In this work, we have systematically studied structural, electronic and magnetic properties of atomic scale defects in 2D transition metal dichalcogenides MX 2 , (M = Mo and W; X = S, Se and Te) by density functional theory. Various types of defects, e.g., X vacancy, X interstitial, M vacancy, M interstitial, MX and XX double vacancies have been considered. It has been found that the X interstitial has the lowest formation energy (∼ 1 eV) for all the systems in the X-rich condition whereas for M-rich condition, X vacancy has the lowest formation energy except for MTe 2 systems. Both these defects have very high equilibrium defect concentrations at growth temperatures (1000K-1200K) reported in literature. A pair of defects, e.g., two X vacancies or one M and one X vacancies tend to occupy the nearest possible distance. No trace of magnetism has been found for any one of the defects considered. Apart from X interstitial, all other defects have defect states appearing in the band gap, which can greatly affect the electronic and optical properties of the pristine systems. Our calculated optical properties show that the defect states cause optical transitions at ∼ 1.0 eV, which can be beneficial for light emitting devices. The results of our systematic study are expected to guide the experimental nanoengineering of defects to achieve suitable properties related to band gap modifications and characterization of defect fingerprints via optical absorption measurements. arXiv:1509.01445v2 [cond-mat.mes-hall]

We study the effect of doping on band gap in Mg-and Cd-doped zinc oxide nanostructures and molecular clusters. The fabrication of doped nanostructures was carried out via solution route. The lower doping efficiency of Cd than that of Mg has been explained in terms of binding energy. The band gap varied from 3.04 eV in Cd-doped ͑9.1 at. % of Cd͒ nanostructure to 3.99 eV in Mg-doped ͑16.8 at. % of Mg͒ nanostructure. Theoretical analysis using first-principles molecular dynamics techniques on pristine and doped ZnO clusters shows that the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital exhibits a similar variation as does the band gap in nanostructures with the varying concentration of Mg and Cd.

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BackgroundAdolescent students are vulnerable group for tobacco addiction. Tobacco use among school children is becoming a serious problem in developing countries. This study was carried out to estimate the prevalence of tobacco use and to determine associated factors among adolescent students of Kalaiya municipality.MethodsA cross sectional survey was carried out by self-administered questionnaire adapted from Global Youth Tobacco Survey to assess tobacco use among the representative sample of 1540 adolescent students selected by stratified random sampling from December 2014 to May 2015.ResultOverall prevalence of ‘ever users’ of tobacco products was 25.3 %. Prevalence among boys and girls was 31 and 14.4 % respectively. Mean age at initiation of using tobacco was 13.38 ± 1.62 years. The correlates of tobacco use were: sex, ethnicity, family members and friends using tobacco products, and students exposed at home and public place.ConclusionSchool based interventions and tobacco education are necessary to prevent initiation and cessation of tobacco use. Legislations related to tobacco control should be enforced to decrease availability, accessibility and affordability of tobacco products. Social norms of tobacco use among parents and others at home as well as at public place should be modified to curb the tobacco use among school students.

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