Abstract: The capability of exploiting the electronic charge and
spin properties simultaneously in a single material has made diluted
magnetic semiconductors (DMS) remarkable in the field of
spintronics. We report the designing of DMS based on zinc-blend
ZnO doped with Cr impurity. The full potential linearized augmented
plane wave plus local orbital FP-L(APW+lo) method in density
functional theory (DFT) has been adapted to carry out these
investigations. For treatment of exchange and correlation energy,
generalized gradient approximations have been used. Introducing Cr
atoms in the matrix of ZnO has induced strong magnetic moment
with ferromagnetic ordering at stable ground state. Cr:ZnO was found
to favor the short range magnetic interaction that
reflect tendency of Cr clustering. The electronic structure of ZnO is
strongly influenced in the presence of Cr impurity atoms where
impurity bands appear in the band gap.
Abstract: Using the first-principles full-potential linearized
augmented plane wave plus local orbital (FP-LAPW+lo) method
based on density functional theory (DFT), we have investigated the
electronic structure and magnetism of full Heusler alloys Co2ZrGe
and Co2NbB. These compounds are predicted to be half-metallic
ferromagnets (HMFs) with a total magnetic moment of 2.000 B per
formula unit, well consistent with the Slater-Pauling rule.
Calculations show that both the alloys have an indirect band gaps, in
the minority-spin channel of density of states (DOS), with values of
0.58 eV and 0.47 eV for Co2ZrGe and Co2NbB, respectively.
Analysis of the DOS and magnetic moments indicates that their
magnetism is mainly related to the d-d hybridization between the Co
and Zr (or Nb) atoms. The half-metallicity is found to be relatively
robust against volume changes. In addition, an atom inside molecule
AIM formalism and an electron localization function ELF were also
adopted to study the bonding properties of these compounds, building
a bridge between their electronic and bonding behavior.
As they have a good crystallographic compatibility with the lattice of
semiconductors used industrially and negative calculated cohesive
energies with considerable absolute values these two alloys could be
promising magnetic materials in the spintronic field.
Abstract: The Al-MoO3-P-CdTe-Al MOS sandwich structures
were fabricated by vacuum deposition method on cleaned glass
substrates. Capacitance versus voltage measurements were performed
at different frequencies and sweep rates of applied voltages for oxide
and semiconductor films of different thicknesses. In the negative
voltage region of the C-V curve a high differential capacitance of the
semiconductor was observed and at high frequencies (
Abstract: Semiconductor crystals smaller than about 10 nm,
known as quantum dots, have properties that differ from large
samples, including a band gap that becomes larger for smaller
particles. These properties create several applications for quantum
dots. In this paper new shapes of quantum dot arrays are used to
enhance the photo physical properties of gold nano-particles. This
paper presents a study of the effect of nano-particles shape, array, and
size on their absorption characteristics.
Abstract: The contact resistance between source/drain electrodes
and semiconductor layer is an important parameter affecting electron
transporting performance in the thin film transistor (TFT). In this
work, we introduced a transparent and the solution prossable
single-walled carbon nanotube (SWCNT)/Al-doped ZnO nano particle
(AZO NP) bilayer electrodes showing low contact resistance with
indium-oxide (In2O3) sol gel thin film. By inserting low work function
AZO NPs into the interface between the SWCNTs and the In2O3 which
has a high energy barrier, we could obtain an electrical Ohmic contact
between them. Finally, with the SWCNT-AZO NP bilayer electrodes,
we successfully fabricated a TFT showing a field effect mobility of
5.38 cm2/V·s at 250°C.
Abstract: Adsorption of a boron nitride nanotube (BNNT) was
examined toward ethylacetylene (C4H6) molecule by using density
functional theory (DFT) calculations at the B3LYP/6-31G (d) level,
and it was found that the adsorption energy (Ead) of ethylacetylene
the pristine nanotubes is about -1.60kcal/mol. But when nanotube has
been doped with Si and Al atoms, the adsorption energy of
ethylacetylene molecule was increased. Calculation showed that
when the nanotube is doping by Al, the adsorption energy is about -
24.19kcal/mol and also the amount of HOMO/LUMO energy gap
(Eg) will reduce significantly. Boron nitride nanotube is a suitable
adsorbent for ethylacetylene and can be used in separation processes
ethylacetylene. It is seem that nanotube (BNNT) is a suitable
semiconductor after doping, and the doped BNNT in the presence of
ethylacetylene an electrical signal is generating directly and therefore
can potentially be used for ethylacetylene sensors.
Abstract: A Silver (Ag) thin film is introduced as a template and
doping source for vertically aligned p–type ZnO nanorods. ZnO
nanorods were grown using an ammonium hydroxide based
hydrothermal process. During the hydrothermal process, the Ag thin
film was dissolved to generate Ag ions in the solution. The Ag ions can
contribute to doping in the wurzite structure of ZnO and the (111)
grain of Ag thin film can be the epitaxial temporal template for the
(0001) plane of ZnO. Hence, Ag–doped p–type ZnO nanorods were
successfully grown on the substrate, which can be an electrode or
semiconductor for the device application. To demonstrate the
potentials of this idea, p–n diode was fabricated and its electrical
characteristics were demonstrated.
Abstract: This paper presents nonlinear pulse propagation characteristics for different input optical pulse shapes with various input pulse energy levels in semiconductor optical amplifiers. For simulation of nonlinear pulse propagation, finite-difference beam propagation method is used to solve the nonlinear Schrödinger equation. In this equation, gain spectrum dynamics, gain saturation are taken into account which depends on carrier depletion, carrier heating, spectral-hole burning, group velocity dispersion, self-phase modulation and two photon absorption. From this analysis, we obtained the output waveforms and spectra for different input pulse shapes as well as for different input energies. It shows clearly that the peak position of the output waveforms are shifted toward the leading edge which due to the gain saturation of the SOA for higher input pulse energies. We also analyzed and compared the normalized difference of full-width at half maximum for different input pulse shapes in the SOA.
Abstract: Rhodamine B (RB) is a toxic dye used extensively in
textile industry, which must be remediated before its drainage to
environment. In the present study, supported gold nanoparticles on
commercially available titania and zincite were successfully prepared
and then their activity on the photodegradation of RB under UV A
light irradiation were evaluated. The synthesized photocatalysts were
characterized by ICP, BET, XRD, and TEM. Kinetic results showed
that Au/TiO2 was an inferior photocatalyst to Au/ZnO. This
observation could be attributed to the strong reflection of UV
irradiation by gold nanoparticles over TiO2 support.
Abstract: We report on the use of strong external optical
feedback to enhance the modulation response of semiconductor lasers
over a frequency passband around modulation frequencies higher
than 60 GHz. We show that this modulation enhancement is a type of
photon-photon resonance (PPR) of oscillating modes in the external
cavity formed between the laser and the external reflector. The study
is based on a time-delay rate equation model that takes into account
both the strong feedback and multiple reflections in the external
cavity. We examine the harmonic and intermodulation distortions
associated with single and two-tone modulations in the mm-wave
band of the resonant modulation. We show that compared with
solitary lasers modulated around the carrier-photon resonance
frequency, the present mm-wave modulated signal has lower
distortions.
Abstract: We model and simulate the combined effect of fiber
dispersion and frequency chirp of a directly modulated high-speed
laser diode on the figures of merit of a non-amplified 40-Gbps optical
fiber link. We consider both the return to zero (RZ) and non-return to
zero (NRZ) patterns of the pseudorandom modulation bits. The
performance of the fiber communication system is assessed by the
fiber-length limitation due to the fiber dispersion. We study the
influence of replacing standard single-mode fibers by non-zero
dispersion-shifted fibers on the maximum fiber length and evaluate
the associated power penalty. We introduce new dispersion
tolerances for 1-dB power penalty of the RZ and NRZ 40-Gbps
optical fiber links.
Abstract: This paper contains 2 main parts. In the first part of paper we simulated and studied three types of electrode patterns used in various industries for suspension and handling of the semiconductor and glass and we selected the best pattern by evaluating the electrostatic force, which was comb pattern electrode.
In the second part we investigated the parameters affecting the amount of electrostatic force such as the gap between surface and electrode (g), the electrode width (w), the gap between electrodes (t), the surface permittivity and electrode length and methods of improvement of adhesion force by changing these values.
Abstract: We introduced an all-optical multicasting
characteristics with wavelength conversion based on a novel
all-optical triode using negative feedback semiconductor optical
amplifier. This study was demonstrated with a transfer speed of 10
Gb/s to a non-return zero 231-1 pseudorandom bit sequence system.
This multi-wavelength converter device can simultaneously provide
three channels of output signal with the support of non-inverted and
inverted conversion. We studied that an all-optical multicasting and
wavelength conversion accomplishing cross gain modulation is
effective in a semiconductor optical amplifier which is effective to
provide an inverted conversion thus negative feedback. The
relationship of received power of back to back signal and output
signals with wavelength 1535 nm, 1540 nm, 1545 nm, 1550 nm, and
1555 nm with bit error rate was investigated. It was reported that the
output signal wavelengths were successfully converted and modulated
with a power penalty of less than 8.7 dB, which the highest is 8.6 dB
while the lowest is 4.4 dB. It was proved that all-optical multicasting
and wavelength conversion using an optical triode with a negative
feedback by three channels at the same time at a speed of 10 Gb/s is a
promising device for the new wavelength conversion technology.
Abstract: The detection of environmental gases, 12CO2, 13CO2,
and CH4, using near-infrared semiconductor lasers with a short
laser path length is studied by means of wavelength-modulation
spectroscopy. The developed system is compact and has high
sensitivity enough to detect the absorption peaks of isotopic 13CO2
of a 3-% CO2 gas at 2 μm with a path length of 2.4 m, where
its peak size is two orders of magnitude smaller than that of the
ordinary 12CO2 peaks. In addition, the detection of 12CO2 peaks of
a 385-ppm (0.0385-%) CO2 gas in the air is made at 2 μm with a
path length of 1.4 m. Furthermore, in pursuing the detection of an
ancient environmental CH4 gas confined to a bubble in ice at the
polar regions, measurements of the absorption spectrum for a trace
gas of CH4 in a small area are attempted. For a 100-% CH4 gas
trapped in a ∼ 1 mm3 glass container, the absorption peaks of CH4
are obtained at 1.65 μm with a path length of 3 mm, and also the
gas pressure is extrapolated from the measured data.
Abstract: The semiconductor industry is placing an increased
emphasis on emerging materials and devices that may provide
improved performance, or provide novel functionality for devices.
Recently, graphene, as a true two-dimensional carbon material, has
shown fascinating applications in electronics. In this paper detailed
discussions are introduced for possible applications of grapheme
Transistor in RF and digital devices.
Abstract: This research presents the design, fabrication and application of a flavor sensor for an integrated electronic tongue and electronic nose that can allow rapid characterization of multi-component mixtures in a solution. The odor gas and liquid are separated using hydrophobic porous membrane in micro fluidic channel. The sensor uses an array composed of microbeads in micromachined cavities localized on silicon wafer. Sensing occurs via colorimetric and fluorescence changes to receptors and indicator molecules that are attached to termination sites on the polymeric microbeads. As a result, the sensor array system enables simultaneous and near-real-time analyses using small samples and reagent volumes with the capacity to incorporate significant redundancies. One of the key parts of the system is a passive pump driven only by capillary force. The hydrophilic surface of the fluidic structure draws the sample into the sensor array without any moving mechanical parts. Since there is no moving mechanical component in the structure, the size of the fluidic structure can be compact and the fabrication becomes simple when compared to the device including active microfluidic components. These factors should make the proposed system inexpensive to mass-produce, portable and compatible with biomedical applications.
Abstract: The application of today's semiconductor transistors in high power UHF DVB-T linear amplifiers has evolved significantly by utilizing LDMOS technology. This fact provides engineers with the option to design a single transistor signal amplifier which enables output power and linearity that was unobtainable previously using bipolar junction transistors or later type first generation MOSFETS. The quiescent current stability in terms of thermal variations of the LDMOS guarantees a robust operation in any topology of DVB-T signal amplifiers. Otherwise, progressively uncontrolled heat dissipation enhancement on the LDMOS case can degrade the amplifier’s crucial parameters in regards to the gain, linearity and RF stability, resulting in dysfunctional operation or a total destruction of the unit. This paper presents one more sophisticated approach from the traditional biasing circuits used so far in LDMOS DVB-T amplifiers. It utilizes a microprocessor control technology, providing stability in topologies where IDQ must be perfectly accurate.
Abstract: The research work covered in this study includes the morphological structure and optical properties of TiO2-coated silk fibroin (SF) filters at 2.5% wt. TiO2/vol. PVA solution. SEM micrographs revealed the fibrous morphology of the TiO2-coated SF filters. An average diameter of the SF fiber was estimated to be approximately 10µm. Also, it was confirmed that TiO2 can be adhered more on SF filter surface at higher TiO2 dosages. The activity of semiconductor materials was studied by UV-VIS spectrophotometer method. The spectral data recorded shows the strong cut off at 390 nm. The calculated band-gap energy was about 3.19 eV. The photocatalytic activity of the filter was tested for gaseous formaldehyde removal in a modeling room with the total volume of 2.66 m3. The highest removal efficiency (54.72 ± 1.75%) was obtained at the initial formaldehyde concentration of about 5.00 ± 0.50ppm.
Abstract: This paper presents advances in pulse width modulation techniques which refers to a method of carrying information on train of pulses and the information be encoded in the width of pulses. Pulse Width Modulation is used to control the inverter output voltage. This is done by exercising the control within the inverter itself by adjusting the ON and OFF periods of inverter. By fixing the DC input voltage we get AC output voltage. In variable speed AC motors the AC output voltage from a constant DC voltage is obtained by using inverter. Recent developments in power electronics and semiconductor technology have lead improvements in power electronic systems. Hence, different circuit configurations namely multilevel inverters have became popular and considerable interest by researcher are given on them. A fast space-vector pulse width modulation (SVPWM) method for five-level inverter is also discussed. In this method, the space vector diagram of the five-level inverter is decomposed into six space vector diagrams of three-level inverters. In turn, each of these six space vector diagrams of three-level inverter is decomposed into six space vector diagrams of two-level inverters. After decomposition, all the remaining necessary procedures for the three-level SVPWM are done like conventional two-level inverter. The proposed method reduces the algorithm complexity and the execution time. It can be applied to the multilevel inverters above the five-level also. The experimental setup for three-level diode-clamped inverter is developed using TMS320LF2407 DSP controller and the experimental results are analyzed.
Abstract: Computer software to calculate electron mobility with respect to different scattering mechanism has been developed. This software is adopted completely Graphical User Interface (GUI) technique and its interface has been designed by Microsoft Visual basic 6.0. As a case study the electron mobility of n-GaN was performed using this software. The behavior of the mobility for n-GaN due to elastic scattering processes and its relation to temperature and doping concentration were discussed. The results agree with other available theoretical and experimental data.