Der Waals Gap Research Articles

The effect of van der Waal's gap expansions on the surface electronic structure of layered topological insulators

On the basis of relativistic ab initio calculations, we show that an expansion of van der Waal's (vdW) spacings in layered topological insulators caused by intercalation of deposited atoms, leads to the simultaneous emergence of parabolic and M-shaped two-dimensional electron gas (2DEG) bands as well as Rashba-splitting of the former states. The expansion of vdW spacings and the emergence of the 2DEG states localized in the (sub)surface region are also accompanied by a relocation of the topological surface state to the lower quintuple layers, that can explain the absence of inter-band scattering found experimentally.

Synthesis and Crystal Structure of Indium Tellurium Trioxide Bromide

The pale yellow air-stable compound InTeO3Br could be obtained by the reaction of In, TeO2, Te and Br2. The compound crystallizes in the monoclinic crystal system (a=8.2596 (4) Å, b = 6.8752(3) Å, c = 7.1394 (3) Å, β = 103.121 (2)ˆ, Z = 4, space group = P21/c),[1] isotypic to the corresponding chloride compound, InTeO3Cl.[2] The compound forms a layered structure and these layers are separated by van der Waal's gaps. InO4Br2 octahedra linked with the TeO3 by sharing common corners are the typical structural building blocks for the title compound.

Comparison of the oxidizing ability of graphite and fullerite

This study is devoted to the comparison of the oxidizing ability of graphite and fullerite towards the three heavy alkali metals. These elements are able to intercalate very easily into graphite and fullerite, leading to various binary compounds. In the case of graphite, that is 2D host material, the alkali metal atoms intercalate in the bidimensional van der Waals's gap. These latter can be systematically occupied (stage 1 compound) or not (stages 2, 3…); the alkali metal concentration decreases from the first to the higher stages. On the other hand, C 60 fullerite is OD host material, and the alkali metal atoms intercalate into the octahedral and tetrahedral sites of the fullerite classical FCC structure. According to the cases, these interstitial sites can be more or less occupied, leading to several well defined phases. For all these compounds, a charge transfer occurs between carbon host material and alkali metal, that greatly reduces graphite and fullerite, so that the binary compounds are considered as salts, that is, graphitides and fullendes, respectively. We have shown that fullerite is much more oxidizing than graphite. This latter indeed is strongly (in cesium) or even completely (in rubidium and potassium) striped of its alkali atoms by fullerite. In other words, graphitides are partly or entirely oxidized by fullerite.

Intercalation of aliphatic amines into layered structure of vanadyl phosphate

Layered complexes VOPO 4·2RNH 2 (R means aliphatic unbranched chain C 1-C 10) have been prepared and characterized by their basal spacings, DTA and IR spectra. The observed alternation of the basal spacing increments with the number of the carbon atoms of the chain indicates an oblique arrangement of these chains in the van der Waal's gap.

Positron lifetime studies in pure and chromium intercalated 2HNbSe2

AbstractThe layered 2 HNbSe2 belongs to a class of very interesting low dimensional conductors which exhibits CDW instability at 32 K. In our earlier paper we have established the two dimensionality of the Fermi surface, in these layered compounds by positron angular correlation technique. The reduction in Fermi level along the basal plane due to CDW transition has been already demonstrated by the Japanese group. But the sensitivity of positron lifetime and Doppler broadening techniques for CDW transition is controversial. The Japanese group report drastic changes in Doppler broadening parameters whereas the American group do not find such a change. Positron lifetime measurements have been performed on pure and Cr intercalated 2 HNbSe2 with Cr concentration 0.25, 0.33, and 0.5 with a view to assess the origin of the second lifetime component. The results show that there are two lifetime component τ1 ∼ 205 ps and τ2 ∼ 440 ps having intensity I2 ∼ 29%. On Chromium intercalation the intensity I2 decreases systematically. The trapping rate of positrons shows a systematic decrease with increase of Cr content indicating that the second lifetime arises due to positron annihilation in van der Waal's gap. The defect free annihilation rate λf was found to increase on intercalation indicating a charge transfer from the guest intercalates to the host MCh2 conduction bands.

Intercalation of aliphatic alcohol mixtures into the layered lattice of unhydrated vanadyl sulphate

The mixed intercalates of the type VOSO 4·(2 − x)C p · xC q have been prepared by reaction of unhydrated layered VOSO 4 with liquid binary mixtures of the aliphatic alcohols. Symbols C p and C q mark two different unbranched primary aliphatic alcohols, p and q are numbers of carbon atoms in their molecules ( p< q). For q= p+1 the value of x changes continuously in the interval 〈0–2〉. For q > p + 2 these values range in intervals 〈0–0.05〉, 〈0.9–1.1〉 and (1.75−2). Relations between basal spacings of the formed layered complexes and their composition and the composition of the liquid alcohol (C 2 to C 7) mixtures were studied for fifteen systems. The schematic explanation of the arrangement of the alcohol molecules in van der Waal's gap is proposed.

Layer-type complexes consisting of VOSO 4 or VOPO 4 and aliphatic alcohols

The intercalates of unhydrated VOSO 4 and VOPO 4 with alcohols (C 1 to C 8) have been prepared and characterized by their compositions, basal spacings and thermal stabilities. X-ray powder studies show that the layered structures of VOSO 4 and VOPO 4 lattices are maintained in these complexes. The alcohol molecules are penetrated into van der Waal's gaps of the host lattices and form bimolecular layers. The observed alternation of the basal spacing increments with the number of carbon atoms of the linear aliphatic chain is explained from the arrangement of these chains.

Structure determination of ZnPS 3

ZnPS 3 structure determination was performed from single crystal diffraction data. The structure refinement was conducted from 634 reflexions and 29 variables in C2/m space group to R = 4.0%. The phase exhibits the expected MPS 3 layered structure (CdCl 2 type). The particular behavior of the MPS 3 atomic species respective to the cation size and their electronic configuration as pointed out in the other MPS 3s (M  Mn, Fe, Co, Ni, Cd) is confirmed by the present study. Within error margin, the phase was found to be stoichiometric with empty Van der Waal's gap.