Search for: semiconductor-quantum-dots
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    Enhancement of Mn luminescence in ZnS:Mn multi-quantum-well structures

    , Article Applied Physics Letters ; Volume 83, Issue 22 , 2003 , Pages 4616-4618 ; 00036951 (ISSN) Taghavinia, N ; Makino, H ; Yao, T ; Sharif University of Technology
    The efficiency of Mn luminescence is enhanced in low-thickness ZnS:Mn layers. While various hypotheses can be considered to explain the phenomenon, it seems more reasonable to consider the luminescence enhancement effect a result of the formation of dot-like regions with higher local Mn concentration  

    Quantum optics of a quantum dot embedded in a photonic crystal cavity

    , Article Photonic Crystal Materials and Devices VII, San Jose, CA, 21 January 2008 through 23 January 2008 ; Volume 6901 , 2008 ; 0277786X (ISSN); 9780819470768 (ISBN) Sodagar, M ; Khorasani, S ; Atabaki, A. H ; Adibi, A ; Sharif University of Technology
    In this paper we analyze a disk-like quantum dot embedded in an engineered two-dimensional (2D) photonic crystal cavity as an artificial atom. In this quantum dot electron and hole form an exciton where photon and electron-hole bound state can interact. Within the engineered electromagnetic vacuum of the PBG material, the exciton can emit and reabsorb a photon. If the exciton energy lies near the photonic band gap edge the exciton level splits into two levels. This is similar to the interaction of field and an atom in a high Q cavity. Here excitonic states are evaluated taking in to account the band mixing for holes. Also energy associated with dressed exction is evaluated  

    From continuous to quantized charging phenomena in few nanocrystals MOS structures

    , Article 11th International Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technlogy, GADEST 2005, Giens, 25 September 2005 through 30 September 2005 ; Volume 108-109 , 2005 , Pages 25-32 ; 10120394 (ISSN); 3908451132 (ISBN); 9783908451136 (ISBN) BenAssayag, G ; Shalchian, M ; Grisolia, J ; Bonafos, C ; Atarodi, S. M ; Claverie, A ; Sharif University of Technology
    Trans Tech Publications Ltd  2005
    In this paper, we present a study on the contribution of silicon nanocrystals to the electrical transport characteristics of large (100 μm × 100 μm) and small (100 nm × 100 nm) metaloxide-semiconductor (MOS) capacitors at room temperature. A layer of silicon nanocrystals is synthesized within the oxide of these capacitors by ultra-low energy ion implantation and annealing. Several features including negative differential resistance (NDR), sharp current peaks and random telegraph signal (RTS) are demonstrated in the current-voltage and current-time characteristics of these capacitors. These features have been associated to charge storage in silicon nanocrystals and to the resulting Coulomb... 

    Theory and simulation of cavity quantum electro-dynamics in multi-partite quantum complex systems

    , Article Applied Physics A: Materials Science and Processing ; Vol. 115, issue. 2 , 2014 , p. 595-603 Alidoosty Shahraki, M ; Khorasani, S ; Aram, M. H ; Sharif University of Technology
    The cavity quantum electrodynamics of various complex systems is here analyzed using a general versatile code developed in this research. Such quantum multi-partite systems normally consist of an arbitrary number of quantum dots in interaction with an arbitrary number of cavity modes. As an example, a nine-partition system is simulated under different coupling regimes, consisting of eight emitters interacting with one cavity mode. Two-level emitters (e.g. quantum dots) are assumed to have an arrangement in the form of a linear chain, defining the mutual dipole-dipole interactions. It was observed that plotting the system trajectory in the phase space reveals a chaotic behavior in the... 

    Analysis of transient response and instability in fiber ring resonators containing an erbium-doped fiber amplifier and quantum dot-doped fiber saturable absorber

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 30, Issue 12 , December , 2013 , Pages 3215-3224 ; 07403224 (ISSN) Tofighi, S ; Bahrampour, A. R ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    In this paper, the transient response of a double coupler fiber ring resonator containing an erbium-doped fiber amplifier (EDFA) in half part of the fiber ring resonator and a quantum dot-doped fiber (QDF) saturable absorber in the other half, is investigated. It is demonstrated that, depending on the device parameters and the input power of the signal and pump, various types of dynamic behaviors (such as bistability, monostability, and regenerative pulsation) can be observed in this intrinsic, optical bistable device. The proposed device can be exploited by optical communication networks to realize all-optical functionalities  

    Optical bistability in fiber ring resonator containing an erbium doped fiber amplifier and quantum dot doped fiber saturable absorber

    , Article Applied Optics ; Volume 51, Issue 29 , 2012 , Pages 7016-7024 ; 1559128X (ISSN) Tofighi, S ; Farshemi, S. S ; Sajjad, B ; Shahshahani, F ; Bahrampour, A. R ; Sharif University of Technology
    In this paper we study the optical bistability in a double coupler fiber ring resonator which consists of an erbium doped fiber amplifier (EDFA) in half part of the fiber ring and a quantum dot doped fiber (QDF) saturable absorber in the other half. The bistability is provided by the QDF section of the ring resonator. The EDFA is employed to reduce the switching power. The transmitted and reflected bistability characteristics are investigated. It is shown that the switching power for this new bistable device is less than 10 mW  

    Enhancement of Kerr nonlinearity at long wavelength in a quantum dot nanostructure

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 43, Issue 10 , August , 2011 , Pages 1759-1762 ; 13869477 (ISSN) Hossein Asadpour, S ; Sahrai, M ; Sadighi Bonabi, R ; Soltani, A ; Mahrami, H ; Sharif University of Technology
    The giant Kerr nonlinearity with reduced linear and nonlinear absorption in a four-level quantum dot by employing the tunnel coupling is investigated. It is shown that by enhancement of tunnel coupling value the Kerr nonlinearity increases and at the same time linear and nonlinear absorption reduces at the long wavelength which is very important for communicational applications. Enhanced of Kerr nonlinearity in a double quantum dots is investigated. It is found that the electron tunneling has an essential role to reducing the linear absorption and increasing the Kerr nonlinearity at long wavelength  

    A new approach to flexible humidity sensors using graphene quantum dots

    , Article Journal of Materials Chemistry C ; Volume 5, Issue 35 , 2017 , Pages 8966-8973 ; 20507534 (ISSN) Hosseini, Z. S ; Iraji Zad, A ; Ghiass, M. A ; Fardindoost, S ; Hatamie, S ; Sharif University of Technology
    Highly sensitive flexible humidity sensors based on graphene quantum dots (GQDs) were developed. The GQDs were prepared using a facile hydrothermal method and characterized considering morphological, structural, and compositional experiments. Then, their humidity sensing properties in correlation with flexibility characteristics were investigated. Good selectivity and response (∼390 for a RH change of 99%), broad detection range (1-100% RH), rather short response and recovery times (12 and 43 s, respectively) as well as flexibility were obtained, demonstrating that the GQD sensors have potential for application in wearable electronics and RH monitoring. Detection of hydrogen (H2) gas by the... 

    Tunable spherical graphene surface plasmon amplification by stimulated emission of radiation

    , Article Journal of Nanophotonics ; Volume 13, Issue 2 , 2019 ; 19342608 (ISSN) Ardakani, S. B ; Faez, R ; Sharif University of Technology
    SPIE  2019
    A structure is suggested for spasing. The presented surface plasmon amplification by stimulated emission of Radiation (SPASER) is made up of a graphene nanosphere, which supports localized surface plasmon modes, and a quantum dot array, acting as a gain medium. The gain medium is pumped by an external light source. Since all the plasmons are carried on a graphene platform, the structure features coherent surface plasmons with high confinement and large life time. All the structures are analyzed theoretically using full quantum mechanical description. The main advantage of the proposed SPASER is its simple tuning capability of changing graphene's Fermi level, which is performed by either... 

    Optical nanoprobes for chiral discrimination

    , Article Analyst ; Volume 145, Issue 20 , 2020 , Pages 6416-6434 Bigdeli, A ; Ghasemi, F ; Fahimi Kashani, N ; Abbasi Moayed, S ; Orouji, A ; Jafar Nezhad Ivrigh, Z ; Shahdost Fard, F ; Hormozi Nezhad, M. R ; Sharif University of Technology
    Royal Society of Chemistry  2020
    Chiral discrimination has always been a hot topic in chemical, food and pharmaceutical industries, especially when dealing with chiral drugs. Enantiomeric recognition not only leads to better understanding of the mechanism of molecular recognition in biological systems, but may further assist in developing useful molecular devices in biochemical and pharmaceutical studies. By emerging nanotechnology and exploiting nanomaterials in sensing applications, a great deal of attention has been given to the design of optical nanoprobes that are able to discriminate enantiomers of chiral analytes. This review explains how engineering nanoparticles (NPs) with desired physicochemical properties allows... 

    Quantum dots for photocatalysis: synthesis and environmental applications

    , Article Green Chemistry ; Volume 23, Issue 14 , 2021 , Pages 4931-4954 ; 14639262 (ISSN) Jouyandeh, M ; Mousavi Khadem, S ; Habibzadeh, S ; Esmaeili, A ; Abida, O ; Vatanpour, V ; Rabiee, N ; Bagherzadeh, M ; Iravani, S ; Saeb, M. R ; Varma, Rajender. S ; Sharif University of Technology
    Royal Society of Chemistry  2021
    Quantum dots (QDs) with unique properties have been widely employed for energy, environmental, and health care applications. Green natural resources, because of their renewability, sustainability, abundance, low cost, and environmental-friendliness, can be utilized for the synthesis of diverse nanoarchitectures. This critical review highlights the recent advancements in the greener and sustainable synthesis of carbon, graphene and metal-based QDs, as well as their significant environmental applications such as photocatalytic hydrogen production, degradation of hazardous contaminants/pollutants and reduction of CO2, with emphasis on the important challenges and future perspectives. © The... 

    Analytical results on coherent conductance in a general periodic quantum dot: Transfer matrix method

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 28, Issue 2 , 2005 , Pages 150-161 ; 13869477 (ISSN) Mardaani, M ; Shokri, A. A ; Esfarjani, K ; Sharif University of Technology
    In this work, we study the conductance of a general periodic quantum dot (QD) attached to ideal semi-infinite uniform metallic leads (nanocrystals), fully analytically. We propose a new general formula which relates conductance to transfer matrix (TM) for an isolated cell in the periodic dot. The equation describes exactly the dependence of the transmission coefficient (TC) on Fermi energy, dot-size, dot-lead coupling, and gate voltage for an arbitrary periodic dot. Then, we derive a nonlinear equation which gives the resonance, bound, and surface state energies. Finally, the TC has been calculated for gapless, single, and double gap models exactly. Moreover, we have also calculated the... 

    Spin filtering and spin diode devices in quantum wire systems

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 27, Issue 3 , 2005 , Pages 325-331 ; 13869477 (ISSN) Shokri, A. A ; Mardaani, M ; Esfarjani, K ; Sharif University of Technology
    Theoretical studies on the spin-dependent transmission and current-voltage characteristic in a mesoscopic system, which consists of two semi-infinite ferromagnetic (FM) leads (as source and drain) separated by a typical periodic quantum dot (QD) are presented. The calculations are based on the tight-binding model and transfer matrix method, and investigate the magnetoresistance (MR) and the spin polarization within the Landauer-Büttiker formalism. The spin-dependent transport behavior can be controlled via a gate voltage and an applied bias in the ballistic regime. The numerical results are shown for a periodic polymer chain with nonmagnetic (NM) and FM leads, and also, with two FM leads.... 

    Simply synthesized TiO2 nanorods as an effective scattering layer for quantum dot sensitized solar cells

    , Article Chinese Physics B ; Vol. 23, issue. 4 , 2014 Samadpour, M ; Zad, A. I ; Molaei, M ; Sharif University of Technology
    TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc = 497 mV, Jsc = 11.32 mA/cm2, FF = 0.54), in optimized structures. High efficiency can be obtained... 

    Monolithic quantum dot sensitized solar cells

    , Article Journal of Physics D: Applied Physics ; Volume 46, Issue 48 , December , 2013 ; 00223727 (ISSN) Samadpour, M ; Ghane, Z ; Ghazyani, N ; Tajabadi, F ; Taghavinia, N ; Sharif University of Technology
    We report a new design of solar cells based on semiconductor quantum dots (QDs), monolithic quantum dot sensitized solar cells (MQDSCs). MQDSCs offer the prospect of having lower cost and a simpler manufacturing process in comparison to conventional double substrate QDSCs. Our proposed monolithic QDSCs have a triple-layer structure, composed of a CdS sensitized mesoporous TiO2 photoanode, a scattering layer made by a core-shell structure of TiO 2/SiO2, and a carbon active/graphite counter electrode layer, which are all deposited on a single fluorine doped tin oxide (FTO) glass substrate. Mesoporous TiO2 was sensitized with CdS QDs by successive ionic layer adsorption and reaction. Here,... 

    Self-assembled, nanowire network electrodes for depleted bulk heterojunction solar cells

    , Article Advanced Materials ; Volume 25, Issue 12 , January , 2013 , Pages 1769-1773 ; 09359648 (ISSN) Lan, X ; Bai, J ; Masala, S ; Thon, S. M ; Ren, Y ; Kramer, I. J ; Hoogland, S ; Simchi, A ; Koleilat, G. I ; Paz-Soldan, D ; Ning, Z ; Labelle, A. J ; Kim, J. Y ; Jabbour, G ; Sargent, E. H ; Sharif University of Technology
    Herein, a solution-processed, bottom-up-fabricated, nanowire network electrode is developed. This electrode features a ZnO template which is converted into locally connected, infiltratable, TiO2 nanowires. This new electrode is used to build a depleted bulk heterojunction solar cell employing hybrid-passivated colloidal quantum dots. The new electrode allows the application of a thicker, and thus more light-absorbing, colloidal quantum dot active layer, from which charge extraction of an efficiency comparable to that obtained from a thinner, planar device could be obtained  

    Relative intensity noise study in two mode quantum dot laser

    , Article Optica Applicata ; Volume 41, Issue 4 , 2011 , Pages 961-970 ; 00785466 (ISSN) Horri, A ; Mirmoeini, S. Z ; Faez, R ; Sharif University of Technology
    In this paper, for the first time, we present a semiclassical noise model for InAs/GaAs quantum dot (QD) laser considering two photon modes, i.e., ground and first excited states lasing. This model is based on the five level rate equations. By using this model, the effect of temperature variations on relative intensity noise (RIN) of QD laser is investigated. We find that the RIN significantly degrades when excited state (ES) lasing emerges at high temperature. Furthermore, we investigate the influence of the quantum dot numbers on the RIN properties  

    Hybrid nanomaterials containing PAMAM, polyrotaxane and quantum dot blocks

    , Article Nano ; Volume 6, Issue 3 , June , 2011 , Pages 239-249 ; 17932920 (ISSN) Adeli, M ; Sarabi, R. S ; Sadeghi, E ; Sharif University of Technology
    Pseudopolyrotaxanes, Ps-PR, consisting of α-cyclodextrin rings, polyethylene glycol axes and end triazine groups were prepared and then were capped by amino-functionalized quantum dots, NH 2-QDs, to achieve polyrotaxanes. The amino-functionalized QDs stoppers of polyrotaxanes were used as core to synthesize polyamidoamine, PAMAM, dendrons divergently and hybrid nanomaterials were obtained. Synthesized hybrid nanomaterials were characterized by different spectroscopy, microscopy and thermal analysis methods. They were freely soluble in water and their aqueous solutions were stable at room temperature over several months. Due to their biocompatible backbone, high functionality and water... 

    A small signal circuit model of two mode InAs/GaAs quantum dot laser

    , Article IEICE Electronics Express ; Volume 8, Issue 4 , 2011 , Pages 245-251 ; 13492543 (ISSN) Horri, A ; Faez, R ; Hoseini, H. R ; Sharif University of Technology
    In this paper, for the first time, we present a small signal circuit model of quantum dot laser considering two photon modes, i.e., ground and first excited states lasing. By using the presented model, effect of temperature variations on modulation response of quantum dot laser is investigated. Simulation results of modulation response are in agreement with the numerical and experimental results reported by other researchers  

    Quasi core/shell lead sulfide/graphene quantum dots for bulk heterojunction solar cells

    , Article Journal of Physical Chemistry C ; Volume 119, Issue 33 , 2015 , Pages 18886-18895 ; 19327447 (ISSN) Tavakoli, M. M ; Aashuri, H ; Simchi, A ; Kalytchuk, S ; Fan, Z ; Sharif University of Technology
    American Chemical Society  2015
    Hybrid nanostructures combining semiconductor quantum dots and graphene are attracting increasing attention because of their optoelectronic properties promising for photovoltaic applications. We present a hot-injection synthesis of a colloidal nanostructure which we define as quasi core/shell PbS/graphene quantum dots due to the incomplete passivation of PbS surfaces with an ultrathin layer of graphene. Simulation by density functional theory of a prototypical model of a nonstoichiometric Pb-rich core (400 atoms) coated by graphene (20 atoms for each graphene sheet) indicates the possibility of surface passivation of (111) planes of PbS with graphene resulting in a decrease in trap states...