Chemical studies of the passivation of GaAs surface recombination using sulfides and thiols

Steady-state photoluminescence, time-resolved photoluminescence, and x-ray photoelectron spectroscopy have been used to study the electrical and chemical properties of GaAs surfaces exposed to inorganic and organic sulfur donors. Despite a wide variation in S2–(aq) concentration, variation of the pH of aqueous HS–solutions had a small effect on the steady-state n-type GaAs photoluminescence intensity, with surfaces exposed to pH=8, 0.1-M HS–(aq) solutions displaying comparable luminescence intensity relative to those treated with pH=14, 1.0-M Na2S·9H2O(aq). Organic thiols (R-SH, where R=–CH2CH2SH or –C6H4Cl) dissolved in nonaqueous solvents were found to effect increases in steady-state luminescence yields and in time-resolved luminescence decay lifetimes of (100)-oriented GaAs. X-ray photoelectron spectroscopy showed that exposure of GaAs surfaces to these organic systems yielded thiols bound to the GaAs surface, but such exposure did not remove excess elemental As and did not form a detectable As2S3 overlayer on the GaAs. These results imply that complete removal of As0 or formation of monolayers of As2S3 is not necessary to effect a reduction in the recombination rate at etched GaAs surfaces. Other compounds that do not contain sulfur but that are strong Lewis bases, such as methoxide ion, also improved the GaAs steady-state photoluminescence intensity. These results demonstrate that a general class of electron-donating reagents can be used to reduce nonradiative recombination at GaAs surfaces, and also imply that prior models focusing on the formation of monolayer coverages of As2S3 and Ga2S3 are not adequate to describe the passivating behavior of this class of reagents. The time-resolved, high level injection experiments clearly demonstrate that a shift in the equilibrium surface Fermi-level energy is not sufficient to explain the luminescence intensity changes, and confirm that HS– and thiol-based reagents induce substantial reductions in the surface recombination velocity through a change in the GaAs surface state recombination rate

Phosphorus and sulphur interactions, 1978.

Yield results, 78AL3, 78KE4, 78M08, 78BY3, 78BA8, 78BU3, 78N04, 78A7, 78C4, 78B4, 78MA2. Soil sampling data

Wheat responses to levels, sources and times of application of nitrogen.

Trial 90M055 Associated work: 90NO112, 105,104.111, 90MO53, 54,56 Location: Dandaragan This project characterizes the dynamics of nitrogen supply to a wheat crop at each of the sites on which various methods of making fertilizer recommendation were tested. It supposedly provides the optimum nitrogen fertilizer regime as well as detailed information on nitrogen supply and demand so that results can be made transferable to other situations. Trial 90MO56 Related trials: 90NO104, 105, 111, 112; 90MO53, 54,55 Tactical nitrogen application for wheat Location: Danaragan This project compares tactical and strategic methods for determining nitrogen requirements of wheat. The tactical methods depend on updating estimates of yield potential and nitrogen status of the crop as the season progresses

UpLIFTIng PFI: does LIFT improve public-private procurement?

The Private Finance Initiative (PFI) and Local Improvement Finance Trust (LIFT) were both introduced by the UK government as part of a drive to improve public service provision. Both PFI and LIFT focus on leveraging the key strengths of the public and private sectors when developing new facilities. This paper does not seek to question the need for new infrastructure, but rather discusses the difficulties encountered when trying to analyse LIFT as a system and when evaluating whether it can address earlier concerns about the PFI procurement process. Our analysis suggests that it is difficult to predict whether LIFT will be capable of delivering on its promise of providing cost-effective, bespoke Primary Care facilities

Improving cost-effectiveness of hypertension management at a community health centre

Objectives. To describe the pattern of prescribing for hypertension at a community health centre (CHC) and to evaluate the impact of introducing treatment guidelines and restricting availability of less cost-effective antihypertensive drugs on prescribing patterns, costs of drug treatment and blood pressure (BP) control.Design. Before/after intervention study.Setting. Medium-sized CHC in the Cape Flats area of Cape Town.Subjects. 1 084 hypertensive patients attending the CHC, who had at least two prescriptions for antihypertensive drugs during a 1-year period starting on 1 January 1992. Interventions. 1. Implementation of stepped-care guidelines for hypertension, specifying treatment with more cost-effective drugs and minimising drug treatment. 2. Reducing availability for routine prescribing by CHC doctors of 10 less cost-effective antihypertensive drugs or drug combinations.Outcome measures. 1. Mean number of drugs prescribed per patient. 2. Proportion of prescriptions for: each major class of antihypertensive drug; restricted availability and freely prescribable drugs; and more and less cost-effective drugs. 3. Mean monthly cost of drugs prescribed per patient. 4. Mean blood pressure and proportion of BP readings controlled (<160/95 mmHg) or uncontrolled (≥160/95 mmHg).Results. A mean of 1.7 active drugs was prescribed per patient per visit. The most frequently prescribed drugs were thiazide-like diuretics (44.8%), centrally acting agents (28.4%) and b-blockers (13.2%). Mean monthly drug costs per patient decreased significantly by R1.99 (24.2%) from R8.24 to R6.25 between the first and last prescription for each patient (exclusive of any reduction due to withdrawal of treatment). This was attributable to reduced prescribing of more expensive drugs withdrawn from routine use and a 51.1% increase in prescribing of the most cost-effective drugs. The overall annual cost-saving of the changes in prescribing for this CHC are estimated at R75 150. Blood pressure control did not change significantly.Conclusion. The pattern of changes in prescribing and drug costs was consistent with a causal effect of the interventions. The study demonstrates the potential forimproving cost-effectiveness of hypertension care in primary care in South Africa and the potential for research in this setting

Hypertension care at a Cape Town community health centre

Objectives. To describe the demographic profile of hypertensive patients and the quality of care for hypertension at a Cape Town community health centre (CHC).Design. Prospective, descriptive study.Setting and subjects. Medium-sized CHC, attended by 1098 hypertensive patients during a 1-year period from 1 January 1992.Outcome measures. Default rate - proportion of due visits not attended. Loss to follow-up - proportion of patients persistently defaulting or not responding to recall. Frequency of blood pressure measurement - per 12 due visits. Compliance - proportion of patients collecting ≥ 75% of antihypertensive drugs. Blood pressure control - mean blood pressure of aggregated readings; and proportion controlled (<160/95 mmHg) on the basis of all blood pressure readings and mean blood pressures of individual patients with two or more readings during the study period.Results. More than half (51.6%) of the hypertensive patients were aged ≥ 65 years; 81.7% were female. The default rate was between 11.9% and 19.4%. Compliance was high (76.9%). Loss to follow-up was 8.1 %. Blood pressure was recorded a mean of 4.0 times per 12 due visits. There were no significant gender differences with regard to these measures. Mean blood pressure was 158.3/89.6 mmHg. Over half (56.7%) of all individual readings over the year were uncontrolled and 51.4% of patients were found to be uncontrolled when categorised by their mean blood pressure. Control was significantly poorer among women ≥ 65 years.Conclusion. We found better compliance, more frequent blood pressure measurement, and lower defaulting and loss to follow-up compared with previous South African studies in similar settings. Despite this, blood pressure control was mediocre. Possible explanations for this are discussed. The low proportion of male hypertensives attending the CHC suggests that the accessibility or acceptability of care is poor for this group. The study illustrates the potential for research in this setting and for the use of computers to monitor the quality of primary care.