Browsing by Author "Gunawardhana, N."

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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.
The land transportation depicted in Mahāvaṃsa and Dīpavaṃsa from 6th B.C.E to the 3rd C.E
(The International Conference on Land Transportation, Locomotive Heritage and Road Culture - 2017, 2017) Gunawardhana, N.
According to the written records like the Mahāvaṃsa and the Dīpavaṃsa history of Sri Lanka may have begun from the arrival of the prince Vijaya circa 6th B.C.E. Although the history begins from the 6th century B.C.E., the literary sources were not recorded till the 4th century C.E. The first Chronicle, the Dīpavaṃsa was written between the 4th and 5th C.E., while the Mahāvaṃsa was written a century later in the 5th or 6th C.E. The authors of these Chronicles belonging to the Mahā Vihāra of the orthodox tendency and they have exaggerate the works of some kings who have been sympathetic towards the Mahā Vihāra while those like Mahāsēna who were ardent supporter of the Mahāyāna were criticized. It is also necessary to bear in mind that most of the accounts of these authors are subjected to usual exaggerations. The authors of these Chronicles of the 4th and the 5th centuries impose their values and partial judgments over the events that have taken place in the 6th century B.C.E. The Mahāvaṃsa and the Dīpavaṃsa shed light on the land transportation in ancient Sri Lanka from the 6th B.C.E. The Immigration of Aryan, prove the fact that the land roads were connected with the ports like Mahātittha, Gōkaṇṇa, Jambukōlapattana etc. All these land routes are connected with ancient capital city of Anurādhapura. This paper proposes to discuss the significance of all the transportation methods as well. These accumulated data are analyzed to evaluate the above mentioned topic.
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.
Tuning the carboxylic groups and increasing the number of defects in graphene oxide nano sheets by changing the oxidation duration of modified Hummers method
(Faculty of Graduate Studies, University of Kelaniya Sri Lanka, 2022) Premadasa, P. M.; Panamaldeniya, S. A.; Munasinghe, M. A. H. M.; Gunawardhana, N.
Graphene Oxide (GO) is a 2-D monolayer/ few stacked layers material synthesized from graphite by introducing oxygen-containing functional groups (carboxylic, hydroxyl, and epoxy) to the graphene sheet. GO has both SP2 and SP3 hybridized carbon atoms, which are decorated by oxygen-containing functional groups. GO is extensively investigated in the translational research rather than fundamental research due to the broad range of applications in the synthesis of energy storage devices as fuel cells. The Modified Hummers method is the most frequently used method for the synthesis of GO. In this work, we have used the oxidation duration of the modified Hummers’ method to tune the carboxylic groups that are attached to the GO sheets with a higher number of defects because the more COOH groups with higher number of defects could enhance the activity of the GO. Here, grinded vain graphite, KMnO4 (an oxidizing agent), and H2O2 were used as basic precursors and three distinct GO materials were synthesized by varying the oxidation durations as 24, 48, and 72 hours for GO-1, GO-2, and GO-3. SEM, PXRD, FTIR, and RAMAN techniques were used to examine the qualitative and quantitative variations in COOH bonds in all three materials. According to the observed SEM images, the sheet morphology is visible in all three materials. But, the GO-3 sample exhibits a cloud-like structure with sheet morphology. It suggests that changing the oxidation time affected the number of defects in the materials. Next, the PXRD spectrums were observed to analyze interlayer spacing of GO sheets. Characteristic peaks of PXRD were obtained between 10° and 12°, but the d-spacing value increased with the oxidation duration of the materials. According to the observed FTIR spectrums, the peak intensities relevant to the carboxylic bonds at 1756cm-1 enhanced with the oxidation duration while all the other peaks remained the same. Stronger vibration relevant to the COOH indicates the production of COOH bonds and GO-3 contains more COOH bonds rather than other two materials. The Raman analysis shows that the intensity of the G and D peaks has grown with the length of oxidation. With the rise in oxidation duration, the FWHM (full width half maximum) of band G, which indicates the presence of SP3 bonding in the materials have also increased. Similarly, the oxidation duration affected the nature of the D band which confirmed the increment of number of defects with oxidation duration. In conclusion, the oxidation duration of the modified Hummers’ method directly influences the formation of COOH bonds, and the number of COOH bonds increase with oxidation duration.