Omar Manasreh

An Electrochemical Glucose Sensor Based on Zinc Oxide Nanorods

A glucose electrochemical sensor based on zinc oxide (ZnO) nanorods was investigated. The hydrothermal sol–gel growth method was utilized to grow ZnO nanorods on indium tin oxide-coated glass substrates. The total active area of the working electrode was 0.3 × 0.3 cm2 where titanium metal was deposited to enhance the contact. Well aligned hexagonal structured ZnO nanorods with a diameter from 68 to 116 nm were obtained. The excitonic peak obtained from the absorbance spectroscopy was observed at ~370 nm. The dominant peak of Raman spectroscopy measurement was at 440 cm−1, matching with the lattice vibration of ZnO. The uniform distribution of the GOx and Nafion membrane that has been done using spin coating technique at 4000 rotations per minute helps in enhancing the ion exchange and increasing the sensitivity of the fabricated electrochemical sensor. The amperometric response of the fabricated electrochemical sensor was 3 s. The obtained sensitivity of the fabricated ZnO electrochemical sensor was 10.911 mA/mM·cm2 and the lower limit of detection was 0.22 µM.

InGaAs Quantum Well Grown on High-Index Surfaces for Superluminescent Diode Applications

The morphological and optical properties of In0.2Ga0.8As/GaAs quantum wells grown on various substrates are investigated for possible application to superluminescent diodes. The In0.2Ga0.8As/GaAs quantum wells are grown by molecular beam epitaxy on GaAs (100), (210), (311), and (731) substrates. A broad photoluminescence emission peak (~950 nm) with a full width at half maximum (FWHM) of 48 nm is obtained from the sample grown on (210) substrate at room temperature, which is over four times wider than the quantum well simultaneously grown on (100) substrate. On the other hand, a very narrow photoluminescence spectrum is observed from the sample grown on (311) with FWHM = 7.8 nm. The results presented in this article demonstrate the potential of high-index GaAs substrates for superluminescent diode applications.

Modeling and optimization of Au-GaAs plasmonic nanoslit array structures for enhanced near-infrared photodetector applications

Abstract. This theoretical work explores how various geometries of Au plasmonic nanoslit array structures improve the total optical enhancement in GaAs photodetectors. Computational models studied these characteristics. Varying the electrode spacing, width, and thickness drastically affected the enhancement in the GaAs. Peaks in enhancement decayed as Au widths and thicknesses increased. These peaks are resonant with the incident near-infrared wavelength. The enhancement values were found to increase with decreasing electrode spacing. Additionally, a calculation was conducted for a model containing Ti between the Au and the GaAs to simulate the necessary adhesion layer. It was found that optical enhancement in the GaAs decreases for increasing Ti layer thickness. Optimal dimensions for the Au electrode include a width of 240 nm, thickness of 60 nm, electrode spacing of 5 nm, and a minimum Ti thickness. Optimal design has been shown to improve enhancement to values that are up to 25 times larger than for nonoptimized geometries and up to 300 times over structures with large electrode spacing. It was also found that the width of the metal in the array plays a more significant role in affecting the field enhancement than does the period of the array.

Hot Electrons in Microscale Thin-Film Schottky Barriers for Enhancing Near-Infrared Detection

Metallic microstructures composed from Au thin films were designed and fabricated to enhance the near-infrared detection of photodetectors based on GaAs. The devices showed significant increase in the photocurrent and the spectral response due to the generation of hot electrons in the Au thin films and their injection into the semiconductor. Enhancement in the order of 120% was achieved in the photocurrent after applying an array of Au thin films with a thickness of 10 nm. Furthermore, a photocurrent-sweep using red laser showed an increase in the photocurrent of the device, as the laser was swept over the Au thin film. The effect of adding Ti adhesive layer on damping the photocurrent enhancement was further studied by varying the thickness of Ti between 0 and 4 nm.

Computational electromagnetic analysis of plasmonic effects in interdigital photodetectors

Plasmonic nanostructures have been shown to act as optical antennas that enhance optical devices. This study focuses on computational electromagnetic (CEM) analysis of GaAs photodetectors with gold interdigital electrodes. Experiments have shown that the photoresponse of the devices depend greatly on the electrode spacing and the polarization of the incident light. Smaller electrode spacing and transverse polarization give rise to a larger photoresponse. This computational study will simulate the optical properties of these devices to determine what plasmonic properties and optical enhancement these devices may have. The models will be solving Maxwell’s equations with a finite element method (FEM) algorithm provided by the software COMSOL Multiphysics 4.4. The preliminary results gathered from the simulations follow the same trends that were seen in the experimental data collected, that the spectral response increases when the electrode spacing decreases. Also the simulations show that incident light with the electric field polarized transversely across the electrodes produced a larger photocurrent as compared with longitudinal polarization. This dependency is similar to other plasmonic devices. The simulation results compare well with the experimental data. This work also will model enhancement effects in nanostructure devices with dimensions that are smaller than the current samples to lead the way for future nanoscale devices. By seeing the potential effects that the decreased spacing could have, it opens the door to a new set of devices on a smaller scale, potentially ones with a higher level of enhancement for these devices. In addition, the precise modeling and understanding of the effects of the parameters provides avenues to optimize the enhancement of these structures making more efficient photodetectors. Similar structures could also potentially be used for enhanced photovoltaics as well.

Performance enhancement of InAs quantum dots solar cells by using nanostructured antireflection coating with hydrophobic properties

Abstract. Enhancement of the performance of an InAs quantum dots (QDs) solar cell was investigated by using a nanostructured antireflection coating with hydrophobic properties. The surface modification was performed by growing ZnO nanoneedles on top of an InAs QDs solar cell’s surface, then the nanoneedles’ hydrophobicity treatment was achieved by using stearic acid. The QDs solar cell’s performance remarkably improved by 50% as noticed in the power conversion efficiency, external quantum efficiency, and spectral response after the surface modification. Additionally, the contact angle of the hydrophobic surface was found to be 153 deg.

Structural characteristics of Au-GaAs nanostructures for increased plasmonic optical enhancement

This research has been performed to improve upon optical qualities exhibited by metallic-semiconductor nanostructures in terms of their ability to excite electrons and generate current through the fabricated device. Plasmonic interactions become very influential at this scale, and can play an important role in the generation of photocurrent throughout the semiconductor. When the device is fabricated to promote the coupling of these radiated electromagnetic fields, a very substantial optical enhancement becomes evident. A GaAs substrate with an array of Au nanowires attached to the surface is studied to determine structural qualities that promote this enhancement. Using computational electromagnetic modeling and analysis, the effect of the Ti adhesion layer and various structural qualities are analyzed to promote photocurrent generation. Emphasis is placed on the amount of enhancement occurring in the semiconductor layer of the model. The photocurrent is then calculated mathematically and generalized for optimization of the device.

Intersubband Transitions in Quantum Wells Infrared Photodetector

Over the past two decades, infrared detection has become an important application. There have been many theoretical and experimental studies focused on the intersubband transitions in multiple quantum well systems. We report on the two-color multiple quantum well infrared photodetector. The reported detector consists of two stacks of InGaAs wells and AlGaAs barriers grown on semi-insulating GaAs substrate for mid-wavelength infrared detection. The photoresponse was measured and analyzed on this device, which confirm presence of the intersubband transitions at 6.3 mum and 5.5 mum. In addition, the transfer matrix method is used to estimate the peak position energies of the intersubband transitions in the two stacks. Furthermore, the temperature dependence of photoresponse was measured under a bias voltage of -2.5V. The photoresponse was remained observable at temperature as high as 110K.

Effect of ligand exchange on the photoresponsivity of near-infrared sensors based on PbSe nanocrystals

The effect of ligand exchange was investigated on the optical and electrical characteristics of near-infrared sensors fabricated from PbSe nanocrystals. Different ligands such as oleic acid, ethanedithiol, and mercaptoacetic acid were used to cap the nanocrystals. The bandgap of the PbSe nanocrystals was measured using the optical absorption and tuned into the near-infrared region by controlling the growth time. The electrical properties of the sensors fabricated from the PbSe nanocrystals treated with different ligands were extracted by measuring the current-voltage characteristics. Furthermore, the optical properties of the different sensors were found by measuring the spectral response of each sensor.

Fabrication of nanoelectrode ensembles using silicon nanowires in an electrochemical glucose sensor

Gold (Au) nanoelectrode ensembles (NEEs) were investigated after the synthesis of silicon nanowires using the metal assisted chemical etching technique. Structural and non-destructive optical characterization of silicon nanowires are carried out to determine its morphology and crystallinity. The cyclic voltammetry technique is used to determine the oxidation-reduction potentials of the sensor at different voltage scan rates of 100, 200, and 300 mV/s. Amperometric measurement at a fixed oxidation potential of 0.6 V is performed to measure the sensitivity, response time, and detection limit of the sensor. The presence of Au NEEs improve the signal to noise ratio of the sensor. Therefore, the sensor exhibits a high sensitivity of 0.4 mA/mM cm2 with a response time of 1 s, and a limit of detection 0.077 mM.