92 research outputs found
Wavelength selective filter based on polarization control in a photonic bandgap structure with a defect
We present a technique for achieving wavelength specific half-wave retardation upon reflection from an asymmetric one-dimensional photonic band-gap structure with a defect. The approach is based on a high finesse Gires-Tournois type interferometer and makes use of the large mode splitting of TE and TM defect modes that occurs in structures with a wide photonic band-gap. We use this structure to demonstrate a polarization-based selective tuneable filter with a narrow pass-band and wide rejection-band
ElectronāInduced Perpendicular Graphene Sheets Embedded Porous Carbon Film for Flexible Touch Sensors
Graphene-based materials on wearable electronics and bendable displays have received considerable attention for the mechanical flexibility, superior electrical conductivity, and high surface area, which are proved to be one of the most promising candidates of stretching and wearable sensors. However, polarized electric charges need to overcome the barrier of graphene sheets to cross over flakes to penetrate into the electrode, as the graphene planes are usually parallel to the electrode surface. By introducing electron-induced perpendicular graphene (EIPG) electrodes incorporated with a stretchable dielectric layer, a flexible and stretchable touch sensor with āin-sheet-charges-transportationā is developed to lower the resistance of carrier movement. The electrode was fabricated with porous nanostructured architecture design to enable wider variety of dielectric constants of only 50-Ī¼m-thick Ecoflex layer, leading to fast response time of only 66 ms, as well as high sensitivities of 0.13 kPaā1 below 0.1 kPa and 4.41 MPaā1 above 10 kPa, respectively. Moreover, the capacitance-decrease phenomenon of capacitive sensor is explored to exhibit an object recognition function in one pixel without any other integrated sensor. This not only suggests promising applications of the EIPG electrode in flexible touch sensors but also provides a strategy for internet of things security functions.The authors thank the National Key R&D
Program of China (Grant No. 2018YFB1306100), China Postdocā
toral Science Foundation (Grant No. 2019M653607), the Fundaā
mental Research Funds for the Central Universities and SEM facilā
ity of the ANFF ACT node at the Australian National University
Photonic crystal slot nanobeam slow light waveguides for refractive index sensing
We present the design, fabrication, and photoluminescence experiment of InGaAsP photonic crystal
slot nanobeam slow light waveguides with embedded InAs quantum dots. The strong confinement
of electric field in the slot region is confirmed by the measured record high sensitivity of 7 x
10 (2) nm per refractive index unit RIU to the refractive index change of the environment. A
cavity, formed by locally deflecting the two beams toward each other, gives an even higher
sensitivity of about 9x10(2) nm/RIU.The authors acknowledge the support from the BrainBridge
project ZJU-TU/e and Philips Research collaboration,
AOARD, and the National Natural Science Foundation of
China Grant No. 60907018
InGaAsP photonic crystal slot nanobeam waveguides for refractive index sensing
Results are presented on the use of InGaAsP photonic crystal nanobeam slot waveguides for refractive index sensing. These sensors are read remote-optically through photoluminescence, which is generated by built-in InGaAs quantum dots. The nanobeams are designed to maximize the electromagnetic field intensity in the slot region, which resulted in record-high sensitivities in the order of 700 nm/RIU (refractive index unit). A cavity, created by locally deflecting the two beams towards each other through overetching, is shown to improve the sensitivity by about 20%
Enhanced luminescence from GaN nanopillar arrays fabricated using a top-down process
We report the fabrication of GaN nanopillar arrays with good structural uniformity using the top-down approach. The photoluminescence intensity from the nanopillar arrays is enhanced compared to the epilayer. We use finite difference time domain simulations to show that the enhancement in photoluminescence intensity from the nanopillar arrays is a result of anti-reflection properties of the arrays that result in enhanced light absorption and increase light extraction efficiency compared to the epilayer. The measured quantum efficiency of the nanopillars is comparable to that of an epitaxially grown GaN epilayer.ARC grant DP140103278 (2014-2016) - H.H. Tan, Nitride-based Compound Semiconductors for Solar Water Splittin
Post-processing approach for tuning multi-layered metamaterials
We propose a post-processing approach to efficiently tune the resonance frequency in double-layered terahertz metamaterials separated by a bonding agent. By heating the bonding agent, it is possible to move one metamaterial layer laterally with respect to the other. This changes the coupling between adjacent layers, thereby shifting the resonance frequency. The resonance frequency of the stacked layers continuously shifts as a function of the lateral displacement, reaching a maximum shift of 92āGHz (31% of the center frequency). We discuss the effects of vertical separation on the tunability of the two-layered structure. The post-processing approach is rather general and can be applied to different paired metamaterials in various wavelength ranges, paving the way to efficiently assemble and fine tune metamaterial sensors and filters.The authors would like to acknowledge the financial
support provided by the Australian Research Council and the
Asian Office of Aerospace Research and DevelopmentāU.S.
Air Force
Liquid crystal based nonlinear fishnet metamaterials
We study experimentally the nonlinear properties of fishnet metamaterials infiltrated with nematic liquid crystals and find that moderate laser powers result in significant changes of the optical transmission of the composite structures. We also show that the nonlinear response of our structure can be further tuned with a bias electric field, enabling the realization of electrically tunable nonlinear metamaterials.We acknowledge the support by the Australian Research
Council, the Australian National Computational Infrastructure,
and the ACT Node of Australian National Fabrication
Facility
Radiation tolerance of two-dimensional material-based devices for space applications
Characteristic for devices based on two-dimensional materials are their low size, weight and power requirements. This makes them advantageous for use in space instrumentation, including photovoltaics, batteries, electronics, sensors and light sources for long-distance quantum communication. Here we present a comprehensive study on combined radiation effects in Earth's atmosphere on various devices based on these nanomaterials. Using theoretical modeling packages, we estimate relevant radiation levels and then expose field-effect transistors, single-photon sources and monolayers as building blocks for future electronics to gamma-rays, protons and electrons. The devices show negligible change in performance after the irradiation, suggesting robust suitability for space use. Under excessive gamma-radiation, however, monolayer WS2 shows decreased defect densities, identified by an increase in photoluminescence, carrier lifetime and a change in doping ratio proportional to the photon flux. The underlying mechanism is traced back to radiation-induced defect healing, wherein dissociated oxygen passivates sulfur vacancies.This work was funded by the Australian Research Council (CE170100012, FL150100019, DE140100805, DE170100169, DE160100098 and DP180103238). We acknowledge financial support from ANU PhD scholarships, the China Scholarship Council and the ANU Major Equipment Committee fund (No. 14MEC34)
Radiation tolerance of two-dimensional material-based devices for space applications
Characteristic for devices based on two-dimensional materials are their low
size, weight and power requirements. This makes them advantageous for use in
space instrumentation, including photovoltaics, batteries, electronics, sensors
and light sources for long-distance quantum communication. Here, we present for
the first time a comprehensive study on combined radiation effects in earth's
atmosphere on various devices based on these nanomaterials. Using theoretical
modeling packages, we estimate relevant radiation levels and then expose
field-effect transistors, single-photon sources and monolayers as building
blocks for future electronics to gamma-rays, protons and electrons. The devices
show negligible change in performance after the irradiation, suggesting robust
suitability for space use. Under excessive -radiation, however,
monolayer WS showed decreased defect densities, identified by an increase
in photoluminescence, carrier lifetime and a change in doping ratio
proportional to the photon flux. The underlying mechanism was traced back to
radiation-induced defect healing, wherein dissociated oxygen passivates sulfur
vacancies
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