Khaled Kirah

Integrated optical sensor using hybrid plasmonics for lab on chip applications

We propose a novel, compact plasmonic sensing structure based on a metal–insulator–metal waveguide hybridly-coupled to a rectangular side cavity. The structure has been numerically investigated using the finite-difference time-domain method. Transmission spectra obtained from numerical simulations are used to analyze the sensing characteristics of the structure. The effects of the geometrical parameters on transmission and sensing of the structure are studied. With optimum design, sensitivity can reach as high as 1500 nm per refractive-index unit around the resonance wavelength of 1550 nm with a cavity area of 1 μm2. The proposed structure can potentially be applied in on-chip pressure and gas micro-sensors.

High Sensitivity Hybrid Plasmonic Rectangular Resonator for Gas Sensing Applications

A compact plasmonic rectangular sensor of effective fabrication cost is proposed. A hybrid coupling mechanism is utilized. The structure is optimized using numerical simulations. A high sensitivity of 1385 nm/RIU is reached at wavelength of 1.55 μm.

Nanowire photovoltaic efficiency enhancement using plasmonic coupled nano-fractal antennas.

We suggest the use of nano-fractal antennas for plasmonic coupling to enhance nanowire (NW) photovoltaic power conversion efficiency. Silicon radial pn junction NWs positioned inside Apollonian and Sierpinski nano-fractal antennas are simulated with different topologies and NW lengths. An enhancement in power conversion efficiency ranging from 12% to up to 24% over the same NW without antenna case is achieved.

Simulation of an asymmetric contacted carbon nanotube for solar-energy harvesting

Nanostructured materials offer great prospects in helping solar-energy harvesting devices to achieve their envisioned performances. Carbon nanotubes (CNT)-based devices were among the first to be proposed for this task. These devices are based on CNT field-effect transistors and CNT diodes. In this paper, the photovoltaic behavior of a diode structure formed from an asymmetrically contacted intrinsic CNT with scandium and palladium electrodes as source and drain, respectively, is investigated. A semi-classical simulator, which combines a quantum solution, for transmission through the electrodes/CNT interfaces with the semi-classical drift-diffusion equation and continuity equation for charge transport in the CNT has been built. The obtained simulation outcomes are compared with the available published experimental results.

Simulation of carbon nanotube photovoltaic arrays

Exploring renewable, sustainable and green energy resources is a critical challenge for scientists and engineers. Large-scale ambient energy, such as the solar energy is available but current technologies are not yet ready to capture it with great efficiency. The sun radiates visible light and also infrared energy, some of which is soaked up by the earth and later released as radiation for hours after sunset. In this study, the use of arrays of carbon nanotubes (CNT) Field Effect Transistors (FET) as photovoltaic (PV) elements is investigated. The interaction between electromagnetic waves and the CNT array is simulated using COMSOL Multiphysics in order to calculate the amount of absorbed power. The effects of the distribution of PV elements on the array performance are studied in order to maximize power absorption for the same number of elements.

Enhancing the absorption capabilities of thin-film solar cells using sandwiched light trapping structures

A novel structure for thin-film solar cells is simulated with the purpose of maximizing the absorption of light in the active layer and of reducing the parasitic absorption in other layers. In the proposed structure, the active layer is formed from an amorphous silicon thin film sandwiched between silicon nanowires from above and photonic crystal structures from below. The upper electrical contact consists of an indium tin oxide layer, which serves also as an antireflection coating. A metal backreflector works additionally as the other contact. The simulation was done using a new reliable, efficient and generic optoelectronic approach. The suggested multiscale simulation model integrates the finite-difference time-domain algorithm used in solving Maxwells equation in three dimensions with a commercial simulation platform based on the finite element method for carrier transport modeling. The absorption profile, the external quantum efficient, and the power conversion efficiency of the suggested solar cell are calculated. A noticeable enhancement is found in all the characteristics of the novel structure with an estimated 32% increase in the total conversion efficiency over a cell without any light trapping mechanisms.

Fractal topologies for efficient solar energy harvesting systems

When constructing efficient solar energy harvesting systems, it is important to connect the photovoltaic (PV) elements in the configuration which maximizes the absorbed solar energy. This undoubtedly gives the best possible efficiency for the system. The usage of fractal topologies to arrange the PV elements spatially is suggested. Our goal is to find the best possible configuration for the same number of elements. Carbon nanotubes (CNTs) diodes are chosen to be the PV elements. The interaction between electromagnetic waves and the CNT array is simulated using a Multi-physics SW package in order to calculate the amount of absorbed energy.

Theoretical and experimental analysis of the fabrication tolerance on deeply etched silicon/air Bragg micromirrors

Modelling and analysis of the technological tolerance and artifacts of deeply-etched Bragg micromirrors and their impact on the performance is presented. Si/Air Bragg micromirrors with 150 µm etching depth and Si/Air layer thickness of about 3.8 µm / 3.6 µm are fabricated on Si wafer using the Deep Reactive Ion Etching technology (DRIE); designed to operate at a central wavelength of 1600 nm. For such high aspect ratio DRIE, the side-effects of the technology such as over-etching and surface roughness can be significant. Optical measurements for the multi-band spectral response are used to characterize the performance of the fabricated micromirrors and estimate the technological parameters. It was found that the central wavelength shifts monotonically with the over-etching at a rate of 0.45 nm / nm. The dependence of the 3-dB bandwidth and mirror reflectivity is non-monotonic with the over-etching. The surface roughness leads to shift in the central wavelength in addition to degradation in the bandwidth and mirror reflectivity. The presented results are important to understand the technological impact on optical filters and sensors based on the Bragg micromirrors.

Inkjet Printing of a 20 GHz Coplanar Waveguide Monopole Antenna Using Copper Oxide Nanoparticles on Flexible Substrates : Effect of Drop Spacing on Antenna Performance

Coplanar monopole antennas printed using copper oxide nanoparticles on flexible substrates are characterized in order to study the effect of the ink drop spacing on the antenna parameters. Polyethylene Terephthalate and Epson paper were the chosen flexible substrates, and the antennas were designed to operate at 20 GHz. A maximum conductivity of 2.8 × 107 Ω−1m−1 was obtained for the films printed on Polyethylene Terephthalate using a drop spacing of 20μm. The corresponding antenna achieved a gain and an efficiency of 1.82 dB and 97.6%, respectively. Experiments showed that smaller drop spacings lead to bulging of the printed lines while the antenna performance worsens for longer ones. At the same drop spacing, antennas printed on Epson paper substrate showed a −10 dB return loss bandwidth which extended from 17.9 GHz to 23.3 GHz, leading to a fractional bandwidth of 26.0%.

Optical investigation of porous TiO2 in mesostructured solar cells

Porous TiO2 films are a crucial part of mesostructured solar cells (MSCs), both dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). However, the literature does not provide a clear description of the optical properties especially of the refractive index and scattering for those films relevant to MSCs. In DSSCs, two different porous TiO2 layers are included, the mesoporous active layer and the blocking layer. While the first is essential for the charge separation, electron collection and ion conduction, the second is intended for suppressing the loss of generated electrons to the electrolyte. Both layers consist of the same chemical compound, TiO2, but they have different porosities. For PSCs, the perovskite is deposited on a mesoporous TiO2 structure for enhancing the I–V characteristics This paper investigates TiO2 films really used in fabricated MSCs. We utilize a technique allowing the determination of the effective refractive index and the film porosity for two different film kinds fabricated using sol-gel methods, discussed in our previous work, to determine the thickness of TiO2 films typically used in fabricating MSCs.