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Microstructural analysis and transport properties of MoO and MoC nanostructures prepared by focused electron beam-induced deposition.

ABSTRACT: By electron-beam-induced deposition, we have succeeded in the direct fabrication of nanowires of molybdenum oxide (MoOx) and molybdenum carbide (MoC) on a SiO2 substrate set in a scanning electron microscope. In order to prepare MoOx specimens of high purity, a precursor gas of molybdenum hexacarbonyl [Mo(CO)6] is used, mixed with oxygen gas. On the other hand, MoC is grown by mixing H2O gas with the precursor gas. The electrical transport properties of the nanowires are investigated by the DC four-terminal method. A highly resistive MoOx nanowire prepared from an as-deposited specimen by annealing in air shows nonlinear current-voltage characteristics and a high photoconductivity. The resistivity ρ of an as-deposited amorphous MoC (a-MoC) nanowire takes its maximum at a temperature T ≈ 10 K and decreases to ≈ 0 with decreasing temperature. This behavior of ρ(T) indicates the possible occurrence of superconductivity in a-MoC nanowires. The characteristic of ρ(T) below the superconducting transition temperature Tc ≈ 4 K can be well explained by the quantum phase-slip model with a coherence length ξ(0) ≈ 8 nm at T = 0.

SUBMITTER: Makise K

PROVIDER: S-EPMC4102898 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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Project description:Solid state nanopores are central structures for many applications. To date, much effort has been spent on controlled fabrication of single nanopores, while relatively little work has focused on large scale fabrication of arrays of nanopores. In this work we show wafer-scale fabrication of plasmonic nanopores in 50 nm thick silicon nitride membranes with one or two 30 nm gold films, using electron beam lithography with a negative resist or a new version of colloidal lithography. Both approaches offer good control of pore diameter (even below 100 nm) and with high yield (>90%) of intact membranes. Colloidal lithography has the advantage of parallel patterning without expensive equipment. Despite its serial nature, electron beam lithography provides high throughput and can make arbitrary array patterns. Importantly, both methods prevent metal from ending up on the membrane pore sidewalls. The new fabrication methods make it possible to compare the optical properties of structurally identical plasmonic nanopore arrays with either long-range order (e-beam) or short-range order (colloidal). The resonance features in the extinction spectrum are very similar for both structures when the pitch is the same as the characteristic spacing in the self-assembled colloidal pattern. Long-range ordering slightly enhances the magnitude of the extinction maximum and blueshift the transmission maximum by tens of nm. Upon reducing the diameter in long-range ordered arrays, the resonance is reduced in magnitude and the transmission maximum is further blue shifted, just like for short-range ordered arrays. These effects are well explained by interpreting the spectra as Fano interference between the grating-type excitation of propagating surface plasmons and the broad transmission via individual pores in the metal film. Furthermore, we find that only the short-range ordered arrays scatter light, which we attribute to the highly limited effective period in the short-range ordered system and the corresponding lack of coherent suppression of scattering by interference effects.

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Microstructural analysis and transport properties of MoO and MoC nanostructures prepared by focused electron beam-induced deposition.

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