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.

Single-Layer Behavior and Its Breakdown in Twisted Graphene Layers

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

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

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

Profiles of Drug Substances, Excipients, and Related Methodology

Synthesis of novel inhibitors of α-glucosidase based on the benzothiazole skeleton containing benzohydrazide moiety and their molecular docking studies

Isatin based Schiff bases as inhibitors of α-glucosidase: Synthesis, characterization, in vitro evaluation and molecular docking studies.

Design of novel inorganic alkaline earth metal doped aluminum nitride complexes (AEM@Al12N12) with high chemical stability, improved electronic properties and large nonlinear optical response

Herein, we present the detailed comparative study on geometric, electronic, optical and non-linear optical response of alkalis and superalkalis doped twisted graphene. The results illustrate that alkali metals and superalkalis interact with the central ring of the twisted graphene through non-covalent interactions which demonstrate the stability of the resultant complexes. NBO charges indicate the transfer of electrons from dopant (alkali metal atoms and superalkalis) towards twisted graphene sheet. Superalkalis doped twisted graphene complexes exhibit higher first hyperpolarizability values compared to alkali metals analogues. Among superalkalis doped complexes, K3O@C104H52 shows the highest βo value of 1.68 × 105 au. In frequency dependent first hyperpolarizability analysis, strong second harmonic generation (SHG) response of K3O@C32H15 complex is observed at both selected resonance frequency values (532 nm and1064 nm) whereas EOPE value of K3O@C32H15 complex shows higher induced response at 1064 nm wavelength. The static hyperpolarizability (βo) further increases under the influence of applied electric field. Among all complexes, Li3O@C32H15 graphene complex has the highest βo value (1.40 × 105 au) under applied electric field along x axis when sheet is in y-z plane. This analysis will be an important guideline for future studies on twisted graphene based NLO materials.

Surface functionalization of twisted graphene C32H15 and C104H52 derivatives with alkalis and superalkalis for NLO response; a DFT study.

Density functional theory calculations are performed to evaluate the sensing ability of polypyrrole for oxynitrogen analytes. Interaction energies of PPy-X (X = NO2−, NO2, and NO) are calculated at B3LYP-CP/6-31G(d) and B3LYP/6-31G(d) levels of theory and compared with the high level calibrated method (M05-2X/aug-cc-pVDZ). B3LYP-CP/6-31G(d) gives the best correlation with the high level calibrated method compared to B3LYP/6-31G(d). Interaction of oligopyrrole with analytes shows a significant effect on the geometric and electronic properties; the conjugation is increased in the pyrrole oligomers and movement of charge is increased over the polymeric backbone. The charge is transferred from analytes to pyrrole oligomers (except nPy-NO2), and a more pronounced effect of charge transfer is observed in the case of nitrite ion (NO2−) compared to NO. In nPy-NO2, the charge is transferred from polymer to analyte. This transfer of charge indicates the n-type doping effect of analytes. The HOMO-LUMO gap decreases after interaction with analytes, which results in a drop of resistance (conductivity increases). These theoretical outcomes are consistent with the experimental results; polypyrrole has more sensing ability toward the nitrite anion (NO2−).

Sensor applications of polypyrrole for oxynitrogen analytes: a DFT study

The geometric, electronic and nonlinear properties of exohedral and endohedral single and multiple alkali metal (Li, Na and K) atom doped C24 fullerene are studied. First, the most stable orientations at the most stable spin state are evaluated. Complexes with odd metal atoms are stable at doublet spin state and complexes with even number of metal atoms are stable at singlet spin state. Thermodynamic analysis shows that Li4C24 among all complexes with highest thermodynamic stability has interaction energy of −190.78 kcal mol−1. The energy gaps (GH-L) are fairly reduced in single and multi-doped cages, and the lowest energy gap is observed for K4C24 complex. NBO analysis is performed to validate the charge transfer from alkali metal toward C24. The largest amount of charge (0.95 |e|) transfer is monitored in exohedral K2C24 complex where the highest charge transfer is for potassium (K) metal. Total density of states (TDOS) spectra of doped complexes justify the involvement of alkali metals and nanocage in new HOMO formation for the excess electrons. First hyperpolarizability is descriptor of NLO properties of single and multi-doped complexes are calculated. It is observed that doping of alkali metal atoms (Li, Na and K) greatly enhances the first hyperpolarizability. Among all the complexes of C24, Na3C24 shows the highest hyperpolarizability value of 2.74 × 105 au. The results of this study are a guideline for the computational designing of highly efficient and thermodynamically stable complexes for the optical and optoelectronic technologies.

Naveen Kosar

Papers

Design of novel inorganic alkaline earth metal doped aluminum nitride complexes (AEM@Al12N12) with high chemical stability, improved electronic properties and large nonlinear optical response

Surface functionalization of twisted graphene C32H15 and C104H52 derivatives with alkalis and superalkalis for NLO response; a DFT study.

Sensor applications of polypyrrole for oxynitrogen analytes: a DFT study

DFT studies of single and multiple alkali metals doped C24 fullerene for electronics and nonlinear optical applications.

Halides encapsulation in aluminum/boron phosphide nanoclusters: An effective strategy for high cell voltage in Na-ion battery