No abstract

In this article, we present the results of a gap-plasmon tip-enhanced Raman scattering study of MoS monolayers deposited on a periodic array of Au nanostructures on a silicon substrate forming a two dimensional (2D) crystal/plasmonic heterostructure. We observe a giant Raman enhancement of the phonon modes in the MoS monolayer located in the plasmonic gap between the Au tip apex and Au nanoclusters. Tip-enhanced Raman mapping allows us to determine the gap-plasmon field distribution responsible for the formation of hot spots. These hot spots provide an unprecedented giant Raman enhancement of 5.6 × 10 and a spatial resolution as small as 2.3 nm under ambient conditions. Moreover, due to strong hot electron doping in the order of 1.8 × 10 cm, we observe a structural change of MoS from the 2H to the 1T phase. Owing to the very good spatial resolution, we are able to spatially resolve those doping sites. To the best of our knowledge, this is the first time reporting of such a phenomenon with nm spatial resolution. Our results will open the perspectives of optical diagnostics with nanometer resolution for many other 2D materials.

No abstract

We present the results of the comparative study of the influence of disorder on transport properties in continuous and nanoperforated TiN films. We show that nanopatterning turns a thin TiN film into an array of superconducting weak links and stimulates both, the disorder-and magnetic field-driven superconductor-to-insulator transitions, pushing them to lower degree of disorder. We find that nanopatterning enhances the role of the two-dimensional Coulomb interaction in the system transforming the originally insulating film into a more pronounced insulator. We observe magnetoresistance oscillations reflecting collective behaviour of the multiconnected nanopatterned superconducting film in the wide range of temperatures and uncover the physical mechanism of these oscillations as phase slips in superconducting weak link network.That a thin film of the same material can be a superconductor but can very well turn an insulator, is one of the most remarkable aspects of disordered superconductors [1][2][3][4][5][6][7]. The engine driving the transition between the superconducting and insulating states is disorder the effect of which is two-fold. On the one hand, disorder limits the electron diffusion enhancing thus the Coulomb electron-electron interaction which competes with the Cooper pairing [8,9]. The latter in an interplay with the disorder-induced inhomogeneities localizes Cooper pairs to form an insulating state, Cooper-pair insulator. A restricted geometry is critical to effects of disorder -for the insulating state to be observed the superconducting material is to be thinned down till its thickness d becomes comparable to or smaller than the superconducting coherence length ξ. One of the major experimental challenges in these studies remains the optimization of material parameters taking it to the closest proximity of the direct superconductor-insulator transition and identifying the systems that exhibit such a transition at available temperatures. In this Letter we meet this challenge via creating a metamaterial with the desirable properties, the multiconnected thin superconducting film. We show that nanopatterning a thin TiN film into a regular sievelike configuration turns it into an array of weak links and, therefore, stimulates the direct superconductor-toinsulator transition. Depending on the original degree of disorder it either suppresses the critical temperature T c , or drives the initially superconducting film into an insulating state, or else, transforms the originally insulating film into an even more pronounced insulator.As a starting material we have chosen a 5 nm thin TiN film which was identical by its parameters to those that experienced the superconductor-insulator transition after soft plasma etching [10][11][12][13] and which were fully characterized by the high resolution electron beam, infrared [14], and low-temperature scanning tunnelling spectroscopy [15]. The smooth, continuous, and uniform TiN film was formed on the Si/SiO 2 substrate by atomic layer deposition. The film had the super...

Articles you may be interested inSplit-gate quantum point contacts with tunable channel length

The properties of silicon-on-insulator nanowires (SOI NWs) fabricated by means of electron lithography and gas etching of SOI in XeF 2 or SF 6 :CFCl 3 have been investigated. The method used to fabricate the nanowires was found to require no additional anneal to be given to the final structure for defect removal after nanostructuring. The sensitivity of SOI NWs to negative protein BSA molecules in the pH 7.4 buffer solution was shown to be as high as 1 femtomoles. The gate characteristics of SOI NWs were used to determine the charge density of particles adsorbed on the NW surface. A charge density of 4.6 × 10 11 cm −2 was estimated for a 1 femtomole protein concentration. The combined use of open-channel structures with top gates was employed for determining the charge state of structure surfaces after different chemical treatments. Chemical treatments giving rise to a density of the negative charges on the surface of NWs ranging in the interval (7-23) × 10 11 cm −2 were examined. Treatments in methanol (after removal of the native oxide) were found to provide stabilization of the SOI surface over a 3-h interval after the treatments.

We look to understand the enhancement and spatial resolution of a tip-enhanced Raman scattering (TERS) system containing a metal tip and plasmonic substrate.

We report on the observation of the giant photoconductance of a quantum point contact (QPC) in tunneling regime excited by terahertz radiation. Studied QPCs are formed in a GaAs/AlGaAs heterostructure with a high-electron-mobility two-dimensional electron gas. We demonstrate that irradiation of strongly negatively biased QPCs by laser radiation with frequency f = 0.69 THz and intensity 50 mW/cm 2 results in two orders of magnitude enhancement of the QPC conductance. The effect has a superlinear intensity dependence and increases with the dark conductivity decrease. It is also characterized by strong polarization and frequency dependencies. We demonstrate that all experimental findings can be well explained by the photon-mediated tunneling through the QPC. Corresponding calculations are in a good agreement with the experiment.