Seung-Bo Shim

A mechanical memory with a dc modulation of nonlinear resonance

We present a mechanical memory device based on dynamic motion of a nanoelectromechanical (NEM) resonator. The NEM resonator exhibits clear nonlinear resonance characteristics which can be controlled by the dc bias voltage. For memory operations, the NEM resonator is driven to the nonlinear resonance region, and binary values are assigned to the two allowed states on the bifurcation branch. The transition between memory states is achieved by modulating the nonlinear resonance characteristics with dc bias voltage. Our device works at room temperature and modest vacuum conditions with a maximum operation frequency of about 5 kHz.

Broadband Surface Plasmon Lasing in One-dimensional Metallic Gratings on Semiconductor

We report surface plasmon (SP) lasing in metal/semiconductor nanostructures, where one-dimensional periodic silver slit gratings are placed on top of an InGaAsP layer. The SP nature of the lasing is confirmed from the emission wavelength governed by the grating period, polarization analysis, spatial coherence, and comparison with the linear transmission. The excellent performance of the device as an SP source is demonstrated by its tunable emission in the 400-nm-wide telecom wavelength band at room temperature. We show that the stimulated emission enhanced by the Purcell effect enables successful SP lasing at high energies above the gap energy of the gain. We also discuss the dependence of the lasing efficiency on temperature, grating dimension, and type of metal.

Electrical conductance change of graphene-based devices upon surface modification for detecting botulinum neurotoxin

We report an electric conductance change in a graphene-based device upon molecular adsorption for detecting botulinum neurotoxin (BoNT) using the antibody–antigen binding strategy. This device consists of a 400-µm-wide monolayer of graphene between the source and drain electrodes. As-fabricated devices exhibit p-type behaviors. After modifying graphene with linkers and antibodies, BoNT detection was performed by dropping a target solution and measuring the conductance change of the devices. The immobilization of linkers on graphene decreases the electrical conductance as a result of electron transfer from linkers to graphene. However, the conductance change caused by the adsorption of antibodies or BoNTs is ascribed to the top-gating effects of the molecules adsorbed on graphene. The normalized conductance change of the graphene-based device upon antibody–BoNT binding was greater than 5%.

Electrical Field Gradient Pumping of Parametric Oscillation in a High-Frequency Nanoelectromechanical Resonator

We report on enhancements in the gain of silicon nitride (SiNx) nanomechanical resonators by parametric amplification using a dielectric gradient force pumping. With this technique, high mechanical quality factors (Q) of over 20,000 at resonant frequency of 6.79 MHz are achieved even at room temperature. By applying a constant electric bias voltage (Vdc), we show the resonant frequency to be dependent on static tension. To periodically modulate the spring constant of the resonator, a parametric pumping signal twice its resonant frequency (2f0) is applied simultaneously with the Vdc, and at room temperature, the phase-sensitive parametric gain is 9.62.

Development of π–Shape Parametric Resonators Including Torsional Self Pumping Springs

Materializing NEMS devices incorporating nonlinear dynamics is of fundamental importance in the field of small-scale mechanics and general science. Among these, parametric amplification draws considerable attention due to its unique characteristic. In this paper, we introduce novel designs for mechanically pumped parametric resonators in which torsional pumping springs are linked. The proposed parametric resonators can increase signal amplitude by matching resonances in a cantilever and beam. Amplitudes of resonators increase when resonances of cantilevers are amplified by torsional pumping from linked beams. In an attempt to transmit pure torsion (not displacement), zero-displacement points method is suggested, and the analytical prediction results are further verified by the corresponding simulation results obtained from COMSOL Multiphysics® . The π-shape resonators are fabricated by surface nano-machining process, and the horizontal dimensions of fabricated beams and cantilever are 31.6 um and 8 um, respectively. By using magnetomotive method, resonance frequencies are measured. Finally frequency matching is performed by DC tuning. When 54 V is applied, fdrive and fpump increase 0.78% and 0.16%, and the frequencies are exactly matched as 4.463 MHz.Copyright