Varghese Swamy

Nanostructuring Mixed‐Dimensional Perovskites: A Route Toward Tunable, Efficient Photovoltaics

2D perovskites is one of the proposed strategies to enhance the moisture resistance, since the larger organic cations can act as a natural barrier. Nevertheless, 2D perovskites hinder the charge transport in certain directions, reducing the solar cell power conversion efficiency. A nanostructured mixed-dimensionality approach is presented to overcome the charge transport limitation, obtaining power conversion efficiencies over 9%.

Enhancing moisture tolerance in efficient hybrid 3D/2D perovskite photovoltaics

Surface imperfections in perovskite films upon crystallization may trigger trap-assisted non-radiative recombination which is a dominant recombination mechanism that potentially restricts the performance of solar devices. In this work, 2D alkylammonium halide perovskites are formed on the 3D perovskite structure to passivate interfacial defects and vacancies and enhance moisture tolerance. The hybrid 3D/2D perovskite films possess longer photoluminescence lifetimes, as well as lower trap state densities, indicating the passivation of cationic and halide vacancies on the surface or grain boundaries, thereby reducing the non-radiative recombination pathways. More importantly, the hybrid 3D/2D perovskite exhibits higher ambient stability than a pure 3D perovskite where the hydrophobic nature of the long aliphatic carbon chains in the 2D perovskite provide an additional moisture repelling effect to the entire perovskite film. With this approach, the power conversion efficiency of perovskite solar cells was improved from 14.17% to 15.74% along with improved device stability. The hybrid 3D/2D perovskite solar cell retained 86% of its initial power conversion efficiency whereas the control device lost almost 40% of its overall efficiency. Thus, the hybrid 3D/2D perovskite structure is an alternative solution for modulating defects and trap-state densities in high efficiency perovskite solar cells with simultaneously enhanced moisture stability.

Multilayer graphene electrodes for one-port surface acoustic wave resonator mass sensor

A one-port surface acoustic wave (SAW) resonator mass sensor composed of multilayer graphene (MLG) electrodes was investigated by the finite element method (FEM) and analyses were carried out to study the enhancement of sensitivity and the secondary effects caused by MLG electrodes on the performance of the resonator. Unlike metal electrodes, MLG electrode offers elastic loading to the contact surface, as evidenced by the increase in the surface velocity of the SAW device. In terms of the sensitivity of the mass sensor, MLG electrode showed the largest center frequency shift in response to a change in mass loading, as well as when used as a gas sensor to detect volatile organic compounds (VOCs). Also, MLG electrodes offered the least triple transit signal (TTS) and bulk acoustic wave (BAW) generations compared with Al and Au–Cr electrodes. Thus, the one-port SAW resonator with graphene electrodes not only possesses excellent performance characteristics but also gives rise to new opportunities in the development of highly sensitive mass sensors.

Revisiting seismic hazard assessment for Peninsular Malaysia using deterministic and probabilistic approaches

Seismic hazard assessments, both deterministic and probabilistic, for Peninsular Malaysia have been carried out using peak ground acceleration (PGA) data recorded between 2004 and 2016 by the Malaysian Meteorological Department using triaxial accelerometers placed at 19 seismic stations on the peninsula. Seismicity source modelling for the deterministic seismic hazard assessment (DSHA) used historical point sources whereas in the probabilistic (PSHA) approach, line and areal sources were used. The earthquake sources comprised the Sumatran subduction zone (SSZ), Sumatran fault zone (SFZ) and local intraplate (LI) faults. Gutenberg–Richter law b value for the various zones identified within the SSZ ranged between 0.56 and 1.06 (mean= 0.82) and for the zones within the SFZ, between 0.57 and 1.03 (mean= 0.89). Suitable ground motion prediction equations (GMPEs) for Peninsular Malaysia along with other pertinent information were used for constructing a logic tree for PSHA of the region. The DSHA “critical-worst” scenario suggests PGAs of 0.07–0.80 ms−2 (0.7–8.2 percent g), whilst the PSHA suggests mean PGAs of 0.11–0.55 ms−2 (0.5–5.4 percent g) and 0.20–1.02 ms−2 (1.9–10.1 percent g) at 10 % and 2 % probability of exceedance in 50 years, respectively. DSHA and PSHA, despite using different source models and methodologies, both conclude that the centralwestern cities of Peninsular Malaysia, located between 2 and 4 N, are most susceptible to high PGAs, due to neighbouring active Sumatran sources, SFZ and SSZ. Of the two Sumatran sources, surprisingly, the relatively less active SFZ source with low magnitude seismicity appeared as the major contributor due to its proximity. However, potential hazards due to SSZ mega-earthquakes should not be dismissed. Finally, DSHA performed using the limited LI seismic data from the Bukit Tinggi fault at a reasonable moment magnitude (Mw) value of 5.0 predicted a PGA of ∼ 0.40 ms−2 at Kuala Lumpur.

Low cost batch fabrication of microdevices using ultraviolet light-emitting diode photolithography technique

Solid-state technology has enabled the use of light-emitting diodes (LEDs) in lithography systems due to their low cost, low power requirement, and higher efficiency relative to the traditional mercury lamp. Uniform irradiance distribution is essential for photolithography to ensure the critical dimension (CD) of the feature fabricated. However, light illuminated from arrays of LEDs can have nonuniform irradiance distribution, which can be a problem when using LED arrays as a source to batch-fabricate multiple devices on a large wafer piece. In this study, the irradiance distribution of an UV LED array was analyzed, and the separation distance between light source and mask optimized to obtain maximum irradiance uniformity without the use of a complex lens. Further, employing a diffuser glass enhanced the fabrication process and the CD loss was minimized to an average of 300 nm. To assess the performance of the proposed technology, batch fabrication of surface acoustic wave devices on lithium niobate substrate was carried out, and all the devices exhibited identical insertion loss of −18  dB at a resonance frequency of 39.33 MHz. The proposed low-cost UV lithography setup can be adapted in academic laboratories for research and teaching on microdevices.

Legumain Targeting Peptide Conjugated Fluorescent Porous Silicon Nanoparticles for Breast Cancer Imaging

Porous silicon (PSi) with a suite of most desirable biomaterial properties has attracted great attention as a multifunctional nanoplatform for bioimaging and drug delivery. Various surface functionalization treatments have been reported for PSi to use as an active tumor cell targeting nanovector. In this study, we investigated surface functionalization treatments using a peptide that is specific to the emerging biomarker legumain. The PSi nanoparticles were coated with dextran and subsequently two types of legumain targeting peptide, Y-shaped and linear chain, were conjugated to produce the functionalized PSi. The functionalized (ligand-conjugated) PSi materials were characterized for morphology, size, functional groups, and fluorescence response using electron and fluorescence microscopy and vibrational spectroscopy techniques. Fluorescence microscopy imaging with two excitation wavelengths (450 nm and 600 nm) suggests comparable fluorescence response of the conjugated PSi to “bare” PSi and the suitability of the PSi functionalized with peptide for bioimaging.

Data analytic engineering and its application in earthquake engineering: An overview

This paper deliberates the challenges of using regression models for earthquake data analysis and compares them with the field measurements. Regression analyses to model the peak ground acceleration (PGA) data are discussed with magnitude and distance as variables. Suitability of the models are further compared with the ground motion (PGA) field records obtained from the seismic stations within the peninsular Malaysia. Far field (distance above 300km from the epicenter) and local earthquakes within 50-300km with a wide range of moment magnitude (1.0-9.1) are considered in this study. Result from the regression models showed significant error between the predicted and field data. Further discussion highlights that the ground motion prediction equation (GMPE) is a function of multiple variables developed from the specific site properties. The paper concludes with a note showing the significance of statistical input and analysis in the GMPEs to achieve a more realistic earthquake data prediction model.