Tunnelling Characteristics of Stone-Wales Defects in Monolayers of Sn and Group-V Elements

Topological defects in ultrathin layers are often formed during synthesis and processing, thereby, strongly influencing their electronic properties . In this paper, we investigate the role of Stone-Wales (SW) defects in modifying the electronic properties of the monolayers of Sn and group-V elements. The calculated results find the electronic properties of stanene (monolayer of Sn atoms) to be strongly dependent on the concentration of SW-defects e.g., defective stanene has nearly zero band gap (~ 0.03 eV) for the defect concentration of 2.2 x 10^13 cm^-2 which opens up to 0.2 eV for the defect concentration of 3.7 x 10^13 cm^-2. In contrast, SW-defects appear to induce conduction states in the semiconducting monolayers of group-V elements. These conduction states act as channels for electron tunnelling, and the calculated tunnelling characteristics show the highest differential conductance for the negative bias with the asymmetric current-voltage characteristics. On the other hand, the highest differential conductance was found for the positive bias in stanene. Simulated STM topographical images of stanene and group-V monolayers show distinctly different features in terms of their cross-sectional views and distance-height profiles which can serve as fingerprints to identify the topological defects in the monolayers of group-IV and group-V elements in experiments.Comment: 18 pages, 5 figures, 1 tabl

Reactivity of neutral and charged B13 clusters with O2: A theoretical study

The chemical reactivity of neutral, cationic, and anionic species of the gas phase B13 cluster with molecular oxygen, O2, was investigated using density functional theory. All three species of B 13 interact with an oxygen molecule to generate a variety of stable isomers, with those representing a dissociative chemisorption process forming the most stable configurations. Our results also show site-specific bonding of oxygen to the B13(+/0/-) cluster. The effect of sequential ionization on the formation of products is pronounced. In ionic B13 clusters, in addition to energetics, the spin of the reactants and products plays a vital role in determining the most favorable product channel. In addition, this study reveals a richness of phenomena requiring a unified consideration of energy, geometry, spin conversion, and details of the electronic structure not previously illustrated for the reactivity of boron clusters. © 2010 American Institute of Physics

Monolayer, Bilayer and Heterostructures of Green Phosphorene for Water Splitting and Photovoltaics

We report the results of density functional theory (DFT) based calculations on monolayer and bilayer green phosphorene and their heterostructures with MoSe2. Both monolayer and bilayer green phosphorene are direct band gap semiconductors and possess anisotropic carrier mobility as high as 10^{4} cm^{2}V^{-1}s^{-1}. In bilayers, pressure of about 9 GPa induces the semiconductor-metal transition. Moreover, the band gap depends strongly on the thickness of the films and the external electric field. By employing strain-engineering under suitable solution conditions, monolayer and AC-stacked bilayer green phosphorene offer the band edge alignments which can be used for water splitting. The upper limit of the power conversion efficiencies for monolayer, AB- and AC-stacked bilayer green phosphorene heterostructures with MoSe_{2} is calculated to be 18-21 %. Our results show the possibility of green phosphorene to be used as photocatalytic and photovoltaic material in the energy-related applications.Comment: 23 pages, 7 figures, 2 table

Two Dimensional Allotropes of Arsenene with Wide Range of High and Anisotropic Carrier Mobility

Considering the rapid development of experimental techniques for fabricating 2D materials in recent years, various monolayers are expected to be experimentally realized in the near future. Motivated by the recent research activities focused on the honeycomb arsenene monolayers, stability and carrier mobility of non-honeycomb and porous allotropic arsenene are determined using first principles calculations. In addition to five honeycomb structures of arsenene, a total of eight other structures are considered in this study. An extensive analysis comprising energetics, phonon spectra and mechanical properties confirms that these structures are energetically and dynamically stable. All these structures are semiconductors with a broad range of band gap varying from ~1 eV to ~2.5 eV. Significantly, these monolayer allotropes possess anisotropic carrier mobilities as high as several hundred cm^{2}V^{-1}s^{-1} which is comparable with the well-known 2D materials such as black phosphorene and monolayer MoS_{2}. Combining such broad band gaps and superior carrier mobilities, these monolayer allotropes can be promising candidates for the superior performance of the next generation nanoscale devices. We further explore these monolayer allotropes for photocatalytic water splitting and find that arsenene monolayers have potential for usage as visible light driven photocatalytic water splitting.Comment: 31 pages, 8 figures, 3 table

Electronic conduction in a three-terminal molecular transistor

The electronic conduction of a novel, three-terminal molecular architecture, analogous to a heterojunction bipolar transistor is studied. In this architecture, two diode arms consisting of donor-acceptor molecular wires fuse through a ring, while a gate modulating wire is a \pi-conjugated wire. The calculated results show the enhancement or depletion mode of a transistor by applying a gate field along the positive or negative direction. A small gate field is required to switch on the current in the proposed architecture. The changes in the electronic conduction can be attributed to the intrinsic dipolar molecular architecture in terms of the evolution of molecular wavefunctions, specifically the one associated with the terphenyl group of the modulating wire in the presence of the gate field.Comment: 13 pages, 5 figure

Centile values for serum lipids and blood pressure for Asian Indian adolescents

BACKGROUND: Reference data for plasma lipids and blood pressure are not available for Asian Indian adolescents. This study aimed to develop representative age- and sex- specific percentile reference data for serum lipids [total cholesterol (TC), triglycerides (TG), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), non-HDL cholesterol] and blood pressure for urban Asian Indian adolescents aged 14–18 years. The sample consisted of 680 boys and 521 girls aged 14–18 years from the cross-sectional population survey, Epidemiological Study of Adolescents and Young Adults (ESAY) for whom the data for serum lipid levels and blood pressure were recorded. Smoothed age- and sex- specific 5(th), 10(th), 25(th), 50(th), 75(th), 85(th), 90(th )and 95(th )percentiles where derived using LMS regression. RESULTS: Percentile-based reference data for serum lipids and blood pressure are presented for adolescent Asian Indian boys and girls for the first time. Asian Indian adolescents had lower levels of serum TC, LDL-C and HDL-C and higher TG than their counterparts in the USA. Interesting trends in TC and HDL-C levels where observed, which might reflect changes in dietary pattern and physical activity in this age group in India. CONCLUSION: These reference data could be used to identify adolescents with an elevated risk of developing dyslipidemia, hypertension and cardiovascular disorders, to plan and implement preventive policies, and to study temporal trends

CIFKAS A Measurer of Functional Disability Status in Knee Osteoarthritis

Knee osteoarthritis (OA) results in structural and functional abnormalities and reduced functional performance abilities. In developing countries majority of population lives in rural areas having limited resources and socio-cultural biodiversity. Their personal, socio-cultural and occupational habits vary and need to be addressed. So a culturally relevant and contextually appropriate, Composite Indian Functional Knee Assessment Scale (CIFKAS) for measuring the functional status in knee osteoarthritis was formulated. 128 participants from various geographical regions of India of age range 40 to 60 years using convenient sampling were included and informed consent signed by the participants. Each participant was assigned to one of the two groups. 39 participants in group A reported no episode of knee pain while 89 participants in group B reported at least one episode of knee pain in the last two months. Each participant was assessed on Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and CIFKAS and statistical analysis was done. The Pearson correlation coefficient calculated for all 128 subjects for pain, physical functional abilities and total functional disability score were 0.878, 0.925 and 0.945 respectively. Between group analysis was done using Independent t test and p value was found to be not significant for pain (≤178), highly significant for physical functional abilities (p≤0001) and very significant for total functional disability status score (p≤004). The results indicate that both WOMAC and CIFKAS are highly correlated and there is no difference between the two for measuring pain, but for functional ability and overall functional disability status within their functional context, CIFKAS is a better tool than WOMAC.KEYWORDS: Knee osteoarthritis; Functional disability; Socio-cultural biodiversities; Functional contextInternet Journal of Medical Update 2012 January;7(1):47-5