M. Matin

Titanium and magnesium Co-alloyed hematite thin films for photoelectrochemical water splitting

Using a combination of density functional theory calculation and materials synthesis and characterization we examine the properties of charge-compensated Ti and Mg co-alloyed hematite thin films for the application of photoelectrochemical (PEC) water splitting. We find that the charge-compensated co-alloying results in the following effects: (1) It enhances the solubility of Mg and Ti, which leads to reduced electron effective mass and therefore increased electron mobility; (2) It tunes the carrier density and therefore allows the optimization of electrical conductivity; and (3) It reduces the density of charged defects and therefore reduces carrier recombination. As a result, the Ti and Mg co-alloyed hematite thin films exhibit improved water oxidation photocurrent magnitudes as compared to pure hematite thin films. Our results suggest that charge-compensated co-alloying is a plausible approach for engineering hematite for the application of PEC water splitting.

Hybrid plasmonic nanosandwich structures

Hybrid plasmonic nanoprisms in the form of gold (Au)-dielectric- silver (Ag) sandwich structures have been designed and simulated using Finite-difference time-domain (FDTD) simulation technique. Simulations results show two dipole resonant peaks for the hybrid sandwich structure. Also, a strong wavelength dependence of the plasmonic resonance peaks on the edge length and the thickness of gold and silver layers. The increase in edge length and thicknesses were found red shift to the plasmonic peak of the nanostructures. Furthermore, the resonant wavelengths and relative strength of the two dipole plasmonic peaks are demonstrated to be tunable.

Implementation of a photonic antenna in optical OFDM link

The integration of photonic antennas with radio over fiber (RoF) systems can serve high dense populated areas such as airports, shopping centers, dead-zone areas and tunnels. In this paper, we present an optical wireless communication downlink with a photonic antenna. Our proposed radio over fiber (RoF) system is to carry modulated orthogonal frequency division multiplexing (OFDM) signals with a 2.4 GHz radio frequency over a cost effective optical link. A comparison of using a photonic antenna as a passive and an active in the RoF system is presented. The active photonic antenna (APHA) is mounted at the end of the optical link to the photodiode as a package of a band-pass filter (BPF) and a radio frequency power amplifier. The photonic antenna scattering parameters are implemented into the optical system simulation tools with various fiber length and free space loss (FSL). The wireless link is implemented for a transmission distance up to 100 meters. The transmitted signal is fully carried over a radio frequency signal and then optically carried over a standard single mode fiber (SSMF). The measurements of the EIPR and SNR were done with 0 dBm RF input into the directly modulated laser (DML) for all the simulations. The results show that the analog optical wireless link is very suitable to carry the OFDM signals. Moreover, the active photonic antenna provides sufficient service for more than 30 meters compared to the passive antenna.

Photonics-based millimeter-wave generation and transmission for wireless/fiber links

Millimeter-waves have found wide application in various fields. In this paper, three ways of millimeter-wave generation are discussed. By modeling these three systems and applying different situations of transmission links and fixed bit rate of 2.5 Gb/s, different results were found. These results showed that each system has its own strengths and weaknesses based on the type of link and distance.

A model for simulation of electrically evoked auditory brainstem responses

An important aspect of research in the continued development of cochlear implants is the in vivo assessment of signal processing algorithms. One technique that has been used is evoked potentials, the recording of neural responses to auditory stimulation. Depending on the latency of the observed response, the evoked potential indicates neural activity at the various neurological structures of the auditory system. Electrically evoked ABRs are commonly measured in hearing-impaired patients who have cochlear implants, via electrical stimulation delivered by electrodes in the implanted array. This research explores the use of MATLAB for the purpose of developing a model for electrically evoked auditory brainstem responses (ABRs). The simulation model developed in this study takes as its input the stimulus current intensity level, and uses function vectors and equations derived from measured ABRs, to generate an approximation of the evoked surface potentials. A function vector is used to represent the combined firing of the neurons of the auditory nervous system that are needed to elicit a measurable response. Equations have been derived to represent the latency and stimulus amplitude scaling functions. The simulation also accounts for other neural activity that can be present in and contaminate an ABR recording, and reduces it through time-locked averaging of the simulated response. In the MATLAB simulation, the model performs well and delivers results that compare favorably with the results measured from the research subjects.

Synthesis and characterization of titanium doped hematite for photoelectrochemical water splitting

Hematite is a potential candidate for hydrogen production by photoelectrochemical (PEC) decomposition of water due to its good bad gap and excellent chemical stability. However, its poor conductivity limits its PEC performance. Titanium has been predicted to be a good choice of dopant for improving the conductivity. Most of the Ti-doped hematite films are produced by solution based method. However, such procedure may introduce impurities. RF sputtering is a clean vacuum deposition technique, which is perfect for the synthesis of metal oxide. In this paper, we report our synthesis of Tidoped hematite thin films by RF magnetron co-sputtering of iron oxide and titanium targets at various conditions. Our work shows that the structure and morphology of iron oxide can be modified by controlling the doping concentration of titanium. Moreover, we confirmed that the PEC performance of Ti-doped iron oxide film is significantly better than the undoped one.

Dispersion and nonlinear effects in OFDM-RoF system

The radio-over-fiber (RoF) network has been a proven technology to be the best candidate for the wireless-access technology, and the orthogonal frequency division multiplexing (OFDM) technique has been established as the core technology in the physical layer of next generation wireless communication system, as a result OFDM-RoF has drawn attentions worldwide and raised many new research topics recently. At the present time, the trend of information industry is towards mobile, wireless, digital and broadband. The next generation network (NGN) has motivated researchers to study higher-speed wider-band multimedia communication to transmit (voice, data, and all sorts of media such as video) at a higher speed. The NGN would offer services that would necessitate broadband networks with bandwidth higher than 2Mbit/s per radio channel. Many new services emerged, such as Internet Protocol TV (IPTV), High Definition TV (HDTV), mobile multimedia and video stream media. Both speed and capacity have been the key objectives in transmission. In the meantime, the demand for transmission bandwidth increased at a very quick pace. The coming of 4G and 5G era will provide faster data transmission and higher bit rate and bandwidth. Taking advantages of both optical communication and wireless communication, OFDM Radio over Fiber (OFDM-RoF) system is characterized by its high speed, large capacity and high spectral efficiency. However, up to the present there are some problems to be solved, such as dispersion and nonlinearity effects. In this paper we will study the dispersion and nonlinearity effects and their elimination in OFDM-radio-over-fiber system.

Application of Mott-Gurney law to model the current-voltage relationship of PPV/CN-PPV with a thin-metal anode buffer

In this paper, we derive the Mott-Gurney Law for space-charge-limited current and model the current density characteristics for a bilayer polymer light emitting diode (ITO/PPV/CN-PPV/Al). The organic material is assumed to be trap free and the influence of electric field on the carrier mobilities is neglected. Since the hole energy barrier between the ITO and PPV is less than 0.60 eV, the bottleneck for current flow is bulk-limited, resulting in space-charge-limited current. We discuss future plans for interposing a thin-layer of metal (Au, Pt, Pd, or AuPd) between the ITO and PPV. Experimental data will be compared to the J-V curve produced in this model, providing insight on how the metal buffer influences the range of potentials for which the current is space-charge-limited. Finally, the emissive spectrum is modeled with consideration of phonon-exciton coupling.

Simulation of push-pull inverter using wide bandgap devices

This paper discusses the use of wide bandgap devices (SiC-MOSFET) in the design of a push-pull inverter which provides inexpensive low power dc-ac inverters. The parameters used were 1200V SiC MOSFET(C2M0040120D) made by power company ROHM. This modeling was created using parameters that were provided from a device datasheet. The spice model is provided by this company to study the effect of adding this component on push-pull inverter ordinary circuit and compared results between SiC MOSFET and silicon MOSFET (IRFP260M). The results focused on Vout and Vmos stability as well as on output power and MOSFET power loss because it is a very crucial aspect on DC-AC inverter design. These results are done using the National Instrument simulation program (Multisim 14). It was found that power loss is better in the 12 and 15 vdc inverter. The Vout in the SIC MOSFET circuit shows more stability in the high current low resistance load in comparison to the Silicon MOSFET circuit and this will improve the overall performance of the circuit.

Plasmonic excitation for high-efficiency photovoltaics

Photovoltaic absorbers ought to be optically thick to allow almost total light absorption and photocarrier current collection. They are typically semiconductors with a thickness more than the optical absorption length. When the absorber layer thickness is reduced significantly, then the quality of the absorber material could considerably increase by allowing resourceful photocarrier collection across tiny distances in structures such as quantum wells or quantum dots. For absorber layers with fine surface passivation, the capability to reduce the solar cell base thickness by means of plasmonic design improves carrier collection. The objective of this paper is to show how plasmonics could be exploited to our benefit in high efficiency photovoltaics.