Lithium intercalation edge effects and doping implications for graphite anodes

The interface between the electrolyte and graphite anodes plays an important role for lithium (Li) intercalation and has significant impact on the charging/discharging performance of Lithium-Ion Batteries (LIBs). However, atomistic understanding of interface effects that would allow the interface to be rationally optimized for application needs is largely missing. Here we comprehensively study the energetics of Li intercalation near the main non-basal surfaces of graphite, namely the armchair and zigzag edges. We find that edge sites at both surfaces bind Li more strongly than in the bulk of graphite. Therefore, lithiation of these sites is expected to proceed at higher voltages than in the bulk. Furthermore, this effect is significantly more pronounced at the zigzag edge compared to the armchair edge due to its unique electronic structure. The “peculiar” topologically stabilized electronic surface state found at zigzag edges strongly interacts with Li, thereby changing Li diffusion behavior at the surface as well. Finally, we investigate boron (B)/nitrogen (N) doping as a promising strategy to tune the Li intercalation behavior at both edge systems, which could lead to enhanced intercalation kinetics in B/N doped graphite anodes

Development of ferromagnetism in the doped topological insulator Bi_(2−x)Mn_xTe_3

The development of ferromagnetism in Mn-doped Bi_2Te_3 is characterized through measurements on a series of single crystals with different Mn content. Scanning tunneling microscopy analysis shows that the Mn substitutes on the Bi sites, forming compounds of the type Bi_(2−x)Mn_xTe_3, and that the Mn substitutions are randomly distributed, not clustered. Mn doping first gives rise to local magnetic moments with Curie-like behavior, but by the compositions Bi_(1.96)Mn_(0.04)Te_3 and Bi_(1.91)Mn_(0.09)Te_3, a second-order ferromagnetic transition is observed, with T_C∼9–12 K. The easy axis of magnetization in the ferromagnetic phase is perpendicular to the Bi2Te3 basal plane. Thermoelectric power and Hall effect measurements show that the Mn-doped Bi_2Te_3 crystals are p-type. Angle-resolved photoemission spectroscopy measurements show that the topological surface states that are present in pristine Bi_2Te_3 are also present at 15 K in ferromagnetic Mn-doped Bi2−xMnxTe3 and that the dispersion relations of the surface states are changed in a subtle fashion

Scanning tunneling spectroscopy of a dilute two-dimensional electron system exhibiting Rashba spin splitting

Using scanning tunneling spectroscopy (STS) at 5 K in B-fields up to 7 T, we investigate the local density of states of a two-dimensional electron system (2DES) created by Cs adsorption on p-type InSb(110). The 2DES, which in contrast to previous STS studies exhibits a 2D Fermi level, shows standing waves at B = 0 T with corrugations decreasing with energy and with wave numbers in accordance with theory. In magnetic field percolating drift states are observed within the disorder broadened Landau levels. Due to the large electric field perpendicular to the surface, a beating pattern of the Landau levels is found and explained quantitatively by Rashba spin splitting within the lowest 2DES subband. The Rashba splitting does not contribute significantly to the standing wave patterns in accordance with theory.Comment: 9 pages, 9 figures, submitted to Phys. Rev.

Quantum galvanomagnetic and thermomagnetic effects in graphite to 18.3 teslas /180 kG/ at low temperatures

Quantum galvanomagnetic and thermomagnetic effects in graphite in magnetic fields at low temperature

Effects of CdCl2 treatment on deep levels in CdTe and their implications on thin film solar cells; A comprehensive photoluminescence study

This work is aimed at studying defect level distributions in the bandgap of CdTe thin films, used for solar cell development. In particular, the effects of CdCl2 treatment on the defect levels are the main objectives of this research. Four different CdTe thin films were electroplated using three different Cd-precursors (CdSO4, Cd(NO3)2 and CdCl2), and bulk CdTe wafers purchased from industry (Eagle Pitcher and University Wafers in US) were studied using low temperature photoluminescence. The finger prints of defects, 0.55 eV below the conduction band down to the valence band edge were investigated. In all of the CdTe layers, four electron trap levels were observed with varying intensities but at very similar energy positions, indicating that the origin of these defects are mainly from native defects. CdCl2 treatment and annealing eliminates two defect levels and the mid-gap recombination centres are reduced drastically by this processing step. The optical bandgap of all four as-deposited CdTe layers is ~1.50 eV, and reduces to ~1.47 eV after CdCl2 treatment. The material grown using the CdCl2 precursor seems to produce CdTe material with the cleanest bandgap, most probably due to the built-in CdCl2 treatment while growing the material