Atomic resolution top-down nanofabrication with low-current focused-ion-beam thinning

a b s t r a c t Techniques for scalable fabrication of one-dimensional or quasi-one-dimensional nanowires are of great importance to observe quantum size effects and build quantum information devices. In this work, we developed a technique for size reduction of both lateral and freestanding tungsten composite nanostructures using focused-ion-beam (FIB) thinning. Different exposure times and ion-beam currents were used to control the final size and the thinning rate and accuracy of a group of nanowires, an individual nanowire and a portion of a nanowire by low-current site-specific milling. A transmission electron microscope image of a thinned superconducting tungsten composite nanowire with width reduced from 80 nm to 50 nm shows uniform shrinking along the length of the wire and high resolution image shows no obvious changes of the morphology after thinning. The variation of the superconducting critical current density upon thinning is insignificant; it is 1.7 Â 10 5 and 1.4 Â 10 5 A/cm 2 at 4.26 K for the as-deposited and wire with width reduced to 50 nm, respectively. These results suggest that FIB-milling is a potential approach for controllable size reduction enabling the observation of size-and quantum effects

A training effect on electrical properties in nanoscale BiFeO3

We report our observation of the training effect on dc electrical properties in a nanochain of BiFeO3 as a result of large scale migration of defects under the combined influence of electric field and Joule heating. We show that an optimum number of cycles of electric field within the range zero to similar to 1.0 MV cm(-1) across a temperature range 80-300 K helps in reaching the stable state via a glass-transition-like process in the defect structure. Further treatment does not give rise to any substantial modification. We conclude that such a training effect is ubiquitous in pristine nanowires or chains of oxides and needs to be addressed for applications in nanoelectronic devices

Quantum-Dot-Bead-Based Fluorescence-Linked Immunosorbent Assay for Sensitive Detection of Cry2A Toxin in Cereals Using Nanobodies

In this study, a quantum-dot-bead (QB)-based fluorescence-linked immunosorbent assay (FLISA) using nanobodies was established for sensitive determination of the Cry2A toxin in cereal. QBs were used as the fluorescent probe and conjugated with a Cry2A polyclonal antibody. An anti-Cry2A nanobody P2 was expressed and used as the capture antibody. The results revealed that the low detection limit of the developed QB-FLISA was 0.41 ng/mL, which had a 19-times higher sensitivity than the traditional colorimetric ELISA. The proposed assay exhibited a high specificity for the Cry2A toxin, and it had no evident cross-reactions with other Cry toxins. The recoveries of Cry2A from the spiked cereal sample ranged from 86.6–117.3%, with a coefficient of variation lower than 9%. Moreover, sample analysis results of the QB-FLISA and commercial ELISA kit correlated well with each other. These results indicated that the developed QB-FLISA provides a potential approach for the sensitive determination of the Cry2A toxin in cereals

High-Quality Reduced Graphene Oxide Electrodes for Sub-Kelvin Studies of Molecular Monolayer Junctions

Electron transport phenomena in molecular monolayers are complex and potentially different from those of single molecules because of, for example, molecule–molecule interactions. Unfortunately, access to detailed mechanistic investigations of molecular monolayer junctions at ultralow temperatures is typically hampered by the narrow range of operating temperatures for most large-area device platforms. Here, we present a highly optimized chemically derived graphene material with a near temperature-independent conductance profile. Using this material as a conducting interlayer electrode in solid-state molecular electronic devices, we show robust and reliable large-area molecular junction operation at temperatures ranging from room temperature to below 1 K, and we demonstrate the ability to measure inelastic electron tunneling spectroscopy of a conjugated molecular monolayer at cryogenic temperatures

The concept and realization of nanostructure fabrication using free-standing metallic wires with rapid thermal annealing

Free-standing metallic nanostructures are considered to be highly relevant to many branches of science and technology with applications of three dimensional metallic nanostructures ranging from optical reflectors, actuators, and antenna, to free-standing electrodes, mechanical, optical, and electrical resonators and sensors. Strain-induced out-of-plane fabrication has emerged as an effective method which uses relaxation of strain-mismatched materials. In this work, we report a study of the thermal annealing-induced shape modification of free-standing nanostructures, which was achieved by introducing compositional or microstructural nonuniformity to the nanowires. In particular gradient, segmented and striped hetero-nanowires were grown by focused-ion-beam-induced chemical vapor deposition, followed by rapid thermal annealing in a N2 atmosphere. Various free-standing nanostructures were produced as a result of the crystalline/grain growth and stress relief