Physics

Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/3750

Browse

Filters

Settings

Search Results

Now showing 1 - 10 of 248
  • No Thumbnail Available
    Item
    Synthesis of TIO2-(B) nanobelts for acetone sensing
    (Sensors, 2023) Kumarage, G. W. C.; Panamaldeniya, S. A.; Maddumage, D. C.; Moumen, A.; Maraloiu, V. A.; Mihalcea, C. G.; Negrea, R. F.; Dassanayake, B. S.; Gunawardhana, N.; Zappa, D.; Galstyan, V.; Comini, E.
    Titanium dioxide nanobelts were prepared via the alkali-hydrothermal method for application in chemical gas sensing. The formation process of TiO2-(B) nanobelts and their sensing properties were investigated in detail. FE-SEM was used to study the surface of the obtained structures. The TEM and XRD analyses show that the prepared TiO2 nanobelts are in the monoclinic phase. Furthermore, TEM shows the formation of porous-like morphology due to crystal defects in the TiO2-(B) nanobelts. The gas-sensing performance of the structure toward various concentrations of hydrogen, ethanol, acetone, nitrogen dioxide, and methane gases was studied at a temperature range between 100 and 500 °C. The fabricated sensor shows a high response toward acetone at a relatively low working temperature (150 °C), which is important for the development of low-power-consumption functional devices. Moreover, the obtained results indicate that monoclinic TiO2-B is a promising material for applications in chemo-resistive gas detectors.
  • No Thumbnail Available
    Item
    Exploring MBH–P scaling relations in spiral galaxies: a comparative analysis of inner and outer arm structures
    (2024) Hettiarachchi, Sanjaya; Hewageegana, Prabath; Abdeen, Shameer
    We study the galactic spiral arm pitch angle dependence with wavelength as predicted by the density wave theory. A sample of 10 barred and unbarred spiral galaxies with two distinct, well-defined arms is used for the measurements. The data sample consists of galaxies with inner arms and galaxies with both inner and outer arms. We use six wavebands, namely 3.6 μm, 8.0 μm, B band, H α, H I, and CO for the image analysis. The pitch angles are visually measured with the PYTHON-OL SCRIPT and more precise measurements are obtained using SPIRALITY. We find a 1:1 correlation between pitch angle measurements in the 3.6 and 8.0 μm bands. We predict supermassive black hole (SMBH) masses for 3.6 μm waveband pitch angles using a standard scaling relation. We find that the black hole mass of a galaxy with both inner and outer arms is determined by the average pitch angle of the inner arms. Using only galaxies with inner arms, we find an SMBH mass–pitch angle relation of log(MBH/M⊙) = (7.11 ± 0.33) + (0.003 ± 0.017)P. Using only galaxies with both inner and outer arms, we find an SMBH mass–pitch angle relation of log(MBH/M⊙) = (7.56 ± 0.28) - (0.038 ± 0.013)P.
  • No Thumbnail Available
    Item
    Cu2O Homojunction Solar Cells: Efficiency Enhancement with a High Short Circuit Current
    (2024) Thejasiri, S. A. A. B.; Jayathilaka, K. M. D. C.; Kafi, F. S. B.; Kumara, L. S. R.; Seo, O.; Yasuno, S.; Sakata, O.; Siripala, W.; Wijesundera, R. P.
    Cu2O homojunction solar cells were fabricated using potentiostatic electrodeposition technique. n-Cu2O thin films were grown in an acetate bath while p-Cu2O thin films were grown in a lactate bath. In the growth of n-Cu2O films, cupric acetate concentration, pH and temperature of the bath, deposition potential and duration (film thickness) and annealing temperature were investigated. In the growth of p-Cu2O on n-Cu2O, concentration of copper sulphate and lactic acid solutions, pH and temperature of the bath, deposition potential and duration were investigated. In addition, the procedure of sulfidation of p-Cu2O film surface using (NH4)2S vapor, before depositing Au front contact, was also optimized to enhance the photoactive performance. The structural, morphological and optoelectronic properties of the Cu2O films were investigated using scanning electron microscopy (SEMs), high energy X-ray diffraction (HEXRD), hard X-ray photoelectron spectroscopy (HAXPES), spectral response and current–voltage (J-V) measurements. The best Cu2O homojunction solar cell exhibited Voc = 460 mV, Jsc = 12.99 mA·cm−2, FF = 42% and η = 2.51%, under AM 1.5 illumination. Efficiency enhancement with the record high Jsc value for the Cu2O homojunction solar cell has mainly been due to the optimization of pH of the n-Cu2O deposition bath and lactic acid concentration of the p-Cu2O deposition bath.
  • No Thumbnail Available
    Item
    Electrodeposited thin film SnO2 photoelectrode for PEC applications
    (Institute of Physics, Sri Lanka, 2024) Kafi, F.S.B.; Gunaratna, B.H.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.
    Tin oxide (SnO2) is a promising semiconductor material to develop photoelectrodes for photoelectrochemical (PEC) cells. Indeed, an effective PEC cell could be developed only if the photoelectrode is stable and free of corrosion in the selected electrolytic solution. In other words, the choice of an electrolyte for a PEC cell determines the stability of the photoelectrode in the PEC cell. In this study, we propose aqueous 0.1 M sodium nitrate (NaNO3) as an effective electrolyte for the PEC cell where thin film SnO2 is a photoelectrode. Current-voltage (I-V) measurements obtained by illuminated chopped ultra violate (UV) radiation established the electrodeposited thin films of SnO2 are stable and free of corrosion/photocorrosion in our PEC cell. In addition, we report the dependence of the photoresponses of electrodeposited thin film SnO2 in this PEC on the bath temperature and the deposition time.
  • No Thumbnail Available
    Item
    Enhancement of Photo-Electrical Properties of CdS Thin Films: Effect of N2 Purging and N2 Annealing
    (2024) Sankalpa, Gayan K. L.; Kumarasinghe, Gayan R. K. K. G. R.; Dassanayake, Buddhika S.; Kumarage, Gayan W. C.
    The impact of N2 purging in the CdS deposition bath and subsequent N2 annealing is examined and contrasted with conventional CdS films, which were deposited without purging and annealed in ambient air. All films were fabricated using the chemical bath deposition method at a temperature of 80 ◦C on fluorine-doped tin oxide glass slides (FTO). N2 purged films were deposited by introducing nitrogen gas into the deposition bath throughout the CdS deposition process. Subsequently, both N2 purged and un-purged films underwent annealing at temperatures ranging from 100 to 500 ◦C for one hour, either in a nitrogen or ambient air environment. Photoelectrochemical (PEC) cell studies reveal that films subjected to both N2 purging and N2 annealing exhibit a notable enhancement of 37.5% and 27% in ISC (short-circuit current) and VOC (open-circuit voltage) values, accompanied by a 5% improvement in optical transmittance compared to conventional CdS thin films. The films annealed at 300 ◦C demonstrate the highest ISC, VOC, and VFB values, 55 μA, 0.475 V, and−675 mV, respectively. The improved optoelectrical properties in both N2-purged and N2-annealed films are attributed to their well-packed structure, enhanced interconnectivity, and a higher sulfur to cadmium ratio of 0.76 in the films.
  • No Thumbnail Available
    Item
    Nb2O5 Microcolumns for Ethanol Sensing
    (2024) Kumarage, Gayan W. C.; Panamaldeniya, Shasika A.; Maraloiu, Valentin A.; Dassanayake, Buddhika S.; Gunawardhana, Nanda; Comini, Elisabetta
    Pseudohexagonal Nb2O5 microcolumns spanning a size range of 50 to 610 nm were synthesized utilizing a cost-effective hydrothermal process (maintained at 180 ◦C for 30 min), followed by a subsequent calcination step at 500 ◦C for 3 h. Raman spectroscopy analysis unveiled three distinct reflection peaks at 220.04 cm−1, 602.01 cm−1, and 735.3 cm−1, indicative of the pseudohexagonal crystal lattice of Nb2O5. The HRTEM characterization confirmed the inter-lattice distance of 1.8 Å for the 110 plain and 3.17 Å for the 100 plain. The conductometry sensors were fabricated by drop-casting a dispersion of Nb2O5 microcolumns, in ethanol, on Pt electrodes. The fabricated sensors exhibited excellent selectivity in detecting C2H5OH (ΔG/G = 2.51 for 10 ppm C2H5OH) when compared to a variety of tested gases, including CO, CO2, NO2, H2, H2S, and C3H6O. The optimal operating temperature for this selective detection was determined to be 500 ◦C in a dry air environment. Moreover, the sensors demonstrated exceptional repeatability over the course of three testing cycles and displayed strong humidity resistance, even when exposed to 90% relative humidity. This excellent humidity resistance gas sensing property can be attributed to their nanoporous nature and elevated operating temperature.
  • No Thumbnail Available
    Item
    Efficiency boost of inverted polymer solar cells using electrodeposited n-type Cu2O electrons selective transport layers (ESTLs)
    (National Science Foundation of Sri Lanka, 2023) Wanninayake, WTMAPK; Namawardana, DGKK; Wanigasekara, RMG; Jayathilaka, KMDC; Wijesundera, RP; Siripala, W; Malik, MI
    Polymer solar cells (PSCs) have attracted tremendous interest as suitable candidates for harnessing solarenergy in the recent years. The inherent optoelectronic properties of the inorganic transition metal oxide, negative type cuprous oxide (n-Cu2O), makes it an attractive candidate to improve the performance of PSCs when incorporated as the electron selective transport layers (ESTLs) in the device. In this study, inverted PSCs were fabricated on stainless steel (SS) substrates with n-Cu2O as the ESTL. The n-Cu2O films were prepared by electrodeposition method, followed by annealing under ambient conditions. The active layer material was prepared as bulk heterojunction blend using regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). Poly-(4,3-ethylene dioxythiophene):poly(styrenesulphonate) (PEDOT:PSS) was used as the hole transport layer (HTL) and the final device structure was SS/n-Cu2O/P3HT:PCBM/PEDOT:PSS/Au. Annealing of the n-Cu2O ESTL in air was optimized observing the photoactive performance of the device. Optoelectronic performance of the devices was characterized using spectral response and dark and light current-voltage (I-V) measurements. n-Cu2O ESTL- incorporated devices have absorbed more photons in the short wavelength region of 450‒600 nm with the annealing of n-Cu2O ESTL due to the reduction of electron-hole recombination. The performance of the devices was significantly increased after incorporating pre-annealed n-Cu2O ESTL at 175 °C for 30 min in air. The maximum power conversion efficiency (PCE) was 0.35%.
  • No Thumbnail Available
    Item
    Enhancing the Photovoltaic Performance of Cd(1􀀀x)ZnxS Thin Films Using Seed Assistance and EDTA Treatment
    (Faculty of Science, University of Kelaniya Sri Lanka, 2023) Kumarage, G. W. C.; Wijesundera, Ruwan P.; Comini, Elisabetta; Dassanayake, Buddhika S.
    This research article provides a comprehensive investigation into the optoelectronic characteristics of three distinct types of cadmium sulfide (CdS) thin films, namely: (a) conventionally prepared CdS thin films using chemical bath deposition (CBD-CdS), (b) CdS thin films produced via chemical bath deposition with the inclusion of zinc (CBD-Cd(1􀀀x)ZnxS, x = 0.3), and (c) CdS thin films synthesized using a seed-assisted approach, treated with ethylenediaminetetraacetic acid (EDTA), and incorporating zinc (ED/CBD + EDTA-Cd(1􀀀x)ZnxS). The investigation reveals that the crystallite size of these thin films decreases upon the addition of EDTA to the reaction solution, leading to an increase in the inter-planar spacing and dislocation density. Furthermore, a blue shift in the transmittance edge of the ED/CBD + EDTA-Cd(1􀀀x)ZnxS samples compared to CBD-CdS implies modifications in the band gaps of the deposited films. The incorporation of Zn2+ into the reaction solution results in an increased band gap value of up to 2.42 eV. This suggests that Cd(1􀀀x)ZnxS thin films permit more efficient photon transmission compared to conventional CdS. Among the three types of films studied, ED/CBD + EDTA-Cd(1􀀀x)ZnxS exhibits the highest optical band gap of 2.50 eV. This increase in the optical band gap is attributed to the smaller crystallite size and the splitting of the tail levels from the band structure. Additionally, the increment in the optical band gap leads to reduced light absorption at longer wavelengths, thereby enhancing the electrical properties. Notably, ED/CBD + EDTA-Cd(1􀀀x)ZnxS thin films demonstrate improved photovoltaic performance in a photoelectrochemical (PEC) cell, characterized by enhanced open-circuit voltage (363 mV, VOC), short-circuit current (35.35 A, ISC), and flat-band voltage (􀀀692 mV, Vfb). These improvements are attributed to the better adhesion of CdS to the fluorine-doped tin oxide (FTO) substrate and improved inter-particle connectivity.
  • No Thumbnail Available
    Item
    Growth and Characterization of Seed‑Assisted, EDTA‑Treated, Chemical Bath‑Deposited CdS
    (Journal of Electronic Materials, 2021) Kumarage, W. G. C.; Wijesundera, R. P.; Seneviratne, V. A.; Jayalath, C. P.; Gunawardhana, N.; Kaur, N.; Comini, E.; Dassanayake, B. S.
    A simple low-cost method to enhance the electrical properties including open-circuit voltage (VOC), flat-band potential (Vfb) and short-circuit current (ISC) in the photoelectrochemical (PEC) cell of cadmium sulfide (CdS) thin films is presented. The PEC cell properties were determined using the configuration Pt/0.1 M Na2S2O3/ CdS. Three different sets of CdS thin films were grown: (a) chemical bath-deposited CdS (CBD-CdS), (b) electrodeposited seed-assisted CBD-CdS (ED/CBD-CdS) and (c) ED/CBD-CdS deposited under the presence of ethylenediaminetetraacetic acid (EDTA) in a reaction solution of CBD (ED/(CBD+EDTA)-CdS). The FE-SEM images suggested the formation of clusters with spherical shape in the presence of a seed layer. All the samples grown with seed layers demonstrated improved ISC and VOC values in the PEC cell compared to the CBD-CdS films due to better contact between the substrate and CBD-CdS. Furthermore, the carrier concentration (ND) and Vfb were also found to improve due to the introduction of the seed layer. In the case of ED/(CBD+EDTA)-CdS, the cluster size was found to be smaller, giving rise to a larger effective surface area. The improved effective surface area, interparticle connections and adhesion of CdS to the FTO substrate resulted in superior electrical properties of ED/(CBD+EDTA)-CdS compared to ED/CBD-CdS and CBD-CdS films.
  • No Thumbnail Available
    Item
    Fabrication of inverted organic solar cells on stainless steel substrate with electrodeposited and spin coated ZnO buffer layers
    (Journal of Polymer Engineering, 2022) Namawardana, D. G. K. K.; Wanigasekara, R. M. G.; Wanninayake, W. T. M. A. P. K.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.; Malik, M. I.
    Polymer based organic solar cells (OSCs) are of tremendous interest as suitable candidates for producing clean and renewable energy in recent years. In this study, inverted OSCs on stainless steel (SS) substrate with zinc oxide (ZnO) as the electron selective transport layer (ESTL), are investigated, occupying bulk heterojunction blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl- C61-butyric acid methyl ester (PCBM) as the active material and poly-(4,3-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer (HTL). The device structure is SS/ZnO/P3HT:PCBM/PEDOT:PSS/Au. ZnO films are prepared by spin coating and electrodeposition techniques, followed by annealing under ambient conditions. The insertion of ZnO layer between the SS substrate and active layer has improved short-circuit current ( Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE) compared to those of the reference cell without ZnO layer, achieving the highest efficiency of 0.66% for the device with spin coated ZnO from sol–gel technique. This enhancement can be attributed to the effective electron extraction and the increased crystallinity of ZnO after annealing treatments at higher temperatures as further confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses.