI) percent weight loss, adjusted for baseline BMI, was significantly different between ConTxt plus health-coaching calls and the control group (-3.0 [-4.99 to -1.04], p = 0.003) but not between the ConTxt-only and the control group (-1.07 [-3.05 to 0.92], p = 0.291). Differences between ConTxt plus health-coaching calls and ConTxt only were not significant (-1.95 [-3.96 to 0.06], p = 0.057). These findings were consistent across other weight-related secondary outcomes, including changes in absolute weight, BMI, and percent body fat at 12 months. Exploratory subgroup analyses suggested that Spanish speakers responded more favorably to ConTxt plus health-coaching calls than English speakers (Spanish contrast: -7.90 [-11.94 to -3.86], p < 0.001; English contrast: -1.82 [-4.03 to 0.39], p = 0.107). Limitations include the unblinded delivery of the intervention and recruitment of a predominantly female sample from a single site. CONCLUSIONS:A 1-year intervention that delivered theory- and evidence-based weight loss content via daily personalized, tailored, and interactive SMS was most effective when combined with brief, monthly phone calls. TRIAL REGISTRATION:ClinicalTrials.gov NCT01171586

Surface transfer doping of diamond: a review

Ultra-wide bandgap materials show great promise as a solution to some of the limitations of current state of the art semiconductor technology. Among these, diamond has exhibited great potential for use in high-power, high-temperature electronics, as well as sensing and quantum applications. Yet, significant challenges associated with impurity doping of the constrained diamond lattice remain a primary impediment towards the development of diamond-based electronic devices. An alternative approach, used with continued success to unlock the use of diamond for semiconductor applications, has been that of ‘surface transfer doping’ - a process by which intrinsically insulating diamond surfaces can be made semiconducting without the need for traditional impurity doping. Here, we present a review of progress in surface transfer doping of diamond, both a history and current outlook of this highly exploitable attribute

Optimization of ohmic contact for AlGaN/ GaN HEMT on low resistivity silicon

In this article, we report the optimization of ohmic contact formation on AlGaN/GaN on low-resistivity silicon. For achieving this, a strategy of uneven AlGaN/GaN was introduced through patterned etching of the substrate under the contact. Various pattern designs (holes, horizontal lines, vertical lines, grid) and varied etch depth (above and below the 2-D electron gas) were investigated. Furthermore, a study of planar and nonplanar ohmic metallization was investigated. Compared to a traditional fabrication strategy, we observed a reduced contact resistance from 0.35 to 0.27 Ω · mm by employing a grid etching approach with a “below channel” etch depth and nonplanar ohmic metallization. In general, measurements of “below channel” test structures exhibited improved contact resistance compared to “above channel” in both planar and nonplanar ohmic metallizatio

Thermal performance of diamond field-effect transistors

In this report, the thermal performance of a hydrogen (H)-terminated diamond field-effect transistor (FET) is investigated using Raman spectroscopy and electrothermal device modeling. First, the thermal conductivity (κdiamond) of the active diamond channel was determined by measuring the temperature rise of transmission line measurement structures under various heat flux conditions using nanoparticle-assisted Raman thermometry. Using this approach, κdiamond was estimated to be 1860 W/m K with a 95% confidence interval ranging from 1610 to 2120 W/m K. In conjunction with measured electrical output characteristics, this κ was used as an input parameter for an electrothermal device model of an H-terminated diamond FET. The simulated thermal response showed good agreement with surface temperature measurements acquired using nanoparticle-assisted Raman thermometry. These diamond-based structures were highly efficient at dissipating heat from the active device channel with measured device thermal resistances as low as ∼1 mm K/W. Using the calibrated electrothermal device model, the diamond FET was able to operate at a very high power density of 40 W/mm with a simulated temperature rise of ∼33 K. Finally, the thermal resistance of these lateral diamond FETs was compared to lateral transistor structures based on other ultrawide bandgap materials (Al0.70Ga0.30N, β-Ga2O3) and wide bandgap GaN for benchmarking. These results indicate that the thermal resistance of diamond-based lateral transistors can be up to ∼10× lower than GaN-based devices and ∼50× lower than other UWBG devices

SUPPORT-AF: Piloting a Multi-Faceted, Electronic Medical Record-Based Intervention to Improve Prescription of Anticoagulation

Background: Only 50% of eligible atrial fibrillation ( AF ) patients receive anticoagulation ( AC ). Feasibility and effectiveness of electronic medical record (EMR)-based interventions to profile and raise provider AC percentage is poorly understood. The SUPPORT-AF (Supporting Use of AC Through Provider Profiling of Oral AC Therapy for AF) study aims to improve rates of adherence to AC guidelines by developing and delivering supportive tools based on the EMR to providers treating patients with AF. Methods and Results: We emailed cardiologists and community-based primary care providers affiliated with our institution reports of their AC percentage relative to peers. We also sent an electronic medical record-based message to these providers the day before an appointment with an atrial fibrillation patient who was eligible but not receiving AC . The electronic medical record message asked the provider to discuss AC with the patient if he or she deemed it appropriate. To assess feasibility, we tracked provider review of our correspondence. We also tracked the change in AC for intervention providers relative to alternate primary care providers not receiving our intervention. We identified 3786, 1054, and 566 patients cared for by 49 cardiology providers, 90 community-based primary care providers, and 88 control providers, respectively. At baseline, the percentage of AC was 71.3%, 63.5%, and 58.3% for these 3 respective groups. Intervention providers reviewed our e-mails and electronic medical record messages 45% and 96% of the time, respectively. For providers responding, patient refusal was the most common reason for patients not being on AC (21%) followed by high bleeding risk (19%). At follow-up 10 weeks later, change in AC was no different for either cardiology or community-based primary care providers relative to controls (0.2% lower and 0.01% higher, respectively). Conclusions: Our intervention profiling AC was feasible, but not sufficient to increase AC in our population

Unveiling Soft Gamma-Ray Repeaters with INTEGRAL

Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and studied in detail for the first time at hard-X/soft gamma rays. This has produced a wealth of new scientific results, which we will review here. Since SGR 1806-20 was particularly active during the last two years, more than 300 short bursts have been observed with INTEGRAL. and their characteristics have been studied with unprecedented sensitivity in the 15-200 keV range. A hardness-intensity anticorrelation within the bursts has been discovered and the overall Number-Intensity distribution of the bursts has been determined. In addition, a particularly active state, during which ~100 bursts were emitted in ~10 minutes, has been observed on October 5 2004, indicating that the source activity was rapidly increasing. This eventually led to the Giant Flare of December 27th 2004, for which a possible soft gamma-ray (>80 keV) early afterglow has been detected. The deep observations allowed us to discover the persistent emission in hard X-rays (20-150 keV) from 1806-20 and 1900+14, the latter being in a quiescent state, and to directly compare the spectral characteristics of all Magnetars (two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL.Comment: 8 pages, 7 figures, Presented at the conference "Isolated Neutron Stars: from the Surface to the Interior", London, UK, 24-28 April 200

Simultaneous quantification of 12 different nucleotides and nucleosides released from renal epithelium and in human urine samples using ion-pair reversed-phase HPLC

Nucleotides and nucleosides are not only involved in cellular metabolism but also act extracellularly via P1 and P2 receptors, to elicit a wide variety of physiological and pathophysiological responses through paracrine and autocrine signalling pathways. For the first time, we have used an ion-pair reversed-phase high-performance liquid chromatography ultraviolet (UV)-coupled method to rapidly and simultaneously quantify 12 different nucleotides and nucleosides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, adenosine, uridine triphosphate, uridine diphosphate, uridine monophosphate, uridine, guanosine triphosphate, guanosine diphosphate, guanosine monophosphate, guanosine): (1) released from a mouse renal cell line (M1 cortical collecting duct) and (2) in human biological samples (i.e., urine). To facilitate analysis of urine samples, a solid-phase extraction step was incorporated (overall recovery rate ? 98 %). All samples were analyzed following injection (100 ?l) into a Synergi Polar-RP 80 Å (250 × 4.6 mm) reversed-phase column with a particle size of 10 ?m, protected with a guard column. A gradient elution profile was run with a mobile phase (phosphate buffer plus ion-pairing agent tetrabutylammonium hydrogen sulfate; pH 6) in 2-30 % acetonitrile (v/v) for 35 min (including equilibration time) at 1 ml min(-1) flow rate. Eluted compounds were detected by UV absorbance at 254 nm and quantified using standard curves for nucleotide and nucleoside mixtures of known concentration. Following validation (specificity, linearity, limits of detection and quantitation, system precision, accuracy, and intermediate precision parameters), this protocol was successfully and reproducibly used to quantify picomolar to nanomolar concentrations of nucleosides and nucleotides in isotonic and hypotonic cell buffers that transiently bathed M1 cells, and urine samples from normal subjects and overactive bladder patients