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    Optical conductivity of triple point fermions

    , Article Journal of Physics Condensed Matter ; Volume 33, Issue 12 , 2021 ; 09538984 (ISSN) Habibi, A ; Farajollahpour, T ; Jafari, S. A ; Sharif University of Technology
    IOP Publishing Ltd  2021
    As a low-energy effective theory on non-symmorphic lattices, we consider a generic triple point fermion Hamiltonian, which is parameterized by an angular parameter λ. We find strong λ dependence in both Drude and interband optical absorption of these systems. The deviation of the T2 coefficient of the Drude weight from Dirac/Weyl fermions can be used as a quick way to optically distinguish the triple point degeneracies from the Dirac/Weyl degeneracies. At the particular λ = π/6 point, we find that the 'helicity' reversal optical transition matrix element is identically zero. Nevertheless, deviating from this point, the helicity reversal emerges as an absorption channel. © 2021 IOP Publishing... 

    Modeling of laser thermal and hydrodynamic effects on a dilute suspension of micro-particles in water

    , Article Journal of Mechanical Science and Technology ; Vol. 28, issue. 3 , 2014 , p. 1017-1026 Zabetian, M ; Saidi, M. H ; Saidi, M. S ; Shafii, M. B ; Sharif University of Technology
    Particle manipulation using laser beam is almost a new and contactless technique in particulate sciences. The method is based on the radiation pressure of light photons on the particles suspended in a semi-transparent fluid. Applications of the technique mainly cover microscopic separation and detection of biological objects. In this work, a theoretical study is conducted to investigate the hydrodynamic and thermal effects on a particulate flow in a mini-channel. Laser thermal effects are studied as a result of light absorption either in fluid or dispersed phase. An analytical model is developed to be the real simulator of a test bed developed by the authors. The main objective of performed... 

    Excitation spectrum of correlated Dirac fermions

    , Article Journal of Physics: Conference Series, 14 January 2015 through 15 January 2015 ; Volume 603, Issue 1 , January , 2015 ; 17426588 (ISSN) Jalali, Z ; Jafari, S. A ; Suzumura Y ; Matsuura H ; Fuseya Y ; Ogata M ; Sharif University of Technology
    Institute of Physics Publishing  2015
    Motivated by the puzzling optical conductivity measurements in graphene, we speculate on the possible role of strong electronic correlations on the two-dimensional Dirac fermions. In this work we employ the slave-particle method to study the excitations of the Hubbard model on honeycomb lattice, away from half-filling. Since the ratio U/t ≈ 3.3 in graphene is not infinite, double occupancy is not entirely prohibited and hence a finite density of doublonscan be generated. We therefore extend the Ioff-Larkin composition rule to include a finite density of doublons. We then investigate the role played by each of these auxiliary particles in the optical absorption of strongly correlated Dirac... 

    Optical properties of defected silicene: the many-body approach

    , Article Optical and Quantum Electronics ; Volume 48, Issue 7 , 2016 ; 03068919 (ISSN) Zakerian, F ; Berahman, M ; Sharif University of Technology
    Springer New York LLC  2016
    Abstract: The electronic structure and excitonic optical properties of pristine and defected silicene are investigated within many-body Green’s function and Bethe–Salpeter equation formalism. We show that compared with pristine one, defects can significantly alter band structure and form much better metallic characteristics. Also, it is shown that low defects in pristine silicene can considerably alter optical absorption peaks and change these peaks to the lower energies. Such effect is illustrated for 5 % defects in the pristine silicene and two main peaks in the optical spectrum are shown, one in low energies and another wider one in the higher energies. These peaks can be used as a tool... 

    Fabrication of dual-phase TiO2/WO3with post-illumination photocatalytic memory

    , Article New Journal of Chemistry ; Volume 44, Issue 46 , 2020 , Pages 20375-20386 Mokhtarifar, M ; Nguyen, D. T ; Diamanti, M. V ; Kaveh, R ; Asa, M ; Sakar, M ; Pedeferri, M ; Do, T. O ; Sharif University of Technology
    Royal Society of Chemistry  2020
    This study describes the synthesis of TiO2/WO3 composite systems with a varying concentration of WO3 by a glucose-template assisted method and demonstrates their round-the-clock photoactivity performance towards the degradation of methanol (MeOH) under illumination and dark conditions. XRD results indicated a biphasic anatase-rutile nature of TiO2, with tunable concentrations with respect to the WO3 loading. WO3 incorporation extended the light absorption of the system towards visible light, increasing the observed photoactivity. The obtained results were further validated using photo-electrochemical investigations such as photocurrent measurements and the impedance response of the systems.... 

    An optical study of cobalt nanowires dispersed in liquid phase

    , Article Optics Communications ; Volume 274, Issue 2 , 2007 , Pages 471-476 ; 00304018 (ISSN) Azarian, A ; Iraji zad, A ; Dolati, A ; Sharif University of Technology
    The Co nanowires were electrodeposited in polycarbonate membrane (PCT). SEM, TEM and XPS techniques were used to characterize the morphology, structure and size of nanowires as well as chemical composition. The influence of different mediums was studied on the optical absorption of dispersed cobalt nanowires. The absorption spectrum of cobalt nanowires in water showed a broad shoulder at 290 nm, but in ethanol solution it was not observed in the visible region of the spectra up to 200 nm. Cobalt nanowires dispersed in methanol presented a peak at 236 nm. We attribute the data to oxidation of cobalt in water and low dielectric constant of methanol relative to ethanol and water. We found... 

    Performance analysis of spectral-phase-encoded optical CDMA system using two-photon-absorption receiver structure for asynchronous and slot-level synchronous transmitters

    , Article Journal of Lightwave Technology ; Volume 25, Issue 6 , 2007 , Pages 1638-1645 ; 07338724 (ISSN) Jamshidi, K ; Salehi, J. A ; Sharif University of Technology
    In this paper, we analyze the performance of a nonlinear two-photon-absorption (TPA) receiver and compare its performance with that of a single-photon-absorption (SPA) receiver in the context of spectral-phase-encoded optical code-division multiple access (CDMA) technique. The performances for the above systems are evaluated for two different transmission scenarios, namely, asynchronous and slot-level synchronous transmitters. Performance evaluation includes different sources of degradation such as multiple-access interference, noise due to optical amplification, shot noise, and thermal noise. In obtaining the performance, the mean and variance of the received signal in each of the above... 

    A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

    , Article Optics Communications ; Volume 265, Issue 1 , 2006 , Pages 283-300 ; 00304018 (ISSN) Bahrampour, A. R ; Mahjoei, M ; Rasouli, A ; Sharif University of Technology
    In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop... 

    Enhancement in solar driven water splitting by Au–Pd nanoparticle decoration of electrochemically grown ZnO nanorods

    , Article Journal of Applied Electrochemistry ; Volume 46, Issue 8 , 2016 , Pages 819-827 ; 0021891X (ISSN) Siavash Moakhar, R ; Kushwaha, A ; Jalali, M ; Goh, G. K. L ; Dolati, A ; Ghorbani, M ; Sharif University of Technology
    Springer Netherlands 
    Oriented ZnO nanorods were grown directly on fluorine doped tin oxide substrates by a single bath electrodeposition process. A pulse potential at the beginning of growth improved the density and orientation of the nanorods. Pulse potential grown ZnO nanorod films showed better harvesting of visible light and enhanced the light driven water splitting performance in comparison to nanorods grown without any pulse potential. To further improve the water splitting activity, the nanorods were decorated with gold–palladium nanoparticles by sputtering. This caused visible light absorption to increase due to a plasmonic effect and the photoelectrochemical water splitting performance to further... 

    Design and tailoring of one-dimensional ZnO nanomaterials for photocatalytic degradation of organic dyes: a review

    , Article Research on Chemical Intermediates ; Volume 45, Issue 4 , 2019 , Pages 2197-2254 ; 09226168 (ISSN) Samadi, M ; Zirak, M ; Naseri, A ; Kheirabadi, M ; Ebrahimi, M ; Moshfegh, A. Z ; Sharif University of Technology
    Springer Netherlands  2019
    Abstract: Photocatalysis using semiconductors has emerged as a promising wastewater treatment process to overcome the major challenges faced by conventional technologies. The advantages of ZnO nanomaterials over other semiconductors, and their structure-dependent properties, make them important building blocks in nanotechnology as multifunctional materials. Moreover, it has been confirmed that ZnO nanomaterials can exhibit high performance in photodegradation of organic dyes for treatment of industrial effluent. The wurtzite structure of ZnO contains polar and nonpolar planes; the low surface energy and thermodynamic stability of the nonpolar planes enable formation of one-dimensional (1D)... 

    Mechanistic insights into photogenerated electrons store-and-discharge in hydrogenated glucose template synthesized Pt: TiO2/WO3 photocatalyst for the round-the-clock decomposition of methanol

    , Article Materials Research Bulletin ; Volume 137 , 2021 ; 00255408 (ISSN) Mokhtarifar, M ; Nguyen, D. T ; Sakar, M ; Pedeferri, M ; Asa, M ; Kaveh, R ; Diamanti, M. V ; Do, T. O ; Sharif University of Technology
    Elsevier Ltd  2021
    This study demonstrates the glucose-template assisted synthesis of hydrogen-treated Pt: TiO2/WO3 composites, and their round-the-clock photoactivity towards methanol (MeOH) degradation under light illumination and in dark. XRD indicated increasing rutile fraction in TiO2 as a function of template removal, WO3 crystallinity and H2 treatment process. The presence of oxygen vacancies in WO3 was confirmed by XPS. Lower recombination rate and higher surface area were observed in the optimized H2-Pt-G:TiO2/WO3 catalyst. The presence of oxygen vacancies and optical enhancements due to the synergistic interactions of the multi-system (TiO2, WO3 and Pt) extended the visible light absorption of the... 

    Extreme light absorption in a necking-free monolayer of resonant-size nanoparticles for photoelectrochemical cells

    , Article Journal of Optics (United Kingdom) ; Vol. 16, issue. 7 , 2014 ; ISSN: 20408978 Dabirian, A ; Sharif University of Technology
    Semiconductor photoelectrodes for water oxidation that absorb visible light usually have poor electronic transport properties and small optical absorption coefficients near their absorption edge. Therefore, innovative designs that lead to significant optical absorption in relatively thin layers of these compounds are highly desirable. Here, using full-field electromagnetic optical simulations, we demonstrate that a monolayer of resonant-size BiVO4 spheres can provide enhancement up to a factor of two in solar light absorption relative to dense planar layers. In this monolayer, BiVO4 spheres do not need to be interconnected; therefore, such monolayers are flexible and their fabrication... 

    Improved charge collection efficiency of hollow sphere/nanoparticle composite TiO 2 electrodes for solid state dye sensitized solar cells

    , Article Current Applied Physics ; Volume 13, Issue 2 , March , 2013 , Pages 371-376 ; 15671739 (ISSN) Sadoughi, G ; Mohammadpour, R ; Irajizad, A ; Taghavinia, N ; Dadgostar, S ; Samadpour, M ; Tajabadi, F ; Sharif University of Technology
    The photoanodes of solid state dye sensitized solar cells (ss-DSCs) embedded with different contents of TiO 2 hollow spheres (HSs) were prepared and the photovoltaic performances were systematically characterized. TiO 2 hollow spheres were synthesized by a facile sacrificial templating method, grounded and added in different ratios to TiO 2 nanoparticle (NP) paste, from which composite HS/NP electrodes were fabricated. The composite photoanodes include hollow spheres of 300-700 nm with enhanced light scattering characteristics in visible range which leads to improved light absorption in conventional thin film electrodes of ss-DSC. By optimizing the amount of HSs in the paste, 40% improvement... 

    Resonant optical absorption and defect control in Ta3N 5 photoanodes

    , Article Applied Physics Letters ; Volume 102, Issue 3 , 2013 ; 00036951 (ISSN) Dabirian, A ; Van De Krol, R ; Sharif University of Technology
    In this study, we explore resonance-enhanced optical absorption in Ta 3N5 photoanodes for water splitting. By using a reflecting Pt back-contact and appropriate Ta3N5 film thickness, the resonance frequency can be tuned to energies just above the bandgap, where the optical absorption is normally weak. The resonance results in a significant improvement in the photoanode's incident photon-to-current efficiency. The Ta3N5 films are made by high-temperature nitridation of Ta2O5. The nitridation time is found to be critical, as extended nitridation result in the formation of nitrogen vacancies through thermal reduction. These insights give important clues for the development of efficient... 

    Thermal interaction of laser beam with particulate flow in mini-channels

    , Article ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2011, 19 June 2011 through 22 June 2011 ; Volume 2 , June , 2011 , Pages 355-366 ; 9780791844649 (ISBN) Zabetian, M ; Saidi, M. S ; Saidi, M. H ; Shafii, M. B ; Sharif University of Technology
    Optical propulsion via laser source is a relatively new and non-contact tool for manipulation of microscopic objects. The method is based on the radiation pressure of light photons on the micron sized particles. Applications of the technique mainly cover microscopic separation, purification and cellular studies. Due to high power intensity of laser beams, absorption of light may result in heating and damage of objects to be manipulated. In addition, the difference between heated and cold zones can lead to a naturally driven flow around the objects. So precisely controlled conditions should be set up to avoid thermal effects. In this work, a theoretical study is conducted to investigate the... 

    Aggregates of plasmonic nanoparticles for broadband light trapping in dye-sensitized solar cells

    , Article Journal of Optics (United Kingdom) ; Volume 18, Issue 1 , November , 2015 ; 20408978 (ISSN) Sharifi, N ; Dabirian, A ; Danaei, D ; Taghavinia, N ; Sharif University of Technology
    Institute of Physics Publishing  2015
    Metallic nanoparticles (NPs) have not been effective in improving the overall performance of the cells with micrometer-thick absorbing layers mainly due to the parasitic optical dissipation in the metal. Here, using both experiment and theory, we demonstrate that aggregates of metallic NPs enhance the light absorption of dye-sensitized solar cells of a few micrometer-thick light absorbing layers. The composite electrode containing the optimal concentration of 5 wt% Au@SiO2 aggregates shows the enhancement of 80% and 52% in external quantum efficiency and photocurrent density, respectively. The superior performance of the aggregates relative to NP is attributed to their larger scattering... 

    Photonic design of embedded dielectric scatterers for dye sensitized solar cells

    , Article RSC Advances ; Volume 5, Issue 42 , Mar , 2015 , Pages 33098-33104 ; 20462069 (ISSN) Malekshahi Byranvand, M ; Dabirian, A ; Nemati Kharat, A ; Taghavinia, N ; Sharif University of Technology
    Embedded dielectric scatterers comprise an important approach for light trapping in dye-sensitized solar cells (DSCs) due to their simple fabrication process. The challenge in applying these scatterers lies in finding the optimal dimensions and concentration of the scatterers. This requires many experiments and it is often quite difficult to have a starting point for optimizing the concentration. Based on theories of light propagation in random media, we propose a simple model for DSCs with embedded silica spherical particles. Then, by full-wave optical calculations, we determine a narrow range for the concentration of silica particles that leads to the largest optical absorption in the... 

    Optical absorption and electronic spectra of chlorophylls a and b

    , Article RSC Advances ; Volume 6, Issue 111 , 2016 , Pages 109778-109785 ; 20462069 (ISSN) Hedayatifar, L ; Irani, E ; Mazarei, M ; Rasti, S ; Azar, Y. T ; Rezakhani, A. T ; Mashaghi, A ; Shayeganfar, F ; Anvari, M ; Heydari, T ; Tabar, A. R ; Nafari, N ; Vesaghi, M. A ; Asgari, R ; Rahimi Tabar, M. R ; Sharif University of Technology
    Royal Society of Chemistry  2016
    Photosynthesis includes capturing sunlight by an assembly of molecules, called chlorophylls, and directing the harvested energy in the form of electronic excitations to the reaction center. Here we report, using real-space density functional theory and time-dependent density functional theory together with GW calculations, the optical and electronic properties of the two main chlorophylls in green plants, namely, chlorophylls a and b. Furthermore, we estimate the dipole and primitive quadrupole electric moments of these molecules. We employ Casida's assignment ansatz to study the absorption spectra of the chlorophylls in the two main red and blue regions at various environments with... 

    The role of a vapor-assisted solution process on tailoring the chemical composition and morphology of mixed-halide perovskite solar cells

    , Article CrystEngComm ; Volume 20, Issue 31 , 2018 , Pages 4428-4435 ; 14668033 (ISSN) Tafazoli, S ; Timasi, N ; Nouri, E ; Mohammadi, M. R ; Sharif University of Technology
    Royal Society of Chemistry  2018
    Herein, we report a modified two-step method to construct a uniform and pinhole-free polycrystalline perovskite film with large grains up to the microscale using lead mixed-halide (PbI2-PbCl2) precursor solutions to guarantee the device functioning. Commonly used sequential deposition methods based on dip- and spin-coatings are combined with a vapor-assisted solution process to improve the perovskite morphology and tune the residual lead mixed-halides. These can enhance the optical absorption and efficiency of perovskite solar cell (PSC) devices. The impact of the Cl content in the lead mixed-halide precursors and the employed preparation methods on the photovoltaic performance of PSCs are... 

    Jamming resistance capabilities of spectrally phase encoded OCDMA communication systems with optimum and suboptimum (nonlinear two-photon-absorption) receiver structures

    , Article Journal of Lightwave Technology ; Volume 27, Issue 22 , 2009 , Pages 5010-5021 ; 07338724 (ISSN) Emadi, M. J ; Salehi, J. A ; Sharif University of Technology
    In this paper, we study three types of jammers, namely, pulse-jammer, partial-band jammer, and follower-jammer, in a typical fiber-optic-based spectrally phase-encoded optical code division multiple-access (SPE-OCDMA) system. We analyze, mathematically, the effects of the aforementioned jammers on the performance of an SPE-OCDMA system for two scenarios, namely, ideal noiseless channel with an ideal optimum receiver and an ultrahigh-speed nonlinear receiver based on two-photon-absorption (TPA) in a noisy channel. Also, for each of the above cases, two types of modulation, namely, ON-OFF keying (OOK) and two-code keying (2CK) are investigated and their system performances are compared. It is...