We report on highly sensitive and flexible biosensors for noninvasive lactate and alcohol monitoring in human perspiration based on zinc oxide (ZnO) nanostructures that does not require linker layer for surface functionalization due to the high isoelectric point of ZnO. Towards fabrication of the biosensors, two-dimensional (2D) ZnO nanoflakes (NFs) were synthesized on flexible polyethylene terephthalate (PET) substrates employing single step sonochemical method after which lactate oxidase (LOx) and anti-body for ethyl glucuronide (EtG)-a metabolite of ethanol were immobilized atop without a linker layer. The cyclic voltammetry (CV) measurements in the concentration range of 10pM-10μM for lactate and 4.5 μM-0.45 M for EtG yielded minimum limit of detection of 10 pM and 4.5 μM, respectively for the electrode area of 0.5 × 0.5 cm2. Moreover, lactate sensor with ZnO NF electrodes demonstrated four times higher sensitivity compared to the ones with gold electrode that required DTSP linker layer for surface functionalization. High isoelectric point allows a direct, stable pathway for rapid electron transport without any mediator when an analyte is immobilized on NFs and improves electron transfer rate.
Plasmonic ultraviolet (UV) photodetectors have witnessed ongoing and tremendous enhancements in quantum efficiency and responsivity. Here, we go beyond regular plasmonic detectors by using periodic arrays of fractal aluminum nanostructures as Cayley trees deposited on a Ga2O3 substrate to generate photocurrent. We show that the proposed aluminum Cayley trees are able to support and intensify strong broad plasmon resonant modes across the UV to the visible spectrum. It is shown that the Cayley trees can be tailored to facilitate strong absorption at high energies (short wavelengths), resulting formation of hot carriers. Having perfect compatibility to operate at the UV spectrum, fractal aluminum structures and Ga2O3 substrate help to increase the produced photocurrent remarkably. Presence of Ga2O3 layer blue-shifts the peak of absorption to higher energies and helps to generate hot carriers at deeper UV wavelengths.
In this paper, we have experimentally demonstrated the engineering of semi-metal single layer CVD Graphene’s bandgap by decorating with randomly distributed ZnO nano-seed grown by sonication of Zinc acetate dehydrate. The proximity of nanoparticles and Graphene breaks Graphene’s sublattice symmetry and opens-up a bandgap. The 2-D/G ratio of Raman spectroscopy of decorated Graphene along with a peak at 432.39 cm-1 confirmed presence of ZnO on single layer Graphene. The introduced bandgap was measured from the slope of Arrhenius plot. Graphene with significant bandgap introduced by the proposed methods could be used for devices intended for digital and logic applications.
We introduce a platform based on plasmonic metamaterials to design various optical devices. A simple structure brokenring
with a nanodisk at the center is utilized to excite and hybridize the plasmon resonant modes. We show that the
proposed nanoantenna is able to support strong sub- and superradiant plasmon resonances because of its unique
geometrical features. Using the concentric ring/disk in a dimer orientation as a nanoantenna on a multilayer metasurface
consisting of graphene monolayer, we induced double sharp plasmonic Fano resonant modes in the transmission window
across the visible to the near-infrared region. Considering the strong polarization-dependency of the broken-ring/disk
dimer antenna, it is shown that the proposed plasmonic metamaterial can be tailored as an optical router device for fast
switching applications. This understanding opens new paths to employ plasmonic metamaterials with simple geometrical
nanoscale blocks for sensing and switching applications.
In this work, we propose a novel Graphene field effect transistor (GFET) with ohmic Source/Drain contacts having capacitive extension towards the Gate. The ohmic contacts of the proposed GFET are used for DC biasing as like as conventional GFETs whereas their extended parts which are capacitively coupled to the channel reduce access region length as well as the access resistance and provide a low impedance route for the high frequency RF signal. Reduction of access resistance along with the paralleling of ohmic contact resistance and real part of capacitive impedance result in an overall lower Source/Drain resistance which eventually increases the current gain cut-off frequency, fT. We have studied and compared the DC and RF characteristics of the baseline conventional GFET and proposed GFET using analytical and numerical techniques.
We propose and extensively analyze a novel Graphene-FET (GFET) with two capacitively coupled field-controlling electrodes (FCE) at the ungated access regions between gate and source/drain. The FCEs are proposed to be positioned both on top and bottom of the device. The FCEs could be independently biased to modulate sheet carrier concentration and thereby the resistance in the ungated regions. The reduction of source/drain access resistance results in increased cut off frequency compared to those of conventional GFETs with the same geometry. The DC and improved RF characteristics of the proposed device have been studied using both analytical and numerical techniques and compared with the baseline designs.
Analytical and numerical studies of the dispersion properties of grating gated THz plasmonic structures show that
the plasmonic crystal dispersion relation can be represented in terms of effective index of the dielectric medium
around the 2DEG for the plasmons. Forbidden energy band gaps are observed at Brillion zone boundaries of the
plasmonic crystal. FDTD calculations predict the existence of the plasmonic modes with symmetrical, antisymmetrical
and asymmetrical charge distributions. Breaking the translational symmetry of the crystal lattice by
changing the electron concentration of the two dimensional electron gas (2DEG) under a single gate line in every 9th gate induces a cavity state. The induced cavity state supports a weekly-coupled cavity mode.
We theoretically investigated and designed a tunable, compact THz source in 1-10 THz range based on a nonlinear
optical microdisk resonator. The lack of tunable THz source operating at room temperature is still one of the major
impediments for the applications of THz radiation. The proposed device on an insulated borosilicate glass substrate
consists of a nonlinear optical disk resonator on top of another disk capable of sustaining THz modes. A pair of Si
optical waveguides is coupled to the nonlinear microdisk in order to carry the two input optical waves. Another pair of Si
THz waveguides is placed beneath the input optical waveguides to couple out the generated THz radiation from the disk
to receiver antenna. Both optical and THz disks are engineered optimally with necessary effective mode indices in order
to satisfy the phase matching condition. We present the simulation results of our proposed device using a commercial
finite element simulation tool. A distinguished THz peak coincident exactly with the theoretical calculations involving
DFG is observed in frequency spectrum of electric field in the microdisk resonator. Our device has the potential to
enable tunable, compact THz emitters and on-chip integrated spectrometers.
We designed and theoretically investigated nonlinear optical micro-ring resonators for tunable terahertz (THz) emission
in 1-10 THz range by using difference frequency generation (DFG) phenomenon with large second order optical
nonlinearity (χ(2)). Our design consists of a nonlinear ring resonator and another ring underneath capable of sustaining high-Q resonant modes for infrared pump beams and the generated THz radiation, respectively. The nonlinear ring
resonator generates THz through DFG by mixing the input waves carried by a pair of waveguides. The proposed device
can be a viable platform for tunable, compact THz emitters and on-chip integrated spectrometers.
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