Opto Field-Effect Transistors for Detecting Quercetin-Cu Complex.

In this study, we explored the potential of applying biosensors based on silicon nanowire field-effect transistors (bio-NWFETs) as molecular absorption sensors. Using quercetin and Copper (Cu) ion as an example, we demonstrated the use of an opto-FET approach for the detection of molecular interactions. We found that photons with wavelengths of 450 nm were absorbed by the molecular complex, with the absorbance level depending on the Cu concentration.

Fabry-Perot interferometric calibration of van der Waals material-based nanomechanical resonators.

One of the challenges in integrating nanomechanical resonators made from van der Waals materials in optoelectromechanical technologies is characterizing their dynamic properties from vibrational displacement. Multiple calibration schemes using optical interferometry have tackled this challenge. However, these techniques are limited only to optically thin resonators with an optimal vacuum gap height and substrate for interferometric detection.

Photothermal Responsivity of van der Waals Material-Based Nanomechanical Resonators.

Nanomechanical resonators made from van der Waals materials (vdW NMRs) provide a new tool for sensing absorbed laser power. The photothermal response of vdW NMRs, quantified from the resonant frequency shifts induced by optical absorption, is enhanced when incorporated in a Fabry-Pérot (FP) interferometer. Along with the enhancement comes the dependence of the photothermal response on NMR displacement, which lacks investigation.

Correlation between the optical absorption and twisted angle of bilayer graphene observed by high-resolution reflectance confocal laser microscopy.

We report a systematic study of the optical absorption of twisted bilayer graphene (tBLG) across a large range of twist angles from 0° to 30° using a high-resolution reflectance confocal laser microscopy (RCLM) system. The high-quality single crystalline tBLG was synthesized via the efficient plasma enhanced chemical vapor deposition techniques without the need of active heating. The sensitivity of acquired images from the RCLM were better than conventional optical microscopes.

Imaging Off-Resonance Nanomechanical Motion as Modal Superposition.

Observation of resonance modes is the most straightforward way of studying mechanical oscillations because these modes have maximum response to stimuli. However, a deeper understanding of mechanical motion can be obtained by also looking at modal responses at frequencies in between resonances. Here, an imaging of the modal responses for a nanomechanical drum driven off resonance is presented.

Ultralow Schottky Barriers in Hexagonal Boron Nitride-Encapsulated Monolayer WSe Tunnel Field-Effect Transistors.

To explore the potential of field-effect transistors (FETs) based on monolayers (MLs) of the two-dimensional semiconducting channel (SC) for spintronics, the two most important issues are to ensure the formation of variable low-resistive tunnel ferromagnetic contacts (FCs) and to preserve intrinsic properties of the SC during fabrication. Large Schottky barriers lead to the formation of high resistive contacts, and methods adopted to control the barriers often alter the intrinsic properties of the SC. This work aims at addressing both issues in fully encapsulated ML WSe FETs using bilayer hexagonal boron nitride (h-BN) as a tunnel barrier at the FC/SC interface.

Observation of Wigner crystal phase and ripplon-limited mobility behavior in monolayer CVD MoS with grain boundary.

Two-dimensional electron gas (2DEG) is crucial in condensed matter physics and is present on the surface of liquid helium and at the interface of semiconductors. Monolayer MoS of 2D materials also contains 2DEG in an atomic layer as a field effect transistor (FET) ultrathin channel. In this study, we synthesized double triangular MoS through a chemical vapor deposition method to obtain grain boundaries for forming a ripple structure in the FET channel.

Quadratic Characteristics of Environment Induced Voltage Shot Noise in Josephson Junctions.

We investigate theoretically and experimentally the environment-induced voltage shot noise in current biased Josephson junctions induced by phase particle tunneling. Quantum mechanical treatment based on the Caldeira-Leggett model with tight-binding formulation in local Wannier bases gives a clear picture of the voltage shot noise. A universal form of the zero-frequency noise spectrum is obtained, which exhibits a quadratic dependence on the mean voltage in small bias region.

High-Current Gain Two-Dimensional MoS₂-Base Hot-Electron Transistors.

The vertical transport of nonequilibrium charge carriers through semiconductor heterostructures has led to milestones in electronics with the development of the hot-electron transistor. Recently, significant advances have been made with atomically sharp heterostructures implementing various two-dimensional materials. Although graphene-base hot-electron transistors show great promise for electronic switching at high frequencies, they are limited by their low current gain.

Probing Spin Accumulation induced Magnetocapacitance in a Single Electron Transistor.

The interplay between spin and charge in solids is currently among the most discussed topics in condensed matter physics. Such interplay gives rise to magneto-electric coupling, which in the case of solids was named magneto-electric effect, as predicted by Curie on the basis of symmetry considerations. This effect enables the manipulation of magnetization using electrical field or, conversely, the manipulation of electrical polarization by magnetic field.

Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics.

High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation.

Effect of focused ion beam deposition induced contamination on the transport properties of nano devices.

Focused ion beam (FIB) deposition produces unwanted particle contamination beyond the deposition point. This is due to the FIB having a Gaussian distribution. This work investigates the spatial extent of this contamination and its influence on the electrical properties of nano-electronic devices.

Polymer-free patterning of graphene at sub-10-nm scale by low-energy repetitive electron beam.

A polymer-free technique for generating nanopatterns on both synthesized and exfoliated graphene sheets is proposed and demonstrated. A low-energy (5-30 keV) scanning electron beam with variable repetition rates is used to etch suspended and unsuspended graphene sheets on designed locations. The patterning mechanisms involve a defect-induced knockout process in the initial etching stage and a heat-induced curling process in a later stage.

Resonant tunneling through discrete quantum states in stacked atomic-layered MoS2.

Two-dimensional crystals can be assembled into three-dimensional stacks with atomic layer precision, which have already shown plenty of fascinating physical phenomena and been used for prototype vertical-field-effect-transistors.1,2 In this work, interlayer electron tunneling in stacked high-quality crystalline MoS2 films were investigated. A trilayered MoS2 film was sandwiched between top and bottom electrodes with an adjacent bottom gate, and the discrete energy levels in each layer could be tuned by bias and gate voltages.

Improving nanowire sensing capability by electrical field alignment of surface probing molecules.

We argue that the structure ordering of self-assembled probing molecular monolayers is essential for the reliability and sensitivity of nanowire-based field-effect sensors because it can promote the efficiency for molecular interactions as well as strengthen the molecular dipole field experienced by the nanowires. In the case of monolayers, we showed that structure ordering could be improved by means of electrical field alignment. This technique was then employed to align multilayer complexes for nanowire sensing applications.

Photo-response of a nanopore device with a single embedded ZnO nanoparticle.

The photo-response of a ZnO nanoparticle embedded in a nanopore made on a silicon nitride membrane is investigated. The ZnO nanoparticle is manipulated onto the nanopore and sandwiched between aluminum contact electrodes from both the top and bottom. The asymmetric device structure facilitates current-voltage rectification that enables photovoltaic capacity.

Monitoring extracellular K+ flux with a valinomycin-coated silicon nanowire field-effect transistor.

A silicon nanowire field-effect transistor (SiNW-FET) coated with a polyvinyl chloride (PVC) membrane containing valinomycin (VAL) was employed as a biosensor (referred to as VAL-PVC/SiNW-FET) to detect the K(+)-efflux from live chromaffin cells. The detection sensitivity of K(+) with the VAL-PVC/SiNW-FET covers a broad range of concentrations from 10(-6) to 10(-2) M. The apparent association constants between VAL and Li(+), Na(+), K(+), and Cs(+) in Tris buffer solution were determined to be 67±42, 120±23, 5974±115, and 4121±140 M(-1), respectively.

Voltage controlled photoluminescence blinking in CdSe nano-particles.

Voltage controlled photoluminescence (PL) blinking behavior in CdSe nano-particles (NPs) is studied. The NPs are sandwiched between a p-type silicon substrate and a thin Au electrode, which serve respectively as source and drain electrodes. The blinking PL from the NPs can be controlled by the bias voltage across the two electrodes.

Direct observation of electron dephasing due to inelastic scattering from defects in weakly disordered AuPd wires.

To identify and investigate the mechanisms of electron-phonon (e-ph) relaxation in weakly disordered metallic conductors, we measure the electron dephasing rate in a series of suspended and supported 15-nm thick AuPd wires. In a wide temperature range, from ∼8  K to above 20 K, the e-ph interaction dominates in the dephasing processes. The corresponding relaxation rate reveals a quadratic temperature dependence, τ(e-ph)(-1)=A(ep)T2, where A(ep)≈5×10(9)  K(-2)  s(-1) is essentially the same for all samples studied.

Coaxial metal-oxide-semiconductor (MOS) Au/Ga2O3/GaN nanowires.

Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C.

Exocytosis of a single bovine adrenal chromaffin cell: the electrical and morphological studies.

Exocytosis of a single bovine adrenal chromaffin cell, triggered by histamine stimulation, was investigated via the electric responses detected with single-walled carbon-nanotube field-effect transistors (SWCNT-FET) and the morphological changes acquired by atomic force microscopy (AFM). Secretion of chromogranin A (CgA), stored in the vesicles of a single chromaffin cell, can be monitored in situ by the antibody against CgA (CgA-antibody) functionalized on the SWCNT-FET devices. The SWCNT-FET can further discriminate the amount of released CgA with different levels of histamine stimulations.