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Quasi-1D van der Waals materials, such as transition metal trichalcogenides, have strong covalent bonds in one direction and weaker bonds in cross-plane directions. They can be prepared as crystalline nanowires or nanoribbons consisting of 1D atomic threads, i.e., chains. We have examined the current carrying capacity of ZrTe3 nanoribbons using a set of structures fabricated by the shadow mask method. The bulk crystals were synthesized by the chemical vapor transport method and exfoliated onto Si/SiO2 substrates. It was found that ZrTe3 nanoribbons reveal an exceptionally high current density, on the order of ~100 MA/cm2, at the peak of the stressing DC current. The low-frequency noise was of 1/ ${f}$ type near room temperature ( ${f}$ is the frequency). The noise amplitude scaled with the resistance, following the trend established for other low-dimensional materials. The high current density in ZrTe3 can be attributed to the single-crystal nature of quasi-1D van der Waals materials. [ABSTRACT FROM AUTHOR]

The controlled tunability of superconductivity in low-dimensional materials may enable new quantum devices. Particularly in triplet or topological superconductors, tunneling devices such as Josephson junctions, etc., can demonstrate exotic functionalities. The tunnel barrier, an insulating or normal material layer separating two superconductors, is a key component for the junctions. Thin layers of NbSe 2 have been shown as a superconductor with strong spin orbit coupling, which can give rise to topological superconductivity if driven by a large magnetic exchange field. Here we demonstrate the superconductor-insulator transitions in epitaxially grown few-layer NbSe 2 with wafer-scale uniformity on insulating substrates. We provide the electrical transport, Raman spectroscopy, cross-sectional transmission electron microscopy, and X-ray diffraction characterizations of the insulating phase. We show that the superconductor-insulator transition is driven by strain, which also causes characteristic energy shifts of the Raman modes. Our observation paves the way for high-quality heterojunction tunnel barriers to be seamlessly built into epitaxial NbSe 2 itself, thereby enabling highly scalable tunneling devices for superconductor-based quantum electronics.

We investigated thermal properties of the epoxy-based composites with the high loading fraction-up to f ≈ 45 vol %-of the randomly oriented electrically conductive graphene fillers and electrically insulating boron nitride fillers. It was found that both types of the composites revealed a distinctive thermal percolation threshold at the loading fraction f T > 20 vol %. The graphene loading required for achieving thermal percolation, f T , was substantially higher than the loading, f E , for electrical percolation. Graphene fillers outperformed boron nitride fillers in the thermal conductivity enhancement. It was established that thermal transport in composites with high filler loadings, f ≥ f T , is dominated by heat conduction via the network of percolating fillers. Unexpectedly, we determined that the thermal transport properties of the high loading composites were influenced strongly by the cross-plane thermal conductivity of the quasi-two-dimensional fillers. The obtained results shed light on the debated mechanism of the thermal percolation, and facilitate the development of the next generation of the efficient thermal interface materials for electronic applications.

It is of paramount importance to improve the control over large area growth of high quality molybdenum disulfide (MoS 2 ) and other types of 2D dichalcogenides. Such atomically thin materials have great potential for use in electronics, and are thought to make possible the first real applications of spintronics. Here in, a facile and reproducible method of producing wafer scale atomically thin MoS 2 layers has been developed using the incorporation of a chelating agent in a common organic solvent, dimethyl sulfoxide (DMSO). Previously, solution processing of a MoS 2 precursor, ammonium tetrathiomolybdate ((NH 4 ) 2 MoS 4 ), and subsequent thermolysis was used to produce large area MoS 2 layers. Our work here shows that the use of ethylenediaminetetraacetic acid (EDTA) in DMSO exerts superior control over wafer coverage and film thickness, and the results demonstrate that the chelating action and dispersing effect of EDTA is critical in growing uniform films. Raman spectroscopy, photoluminescence (PL), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and high-resolution scanning transmission electron microscopy (HR-STEM) indicate the formation of homogenous few layer MoS 2 films at the wafer scale, resulting from the novel chelant-in-solution method.

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.

The production of antileukemic enzyme methionine γ-lyase (MGL) in distinctly related bacteria, Citrobacter freundii and in their recombinants expressing the Vitresocilla hemoglobin (VHb) has been studied. This study concerns the potential of Citrobacter freundii expressing the Vitreoscilla hemoglobin gene (vgb) for the methionine γ- liyase production. Methionine γ- liyase production by Citrobacter freundii and its vgb(-) and vgb(+) bearing recombinant strain was studied in shake-flasks under 200 rpm agitation, culture medium and 30 °C in a time-course manner. The vgb(+) and especially the carbon type had a dramatic effect on methionine γ- liyase production. The vgb(+) strain of C. freundii had about 2-fold and 3.1-fold higher levels of MGL than the host and vgb(-) strain, respectively.

Given the well-established beneficial effects of Vitreoscilla hemoglobin (VHb) on heterologous organisms, the potential of this protein for the production of L-DOPA and dopamine in two bacteria, Citrobacter freundii and Erwinia herbicola, was investigated. The constructed recombinants bearing the VHb gene (vgb(+)) had substantially higher levels of cytoplasmic L-DOPA (112 mg/L for C. freundii and 97 mg/L for E. herbicola) than their respective hosts (30.4 and 33.8 mg/L) and the vgb(-) control strains (35.6 and 35.8 mg/L). Further, the vgb(+) recombinants of C. freundii and E. herbicola had 20-fold and about two orders of magnitude higher dopamine levels than their hosts, repectively. The activity of tyrosine phenol-lyase, the enzyme converting L-tyrosine to L-DOPA, was well-correlated to cytoplasmic L-DOPA levels. As cultures aged, higher tyrosine phenol-lyase activity of the vgb(+) strains was more apparent.

A new contrast agent has been developed for the opacification of the esophageal lumen in Magnetic Resonance (MR) Imaging. The contrast agent consists of an emulsion of low-density and high-viscosity barium paste employed for the CT study of the esophagus (E.Z.E.M., Westbury, USA) and a small amount of Gadolinium-DTPA (Magnevist, Schering, Germany), diluted in 3 ml of saline solution. In vitro evaluation of the contrast solution showed high-signal intensity on T1-weighted SE sequences. The study was subsequently performed on 5 healthy volunteers and 30 subjects with clinical indication for MR Imaging of the chest. The complete opacification of the esophagus was obtained in 12 of the 16 patients (75%) who presented no pathological involvement of the esophagus. The esophageal lumen was completely opacified in 8 patients with esophageal carcinoma and in 1 case of esophageal leiomyoma. In the cases with esophageal carcinoma, lumen opacification allowed the evaluation of tumor growth (concentric or eccentric), a more detailed definition of tumor extent, with assessment of neoplastic wall thickening, and the evaluation of the possible infiltration of adjacent organs. Lumen opacification was obtained in 8 of 10 patients (80%) affected with other chest conditions secondarily involving the esophagus. In these cases, lumen opacification helped to localize the esophagus and to evaluate its involvement by adjacent tumors.