Naveen Kosar

Bio: Naveen Kosar is an academic researcher from University of Management and Technology. The author has contributed to research in topics: Hyperpolarizability & Density functional theory. The author has an hindex of 13, co-authored 36 publications receiving 491 citations. Previous affiliations of Naveen Kosar include COMSATS Institute of Information Technology & Hazara University.

Design of novel superalkali doped silicon carbide nanocages with giant nonlinear optical response

Abstract: In this study, the electronic and nonlinear optical (NLO) properties of a novel class of superalkalis (Li2F, Li3O and Li4N) doped silicon carbide (Si12C12) nanocages are investigated by using density functional theory (DFT) calculations. Computational results reveal that these complexes are quite stable and superalkalis prefer Sitop position of the nanocage energetically to be chemisorbed. The doping of superalkalis effectively reduced the HOMO–LUMO energy gap and transformed Si12C12 nanocage from insulator to n-type semiconductor. More interestingly, these complexes exhibited significantly large first hyperpolarizabilities (βo) in the range of 2141–19864 au. This remarkable increase in first hyperpolarizability (βo) values is due to small transition energies ΔE, which comes from the corresponding charge transfer from superalkali to the nanocage. The NLO response of the superalkali-doped Si12C12 nanocage was much better to those of their alkali-metal-doped analogs. Moreover, frequency dependent hyperpolarizability calculations are performed in the range of 400–1600 nm including 532 and 1064 nm for commonly used lasers. The TD-DFT analysis reveals that these complexes possess enough transparency in the UV region which is required besides large NLO response for practical applications in the field of opto-electronics. This study will provide new insights for designing of novel NLO materials having useful applications in all-optical switching, wavelength conversion and harmonic generation.

Theoretical study on novel superalkali doped graphdiyne complexes: Unique approach for the enhancement of electronic and nonlinear optical response.

Abstract: Based on DFT calculations, we have explored the changes in geometric, electronic and nonlinear optical (NLO) properties of M3O and M3S (M = Li, Na and K) doped graphdiyne. The doping of superalkalis not only changes the electronic properties of GDY but also remarkably alters the NLO properties. Stabilities of doped GDY are evaluated through interaction energies. HOMO-LUMO gap, NBO, polarizability and first hyperpolarizability (βo) calculations at hybrid (B3LYP) and long-range corrected methods (CAM-B3LYP, LC-BLYP and ωB97XD) are performed for studying the NLO properties of doped GDY complexes. Significantly high values of βo are observed for all doped structures, especially for Na3S@GDY (1.36×105 au). Reduction in HOMO-LUMO gap concomitant with increase of βo value is attributed to the strong interaction of Na3S with GDY. The partial density of states (PDOS) spectra strongly support the existence of excess electrons. To rationalize the trends in first hyperpolarizability of doped GDY, two level model calculations are also performed. This study of super alkalis doped GDY will be advantageous for promoting the potential applications of the nanostructures in designing new types of electronic nanodevices and production of high performance nonlinear optical materials.

Theoretical study on a boron phosphide nanocage doped with superalkalis: novel electrides having significant nonlinear optical response

Abstract: Three series of compounds Li2F@B12P12, Li3O@B12P12 and Li4N@B12P12 are theoretically designed and investigated for their nonlinear optical response using density functional theory (DFT). Computational results reveal that isomers VIII and X are inorganic electrides whereas the others are excess electron systems. Interaction energies reveal that these systems are quite stable and superalkalis are chemisorbed on the nanocage. Doping of a B12P12 nanocage with superalkali brings a considerable increase in the first hyperpolarizability response of the system. The highest first hyperpolarizability (β0 = 3.48 × 105 a.u.) along with good ultraviolet transparency is observed for isomer III of Li2F@B12P12. Moreover, all three series of compounds are systemically studied for the effect of different superalkalis and different doping positions on the nonlinear optical response. This study will be advantageous for promoting the potential applications of the fullerene-like superalkali doped B12P12 nanostructures in new types of electronic nanodevices and high-performance nonlinear optical materials with good ultraviolet transparency.

Single-Layer Behavior and Its Breakdown in Twisted Graphene Layers

Abstract: We report high magnetic field scanning tunneling microscopy and Landau level spectroscopy of twisted graphene layers grown by chemical vapor deposition. For twist angles exceeding ~3° the low energy carriers exhibit Landau level spectra characteristic of massless Dirac fermions. Above 20° the layers effectively decouple and the electronic properties are indistinguishable from those in single-layer graphene, while for smaller angles we observe a slowdown of the carrier velocity which is strongly angle dependent. At the smallest angles the spectra are dominated by twist-induced van Hove singularities and the Dirac fermions eventually become localized. An unexpected electron-hole asymmetry is observed which is substantially larger than the asymmetry in either single or untwisted bilayer graphene.

RESEARCH NOTE The First Preparation of Silicon Carbide Nanotubes by Shape Memory Synthesis and Their Catalytic Potential

Abstract: Two main innovations are presented in this article. (1) The first reproducible synthesis of silicon carbide nanotubes of different internal and external diameters. The method used, the shape memory synthesis, is based on the gas‐solid reaction between a vapor of SiO and nanotubes of carbon for the high diameters, and nanofibers of carbon for the small diameters. (2) A significant increase in the rate of a catalytic reaction (oxidation of H2S in S) probably due to a microscopic increase of the partial pressure of H2S inside the nanotubes, produced by condensation and microcapillarity, while the macroscopic partial pressure outside the tubes remains unchanged. This phenomenon could be extended to many other reactions, with polar gaseous reactants which are prone to condensation by capillarity at the usual temperatures of catalytic reaction, or with liquid phase reaction by an overconcentration of one of the reactants inside the tubes. c ∞ 2001 Academic Press

Profiles of Drug Substances, Excipients, and Related Methodology

Abstract: Volumes in this widely revered series present comprehensive reviews of drug substances and additional materials, with critical review chapters that summarize information related to the characterization of drug substances and excipients. This organizational structure meets the needs of the pharmaceutical community and allows for the development of a timely vehicle for publishing review materials on this topic. The scope of the Profiles series encompasses review articles and database compilations that fall within one of the following six broad categories: Physical profiles of drug substances and excipients; Analytical profiles of drug substances and excipients; Drug metabolism and pharmacokinetic profiles of drug substances and excipients; Methodology related to the characterization of drug substances and excipients; Methods of chemical synthesis; and Reviews of the uses and applications for individual drug substances, classes of drug substances, or excipients. * Contributions from leading authorities * Informs and updates on all the latest developments in the field