Mesoscopic irregularly ordered and even amorphous self-assembled electronic structures were recently reported in two-dimensional metallic dichalcogenides (TMDs), created and manipulated with short light pulses or by charge injection. Apart from promising new all-electronic memory devices, such states are of great fundamental importance, since such aperiodic states cannot be described in terms of conventional charge-density-wave (CDW) physics. In this paper, we address the problem of metastable mesoscopic configurational charge ordering in TMDs with a sparsely filled charged lattice gas model in which electrons are subject only to screened Coulomb repulsion. The model correctly predicts commensurate CDW states corresponding to different TMDs at magic filling fractions = / / / / / f 1 3, 1 4, 1 9, 1 13, 1 16.mDoping away from f m results either in multiple neardegenerate configurational states, or an amorphous state at the correct density observed by scanning tunnelling microscopy. Quantum fluctuations between degenerate states predict a quantum charge liquid at low temperatures, revealing a new generalized viewpoint on both regular, irregular and amorphous charge ordering in transition metal dichalcogenides.

The basic and the charge density wave (CDW) structures of the monoclinic NbS3-II polymorph were studied by synchrotron x-ray diffraction, ab-initio calculation, simulation of electron diffraction patterns and by atomicresolution transmission electron and low-temperature scanning tunneling microscopies. It is shown that the basic structure belongs to the space group P 21/m and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns (a0 = 0.96509(8) nm, b0 = 0.33459(2) nm, c0 = 1.9850(1) nm, β0 = 110.695(4) • ), with all Nb and S atoms in 2e special positions. The two CDWs, with q1 = (0, 0.298,0) and q2 = (0, 0.352, 0), form their own modulation unit cells (am = 2a0, bm = b0/qjb, cm = c0, βm = β0) and are ordered pairwise along adjacent isosceles TP columns. The symmetries of both qj modes belong to the space group Cm and are related according to the 2a special positions. If considered as long-period commensurate, the entire modulated structure with both CDWs included is best described with an enlarged unit cell (a = 2a0, b = 37b0, c = c0, β = β0), with all Nb and S atoms in 1a positions of the space group P 1.

We used a 16-channel e-nose demonstrator based on micro-capacitive sensors with functionalized surfaces to measure the response of 30 different sensors to the vapours from 11 different substances, including the explosives 1,3,5-trinitro-1,3,5-triazinane (RDX), 1-methyl-2,4-dinitrobenzene (DNT) and 2-methyl-1,3,5-trinitrobenzene (TNT). A classification model was developed using the Random Forest machine-learning algorithm and trained the models on a set of signals, where the concentration and flow of a selected single vapour were varied independently. It is demonstrated that our classification models are successful in recognizing the signal pattern of different sets of substances. An excellent accuracy of 96% was achieved for identifying the explosives from among the other substances. These experiments clearly demonstrate that the silane monolayers used in our sensors as receptor layers are particularly well suited to selecting and recognizing TNT and similar types of explosives from among other substances.

No abstract

No abstract