Polycrystalline lead selenide thin film has now emerged as a promising choice for low-cost and uncooled MWIR detectors and arrays operating at room temperature within the 3~5 µm wavelength range. LCDG (Laser Components Detector Groups) has successfully fabricated a new version of PbSe thin films using the chemical bath deposition (CBD) method on quartz substrates, enabling the development of infrared detectors and arrays with robust and high production yield. To achieve efficient activation of the PbSe thin film, LCDG investigates PbSe material from chemical reaction of the bath deposition to final packaging to meet various customer specifications and establishes PbSe detectors based on nano- and micro-particles embedded PbSe thin film, resulting in exceptional MWIR photoconductive response at room temperature. The characterization of PbSe thin film reveals the presence of various nanostructures, such as nano- and micro-particles as well as Pb-oxide phases and Pb-iodine phase carrier transporting channels. This paper reports the MWIR performance of the uncooled LCDG’s PbSe detector, focusing on responsivity, EQE, 1/f noise and FTIR spectral response (77K-340K), and D*.
The hybrid metal/quantum dots (QDs) structures were synthesized and characterized with different thicknesses of silica shells by uncomplicated and typical methods. By engineering the shell thickness and Au nanoparticles (Au NPs) core size with shapes, the interaction between Au NPs and QDs could be adjusted flexibly to witness the energy transfer process thoroughly. The improvement of the emission intensity and the reduction in the PL lifetime with the appropriate thickness of silica layer were obtained. Likewise, the energy transfer efficiency between QDs donor-acceptor pairs was inferred as the dominance of larger QDs with hybrid structures. The quenching of QDs donors and the enhancement of QDs acceptors in PL emission intensity were determined by the different core-shell structures. Finally, as-prepared metal/silica/QDs structures have been explored for bio-imaging applications, leading to enhanced light absorption and sensitivity.
We report a localized surface plasmon resonance (LSPR) sensor that consists of noble metal and ferromagnetic material. This hybrid system offers tunable LSPR frequencies by the refractive index change of the surrounding medium as well as the external magnetic field around the nanostructures. We used a gold nanoparticle with Co and Fe. The thin ferromagnetic layers coated on gold nanoparticles have a linear dependence between relative permittivity with an applied magnetic field. The underlying mechanism is the change of the dielectric constant of the ferromagnetic film when it has aligned magnetization in the same direction of the external magnetic field. Consequently, change of the LSPR absorption spectrum of the hybrid nanostructures.
We present herein the active PbS-photopolymer waveguide fabricated by vacuum assisted microfluidic (VAM) soft lithography technique. The PbS Quantum Dots (QDs) were synthesized using colloidal chemistry methods with tunable sizes and emission wavelengths, resulting in efficient light emission around 1000 nm center wavelength. The PbS QDs have demonstrated much better solubility in our newly synthesized UV curable polymer than SU-8 photoresist, verified by Photoluminescence (PL) testing. Through refractive index control, the PbS QDs-polymer core material and polymer cladding material can efficiently confine the infrared emitting light with a broad spectral bandwidth of ~180 nm. Both single-mode and multi-mode light emitting waveguides have been realized.
Surface Plasmon Resonance (SPR) is currently being widely studied as it exhibits sensitive optical properties to changes in in the refractive index of the surrounding medium. As novel devices using SPR have been developing rapidly there is a necessity to develop models and simulation environments that will allow for continued development and optimization of these devices. A biological sensing device of interest is the Plasmon FET which has been proven experimentally to have a limit of detection (LOD) of 20pg/ml while being immune to the absorption of the medium. The Plasmon FET is a metal-semiconductor-metal detector which employ functionalized gold nanostructures on a semi-conducting layer. This direct approach has the advantages of not requiring readout optics reducing size and allowing for point-of -care measurements. Using Lumerical FDTD and Device numerical solvers, we can report an advanced simulation environment illustrating several key sensor specifications including LOD, resolution, sensitivity, and dynamic range, for a variety of biological markers providing a comprehensive analysis of a Direct Plasmon-to-Electric conversion device designed to function with colored mediums (eg.whole blood). This model allows for the simulation and optimization of a plasmonic sensor that already o
ers advantages in size, operability, and multiplexing-capability, with real time monitoring.
Surface Plasmon Resonance (SPR) has been widely studied for various application. Due to the highly sensitive optical property to the change of the refractive index of the surrounded medium, there have been lots of reports for biological sensing. Direct Plasmon-to-Electric conversion device using metal nanostructures and semiconductor does not require additional readout optics and the device size and sensing area could be much smaller (1/100 to 1/10 of size) than current technologies. In addition, our sensing platform designed to address the issue of using the colored medium (e.g. whole blood) for detection. The detection signal comes only from plasmonic absorption and is not affected by the absorption from the medium. We developed a plasmonic sensing platform using a metal-semiconductor-metal detector by incorporating gold nanostructures on top of the semiconducting layer. The gold nanostructures are functionalized using antibodies to detect Troponin I, which is very important molecule to prevent hart attacks. In this presentation, we report a successful demonstration of a point-of-care sensing platform to detect cardiac Troponin I using antibody functionalized plasmonic nanostructures. Because the sensors are integrated into a microfluidic channel, it requires only a few µl of sample volume. The limit of detection was 20 pg/ml in our preliminary results, and we successfully demonstrated sensor operation using whole blood. This plasmonic sensor has several advantages such as extremely small size for the point-of-care system, multiplexing capability, no need of complex optical geometry and real-time binding monitoring.
In this work, we present the enhancement of ultraviolet (UV) photodetection of Ag-ZnO thin film deposited by radio frequency magnetron sputtering. The surface morphological, optical, structural, and electrical properties of the deposited thin films were investigated by various characterization techniques. With this Ag-ZnO thin film structure and proper geometry of metal–semiconductor–metal (MSM) interdigitated structure design, photocurrent enhancement has been accomplished. MSM-photodetectors (PDs) using structures of Ag-ZnO gave a 30 times higher magnitude photocurrent at 340 nm of the wavelength. Plasmon-induced hot electrons contributed to improved spectral response to the UV region, while absorption and scattering effect enhanced broadband improvement to a response in the VIS–IR spectrum range. The improvement of Ag-ZnO PD in comparison with ZnO is attributed to the surface plasmon effect using Ag nanodisks. These results indicate that Ag-ZnO thin films can serve as excellent ultraviolet-PD and a very promising candidate for practical applications.
Plasmon field-effect transistor is a hybrid device using nanostructures to detect the plasmonic energy. This device efficiently transfers plasmonic hot electrons from the metal nanostructures to the semiconductor. The transported hot electrons to the electron channel increases transistor drain current. We investigate the efficiency of plasmonic hot carrier harvesting between metal and semiconductor. We analyzed the effect of gold nanoparticle (NP) density and distribution on plasmon FET spectral response. Then, we studied electric field-assisted hot electron transfer and transport using different device structures. The position of plasmonic structures plays an important role in plasmonic energy detection efficiency because the gradient of electric field seen by induced hot electrons varies depending on the distance between drain and source. Both the experimental and simulation results confirm that by fabricating the gold NPs close to source the spectral response increases by 31% in comparison with having gold NPs close to the drain. Our simulation and experimental data suggest important design considerations to improve hot electron collection and conversion using metallic nanostructures for plasmonic energy harvesting.
Localized surface Plasmon Resonance (LSPR) is a nanoscale phenomenon which presents strong resonance associated with noble metal nanostructures. This plasmon resonance based technology enables highly sensitive detection for chemical and biological applications. Recently, we have developed a plasmon field effect transistor (FET) that enables direct plasmonic-to-electric signal conversion with signal amplification. The plasmon FET consists of back-gated field effect transistor incorporated with gold nanoparticles on top of the FET channel. The gold nanostructures are physically separated from transistor electrodes and can be functionalized for a specific biological application. In this presentation, we report a successful demonstration of a model system to detect Con A proteins using Carbohydrate linkers as a capture molecule. The plasmon FET detected a very low concentration of Con A (0.006 mg/L) while it offers a wide dynamic range of 0.006-50 mg/L. In this demonstration, we used two-color light sources instead of a bulky spectrometer to achieve high sensitivity and wide dynamic range. The details of two-color based differential measurement method will be discussed. This novel protein-based sensor has several advantages such as extremely small size for point-of-care system, multiplexing capability, no need of complex optical geometry.
The potential of using a DNA biopolymer in an electro-optic device is presented. A complex of DNA with the
cationic surfactant cetyltrimethylammonium-chloride (CTMA) was used to obtain an organic-soluble DNA material
(DNA-CTMA). Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) was added to the DNACTMA
to increase the electrical conductivity of the biopolymer. The CW absorbance and time-resolved
photoluminescence of the resulting DNA-CTMA and DNA-CTMA-PEDOT:PSS were investigated. Both DNA
materials have absorbance peaks at ~260 nm and a broad, Stokes shifted, photoluminescence peak around 470nm.
The photoluminescence lifetime of the materials was observed to decrease with increasing UV excitation.
Specifically, excitation with a high power ultrafast (~150fs) UV (266nm) laser pulse resulted in a drastic decrease
in the photoluminescence lifetime decreases after a few minutes. Moreover, the observed decrease was faster in an
air ambient than in a nitrogen ambient. This is most likely due to photo-oxidation that degrades the polymer surface
resulting in an increase in the non-radiative recombination. In order to investigate the photoconductivity of these
two materials, metal-biopolymer-metal (MBM) ultraviolet photodetectors with interdigitated electrodes were
fabricated and characterized. The photoresponsivity of these devices was limited by the transport dynamics within
the film. The prospects for the use of these materials in optical devices will be discussed.
Mesoporous materials, such as porous silicon and porous polymer gratings (Bragg structures), offer an attractive platform for the encapsulation of chemical and biological recognition elements. These materials include the advantages of high surface to volume ratio, biocompatibility, functionality with various recognition elements, and the ability to modify the material surface/volume properties and porosity. Two porous structures were used for chemical and biological sensing: porous silicon and porous polymer photonic bandgap structures. Specifically, a new dry etching manufacturing technique employing xenon difluoride (XeF2) based etching was used to produce porous silicon Porous silicon continues to be extensively researched for various optical and electronic devices and applications in chemical and biological sensing are abundant. The dry etching technique to manufacture porous silicon offers a simple and efficient alternative to the traditional wet electrochemical etching using hydrofluoric acid. This new porous silicon material was characterized for its pore size and morphology using top and cross-sectional views from scanning electron microscopy. Its optical properties were determined by angular dependence of reflectance measurements. A new class of holographically ordered porous polymer gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. As an alternative structure and fabrication process, porous polymer gratings that include a volatile solvent as the phase separation fluid was fabricated. Porous silicon and porous polymer materials were used as substrates to encapsulate gaseous oxygen (O2) responsive luminophores in their nanostructured pores. These substrate materials behave as optical interference filters that allow efficient and selective detection of the wavelengths of interest in optical sensors.
KEYWORDS: Nanocrystals, Photoresistors, Ultraviolet radiation, Polymers, Solar cells, Absorption, Quantum dots, Quantum efficiency, Solar energy, Control systems
To achieve efficient carrier extraction from nanocrystal quantum dots, we introduce a novel tandem cell device
using PbSe nanocrystal quantum dots and a P3HT/PCBM bulk hetero junction cell. The device is fabricated using an all
solution based process. The device consists of a hydrazine treated PbSe nanocrystal photoconductive film coupled to
the P3HT/PCBM bulk hetero junction cell. In this work, the photocurrent from the PbSe nanocrystal photoconductive
layer, and the role of carrier multiplication at UV wavelengths, is elucidated. By using light biased spectral response
measurements, we successfully demonstrate an enhancement of quantum efficiency at photon energies greater than three
times the bandgap of the PbSe nanocrystals. Additionally, this tandem structured device shows a self-passivation
property that provides protection from UV irradiation to the underlying polymer cell.
A methodology for enabling biochemical sensing applications using porous polymer photonic bandgap structures is presented. Specifically, we demonstrate an approach to encapsulation of chemical and biological recognition elements within the pores of these structures. This sensing platform is built on our recently demonstrated nanofabrication technique using holographic interferometry of a photo-activated mixture that includes a volatile solvent as well as monomers, photoinitiators, and co-initiators. Evaporation of the solvent after polymerization yields nanoporous polymeric 1D photonic bandgap structures that can be directly integrated into optical sensor systems that we have previously developed. More importantly, these composite structures are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of biochemical recognition elements. As a specific example of a prototype device, we demonstrate an oxygen (O2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. Finally, we report initial results of extending this technique to the development of a hydrophilic porous polymer photonic bandgap structure for sensing in aqueous environments. The ability to control the hydrophilic/hydrophobic nature of these materials has direct impact on chemical and biological sensing.
The development of porous nanostructured materials, such as polymer Bragg gratings, offer an attractive and unique platform for chemical and biological recognition elements. Much of the efforts in polymeric gratings have been focused on holographic polymer dispersed liquid crystal (H-PDLC) gratings with demonstrated applications in switching, lasing, and display devices. Here, we present the application of porous polymer photonic bandgap structures produced using a modified holographic method that includes a solvent as a phase separation fluid. The resulting gratings are simple to fabricate, stable, tunable, and highly versatile. Moreover, these acrylate porous polymer photonic bandgap structures were generated using a simple one-beam setup. In this paper, we describe the application of these nanoporous polymer gratings as a general template for biochemical recognition elements. As a prototype, we developed an oxygen (O2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. Thus, the obtained O2 sensors performed through the full-scale range (0%-100%) with a response time of less than 1 second. Most importantly, the use of the inherent property of these gratings to transmit or reflect a particular wavelength spectrum, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest.
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