Quantum of solace: Fluorescent carbon dots (surface‐passivated carbon nanoparticles) are developed as an alternative to classical semiconductor quantum dots. Gel column chromatography afforded carbon dots with emission yields close to 60 %. Their optical properties resemble band‐gap transitions found in nanoscale semiconductors, thus suggesting that nanoscale carbon particles acquire essentially semiconductorlike characteristics.

Edge-enriched transition metal dichalcogenides, such as WS 2 , are promising electrocatalysts for sustainable production of H 2 through the electrochemical hydrogen evolution reaction (HER). The reliable and controlled growth of such edge-enriched electrocatalysts at low temperatures has, however, remained elusive. In this work, we demonstrate how plasma-enhanced atomic layer deposition (PEALD) can be used as a new approach to nanoengineer and enhance the HER performance of WS 2 by maximizing the density of reactive edge sites at a low temperature of 300 °C. By altering the plasma gas composition from H 2 S to H 2 + H 2 S during PEALD, we could precisely control the morphology and composition and, consequently, the edge-site density as well as chemistry in our WS 2 films. The precise control over edge-site density was verified by evaluating the number of exposed edge sites using electrochemical copper underpotential depositions. Subsequently, we demonstrate the HER performance of the edge-enriched WS 2 electrocatalyst, and a clear correlation among plasma conditions, edge-site density, and the HER performance is obtained. Additionally, using density functional theory calculations we provide insights and explain how the addition of H 2 to the H 2 S plasma impacts the PEALD growth behavior and, consequently, the material properties, when compared to only H 2 S plasma.

Quantum of solace: Fluorescent carbon dots (surface‐passivated carbon nanoparticles) are developed as an alternative to classical semiconductor quantum dots. Gel column chromatography afforded carbon dots with emission yields close to 60 %. Their optical properties resemble band‐gap transitions found in nanoscale semiconductors, thus suggesting that nanoscale carbon particles acquire essentially semiconductorlike characteristics.

We report on the current-carrying capacity of the nanowires made from the quasi-1D van der Waals metal tantalum triselenide capped with quasi-2D boron nitride. The chemical vapor transport method followed by chemical and mechanical exfoliation were used to fabricate the mm-long TaSe3 wires with the lateral dimensions in the 20 to 70 nm range. Electrical measurements establish that the TaSe3/h-BN nanowire heterostructures have a breakdown current density exceeding 10 MA cm(-2)-an order-of-magnitude higher than that for copper. Some devices exhibited an intriguing step-like breakdown, which can be explained by the atomic thread bundle structure of the nanowires. The quasi-1D single crystal nature of TaSe3 results in a low surface roughness and in the absence of the grain boundaries. These features can potentially enable the downscaling of the nanowires to lateral dimensions in a few-nm range. Our results suggest that quasi-1D van der Waals metals have potential for applications in the ultimately downscaled local interconnects.

We report results of investigation of the low-frequency electronic excess noise in quasi-1D nanowires of TaSe3 capped with quasi-2D h-BN layers. Semi-metallic TaSe3 is a quasi-1D van der Waals material with exceptionally high breakdown current density. It was found that TaSe3 nanowires have lower levels of the normalized noise spectral density, SI/I 2 , compared to carbon nanotubes and graphene (I is the current). The temperature-dependent measurements revealed that the low-frequency electronic 1/f noise becomes the 1/f 2 -type as temperature increases to ~400 K, suggesting the onset of electromigration (f is the frequency). Using the Dutta-Horn random fluctuation model of the electronic noise in metals we determined that the noise activation energy for quasi-1D TaSe3 nanowires is approximately EP≈1.0 eV. In the framework of the empirical noise model for metallic interconnects, the extracted activation energy, related to electromigration, is EA=0.88 eV, consistent with that for Cu and Al interconnects. Our results shed light on the physical mechanism of low-frequency 1/f noise in quasi-1D van der Waals semi-metals and suggest that such material systems have potential for ultimately downscaled local interconnect applications.Keywords: quasi-1D materials; van der Waals materials; low-frequency noise; interconnects 2 | P a g e The investigations of the two-dimensional layers and heterostructures revealed new physics and demonstrated promising applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Starting with graphene [3][4][5], and spreading to a wide range of layered van der Waals materials [6][7][8][9][10], successful isolation of individual atomic layers from their respective bulk crystals by mechanical exfoliation led to the fast growing research activities in the 2D materials. In contrast to the layered van der Waals materials that yield 2D crystals, materials, such as TaSe3 and TiS3 [15][16][17] yield the quasi-onedimensional (1D) van der Waals crystal structures. These materials belong to the group of the transition metal trichalcogenides MX3 (where M = Mo, W, and other transition metals; X = S, Se, Te). In the monoclinic crystal structure of TaSe3, the trigonal prismatic TaSe3 units form continuous chains extending along the b axis and leading to fiber-and needle-like crystals with anisotropic semi-metallic or metallic properties. The quasi-1D atomic threads are weakly bound in bundles by the van der Waals forces. As a consequence, the mechanical exfoliation of the MX3 crystals results not in the 2D layers but rather in the quasi-1D van der Waals nanowires. We have recently demonstrated quasi-1D TaSe3 nanowires with the record high current density exceeding JB~10 MA/cm 2 , which is an order of magnitude larger than that for the Cu interconnects [18].In this Letter, we report on the excess low-frequency electronic noise in quasi-1D nanowires of TaSe3 capped with the quasi-2D h-BN layers. The h-BN capping was used as a surface passivation protecting from environmental exposure. The measuremen...

We investigated low-frequency noise in two-dimensional (2D) charge density wave (CDW) systems, 1 T-TaS thin films, as they were driven from the nearly commensurate (NC) to incommensurate (IC) CDW phases by voltage and temperature stimuli. This study revealed that noise in 1 T-TaS has two pronounced maxima at the bias voltages, which correspond to the onset of CDW sliding and the NC-to-IC phase transition. We observed unusual Lorentzian features and exceptionally strong noise dependence on electric bias and temperature, leading to the conclusion that electronic noise in 2D CDW systems has a unique physical origin different from known fundamental noise types. We argue that noise spectroscopy can serve as a useful tool for understanding electronic transport phenomena in 2D CDW materials characterized by coexistence of different phases and strong pinning.

We report on switching among three charge-density-wave phases -commensurate, nearly commensurate, incommensurate -and the high-temperature normal metallic phase in thin-film 1T-TaS2 devices induced by application of an in-plane electric field. The electric switching among all phases has been achieved over a wide temperature range, from 77 K to 400 K. The low-frequency electronic noise spectroscopy has been used as an effective tool for monitoring the transitions, particularly the switching from the incommensurate charge-density-wave phase to the normal metal phase. The noise spectral density exhibits sharp increases at the phase transition points, which correspond to the step-like changes in resistivity. Assignment of the phases is consistent with low-field resistivity measurements over the temperature range from 77 K to 600 K. Analysis of the experimental data and calculations of heat dissipation suggest that Joule heating plays a dominant role in the electric-field induced transitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The possibility of electrical switching among four different phases of 1T-TaS2 is a promising step toward nanoscale device applications. The results also demonstrate the potential of noise spectroscopy for investigating and identifying phase transitions in materials. Keywords: charge-density-wave effects; van der Waals materials; resistive switching, lowfrequency noise, 1T-TaS2; normal metallic phase Electric Switching of the Charge-Density-Wave and Normal Metallic Phases in 1T-TaS2 Thin-Film Devices -UC Riverside 2019 3 | P a g eSwitching between various material phases at room temperature by the application of electric field has the potential of becoming a new device paradigm for future electronic and optoelectronic technologies 1-4 . Among the promising material candidates, which must exhibit phase changes characterized by abrupt resistivity changes and hysteresis, is the 1T polymorph of tantalum disulfide (TaS2). The quasi-two-dimensional (2D) van der Waals layered crystalline 1T-TaS2 exhibits charge-density-wave (CDW) effects, i.e. periodic modulation of the charge density and the underlying lattice resulting from the interplay between the electron-electron and electronphonon interactions [5][6][7][8][9][10][11][12][13]14 . The CDW state becomes fully commensurate with the lattice below ~200 K 15-17 . The commensurate CDW (C-CDW) consists of a √13 × √13 reconstruction within the basal plane that forms a star-of-David pattern in which each star contains 13 Ta atoms. The Fermi surface, composed of 1 d-electron per star, is unstable, so that the lattice reconstruction is accompanied by a Mott-Hubbard transition that fully gaps the Fermi surface and increases the resistance 15,18-21 . As the temperature increases above 180 K, the C-CDW phase breaks up into a nearly commensurate CDW (NC-CDW) phase that consists of ordered C-CDW regions separated by domain walls 22 . This C-CDW to NC-CDW transition is revealed as an abrupt change in the resistance with a large hysteresis window i...

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