Research Articles (Physics)

Permanent URI for this collection


Recent Submissions

Now showing 1 - 4 of 4
  • ItemOpen Access
    Bias and illumination-dependent room temperature negative differential conductance in Ni-doped ZnO/p-Si Schottky photodiodes for quantum optics applications
    (Cell Press, 2023) Ocaya, Richard O.; Orman, Yusuf; Al-Sehemi, Abdullah G.; Dere, Aysegul; Al-Ghamdi, Ahmed A.; Yakuphanoglu, Fahrettin
    In this article, evidence for the existence of illumination and bias-dependent negative differential conductance (NDC) in Ni-doped Al/ZnO/p-Si Schottky diodes, and the possible mechanism for its origin, are presented. The atomic percentages of Ni doping were 0%, 3%, 5%, and 10%. NDC is observed between -1.5 V to -0.5 V in reverse bias under illumination, but only at certain doping levels and specific forward bias. Furthermore, the devices show excellent optoelectronic characteristics in the photoconductive and photovoltaic modes, with device open circuit voltages ranging from 0.03 V to 0.6 V under illumination.
  • ItemOpen Access
    The vanishing of the primary emission region in PKS 1510–089
    (American Astronomical Society, 2023) Aharonian, F.; Ait Benkhali, F.; Aschersleben, J.; Ashkar, H.; Backes, M.; Barbosa Martins, V.; Barnard, J.; Batzofin, R.; Becherini, Y.; Berge, D.; Bernlohr, K.; Bi, B.; de Bony de Lavergne, M.; Bottcher, M.; Boisson, C.; Bolmont, J.; Borowska, J.; Bouyahiaoui, M; Bradascio, F.; Breuhaus, M.; Brose, R.; Brown, A. M.; Brun, F.; Bruno, B.; Bulik, T.; Burger-Scheidlin, C.; Caroff, S.; Casanova, S.; Cecil, R.; Celic, J.; Cerruti, M.; Chand, T.; Chandra, S.; Chen, A.; Chibueze, J.; Chibueze, O.; Cotter, G.; Damascene Mbarubucyeye, J.; Davids, I. D.; Djannati-Atai, A.; Dmytriiev, A.; Doroshenko, V.; Egberts, K.; Einecke, S.; Ernenwein, J.-P.; Fegan, S.; Fontaine, G.; Fussling, M.; Funk, S.; Gabici, S.; Ghafourizadeh, S.; Giavitto, G.; Glawion, D.; Glicenstein, J. F.; Goswami, P.; Grolleron, G.; Haerer, L.; Hofmann, W.; Holch, T. L.; Holler, M.; Horns, D.; Jamrozy, M.; Jankowsky, F.; Joshi, V.; Jung-Richardt, I.; Kasai, E.; Katarzynski, K.; Khatoon, R.; Khelifi, B.; Kluzniak, W.; Komin, N.; Kosack, K.; Kostunin, D.; Lang, R. G.; Le Stum, S.; Leitl, F.; Lemiere, A.; Lenain, J.-P.; Leuschner, F.; Luashvili, A.; Mackey, J.; Marandon, V.; Marchegiani, P.; Marti-Devesa, G.; Marx, R.; Mehta, A.; Meyer, M.; Mitchell, A.; Moderski, R.; Mohrmann, L.; Montanari, A.; Moulin, E.; de Naurois, M.; Niemiec, J.; Priyana Noel, A.; O'Brien, P.; Ohm, S.; Olivera-Nieto, L.; de Ona Wilhelmi, E.; Ostrowski, M.; Panny, S.; Panter, M.; Peron, G.; Prokhorov, D. A.; Ren, H.; Rieger, F.; Rowell, G.; Rudak, B.; Rueda Ricarte, H.; Ruiz-Velasco, E.; Sahakian, V.; Salzmann, H.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schussler, F.; Schutte, H. M.; Schwanke, U.; Shapopi, J. N. S.; Sol, H.; Specovius, A.; Spencer, S.; Stawarz, K.; Steenkamp, R.; Steinmassl, S.; Steppa, C.; Sushch, I.; Suzuki, H.; Takahashi, T.; Tanaka, T.; Terrier, R.; Tsuji, N.; van Eldik, C.; van Soelen, B.; Vecchi, M.; Veh, J.; Vink, J.; Wach, T.; Wagner, S. J.; Wierzcholska, A.; Zacharias, M.; Zargaryan, D.; Zdziarski, A. A.; Zech, A.; Zouari, S.; Zywucka, N.; Buckley, D. A. H.; Cooper, J.; Groenewald, D.; H.E.S.S., Collaboration
    In 2021 July, PKS 1510−089 exhibited a significant flux drop in the high-energy γ-ray (by a factor 10) and optical (by a factor 5) bands and remained in this low state throughout 2022. Similarly, the optical polarization in the source vanished, resulting in the optical spectrum being fully explained through the steady flux of the accretion disk and the broad-line region. Unlike the aforementioned bands, the very-high-energy γ-ray and X-ray fluxes did not exhibit a significant flux drop from year to year. This suggests that the steady-state very-high-energy γ-ray and X-ray fluxes originate from a different emission region than the vanished parts of the high-energy γ-ray and optical jet fluxes. The latter component has disappeared through either a swing of the jet away from the line of sight or a significant drop in the photon production efficiency of the jet close to the black hole. Either change could become visible in high-resolution radio images.
  • ItemOpen Access
    Data of electronic, reactivity, optoelectronic, linear and non-linear optical parameters of doping graphene oxide nanosheet with aluminum atom
    (Elsevier, 2022) Foadin, Crevain Souop Tala; Nya, Fridolin Tchangnwa; Malloum, Alhadji; Conradie, Jeanet
    We have established a design to increase the absorption capacity, optoelectronic, linear and nonlinear optical prop- erties of the graphene oxide nanosheet (GON) based on the coronene molecule [C 24 H 12 ] with the help of doping, using the aluminum atom. The attachment of functional groups to the coronene surface was defined according to the Lerf-Klinowski model, based on experimental predic- tions [1] . Two GON structures (GON1 and GON2 with for- mula (C 24 H 11 )(O)(OH)COOH)) have been proposed for this purpose, and it should be noted that each of them is dis- tinguished by a different distribution of functional groups within their honeycomb lattice. A series of substitutions of the carbon atoms of the two isomers considered GON1 and GON2 were performed with the aluminum atom, resulting in the abbreviated derivative systems GON1-Alx and GON2- Alx ( x = 1–6), respectively to each of the GON1 and GON2 units. In this work, we provide data carried out in the gas phase, from density functional theory (DFT) methods that al- lowed us to understand the effects of aluminum atom dop- ing on the circular graphene oxide nanosheets. First, we report the wavenumber data related to the IR spectrum peak characteristics computed at the B3LYP, B3LYP-D3 and ωB97XD/6–31 + G(d,p) levels of theory, that allowed us to val- idate the designs of both proposed graphene oxide models. Then, we provide electronic, reactivity, optoelectronic, linear and nonlinear optical data parameters of both graphene ox- ide nanosheets and their aluminum-doped derivatives com- puted at the B3LYP, B3LYP-D3 and /6-31 + G(d,p) levels of the- ory. Finally the UV-vis spectra of the investigated compounds evaluated from time-dependent (TD) B3LYP and B3LYP-D3/6- 31 + G(d,p) levels of theory and the HOMO & LUMO orbitals of the derivatives of graphene oxide isomers computed at the B3LYP/6-31 + G(d,p) level of theory are provided. In addi- tion, the raw data of UV-vis spectra, optoelectronic parame- ters, Cartesian coordinates of all studied compounds and also those of IR spectra of both studied graphene oxide models are provided as supplementary file. The data reported in this work are useful to expose some specific positions of alu- minum within circular model of graphene oxide nanosheet that improve its electronic, reactive, optoelectronic, linear and nonlinear optical characteristics. All the formulas and de- tails of calculation performed to obtain the data reported in this work are provided in our previous work (Foadin et al., 2020) and summarized in the experimental section of this paper. To learn more about the ideal doping positions of the aluminum atom within both proposed graphene oxide de- signs that increase their electronic, reactivity, optoelectronic, linear optical and nonlinear optical properties, respectively, please see the corresponding main research paper (Foadin et al., 2022).
  • ItemOpen Access
    AutoCal: A software application for calibrating photometric data
    (Academy of Science of South Africa (ASSAf), 2016) Wium, Daniël J.; Van Soelen, Brian
    We present a software application for the calibration of stellar magnitudes in the absence of standard stars. It uses an existing algorithm to match stars in the target’s field of view to catalogue entries and computes the average offset between the two sets of magnitudes using a weighted least-squares approach. This offset is used to calibrate the target’s instrumental magnitude. The software application was used to calibrate magnitudes for six Be/X-ray binary sources in the Small Magellanic Cloud and the results were compared with published results for these sources. Where comparisons were possible, our results agreed with those results within the uncertainties specified. Infrared variability was found for all six of the sources tested. The interactive outlier removal that was made possible by our software allowed for smaller uncertainties to be reported for our results.