Doping Dependence of Thermal Oxidation on n-type 4H-SiC

The doping dependence of dry thermal oxidation rates in n-type 4H-SiC was investigated. The oxidation was performed in the temperature range 1000C to 1200C for samples with nitrogen doping in the range of 6.5e15/cm3 to 9.3e18/cm3, showing a clear doping dependence. Samples with higher doping concentrations displayed higher oxidation rates. The results were interpreted using a modified Deal-Grove model. Linear and parabolic rate constants and activation energies were extracted. Increasing nitrogen led to an increase in linear rate constant pre-exponential factor from 10-6m/s to 10-2m/s and the parabolic rate constant pre-exponential factor from 10e9m2/s to 10e6m2/s. The increase in linear rate constant was attributed to defects from doping-induced lattice mismatch, which tend to be more reactive than bulk crystal regions. The increase in the diffusion-limited parabolic rate constant was attributed to degradation in oxide quality originating from the doping-induced lattice mismatch. This degradation was confirmed by the observation of a decrease in optical density of the grown oxide films from 1.4 to 1.24. The linear activation energy varied from 1.6eV to 2.8eV, while the parabolic activation energy varied from 2.7eV to 3.3eV, increasing with doping concentration. These increased activation energies were attributed to higher nitrogen content, leading to an increase in effective bond energy stemming from the difference in C-Si (2.82eV) and Si-N (4.26eV) binding energies. This work provides crucial information in the engineering of SiO2 dielectrics for SiC MOS structures, which typically involve regions of very different doping concentrations, and suggests that thermal oxidation at high doping concentrations in SiC may be defect mediated.Comment: 13 pages. 9 figures, accepted as a transiction in IEEE electron device. TED MS#8035

Physicochemical properties of various alginate-based raft-forming antacid products: a comparative study

Background: Alginate-based, raft-forming antacid products with reflux suppressant activity are complex formulations expected to achieve effective raft formation and cause elimination or displacement of the acid pocket, which is typically manifested in gastroesophageal reflux disease (GERD).Methods: In the present study, six alginate-based raft-forming products commercially available in the Indian market were compared in terms of their acid neutralization properties, strength, resilience and structural and thermal properties of their rafts. Percent alginate content was also determined.Results: Rafts of products containing calcium-based antacids formed voluminous, porous and floating rafts within seconds of addition to the simulated gastric fluid (SGF) compared with the products that contained aluminium and magnesium-based antacids. Marked differences were not evident in the ANC (acid neutralization capacity) values of the various products. No correlation was observed between ANC and raft-forming capacity or duration of neutralization. Raft structures affected their neutralization profiles. Rafts of porous and absorbent nature could retain their ANC probably due to release of trapped antacids. Further, raft strengths of only two products were above the British Pharmacopoeia specification of not less than 7.5 g. Sodium alginate content was within specifications (85-115%) for three of the six products.Conclusions: Raft-forming formulations with higher alginate content and calcium-based antacids have better physicochemical properties such as ANC, neutralization profiles, raft strength and raft resilience than those with lower alginate content or those containing aluminium or magnesium-based antacids

A study of knowledge, attitude and practice on use of antibiotics and its resistance among the doctors and interns at urban tertiary care hospital: an interventional study

Background: Infections due to resistant micro-organisms considerably increase the mortality rate, treatment cost, disease spread and duration of illness. The development of antibiotic resistance (AMR) is increasing steadily increasing over the last 10-15 years, which is a real threat to disease management. Many studies states that about 20-50% of antibiotic use unnecessary so decreasing the use of antibiotics is the first step to curb the AMR.Methods: A questionnaire based prospective interventional study among the doctors. Systemic random sampling was applied. The pre tested structured questionnaire was used. Data’s were summarised in the excel sheet, analysed by proportions, percentages and other statistical methods like Student t test, Fisher test and Chi square test were used to check the association. The p>0.05 was considered as significant.Results: Out of 200 doctors, preliminary screening of 170 was included in the study and finally 156 participants were actively selected for analysis of results. Out of 156 participants, 55.1% were MBBS Intern and 44.9% were doctors. High significance (p=0.0001) were found between pre and post knowledge, attitude and practice of doctors.Conclusions: Further modes of studies have to perform to identify the determinants of attitude behaviour and motivation that lead people to use and misuse antibiotics. For effective outcome many more qualitative and quantitative studies are required. In addition, health care system should follow proper regulation and prescription policy as well as controls for prescription of antibiotic drugs

Thickness Estimation of Epitaxial Graphene on SiC using Attenuation of Substrate Raman Intensity

A simple, non-invasive method using Raman spectroscopy for the estimation of the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is presented, enabling simultaneous determination of thickness, grain size and disorder using the spectra. The attenuation of the substrate Raman signal due to the graphene overlayer is found to be dependent on the graphene film thickness deduced from X-ray photoelectron spectroscopy and transmission electron microscopy of the surfaces. We explain this dependence using an absorbing overlayer model. This method can be used for mapping graphene thickness over a region and is capable of estimating thickness of multilayer graphene films beyond that possible by XPS and Auger electron spectroscopy (AES).Comment: 14 pages, 9 figure

High purity semi-insulating 4H-SiC epitaxial layers by Defect-Competition Epitaxy

Thick, high-purity semi-insulating (SI)homoepitaxial layers on Si-face 4H-SiC weregrownsystematically, with resistivity \geq 109{\Omega}-cmby maintaining high C/Si ratios 1.3-15 during growth.Comparison of secondary ion mass spectra betweenlow-dopedepilayers grown at C/Si ratio<1.3andSI-epilayers grown at C/Si ratio>1.3 showed little difference in residual impurity concentrations. A reconciliation of impurity concentration with measured resistivity indicated a compensating trap concentration of ~1015cm-3present only in the SI-epilayers. High- resolution photo induced transient spectroscopy (HRPITS) identified themas Si-vacancy related deep centers, with no detectable EH6/7 and Z1/2levels. Recombination lifetimes ~5ns suggest application in fast-switching power devices.Comment: Submitted to Applied Physics Letter