arXiv subjects

Roberto De Alba

Publications and source records attributed to Roberto De Alba.

4 recordsLinked to original sources

arXiv2016

Low-power photothermal self-oscillation of bimetallic nanowires

We investigate the nonlinear mechanics of a bimetallic, optically absorbing SiN-Nb nanowire in the presence of incident laser light and a reflecting Si mirror. Situated in a standing wave of optical intensity and subject to photothermal forces, the nanowire undergoes self-induced oscillations at low incident light thresholds of $<1\, \rm{μW}$ due to engineered strong temperature-position ($T$-$z$) coupling. Along with inducing self-oscillation, laser light causes large changes to the mechanical resonant frequency $ω_0$ and equilibrium position $z_0$ that cannot be neglected. We present experimental results and a theoretical model for the motion under laser illumination. In the model, we solve the governing nonlinear differential equations by perturbative means to show that self-oscillation amplitude is set by the competing effects of direct $T$-$z$ coupling and $2ω_0$ parametric excitation due to $T$-$ω_0$ coupling. We then study the linearized equations of motion to show that the optimal thermal time constant $τ$ for photothermal feedback is $τ\to \infty$ rather than the widely reported $ω_0 τ= 1$. Lastly, we demonstrate photothermal quality factor ($Q$) enhancement of driven motion as a means to counteract air damping. Understanding photothermal effects on micromechanical devices, as well as nonlinear aspects of optics-based motion detection, can enable new device applications as oscillators or other electronic elements with smaller device footprints and less stringent ambient vacuum requirements.

cond-mat.mes-hall↗

arXiv2016

Transfer Printing of CVD Graphene FETs on Patterned Substrates

We describe a simple and scalable method for the transfer of CVD graphene for the fabrication of field effect transistors. This is a dry process that uses a modified RCA cleaning step to improve the surface quality. In contrast to conventional fabrication routes where lithographic steps are performed after the transfer, here graphene is transferred to a pre-patterned substrate. The resulting FET devices display nearly zero Dirac voltage, and the contact resistance between the graphene and metal contacts is on the order of 910 +- 340 Ohm-micrometer. This approach enables formation of conducting graphene channel lengths up to one millimeter. The resist-free transfer process provides a clean graphene surface that is promising for use in high sensitivity graphene FET biosensors.

cond-mat.mes-hall↗

arXiv2016

Detection of DNA and Poly-L-Lysine using CVD Graphene-channel FET Biosensors

A graphene channel field-effect biosensor is demonstrated for detecting the binding of double-stranded DNA and poly-l-lysine. Sensors consist of CVD graphene transferred using a clean, etchant-free transfer method. The presence of DNA and poly-l-lysine are detected by the conductance change of the graphene transistor. A readily measured shift in the Dirac Voltage (the voltage at which the graphenes resistance peaks) is observed after the graphene channel is exposed to solutions containing DNA or poly-l-lysine. The Dirac voltage shift is attributed to the binding/unbinding of charged molecules on the graphene surface. The polarity of the response changes to positive direction with poly-l-lysine and negative direction with DNA. This response results in detection limits of 8 pM for 48.5 kbp DNA and 11 pM for poly-l-lysine. The biosensors are easy to fabricate, reusable and are promising as sensors of a wide variety of charged biomolecules

cond-mat.mes-hall↗

arXiv2014

Evanescent field optical readout of graphene mechanical motion at room temperature

Graphene mechanical resonators have recently attracted considerable attention for use in precision force and mass sensing applications. To date, readout of their oscillatory motion has typically required cryogenic conditions to achieve high sensitivity, restricting their range of applications. Here we report the first demonstration of evanescent optical readout of graphene motion, using a scheme which does not require cryogenic conditions and exhibits enhanced sensitivity and bandwidth at room temperature. We utilise a high $Q$ microsphere to enable evanescent readout of a 70 $μ$m diameter graphene drum resonator with a signal-to-noise ratio of greater than 25 dB, corresponding to a transduction sensitivity of $S_{N}^{1/2} = $ 2.6 $\times 10^{-13}$ m $\mathrm{Hz}^{-1/2}$. The sensitivity of force measurements using this resonator is limited by the thermal noise driving the resonator, corresponding to a force sensitivity of $F_{min} = 1.5 \times 10^{-16}$ N ${\mathrm{Hz}}^{-1/2}$ with a bandwidth of 35 kHz at room temperature (T = 300 K). Measurements on a 30 $μ$m graphene drum had sufficient sensitivity to resolve the lowest three thermally driven mechanical resonances.

cond-mat.mes-hall↗