Field-Effect Transistors (FETs) are the key building blocks in a wide range of electronic applications such as sensors and electrical switches. The emergence of Organic Field-Effect Transistors (OFETs) unveiled special features, which have taken the application of FETs into uncharted territories. These unique features include but are not limited to, low- cost processing, lightweight, mechanical flexibility, biocompatibility, broad material availability, etc. Similar to their inorganic counterparts, doping organic semiconductors (OSC) can significantly alter or improve their electrical and optoelectronic properties, resulting in doping induced OFET multi-functionalities. In this study, the impact of multi-doping on the OFET device performance and functionalities has been systematically investigated and evaluated under varying conditions of light, heat, and gate voltages. The experimental results appear to support the proposed hypothesis behind the multi-functionality of the system under study. The present work will provide valuable scientific insights for the advancement of OFET based sensors, switches, and modulators.
Graphene is a two-dimensional material and has demonstrated an exceptional electronic and photonic properties for unlimited applications including its use in extreme environments of the space. There are several known techniques of formation of graphene onto different types of substrates such as the substrate transfer process and direct deposition. In this work, we deposited monolayer graphene over copper and nickel substrates in NanoCVD-8G Graphene reactor using argon plasma, and methane as a carbon source and studied effects of gamma irradiation using Cobalt-60 source. Radiation effects on crystalline structure of graphene is examined using Raman Spectroscopy and X-ray Photo Electron Spectroscopy (XPS). In our experiment, we used irradiation dose from 1 kGy to 2.65 kGy for different samples of graphene over copper and nickel substrates. For the graphene grown on the nickel substrates, we exposed the irradiation dose of 1.0 kGy and 2.5 kGy on two samples, respectively. For the graphene grown on the copper substrates, we exposed 1.25 kGy, 1.75 kGy, and 2.65 kGy irradiation dose on three samples, respectively. We observed D-peak in graphene deposited over nickel and copper substrates caused by disordered structure of graphene after Co-60 exposure. After the Raman spectroscopy and XPS studies, same amount of irradiation was used for second set of irradiation dose experiment. XPS data on Co-60 exposed samples showed four peaks positioned at 284.8eV, 285.3eV, 286.0 eV and 288.5 eV for C-C, C-OH, C-O-C and COOH bonds, respectively. Analysis of the results shows weakening of C-C bonds and formation of C-OH, C-O-C and COOH bonds implying reduced electrical conductivity of graphene.
Contamination control engineers provide critical plans to monitor, mitigate, and reduce the impact of molecular and particulate contamination on spacecraft systems. Witness monitoring programs are dependable methods that utilize strategically placed witness samples on space flight hardware to monitor particulate and molecular contaminants during the assembly, integration, and test (AI&T) phases. Traditionally, optical characterization of these witness plates is the tool to determine the presence of molecular films on space flight hardware in the AI&T environment. Once a visual inspection or optical measurement identifies the presence of a contaminant, analysts collect tape lifts and wipe samples from the witness plate for analysis in an analytical lab with a potential contaminant identified within 24 hours. To speed up this process and reduce the impact to project schedule and cost the use of a non-invasive and in situ method for optical witness plate program with portable Raman spectroscopy to detect molecular contamination on spacecraft was explored.
Devices with increased sensitivities are needed for various applications including the detection of chemical and biological agents. This paper presents the design of microelectromechanical systems (MEMS) devices that incorporate lead zirconate titanate (PZT) films in order to realize highly sensitive sensors. In this work, the piezoelectric properties of the PZT are exploited to produce sensors that perform optimally for mass sensing applications. The sensor is designed to operate as a thin-film bulk acoustic resonator (TFBAR) whereas a piezoelectric is sandwiched between electrodes and senses a change in mass by measuring a change in resonance frequency. Modeling of the TFBAR sensor, using finite element analysis software COMSOL, was performed to examine optimal device design parameters and is presented in this paper. The effect of the PZT thickness on device resonance is also presented. The piezoelectric properties of the PZT is based on its crystal structure, therefore, optimization of the PZT film growth parameters is also described in this work. A detailed description of the fabrication process flow developed based on the optimization of the device design and film growth is also given. The TFBAR sensor consists of 150 nm of PZT, 150nm of silicon dioxide, silicon substrate, titanium/platinum bottom electrodes, and aluminum top electrodes. The top electrodes are segmented to increase the sensitivity of the sensor. The resonance frequency of the device is 3.2 GHz.
We investigated the optical and optoelectronic properties of vertically aligned Al:ZnO nanorod arrays synthesized by the hydrothermal technique at a considerably low temperature on a sputtered Al:ZnO seed layer. The nanorod arrays maintained remarkable alignment along the c-axis over a large area. The seed layers and nanorod arrays showed various optical band gaps. Investigation of the optoelectronic properties of nanorod arrays on Al:ZnO/p-Si seed layer with SiO2 revealed that the photocurrent is significantly reduced in nanorod arrays on a AZO/SiO2/p-Si heterojunction due to multiple scattering phenomena associated with nanorod arrays. This research may open up venues for various optical and opto-electronic applications where highly aligned nanostructures are desired.
We report here the investigation of Al-doped ZnO films fabricated by the RF magnetron deposition technique. The films
show excellent crystalline quality with atomically smooth surface morphology. The Al-doped ZnO films have been
characterized in detail using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy UV-visible
spectrophotometer and four probe technique. It was found that the morphological, structural, electrical and optical
properties of Al-doped ZnO films are greatly dependent on substrate temperature. XRD patterns show that all the films
are well crystallized with hexagonal wurtzite structure with preferred orientation along (0 0 2) plane. The electrical
resistivity of Al-doped ZnO films decreases with increasing substrate temperature and was found to be close to 1.5 × 10-3
ohm-cm and transmittance >85% in the visible region.
We report on the growth of vertically aligned Al:ZnO nanorod arrays synthesized by the hydrothermal technique at
considerably low temperature on a sputtered Al:ZnO seed layer. The morphology demonstrates that the nanorod arrays
maintain remarkable alignment along the c-axis over a large area. The optoelectronic properties of nanorod arrays on
Al:ZnO/p-Si seed layer with SiO2 have been illustrated. The photocurrent is significantly reduced in nanorod arrays on
AZO/SiO2/p-Si heterojunction due to multiple scattering phenomena associated with the nanorod arrays. The optical
properties of the AZO film with and without the AZO nanorod arrays were investigated. Also the effects of an
intermediate layer in the AZO/P-Si heterojunction structure with and without the AZO nanorod array present were
explored. All the various intermediate layers displayed photovoltaic effect behavior, especially with the AZO/SiO2/P-Si
heterojunction structure, which exhibited ideal diode behavior. The optoelectronic properties of nanorod arrays on
AZO/P-Si seed layer with SiO2 have been illustrated. The photocurrent is significantly reduced in nanorod arrays on
AZO/SiO2/P-Si heterojunction due to multiple scattering phenomena associated with the nanorod arrays. The results
have tremendous impact for sensor fabrication, including glucose sensor.
Layered lithiated transition metal oxides have been extensively developed and investigated as a cathode materials for
lithium ion batteries due to the following advantages, such as high output voltage of 3.6 V, high energy density larger
than 450Wh/dm3, low self-discharge rate less than 10%, no memory effect resulting in long cycle lives for more than
1000 times charging and discharging, free maintenance and no environmental pollution. The cathode materials in lithium
ion battery are generally in the form of LiMO2 (M= Co, Ni, Mn, etc). Currently, lithium vanadium oxides also were
studied. It is well known that the synthetic condition and methods are closely related to the electrochemical properties of
lithium ion batteries. In this work, the wet chemical sol gel techniques have been used to synthesize LiNiO2 and LiV3O8.
In this study, the LiNiO2 particles and LiV3O8 nanorods were successfully synthesized by sol-gel wet chemical methods.
Annealing heat treatment influence the crystallinity of the final product, which may be consequently affected their
electrochemical performance.
A. Pradhan, R. Mundle, K. Zhang, T. Holloway, O. Amponsah, D. Biswal, R. Konda, C. White, H. Dondapati, K. Santiago, T. Birdsong, M. Arslan, B. Peeples, D. Shaw, J. Smak, C. Samataray, M. Bahoura
Magnetic nanoparticles of CoFe2O4 have been synthesized under an applied magnetic field through a co-precipitation
method followed by thermal treatments at different temperatures, producing nanoparticles of varying size. The
magnetic behavior of these nanoparticles of varying size was investigated. As-grown nanoparticles demonstrate
superparamagnetism above the blocking temperature, which is dependent on the particle size. The anomalous
magnetic behavior is attributed to the preferred Co ions and vacancies arrangements when the CoFe2O4 nanoparticles
were synthesized under applied magnetic field. Furthermore, this magnetic property is strongly dependent on the high
temperature heat treatments, which produce Co ions and vacancies disorder. We performed the fabrication of
condensed and mesoporous silica coated CoFe2O4 magnetic nanocomposites. The CoFe2O4 magnetic nanoparticles
were encapsulated with well-defined silica layer. The mesopores in the shell were fabricated as a consequence of
removal of organic group of the precursor through annealing. The NiO nanoparticles were loaded into the
mesoporous silica. The mesoporous silica coated magnetic nanostructure loaded with NiO as a final product may
have potential use in the field of biomedical applications.
Growth mechanism of ZnO nanorod arrays on ZnO seed layer investigated by electric and Kelvin probe
force microscopy. Both electric and Kelvin force probe microscopy was used to investigate the surface potentials on
the ZnO seed layer, which shows a remarkable dependence on the annealing temperature. The optimum temperature
for the growth of nanorod arrays normal to the surface was found to be at 600 °C, which is in the range of right
surface potentials and energy measured between 500 °C and 700 °C. We demonstrated from both EFM and Kelvin
force probe microscopy studies that surface potential controls the growth of ZnO nanorods. This study will provide
important understanding of growth of other nanostructures. ZnO nanolayers were also grown by atomic layer
deposition techniques. These nanolayers of ZnO demonstrate remarkable optical and electrical properties. These
nanolayers were patterned by the Electron Beam Lithography (EBL) technique.
A major goal of nanotechnology is to couple the self-assembly of molecular nanostructures with
conventional lithography, using either or both bottom-up and top-down fabrication methods, that would enable us to
register individual molecular nanostructures onto the functional devices. However, combining the nanofabrication
technique with high resolution Electron Beam Lithography, we can achieve 3D bimolecular or/and DNA origami that
will be able to identify nucleic acid sequences, antigen targets, and other molecules, as for a perfect nano-biosensor.
We have explored some of the nanopatterning using EBL in order to fabricate biomolecule sensing on a single chip
with sub nm pitch. The applications are not limited for the bioactivity, but for enhancing immunoreactions, cell
culture dishes, and tissue engineering applications.
Multicomponent semiconductor oxides mainly composed of elements like indium, zinc, tin or gallium are very
promising new class of materials for application in transparent electronics, multifunctional sensors and other electronic
applications. The major characteristic of these materials is high mobility, and the electrical behavior is a consequence of
a conduction band primarily derived from spherically symmetric heavy-metal cationns orbital with (n-1)d10ns0 (n ≥4)
electronic configuration. The carrier transport becomes insensitive to the degree of disorder of the film, and makes this
class of quasi-polycrystalline and amorphous semiconductors attractive for numerous applications.We report here on the
environmental sensing, such as ultra-violet-radiation and various gases of pulsed-laser deposited composite
semiconductor films. These films demonstrate outstanding sensing capability from measuring the surface resistivity
taking into account the absorption of sensing species. Our results show new possibilities for the low-cost high
performance environmental sensors for numerous potential applications. The details of the results will be presented.
We have studied ferroelectric properties of Pb (Zr0.6Ti0.4) O3(PZT)/SrTiO3 thin films grown on
platinized silicon substrates using pulsed-laser deposition and magnetron sputtering technique.
The spontaneous polarization (Ps) and remnant polarization (Pr) varies between 15.5 K and 100
K from 33-38 μC/cm2 and 25-30 μC/cm2,respectively. Similar values of Ps and Pr were also
observed until temperature reached to 300K. However, more pronounced ferroelectric hysteresis
loops were observed between T= 323 to 353 K. The Ps and Pr remain around 36-40 μC/cm2and
23-28 μC/cm2, respectively, between T = 323 to 353 K. The remnant polarization remains fairly
consistent over the chosen temperature range. X-ray diffraction and high-resolution microscopic
studies reveal that the Pb (Zr0.6Ti0.4) O3 layers are superior in crystalline quality than that of
SrTiO3. The PZT in multilayered films show remarkably enhanced polarization properties
relative to their single layers on the same substrates. The collective contribution of dipole
moments from each layer is the reason for such enhancement in polarization properties. This
growth strategy may be very useful for fabrication of sensitive sensing and other relevant
devices.
Nanometer-sized particles have novel optical, electronic, magnetic or structural properties and are currently under
intense development for application in cancer, cardiovascular diseases, and degenerative neurological disorders such as
alzheimer's disease. Targeted nanoparticle drugs offer significant advantages in improving cancer therapeutic efficacy
and simultaneously reducing drug toxicity. We report here the synthesis, characterization and toxicity test of FeCo and
Eu: Gd2O3 nanoparticles. Chemical routes, such ad coprecipitation and sol-gel techniques were used for the synthesis of
the nanoparticles, and the surface of the nanoparticles was coated with silica. Structural and microstructural studies
reveal that both type of nanoparticles 20 nm in size with very narrow size distribution. These nanoparticles demonstrate
strong magnetic and optical properties at room temperature. Toxicity test shows that FeCo nanoparticles are very toxic,
however toxicity decreases when the nanoparticles were coated with a thin layer of silica. However toxicity decreases
when the nanoparticles were coated with a thin layer of silica. However, both uncoated and coated Eu:Gd2O3
nanoparticles show significantly reduced toxicity. Our results suggest that these nanoparticles are useful for biomedical
applications. The detail of the results will be presented.
We have demonstrated that an addition of highly concentrated rhodamine 6G chloride dye to the PMMA film adjacent to
a silver film causes three-fold reduction of the imaginary part of the dielectric constant of Ag (absorption loss in metal)
and 30% elongation of the propagation length of surface plasmon polaritons (SPP). The possibility to elongate the SPP
propagation length without optical gain opens a new technological dimension to low-loss nanoplasmonics.
In this work, we report the substantial compensation of loss of propagating SPPs at the interface between silver film and
optically pumped polymer with dye. The large magnitude of the effect, nearly threefold change of the reflectivity,
enables a variety of applications of "active" nanoplasmonics. In order to quantify the observed phenomenon, we have
extended the theoretical formalism relating the reflectivity in ATR experiment and the SPP propagation length to the
case of active dielectric media.
We demonstrate first anti-Stokes laser in which only one pumping photon is required to produce one higher-energy emission photon. The difference of energy is drawn from phonons. This regime is realized in GaAs random laser. We also propose a laser system based on an anti-Stokes laser, which can be pumped by heat only. The temperature of the heater does not need to be high. The heat pumping energy (at practically no cost) can be provided via thermal contact of the laser element with an ambient environment, such as atmosphere, ocean, ground, etc.
Stimulated emission can be obtained in small volumes of scattering laser materials without cavity or any special optical design. Such sources of stimulated emission are known as random lasers. In random lasers, amplifying laser medium provides for gain, and scatterers (powder particles, air gaps between particles, etc.) provide for stimulated emission feedback. Above certain threshold pumping energy, the emission characteristics of random lasers change dramatically: the emission spectrum collapses to one or several narrow lines and one or several short emission pulses appear in response to a relatively long pumping pulse. Solid-state random lasers based on rare-earth doped dielectrics, dielectrics with color centers, semiconductors, scattering polymers, etc., offer challenging and not yet completely understood physics as well as promising applications, including express testing of laser materials, identification, and information processing. The focus of our presentation is on optically pumped neodymium random lasers. In particular, we discuss the dependence of the photon mean free path lt, the threshold energy density Eth/S and the slope efficiency in neodymium random lasers as a function of the mean particles size s. The experimental results are compared with the predictions of the developed models.
Stimulated emission in Nd0.5La0.5Al3(BO3)4 ceramic random laser was studied at different diameters of the pumped spot d. The developed heuristic model adequately describes the dependence of threshold pumping energy density versus d at d greater or equal to 150 micrometer. At small pumping beam diameter (less than 100 micrometer), very bright and strongly localized emission spot was observed in the center of the pumped area. The spectrum of the bright-spot emission appeared to be similar to that of 'continuum wave' light sources.
A future polymer based electro-optical (EO) modulator has several advantages over a current commercial Lithium Niobate EO modulator, a key device that encodes electronic signals into optical signals. These advantages include larger bandwidth (over 100 GHz), lower drive voltage (less then 1 volt), more cost effective, etc. However, one major challenge for EO polymer development is materials stability, including short term and long term SHG (NLO chromophore orientation) stability. Since the modulator fabrication and packaging processes typically require heating temperatures of 200-250oC for up to 10 minutes, yet the SHG thermal stability of most NLO polymers developed so far only reach about 150oC. In order to overcome this challenge, either modulator processing temperatures are reduced, or SHG thermal stability of EO polymers be increased. Polymer crosslinking technique is one of the most versatile and effective methods for fabricating and stabilizing polymer nano structures at high temperatures. Among various NLO polymer crosslinking schemes developed so far, fumaryl chloride (FC) and maleic anhydride (MA) derived crosslinked polyester system seems to be a versatile and convenient scheme. This scheme also looks attractive for low loss applications at 1550 nm. FC/MA crosslinking systems also offer visible light photolithographic fabrication advantage during waveguide fabrication.
The synthesis and characterization of maleate type crosslinkable nonlinear optical (NLO) polymers derived form maleic anhydride and fumaryl chloride is described. Preliminary results demonstrated this is a convenient, inexpensive, and versatile method of fabricating crosslinked NLO polymer thin films. These maleate type polyesters containing NLO chromophores such as Disperse Red 19 are capable of crosslinking to form a hardened lattice under thermal or high-energy radiation conditions. Crosslinking is a critical nano-scale technique for second order nonlinear optical as well as other potential photonic applications where molecular orientations need to be aligned and be stabilized against molecular thermal motions. Photolithographic techniques may be readily employed in this system to fabricate patterned polymer waveguide.
A novel phase-matching technique for coherent THz-wave generation was proposed. This approach uses cross- Reststrahlen band dispersion compensation phase-matching in a collinear optical mixing technique using isotropic, semiconductor nonlinear crystals. The pump and signal sources are in the near-IR transmission window of the nonlinear crystal and the generated idler wave is in the far-IR transmission window, on the other side of the crystal's Reststrahlen band. The choice of the nonlinear crystal for frequency conversion from the near-IR to the far-IR is highly dependent on the optical properties of the nonlinear crystal being used as the frequency converter element. We evaluate the use of the proposed phase-matching technique with a variety of III-V and II-VI compounds taking into account their optical dispersion and their phase- matching properties. Theoretical projections of the device performance such as perfect phase-matching conditions, coherence length and wavelength tuning range for different nonlinear crystals are compared.
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