In this work, we have studied photo-electronic current transport in a back-gated graphene field-effect transistor. Under the light illumination, band bending at the metal/graphene interface develops a built-in potential which generates photonic current at varying back-gate biases. A typical MOSFET type back-gated transistor structure uses a monolayer graphene as the channel layer formed over the silicon dioxide/silicon substrate. It is shown that the photo-electronic current consists of current contributions from photovoltaic, photo-thermoelectric and photo-bolometric effects. A maximum external responsivity close to 0.0009A/W is achieved at 30μW laser power source and 633nm wavelength.
Aluminum (Al) doped ZnO with very high Al concentration acts as metal regarding its electrical conductivity. ZnO offers many advantages over the commonly-known metals being used today as electrode materials for nuclear detector fabrication. Often, the common metals show poor adhesion to CdZnTe or CdTe surfaces and have a tendency to peel off. In addition, there is a large mismatch of the coefficients of thermal expansion (CTE) between the metals and underlying CdZnTe, which is one of the reasons for mechanical degradation of the contact. In contrast ZnO has a close match of the CTE with CdZnTe and possesses 8-20 times higher hardness than the commonly-used metals. In this presentation, we will explore and discuss the properties of CdZnTe detectors with ZnO:Al contacts.
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.
Magnetic nanoparticles have been used in a wide array of industrial and biomedical applications due to their
unique properties at the nanoscale level. They are extensively used in magnetic resonance imaging (MRI), magnetic
hyperthermia treatment, drug delivery, and in assays for biological separations. Furthermore, superparamagnetic
nanoparticles are of large interest for in vivo applications. However, these unmodified nanoparticles aggregate and
consequently lose their superparamagnetic behaviors, due to high surface to volume ratio and strong dipole to dipole
interaction. For these reasons, surface coating is necessary for the enhancement and effectiveness of magnetic
nanoparticles to be used in various applications. In addition to providing increased stability to the nanoparticles in
different solvents or media, stabilizers such as surfactants, organic/inorganic molecules, polymer and co-polymers
are employed as surface coatings, which yield magnetically responsive systems. In this work we present the
synthesis and magnetic characterization of Fe3O4 nanoparticles coated with 3-aminopropyltriethoxy silane (APS)
and citric acid. The particles magnetic hysteresis was measured by a superconducting quantum interference device
(SQUID) magnetometer with an in-plane magnetic field. The uncoated and coated magnetic nanoparticles were
characterized by using fourier transform infrared (FTIR), UV-vis, X-ray diffraction, transmission electron
microscopy, and thermo-gravimetric analysis.
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.
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.
This paper presents the design of glucose sensors that will be integrated with advanced nano-materials, bio-coatings and
electronics to create novel devices that are highly sensitive, inexpensive, accurate, and reliable. In the work presented, a
glucose biosensor and its fabrication process flow have been designed. The device is based on electrochemical sensing
using a working electrode with bio-functionalized zinc oxide (ZnO) nano-rods. Among all metal oxide nanostructures,
ZnO nano-materials play a significant role as a sensing element in biosensors due to their properties such as high
isoelectric point (IEP), fast electron transfer, non-toxicity, biocompatibility, and chemical stability which are very crucial
parameters to achieve high sensitivity. Amperometric enzyme electrodes based on glucose oxidase (GOx) are used due
to their stability and high selectivity to glucose. The device also consists of silicon dioxide and titanium layers as well as
platinum working and counter electrodes and a silver/silver chloride reference electrode. Currently, the biosensors are
being fabricated using the process flow developed. Once completed, the sensors will be bio-functionalized and tested to
characterize their performance, including their sensitivity and stability.
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.
We report on the growth and characterization of ZnO nanorods using chemical vapor deposition
(CVP) with and without graphite, wet chemical reaction and gold attached ZnO nanorods called
nanocomposites. Various novel arrangements of growth of uniform one dimensional ZnO nanostructures
were observed. The ZnO nanostructures and the composite materials were examined by X-ray diffraction
(XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), The results of
characterization demonstrated that ZnO nanostructures are one dimensional, the nanocomposites consist of
both gold nanoparticles and ZnO nanorods. The result also shows that the gold nanoparticles were tightly
attached on the nanorod surface. Our results suggest that ZnO nanostructures and nanocomposites are
useful for solar cell, sensor applications. The detail of the results will be presented.
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 report here the synthesis of ZnO films by the pulsed-laser deposition technique using various novel conditions. The
dopants are As, Ga, Al and N. The films show excellent crystalline quality with atomically smooth surface morphology.
The electrical resistivity was found to be close to 2 x~10-4 ohm-cm and transmittance >85% with both Ga and Al doping.
Doping with As shows several distinct transitions in their electrical resistivity and strong aging effects. On the other
hand, doping with Mn in ZnO reduces the grain size. On the other hand, doping with trivalent Er ions in ZnO films
causes two effects: for high doping (>8 wt%), a substantial enhancement of diagonal piezo-optic effect (up to 3.7*10-13
m2/N at &lgr;=633 nm) was observed due to creation of additional dipole moments at the interface of the film and the
substrate, and higher electrical conductivity with enhanced 1.54 &mgr;m emission was demonstrated at room temperature for
low concentration (<2 wt%) of Er. Furthermore, no quenching effects in emission characteristics at 1.54 &mgr;m were
observed up to 2 wt % of Er-doping in ZnO at room-temperature.
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