PS-based Devices Research Articles

A Joint Optimization Framework for IRS-Assisted Energy Self-Sustainable IoT Networks

Energy self-sustainability is critically important for future Internet of Things (IoT) networks to support an ever-growing massive number of wireless devices with low maintenance cost and high spectrum/energy efficiency. Power-splitting (PS)-based simultaneous wireless information and power transfer (PS-SWIPT) is a promising solution to realize it. However, the performance of PS-SWIPT is severely influenced by the channel attenuation caused by the detrimental radio propagation environment. Intelligent reflecting surface (IRS) is an emerging technology that can reconfigure the incident signal with considerable array gain so as to improve the PS-SWIPT performance. Thus, in this article, we investigate the weighted sumrate (WSR) maximization problem of the IRS-assisted multi-input–multioutput (MIMO) PS-SWIPT IoT network with multiple low-power IoT PS-based devices (PSDs). The formulated problem is nonconvex and arduous to tackle due to the presence of the intricately coupled variables and the mutually exclusive constraints. To the best of our knowledge, the problem is not addressed yet and cannot be solved by employing the existing methods directly. To cope with the problem, we develop a joint optimization framework that decomposes the original problem into several subproblems that can be solved alternately. Simulation results confirm the effectiveness of IRS to improve the WSR of the PS-SWIPT energy self-sustainable IoT networks and demonstrate that the proposed algorithm outperforms benchmark methods considerably.

Thermal carbonization of nanoporous silicon: Formation of carbon nanofibres without a metal catalyst

An interesting phenomenon is observed while carrying out thermal carbonization of porous silicon (PS) with an aim to arrest the natural surface degradation, and it is a burning issue for PS-based device applications. A tubular carbon structure has been observed on the PS surface. Raman, Fourier transform infrared spectroscopy (FTIR) and electron microscope studies, revealed that the tubular structure is nothing but amorphous carbon nanofibres sprouted within the pores in the absence of a metal catalyst, for which a suitable explanation is proposed.

Integration of multiple components in polystyrene-based microfluidic devices part II: cellular analysis

In Part II of this series describing the use of polystyrene (PS) devices for microfluidic-based cellular assays: various cellular types and detection strategies are employed to determine three fundamental assays often associated with cells. Specifically, using either integrated electrochemical sensing or optical measurements with a standard multi-well plate reader, cellular uptake, production, or release of important cellular analytes are determined on a PS-based device. One experiment involved the fluorescence measurement of nitric oxide (NO) produced within an endothelial cell line following stimulation with ATP. The result was a four-fold increase in NO production (as compared to a control), with this receptor-based mechanism of NO production verifying the maintenance of cell receptors following immobilization onto the PS substrate. The ability to monitor cellular uptake was also demonstrated by optical determination of Ca(2+) into endothelial cells following stimulation with the Ca(2+) ionophore A20317. The result was a significant increase (42%) in the calcium uptake in the presence of the ionophore, as compared to a control (17%) (p < 0.05). Finally, the release of catecholamines from a dopaminergic cell line (PC 12 cells) was electrochemically monitored, with the electrodes being embedded into the PS-based device. The PC 12 cells had better adherence on the PS devices, as compared to use of PDMS. Potassium-stimulation resulted in the release of 114 ± 11 μM catecholamines, a significant increase (p < 0.05) over the release from cells that had been exposed to an inhibitor (reserpine, 20 ± 2 μM of catecholamines). The ability to successfully measure multiple analytes, generated in different means from various cells under investigation, suggests that PS may be a useful material for microfluidic device fabrication, especially considering the enhanced cell adhesion to PS, its enhanced rigidity/amenability to automation, and its ability to enable a wider range of analytes to be investigated, even analytes with a high degree of hydrophobicity.

Fabrication and chemical surface modification of nanoporous silicon for biosensing applications

In this work, porous silicon (PS) films with varied porosity (68–82%) were formed on the p-type, boron-doped silicon wafer (100) by the electrochemical anodisation in an aqueous hydrofluoric acid and isopropyl alcohol solution at different current densities (I d) ranging from 20–70 mA cm−2, respectively. Biofunctionalisation of the PS surface was carried out by chemically modifying the surface of PS by the deposition of 3-aminopropyltriethoxysilane thermally leading to high density of amine groups covering the PS surface. This further promotes the immobilisation of immunoglobulin (human IgG and goat anti-human IgG binding) on to the PS surface. Formation of nanostructured PS and the attachment of antibody–antigen to its surface were characterised using photoluminescence (PL), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques, respectively. The possibility of using these structures as biosensors has been explored based on the significant changes in the PL spectra before and after exposing the PS optical structures to biomolecules. These experimental results open the possibility of developing optical biosensors based on the variation of the PL position of the PL spectra of PS-based devices.

Porous silicon optical cavity structure applied to high sensitivity organic solvent sensor

The present work reports the thermal annealing process, the number of layer and electrochemical process effect in the optical response quality of Bragg and microcavity devices that were applied as organic solvent sensors. These devices have been obtained by using porous silicon (PS) technology. The optical characterization of the Bragg reflector, before annealing, showed a broad photonic band-gap structure with blue shifted and narrowed after annealing process. The electrochemical process used to obtain the PS-based device imposes the limit in the number of layers because of the chemical dissolution effect. The interface roughness minimizations in the devices have been achieved by using the double electrochemical cell setup. The microcavity devices showed to have a good sensibility for organic solvent detection. The thermal annealed device showed better sensibility feature and this result was attributed to passivation of the surface devices.

Porous silicon based structures for the electrical biosensing of glucose

Porous silicon (PS), which is composed of silicon crystals with typical sizes in the range of a few nanometers, shows high specific surface. Thus, its particular surface morphology makes this material very suitable for its use in the field of sensing. Accordingly, PS-based devices with the structure metal/PS/silicon/metal were developed to be used as electrical biosensors. Current–voltage measurements have shown that these devices typically show rectifying characteristics. In addition, it has been found that the current–voltage characteristics show a strong variation as a function of the presence/absence and concentration of biomolecules onto the surface of PS, both for longitudinal and transversal conduction. The present work describes our findings in the correlation between biomolecule surface concentration and current for a given voltage.

Electrical properties of metal/porous silicon/p-Si structures with thin porous silicon layer

Porous silicon (PS) based metal/PS/p-Si structures with PS layer of different thickness were prepared on moderate- and high-resistivity substrates. Measurements of current–voltage (I–V) characteristics and impedance at various temperatures were used for the investigation of the electrical properties of these structures. Electrical properties of the structures with relatively thin (1 μm) PS layer significantly differ from those of thick structures. The exponential forward bias I–V dependencies for thin structures spread over several orders of magnitude with a low value of quality factor (close to 2) and have activation temperature dependencies with an activation energy equal to half the c-Si band gap. The reverse current has a square root dependence on the reverse bias voltage and the activation energy is equal to half the c-Si band gap. Therefore, it was concluded that the reverse and forward currents in thin PS-based device structures were determined by the generation and recombination of carriers in the depletion region of the c-Si substrate. It was shown that a large area spreading current exists in structures made on highly resistive substrates, which appears to be due to a highly conductive inverse (n-type) layer formed in the p-Si substrate at the PS/p-Si heterojunction. The spreading effect leads to high reverse currents and high capacitance of the device structures made on highly resistive substrates.

Development and characterization of porous silicon based photodiodes

Porous silicon (PS) based photodiodes have been developed from multicrystalline n +/p junctions, since this material can efficiently be employed to reduce optical reflection and to enhance absorption. These devices show a strong rectifying characteristic, in which the reverse and short-circuit current strongly depends on the presence of light. According to this, their use as solar sensors is considered as a practical application of PS-based photodiodes. The electrical performance (forward and reversed biased) of the PS-based devices under standard conditions of illumination and temperature has been determined. The angular dependence of the electrical response as a function of incidence light has also been established showing a cosine-type behavior. The degradation of these devices after extended photon irradiation as well as after long periods of atmospheric exposure has been found to be small. Finally, the variation of the electrical response under standard illumination conditions of PS-based photodetectors has also been estimated by varying the device working temperature from 10 up to 80°C.

Transport of carriers in thin Metal/PS/c-Si device Structures based on Porous Silicon

AbstractThin porous silicon (PS) based metal/PS/p-c-Si structures were prepared on moderate-and high- resistivity substrates. Measurements of current-voltage (I-V) dependencies and impedance at various temperatures were used for the investigation of carrier transport in these structures. The exponential forward bias I-Vdependencies for both types of structures spread over several orders of magnitude with a low value of quality factor (close to 2) and have activation temperature dependencies with an activation energy equal to half the c-Si band gap. The reverse current has a square root dependence on the reverse bias voltage and the activation energy is equal to half the c-Si band gap. Therefore, it was concluded that the reverse and forward currents in thin PS-based device structures were determined by the generation and recombination of carriers in the depletion region of the c-Si substrate. It was shown that a large area spreading current exists in structures made on highly resistive substrates, which appears to be due to a highly conductive inverse (n-type) layer formed in the c-Si substrate at the PS/c-Si heterojunction.