Displaying publications 41 - 60 of 283 in total

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  1. Structural and optical properties investigation on h-bonded 1d helical selfassembly of 1,1-dibenzyl-3-(2-bromobenzoyl)thiourea molecules for nonlinear optical application
    Wun Fui Mark-Lee, Mohammad B. Kassim, Mohd Faizal Md Nasir
    Sains Malaysiana, 2018;47:741-747.
    A benzoylthiourea molecule namely 1,1-dibenzyl-3-(2-bromobenzoyl)thiourea (2BrBT) was synthesized and characterized
    by C, H, N and S elemental, mass spectrometry and spectroscopic analyses (infrared, ultraviolet-visible and nuclear
    magnetic resonance). The 2BrBT compound crystallized in a tetragonal system with the space group P43 and exhibits
    an acentric crystalline packing due to the presence of intermolecular H-bonding network that forms a self-assembly
    of 1D helical motif. The asymmetric delocalisation of electrons in the molecule retains its transparency throughout the
    visible and near-infrared region and hence, essentially propagates the macroscopic helical motif in the solid state. The
    highest-occupied and lowest-unoccupied molecular orbital (HOMO/LUMO) are mainly found on the thiourea moiety and
    the benzoylthiourea fragment, respectively and shows an optical bandgap of 3.50 eV. The influence of its geometrical
    characteristics to the optical properties of 2BrBT is established and discussed in view of nonlinear optical (NLO)
    application.
    Matched MeSH terms: Electrons
  2. Effect of nonmetals (B, O, P, and S) doped with porous g-C3N4 for improved electron transfer towards photocatalytic CO2 reduction with water into CH4
    Arumugam M, Tahir M, Praserthdam P
    Chemosphere, 2022 Jan;286(Pt 2):131765.
    PMID: 34371351 DOI: 10.1016/j.chemosphere.2021.131765
    Photocatalytic conversion of carbon dioxide (CO2) into gaseous hydrocarbon fuels is an auspicious way to produce renewable fuels in addition to greenhouse gas emission mitigation. In this work, non-metals (B, O, P, and S) doped graphitic carbon nitride (g-C3N4) was prepared via solid-state polycondensation of urea for photocatalytic CO2 reduction into highly needed methane (CH4) with water under UV light irradiation. The various physicochemical characterization results reveal the successful incorporation of B, O, P, and S elements in the g-C3N4 matrix. The maximum CH4 yield of 55.10 nmol/(mLH2O.gcat) over S-doped g-C3N4 has been obtained for CO2 reduction after 7 h of irradiation. This amount of CH4 production was 1.9, 1.4, 1.7, and 2.4-folds higher than B, O, P and bare g-C3N4 samples. The doping of S did not enlarge the surface area and photon absorption ability of the g-C3N4 sample, but this significant improvement was evidently due to effective charge separation and migration. The observed results imply that the doping of non-metal elements provides improved charge separation and is an effective way to boost photocatalyst performance. This work offers an auspicious approach to design non-metal doped g-C3N4 photocatalysts for renewable fuel production and would be promising for other energy application.
    Matched MeSH terms: Electrons
  3. Fulltext Tunable Open Circuit Voltage by Engineering Inorganic Cesium Lead Bromide/Iodide Perovskite Solar Cells
    Ng CH, Ripolles TS, Hamada K, Teo SH, Lim HN, Bisquert J, et al.
    Sci Rep, 2018 02 06;8(1):2482.
    PMID: 29410450 DOI: 10.1038/s41598-018-20228-0
    Perovskite solar cells based on series of inorganic cesium lead bromide and iodide mixture, CsPbBr3-xI x , where x varies between 0, 0.1, 0.2, and 0.3 molar ratio were synthesized by two step-sequential deposition at ambient condition to design the variations of wide band gap light absorbers. A device with high overall photoconversion efficiency of 3.98 % was obtained when small amount of iodide (CsPbBr2.9I0.1) was used as the perovskite and spiro-OMeTAD as the hole transport material (HTM). We investigated the origin of variation in open circuit voltage, Voc which was shown to be mainly dependent on two factors, which are the band gap of the perovskite and the work function of the HTM. An increment in Voc was observed for the device with larger perovskite band gap, while keeping the electron and hole extraction contacts the same. Besides, the usage of bilayer P3HT/MoO3 with deeper HOMO level as HTM instead of spiro-OMeTAD, thus increased the Voc from 1.16 V to 1.3 V for CsPbBr3 solar cell, although the photocurrent is lowered due to charge extraction issues. The stability studies confirmed that the addition of small amount of iodide into the CsPbBr3 is necessarily to stabilize the cell performance over time.
    Matched MeSH terms: Electrons
  4. Enhanced simultaneous degradation of simulated dyes using ZnO/GCN heterojunction photocatalyst
    Isa EDM, Jusoh NWC, Rodzi AAM
    Environ Sci Pollut Res Int, 2023 Nov;30(55):116921-116933.
    PMID: 37178288 DOI: 10.1007/s11356-023-27576-z
    The scarcity of water leads to research nowadays to focus on techniques for treating wastewater. Photocatalysis emerged as a technique of interest due to its nature of friendliness. It utilizes light and catalyst to degrade the pollutants. One of the popular catalysts to be used is zinc oxide (ZnO), but its usage is limited due to the high recombination rate of electron-hole pair. Herein, in this study, ZnO is modified with graphitic carbon nitride (GCN), and the GCN loading amount was varied to study the impact on photocatalytic degradation of mixed dye solution. To the best of our knowledge, this is the first work that reports on the degradation of mixed dye solution using modified ZnO with GCN. Structural analysis showed that GCN is present in the composites which proves the success of the modification. Photocatalytic activity revealed that the composite with 5 wt% loading of GCN showed the best activity at a catalyst dosage of 1 g/L with degradation rates of 0.0285, 0.0365, 0.0869, and 0.1758 min-1 for methyl red, methyl orange, rhodamine B, and methylene blue dyes, respectively. This observation is expected due to the formation of heterojunction between ZnO and GCN which creates a synergistic effect and thus led to an improvement in the photocatalytic activity. Based on these results, ZnO modified with GCN has a good potential to be used in the treatment of textile wastewater which consists of various dye mixtures.
    Matched MeSH terms: Electrons
  5. Fulltext Reversible structure manipulation by tuning carrier concentration in metastable Cu2S
    Tao J, Chen J, Li J, Mathurin L, Zheng JC, Li Y, et al.
    Proc Natl Acad Sci U S A, 2017 09 12;114(37):9832-9837.
    PMID: 28855335 DOI: 10.1073/pnas.1709163114
    The optimal functionalities of materials often appear at phase transitions involving simultaneous changes in the electronic structure and the symmetry of the underlying lattice. It is experimentally challenging to disentangle which of the two effects--electronic or structural--is the driving force for the phase transition and to use the mechanism to control material properties. Here we report the concurrent pumping and probing of Cu2S nanoplates using an electron beam to directly manipulate the transition between two phases with distinctly different crystal symmetries and charge-carrier concentrations, and show that the transition is the result of charge generation for one phase and charge depletion for the other. We demonstrate that this manipulation is fully reversible and nonthermal in nature. Our observations reveal a phase-transition pathway in materials, where electron-induced changes in the electronic structure can lead to a macroscopic reconstruction of the crystal structure.
    Matched MeSH terms: Electrons
  6. Fulltext Open-gated pH sensor fabricated on an undoped-AlGaN/GaN HEMT structure
    Abidin MS, Hashim AM, Sharifabad ME, Rahman SF, Sadoh T
    Sensors (Basel), 2011;11(3):3067-77.
    PMID: 22163786 DOI: 10.3390/s110303067
    The sensing responses in aqueous solution of an open-gated pH sensor fabricated on an AlGaN/GaN high-electron-mobility-transistor (HEMT) structure are investigated. Under air-exposed ambient conditions, the open-gated undoped AlGaN/GaN HEMT only shows the presence of a linear current region. This seems to show that very low Fermi level pinning by surface states exists in the undoped AlGaN/GaN sample. In aqueous solution, typical current-voltage (I-V) characteristics with reasonably good gate controllability are observed, showing that the potential of the AlGaN surface at the open-gated area is effectively controlled via aqueous solution by the Ag/AgCl gate electrode. The open-gated undoped AlGaN/GaN HEMT structure is capable of distinguishing pH level in aqueous electrolytes and exhibits linear sensitivity, where high sensitivity of 1.9 mA/pH or 3.88 mA/mm/pH at drain-source voltage, V(DS) = 5 V is obtained. Due to the large leakage current where it increases with the negative gate voltage, Nernstian like sensitivity cannot be determined as commonly reported in the literature. This large leakage current may be caused by the technical factors rather than any characteristics of the devices. Surprisingly, although there are some imperfections in the device preparation and measurement, the fabricated devices work very well in distinguishing the pH levels. Suppression of current leakage by improving the device preparation is likely needed to improve the device performance. The fabricated device is expected to be suitable for pH sensing applications.
    Matched MeSH terms: Electrons*; Transistors, Electronic*
  7. Electronic properties and gas adsorption behaviour of pristine, silicon-, and boron-doped (8, 0) single-walled carbon nanotube: A first principles study
    Azam MA, Alias FM, Tack LW, Seman RNAR, Taib MFM
    J Mol Graph Model, 2017 08;75:85-93.
    PMID: 28531817 DOI: 10.1016/j.jmgm.2017.05.003
    Carbon nanotubes (CNTs) have received enormous attention due to their fascinating properties to be used in various applications including electronics, sensing, energy storage and conversion. The first principles calculations within density functional theory (DFT) have been carried out in order to investigate the structural, electronic and optical properties of un-doped and doped CNT nanostructures. O2, CO2, and CH3OH have been chosen as gas molecules to study the adsorption properties based on zigzag (8,0) SWCNTs. The results demonstrate that the adsorption of O2, CO2, and CH3OH gas molecules on pristine, Si-doped and B-doped SWCNTs are either physisorption or chemisorption. Moreover, the electronic properties indicating SWCNT shows significant improvement toward gas adsorption which provides the impact of selecting the best gas sensor materials towards detecting gas molecule. Therefore, these pristine, Si-, and B-doped SWCNTs can be considered to be very good potential candidates for sensing application.
    Matched MeSH terms: Electrons*
  8. Reactive Black 5 as electron donor and/or electron acceptor in dual chamber of solar photocatalytic fuel cell
    Khalik WF, Ho LN, Ong SA, Voon CH, Wong YS, Yusuf SY, et al.
    Chemosphere, 2018 Jul;202:467-475.
    PMID: 29579681 DOI: 10.1016/j.chemosphere.2018.03.113
    The role of azo dye Reactive Black 5 (RB5) as an electron donor and/or electron acceptor could be distinguished in dual chamber of photocatalytic fuel cell (PFC). The introduction of RB5 in anode chamber increased the voltage generation in the system since degradation of RB5 might produce electrons which also would transfer through external circuit to the cathode chamber. The removal efficiency of RB5 with open and closed circuit was 8.5% and 13.6%, respectively and removal efficiency for open circuit was low due to the fact that recombination of electron-hole pairs might happen in anode chamber since without connection to the cathode, electron cannot be transferred. The degradation of RB5 in cathode chamber with absence of oxygen showed that electrons from anode chamber was accepted by dye molecules to break its azo bond. The presence of oxygen in cathode chamber would improve the oxygen reduction rate which occurred at Platinum-loaded carbon (Pt/C) cathode electrode. The Voc, Jsc and Pmax for different condition of ultrapure water at cathode chamber also affected their fill factor. The transportation of protons to cathode chamber through Nafion membrane could decrease the pH of ultrapure water in cathode chamber and undergo hydrogen evolution reaction in the absence of oxygen which then increased degradation rate of RB5 as well as its electricity generation.
    Matched MeSH terms: Electrons*
  9. Enhancing the radiation dose detection sensitivity of optical fibres
    Bradley DA, Mahdiraji GA, Ghomeishi M, Dermosesian E, Adikan FR, Rashid HA, et al.
    Appl Radiat Isot, 2015 Jun;100:43-9.
    PMID: 25533626 DOI: 10.1016/j.apradiso.2014.12.005
    A method for improving the thermoluminescence (TL) yield of silica-based optical fibres is demonstrated. Using silica obtained from a single manufacturer, three forms of pure (undoped) fibre (capillary-, flat-, and photonic crystal fibre (PCF)) and two forms of Ge-doped fibre (capillary- and flat-fibre) were fabricated. The pure fibre samples were exposed to 6 and 21MeV electrons, the doped fibres to 6MV photons. The consistent observation of large TL yield enhancement is strongly suggestive of surface-strain defects generation. For 6MeV irradiations of flat-fibre and PCF, respective TL yields per unit mass of about 12.0 and 17.5 times that of the undoped capillary-fibre have been observed. Similarly, by making a Ge-doped capillary-fibre into flat-fibre, the TL response is found to increase by some 6.0 times. Thus, in addition to TL from the presence of a dopant, the increase in fused surface areas of flat-fibres and PCF is seen to be a further important source of TL. The glow-curves of the undoped fibres have been analysed by computational deconvolution. Trap centre energies have been estimated and compared for the various fibre samples. Two trap centre types observed in capillary-fibre are also observed in flat-fibre and PCF. An additional trap centre in flat-fibre and one further trap centre in PCF are observed when compared to capillary fibre. These elevated-energy trap centres are linked with strain-generated defects in the collapsed regions of the flat fibre and PCF.
    Matched MeSH terms: Electrons
  10. Differential cross sections for intermediate-energy electron scattering from α-tetrahydrofurfuryl alcohol: excitation of electronic-states
    Chiari L, Duque HV, Jones DB, Thorn PA, Pettifer Z, da Silva GB, et al.
    J Chem Phys, 2014 Jul 14;141(2):024301.
    PMID: 25028013 DOI: 10.1063/1.4885856
    We report on measurements of differential cross sections (DCSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol (THFA). The energy range of these experiments was 20-50 eV, while the scattered electron was detected in the 10°-90° angular range. There are currently no other experimental data or theoretical computations against which we can directly compare the present measured results. Nonetheless, we are able to compare our THFA DCSs with earlier cross section measurements for Rydberg-state electronic excitation for tetrahydrofuran, a similar cyclic ether, from Do et al. [J. Chem. Phys. 134, 144302 (2011)]. In addition, "rotationally averaged" elastic DCSs, calculated using our independent atom model with screened additivity rule correction approach are also reported. Those latter results give integral cross sections consistent with the optical theorem, and supercede those from the only previous study of Milosavljević et al. [Eur. Phys. J. D 40, 107 (2006)].
    Matched MeSH terms: Electrons
  11. Fulltext Monte Carlo dose calculation in dental amalgam phantom
    Aziz MZ, Yusoff AL, Osman ND, Abdullah R, Rabaie NA, Salikin MS
    J Med Phys, 2015 Jul-Sep;40(3):150-5.
    PMID: 26500401 DOI: 10.4103/0971-6203.165080
    It has become a great challenge in the modern radiation treatment to ensure the accuracy of treatment delivery in electron beam therapy. Tissue inhomogeneity has become one of the factors for accurate dose calculation, and this requires complex algorithm calculation like Monte Carlo (MC). On the other hand, computed tomography (CT) images used in treatment planning system need to be trustful as they are the input in radiotherapy treatment. However, with the presence of metal amalgam in treatment volume, the CT images input showed prominent streak artefact, thus, contributed sources of error. Hence, metal amalgam phantom often creates streak artifacts, which cause an error in the dose calculation. Thus, a streak artifact reduction technique was applied to correct the images, and as a result, better images were observed in terms of structure delineation and density assigning. Furthermore, the amalgam density data were corrected to provide amalgam voxel with accurate density value. As for the errors of dose uncertainties due to metal amalgam, they were reduced from 46% to as low as 2% at d80 (depth of the 80% dose beyond Zmax) using the presented strategies. Considering the number of vital and radiosensitive organs in the head and the neck regions, this correction strategy is suggested in reducing calculation uncertainties through MC calculation.
    Matched MeSH terms: Electrons
  12. Nanostructured SnO2-Ge Multi-layer thin Films with Quantum Confinement Effects for Solar Cell
    Khan AF, Sajjad W, Rahim NA
    Recent Pat Nanotechnol, 2016;10(1):77-82.
    PMID: 27018275
    BACKGROUND: It is well-known that multi-layer films with nanostructure can give novel properties by interfacial phenomenon and quantum confinement effects. Nanostructured multi-layer thin films are presently being analyzed for their vast applications in the area of optoelectronics technology particularly photovoltaics. Hereof, two dimensional thin films with nanostructure are of prime importance due to their structure dependent optical, electrical, and opto-electronic properties. It has been revealed that these films exhibit quantum confinement effects with band gap engineering. The main focus of the research is to evaluate the effect on structural and optical properties with number of layers.

    METHODS: Nanostructured SnO2-Ge multi-layer thin films were fabricated using electron beam evaporation and resistive heating techniques. Alternate layers of SnO2 and Ge were deposited on glass substrate at a substrate temperature of 300 °C in order to obtain uniform and homogeneous deposition. The substrate temperature of 300 °C has been determined to be effective for the deposition of these multi-layer films from our previous studies. The films were characterized by investigating their structural and optical properties. The structural properties of the as-deposited films were characterized by Rutherford Backscattering Spectroscopy (RBS) and Raman spectroscopy and optical properties by Ultra-Violet-Near infrared (UV-VIS-NIR) spectroscopy.

    RESULTS: RBS studies confirmed that the layer structure has been effectively formed. Raman spectroscopy results show that the peaks of both Ge and SnO2 shifts towards lower wavenumbers (in comparison with bulk Ge and SnO2, suggesting that the films consist of nanostructures and demonstrate quantum confinement effects. UV-VIS-NIR spectroscopy showed an increase in the band gap energy of Ge and SnO2 and shifting of transmittance curves toward higher wavelength by increasing the number of layers. The band gap lies in the range of 0.9 to 1.2 eV for Ge, while for SnO2, it lies between 1.7 to 2.1 eV.

    CONCLUSION: Analysis of results suggests that the nanostructured SnO2-Ge multi-layer thin film can work as heterojunction materials with quantum confinement effects. Accordingly, the present SnO2-Ge multi-layer films may be employed for photovoltaic applications. Few relevant patents to the topic have been reviewed and cited.

    Matched MeSH terms: Electrons
  13. Tunable Spectrum Selectivity for Multiphoton Absorption with Enhanced Visible Light Trapping in ZnO Nanorods
    Tan KH, Lim FS, Toh AZY, Zheng XX, Dee CF, Majlis BY, et al.
    Small, 2018 May;14(20):e1704053.
    PMID: 29665226 DOI: 10.1002/smll.201704053
    Observation of visible light trapping in zinc oxide (ZnO) nanorods (NRs) correlated to the optical and photoelectrochemical properties is reported. In this study, ZnO NR diameter and c-axis length respond primarily at two different regions, UV and visible light, respectively. ZnO NR diameter exhibits UV absorption where large ZnO NR diameter area increases light absorption ability leading to high efficient electron-hole pair separation. On the other hand, ZnO NR c-axis length has a dominant effect in visible light resulting from a multiphoton absorption mechanism due to light reflection and trapping behavior in the free space between adjacent ZnO NRs. Furthermore, oxygen vacancies and defects in ZnO NRs are associated with the broad visible emission band of different energy levels also highlighting the possibility of the multiphoton absorption mechanism. It is demonstrated that the minimum average of ZnO NR c-axis length must satisfy the linear regression model of Z p,min = 6.31d to initiate the multiphoton absorption mechanism under visible light. This work indicates the broadening of absorption spectrum from UV to visible light region by incorporating a controllable diameter and c-axis length on vertically aligned ZnO NRs, which is important in optimizing the design and functionality of electronic devices based on light absorption mechanism.
    Matched MeSH terms: Electrons
  14. Fulltext Dataset on structure and mechanical properties of electrospun polyacrylonitrile nanofibrous mesh reinforced by halloysite nanotubes
    Goh KL, Makaremi M, Pasbakhsh P, De Silva R, Zivkovic V
    Data Brief, 2018 Dec;21:2170-2178.
    PMID: 30555856 DOI: 10.1016/j.dib.2018.11.039
    The mechanical properties of electrospun polyacrylonitrile (PAN)-based membranes for ultrafiltration, such as oil-water separation and heavy metals from water, are often characterised in the dry state but little is known about the membrane properties in the hydrated state. This dataset comprised mechanical properties and structure-related properties of electrospun PAN-based membranes. The mechanical dataset described the yield strength and strain, stiffness, resilience energy, fracture strength, strain at fracture and fracture toughness of electrospun neat PAN and halloysite nanotube (HNT) reinforced PAN membranes in both hydrated and dry states. The data related to the hydrated state were derived from direct measurements of the mechanical properties of the PAN-based membrane using a novel environmental micromechanical tester. The structure-related dataset comprised electron micrographs and quantitative measurements (fibre diameter and pore diameter) derived from the micrographs. For further interpretation and discussion of the dataset, the reader is referred to the research data article, "Direct measurement of the elasticity and fracture properties of electrospun polyacrylonitrile/halloysite fibrous mesh in water" (Govindasamy et al., 2014).
    Matched MeSH terms: Electrons
  15. Growth conditions of graphene grown in chemical vapour deposition (CVD)
    Mohamad Shukri Sirat, Edhuan Ismail, Hadi Purwanto, Mohd Hanafi Ani, Mohd Asyadi Azam Mohd Abid
    Sains Malaysiana, 2017;46:1033-1038.
    The fabrication of high quality graphene has become the main interest in current chemical vapour deposition (CVD) method due to the scalability for mass production of graphene-based electronic devices. The quality of graphene is determined by defect density, number of layers and properties changed such as electron mobility, transparency and conductivity as compared to the pristine graphene. Here, we did a study on the effects of reaction conditions such as methane, CH4 concentration and deposition time towards the quality of graphene produced. We found that by lowering both CH4 concentration down to 20% and deposition time to 5 min, a better quality graphene was produced with higher I2D/IG ratio of 0.82 compared to other reaction condition. Through the analysis, we concluded that there are two important parameters to be controlled to obtain high quality graphene.
    Matched MeSH terms: Electrons
  16. Optical Properties of Azo-Benzothiazole Side Chain Liquid Crystalline Polymers: Effect of Solvents, Substituents and Temperatures
    Dzulkharnien NSF, Karim MR, Zahid NI, Rahman NMMA, Abdullah I, Salleh NM
    J Fluoresc, 2019 Jul;29(4):1049-1056.
    PMID: 31338718 DOI: 10.1007/s10895-019-02418-9
    The optical properties of a series of side chain liquid crystalline polymers (P1-P3) containing azo-benzothiazole mesogen with different terminal substituents (-H, -CH3 and -OCH2CH3) in four organic solvents of varying polarity have been investigated by absorption and fluorescence spectral analysis. Solvatochromic studies of P1-P3 did not show any regular variation on the absorption and emission intensities with changing the polarity of solvent. Theoretical studies were performed based on different solvent correlation methods such as Dimroth-Reichardt and Kamlet-Taft methods to investigate the solute-solvent interactions. Both absorption and emission maxima of investigated polymers were bathochromically shifted with the replacement of sixth position hydrogen atom by electron donating groups in benzothiazole moiety. The emission intensities of the studied polymers showed decreasing trend with increasing temperature.
    Matched MeSH terms: Electrons
  17. Observation of the Production of Three Massive Gauge Bosons at sqrt[s]=13  TeV
    Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Bergauer T, Dragicevic M, et al.
    Phys Rev Lett, 2020 Oct 09;125(15):151802.
    PMID: 33095594 DOI: 10.1103/PhysRevLett.125.151802
    The first observation is reported of the combined production of three massive gauge bosons (VVV with V=W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 137  fb^{-1}. The searches for individual WWW, WWZ, WZZ, and ZZZ production are performed in final states with three, four, five, and six leptons (electrons or muons), or with two same-sign leptons plus one or two jets. The observed (expected) significance of the combined VVV production signal is 5.7 (5.9) standard deviations and the corresponding measured cross section relative to the standard model prediction is 1.02_{-0.23}^{+0.26}. The significances of the individual WWW and WWZ production are 3.3 and 3.4 standard deviations, respectively. Measured production cross sections for the individual triboson processes are also reported.
    Matched MeSH terms: Electrons
  18. Photoluminescence Investigation of Carrier Localization in Colloidal PbS and PbS/MnS Quantum Dots
    Zaini MS, Liew JYC, Alang Ahmad SA, Mohmad AR, Ahmad Kamarudin M
    ACS Omega, 2020 Dec 08;5(48):30956-30962.
    PMID: 33324803 DOI: 10.1021/acsomega.0c03768
    The existence of surface organic capping ligands on quantum dots (QDs) has limited the potential in QDs emission properties and energy band gap structure alteration as well as the carrier localization. This drawback can be addressed via depositing a thin layer of a semiconductor material on the surface of QDs. Herein, we report on the comparative study for photoluminescent (PL) properties of PbS and PbS/MnS QDs. The carrier localization effect due to the alteration of energy band gap structure and carrier recombination mechanism in the QDs were investigated via PL measurements in a temperature range of 10-300 K with the variation of the excitation power from 10 to 200 mW. For PbS QDs, the gradient of integrated PL intensity (IPL) as a function of excitation power density graph was less than unity. When the MnS shell layer was deposited onto the PbS core, the PL emission exhibited a blue shift, showing dominant carrier recombination. It was also found that the full width half-maximum showed a gradual broadening with the increasing temperature, affirming the electron-phonon interaction.
    Matched MeSH terms: Electrons
  19. Electronic structure and optical properties of the dialkali metal monotelluride compounds: Ab initio study
    Souadia Z, Bouhemadou A, Bin-Omran S, Khenata R, Al-Douri Y, Al Essa S
    J Mol Graph Model, 2019 07;90:77-86.
    PMID: 31031219 DOI: 10.1016/j.jmgm.2019.04.008
    Structural parameters, electronic structure and optical properties of the dialkali metal monotelluride M2Te (M = Li, Na, K and Rb) compounds in the cubic antifluorite structure were investigated via ab initio calculations using the all electron linearized augmented plane wave approach based on density functional theory with and without including spin-orbit coupling (SOC). The exchange-correlation interactions were described within the PBEsol version of the generalized gradient approximation and Tran-Blaha modified Becke-Johnson potential (TB-mBJ). Optimized equilibrium lattice parameters are in excellent accordance with existing measured ones. Computed energy band dispersions show that the studied compounds are large band gap materials. Inclusion of SOC reduces the band gap value compared to the corresponding one calculated without including SOC. Determination of the energy band character and interatomic bonding nature are performed using the densities of states diagrams and charge density distribution map. Linear optical function spectra are predicted for a wide energy range and the origin of the dielectric function spectrum peaks are determined.
    Matched MeSH terms: Electrons
  20. Fulltext First-Principles Studies for Electronic Structure and Optical Properties of Strontium Doped β-Ga2O3
    Kean Ping L, Mohamed MA, Kumar Mondal A, Mohamad Taib MF, Samat MH, Berhanuddin DD, et al.
    Micromachines (Basel), 2021 Mar 24;12(4).
    PMID: 33804978 DOI: 10.3390/mi12040348
    The crystal structure, electron charge density, band structure, density of states, and optical properties of pure and strontium (Sr)-doped β-Ga2O3 were studied using the first-principles calculation based on the density functional theory (DFT) within the generalized-gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE). The reason for choosing strontium as a dopant is due to its p-type doping behavior, which is expected to boost the material's electrical and optical properties and maximize the devices' efficiency. The structural parameter for pure β-Ga2O3 crystal structure is in the monoclinic space group (C2/m), which shows good agreement with the previous studies from experimental work. Bandgap energy from both pure and Sr-doped β-Ga2O3 is lower than the experimental bandgap value due to the limitation of DFT, which will ignore the calculation of exchange-correlation potential. To counterbalance the current incompatibilities, the better way to complete the theoretical calculations is to refine the theoretical predictions using the scissor operator's working principle, according to literature published in the past and present. Therefore, the scissor operator was used to overcome the limitation of DFT. The density of states (DOS) shows the hybridization state of Ga 3d, O 2p, and Sr 5s orbital. The bonding population analysis exhibits the bonding characteristics for both pure and Sr-doped β-Ga2O3. The calculated optical properties for the absorption coefficient in Sr doping causes red-shift of the absorption spectrum, thus, strengthening visible light absorption. The reflectivity, refractive index, dielectric function, and loss function were obtained to understand further this novel work on Sr-doped β-Ga2O3 from the first-principles calculation.
    Matched MeSH terms: Electrons
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