Proceedings for the Alaska Meeting on Fundamental Optical Processes in Semiconductors (AMFOPS 󈧅) Held in Girdwood, Alaska on August 5-10, 2001

DTIC Science & Technology

2002-05-31

Arizona Jagdeep Shah Lucent Technologies Advisory Committee Yasuhiko Arakawa University of Tokyo David Citrin Washington State University Hartmut...the dipole moment of the exciton in the dot. WA2 Fabrication and Optical Properties of Quantum Dots: GaN-Based and InAs Quantum Dots Yasuhiko

Optical Properties of Fluorescent Mixtures: Comparing Quantum Dots to Organic Dyes

ERIC Educational Resources Information Center

Hutchins, Benjamin M.; Morgan, Thomas T.; Ucak-Astarlioglu, Mine G.; Wlilliams, Mary Elizabeth

2007-01-01

The study describes and compares the size-dependent optical properties of organic dyes with those of semiconductor nanocrystals or quantum dots (QDs). The analysis shows that mixtures of QDs contain emission colors that are sum of the individual QD components.

Cryptography based on the absorption/emission features of multicolor semiconductor nanocrystal quantum dots.

PubMed

Zhou, Ming; Chang, Shoude; Grover, Chander

2004-06-28

Further to the optical coding based on fluorescent semiconductor quantum dots (QDs), a concept of using mixtures of multiple single-color QDs for creating highly secret cryptograms based on their absorption/emission properties was demonstrated. The key to readout of the optical codes is a group of excitation lights with the predetermined wavelengths programmed in a secret manner. The cryptograms can be printed on the surfaces of different objects such as valuable documents for security purposes.

Surface Plasmon Enhanced Sensitive Detection for Possible Signature of Majorana Fermions via a Hybrid Semiconductor Quantum Dot-Metal Nanoparticle System

PubMed Central

Chen, Hua-Jun; Zhu, Ka-Di

2015-01-01

In the present work, we theoretically propose an optical scheme to detect the possible signature of Majorana fermions via the optical pump-probe spectroscopy, which is very different from the current tunneling measurement based on electrical methods. The scheme consists of a metal nanoparticle and a semiconductor quantum dot coupled to a hybrid semiconductor/superconductor heterostructures. The results show that the probe absorption spectrum of the quantum dot presents a distinct splitting due to the existence of Majorana fermions. Owing to surface plasmon enhanced effect, this splitting will be more obvious, which makes Majorana fermions more easy to be detectable. The technique proposed here open the door for new applications ranging from robust manipulation of Majorana fermions to quantum information processing based on Majorana fermions. PMID:26310929

Optically programmable electron spin memory using semiconductor quantum dots.

PubMed

Kroutvar, Miro; Ducommun, Yann; Heiss, Dominik; Bichler, Max; Schuh, Dieter; Abstreiter, Gerhard; Finley, Jonathan J

2004-11-04

The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.

Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots.

PubMed

de Weerd, Chris; Shin, Yonghun; Marino, Emanuele; Kim, Joosung; Lee, Hyoyoung; Saeed, Saba; Gregorkiewicz, Tom

2017-10-31

Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other applications. Ideal materials for these applications should feature efficient radiative recombination and absorption transitions, altogether with spectral tunability over a wide range. Group IV semiconductor quantum dots can fulfill these requirements and serve as an alternative to the commonly used direct bandgap materials containing toxic and/or rare elements. Here, we present optical properties of butyl-terminated Si and Ge quantum dots and compare them to those of graphene quantum dots, finding them remarkably similar. We investigate their time-resolved photoluminescence emission as well as the photoluminescence excitation and linear absorption spectra. We contemplate that their emission characteristics indicate a (semi-) resonant activation of the emitting channel; the photoluminescence excitation shows characteristics similar to those of a molecule. The optical density is consistent with band-to-band absorption processes originating from core-related states. Hence, these observations strongly indicate a different microscopic origin for absorption and radiative recombination in the three investigated quantum dot systems.

Emission polarization control in semiconductor quantum dots coupled to a photonic crystal microcavity.

PubMed

Gallardo, E; Martínez, L J; Nowak, A K; van der Meulen, H P; Calleja, J M; Tejedor, C; Prieto, I; Granados, D; Taboada, A G; García, J M; Postigo, P A

2010-06-07

We study the optical emission of single semiconductor quantum dots weakly coupled to a photonic-crystal micro-cavity. The linearly polarized emission of a selected quantum dot changes continuously its polarization angle, from nearly perpendicular to the cavity mode polarization at large detuning, to parallel at zero detuning, and reversing sign for negative detuning. The linear polarization rotation is qualitatively interpreted in terms of the detuning dependent mixing of the quantum dot and cavity states. The present result is relevant to achieve continuous control of the linear polarization in single photon emitters.

High-power quantum-dot tapered tunable external-cavity lasers based on chirped and unchirped structures.

PubMed

Haggett, Stephanie; Krakowski, Michel; Montrosset, Ivo; Cataluna, Maria Ana

2014-09-22

A high-power tunable external cavity laser configuration with a tapered quantum-dot semiconductor optical amplifier at its core is presented, enabling a record output power for a broadly tunable semiconductor laser source in the 1.2 - 1.3 µm spectral region. Two distinct optical amplifiers are investigated, using either chirped or unchirped quantum-dot structures, and their merits are compared, considering the combination of tunability and high output power generation. At 1230 nm, the chirped quantum-dot laser achieved a maximum power of 0.62 W and demonstrated nearly 100-nm tunability. The unchirped laser enabled a tunability range of 32 nm and at 1254 nm generated a maximum power of 0.97 W, representing a 22-fold increase in output power compared with similar narrow-ridge external-cavity lasers at the same current density.

Plasmonic giant quantum dots: Hybrid nanostructures for truly simultaneous optical imaging, photothermal effect and thermometry

DOE PAGES

Karan, Niladri S.; Keller, Aaron M.; Sampat, Siddharth; ...

2015-02-09

Hybrid semiconductor–metal nanoscale constructs are of both fundamental and practical interest. Semiconductor nanocrystals are active emitters of photons when stimulated optically, while the interaction of light with nanosized metal objects results in scattering and ohmic damping due to absorption. In a combined structure, the properties of both components can be realized together. At the same time, metal–semiconductor coupling may intervene to modify absorption and/or emission processes taking place in the semiconductor, resulting in a range of effects from photoluminescence quenching to enhancement. We show here that photostable ‘giant’ quantum dots when placed at the center of an ultrathin gold shellmore » retain their key optical property of bright and blinking-free photoluminescence, while the metal shell imparts efficient photothermal transduction. The latter is despite the highly compact total particle size (40–60 nm “inorganic” diameter and <100 nm hydrodynamic diameter) and the very thin nature of the optically transparent Au shell. Furthermore, the sensitivity of the quantum dot emission to local temperature provides a novel internal thermometer for recording temperature during infrared irradiation-induced photothermal heating.« less

Influence of optical pumping wavelength on the ultrafast gain and phase recovery acceleration of quantum-dot semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Kim, Jungho

2013-10-01

We numerically investigate the influence of the optical pumping wavelength on the ultrafast gain and phase recovery acceleration of quantum-dot (QD) semiconductor optical amplifiers (SOAs) by solving 1088 coupled rate equations. The temporal variations of the gain and phase recovery response at the ground state (GS) of QDs are calculated at various signal wavelengths when the optical pumping wavelengths at the excited state (ES) of QDs are varied. The phase recovery response is fastest when the wavelength of the signal and pumping beams corresponds to the respective emission wavelength of the GS and the ES in the same size of QDs. The absorption efficiency of the optical pumping beam at the ES is determined by the Lorentzian line shape function of the homogeneous broadening.

Few-Photon Model of the Optical Emission of Semiconductor Quantum Dots

NASA Astrophysics Data System (ADS)

Richter, Marten; Carmele, Alexander; Sitek, Anna; Knorr, Andreas

2009-08-01

The Jaynes-Cummings model provides a well established theoretical framework for single electron two level systems in a radiation field. Similar exactly solvable models for semiconductor light emitters such as quantum dots dominated by many particle interactions are not known. We access these systems by a generalized cluster expansion, the photon-probability cluster expansion: a reliable approach for few-photon dynamics in many body electron systems. As a first application, we discuss vacuum Rabi oscillations and show that their amplitude determines the number of electrons in the quantum dot.

Electric field induced optical gain of a hydrogenic impurity in a Cd{sub 0.8}Zn{sub 0.2}Se/ZnSe parabolic quantum dot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jasmine, P. Christina Lily; Peter, A. John, E-mail: a.john.peter@gmail.com

The dependence of electric field on the electronic and optical properties is investigated in a Cd{sub 0.8}Zn{sub 0.2}Se/ZnSe quantum dot. The hydrogenic binding energy, in the presence of electric field, is calculated with the spatial confinement effect. The electric field dependent optical gain with the photon energy is found using compact density matrix method. The results show that the electric field has a great influence on the optical properties of II-VI semiconductor quantum dot.

Single photon sources with single semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Shan, Guang-Cun; Yin, Zhang-Qi; Shek, Chan Hung; Huang, Wei

2014-04-01

In this contribution, we briefly recall the basic concepts of quantum optics and properties of semiconductor quantum dot (QD) which are necessary to the understanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantum emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as optical properties of the QDs. We then review the localization of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and performances in terms of strong coupling regime, efficiency, directionality, and polarization control. Furthermore, we will discuss the recent progress on the fabrication of single photon sources, and various approaches for embedding single QDs into microcavities or photonic crystal nanocavities and show how to extend the wavelength range. We focus in particular on new generations of electrically driven QD single photon source leading to high repetition rates, strong coupling regime, and high collection efficiencies at elevated temperature operation. Besides, new developments of room temperature single photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for practical single-photon sources are also discussed.

Classical and quantum optical correlation effects between single quantum dots: The role of the hopping photon

NASA Astrophysics Data System (ADS)

Hughes, S.; Gotoh, H.; Kamada, H.

2006-09-01

We present a theoretical study of photon-coupled single quantum dots in a semiconductor. A series of optical effects are demonstrated, including a subradiant dark resonance, superradiance, reversible spontaneous emission decay, and pronounced exciton entanglement. Both classical and quantum optical approaches are presented using a self-consistent formalism that treats real and virtual photon exchange on an equal footing and can account for different quantum dot properties, surface effects, and retardation in the dipole-dipole coupling, all of which are shown to play a non-negligible role.

Phase Recovery Acceleration of Quantum-Dot Semiconductor Optical Amplifiers by Optical Pumping to Quantum-Well Wetting Layer

NASA Astrophysics Data System (ADS)

Kim, Jungho

2013-11-01

We theoretically investigate the phase recovery acceleration of quantum-dot (QD) semiconductor optical amplifiers (SOAs) by means of the optical pump injection to the quantum-well (QW) wetting layer (WL). We compare the ultrafast gain and phase recovery responses of QD SOAs in either the electrical or the optical pumping scheme by numerically solving 1088 coupled rate equations. The ultrafast gain recovery responses on the order of sub-picosecond are nearly the same for the two pumping schemes. The ultrafast phase recovery is not significantly accelerated by increasing the electrical current density, but greatly improved by increasing the optical pumping power to the QW WL. Because the phase recovery time of QD SOAs with the optical pumping scheme can be reduced down to several picoseconds, the complete phase recovery can be achieved when consecutive pulse signals with a repetition rate of 100 GHz is injected.

Monolithically integrated quantum dot optical modulator with Semiconductor optical amplifier for short-range optical communications

NASA Astrophysics Data System (ADS)

Yamamoto, Naokatsu; Akahane, Kouichi; Umezawa, Toshimasa; Kawanishi, Tetsuya

2015-04-01

A monolithically integrated quantum dot (QD) optical gain modulator (OGM) with a QD semiconductor optical amplifier (SOA) was successfully developed. Broadband QD optical gain material was used to achieve Gbps-order high-speed optical data transmission, and an optical gain change as high as approximately 6-7 dB was obtained with a low OGM voltage of 2.0 V. Loss of optical power due to insertion of the device was also effectively compensated for by the SOA section. Furthermore, it was confirmed that the QD-OGM/SOA device helped achieve 6.0-Gbps error-free optical data transmission over a 2.0-km-long photonic crystal fiber. We also successfully demonstrated generation of Gbps-order, high-speed, and error-free optical signals in the >5.5-THz broadband optical frequency bandwidth larger than the C-band. These results suggest that the developed monolithically integrated QD-OGM/SOA device will be an advantageous and compact means of increasing the usable optical frequency channels for short-reach communications.

Plasmonic giant quantum dots: hybrid nanostructures for truly simultaneous optical imaging, photothermal effect and thermometry† †Electronic supplementary information (ESI) available: Further information on Au shelling chemistry and imaging of the Au shell by electron microscopy. Figures and Movie. See DOI: 10.1039/c5sc00020c

PubMed Central

Karan, Niladri S.; Keller, Aaron M.; Sampat, Siddharth; Roslyak, Oleksiy; Arefin, Ayesha; Hanson, Christina J.; Casson, Joanna L.; Desireddy, Anil; Ghosh, Yagnaseni; Piryatinski, Andrei; Iyer, Rashi; Htoon, Han; Malko, Anton V.

2015-01-01

Hybrid semiconductor–metal nanoscale constructs are of both fundamental and practical interest. Semiconductor nanocrystals are active emitters of photons when stimulated optically, while the interaction of light with nanosized metal objects results in scattering and ohmic damping due to absorption. In a combined structure, the properties of both components can be realized together. At the same time, metal–semiconductor coupling may intervene to modify absorption and/or emission processes taking place in the semiconductor, resulting in a range of effects from photoluminescence quenching to enhancement. We show here that photostable ‘giant’ quantum dots when placed at the center of an ultrathin gold shell retain their key optical property of bright and blinking-free photoluminescence, while the metal shell imparts efficient photothermal transduction. The latter is despite the highly compact total particle size (40–60 nm “inorganic” diameter and <100 nm hydrodynamic diameter) and the very thin nature of the optically transparent Au shell. Importantly, the sensitivity of the quantum dot emission to local temperature provides a novel internal thermometer for recording temperature during infrared irradiation-induced photothermal heating. PMID:29163879

Semiconductor Quantum Dots for Biomedicial Applications

PubMed Central

Shao, Lijia; Gao, Yanfang; Yan, Feng

2011-01-01

Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can be used as labels for the electrochemical detection of DNA or proteins. This article reviews the synthesis and toxicity of QDs and their optical and electrochemical bioanalytical applications. Especially the application of QDs in biomedicine such as delivering, cell targeting and imaging for cancer research, and in vivo photodynamic therapy (PDT) of cancer are briefly discussed. PMID:22247690

Quantum memory on a charge qubit in an optical microresonator

NASA Astrophysics Data System (ADS)

Tsukanov, A. V.

2017-10-01

A quantum-memory unit scheme on the base of a semiconductor structure with quantum dots is proposed. The unit includes a microresonator with single and double quantum dots performing frequencyconverter and charge-qubit functions, respectively. The writing process is carried out in several stages and it is controlled by optical fields of the resonator and laser. It is shown that, to achieve high writing probability, it is necessary to use high-Q resonators and to be able to suppress relaxation processes in quantum dots.

Effect of wetting-layer density of states on the gain and phase recovery dynamics of quantum-dot semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Kim, Jungho; Yu, Bong-Ahn

2015-03-01

We numerically investigate the effect of the wetting-layer (WL) density of states on the gain and phase recovery dynamics of quantum-dot semiconductor optical amplifiers in both electrical and optical pumping schemes by solving 1088 coupled rate equations. The temporal variations of the ultrafast gain and phase recovery responses at the ground state (GS) are calculated as a function of the WL density of states. The ultrafast gain recovery responses do not significantly depend on the WL density of states in the electrical pumping scheme and the three optical pumping schemes such as the optical pumping to the WL, the optical pumping to the excited state ensemble, and the optical pumping to the GS ensemble. The ultrafast phase recovery responses are also not significantly affected by the WL density of states except the optical pumping to the WL, where the phase recovery component caused by the WL becomes slowed down as the WL density of states increases.

Voltage-controlled quantum light from an atomically thin semiconductor

NASA Astrophysics Data System (ADS)

Chakraborty, Chitraleema; Kinnischtzke, Laura; Goodfellow, Kenneth M.; Beams, Ryan; Vamivakas, A. Nick

2015-06-01

Although semiconductor defects can often be detrimental to device performance, they are also responsible for the breadth of functionality exhibited by modern optoelectronic devices. Artificially engineered defects (so-called quantum dots) or naturally occurring defects in solids are currently being investigated for applications ranging from quantum information science and optoelectronics to high-resolution metrology. In parallel, the quantum confinement exhibited by atomically thin materials (semi-metals, semiconductors and insulators) has ushered in an era of flatland optoelectronics whose full potential is still being articulated. In this Letter we demonstrate the possibility of leveraging the atomically thin semiconductor tungsten diselenide (WSe2) as a host for quantum dot-like defects. We report that this previously unexplored solid-state quantum emitter in WSe2 generates single photons with emission properties that can be controlled via the application of external d.c. electric and magnetic fields. These new optically active quantum dots exhibit excited-state lifetimes on the order of 1 ns and remarkably large excitonic g-factors of 10. It is anticipated that WSe2 quantum dots will provide a novel platform for integrated solid-state quantum photonics and quantum information processing, as well as a rich condensed-matter physics playground with which to explore the coupling of quantum dots and atomically thin semiconductors.

Ultra-broad band, low power, highly efficient coherent wavelength conversion in quantum dot SOA.

PubMed

Contestabile, G; Yoshida, Y; Maruta, A; Kitayama, K

2012-12-03

We report broadband, all-optical wavelength conversion over 100 nm span, in full S- and C-band, with positive conversion efficiency with low optical input power exploiting dual pump Four-Wave-Mixing in a Quantum Dot Semiconductor Optical Amplifier (QD-SOA). We also demonstrate by Error Vector Magnitude analysis the full transparency of the conversion scheme for coherent modulation formats (QPSK, 8-PSK, 16-QAM, OFDM-16QAM) in the whole C-band.

Semiconductor Nanomaterials-Based Fluorescence Spectroscopic and Matrix-Assisted Laser Desorption/Ionization (MALDI) Mass Spectrometric Approaches to Proteome Analysis

PubMed Central

Kailasa, Suresh Kumar; Cheng, Kuang-Hung; Wu, Hui-Fen

2013-01-01

Semiconductor quantum dots (QDs) or nanoparticles (NPs) exhibit very unusual physico-chemcial and optical properties. This review article introduces the applications of semiconductor nanomaterials (NMs) in fluorescence spectroscopy and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for biomolecule analysis. Due to their unique physico-chemical and optical properties, semiconductors NMs have created many new platforms for investigating biomolecular structures and information in modern biology. These semiconductor NMs served as effective fluorescent probes for sensing proteins and cells and acted as affinity or concentrating probes for enriching peptides, proteins and bacteria proteins prior to MALDI-MS analysis. PMID:28788422

Monolithically integrated quantum dot optical modulator with semiconductor optical amplifier for thousand and original band optical communication

NASA Astrophysics Data System (ADS)

Yamamoto, Naokatsu; Akahane, Kouichi; Umezawa, Toshimasa; Matsumoto, Atsushi; Kawanishi, Tetsuya

2016-04-01

A monolithically integrated quantum dot (QD) optical gain modulator (OGM) with a QD semiconductor optical amplifier (SOA) was successfully developed with T-band (1.0 µm waveband) and O-band (1.3 µm waveband) QD optical gain materials for Gbps-order, high-speed optical data generation. The insertion loss due to coupling between the device and the optical fiber was effectively compensated for by the SOA section. It was also confirmed that the monolithic QD-OGM/SOA device enabled >4.8 Gbps optical data generation with a clear eye opening in the T-band. Furthermore, we successfully demonstrated error-free 4.8 Gbps optical data transmissions in each of the six wavelength channels over a 10-km-long photonic crystal fiber using the monolithic QD-OGM/SOA device in multiple O-band wavelength channels, which were generated by the single QD gain chip. These results suggest that the monolithic QD-OGM/SOA device will be advantageous in ultra-broadband optical frequency systems that utilize the T+O-band for short- and medium-range optical communications.

Unbound states in quantum heterostructures

PubMed Central

Bastard, G

2006-01-01

We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron – hole states. The part played by Auger scattering in Quantum Dots is also discussed.

Development and Application of Explicitly Correlated Wave Function Based Methods for the Investigation of Optical Properties of Semiconductor Nanomaterials

NASA Astrophysics Data System (ADS)

Elward, Jennifer Mary

Semiconductor nanoparticles, or quantum dots (QDs), are well known to have very unique optical and electronic properties. These properties can be controlled and tailored as a function of several influential factors, including but not limited to the particle size and shape, effect of composition and heterojunction as well as the effect of ligand on the particle surface. This customizable nature leads to extensive experimental and theoretical research on the capabilities of these quantum dots for many application purposes. However, in order to be able to understand and thus further the development of these materials, one must first understand the fundamental interaction within these nanoparticles. In this thesis, I have developed a theoretical method which is called electron-hole explicitly correlated Hartee-Fock (eh-XCHF). It is a variational method for solving the electron-hole Schrodinger equation and has been used in this work to study electron-hole interaction in semiconductor quantum dots. The method was benchmarked with respect to a parabolic quantum dot system, and ground state energy and electron-hole recombination probability were computed. Both of these properties were found to be in good agreement with expected results. Upon successful benchmarking, I have applied the eh-XCHF method to study optical properties of several quantum dot systems including the effect of dot size on exciton binding energy and recombination probability in a CdSe quantum dot, the effect of shape on a CdSe quantum dot, the effect of heterojunction on a CdSe/ZnS quantum dot and the effect of quantum dot-biomolecule interaction within a CdSe-firefly Luciferase protein conjugate system. As metrics for assessing the effect of these influencers on the electron-hole interaction, the exciton binding energy, electron-hole recombination probability and the average electron-hole separation distance have been computed. These excitonic properties have been found to be strongly infuenced by the changing composition of the particle. It has also been found through this work that the explicitly correlated method performs very well when computing these properties as it provides a feasible computational route to compare to both experimental and other theoretical results.

Effects of increasing number of rings on the ion sensing ability of CdSe quantum dots: a theoretical study

NASA Astrophysics Data System (ADS)

Malik, Pragati; Kakkar, Rita

2018-04-01

A computational study on the structural and electronic properties of a special class of artificial atoms, known as quantum dots, has been carried out. These are semiconductors with unique optical and electronic properties and have been widely used in various applications, such as bio-sensing, bio-imaging, and so on. We have considered quantum dots belonging to II-VI types of semiconductors, due to their wide band gap, possession of large exciton binding energies and unique optical and electronic properties. We have studied their applications as chemical ion sensors by beginning with the study of the ion sensing ability of (CdSe) n ( n = 3, 6, 9 which are in the size range of 0.24, 0.49, 0.74 nm, respectively) quantum dots for cations of the zinc triad, namely Zn2+, Cd2+, Hg2+, and various anions of biological and environmental importance, and studied the effect of increasing number of rings on their ion sensing ability. The various structural, electronic, and optical properties, their interaction energies, and charge transfer on interaction with metal ions and anions have been calculated and reported. Our studies indicate that the CdSe quantum dots can be employed as sensors for both divalent cations and anions, but they can sense cations better than anions.

Experimental observation of Fano effect in Ag nanoparticle-CdTe quantum dot hybrid system

NASA Astrophysics Data System (ADS)

Gurung, Sabina; Jayabalan, J.; Singh, Asha; Khan, Salahuddin; Chari, Rama

2018-04-01

We have experimentally measured the optical properties of Ag nanoparticle-CdTe quantum dot hybrid system and compared it with that of bare CdTe quantum dot colloid. It has been shown that the photoluminescence line shape of CdTe quantum dots becomes asymmetric in presence of Ag nanoparticles. The observed changes in the PL spectrum closely match the expected changes in the line shape due to Fano interaction between discrete level and continuum levels. Our experiment shows that a very small fraction of metal nanoparticles in the metal-semiconductor hybrid is sufficient to induce such changes in line shape which is in contrary to the earlier reported theoretical prediction on metal-semiconductor hybrid.

High-performance semiconductor quantum-dot single-photon sources

NASA Astrophysics Data System (ADS)

Senellart, Pascale; Solomon, Glenn; White, Andrew

2017-11-01

Single photons are a fundamental element of most quantum optical technologies. The ideal single-photon source is an on-demand, deterministic, single-photon source delivering light pulses in a well-defined polarization and spatiotemporal mode, and containing exactly one photon. In addition, for many applications, there is a quantum advantage if the single photons are indistinguishable in all their degrees of freedom. Single-photon sources based on parametric down-conversion are currently used, and while excellent in many ways, scaling to large quantum optical systems remains challenging. In 2000, semiconductor quantum dots were shown to emit single photons, opening a path towards integrated single-photon sources. Here, we review the progress achieved in the past few years, and discuss remaining challenges. The latest quantum dot-based single-photon sources are edging closer to the ideal single-photon source, and have opened new possibilities for quantum technologies.

PREFACE: Proceedings of the First Workshop of the EU RT Network `Photon-Mediated Phenomena in Semiconductor Nanostructures' (Gregynog, Wales, UK, 28--31 March 2003)

NASA Astrophysics Data System (ADS)

Ivanov, Alexei L.

2004-09-01

The EU Research Training Network `Photon-Mediated Phenomena in Semiconductor Nanostructures' (HPRN-CT-2002-00298) comprises seven teams from across Europe: Cambridge, Cardiff, Dortmund, Heraklion, Grenoble, Lund and Paderborn (for details see the Network website http://www.astro.cardiff.ac.uk/research/PMPnetwork/index.html). The first workshop of the Network was held at Gregynog Hall, a conference centre in the beautiful countryside of mid-Wales. There were 44 participants who attended the meeting (7 from France, 2 from Japan, 3 from Germany, 1 from Greece, 2 from Russia, 3 from Sweden, 23 from UK and 3 from USA). Of these, 57% were students and young postdoctoral research associates. The talks presented at the meeting were mainly devoted to linear and nonlinear optics of semiconductor nanostructures. Thus the review and research papers included in this special issue of Journal of Physics: Condensed Matter deal with the exciton-mediated optical phenomena in semiconductor quantum wires, quantum wells, planar and spherical microcavities and self-assembled quantum dots. The specific topics covered by the proceedings are exciton-mediated optics, including lasing, of semiconductor quantum wires Bose-Einstein condensation of excitons and microcavity polaritons diffusion, thermalization and photoluminescence of free carriers and excitons in GaAs coupled quantum wells polaritons in semiconductor microcavities exciton-mediated optics of semiconductor photonic dots optical nonlinearities of biexciton waves optics of self-assembled quantum dots photosensitive metal oxides films On the first day of the workshop, a special session on presentation skills, lead by Mike Edmunds, was organized for the young researchers. The meeting concluded with a round-table discussion at which key questions on research, organization and management of the Network were identified and discussed. The second workshop of the Network, organized and chaired by George Kiriakidis, took place at Hersonissos (Crete, Greece) in October 2003. The forthcoming third workshop, organized by Detlef Schikora and Ulrike Woggon, will be held in Paderborn (conference part) and Dortmund (training part) from 4 October 4 through 7 October 2004 (for details visit the Network website). Finally, I would like to thank my colleagues, Celestino Creatore, Nikolay Nikolaev, Lois Smallwood and Andrew Smith, for their help with preparation of the Proceedings.

Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

NASA Astrophysics Data System (ADS)

Dey, Anup; Maiti, Biswajit; Chanda Sarkar, Debasree

2014-04-01

A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k→) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1-xCdxTe, and In1-xGaxAsyP1-y lattice matched to InP, as example of III-V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

Electroluminescence Studies on Longwavelength Indium Arsenide Quantum Dot Microcavities Grown on Gallium Arsenide

DTIC Science & Technology

2011-12-01

communication links using VCSEL arrays [1, 2], medical imaging using super luminescent diodes [3], and tunable lasers capable of remotely sensing...increase the efficiency of solar cells [6, 7, 8], vastly improve photo detector sensitivity [9], and provide optical memory storage densities predicted...semiconductor lasers” Applied Physics B: Lasers and Optics, Volume 90, Number 2, 2008, Pages 339-343. 6. Nozik, A.J. “Quantum dot solar cells

Artful and multifaceted applications of carbon dot in biomedicine.

PubMed

Jaleel, Jumana Abdul; Pramod, K

2018-01-10

Carbon dots (C-dots) are luminescent carbon nanomaterial having good biocompatibility and low toxicity. The characteristic fluorescence emission property of C-dots establishes their role in optical imaging. C-dots which are superior to fluorescent dyes and semiconductor quantum dots act as a safer in vivo imaging probe. Apart from their bioimaging application, other applications in biomedicine such as drug delivery, cancer therapy, and gene delivery were studied. In this review, we present multifaceted applications of C-dots along with their synthesis, surface passivation, doping, and toxicity profile. Copyright © 2017 Elsevier B.V. All rights reserved.

Direct photonic coupling of a semiconductor quantum dot and a trapped ion.

PubMed

Meyer, H M; Stockill, R; Steiner, M; Le Gall, C; Matthiesen, C; Clarke, E; Ludwig, A; Reichel, J; Atatüre, M; Köhl, M

2015-03-27

Coupling individual quantum systems lies at the heart of building scalable quantum networks. Here, we report the first direct photonic coupling between a semiconductor quantum dot and a trapped ion and we demonstrate that single photons generated by a quantum dot controllably change the internal state of a Yb^{+} ion. We ameliorate the effect of the 60-fold mismatch of the radiative linewidths with coherent photon generation and a high-finesse fiber-based optical cavity enhancing the coupling between the single photon and the ion. The transfer of information presented here via the classical correlations between the σ_{z} projection of the quantum-dot spin and the internal state of the ion provides a promising step towards quantum-state transfer in a hybrid photonic network.

Characterization of CuCl quantum dots grown in NaCl single crystals via optical measurements, X-ray diffraction, and transmission electron microscopy

NASA Astrophysics Data System (ADS)

Miyajima, Kensuke; Akatsu, Tatsuro; Itoh, Ken

2018-05-01

We evaluated the crystal size, shape, and alignment of the lattice planes of CuCl quantum dots (QDs) embedded in NaCl single crystals by optical measurements, X-ray diffraction (XRD) patterns, and transmission electron microscopy (TEM). We obtained, for the first time, an XRD pattern and TEM images for CuCl QDs in NaCl crystals. The XRD pattern showed that the lattice planes of the CuCl QDs were parallel to those of the NaCl crystals. In addition, the size of the QDs was estimated from the diffraction width. It was apparent from the TEM images that almost all CuCl QDs were polygonal, although some cubic QDs were present. The mean size and size distribution of the QDs were also obtained. The dot size obtained from optical measurements, XRD, and TEM image were almost consistent. Our new findings can help to reveal the growth mechanism of semiconductor QDs embedded in a crystallite matrix. In addition, this work will play an important role in progressing the study of optical phenomena originating from assembled semiconductor QDs.

Semiconductor quantum dot-sensitized solar cells.

PubMed

Tian, Jianjun; Cao, Guozhong

2013-10-31

Semiconductor quantum dots (QDs) have been drawing great attention recently as a material for solar energy conversion due to their versatile optical and electrical properties. The QD-sensitized solar cell (QDSC) is one of the burgeoning semiconductor QD solar cells that shows promising developments for the next generation of solar cells. This article focuses on recent developments in QDSCs, including 1) the effect of quantum confinement on QDSCs, 2) the multiple exciton generation (MEG) of QDs, 3) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions for future research on QDSCs. Although the efficiency of QDSCs is still low, we think there will be major breakthroughs in developing QDSCs in the future.

Quantum Entanglement of Quantum Dot Spin Using Flying Qubits

DTIC Science & Technology

2015-05-01

QUANTUM ENTANGLEMENT OF QUANTUM DOT SPIN USING FLYING QUBITS UNIVERSITY OF MICHIGAN MAY 2015 FINAL TECHNICAL REPORT APPROVED FOR PUBLIC RELEASE...To) SEP 2012 – DEC 2014 4. TITLE AND SUBTITLE QUANTUM ENTANGLEMENT OF QUANTUM DOT SPIN USING FLYING QUBITS 5a. CONTRACT NUMBER FA8750-12-2-0333...been to advance the frontier of quantum entangled semiconductor electrons using ultrafast optical techniques. The approach is based on

Direct optical state preparation of the dark exciton in a quantum dot

NASA Astrophysics Data System (ADS)

Lüker, S.; Kuhn, T.; Reiter, D. E.

2015-11-01

Because of their weak coupling to the electromagnetic field, dark excitons in semiconductor quantum dots possess extremely long lifetimes, which makes them attractive candidates for quantum information processing. On the other hand, the preparation and manipulation of dark states is challenging, because commonly used optical excitation mechanisms are not applicable. We propose an efficient mechanism for the deterministic preparation of the dark exciton exploiting the application of a tilted magnetic field and the optical excitation with a chirped, i.e., frequency modulated, laser pulse.

Quantum dots and nanocomposites.

PubMed

Mansur, Herman Sander

2010-01-01

Quantum dots (QDs), also known as semiconducting nanoparticles, are promising zero-dimensional advanced materials because of their nanoscale size and because they can be engineered to suit particular applications such as nonlinear optical devices (NLO), electro-optical devices, and computing applications. QDs can be joined to polymers in order to produce nanocomposites which can be considered a scientific revolution of the 21st century. One of the fastest moving and most exciting interfaces of nanotechnology is the use of QDs in medicine, cell and molecular biology. Recent advances in nanomaterials have produced a new class of markers and probes by conjugating semiconductor QDs with biomolecules that have affinities for binding with selected biological structures. The nanoscale of QDs ensures that they do not scatter light at visible or longer wavelengths, which is important in order to minimize optical losses in practical applications. Moreover, at this scale, quantum confinement and surface effects become very important and therefore manipulation of the dot diameter or modification of its surface allows the properties of the dot to be controlled. Quantum confinement affects the absorption and emission of photons from the dot. Thus, the absorption edge of a material can be tuned by control of the particle size. This paper reviews developments in the myriad of possibilities for the use of semiconductor QDs associated with molecules producing novel hybrid nanocomposite systems for nanomedicine and bioengineering applications.

Quantum dots and nanoparticles for photodynamic and radiation therapies of cancer

PubMed Central

Juzenas, Petras; Chen, Wei; Sun, Ya-Ping; Coelho, Manuel Alvaro Neto; Generalov, Roman; Generalova, Natalia; Christensen, Ingeborg Lie

2009-01-01

Semiconductor quantum dots and nanoparticles composed of metals, lipids or polymers have emerged with promising applications for early detection and therapy of cancer. Quantum dots with unique optical properties are commonly composed of cadmium contained semiconductors. Cadmium is potentially hazardous, and toxicity of such quantum dots to living cells, and humans, is not yet systematically investigated. Therefore, search for less toxic materials with similar targeting and optical properties is of further interest. Whereas, the investigation of luminescence nanoparticles as light sources for cancer therapy is very interesting. Despite advances in neurosurgery and radiotherapy the prognosis for patients with malignant gliomas has changed little for the last decades. Cancer treatment requires high accuracy in delivering ionizing radiation to reduce toxicity to surrounding tissues. Recently some research has been focused in developing photosensitizing quantum dots for production of radicals upon absorption of visible light. In spite of the fact that visible light is safe, this approach is suitable to treat only superficial tumours. Ionizing radiation (X-rays and gamma rays) penetrate much deeper thus offering a big advantage in treating patients with tumours in internal organs. Such concept of using quantum dots and nanoparticles to yield electrons and radicals in photodynamic and radiation therapies as well their combination is reviewed in this article. PMID:18840487

Hybrid quantum-classical modeling of quantum dot devices

NASA Astrophysics Data System (ADS)

Kantner, Markus; Mittnenzweig, Markus; Koprucki, Thomas

2017-11-01

The design of electrically driven quantum dot devices for quantum optical applications asks for modeling approaches combining classical device physics with quantum mechanics. We connect the well-established fields of semiclassical semiconductor transport theory and the theory of open quantum systems to meet this requirement. By coupling the van Roosbroeck system with a quantum master equation in Lindblad form, we introduce a new hybrid quantum-classical modeling approach, which provides a comprehensive description of quantum dot devices on multiple scales: it enables the calculation of quantum optical figures of merit and the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way. We construct the interface between both theories in such a way, that the resulting hybrid system obeys the fundamental axioms of (non)equilibrium thermodynamics. We show that our approach guarantees the conservation of charge, consistency with the thermodynamic equilibrium and the second law of thermodynamics. The feasibility of the approach is demonstrated by numerical simulations of an electrically driven single-photon source based on a single quantum dot in the stationary and transient operation regime.

Phonon impact on optical control schemes of quantum dots: Role of quantum dot geometry and symmetry

NASA Astrophysics Data System (ADS)

Lüker, S.; Kuhn, T.; Reiter, D. E.

2017-12-01

Phonons strongly influence the optical control of semiconductor quantum dots. When modeling the electron-phonon interaction in several theoretical approaches, the quantum dot geometry is approximated by a spherical structure, though typical self-assembled quantum dots are strongly lens-shaped. By explicitly comparing simulations of a spherical and a lens-shaped dot using a well-established correlation expansion approach, we show that, indeed, lens-shaped dots can be exactly mapped to a spherical geometry when studying the phonon influence on the electronic system. We also give a recipe to reproduce spectral densities from more involved dots by rather simple spherical models. On the other hand, breaking the spherical symmetry has a pronounced impact on the spatiotemporal properties of the phonon dynamics. As an example we show that for a lens-shaped quantum dot, the phonon emission is strongly concentrated along the direction of the smallest axis of the dot, which is important for the use of phonons for the communication between different dots.

Ring-shaped active mode-locked tunable laser using quantum-dot semiconductor optical amplifier

NASA Astrophysics Data System (ADS)

Zhang, Mingxiao; Wang, Yongjun; Liu, Xinyu

2018-03-01

In this paper, a lot of simulations has been done for ring-shaped active mode-locked lasers with quantum-dot semiconductor optical amplifier (QD-SOA). Based on the simulation model of QD-SOA, we discussed about the influence towards mode-locked waveform frequency and pulse caused by QD-SOA maximum mode peak gain, active layer loss coefficient, bias current, incident light pulse, fiber nonlinear coefficient. In the meantime, we also take the tunable performance of the laser into consideration. Results showed QD-SOA a better performance than original semiconductor optical amplifier (SOA) in recovery time, line width, and nonlinear coefficients, which makes it possible to output a locked-mode impulse that has a higher impulse power, narrower impulse width as well as the phase is more easily controlled. After a lot of simulations, this laser can realize a 20GHz better locked-mode output pulse after 200 loops, where the power is above 17.5mW, impulse width is less than 2.7ps, moreover, the tunable wavelength range is between 1540nm-1580nm.

PREFACE: Quantum Dot 2010

NASA Astrophysics Data System (ADS)

Taylor, Robert A.

2010-09-01

These conference proceedings contain the written papers of the contributions presented at Quantum Dot 2010 (QD2010). The conference was held in Nottingham, UK, on 26-30 April 2010. The conference addressed topics in research on: 1. Epitaxial quantum dots (including self-assembled and interface structures, dots defined by electrostatic gates etc): optical properties and electron transport quantum coherence effects spin phenomena optics of dots in cavities interaction with surface plasmons in metal/semiconductor structures opto-electronics applications 2. Novel QD structures: fabrication and physics of graphene dots, dots in nano-wires etc 3. Colloidal quantum dots: growth (shape control and hybrid nanocrystals such as metal/semiconductor, magnetic/semiconductor) assembly and surface functionalisation optical properties and spin dynamics electrical and magnetic properties applications (light emitting devices and solar cells, biological and medical applications, data storage, assemblers) The Editors Acknowledgements Conference Organising Committee: Maurice Skolnick (Chair) Alexander Tartakovskii (Programme Chair) Pavlos Lagoudakis (Programme Chair) Max Migliorato (Conference Secretary) Paola Borri (Publicity) Robert Taylor (Proceedings) Manus Hayne (Treasurer) Ray Murray (Sponsorship) Mohamed Henini (Local Organiser) International Advisory Committee: Yasuhiko Arakawa (Tokyo University, Japan) Manfred Bayer (Dortmund University, Germany) Sergey Gaponenko (Stepanov Institute of Physics, Minsk, Belarus) Pawel Hawrylak (NRC, Ottawa, Canada) Fritz Henneberger (Institute for Physics, Berlin, Germany) Atac Imamoglu (ETH, Zurich, Switzerland) Paul Koenraad (TU Eindhoven, Nethehrlands) Guglielmo Lanzani (Politecnico di Milano, Italy) Jungil Lee (Korea Institute of Science and Technology, Korea) Henri Mariette (CNRS-CEA, Grenoble, France) Lu Jeu Sham (San Diego, USA) Andrew Shields (Toshiba Research Europe, Cambridge, UK) Yoshihisa Yamamoto (Stanford University, USA) Artur Zrenner (Paderborn University, Germany) International Programme Committee: Alexander Eychmüller (TU Dresden, Germany) Jonathan Finley (TU Munich, Germany) Dan Gammon (NRL, Washington, USA) Alexander Govorov (Ohio University, USA) Neil Greenham (Cavendish Laboratory, UK) Vladimir Korenev (Ioffe Institute, Russia) Leo Kouwenhoven (TU Delft, Netherlands) Wolfgang Langbein (Cardiff University, UK) Xavier Marie (CNRS Toulouse, France) David Ritchie (Cambridge, UK) Andrew Sachrajda (IMS, Ottawa, Canada) Katerina Soulantica (University of Toulouse, France) Seigo Tarucha (University of Tokyo, Japan) Carlos Tejedor (UAM, Madrid, Spain) Euijoon Yoon (Seoul National University, Korea) Ulrike Woggon (Tu Berlin, Germany) Proceedings edited and compiled by Profesor Robert A Taylor, University of Oxford

Ultrafast optical control of individual quantum dot spin qubits.

PubMed

De Greve, Kristiaan; Press, David; McMahon, Peter L; Yamamoto, Yoshihisa

2013-09-01

Single spins in semiconductor quantum dots form a promising platform for solid-state quantum information processing. The spin-up and spin-down states of a single electron or hole, trapped inside a quantum dot, can represent a single qubit with a reasonably long decoherence time. The spin qubit can be optically coupled to excited (charged exciton) states that are also trapped in the quantum dot, which provides a mechanism to quickly initialize, manipulate and measure the spin state with optical pulses, and to interface between a stationary matter qubit and a 'flying' photonic qubit for quantum communication and distributed quantum information processing. The interaction of the spin qubit with light may be enhanced by placing the quantum dot inside a monolithic microcavity. An entire system, consisting of a two-dimensional array of quantum dots and a planar microcavity, may plausibly be constructed by modern semiconductor nano-fabrication technology and could offer a path toward chip-sized scalable quantum repeaters and quantum computers. This article reviews the recent experimental developments in optical control of single quantum dot spins for quantum information processing. We highlight demonstrations of a complete set of all-optical single-qubit operations on a single quantum dot spin: initialization, an arbitrary SU(2) gate, and measurement. We review the decoherence and dephasing mechanisms due to hyperfine interaction with the nuclear-spin bath, and show how the single-qubit operations can be combined to perform spin echo sequences that extend the qubit decoherence from a few nanoseconds to several microseconds, more than 5 orders of magnitude longer than the single-qubit gate time. Two-qubit coupling is discussed, both within a single chip by means of exchange coupling of nearby spins and optically induced geometric phases, as well as over longer-distances. Long-distance spin-spin entanglement can be generated if each spin can emit a photon that is entangled with the spin, and these photons are then interfered. We review recent work demonstrating entanglement between a stationary spin qubit and a flying photonic qubit. These experiments utilize the polarization- and frequency-dependent spontaneous emission from the lowest charged exciton state to single spin Zeeman sublevels.

Color-selective photodetection from intermediate colloidal quantum dots buried in amorphous-oxide semiconductors.

PubMed

Cho, Kyung-Sang; Heo, Keun; Baik, Chan-Wook; Choi, Jun Young; Jeong, Heejeong; Hwang, Sungwoo; Lee, Sang Yeol

2017-10-10

We report color-selective photodetection from intermediate, monolayered, quantum dots buried in between amorphous-oxide semiconductors. The proposed active channel in phototransistors is a hybrid configuration of oxide-quantum dot-oxide layers, where the gate-tunable electrical property of silicon-doped, indium-zinc-oxide layers is incorporated with the color-selective properties of quantum dots. A remarkably high detectivity (8.1 × 10 13 Jones) is obtained, along with three major findings: fast charge separation in monolayered quantum dots; efficient charge transport through high-mobility oxide layers (20 cm 2  V -1  s -1 ); and gate-tunable drain-current modulation. Particularly, the fast charge separation rate of 3.3 ns -1 measured with time-resolved photoluminescence is attributed to the intermediate quantum dots buried in oxide layers. These results facilitate the realization of efficient color-selective detection exhibiting a photoconductive gain of 10 7 , obtained using a room-temperature deposition of oxide layers and a solution process of quantum dots. This work offers promising opportunities in emerging applications for color detection with sensitivity, transparency, and flexibility.The development of highly sensitive photodetectors is important for image sensing and optical communication applications. Cho et al., report ultra-sensitive photodetectors based on monolayered quantum dots buried in between amorphous-oxide semiconductors and demonstrate color-detecting logic gates.

Optical Pulse Interactions in Nonlinear Excited State Materials

DTIC Science & Technology

2008-07-14

described below. 2.5 Overview of Semiconductor Quantum Dot A quantum dot (QD) is a quasi -zero-dimensional object where the carrier movement is...a particle of mass M (e.g., an electron) having a potential energy can be described by a wavefunction that satisfies the following Schrödinger...dot (QD) is a quasi -zero-dimensional object where the carrier movement is restricted in three dimensions. The bulk crystalline structure of the

Coherently-enabled environmental control of optics and energy transfer pathways of hybrid quantum dot-metallic nanoparticle systems.

PubMed

Hatef, Ali; Sadeghi, Seyed M; Fortin-Deschênes, Simon; Boulais, Etienne; Meunier, Michel

2013-03-11

It is well-known that optical properties of semiconductor quantum dots can be controlled using optical cavities or near fields of localized surface plasmon resonances (LSPRs) of metallic nanoparticles. In this paper we study the optics, energy transfer pathways, and exciton states of quantum dots when they are influenced by the near fields associated with plasmonic meta-resonances. Such resonances are formed via coherent coupling of excitons and LSPRs when the quantum dots are close to metallic nanorods and driven by a laser beam. Our results suggest an unprecedented sensitivity to the refractive index of the environment, causing significant spectral changes in the Förster resonance energy transfer from the quantum dots to the nanorods and in exciton transition energies. We demonstrate that when a quantum dot-metallic nanorod system is close to its plasmonic meta-resonance, we can adjust the refractive index to: (i) control the frequency range where the energy transfer from the quantum dot to the metallic nanorod is inhibited, (ii) manipulate the exciton transition energy shift of the quantum dot, and (iii) disengage the quantum dot from the metallic nanoparticle and laser field. Our results show that near meta-resonances the spectral forms of energy transfer and exciton energy shifts are strongly correlated to each other.

Nano-scale measurement of biomolecules by optical microscopy and semiconductor nanoparticles

PubMed Central

Ichimura, Taro; Jin, Takashi; Fujita, Hideaki; Higuchi, Hideo; Watanabe, Tomonobu M.

2014-01-01

Over the past decade, great developments in optical microscopy have made this technology increasingly compatible with biological studies. Fluorescence microscopy has especially contributed to investigating the dynamic behaviors of live specimens and can now resolve objects with nanometer precision and resolution due to super-resolution imaging. Additionally, single particle tracking provides information on the dynamics of individual proteins at the nanometer scale both in vitro and in cells. Complementing advances in microscopy technologies has been the development of fluorescent probes. The quantum dot, a semi-conductor fluorescent nanoparticle, is particularly suitable for single particle tracking and super-resolution imaging. This article overviews the principles of single particle tracking and super resolution along with describing their application to the nanometer measurement/observation of biological systems when combined with quantum dot technologies. PMID:25120488

Analytical model of ground-state lasing phenomenon in broadband semiconductor quantum dot lasers

NASA Astrophysics Data System (ADS)

Korenev, Vladimir V.; Savelyev, Artem V.; Zhukov, Alexey E.; Omelchenko, Alexander V.; Maximov, Mikhail V.

2013-05-01

We introduce an analytical approach to the description of broadband lasing spectra of semiconductor quantum dot lasers emitting via ground-state optical transitions of quantum dots. The explicit analytical expressions describing the shape and the width of lasing spectra as well as their temperature and injection current dependences are obtained in the case of low homogeneous broadening. It is shown that in this case these dependences are determined by only two dimensionless parameters, which are the dispersion of the distribution of QDs over the energy normalized to the temperature and loss-to-maximum gain ratio. The possibility of optimization of laser's active region size and structure by using the intentionally introduced disorder is also carefully considered.

Size-Dependent Optoelectronic Properties and Controlled Doping of Semiconductor Quantum Dots

NASA Astrophysics Data System (ADS)

Engel, Jesse Hart

Given a rapidly developing world, the need exists for inexpensive renewable energy alternatives to help avoid drastic climate change. Photovoltaics have the potential to fill the energy needs of the future, but significant cost decreases are necessary for widespread adoption. Semiconductor nanocrystals, also known as quantum dots, are a nascent technology with long term potential to enable inexpensive and high efficiency photovoltaics. When deposited as a film, quantum dots form unique nanocomposites whose electronic and optical properties can be broadly tuned through manipulation of their individual constituents. The contents of this thesis explore methods to understand and optimize the optoelectronic properties of PbSe quantum dot films for use in photovoltaic applications. Systematic optimization of photovoltaic performance is demonstrated as a function of nanocrystal size, establishing the potential for utilizing extreme quantum confinement to improve device energetics and alignment. Detailed investigations of the mechanisms of electrical transport are performed, revealing that electronic coupling in quantum dot films is significantly less than often assumed based on optical shifts. A method is proposed to employ extended regions of built-in electrical field, through controlled doping, to sidestep issues of poor transport. To this end, treatments with chemical redox agents are found to effect profound and reversible doping within nanocrystal films, sufficient to enable their use as chemical sensors, but lacking the precision required for optoelectronic applications. Finally, a novel doping method employing "redox buffers" is presented to enact precise, stable, and reversible charge-transfer doping in porous semiconductor films. An example of oxidatively doping PbSe quantum dot thin films is presented, and the future potential for redox buffers in photovoltaic applications is examined.

Spontaneous generation of frequency combs in QD lasers

NASA Astrophysics Data System (ADS)

Columbo, Lorenzo Luigi; Bardella, Paolo; Gioannini, Mariangela

2018-02-01

We report a systematic analysis of the phenomenon of self-generation of optical frequency combs in single section Fabry-Perot Quantum Dot lasers using a Time Domain Travelling Wave model. We show that the carriers grating due to the standing wave pattern (spatial hole burning) peculiar of Quantum Dots laser and the Four Wave Mixing are the key ingredients to explain spontaneous Optical Frequency Combs in these devices. Our results well agree with recent experimental evidences reported in semiconductor lasers based on Quantum Dots and Quantum Dashes active material and pave the way to the development of a simulation tool for the design of these comb laser sources for innovative applications in the field of high-data rate optical communications.

Biomolecule/nanomaterial hybrid systems for nanobiotechnology.

PubMed

Tel-Vered, Ran; Yehezkeli, Omer; Willner, Itamar

2012-01-01

The integration of biomolecules with metallic or semiconductor nanoparticles or carbon nanotubes yields new hybrid nanostructures of unique features that combine the properties of the biomolecules and of the nano-elements. These unique features of the hybrid biomolecule/nanoparticle systems provide the basis for the rapid development of the area of nanobiotechnology. Recent advances in the implementation of hybrid materials consisting of biomolecules and metallic nanoparticles or semiconductor quantum dots will be discussed. The following topics will be exemplified: (i) The electrical wiring of redox enzymes with electrodes by means of metallic nanoparticles or carbon nanotubes, and the application of the modified electrodes as amperometric biosensors or for the construction of biofuel cells. (ii) The biocatalytic growth of metallic nanoparticles as a means to construct optical or electrical sensors. (iii) The functionalization of semiconductor quantum dots with biomolecules and the application of the hybrid nanostructures for developing different optical sensors, including intracellular sensor systems. (iv) The use of biomolecule-metallic nanoparticle nanostructures as templates for growing metallic nanowires, and the construction of fuel-driven nano-transporters.

Temperature characteristics of epitaxially grown InAs quantum dot micro-disk lasers on silicon for on-chip light sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Yating; Li, Qiang; Lau, Kei May, E-mail: eekmlau@ust.hk

2016-07-04

Temperature characteristics of optically pumped micro-disk lasers (MDLs) incorporating InAs quantum dot active regions are investigated for on-chip light sources. The InAs quantum dot MDLs were grown on V-groove patterned (001) silicon, fully compatible with the prevailing complementary metal oxide-semiconductor technology. By combining the high-quality whispering gallery modes and 3D confinement of injected carriers in quantum dot micro-disk structures, we achieved lasing operation from 10 K up to room temperature under continuous optical pumping. Temperature dependences of the threshold, lasing wavelength, slope efficiency, and mode linewidth are examined. An excellent characteristic temperature T{sub o} of 105 K has been extracted.

Optical activity of helical quantum-dot supercrystals

NASA Astrophysics Data System (ADS)

Baimuratov, A. S.; Tepliakov, N. V.; Gun'ko, Yu. K.; Baranov, A. V.; Federov, A. V.; Rukhlenko, I. D.

2017-01-01

The size of chiral nanoparticles is much smaller than the optical wavelength. As a result, the difference in interaction of enantiomers with circularly polarized light of different handedness is practically unobservable. Due to the large mismatch in scale, the problem of enhancement of enantioselectivity of optical properties of nanoparticles is particularly important for modern photonics. In this work, we show that ordering of achiral nanoparticles into a chiral supercrystal with dimensions comparable to the wavelength of light allows achieving nearly total dissymmetry of optical absorption and demonstrate this using a helical super-crystal made of semiconductor quantum dots as an example. The proposed approach may find numerous applications in various optical and analytical methods used in biomedicine, chemistry, and pharmacology.

Ultrashort, high power, and ultralow noise mode-locked optical pulse generation using quantum-dot semiconductor lasers

NASA Astrophysics Data System (ADS)

Choi, Myoung-Taek

This dissertation explores various aspects and potential of optical pulse generation based on active, passive, and hybrid mode-locked quantum dot semiconductor lasers with target applications such as optical interconnect and high speed signal processing. Design guidelines are developed for the single mode operation with suppressed reflection from waveguide discontinuities. The device fabrication procedure is explained, followed by characteristics of FP laser, SOA, and monolithic two-section devices. Short pulse generation from an external cavity mode-locked QD two-section diode laser is studied. High quality, sub-picosecond (960 fs), high peak power (1.2 W) pulse trains are obtained. The sign and magnitude of pulse chirp were measured for the first time. The role of the self-phase modulation and the linewidth enhancement factor in QD mode-locked lasers is addressed. The noise performance of two-section mode-locked lasers and a SOA-based ring laser was investigated. Significant reduction of the timing jitter under hybrid mode-locked operation was achieved owing to more than one order of magnitude reduction of the linewidth in QD gain media. Ultralow phase noise performance (integrated timing jitter of a few fs at a 10 GHz repetition rate) was demonstrated from an actively mode-locked unidirectional ring laser. These results show that quantum dot mode-locked lasers are strong competitors to conventional semiconductor lasers in noise performance. Finally we demonstrated an opto-electronic oscillator (OEO) and coupled opto-electronic oscillators (COEO) which have the potential for both high purity microwave and low noise optical pulse generation. The phase noise of the COEO is measured by the photonic delay line frequency discriminator method. Based on this study we discuss the prospects of the COEO as a low noise optical pulse source.

Interband optical pulse injection locking of quantum dot mode-locked semiconductor laser.

PubMed

Kim, Jimyung; Delfyett, Peter J

2008-07-21

We experimentally demonstrate optical clock recovery from quantum dot mode-locked semiconductor lasers by interband optical pulse injection locking. The passively mode-locked slave laser oscillating on the ground state or the first excited state transition is locked through the injection of optical pulses generated via the opposite transition bands, i.e. the first excited state or the ground state transition from the hybridly mode-locked master laser, respectively. When an optical pulse train generated via the first excited state from the master laser is injected to the slave laser oscillating via ground state, the slave laser shows an asymmetric locking bandwidth around the nominal repetition rate of the slave laser. In the reverse injection case of, i.e. the ground state (master laser) to the first excited state (slave laser), the slave laser does not lock even though both lasers oscillate at the same cavity frequency. In this case, the slave laser only locks to higher injection rates as compared to its own nominal repetition rate, and also shows a large locking bandwidth of 6.7 MHz.

Site-controlled quantum dots fabricated using an atomic-force microscope assisted technique

PubMed Central

Usuki, T; Ohshima, T; Sakuma, Y; Kawabe, M; Okada, Y; Takemoto, K; Miyazawa, T; Hirose, S; Nakata, Y; Takatsu, M; Yokoyama, N

2006-01-01

An atomic-force microscope assisted technique is developed to control the position and size of self-assembled semiconductor quantum dots (QDs). Presently, the site precision is as good as ± 1.5 nm and the size fluctuation is within ± 5% with the minimum controllable lateral diameter of 20 nm. With the ability of producing tightly packed and differently sized QDs, sophisticated QD arrays can be controllably fabricated for the application in quantum computing. The optical quality of such site-controlled QDs is found comparable to some conventionally self-assembled semiconductor QDs. The single dot photoluminescence of site-controlled InAs/InP QDs is studied in detail, presenting the prospect to utilize them in quantum communication as precisely controlled single photon emitters working at telecommunication bands.

Tunable Quantum Dot Solids: Impact of Interparticle Interactions on Bulk Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sinclair, Michael B.; Fan, Hongyou; Brener, Igal

2015-09-01

QD-solids comprising self-assembled semiconductor nanocrystals such as CdSe are currently under investigation for use in a wide array of applications including light emitting diodes, solar cells, field effect transistors, photodetectors, and biosensors. The goal of this LDRD project was develop a fundamental understanding of the relationship between nanoparticle interactions and the different regimes of charge and energy transport in semiconductor quantum dot (QD) solids. Interparticle spacing was tuned through the application of hydrostatic pressure in a diamond anvil cell, and the impact on interparticle interactions was probed using x-ray scattering and a variety of static and transient optical spectroscopies. Duringmore » the course of this LDRD, we discovered a new, previously unknown, route to synthesize semiconductor quantum wires using high pressure sintering of self-assembled quantum dot crystals. We believe that this new, pressure driven synthesis approach holds great potential as a new tool for nanomaterials synthesis and engineering.« less

A dark-field microscope for background-free detection of resonance fluorescence from single semiconductor quantum dots operating in a set-and-forget mode

NASA Astrophysics Data System (ADS)

Kuhlmann, Andreas V.; Houel, Julien; Brunner, Daniel; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D.; Warburton, Richard J.

2013-07-01

Optically active quantum dots, for instance self-assembled InGaAs quantum dots, are potentially excellent single photon sources. The fidelity of the single photons is much improved using resonant rather than non-resonant excitation. With resonant excitation, the challenge is to distinguish between resonance fluorescence and scattered laser light. We have met this challenge by creating a polarization-based dark-field microscope to measure the resonance fluorescence from a single quantum dot at low temperature. We achieve a suppression of the scattered laser exceeding a factor of 107 and background-free detection of resonance fluorescence. The same optical setup operates over the entire quantum dot emission range (920-980 nm) and also in high magnetic fields. The major development is the outstanding long-term stability: once the dark-field point has been established, the microscope operates for days without alignment. The mechanical and optical designs of the microscope are presented, as well as exemplary resonance fluorescence spectroscopy results on individual quantum dots to underline the microscope's excellent performance.

Recent advances in biocompatible semiconductor nanocrystals for immunobiological applications.

PubMed

Nanda, Sitansu Sekhar; Kim, Min Jik; Kim, Kwangmeyung; Papaefthymiou, Georgia C; Selvan, Subramanian Tamil; Yi, Dong Kee

2017-11-01

Quantum confinement in inorganic semiconductor nanocrystals produces brightly luminescent nanoparticles endowed with unique photo-physical properties, such as tunable optical properties. These have found widespread applications in nanotechnology. The ability to render such nanostructures biocompatible, while maintaining their tunable radiation in the visible range of the electromagnetic spectrum, renders them appropriate for bio-applications. Promising in vitro and in vivo diagnostic applications have been demonstrated, such as fluorescence-based detection of biological interactions, single molecule tracking, multiplexing and immunoassaying. In particular, these fluorescent inorganic semiconductor nanocrystals, generally known as quantum dots, have the potential of remarkable immunobiological applications. This review focuses on the current status of biocompatible quantum dots and their applications in immunobiology - immunosensing, immunofluorescent imaging and immunotherapy. Copyright © 2017 Elsevier B.V. All rights reserved.

Generation of heralded entanglement between distant quantum dot hole spins

NASA Astrophysics Data System (ADS)

Delteil, Aymeric

Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, some of the major challenges are the efficient generation of entanglement between stationary (spin) and propagating (photon) qubits, the transfer of information from flying to stationary qubits, and the efficient generation of entanglement between distant stationary (spin) qubits. In this talk, I will present such experimental implementations achieved in our team with semiconductor self-assembled quantum dots.Not only are self-assembled quantum dots good single-photon emitters, but they can host an electron or a hole whose spin serves as a quantum memory, and then present spin-dependent optical selection rules leading to an efficient spin-photon quantum interface. Moreover InGaAs quantum dots grown on GaAs substrate can profit from the maturity of III-V semiconductor technology and can be embedded in semiconductor structures like photonic cavities and Schottky diodes.I will report on the realization of heralded quantum entanglement between two semiconductor quantum dot hole spins separated by more than five meters. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments carried out in other systems.Our results extend previous demonstrations in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of artificial atoms in semiconductor nanostructures that allow for on-chip integration of electronic and photonic elements. This work lays the groundwork for the realization of quantum repeaters and quantum networks on a chip.

Coulomb Mediated Hybridization of Excitons in Coupled Quantum Dots.

PubMed

Ardelt, P-L; Gawarecki, K; Müller, K; Waeber, A M; Bechtold, A; Oberhofer, K; Daniels, J M; Klotz, F; Bichler, M; Kuhn, T; Krenner, H J; Machnikowski, P; Finley, J J

2016-02-19

We report Coulomb mediated hybridization of excitonic states in optically active InGaAs quantum dot molecules. By probing the optical response of an individual quantum dot molecule as a function of the static electric field applied along the molecular axis, we observe unexpected avoided level crossings that do not arise from the dominant single-particle tunnel coupling. We identify a new few-particle coupling mechanism stemming from Coulomb interactions between different neutral exciton states. Such Coulomb resonances hybridize the exciton wave function over four different electron and hole single-particle orbitals. Comparisons of experimental observations with microscopic eight-band k·p calculations taking into account a realistic quantum dot geometry show good agreement and reveal that the Coulomb resonances arise from broken symmetry in the artificial semiconductor molecule.

Multi-dimensional coherent optical spectroscopy of semiconductor nanostructures: Collinear and non-collinear approaches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nardin, Gaël; Li, Hebin; Autry, Travis M.

2015-03-21

We review our recent work on multi-dimensional coherent optical spectroscopy (MDCS) of semiconductor nanostructures. Two approaches, appropriate for the study of semiconductor materials, are presented and compared. A first method is based on a non-collinear geometry, where the Four-Wave-Mixing (FWM) signal is detected in the form of a radiated optical field. This approach works for samples with translational symmetry, such as Quantum Wells (QWs) or large and dense ensembles of Quantum Dots (QDs). A second method detects the FWM in the form of a photocurrent in a collinear geometry. This second approach extends the horizon of MDCS to sub-diffraction nanostructures,more » such as single QDs, nanowires, or nanotubes, and small ensembles thereof. Examples of experimental results obtained on semiconductor QW structures are given for each method. In particular, it is shown how MDCS can assess coupling between excitons confined in separated QWs.« less

Semiconductor quantum dots: synthesis and water-solubilization for biomedical applications.

PubMed

Yu, William W

2008-10-01

Quantum dots (QDs) are generally nanosized inorganic particles. They have distinctive size-dependent optical properties due to their very small size (mostly < 10 nm). QDs are regarded as promising new fluorescent materials for biological labeling and imaging because of their superior properties compared with traditional organic molecular dyes. These properties include high quantum efficiency, long-term photostability and very narrow emission but broad absorption spectra. Recent developments in synthesizing high quality semiconductor QDs (mainly metal-chalcogenide compounds) and forming biocompatible structures for biomedical applications are discussed in this paper. This information may facilitate the research to create new materials/technologies for future clinical applications.

Deterministic radiative coupling of two semiconductor quantum dots to the optical mode of a photonic crystal nanocavity.

PubMed

Calic, M; Jarlov, C; Gallo, P; Dwir, B; Rudra, A; Kapon, E

2017-06-22

A system of two site-controlled semiconductor quantum dots (QDs) is deterministically integrated with a photonic crystal membrane nano-cavity. The two QDs are identified via their reproducible emission spectral features, and their coupling to the fundamental cavity mode is established by emission co-polarization and cavity feeding features. A theoretical model accounting for phonon interaction and pure dephasing reproduces the observed results and permits extraction of the light-matter coupling constant for this system. The demonstrated approach offers a platform for scaling up the integration of QD systems and nano-photonic elements for integrated quantum photonics applications.

Tuning optical properties of water-soluble CdTe quantum dots for biological applications

NASA Astrophysics Data System (ADS)

Schulze, Anne S.; Tavernaro, Isabella; Machka, Friederike; Dakischew, Olga; Lips, Katrin S.; Wickleder, Mathias S.

2017-02-01

In this study, two different synthetic methods in aqueous solution are presented to tune the optical properties of CdTe and CdSe semiconductor nanoparticles. Additionally, the influence of different temperatures, pressures, precursor ratios, surface ligands, bases, and core components in the synthesis was investigated with regard to the particle sizes and optical properties. As a result, a red shift of the emission and absorption maxima with increasing reaction temperature (100 to 220°C), pressure (1 to 25 bar), and different ratios of core components of alloyed semiconductor nanoparticles could be observed without a change of the particle size. An increase in particle size from 2.5 to 5 nm was only achieved by variation of the mercaptocarboxylic acid ligands in combination with the reaction time and used base. To get a first hint on the cytotoxic effects and cell uptake of the synthesized quantum dots, in vitro tests mesenchymal stem cells (MSCs) were carried out.

MURI Center for Photonic Quantum Information Systems

DTIC Science & Technology

2009-10-16

conversion; solid- state quantum gates based on quantum dots in semiconductors and on NV centers in diamond; quantum memories using optical storage...of our high-speed quantum cryptography systems, and also by continuing to work on quantum information encoding into transverse spatial modes. 14...make use of cavity QED effects for quantum information processing, the quantum dot needs to be addressed coherently . We have probed the QD-cavity

Room-temperature lasing in a single nanowire with quantum dots

NASA Astrophysics Data System (ADS)

Tatebayashi, Jun; Kako, Satoshi; Ho, Jinfa; Ota, Yasutomo; Iwamoto, Satoshi; Arakawa, Yasuhiko

2015-08-01

Semiconductor nanowire lasers are promising as ultrasmall, highly efficient coherent light emitters in the fields of nanophotonics, nano-optics and nanobiotechnology. Although there have been several demonstrations of nanowire lasers using homogeneous bulk gain materials or multi-quantum-wells/disks, it is crucial to incorporate lower-dimensional quantum nanostructures into the nanowire to achieve superior device performance in relation to threshold current, differential gain, modulation bandwidth and temperature sensitivity. The quantum dot is a useful and essential nanostructure that can meet these requirements. However, difficulties in forming stacks of quantum dots in a single nanowire hamper the realization of lasing operation. Here, we demonstrate room-temperature lasing of a single nanowire containing 50 quantum dots by properly designing the nanowire cavity and tailoring the emission energy of each dot to enhance the optical gain. Our demonstration paves the way toward ultrasmall lasers with extremely low power consumption for integrated photonic systems.

Optical Amplification of Spin Noise Spectroscopy via Homodyne Detection

NASA Astrophysics Data System (ADS)

Sterin, Pavel; Wiegand, Julia; Hübner, Jens; Oestreich, Michael

2018-03-01

Spin noise (SN) spectroscopy measurements on delicate semiconductor spin systems, like single (In,Ga)As quantum dots, are currently not limited by optical shot noise but rather by the electronic noise of the detection system. We report on a realization of homodyne SN spectroscopy enabling shot-noise-limited SN measurements. The proof-of-principle measurements on impurities in an isotopically enriched rubidium atom vapor show that homodyne SN spectroscopy can be utilized even in the low-frequency spectrum, which facilitates advanced semiconductor spin research like higher order SN measurements on spin qubits.

Semiconductor Quantum Dots with Photoresponsive Ligands.

PubMed

Sansalone, Lorenzo; Tang, Sicheng; Zhang, Yang; Thapaliya, Ek Raj; Raymo, Françisco M; Garcia-Amorós, Jaume

2016-10-01

Photochromic or photocaged ligands can be anchored to the outer shell of semiconductor quantum dots in order to control the photophysical properties of these inorganic nanocrystals with optical stimulations. One of the two interconvertible states of the photoresponsive ligands can be designed to accept either an electron or energy from the excited quantum dots and quench their luminescence. Under these conditions, the reversible transformations of photochromic ligands or the irreversible cleavage of photocaged counterparts translates into the possibility to switch luminescence with external control. As an alternative to regulating the photophysics of a quantum dot via the photochemistry of its ligands, the photochemistry of the latter can be controlled by relying on the photophysics of the former. The transfer of excitation energy from a quantum dot to a photocaged ligand populates the excited state of the species adsorbed on the nanocrystal to induce a photochemical reaction. This mechanism, in conjunction with the large two-photon absorption cross section of quantum dots, can be exploited to release nitric oxide or to generate singlet oxygen under near-infrared irradiation. Thus, the combination of semiconductor quantum dots and photoresponsive ligands offers the opportunity to assemble nanostructured constructs with specific functions on the basis of electron or energy transfer processes. The photoswitchable luminescence and ability to photoinduce the release of reactive chemicals, associated with the resulting systems, can be particularly valuable in biomedical research and can, ultimately, lead to the realization of imaging probes for diagnostic applications as well as to therapeutic agents for the treatment of cancer.

Semiconductor particles in bilayer lipid membranes. Formation, characterization, and photoelectrochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, X.K.; Baral, S.B.; Rolandi, R.

Bilayer lipid membranes (BLMs) have been formed from bovine brain phosphatidylserine (PS), glyceryl monooleate (GMO), and a ploymerizable surfactant, (n-C/sub 15/H/sub 31/CO/sub 2/(CH/sub 2/))/sub 2/N/sup +/(CH/sub 3/)CH/sub 2/C/sub 6/H/sub 4/CH==CH/sub 2/Cl/sup -/(STYRS). These BLMs were then used to provide matrices for the in situ generation of microcrystalline CdS, CuS, Cu/sub 2/S, PbS, ZnS, HgS, and In/sub 2/S/sub 3/. Semiconductors were formed by injecting appropriate metal ion precursors and H/sub 2/S into the bathing solutions on opposite sides of the BLM. Their presence was established by voltage-dependent capacitance measurements, absorption spectroscopy, and optical microscopy. Subsequent to the injection of H/sub 2/S,more » the first observable change was the appearance of fairly uniform white dots on the black film. These dots rapidly moved around and grew in size, forming islands that then merged with themselves and with a second generation of dots, which ultimately led to a continuous film that continued to grow in thickness. Film formation and growth were monitored by simultaneous optical thickness and capacitance measurements. These data were treated in terms of an equivalent R-C circuit and allowed for the assessment of the semiconductor penetration depth into the BLM. This value for a GMO-BLM-supported In/sub 2/S/sub 3/ film was determined to be 24 A. Bandgap excitation, by nanosecond-pulsed or continuous illumination of the BLM-supported semiconductor film, led to observable photoelectric effects. Visible light (lambda > 350 nm) excitation into STYRS-BLM-supported CdS led to polymerization of the styrene moiety of STYRS. BLM-supported semiconductors remained stable for days.« less

Emission switching in carbon dots coated CdTe quantum dots driving by pH dependent hetero-interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Xiao; Wang, Hao; Yi, Qinghua

2015-11-16

Due to the different emission mechanism between fluorescent carbon dots and semiconductor quantum dots (QDs), it is of interest to explore the potential emission in hetero-structured carbon dots/semiconducting QDs. Herein, we design carbon dots coated CdTe QDs (CDQDs) and investigate their inherent emission. We demonstrate switchable emission for the hetero-interactions of the CDQDs. Optical analyses indicate electron transfer between the carbon dots and the CdTe QDs. A heterojunction electron process is proposed as the driving mechanism based on N atom protonation of the carbon dots. This work advances our understanding of the interaction mechanism of the heterostructured CDQDs and benefitsmore » the future development of optoelectronic nanodevices with new functionalities.« less

Non-blinking quantum dot with a plasmonic nanoshell resonator

NASA Astrophysics Data System (ADS)

Ji, Botao; Giovanelli, Emerson; Habert, Benjamin; Spinicelli, Piernicola; Nasilowski, Michel; Xu, Xiangzhen; Lequeux, Nicolas; Hugonin, Jean-Paul; Marquier, Francois; Greffet, Jean-Jacques; Dubertret, Benoit

2015-02-01

Colloidal semiconductor quantum dots are fluorescent nanocrystals exhibiting exceptional optical properties, but their emission intensity strongly depends on their charging state and local environment. This leads to blinking at the single-particle level or even complete fluorescence quenching, and limits the applications of quantum dots as fluorescent particles. Here, we show that a single quantum dot encapsulated in a silica shell coated with a continuous gold nanoshell provides a system with a stable and Poissonian emission at room temperature that is preserved regardless of drastic changes in the local environment. This novel hybrid quantum dot/silica/gold structure behaves as a plasmonic resonator with a strong Purcell factor, in very good agreement with simulations. The gold nanoshell also acts as a shield that protects the quantum dot fluorescence and enhances its resistance to high-power photoexcitation or high-energy electron beams. This plasmonic fluorescent resonator opens the way to a new family of plasmonic nanoemitters with robust optical properties.

Continuous wave terahertz radiation from an InAs/GaAs quantum-dot photomixer device

NASA Astrophysics Data System (ADS)

Kruczek, T.; Leyman, R.; Carnegie, D.; Bazieva, N.; Erbert, G.; Schulz, S.; Reardon, C.; Reynolds, S.; Rafailov, E. U.

2012-08-01

Generation of continuous wave radiation at terahertz (THz) frequencies from a heterodyne source based on quantum-dot (QD) semiconductor materials is reported. The source comprises an active region characterised by multiple alternating photoconductive and QD carrier trapping layers and is pumped by two infrared optical signals with slightly offset wavelengths, allowing photoconductive device switching at the signals' difference frequency ˜1 THz.

Acoustically regulated optical emission dynamics from quantum dot-like emission centers in GaN/InGaN nanowire heterostructures

NASA Astrophysics Data System (ADS)

Lazić, S.; Chernysheva, E.; Hernández-Mínguez, A.; Santos, P. V.; van der Meulen, H. P.

2018-03-01

We report on experimental studies of the effects induced by surface acoustic waves on the optical emission dynamics of GaN/InGaN nanowire quantum dots. We employ stroboscopic optical excitation with either time-integrated or time-resolved photoluminescence detection. In the absence of the acoustic wave, the emission spectra reveal signatures originated from the recombination of neutral exciton and biexciton confined in the probed nanowire quantum dot. When the nanowire is perturbed by the propagating acoustic wave, the embedded quantum dot is periodically strained and its excitonic transitions are modulated by the acousto-mechanical coupling. Depending on the recombination lifetime of the involved optical transitions, we can resolve acoustically driven radiative processes over time scales defined by the acoustic cycle. At high acoustic amplitudes, we also observe distortions in the transmitted acoustic waveform, which are reflected in the time-dependent spectral response of our sensor quantum dot. In addition, the correlated intensity oscillations observed during temporal decay of the exciton and biexciton emission suggest an effect of the acoustic piezoelectric fields on the quantum dot charge population. The present results are relevant for the dynamic spectral and temporal control of photon emission in III-nitride semiconductor heterostructures.

White/blue-emitting, water-dispersible CdSe quantum dots prepared by counter ion-induced polymer collapse

NASA Astrophysics Data System (ADS)

Wang, Jing; Goh, Jane Betty; Goh, M. Cynthia; Giri, Neeraj Kumar; Paige, Matthew F.

2015-09-01

The synthesis and characterization of water-dispersible, luminescent CdSe/ZnS semiconductor quantum dots that exhibit nominal "white" fluorescence emission and have potential applications in solid-state lighting is described. The nanomaterials, prepared through counter ion-induced collapse and UV cross-linking of high-molecular weight polyacrylic acid in the presence of appropriate aqueous inorganic ions, were of ∼2-3 nm diameter and could be prepared in gram quantities. The quantum dots exhibited strong luminescence emission in two bands, the first in the blue-region (band edge) of the optical spectrum and the second, a broad emission in the red-region (attributed to deep trap states) of the optical spectrum. Because of the relative strength of emission of the band edge and deep trap state luminescence, it was possible to achieve visible white luminescence from the quantum dots in aqueous solution and in dried, solid films. The optical spectroscopic properties of the nanomaterials, including ensemble and single-molecule spectroscopy, was performed, with results compared to other white-emitting quantum dot systems described previously in the literature.

Controlled waveguide coupling for photon emission from colloidal PbS quantum dot using tunable microcavity made of optical polymer and silicon

NASA Astrophysics Data System (ADS)

Nozaka, Takahiro; Mukai, Kohki

2016-04-01

A tunable microcavity device composed of optical polymer and Si with a colloidal quantum dot (QD) is proposed as a single-photon source for planar optical circuit. Cavity size is controlled by electrostatic micromachine behavior with the air bridge structure to tune timing of photon injection into optical waveguide from QD. Three-dimensional positioning of a QD in the cavity structure is available using a nanohole on Si processed by scanning probe microscope lithography. We fabricated the prototype microcavity with PbS-QD-mixed polymenthyl methacrylate on a SOI (semiconductor-on-insulator) substrate to show the tunability of cavity size as the shift of emission peak wavelength of QD ensemble.

1.55 µm InAs/GaAs Quantum Dots and High Repetition Rate Quantum Dot SESAM Mode-locked Laser

NASA Astrophysics Data System (ADS)

Zhang, Z. Y.; Oehler, A. E. H.; Resan, B.; Kurmulis, S.; Zhou, K. J.; Wang, Q.; Mangold, M.; Süedmeyer, T.; Keller, U.; Weingarten, K. J.; Hogg, R. A.

2012-06-01

High pulse repetition rate (>=10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ~2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.

Anisotropy-Induced Quantum Interference and Population Trapping between Orthogonal Quantum Dot Exciton States in Semiconductor Cavity Systems

NASA Astrophysics Data System (ADS)

Hughes, Stephen; Agarwal, Girish S.

2017-02-01

We describe how quantum dot semiconductor cavity systems can be engineered to realize anisotropy-induced dipole-dipole coupling between orthogonal dipole states in a single quantum dot. Quantum dots in single-mode cavity structures as well as photonic crystal waveguides coupled to spin states or linearly polarized excitons are considered. We demonstrate how the dipole-dipole coupling can control the radiative decay rate of excitons and form pure entangled states in the long time limit. We investigate both field-free entanglement evolution and coherently pumped exciton regimes, and show how a double-field pumping scenario can completely eliminate the decay of coherent Rabi oscillations and lead to population trapping. In the Mollow triplet regime, we explore the emitted spectra from the driven dipoles and show how a nonpumped dipole can take on the form of a spectral triplet, quintuplet, or a singlet, which has applications for producing subnatural linewidth single photons and more easily accessing regimes of high-field quantum optics and cavity-QED.

Anisotropy-Induced Quantum Interference and Population Trapping between Orthogonal Quantum Dot Exciton States in Semiconductor Cavity Systems.

PubMed

Hughes, Stephen; Agarwal, Girish S

2017-02-10

We describe how quantum dot semiconductor cavity systems can be engineered to realize anisotropy-induced dipole-dipole coupling between orthogonal dipole states in a single quantum dot. Quantum dots in single-mode cavity structures as well as photonic crystal waveguides coupled to spin states or linearly polarized excitons are considered. We demonstrate how the dipole-dipole coupling can control the radiative decay rate of excitons and form pure entangled states in the long time limit. We investigate both field-free entanglement evolution and coherently pumped exciton regimes, and show how a double-field pumping scenario can completely eliminate the decay of coherent Rabi oscillations and lead to population trapping. In the Mollow triplet regime, we explore the emitted spectra from the driven dipoles and show how a nonpumped dipole can take on the form of a spectral triplet, quintuplet, or a singlet, which has applications for producing subnatural linewidth single photons and more easily accessing regimes of high-field quantum optics and cavity-QED.

Manipulating Nonlinear Emission and Cooperative Effect of CdSe/ZnS Quantum Dots by Coupling to a Silver Nanorod Complex Cavity

PubMed Central

Nan, Fan; Cheng, Zi-Qiang; Wang, Ya-Lan; Zhang, Qing; Zhou, Li; Yang, Zhong-Jian; Zhong, Yu-Ting; Liang, Shan; Xiong, Qihua; Wang, Qu-Quan

2014-01-01

Colloidal semiconductor quantum dots have three-dimensional confined excitons with large optical oscillator strength and gain. The surface plasmons of metallic nanostructures offer an efficient tool to enhance exciton-exciton coupling and excitation energy transfer at appropriate geometric arrangement. Here, we report plasmon-mediated cooperative emissions of approximately one monolayer of ensemble CdSe/ZnS quantum dots coupled with silver nanorod complex cavities at room temperature. Power-dependent spectral shifting, narrowing, modulation, and amplification are demonstrated by adjusting longitudinal surface plasmon resonance of silver nanorods, reflectivity and phase shift of silver nanostructured film, and mode spacing of the complex cavity. The underlying physical mechanism of the nonlinear excitation energy transfer and nonlinear emissions are further investigated and discussed by using time-resolved photoluminescence and finite-difference time-domain numerical simulations. Our results suggest effective strategies to design active plasmonic complex cavities for cooperative emission nanodevices based on semiconductor quantum dots. PMID:24787617

Electrical control of single hole spins in nanowire quantum dots.

PubMed

Pribiag, V S; Nadj-Perge, S; Frolov, S M; van den Berg, J W G; van Weperen, I; Plissard, S R; Bakkers, E P A M; Kouwenhoven, L P

2013-03-01

The development of viable quantum computation devices will require the ability to preserve the coherence of quantum bits (qubits). Single electron spins in semiconductor quantum dots are a versatile platform for quantum information processing, but controlling decoherence remains a considerable challenge. Hole spins in III-V semiconductors have unique properties, such as a strong spin-orbit interaction and weak coupling to nuclear spins, and therefore, have the potential for enhanced spin control and longer coherence times. A weaker hyperfine interaction has previously been reported in self-assembled quantum dots using quantum optics techniques, but the development of hole-spin-based electronic devices in conventional III-V heterostructures has been limited by fabrication challenges. Here, we show that gate-tunable hole quantum dots can be formed in InSb nanowires and used to demonstrate Pauli spin blockade and electrical control of single hole spins. The devices are fully tunable between hole and electron quantum dots, which allows the hyperfine interaction strengths, g-factors and spin blockade anisotropies to be compared directly in the two regimes.

Decoherence processes during optical manipulation of excitonic qubits in semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Wang, Q. Q.; Muller, A.; Bianucci, P.; Rossi, E.; Xue, Q. K.; Takagahara, T.; Piermarocchi, C.; MacDonald, A. H.; Shih, C. K.

2005-07-01

Using photoluminescence spectroscopy, we have investigated the nature of Rabi oscillation damping during optical manipulation of excitonic qubits in self-assembled quantum dots. Rabi oscillations were recorded by varying the pulse amplitude for fixed pulse durations between 4ps and 10ps . Up to five periods are visible, making it possible to quantify the excitation dependent damping. We find that this damping is more pronounced for shorter pulse widths and show that its origin is the nonresonant excitation of carriers in the wetting layer, most likely involving bound-to-continuum and continuum-to-bound transitions.

Synthesis of carbon-based quantum dots from starch extracts: Optical investigations.

PubMed

Al-Douri, Y; Badi, N; Voon, C H

2018-03-01

Carbon-based quantum dots (C-QDs) were synthesized through microwave-assisted carbonization of an aqueous starch suspension mediated by sulphuric and phosphoric acids. The as-prepared C-QDs showed blue, green and yellow luminescence without the addition of any surface-passivating agent. The C-QDs were further analyzed by UV-vis spectroscopy to measure the optical response of the organic compound. The energy gaps revealed narrow sizing of C-QDs in the semiconductor range. The optical refractive index and dielectric constant were investigated. The C-QDs size distribution was characterized. The results suggested an easy route to the large scale production of C-QDs materials. Copyright © 2017 John Wiley & Sons, Ltd.

Nonlinear optical switching and optical limiting in colloidal CdSe quantum dots investigated by nanosecond Z-scan measurement

NASA Astrophysics Data System (ADS)

Valligatla, Sreeramulu; Haldar, Krishna Kanta; Patra, Amitava; Desai, Narayana Rao

2016-10-01

The semiconductor nanocrystals are found to be promising class of third order nonlinear optical materials because of quantum confinement effects. Here, we highlight the nonlinear optical switching and optical limiting of cadmium selenide (CdSe) quantum dots (QDs) using nanosecond Z-scan measurement. The intensity dependent nonlinear absorption and nonlinear refraction of CdSe QDs were investigated by applying the Z-scan technique with 532 nm, nanosecond laser pulses. At lower intensities, the nonlinear process is dominated by saturable absorption (SA) and it is changed to reverse saturable absorption (RSA) at higher intensities. The SA behaviour is attributed to the ground state bleaching and the RSA is ascribed to free carrier absorption (FCA) of CdSe QDs. The nonlinear optical switching behaviour and reverse saturable absorption makes CdSe QDs are good candidate for all-optical device and optical limiting applications.

Optical Biosensors Based on Semiconductor Nanostructures

PubMed Central

Martín-Palma, Raúl J.; Manso, Miguel; Torres-Costa, Vicente

2009-01-01

The increasing availability of semiconductor-based nanostructures with novel and unique properties has sparked widespread interest in their use in the field of biosensing. The precise control over the size, shape and composition of these nanostructures leads to the accurate control of their physico-chemical properties and overall behavior. Furthermore, modifications can be made to the nanostructures to better suit their integration with biological systems, leading to such interesting properties as enhanced aqueous solubility, biocompatibility or bio-recognition. In the present work, the most significant applications of semiconductor nanostructures in the field of optical biosensing will be reviewed. In particular, the use of quantum dots as fluorescent bioprobes, which is the most widely used application, will be discussed. In addition, the use of some other nanometric structures in the field of biosensing, including porous semiconductors and photonic crystals, will be presented. PMID:22346691

Growth of group II-VI semiconductor quantum dots with strong quantum confinement and low size dispersion

NASA Astrophysics Data System (ADS)

Pandey, Praveen K.; Sharma, Kriti; Nagpal, Swati; Bhatnagar, P. K.; Mathur, P. C.

2003-11-01

CdTe quantum dots embedded in glass matrix are grown using two-step annealing method. The results for the optical transmission characterization are analysed and compared with the results obtained from CdTe quantum dots grown using conventional single-step annealing method. A theoretical model for the absorption spectra is used to quantitatively estimate the size dispersion in the two cases. In the present work, it is established that the quantum dots grown using two-step annealing method have stronger quantum confinement, reduced size dispersion and higher volume ratio as compared to the single-step annealed samples. (

Linearly polarized light emission from quantum dots with plasmonic nanoantenna arrays.

PubMed

Ren, Mengxin; Chen, Mo; Wu, Wei; Zhang, Lihui; Liu, Junku; Pi, Biao; Zhang, Xinzheng; Li, Qunqing; Fan, Shoushan; Xu, Jingjun

2015-05-13

Polarizers provide convenience in generating polarized light, meanwhile their adoption raises problems of extra weight, cost, and energy loss. Aiming to realize polarizer-free polarized light sources, herein, we present a plasmonic approach to achieve direct generation of linearly polarized optical waves at the nanometer scale. Periodic slot nanoantenna arrays are fabricated, which are driven by the transition dipole moments of luminescent semiconductor quantum dots. By harnessing interactions between quantum dots and scattered fields from the nanoantennas, spontaneous emission with a high degree of linear polarization is achieved from such hybrid antenna system with polarization perpendicular to antenna slot. We also demonstrate that the polarization is engineerable in aspects of both spectrum and magnitude by tailoring plasmonic resonance of the antenna arrays. Our findings will establish a basis for the development of innovative polarized light-emitting devices, which are useful in optical displays, spectroscopic techniques, optical telecommunications, and so forth.

Demonstration of quantum entanglement between a single electron spin confined to an InAs quantum dot and a photon.

PubMed

Schaibley, J R; Burgers, A P; McCracken, G A; Duan, L-M; Berman, P R; Steel, D G; Bracker, A S; Gammon, D; Sham, L J

2013-04-19

The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot's excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×10(3) s(-1). This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network.

Development of Highly Ordered Heterostructured Semiconductor Nanowire Arrays for Sub-Wavelength Optical Devices

DTIC Science & Technology

2007-06-01

properties of nanowires" J. Appl. Phys 98, 094306 (2005) 9. Harry E. Ruda and Alexander Shik, "Polarization-sensitive optical properties of metallic and...34Biexcitons in parabolic quantum dots", Phys. Rev. B. 73, 125321 (2006). 11. M. Blumin, H.E. Ruda, I. Savelyev , A Shik and H. Wang, "Self-assembled InAs

Self-generation of optical frequency comb in single section quantum dot Fabry-Perot lasers: a theoretical study.

PubMed

Bardella, Paolo; Columbo, Lorenzo Luigi; Gioannini, Mariangela

2017-10-16

Optical Frequency Comb (OFC) generated by semiconductor lasers are currently widely used in the extremely timely field of high capacity optical interconnects and high precision spectroscopy. In the last decade, several experimental evidences of spontaneous OFC generation have been reported in single section Quantum Dot (QD) lasers. Here we provide a physical understanding of these self-organization phenomena by simulating the multi-mode dynamics of a single section Fabry-Perot (FP) QD laser using a Time-Domain Traveling-Wave (TDTW) model that properly accounts for coherent radiation-matter interaction in the semiconductor active medium and includes the carrier grating generated by the optical standing wave pattern in the laser cavity. We show that the latter is the fundamental physical effect at the origin of the multi-mode spectrum appearing just above threshold. A self-mode-locking regime associated with the emission of OFC is achieved for higher bias currents and ascribed to nonlinear phase sensitive effects as Four Wave Mixing (FWM). Our results explain in detail the behaviour observed experimentally by different research groups and in different QD and Quantum Dash (QDash) devices.

Quantum Dots for Live Cell and In Vivo Imaging

PubMed Central

Walling, Maureen A; Novak, Jennifer A; Shepard, Jason R. E

2009-01-01

In the past few decades, technology has made immeasurable strides to enable visualization, identification, and quantitation in biological systems. Many of these technological advancements are occurring on the nanometer scale, where multiple scientific disciplines are combining to create new materials with enhanced properties. The integration of inorganic synthetic methods with a size reduction to the nano-scale has lead to the creation of a new class of optical reporters, called quantum dots. These semiconductor quantum dot nanocrystals have emerged as an alternative to organic dyes and fluorescent proteins, and are brighter and more stable against photobleaching than standard fluorescent indicators. Quantum dots have tunable optical properties that have proved useful in a wide range of applications from multiplexed analysis such as DNA detection and cell sorting and tracking, to most recently demonstrating promise for in vivo imaging and diagnostics. This review provides an in-depth discussion of past, present, and future trends in quantum dot use with an emphasis on in vivo imaging and its related applications. PMID:19333416

Above threshold spectral dependence of linewidth enhancement factor, optical duration and linear chirp of quantum dot lasers.

PubMed

Kim, Jimyung; Delfyett, Peter J

2009-12-07

The spectral dependence of the linewidth enhancement factor above threshold is experimentally observed from a quantum dot Fabry-Pérot semiconductor laser. The linewidth enhancement factor is found to be reduced when the quantum dot laser operates approximately 10 nm offset to either side of the gain peak. It becomes significantly reduced on the anti-Stokes side as compared to the Stokes side. It is also found that the temporal duration of the optical pulses generated from quantum dot mode-locked lasers is shorter when the laser operates away from the gain peak. In addition, less linear chirp is impressed on the pulse train generated from the anti-Stokes side whereas the pulses generated from the gain peak and Stokes side possess a large linear chirp. These experimental results imply that enhanced performance characteristics of quantum dot lasers can be achieved by operating on the anti-Stokes side, approximately 10 nm away from the gain peak.

Interference Lithography for Optical Devices and Coatings

DTIC Science & Technology

2010-01-01

semiconductor quantum dots. J. Chem. Phys. 2004, 121, 7421. 100. Jeon, S.; Braun, P. V., Hydrothermal Synthesis of Er-Doped Luminescent TiO2 Nanoparticles ...Silica Nanoparticle Synthesis .....................................................................23 2.2.2 Polymer Matrix Formulation...41 CHAPTER 3: NANOPARTICLE SYNTHESIS , FUNCTIONALIZATION, AND INCORPORATION INTO

Observation of entanglement between a quantum dot spin and a single photon.

PubMed

Gao, W B; Fallahi, P; Togan, E; Miguel-Sanchez, J; Imamoglu, A

2012-11-15

Entanglement has a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, a main challenge is the efficient generation of entanglement between stationary (spin) and propagating (photon) quantum bits. Here we report the observation of quantum entanglement between a semiconductor quantum dot spin and the colour of a propagating optical photon. The demonstration of entanglement relies on the use of fast, single-photon detection, which allows us to project the photon into a superposition of red and blue frequency components. Our results extend the previous demonstrations of single-spin/single-photon entanglement in trapped ions, neutral atoms and nitrogen-vacancy centres to the domain of artificial atoms in semiconductor nanostructures that allow for on-chip integration of electronic and photonic elements. As a result of its fast optical transitions and favourable selection rules, the scheme we implement could in principle generate nearly deterministic entangled spin-photon pairs at a rate determined ultimately by the high spontaneous emission rate. Our observation constitutes a first step towards implementation of a quantum network with nodes consisting of semiconductor spin quantum bits.

Quantum Dots in Diagnostics and Detection: Principles and Paradigms

PubMed Central

Pisanic, T. R.; Zhang, Y.; Wang, T. H.

2014-01-01

Quantum dots are semiconductor nanocrystals that exhibit exceptional optical and electrical behaviors not found in their bulk counterparts. Following seminal work in the development of water-soluble quantum dots in the late 1990's, researchers have sought to develop interesting and novel ways of exploiting the extraordinary properties of quantum dots for biomedical applications. Since that time, over 10,000 articles have been published related to the use of quantum dots in biomedicine, many of which regard their use in detection and diagnostic bioassays. This review presents a didactic overview of fundamental physical phenomena associated with quantum dots and paradigm examples of how these phenomena can and have been readily exploited for manifold uses in nanobiotechnology with a specific focus on their implementation in in vitro diagnostic assays and biodetection. PMID:24770716

Coherent electron{endash}hole correlations in quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joensson, L.; Steiner, M.M.; Wilkins, J.W.

1997-03-01

Using numerical time propagation of the electron{endash}hole wave function, we demonstrate how various coherent correlation effects can be observed by laser excitation of a nanoscale semiconductor quantum dot. The lowest-lying states of an electron{endash}hole pair, when appropriately excited by a laser pulse, give rise to charge oscillations that are manifested by beatings in the optical or intraband polarizations. A GaAs 5{times}25{times}25 nm{sup 3} dot in the effective-mass approximation, including the screened Coulomb interaction between the electron and a heavy or light hole, is simulated. {copyright} {ital 1997 American Institute of Physics.}

Quantum Confined Semiconductors

DTIC Science & Technology

2015-02-01

diodes [8-10], metamaterials [11-13], and solar cells [14,15]. As a consequence, the optical and electrical stability of colloidal quantum dots...PbS quantum dot solar cells with high fill factor,” ACS Nano, 4 (7), 3743–3752 (2010). [15] Gur, I., Fromer, N. A., Geier, M. L. and Alivisatos, A...P., “Air-stable all-inorganic nanocrystal solar cells processed from solution,” Sci. 310, 462–465 (2005). [16] Dai, Q., Wang, Y. N., Zhang, Y

Modeling and studying of white light emitting diodes based on CdS/ZnS spherical quantum dots

NASA Astrophysics Data System (ADS)

Hasanirokh, K.; Asgari, A.

2018-07-01

In this paper, we propose a quantum dot (QD) based white light emitting diode (WLED) structure to study theoretically the material gain and quantum efficiency of the system. We consider the spherical QDs with a II-VI semiconductor core (CdS) that covered with a wider band gap semiconductor acting as a shell (ZnS). In order to generate white light spectrum, we use layers with different dot size that can emit blue, green and red colors. The blue emission originating from CdS core combines to green/orange components originating from ZnS shell and creates an efficiency white light emission. To model this device, at first, we solve Schrödinger and Poisson equations self consistently and obtain eigen energies and wave functions. Then, we calculate the optical gain and internal quantum efficiency (IQE) of a CdS/ZnS LED sample. We investigate the structural parameter effects on the optical properties of the WLED. The numerical results show that the gain profile and IQE curves depend strongly on the structural parameters such as dot size, carrier density and volume scaling parameter. The gain profile becomes higher and wider with increasing the core radius while it becomes less and narrower with increasing the shell thickness. Furthermore, it is found that the volume scaling parameter can manage the system quantum efficiency.

Small signal analysis of four-wave mixing in InAs/GaAs quantum-dot semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Ma, Shaozhen; Chen, Zhe; Dutta, Niloy K.

2009-02-01

A model to study four-wave mixing (FWM) wavelength conversion in InAs-GaAs quantum-dot semiconductor optical amplifier is proposed. Rate equations involving two QD states are solved to simulate the carrier density modulation in the system, results show that the existence of QD excited state contributes to the ultra fast recover time for single pulse response by serving as a carrier reservoir for the QD ground state, its speed limitations are also studied. Nondegenerate four-wave mixing process with small intensity modulation probe signal injected is simulated using this model, a set of coupled wave equations describing the evolution of all frequency components in the active region of QD-SOA are derived and solved numerically. Results show that better FWM conversion efficiency can be obtained compared with the regular bulk SOA, and the four-wave mixing bandwidth can exceed 1.5 THz when the detuning between pump and probe lights is 0.5 nm.

Simultaneous multichannel wavelength multicasting and XOR logic gate multicasting for three DPSK signals based on four-wave mixing in quantum-dot semiconductor optical amplifier.

PubMed

Qin, Jun; Lu, Guo-Wei; Sakamoto, Takahide; Akahane, Kouichi; Yamamoto, Naokatsu; Wang, Danshi; Wang, Cheng; Wang, Hongxiang; Zhang, Min; Kawanishi, Tetsuya; Ji, Yuefeng

2014-12-01

In this paper, we experimentally demonstrate simultaneous multichannel wavelength multicasting (MWM) and exclusive-OR logic gate multicasting (XOR-LGM) for three 10Gbps non-return-to-zero differential phase-shift-keying (NRZ-DPSK) signals in quantum-dot semiconductor optical amplifier (QD-SOA) by exploiting the four-wave mixing (FWM) process. No additional pump is needed in the scheme. Through the interaction of the input three 10Gbps DPSK signal lights in QD-SOA, each channel is successfully multicasted to three wavelengths (1-to-3 for each), totally 3-to-9 MWM, and at the same time, three-output XOR-LGM is obtained at three different wavelengths. All the new generated channels are with a power penalty less than 1.2dB at a BER of 10(-9). Degenerate and non-degenerate FWM components are fully used in the experiment for data and logic multicasting.

Coherent control of optical absorption and the energy transfer pathway of an infrared quantum dot hybridized with a VO2 nanoparticle

NASA Astrophysics Data System (ADS)

Hatef, Ali; Zamani, Naser; Johnston, William

2017-04-01

We systematically investigate the optical response of a semiconductor quantum dot (QD) hybridized with a vanadium dioxide nanoparticle (VO2NP) in the infrared (IR) region. The VO2NP features a semiconductor to metal phase change characteristic below and above a critical temperature that leads to an abrupt change in the particle’s optical properties. This feature means that the QD-VO2NP hybrid system can support the coherent coupling of exciton-polaritons and exciton-plasmon polaritons in the semiconductor and metal phases of the VO2NP, respectively. In our calculations, the VO2NP phase transition is modelled with a filling fraction (f), representing the fraction of the VO2NP in the metallic phase. The phase transition is driven by the hybrid system’s interaction with a continuous wave (CW) IR laser field. In this paper, we show how control over the filling fraction results in the enhancement or suppression of the QD’s linear absorption. These variations in the QD absorption is due to dramatic changes in the effective local field experienced by the QD and the non-radiative energy transfer from the QD to the VO2NP. The presented results have the potential to be applied to the design of thermal sensors at the nanoscale.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bishnoi, Dimple

In this paper, we demonstrate theoretically that the Quantum dots are quite interesting for the electronics industry. Semiconductor quantum dots (QDs) are nanometer-scale crystals, which have unique photo physical, quantum electrical properties, size-dependent optical properties, There small size means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Cheaper than modern commercial solar cells while making use of a wider variety of photon energies, including “waste heat” from the sun’s energy. Quantum dots can be used in tandem cells, which are multi junction photovoltaic cells or in the intermediate bandmore » setup. PbSe (lead selenide) is commonly used in quantum dot solar cells.« less

A semiconductor photon-sorter

NASA Astrophysics Data System (ADS)

Bennett, A. J.; Lee, J. P.; Ellis, D. J. P.; Farrer, I.; Ritchie, D. A.; Shields, A. J.

2016-10-01

Obtaining substantial nonlinear effects at the single-photon level is a considerable challenge that holds great potential for quantum optical measurements and information processing. Of the progress that has been made in recent years one of the most promising methods is to scatter coherent light from quantum emitters, imprinting quantum correlations onto the photons. We report effective interactions between photons, controlled by a single semiconductor quantum dot that is weakly coupled to a monolithic cavity. We show that the nonlinearity of a transition modifies the counting statistics of a Poissonian beam, sorting the photons in number. This is used to create strong correlations between detection events and to create polarization-correlated photons from an uncorrelated stream using a single spin. These results pave the way for semiconductor optical switches operated by single quanta of light.

Intermediate-band photosensitive device with quantum dots embedded in energy fence barrier

DOEpatents

Forrest, Stephen R.; Wei, Guodan

2010-07-06

A plurality of layers of a first semiconductor material and a plurality of dots-in-a-fence barriers disposed in a stack between a first electrode and a second electrode. Each dots-in-a-fence barrier consists essentially of a plurality of quantum dots of a second semiconductor material embedded between and in direct contact with two layers of a third semiconductor material. Wave functions of the quantum dots overlap as at least one intermediate band. The layers of the third semiconductor material are arranged as tunneling barriers to require a first electron and/or a first hole in a layer of the first material to perform quantum mechanical tunneling to reach the second material within a respective quantum dot, and to require a second electron and/or a second hole in a layer of the first semiconductor material to perform quantum mechanical tunneling to reach another layer of the first semiconductor material.

Demonstration of Quantum Entanglement between a Single Electron Spin Confined to an InAs Quantum Dot and a Photon

NASA Astrophysics Data System (ADS)

Schaibley, J. R.; Burgers, A. P.; McCracken, G. A.; Duan, L.-M.; Berman, P. R.; Steel, D. G.; Bracker, A. S.; Gammon, D.; Sham, L. J.

2013-04-01

The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot’s excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×103s-1. This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network.

Hot electron dynamics at semiconductor surfaces: Implications for quantum dot photovoltaics

NASA Astrophysics Data System (ADS)

Tisdale, William A., III

Finding a viable supply of clean, renewable energy is one of the most daunting challenges facing the world today. Solar cells have had limited impact in meeting this challenge because of their high cost and low power conversion efficiencies. Semiconductor nanocrystals, or quantum dots, are promising materials for use in novel solar cells because they can be processed with potentially inexpensive solution-based techniques and because they are predicted to have novel optoelectronic properties that could enable the realization of ultra-efficient solar power converters. However, there is a lack of fundamental understanding regarding the behavior of highly-excited, or "hot," charge carriers near quantum-dot and semiconductor interfaces, which is of paramount importance to the rational design of high-efficiency devices. The elucidation of these ultrafast hot electron dynamics is the central aim of this Dissertation. I present a theoretical framework for treating the electronic interactions between quantum dots and bulk semiconductor surfaces and propose a novel experimental technique, time-resolved surface second harmonic generation (TR-SHG), for probing these interactions. I then describe a series of experimental investigations into hot electron dynamics in specific quantum-dot/semiconductor systems. A two-photon photoelectron spectroscopy (2PPE) study of the technologically-relevant ZnO(1010) surface reveals ultrafast (sub-30fs) cooling of hot electrons in the bulk conduction band, which is due to strong electron-phonon coupling in this highly polar material. The presence of a continuum of defect states near the conduction band edge results in Fermi-level pinning and upward (n-type) band-bending at the (1010) surface and provides an alternate route for electronic relaxation. In monolayer films of colloidal PbSe quantum dots, chemical treatment with either hydrazine or 1,2-ethanedithiol results in strong and tunable electronic coupling between neighboring quantum dots. A TR-SHG study of these electronically-coupled quantum-dot films reveals temperature-activated cooling of hot charge carriers and coherent excitation of a previously-unidentified surface optical phonon. Finally, I report the first experimental observation of ultrafast electron transfer from the higher excited states of a colloidal quantum dot (PbSe) to delocalized conduction band states of a widely-used electron acceptor (TiO2). The electric field resulting from ultrafast (<50fs) separation of charge carriers across the PbSe/TiO2(110) interface excites coherent vibration of the TiO2 surface atoms, whose collective motions can be followed in real time.

Bioengineered II-VI semiconductor quantum dot-carboxymethylcellulose nanoconjugates as multifunctional fluorescent nanoprobes for bioimaging live cells

NASA Astrophysics Data System (ADS)

Mansur, Alexandra A. P.; Mansur, Herman S.; Mansur, Rafael L.; de Carvalho, Fernanda G.; Carvalho, Sandhra M.

2018-01-01

Colloidal semiconductor quantum dots (QDs) are light-emitting ultra-small nanoparticles, which have emerged as a new class of nanoprobes with unique optical properties for bioimaging and biomedical diagnostic. However, to be used for most biomedical applications the biocompatibility and water-solubility are mandatory that can achieved through surface modification forming QD-nanoconjugates. In this study, semiconductor II-VI quantum dots of type MX (M = Cd, Pb, Zn, X = S) were directly synthesized in aqueous media and at room temperature using carboxymethylcellulose sodium salt (CMC) behaving simultaneously as stabilizing and surface biofunctional ligand. These nanoconjugates were extensively characterized using UV-visible spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, dynamic light scattering and zeta potential. The results demonstrated that the biopolymer was effective on nucleating and stabilizing the colloidal nanocrystals of CdS, ZnS, and PbS with the average diameter ranging from 2.0 to 5.0 nm depending on the composition of the semiconductor core, which showed quantum-size confinement effect. These QD/polysaccharide conjugates showed luminescent activity from UV-visible to near-infrared range of the spectra under violet laser excitation. Moreover, the bioassays performed proved that these novel nanoconjugates were biocompatible and behaved as composition-dependent fluorescent nanoprobes for in vitro live cell bioimaging with very promising perspectives to be used in numerous biomedical applications and nanomedicine.

Emerging technologies for high performance infrared detectors

NASA Astrophysics Data System (ADS)

Tan, Chee Leong; Mohseni, Hooman

2018-01-01

Infrared photodetectors (IRPDs) have become important devices in various applications such as night vision, military missile tracking, medical imaging, industry defect imaging, environmental sensing, and exoplanet exploration. Mature semiconductor technologies such as mercury cadmium telluride and III-V material-based photodetectors have been dominating the industry. However, in the last few decades, significant funding and research has been focused to improve the performance of IRPDs such as lowering the fabrication cost, simplifying the fabrication processes, increasing the production yield, and increasing the operating temperature by making use of advances in nanofabrication and nanotechnology. We will first review the nanomaterial with suitable electronic and mechanical properties, such as two-dimensional material, graphene, transition metal dichalcogenides, and metal oxides. We compare these with more traditional low-dimensional material such as quantum well, quantum dot, quantum dot in well, semiconductor superlattice, nanowires, nanotube, and colloid quantum dot. We will also review the nanostructures used for enhanced light-matter interaction to boost the IRPD sensitivity. These include nanostructured antireflection coatings, optical antennas, plasmonic, and metamaterials.

Entanglement distribution schemes employing coherent photon-to-spin conversion in semiconductor quantum dot circuits

NASA Astrophysics Data System (ADS)

Gaudreau, Louis; Bogan, Alex; Korkusinski, Marek; Studenikin, Sergei; Austing, D. Guy; Sachrajda, Andrew S.

2017-09-01

Long distance entanglement distribution is an important problem for quantum information technologies to solve. Current optical schemes are known to have fundamental limitations. A coherent photon-to-spin interface built with quantum dots (QDs) in a direct bandgap semiconductor can provide a solution for efficient entanglement distribution. QD circuits offer integrated spin processing for full Bell state measurement (BSM) analysis and spin quantum memory. Crucially the photo-generated spins can be heralded by non-destructive charge detection techniques. We review current schemes to transfer a polarization-encoded state or a time-bin-encoded state of a photon to the state of a spin in a QD. The spin may be that of an electron or that of a hole. We describe adaptations of the original schemes to employ heavy holes which have a number of attractive properties including a g-factor that is tunable to zero for QDs in an appropriately oriented external magnetic field. We also introduce simple throughput scaling models to demonstrate the potential performance advantage of full BSM capability in a QD scheme, even when the quantum memory is imperfect, over optical schemes relying on linear optical elements and ensemble quantum memories.

Synthesis of Zn-In-S Quantum Dots with Tunable Composition and Optical Properties.

PubMed

Wang, Xianliang; Damasco, Jossana; Shao, Wei; Ke, Yujie; Swihart, Mark T

2016-03-03

II-III-VI semiconductors are of interest due to their chemical stability and composition-tunable optical properties. Here, we report a methodology for the synthesis of monodisperse zinc-indium-sulfide (ZIS) alloy quantum dots (QDs, mean diameter from ∼2 to 3.5 nm) with an In content substantially below that of the stoichiometric ZnIn2 S4 compound. The effects of indium incorporation on the size, lattice constant, and optical properties of ZIS QDs are elucidated. In contrast to previous reports, we employ sulfur dissolved in oleic acid as the sulfur donor rather than thioacetamide (TAA). The size of the ZIS QDs and their crystal lattice constant increased with increasing In incorporation, but they maintained the cubic sphalerite phase of ZnS, rather than the hexagonal phase typical of ZnIn2 S4 . The QDs' absorbance onset at UV wavelengths red-shifts with increasing In content and the accompanying increase in NC size. The ZIS NCs and related materials, whose synthesis is enabled by the approach presented here, provide new opportunities to apply II-III-VI semiconductors in solution-processed UV optoelectronics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-Performance, Solution-Processed Quantum Dot Light-Emitting Field-Effect Transistors with a Scandium-Incorporated Indium Oxide Semiconductor.

PubMed

He, Penghui; Jiang, Congbiao; Lan, Linfeng; Sun, Sheng; Li, Yizhi; Gao, Peixiong; Zhang, Peng; Dai, Xingqiang; Wang, Jian; Peng, Junbiao; Cao, Yong

2018-05-22

Light-emitting field-effect transistors (LEFETs) have attained great attention due to their special characteristics of both the switching capacity and the electroluminescence capacity. However, high-performance LEFETs with high mobility, high brightness, and high efficiency have not been realized due to the difficulty in developing high electron and hole mobility materials with suitable band structures. In this paper, quantum dot hybrid LEFETs (QD-HLEFETs) combining high-luminous-efficiency quantum dots (QDs) and a solution-processed scandium-incorporated indium oxide (Sc:In 2 O 3 ) semiconductor were demonstrated. The red QD-HLEFET showed high electrical and optical performance with an electron mobility of 0.8 cm 2 V -1 s -1 , a maximum brightness of 13 400 cd/m 2 , and a maximum external quantum efficiency of 8.7%. The high performance of the QD-HLEFET is attributed to the good energy band matching between Sc:In 2 O 3 and QDs and the balanced hole and electron injection (less exciton nonradiative recombination). In addition, incorporation of Sc into In 2 O 3 can suppress the oxygen vacancy and free carrier generation and brings about excellent current and optical modulation (the on/off current ratio is 10 5 and the on/off brightness ratio is 10 6 ).

Highly efficient quantum dot-based photoconductive THz materials and devices

NASA Astrophysics Data System (ADS)

Rafailov, E. U.; Leyman, R.; Carnegie, D.; Bazieva, N.

2013-09-01

We demonstrate Terahertz (THz) signal sources based on photoconductive (PC) antenna devices comprising active layers of InAs semiconductor quantum dots (QDs) on GaAs. Antenna structures comprised of multiple active layers of InAs:GaAs PC materials are optically pumped using ultrashort pulses generated by a Ti:Sapphire laser and CW dualwavelength laser diodes. We also characterised THz output signals using a two-antenna coherent detection system. We discuss preliminary performance data from such InAs:GaAs THz devices which exhibit efficient emission of both pulsed and continuous wave (CW) THz signals and significant optical-to-THz conversion at both absorption wavelength ranges, <=850 nm and <=1300 nm.

Scalable quantum computer architecture with coupled donor-quantum dot qubits

DOEpatents

Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

2014-08-26

A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

Decoupling the effects of confinement and passivation on semiconductor quantum dots.

PubMed

Rudd, Roya; Hall, Colin; Murphy, Peter J; Reece, Peter J; Charrault, Eric; Evans, Drew

2016-07-20

Semiconductor (SC) quantum dots (QDs) have recently been fabricated by both chemical and plasma techniques for specific absorption and emission of light. Their optical properties are governed by the size of the QD and the chemistry of any passivation at their surface. Here, we decouple the effects of confinement and passivation by utilising DC magnetron sputtering to fabricate SC QDs in a perfluorinated polyether oil. Very high band gaps are observed for fluorinated QDs with increasing levels of quantum confinement (from 4.2 to 4.6 eV for Si, and 2.5 to 3 eV for Ge), with a shift down to 3.4 eV for Si when oxygen is introduced to the passivation layer. In contrast, the fluorinated Si QDs display a constant UV photoluminescence (3.8 eV) irrespective of size. This ability to tune the size and passivation independently opens a new opportunity to extending the use of simple semiconductor QDs.

Quantum memory node based on a semiconductor double quantum dot in a laser-controlled optical resonator

NASA Astrophysics Data System (ADS)

Tsukanov, A. V.; Kateev, I. Yu

2017-08-01

The concept of a quantum node consisting of a memory qubit and a frequency convertor is proposed and analysed. The memory qubit is presented by a semiconductor four-level double quantum dot (DQD) placed in an optical microresonator (MR). The DQD contains an electron in the quantised part of the conduction band and the MR can be populated by a certain number of photons. The DQD and MR states are controlled be applying the laser and electrostatic fields. The difference between the telecommunication frequency of the photon (transport qubit) supplied to the system through a waveguide and the frequency of the electronic transition in the DQD is compensated for using an auxiliary element, i.e. a frequency convertor based on a single quantum dot (QD). This design allows the electron - photon state of the hybrid system to be controlled by an appropriate variation of the field parameters and the switching between resonance and nonresonance DQD and MR interaction regimes. As an example, a GaAs DQD placed in a microdisk MR is studied. A numerical technique for modelling an optical spectrum of a microdisk MR with an additional layer (AL) deposited on its surface is developed. Using this technique, the effect of the AL on the MR eigenmode properties is investigated and the possibility of tuning its frequency to the QD electronic transition frequency by depositing an AL on the disk surface is demonstrated.

Arbitrary Multicolor Photodetection by Hetero-integrated Semiconductor Nanostructures

PubMed Central

Sang, Liwen; Hu, Junqing; Zou, Rujia; Koide, Yasuo; Liao, Meiyong

2013-01-01

The typical photodetectors can only detect one specific optical spectral band, such as InGaAs and graphene-PbS quantum dots for near-infrared (NIR) light detection, CdS and Si for visible light detection, and ZnO and III-nitrides for UV light detection. So far, none of the developed photodetector can achieve the multicolor detection with arbitrary spectral selectivity, high sensitivity, high speed, high signal-to-noise ratio, high stability, and simplicity (called 6S requirements). Here, we propose a universal strategy to develop multicolor photodetectors with arbitrary spectral selectivity by integrating various semiconductor nanostructures on a wide-bandgap semiconductor or an insulator substrate. Because the photoresponse of each spectral band is determined by each semiconductor nanostructure or the semiconductor substrate, multicolor detection satisfying 6S requirements can be readily satisfied by selecting the right semiconductors. PMID:23917790

The Physics of Ultracold Sr2 Molecules: Optical Production and Precision Measurement

NASA Astrophysics Data System (ADS)

Osborn, Christopher Butler

Colloidal quantum dots have desirable optical properties which can be exploited to realize a variety of photonic devices and functionalities. However, colloidal dots have not had a pervasive utility in photonic devices because of the absence of patterning methods. The electronic chip industry is highly successful due to the well-established lithographic procedures. In this thesis we borrow ideas from the semiconductor industry to develop lithographic techniques that can be used to pattern colloidal quantum dots while ensuring that the optical properties of the quantum dots are not affected by the process. In this thesis we have developed colloidal quantum dot based waveguide structures for amplification and switching applications for all-optical signal processing. We have also developed colloidal quantum dot based light emitting diodes. We successfully introduced CdSe/ZnS quantum dots into a UV curable photo-resist, which was then patterned to realize active devices. In addition, "passive" devices (devices without quantum dots) were integrated to "active" devices via waveguide couplers. Use of photo-resist devices offers two distinct advantages. First, they have low scattering loss and secondly, they allow good fiber to waveguide coupling efficiency due to the low refractive index which allows for large waveguide cross-sections while supporting single mode operation. Practical planar photonic devices and circuits incorporating both active and passive structures can now be realized, now that we have patterning capabilities of quantum dots while maintaining the original optical attributes of the system. In addition to the photo-resist host, we also explored the incorporation of colloidal quantum dots into a dielectric silicon dioxide and silicon nitride one-dimensional microcavity structures using low temperature plasma enhanced chemical vapor deposition. This material system can be used to realize microcavity light emitting diodes that can be realized on any substrate. As a proof of concept demonstration we show a 1550 nm emitting all-dielectric vertical cavity structure embedded with PbS quantum dots. Enhancement in spontaneous emission from the dots embedded in the microcavity is also demonstrated.

Metal-Insulator-Semiconductor Photodetectors

PubMed Central

Lin, Chu-Hsuan; Liu, Chee Wee

2010-01-01

The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III–V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows. PMID:22163382

Theoretical Investigation of Optical Detection and Recognition of Single Biological Molecules Using Coherent Dynamics of Exciton-Plasmon Coupling

PubMed Central

Sadeghi, S. M.; Hood, B.; Patty, K. D.; Mao, C.-B.

2013-01-01

We use quantum coherence in a system consisting of one metallic nanorod and one semi-conductor quantum dot to investigate a plasmonic nanosensor capable of digital optical detection and recognition of single biological molecules. In such a sensor the adsorption of a specific molecule to the nanorod turns off the emission of the system when it interacts with an optical pulse having a certain intensity and temporal width. The proposed quantum sensors can count the number of molecules of the same type or differentiate between molecule types with digital optical signals that can be measured with high certainty. We show that these sensors are based on the ultrafast upheaval of coherent dynamics of the system and the removal of coherent blockage of energy transfer from the quantum dot to the nanorod once the adsorption process has occurred. PMID:24040424

III-V quantum light source and cavity-QED on silicon.

PubMed

Luxmoore, I J; Toro, R; Del Pozo-Zamudio, O; Wasley, N A; Chekhovich, E A; Sanchez, A M; Beanland, R; Fox, A M; Skolnick, M S; Liu, H Y; Tartakovskii, A I

2013-01-01

Non-classical light sources offer a myriad of possibilities in both fundamental science and commercial applications. Single photons are the most robust carriers of quantum information and can be exploited for linear optics quantum information processing. Scale-up requires miniaturisation of the waveguide circuit and multiple single photon sources. Silicon photonics, driven by the incentive of optical interconnects is a highly promising platform for the passive optical components, but integrated light sources are limited by silicon's indirect band-gap. III-V semiconductor quantum-dots, on the other hand, are proven quantum emitters. Here we demonstrate single-photon emission from quantum-dots coupled to photonic crystal nanocavities fabricated from III-V material grown directly on silicon substrates. The high quality of the III-V material and photonic structures is emphasized by observation of the strong-coupling regime. This work opens-up the advantages of silicon photonics to the integration and scale-up of solid-state quantum optical systems.

CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

PubMed Central

Gomes, Suzete A.O.; Vieira, Cecilia Stahl; Almeida, Diogo B.; Santos-Mallet, Jacenir R.; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Feder, Denise

2011-01-01

Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

Self-assembling complexes of quantum dots and scFv antibodies for cancer cell targeting and imaging.

PubMed

Zdobnova, Tatiana A; Stremovskiy, Oleg A; Lebedenko, Ekaterina N; Deyev, Sergey M

2012-01-01

Semiconductor quantum dots represent a novel class of fluorophores with unique physical and chemical properties which could enable a remarkable broadening of the current applications of fluorescent imaging and optical diagnostics. Complexes of quantum dots and antibodies are promising visualising agents for fluorescent detection of selective biomarkers overexpressed in tumor tissues. Here we describe the construction of self-assembling fluorescent complexes of quantum dots and anti-HER1 or anti-HER2/neu scFv antibodies and their interactions with cultured tumor cells. A binding strategy based on a very specific non-covalent interaction between two proteins, barnase and barstar, was used to connect quantum dots and the targeting antibodies. Such a strategy allows combining the targeting and visualization functions simply by varying the corresponding modules of the fluorescent complex.

Self-Assembling Complexes of Quantum Dots and scFv Antibodies for Cancer Cell Targeting and Imaging

PubMed Central

Zdobnova, Tatiana A.; Stremovskiy, Oleg A.; Lebedenko, Ekaterina N.; Deyev, Sergey M.

2012-01-01

Semiconductor quantum dots represent a novel class of fluorophores with unique physical and chemical properties which could enable a remarkable broadening of the current applications of fluorescent imaging and optical diagnostics. Complexes of quantum dots and antibodies are promising visualising agents for fluorescent detection of selective biomarkers overexpressed in tumor tissues. Here we describe the construction of self-assembling fluorescent complexes of quantum dots and anti-HER1 or anti-HER2/neu scFv antibodies and their interactions with cultured tumor cells. A binding strategy based on a very specific non-covalent interaction between two proteins, barnase and barstar, was used to connect quantum dots and the targeting antibodies. Such a strategy allows combining the targeting and visualization functions simply by varying the corresponding modules of the fluorescent complex. PMID:23133578

Monolithically integrated quantum dot optical gain modulator with semiconductor optical amplifier for 10-Gb/s photonic transmission

NASA Astrophysics Data System (ADS)

Yamamoto, Naokatsu; Akahane, Kouichi; Umezawa, Toshimasa; Kawanishi, Tetsuya

2015-03-01

Short-range interconnection and/or data center networks require high capacity and a large number of channels in order to support numerous connections. Solutions employed to meet these requirements involve the use of alternative wavebands to increase the usable optical frequency range. We recently proposed the use of the T- and O-bands (Thousand band: 1000-1260 nm, Original band: 1260-1360 nm) as alternative wavebands because large optical frequency resources (>60 THz) can be easily employed. In addition, a simple and compact Gb/s-order high-speed optical modulator is a critical photonic device for short-range communications. Therefore, to develop an optical modulator that acts as a highfunctional photonic device, we focused on the use of self-assembled quantum dots (QDs) as a three-dimensional (3D) confined structure because QD structures are highly suitable for realizing broadband optical gain media in the T+O bands. In this study, we use the high-quality broadband QD optical gain to develop a monolithically integrated QD optical gain modulator (QD-OGM) device that has a semiconductor optical amplifier (QD-SOA) for Gb/s-order highspeed optical data generation in the 1.3-μm waveband. The insertion loss of the device can be compensated through the SOA, and we obtained an optical gain change of up to ~7 dB in the OGM section. Further, we successfully demonstrate a 10-Gb/s clear eye opening using the QD-OGM/SOA device with a clock-data recovery sequence at the receiver end. These results suggest that the monolithic QD-EOM/SOA is suitable for increasing the number of wavelength channels for smart short-range communications.

Artificial Neuron Based on Integrated Semiconductor Quantum Dot Mode-Locked Lasers

NASA Astrophysics Data System (ADS)

Mesaritakis, Charis; Kapsalis, Alexandros; Bogris, Adonis; Syvridis, Dimitris

2016-12-01

Neuro-inspired implementations have attracted strong interest as a power efficient and robust alternative to the digital model of computation with a broad range of applications. Especially, neuro-mimetic systems able to produce and process spike-encoding schemes can offer merits like high noise-resiliency and increased computational efficiency. Towards this direction, integrated photonics can be an auspicious platform due to its multi-GHz bandwidth, its high wall-plug efficiency and the strong similarity of its dynamics under excitation with biological spiking neurons. Here, we propose an integrated all-optical neuron based on an InAs/InGaAs semiconductor quantum-dot passively mode-locked laser. The multi-band emission capabilities of these lasers allows, through waveband switching, the emulation of the excitation and inhibition modes of operation. Frequency-response effects, similar to biological neural circuits, are observed just as in a typical two-section excitable laser. The demonstrated optical building block can pave the way for high-speed photonic integrated systems able to address tasks ranging from pattern recognition to cognitive spectrum management and multi-sensory data processing.

Artificial Neuron Based on Integrated Semiconductor Quantum Dot Mode-Locked Lasers

PubMed Central

Mesaritakis, Charis; Kapsalis, Alexandros; Bogris, Adonis; Syvridis, Dimitris

2016-01-01

Neuro-inspired implementations have attracted strong interest as a power efficient and robust alternative to the digital model of computation with a broad range of applications. Especially, neuro-mimetic systems able to produce and process spike-encoding schemes can offer merits like high noise-resiliency and increased computational efficiency. Towards this direction, integrated photonics can be an auspicious platform due to its multi-GHz bandwidth, its high wall-plug efficiency and the strong similarity of its dynamics under excitation with biological spiking neurons. Here, we propose an integrated all-optical neuron based on an InAs/InGaAs semiconductor quantum-dot passively mode-locked laser. The multi-band emission capabilities of these lasers allows, through waveband switching, the emulation of the excitation and inhibition modes of operation. Frequency-response effects, similar to biological neural circuits, are observed just as in a typical two-section excitable laser. The demonstrated optical building block can pave the way for high-speed photonic integrated systems able to address tasks ranging from pattern recognition to cognitive spectrum management and multi-sensory data processing. PMID:27991574

Bistable four-wave mixing response in a semiconductor quantum dot coupled to a photonic crystal nanocavity.

PubMed

Li, Jian-Bo; Xiao, Si; Liang, Shan; He, Meng-Dong; Luo, Jian-Hua; Kim, Nam-Chol; Chen, Li-Qun

2017-10-16

We perform a theoretical study of the bistable four-wave mixing (FWM) response in a coupled system comprised of a semiconductor quantum dot (SQD) and a photonic crystal (PC) nanocavity in which the SQD is embedded. It is shown that the shape of the FWM spectrum can switch among single-peaked, double-peaked, triple-peaked, and four-peaked arising from the vacuum Rabi splitting and the exciton-nanocavity coupling. Especially, we map out bistability phase diagrams within a parameter subspace of the system, and find that it is easy to turn on or off the bistable FWM response by only adjusting the excitation frequency or the pumping intensity. Our results offer a feasible means for measuring the SQD-PC nanocavity coupling strength and open a new avenue to design optical switches and memories.

Quantum Dots for Molecular Diagnostics of Tumors

PubMed Central

Zdobnova, T.A.; Lebedenko, E.N.; Deyev, S.М.

2011-01-01

Semiconductor quantum dots (QDs) are a new class of fluorophores with unique physical and chemical properties, which allow to appreciably expand the possibilities for the current methods of fluorescent imaging and optical diagnostics. Here we discuss the prospects of QD application for molecular diagnostics of tumors ranging from cancer-specific marker detection on microplates to non-invasive tumor imagingin vivo. We also point out the essential problems that require resolution in order to clinically promote QD, and we indicate innovative approaches to oncology which are implementable using QD. PMID:22649672

The analytical approach to optimization of active region structure of quantum dot laser

NASA Astrophysics Data System (ADS)

Korenev, V. V.; Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V.

2014-10-01

Using the analytical approach introduced in our previous papers we analyse the possibilities of optimization of size and structure of active region of semiconductor quantum dot lasers emitting via ground-state optical transitions. It is shown that there are optimal length' dispersion and number of QD layers in laser active region which allow one to obtain lasing spectrum of a given width at minimum injection current. Laser efficiency corresponding to the injection current optimized by the cavity length is practically equal to its maximum value.

Quantum dot SOA/silicon external cavity multi-wavelength laser.

PubMed

Zhang, Yi; Yang, Shuyu; Zhu, Xiaoliang; Li, Qi; Guan, Hang; Magill, Peter; Bergman, Keren; Baehr-Jones, Thomas; Hochberg, Michael

2015-02-23

We report a hybrid integrated external cavity, multi-wavelength laser for high-capacity data transmission operating near 1310 nm. This is the first demonstration of a single cavity multi-wavelength laser in silicon to our knowledge. The device consists of a quantum dot reflective semiconductor optical amplifier and a silicon-on-insulator chip with a Sagnac loop mirror and microring wavelength filter. We show four major lasing peaks from a single cavity with less than 3 dB power non-uniformity and demonstrate error-free 4 × 10 Gb/s data transmission.

Inorganic Chemistry Solutions to Semiconductor Nanocrystal Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alvarado, Samuel R.; Guo, Yijun; Ruberu, T. Purnima A.

2014-03-15

The optoelectronic and chemical properties of semiconductor nanocrystals heavily depend on their composition, size, shape and internal structure, surface functionality, etc. Available strategies to alter these properties through traditional colloidal syntheses and ligand exchange methods place a premium on specific reaction conditions and surfactant combinations. In this invited review, we apply a molecular-level understanding of chemical precursor reactivity to reliably control the morphology, composition and intimate architecture (core/shell vs. alloyed) of semiconductor nanocrystals. We also describe our work aimed at achieving highly selective, low-temperature photochemical methods for the synthesis of semiconductor–metal and semiconductor–metal oxide photocatalytic nanocomposites. In addition, we describemore » our work on surface modification of semiconductor nanocrystal quantum dots using new approaches and methods that bypass ligand exchange, retaining the nanocrystal's native ligands and original optical properties, as well as on spectroscopic methods of characterization useful in determining surface ligand organization and chemistry. Using recent examples from our group and collaborators, we demonstrate how these efforts have lead to faster, wider and more systematic application of semiconductor nanocrystal-based materials to biological imaging and tracking, and to photocatalysis of unconventional substrates. We believe techniques and methods borrowed from inorganic chemistry (including coordination, organometallic and solid state chemistry) have much to offer in reaching a better understanding of the synthesis, functionalization and real-life application of such exciting materials as semiconductor nanocrystals (quantum dots, rods, tetrapods, etc.).« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lafuente-Sampietro, A.; CNRS, Institut Néel, F-38000 Grenoble; Institute of Materials Science, University of Tsukuba, 305-8573 Tsukuba

We studied the spin dynamics of a Cr atom incorporated in a II-VI semiconductor quantum dot using photon correlation techniques. We used recently developed singly Cr-doped CdTe/ZnTe quantum dots to access the spin of an individual magnetic atom. Auto-correlation of the photons emitted by the quantum dot under continuous wave optical excitation reveals fluctuations of the localized spin with a timescale in the 10 ns range. Cross-correlation gives quantitative transfer time between Cr spin states. A calculation of the time dependence of the spin levels population in Cr-doped quantum dots shows that the observed spin dynamics is dominated by the exciton-Crmore » interaction. These measurements also provide a lower bound in the 20 ns range for the intrinsic Cr spin relaxation time.« less

A Study on the Applications of Quantum Optical Coherence to Nano-Optics

NASA Astrophysics Data System (ADS)

Hakami, Jabir Wali

Optically controlled dipole-dipole interaction at submicrometers and subwavelength scales leads to many interesting phenomenon and remarkable potential applications in quantum optics, condensed matter physics, and today's micro-devices. In this dissertation, we study the applications of quantum optical coherence to nano-optics in the following systems and aspects. On the one hand, chiral metamaterials has been previously reported as excellent candidates to realize both attractive and repulsive Casimir forces, where the existence of a repulsive Casimir force depends upon the strength of the chirality. On the other hand, nanoscale integration of metal nanoparticles and semiconductors is particularly interesting because the strengths of both materials are combined in such a hybrid system. In the first part of this work, we proposed a technical scheme to coherently control of the Casimir interaction energy with two identical chirality mediums. We took explicit caution regarding the requirements of passivity and causal response of the materials, since these requirements are essential for the application of the Lifshitz formula. The rare-earth metals' atomic species, for instance, dysprosium, is proposed as an applicable medium for the forthcoming studies of possible experimental implementation of our technique. Secondly, we fully investigated the coherent control of the quantum optical properties of spontaneous emission spectra of a semiconductor quantum dot coupled to a metallic nanoparticle. The properties of the spontaneous emission spectra of such a system are studied in detail with and without involving the coherent field. The Rabi splitting effect in the spectrum emitted by the quantum dot under particular conditions is predicted for different sizes of the metal nanoparticles. We show that the spontaneous emission spectra of the transition coupled to surface plasmons may be further modified by adjusting the external coherent control on the adjacent transitions. In the third part, we propose a robust protocol to study the entanglement generation in a hybrid structure consisting of two quantum dots in the proximity of a metallic nanoshell. The entanglement arises impulsively due to common coupling to the plasmonic nanostructure, without demanding postselective measurement or mediating the dissipative environment. The long-lived entangled states can be created deterministically by optimizing the shell thickness as well as the ratio of the distances between the quantum dots and the surface of the shell. The loss of the system is greatly reduced even when the quantum dots are ultraclose to the shell, which signifies a slow decay rate of the coherence information and longtime entanglement preservation.

Giant nonlinear interaction between two optical beams via a quantum dot embedded in a photonic wire

NASA Astrophysics Data System (ADS)

Nguyen, H. A.; Grange, T.; Reznychenko, B.; Yeo, I.; de Assis, P.-L.; Tumanov, D.; Fratini, F.; Malik, N. S.; Dupuy, E.; Gregersen, N.; Auffèves, A.; Gérard, J.-M.; Claudon, J.; Poizat, J.-Ph.

2018-05-01

Optical nonlinearities usually appear for large intensities, but discrete transitions allow for giant nonlinearities operating at the single-photon level. This has been demonstrated in the last decade for a single optical mode with cold atomic gases, or single two-level systems coupled to light via a tailored photonic environment. Here, we demonstrate a two-mode giant nonlinearity with a single semiconductor quantum dot (QD) embedded in a photonic wire antenna. We exploit two detuned optical transitions associated with the exciton-biexciton QD level scheme. Owing to the broadband waveguide antenna, the two transitions are efficiently interfaced with two free-space laser beams. The reflection of one laser beam is then controlled by the other beam, with a threshold power as low as 10 photons per exciton lifetime (1.6 nW ). Such a two-color nonlinearity opens appealing perspectives for the realization of ultralow-power logical gates and optical quantum gates, and could also be implemented in an integrated photonic circuit based on planar waveguides.

Synthesis of Bi2S3 quantum dots for sensitized solar cells by reverse SILAR

NASA Astrophysics Data System (ADS)

Singh, Navjot; Sharma, J.; Tripathi, S. K.

2016-05-01

Quantum Dot Sensitized Solar cells (QDSSC) have great potential to replace silicon-based solar cells. Quantum dots of various materials and sizes could be used to convert most of the visible light into the electrical current. This paper put emphasis on the synthesis of Bismuth Sulphide quantum dots and selectivity of the anionic precursor by Successive Ionic Layer Adsorption Reaction (SILAR). Bismuth Sulfide (Bi2S3) (group V - Vi semiconductor) is strong contestant for cadmium free solar cells due to its optimum band gap for light harvesting. Optical, structural and electrical measurements are reported and discussed. Problem regarding the choice of precursor for anion extraction is discussed. Band gap of the synthesized quantum dots is 1.2 eV which does not match with the required energy band gap of bismuth sulfide that is 1.7eV.

Highly efficient non-degenerate four-wave mixing under dual-mode injection in InP/InAs quantum-dash and quantum-dot lasers at 1.55 μm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadeev, T., E-mail: tagir@mailbox.tu-berlin.de; Arsenijević, D.; Huang, H.

2015-11-09

This work reports on non-degenerate four-wave mixing under dual-mode injection in metalorganic vapor phase epitaxy grown InP/InAs quantum-dash and quantum dot Fabry-Perot laser operating at 1550 nm. High values of normalized conversion efficiency of −18.6 dB, optical signal-to-noise ratio of 37 dB, and third order optical susceptibility normalized to material gain χ{sup (3)}/g{sub 0} of ∼4 × 10{sup −19} m{sup 3}/V{sup 3} are measured for 1490 μm long quantum-dash lasers. These values are similar to those obtained with distributed-feedback lasers and semiconductor optical amplifiers, which are much more complicated to fabricate. On the other hand, due to the faster gain saturation and enhanced modulation of carriermore » populations, quantum-dot lasers demonstrate 12 dB lower conversion efficiency and 4 times lower χ{sup (3)}/g{sub 0} compared to quantum dash lasers.« less

Molecular profiling of single cancer cells and clinical tissue specimens with semiconductor quantum dots

PubMed Central

Xing, Yun; Smith, Andrew M; Agrawal, Amit; Ruan, Gang; Nie, Shuming

2006-01-01

Semiconductor quantum dots (QDs) are a new class of fluorescent labels with broad applications in biomedical imaging, disease diagnostics, and molecular and cell biology. In comparison with organic dyes and fluorescent proteins, quantum dots have unique optical and electronic properties such as size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. Recent advances have led to multifunctional nanoparticle probes that are highly bright and stable under complex in vitro and in vivo conditions. New designs involve encapsulating luminescent QDs with amphiphilic block copolymers, and linking the polymer coating to tumor-targeting ligands and drug-delivery functionalities. These improved QDs have opened new possibilities for real-time imaging and tracking of molecular targets in living cells, for multiplexed analysis of biomolecular markers in clinical tissue specimens, and for ultrasensitive imaging of malignant tumors in living animal models. In this article, we briefly discuss recent developments in bioaffinity QD probes and their applications in molecular profiling of individual cancer cells and clinical tissue specimens. PMID:17722280

Optical response of hybrid semiconductor quantum dot-metal nanoparticle system: Beyond the dipole approximation

NASA Astrophysics Data System (ADS)

Mohammadzadeh, Atefeh; Miri, MirFaez

2018-01-01

We study the response of a semiconductor quantum dot-metal nanoparticle system to an external field E 0 cos ( ω t ) . The borders between Fano, double peaks, weak transition, strong transition, and bistability regions of the phase diagram move considerably as one regards the multipole effects. The exciton-induced transparency is an artifact of the dipole approximation. The absorption of the nanoparticle, the population inversion of the quantum dot, the upper and lower limits of intensity where bistability occurs, the characteristic time to reach the steady state, and other features of the hybrid system change due to the multipole effects. The phase diagrams corresponding to the fields parallel and perpendicular to the axis of system are quite distinguishable. Thus, both the intensity and the polarization of the incident field can be used to control the system. In particular, the incident polarization can be used to switch on and switch off the bistable behavior. For applications such as miniaturized bistable devices and nanosensors sensitive to variations of the dielectric constant of the surrounding medium, multipole effects must be considered.

Synthesis of colloidal Zn(Te,Se) alloy quantum dots

NASA Astrophysics Data System (ADS)

Asano, H.; Arai, K.; Kita, M.; Omata, T.

2017-10-01

Colloidal Zn(Te1-x Se x ) quantum dots (QDs), which are highly mismatched semiconductor alloys, were synthesized by the hot injection of an organometallic solution, and the composition and size dependence of their optical gap were studied together with the theoretical calculation using the finite-depth-well effective mass approximation. The optical gaps exhibited considerable negative deviation from the mole fraction weighted mean optical gaps of ZnTe and ZnSe, i.e. a large optical gap bowing was observed, similar to the bulk and thin-film alloys. The composition and size dependence of optical gaps agreed well with theoretically calculated ones employing a bowing parameter similar to that of the bulk alloys; therefore, the extent of the optical gap bowing in these alloy QDs is concluded to be the same as that in bulk and thin-film alloys. The optical gaps of Zn(Te1-x Se x ) QDs with diameters of 3.5-5 nm, where x ~ 0.35, were close to the energy corresponding to green light, indicating that those QDs are very promising as green QD-phosphors.

Semiconductor Quantum Dots for Bioimaging and Biodiagnostic Applications

NASA Astrophysics Data System (ADS)

Kairdolf, Brad A.; Smith, Andrew M.; Stokes, Todd H.; Wang, May D.; Young, Andrew N.; Nie, Shuming

2013-06-01

Semiconductor quantum dots (QDs) are light-emitting particles on the nanometer scale that have emerged as a new class of fluorescent labels for chemical analysis, molecular imaging, and biomedical diagnostics. Compared with traditional fluorescent probes, QDs have unique optical and electronic properties such as size-tunable light emission, narrow and symmetric emission spectra, and broad absorption spectra that enable the simultaneous excitation of multiple fluorescence colors. QDs are also considerably brighter and more resistant to photobleaching than are organic dyes and fluorescent proteins. These properties are well suited for dynamic imaging at the single-molecule level and for multiplexed biomedical diagnostics at ultrahigh sensitivity. Here, we discuss the fundamental properties of QDs; the development of next-generation QDs; and their applications in bioanalytical chemistry, dynamic cellular imaging, and medical diagnostics. For in vivo and clinical imaging, the potential toxicity of QDs remains a major concern. However, the toxic nature of cadmium-containing QDs is no longer a factor for in vitro diagnostics, so the use of multicolor QDs for molecular diagnostics and pathology is probably the most important and clinically relevant application for semiconductor QDs in the immediate future.

Semiconductor quantum dots for bioimaging and biodiagnostic applications.

PubMed

Kairdolf, Brad A; Smith, Andrew M; Stokes, Todd H; Wang, May D; Young, Andrew N; Nie, Shuming

2013-01-01

Semiconductor quantum dots (QDs) are light-emitting particles on the nanometer scale that have emerged as a new class of fluorescent labels for chemical analysis, molecular imaging, and biomedical diagnostics. Compared with traditional fluorescent probes, QDs have unique optical and electronic properties such as size-tunable light emission, narrow and symmetric emission spectra, and broad absorption spectra that enable the simultaneous excitation of multiple fluorescence colors. QDs are also considerably brighter and more resistant to photobleaching than are organic dyes and fluorescent proteins. These properties are well suited for dynamic imaging at the single-molecule level and for multiplexed biomedical diagnostics at ultrahigh sensitivity. Here, we discuss the fundamental properties of QDs; the development of next-generation QDs; and their applications in bioanalytical chemistry, dynamic cellular imaging, and medical diagnostics. For in vivo and clinical imaging, the potential toxicity of QDs remains a major concern. However, the toxic nature of cadmium-containing QDs is no longer a factor for in vitro diagnostics, so the use of multicolor QDs for molecular diagnostics and pathology is probably the most important and clinically relevant application for semiconductor QDs in the immediate future.

Semiconductor Quantum Dots for Bioimaging and Biodiagnostic Applications

PubMed Central

Kairdolf, Brad A.; Smith, Andrew M.; Stokes, Todd H.; Wang, May D.; Young, Andrew N.; Nie, Shuming

2013-01-01

Semiconductor quantum dots (QDs) are light-emitting particles on the nanometer scale that have emerged as a new class of fluorescent labels for chemical analysis, molecular imaging, and biomedical diagnostics. Compared with traditional fluorescent probes, QDs have unique optical and electronic properties such as size-tunable light emission, narrow and symmetric emission spectra, and broad absorption spectra that enable the simultaneous excitation of multiple fluorescence colors. QDs are also considerably brighter and more resistant to photobleaching than are organic dyes and fluorescent proteins. These properties are well suited for dynamic imaging at the single-molecule level and for multiplexed biomedical diagnostics at ultrahigh sensitivity. Here, we discuss the fundamental properties of QDs; the development of next-generation QDs; and their applications in bioanalytical chemistry, dynamic cellular imaging, and medical diagnostics. For in vivo and clinical imaging, the potential toxicity of QDs remains a major concern. However, the toxic nature of cadmium-containing QDs is no longer a factor for in vitro diagnostics, so the use of multicolor QDs for molecular diagnostics and pathology is probably the most important and clinically relevant application for semiconductor QDs in the immediate future. PMID:23527547

Monte Carlo simulations of quantum dot solar concentrators: ray tracing based on fluorescence mapping

NASA Astrophysics Data System (ADS)

Schuler, A.; Kostro, A.; Huriet, B.; Galande, C.; Scartezzini, J.-L.

2008-08-01

One promising application of semiconductor nanostructures in the field of photovoltaics might be quantum dot solar concentrators. Quantum dot containing nanocomposite thin films are synthesized at EPFL-LESO by a low cost sol-gel process. In order to study the potential of the novel planar photoluminescent concentrators, reliable computer simulations are needed. A computer code for ray tracing simulations of quantum dot solar concentrators has been developed at EPFL-LESO on the basis of Monte Carlo methods that are applied to polarization-dependent reflection/transmission at interfaces, photon absorption by the semiconductor nanocrystals and photoluminescent reemission. The software allows importing measured or theoretical absorption/reemission spectra describing the photoluminescent properties of the quantum dots. Hereby the properties of photoluminescent reemission are described by a set of emission spectra depending on the energy of the incoming photon, allowing to simulate the photoluminescent emission using the inverse function method. By our simulations, the importance of two main factors is revealed, an emission spectrum matched to the spectral efficiency curve of the photovoltaic cell, and a large Stokes shift, which is advantageous for the lateral energy transport. No significant energy losses are implied when the quantum dots are contained within a nanocomposite coating instead of being dispersed in the entire volume of the pane. Together with the knowledge on the optoelectronical properties of suitable photovoltaic cells, the simulations allow to predict the total efficiency of the envisaged concentrating PV systems, and to optimize photoluminescent emission frequencies, optical densities, and pane dimensions.

Experimental methods of post-growth tuning of the excitonic fine structure splitting in semiconductor quantum dots

PubMed Central

2012-01-01

Deterministic sources of polarization entangled photon pairs on demand are considered as important building blocks for quantum communication technology. It has been demonstrated that semiconductor quantum dots (QDs), which exhibit a sufficiently small excitonic fine structure splitting (FSS) can be used as triggered, on-chip sources of polarization entangled photon pairs. As-grown QDs usually do not have the required values of the FSS, making the availability of post-growth tuning techniques highly desired. This article reviews the effect of different post-growth treatments and external fields on the FSS such as thermal annealing, magnetic fields, the optical Stark effect, electric fields, and anisotropic stress. As a consequence of the tuning of the FSS, for some tuning techniques a rotation of the polarization of the emitted light is observed. The joint modification of polarization orientation and FSS can be described by an anticrossing of the bright excitonic states. PMID:22726724

Quantum dot-polymer conjugates for stable luminescent displays.

PubMed

Ghimire, Sushant; Sivadas, Anjaly; Yuyama, Ken-Ichi; Takano, Yuta; Francis, Raju; Biju, Vasudevanpillai

2018-05-23

The broad absorption of light in the UV-Vis-NIR region and the size-based tunable photoluminescence color of semiconductor quantum dots make these tiny crystals one of the most attractive antennae in solar cells and phosphors in electrooptical devices. One of the primary requirements for such real-world applications of quantum dots is their stable and uniform distribution in optically transparent matrices. In this work, we prepare transparent thin films of polymer-quantum dot conjugates, where CdSe/ZnS quantum dots are uniformly distributed at high densities in a chitosan-polystyrene copolymer (CS-g-PS) matrix. Here, quantum dots in an aqueous solution are conjugated to the copolymer by a phase transfer reaction. With the stable conjugation of quantum dots to the copolymer, we prevent undesired phase separation between the two and aggregation of quantum dots. Furthermore, the conjugate allows us to prepare transparent thin films in which quantum dots are uniformly distributed at high densities. The CS-g-PS copolymer helps us in not only preserving the photoluminescence properties of quantum dots in the film but also rendering excellent photostability to quantum dots at the ensemble and single particle levels, making the conjugate a promising material for photoluminescence-based devices.

Strong plasmonic enhancement of biexciton emission: controlled coupling of a single quantum dot to a gold nanocone antenna

DOE PAGES

Matsuzaki, Korenobu; Vassant, Simon; Liu, Hsuan-Wei; ...

2017-02-14

Multiexcitonic transitions and emission of several photons per excitation comprise a very attractive feature of semiconductor quantum dots for optoelectronics applications. However, these higher-order radiative processes are usually quenched in colloidal quantum dots by Auger and other nonradiative decay channels. To increase the multiexcitonic quantum efficiency, several groups have explored plasmonic enhancement, so far with moderate results. By controlled positioning of individual quantum dots in the near field of gold nanocone antennas, we enhance the radiative decay rates of monoexcitons and biexcitons by 109 and 100 folds at quantum efficiencies of 60 and 70%, respectively, in very good agreement withmore » the outcome of numerical calculations. We discuss the implications of our work for future fundamental and applied research in nano-optics.« less

Microfluidic Technology: Uncovering the Mechanisms of Nanocrystal Nucleation and Growth.

PubMed

Lignos, Ioannis; Maceiczyk, Richard; deMello, Andrew J

2017-05-16

The controlled and reproducible formation of colloidal semiconductor nanocrystals (or quantum dots) is of central importance in nanoscale science and technology. The tunable size- and shape-dependent properties of such materials make them ideal candidates for the development of efficient and low-cost displays, solar cells, light-emitting devices, and catalysts. The formidable difficulties associated with the macroscale preparation of semiconductor nanocrystals (possessing bespoke optical and chemical properties) result from the fact that underlying reaction mechanisms are complex and that the reactive environment is difficult to control. Automated microfluidic reactors coupled with monitoring systems and optimization algorithms aim to elucidate complex reaction mechanisms that govern both nucleation and growth of nanocrystals. Such platforms are ideally suited for the efficient optimization of reaction parameters, assuring the reproducible synthesis of nanocrystals with user-defined properties. This Account aims to inform the nanomaterials community about how microfluidic technologies can supplement flask experimentation for the ensemble investigation of formation mechanisms and design of semiconductor nanocrystals. We present selected studies outlining the preparation of quantum dots using microfluidic systems with integrated analytics. Such microfluidic reaction systems leverage the ability to extract real-time information regarding optical, structural, and compositional characteristics of quantum dots during nucleation and growth stages. The Account further highlights our recent research activities focused on the development and application of droplet-based microfluidics with integrated optical detection systems for the efficient and rapid screening of reaction conditions and a better understanding of the mechanisms of quantum dot synthesis. We describe the features and operation of fully automated microfluidic reactors and their subsequent application to high-throughput parametric screening of metal chalcogenides (CdSe, PbS, PbSe, CdSeTe), ternary and core/shell heavy metal-free quantum dots (CuInS 2 , CuInS 2 /ZnS), and all-inorganic perovskite nanocrystals (CsPbX 3 , X = Cl, Br, I) syntheses. Critically, concurrent absorption and photoluminescence measurements on millisecond to second time scales allow the extraction of basic parameters governing nanocrystal formation. Moreover, experimental data obtained from such microfluidic platforms can be directly supported by theoretical models of nucleation and growth. To this end, we also describe the use of metamodeling algorithms able to accurately predict optimized conditions of CdSe synthesis using a minimal number of sample parameters. Importantly, we discuss future challenges that must be addressed before microfluidic technologies are in a position to be widely adopted for the on-demand formation of nanocrystals. From a technology perspective, these challenges include the development of novel engineering platforms for the formation of complex architectures, the integration of monitoring systems able to harvest photophysical and structural information, the incorporation of continuous purification systems, and the application of optimization algorithms to multicomponent quantum dot systems.

Properties and applications of quantum dot heterostructures grown by molecular beam epitaxy

PubMed Central

2006-01-01

One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two: quantum wires and quantum dots, in order to realize novel devices that make use of low-dimensional confinement effects. One of the promising fabrication methods is to use self-organized three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. This article is intended to convey the flavour of the subject by focussing on the structural, optical and electronic properties and device applications of self-assembled quantum dots and to give an elementary introduction to some of the essential characteristics.

III–V quantum light source and cavity-QED on Silicon

PubMed Central

Luxmoore, I. J.; Toro, R.; Pozo-Zamudio, O. Del; Wasley, N. A.; Chekhovich, E. A.; Sanchez, A. M.; Beanland, R.; Fox, A. M.; Skolnick, M. S.; Liu, H. Y.; Tartakovskii, A. I.

2013-01-01

Non-classical light sources offer a myriad of possibilities in both fundamental science and commercial applications. Single photons are the most robust carriers of quantum information and can be exploited for linear optics quantum information processing. Scale-up requires miniaturisation of the waveguide circuit and multiple single photon sources. Silicon photonics, driven by the incentive of optical interconnects is a highly promising platform for the passive optical components, but integrated light sources are limited by silicon's indirect band-gap. III–V semiconductor quantum-dots, on the other hand, are proven quantum emitters. Here we demonstrate single-photon emission from quantum-dots coupled to photonic crystal nanocavities fabricated from III–V material grown directly on silicon substrates. The high quality of the III–V material and photonic structures is emphasized by observation of the strong-coupling regime. This work opens-up the advantages of silicon photonics to the integration and scale-up of solid-state quantum optical systems. PMID:23393621

Photovoltage field-effect transistors

NASA Astrophysics Data System (ADS)

Adinolfi, Valerio; Sargent, Edward H.

2017-02-01

The detection of infrared radiation enables night vision, health monitoring, optical communications and three-dimensional object recognition. Silicon is widely used in modern electronics, but its electronic bandgap prevents the detection of light at wavelengths longer than about 1,100 nanometres. It is therefore of interest to extend the performance of silicon photodetectors into the infrared spectrum, beyond the bandgap of silicon. Here we demonstrate a photovoltage field-effect transistor that uses silicon for charge transport, but is also sensitive to infrared light owing to the use of a quantum dot light absorber. The photovoltage generated at the interface between the silicon and the quantum dot, combined with the high transconductance provided by the silicon device, leads to high gain (more than 104 electrons per photon at 1,500 nanometres), fast time response (less than 10 microseconds) and a widely tunable spectral response. Our photovoltage field-effect transistor has a responsivity that is five orders of magnitude higher at a wavelength of 1,500 nanometres than that of previous infrared-sensitized silicon detectors. The sensitization is achieved using a room-temperature solution process and does not rely on traditional high-temperature epitaxial growth of semiconductors (such as is used for germanium and III-V semiconductors). Our results show that colloidal quantum dots can be used as an efficient platform for silicon-based infrared detection, competitive with state-of-the-art epitaxial semiconductors.

Pulse propagation and optically controllable switch in coupled semiconductor-double-quantum-dot nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamedi, H. R., E-mail: hamid.r.hamedi@gmail.com, E-mail: hamid.hamedi@tfai.vu.lt

The problem of pulse propagation is theoretically investigated through a coupled semiconductor-double-quantum-dot (SDQD) nanostructure. Solving the coupled Maxwell–Bloch equations for the SDQD and field simultaneously, the dynamic control of pulse propagation through the medium is numerically explored. It is found that when all the control fields are in exact resonance with their corresponding transitions, a weak Gaussian-shaped probe pulse is transmitted through the medium nearly without any significant absorption and losses so that it can preserve its shape for quite a long propagation distance. In contrast, when one of the control fields is not in resonance with its corresponding transition,more » the probe pulse will be absorbed by the QD medium after a short distance. Then we consider the probe pulses with higher intensities. It is realized that an intense probe pulse experiences remarkable absorption and broadening during propagation. Finally, we demonstrate that this SDQD system can be employed as an optically controllable switch for the wave propagation to transit from an absorbing phase to a perfect transparency for the probe field. The required time for such switch is also estimated through realistic values.« less

Optically Active CdSe-Dot/CdS-Rod Nanocrystals with Induced Chirality and Circularly Polarized Luminescence.

PubMed

Cheng, Jiaji; Hao, Junjie; Liu, Haochen; Li, Jiagen; Li, Junzi; Zhu, Xi; Lin, Xiaodong; Wang, Kai; He, Tingchao

2018-05-30

Ligand-induced chirality in semiconductor nanocrystals (NCs) has attracted attention because of the tunable optical properties of the NCs. Induced circular dichroism (CD) has been observed in CdX (X = S, Se, Te) NCs and their hybrids, but circularly polarized luminescence (CPL) in these fluorescent nanomaterials has been seldom reported. Herein, we describe the successful preparation of l- and d-cysteine-capped CdSe-dot/CdS-rods (DRs) with tunable CD and CPL behaviors and a maximum anisotropic factor ( g lum ) of 4.66 × 10 -4 . The observed CD and CPL activities are sensitive to the relative absorption ratio of the CdS shell to the CdSe core, suggesting that the anisotropic g-factors in both CD and CPL increase to some extent for a smaller shell-to-core absorption ratio. In addition, the molar ratio of chiral cysteine to the DRs is investigated. Instead of enhancing the chiral interactions between the chiral molecules and DRs, an excess of cysteine molecules in aqueous solution inhibits both the CD and CPL activities. Such chiral and emissive NCs provide an ideal platform for the rational design of semiconductor nanomaterials with chiroptical properties.

Quantum state reconstruction and photon number statistics for low dimensional semiconductor opto-electronic devices

NASA Astrophysics Data System (ADS)

Böhm, Fabian; Grosse, Nicolai B.; Kolarczik, Mirco; Herzog, Bastian; Achtstein, Alexander; Owschimikow, Nina; Woggon, Ulrike

2017-09-01

Quantum state tomography and the reconstruction of the photon number distribution are techniques to extract the properties of a light field from measurements of its mean and fluctuations. These techniques are particularly useful when dealing with macroscopic or mesoscopic systems, where a description limited to the second order autocorrelation soon becomes inadequate. In particular, the emission of nonclassical light is expected from mesoscopic quantum dot systems strongly coupled to a cavity or in systems with large optical nonlinearities. We analyze the emission of a quantum dot-semiconductor optical amplifier system by quantifying the modifications of a femtosecond laser pulse propagating through the device. Using a balanced detection scheme in a self-heterodyning setup, we achieve precise measurements of the quadrature components and their fluctuations at the quantum noise limit1. We resolve the photon number distribution and the thermal-to-coherent evolution in the photon statistics of the emission. The interferometric detection achieves a high sensitivity in the few photon limit. From our data, we can also reconstruct the second order autocorrelation function with higher precision and time resolution compared with classical Hanbury Brown-Twiss experiments.

Monolayer semiconductor nanocavity lasers with ultralow thresholds.

PubMed

Wu, Sanfeng; Buckley, Sonia; Schaibley, John R; Feng, Liefeng; Yan, Jiaqiang; Mandrus, David G; Hatami, Fariba; Yao, Wang; Vučković, Jelena; Majumdar, Arka; Xu, Xiaodong

2015-04-02

Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter, providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots, extreme difficulty in current injection, and lack of compatibility with electronic circuits. Here we report a new lasing strategy: an atomically thin crystalline semiconductor--that is, a tungsten diselenide monolayer--is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.

Monolayer semiconductor nanocavity lasers with ultralow thresholds

NASA Astrophysics Data System (ADS)

Wu, Sanfeng; Buckley, Sonia; Schaibley, John R.; Feng, Liefeng; Yan, Jiaqiang; Mandrus, David G.; Hatami, Fariba; Yao, Wang; Vučković, Jelena; Majumdar, Arka; Xu, Xiaodong

2015-04-01

Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter, providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots, extreme difficulty in current injection, and lack of compatibility with electronic circuits. Here we report a new lasing strategy: an atomically thin crystalline semiconductor--that is, a tungsten diselenide monolayer--is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.

Enhancement of carrier lifetimes in type-II quantum dot/quantum well hybrid structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Couto, O. D. D., E-mail: odilon@ifi.unicamp.br; Almeida, P. T. de; Santos, G. E. dos

We investigate optical transitions and carrier dynamics in hybrid structures containing type-I GaAs/AlGaAs quantum wells (QWs) and type-II GaSb/AlGaAs quantum dots (QDs). We show that the optical recombination of photocreated electrons confined in the QWs with holes in the QDs and wetting layer can be modified according to the QW/QD spatial separation. In particular, for low spacer thicknesses, the QW optical emission can be suppressed due to the transference of holes from the QW to the GaSb layer, favoring the optical recombination of spatially separated carriers, which can be useful for optical memory and solar cell applications. Time-resolved photoluminescence (PL)more » measurements reveal non-exponential recombination dynamics. We demonstrate that the PL transients can only be quantitatively described by considering both linear and quadratic terms of the carrier density in the bimolecular recombination approximation for type-II semiconductor nanostructures. We extract long exciton lifetimes from 700 ns to 5 μs for QDs depending on the spacer layer thickness.« less

Precise Control of Quantum Confinement in Cesium Lead Halide Perovskite Quantum Dots via Thermodynamic Equilibrium.

PubMed

Dong, Yitong; Qiao, Tian; Kim, Doyun; Parobek, David; Rossi, Daniel; Son, Dong Hee

2018-05-09

Cesium lead halide (CsPbX 3 ) nanocrystals have emerged as a new family of materials that can outperform the existing semiconductor nanocrystals due to their superb optical and charge-transport properties. However, the lack of a robust method for producing quantum dots with controlled size and high ensemble uniformity has been one of the major obstacles in exploring the useful properties of excitons in zero-dimensional nanostructures of CsPbX 3 . Here, we report a new synthesis approach that enables the precise control of the size based on the equilibrium rather than kinetics, producing CsPbX 3 quantum dots nearly free of heterogeneous broadening in their exciton luminescence. The high level of size control and ensemble uniformity achieved here will open the door to harnessing the benefits of excitons in CsPbX 3 quantum dots for photonic and energy-harvesting applications.

Inkjet printed fluorescent nanorod layers exhibit superior optical performance over quantum dots

NASA Astrophysics Data System (ADS)

Halivni, Shira; Shemesh, Shay; Waiskopf, Nir; Vinetsky, Yelena; Magdassi, Shlomo; Banin, Uri

2015-11-01

Semiconductor nanocrystals exhibit unique fluorescence properties which are tunable in size, shape and composition. The high quantum yield and enhanced stability have led to their use in biomedical imaging and flat panel displays. Here, semiconductor nanorod based inkjet inks are presented, overcoming limitations of the commonly reported quantum dots in printing applications. Fluorescent seeded nanorods were found to be outstanding candidates for fluorescent inks, due to their low particle-particle interactions and negligible self-absorption. This is manifested by insignificant emission shifts upon printing, even in highly concentrated printed layers and by maintenance of a high fluorescence quantum yield, unlike quantum dots which exhibit fluorescence wavelength shifts and quenching effects. This behavior results from the reduced absorption/emission overlap, accompanied by low energy transfer efficiencies between the nanorods as supported by steady state and time resolved fluorescence measurements. The new seeded nanorod inks enable patterning of thin fluorescent layers, for demanding light emission applications such as signage and displays.Semiconductor nanocrystals exhibit unique fluorescence properties which are tunable in size, shape and composition. The high quantum yield and enhanced stability have led to their use in biomedical imaging and flat panel displays. Here, semiconductor nanorod based inkjet inks are presented, overcoming limitations of the commonly reported quantum dots in printing applications. Fluorescent seeded nanorods were found to be outstanding candidates for fluorescent inks, due to their low particle-particle interactions and negligible self-absorption. This is manifested by insignificant emission shifts upon printing, even in highly concentrated printed layers and by maintenance of a high fluorescence quantum yield, unlike quantum dots which exhibit fluorescence wavelength shifts and quenching effects. This behavior results from the reduced absorption/emission overlap, accompanied by low energy transfer efficiencies between the nanorods as supported by steady state and time resolved fluorescence measurements. The new seeded nanorod inks enable patterning of thin fluorescent layers, for demanding light emission applications such as signage and displays. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06248a

External control of semiconductor nanostructure lasers

NASA Astrophysics Data System (ADS)

Naderi, Nader A.

2011-12-01

Novel semiconductor nanostructure laser diodes such as quantum-dot and quantum-dash are key optoelectronic candidates for many applications such as data transmitters in ultra fast optical communications. This is mainly due to their unique carrier dynamics compared to conventional quantum-well lasers that enables their potential for high differential gain and modified linewidth enhancement factor. However, there are known intrinsic limitations associated with semiconductor laser dynamics that can hinder the performance including the mode stability, spectral linewidth, and direct modulation capabilities. One possible method to overcome these limitations is through the use of external control techniques. The electrical and/or optical external perturbations can be implemented to improve the parameters associated with the intrinsic laser's dynamics, such as threshold gain, damping rate, spectral linewidth, and mode selectivity. In this dissertation, studies on the impact of external control techniques through optical injection-locking, optical feedback and asymmetric current bias control on the overall performance of the nanostructure lasers were conducted in order to understand the associated intrinsic device limitations and to develop strategies for controlling the underlying dynamics to improve laser performance. In turn, the findings of this work can act as a guideline for making high performance nanostructure lasers for future ultra fast data transmitters in long-haul optical communication systems, and some can provide an insight into making a compact and low-cost terahertz optical source for future implementation in monolithic millimeter-wave integrated circuits.

Towards Violation of Classical Inequalities using Quantum Dot Resonance Fluorescence

NASA Astrophysics Data System (ADS)

Peiris, Manoj

Self-assembled semiconductor quantum dots have attracted considerable interest recently, ranging from fundamental studies of quantum optics to advanced applications in the field of quantum information science. With their atom-like properties, quantum dot based nanophotonic devices may also substantially contribute to the development of quantum computers. This work presents experimental progress towards the understanding of light-matter interactions that occur beyond well-understood monochromatic resonant light scattering processes in semiconductor quantum dots. First, we report measurements of resonance fluorescence under bichromatic laser excitation. With the inclusion of a second laser, both first-order and second-order correlation functions are substantially altered. Under these conditions, the scattered light exhibits a rich spectrum containing many spectral features that lead to a range of nonlinear multiphoton dynamics. These observations are discussed and compared with a theoretical model. Second, we investigated the light scattered by a quantum dot in the presence of spectral filtering. By scanning the tunable filters placed in front of each detector of a Hanbury-Brown and Twiss setup and recording coincidence measurements, a \\two-photon spectrum" has been experimentally reconstructed for the first time. The two-photon spectrum contains a wealth of information about the cascaded emission involved in the scattering process, such as transitions occurring via virtual intermediate states. Our measurements also reveal that the scattered frequency-filtered light from a quantum dot violates the Cauchy-Schwarz inequality. Finally, Franson-interferometry has been performed using spectrally filtered light from quantum dot resonance fluorescence. Visibilities exceeding the classical limit were demonstrated by using a pair of folded Mach-Zehnder interferometers, paving the way for producing single time-energy entangled photon pairs that could violate Bell's inequalities.

Design strategy for terahertz quantum dot cascade lasers.

PubMed

Burnett, Benjamin A; Williams, Benjamin S

2016-10-31

The development of quantum dot cascade lasers has been proposed as a path to obtain terahertz semiconductor lasers that operate at room temperature. The expected benefit is due to the suppression of nonradiative electron-phonon scattering and reduced dephasing that accompanies discretization of the electronic energy spectrum. We present numerical modeling which predicts that simple scaling of conventional quantum well based designs to the quantum dot regime will likely fail due to electrical instability associated with high-field domain formation. A design strategy adapted for terahertz quantum dot cascade lasers is presented which avoids these problems. Counterintuitively, this involves the resonant depopulation of the laser's upper state with the LO-phonon energy. The strategy is tested theoretically using a density matrix model of transport and gain, which predicts sufficient gain for lasing at stable operating points. Finally, the effect of quantum dot size inhomogeneity on the optical lineshape is explored, suggesting that the design concept is robust to a moderate amount of statistical variation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habercorn, Lasse; Merkl, Jan-Philip; Kloust, Hauke Christian

With the polymer encapsulation of quantum dots via seeded emulsion polymerization we present a powerful tool for the preparation of fluorescent nanoparticles with an extraordinary stability in aqueous solution. The method of the seeded emulsion polymerization allows a straightforward and simple in situ functionalization of the polymer shell under preserving the optical properties of the quantum dots. These requirements are inevitable for the application of semiconductor nanoparticles as markers for biomedical applications. Polymer encapsulated quantum dots have shown only a marginal loss of quantum yields when they were exposed to copper(II)-ions. Under normal conditions the quantum dots were totally quenchedmore » in presence of copper(II)-ions. Furthermore, a broad range of in situ functionalized polymer-coated quantum dots were obtained by addition of functional monomers or surfactants like fluorescent dye molecules, antibodies or specific DNA aptamers. Furthermore the emulsion polymerization can be used to prepare multifunctional hybrid systems, combining different nanoparticles within one construct without any adverse effect of the properties of the starting materials.{sup 1,2}.« less

Downconversion quantum interface for a single quantum dot spin and 1550-nm single-photon channel.

PubMed

Pelc, Jason S; Yu, Leo; De Greve, Kristiaan; McMahon, Peter L; Natarajan, Chandra M; Esfandyarpour, Vahid; Maier, Sebastian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Hadfield, Robert H; Forchel, Alfred; Yamamoto, Yoshihisa; Fejer, M M

2012-12-03

Long-distance quantum communication networks require appropriate interfaces between matter qubit-based nodes and low-loss photonic quantum channels. We implement a downconversion quantum interface, where the single photons emitted from a semiconductor quantum dot at 910 nm are downconverted to 1560 nm using a fiber-coupled periodically poled lithium niobate waveguide and a 2.2-μm pulsed pump laser. The single-photon character of the quantum dot emission is preserved during the downconversion process: we measure a cross-correlation g(2)(τ = 0) = 0.17 using resonant excitation of the quantum dot. We show that the downconversion interface is fully compatible with coherent optical control of the quantum dot electron spin through the observation of Rabi oscillations in the downconverted photon counts. These results represent a critical step towards a long-distance hybrid quantum network in which subsystems operating at different wavelengths are connected through quantum frequency conversion devices and 1.5-μm quantum channels.

Designing quantum dots for solotronics.

PubMed

Kobak, J; Smoleński, T; Goryca, M; Papaj, M; Gietka, K; Bogucki, A; Koperski, M; Rousset, J-G; Suffczyński, J; Janik, E; Nawrocki, M; Golnik, A; Kossacki, P; Pacuski, W

2014-01-01

Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory.

Designing quantum dots for solotronics

PubMed Central

Kobak, J.; Smoleński, T.; Goryca, M.; Papaj, M.; Gietka, K.; Bogucki, A.; Koperski, M.; Rousset, J.-G.; Suffczyński, J.; Janik, E.; Nawrocki, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

2014-01-01

Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory. PMID:24463946

Edge physics of the quantum spin Hall insulator from a quantum dot excited by optical absorption.

PubMed

Vasseur, Romain; Moore, Joel E

2014-04-11

The gapless edge modes of the quantum spin Hall insulator form a helical liquid in which the direction of motion along the edge is determined by the spin orientation of the electrons. In order to probe the Luttinger liquid physics of these edge states and their interaction with a magnetic (Kondo) impurity, we consider a setup where the helical liquid is tunnel coupled to a semiconductor quantum dot that is excited by optical absorption, thereby inducing an effective quantum quench of the tunneling. At low energy, the absorption spectrum is dominated by a power-law singularity. The corresponding exponent is directly related to the interaction strength (Luttinger parameter) and can be computed exactly using boundary conformal field theory thanks to the unique nature of the quantum spin Hall edge.

Low-Loss Optical Metamaterials Based on Mie Resonances in Semiconductor Nanoparticle Composites

DTIC Science & Technology

2012-12-13

Brillouin zone where two transverse bands with linear dispersion intersect a flat longitudinal band, resulting in triple degeneracy. The fields in the...transmission pattern through Fourier plane imaging. This was accomplished by focusing a laser beam within the structure using a high numerical...conditions, a high frequency magnetic response could be created in metamaterials formed from composites of quantum dots utilizing excitonic resonances

Cavity QED analysis of an exciton-plasmon hybrid molecule via the generalized nonlocal optical response method

NASA Astrophysics Data System (ADS)

Hapuarachchi, Harini; Premaratne, Malin; Bao, Qiaoliang; Cheng, Wenlong; Gunapala, Sarath D.; Agrawal, Govind P.

2017-06-01

A metal nanoparticle coupled to a semiconductor quantum dot forms a tunable hybrid system which exhibits remarkable optical phenomena. Small metal nanoparticles possess nanocavitylike optical concentration capabilities due to the presence of strong dipolar excitation modes in the form of localized surface plasmons. Semiconductor quantum dots have strong luminescent capabilities widely used in many applications such as biosensing. When a quantum dot is kept in the vicinity of a metal nanoparticle, a dipole-dipole coupling occurs between the two nanoparticles giving rise to various optical signatures in the scattered spectra. This coupling makes the two nanoparticles behave like a single hybrid molecule. Hybrid molecules made of metal nanoparticles (MNPs) and quantum dots (QDs) under the influence of an external driving field have been extensively studied in literature, using the local response approximation (LRA). However, such previous work in this area was not adequate to explain some experimental observations such as the size-dependent resonance shift of metal nanoparticles which becomes quite significant with decreasing diameter. The nonlocal response of metallic nanostructures which is hitherto disregarded by such studies is a main reason for such nonclassical effects. The generalized nonlocal optical response (GNOR) model provides a computationally less-demanding path to incorporate such properties into the theoretical models. It allows unified theoretical explanation of observed experimental phenomena which previously seemed to require ab initio microscopic theory. In this paper, we analyze the hybrid molecule in an external driving field as an open quantum system using a cavity-QED approach. In the process, we quantum mechanically model the dipole moment operator and the dipole response field of the metal nanoparticle taking the nonlocal effects into account. We observe that the spectra resulting from the GNOR based model effectively demonstrate the experimentally observed size dependent amplitude scaling, linewidth broadening, and resonance shift phenomena compared to the respective LRA counterparts. Then, we provide a comparison between our suggested GNOR based cavity-QED model and the conventional LRA model, where it becomes evident that our analytical model provides a close match to the experimentally suggested behavior. Furthermore, we show that the Rayleigh scattering spectra of the MNP-QD hybrid molecule possess an asymmetric Fano interference pattern that is tunable to suit various applications.

Doping effect in Si nanocrystals

NASA Astrophysics Data System (ADS)

Li, Dongke; Xu, Jun; Zhang, Pei; Jiang, Yicheng; Chen, Kunji

2018-06-01

Intentional doping in semiconductors is a fundamental issue since it can control the conduction type and ability as well as modify the optical and electronic properties. To realize effective doping is the basis for developing semiconductor devices. However, by reducing the size of a semiconductor, like Si, to the nanometer scale, the doping effects become complicated due to the coupling between the quantum confinement effect and the surfaces and/or interfaces effect. In particular, by introducing phosphorus or boron impurities as dopants into material containing Si nanocrystals with a dot size of less than 10 nm, it exhibits different behaviors and influences on the physical properties from its bulk counterpart. Understanding the doping effects in Si nanocrystals is currently a challenge in order to further improve the performance of the next generation of nano-electronic and photonic devices. In this review, we present an overview of the latest theoretical studies and experimental results on dopant distributions and their effects on the electronic and optical properties of Si nanocrystals. In particular, the advanced characterization techniques on dopant distribution, the carrier transport process as well as the linear and nonlinear optical properties of doped Si nanocrystals, are systematically summarized.

Nanoscale chirality in metal and semiconductor nanoparticles

PubMed Central

Thomas, K. George

2016-01-01

The field of chirality has recently seen a rejuvenation due to the observation of chirality in inorganic nanomaterials. The advancements in understanding the origin of nanoscale chirality and the potential applications of chiroptical nanomaterials in the areas of optics, catalysis and biosensing, among others, have opened up new avenues toward new concepts and design of novel materials. In this article, we review the concept of nanoscale chirality in metal nanoclusters and semiconductor quantum dots, then focus on recent experimental and theoretical advances in chiral metal nanoparticles and plasmonic chirality. Selected examples of potential applications and an outlook on the research on chiral nanomaterials are additionally provided. PMID:27752651

Nanoscale chirality in metal and semiconductor nanoparticles.

PubMed

Kumar, Jatish; Thomas, K George; Liz-Marzán, Luis M

2016-10-18

The field of chirality has recently seen a rejuvenation due to the observation of chirality in inorganic nanomaterials. The advancements in understanding the origin of nanoscale chirality and the potential applications of chiroptical nanomaterials in the areas of optics, catalysis and biosensing, among others, have opened up new avenues toward new concepts and design of novel materials. In this article, we review the concept of nanoscale chirality in metal nanoclusters and semiconductor quantum dots, then focus on recent experimental and theoretical advances in chiral metal nanoparticles and plasmonic chirality. Selected examples of potential applications and an outlook on the research on chiral nanomaterials are additionally provided.

Plasma Reflection in Multigrain Layers of Narrow-Bandgap Semiconductors

NASA Astrophysics Data System (ADS)

Zhukov, N. D.; Shishkin, M. I.; Rokakh, A. G.

2018-04-01

Qualitatively similar spectral characteristics of plasma-resonance reflection in the region of 15-25 μm were obtained for layers of electrodeposited submicron particles of InSb, InAs, and GaAs and plates of these semiconductors ground with M1-grade diamond powder. The most narrow-bandgap semiconductor InSb (intrinsic absorption edge ˜7 μm) is characterized by an absorption band at 2.1-2.3 μm, which is interpreted in terms of the model of optical excitation of electrons coupled by the Coulomb interaction. The spectra of a multigrain layer of chemically deposited PbS nanoparticles (50-70 nm) exhibited absorption maxima at 7, 10, and 17 μm, which can be explained by electron transitions obeying the energy-quantization rules for quantum dots.

Optical coefficients in a semiconductor quantum ring: Electric field and donor impurity effects

NASA Astrophysics Data System (ADS)

Duque, C. M.; Acosta, Ruben E.; Morales, A. L.; Mora-Ramos, M. E.; Restrepo, R. L.; Ojeda, J. H.; Kasapoglu, E.; Duque, C. A.

2016-10-01

The electron states in a two-dimensional quantum dot ring are calculated in the presence of a donor impurity atom under the effective mass and parabolic band approximations. The effect of an externally applied electric field is also taken into account. The wavefunctions are obtained via the exact diagonalization of the problem Hamiltonian using a 2D expansion within the adiabatic approximation. The impurity-related optical response is analyzed via the optical absorption, relative refractive index change and the second harmonics generation. The dependencies of the electron states and these optical coefficients with the changes in the configuration of the quantum ring system are discussed in detail.

Nonlinear optical spectra having characteristics of Fano interferences in coherently coupled lowest exciton biexciton states in semiconductor quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gotoh, Hideki, E-mail: gotoh.hideki@lab.ntt.co.jp; Sanada, Haruki; Yamaguchi, Hiroshi

2014-10-15

Optical nonlinear effects are examined using a two-color micro-photoluminescence (micro-PL) method in a coherently coupled exciton-biexciton system in a single quantum dot (QD). PL and photoluminescence excitation spectroscopy (PLE) are employed to measure the absorption spectra of the exciton and biexciton states. PLE for Stokes and anti-Stokes PL enables us to clarify the nonlinear optical absorption properties in the lowest exciton and biexciton states. The nonlinear absorption spectra for excitons exhibit asymmetric shapes with peak and dip structures, and provide a distinct contrast to the symmetric dip structures of conventional nonlinear spectra. Theoretical analyses with a density matrix method indicatemore » that the nonlinear spectra are caused not by a simple coherent interaction between the exciton and biexciton states but by coupling effects among exciton, biexciton and continuum states. These results indicate that Fano quantum interference effects appear in exciton-biexciton systems at QDs and offer important insights into their physics.« less

On-demand semiconductor single-photon source with near-unity indistinguishability.

PubMed

He, Yu-Ming; He, Yu; Wei, Yu-Jia; Wu, Dian; Atatüre, Mete; Schneider, Christian; Höfling, Sven; Kamp, Martin; Lu, Chao-Yang; Pan, Jian-Wei

2013-03-01

Single-photon sources based on semiconductor quantum dots offer distinct advantages for quantum information, including a scalable solid-state platform, ultrabrightness and interconnectivity with matter qubits. A key prerequisite for their use in optical quantum computing and solid-state networks is a high level of efficiency and indistinguishability. Pulsed resonance fluorescence has been anticipated as the optimum condition for the deterministic generation of high-quality photons with vanishing effects of dephasing. Here, we generate pulsed single photons on demand from a single, microcavity-embedded quantum dot under s-shell excitation with 3 ps laser pulses. The π pulse-excited resonance-fluorescence photons have less than 0.3% background contribution and a vanishing two-photon emission probability. Non-postselective Hong-Ou-Mandel interference between two successively emitted photons is observed with a visibility of 0.97(2), comparable to trapped atoms and ions. Two single photons are further used to implement a high-fidelity quantum controlled-NOT gate.

A quantum dot single-photon source with on-the-fly all-optical polarization control and timed emission.

PubMed

Heinze, Dirk; Breddermann, Dominik; Zrenner, Artur; Schumacher, Stefan

2015-10-05

Sources of single photons are key elements for applications in quantum information science. Among the different sources available, semiconductor quantum dots excel with their integrability in semiconductor on-chip solutions and the potential that photon emission can be triggered on demand. Usually, the photon is emitted from a single-exciton ground state. Polarization of the photon and time of emission are either probabilistic or pre-determined by electronic properties of the system. Here, we study the direct two-photon emission from the biexciton. The two-photon emission is enabled by a laser pulse driving the system into a virtual state inside the band gap. From this intermediate state, the single photon of interest is then spontaneously emitted. We show that emission through this higher-order transition provides a versatile approach to generate a single photon. Through the driving laser pulse, polarization state, frequency and emission time of the photon can be controlled on-the-fly.

Electro-mechanical control of an on-chip optical beam splitter containing an embedded quantum emitter.

PubMed

Bishop, Z K; Foster, A P; Royall, B; Bentham, C; Clarke, E; Skolnick, M S; Wilson, L R

2018-05-01

We demonstrate electro-mechanical control of an on-chip GaAs optical beam splitter containing a quantum dot single-photon source. The beam splitter consists of two nanobeam waveguides, which form a directional coupler (DC). The splitting ratio of the DC is controlled by varying the out-of-plane separation of the two waveguides using electromechanical actuation. We reversibly tune the beam splitter between an initial state, with emission into both output arms, and a final state with photons emitted into a single output arm. The device represents a compact and scalable tuning approach for use in III-V semiconductor integrated quantum optical circuits.

Boosting the efficiency of quantum dot sensitized solar cells through modulation of interfacial charge transfer.

PubMed

Kamat, Prashant V

2012-11-20

The demand for clean energy will require the design of nanostructure-based light-harvesting assemblies for the conversion of solar energy into chemical energy (solar fuels) and electrical energy (solar cells). Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in these nanostructures. This Account focuses on photoinduced electron transfer processes in quantum dot sensitized solar cells (QDSCs) and discusses strategies to overcome the limitations of various interfacial electron transfer processes. The heterojunction of two semiconductor nanocrystals with matched band energies (e.g., TiO(2) and CdSe) facilitates charge separation. The rate at which these separated charge carriers are driven toward opposing electrodes is a major factor that dictates the overall photocurrent generation efficiency. The hole transfer at the semiconductor remains a major bottleneck in QDSCs. For example, the rate constant for hole transfer is 2-3 orders of magnitude lower than the electron injection from excited CdSe into oxide (e.g., TiO(2)) semiconductor. Disparity between the electron and hole scavenging rate leads to further accumulation of holes within the CdSe QD and increases the rate of electron-hole recombination. To overcome the losses due to charge recombination processes at the interface, researchers need to accelerate electron and hole transport. The power conversion efficiency for liquid junction and solid state quantum dot solar cells, which is in the range of 5-6%, represents a significant advance toward effective utilization of nanomaterials for solar cells. The design of new semiconductor architectures could address many of the issues related to modulation of various charge transfer steps. With the resolution of those problems, the efficiencies of QDSCs could approach those of dye sensitized solar cells (DSSC) and organic photovoltaics.

Self-assembled quantum dots in a liquid-crystal-tunable microdisk resonator

NASA Astrophysics Data System (ADS)

Piegdon, Karoline A.; Offer, Matthias; Lorke, Axel; Urbanski, Martin; Hoischen, Andreas; Kitzerow, Heinz-S.; Declair, Stefan; Förstner, Jens; Meier, Torsten; Reuter, Dirk; Wieck, Andreas D.; Meier, Cedrik

2010-09-01

GaAs-based semiconductor microdisks with high quality whispering gallery modes ( Q>4000) have been fabricated. A layer of self-organized InAs quantum dots (QDs) served as a light source to feed the optical modes at room temperature. In order to achieve frequency tuning of the optical modes, the microdisk devices have been immersed in 4-cyano-4-pentylbiphenyl (5CB), a liquid crystal (LC) with a nematic phase below the clearing temperature of TC≈34C. We have studied the device performance in the temperature range of T=20-50C, in order to investigate the influence of the nematic-isotropic phase transition on the optical modes. Moreover, we have applied an AC electric field to the device, which leads in the nematic phase to a reorientation of the anisotropic dielectric tensor of the liquid crystal. This electrical anisotropy can be used to achieve electrical tunability of the optical modes. Using the finite-difference time domain (FDTD) technique with an anisotropic material model, we are able to describe the influence of the liquid crystal qualitatively.

Semiconductor quantum dot scintillation under gamma-ray irradiation.

PubMed

Létant, S E; Wang, T-F

2006-12-01

We recently demonstrated the ability of semiconductor quantum dots to convert alpha radiation into visible photons. In this letter, we report on the scintillation of quantum dots under gamma irradiation and compare the energy resolution of the 59 keV line of americium-241 obtained with our quantum dot-glass nanocomposite to that of a standard sodium iodide scintillator. A factor 2 improvement is demonstrated experimentally and interpreted theoretically using a combination of energy-loss and photon-transport models.

Control of spontaneous emission of quantum dots using correlated effects of metal oxides and dielectric materials

NASA Astrophysics Data System (ADS)

Sadeghi, S. M.; Wing, W. J.; Gutha, R. R.; Capps, L.

2017-03-01

We study the emission dynamics of semiconductor quantum dots in the presence of the correlated impact of metal oxides and dielectric materials. For this we used layered material structures consisting of a base substrate, a dielectric layer, and an ultrathin layer of a metal oxide. After depositing colloidal CdSe/ZnS quantum dots on the top of the metal oxide, we used spectral and time-resolved techniques to show that, depending on the type and thickness of the dielectric material, the metal oxide can characteristically change the interplay between intrinsic excitons, defect states, and the environment, offering new material properties. Our results show that aluminum oxide, in particular, can strongly change the impact of amorphous silicon on the emission dynamics of quantum dots by balancing the intrinsic near band emission and fast trapping of carriers. In such a system the silicon/aluminum oxide charge barrier can lead to large variation of the radiative lifetime of quantum dots and control of the photo-ejection rate of electrons in quantum dots. The results provide unique techniques to investigate and modify physical properties of dielectrics and manage optical and electrical properties of quantum dots.

Control of spontaneous emission of quantum dots using correlated effects of metal oxides and dielectric materials.

PubMed

Sadeghi, S M; Wing, W J; Gutha, R R; Capps, L

2017-03-03

We study the emission dynamics of semiconductor quantum dots in the presence of the correlated impact of metal oxides and dielectric materials. For this we used layered material structures consisting of a base substrate, a dielectric layer, and an ultrathin layer of a metal oxide. After depositing colloidal CdSe/ZnS quantum dots on the top of the metal oxide, we used spectral and time-resolved techniques to show that, depending on the type and thickness of the dielectric material, the metal oxide can characteristically change the interplay between intrinsic excitons, defect states, and the environment, offering new material properties. Our results show that aluminum oxide, in particular, can strongly change the impact of amorphous silicon on the emission dynamics of quantum dots by balancing the intrinsic near band emission and fast trapping of carriers. In such a system the silicon/aluminum oxide charge barrier can lead to large variation of the radiative lifetime of quantum dots and control of the photo-ejection rate of electrons in quantum dots. The results provide unique techniques to investigate and modify physical properties of dielectrics and manage optical and electrical properties of quantum dots.

Monolayer semiconductor nanocavity lasers with ultralow thresholds

DOE PAGES

Wu, Sanfeng; Buckley, Sonia; Schaibley, John R.; ...

2015-03-16

Engineering the electromagnetic environment of a nanoscale light emitter by a photonic cavity can significantly enhance its spontaneous emission rate through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter 1–5, providing the ultimate low-threshold laser system with small footprint, low power consumption and ultrafast modulation. A state-of-the-art ultra-low threshold nanolaser has been successfully developed though embedding quantum dots into photonic crystal cavity (PhCC) 6–8. However, several core challenges impede the practical applications of this architecture, including the random positions and compositional fluctuations of the dots 7, extreme difficulty in currentmore » injection8, and lack of compatibility with electronic circuits 7,8. Here, we report a new strategy to lase, where atomically thin crystalline semiconductor, i.e., a tungsten-diselenide (WSe 2) monolayer, is nondestructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PhCC. A new type of continuous-wave nanolaser operating in the visible regime is achieved with an optical pumping threshold as low as 27 nW at 130 K, similar to the value achieved in quantum dot PhCC lasers 7. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within 1 nm of the PhCC surface. The surface-gain geometry allows unprecedented accessibilities to multi-functionalize the gain, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.« less

Förster Resonance Energy Transfer between Quantum Dot Donors and Quantum Dot Acceptors

PubMed Central

Chou, Kenny F.; Dennis, Allison M.

2015-01-01

Förster (or fluorescence) resonance energy transfer amongst semiconductor quantum dots (QDs) is reviewed, with particular interest in biosensing applications. The unique optical properties of QDs provide certain advantages and also specific challenges with regards to sensor design, compared to other FRET systems. The brightness and photostability of QDs make them attractive for highly sensitive sensing and long-term, repetitive imaging applications, respectively, but the overlapping donor and acceptor excitation signals that arise when QDs serve as both the donor and acceptor lead to high background signals from direct excitation of the acceptor. The fundamentals of FRET within a nominally homogeneous QD population as well as energy transfer between two distinct colors of QDs are discussed. Examples of successful sensors are highlighted, as is cascading FRET, which can be used for solar harvesting. PMID:26057041

Quantum dots in imaging, drug delivery and sensor applications

PubMed Central

Matea, Cristian T; Mocan, Teodora; Tabaran, Flaviu; Pop, Teodora; Mosteanu, Ofelia; Puia, Cosmin; Iancu, Cornel; Mocan, Lucian

2017-01-01

Quantum dots (QDs), also known as nanoscale semiconductor crystals, are nanoparticles with unique optical and electronic properties such as bright and intensive fluorescence. Since most conventional organic label dyes do not offer the near-infrared (>650 nm) emission possibility, QDs, with their tunable optical properties, have gained a lot of interest. They possess characteristics such as good chemical and photo-stability, high quantum yield and size-tunable light emission. Different types of QDs can be excited with the same light wavelength, and their narrow emission bands can be detected simultaneously for multiple assays. There is an increasing interest in the development of nano-theranostics platforms for simultaneous sensing, imaging and therapy. QDs have great potential for such applications, with notable results already published in the fields of sensors, drug delivery and biomedical imaging. This review summarizes the latest developments available in literature regarding the use of QDs for medical applications. PMID:28814860

Quantum dots in imaging, drug delivery and sensor applications.

PubMed

Matea, Cristian T; Mocan, Teodora; Tabaran, Flaviu; Pop, Teodora; Mosteanu, Ofelia; Puia, Cosmin; Iancu, Cornel; Mocan, Lucian

2017-01-01

Quantum dots (QDs), also known as nanoscale semiconductor crystals, are nanoparticles with unique optical and electronic properties such as bright and intensive fluorescence. Since most conventional organic label dyes do not offer the near-infrared (>650 nm) emission possibility, QDs, with their tunable optical properties, have gained a lot of interest. They possess characteristics such as good chemical and photo-stability, high quantum yield and size-tunable light emission. Different types of QDs can be excited with the same light wavelength, and their narrow emission bands can be detected simultaneously for multiple assays. There is an increasing interest in the development of nano-theranostics platforms for simultaneous sensing, imaging and therapy. QDs have great potential for such applications, with notable results already published in the fields of sensors, drug delivery and biomedical imaging. This review summarizes the latest developments available in literature regarding the use of QDs for medical applications.

Multicolor quantum dot-encoded microspheres for the fluoroimmunoassays of chicken newcastle disease and goat pox virus.

PubMed

Yuan, Pingfan; Ma, Qiang; Meng, Rizeng; Wang, Chao; Dou, Wenchao; Wang, Guannan; Su, Xingguang

2009-05-01

Semiconductor nanocrystals (or quantum dots, QDs) have the potential to overcome some of the limitations encountered by traditional fluorophores in fluorescence labeling applications. The unique spectroscopic properties of QDs make them hold immense promise as versatile labels for biological applications. In this work, we employ the layer-by-layer (LbL) method for the construction of bio-functional multicolor QD-encoded microspheres. Polystyrene microspheres with diameter of 3 microm were used as templates for the deposition of different sized CdTe QDs/polyelectrolyte multilayers. Two different antigens, Chicken newcastle disease (CND) antigen and goat pox virus (GPV) antigen, were conjugated to two kinds of biofunctional multicolor microspheres with different optical encoding. The multicolor microspheres can capture corresponding antibodies labeled with QDs, QDs-CND antibody and QDs-GPV antibody in the fluoroimmunoassays. The microspheres can be distinguished from each other based on their optical encoding.

‘Green’-synthesized near-infrared PbS quantum dots with silica-PEG dual-layer coating: ultrastable and biocompatible optical probes for in vivo animal imaging

NASA Astrophysics Data System (ADS)

Wang, D.; Qian, J.; Cai, F.; He, S.; Han, S.; Mu, Y.

2012-06-01

In this paper, PbS semiconductor quantum dots (QDs) with near-infrared (NIR) photoluminescence were synthesized in oleic acid and paraffin liquid mixture by using an easily handled and ‘green’ approach. Surface functionalization of the QDs was accomplished with a silica and polyethylene glycol (PEG) phospholipid dual-layer coating and the excellent chemical stability of the nanoparticles is demonstrated. We then successfully applied the ultrastable PbS QDs to in vivo sentinel lymph node (SLN) mapping of mice. Histological analyses were also carried out to ensure that the intravenously injected nanoparticles did not produce any toxicity to the organism of mice. These experimental results suggested that our ultrastable NIR PbS QDs can serve as biocompatible and efficient probes for in vivo optical bioimaging and has great potentials for disease diagnosis and clinical therapies in the future.

High-fidelity quantum gates on quantum-dot-confined electron spins in low-Q optical microcavities

NASA Astrophysics Data System (ADS)

Li, Tao; Gao, Jian-Cun; Deng, Fu-Guo; Long, Gui-Lu

2018-04-01

We propose some high-fidelity quantum circuits for quantum computing on electron spins of quantum dots (QD) embedded in low-Q optical microcavities, including the two-qubit controlled-NOT gate and the multiple-target-qubit controlled-NOT gate. The fidelities of both quantum gates can, in principle, be robust to imperfections involved in a practical input-output process of a single photon by converting the infidelity into a heralded error. Furthermore, the influence of two different decay channels is detailed. By decreasing the quality factor of the present microcavity, we can largely increase the efficiencies of these quantum gates while their high fidelities remain unaffected. This proposal also has another advantage regarding its experimental feasibility, in that both quantum gates can work faithfully even when the QD-cavity systems are non-identical, which is of particular importance in current semiconductor QD technology.

The influence of the quantum dot/polymethylmethacrylate composite preparation method on the stability of its optical properties under laser radiation

NASA Astrophysics Data System (ADS)

Zvaigzne, M. A.; Martynov, I. L.; Krivenkov, V. A.; Samokhvalov, P. S.; Nabiev, I. R.

2017-01-01

Photoluminescent semiconductor nanocrystals, quantum dots (QDs), are nowadays one of the most promising materials for developing a new generation of fluorescent labels, new types of light-emitting devices and displays, flexible electronic components, and solar panels. In many areas the use of QDs is associated with an intense optical excitation, which, in the case of a prolonged exposure, often leads to changes in their optical characteristics. In the present work we examined how the method of preparation of quantum dot/polymethylmethacrylate (QD/PMMA) composite influenced the stability of the optical properties of QD inside the polymer matrix under irradiation by different laser harmonics in the UV (355 nm) and visible (532 nm) spectral regions. The composites were synthesized by spin-coating and radical polymerization methods. Experiments with the samples obtained by spin-coating showed that the properties of the QD/PMMA films remain almost constant at values of the radiation dose below 10 fJ per particle. Irradiating the composites prepared by the radical polymerization method, we observed a monotonic increase in the luminescence quantum yield (QY) accompanied by an increase in the luminescence decay time regardless of the wavelength of the incident radiation. We assume that the observed difference in the optical properties of the samples under exposure to laser radiation is associated with the processes occurring during radical polymerization, in particular, with charge transfer from the radical particles inside QDs. The results of this study are important for understanding photophysical properties of composites on the basis of QDs, as well as for selection of the type of polymer and the composite synthesis method with quantum dots that would allow one to avoid the degradation of their luminescence.

Optical pumping of a single hole spin in a p-doped quantum dot coupled to a metallic nanoparticle

NASA Astrophysics Data System (ADS)

Antón, M. A.; Carreño, F.; Melle, Sonia; Calderón, Oscar G.; Cabrera-Granado, E.; Singh, Mahi R.

2013-05-01

The preparation of quantum states with a defined spin is analyzed in a hybrid system consisting of a p-doped semiconductor quantum dot (QD) coupled to a metallic nanoparticle. The quantum dot is described as a four-level atom-like system using the density matrix formalism. The lower levels are Zeeman-split hole spin states and the upper levels correspond to positively charged excitons containing a spin-up, spin-down hole pair and a spin electron. A metallic nanoparticle with spheroidal geometry is placed in close proximity to the quantum dot, and its effects are considered in the quasistatic approximation. A linearly polarized laser field drives two of the optical transitions of the QD and produces localized surface plasmons in the nanoparticle which act back upon the QD. The frequencies of these localized plasmons are very different along the two principal axes of the nanoparticle, thus producing an anisotropic modification of the spontaneous emission rates of the allowed optical transitions which is accompanied by local-field corrections. This effect translates into a preferential acceleration of some of the optical pathways and therefore into a fast initialization of the QD by excitation with a short optical pulse. The population transfer between the lower levels of the QD and the fidelity is analyzed as a function of the nanoparticle's aspect ratio, the external magnetic field, and the Rabi frequency of the driving field. It is also shown that the main effect of the local-field corrections is a lengthening of the time elapsed to reach the steady-state. The hole spin is predicted to be successfully cooled from 5 to 0.04 K at a magnetic field of 4.6 T applied in the Voigt geometry.

Fano Effect and Quantum Entanglement in Hybrid Semiconductor Quantum Dot-Metal Nanoparticle System.

PubMed

He, Yong; Zhu, Ka-Di

2017-06-20

In this paper, we review the investigation for the light-matter interaction between surface plasmon field in metal nanoparticle (MNP) and the excitons in semiconductor quantum dots (SQDs) in hybrid SQD-MNP system under the full quantum description. The exciton-plasmon interaction gives rise to the modified decay rate and the exciton energy shift which are related to the exciton energy by using a quantum transformation method. We illustrate the responses of the hybrid SQD-MNP system to external field, and reveal Fano effect shown in the absorption spectrum. We demonstrate quantum entanglement between two SQD mediated by surface plasmon field. In the absence of a laser field, concurrence of quantum entanglement will disappear after a few ns. If the laser field is present, the steady states appear, so that quantum entanglement produced will reach a steady-state entanglement. Because one of all optical pathways to induce Fano effect refers to the generation of quantum entangled states, It is shown that the concurrence of quantum entanglement can be obtained by observation for Fano effect. In a hybrid system including two MNP and a SQD, because the two Fano quantum interference processes share a segment of all optical pathways, there is correlation between the Fano effects of the two MNP. The investigations for the light-matter interaction in hybrid SQD-MNP system can pave the way for the development of the optical processing devices and quantum information based on the exciton-plasmon interaction.

Fano Effect and Quantum Entanglement in Hybrid Semiconductor Quantum Dot-Metal Nanoparticle System

PubMed Central

He, Yong; Zhu, Ka-Di

2017-01-01

In this paper, we review the investigation for the light-matter interaction between surface plasmon field in metal nanoparticle (MNP) and the excitons in semiconductor quantum dots (SQDs) in hybrid SQD-MNP system under the full quantum description. The exciton-plasmon interaction gives rise to the modified decay rate and the exciton energy shift which are related to the exciton energy by using a quantum transformation method. We illustrate the responses of the hybrid SQD-MNP system to external field, and reveal Fano effect shown in the absorption spectrum. We demonstrate quantum entanglement between two SQD mediated by surface plasmon field. In the absence of a laser field, concurrence of quantum entanglement will disappear after a few ns. If the laser field is present, the steady states appear, so that quantum entanglement produced will reach a steady-state entanglement. Because one of all optical pathways to induce Fano effect refers to the generation of quantum entangled states, It is shown that the concurrence of quantum entanglement can be obtained by observation for Fano effect. In a hybrid system including two MNP and a SQD, because the two Fano quantum interference processes share a segment of all optical pathways, there is correlation between the Fano effects of the two MNP. The investigations for the light-matter interaction in hybrid SQD-MNP system can pave the way for the development of the optical processing devices and quantum information based on the exciton-plasmon interaction. PMID:28632165

Synthesis and characterization of colloidal ZnTe nanocrystals and ZnTe/ZnSe quantum dots

NASA Astrophysics Data System (ADS)

Gonzales, Gavin P.; Alas, Gema; Senthil, Arjun; Withers, Nathan J.; Minetos, Christina; Sandoval, Alejandro; Ivanov, Sergei A.; Smolyakov, Gennady A.; Huber, Dale L.; Osiński, Marek

2018-02-01

Quantum dots (QDs) emitting in the visible are of interest for many biomedical applications, including bioimaging, biosensing, drug targeting, and photodynamic therapy. However, a significant limitation is that QDs typically contain cadmium, which makes prospects for their FDA approval very unlikely. Previous work has focused on InP and ZnO as alternative semiconductor materials for QDs. However, these nanoparticles have also been shown to be cytotoxic. High-efficiency luminescent ZnTe-based QDs could be a reasonable alternative to Cd-containing QDs. In this paper, we present preliminary results of our recent studies of ZnTe-based QDs, including their synthesis, structural characterization, and optical properties.

Raman spectroscopy of magneto-phonon resonances in graphene and graphite

NASA Astrophysics Data System (ADS)

Goler, Sarah; Yan, Jun; Pellegrini, Vittorio; Pinczuk, Aron

2012-08-01

The magneto-phonon resonance or MPR occurs in semiconductor materials when the energy spacing between Landau levels is continuously tuned to cross the energy of an optical phonon mode. MPRs have been largely explored in bulk semiconductors, in two-dimensional systems and in quantum dots. Recently there has been significant interest in the MPR interactions of the Dirac fermion magneto-excitons in graphene, and a rich splitting and anti-crossing phenomena of the even parity E2g long wavelength optical phonon mode have been theoretically proposed and experimentally observed. The MPR has been found to crucially depend on disorder in the graphene layer. This is a feature that creates new venues for the study of interplays between disorder and interactions in the atomic layers. We review here the fundamentals of MRP in graphene and the experimental Raman scattering works that have led to the observation of these phenomena in graphene and graphite.

Structured illumination diffuse optical tomography for noninvasive functional neuroimaging in mice.

PubMed

Reisman, Matthew D; Markow, Zachary E; Bauer, Adam Q; Culver, Joseph P

2017-04-01

Optical intrinsic signal (OIS) imaging has been a powerful tool for capturing functional brain hemodynamics in rodents. Recent wide field-of-view implementations of OIS have provided efficient maps of functional connectivity from spontaneous brain activity in mice. However, OIS requires scalp retraction and is limited to superficial cortical tissues. Diffuse optical tomography (DOT) techniques provide noninvasive imaging, but previous DOT systems for rodent neuroimaging have been limited either by sparse spatial sampling or by slow speed. Here, we develop a DOT system with asymmetric source-detector sampling that combines the high-density spatial sampling (0.4 mm) detection of a scientific complementary metal-oxide-semiconductor camera with the rapid (2 Hz) imaging of a few ([Formula: see text]) structured illumination (SI) patterns. Analysis techniques are developed to take advantage of the system's flexibility and optimize trade-offs among spatial sampling, imaging speed, and signal-to-noise ratio. An effective source-detector separation for the SI patterns was developed and compared with light intensity for a quantitative assessment of data quality. The light fall-off versus effective distance was also used for in situ empirical optimization of our light model. We demonstrated the feasibility of this technique by noninvasively mapping the functional response in the somatosensory cortex of the mouse following electrical stimulation of the forepaw.

Epitaxial Zn quantum dots coherently grown on Si(1 1 1): growth mechanism, nonlinear optical and chemical states analyses

NASA Astrophysics Data System (ADS)

Huang, Bo-Jia; Kao, Li-Chi; Brahma, Sanjaya; Jeng, Yu-En; Chiu, Shang-Jui; Ku, Ching-Shun; Lo, Kuang-Yao

2017-05-01

Oxide- and defect-free metal/semiconductor interface is important to improve Ohmic contact for the suppression of electron scattering and the avoidance of an extrinsic surface state in estimating the barrier of the Schottky contact at the nanodevice interface. This study reports the growth mechanism of Zn quantum dots coherently grown on Si(1 1 1) and the physical phenomena of the crystalline, nonlinear optics, and the chemical states of Zn quantum dots. Epitaxial Zn quantum dots were coherently formed on a non-oxide Si(1 1 1) surface through the liquid- to solid-phase transformation as a result of pattern matching between the Zn(0 0 2) and Si(1 1 1) surfaces. The growth mechanism of constrained Zn quantum dots grown through strategic magnetron radio frequency sputtering is complex. Some factors, such as substrate temperature, hydrogen gas flow, and negative DC bias, influence the configuration of epitaxial Zn quantum dots. In particular, hydrogen gas plays an important role in reducing the ZnO+ and native oxide that is bombarded by accelerated ions, thereby enhancing the Zn ion surface diffusion. The reduction reaction can be inspected by distinguishing the chemical states of ZnO/Zn quantum dots from natural oxidation or the states of Zn 3d through the analysis of x-ray absorption near the edge structure spectrum. The complex growth mechanism can be systematically understood by analyzing a noncancelled anisotropic 3 m dipole from reflective second harmonic generation and inspecting the evolution between the Zn(0 0 2) and Zn(1 1 1) peaks of the collective ZnO/Zn quantum dots in synchrotron XRD.

Tuning Optoelectronic Properties of the Graphene-Based Quantum Dots C16- xSi xH10 Family.

PubMed

Ramadan, F-Z; Ouarrad, H; Drissi, L B

2018-06-07

The electronic and optical properties of graphene-based quantum dots (QDs) are investigated using DFT and many-body perturbation theory. Formation energy, hardeness and electrophilicity show that all structures, from pyrene to silicene QD passing through 15 CSi QD configurations, are energetically and chemically stable. It is also found that they are reactive which implies their favorable character for the possible electronic transport and conductivity. The electronic and optical properties are very sensitive to the number and position of the substituted silicon atoms as well as the directions of the light polarization. Moreover, quantum confinement effects make the exciton binding energy of CSi quantum dots larger than those of their higher dimensional allotropes such as silicene, graphene, and SiC sheet and nanotube. It is also higher those of other shapes of quantum dots like hexagonal graphene QDs and can be tailored from the ultraviolet region to the visible one. The values of the singlet-triplet splitting determined for the X- and Y-light polarized indicate that all configurations have a high fluorescence quantum yield compared to the yield of typical semiconductors, which makes them very promising for various applications such as the light-emitting diode material and nanomedicine.

Analysis of Phase Separation in Czochralski Grown Single Crystal Ilmenite

NASA Technical Reports Server (NTRS)

Wilkins, R.; Powell, Kirk St. A.; Loregnard, Kieron R.; Lin, Sy-Chyi; Muthusami, Jayakumar; Zhou, Feng; Pandey, R. K.; Brown, Geoff; Hawley, M. E.

1998-01-01

Ilmenite (FeTiOs) is a wide bandgap semiconductor with an energy gap of 2.58 eV. Ilmenite has properties suited for radiation tolerant applications, as well as a variety of other electronic applications. Single crystal ilmenite has been grown from the melt using the Czochralski method. Growth conditions have a profound effect on the microstructure of the samples. Here we present data from a variety of analytical techniques which indicate that some grown crystals exhibit distinct phase separation during growth. This phase separation is apparent for both post-growth annealed and unannealed samples. Under optical microscopy, there appear two distinct areas forming a matrix with an array of dots on order of 5 pm diameter. While appearing bright in the optical micrograph, atomic force microscope (AFM) shows the dots to be shallow pits on the surface. Magnetic force microscope (MFM) shows the dots to be magnetic. Phase identification via electron microprobe analysis (EMPA) indicates two major phases in the unannealed samples and four in the annealed samples, where the dots appear to be almost pure iron. This is consistent with micrographs taken with a scanning probe microscope used in the magnetic force mode. Samples that do not exhibit the phase separation have little or no discernible magnetic structure detectable by the MFM.

InGaN/GaN quantum dots as optical probes for the electric field at the GaN/electrolyte interface

NASA Astrophysics Data System (ADS)

Teubert, J.; Koslowski, S.; Lippert, S.; Schäfer, M.; Wallys, J.; Dimitrakopulos, G.; Kehagias, Th.; Komninou, Ph.; Das, A.; Monroy, E.; Eickhoff, M.

2013-08-01

We investigated the electric-field dependence of the photoluminescence-emission properties of InGaN/GaN quantum dot multilayers in contact with an electrolyte. Controlled variations of the surface potential were achieved by the application of external electric fields using the electrolytic Schottky contact and by variation of the solution's pH value. Prior to characterization, a selective electrochemical passivation process was required to suppress leakage currents. The quantum dot luminescence is strongly affected by surface potential variations, i.e., it increases exponentially with cathodic bias and acidic pH values. The results cannot be explained by a modification of intra-dot polarization induced electric fields via the quantum confined Stark effect but are attributed to the suppression/enhancement of non-radiative recombination processes, i.e., mainly hole transfer into the electrolyte. The results establish a link between the photoluminescence intensity and the magnitude of electric fields at the semiconductor/electrolyte interface.

Spin-orbit qubit in a semiconductor nanowire.

PubMed

Nadj-Perge, S; Frolov, S M; Bakkers, E P A M; Kouwenhoven, L P

2010-12-23

Motion of electrons can influence their spins through a fundamental effect called spin-orbit interaction. This interaction provides a way to control spins electrically and thus lies at the foundation of spintronics. Even at the level of single electrons, the spin-orbit interaction has proven promising for coherent spin rotations. Here we implement a spin-orbit quantum bit (qubit) in an indium arsenide nanowire, where the spin-orbit interaction is so strong that spin and motion can no longer be separated. In this regime, we realize fast qubit rotations and universal single-qubit control using only electric fields; the qubits are hosted in single-electron quantum dots that are individually addressable. We enhance coherence by dynamically decoupling the qubits from the environment. Nanowires offer various advantages for quantum computing: they can serve as one-dimensional templates for scalable qubit registers, and it is possible to vary the material even during wire growth. Such flexibility can be used to design wires with suppressed decoherence and to push semiconductor qubit fidelities towards error correction levels. Furthermore, electrical dots can be integrated with optical dots in p-n junction nanowires. The coherence times achieved here are sufficient for the conversion of an electronic qubit into a photon, which can serve as a flying qubit for long-distance quantum communication.

Design of cadmium-free colloidal II-VI semiconductor quantum dots exhibiting RGB emission

NASA Astrophysics Data System (ADS)

Asano, Hiroshi; Omata, Takahisa

2017-04-01

The size and composition dependence of the optical gap of colloidal alloyed quantum dots (QDs) of Zn(Te1-xSex) and Zn(Te1-xSx) were calculated by the finite-depth-well effective mass approximation method. QDs that exhibited red, green and blue emission were explored to develop cadmium-free II-VI chalcogenide-based QD-phosphors. We considered that highly monodisperse colloidal QDs with diameters of 3-6 nm are easy to synthesize and II-VI semiconductor QDs usually exhibit a Stokes shift ranging between 50 and 150 meV. We showed that Zn(Te1-xSex) QDs with 0.02≤x≤0.68, and 0≤x≤0.06, and 0.66≤x≤0.9 may be expected to exhibit green, and blue emission, respectively. Zn(Te1-xSx) QDs with 0.26≤x≤0.37, 0.01≤x≤0.2 and 0.45≤x≤0.61, 0≤x≤0.02, and 0.63≤x≤0.72, should give red, green and blue emission respectively. On the basis of our calculations, we showed that Zn(Te,Se) and Zn(Te,S) QDs are very promising cadmium-free II-VI chalcogenide semiconductor QD phosphors.

Electro-mechanical control of an on-chip optical beam splitter containing an embedded quantum emitter

NASA Astrophysics Data System (ADS)

Bishop, Z. K.; Foster, A. P.; Royall, B.; Bentham, C.; Clarke, E.; Skolnick, M. S.; Wilson, L. R.

2018-05-01

We demonstrate electro-mechanical control of an on-chip GaAs optical beam splitter containing a quantum dot single-photon source. The beam splitter consists of two nanobeam waveguides, which form a directional coupler (DC). The splitting ratio of the DC is controlled by varying the out-of-plane separation of the two waveguides using electro-mechanical actuation. We reversibly tune the beam splitter between an initial state, with emission into both output arms, and a final state with photons emitted into a single output arm. The device represents a compact and scalable tuning approach for use in III-V semiconductor integrated quantum optical circuits.

Fluorescence Stability of Mercaptopropionic Acid Capped Cadmium Telluride Quantum Dots in Various Biochemical Buffers.

PubMed

Borse, Vivek; Kashikar, Adisha; Srivastava, Rohit

2018-04-01

Quantum dots are the semiconductor nanocrystals having unique optical and electronic properties. Quantum dots are category of fluorescent labels utilized for biological tagging, biosensing, bioassays, bioimaging and in vivo imaging as they exhibit very small size, signal brightness, photostability, tuning of light emission range, longer photoluminescence decay time as compared to organic dyes. In this work, we have synthesized and characterized mercaptopropionic acid capped cadmium telluride quantum dots (MPA-CdTe QDs) using hydrothermal method. The study further reports fluorescence intensity stability of quantum dots suspended in different buffers of varying concentration (1-100 mM), stored at various photophysical conditions. Fluorescence intensity values were reduced with increase in buffer concentration. When the samples were stored at room temperature in ambient light condition the quantum dots suspended in different buffers lost the fluorescence intensity after day 15 (except TRIS II). Fluorescence intensity values were found stable for more than 30 days when the samples were stored in dark condition. Samples stored in refrigerator displayed modest fluorescence intensity even after 300 days of storage. Thus, storage of MPA-CdTe QDs in refrigerator may be the suitable choice to maintain its fluorescence stability for longer time for further application.

Laser direct-write and crystallization of FeSi II micro-dot array for NIR light-emitting device application

NASA Astrophysics Data System (ADS)

Narazaki, Aiko; Kurosaki, Ryozo; Sato, Tadatake; Kawaguchi, Yoshizo; Niino, Hiroyuki

2007-02-01

We printed FeSi II micro-dot array on various kinds of substrates utilizing laser-induced forward transfer (LIFT). An amorphous FeSi II was deposited by sputtering on a transparent plate as a source film. A single KrF excimer laser pulse through a mask-projection system was imaged with a small micrometer-sized grid pattern onto a film/plate interface, resulting in the deposition of FeSi II micro-dot array on a facing substrate with a high number density of 10 4 mm -2. FeSi II in the β crystalline phase is a promising eco-friendly semiconductor because of NIR electroluminescence used for optical networking as well as abundant components reserve on the earth and non-toxicity. However, the β-FeSi II film fabrication generally required high-temperature multi-processes which hamper its integration and performance reproducibility. Using the LIFT of micro-dot array, we succeeded in room-temperature preparation of β-FeSi II. Micro-Raman spectroscopy confirmed the β crystalline phase in the micro-dots deposited on an unheated silica glass substrate. Thus, the LIFT is useful for integrating functional micro-dot array accompanied by the crystallization at lower temperatures.

CdSe quantum dot sensitized solar cells. Shuttling electrons through stacked carbon nanocups.

PubMed

Farrow, Blake; Kamat, Prashant V

2009-08-12

The charge separation between excited CdSe semiconductor quantum dots and stacked-cup carbon nanotubes (SCCNTs) has been successfully tapped to generate photocurrent in a quantum dot sensitized solar cell (QDSC). By employing an electrophoretic deposition technique we have cast SCCNT-CdSe composite films on optically transparent electrodes (OTEs). The quenching of CdSe emission, as well as transient absorption measurements, confirms ultrafast electron transfer to SCCNTs. The rate constant for electron transfer increases from 9.51 x 10(9) s(-1) to 7.04 x 10(10) s(-1) as we decrease the size of CdSe nanoparticles from 4.5 to 3 nm. The ability of SCCNTs to collect and transport electrons from excited CdSe has been established from photocurrent measurements. The morphological and excited state properties of SCCNT-CdSe composites demonstrate their usefulness in energy conversion devices.

Quantum teleportation from a propagating photon to a solid-state spin qubit

NASA Astrophysics Data System (ADS)

Gao, W. B.; Fallahi, P.; Togan, E.; Delteil, A.; Chin, Y. S.; Miguel-Sanchez, J.; Imamoğlu, A.

2013-11-01

A quantum interface between a propagating photon used to transmit quantum information and a long-lived qubit used for storage is of central interest in quantum information science. A method for implementing such an interface between dissimilar qubits is quantum teleportation. Here we experimentally demonstrate transfer of quantum information carried by a photon to a semiconductor spin using quantum teleportation. In our experiment, a single photon in a superposition state is generated using resonant excitation of a neutral dot. To teleport this photonic qubit, we generate an entangled spin-photon state in a second dot located 5 m away and interfere the photons from the two dots in a Hong-Ou-Mandel set-up. Thanks to an unprecedented degree of photon-indistinguishability, a coincidence detection at the output of the interferometer heralds successful teleportation, which we verify by measuring the resulting spin state after prolonging its coherence time by optical spin-echo.

Quantum teleportation from a propagating photon to a solid-state spin qubit.

PubMed

Gao, W B; Fallahi, P; Togan, E; Delteil, A; Chin, Y S; Miguel-Sanchez, J; Imamoğlu, A

2013-01-01

A quantum interface between a propagating photon used to transmit quantum information and a long-lived qubit used for storage is of central interest in quantum information science. A method for implementing such an interface between dissimilar qubits is quantum teleportation. Here we experimentally demonstrate transfer of quantum information carried by a photon to a semiconductor spin using quantum teleportation. In our experiment, a single photon in a superposition state is generated using resonant excitation of a neutral dot. To teleport this photonic qubit, we generate an entangled spin-photon state in a second dot located 5 m away and interfere the photons from the two dots in a Hong-Ou-Mandel set-up. Thanks to an unprecedented degree of photon-indistinguishability, a coincidence detection at the output of the interferometer heralds successful teleportation, which we verify by measuring the resulting spin state after prolonging its coherence time by optical spin-echo.

Holographic assembly of semiconductor CdSe quantum dots in polymer for volume Bragg grating structures with diffraction efficiency near 100%

NASA Astrophysics Data System (ADS)

Liu, Xiangming; Tomita, Yasuo; Oshima, Juro; Chikama, Katsumi; Matsubara, Koutatsu; Nakashima, Takuya; Kawai, Tsuyoshi

2009-12-01

We report on the fabrication of centimeter-size transmission Bragg gratings in semiconductor CdSe quantum dots dispersed 50 μm thick photopolymer films. This was done by holographic assembly of CdSe quantum dots in a photopolymerizable monomer blend. Periodic patterning of CdSe quantum dots in polymer was confirmed by a fluorescence microscope and confocal Raman imaging. The diffraction efficiency from the grating of 1 μm spacing was near 100% in the green with 0.34 vol % CdSe quantum dots, giving the refractive index modulation as large as 5.1×10-3.

Prospects and fundamental limitations of room temperature, non-avalanche, semiconductor photon-counting sensors (Conference Presentation)

NASA Astrophysics Data System (ADS)

Ma, Jiaju; Zhang, Yang; Wang, Xiaoxin; Ying, Lei; Masoodian, Saleh; Wang, Zhiyuan; Starkey, Dakota A.; Deng, Wei; Kumar, Rahul; Wu, Yang; Ghetmiri, Seyed Amir; Yu, Zongfu; Yu, Shui-Qing; Salamo, Gregory J.; Fossum, Eric R.; Liu, Jifeng

2017-05-01

This research investigates the fundamental limits and trade-space of quantum semiconductor photodetectors using the Schrödinger equation and the laws of thermodynamics.We envision that, to optimize the metrics of single photon detection, it is critical to maximize the optical absorption in the minimal volume and minimize the carrier transit process simultaneously. Integration of photon management with quantum charge transport/redistribution upon optical excitation can be engineered to maximize the quantum efficiency (QE) and data rate and minimize timing jitter at the same time. Due to the ultra-low capacitance of these quantum devices, even a single photoelectron transfer can induce a notable change in the voltage, enabling non-avalanche single photon detection at room temperature as has been recently demonstrated in Si quanta image sensors (QIS). In this research, uniform III-V quantum dots (QDs) and Si QIS are used as model systems to test the theory experimentally. Based on the fundamental understanding, we also propose proof-of-concept, photon-managed quantum capacitance photodetectors. Built upon the concepts of QIS and single electron transistor (SET), this novel device structure provides a model system to synergistically test the fundamental limits and tradespace predicted by the theory for semiconductor detectors. This project is sponsored under DARPA/ARO's DETECT Program: Fundamental Limits of Quantum Semiconductor Photodetectors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Guohua; Czaplewski, David A.; Lenferink, Erik J.

Three-dimensional confinement allows semiconductor quantum dots to exhibit size-tunable electronic and optical properties that enable a wide range of opto-electronic applications from displays, solar cells and bio-medical imaging to single-electron devices. Additional modalities such as spin and valley properties in monolayer transition metal dichalcogenides provide further degrees of freedom requisite for information processing and spintronics. In nanostructures, however, spatial confinement can cause hybridization that inhibits the robustness of these emergent properties. Here in this paper, we show that laterally-confined excitons in monolayer MoS 2 nanodots can be created through top-down nanopatterning with controlled size tunability. Unlike chemically-exfoliated monolayer nanoparticles, themore » lithographically patterned monolayer semiconductor nanodots down to a radius of 15 nm exhibit the same valley polarization as in a continuous monolayer sheet. The inherited bulk spin and valley properties, the size dependence of excitonic energies, and the ability to fabricate MoS 2 nanostructures using semiconductor-compatible processing suggest that monolayer semiconductor nanodots have potential to be multimodal building blocks of integrated optoelectronics and spintronics systems« less

Quantum quench of Kondo correlations in optical absorption.

PubMed

Latta, C; Haupt, F; Hanl, M; Weichselbaum, A; Claassen, M; Wuester, W; Fallahi, P; Faelt, S; Glazman, L; von Delft, J; Türeci, H E; Imamoglu, A

2011-06-29

The interaction between a single confined spin and the spins of an electron reservoir leads to one of the most remarkable phenomena of many-body physics--the Kondo effect. Electronic transport measurements on single artificial atoms, or quantum dots, have made it possible to study the effect in great detail. Here we report optical measurements on a single semiconductor quantum dot tunnel-coupled to a degenerate electron gas which show that absorption of a single photon leads to an abrupt change in the system Hamiltonian and a quantum quench of Kondo correlations. By inferring the characteristic power-law exponents from the experimental absorption line shapes, we find a unique signature of the quench in the form of an Anderson orthogonality catastrophe, induced by a vanishing overlap between the initial and final many-body wavefunctions. We show that the power-law exponent that determines the degree of orthogonality can be tuned using an external magnetic field, which unequivocally demonstrates that the observed absorption line shape originates from Kondo correlations. Our experiments demonstrate that optical measurements on single artificial atoms offer new perspectives on many-body phenomena previously studied using transport spectroscopy only.

Size-tunable Lateral Confinement in Monolayer Semiconductors

DOE PAGES

Wei, Guohua; Czaplewski, David A.; Lenferink, Erik J.; ...

2017-06-12

Three-dimensional confinement allows semiconductor quantum dots to exhibit size-tunable electronic and optical properties that enable a wide range of opto-electronic applications from displays, solar cells and bio-medical imaging to single-electron devices. Additional modalities such as spin and valley properties in monolayer transition metal dichalcogenides provide further degrees of freedom requisite for information processing and spintronics. In nanostructures, however, spatial confinement can cause hybridization that inhibits the robustness of these emergent properties. Here in this paper, we show that laterally-confined excitons in monolayer MoS 2 nanodots can be created through top-down nanopatterning with controlled size tunability. Unlike chemically-exfoliated monolayer nanoparticles, themore » lithographically patterned monolayer semiconductor nanodots down to a radius of 15 nm exhibit the same valley polarization as in a continuous monolayer sheet. The inherited bulk spin and valley properties, the size dependence of excitonic energies, and the ability to fabricate MoS 2 nanostructures using semiconductor-compatible processing suggest that monolayer semiconductor nanodots have potential to be multimodal building blocks of integrated optoelectronics and spintronics systems« less

Submicron polymer particles containing fluorescent semiconductor nanocrystals CdSe/ZnS for bioassays.

PubMed

Generalova, Alla N; Sizova, Svetlana V; Zdobnova, Tatiana A; Zarifullina, Margarita M; Artemyev, Michail V; Baranov, Alexander V; Oleinikov, Vladimir A; Zubov, Vitaly P; Deyev, Sergey M

2011-02-01

This study aimed to design a panel of uniform particulate biochemical reagents and to test them in specific bioassays. These reagents are polymer particles of different sizes doped with semiconductor nanocrystals and conjugated with either full-size antibodies or recombinant mini-antibodies (4D5 scFv fragment) designed by genetic engineering approaches. A panel of highly fluorescent polymer particles (150-800 nm) were formed by embedding CdSe/ZnS nanocrystals (quantum dots) into preformed polyacrolein and poly(acrolein-co-styrene) particles. Morphology, content and fluorescence characteristics of the prepared materials were studied by laser correlation spectroscopy, spectrophotometry, optical and fluorescent microscopy and fluorimetry. The obtained fluorescent particles sensitized by anti-Yersinia pestis antibodies were used for rapid agglutination glass test suitable for screening analysis of Y. pestis antigen and for microtiter particle agglutination, which, owing to its speed and simplicity, is very beneficial for diagnostic detection of Y. pestis antigen. Recombinant 4D5 scFv antibodies designed and conjugated with polymer particles containing quantum dots provide multipoint highly specific binding with cancer marker HER2/neu on the surface of SKOV-3 cell.

Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain

PubMed Central

Chekhovich, E.A.; Hopkinson, M.; Skolnick, M.S.; Tartakovskii, A.I.

2015-01-01

Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear–nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2–4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging. PMID:25704639

Experimental optimal maximum-confidence discrimination and optimal unambiguous discrimination of two mixed single-photon states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steudle, Gesine A.; Knauer, Sebastian; Herzog, Ulrike

2011-05-15

We present an experimental implementation of optimum measurements for quantum state discrimination. Optimum maximum-confidence discrimination and optimum unambiguous discrimination of two mixed single-photon polarization states were performed. For the latter the states of rank 2 in a four-dimensional Hilbert space are prepared using both path and polarization encoding. Linear optics and single photons from a true single-photon source based on a semiconductor quantum dot are utilized.

Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons

NASA Astrophysics Data System (ADS)

Wolters, Janik; Buser, Gianni; Horsley, Andrew; Béguin, Lucas; Jöckel, Andreas; Jahn, Jan-Philipp; Warburton, Richard J.; Treutlein, Philipp

2017-08-01

Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δ f =0.66 GHz , the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure ηe2 e 50 ns=3.4 (3 )% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency ηint=17 (3 )%. Straightforward technological improvements can boost the end-to-end-efficiency to ηe 2 e≈35 %; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9 ×10-3 photons is dominated by atomic fluorescence, and for input pulses containing on average μ1=0.27 (4 ) photons, the signal to noise level would be unity.

Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons.

PubMed

Wolters, Janik; Buser, Gianni; Horsley, Andrew; Béguin, Lucas; Jöckel, Andreas; Jahn, Jan-Philipp; Warburton, Richard J; Treutlein, Philipp

2017-08-11

Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δf=0.66  GHz, the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure η_{e2e}^{50  ns}=3.4(3)% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency η_{int}=17(3)%. Straightforward technological improvements can boost the end-to-end-efficiency to η_{e2e}≈35%; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9×10^{-3} photons is dominated by atomic fluorescence, and for input pulses containing on average μ_{1}=0.27(4) photons, the signal to noise level would be unity.

Electrically tunable dynamic nuclear spin polarization in GaAs quantum dots at zero magnetic field

NASA Astrophysics Data System (ADS)

Manca, M.; Wang, G.; Kuroda, T.; Shree, S.; Balocchi, A.; Renucci, P.; Marie, X.; Durnev, M. V.; Glazov, M. M.; Sakoda, K.; Mano, T.; Amand, T.; Urbaszek, B.

2018-04-01

In III-V semiconductor nano-structures, the electron and nuclear spin dynamics are strongly coupled. Both spin systems can be controlled optically. The nuclear spin dynamics are widely studied, but little is known about the initialization mechanisms. Here, we investigate optical pumping of carrier and nuclear spins in charge tunable GaAs dots grown on 111A substrates. We demonstrate dynamic nuclear polarization (DNP) at zero magnetic field in a single quantum dot for the positively charged exciton X+ state transition. We tune the DNP in both amplitude and sign by variation of an applied bias voltage Vg. Variation of ΔVg on the order of 100 mV changes the Overhauser splitting (nuclear spin polarization) from -30 μeV (-22%) to +10 μeV (+7%) although the X+ photoluminescence polarization does not change sign over this voltage range. This indicates that absorption in the structure and energy relaxation towards the X+ ground state might provide favourable scenarios for efficient electron-nuclear spin flip-flops, generating DNP during the first tens of ps of the X+ lifetime which is on the order of hundreds of ps. Voltage control of DNP is further confirmed in Hanle experiments.

Diffusion doping in quantum dots: bond strength and diffusivity.

PubMed

Saha, Avijit; Makkar, Mahima; Shetty, Amitha; Gahlot, Kushagra; A R, Pavan; Viswanatha, Ranjani

2017-02-23

Semiconducting materials uniformly doped with optical or magnetic impurities have been useful in a number of potential applications. However, clustering or phase separation during synthesis has made this job challenging. Recently the "inside out" diffusion doping was proposed to be successful in obtaining large sized quantum dots (QDs) uniformly doped with a dilute percentage of dopant atoms. Herein, we demonstrate the use of basic physical chemistry of diffusion to control the size and concentration of the dopants within the QDs for a given transition metal ion. We have studied three parameters; the bond strength of the core molecules and the diffusion coefficient of the diffusing metal ion are found to be important while the ease of cation exchange was not highly influential in the control of size and concentration of the single domain dilute magnetic semiconductor quantum dots (DMSQDs) with diverse dopant ions M 2+ (Fe 2+ , Ni 2+ , Co 2+ , Mn 2+ ). Steady state optical emission spectra reveal that the dopants are incorporated inside the semiconducting CdS and the emission can be tuned during shell growth. We have shown that this method enables control over doping percentage and the QDs show a superior ferromagnetic response at room temperature as compared to previously reported systems.

SEMICONDUCTOR PHYSICS: Properties of the two- and three-dimensional quantum dot qubit

NASA Astrophysics Data System (ADS)

Shihua, Chen

2010-05-01

On the condition of electric-longitudinal-optical (LO) phonon strong coupling in both two- and three-dimensional parabolic quantum dots (QDs), we obtain the eigenenergies of the ground state (GS) and the first excited state (ES), the eigenfunctions of the GS and the first ES by using a variational method of Pekar type. This system in QD may be employed as a quantum system-quantum bit (qubit). When the electron is in the superposition state of the GS and the first ES, we obtain the time evolution of the electron density. The relations of both the electron probability density and the period of oscillation with the electric-LO phonon coupling strength and confinement length are discussed.

Fast detection of Listeria monocytogenes through a nanohybrid quantum dot complex.

PubMed

Donoso, Wendy; Castro, Ricardo I; Guzmán, Luis; López-Cabaña, Zoraya; Nachtigall, Fabiane M; Santos, Leonardo S

2017-09-01

Listeria monocytogenes is a recognized foodborne pathogen that causes listeriosis in susceptible consumers. Currently, the detection systems for Listeria in food detect live and dead bacteria, being the viable microorganisms most relevant for their ability to cause sickness in the population at risk. For this reason, a new nanohybrid compound was developed for the optical detection of Listeria that was based on polyamidoamine dendrimers functionalized with an auxotrophic cofactor (lipoic acid), together with the coupling of fluorescent semiconductor crystals (quantum dots). The nanohybrid sensor has a detection limit for viable L. monocytogenes of 5.19 × 10 3 colony-forming units per milliliter under epifluorescence microscopy. It was specific when used among other pathogens commonly found in food.

Nanoscale solid-state quantum computing

NASA Astrophysics Data System (ADS)

Ardavan, A.; Austwick, M.; Benjamin, S.C.; Briggs, G.A.D.; Dennis, T.J.S.; Ferguson, A.; Hasko, D.G.; Kanai, M.; Khlobystov, A.N.; Lovett, B.W.; Morley, G.W.; Oliver, R.A.; Pettifor, D.G.; Porfyrakis, K.; Reina, J.H.; Rice, J.H.; Smith, J.D.; Taylor, R.A.; Williams, D.A.; Adelmann, C.; Mariette, H.; Hamers, R.J.

2003-07-01

Most experts agree that it is too early to say how quantum computers will eventually be built, and several nanoscale solid-state schemes are being implemented in a range of materials. Nanofabricated quantum dots can be made in designer configurations, with established technology for controlling interactions and for reading out results. Epitaxial quantum dots can be grown in vertical arrays in semiconductors, and ultrafast optical techniques are available for controlling and measuring their excitations. Single-walled carbon nanotubes can be used for molecular self-assembly of endohedral fullerenes, which can embody quantum information in the electron spin. The challenges of individual addressing in such tiny structures could rapidly become intractable with increasing numbers of qubits, but these schemes are amenable to global addressing methods for computation.

Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor

PubMed Central

Branny, Artur; Kumar, Santosh; Proux, Raphaël; Gerardot, Brian D

2017-01-01

An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. We create point-like strain perturbations in mono- and bi-layer WSe2 which locally modify the band-gap, leading to efficient funnelling of excitons towards isolated strain-tuned quantum emitters that exhibit high-purity single photon emission. We achieve near unity emitter creation probability and a mean positioning accuracy of 120±32 nm, which may be improved with further optimization of the nanopillar dimensions. PMID:28530219

Tunable room-temperature spin-selective optical Stark effect in solution-processed layered halide perovskites.

PubMed

Giovanni, David; Chong, Wee Kiang; Dewi, Herlina Arianita; Thirumal, Krishnamoorthy; Neogi, Ishita; Ramesh, Ramamoorthy; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

2016-06-01

Ultrafast spin manipulation for opto-spin logic applications requires material systems that have strong spin-selective light-matter interaction. Conventional inorganic semiconductor nanostructures [for example, epitaxial II to VI quantum dots and III to V multiple quantum wells (MQWs)] are considered forerunners but encounter challenges such as lattice matching and cryogenic cooling requirements. Two-dimensional halide perovskite semiconductors, combining intrinsic tunable MQW structures and large oscillator strengths with facile solution processability, can offer breakthroughs in this area. We demonstrate novel room-temperature, strong ultrafast spin-selective optical Stark effect in solution-processed (C6H4FC2H4NH3)2PbI4 perovskite thin films. Exciton spin states are selectively tuned by ~6.3 meV using circularly polarized optical pulses without any external photonic cavity (that is, corresponding to a Rabi energy of ~55 meV and equivalent to applying a 70 T magnetic field), which is much larger than any conventional system. The facile halide and organic replacement in these perovskites affords control of the dielectric confinement and thus presents a straightforward strategy for tuning light-matter coupling strength.

Reconfigurable exciton-plasmon interconversion for nanophotonic circuits

PubMed Central

Lee, Hyun Seok; Luong, Dinh Hoa; Kim, Min Su; Jin, Youngjo; Kim, Hyun; Yun, Seokjoon; Lee, Young Hee

2016-01-01

The recent challenges for improving the operation speed of nanoelectronics have motivated research on manipulating light in on-chip integrated circuits. Hybrid plasmonic waveguides with low-dimensional semiconductors, including quantum dots and quantum wells, are a promising platform for realizing sub-diffraction limited optical components. Meanwhile, two-dimensional transition metal dichalcogenides (TMDs) have received broad interest in optoelectronics owing to tightly bound excitons at room temperature, strong light-matter and exciton-plasmon interactions, available top-down wafer-scale integration, and band-gap tunability. Here, we demonstrate principal functionalities for on-chip optical communications via reconfigurable exciton-plasmon interconversions in ∼200-nm-diameter Ag-nanowires overlapping onto TMD transistors. By varying device configurations for each operation purpose, three active components for optical communications are realized: field-effect exciton transistors with a channel length of ∼32 μm, field-effect exciton multiplexers transmitting multiple signals through a single NW and electrical detectors of propagating plasmons with a high On/Off ratio of∼190. Our results illustrate the unique merits of two-dimensional semiconductors for constructing reconfigurable device architectures in integrated nanophotonic circuits. PMID:27892463

Engineering of Semiconductor Nanocrystals for Light Emitting Applications

PubMed Central

Todescato, Francesco; Fortunati, Ilaria; Minotto, Alessandro; Signorini, Raffaella; Jasieniak, Jacek J.; Bozio, Renato

2016-01-01

Semiconductor nanocrystals are rapidly spreading into the display and lighting markets. Compared with liquid crystal and organic LED displays, nanocrystalline quantum dots (QDs) provide highly saturated colors, wide color gamut, resolution, rapid response time, optical efficiency, durability and low cost. This remarkable progress has been made possible by the rapid advances in the synthesis of colloidal QDs and by the progress in understanding the intriguing new physics exhibited by these nanoparticles. In this review, we provide support to the idea that suitably engineered core/graded-shell QDs exhibit exceptionally favorable optical properties, photoluminescence and optical gain, while keeping the synthesis facile and producing QDs well suited for light emitting applications. Solid-state laser emitters can greatly profit from QDs as efficient gain materials. Progress towards fabricating low threshold, solution processed DFB lasers that are optically pumped using one- and two-photon absorption is reviewed. In the field of display technologies, the exploitation of the exceptional photoluminescence properties of QDs for LCD backlighting has already advanced to commercial levels. The next big challenge is to develop the electroluminescence properties of QD to a similar state. We present an overview of QLED devices and of the great perspectives for next generation display and lighting technologies. PMID:28773794

Entangling quantum-logic gate operated with an ultrabright semiconductor single-photon source.

PubMed

Gazzano, O; Almeida, M P; Nowak, A K; Portalupi, S L; Lemaître, A; Sagnes, I; White, A G; Senellart, P

2013-06-21

We demonstrate the unambiguous entangling operation of a photonic quantum-logic gate driven by an ultrabright solid-state single-photon source. Indistinguishable single photons emitted by a single semiconductor quantum dot in a micropillar optical cavity are used as target and control qubits. For a source brightness of 0.56 photons per pulse, the measured truth table has an overlap with the ideal case of 68.4±0.5%, increasing to 73.0±1.6% for a source brightness of 0.17 photons per pulse. The gate is entangling: At a source brightness of 0.48, the Bell-state fidelity is above the entangling threshold of 50% and reaches 71.0±3.6% for a source brightness of 0.15.

Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties

NASA Technical Reports Server (NTRS)

Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher

1995-01-01

One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.

Probing into hybrid organic-molecule and InAs quantum-dots nanosystem with multistacked dots-in-a-well units

NASA Astrophysics Data System (ADS)

Chen, Miaoxiang; Kobashi, Kazufumi

2012-09-01

Hybridizing air-stable organic-molecules with advanced III-V semiconductor quantum-dots (QDs) structures can be utilized to create a new generation of biochemical sensing devices. In order to enhance their optical performances, the active regions in these QDs structures commonly consist of multistacked dots-in-a-well (DWELL) units. The effects of grafted molecules on the performances of the QDs structures with multistacked DWELLs, however, still remain unclear. Here, we show the significant improvements in the optical properties of InAs QDs in a hybrid nanosystem obtained by grafting biocompatible diazonium salt compound (amine donor) atop InAs QDs structure. Since its interface between the QDs structure and molecular monolayer retains an uncontaminated and non-oxidized condition, the nanosystem is an ideal platform to study the intrinsic properties of charge-carrier transport inside the system. Because of the complexity of the energy-levels in the QDs structure due to the existing surface QDs and DWELLs, selective excitation wavelengths (400, 633, and 885 nm, respectively) with different photo-energies are used to exactly analyze the complete charging mechanism in these QDs. A clear view of charge-carrier transfer inside the nanosystem is revealed by employing photoluminescence technique under selective-wavelength excitations. The present work provides new quantitative evidences for exploiting inorganic QDs applications in complex biological systems.

Optical gain in colloidal quantum dots achieved with direct-current electrical pumping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Jaehoon; Park, Young-Shin; Klimov, Victor Ivanovich

Chemically synthesized semiconductor quantum dots (QDs) can potentially enable solution-processable laser diodes with a wide range of operational wavelengths, yet demonstrations of lasing from the QDs are still at the laboratory stage. An important challenge—realization of lasing with electrical injection—remains unresolved, largely due to fast nonradiative Auger recombination of multicarrier states that represent gain-active species in the QDs. Here in this paper, we present population inversion and optical gain in colloidal nanocrystals realized with direct-current electrical pumping. Using continuously graded QDs, we achieve a considerable suppression of Auger decay such that it can be outpaced by electrical injection. Further, wemore » apply a special current-focusing device architecture, which allows us to produce high current densities (j) up to ~18 A cm -2 without damaging either the QDs or the injection layers. The quantitative analysis of electroluminescence and current-modulated transmission spectra indicates that with j = 3-4 A cm -2 we achieve the population inversion of the band-edge states.« less

Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission

PubMed Central

Sapienza, Luca; Davanço, Marcelo; Badolato, Antonio; Srinivasan, Kartik

2015-01-01

Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30 nm (<10 nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices. To that end, we create QD single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48%±5% into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50%), low multiphoton probability (g(2)(0) <1%), and a significant Purcell enhancement factor (≈3). PMID:26211442

Optical gain in colloidal quantum dots achieved with direct-current electrical pumping

NASA Astrophysics Data System (ADS)

Lim, Jaehoon; Park, Young-Shin; Klimov, Victor I.

2018-01-01

Chemically synthesized semiconductor quantum dots (QDs) can potentially enable solution-processable laser diodes with a wide range of operational wavelengths, yet demonstrations of lasing from the QDs are still at the laboratory stage. An important challenge--realization of lasing with electrical injection--remains unresolved, largely due to fast nonradiative Auger recombination of multicarrier states that represent gain-active species in the QDs. Here we present population inversion and optical gain in colloidal nanocrystals realized with direct-current electrical pumping. Using continuously graded QDs, we achieve a considerable suppression of Auger decay such that it can be outpaced by electrical injection. Further, we apply a special current-focusing device architecture, which allows us to produce high current densities (j) up to ~18 A cm-2 without damaging either the QDs or the injection layers. The quantitative analysis of electroluminescence and current-modulated transmission spectra indicates that with j = 3-4 A cm-2 we achieve the population inversion of the band-edge states.

Optical gain in colloidal quantum dots achieved with direct-current electrical pumping

DOE PAGES

Lim, Jaehoon; Park, Young-Shin; Klimov, Victor Ivanovich

2017-11-20

Chemically synthesized semiconductor quantum dots (QDs) can potentially enable solution-processable laser diodes with a wide range of operational wavelengths, yet demonstrations of lasing from the QDs are still at the laboratory stage. An important challenge—realization of lasing with electrical injection—remains unresolved, largely due to fast nonradiative Auger recombination of multicarrier states that represent gain-active species in the QDs. Here in this paper, we present population inversion and optical gain in colloidal nanocrystals realized with direct-current electrical pumping. Using continuously graded QDs, we achieve a considerable suppression of Auger decay such that it can be outpaced by electrical injection. Further, wemore » apply a special current-focusing device architecture, which allows us to produce high current densities (j) up to ~18 A cm -2 without damaging either the QDs or the injection layers. The quantitative analysis of electroluminescence and current-modulated transmission spectra indicates that with j = 3-4 A cm -2 we achieve the population inversion of the band-edge states.« less

Electrically driven quantum light emission in electromechanically tuneable photonic crystal cavities

NASA Astrophysics Data System (ADS)

Petruzzella, M.; Pagliano, F. M.; Zobenica, Ž.; Birindelli, S.; Cotrufo, M.; van Otten, F. W. M.; van der Heijden, R. W.; Fiore, A.

2017-12-01

A single quantum dot deterministically coupled to a photonic crystal environment constitutes an indispensable elementary unit to both generate and manipulate single-photons in next-generation quantum photonic circuits. To date, the scaling of the number of these quantum nodes on a fully integrated chip has been prevented by the use of optical pumping strategies that require a bulky off-chip laser along with the lack of methods to control the energies of nano-cavities and emitters. Here, we concurrently overcome these limitations by demonstrating electrical injection of single excitonic lines within a nano-electro-mechanically tuneable photonic crystal cavity. When an electrically driven dot line is brought into resonance with a photonic crystal mode, its emission rate is enhanced. Anti-bunching experiments reveal the quantum nature of these on-demand sources emitting in the telecom range. These results represent an important step forward in the realization of integrated quantum optics experiments featuring multiple electrically triggered Purcell-enhanced single-photon sources embedded in a reconfigurable semiconductor architecture.

Engineering a Robust Photovoltaic Device with Quantum Dots and Bacteriorhodopsin

PubMed Central

2015-01-01

We present a route toward a radical improvement in solar cell efficiency using resonant energy transfer and sensitization of semiconductor metal oxides with a light-harvesting quantum dot (QD)/bacteriorhodopsin (bR) layer designed by protein engineering. The specific aims of our approach are (1) controlled engineering of highly ordered bR/QD complexes; (2) replacement of the liquid electrolyte by a thin layer of gold; (3) highly oriented deposition of bR/QD complexes on a gold layer; and (4) use of the Forster resonance energy transfer coupling between bR and QDs to achieve an efficient absorbing layer for dye-sensitized solar cells. This proposed approach is based on the unique optical characteristics of QDs, on the photovoltaic properties of bR, and on state-of-the-art nanobioengineering technologies. It permits spatial and optical coupling together with control of hybrid material components on the bionanoscale. This method paves the way to the development of the solid-state photovoltaic device with the efficiency increased to practical levels. PMID:25383133

Single-shot quantum nondemolition measurement of a quantum-dot electron spin using cavity exciton-polaritons

NASA Astrophysics Data System (ADS)

Puri, Shruti; McMahon, Peter L.; Yamamoto, Yoshihisa

2014-10-01

We propose a scheme to perform single-shot quantum nondemolition (QND) readout of the spin of an electron trapped in a semiconductor quantum dot (QD). Our proposal relies on the interaction of the QD electron spin with optically excited, quantum well (QW) microcavity exciton-polaritons. The spin-dependent Coulomb exchange interaction between the QD electron and cavity polaritons causes the phase and intensity response of left circularly polarized light to be different than that of right circularly polarized light, in such a way that the QD electron's spin can be inferred from the response to a linearly polarized probe reflected or transmitted from the cavity. We show that with careful device design it is possible to essentially eliminate spin-flip Raman transitions. Thus a QND measurement of the QD electron spin can be performed within a few tens of nanoseconds with fidelity ˜99.95%. This improves upon current optical QD spin readout techniques across multiple metrics, including speed and scalability.

Synthesis and characterization of CdSe/ZnS quantum dots conjugated with poly (ethylene glycol) diamine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bharti, Shivani; Tripathi, S. K., E-mail: surya@pu.ac.in; Kaur, Gurvir

2015-08-28

Bio-functionalization or surface modification is an important technique to obtain biocompatibility in semiconductor nanoparticles for biomedical applications. In this study semiconductor core/shell quantum dots of CdSe/ZnS have been prepared by chemical reduction method and then further PEGylated using Poly(ethylene glycol) diamine of M{sub w} 2000. They were characterized by UV-vis spectroscopy & Fourier transform infrared spectroscopy. The results reveals the successful PEGylation of CdSe/ZnS quantum dots.

Quantifying the cellular uptake of semiconductor quantum dot nanoparticles by analytical electron microscopy.

PubMed

Hondow, Nicole; Brown, M Rowan; Starborg, Tobias; Monteith, Alexander G; Brydson, Rik; Summers, Huw D; Rees, Paul; Brown, Andy

2016-02-01

Semiconductor quantum dot nanoparticles are in demand as optical biomarkers yet the cellular uptake process is not fully understood; quantification of numbers and the fate of internalized particles are still to be achieved. We have focussed on the characterization of cellular uptake of quantum dots using a combination of analytical electron microscopies because of the spatial resolution available to examine uptake at the nanoparticle level, using both imaging to locate particles and spectroscopy to confirm identity. In this study, commercially available quantum dots, CdSe/ZnS core/shell particles coated in peptides to target cellular uptake by endocytosis, have been investigated in terms of the agglomeration state in typical cell culture media, the traverse of particle agglomerates across U-2 OS cell membranes during endocytosis, the merging of endosomal vesicles during incubation of cells and in the correlation of imaging flow cytometry and transmission electron microscopy to measure the final nanoparticle dose internalized by the U-2 OS cells. We show that a combination of analytical transmission electron microscopy and serial block face scanning electron microscopy can provide a comprehensive description of the internalization of an initial exposure dose of nanoparticles by an endocytically active cell population and how the internalized, membrane bound nanoparticle load is processed by the cells. We present a stochastic model of an endosome merging process and show that this provides a data-driven modelling framework for the prediction of cellular uptake of engineered nanoparticles in general. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Single-electron-occupation metal-oxide-semiconductor quantum dots formed from efficient poly-silicon gate layout

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carroll, Malcolm S.; rochette, sophie; Rudolph, Martin

We introduce a silicon metal-oxide-semiconductor quantum dot structure that achieves dot-reservoir tunnel coupling control without a dedicated barrier gate. The elementary structure consists of two accumulation gates separated spatially by a gap, one gate accumulating a reservoir and the other a quantum dot. Control of the tunnel rate between the dot and the reservoir across the gap is demonstrated in the single electron regime by varying the reservoir accumulation gate voltage while compensating with the dot accumulation gate voltage. The method is then applied to a quantum dot connected in series to source and drain reservoirs, enabling transport down tomore » the single electron regime. Finally, tuning of the valley splitting with the dot accumulation gate voltage is observed. This split accumulation gate structure creates silicon quantum dots of similar characteristics to other realizations but with less electrodes, in a single gate stack subtractive fabrication process that is fully compatible with silicon foundry manufacturing.« less

The Application of Fluorescent Quantum Dots to Confocal, Multiphoton, and Electron Microscopic Imaging

PubMed Central

Deerinck, Thomas J.

2009-01-01

Fluorescent quantum dots are emerging as an important tool for imaging cells and tissues, and their unique optical and physical properties have captured the attention of the research community. The most common types of commercially available quantum dots consist of a nanocrystalline semiconductor core composed of cadmium selenide with a zinc sulfide capping layer and an outer polymer layer to facilitate conjugation to targeting biomolecules such as immunoglobulins. They exhibit high fluorescent quantum yields and have large absorption cross-sections, possess excellent photostability, and can be synthesized so that their narrow-band fluorescence emission can occur in a wide spectrum of colors. These properties make them excellent candidates for serving as multiplexing molecular beacons using a variety of imaging modalities including highly correlated microscopies. Whereas much attention has been focused on quantum-dot applications for live-cell imaging, we have sought to characterize and exploit their utility for enabling simultaneous multiprotein immunolabeling in fixed cells and tissues. Considerations for their application to immunolabeling for correlated light and electron microscopic analysis are discussed. PMID:18337229

Unveiling the composite structures of emissive consolidated p-i-n junction nanocells for white light emission.

PubMed

Lee, Kyu Seung; Shim, Jaeho; Lee, Hyunbok; Yim, Sang-Youp; Angadi, Basavaraj; Lim, Byungkwon; Son, Dong Ick

2018-06-08

Hybrid organic-Red-Green-Blue (RGB) color quantum dots were incorporated into consolidated p(polymer)-i(RGB quantum dots)-n(small molecules) junction structures to fabricate a single active layer for a light emitting diode device for white electroluminescence. The semiconductor RGB quantum dots, as an intrinsic material, were electrostatically bonded between functional groups of the p-type polymer organic material core surface and the n-type small molecular organic material shell surface. The ZnCdSe/ZnS and CdSe/ZnS quantum dots distributed uniformly and isotropically surrounding the polymer core which in turn was surrounded by small molecular organic materials. In the present study, we have identified the mechanisms of chemical synthesis and interactions of the p-i-n junction nanocell structure through modeling studies by DFT calculations. We have also investigated optical, structural and electrical properties along with the carrier transport mechanism of the light emitting diodes which have a single active layer of consolidated p-i-n junction nanocells for white electroluminescence.

Cavity-Mediated Coherent Coupling between Distant Quantum Dots

NASA Astrophysics Data System (ADS)

Nicolí, Giorgio; Ferguson, Michael Sven; Rössler, Clemens; Wolfertz, Alexander; Blatter, Gianni; Ihn, Thomas; Ensslin, Klaus; Reichl, Christian; Wegscheider, Werner; Zilberberg, Oded

2018-06-01

Scalable architectures for quantum information technologies require one to selectively couple long-distance qubits while suppressing environmental noise and cross talk. In semiconductor materials, the coherent coupling of a single spin on a quantum dot to a cavity hosting fermionic modes offers a new solution to this technological challenge. Here, we demonstrate coherent coupling between two spatially separated quantum dots using an electronic cavity design that takes advantage of whispering-gallery modes in a two-dimensional electron gas. The cavity-mediated, long-distance coupling effectively minimizes undesirable direct cross talk between the dots and defines a scalable architecture for all-electronic semiconductor-based quantum information processing.

Control of electromagnetically induced transparency via a hybrid semiconductor quantum dot-vanadium dioxide nanoparticle system

NASA Astrophysics Data System (ADS)

Zamani, Naser; Hatef, Ali; Nadgaran, Hamid; Keshavarz, Alireza

2017-07-01

We numerically investigate the electromagnetically induced transparency (EIT) of a hybrid system consisting of a three-level quantum dot (QD) in the vicinity of vanadium dioxide nanoparticle (VO2NP). VO2NP has semiconductor and metallic phases where the transition between the two phases occurs around a critical temperature. When the QD-VO2NP hybrid system interacts with continuous wave laser fields in an infrared regime, it supports a coherent coupling of exciton-polariton and exciton-plasmon polariton in semiconductor and metal phases of VO2NP, respectively. In our calculations a filling fraction factor controls the VO2NP phase transition. A probe and control laser field configuration is studied for the hybrid system to measure the absorption of QD through the filling fraction factor manipulations. We show that for the VO2NP semiconductor phase and proper geometrical configuration, the absorption spectrum profile of the QD represents an EIT with two peaks and a clear minimum. These two peaks merge to one through the VO2NP phase transition to metal. We also show that the absorption spectrum profile is modified by different orientations of the laser fields with the axis of the QD-VO2NP hybrid system. The innovation in comparison to other research in the field is that robust variation in the absorption profile through EIT is due to the phase transition in VO2NP without any structural change in the QD-VO2NP hybrid system. Our results can be employed to design nanothermal sensors, optical nanoswitches, and energy transfer devices.

Synthesis and Characterization of Quantum Dots: A Case Study Using PbS

ERIC Educational Resources Information Center

Pan, Yi; Li, Yue Ru; Zhao, Yu; Akins, Daniel L.

2015-01-01

A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a…

A Quantum Dot with Spin-Orbit Interaction--Analytical Solution

ERIC Educational Resources Information Center

Basu, B.; Roy, B.

2009-01-01

The practical applicability of a semiconductor quantum dot with spin-orbit interaction gives an impetus to study analytical solutions to one- and two-electron quantum dots with or without a magnetic field.

Experimental investigation of different regimes of mode-locking in a high repetition rate passively mode-locked semiconductor quantum-dot laser.

PubMed

Kéfélian, Fabien; O'Donoghue, Shane; Todaro, Maria Teresa; McInerney, John; Huyet, Guillaume

2009-04-13

We report experimental investigations on a two-section 16-GHz repetition rate InAs/GaAs quantum dot passively mode-locked laser. Near the threshold current, pseudo-periodic Q-switching with complex dynamics is exhibited. Mode-locking operation regimes characterized by different repetition rates and timing jitter levels are encountered up to twice the threshold current. Evolution of the RF spectrum and optical spectrum with current is compared. The different mode-locked regimes are shown to be associated with different spectral and temporal shapes, ranging from 1.3 to 6 ps. This point is discussed by introducing the existence of two different supermodes. Repetition rate evolution and timing jitter increase is attributed to the coupling between the dominant and the secondary supermodes.

Preliminary Study of ZnS:Mn2+ Quantum Dots Response Under UV and X-Ray Irradiation

NASA Astrophysics Data System (ADS)

Saatsakis, G.; Valais, I.; Michail, C.; Fountzoula, C.; Fountos, G.; Koukou, V.; Martini, N.; Kalyvas, N.; Bakas, A.; Sianoudis, I.; Kandarakis, I.; Panayiotakis, G. S.

2017-11-01

Quantum Dots are semiconductor nanocrystals, with their optical properties controlled by their size, shape and material composition. The aim of the present study is to examine the scintillation properties of Manganese Doped Zinc Sulfide (ZnS:Mn 2+) Quantum Dot (QDs) nanocrystals under UV and X-ray irradiation. ZnS:Mn 2+ Quantum Dots, with typical diameter of ZnS dots of 13-20nm (also called scintillation QDs, stQDs), were developed and acquired by Mesolight Inc. The initial stQD sample was a solution of 75mg of ZnS:Mn 2+ dissolved in 100μL of Toluene, having a concentration of 75% w/v. Emission characteristics under UV and X-Ray excitation were examined. Two ultraviolet sources were incorporated (315 nm and 365 nm) as well as a medical X-ray tube with tube voltage from 50 to 130 kVp. Parameters such as Energy Quantum Efficiency under UV excitation and Luminescence Efficiency-LE (light energy flux over exposure rate) under X-ray excitation were examined. Luminescence Efficiency (LE) of ZnS:Mn 2+ was higher than that exhibited by previously examined QDs, (ZnCdSeS:ZnS and ZnCuInS:ZnS). The ability of ZnS:Mn 2+ to transform UV photons energy into optical photons energy, tends to increase while the incident UV wavelength decreases. Energy Quantum Efficiency of the sample exhibited a 6% increase when exposed to 315nm UV light compared to 365 nm. The emission spectrum of the stQDs, exhibited a narrow peak (~585nm) in the yellow range.

Theory of few photon dynamics in light emitting quantum dot devices

NASA Astrophysics Data System (ADS)

Carmele, Alexander; Richter, Marten; Sitek, Anna; Knorr, Andreas

2009-10-01

We present a modified cluster expansion to describe single-photon emitters in a semiconductor environment. We calculate microscopically to what extent semiconductor features in quantum dot-wetting layer systems alter the exciton and photon dynamics in comparison to the atom-like emission dynamics. We access these systems by the photon-probability-cluster-expansion: a reliable approach for few photon dynamics in many body electron systems. As a first application, we show that the amplitude of vacuum Rabi flops determines the number of electrons in the quantum dot.

Integration of semiconductor quantum dots into nano-bio-chip systems for enumeration of CD4+ T cell counts at the point-of-need†‡

PubMed Central

Jokerst, Jesse V.; Floriano, Pierre N.; Christodoulides, Nicolaos; Simmons, Glennon W.; McDevitt, John T.

2010-01-01

Recent humanitarian efforts have led to the widespread release of antiretroviral drugs for the treatment of the more than 33 million HIV afflicted people living in resource-scarce settings. Here, the enumeration of CD4+ T lymphocytes is required to establish the level at which the immune system has been compromised. The gold standard method used in developed countries, based on flow cytometry, though widely accepted and accurate, is precluded from widespread use in resource-scarce settings due to its high expense, high technical requirements, difficulty in operation-maintenance and the lack of portability for these sophisticated laboratory-confined systems. As part of continuing efforts to develop practical diagnostic instrumentation, the integration of semiconductor nanocrystals (quantum dots, QDs) into a portable microfluidic-based lymphocyte capture and detection device is completed. This integrated system is capable of isolating and counting selected lymphocyte sub-populations (CD3+CD4+) from whole blood samples. By combining the unique optical properties of the QDs with the sample handling capabilities and cost effectiveness of novel microfluidic systems, a practical, portable lymphocyte measurement modality that correlates nicely with flow cytometry (R2 = 0.97) has been developed. This QD-based system reduces the optical requirements significantly relative to molecular fluorophores and the mini-CD4 counting device is projected to be suitable for use in both point-of-need and resource-scarce settings. PMID:19023471

Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin

NASA Astrophysics Data System (ADS)

He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven

2017-08-01

Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796 ±0.020 . Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.

Spectra, current flow, and wave-function morphology in a model PT -symmetric quantum dot with external interactions

NASA Astrophysics Data System (ADS)

Tellander, Felix; Berggren, Karl-Fredrik

2017-04-01

In this paper we use numerical simulations to study a two-dimensional (2D) quantum dot (cavity) with two leads for passing currents (electrons, photons, etc.) through the system. By introducing an imaginary potential in each lead the system is made symmetric under parity-time inversion (PT symmetric). This system is experimentally realizable in the form of, e.g., quantum dots in low-dimensional semiconductors, optical and electromagnetic cavities, and other classical wave analogs. The computational model introduced here for studying spectra, exceptional points (EPs), wave-function symmetries and morphology, and current flow includes thousands of interacting states. This supplements previous analytic studies of few interacting states by providing more detail and higher resolution. The Hamiltonian describing the system is non-Hermitian; thus, the eigenvalues are, in general, complex. The structure of the wave functions and probability current densities are studied in detail at and in between EPs. The statistics for EPs is evaluated, and reasons for a gradual dynamical crossover are identified.

Far-field nanoscopy on a semiconductor quantum dot via a rapid-adiabatic-passage-based switch

NASA Astrophysics Data System (ADS)

Kaldewey, Timo; Kuhlmann, Andreas V.; Valentin, Sascha R.; Ludwig, Arne; Wieck, Andreas D.; Warburton, Richard J.

2018-02-01

The diffraction limit prevents a conventional optical microscope from imaging at the nanoscale. However, nanoscale imaging of molecules is possible by exploiting an intensity-dependent molecular switch1-3. This switch is translated into a microscopy scheme, stimulated emission depletion microscopy4-7. Variants on this scheme exist3,8-13, yet all exploit an incoherent response to the lasers. We present a scheme that relies on a coherent response to a laser. Quantum control of a two-level system proceeds via rapid adiabatic passage, an ideal molecular switch. We implement this scheme on an ensemble of quantum dots. Each quantum dot results in a bright spot in the image with extent down to 30 nm (λ/31). There is no significant loss of intensity with respect to confocal microscopy, resulting in a factor of 10 improvement in emitter position determination. The experiments establish rapid adiabatic passage as a versatile tool in the super-resolution toolbox.

Magneto-optical studies of quantum dots

NASA Astrophysics Data System (ADS)

Russ, Andreas Hans

Significant effort in condensed matter physics has recently been devoted to the field of "spintronics" which seeks to utilize the spin degree of freedom of electrons. Unlike conventional electronics that rely on the electron charge, devices exploiting their spin have the potential to yield new and novel technological applications, including spin transistors, spin filters, and spin-based memory devices. Any such application has the following essential requirements: 1) Efficient electrical injection of spin-polarized carriers; 2) Long spin lifetimes; 3) Ability to control and manipulate electron spins; 4) Effective detection of spin-polarized carriers. Recent work has demonstrated efficient electrical injection from ferromagnetic contacts such as Fe and MnAs, utilizing a spin-Light Emitting Diode (spin-LED) as a method of detection. Semiconductor quantum dots (QDs) are attractive candidates for satisfying requirements 2 and 3 as their zero dimensionality significantly suppresses many spin-flip mechanisms leading to long spin coherence times, as well as enabling the localization and manipulation of a controlled number of electrons and holes. This thesis is composed of three projects that are all based on the optical properties of QD structures including: I) Intershell exchange between spin-polarized electrons occupying adjacent shells in InAs QDs; II) Spin-polarized multiexitons in InAs QDs in the presence of spin-orbit interactions; III) The optical Aharonov-Bohm effect in AlxGa1-xAs/AlyGa1-yAs quantum wells (QWs). In the following we introduce some of the basic optical properties of quantum dots, describe the main tool (spin-LED) employed in this thesis to inject and detect spins in these QDs, and conclude with the optical Aharonov-Bohm effect (OAB) in type-II QDs.

Late Quaternary to Holocene Geology, Geomorphology and Glacial History of Dawson Creek and Surrounding area, Northeast British Columbia, Canada

NASA Astrophysics Data System (ADS)

Henry, Edward Trowbridge

Semiconductor quantum dots in silicon demonstrate exceptionally long spin lifetimes as qubits and are therefore promising candidates for quantum information processing. However, control and readout techniques for these devices have thus far employed low frequency electrons, in contrast to high speed temperature readout techniques used in other qubit architectures, and coupling between multiple quantum dot qubits has not been satisfactorily addressed. This dissertation presents the design and characterization of a semiconductor charge qubit based on double quantum dot in silicon with an integrated microwave resonator for control and readout. The 6 GHz resonator is designed to achieve strong coupling with the quantum dot qubit, allowing the use of circuit QED control and readout techniques which have not previously been applicable to semiconductor qubits. To achieve this coupling, this document demonstrates successful operation of a novel silicon double quantum dot design with a single active metallic layer and a coplanar stripline resonator with a bias tee for dc excitation. Experiments presented here demonstrate quantum localization and measurement of both electrons on the quantum dot and photons in the resonator. Further, it is shown that the resonator-qubit coupling in these devices is sufficient to reach the strong coupling regime of circuit QED. The details of a measurement setup capable of performing simultaneous low noise measurements of the resonator and quantum dot structure are also presented here. The ultimate aim of this research is to integrate the long coherence times observed in electron spins in silicon with the sophisticated readout architectures available in circuit QED based quantum information systems. This would allow superconducting qubits to be coupled directly to semiconductor qubits to create hybrid quantum systems with separate quantum memory and processing components.

Dynamics of a Cr spin in a semiconductor quantum dot: Hole-Cr flip-flops and spin-phonon coupling

NASA Astrophysics Data System (ADS)

Lafuente-Sampietro, A.; Utsumi, H.; Sunaga, M.; Makita, K.; Boukari, H.; Kuroda, S.; Besombes, L.

2018-04-01

A detailed analysis of the photoluminescence (PL) intensity distribution in singly Cr-doped CdTe/ZnTe quantum dots (QDs) is performed. First of all, we demonstrate that hole-Cr flip-flops induced by an interplay of the hole-Cr exchange interaction and the coupling with acoustic phonons are the main source of spin relaxation within the exciton-Cr complex. This spin flip mechanism appears in the excitation power dependence of the PL of the exciton as well as in the intensity distribution of the resonant PL. The resonant optical pumping of the Cr spin which was recently demonstrated can also be explained by these hole-Cr flip-flops. Despite the fast exciton-Cr spin dynamics, an analysis of the PL intensity under magnetic field shows that the hole-Cr exchange interaction in CdTe/ZnTe QDs is antiferromagnetic. In addition to the Cr spin dynamics induced by the interaction with carriers' spin, we finally demonstrate using time resolved optical pumping measurements that a Cr spin interacts with nonequilibrium acoustic phonons generated during the optical excitation inside or near the QD.

Spatially selective assembly of quantum dot light emitters in an LED using engineered peptides.

PubMed

Demir, Hilmi Volkan; Seker, Urartu Ozgur Safak; Zengin, Gulis; Mutlugun, Evren; Sari, Emre; Tamerler, Candan; Sarikaya, Mehmet

2011-04-26

Semiconductor nanocrystal quantum dots are utilized in numerous applications in nano- and biotechnology. In device applications, where several different material components are involved, quantum dots typically need to be assembled at explicit locations for enhanced functionality. Conventional approaches cannot meet these requirements where assembly of nanocrystals is usually material-nonspecific, thereby limiting the control of their spatial distribution. Here we demonstrate directed self-assembly of quantum dot emitters at material-specific locations in a color-conversion LED containing several material components including a metal, a dielectric, and a semiconductor. We achieve a spatially selective immobilization of quantum dot emitters by using the unique material selectivity characteristics provided by the engineered solid-binding peptides as smart linkers. Peptide-decorated quantum dots exhibited several orders of magnitude higher photoluminescence compared to the control groups, thus, potentially opening up novel ways to advance these photonic platforms in applications ranging from chemical to biodetection.

Low temperature nano-spin filtering using a diluted magnetic semiconductor core-shell quantum dot

NASA Astrophysics Data System (ADS)

Chattopadhyay, Saikat; Sen, Pratima; Andrews, Joshep Thomas; Sen, Pranay Kumar

2014-07-01

The spin polarized electron transport properties and spin polarized tunneling current have been investigated analytically in a diluted magnetic semiconductor core-shell quantum dot in the presence of applied electric and magnetic fields. Assuming the electron wave function to satisfy WKB approximation, the electron energy eigenvalues have been calculated. The spin polarized tunneling current and the spin dependent tunneling coefficient are obtained by taking into account the exchange interaction and Zeeman splitting. Numerical estimates made for a specific diluted magnetic semiconductor, viz., Zn1-xMnxSe/ZnS core-shell quantum dot establishes the possibility of a nano-spin filter for a particular biasing voltage and applied magnetic field. Influence of applied voltage on spin polarized electron transport has been investigated in a CSQD.

Simultaneous deterministic control of distant qubits in two semiconductor quantum dots.

PubMed

Gamouras, A; Mathew, R; Freisem, S; Deppe, D G; Hall, K C

2013-10-09

In optimal quantum control (OQC), a target quantum state of matter is achieved by tailoring the phase and amplitude of the control Hamiltonian through femtosecond pulse-shaping techniques and powerful adaptive feedback algorithms. Motivated by recent applications of OQC in quantum information science as an approach to optimizing quantum gates in atomic and molecular systems, here we report the experimental implementation of OQC in a solid-state system consisting of distinguishable semiconductor quantum dots. We demonstrate simultaneous high-fidelity π and 2π single qubit gates in two different quantum dots using a single engineered infrared femtosecond pulse. These experiments enhance the scalability of semiconductor-based quantum hardware and lay the foundation for applications of pulse shaping to optimize quantum gates in other solid-state systems.

Quantum control and process tomography of a semiconductor quantum dot hybrid qubit.

PubMed

Kim, Dohun; Shi, Zhan; Simmons, C B; Ward, D R; Prance, J R; Koh, Teck Seng; Gamble, John King; Savage, D E; Lagally, M G; Friesen, Mark; Coppersmith, S N; Eriksson, Mark A

2014-07-03

The similarities between gated quantum dots and the transistors in modern microelectronics--in fabrication methods, physical structure and voltage scales for manipulation--have led to great interest in the development of quantum bits (qubits) in semiconductor quantum dots. Although quantum dot spin qubits have demonstrated long coherence times, their manipulation is often slower than desired for important future applications, such as factoring. Furthermore, scalability and manufacturability are enhanced when qubits are as simple as possible. Previous work has increased the speed of spin qubit rotations by making use of integrated micromagnets, dynamic pumping of nuclear spins or the addition of a third quantum dot. Here we demonstrate a qubit that is a hybrid of spin and charge. It is simple, requiring neither nuclear-state preparation nor micromagnets. Unlike previous double-dot qubits, the hybrid qubit enables fast rotations about two axes of the Bloch sphere. We demonstrate full control on the Bloch sphere with π-rotation times of less than 100 picoseconds in two orthogonal directions, which is more than an order of magnitude faster than any other double-dot qubit. The speed arises from the qubit's charge-like characteristics, and its spin-like features result in resistance to decoherence over a wide range of gate voltages. We achieve full process tomography in our electrically controlled semiconductor quantum dot qubit, extracting high fidelities of 85 per cent for X rotations (transitions between qubit states) and 94 per cent for Z rotations (phase accumulation between qubit states).

Thermally activated delayed photoluminescence from pyrenyl-functionalized CdSe quantum dots

NASA Astrophysics Data System (ADS)

Mongin, Cédric; Moroz, Pavel; Zamkov, Mikhail; Castellano, Felix N.

2018-02-01

The generation and transfer of triplet excitons across semiconductor nanomaterial-molecular interfaces will play an important role in emerging photonic and optoelectronic technologies, and understanding the rules that govern such phenomena is essential. The ability to cooperatively merge the photophysical properties of semiconductor quantum dots with those of well-understood and inexpensive molecular chromophores is therefore paramount. Here we show that 1-pyrenecarboxylic acid-functionalized CdSe quantum dots undergo thermally activated delayed photoluminescence. This phenomenon results from a near quantitative triplet-triplet energy transfer from the nanocrystals to 1-pyrenecarboxylic acid, producing a molecular triplet-state 'reservoir' that thermally repopulates the photoluminescent state of CdSe through endothermic reverse triplet-triplet energy transfer. The photoluminescence properties are systematically and predictably tuned through variation of the quantum dot-molecule energy gap, temperature and the triplet-excited-state lifetime of the molecular adsorbate. The concepts developed are likely to be applicable to semiconductor nanocrystals interfaced with molecular chromophores, enabling potential applications of their combined excited states.

Optical investigations of nanostructured oxides and semiconductors

NASA Astrophysics Data System (ADS)

Irvin, Patrick Richard

This work is motivated by the prospect of building a quantum computer: a device that would allow physicists to explore quantum mechanics more deeply, and allow everyone else to keep their credit card numbers safe on the Internet. In this thesis we explore two classes of materials that are relevant to a proposed quantum computer architecture: oxides and semiconductors. Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. We investigate strained-SrTiO 3, which is ferroelectric at room-temperature, and a composite material of (Ba,Sr)TiO3 and MgO. We present optical techniques to measure electron spin dynamics with GHz dynamical bandwidth, transform-limited spectral selectivity, and phase-sensitive detection. We demonstrate this technique by measuring GHz-spin precession in n-GaAs. We also describe our efforts to optically probe InAs/GaAs and GaAs/AlGaAs quantum dots. Nanoscale devices with photonic properties have been the subject of intense research over the past decade. Potential nanophotonic applications include communications, polarization-sensitive detectors, and solar power generation. Here we show photosensitivity of a nanoscale detector written at the interface between two oxides.

Ultrafast Single and Multiexciton Energy Transfer in Semiconductor Nanoplatelets

NASA Astrophysics Data System (ADS)

Schaller, Richard

Photophysical processes such as fluorescence resonance energy transfer (FRET) enable optical antennas, wavelength down-conversion in light-emitting diodes (LEDs), and optical bio-sensing schemes. The rate and efficiency of this donor to acceptor transfer of excitation between chromophores dictates the utility of FRET and can unlock new device operation motifs including quantum-funnel solar cells and reduced gain thresholds. However, the fastest reported FRET time constants involving spherical quantum dots (QDs) (0.12-1 ns), do not outpace biexciton Auger recombination (0.01-0.1 ns), which impedes multiexciton-driven applications including electrically-pumped lasers and carrier-multiplication-enhanced photovoltaics. Precisely controlled, few-monolayer thick semiconductor nano-platelets with tens-of-nanometer diameters exhibit intense optical transitions and hundreds-of-picosecond Auger recombination, but heretofore lack FRET characterizations. We examine binary CdSe NPL solids and show that inter-plate FRET (~6-23 ps, presumably for co-facial arrangements) can occur 15-50 times faster than Auger recombination and demonstrate multiexcitonic FRET, making such materials ideal candidates for advanced technologies. This work was performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility under Contract No. DE-AC02-06CH11357.

Optical bandgap of semiconductor nanostructures: Methods for experimental data analysis

NASA Astrophysics Data System (ADS)

Raciti, R.; Bahariqushchi, R.; Summonte, C.; Aydinli, A.; Terrasi, A.; Mirabella, S.

2017-06-01

Determination of the optical bandgap (Eg) in semiconductor nanostructures is a key issue in understanding the extent of quantum confinement effects (QCE) on electronic properties and it usually involves some analytical approximation in experimental data reduction and modeling of the light absorption processes. Here, we compare some of the analytical procedures frequently used to evaluate the optical bandgap from reflectance (R) and transmittance (T) spectra. Ge quantum wells and quantum dots embedded in SiO2 were produced by plasma enhanced chemical vapor deposition, and light absorption was characterized by UV-Vis/NIR spectrophotometry. R&T elaboration to extract the absorption spectra was conducted by two approximated methods (single or double pass approximation, single pass analysis, and double pass analysis, respectively) followed by Eg evaluation through linear fit of Tauc or Cody plots. Direct fitting of R&T spectra through a Tauc-Lorentz oscillator model is used as comparison. Methods and data are discussed also in terms of the light absorption process in the presence of QCE. The reported data show that, despite the approximation, the DPA approach joined with Tauc plot gives reliable results, with clear advantages in terms of computational efforts and understanding of QCE.

Tunable room-temperature spin-selective optical Stark effect in solution-processed layered halide perovskites

PubMed Central

Giovanni, David; Chong, Wee Kiang; Dewi, Herlina Arianita; Thirumal, Krishnamoorthy; Neogi, Ishita; Ramesh, Ramamoorthy; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

2016-01-01

Ultrafast spin manipulation for opto–spin logic applications requires material systems that have strong spin-selective light-matter interaction. Conventional inorganic semiconductor nanostructures [for example, epitaxial II to VI quantum dots and III to V multiple quantum wells (MQWs)] are considered forerunners but encounter challenges such as lattice matching and cryogenic cooling requirements. Two-dimensional halide perovskite semiconductors, combining intrinsic tunable MQW structures and large oscillator strengths with facile solution processability, can offer breakthroughs in this area. We demonstrate novel room-temperature, strong ultrafast spin-selective optical Stark effect in solution-processed (C6H4FC2H4NH3)2PbI4 perovskite thin films. Exciton spin states are selectively tuned by ~6.3 meV using circularly polarized optical pulses without any external photonic cavity (that is, corresponding to a Rabi energy of ~55 meV and equivalent to applying a 70 T magnetic field), which is much larger than any conventional system. The facile halide and organic replacement in these perovskites affords control of the dielectric confinement and thus presents a straightforward strategy for tuning light-matter coupling strength. PMID:27386583

Delay induced high order locking effects in semiconductor lasers

NASA Astrophysics Data System (ADS)

Kelleher, B.; Wishon, M. J.; Locquet, A.; Goulding, D.; Tykalewicz, B.; Huyet, G.; Viktorov, E. A.

2017-11-01

Multiple time scales appear in many nonlinear dynamical systems. Semiconductor lasers, in particular, provide a fertile testing ground for multiple time scale dynamics. For solitary semiconductor lasers, the two fundamental time scales are the cavity repetition rate and the relaxation oscillation frequency which is a characteristic of the field-matter interaction in the cavity. Typically, these two time scales are of very different orders, and mutual resonances do not occur. Optical feedback endows the system with a third time scale: the external cavity repetition rate. This is typically much longer than the device cavity repetition rate and suggests the possibility of resonances with the relaxation oscillations. We show that for lasers with highly damped relaxation oscillations, such resonances can be obtained and lead to spontaneous mode-locking. Two different laser types-—a quantum dot based device and a quantum well based device—are analysed experimentally yielding qualitatively identical dynamics. A rate equation model is also employed showing an excellent agreement with the experimental results.

Delay induced high order locking effects in semiconductor lasers.

PubMed

Kelleher, B; Wishon, M J; Locquet, A; Goulding, D; Tykalewicz, B; Huyet, G; Viktorov, E A

2017-11-01

Multiple time scales appear in many nonlinear dynamical systems. Semiconductor lasers, in particular, provide a fertile testing ground for multiple time scale dynamics. For solitary semiconductor lasers, the two fundamental time scales are the cavity repetition rate and the relaxation oscillation frequency which is a characteristic of the field-matter interaction in the cavity. Typically, these two time scales are of very different orders, and mutual resonances do not occur. Optical feedback endows the system with a third time scale: the external cavity repetition rate. This is typically much longer than the device cavity repetition rate and suggests the possibility of resonances with the relaxation oscillations. We show that for lasers with highly damped relaxation oscillations, such resonances can be obtained and lead to spontaneous mode-locking. Two different laser types--a quantum dot based device and a quantum well based device-are analysed experimentally yielding qualitatively identical dynamics. A rate equation model is also employed showing an excellent agreement with the experimental results.

Plasmonic Control of Radiation and Absorption Processes in Semiconductor Quantum Dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paiella, Roberto; Moustakas, Theodore D.

This document reviews a research program funded by the DOE Office of Science, which has been focused on the control of radiation and absorption processes in semiconductor photonic materials (including III-nitride quantum wells and quantum dots), through the use of specially designed metallic nanoparticles (NPs). By virtue of their strongly confined plasmonic resonances (i.e., collective oscillations of the electron gas), these nanostructures can concentrate incident radiation into sub-wavelength “hot spots” of highly enhanced field intensity, thereby increasing optical absorption by suitably positioned absorbers. By reciprocity, the same NPs can also dramatically increase the spontaneous emission rate of radiating dipoles locatedmore » within their hot spots. The NPs can therefore be used as optical antennas to enhance the radiation output of the underlying active material and at the same time control the far-field pattern of the emitted light. The key accomplishments of the project include the demonstration of highly enhanced light emission efficiency as well as plasmonic collimation and beaming along geometrically tunable directions, using a variety of plasmonic excitations. Initial results showing the reverse functionality (i.e., plasmonic unidirectional absorption and photodetection) have also been generated with similar systems. Furthermore, a new paradigm for the near-field control of light emission has been introduced through rigorous theoretical studies, based on the use of gradient metasurfaces (i.e., optical nanoantenna arrays with spatially varying shape, size, and/or orientation). These activities have been complemented by materials development efforts aimed at the synthesis of suitable light-emitting samples by molecular beam epitaxy. In the course of these efforts, a novel technique for the growth of III-nitride quantum dots has also been developed (droplet heteroepitaxy), with several potential advantages in terms of compositional and geometrical control. The results of these studies provide fundamental new understanding of optical processes at the nanoscale, including near-field energy transfer between quantum emitters and photonic nanostructures, dissipation phenomena of plasmonic excitations, and radiation from nanoantennas. Furthermore, they may open the way to entirely new device concepts and applications, in a broad range of disciplines including optoelectronics, sensing, spectroscopy, photovoltaics, and quantum information science. A specific application of particularly strong relevance to the DOE mission is the development of energy efficient LED active materials for solid-state lighting, based on plasmonic enhancement effects.« less

Optical Spectra of the Jaynes-Cummings Ladder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laussy, Fabrice P.; Valle, Elena del

2009-06-29

We explore how the Jaynes-Cummings ladder transpires in the emitted spectra of a two-level system in strong coupling with a single mode of light. We focus on the case of very strong coupling, that would be achieved with systems of exceedingly good quality (very long lifetimes for both the emitter and the cavity). We focus on the incoherent regime of excitation, that is realized with semiconductors quantum dots in microcavities, and discuss how reasonable is the understanding of the systems in terms of transitions between dressed states of the Jaynes-Cummings Hamiltonian.

Electrical control of optical orientation of neutral and negatively charged excitons in an n -type semiconductor quantum well

NASA Astrophysics Data System (ADS)

Dzhioev, R. I.; Korenev, V. L.; Lazarev, M. V.; Sapega, V. F.; Gammon, D.; Bracker, A. S.

2007-01-01

We report electric field induced increase of spin orientation of negatively charged excitons (trions) localized in n -type GaAs/AlGaAs quantum well. Under resonant excitation of free neutral heavy-hole excitons, the polarization of trions increases dramatically with electrical injection of electrons. The polarization enhancement correlates strongly with trion/exciton luminescence intensity ratio. This effect results from a very efficient trapping of free neutral excitons by the quantum well interfacial fluctuations (“natural” quantum dots) containing resident electrons.

Quantum many-body correlations in collective phonon-excitations

NASA Astrophysics Data System (ADS)

Droenner, Leon; Kabuss, Julia; Carmele, Alexander

2018-02-01

We present a theoretical study of a many-emitter phonon laser based on optically driven semiconductor quantum dots placed within an acoustic nanocavity. A transformation of the phonon laser Hamiltonian leads to a Tavis-Cummings type interaction with an unexpected additional many-emitter energy shift. This many-emitter interaction with the cavity mode results in a variety of phonon resonances which dependent strongly on the number of participating emitters. These collective resonances show the highest phonon output. Furthermore, we show that the output can be increased even more via lasing at the two phonon resonance.

Microscopic theory of cation exchange in CdSe nanocrystals.

PubMed

Ott, Florian D; Spiegel, Leo L; Norris, David J; Erwin, Steven C

2014-10-10

Although poorly understood, cation-exchange reactions are increasingly used to dope or transform colloidal semiconductor nanocrystals (quantum dots). We use density-functional theory and kinetic Monte Carlo simulations to develop a microscopic theory that explains structural, optical, and electronic changes observed experimentally in Ag-cation-exchanged CdSe nanocrystals. We find that Coulomb interactions, both between ionized impurities and with the polarized nanocrystal surface, play a key role in cation exchange. Our theory also resolves several experimental puzzles related to photoluminescence and electrical behavior in CdSe nanocrystals doped with Ag.

Self Assembled Semiconductor Quantum Dots for Spin Based All Optical and Electronic Quantum Computing

DTIC Science & Technology

2008-04-17

resolution TEM images (see Fig. 10) also show that ZnO nanocrystals nucleate on Fig. 9 SEM images of ZnO nanorods grown on (a) Si(001) and b) GaN/Al2O3... electrodeposition in a non-aqueous solution. The solution consisted of ZnClO4 (10.5 gm), LiClO4 (2.5 gm) and dimethyl sulfoxide (250 ml). The porous...valent Zn atoms which were selectively electrodeposited within the pores since they offered the least impedance path for the ac current

Design of hybrid laser structures with QD-RSOA and silicon photonic mirrors

NASA Astrophysics Data System (ADS)

Gioannini, Mariangela; Benedetti, Alessio; Bardella, Paolo; Bovington, Jock; Traverso, Matt; Siriani, Dominic; Gothoskar, Prakash

2018-02-01

We compare the design of three different single mode laser structures consisting in a Reflective Semiconductor Optical Amplifier coupled to a silicon photonic external cavity mirror. The three designs differ for the mirror structure and are compared in terms of SOA power consumption and side mode suppression ratio (SMSR). Assuming then a Quantum Dot active material, we simulate the best laser design using a numerical model that includes the peculiar physical characteristics of the QD gain medium. The simulated QD laser CW characteristics are shown and discussed.

PREFACE: Semiconductor Nanostructures towards Electronic and Optoelectronic Device Applications II (Symposium K, E-MRS 2009 Spring Meeting)

NASA Astrophysics Data System (ADS)

Nötzel, Richard

2009-07-01

This volume of IOP Conference Series: Materials Science and Engineering contains papers that were presented at the special symposium K at the EMRS 2009 Spring Meeting held 8-12 June in Strasbourg, France, which was entitled 'Semiconductor Nanostructures towards Electronic and Optoelectronic Device Applications II'. Thanks to the broad interest a large variety of quantum dots and quantum wires and related nanostructures and their application in devices could be covered. There was significant progress in the epitaxial growth of semiconductor quantum dots seen in the operation of high-power, as well as mode locked laser diodes and the lateral positioning of quantum dots on patterned substrates or by selective area growth for future single quantum dot based optoelectronic and electronic devices. In the field of semiconductor nanowires high quality, almost twin free structures are now available together with a new degree of freedom for band structure engineering based on alternation of the crystal structure. In the search for Si based light emitting structures, nanocrystals and miniband-related near infrared luminescence of Si/Ge quantum dot superlattices with high quantum efficiency were reported. These highlights, among others, and the engaged discussions of the scientists, engineers and students brought together at the symposium emphasize how active the field of semiconductor nanostructures and their applications in devices is, so that we can look forward to the progress to come. Guest Editor Richard Nötzel COBRA Research Institute Department of Applied Physics Eindhoven University of Technology 5600 MB Eindhoven The Netherlands Tel.: +31 40 247 2047; fax: +31 40 246 1339 E-mail address: r.noetzel@tue.nl

Exchange interaction and the tunneling induced transparency in coupled quantum dots

NASA Astrophysics Data System (ADS)

Borges, Halyne; Alcalde, Augusto; Ulloa, Sergio

2014-03-01

Stacked semiconductor quantum dots coupled by tunneling are unique ``quantum molecule'' where it is possible to create a multilevel structure of excitonic states. This structure allows the investigation of quantum interference processes and their control via electric external fields. In this work, we investigate the optical response of a quantum molecule coherently driven by a polarized laser, considering the splitting in excitonic levels caused by isotropic and anisotropic exchange interactions. In our model we consider interdot transitions mediated by the the hole tunneling between states with the same total spin and, between bright and dark exciton states. Using realistic experimental parameters, we demonstrate that the excitonic states coupled by tunneling exhibit an enriched and controllable optical response. Our results show that through the appropriate control of the external electric field and light polarization, the tunneling coupling establishes an efficient destructive quantum interference path that creates a transparency window in the absorption spectra, whenever states of appropriate symmetry are mixed by the hole tunneling. We explore the relevant parameters space that would allows with the experiments. CAPES, INCT-IQ and MWN/CIAM-NSF.

Four-wave mixing in an asymmetric double quantum dot molecule

NASA Astrophysics Data System (ADS)

Kosionis, Spyridon G.

2018-06-01

The four-wave mixing (FWM) effect of a weak probe field, in an asymmetric semiconductor double quantum dot (QD) structure driven by a strong pump field is theoretically studied. Similarly to the case of examining several other nonlinear optical processes, the nonlinear differential equations of the density matrix elements are used, under the rotating wave approximation. By suitably tuning the intensity and the frequency of the pump field as well as by changing the value of the applied bias voltage, a procedure used to properly adjust the electron tunneling coupling, we control the FWM in the same way as several other nonlinear optical processes of the system. While in the weak electron tunneling regime, the impact of the pump field intensity on the FWM is proven to be of crucial importance, for even higher rates of the electron tunneling it is evident that the intensity of the pump field has only a slight impact on the form of the FWM spectrum. The number of the spectral peaks, depends on the relation between specific parameters of the system.

Optically pumped quantum-dot Cd(Zn)Se/ZnSe laser and microchip converter for yellow-green spectral region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lutsenko, E V; Voinilovich, A G; Rzheutskii, N V

2013-05-31

The room temperature laser generation in the yellow-green ({lambda} = 558.5-566.7 nm) spectral range has been demonstrated under optical pumping by a pulsed nitrogen laser of Cd(Zn)Se/ZnSe quantum dot heterostructures. The maximum achieved laser wavelength was as high as {lambda} = 566.7 nm at a laser cavity length of 945 {mu}m. High values of both the output pulsed power (up to 50 W) and the external differential quantum efficiency ({approx}60%) were obtained at a cavity length of 435 {mu}m. Both a high quality of the laser heterostructure and a low lasing threshold ({approx}2 kW cm{sup -2}) make it possible tomore » use a pulsed InGaN laser diode as a pump source. A laser microchip converter based on this heterostructure has demonstrated a maximum output pulse power of {approx}90 mW at {lambda} = 560 nm. The microchip converter was placed in a standard TO-18 (5.6 mm in diameter) laser diode package. (semiconductor lasers. physics and technology)« less

The analytical approach to the multi-state lasing phenomenon in undoped and p-doped InAs/InGaAs semiconductor quantum dot lasers

NASA Astrophysics Data System (ADS)

Korenev, Vladimir V.; Savelyev, Artem V.; Zhukov, Alexey E.; Omelchenko, Alexander V.; Maximov, Mikhail V.

2014-05-01

We introduce an analytical approach to the multi-state lasing phenomenon in p-doped and undoped InAs/InGaAs quantum dot lasers which were studied both theoretically and experimentally. It is shown that the asymmetry in charge carrier distribution in quantum dots as well as hole-to-electron capture rate ratio jointly determine laser's behavior in such a regime. If the ratio is lower than a certain critical value, the complete quenching of ground-state lasing takes place at sufficiently high injection currents; at higher values of the ratio, our model predicts saturation of the ground-state power. It was experimentally shown that the modulation p-doping of laser's active region results in increase of output power emitted via the ground-state optical transitions of quantum dots and in enhancement of the injection currents range in which multi-state lasing takes place. The maximum temperature at which multi-state lasing exists was increased by about 50°C in the p-doped samples. These effects are qualitatively explained in the terms of the proposed model.

Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots

NASA Astrophysics Data System (ADS)

Meinardi, Francesco; Ehrenberg, Samantha; Dhamo, Lorena; Carulli, Francesco; Mauri, Michele; Bruni, Francesco; Simonutti, Roberto; Kortshagen, Uwe; Brovelli, Sergio

2017-02-01

Building-integrated photovoltaics is gaining consensus as a renewable energy technology for producing electricity at the point of use. Luminescent solar concentrators (LSCs) could extend architectural integration to the urban environment by realizing electrode-less photovoltaic windows. Crucial for large-area LSCs is the suppression of reabsorption losses, which requires emitters with negligible overlap between their absorption and emission spectra. Here, we demonstrate the use of indirect-bandgap semiconductor nanostructures such as highly emissive silicon quantum dots. Silicon is non-toxic, low-cost and ultra-earth-abundant, which avoids the limitations to the industrial scaling of quantum dots composed of low-abundance elements. Suppressed reabsorption and scattering losses lead to nearly ideal LSCs with an optical efficiency of η = 2.85%, matching state-of-the-art semi-transparent LSCs. Monte Carlo simulations indicate that optimized silicon quantum dot LSCs have a clear path to η > 5% for 1 m2 devices. We are finally able to realize flexible LSCs with performances comparable to those of flat concentrators, which opens the way to a new design freedom for building-integrated photovoltaics elements.

Interband emission energy in a dilute nitride quaternary semiconductor quantum dot for longer wavelength applications

NASA Astrophysics Data System (ADS)

Mageshwari, P. Uma; Peter, A. John; Lee, Chang Woo; Duque, C. A.

2016-07-01

Excitonic properties are studied in a strained Ga1-xInxNyAs1-y/GaAs cylindrical quantum dot. The optimum condition for the desired band alignment for emitting wavelength 1.55 μm is investigated using band anticrossing model and the model solid theory. The band gap and the band discontinuities of a Ga1-xInxNyAs1-y/GaAs quantum dot on GaAs are computed with the geometrical confinement effect. The binding energy of the exciton, the oscillator strength and its radiative life time for the optimum condition are found taking into account the spatial confinement effect. The effects of geometrical confinement and the nitrogen incorporation on the interband emission energy are brought out. The result shows that the desired band alignment for emitting wavelength 1.55 μm is achieved for the inclusion of alloy contents, y=0.0554% and x=0.339% in Ga1-xInxNyAs1-y/GaAs quantum dot. And the incorporation of nitrogen and indium shows the red-shift and the geometrical confinement shows the blue-shift. And it can be applied for fibre optical communication networks.

Quantum Dots Based Rad-Hard Computing and Sensors

NASA Technical Reports Server (NTRS)

Fijany, A.; Klimeck, G.; Leon, R.; Qiu, Y.; Toomarian, N.

2001-01-01

Quantum Dots (QDs) are solid-state structures made of semiconductors or metals that confine a small number of electrons into a small space. The confinement of electrons is achieved by the placement of some insulating material(s) around a central, well-conducting region. Thus, they can be viewed as artificial atoms. They therefore represent the ultimate limit of the semiconductor device scaling. Additional information is contained in the original extended abstract.

Hybrid structures based on gold nanoparticles and semiconductor quantum dots for biosensor applications.

PubMed

Kurochkina, Margarita; Konshina, Elena; Oseev, Aleksandr; Hirsch, Soeren

2018-01-01

The luminescence amplification of semiconductor quantum dots (QD) in the presence of self-assembled gold nanoparticles (Au NPs) is one of way for creating biosensors with highly efficient transduction. The objective of this study was to fabricate the hybrid structures based on semiconductor CdSe/ZnS QDs and Au NP arrays and to use them as biosensors of protein. In this paper, the hybrid structures based on CdSe/ZnS QDs and Au NP arrays were fabricated using spin coating processes. Au NP arrays deposited on a glass wafer were investigated by optical microscopy and absorption spectroscopy depending on numbers of spin coating layers and their baking temperature. Bovine serum albumin (BSA) was used as the target protein analyte in a phosphate buffer. A confocal laser scanning microscope was used to study the luminescent properties of Au NP/QD hybrid structures and to test BSA. The dimensions of Au NP aggregates increased and the space between them decreased with increasing processing temperature. At the same time, a blue shift of the plasmon resonance peak in the absorption spectra of Au NP arrays was observed. The deposition of CdSe/ZnS QDs with a core diameter of 5 nm on the surface of the Au NP arrays caused an increase in absorption and a red shift of the plasmon peak in the spectra. The exciton-plasmon enhancement of the QDs' photoluminescence intensity has been obtained at room temperature for hybrid structures with Au NPs array pretreated at temperatures of 100°C and 150°C. It has been found that an increase in the weight content of BSA increases the photoluminescence intensity of such hybrid structures. The ability of the qualitative and quantitative determination of protein content in solution using the Au NP/QD structures as an optical biosensor has been shown experimentally.

Hybrid structures based on gold nanoparticles and semiconductor quantum dots for biosensor applications

PubMed Central

Kurochkina, Margarita; Konshina, Elena; Oseev, Aleksandr; Hirsch, Soeren

2018-01-01

Background The luminescence amplification of semiconductor quantum dots (QD) in the presence of self-assembled gold nanoparticles (Au NPs) is one of way for creating biosensors with highly efficient transduction. Aims The objective of this study was to fabricate the hybrid structures based on semiconductor CdSe/ZnS QDs and Au NP arrays and to use them as biosensors of protein. Methods In this paper, the hybrid structures based on CdSe/ZnS QDs and Au NP arrays were fabricated using spin coating processes. Au NP arrays deposited on a glass wafer were investigated by optical microscopy and absorption spectroscopy depending on numbers of spin coating layers and their baking temperature. Bovine serum albumin (BSA) was used as the target protein analyte in a phosphate buffer. A confocal laser scanning microscope was used to study the luminescent properties of Au NP/QD hybrid structures and to test BSA. Results The dimensions of Au NP aggregates increased and the space between them decreased with increasing processing temperature. At the same time, a blue shift of the plasmon resonance peak in the absorption spectra of Au NP arrays was observed. The deposition of CdSe/ZnS QDs with a core diameter of 5 nm on the surface of the Au NP arrays caused an increase in absorption and a red shift of the plasmon peak in the spectra. The exciton–plasmon enhancement of the QDs’ photoluminescence intensity has been obtained at room temperature for hybrid structures with Au NPs array pretreated at temperatures of 100°C and 150°C. It has been found that an increase in the weight content of BSA increases the photoluminescence intensity of such hybrid structures. Conclusion The ability of the qualitative and quantitative determination of protein content in solution using the Au NP/QD structures as an optical biosensor has been shown experimentally. PMID:29731613

Quantum Dots in a Polymer Composite: A Convenient Particle-in-a-Box Laboratory Experiment

ERIC Educational Resources Information Center

Rice, Charles V.; Giffin, Guinevere A.

2008-01-01

Semiconductor quantum dots are at the forefront of materials science chemistry with applications in biological imaging and photovoltaic technologies. We have developed a simple laboratory experiment to measure the quantum-dot size from fluorescence spectra. A major roadblock of quantum-dot based exercises is the particle synthesis and handling;…

Gate-controlled electromechanical backaction induced by a quantum dot

NASA Astrophysics Data System (ADS)

Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

2016-04-01

Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter.

Nuclear spin cooling by electric dipole spin resonance and coherent population trapping

NASA Astrophysics Data System (ADS)

Li, Ai-Xian; Duan, Su-Qing; Zhang, Wei

2017-09-01

Nuclear spin fluctuation suppression is a key issue in preserving electron coherence for quantum information/computation. We propose an efficient way of nuclear spin cooling in semiconductor quantum dots (QDs) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. The EDSR can enhance the spin flip-flop rate and may bring out bistability under certain conditions. By tuning the optical fields, we can avoid the EDSR induced bistability and obtain highly polarized nuclear spin state, which results in long electron coherence time. With the help of CPT and EDSR, an enhancement of 1500 times of the electron coherence time can been obtained after a 500 ns preparation time.

Signatures of Förster and Dexter transfer processes in coupled nanostructures for linear and two-dimensional coherent optical spectroscopy

NASA Astrophysics Data System (ADS)

Specht, Judith F.; Richter, Marten

2015-03-01

In this manuscript, we study the impact of the two Coulomb induced resonance energy transfer processes, Förster and Dexter coupling, on the spectral signatures obtained by double quantum coherence spectroscopy. We show that the specific coupling characteristics allow us to identify the underlying excitation transfer mechanism by means of specific signatures in coherent spectroscopy. Therefore, we control the microscopic calculated coupling strength of spin preserving and spin flipping Förster transfer processes by varying the mutual orientation of the two quantum emitters. The calculated spectra reveal the optical selection rules altered by Förster and Dexter coupling between two semiconductor quantum dots. We show that Dexter coupling between bright and dark two-exciton states occurs.

Dynamical thermal effects in InGaAsP microtubes at telecom wavelengths.

PubMed

Tian, Zhaobing; Bianucci, Pablo; Roche, Philip J R; Dastjerdi, M Hadi Tavakoli; Mi, Zetian; Poole, Philip J; Kirk, Andrew G; Plant, David V

2012-07-01

We report on the observation of a dynamical thermal effect in InGaAsP microtubes at telecom wavelengths. The microtubes are fabricated by releasing a strained semiconductor bilayer and are picked up by abruptly tapered optical fibers for subsequent coupling with adiabatically tapered optical fibers. As a result of absorption by InAs quantum dots embedded in the tube structure, these microtubes show dynamical thermal effects at wavelengths around 1525 nm and 1578 nm, while they are passive at longer wavelengths near 1634 nm. The photon absorption induced thermal effect is visualized by generating a pair of microbottles. The dynamical thermal effect can be avoided or exploited for passive or active applications by utilizing appropriate resonance wavelengths.

Integrated InAs/InP quantum-dot coherence comb lasers (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lu, Zhenguo; Liu, Jiaren; Poole, Philip J.; Song, Chun-Ying; Webber, John; Mao, Linda; Chang, Shoude; Ding, Heping; Barrios, Pedro J.; Poitras, Daniel; Janz, Siegfried

2017-02-01

Current communication networks needs to keep up with the exponential growth of today's internet traffic, and telecommunications industry is looking for radically new integrated photonics components for new generation optical networks. We at National Research Council (NRC) Canada have successfully developed nanostructure InAs/InP quantum dot (QD) coherence comb lasers (CCLs) around 1.55 μm. Unlike uniform semiconductor layers in most telecommunication lasers, in these QD CCLs light is emitted and amplified by millions of semiconductor QDs less than 60 nm in diameter. Each QD acts like an isolated light source acting independently of its neighbours, and each QD emits light at its own unique wavelength. The end result is a QD CCL is more stable and has ultra-low timing jitter. But most importantly, a single QD CCL can simultaneously produce 50 or more separate laser beams at distinct wavelengths over the telecommunications C-band. Utilizing those unique properties we have put considerable effort well to design, grow and fabricate InAs/InP QD gain materials. After our integrated packaging and using electrical feedback-loop control systems, we have successfully demonstrated ultra-low intensity and phase noise, frequency-stabilized integrated QD CCLs with the repetition rates from 10 GHz to 100 GHz and the total output power up to 60 mW at room temperature. We have investigated their relative intensity noises, phase noises, RF beating signals and other performance of both filtered individual channel and the whole CCLs. Those highly phase-coherence comb lasers are the promising candidates for flexible bandwidth terabit coherent optical networks and signal processing applications.

Semiconductor quantum dot super-emitters: spontaneous emission enhancement combined with suppression of defect environment using metal-oxide plasmonic metafilms

NASA Astrophysics Data System (ADS)

Sadeghi, Seyed M.; Wing, Waylin J.; Gutha, Rithvik R.; Sharp, Christina

2018-01-01

We demonstrate that a metal-oxide plasmonic metafilm consisting of a Si/Al oxide junction in the vicinity of a thin gold layer can quarantine excitons in colloidal semiconductor quantum dots against their defect environments. This process happens while the plasmon fields of the gold layer enhance spontaneous emission decay rates of the quantum dots. We study the emission dynamics of such quantum dots when the distance between the Si/Al oxide junction and the gold thin layer is varied. The results show that for distances less than a critical value the lifetime of the quantum dots can be elongated while they experience intense plasmon fields. This suggests that the metal-oxide metafilm can keep photo-excited electrons in the cores of the quantum dots, suppressing their migration to the surface defect sites. This leads to suppression of Auger recombination, offering quantum dot super-emitters with emission that is enhanced not only by the plasmon fields (Purcell effect), but also by strong suppression of the non-radiative decay caused by the defect sites.

Quantum-dot temperature profiles during laser irradiation for semiconductor-doped glasses

NASA Astrophysics Data System (ADS)

Nagpal, Swati

2002-12-01

Temperature profiles around laser irradiated CdX (X=S, Se, and Te) quantum dots in borosilicate glasses were theoretically modeled. Initially the quantum dots heat up rapidly, followed by a gradual increase of temperature. Also it is found that larger dots reach higher temperatures for the same pulse characteristics. After the pulse is turned off, the dots initially cool rapidly, followed by a gradual decrease in temperature.

Biodetection using fluorescent quantum dots

NASA Astrophysics Data System (ADS)

Speckman, Donna M.; Jennings, Travis L.; LaLumondiere, Steven D.; Klimcak, Charles M.; Moss, Steven C.; Loper, Gary L.; Beck, Steven M.

2002-07-01

Multi-pathogen biosensors that take advantage of sandwich immunoassay detection schemes and utilize conventional fluorescent dye reporter molecules are difficult to make into extremely compact and autonomous packages. The development of a multi-pathogen, immunoassay-based, fiber optic detector that utilizes varying sized fluorescent semiconductor quantum dots (QDs) as the reporter labels has the potential to overcome these problems. In order to develop such a quantum dot-based biosensor, it is essential to demonstrate that QDs can be attached to antibody proteins, such that the specificity of the antibody is maintained. We have been involved in efforts to develop a reproducible method for attaching QDs to antibodies for use in biodetection applications. We have synthesized CdSe/ZnS core-shell QDs of differing size, functionalized their surfaces with several types of organic groups for water solubility, and covalently attached these functionalized QDs to rabbit anti-ovalbumin antibody protein. We also demonstrated that these labeled antibodies exhibit selective binding to ovalbumin antigen. We characterized the QDs at each step in the overall synthesis by UV-VIS absorption spectroscopy and by picosecond (psec) transient photoluminescence (TPL) spectroscopy. TPL spectroscopy measurements indicate that QD lifetime depends on the size of the QD, the intensity of the optical excitation source, and whether or not they are functionalized and conjugated to antibodies. We describe details of these experiments and discuss the impact of our results on our biosensor development program.

Resonance fluorescence spectrum of a p-doped quantum dot coupled to a metallic nanoparticle

NASA Astrophysics Data System (ADS)

Carreño, F.; Antón, M. A.; Arrieta-Yáñez, Francisco

2013-11-01

The resonance fluorescence spectrum (RFS) of a hybrid system consisting of a p-doped semiconductor quantum dot (QD) coupled to a metallic nanoparticle (MNP) is analyzed. The quantum dot is described as a four-level atomlike system using the density matrix formalism. The lower levels are Zeeman-split hole spin states and the upper levels correspond to positively charged excitons containing a spin-up, spin-down hole pair and a spin electron. A linearly polarized laser field drives two of the optical transitions of the QD and produces localized surface plasmons in the nanoparticle, which act back upon the QD. The frequencies of these localized plasmons are very different along the two principal axes of the nanoparticle, thus producing an anisotropic modification of the spontaneous emission rates of the allowed optical transitions, which is accompanied by very minor local field corrections. This manifests into dramatic modifications in the RFS of the hybrid system in contrast to the one obtained for the isolated QD. The RFS is analyzed as a function of the nanoparticle's aspect ratio, the external magnetic field applied in the Voigt geometry, and the Rabi frequency of the driving field. It is shown that the spin of the QD is imprinted onto certain sidebands of the RFS, and that the signal at these sidebands can be optimized by engineering the shape of the MNP.

Spectroscopic investigations on the interaction of thioacetamide with ZnO quantum dots and application for its fluorescence sensing

NASA Astrophysics Data System (ADS)

Saha, Dipika; Negi, Devendra P. S.

2018-01-01

The purpose of the present work was to develop a method for the sensing of thioacetamide by using spectroscopic techniques. Thioacetamide is a carcinogen and it is important to detect its presence in food-stuffs. Semiconductor quantum dots are frequently employed as sensing probes since their absorption and fluorescence properties are highly sensitive to the interaction with substrates present in the solution. In the present work, the interaction between thioacetamide and ZnO quantum dots has been investigated by using UV-visible, fluorescence and infrared spectroscopy. Besides, dynamic light scattering (DLS) has also been utilized for the interaction studies. UV-visible absorption studies indicated the bonding of the lone pair of sulphur atom of thioacetamide with the surface of the semiconductor. The fluorescence band of the ZnO quantum dots was found to be quenched in the presence of micromolar concentrations of thioacetamide. The quenching was found to follow the Stern-Volmer relationship. The Stern-Volmer constant was evaluated to be 1.20 × 105 M- 1. Infrared spectroscopic measurements indicated the participation of the sbnd NH2 group and the sulphur atom of thioacetamide in bonding with the surface of the ZnO quantum dots. DLS measurements indicated that the surface charge of the semiconductor was shielded by the thioacetamide molecules.

Microbial synthesis of chalcogenide semiconductor nanoparticles: a review.

PubMed

Jacob, Jaya Mary; Lens, Piet N L; Balakrishnan, Raj Mohan

2016-01-01

Chalcogenide semiconductor quantum dots are emerging as promising nanomaterials due to their size tunable optoelectronic properties. The commercial synthesis and their subsequent integration for practical uses have, however, been contorted largely due to the toxicity and cost issues associated with the present chemical synthesis protocols. Accordingly, there is an immediate need to develop alternative environment-friendly synthesis procedures. Microbial factories hold immense potential to achieve this objective. Over the past few years, bacteria, fungi and yeasts have been experimented with as eco-friendly and cost-effective tools for the biosynthesis of semiconductor quantum dots. This review provides a detailed overview about the production of chalcogen-based semiconductor quantum particles using the inherent microbial machinery. © 2015 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.

Using quantum dot photoluminescence for load detection

NASA Astrophysics Data System (ADS)

Moebius, M.; Martin, J.; Hartwig, M.; Baumann, R. R.; Otto, T.; Gessner, T.

2016-08-01

We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL) of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N',N'-Tetrakis(3-methylphenyl)-3,3'-dimethylbenzidine (HMTPD) and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

Electronic and Optical Properties of Core/Shell Pb16X16/Cd52X52 (X =S, Se, Te) Quantum Dots

NASA Astrophysics Data System (ADS)

Tamukong, Patrick; Mayo, Michael; Kilina, Svetlana

2015-03-01

The electronic and optoelectronic properties of semiconductor quantum dots (QDs) are mediated by surface defects due to the presence of dangling bonds producing trap states within the HOMO-LUMO energy gap, and contributing to fluorescence quenching. Surface capping ligands are generally used to alleviate this problem and increase the quantum yields of QDs. An alternative way is to synthesize core-shell QD structures; i.e., a QD core with a shell of another semiconductor material. We have investigated the effects of Cd52X52 shells on the photoexcited dynamics of Pb16X16 (X =S, Se, Te) QDs. The thin (~ 0.50 nm) shells were found to result largely in type I core/shell structures and a blue shift of the absorption spectra. Our studies revealed fairly strong core-shell hybridization in the electronic states close to the conduction band (CB) edge for Pb16S16andPb16Se16 cores, whereas for the Pb16Te16 core, such CB states were largely shell-like in nature. Nonadiabatic DFT-based dynamics, coupled with the surface hopping method, was used to study the effects of the core and shell compositions on energy relaxation rates in these systems.

The diamagnetic susceptibility of a donor in a semiconductor core shell quantum dot

NASA Astrophysics Data System (ADS)

Sudharshan, M. S.; Subhash, P.; Shaik, Nagoor Babu; Kalpana, P.; Jayakumar, K.; Reuben, A. Merwyn Jasper D.

2015-06-01

The effect of Aluminium concentration, shell thickness and size of the core shell Quantum Dot on the Diamagnetic Susceptibility of a donor in the Core Shell Quantum Dot is calculated in the effective mass approximation using the variational method. The results are presented and discussed.

Bioconjugated Quantum Dots for In Vivo Molecular and Cellular Imaging

PubMed Central

Smith, Andrew M.; Duan, Hongwei; Mohs, Aaron M.; Nie, Shuming

2008-01-01

Semiconductor quantum dots (QDs) are tiny light-emitting particles on the nanometer scale, and are emerging as a new class of fluorescent labels for biology and medicine. In comparison with organic dyes and fluorescent proteins, they have unique optical and electronic properties, with size-tunable light emission, superior signal brightness, resistance to photobleaching, and broad absorption spectra for simultaneous excitation of multiple fluorescence colors. QDs also provide a versatile nanoscale scaffold for designing multifunctional nanoparticles with both imaging and therapeutic functions. When linked with targeting ligands such as antibodies, peptides or small molecules, QDs can be used to target tumor biomarkers as well as tumor vasculatures with high affinity and specificity. Here we discuss the synthesis and development of state-of-the-art QD probes and their use for molecular and cellular imaging. We also examine key issues for in vivo imaging and therapy, such as nanoparticle biodistribution, pharmacokinetics, and toxicology. PMID:18495291

Plasmon-Exciton Interactions Probed Using Spatial Coentrapment of Nanoparticles by Topological Singularities.

PubMed

Ackerman, Paul J; Mundoor, Haridas; Smalyukh, Ivan I; van de Lagemaat, Jao

2015-12-22

We study plasmon-exciton interaction by using topological singularities to spatially confine, selectively deliver, cotrap and optically probe colloidal semiconductor and plasmonic nanoparticles. The interaction is monitored in a single quantum system in the bulk of a liquid crystal medium where nanoparticles are manipulated and nanoconfined far from dielectric interfaces using laser tweezers and topological configurations containing singularities. When quantum dot-in-a-rod particles are spatially colocated with a plasmonic gold nanoburst particle in a topological singularity core, its fluorescence increases because blinking is significantly suppressed and the radiative decay rate increases by nearly an order of magnitude owing to the Purcell effect. We argue that the blinking suppression is the result of the radiative rate change that mitigates Auger recombination and quantum dot ionization, consequently reducing nonradiative recombination. Our work demonstrates that topological singularities are an effective platform for studying and controlling plasmon-exciton interactions.

Plasmon–Exciton Interactions Probed Using Spatial Coentrapment of Nanoparticles by Topological Singularities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackerman, Paul J.; Mundoor, Haridas; Smalyukh, Ivan I.

2015-12-22

We study plasmon-exciton interaction by using topological singularities to spatially confine, selectively deliver, cotrap and optically probe colloidal semiconductor and plasmonic nanoparticles. The interaction is monitored in a single quantum system in the bulk of a liquid crystal medium where nanoparticles are manipulated and nanoconfined far from dielectric interfaces using laser tweezers and topological configurations containing singularities. When quantum dot-in-a-rod particles are spatially colocated with a plasmonic gold nanoburst particle in a topological singularity core, its fluorescence increases because blinking is significantly suppressed and the radiative decay rate increases by nearly an order of magnitude owing to the Purcell effect.more » We argue that the blinking suppression is the result of the radiative rate change that mitigates Auger recombination and quantum dot ionization, consequently reducing nonradiative recombination. Our work demonstrates that topological singularities are an effective platform for studying and controlling plasmon-exciton interactions.« less

Complete quantum control of exciton qubits bound to isoelectronic centres.

PubMed

Éthier-Majcher, G; St-Jean, P; Boso, G; Tosi, A; Klem, J F; Francoeur, S

2014-05-30

In recent years, impressive demonstrations related to quantum information processing have been realized. The scalability of quantum interactions between arbitrary qubits within an array remains however a significant hurdle to the practical realization of a quantum computer. Among the proposed ideas to achieve fully scalable quantum processing, the use of photons is appealing because they can mediate long-range quantum interactions and could serve as buses to build quantum networks. Quantum dots or nitrogen-vacancy centres in diamond can be coupled to light, but the former system lacks optical homogeneity while the latter suffers from a low dipole moment, rendering their large-scale interconnection challenging. Here, through the complete quantum control of exciton qubits, we demonstrate that nitrogen isoelectronic centres in GaAs combine both the uniformity and predictability of atomic defects and the dipole moment of semiconductor quantum dots. This establishes isoelectronic centres as a promising platform for quantum information processing.

Sub-wavelength InAs quantum dot micro-disk lasers epitaxially grown on exact Si (001) substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Yating; Li, Qiang; Lau, Kei May, E-mail: eekmlau@ust.hk

Subwavelength micro-disk lasers (MDLs) as small as 1 μm in diameter on exact (001) silicon were fabricated using colloidal lithography. The micro-cavity gain medium incorporating five-stacked InAs quantum dot layers was grown on a high crystalline quality GaAs-on-V-grooved-Si template with no absorptive intermediate buffers. Under continuous-wave optical pumping, the MDLs on silicon exhibit lasing in the 1.2-μm wavelength range with low thresholds down to 35 μW at 10 K. The MDLs compare favorably with devices fabricated on native GaAs substrates and state-of-the-art work reported elsewhere. Feasibility of device miniaturization can be projected by size-dependent lasing characteristics. The results show a promising path towardsmore » dense integration of photonic components on the mainstream complementary metal–oxide–semiconductor platform.« less

``New'' energy states lead to phonon-less optoelectronic properties in nanostructured silicon

NASA Astrophysics Data System (ADS)

Singh, Vivek; Yu, Yixuan; Korgel, Brian; Nagpal, Prashant

2014-03-01

Silicon is arguably one of the most important technological material for electronic applications. However, indirect bandgap of silicon semiconductor has prevented optoelectronic applications due to phonon assistance required for photon light absorption/emission. Here we show, that previously unexplored surface states in nanostructured silicon can couple with quantum-confined energy levels, leading to phonon-less exciton-recombination and photoluminescence. We demonstrate size dependence (2.4 - 8.3 nm) of this coupling observed in small uniform silicon nanocrystallites, or quantum-dots, by direct measurements of their electronic density of states and low temperature measurements. To enhance the optical absorption of the these silicon quantum-dots, we utilize generation of resonant surface plasmon polariton waves, which leads to several fold increase in observed spectrally-resolved photocurrent near the quantum-confined bandedge states. Therefore, these enhanced light emission and absorption enhancement can have important implications for applications of nanostructured silicon for optoelectronic applications in photovoltaics and LEDs.

Combining atomic force and fluorescence microscopy for analysis of quantum-dot labeled protein–DNA complexes

PubMed Central

Ebenstein, Yuval; Gassman, Natalie; Kim, Soohong; Weiss, Shimon

2011-01-01

Atomic force microscopy (AFM) and fluorescence microscopy are widely used for the study of protein-DNA interactions. While AFM excels in its ability to elucidate structural detail and spatial arrangement, it lacks the ability to distinguish between similarly sized objects in a complex system. This information is readily accessible to optical imaging techniques via site-specific fluorescent labels, which enable the direct detection and identification of multiple components simultaneously. Here, we show how the utilization of semiconductor quantum dots (QDs), serving as contrast agents for both AFM topography and fluorescence imaging, facilitates the combination of both imaging techniques, and with the addition of a flow based DNA extension method for sample deposition, results in a powerful tool for the study of protein-DNA complexes. We demonstrate the inherent advantages of this novel combination of techniques by imaging individual RNA polymerases (RNAP) on T7 genomic DNA. PMID:19452448

Microwave-Driven Coherent Operation of a Semiconductor Quantum Dot Charge Qubit

DTIC Science & Technology

2015-02-16

indicating that understanding high frequency charge noise as well as charge relaxation at the sweet spot will be important for further development. The...Microwave-driven coherent operation of a semiconductor quantum dot charge qubit Dohun Kim,1 D. R. Ward,1 C. B. Simmons,1 John King Gamble,2 Robin...University of Wisconsin-Madison, Madison, WI 53706, USA A most intuitive realization of a qubit is a sin- gle electron charge sitting at two well -defined

Computational models for the berry phase in semiconductor quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prabhakar, S., E-mail: rmelnik@wlu.ca; Melnik, R. V. N., E-mail: rmelnik@wlu.ca; Sebetci, A.

2014-10-06

By developing a new model and its finite element implementation, we analyze the Berry phase low-dimensional semiconductor nanostructures, focusing on quantum dots (QDs). In particular, we solve the Schrödinger equation and investigate the evolution of the spin dynamics during the adiabatic transport of the QDs in the 2D plane along circular trajectory. Based on this study, we reveal that the Berry phase is highly sensitive to the Rashba and Dresselhaus spin-orbit lengths.

Characterization of Strong Light-Matter Coupling in Semiconductor Quantum-Dot Microcavities via Photon-Statistics Spectroscopy

NASA Astrophysics Data System (ADS)

Schneebeli, L.; Kira, M.; Koch, S. W.

2008-08-01

It is shown that spectrally resolved photon-statistics measurements of the resonance fluorescence from realistic semiconductor quantum-dot systems allow for high contrast identification of the two-photon strong-coupling states. Using a microscopic theory, the second-rung resonance of Jaynes-Cummings ladder is analyzed and optimum excitation conditions are determined. The computed photon-statistics spectrum displays gigantic, experimentally robust resonances at the energetic positions of the second-rung emission.

Application of semiconductor fluorescent nanocrystals as optical probes for rapid early viral detection

NASA Astrophysics Data System (ADS)

Bentzen, Elizabeth L.; House, Frances; Tomlinson, Ian D.; Rosenthal, Sandra J.; Crowe, James E.; Wright, David D.

2005-04-01

Fluorescence is a tool widely employed in biological assays. Fluorescent semiconducting nanocrystals, quantum dots (QDs), are beginning to find their way into the tool box of many biologist, chemist and biochemist. These quantum dots are an attractive alternative to the traditional organic dyes due to their broad excitation spectra, narrow emission spectra and photostability. Non-specific binding is a frequently encountered problem with fluorescent labeling in biological assays. In these studies various cell lines were examined for non-specific binding to quantum dots. Evidence suggests that non-specific binding is related to cell type and, may be significantly reduced by functionalizing quantum dots with polyethyleneglycol ligands (PEG). In addition quantum dots were used to detect and monitor the progession of the viral glycoproteins ,F (fusion) and G (attachment), from Respiratory Syncytial Virus (RSV) in HEp-2 cells. RSV is the most common cause of lower respiratory tract infection in children worldwide and the most common cause of hospitalization of infants in the US. Antiviral therapy is available for treatment of RSV but is only effective if given within the first 48 hours of infection. Existing test methods require a virus level of at least 1000-fold of the amount needed for infection of most children and require several days to weeks to obtain results. The use of quantum dots may provide an early, rapid method for detection and provide insight into the trafficking of viral proteins during the course of infection.

Ultrahigh resolution multicolor colocalization of single fluorescent probes

DOEpatents

Weiss, Shimon; Michalet, Xavier; Lacoste, Thilo D.

2005-01-18

A novel optical ruler based on ultrahigh-resolution colocalization of single fluorescent probes is described. Two unique families of fluorophores are used, namely energy-transfer fluorescent beads and semiconductor nanocrystal (NC) quantum dots, that can be excited by a single laser wavelength but emit at different wavelengths. A novel multicolor sample-scanning confocal microscope was constructed which allows one to image each fluorescent light emitter, free of chromatic aberrations, by scanning the sample with nanometer scale steps using a piezo-scanner. The resulting spots are accurately localized by fitting them to the known shape of the excitation point-spread-function of the microscope.

Nuclear spin warm up in bulk n -GaAs

NASA Astrophysics Data System (ADS)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

2016-08-01

We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

Surface Traps in Colloidal Quantum Dots: A Combined Experimental and Theoretical Perspective.

PubMed

Giansante, Carlo; Infante, Ivan

2017-10-19

Surface traps are ubiquitous to nanoscopic semiconductor materials. Understanding their atomistic origin and manipulating them chemically have capital importance to design defect-free colloidal quantum dots and make a leap forward in the development of efficient optoelectronic devices. Recent advances in computing power established computational chemistry as a powerful tool to describe accurately complex chemical species and nowadays it became conceivable to model colloidal quantum dots with realistic sizes and shapes. In this Perspective, we combine the knowledge gathered in recent experimental findings with the computation of quantum dot electronic structures. We analyze three different systems: namely, CdSe, PbS, and CsPbI 3 as benchmark semiconductor nanocrystals showing how different types of trap states can form at their surface. In addition, we suggest experimental healing of such traps according to their chemical origin and nanocrystal composition.

Effect of Γ-X band mixing on the donor binding energy in a Quantum Wire

NASA Astrophysics Data System (ADS)

Vijaya Shanthi, R.; Jayakumar, K.; Nithiananthi, P.

2015-02-01

To invoke the technological applications of heterostructure semiconductors like Quantum Well (QW), Quantum Well Wire (QWW) and Quantum Dot (QD), it is important to understand the property of impurity energy which is responsible for the peculiar electronic & optical behavior of the Low Dimensional Semiconductor Systems (LDSS). Application of hydrostatic pressure P>35kbar drastically alters the band offsets leading to the crossover of Γ band of the well & X band of the barrier resulting in an indirect transition of the carrier and this effect has been studied experimentally and theoretically in a QW structure. In this paper, we have investigated the effect of Γ-X band mixing due to the application of hydrostatic pressure in a GaAs/AlxGa1-xAs QWW system. The results are presented and discussed for various widths of the wire.

Spatially selective hydrogen irradiation of dilute nitride semiconductors: a brief review

NASA Astrophysics Data System (ADS)

Felici, Marco; Pettinari, Giorgio; Biccari, Francesco; Capizzi, Mario; Polimeni, Antonio

2018-05-01

We provide a brief survey of the most recent results obtained by performing spatially selective hydrogen irradiation of dilute nitride semiconductors. The striking effects of the formation of stable N–H complexes in these compounds—coupled to the ultrasharp diffusion profile of H therein—can be exploited to tailor the structural (lattice constant) and optoelectronic (energy gap, refractive index, electron effective mass) properties of the material in the growth plane, with a spatial resolution of a few nm. This can be applied to the fabrication of site-controlled quantum dots (QDs) and wires, but also to the realization of the optical elements required for the on-chip manipulation and routing of qubits in fully integrated photonic circuits. The fabricated QDs—which have shown the ability to emit single photons—can also be deterministically coupled with photonic crystal microcavities, proving their inherent suitability to act as integrated light sources in complex nanophotonic devices.

Photoisomerization-induced manipulation of single-electron tunneling for novel Si-based optical memory.

PubMed

Hayakawa, Ryoma; Higashiguchi, Kenji; Matsuda, Kenji; Chikyow, Toyohiro; Wakayama, Yutaka

2013-11-13

We demonstrated optical manipulation of single-electron tunneling (SET) by photoisomerization of diarylethene molecules in a metal-insulator-semiconductor (MIS) structure. Stress is placed on the fact that device operation is realized in the practical device configuration of MIS structure and that it is not achieved in structures based on nanogap electrodes and scanning probe techniques. Namely, this is a basic memory device configuration that has the potential for large-scale integration. In our device, the threshold voltage of SET was clearly modulated as a reversible change in the molecular orbital induced by photoisomerization, indicating that diarylethene molecules worked as optically controllable quantum dots. These findings will allow the integration of photonic functionality into current Si-based memory devices, which is a unique feature of organic molecules that is unobtainable with inorganic materials. Our proposed device therefore has enormous potential for providing a breakthrough in Si technology.

Single-particle studies of band alignment effects on electron transfer dynamics from semiconductor hetero-nanostructures to single-walled carbon nanotubes.

PubMed

Yuan, Chi-Tsu; Wang, Yong-Gang; Huang, Kuo-Yen; Chen, Ting-Yu; Yu, Pyng; Tang, Jau; Sitt, Amit; Banin, Uri; Millo, Oded

2012-01-24

We utilize single-molecule spectroscopy combined with time-correlated single-photon counting to probe the electron transfer (ET) rates from various types of semiconductor hetero-nanocrystals, having either type-I or type-II band alignment, to single-walled carbon nanotubes. A significantly larger ET rate was observed for type-II ZnSe/CdS dot-in-rod nanostructures as compared to type-I spherical CdSe/ZnS core/shell quantum dots and to CdSe/CdS dot-in-rod structures. Furthermore, such rapid ET dynamics can compete with both Auger and radiative recombination processes, with significance for effective photovoltaic operation. © 2011 American Chemical Society

Long range spin qubit interaction mediated by microcavity polaritons

NASA Astrophysics Data System (ADS)

Piermarocchi, Carlo; Quinteiro, Guillermo F.; Fernandez-Rossier, Joaquin

2007-03-01

Planar microcavities are semiconductor devices that confine the electromagnetic field by means of two parallel semiconductor mirrors. When a quantum well (QW) is placed inside a planar microcavity, the excitons in the QW couple to confined electromagnetic modes. In the strong-coupling regime, excitons and cavity photons give rise to new states, cavity polaritons, which appear in two branches separated by a vacuum Rabi splitting. We study theoretically the dynamics of localized spins in the QW interacting with cavity polaritons. Our calculations consider localized electron spins of shallow neutral donors in GaAs (e.g., Si), but the theory is valid for other impurities and host semiconductors, as well as to charged quantum dots. In the strong-coupling regime, the vacuum Rabi splitting introduces anisotropies in the spin coupling. Moreover, due to their photon-like mass, polaritons provide an extremely long spin coupling range. This suggests the realization of two-qubit all-optical quantum operations within tens of picoseconds with spins localized as far as hundreds of nanometers apart. [G. F. Quinteiro et al., Phys. Rev. Lett. 97 097401, (2006)].

Exciton shelves for charge and energy transport in third-generation quantum-dot devices

NASA Astrophysics Data System (ADS)

Goodman, Samuel; Singh, Vivek; Noh, Hyunwoo; Casamada, Josep; Chatterjee, Anushree; Cha, Jennifer; Nagpal, Prashant

2014-03-01

Quantum dots are semiconductor nanocrystallites with size-dependent quantum-confined energy levels. While they have been intensively investigated to utilize hot-carriers for photovoltaic applications, to bridge the mismatch between incident solar photons and finite bandgap of semiconductor photocells, efficient charge or exciton transport in quantum-dot films has proven challenging. Here we show development of new coupled conjugated molecular wires with ``exciton shelves'', or different energy levels, matched with the multiple energy levels of quantum dots. Using single nanoparticle and ensemble device measurements we show successful extraction and transport of both bandedge and high-energy charge carriers, and energy transport of excitons. We demonstrate using measurements of electronic density of states, that careful matching of energy states of quantum-dot with molecular wires is important, and any mismatch can generate midgap states leading to charge recombination and reduced efficiency. Therefore, these exciton-shelves and quantum dots can lead to development of next-generation photovoltaic and photodetection devices using simultaneous transport of bandedge and hot-carriers or energy transport of excitons in these nanostructured solution-processed films.

Lifetimes of the Vibrational States of DNA Molecules in Functionalized Complexes of Semiconductor Quantum Dots

NASA Astrophysics Data System (ADS)

Bayramov, F. B.; Poloskin, E. D.; Chernev, A. L.; Toporov, V. V.; Dubina, M. V.; Sprung, C.; Lipsanen, H. K.; Bairamov, B. Kh.

2018-01-01

Results of studying nanocrystalline nc-Si/SiO2 quantum dots (QDs) functionalized by short oligonucleotides show that complexes of isolated crystalline semiconductor QDs are unique objects for detecting the manifestation of new quantum confinement phenomena. It is established that narrow lines observed in high-resolution spectra of inelastic light scattering can be used for determining the characteristic time scale of vibrational excitations of separate nucleotide molecules and for studying structural-dynamic properties of fast oscillatory processes in biomacromolecules.

Model of an Injection Semiconductor Quantum-Dot Laser

NASA Astrophysics Data System (ADS)

Koryukin, I. V.

2018-05-01

We propose an asymmetric electron-hole model of an injection semiconductor quantum-dot laser, which correctly allows for relaxation at transitions between the electron and hole levels. Steady-state solutions of the proposed model, conditions for the simultaneous operation at transitions between the ground and first excited state levels, and relaxation oscillations in the two-wave lasing regime are studied. It is shown that the model can be simplified when the relaxation between hole levels is much faster than the relaxation between electron levels.

Development of cadmium-free quantum dot for intracellular labelling through electroporation or lipid-calcium-phosphate

NASA Astrophysics Data System (ADS)

Liu, Ying-Feng; Hung, Wei-Ling; Hou, Tzh-Yin; Huang, Hsiu-Ying; Lin, Cheng-An J.

2016-04-01

Traditional fluorescent labelling techniques has severe photo-bleaching problem such as organic dyes and fluorescent protein. Quantum dots made up of traditional semiconductor (CdSe/ZnS) material has sort of biological toxicity. This research has developed novel Cd-free quantum dots divided into semiconductor (Indium phosphide, InP) and noble metal (Gold). Former has lower toxicity compared to traditional quantum dots. Latter consisting of gold (III) chloride (AuCl3) and toluene utilizes sonochemical preparation and different stimulus to regulate fluorescent wavelength. Amphoteric macromolecule surface technology and ligand Exchange in self-Assembled are involved to develop hydrophilic nanomaterials which can regulate the number of grafts per molecule of surface functional groups. Calcium phosphate (CaP) nanoparticle (NP) with an asymmetric lipid bilayer coating technology developed for intracellular delivery and labelling has synthesized Cd-free quantum dots possessing high brightness and multi-fluorescence successfully. Then, polymer coating and ligand exchange transfer to water-soluble materials to produce liposome nanomaterials as fluorescent probes and enhancing medical applications of nanotechnology.

Controlling the Properties of Matter with Quantum Dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klimov, Victor

2017-03-22

Solar cells and photodetectors could soon be made from new types of materials based on semiconductor quantum dots, thanks to new insights based on ultrafast measurements capturing real-time photoconversion processes. Photoconversion is a process wherein the energy of a photon, or quantum of light, is converted into other forms of energy, for example, chemical or electrical. Semiconductor quantum dots are chemically synthesized crystalline nanoparticles that have been studied for more than three decades in the context of various photoconversion schemes including photovoltaics (generation of photo-electricity) and photo-catalysis (generation of “solar fuels”). The appeal of quantum dots comes from the unmatchedmore » tunability of their physical properties, which can be adjusted by controlling the size, shape and composition of the dots. At Los Alamos, the research connects to the institutional mission of solving national security challenges through scientific excellence, in this case focusing on novel physical principles for highly efficient photoconversion, charge manipulation in exploratory device structures and novel nanomaterials.« less

Ultrafast single photon emitting quantum photonic structures based on a nano-obelisk.

PubMed

Kim, Je-Hyung; Ko, Young-Ho; Gong, Su-Hyun; Ko, Suk-Min; Cho, Yong-Hoon

2013-01-01

A key issue in a single photon source is fast and efficient generation of a single photon flux with high light extraction efficiency. Significant progress toward high-efficiency single photon sources has been demonstrated by semiconductor quantum dots, especially using narrow bandgap materials. Meanwhile, there are many obstacles, which restrict the use of wide bandgap semiconductor quantum dots as practical single photon sources in ultraviolet-visible region, despite offering free space communication and miniaturized quantum information circuits. Here we demonstrate a single InGaN quantum dot embedded in an obelisk-shaped GaN nanostructure. The nano-obelisk plays an important role in eliminating dislocations, increasing light extraction, and minimizing a built-in electric field. Based on the nano-obelisks, we observed nonconventional narrow quantum dot emission and positive biexciton binding energy, which are signatures of negligible built-in field in single InGaN quantum dots. This results in efficient and ultrafast single photon generation in the violet color region.

Mesoscopic Elastic Distortions in GaAs Quantum Dot Heterostructures.

PubMed

Pateras, Anastasios; Park, Joonkyu; Ahn, Youngjun; Tilka, Jack A; Holt, Martin V; Reichl, Christian; Wegscheider, Werner; Baart, Timothy A; Dehollain, Juan Pablo; Mukhopadhyay, Uditendu; Vandersypen, Lieven M K; Evans, Paul G

2018-05-09

Quantum devices formed in high-electron-mobility semiconductor heterostructures provide a route through which quantum mechanical effects can be exploited on length scales accessible to lithography and integrated electronics. The electrostatic definition of quantum dots in semiconductor heterostructure devices intrinsically involves the lithographic fabrication of intricate patterns of metallic electrodes. The formation of metal/semiconductor interfaces, growth processes associated with polycrystalline metallic layers, and differential thermal expansion produce elastic distortion in the active areas of quantum devices. Understanding and controlling these distortions present a significant challenge in quantum device development. We report synchrotron X-ray nanodiffraction measurements combined with dynamical X-ray diffraction modeling that reveal lattice tilts with a depth-averaged value up to 0.04° and strain on the order of 10 -4 in the two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. Elastic distortions in GaAs/AlGaAs heterostructures modify the potential energy landscape in the 2DEG due to the generation of a deformation potential and an electric field through the piezoelectric effect. The stress induced by metal electrodes directly impacts the ability to control the positions of the potential minima where quantum dots form and the coupling between neighboring quantum dots.

Quantum-dot spin-photon entanglement via frequency downconversion to telecom wavelength.

PubMed

De Greve, Kristiaan; Yu, Leo; McMahon, Peter L; Pelc, Jason S; Natarajan, Chandra M; Kim, Na Young; Abe, Eisuke; Maier, Sebastian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Hadfield, Robert H; Forchel, Alfred; Fejer, M M; Yamamoto, Yoshihisa

2012-11-15

Long-distance quantum teleportation and quantum repeater technologies require entanglement between a single matter quantum bit (qubit) and a telecommunications (telecom)-wavelength photonic qubit. Electron spins in III-V semiconductor quantum dots are among the matter qubits that allow for the fastest spin manipulation and photon emission, but entanglement between a single quantum-dot spin qubit and a flying (propagating) photonic qubit has yet to be demonstrated. Moreover, many quantum dots emit single photons at visible to near-infrared wavelengths, where silica fibre losses are so high that long-distance quantum communication protocols become difficult to implement. Here we demonstrate entanglement between an InAs quantum-dot electron spin qubit and a photonic qubit, by frequency downconversion of a spontaneously emitted photon from a singly charged quantum dot to a wavelength of 1,560 nanometres. The use of sub-10-picosecond pulses at a wavelength of 2.2 micrometres in the frequency downconversion process provides the necessary quantum erasure to eliminate which-path information in the photon energy. Together with previously demonstrated indistinguishable single-photon emission at high repetition rates, the present technique advances the III-V semiconductor quantum-dot spin system as a promising platform for long-distance quantum communication.

Spectroscopic investigations on the interaction of thioacetamide with ZnO quantum dots and application for its fluorescence sensing.

PubMed

Saha, Dipika; Negi, Devendra P S

2018-01-15

The purpose of the present work was to develop a method for the sensing of thioacetamide by using spectroscopic techniques. Thioacetamide is a carcinogen and it is important to detect its presence in food-stuffs. Semiconductor quantum dots are frequently employed as sensing probes since their absorption and fluorescence properties are highly sensitive to the interaction with substrates present in the solution. In the present work, the interaction between thioacetamide and ZnO quantum dots has been investigated by using UV-visible, fluorescence and infrared spectroscopy. Besides, dynamic light scattering (DLS) has also been utilized for the interaction studies. UV-visible absorption studies indicated the bonding of the lone pair of sulphur atom of thioacetamide with the surface of the semiconductor. The fluorescence band of the ZnO quantum dots was found to be quenched in the presence of micromolar concentrations of thioacetamide. The quenching was found to follow the Stern-Volmer relationship. The Stern-Volmer constant was evaluated to be 1.20×10 5 M -1 . Infrared spectroscopic measurements indicated the participation of the NH 2 group and the sulphur atom of thioacetamide in bonding with the surface of the ZnO quantum dots. DLS measurements indicated that the surface charge of the semiconductor was shielded by the thioacetamide molecules. Copyright © 2017 Elsevier B.V. All rights reserved.

Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array.

PubMed

Hensgens, T; Fujita, T; Janssen, L; Li, Xiao; Van Diepen, C J; Reichl, C; Wegscheider, W; Das Sarma, S; Vandersypen, L M K

2017-08-02

Interacting fermions on a lattice can develop strong quantum correlations, which are the cause of the classical intractability of many exotic phases of matter. Current efforts are directed towards the control of artificial quantum systems that can be made to emulate the underlying Fermi-Hubbard models. Electrostatically confined conduction-band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical initialization of low-entropy states and readily adhere to the Fermi-Hubbard Hamiltonian. Until now, however, the substantial electrostatic disorder of the solid state has meant that only a few attempts at emulating Fermi-Hubbard physics on solid-state platforms have been made. Here we show that for gate-defined quantum dots this disorder can be suppressed in a controlled manner. Using a semi-automated and scalable set of experimental tools, we homogeneously and independently set up the electron filling and nearest-neighbour tunnel coupling in a semiconductor quantum dot array so as to simulate a Fermi-Hubbard system. With this set-up, we realize a detailed characterization of the collective Coulomb blockade transition, which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition. As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here will enable the investigation of the physics of ever more complex many-body states using quantum dots.

Optical excitations dynamics at hetero-interfaces fullerene/quantum dots

NASA Astrophysics Data System (ADS)

Righetto, Marcello; Privitera, Alberto; Franco, Lorenzo; Bozio, Renato

2017-08-01

Embedding Semiconductor Quantum Dots (QDs) into hybrid organic-inorganic solar cell holds promises for improving photovoltaic performances. Thanks to their strong coupling with electro-magnetic radiation field, QDs represent paradigmatic photon absorbers. Nevertheless, the quest for suitable charge separating hetero-interfaces is still an open challenge. Within this framework, the excited state interactions between QDs and fullerene derivatives are of great interest for ternary solar cells (polymer:QDs:fullerene). In this work, we investigated the exciton dynamics of core/shell CdSe/CdS QDs both in solution and in blends with fullerene derivative (PCBM). By means of transient optical techniques, we aimed to unveil the dynamics of the QDs-PCBM interaction. Indeed, the observed excited state depopulation of QDs in blends is compatible with an excited state interaction living on picosecond timescale. Through electron paramagnetic resonance, we delved into the nature of this interaction, identifying the presence of charge separated states. The concurrence of these observations suggest a fast electron transfer process, where QDs act as donors and PCBM molecules as acceptors, followed by effective charge separation. Therefore, our experimental results indicate the QDs-PCBM heterointerface as suitable exciton separating interface, paving the way for possible applications in photovoltaics.

Accessing the dark exciton spin in deterministic quantum-dot microlenses

NASA Astrophysics Data System (ADS)

Heindel, Tobias; Thoma, Alexander; Schwartz, Ido; Schmidgall, Emma R.; Gantz, Liron; Cogan, Dan; Strauß, Max; Schnauber, Peter; Gschrey, Manuel; Schulze, Jan-Hindrik; Strittmatter, Andre; Rodt, Sven; Gershoni, David; Reitzenstein, Stephan

2017-12-01

The dark exciton state in semiconductor quantum dots (QDs) constitutes a long-lived solid-state qubit which has the potential to play an important role in implementations of solid-state-based quantum information architectures. In this work, we exploit deterministically fabricated QD microlenses which promise enhanced photon extraction, to optically prepare and read out the dark exciton spin and observe its coherent precession. The optical access to the dark exciton is provided via spin-blockaded metastable biexciton states acting as heralding states, which are identified by deploying polarization-sensitive spectroscopy as well as time-resolved photon cross-correlation experiments. Our experiments reveal a spin-precession period of the dark exciton of (0.82 ± 0.01) ns corresponding to a fine-structure splitting of (5.0 ± 0.7) μeV between its eigenstates |↑ ⇑ ±↓ ⇓ ⟩. By exploiting microlenses deterministically fabricated above pre-selected QDs, our work demonstrates the possibility to scale up implementations of quantum information processing schemes using the QD-confined dark exciton spin qubit, such as the generation of photonic cluster states or the realization of a solid-state-based quantum memory.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baart, T. A.; Vandersypen, L. M. K.; Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft

We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate T that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot devices.

Chiral quantum supercrystals with total dissymmetry of optical response

NASA Astrophysics Data System (ADS)

Baimuratov, Anvar S.; Gun'Ko, Yurii K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

2016-03-01

Since chiral nanoparticles are much smaller than the optical wavelength, their enantiomers show little difference in the interaction with circularly polarized light. This scale mismatch makes the enhancement of enantioselectivity in optical excitation of nanoobjects a fundamental challenge in modern nanophotonics. Here we demonstrate that a strong dissymmetry of optical response from achiral nanoobjects can be achieved through their arrangement into chiral superstructures with the length scale comparable to the optical wavelength. This concept is illustrated by the example of the simple helix supercrystal made of semiconductor quantum dots. We show that this supercrystal almost fully absorbs light with one circular polarization and does not absorb the other. The giant circular dichroism of the supercrystal comes from the formation of chiral bright excitons, which are the optically active collective excitations of the entire supercrystal. Owing to the recent advances in assembly and self-organization of nanocrystals in large superparticle structures, the proposed principle of enantioselectivity enhancement has great potential of benefiting various chiral and analytical methods, which are used in biophysics, chemistry, and pharmaceutical science.

All optical quantum control of a spin-quantum state and ultrafast transduction into an electric current.

PubMed

Müller, K; Kaldewey, T; Ripszam, R; Wildmann, J S; Bechtold, A; Bichler, M; Koblmüller, G; Abstreiter, G; Finley, J J

2013-01-01

The ability to control and exploit quantum coherence and entanglement drives research across many fields ranging from ultra-cold quantum gases to spin systems in condensed matter. Transcending different physical systems, optical approaches have proven themselves to be particularly powerful, since they profit from the established toolbox of quantum optical techniques, are state-selective, contact-less and can be extremely fast. Here, we demonstrate how a precisely timed sequence of monochromatic ultrafast (~ 2-5 ps) optical pulses, with a well defined polarisation can be used to prepare arbitrary superpositions of exciton spin states in a semiconductor quantum dot, achieve ultrafast control of the spin-wavefunction without an applied magnetic field and make high fidelity read-out the quantum state in an arbitrary basis simply by detecting a strong (~ 2-10 pA) electric current flowing in an external circuit. The results obtained show that the combined quantum state preparation, control and read-out can be performed with a near-unity (≥97%) fidelity.

Optical Response of Metal Nanoantennas to Femtosecond Pulses

NASA Astrophysics Data System (ADS)

Biswas, Sushmita; Heberle, Albert

2007-03-01

Nanoscale metal antennas are promising devices for focusing light down to dimensions much smaller than the wavelength of light. This focusing can lead to strong optical enhancement of the response of single molecules or quantum dots placed in the antenna gap, as well as strong nonlinearities. The optical response of such antenna, however, is not well understood yet. Here, we will present results of our investigations of the linear and nonlinear optical response of silver nanoscale bowtie antennas to excitation with near-infrared pulses from a femtosecond Ti:sapphire laser. The antennas were fabricated with electron beam lithography and a lift-of process on glass substrates and semiconductor materials. They have lengths of a few hundred nanometers and gaps between 10 and 100 nanometers. We will discuss polarization dependence of the excitation sensitivity, second harmonic generation and other nonlinear effects. References: [1] P. Muhlschlegel et al., Science ,1607(2005). [2] J.N. Farahani et al., Phys. Rev. Lett. 95,017402(2005).

NREL Senior Research Fellow Honored by The Journal of Physical Chemistry |

Science.gov Websites

and quantum size effects in semiconductors and carrier dynamics in semiconductor quantum dots and using hot carrier effects, size quantization, and superlattice concepts that could, in principle, enable

Surface Traps in Colloidal Quantum Dots: A Combined Experimental and Theoretical Perspective

PubMed Central

2017-01-01

Surface traps are ubiquitous to nanoscopic semiconductor materials. Understanding their atomistic origin and manipulating them chemically have capital importance to design defect-free colloidal quantum dots and make a leap forward in the development of efficient optoelectronic devices. Recent advances in computing power established computational chemistry as a powerful tool to describe accurately complex chemical species and nowadays it became conceivable to model colloidal quantum dots with realistic sizes and shapes. In this Perspective, we combine the knowledge gathered in recent experimental findings with the computation of quantum dot electronic structures. We analyze three different systems: namely, CdSe, PbS, and CsPbI3 as benchmark semiconductor nanocrystals showing how different types of trap states can form at their surface. In addition, we suggest experimental healing of such traps according to their chemical origin and nanocrystal composition. PMID:28972763

Photoluminescence spectral study of single cadmium selenide/zinc sulfide colloidal nanocrystals in poly(methyl methacrylate) and quantum dots molecules

NASA Astrophysics Data System (ADS)

Shen, Yaoming

Quantum dots (QDs)and Nano-crystals (NCs) have been studies for decades. Because of the nanoscale quantum confinement, delta shape like energy density states and narrowband emitters properties, they hold great promise for numerous optoelectronics and photonics applications. They could be used for tunable lasers, white LED, Nano-OLED, non-volatile memory and solar cells. They are also the most promising candidates for the quantum computing. The benefits for NCs over QDs is that NCs can be incorporated into a variety of polymers as well as thin films of bulk semiconductors. These exceptional flexibility and structural control distinguish NCs from the more traditional QD structures fabricated using epitaxial growth techniques. In my research of work, I studied the photoluminescence (PL) and absorption character of ensemble NCs incorporated in Polymethyl methacrylate (PMMA). To understand the behavior of the NCs in PMMA, it is important to measure a singe NC to avoid the inhomogenous broading of many NCs. So I particularly studied the behavior of a single NC in PMMA matrix. A microphotoluminescence setup to optically isolate a single nanocrystal is used. Random spectral shift and blinking behavior (on and off) are found. Addition to that, two color spectral shifting, is a major phenomena found in the system. Other interesting results such as PL intensity changes (decreasing or increasing with time) and quenching effect are observed and explained too. From the correlation function, we can distinguish the phonon replicas. The energy of these phonons can be calculated very accurately from the experiment result. The Huang-Rhys factors can be estimated too. Self-assembled semiconductor quantum dots (QDs), from highly strained-layer heteroepitaxy in the Stranski-Krastanow (S-K) growth mode, have been intensively studied because of the delta-function-like density of states, which is significant for optoelectronic applications. Spontaneous formation of semiconductor quantum-dot molecules (QDMs), which are clusters of a few QDs, has attracted attention as a possible implementation of future quantum devices such as quantum cellular antomata. With the advances in crystal growth techniques, the fabrication methods for nanostructures have been improved continuously. Lateral QDMs have been achieved. As a side topic, lateral QDMs have been studied and the result is presented in the last chapter.

Optical orientation in ferromagnet/semiconductor hybrids

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2008-11-01

The physics of optical pumping of semiconductor electrons in ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of a ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of a semiconductor. Spin-spin interactions near the ferromagnet/semiconductor interface play a crucial role in the optical readout and the manipulation of ferromagnetism.

Investigations into the formation of nanocrystalline quantum dot thin films by mist deposition process

NASA Astrophysics Data System (ADS)

Kshirsagar, Aditya

Semiconductor nanocrystalline quantum dots (NQDs) have material properties remarkably different compared to bulk semiconductors with the same material composition. These NQDs have various novel applications in the electronic and photonic industry, such as light emitting diodes (LEDs) and flat-panel displays. In these applications, ultra-thin films of NQDs in the monolayer regime are needed to ensure optimal current transport properties and device efficiency. There is ongoing search to find a suitable method to deposit and pattern such ultra-thin films of quantum dots with few monolayer thicknesses. Several competing approaches are available, each with its pros and cons. This study explores mist deposition as the technique to fill this void. In this study, ultra-thin films of quantum dots are deposited on diverse substrates and are characterized to understand the mechanics of mist deposition. Various applications of blanket deposited and patterned quantum dot films are studied. The results discussed here include atomic force microscopy analysis of the films to study surface morphology, fluorescence microscopy to study light emission and optical microscope images to study patterning techniques. These results demonstrate the ability of mist deposition to form 1-4 monolayers thick, uniform, defect-free patterned films with root mean square (RMS) surface roughness less than 2 nm. LEDs fabricated using mist deposition show a peak luminescence greater than 500 cd/m2 for matched red, yellow and green devices using Alq3 as the electron transport layer, and over 9000 cd/m2 for red devices using ZnO as the electron transport layer, respectively. In addition to the experimental approach to study the process and explore potential applications, simulation and modeling are carried out to understand the various aspects of mist deposition. A mathematical model is presented which discusses the atomization process of the precursor solution, the physics involved during the deposition process, and the mechanics of film formation. Results of film morphology simulation using Monte Carlo techniques and process simulation using multi-physics approach are discussed. Problems in pattern transfer due to electrostatic effects when using shadow masks are presented in a separate chapter.

Properties of Type-II ZnTe/ZnSe Submonolayer Quantum Dots Studied via Excitonic Aharonov- Bohm Effect and Polarized Optical Spectroscopy

NASA Astrophysics Data System (ADS)

Ji, Haojie

In this thesis I develop understanding of the fundamental physical and material properties of type-II ZnTe/ZnSe submonolayer quantum dots (QDs), grown via combination of molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). I use magneto-photoluminescence, including excitonic Aharonov-Bohm (AB) effect and polarized optical spectroscopy as the primary tools in this work. I present previous studies as well as the background of optical and magneto-optical processes in semiconductor nanostructures and introduce the experimental methods in Chapters 1 - 3. In Chapter 4 I focus on the excitonic AB effect in the type-II QDs. I develop a lateral tightly-bound exciton model for ZnTe/ZnSe type-II QDs, using analytical methods and numerical calculations. This explained the magneto-PL observation and allowed for establishing the size and density of the QDs in each sample based on the results of PL and magneto-PL measurements. For samples with larger QDs, I observe behaviors that fall between properties of quantum-dot and quantum-well-like systems due to increased QD densities and their type-II nature. Finally, the decoherence mechanisms of the AB excitons are investigated via the temperature dependent studies of the magneto-PL. It is determined that the AB exciton decoherence is due to transport-like (acoustic phonon) scattering of the electrons moving in the ZnSe barriers, but with substantially smaller magnitude of electron-phonon coupling constant due to relatively strong electron-hole coupling within these type-II QDs. In Chapter 5 I discuss the results of circularly polarized magneto-PL measurements. A model with ultra-long spin-flip time of holes confined to submonolayer QDs is proposed. The g-factor of type-II excitons was extracted from the Zeeman splitting and the g-factor of electrons was obtained by fitting the temperature dependence of the degree of circular polarization (DCP), from which g-factor of holes confined within ZnTe QDs was found. It is shown that it is about three times larger than that of bulk ZnTe. In Chapter 6 I study the optical anisotropy in QDs. I show that all samples exhibit such an effect, and explain it based on non-spherical shape of the QDs. Numerical calculation is applied to calculate degree of linear polarization, and estimate the aspect ratio. The exciton anisotropic exchange splitting is calculated from the magnetic field dependence of the DCP. In the last two chapters I show my achievement on the growth of ZnO nanorods as a core for type-II 1D systems and propose an outlook for future research on the type-II semiconductor heterostructures.

Senior Research Fellow Wins Major International Science Award | News | NREL

Science.gov Websites

generation (MEG) in semiconductor nanocrystals, also called quantum dots, and recently found efficient MEG in silicon quantum dots. He shares the award with Stefan W. Glunz of the Fraunhofer Institute in Germany

Effect of the Semiconductor Quantum Dot Shell Structure on Fluorescence Quenching by Acridine Ligand

NASA Astrophysics Data System (ADS)

Linkov, P. A.; Vokhmintcev, K. V.; Samokhvalov, P. S.; Laronze-Cochard, M.; Sapi, J.; Nabiev, I. R.

2018-02-01

The main line of research in cancer treatment is the development of methods for early diagnosis and targeted drug delivery to cancer cells. Fluorescent semiconductor core/shell nanocrystals of quantum dots (e.g., CdSe/ZnS) conjugated with an anticancer drug, e.g., an acridine derivative, allow real-time tracking and control of the process of the drug delivery to tumors. However, linking of acridine derivatives to a quantum dot can be accompanied by quantum dot fluorescence quenching caused by electron transfer from the quantum dot to the organic molecule. In this work, it has been shown that the structure of the shell of the quantum dot plays the decisive role in the process of photoinduced charge transfer from the quantum dot to the acridine ligand, which is responsible for fluorescence quenching. It has been shown that multicomponent ZnS/CdS/ZnS shells of CdSe cores of quantum dots, which have a relatively small thickness, make it possible to significantly suppress a decrease in the quantum yield of fluorescence of quantum dots as compared to both the classical ZnS thin shell and superthick shells of the same composition. Thus, core/multicomponent shell CdSe/ZnS/CdS/ZnS quantum dots can be used as optimal fluorescent probes for the development of systems for diagnosis and treatment of cancer with the use of anticancer compounds based on acridine derivatives.

Spin relaxation in semiconductor quantum rings and dots--a comparative study.

PubMed

Zipper, Elżbieta; Kurpas, Marcin; Sadowski, Janusz; Maśka, Maciej M

2011-03-23

We calculate spin relaxation times due to spin-orbit-mediated electron-phonon interactions for experimentally accessible semiconductor quantum ring and dot architectures. We elucidate the differences between the two systems due to different confinement. The estimated relaxation times (at B = 1 T) are in the range between a few milliseconds to a few seconds. This high stability of spin in a quantum ring allows us to test it as a spin qubit. A brief discussion of quantum state manipulations with such a qubit is presented.

Decoherence of spin states induced by Rashba coupling for an electron confined to a semiconductor quantum dot in the presence of a magnetic field

NASA Astrophysics Data System (ADS)

Poszwa, A.

2018-05-01

We investigate quantum decoherence of spin states caused by Rashba spin-orbit (SO) coupling for an electron confined to a planar quantum dot (QD) in the presence of a magnetic field (B). The Schrödinger equation has been solved in a frame of second-order perturbation theory. The relationship between the von Neumann (vN) entropy and the spin polarization is obtained. The relation is explicitly demonstrated for the InSb semiconductor QD.

Colloidal-Quantum-Dot Ring Lasers with Active Color Control.

PubMed

le Feber, Boris; Prins, Ferry; De Leo, Eva; Rabouw, Freddy T; Norris, David J

2018-02-14

To improve the photophysical performance of colloidal quantum dots for laser applications, sophisticated core/shell geometries have been developed. Typically, a wider bandgap semiconductor is added as a shell to enhance the gain from the quantum-dot core. This shell is designed to electronically isolate the core, funnel excitons to it, and reduce nonradiative Auger recombination. However, the shell could also potentially provide a secondary source of gain, leading to further versatility in these materials. Here we develop high-quality quantum-dot ring lasers that not only exhibit lasing from both the core and the shell but also the ability to switch between them. We fabricate ring resonators (with quality factors up to ∼2500) consisting only of CdSe/CdS/ZnS core/shell/shell quantum dots using a simple template-stripping process. We then examine lasing as a function of the optical excitation power and ring radius. In resonators with quality factors >1000, excitons in the CdSe cores lead to red lasing with thresholds at ∼25 μJ/cm 2 . With increasing power, green lasing from the CdS shell emerges (>100 μJ/cm 2 ) and then the red lasing begins to disappear (>250 μJ/cm 2 ). We present a rate-equation model that can explain this color switching as a competition between exciton localization into the core and stimulated emission from excitons in the shell. Moreover, by lowering the quality factor of the cavity we can engineer the device to exhibit only green lasing. The mechanism demonstrated here provides a potential route toward color-switchable quantum-dot lasers.

Coupling of Excitons and Discrete Acoustic Phonons in Vibrationally Isolated Quantum Emitters.

PubMed

Werschler, Florian; Hinz, Christopher; Froning, Florian; Gumbsheimer, Pascal; Haase, Johannes; Negele, Carla; de Roo, Tjaard; Mecking, Stefan; Leitenstorfer, Alfred; Seletskiy, Denis V

2016-09-14

The photoluminescence emission by mesoscopic condensed matter is ultimately dictated by the fine-structure splitting of the fundamental exciton into optically allowed and dipole-forbidden states. In epitaxially grown semiconductor quantum dots, nonradiative equilibration between the fine-structure levels is mediated by bulk acoustic phonons, resulting in asymmetric spectral broadening of the excitonic luminescence. In isolated colloidal quantum dots, spatial confinement of the vibrational motion is expected to give rise to an interplay between the quantized electronic and phononic degrees of freedom. In most cases, however, zero-dimensional colloidal nanocrystals are strongly coupled to the substrate such that the charge relaxation processes are still effectively governed by the bulk properties. Here we show that encapsulation of single colloidal CdSe/CdS nanocrystals into individual organic polymer shells allows for systematic vibrational decoupling of the semiconductor nanospheres from the surroundings. In contrast to epitaxially grown quantum dots, simultaneous quantization of both electronic and vibrational degrees of freedom results in a series of strong and narrow acoustic phonon sidebands observed in the photoluminescence. Furthermore, an individual analysis of more than 200 compound particles reveals that enhancement or suppression of the radiative properties of the fundamental exciton is controlled by the interaction between fine-structure states via the discrete vibrational modes. For the first time, pronounced resonances in the scattering rate between the fine-structure states are directly observed, in good agreement with a quantum mechanical model. The unambiguous assignment of mediating acoustic modes to the observed scattering resonances complements the experimental findings. Thus, our results form an attractive basis for future studies on subterahertz quantum opto-mechanics and efficient laser cooling at the nanoscale.

Boundary Condition for Modeling Semiconductor Nanostructures

NASA Technical Reports Server (NTRS)

Lee, Seungwon; Oyafuso, Fabiano; von Allmen, Paul; Klimeck, Gerhard

2006-01-01

A recently proposed boundary condition for atomistic computational modeling of semiconductor nanostructures (particularly, quantum dots) is an improved alternative to two prior such boundary conditions. As explained, this boundary condition helps to reduce the amount of computation while maintaining accuracy.

Phonon-wave-induced resonance fluorescence in semiconductor nanostructures: acoustoluminescence in the terahertz range.

PubMed

Ahn, K J; Milde, F; Knorr, A

2007-01-12

Acoustic wave excitation of semiconductor quantum dots generates resonance fluorescence of electronic intersublevel excitations. Our theoretical analysis predicts acoustoluminescence, in particular, a conversion of acoustic into electromagnetic THz waves over a broad spectral range.

Enhanced oxidation stability of quasi core-shell alloyed CdSeS quantum dots prepared through aqueous microwave synthesis technique.

PubMed

Zhan, Hong-Ju; Zhou, Pei-Jiang; Ma, Rong; Liu, Xi-Jing; He, Yu-Ning; Zhou, Chuan-Yun

2014-01-01

Quasi core shell alloyed CdSeS quantum dots (QDs) have been prepared through a facile aqueous-phase route employing microwave irradiation technique. The optical spectroscopy and structure characterization evidenced the quasi core shell alloyed structures of CdSeS QDs. The X-ray diffraction patterns of the obtained CdSeS QDs displayed peak positions very close to those of bulk cubic CdS crystal structures and the result of X-ray photoelectron spectroscopy data re-confirmed the thick CdS shell on the CdSe core. The TEM images and HRTEM images of the CdSeS QDs ascertained the well-defined spherical particles and a relatively narrow size distribution. On the basis, the stability of the obtained QDs in an oxidative environment was also discussed using etching reaction by H2O2. The experiments result showed the as-prepared QDs present high tolerance towards H2O2, obviously superior to the commonly used CdTe QDs and core-shell CdTe/CdS QDs, which was attributed to the unique quasi core-shell CdSeS crystal structure and the small lattice mismatch between CdSe and CdS semiconductor materials. This assay provided insight to obtain high stable crystal structured semiconductor nanocrystals in the design and synthesis process.

Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control.

PubMed

Sun, Liangfeng; Choi, Joshua J; Stachnik, David; Bartnik, Adam C; Hyun, Byung-Ryool; Malliaras, George G; Hanrath, Tobias; Wise, Frank W

2012-05-06

Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr(-1) m(-2)) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH(2) groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.

Full-mesh T- and O-band wavelength router based on arrayed waveguide gratings.

PubMed

Idris, Nazirul A; Yoshizawa, Katsumi; Tomomatsu, Yasunori; Sudo, Makoto; Hajikano, Tadashi; Kubo, Ryogo; Zervas, Georgios; Tsuda, Hiroyuki

2016-01-11

We propose an ultra-broadband full-mesh wavelength router supporting the T- and O-bands using 3 stages of cascaded arrayed waveguide gratings (AWGs). The router architecture is based on a combination of waveband and channel routing by coarse and fine AWGs, respectively. We fabricated several T-band-specific silica-based AWGs and quantum dot semiconductor optical ampliers as part of the router, and demonstrated 10 Gbps data transmission for several wavelengths throughout a range of 7.4 THz. The power penalties were below 1 dB. Wavelength routing was also demonstrated, where tuning time within a 9.4-nm-wide waveband was below 400 ms.

Fiber-based confocal microscope for cryogenic spectroscopy.

PubMed

Högele, Alexander; Seidl, Stefan; Kroner, Martin; Karrai, Khaled; Schulhauser, Christian; Sqalli, Omar; Scrimgeour, Jan; Warburton, Richard J

2008-02-01

We describe the design and performance of a fiber-based confocal microscope for cryogenic operation. The microscope combines positioning at low temperatures along three space coordinates of millimeter translation and nanometer precision with high stability and optical performance at the diffraction limit. It was successfully tested under ambient conditions as well as at liquid nitrogen (77 K) and liquid helium (4 K) temperatures. The compact nonmagnetic design provides for long term position stability against helium refilling transfers, temperature sweeps, as well as magnetic field variation between -9 and 9 T. As a demonstration of the microscope performance, applications in the spectroscopy of single semiconductor quantum dots are presented.

Semiconductor nanocrystals for novel optical applications

NASA Astrophysics Data System (ADS)

Moon, Jong-Sik

Inspired by the promise of enhanced spectral response, photorefractive polymeric composites photosensitized with semiconductor nanocrystals have emerged as an important class of materials. Here, we report on the photosensitization of photorefractive polymeric composites at visible wavelengths through the inclusion of narrow band-gap semiconductor nanocrystals composed of PbS. Through this approach, internal diffraction efficiencies in excess of 82%, two-beam-coupling gain coefficients in excess of 211 cm-1, and response times 34 ms have been observed, representing some of the best figures-of-merit reported on this class of materials. In addition to providing efficient photosensitization, however, extensive studies of these hybrid composites have indicated that the inclusion of nanocrystals also provides an enhancement in the charge-carrier mobility and subsequent reduction in the photorefractive response time. Through this approach with PbS as charge-carrier, unprecedented response times of 399 micros were observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency and with internal diffraction efficiencies of 72% and two- beam-coupling gain coefficients of 500 cm-1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of the enhanced charge mobility without the accompaniment of superfluous traps. Finally, water soluble InP/ZnS and CdSe/ZnS quantum dots interacted with CPP and Herceptin to apply them as a bio-maker. Both of quantum dots showed the excellent potential for use in biomedical imaging and drug delivery applications. It is anticipated that these approaches can play a significant role in the eventual commercialization of these classes of materials.

Interaction of Water-Soluble CdTe Quantum Dots with Bovine Serum Albumin

PubMed Central

2011-01-01

Semiconductor nanoparticles (quantum dots) are promising fluorescent markers, but it is very little known about interaction of quantum dots with biological molecules. In this study, interaction of CdTe quantum dots coated with thioglycolic acid (TGA) with bovine serum albumin was investigated. Steady state spectroscopy, atomic force microscopy, electron microscopy and dynamic light scattering methods were used. It was explored how bovine serum albumin affects stability and spectral properties of quantum dots in aqueous media. CdTe–TGA quantum dots in aqueous solution appeared to be not stable and precipitated. Interaction with bovine serum albumin significantly enhanced stability and photoluminescence quantum yield of quantum dots and prevented quantum dots from aggregating. PMID:27502633

Reconfigurable quadruple quantum dots in a silicon nanowire transistor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Betz, A. C., E-mail: ab2106@cam.ac.uk; Broström, M.; Gonzalez-Zalba, M. F.

2016-05-16

We present a reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consists of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired with improved silicon fabrication techniques, makes the corner state quantum dot approach a promising candidate for a scalable quantum information architecture.

Photon induced non-linear quantized double layer charging in quaternary semiconducting quantum dots.

PubMed

Nair, Vishnu; Ananthoju, Balakrishna; Mohapatra, Jeotikanta; Aslam, M

2018-03-15

Room temperature quantized double layer charging was observed in 2 nm Cu 2 ZnSnS 4 (CZTS) quantum dots. In addition to this we observed a distinct non-linearity in the quantized double layer charging arising from UV light modulation of double layer. UV light irradiation resulted in a 26% increase in the integral capacitance at the semiconductor-dielectric (CZTS-oleylamine) interface of the quantum dot without any change in its core size suggesting that the cause be photocapacitive. The increasing charge separation at the semiconductor-dielectric interface due to highly stable and mobile photogenerated carriers cause larger electrostatic forces between the quantum dot and electrolyte leading to an enhanced double layer. This idea was supported by a decrease in the differential capacitance possible due to an enhanced double layer. Furthermore the UV illumination enhanced double layer gives us an AC excitation dependent differential double layer capacitance which confirms that the charging process is non-linear. This ultimately illustrates the utility of a colloidal quantum dot-electrolyte interface as a non-linear photocapacitor. Copyright © 2017 Elsevier Inc. All rights reserved.

A simple and facile synthesis of MPA capped CdSe and CdSe/CdS core/shell nanoparticles

NASA Astrophysics Data System (ADS)

Sukanya, D.; Sagayaraj, P.

2015-06-01

II-VI semiconductor nanostructures, in particular, CdSe quantum dots have drawn a lot of attention because of their promising potential applications in biological tagging, photovoltaic, display devices etc. due to their excellent optical properties, high emission quantum yield, size dependent emission wavelength and high photostability. In this paper, we describe the synthesis and properties of mercaptopropionic acid capped CdSe and CdSe/CdS nanoparticles through a simple and efficient co-precipitation method followed by hydrothermal treatment. The growth process, characterization and the optical absorption as a function of wavelength for the synthesized MPA capped CdSe and CdSe/CdS nanoparticles have been determined using X-ray diffraction study (XRD), Ultraviolet-Visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and High Resolution Transmission Electron Microscopy (HRTEM).

Thermal-Error Regime in High-Accuracy Gigahertz Single-Electron Pumping

NASA Astrophysics Data System (ADS)

Zhao, R.; Rossi, A.; Giblin, S. P.; Fletcher, J. D.; Hudson, F. E.; Möttönen, M.; Kataoka, M.; Dzurak, A. S.

2017-10-01

Single-electron pumps based on semiconductor quantum dots are promising candidates for the emerging quantum standard of electrical current. They can transfer discrete charges with part-per-million (ppm) precision in nanosecond time scales. Here, we employ a metal-oxide-semiconductor silicon quantum dot to experimentally demonstrate high-accuracy gigahertz single-electron pumping in the regime where the number of electrons trapped in the dot is determined by the thermal distribution in the reservoir leads. In a measurement with traceability to primary voltage and resistance standards, the averaged pump current over the quantized plateau, driven by a 1-GHz sinusoidal wave in the absence of a magnetic field, is equal to the ideal value of e f within a measurement uncertainty as low as 0.27 ppm.

Two-state semiconductor laser self-mixing velocimetry exploiting coupled quantum-dot emission-states: experiment, simulation and theory

PubMed Central

Gioannini, Mariangela; Dommermuth, Marius; Drzewietzki, Lukas; Krestnikov, Igor; Livshits, Daniil; Krakowski, Michel; Breuer, Stefan

2014-01-01

We exploit the coupled emission-states of a single-chip semiconductor InAs/GaAs quantum-dot laser emitting simultaneously on ground-state (λGS = 1245 nm) and excited-state (λES = 1175 nm) to demonstrate coupled-two-state self-mixing velocimetry for a moving diffuse reflector. A 13 Hz-narrow Doppler beat frequency signal at 317 Hz is obtained for a reflector velocity of 3 mm/s, which exemplifies a 66-fold improvement in width as compared to single-wavelength self-mixing velocimetry. Simulation results reveal the physical origin of this signal, the coupling of excited-state and ground-state photons via the carriers, which is unique for quantum-dot lasers and reproduce the experimental results with excellent agreement. PMID:25321809

Radiation Effects in Nanostructures: Comparison of Proton Irradiation Induced Changes on Quantum Dots and Quantum Wells

NASA Technical Reports Server (NTRS)

Leon, R.; Swift, G.; Magness, B.; Taylor, W.; Tang, Y.; Wang, K.; Dowd, P.; Zhang, Y.

2000-01-01

Successful implementation of technology using self-forming semiconductor Quantum Dots (QDs) has already demonstrated that temperature independent Dirac-delta density of states can be exploited in low current threshold QD lasers and QD infrared photodetectors.

Method and apparatus for use of III-nitride wide bandgap semiconductors in optical communications

DOEpatents

Hui, Rongqing [Lenexa, KS; Jiang, Hong-Xing [Manhattan, KS; Lin, Jing-Yu [Manhattan, KS

2008-03-18

The present disclosure relates to the use of III-nitride wide bandgap semiconductor materials for optical communications. In one embodiment, an optical device includes an optical waveguide device fabricated using a III-nitride semiconductor material. The III-nitride semiconductor material provides for an electrically controllable refractive index. The optical waveguide device provides for high speed optical communications in an infrared wavelength region. In one embodiment, an optical amplifier is provided using optical coatings at the facet ends of a waveguide formed of erbium-doped III-nitride semiconductor materials.

Evaluating the potential of using quantum dots for monitoring electrical signals in neurons

NASA Astrophysics Data System (ADS)

Efros, Alexander L.; Delehanty, James B.; Huston, Alan L.; Medintz, Igor L.; Barbic, Mladen; Harris, Timothy D.

2018-04-01

Success in the projects aimed at providing an advanced understanding of the brain is directly predicated on making critical advances in nanotechnology. This Perspective addresses the unique interface of neuroscience and nanomaterials by considering the foundational problem of sensing neuron membrane voltage and offers a potential solution that may be facilitated by a prototypical nanomaterial. Despite substantial improvements, the visualization of instantaneous voltage changes within individual neurons, whether in cell culture or in vivo, at both the single-cell and network level at high speed remains complex and problematic. The unique properties of semiconductor quantum dots (QDs) have made them powerful fluorophores for bioimaging. What is not widely appreciated, however, is that QD photoluminescence is exquisitely sensitive to proximal electric fields. This property should be suitable for sensing voltage changes that occur in the active neuronal membrane. Here, we examine the potential role of QDs in addressing the important challenge of real-time optical voltage imaging.

Alloy and heterostructure architectures as promising tools for controlling electronic properties of semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Vaxenburg, Roman; Lifshitz, Efrat

2012-02-01

Tunability of energy levels and wavefunctions of carriers in colloidal quantum dots (CQDs) has a marked effect on numerous physical aspects, such as Coulomb interactions and charge separation, which in turn has a direct impact on the functioning of CQD-based opto-electronic devices. The electronic properties of CQDs are conventionally controlled by variation of their size. Here we demonstrate a theoretical approach to engineer the electronic properties of IV-VI CQDs by introducing an alloy composition in core and core/shell heterostructures, having the general chemical formula PbSexS1-x/PbSeyS1-y (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), while maintaining a constant size. The theoretical model considered an effective mass anisotropy and smooth potential step at the core/shell interface. The model revealed the influence induced by variation of chemical composition and core-to-shell division on the band-gap energy, remote states’ density, internal charge separation, electron-hole Coulomb interaction, and optical transition oscillator strength.

Deterministic and robust generation of single photons from a single quantum dot with 99.5% indistinguishability using adiabatic rapid passage.

PubMed

Wei, Yu-Jia; He, Yu-Ming; Chen, Ming-Cheng; Hu, Yi-Nan; He, Yu; Wu, Dian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Lu, Chao-Yang; Pan, Jian-Wei

2014-11-12

Single photons are attractive candidates of quantum bits (qubits) for quantum computation and are the best messengers in quantum networks. Future scalable, fault-tolerant photonic quantum technologies demand both stringently high levels of photon indistinguishability and generation efficiency. Here, we demonstrate deterministic and robust generation of pulsed resonance fluorescence single photons from a single semiconductor quantum dot using adiabatic rapid passage, a method robust against fluctuation of driving pulse area and dipole moments of solid-state emitters. The emitted photons are background-free, have a vanishing two-photon emission probability of 0.3% and a raw (corrected) two-photon Hong-Ou-Mandel interference visibility of 97.9% (99.5%), reaching a precision that places single photons at the threshold for fault-tolerant surface-code quantum computing. This single-photon source can be readily scaled up to multiphoton entanglement and used for quantum metrology, boson sampling, and linear optical quantum computing.

Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

DOE PAGES

Gong, Jianxiao; Steinsultz, Nat; Ouyang, Min

2016-06-08

The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters ( including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring themore » underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. Lastly, this study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen vacancy centres that use these freestanding hybrid nanostructures as building blocks.« less

Discrete quantum dot like emitters in monolayer MoSe{sub 2}: Spatial mapping, magneto-optics, and charge tuning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Branny, Artur; Kumar, Santosh; Gerardot, Brian D., E-mail: b.d.gerardot@hw.ac.uk

Transition metal dichalcogenide monolayers such as MoSe{sub 2}, MoS{sub 2}, and WSe{sub 2} are direct bandgap semiconductors with original optoelectronic and spin-valley properties. Here we report on spectrally sharp, spatially localized emission in monolayer MoSe{sub 2}. We find this quantum dot-like emission in samples exfoliated onto gold substrates and also suspended flakes. Spatial mapping shows a correlation between the location of emitters and the existence of wrinkles (strained regions) in the flake. We tune the emission properties in magnetic and electric fields applied perpendicular to the monolayer plane. We extract an exciton g-factor of the discrete emitters close to −4,more » as for 2D excitons in this material. In a charge tunable sample, we record discrete jumps on the meV scale as charges are added to the emitter when changing the applied voltage.« less

Designing multifunctional quantum dots for bioimaging, detection, and drug delivery

PubMed Central

Zrazhevskiy, Pavel; Sena, Mark; Gao, Xiaohu

2011-01-01

The emerging field of bionanotechnology aims at revolutionizing biomedical research and clinical practice via introduction of nanoparticle-based tools, expanding capabilities of existing investigative, diagnostic, and therapeutic techniques as well as creating novel instruments and approaches for addressing challenges faced by medicine. Quantum dots (QDs), semiconductor nanoparticles with unique photo-physical properties, have become one of the dominant classes of imaging probes as well as universal platforms for engineering of multifunctional nanodevices. Possessing versatile surface chemistry and superior optical features, QDs have found initial use in a variety of in vitro and in vivo applications. However, careful engineering of QD probes guided by application-specific design criteria is becoming increasingly important for successful transition of this technology from proof-of-concept studies towards real-life clinical applications. This review outlines the major design principles and criteria, from general ones to application-specific, governing the engineering of novel QD probes satisfying the increasing demands and requirements of nanomedicine and discusses the future directions of QD-focused bionanotechnology research (critical review, 201 references). PMID:20697629

Ultrafast Room-Temperature Single Photon Emission from Quantum Dots Coupled to Plasmonic Nanocavities.

PubMed

Hoang, Thang B; Akselrod, Gleb M; Mikkelsen, Maiken H

2016-01-13

Efficient and bright single photon sources at room temperature are critical components for quantum information systems such as quantum key distribution, quantum state teleportation, and quantum computation. However, the intrinsic radiative lifetime of quantum emitters is typically ∼10 ns, which severely limits the maximum single photon emission rate and thus entanglement rates. Here, we demonstrate the regime of ultrafast spontaneous emission (∼10 ps) from a single quantum emitter coupled to a plasmonic nanocavity at room temperature. The nanocavity integrated with a single colloidal semiconductor quantum dot produces a 540-fold decrease in the emission lifetime and a simultaneous 1900-fold increase in the total emission intensity. At the same time, the nanocavity acts as a highly efficient optical antenna directing the emission into a single lobe normal to the surface. This plasmonic platform is a versatile geometry into which a variety of other quantum emitters, such as crystal color centers, can be integrated for directional, room-temperature single photon emission rates exceeding 80 GHz.

One-step colloidal synthesis of biocompatible water-soluble ZnS quantum dot/chitosan nanoconjugates

NASA Astrophysics Data System (ADS)

Ramanery, Fábio P.; Mansur, Alexandra AP; Mansur, Herman S.

2013-12-01

Quantum dots (QDs) are luminescent semiconductor nanocrystals with great prospective for use in biomedical and environmental applications. Nonetheless, eliminating the potential cytotoxicity of the QDs made with heavy metals is still a challenge facing the research community. Thus, the aim of this work was to develop a novel facile route for synthesising biocompatible QDs employing carbohydrate ligands in aqueous colloidal chemistry with optical properties tuned by pH. The synthesis of ZnS QDs capped by chitosan was performed using a single-step aqueous colloidal process at room temperature. The nanobioconjugates were extensively characterised by several techniques, and the results demonstrated that the average size of ZnS nanocrystals and their fluorescent properties were influenced by the pH during the synthesis. Hence, novel 'cadmium-free' biofunctionalised systems based on ZnS QDs capped by chitosan were successfully developed exhibiting luminescent activity that may be used in a large number of possible applications, such as probes in biology, medicine and pharmacy.

Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Gong, Jianxiao; Steinsultz, Nat; Ouyang, Min

2016-06-01

The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters (including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring the underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. This study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen-vacancy centres that use these freestanding hybrid nanostructures as building blocks.

Studies on the interaction between 7-(dimethyl amino)-4-(trifluoromethyl)-2H-1-benzopyran-2-one and cadmium sulfide quantum dots

NASA Astrophysics Data System (ADS)

Kuriakose, Alina C.; Pradeep, C.; Nampoori, V. P. N.; Thomas, Sheenu

2018-04-01

Quantum dots (QDs) are well known for their optical properties which differ from those of bulk semiconductors. Herein, we have created an energy transfer platform that combines CdS QDs with a coumarin based dye C485 [7-(dimethyl amino)-4-(trifluoromethyl)-2H-1-benzopyran-2-one]. Spectroscopic studies of energy transfer between the dye donor and CdS QDs as acceptors reveal the occurrence of dynamic quenching. Analysis of the steady-state and time resolved fluorescence measurements of C485 in the presence of CdS QDs infers fluorescence resonance (Förster type) energy transfer (FRET) as responsible for the quenching phenomena. The energy transfer efficiency as well as energy transfer distance for the donor-acceptor pair is calculated using steady-state fluorescence method. Luminescence enhancement of CdS QDs play a critical role in device performance for solar applications and also in the field of biological applications.

Image simulations of quantum dots.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lang, C.; Liao, Xiaozhou; Cockayne, D. J.

2001-01-01

Quantum dot (QD) nanostructures have drawn increased interest in recent years. Their small size leads to quantum confinement of the electrons, which is responsible for their unique electronic and optical properties. They promise to find use in a wide range of devices ranging from semiconductor lasers (Bimberg et al (2001), Ribbat et al (2001)) to quantum computing. The properties of QDs are also determined by their shape and composition. All three parameters (size, shape and composition) have a significant impact on their contrast in the transmission electron microscope (TEM), and consequently the possibility arises that these parameters can be extractedmore » from the images. Zone axis plan view images are especially sensitive to the composition of QDs, and image simulation is an important way to understand how the composition determines the contrast. This paper outlines a method of image simulation of QDs developed by Liao et. al. (1999) and presents an application of the method to QDs in wurtzite InN/GaN.« less

Synthesis and exploitation of InP/ZnS quantum dots for bioimaging

NASA Astrophysics Data System (ADS)

Massadeh, Salam; Xu, Shu; Nann, Thomas

2009-02-01

Nano- and cytotoxicity becomes increasingly more important with an increasing number of potential bio-medical applications for semiconductor Quantum Dots (QDs). Therefore, the frequently used CdSe-based QDs are unsuitable per-se, since cadmium is a highly toxic heavy metal and may leach out of QDs. Cadmium-free QDs have not been available for a long time, because the synthesis of e.g. monodisperes and highly crystalline InP QDs caused many problems. We report on the synthesis of InP/ZnS QDs with optical properties similar to those displayed by typical CdSe/ZnS QDs. A major break-through has been reached by addition of zinc ions into the reaction mixture. Furthermore, the transfer of the InP/ZnS QDs to water and their exploitation for bioanalytical applications are reported. It is shown that InP/ZnS QDs can be used to replace CdSe-based ones for almost any bio-medical application.

Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor.

PubMed

Saha, Avijit; Shetty, Amitha; Pavan, A R; Chattopadhyay, Soma; Shibata, Tomohiro; Viswanatha, Ranjani

2016-07-07

Effective manipulation of magnetic spin within a semiconductor leading to a search for ferromagnets with semiconducting properties has evolved into an important field of dilute magnetic semiconductors (DMS). Although a lot of research is focused on understanding the still controversial origin of magnetism, efforts are also underway to develop new materials with higher magnetic temperatures for spintronics applications. However, so far, efforts toward quantum-dots(QDs)-based DMS materials are plagued with problems of phase separation, leading to nonuniform distribution of dopant ions. In this work, we have developed a strategy to synthesize highly crystalline, single-domain DMS system starting from a small magnetic core and allowing it to diffuse uniformly inside a thick CdS semiconductor matrix and achieve DMS QDs. X-ray absorption fine structure (XAFS) spectroscopy and energy-dispersive X-ray spectroscopy-scanning transmission electron microscopy (STEM-EDX) indicates the homogeneous distribution of magnetic impurities inside the semiconductor QDs leading to superior magnetic property. Further, the versatility of this technique was demonstrated by obtaining ultra large particles (∼60 nm) with uniform doping concentration as well as demonstrating the high quality magnetic response.

Silicon Quantum Dots with Counted Antimony Donor Implants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Meenakshi; Pacheco, Jose L.; Perry, Daniel Lee

2015-10-01

Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. A focused ion beam is used to implant close to quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of ions implanted can be counted to a precision of a single ion. Regular coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization, are observed in devices with counted implants.

The emission wavelength dependent photoluminescence lifetime of the N-doped graphene quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Xingxia; School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210; University of Chinese Academy of Sciences, Beijing 100049

2015-12-14

Aromatic nitrogen doped graphene quantum dots were investigated by steady-state and time-resolved photoluminescence (PL) techniques. The PL lifetime was found to be dependent on the emission wavelength and coincident with the PL spectrum, which is different from most semiconductor quantum dots and fluorescent dyes. This result shows the synergy and competition between the quantum confinement effect and edge functional groups, which may have the potential to guide the synthesis and expand the applications of graphene quantum dots.

Quantum theory of the electronic and optical properties of low-dimensional semiconductor systems

NASA Astrophysics Data System (ADS)

Lau, Wayne Heung

This thesis examines the electronic and optical properties of low-dimensional semiconductor systems. A theory is developed to study the electron-hole generation-recombination process of type-II semimetallic semiconductor heterojunctions based on a 3 x 3 k·p matrix Hamiltonian (three-band model) and an 8 x 8 k·p matrix Hamiltonian (eight-band model). A novel electron-hole generation and recombination process, which is called activationless generation-recombination process, is predicted. It is demonstrated that the current through the type-II semimetallic semiconductor heterojunctions is governed by the activationless electron-hole generation-recombination process at the heterointerfaces, and that the current-voltage characteristics are essentially linear. A qualitative agreement between theory and experiments is observed. The numerical results of the eight-band model are compared with those of the threeband model. Based on a lattice gas model, a theory is developed to study the influence of a random potential on the ionization equilibrium conditions for bound electron-hole pairs (excitons) in III--V semiconductor heterostructures. It is demonstrated that ionization equilibrium conditions for bound electron-hole pairs change drastically in the presence of strong disorder. It is predicted that strong disorder promotes dissociation of excitons in III--V semiconductor heterostructures. A theory of polariton (photon dressed by phonon) spontaneous emission in a III--V semiconductor doped with semiconductor quantum dots (QDs) or quantum wells (QWs) is developed. For the first time, superradiant and subradiant polariton spontaneous emission phenomena in a polariton-QD (QW) coupled system are predicted when the resonance energies of the two identical QDs (QWs) lie outside the polaritonic energy gap. It is also predicted that when the resonance energies of the two identical QDs (QWs) lie inside the polaritonic energy gap, spontaneous emission of polariton in the polariton-QD (QW) coupled system is inhibited and polariton bound states are formed within the polaritonic energy gap. A theory is also developed to study the polariton eigenenergy spectrum, polariton effective mass, and polariton spectral density of N identical semiconductor QDs (QWs) or a superlattice (SL) placed inside a III--V semiconductor. A polariton-impurity band lying within the polaritonic energy gap of the III--V semiconductor is predicted when the resonance energies of the QDs (QWs) lie inside the polaritonic energy gap. Hole-like polariton effective mass of the polariton-impurity band is predicted. It is also predicted that the spectral density of the polariton has a Lorentzian shape if the resonance energies of the QDs (QWs) lie outside the polaritonic gap.

Functionality of bismuth sulfide quantum dots/wires-glass nanocomposite as an optical current sensor with enhanced Verdet constant

NASA Astrophysics Data System (ADS)

Panmand, Rajendra P.; Kumar, Ganapathy; Mahajan, Satish M.; Kulkarni, Milind V.; Amalnerkar, D. P.; Kale, Bharat B.; Gosavi, Suresh. W.

2011-02-01

We report optical studies with magneto-optic properties of Bi2S3 quantum dot/wires-glass nanocomposite. The size of the Q-dot was observed to be in the range 3-15 nm along with 11 nm Q-wires. Optical study clearly demonstrated the size quantization effect with drastic band gap variation with size. Faraday rotation tests on the glass nanocomposites show variation in Verdet constant with Q-dot size. Bi2S3 Q-dot/wires glass nanocomposite demonstrated 190 times enhanced Verdet constant compared to the host glass. Prima facie observations exemplify the significant enhancement in Verdet constant of Q-dot glass nanocomposites and will have potential application in magneto-optical devices.

Shell Filling and Magnetic Anisotropy In A Few Hole Silicon Metal-Oxide-Semiconductor Quantum Dot

NASA Astrophysics Data System (ADS)

Hamilton, Alex; Li., R.; Liles, S. D.; Yang, C. H.; Hudson, F. E.; Veldhorst, M. E.; Dzurak, A. S.

There is growing interest in hole spin states in group IV materials for quantum information applications. The near-absence of nuclear spins in group IV crystals promises long spin coherence times, while the strong spin-orbit interaction of the hole states provides fast electrical spin manipulation methods. However, the level-mixing and magnetic field dependence of the p-orbital hole states is non-trivial in nanostructures, and is not as well understood as for electron systems. In this work, we study the hole states in a gate-defined silicon metal-oxide-semiconductor quantum dot. Using an adjacent charge sensor, we monitor quantum dot orbital level spacing down to the very last hole, and find the standard two-dimensional (2D) circular dot shell filling structure. We can change the shell filling sequence by applying an out-of-plane magnetic field. However, when the field is applied in-plane, the shell filling is not changed. This magnetic field anisotropy suggests that the confined hole states are Ising-like.

16th Russian Youth Conference on Physics of Semiconductors and Nanostructures, Opto- and Nanoelectronics

NASA Astrophysics Data System (ADS)

Suris, Robert A.; Vorobjev, Leonid E.; Firsov, Dmitry A.

2015-01-01

The 16th Russian Youth Conference on Physics of Semiconductors and Nanostructures, Opto- and Nanoelectronics was held on November 24 - 28 at St. Petersburg Polytechnic University. The program of the Conference included semiconductor technology, heterostructures with quantum wells and quantum dots, opto- and nanoelectronic devices, and new materials. A large number of participants with about 200 attendees from many regions of Russia provided a perfect platform for the valuable discussions between students and experienced scientists. The Conference included two invited talks given by a corresponding member of RAS P.S. Kopyev ("Nitrides: the 4th Nobel Prize on semiconductor heterostructures") and Dr. A.V. Ivanchik ("XXI century is the era of precision cosmology"). Students, graduate and postgraduate students presented their results on plenary and poster sessions. The total number of accepted papers published in Russian (the official conference language) was 92. Here we publish 18 of them in English. Like previous years, the participants were involved in the competition for the best report. Certificates and cash prizes were awarded to a number of participants for the presentations selected by the Program Committee. Two special E.F. Gross Prizes were given for the best presentations in semiconductor optics. Works with potential applications were recommended for participation in the following competition for support from the Russian Foundation for Assistance to Small Innovative Enterprises in Science and Technology. The Conference was supported by the Russian Foundation for Basic Research, the "Dynasty" foundation and the innovation company "ATC - Semiconductor Devices", St. Petersburg. The official Conference website is http://www.semicond.spbstu.ru/conf2014-eng.html

Intermediate-band photosensitive device with quantum dots having tunneling barrier embedded in organic matrix

DOEpatents

Forrest, Stephen R.

2008-08-19

A plurality of quantum dots each have a shell. The quantum dots are embedded in an organic matrix. At least the quantum dots and the organic matrix are photoconductive semiconductors. The shell of each quantum dot is arranged as a tunneling barrier to require a charge carrier (an electron or a hole) at a base of the tunneling barrier in the organic matrix to perform quantum mechanical tunneling to reach the respective quantum dot. A first quantum state in each quantum dot is between a lowest unoccupied molecular orbital (LUMO) and a highest occupied molecular orbital (HOMO) of the organic matrix. Wave functions of the first quantum state of the plurality of quantum dots may overlap to form an intermediate band.

Photoacoustic tomography guided diffuse optical tomography for small-animal model

NASA Astrophysics Data System (ADS)

Wang, Yihan; Gao, Feng; Wan, Wenbo; Zhang, Yan; Li, Jiao

2015-03-01

Diffuse optical tomography (DOT) is a biomedical imaging technology for noninvasive visualization of spatial variation about the optical properties of tissue, which can be applied to in vivo small-animal disease model. However, traditional DOT suffers low spatial resolution due to tissue scattering. To overcome this intrinsic shortcoming, multi-modal approaches that incorporate DOT with other imaging techniques have been intensively investigated, where a priori information provided by the other modalities is normally used to reasonably regularize the inverse problem of DOT. Nevertheless, these approaches usually consider the anatomical structure, which is different from the optical structure. Photoacoustic tomography (PAT) is an emerging imaging modality that is particularly useful for visualizing lightabsorbing structures embedded in soft tissue with higher spatial resolution compared with pure optical imaging. Thus, we present a PAT-guided DOT approach, to obtain the location a priori information of optical structure provided by PAT first, and then guide DOT to reconstruct the optical parameters quantitatively. The results of reconstruction of phantom experiments demonstrate that both quantification and spatial resolution of DOT could be highly improved by the regularization of feasible-region information provided by PAT.

Semiconductor Quantum Dots for Applications to Advanced Concepts for Solar Photon Conversion to Electricity and Solar Fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nozik, Arthur J; Beard, Matthew C

The challenge of photoconversion research is to produce photovoltaic electricity at costs much less than those based on fossil fuels. Novel photoactive semiconductors and molecules of various types and structures are discussed for this purpose.

Luminescent manganese-doped CsPbCl3 perovskite quantum dots

NASA Astrophysics Data System (ADS)

Lin, Chun Che; Xu, Kun Yuan; Wang, Da; Meijerink, Andries

2017-04-01

Nanocrystalline cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn2+ or Co2+. Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl4) to the QDs in toluene results in the formation of Mn‒doped CsPbCl3 QDs showing bright orange Mn2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn2+ emission, with all features of the CsPbCl3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs.

Luminescent manganese-doped CsPbCl3 perovskite quantum dots.

PubMed

Lin, Chun Che; Xu, Kun Yuan; Wang, Da; Meijerink, Andries

2017-04-12

Nanocrystalline cesium lead halide perovskites (CsPbX 3 , X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn 2+ or Co 2+ . Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl 4 ) to the QDs in toluene results in the formation of Mn‒doped CsPbCl 3 QDs showing bright orange Mn 2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn 2+ emission, with all features of the CsPbCl 3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn 2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs.

Optical fiber sensors based on nanostructured coatings fabricated by means of the layer-by-layer electrostatic self-assembly method

NASA Astrophysics Data System (ADS)

Arregui, Francisco J.; Matías, Ignacio R.; Claus, Richard O.

2007-07-01

The Layer-by-Layer Electrostatic Self-Assembly (ESA) method has been successfully used for the design and fabrication of nanostructured materials. More specifically, this technique has been applied for the deposition of thin films on optical fibers with the purpose of fabricating different types of optical fiber sensors. In fact, optical fiber sensors for measuring humidity, temperature, pH, hydrogen peroxide, glucose, volatile organic compounds or even gluten have been already experimentally demonstrated. The versatility of this technique allows the deposition of these sensing coatings on flat substrates and complex geometries as well. For instance, nanoFabry-Perots and microgratings have been formed on cleaved ends of optical fibers (flat surfaces) and also sensing coatings have been built onto long period gratings (cylindrical shape), tapered fiber ends (conical shape), biconically tapered fibers or even the internal side of hollow core fibers. Among the different materials used for the construction of these sensing nanostructured coatings, diverse types such as polymers, inorganic semiconductors, colorimetric indicators, fluorescent dyes, quantum dots or even biological elements as enzymes can be found. This technique opens the door to the fabrication of new types of optical fiber sensors.

Basics for the preparation of quantum dots and their interactions with living cells.

PubMed

Jiang, Xiue; Bai, Jing; Wang, Tiantian

2014-01-01

A study of the interactions between nanoparticles and living cells is invaluable in understanding the nano-biological effect and the mechanism of cellular endocytosis. Here we describe two methods for the preparation of semiconductor quantum dots with different physiochemical properties. Furthermore, we describe how to study the interaction of the two quantum dots with living HeLa cells and red blood cells with confocal microscopy.

Enabling two-dimensional fourier transform electronic spectroscopy on quantum dots

NASA Astrophysics Data System (ADS)

Hill, Robert John, Jr.

Colloidal semiconductor nanocrystals exhibit unique properties not seen in their bulk counterparts. Quantum confinement of carriers causes a size-tunable bandgap, making them attractive candidates for solar cells. Fundamental understanding of their spectra and carrier dynamics is obscured by inhomogeneous broadening arising from the size distribution. Because quantum dots have long excited state lifetimes and are sensitive to both air and moisture, there are many potential artifacts in femtosecond experiments. Two-dimensional electronic spectroscopy promises insight into the photo-physics, but required key instrumental advances. Optics that can process a broad bandwidth without distortion are required for a two-dimensional optical spectrometer. To control pathlength differences for femtosecond time delays, hollow retro-reflectors are used on actively stabilized delay lines in interferometers. The fabrication of rigid, lightweight, precision hollow rooftop retroreflectors that allow beams to be stacked while preserving polarization is described. The rigidity and low mass enable active stabilization of an interferometer to within 0.6 nm rms displacement, while the return beam deviation is sufficient for Fourier transform spectroscopy with a frequency precision of better than 1 cm -1. Keeping samples oxygen and moisture free while providing fresh sample between laser shots is challenging in an interferometer. A low-vibration spinning sample cell was designed and built to keep samples oxygen free for days while allowing active stabilization of interferometer displacement to ˜1 nm. Combining these technologies has enabled 2D short-wave infrared spectroscopy on colloidal PbSe nanocrystals. 2D spectra demonstrate the advantages of this key instrumentation while providing valuable insight into the low-lying electronic states of colloidal quantum dots.

Growing High-Quality InAs Quantum Dots for Infrared Lasers

NASA Technical Reports Server (NTRS)

Qiu, Yueming; Uhl, David

2004-01-01

An improved method of growing high-quality InAs quantum dots embedded in lattice-matched InGaAs quantum wells on InP substrates has been developed. InAs/InGaAs/InP quantum dot semiconductor lasers fabricated by this method are capable of operating at room temperature at wavelengths greater than or equal to 1.8 mm. Previously, InAs quantum dot lasers based on InP substrates have been reported only at low temperature of 77 K at a wavelength of 1.9 micrometers. In the present method, as in the prior method, one utilizes metalorganic vapor phase epitaxy to grow the aforementioned semiconductor structures. The development of the present method was prompted in part by the observation that when InAs quantum dots are deposited on an InGaAs layer, some of the InAs in the InGaAs layer becomes segregated from the layer and contributes to the formation of the InAs quantum dots. As a result, the quantum dots become highly nonuniform; some even exceed a critical thickness, beyond which they relax. In the present method, one covers the InGaAs layer with a thin layer of GaAs before depositing the InAs quantum dots. The purpose and effect of this thin GaAs layer is to suppress the segregation of InAs from the InGaAs layer, thereby enabling the InAs quantum dots to become nearly uniform (see figure). Devices fabricated by this method have shown near-room-temperature performance.

Peptide-coated semiconductor quantum dots and their applications in biological imaging of single molecules in live cells and organisms

NASA Astrophysics Data System (ADS)

Pinaud, Fabien Florent

2007-12-01

A new surface chemistry has been developed for the solubilization and biofunctionalization of inorganic semiconductor nanocrystals fluorescent probes, also known as quantum dots. This chemistry is based on the surface coating of quantum dots with custom-designed polycysteine peptides and yields water-soluble, small, monodispersed and colloidally stable probes that remain bright and photostable in complex biological milieus. This peptide coating strategy was successfully tested on several types of core and core-shell quantum dots emitting from the visible (e.g. CdSe/ZnS) to the NIR spectrum range (e.g. CdTe/CdSe/ZnS). By taking advantage of the versatile physico-chemical properties of peptides, a peptide "toolkit" was designed and employed to impart several biological functions to individual quantum dots and control their biochemical activity at the nanometer scale. These biofunctionalized peptide-coated quantum dots were exploited in very diverse biological applications. Near-infrared emitting quantum dot probes were engineered with optimized blood circulation and biodistribution properties for in vivo animal imaging. Visible emitting quantum dots were used for single molecule tracking of raft-associated GPI-anchored proteins in live cells. This last application revealed the presence of discrete and non-caveolar lipid microdomains capable of impeding free lateral diffusions in the plasma membrane of Hela cells. Imaging and tracking of peptide-coated quantum dots provided the first direct evidence that microdomains having the composition and behavior expected for lipid rafts can induce molecular compartmentalization in the membrane of living cells.

Optical signatures of coupled quantum dots.

PubMed

Stinaff, E A; Scheibner, M; Bracker, A S; Ponomarev, I V; Korenev, V L; Ware, M E; Doty, M F; Reinecke, T L; Gammon, D

2006-02-03

An asymmetric pair of coupled InAs quantum dots is tuned into resonance by applying an electric field so that a single hole forms a coherent molecular wave function. The optical spectrum shows a rich pattern of level anticrossings and crossings that can be understood as a superposition of charge and spin configurations of the two dots. Coulomb interactions shift the molecular resonance of the optically excited state (charged exciton) with respect to the ground state (single charge), enabling light-induced coupling of the quantum dots. This result demonstrates the possibility of optically coupling quantum dots for application in quantum information processing.

Optical Signatures of Coupled Quantum Dots

NASA Astrophysics Data System (ADS)

Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Ponomarev, I. V.; Korenev, V. L.; Ware, M. E.; Doty, M. F.; Reinecke, T. L.; Gammon, D.

2006-02-01

An asymmetric pair of coupled InAs quantum dots is tuned into resonance by applying an electric field so that a single hole forms a coherent molecular wave function. The optical spectrum shows a rich pattern of level anticrossings and crossings that can be understood as a superposition of charge and spin configurations of the two dots. Coulomb interactions shift the molecular resonance of the optically excited state (charged exciton) with respect to the ground state (single charge), enabling light-induced coupling of the quantum dots. This result demonstrates the possibility of optically coupling quantum dots for application in quantum information processing.

Resonant electronic excitation energy transfer by exchange mechanism in the quantum dot system

NASA Astrophysics Data System (ADS)

Chikalova-Luzina, O. P.; Samosvat, D. M.; Vyatkin, V. M.; Zegrya, G. G.

2017-11-01

A microscopic theory of nonradiative resonance energy transfer between spherical A3B5 semiconductor quantum dots by the exchange mechanism is suggested. The interdot Coulomb interaction is taken into consideration. It is assumed that the quantum dot-donor and the quantum dot-acceptor are made from the same A3B5 compound and are embedded in the matrix of another material that produces potential barriers for electrons and holes. The dependences of the energy transfer rate on the quantum-dot system parameters are found in the frame of the Kane model that provides the most adequate description of the real spectra of A3B5 semiconductors. The analytical treatment is carried out with using the density matrix method, which enabled us to perform an energy transfer analysis both in the weak-interaction approximation and in the strong-interaction approximation. The numerical calculations showed the saturation of the energy transfer rate at the distances between the donor and the acceptor approaching the contact one. The contributions of the exchange and direct Coulomb intractions can be of the same order at the small distances and can have the same value in the saturation range.

Non-Poissonian photon statistics from macroscopic photon cutting materials.

PubMed

de Jong, Mathijs; Meijerink, Andries; Rabouw, Freddy T

2017-05-24

In optical materials energy is usually extracted only from the lowest excited state, resulting in fundamental energy-efficiency limits such as the Shockley-Queisser limit for single-junction solar cells. Photon-cutting materials provide a way around such limits by absorbing high-energy photons and 'cutting' them into multiple low-energy excitations that can subsequently be extracted. The occurrence of photon cutting or quantum cutting has been demonstrated in a variety of materials, including semiconductor quantum dots, lanthanides and organic dyes. Here we show that photon cutting results in bunched photon emission on the timescale of the excited-state lifetime, even when observing a macroscopic number of optical centres. Our theoretical derivation matches well with experimental data on NaLaF 4 :Pr 3+ , a material that can cut deep-ultraviolet photons into two visible photons. This signature of photon cutting can be used to identify and characterize new photon-cutting materials unambiguously.

Preparation and Characterization of InP/Poly(methyl methacrylate) Nanocomposite Films.

PubMed

Kwon, Younghoon; Kim, Jongsung

2017-04-01

Quantum dots (QDs) are nanocrystalline semiconductors with many unusual optical properties. They exhibit very high fluorescence intensities and possess exceptional stability against photo-bleaching. In this study, we report the preparation of InP QDs-poly(methyl methacrylate) (PMMA) hybrids by fabricating QDs via a thermal decomposition reaction, followed by radical polymerization. The InP QDs were synthesized using indium(III) chloride and tris(dimethylamino)phosphine. Flexible composite films were obtained by radical polymerization using methyl methacrylate (MMA) as the monomer and 2,2′-azobis(2-methylpropionitrile) (AIBN) as a radical initiator. The PL intensity of the QDs was lowered upon composite formation with PMMA. However, the composites exhibited higher thermal stability than pure PMMA.

Charge reconfiguration in arrays of quantum dots

NASA Astrophysics Data System (ADS)

Bayer, Johannes C.; Wagner, Timo; Rugeramigabo, Eddy P.; Haug, Rolf J.

2017-12-01

Semiconductor quantum dots are potential building blocks for scalable qubit architectures. Efficient control over the exchange interaction and the possibility of coherently manipulating electron states are essential ingredients towards this goal. We studied experimentally the shuttling of electrons trapped in serial quantum dot arrays isolated from the reservoirs. The isolation hereby enables a high degree of control over the tunnel couplings between the quantum dots, while electrons can be transferred through the array by gate voltage variations. Model calculations are compared with our experimental results for double, triple, and quadruple quantum dot arrays. We are able to identify all transitions observed in our experiments, including cotunneling transitions between distant quantum dots. The shuttling of individual electrons between quantum dots along chosen paths is demonstrated.

Quantum dot bioconjugates for ultrasensitive nonisotopic detection.

PubMed

Chan, W C; Nie, S

1998-09-25

Highly luminescent semiconductor quantum dots (zinc sulfide-capped cadmium selenide) have been covalently coupled to biomolecules for use in ultrasensitive biological detection. In comparison with organic dyes such as rhodamine, this class of luminescent labels is 20 times as bright, 100 times as stable against photobleaching, and one-third as wide in spectral linewidth. These nanometer-sized conjugates are water-soluble and biocompatible. Quantum dots that were labeled with the protein transferrin underwent receptor-mediated endocytosis in cultured HeLa cells, and those dots that were labeled with immunomolecules recognized specific antibodies or antigens.

Infrared Focal Plane Arrays Based on Semiconductor Quantum Dots

DTIC Science & Technology

2002-01-01

an ensemble of self -assembled InAs/GaAs or InAs/InP quantum dots (QDs) are typically in the range of 10-30 monolayers [1]. Here, we report on InAs...photoconductive properties of QDIPs based on self organized InAs quantum dots grown on In.52Al.48As/InP(100), using the MBE technique. Dr. Gendry grew the...composed of 10 layers of self assembled InAs dots, separated by 500 Å thick InAlAs (lattice matched to the semi-insulating InP substrate) barrier

Biocompatible Quantum Dots for Biological Applications

PubMed Central

Rosenthal, Sandra J.; Chang, Jerry C.; Kovtun, Oleg; McBride, James R.; Tomlinson, Ian D.

2011-01-01

Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, sizetunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots. PMID:21276935

Resonant Scattering of Surface Plasmon Polaritons by Dressed Quantum Dots

DTIC Science & Technology

2014-06-23

Resonant scattering of surface plasmon polaritons by dressed quantum dots Danhong Huang,1 Michelle Easter,2 Godfrey Gumbs,3 A. A. Maradudin,4 Shawn... polariton waves (SPP) by embedded semiconductor quantum dots above the dielectric/metal interface is explored in the strong-coupling regime. In con- trast to...induced polarization field, treated as a source term9 arising from photo-excited electrons, allows for a resonant scattering of surface plasmon- polariton

Double Quantum Dots in Carbon Nanotubes

DTIC Science & Technology

2010-06-02

occupation of one dot is favored by increasing the detuning between the dots, the Coulomb interaction causes strong correlation effects realized by...al- low the measurement and manipulation of the spin de - gree of freedom of the confined electrons1. Such con- trol is at the heart of semiconductor...of an additional val- ley degree of freedom, the two-electron eigenstates can be separated in an orbital part and a spin-valley part that are, to a

Semiconductor quantum dots as Förster resonance energy transfer donors for intracellularly-based biosensors

NASA Astrophysics Data System (ADS)

Field, Lauren D.; Walper, Scott A.; Susumu, Kimihiro; Oh, Eunkeu; Medintz, Igor L.; Delehanty, James B.

2017-02-01

Förster resonance energy transfer (FRET)-based assemblies currently comprise a significant portion of intracellularly based sensors. Although extremely useful, the fluorescent protein pairs typically utilized in such sensors are still plagued by many photophysical issues including significant direct acceptor excitation, small changes in FRET efficiency, and limited photostability. Luminescent semiconductor nanocrystals or quantum dots (QDs) are characterized by many unique optical properties including size-tunable photoluminescence, broad excitation profiles coupled to narrow emission profiles, and resistance to photobleaching, which can cumulatively overcome many of the issues associated with use of fluorescent protein FRET donors. Utilizing QDs for intracellular FRET-based sensing still requires significant development in many areas including materials optimization, bioconjugation, cellular delivery and assay design and implementation. We are currently developing several QD-based FRET sensors for various intracellular applications. These include sensors targeting intracellular proteolytic activity along with those based on theranostic nanodevices for monitoring drug release. The protease sensor is based on a unique design where an intracellularly expressed fluorescent acceptor protein substrate assembles onto a QD donor following microinjection, forming an active complex that can be monitored in live cells over time. In the theranostic configuration, the QD is conjugated to a carrier protein-drug analogue complex to visualize real-time intracellular release of the drug from its carrier in response to an external stimulus. The focus of this talk will be on the design, properties, photophysical characterization and cellular application of these sensor constructs.

Activation of molecular catalysts using semiconductor quantum dots

DOEpatents

Meyer, Thomas J [Chapel Hill, NC; Sykora, Milan [Los Alamos, NM; Klimov, Victor I [Los Alamos, NM

2011-10-04

Photocatalytic materials based on coupling of semiconductor nanocrystalline quantum dots (NQD) and molecular catalysts. These materials have capability to drive or catalyze non-spontaneous chemical reactions in the presence of visible radiation, ultraviolet radiation, or both. The NQD functions in these materials as a light absorber and charge generator. Following light absorption, the NQD activates a molecular catalyst adsorbed on the surface of the NQD via transfer of one or more charges (either electrons or electron-holes) from the NQD to the molecular catalyst. The activated molecular catalyst can then drive a chemical reaction. A photoelectrolytic device that includes such photocatalytic materials is also described.

Intrinsic errors in transporting a single-spin qubit through a double quantum dot

NASA Astrophysics Data System (ADS)

Li, Xiao; Barnes, Edwin; Kestner, J. P.; Das Sarma, S.

2017-07-01

Coherent spatial transport or shuttling of a single electron spin through semiconductor nanostructures is an important ingredient in many spintronic and quantum computing applications. In this work we analyze the possible errors in solid-state quantum computation due to leakage in transporting a single-spin qubit through a semiconductor double quantum dot. In particular, we consider three possible sources of leakage errors associated with such transport: finite ramping times, spin-dependent tunneling rates between quantum dots induced by finite spin-orbit couplings, and the presence of multiple valley states. In each case we present quantitative estimates of the leakage errors, and discuss how they can be minimized. The emphasis of this work is on how to deal with the errors intrinsic to the ideal semiconductor structure, such as leakage due to spin-orbit couplings, rather than on errors due to defects or noise sources. In particular, we show that in order to minimize leakage errors induced by spin-dependent tunnelings, it is necessary to apply pulses to perform certain carefully designed spin rotations. We further develop a formalism that allows one to systematically derive constraints on the pulse shapes and present a few examples to highlight the advantage of such an approach.

Facile synthesis of uniform large-sized InP nanocrystal quantum dots using tris(tert-butyldimethylsilyl)phosphine

PubMed Central

2012-01-01

Colloidal III-V semiconductor nanocrystal quantum dots [NQDs] have attracted interest because they have reduced toxicity compared with II-VI compounds. However, the study and application of III-V semiconductor nanocrystals are limited by difficulties in their synthesis. In particular, it is difficult to control nucleation because the molecular bonds in III-V semiconductors are highly covalent. A synthetic approach of InP NQDs was presented using newly synthesized organometallic phosphorus [P] precursors with different functional moieties while preserving the P-Si bond. Introducing bulky side chains in our study improved the stability while facilitating InP formation with strong confinement at a readily low temperature regime (210°C to 300°C). Further shell coating with ZnS resulted in highly luminescent core-shell materials. The design and synthesis of P precursors for high-quality InP NQDs were conducted for the first time, and we were able to control the nucleation by varying the reactivity of P precursors, therefore achieving uniform large-sized InP NQDs. This opens the way for the large-scale production of high-quality Cd-free nanocrystal quantum dots. PMID:22289352

Renormalization of optical transition strengths in semiconductor nanoparticles due to band mixing

DOE PAGES

Velizhanin, Kirill A.

2016-05-25

We report that unique optical properties of semiconductor nanoparticles (SN) make them very promising in the multitude of applications including lasing, light emission and photovoltaics. In many of these applications it is imperative to understand the physics of interaction of electrons in a SN with external electromagnetic fields on the quantitative level. In particular, the strength of electron–photon coupling determines such important SN parameters as the radiative lifetime and absorption cross section. This strength is often assumed to be fully encoded by the so called Kane momentum matrix element. This parameter, however, pertains to a bulk semiconductor material and, asmore » such, is not sensitive to the quantum confinement effects in SNs. In this work we demonstrate that the quantum confinement, via the so called band mixing, can result in a significant suppression of the strength of electron interaction with electromagnetic field. Within the envelope function formalism we show how this suppression can be described by introducing an effective energy-dependent Kane momentum. Then, the effect of band mixing on the efficiencies of various photoinduced processes can be fully captured by the conventional formulae (e.g., spontaneous emission rate), once the conventional Kane momentum is substituted with the renormalized energy-dependent Kane momentum introduced in here. Lastly, as an example, we evaluate the energy-dependent Kane momentum for spherical PbSe and PbS SNs (i.e., quantum dots) and show that neglecting band mixing in these systems can result in the overestimation of absorption cross sections and emission rates by a factor of ~2.« less

Assessment of Anisotropic Semiconductor Nanorod and Nanoplatelet Heterostructures with Polarized Emission for Liquid Crystal Display Technology.

PubMed

Cunningham, Patrick D; Souza, João B; Fedin, Igor; She, Chunxing; Lee, Byeongdu; Talapin, Dmitri V

2016-06-28

Semiconductor nanorods can emit linear-polarized light at efficiencies over 80%. Polarization of light in these systems, confirmed through single-rod spectroscopy, can be explained on the basis of the anisotropy of the transition dipole moment and dielectric confinement effects. Here we report emission polarization in macroscopic semiconductor-polymer composite films containing CdSe/CdS nanorods and colloidal CdSe nanoplatelets. Anisotropic nanocrystals dispersed in polymer films of poly butyl-co-isobutyl methacrylate (PBiBMA) can be stretched mechanically in order to obtain unidirectionally aligned arrays. A high degree of alignment, corresponding to an orientation factor of 0.87, was achieved and large areas demonstrated polarized emission, with the contrast ratio I∥/I⊥ = 5.6, making these films viable candidates for use in liquid crystal display (LCD) devices. To some surprise, we observed significant optical anisotropy and emission polarization for 2D CdSe nanoplatelets with the electronic structure of quantum wells. The aligned nanorod arrays serve as optical funnels, absorbing unpolarized light and re-emitting light from deep-green to red with quantum efficiencies over 90% and high degree of linear polarization. Our results conclusively demonstrate the benefits of anisotropic nanostructures for LCD backlighting. The polymer films with aligned CdSe/CdS dot-in-rod and rod-in-rod nanostructures show more than 2-fold enhancement of brightness compared to the emitter layers with randomly oriented nanostructures. This effect can be explained as the combination of linearly polarized luminescence and directional emission from individual nanostructures.

Low-power nanophotonics: material and device technology

NASA Astrophysics Data System (ADS)

Thylén, Lars; Holmstrom, Petter; Wosinski, Lech; Lourdudoss, Sebastian

2013-05-01

Development in photonics for communications and interconnects pose increasing requirements on reduction of footprint, power dissipation and cost, as well as increased bandwidth. Nanophotonics integrated photonics has been viewed as a solution to this, capitalizing on development in nanotechnology and an increased understanding of light matter interaction on the nanoscale. The latter can be exemplified by plasmonics and low dimensional semiconductors such as quantum dots (QDs). In this scenario the development of improved electrooptic materials is of great importance, the electrooptic polymers being an example, since they potentially offer superior properties for optical phase modulators in terms of power and integratability. Phase modulators are essential for e.g. the rapidly developing advanced modulation formats, since phase modulation basically can generate any type of modulation. The electrooptic polymers, in combination with plasmonics nanoparticle array waveguides or nanostructured hybrid plasmonic media can give extremely compact and low power dissipation modulators. Low-dimensional semiconductors, e.g. in the shape of QDs, can be employed for modulation or switching functions, offering possibilities for scaling to 2 or 3 dimensions for advanced switching functions. In both the high field confinement plasmonics and QDs, the nanosizing is due to nearfield interactions, albeit being of different physical origin in the two cases. Epitaxial integration of III-V structures on Si plays an important role in developing high-performance light sources on silicon, eventually integrated with silicon electronics. A brief remark on all-optical vs. electronically controlled optical switching systems is also given.

A SELDI-TOF approach to ecotoxicology: comparative profiling of low molecular weight proteins from a marine diatom exposed to CdSe/ZnS quantum dots.

PubMed

Scebba, Francesca; Tognotti, Danika; Presciuttini, Gianluca; Gabellieri, Edi; Cioni, Patrizia; Angeloni, Debora; Basso, Barbara; Morelli, Elisabetta

2016-01-01

Quantum dots (QDs), namely semiconductor nanocrystals, due to their particular optical and electronic properties, have growing applications in device technology, biotechnology and biomedical fields. Nevertheless, the possible threat to human health and the environment have attracted increasing attention as the production and applications of QDs increases rapidly while standard evaluation of safety lags. In the present study we performed proteomic analyses, by means of 2D gel electrophoresis and Surface Enhanced Laser Desorption Ionization-Time of Flight-Mass Spectrometry (SELDI-TOF-MS). We aimed to identify potential biomarkers of exposure to CdSe/ZnS quantum dots. The marine diatom Phaeodactylum tricornutum exposed to 2.5nM QDs was used as a model system. Both 2DE and SELDI showed the presence of differentially expressed proteins. By Principal Component Analysis (PCA) we were able to show that the differentially expressed proteins can discriminate between exposed and not exposed cells. Furthermore, a protein profile specific for exposed cells was obtained by SELDI analysis. To our knowledge, this is the first example of the application of SELDI technology to the analysis of microorganisms used as biological sentinel model of marine environmental pollution. Copyright © 2015 Elsevier Inc. All rights reserved.

Synthetic Developments of Nontoxic Quantum Dots.

PubMed

Das, Adita; Snee, Preston T

2016-03-03

Semiconductor nanocrystals, or quantum dots (QDs), are candidates for biological sensing, photovoltaics, and catalysis due to their unique photophysical properties. The most studied QDs are composed of heavy metals like cadmium and lead. However, this engenders concerns over heavy metal toxicity. To address this issue, numerous studies have explored the development of nontoxic (or more accurately less toxic) quantum dots. In this Review, we select three major classes of nontoxic quantum dots composed of carbon, silicon and Group I-III-VI elements and discuss the myriad of synthetic strategies and surface modification methods to synthesize quantum dots composed of these material systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Current Application of Quantum Dots (QD) in Cancer Therapy: A Review.

PubMed

Babu, Lavanya Thilak; Paira, Priyankar

2017-01-01

Semiconductor quantum dots proved themselves as efficient fluorescent probes in cancer detection and treatment. Their size, high stability, non-photobleaching and water solubility made them a unique fluorophore in place of conventional organic dyes. Newly emerged theranostic drug delivery system using quantum dots helped us in better understanding of the drug delivery mechanism inside the cells. Surface modified Quantum dots and their applications became wide in bioimaging, immunohistochemistry, tracking intracellular drug and intracellular molecules target. We have highlighted various applications of quantum dots in cancer treatment, drug delivery, flow cytometry, and theranostics. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Anisotropic exchange interaction induced by a single photon in semiconductor microcavities

NASA Astrophysics Data System (ADS)

Chiappe, G.; Fernández-Rossier, J.; Louis, E.; Anda, E. V.

2005-12-01

We investigate coupling of localized spins in a semiconductor quantum dot embedded in a microcavity. The lowest cavity mode and the quantum dot exciton are coupled and close in energy, forming a polariton. The fermions forming the exciton interact with localized spins via exchange. Exact diagonalization of a Hamiltonian in which photons, spins, and excitons are treated quantum mechanically shows that a single polariton induces a sizable indirect anisotropic exchange interaction between spins. At sufficiently low temperatures strong ferromagnetic correlations show up without an appreciable increase in exciton population. In the case of a (Cd,Mn)Te quantum dot, Mn-Mn ferromagnetic coupling is still significant at 1 K : spin-spin correlation around 3 for exciton occupation smaller than 0.3. We find that the interaction mediated by photon-polaritons is 10 times stronger than the one induced by a classical field for equal Rabi splitting.

Multi-modal diffuse optical techniques for breast cancer neoadjuvant chemotherapy monitoring (Conference Presentation)

NASA Astrophysics Data System (ADS)

Cochran, Jeffrey M.; Busch, David R.; Ban, Han Y.; Kavuri, Venkaiah C.; Schweiger, Martin J.; Arridge, Simon R.; Yodh, Arjun G.

2017-02-01

We present high spatial density, multi-modal, parallel-plate Diffuse Optical Tomography (DOT) imaging systems for the purpose of breast tumor detection. One hybrid instrument provides time domain (TD) and continuous wave (CW) DOT at 64 source fiber positions. The TD diffuse optical spectroscopy with PMT- detection produces low-resolution images of absolute tissue scattering and absorption while the spatially dense array of CCD-coupled detector fibers (108 detectors) provides higher-resolution CW images of relative tissue optical properties. Reconstruction of the tissue optical properties, along with total hemoglobin concentration and tissue oxygen saturation, is performed using the TOAST software suite. Comparison of the spatially-dense DOT images and MR images allows for a robust validation of DOT against an accepted clinical modality. Additionally, the structural information from co-registered MR images is used as a spatial prior to improve the quality of the functional optical images and provide more accurate quantification of the optical and hemodynamic properties of tumors. We also present an optical-only imaging system that provides frequency domain (FD) DOT at 209 source positions with full CCD detection and incorporates optical fringe projection profilometry to determine the breast boundary. This profilometry serves as a spatial constraint, improving the quality of the DOT reconstructions while retaining the benefits of an optical-only device. We present initial images from both human subjects and phantoms to display the utility of high spatial density data and multi-modal information in DOT reconstruction with the two systems.

Evaluating charge noise acting on semiconductor quantum dots in the circuit quantum electrodynamics architecture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basset, J.; Stockklauser, A.; Jarausch, D.-D.

2014-08-11

We evaluate the charge noise acting on a GaAs/GaAlAs based semiconductor double quantum dot dipole-coupled to the voltage oscillations of a superconducting transmission line resonator. The in-phase (I) and the quadrature (Q) components of the microwave tone transmitted through the resonator are sensitive to charging events in the surrounding environment of the double dot with an optimum sensitivity of 8.5×10{sup −5} e/√(Hz). A low frequency 1/f type noise spectrum combined with a white noise level of 6.6×10{sup −6} e{sup 2}/Hz above 1 Hz is extracted, consistent with previous results obtained with quantum point contact charge detectors on similar heterostructures. The slope ofmore » the 1/f noise allows to extract a lower bound for the double-dot charge qubit dephasing rate which we compare to the one extracted from a Jaynes-Cummings Hamiltonian approach. The two rates are found to be similar emphasizing that charge noise is the main source of dephasing in our system.« less

Controlled Quantum Operations of a Semiconductor Three-Qubit System

NASA Astrophysics Data System (ADS)

Li, Hai-Ou; Cao, Gang; Yu, Guo-Dong; Xiao, Ming; Guo, Guang-Can; Jiang, Hong-Wen; Guo, Guo-Ping

2018-02-01

In a specially designed semiconductor device consisting of three capacitively coupled double quantum dots, we achieve strong and tunable coupling between a target qubit and two control qubits. We demonstrate how to completely switch on and off the target qubit's coherent rotations by presetting two control qubits' states. A Toffoli gate is, therefore, possible based on these control effects. This research paves a way for realizing full quantum-logic operations in semiconductor multiqubit systems.

Los Alamos Quantum Dots for Solar, Display Technology

ScienceCinema

Klimov, Victor

2018-05-01

Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of e-readers and video monitors.

Exploring ultrafast dynamics of excitons and multiexcitons in "giant" nanocrystal quantum dots

NASA Astrophysics Data System (ADS)

Sampat, Siddharth

In this work, we have performed extensive time resolved photoluminescence (PL) studies to further the understanding of charge dynamics in semiconductor nanocrystal quantum dots (QDs). Recent developments in QD synthesis have introduced a new set of QD known as "giant" quantum dots (gQDs) that consist of a CdSe core coated with up to 19 monolayers of a CdS shell. The thick shell layer is grown using a SILAR method resulting in a defect free, alloyed CdSe/CdS interface. This has been attributed to gQDs exhibiting excellent optical properties such as high excitonic quantum yield (QY), prolonged photostability and inhibition of flourescence intermittency ("blinking"), which is regularly observed in conventional QDs. In gQDs, however, owing to unique fabrication methods and material selection, the Auger process is strongly suppressed resulting in efficient radiative recombination of photogenerated excitons as well as high PL QY of charged excitonic and multiexcitonic species. We perform extensive single gQDs studies that establish the role played by gQD shell thickness and core size in governing their optical properties. It is found that both the core and shell dimensions can be tuned in order to achieve the smallest gQDs with the highest vii Auger suppression resulting in photostable dots with high QYs. Next, we perform a study of multiexcitonic species in gQDs that are encapsulated in an insulating SiO2shell. These silica-coated gQDs exhibit strong PL from charged excitons, biexcitons as well as triexcitons. This observation has led to an accurate description of excitonic and multiexcitonic behavior which is modeled using a statistical scaling approach. As a demonstration of the practical applicability of gQDs, energy transfer of excitons as well as multiexcitons to different substrates is studied. Finally, a back gated silicon nanomembrane FET device is discussed that exhibits a large photocurrent increase when sensitized with QDs.

Theory and modelling of light-matter interactions in photonic crystal cavity systems coupled to quantum dot ensembles

NASA Astrophysics Data System (ADS)

Cartar, William K.

Photonic crystal microcavity quantum dot lasers show promise as high quality-factor, low threshold lasers, that can be integrated on-chip, with tunable room temperature opera- tions. However, such semiconductor microcavity lasers are notoriously difficult to model in a self-consistent way and are primarily modelled by simplified rate equation approxima- tions, typically fit to experimental data, which limits investigations of their optimization and fundamental light-matter interaction processes. Moreover, simple cavity mode optical theory and rate equations have recently been shown to fail in explaining lasing threshold trends in triangular lattice photonic crystal cavities as a function of cavity size, and the potential impact of fabrication disorder is not well understood. In this thesis, we develop a simple but powerful numerical scheme for modelling the quantum dot active layer used for lasing in these photonic crystal cavity structures, as an ensemble of randomly posi- tioned artificial two-level atoms. Each two-level atom is defined by optical Bloch equations solved by a quantum master equation that includes phenomenological pure dephasing and an incoherent pump rate that effectively models a multi-level gain system. Light-matter in- teractions of both passive and lasing structures are analyzed using simulation defined tools and post-simulation Green function techniques. We implement an active layer ensemble of up to 24,000 statistically unique quantum dots in photonic crystal cavity simulations, using a self-consistent finite-difference time-domain method. This method has the distinct advantage of capturing effects such as dipole-dipole coupling and radiative decay, without the need for any phenomenological terms, since the time-domain solution self-consistently captures these effects. Our analysis demonstrates a powerful ability to connect with recent experimental trends, while remaining completely general in its set-up; for example, we do not invoke common approximations such as the rotating-wave or slowly-varying envelope approximations, and solve dynamics with zero a priori knowledge.

Quality factor of luminescent solar concentrators and practical concentration limits attainable with semiconductor quantum dots

DOE PAGES

Klimov, Victor I.; Baker, Thomas A.; Lim, Jaehoon; ...

2016-05-09

In this study, luminescent solar concentrators (LSCs) can be utilized as both large-area collectors of solar radiation supplementing traditional photovoltaic cells as well as semitransparent “solar windows” that provide a desired degree of shading and simultaneously serve as power-generation units. An important characteristic of an LSC is a concentration factor (C) that can be thought of as a coefficient of effective enlargement (or contraction) of the area of a solar cell when it is coupled to the LSC. Here we use analytical and numerical Monte Carlo modeling in addition to experimental studies of quantum-dot-based LSCs to analyze the factors thatmore » influence optical concentration in practical devices. Our theoretical model indicates that the maximum value of C achievable with a given fluorophore is directly linked to the LSC quality factor (Q LSC) defined as the ratio of absorption coefficients at the wavelengths of incident and reemitted light. In fact, we demonstrate that the ultimate concentration limit (C 0) realized in large-area devices scales linearly with the LSC quality factor and in the case of perfect emitters and devices without back reflectors is approximately equal to Q LSC. To test the predictions of this model, we conduct experimental studies of LSCs based on visible-light emitting II–VI core/shell quantum dots with two distinct LSC quality factors. We also investigate devices based on near-infrared emitting CuInSe xS 2–x quantum dots for which the large emission bandwidth allows us to assess the impact of varied Q LSC on the concentration factor by simply varying the detection wavelength. In all cases, we find an excellent agreement between the model and the experimental observations, suggesting that the developed formalism can be utilized for express evaluation of prospective LSC performance based on the optical spectra of LSC fluorophores, which should facilitate future efforts on the development of high-performance devices based on quantum dots as well as other types of emitters.« less

Quality factor of luminescent solar concentrators and practical concentration limits attainable with semiconductor quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klimov, Victor I.; Baker, Thomas A.; Lim, Jaehoon

In this study, luminescent solar concentrators (LSCs) can be utilized as both large-area collectors of solar radiation supplementing traditional photovoltaic cells as well as semitransparent “solar windows” that provide a desired degree of shading and simultaneously serve as power-generation units. An important characteristic of an LSC is a concentration factor (C) that can be thought of as a coefficient of effective enlargement (or contraction) of the area of a solar cell when it is coupled to the LSC. Here we use analytical and numerical Monte Carlo modeling in addition to experimental studies of quantum-dot-based LSCs to analyze the factors thatmore » influence optical concentration in practical devices. Our theoretical model indicates that the maximum value of C achievable with a given fluorophore is directly linked to the LSC quality factor (Q LSC) defined as the ratio of absorption coefficients at the wavelengths of incident and reemitted light. In fact, we demonstrate that the ultimate concentration limit (C 0) realized in large-area devices scales linearly with the LSC quality factor and in the case of perfect emitters and devices without back reflectors is approximately equal to Q LSC. To test the predictions of this model, we conduct experimental studies of LSCs based on visible-light emitting II–VI core/shell quantum dots with two distinct LSC quality factors. We also investigate devices based on near-infrared emitting CuInSe xS 2–x quantum dots for which the large emission bandwidth allows us to assess the impact of varied Q LSC on the concentration factor by simply varying the detection wavelength. In all cases, we find an excellent agreement between the model and the experimental observations, suggesting that the developed formalism can be utilized for express evaluation of prospective LSC performance based on the optical spectra of LSC fluorophores, which should facilitate future efforts on the development of high-performance devices based on quantum dots as well as other types of emitters.« less

Variable optical delay using population oscillation and four-wave-mixing in semiconductor optical amplifiers.

PubMed

Su, Hui; Kondratko, Piotr; Chuang, Shun L

2006-05-29

We investigate variable optical delay of a microwave modulated optical beam in semiconductor optical amplifier/absorber waveguides with population oscillation (PO) and nearly degenerate four-wave-mixing (NDFWM) effects. An optical delay variable between 0 and 160 ps with a 1.0 GHz bandwidth is achieved in an InGaAsP/InP semiconductor optical amplifier (SOA) and shown to be electrically and optically controllable. An analytical model of optical delay is developed and found to agree well with the experimental data. Based on this model, we obtain design criteria to optimize the delay-bandwidth product of the optical delay in semiconductor optical amplifiers and absorbers.

Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids.

PubMed

Talgorn, Elise; Gao, Yunan; Aerts, Michiel; Kunneman, Lucas T; Schins, Juleon M; Savenije, T J; van Huis, Marijn A; van der Zant, Herre S J; Houtepen, Arjan J; Siebbeles, Laurens D A

2011-09-25

Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots.

The impact of quantum dot filling on dual-band optical transitions via intermediate quantum states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Jiang, E-mail: jiang.wu@ucl.ac.uk; Passmore, Brandon; Manasreh, M. O.

2015-08-28

InAs/GaAs quantum dot infrared photodetectors with different doping levels were investigated to understand the effect of quantum dot filling on both intraband and interband optical transitions. The electron filling of self-assembled InAs quantum dots was varied by direct doping of quantum dots with different concentrations. Photoresponse in the near infrared and middle wavelength infrared spectral region was observed from samples with low quantum dot filling. Although undoped quantum dots were favored for interband transitions with the absence of a second optical excitation in the near infrared region, doped quantum dots were preferred to improve intraband transitions in the middle wavelengthmore » infrared region. As a result, partial filling of quantum dot was required, to the extent of maintaining a low dark current, to enhance the dual-band photoresponse through the confined electron states.« less

Visible light-sensitive APTES-bound ZnO nanowire toward a potent nanoinjector sensing biomolecules in a living cell

NASA Astrophysics Data System (ADS)

Lee, Jooran; Choi, Sunyoung; Bae, Seon Joo; Yoon, Seok Min; Choi, Joon Sig; Yoon, Minjoong

2013-10-01

Nanoscale cell injection techniques combined with nanoscopic photoluminescence (PL) spectroscopy have been important issues in high-resolution optical biosensing, gene and drug delivery and single-cell endoscopy for medical diagnostics and therapeutics. However, the current nanoinjectors remain limited for optical biosensing and communication at the subwavelength level, requiring an optical probe such as semiconductor quantum dots, separately. Here, we show that waveguided red emission is observed at the tip of a single visible light-sensitive APTES-modified ZnO nanowire (APTES-ZnO NW) and it exhibits great enhancement upon interaction with a complementary sequence-based double stranded (ds) DNA, whereas it is not significantly affected by non-complementary ds DNA. Further, the tip of a single APTES-ZnO NW can be inserted into the subcellular region of living HEK 293 cells without significant toxicity, and it can also detect the enhancement of the tip emission from subcellular regions with high spatial resolution. These results indicate that the single APTES-ZnO NW would be useful as a potent nanoinjector which can guide visible light into intracellular compartments of mammalian cells, and can also detect nanoscopic optical signal changes induced by interaction with the subcellular specific target biomolecules without separate optical probes.Nanoscale cell injection techniques combined with nanoscopic photoluminescence (PL) spectroscopy have been important issues in high-resolution optical biosensing, gene and drug delivery and single-cell endoscopy for medical diagnostics and therapeutics. However, the current nanoinjectors remain limited for optical biosensing and communication at the subwavelength level, requiring an optical probe such as semiconductor quantum dots, separately. Here, we show that waveguided red emission is observed at the tip of a single visible light-sensitive APTES-modified ZnO nanowire (APTES-ZnO NW) and it exhibits great enhancement upon interaction with a complementary sequence-based double stranded (ds) DNA, whereas it is not significantly affected by non-complementary ds DNA. Further, the tip of a single APTES-ZnO NW can be inserted into the subcellular region of living HEK 293 cells without significant toxicity, and it can also detect the enhancement of the tip emission from subcellular regions with high spatial resolution. These results indicate that the single APTES-ZnO NW would be useful as a potent nanoinjector which can guide visible light into intracellular compartments of mammalian cells, and can also detect nanoscopic optical signal changes induced by interaction with the subcellular specific target biomolecules without separate optical probes. Electronic supplementary information (ESI) available: Synthesis of APTES-modified ZnO nanowires, DNA functionalization and spectroscopic measurements with additional fluorescence image ad fluorescence decay times, cell culture, injection of a single nanowire into living cells, subcellular imaging and determination of cytotoxicity. See DOI: 10.1039/c3nr03042c

Fluorescent Quantum Dots for Biological Labeling

NASA Technical Reports Server (NTRS)

McDonald, Gene; Nadeau, Jay; Nealson, Kenneth; Storrie-Lomardi, Michael; Bhartia, Rohit

2003-01-01

Fluorescent semiconductor quantum dots that can serve as "on/off" labels for bacteria and other living cells are undergoing development. The "on/off" characterization of these quantum dots refers to the fact that, when properly designed and manufactured, they do not fluoresce until and unless they come into contact with viable cells of biological species that one seeks to detect. In comparison with prior fluorescence-based means of detecting biological species, fluorescent quantum dots show promise for greater speed, less complexity, greater sensitivity, and greater selectivity for species of interest. There are numerous potential applications in medicine, environmental monitoring, and detection of bioterrorism.

Feasibility of interstitial diffuse optical tomography using cylindrical diffusing fiber for prostate PDT

PubMed Central

Liang, Xing; Wang, Ken Kang-Hsin; Zhu, Timothy C.

2013-01-01

Interstitial diffuse optical tomography (DOT) has been used to characterize spatial distribution of optical properties for prostate photodynamic therapy (PDT) dosimetry. We have developed an interstitial DOT method using cylindrical diffuse fibers (CDFs) as light sources, so that the same light sources can be used for both DOT measurement and PDT treatment. In this novel interstitial CDF-DOT method, absolute light fluence per source strength (in unit of 1/cm2) is used to separate absorption and scattering coefficients. A mathematical phantom and a solid prostate phantom including anomalies with known optical properties were used, respectively, to test the feasibility of reconstructing optical properties using interstitial CDF-DOT. Three dimension spatial distributions of the optical properties were reconstructed for both scenarios. Our studies show that absorption coefficient can be reliably extrapolated while there are some cross talks between absorption and scattering properties. Even with the suboptimal reduced scattering coefficients, the reconstructed light fluence rate agreed with the measured values to within ±10%, thus the proposed CDF-DOT allows greatly improved light dosimetry calculation for interstitial PDT. PMID:23629149

Modification of quantum dots with nucleic acids

NASA Astrophysics Data System (ADS)

Kocherginskaya, P. B.; Romanova, A. V.; Prokhorenko, I. A.; Itkis, Daniil M.; Korshun, V. A.; Goodilin, Eugene A.; Tretyakov, Yuri D.

2011-12-01

The key principles and modern approaches to targeted modification of semiconductor colloidal nanoparticles, quantum dots, which exhibit unique photophysical properties and are a promising class of luminescent markers, are discussed. Attention is given to the preparation of their bioconjugates with nucleic acids, promising tools for biological microchips and resonance energy transfer sensors. The bibliography includes 80 references.

Theoretical optimization of multi-layer InAs/GaAs quantum dots subject to post-growth thermal annealing for tailoring the photoluminescence emission beyond 1.3 μm

NASA Astrophysics Data System (ADS)

Ghosh, K.; Naresh, Y.; Srichakradhar Reddy, N.

2012-07-01

In this paper, we present theoretical analysis and computation for tuning the ground state (GS) photoluminescence (PL) emission of InAs/GaAs quantum dots (QDs) at telecommunication window of 1.3-1.55 μm by optimizing its height and base dimensions through quantum mechanical concepts. For this purpose, numerical modelling is carried out to calculate the quantized energy states of finite dimensional QDs so as to obtain the GS PL emission at or beyond 1.3 μm. Here, we also explored strain field altering the QD size distribution in multilayer heterostructure along with the changes in the PL spectra, simulation on post growth thermal annealing process which blueshifts the operating wavelength away from the vicinity of 1.3 μm and improvement of optical properties by varying the thickness of GaAs spacing. The results are discussed in detail which will serve as an important information tool for device scientist fabricating high quality semiconductor quantum structures with reduced defects at telecommunication wavelengths.

Quantum dot-containing polymer particles with thermosensitive fluorescence.

PubMed

Generalova, Alla N; Oleinikov, Vladimir A; Sukhanova, Alyona; Artemyev, Mikhail V; Zubov, Vitaly P; Nabiev, Igor

2013-01-15

Composite polymer particles consisting of a solid poly(acrolein-co-styrene) core and a poly(N-vinylcaprolactam) (PVCL) polymer shell doped with CdSe/ZnS semiconductor quantum dots (QDs) were fabricated. The temperature response of the composite particles was observed as a decrease in their hydrodynamic diameter upon heating above the lower critical solution temperature of the thermosensitive PVCL polymer. Embedding QDs in the PVCL shell yields particles whose fluorescence is sensitive to temperature changes. This sensitivity was determined by the dependence of the QD fluorescence intensity on the distances between them in the PVCL shell, which reversibly change as a result of the temperature-driven conformational changes in the polymer. The QD-containing thermosensitive particles were assembled with protein molecules in such a way that they retained their thermosensitive properties, including the completely reversible temperature dependence of their fluorescence response. The composite particles developed can be used as local temperature sensors, as carriers for biomolecules, as well as in biosensing and various bioassays employing optical detection schemes. Copyright © 2012 Elsevier B.V. All rights reserved.

Non-blinking (Zn)CuInS/ZnS Quantum Dots Prepared by In Situ Interfacial Alloying Approach

PubMed Central

Zhang, Aidi; Dong, Chaoqing; Li, Liang; Yin, Jinjin; Liu, Heng; Huang, Xiangyi; Ren, Jicun

2015-01-01

Semiconductor quantum dots (QDs) are very important optical nanomaterials with a wide range of potential applications. However, blinking behavior of single QD is an intrinsic drawback for some biological and photoelectric applications based on single-particle emission. Herein we present a rational strategy for fabrication of non-blinking (Zn)CuInS/ZnS QDs in organic phase through in situ interfacial alloying approach. This new strategy includes three steps: synthesis of CuInS QDs, eliminating the interior traps of QDs by forming graded (Zn)CuInS alloyed QDs, modifying the surface traps of QDs by introducing ZnS shells onto (Zn)CuInS QDs using alkylthiols as sulfur source and surface ligands. The suppressed blinking mechanism was mainly attributed to modifying QDs traps from interior to exterior via a step-by-step modification. Non-blinking QDs show high quantum yield, symmetric emission spectra and excellent crystallinity, and will enable applications from biology to optoelectronics that were previously hindered by blinking behavior of traditional QDs. PMID:26458511

InP/ZnSe/ZnS core-multishell quantum dots for improved luminescence efficiency

NASA Astrophysics Data System (ADS)

Greco, Tonino; Ippen, Christian; Wedel, Armin

2012-04-01

Semiconductor quantum dots (QDs) exhibit unique optical properties like size-tunable emission color, narrow emission peak, and high luminescence efficiency. QDs are therefore investigated towards their application in light-emitting devices (QLEDs), solar cells, and for bio-imaging purposes. In most cases QDs made from cadmium compounds like CdS, CdSe or CdTe are studied because of their facile and reliable synthesis. However, due to the toxicity of Cd compounds and the corresponding regulation (e.g. RoHS directive in Europe) these materials are not feasible for customer applications. Indium phosphide is considered to be the most promising alternative because of the similar band gap (InP 1.35 eV, CdSe 1.73 eV). InP QDs do not yet reach the quality of CdSe QDs, especially in terms of photoluminescence quantum yield and peak width. Typically, QDs are coated with another semiconductor material of wider band gap, often ZnS, to passivate surface defects and thus improve luminescence efficiency. Concerning CdSe QDs, multishell coatings like CdSe/CdS/ZnS or CdSe/ZnSe/ZnS have been shown to be advantageous due to the improved compatibility of lattice constants. Here we present a method to improve the luminescence efficiency of InP QDs by coating a ZnSe/ZnS multishell instead of a ZnS single shell. ZnSe exhibits an intermediate lattice constant of 5.67 Å between those of InP (5.87 Å) and ZnS (5.41 Å) and thus acts as a wetting layer. As a result, InP/ZnSe/ZnS is introduced as a new core-shell quantum dot material which shows improved photoluminescence quantum yield (up to 75 %) compared to the conventional InP/ZnS system.

Temperature dependence of Coulomb oscillations in a few-layer two-dimensional WS2 quantum dot.

PubMed

Song, Xiang-Xiang; Zhang, Zhuo-Zhi; You, Jie; Liu, Di; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

2015-11-05

Standard semiconductor fabrication techniques are used to fabricate a quantum dot (QD) made of WS2, where Coulomb oscillations were found. The full-width-at-half-maximum of the Coulomb peaks increases linearly with temperature while the height of the peaks remains almost independent of temperature, which is consistent with standard semiconductor QD theory. Unlike graphene etched QDs, where Coulomb peaks belonging to the same QD can have different temperature dependences, these results indicate the absence of the disordered confining potential. This difference in the potential-forming mechanism between graphene etched QDs and WS2 QDs may be the reason for the larger potential fluctuation found in graphene QDs.

Temperature dependence of Coulomb oscillations in a few-layer two-dimensional WS2 quantum dot

PubMed Central

Song, Xiang-Xiang; Zhang, Zhuo-Zhi; You, Jie; Liu, Di; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

2015-01-01

Standard semiconductor fabrication techniques are used to fabricate a quantum dot (QD) made of WS2, where Coulomb oscillations were found. The full-width-at-half-maximum of the Coulomb peaks increases linearly with temperature while the height of the peaks remains almost independent of temperature, which is consistent with standard semiconductor QD theory. Unlike graphene etched QDs, where Coulomb peaks belonging to the same QD can have different temperature dependences, these results indicate the absence of the disordered confining potential. This difference in the potential-forming mechanism between graphene etched QDs and WS2 QDs may be the reason for the larger potential fluctuation found in graphene QDs. PMID:26538164

Self-assembled InAs/InP quantum dots and quantum dashes: Material structures and devices

NASA Astrophysics Data System (ADS)

Khan, Mohammed Zahed Mustafa; Ng, Tien Khee; Ooi, Boon S.

2014-11-01

The advances in lasers, electronic and photonic integrated circuits (EPIC), optical interconnects as well as the modulation techniques allow the present day society to embrace the convenience of broadband, high speed internet and mobile network connectivity. However, the steep increase in energy demand and bandwidth requirement calls for further innovation in ultra-compact EPIC technologies. In the optical domain, advancement in the laser technologies beyond the current quantum well (Qwell) based laser technologies are already taking place and presenting very promising results. Homogeneously grown quantum dot (Qdot) lasers and optical amplifiers, can serve in the future energy saving information and communication technologies (ICT) as the work-horse for transmitting and amplifying information through optical fiber. The encouraging results in the zero-dimensional (0D) structures emitting at 980 nm, in the form of vertical cavity surface emitting laser (VCSEL), are already operational at low threshold current density and capable of 40 Gbps error-free transmission at 108 fJ/bit. Subsequent achievements for lasers and amplifiers operating in the O-, C-, L-, U-bands, and beyond will eventually lay the foundation for green ICT. On the hand, the inhomogeneously grown quasi 0D quantum dash (Qdash) lasers are brilliant solutions for potential broadband connectivity in server farms or access network. A single broadband Qdash laser operating in the stimulated emission mode can replace tens of discrete narrow-band lasers in dense wavelength division multiplexing (DWDM) transmission thereby further saving energy, cost and footprint. We herein reviewed the1 progress of both Qdots and Qdash devices, based on the InAs/InGaAlAs/InP and InAs/InGaAsP/InP material systems, from the angles of growth and device performance. In particular, we discussed the progress in lasers, semiconductor optical amplifiers (SOA), mode locked lasers, and superluminescent diodes, which are the building blocks of EPIC and ICT. Alternatively, these optical sources are potential candidates for other multi-disciplinary field applications.

Interfacing a quantum dot with a spontaneous parametric down-conversion source

NASA Astrophysics Data System (ADS)

Huber, Tobias; Prilmüller, Maximilian; Sehner, Michael; Solomon, Glenn S.; Predojević, Ana; Weihs, Gregor

2017-09-01

Quantum networks require interfacing stationary and flying qubits. These flying qubits are usually nonclassical states of light. Here we consider two of the leading source technologies for nonclassical light, spontaneous parametric down-conversion and single semiconductor quantum dots. Down-conversion delivers high-grade entangled photon pairs, whereas quantum dots excel at producing single photons. We report on an experiment that joins these two technologies and investigates the conditions under which optimal interference between these dissimilar light sources may be achieved.

Semiconductor nanocrystal quantum dot synthesis approaches towards large-scale industrial production for energy applications

DOE PAGES

Hu, Michael Z.; Zhu, Ting

2015-12-04

This study reviews the experimental synthesis and engineering developments that focused on various green approaches and large-scale process production routes for quantum dots. Fundamental process engineering principles were illustrated. In relation to the small-scale hot injection method, our discussions focus on the non-injection route that could be scaled up with engineering stir-tank reactors. In addition, applications that demand to utilize quantum dots as "commodity" chemicals are discussed, including solar cells and solid-state lightings.

Functionalization of Semiconductor Nanomaterials for Optoelectronic Devices And Components

DTIC Science & Technology

2015-03-04

conversion efficiency of InAs quantum dot solar cell by using a single layer anatase TiO2 anti-reflection coating,” R. Vasan, Y. F. Makableh, J. C...dx.doi.org/10.1557//opl.2013.742 9. “The Optimization of InP/ZnS Core/Shell Nanocrystals and TiO2 Nanotubes for Quantum Dot Sensitized Solar Cells ...Quantum Dots Solar Cells Performance,” J. C. Sarker, Y. F. Makableh, R. Vasan, S. Lee, M. O. Manasreh, and M. Benamara, IEEE J. Photovoltaic. (submitted

Luminescence and transient lifetime studies for energy transfer of PbS QD films

NASA Astrophysics Data System (ADS)

Wang, Joanna S.; Ullrich, Bruno; Dass, Chandriker K.; Das, Anirban; Wai, Chien M.; Brown, Gail J.; Hendrickson, Joshua R.

2017-08-01

Quantum confined semiconductor materials in colloidal form have drawn great attention in scientific communities due to the size-tunability, which controls their optical properties. PbS quantum dots (QDs) are exciting candidates for quantum optics, particularly due to the control of the QD sizes during the synthetic process enabling the realization of precisely tunable emission properties in the near-infrared region. Differently sized pairs of PbS QDs were deposited onto glass substrates to form thin films using supercritical CO2 (sc-CO2) deposition and solvent deposition methods (SDM). The fluorescence and photoluminescence (PL) spectra obtained from these closely packed films prepared by the sc-CO2 method reveal effective Förster resonance energy transfer (FRET) between two different sized dots, while the films composed of three different QD sizes show an even more effective FRET from the smallest to the largest ones. Energy transfer can be observed more directly by temporally resolved PL decay of mixed dots. By means of transient lifetime measurements, a mixed PbS film with 3.1 and 4.7 nm QDs was studied for FRET by time correlated single photon counting. The PL peak of the 3.1 nm QDs is quenched with respect to the emission of the 4.7 nm QDs and decays faster, and the best fit for the lifetime (decay constant)-1 is a biexponential decay mode. The long wavelength decay (4.7 nm QDs) is best fit by a mono-exponential equation. More theoretical and experimental work is required for a thorough understanding of the radiative lifetimes of PbS QDs in mixed QD systems.

Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barettin, Daniele, E-mail: Daniele.Barettin@uniroma2.it; Auf der Maur, Matthias; De Angelis, Roberta

2015-03-07

We report on numerical simulations of InP surface lateral quantum-dot molecules on In{sub 0.48}Ga{sub 0.52 }P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateralmore » quantum-dot molecules. Continuum electromechanical, k{sup →}·p{sup →} bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.« less

Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

NASA Astrophysics Data System (ADS)

Barettin, Daniele; Auf der Maur, Matthias; De Angelis, Roberta; Prosposito, Paolo; Casalboni, Mauro; Pecchia, Alessandro

2015-03-01

We report on numerical simulations of InP surface lateral quantum-dot molecules on In0.48Ga0.52P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k →.p → bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.

Nuclear Spin Nanomagnet in an Optically Excited Quantum Dot

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2007-12-01

Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins—the nuclear spin nanomagnet.

Optical pumping of the electronic and nuclear spin of single charge-tunable quantum dots.

PubMed

Bracker, A S; Stinaff, E A; Gammon, D; Ware, M E; Tischler, J G; Shabaev, A; Efros, Al L; Park, D; Gershoni, D; Korenev, V L; Merkulov, I A

2005-02-04

We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the net charge from positive to neutral to negative with a charge-tunable heterostructure. Negative photoluminescence polarization memory is enhanced by optical pumping of ground state electron spins, which we prove with the first measurements of the Hanle effect on an individual quantum dot. We use the Overhauser effect in a high longitudinal magnetic field to demonstrate efficient optical pumping of nuclear spins for all three charge states of the quantum dot.

Optical Pumping of the Electronic and Nuclear Spin of Single Charge-Tunable Quantum Dots

NASA Astrophysics Data System (ADS)

Bracker, A. S.; Stinaff, E. A.; Gammon, D.; Ware, M. E.; Tischler, J. G.; Shabaev, A.; Efros, Al. L.; Park, D.; Gershoni, D.; Korenev, V. L.; Merkulov, I. A.

2005-02-01

We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the net charge from positive to neutral to negative with a charge-tunable heterostructure. Negative photoluminescence polarization memory is enhanced by optical pumping of ground state electron spins, which we prove with the first measurements of the Hanle effect on an individual quantum dot. We use the Overhauser effect in a high longitudinal magnetic field to demonstrate efficient optical pumping of nuclear spins for all three charge states of the quantum dot.

Nuclear spin nanomagnet in an optically excited quantum dot.

PubMed

Korenev, V L

2007-12-21

Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins-the nuclear spin nanomagnet.

Luminescent manganese-doped CsPbCl3 perovskite quantum dots

PubMed Central

Lin, Chun Che; Xu, Kun Yuan; Wang, Da; Meijerink, Andries

2017-01-01

Nanocrystalline cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn2+ or Co2+. Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl4) to the QDs in toluene results in the formation of Mn‒doped CsPbCl3 QDs showing bright orange Mn2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn2+ emission, with all features of the CsPbCl3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs. PMID:28401894

Terbium to Quantum Dot FRET Bioconjugates for Clinical Diagnostics: Influence of Human Plasma on Optical and Assembly Properties

PubMed Central

Morgner, Frank; Stufler, Stefan; Geißler, Daniel; Medintz, Igor L.; Algar, W. Russ; Susumu, Kimihiro; Stewart, Michael H.; Blanco-Canosa, Juan B.; Dawson, Philip E.; Hildebrandt, Niko

2011-01-01

Förster resonance energy transfer (FRET) from luminescent terbium complexes (LTC) as donors to semiconductor quantum dots (QDs) as acceptors allows extraordinary large FRET efficiencies due to the long Förster distances afforded. Moreover, time-gated detection permits an efficient suppression of autofluorescent background leading to sub-picomolar detection limits even within multiplexed detection formats. These characteristics make FRET-systems with LTC and QDs excellent candidates for clinical diagnostics. So far, such proofs of principle for highly sensitive multiplexed biosensing have only been performed under optimized buffer conditions and interactions between real-life clinical media such as human serum or plasma and LTC-QD-FRET-systems have not yet been taken into account. Here we present an extensive spectroscopic analysis of absorption, excitation and emission spectra along with the luminescence decay times of both the single components as well as the assembled FRET-systems in TRIS-buffer, TRIS-buffer with 2% bovine serum albumin, and fresh human plasma. Moreover, we evaluated homogeneous LTC-QD FRET assays in QD conjugates assembled with either the well-known, specific biotin-streptavidin biological interaction or, alternatively, the metal-affinity coordination of histidine to zinc. In the case of conjugates assembled with biotin-streptavidin no significant interference with the optical and binding properties occurs whereas the histidine-zinc system appears to be affected by human plasma. PMID:22163719

Aptasensor based optical detection of glycated albumin for diabetes mellitus diagnosis

NASA Astrophysics Data System (ADS)

Ghosh, Shreya; Datta, Debopam; Cheema, Mehar; Dutta, Mitra; Stroscio, Michael A.

2017-10-01

Glycated albumin (GA) has been reported as an important biomarker for diabetes mellitus. This study investigates an optical sensor comprised of deoxyribonucleic acid (DNA) aptamer, semiconductor quantum dot and gold (Au) nanoparticle for the detection of GA. The system functions as a ‘turn on’ sensor because an increase in photoluminescence intensity is observed upon the addition of GA to the sensor. This is possibly because of the structure of the DNA aptamer, which folds to form a large hairpin loop before the addition of the analyte and is assumed to open up after the addition of target to the sensor in order to bind to GA. This pushes the quantum dot and the Au nanoparticle away causing an increase in photoluminescence. A linear increase in photoluminescence intensity and quenching efficiency of the sensor is observed as the GA concentration is varied between 0-14 500 nM. Time based photoluminescence studies with the sensor show the decrease in binding rate of the aptamer to the target within a specific time period. The sensor was found to have a higher selectivity towards GA than other control proteins. Further investigation of this simple sensor with greater number of clinical samples can open up avenues for an efficient diagnosis and monitoring of diabetes mellitus when used in conjunction with the traditional method of glucose level monitoring.

Automated setup for spray assisted layer-by-layer deposition.

PubMed

Mundra, Paul; Otto, Tobias; Gaponik, Nikolai; Eychmüller, Alexander

2013-07-01

The design for a setup allowing the layer-by-layer (LbL) assembly of thin films consisting of various colloidal materials is presented. The proposed system utilizes the spray-assisted LbL approach and is capable of autonomously producing films. It provides advantages to existing LbL procedures in terms of process speed and applicability. The setup offers several features that are advantageous for routine operation like an actuated sample holder, stainless steel spraying nozzles, or an optical liquid detection system. The applicability is demonstrated by the preparation of films containing semiconductor nanoparticles, namely, CdSe∕CdS quantum dots and a polyelectolyte. The films of this type are of potential interest for applications in optoelectronic devices such as light-emitting diodes or solar cells.

Fiber-Coupled Cavity-QED Source of Identical Single Photons

NASA Astrophysics Data System (ADS)

Snijders, H.; Frey, J. A.; Norman, J.; Post, V. P.; Gossard, A. C.; Bowers, J. E.; van Exter, M. P.; Löffler, W.; Bouwmeester, D.

2018-03-01

We present a fully fiber-coupled source of high-fidelity single photons. An (In,Ga)As semiconductor quantum dot is embedded in an optical Fabry-Perot microcavity with a robust design and rigidly attached single-mode fibers, which enables through-fiber cross-polarized resonant laser excitation and photon extraction. Even without spectral filtering, we observe that the incident coherent light pulses are transformed into a stream of single photons with high purity (97%) and indistinguishability (90%), which is measured at an in-fiber brightness of 5% with an excellent cavity-mode-to-fiber coupling efficiency of 85%. Our results pave the way for fully fiber-integrated photonic quantum networks. Furthermore, our method is equally applicable to fiber-coupled solid-state cavity-QED-based photonic quantum gates.

Basic modelling of transport in 2D wave-mechanical nanodots and billiards with balanced gain and loss mediated by complex potentials

NASA Astrophysics Data System (ADS)

Berggren, Karl-Fredrik; Tellander, Felix; Yakimenko, Irina

2018-05-01

Non-Hermitian quantum mechanics with parity-time (PT) symmetry is presently gaining great interest, especially within the fields of photonics and optics. Here, we give a brief overview of low-dimensional semiconductor nanodevices using the example of a quantum dot with input and output leads, which are mimicked by imaginary potentials for gain and loss, and how wave functions, particle flow, coalescence of levels and associated breaking of PT symmetry may be analysed within such a framework. Special attention is given to the presence of exceptional points and symmetry breaking. Related features for musical string instruments and ‘wolf-notes’ are outlined briefly with suggestions for further experiments.

Single nickel-related defects in molecular-sized nanodiamonds for multicolor bioimaging: an ab initio study.

PubMed

Thiering, Gergő; Londero, Elisa; Gali, Adam

2014-10-21

Fluorescent nanodiamonds constitute an outstanding alternative to semiconductor quantum dots and dye molecules for in vivo biomarker applications, where the fluorescence comes from optically active point defects acting as color centers in the nanodiamonds. For practical purposes, these color centers should be photostable as a function of the laser power or the surface termination of nanodiamonds. Furthermore, they should exhibit a sharp and nearly temperature-independent zero-phonon line. In this study, we show by hybrid density functional theory calculations that nickel doped nanodiamonds exhibit the desired properties, thus opening the avenue to practical applications. In particular, harnessing the strong quantum confinement effect in molecule-sized nanodiamonds is very promising for achieving multicolor imaging by single nickel-related defects.

Single nickel-related defects in molecular-sized nanodiamonds for multicolor bioimaging: an ab initio study

NASA Astrophysics Data System (ADS)

Thiering, Gergő; Londero, Elisa; Gali, Adam

2014-09-01

Fluorescent nanodiamonds constitute an outstanding alternative to semiconductor quantum dots and dye molecules for in vivo biomarker applications, where the fluorescence comes from optically active point defects acting as color centers in the nanodiamonds. For practical purposes, these color centers should be photostable as a function of the laser power or the surface termination of nanodiamonds. Furthermore, they should exhibit a sharp and nearly temperature-independent zero-phonon line. In this study, we show by hybrid density functional theory calculations that nickel doped nanodiamonds exhibit the desired properties, thus opening the avenue to practical applications. In particular, harnessing the strong quantum confinement effect in molecule-sized nanodiamonds is very promising for achieving multicolor imaging by single nickel-related defects.

Optical intensity dynamics in a five-emitter semiconductor array laser

NASA Astrophysics Data System (ADS)

Williams, Matthew O.; Kutz, J. Nathan

2009-06-01

The intensity dynamics of a five-emitter laser array subject to a linearly decreasing injection current are examined numerically. We have matched the results of the numerical model to an experimental AlGaAs quantum-dot array laser and have achieved the same robust oscillatory power output with a nearly π phase shift between emitters that was observed in experiments. Due to the linearly decreasing injection current, the output power of the waveguide decreases as a function of waveguide number. For injection currents ranging from 380 to 500 mA, the oscillatory behavior persists with only a slight change in phase difference. However, the fundamental frequency of oscillation increases with injection current, and higher harmonics as well as some fine structures are produced.

Photovoltaic Performance of Inverted Polymer Solar Cells Using Hybrid Carbon Quantum Dots and Absorption Polymer Materials

NASA Astrophysics Data System (ADS)

Lim, Hwain; Lee, Kyu Seung; Liu, Yang; Kim, Hak Yong; Son, Dong Ick

2018-05-01

We report the synthesis and characterization of the carbon quantum dots (C-dots) easily obtained from citric acid and ethanediamine, and also investigated structural, optical and electrical properties. The C-dots have extraordinary optical and electrical features such as absorption of ultraviolet range and effective interface for charge separation and transport in active layer, which make them attractive materials for applications in photovoltaic devices (PV). The C-dots play important roles in charge extraction in the PV structures, they can be synthesized by a simple method and used to insert in active layer of polymer solar cells. In this study, we demonstrate that improve charge transport properties of inverted polymer solar cells (iPSCs) with C-dots and structural, optical and electrical properties of C-dots. As a result, iPSCs with C-dots showed enhancement of more than 30% compared with that of the contrast device in power conversion efficiency.

Spin fine structure of optically excited quantum dot molecules

NASA Astrophysics Data System (ADS)

Scheibner, M.; Doty, M. F.; Ponomarev, I. V.; Bracker, A. S.; Stinaff, E. A.; Korenev, V. L.; Reinecke, T. L.; Gammon, D.

2007-06-01

The interaction between spins in coupled quantum dots is revealed in distinct fine structure patterns in the measured optical spectra of InAs/GaAs double quantum dot molecules containing zero, one, or two excess holes. The fine structure is explained well in terms of a uniquely molecular interplay of spin-exchange interactions, Pauli exclusion, and orbital tunneling. This knowledge is critical for converting quantum dot molecule tunneling into a means of optically coupling not just orbitals but also spins.

Quantum Dots Microstructured Optical Fiber for X-Ray Detection

NASA Technical Reports Server (NTRS)

DeHaven, Stan; Williams, Phillip; Burke, Eric

2015-01-01

Microstructured optical fibers containing quantum dots scintillation material comprised of zinc sulfide nanocrystals doped with magnesium sulfide are presented. These quantum dots are applied inside the microstructured optical fibers using capillary action. The x-ray photon counts of these fibers are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The results of the fiber light output and associated effects of an acrylate coating and the quantum dot application technique are discussed.

Quantum dot properties in the multiband envelope-function approximation using boundary conditions based upon first-principles quantum calculations

NASA Astrophysics Data System (ADS)

Flory, Curt A.; Musgrave, Charles B.; Zhang, Zhiyong

2008-05-01

A number of physical processes involving quantum dots depend critically upon the “evanescent” electron eigenstate wave function that extends outside of the material surface into the surrounding region. These processes include electron tunneling through quantum dots, as well as interactions between multiple quantum dot structures. In order to unambiguously determine these evanescent fields, appropriate boundary conditions have been developed to connect the electronic solutions interior to the semiconductor quantum dot to exterior vacuum solutions. In standard envelope function theory, the interior wave function consists of products of band edge and envelope functions, and both must be considered when matching to the external solution. While the envelope functions satisfy tractable equations, the band edge functions are generally not known. In this work, symmetry arguments in the spherically symmetric approximation are used in conjunction with the known qualitative behavior of bonding and antibonding orbitals to catalog the behavior of the band edge functions at the unit cell boundary. This physical approximation allows consolidation of the influence of the band edge functions to two simple surface parameters that are incorporated into the boundary conditions and are straightforwardly computed by using numerical first-principles quantum techniques. These new boundary conditions are employed to analyze an isolated spherically symmetric semiconductor quantum dot in vacuum within the analytical model of Sercel and Vahala [Phys. Rev. Lett. 65, 239 (1990); Phys. Rev. B 42, 3690 (1990)]. Results are obtained for quantum dots made of GaAs and InP, which are compared with ab initio calculations that have appeared in the literature.

The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium Selenide crystals

PubMed Central

Mudd, G. W.; Molas, M. R.; Chen, X.; Zólyomi, V.; Nogajewski, K.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Yusa, G.; Makarovsky, O.; Eaves, L.; Potemski, M.; Fal’ko, V. I.; Patanè, A.

2016-01-01

The electronic band structure of van der Waals (vdW) layered crystals has properties that depend on the composition, thickness and stacking of the component layers. Here we use density functional theory and high field magneto-optics to investigate the metal chalcogenide InSe, a recent addition to the family of vdW layered crystals, which transforms from a direct to an indirect band gap semiconductor as the number of layers is reduced. We investigate this direct-to-indirect bandgap crossover, demonstrate a highly tuneable optical response from the near infrared to the visible spectrum with decreasing layer thickness down to 2 layers, and report quantum dot-like optical emissions distributed over a wide range of energy. Our analysis also indicates that electron and exciton effective masses are weakly dependent on the layer thickness and are significantly smaller than in other vdW crystals. These properties are unprecedented within the large family of vdW crystals and demonstrate the potential of InSe for electronic and photonic technologies. PMID:28008964

The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium Selenide crystals.

PubMed

Mudd, G W; Molas, M R; Chen, X; Zólyomi, V; Nogajewski, K; Kudrynskyi, Z R; Kovalyuk, Z D; Yusa, G; Makarovsky, O; Eaves, L; Potemski, M; Fal'ko, V I; Patanè, A

2016-12-23

The electronic band structure of van der Waals (vdW) layered crystals has properties that depend on the composition, thickness and stacking of the component layers. Here we use density functional theory and high field magneto-optics to investigate the metal chalcogenide InSe, a recent addition to the family of vdW layered crystals, which transforms from a direct to an indirect band gap semiconductor as the number of layers is reduced. We investigate this direct-to-indirect bandgap crossover, demonstrate a highly tuneable optical response from the near infrared to the visible spectrum with decreasing layer thickness down to 2 layers, and report quantum dot-like optical emissions distributed over a wide range of energy. Our analysis also indicates that electron and exciton effective masses are weakly dependent on the layer thickness and are significantly smaller than in other vdW crystals. These properties are unprecedented within the large family of vdW crystals and demonstrate the potential of InSe for electronic and photonic technologies.

Photon-assisted tunneling in an asymmetrically coupled triple quantum dot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Bao-Chuan; Cao, Gang, E-mail: gcao@ustc.edu.cn; Chen, Bao-Bao

The gate-defined quantum dot is regarded as one of the basic structures required for scalable semiconductor quantum processors. Here, we demonstrate a structure that contains three quantum dots scaled in series. The electron number of each dot and the tunnel coupling between them can be tuned conveniently using splitting gates. We tune the quantum dot array asymmetrically such that the tunnel coupling between the right dot and the central dot is much larger than that between the left dot and the central dot. When driven by microwaves, the sidebands of the photon-assisted tunneling process appear not only in the left-to-centralmore » dot transition region but also in the left-to-right dot transition region. These sidebands are both attributed to the left-to-central transition for asymmetric coupling. Our result shows that there is a region of a triple quantum dot structure that remains indistinct when studied with a normal two-dimensional charge stability diagram; this will be helpful in future studies of the scalability of quantum dot systems.« less

Integrated smartphone imaging of quantum dot photoluminescence and Förster resonance energy transfer

NASA Astrophysics Data System (ADS)

Petryayeva, Eleonora; Algar, W. Russ

2015-06-01

Smartphones and other mobile devices are emerging as promising analytical platforms for point-of-care diagnostics, particularly when combined with nanotechnology. For example, we have shown that the optical properties of semiconductor quantum dots (QDs) are well suited to photoluminescence (PL) detection with a smartphone camera. However, this previous work has utilized an external excitation source for interrogation of QD PL. In this proceeding, we demonstrate that the white-light LED photographic flashes built into smartphones can be optically filtered to yield blue light suitable for excitation of QD PL. Measurements were made by recording video with filtered flash illumination and averaging the frames of the video to obtain images with good signal-to-background ratios. These images permitted detection of green-emitting and red-emitting QDs at levels comparable to those possible with excitation using an external long-wave UV lamp. The optical properties of QDs proved to be uniquely suited to smartphone PL imaging, exhibiting emission that was 1-2 orders magnitude brighter than that of common fluorescent dyes under the same conditions. Excitation with the smartphone flash was also suitable for imaging of FRET between green-emitting QD donors and Alexa Fluor 555 (A555) fluorescent dye acceptors. No significant difference in FRET imaging capability was observed between excitation with the smartphone flash and a long-wave UV lamp. Although the smartphone flash did have some disadvantages compared to an external UV lamp, these disadvantages are potentially offset by the benefit of having excitation and detection integrated into the smartphone.

Quantifying the density of surface capping ligands on semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Zhan, Naiqian; Palui, Goutam; Merkl, Jan-Philip; Mattoussi, Hedi

2015-03-01

We have designed a new set of coordinating ligands made of a lipoic acid (LA) anchor and poly(ethylene glycol) (PEG) hydrophilic moiety appended with a terminal aldehyde for the surface functionalization of QDs. This ligand design was combined with a recently developed photoligation strategy to prepare hydrophilic CdSe-ZnS QDs with good control over the fraction of intact aldehyde (-CHO) groups per nanocrystal. We further applied the efficient hydrazone ligation to react aldehyde-QDs with 2-hydrazinopyridine (2-HP). This covalent modification produces QD-conjugates with a well-defined absorption feature at 350 nm ascribed to the hydrazone chromophore. We exploited this unique optical signature to accurately measure the number of aldehyde groups per QD when the fraction of LA-PEG-CHO per nanocrystal was varied. This allowed us to extract an estimate for the number of LA-PEG ligands per QD. These results suggest that hydrazone ligation has the potential to provide a simple and general analytical method to estimate the number of surface ligands for a variety of nanocrystals such as metal, metal oxide and semiconductor nanocrystals.

Nanometric summation architecture based on optical near-field interaction between quantum dots.

PubMed

Naruse, Makoto; Miyazaki, Tetsuya; Kubota, Fumito; Kawazoe, Tadashi; Kobayashi, Kiyoshi; Sangu, Suguru; Ohtsu, Motoichi

2005-01-15

A nanoscale data summation architecture is proposed and experimentally demonstrated based on the optical near-field interaction between quantum dots. Based on local electromagnetic interactions between a few nanometric elements via optical near fields, we can combine multiple excitations at a certain quantum dot, which allows construction of a summation architecture. Summation plays a key role for content-addressable memory, which is one of the most important functions in optical networks.

Solid-state-based analog of optomechanics

DOE PAGES

Naumann, Nicolas L.; Droenner, Leon; Carmele, Alexander; ...

2016-09-01

In this study, we investigate a semiconductor quantum dot as a microscopic analog of a basic optomechanical setup. We show that optomechanical features can be reproduced by the solid-state platform, arising from parallels of the underlying interaction processes, which in the optomechanical case is the radiation pressure coupling and in the semiconductor case the electron–phonon coupling. We discuss bistabilities, lasing, and phonon damping, and recover the same qualitative behaviors for the semiconductor and the optomechanical cases expected for low driving strengths. However, in contrast to the optomechanical case, distinct signatures of higher order processes arise in the semiconductor model.

Preface: phys. stat. sol. (c) 1/8

NASA Astrophysics Data System (ADS)

Amann, Markus C.

2004-07-01

In this special issue of physica status solidi (c) we have included 10 invited papers reviewing the current state-of-the-art and the progress achieved in materials science, semiconductor theory, novel physical mechanisms and advanced device concepts in the field of nanostructured electronic and optoelectronic semiconductor devices. All of these papers were written by previous members of the Collaborative Research Centre 348 Nanometer-Halbleiterbauelemente: Grundlagen - Konzepte - Realisierungen (Nanometer Semiconductor Devices: Fundamentals - Concepts - Realisations), which was funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) during the period from 1991 to 2003. In these twelve years, the researchers in this programme have carried an intense activity directed towards two main objectives. First of all, Fundamentals and Concepts of nanostructure devices and their technology were explored theoretically and experimentally including the effects of low-dimensional structures on carrier transport, optical properties and spin, as well as the enabling epitaxial and nanostructure technologies such as the cleaved-edge-overgrowth technique and the self-assembled growth of quantum dots. A second field of interest was focused towards the design and development of Novel Semiconductor Devices exploiting nanostructure technology. This comprises optical detectors and memories with nanometer lateral dimensions, microwave detectors and sources up to the 300 GHz regime, innovative tunable and surface-emitting semiconductor lasers for the wavelength range 0.9 to 2 m, and nitride-based resonant tunnelling diodes. Some of the device innovations have meanwhile become commercial products proving also the practical importance of this research area. The articles in this special issue relate to the projects of the last three-years' funding period from 2000 to 2003 and are organized along these two We would like to thank the numerous reviewers for their valuable comments and the editorial staff of physica status solidi (c) for their extremely helpful support. The funding by the German Research Foundation over the full project time and the continued monitoring and advice by its representatives Dr. Klaus Wehrberger and Dr. Peter Heil are gratefully acknowledged by all previous members and co-workers of this Collaborative Research Centre.

Resonance energy transfer improves the biological function of bacteriorhodopsin within a hybrid material built from purple membranes and semiconductor quantum dots.

PubMed

Rakovich, Aliaksandra; Sukhanova, Alyona; Bouchonville, Nicolas; Lukashev, Evgeniy; Oleinikov, Vladimir; Artemyev, Mikhail; Lesnyak, Vladimir; Gaponik, Nikolai; Molinari, Michael; Troyon, Michel; Rakovich, Yury P; Donegan, John F; Nabiev, Igor

2010-07-14

Purple membrane (PM) from bacteria Halobacterium salinarum contains a photochromic protein bacteriorhodopsin (bR) arranged in a 2D hexagonal nanocrystalline lattice (Figure 1 ). Absorption of light by the protein-bound chromophore retinal results in pumping the protons through the PM creating an electrochemical gradient which is then used by the ATPases to energize the cellular processes. Energy conversion, photochromism, and photoelectrism are the inherent effects which are employed in many bR technical applications. bR, along with the other photosensitive proteins, is not able to deal with the excess energy of photons in UV and blue spectral region and utilizes less than 0.5% of the energy from the available incident solar light for its biological function. Here, we proceed with optimization of bR functions through the engineering of a "nanoconverter" of solar energy based on semiconductor quantum dots (QDs) tagged with the PM. These nanoconverters are able to harvest light from deep-UV to the visible region and to transfer this additionally collected energy to bR via Förster resonance energy transfer (FRET). We show that specific nanobio-optical and spatial coupling of QDs (donor) and bR retinal (acceptor) provide a means to achieve FRET with efficiency approaching 100%. We have finally demonstrated that the integration of QDs within PM significantly increases the efficiency of light-driven transmembrane proton pumping, which is the main bR biological function. This new QD-PM hybrid material will have numerous optoelectronic, photonic, and photovoltaic applications based on its energy conversion, photochromism, and photoelectrism properties.

Characterization of the Structural and Optical Properties of III-V Semiconductor Materials for Solar Cell Applications

NASA Astrophysics Data System (ADS)

Xie, Hongen

The work contained in this dissertation is focused on the structural and optical properties of III-V semiconductor structures for solar cell applications. By using transmission electron microscopy, many of their structural properties have been investigated, including morphology, defects, and strain relaxation. The optical properties of the semiconductor structures have been studied by photoluminescence and cathodoluminescence. Part of this work is focused on InAs quantum dots (QDs) embedded in AlGaAs matrices. This QD system is important for the realization of intermediate-band solar cells, which has three light absorption paths for high efficiency photovoltaics. The suppression of plastic strain relaxation in the QDs shows a significant improvement of the optoelectronic properties. A partial capping followed by a thermal annealing step is used to achieve spool-shaped QDs with a uniform height following the thickness of the capping layer. This step keeps the height of the QDs below a critical value that is required for plastic relaxation. The spool-shaped QDs exhibit two photoluminescence peaks that are attributed to ground and excited state transitions. The luminescence peak width is associated with the QD diameter distribution. An InAs cover layer formed during annealing is found responsible for the loss of the confinement of the excited states in smaller QDs. The second part of this work is focused on the investigation of the In xGa1-xN thin films having different bandgaps for double-junction solar cells. InxGa1-xN films with x ≤ 0.15 were grown by metal organic chemical vapor deposition. The defects in films with different indium contents have been studied. Their effect on the optical properties of the film have been investigated by cathodoluminescence. InxGa 1-xN films with indium contents higher than 20% were grown by molecular beam epitaxy. The strain relaxation in the films has been measured from electron diffraction patterns taken in cross-sectional TEM specimens. Moire fringes in some of the films reveal interfacial strain relaxation that is explained by a critical thickness model.

Strain-induced vertical self-organization of semiconductor quantum dots: A computational study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shtinkov, N., E-mail: nshtinkov@uottawa.ca

Atomistic strain simulations based on the valence force field method are employed to study the vertical arrangements of semiconductor quantum dot (QD) multilayers. The effects of the QD shape, dimensions, and materials parameters are systematically investigated, varying independently the following parameters: spacer width H, QD lateral spacing D, base b, and height h, slope of the side facets, elastic properties of the dot and the substrate materials, and lattice mismatch between the dot and the substrate. The transition between vertically aligned and anti-aligned structures is found to be determined mainly by the ratios H/D and b/D, as well as bymore » the strain anisotropy of the substrate and to a lesser extent of the QD. The dependence on the QD height h is significant only for steep side facets and large aspect ratios h/b, and the effects of the lattice mismatch strain and the bulk elastic moduli are found to be negligible. The comparison with experimental data shows an excellent agreement with the results from the simulations, demonstrating that the presented analysis results in precise theoretical predictions for the vertical self-organization regime in a wide range of QD materials systems.« less

Competing interactions in semiconductor quantum dots

DOE PAGES

van den Berg, R.; Brandino, G. P.; El Araby, O.; ...

2014-10-14

In this study, we introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions atmore » longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.« less

Electric-field-controlled ferromagnetism in high-Curie-temperature Mn0.05Ge0.95 quantum dots.

PubMed

Xiu, Faxian; Wang, Yong; Kim, Jiyoung; Hong, Augustin; Tang, Jianshi; Jacob, Ajey P; Zou, Jin; Wang, Kang L

2010-04-01

Electric-field manipulation of ferromagnetism has the potential for developing a new generation of electric devices to resolve the power consumption and variability issues in today's microelectronics industry. Among various dilute magnetic semiconductors (DMSs), group IV elements such as Si and Ge are the ideal material candidates because of their excellent compatibility with the conventional complementary metal-oxide-semiconductor (MOS) technology. Here we report, for the first time, the successful synthesis of self-assembled dilute magnetic Mn(0.05)Ge(0.95) quantum dots with ferromagnetic order above room temperature, and the demonstration of electric-field control of ferromagnetism in MOS ferromagnetic capacitors up to 100 K. We found that by applying electric fields to a MOS gate structure, the ferromagnetism of the channel layer can be effectively modulated through the change of hole concentration inside the quantum dots. Our results are fundamentally important in the understanding and to the realization of high-efficiency Ge-based spin field-effect transistors.

Semiconductor quantum dots as an ideal source of polarization-entangled photon pairs on-demand: a review

NASA Astrophysics Data System (ADS)

Huber, Daniel; Reindl, Marcus; Aberl, Johannes; Rastelli, Armando; Trotta, Rinaldo

2018-07-01

More than 80 years have passed since the first publication on entangled quantum states. Over this period, the concept of spookily interacting quantum states became an emerging field of science. After various experiments proving the existence of such non-classical states, visionary ideas were put forward to exploit entanglement in quantum information science and technology. These novel concepts have not yet come out of the experimental stage, mostly because of the lack of suitable, deterministic sources of entangled quantum states. Among many systems under investigation, semiconductor quantum dots are particularly appealing emitters of on-demand, single polarization-entangled photon pairs. While it was originally believed that quantum dots must exhibit a limited degree of entanglement related to decoherence effects typical of the solid-state, recent studies have invalidated this preconception. We review the relevant experiments which have led to these important discoveries and discuss the remaining challenges for the anticipated quantum technologies.

Electrostatically defined silicon quantum dots with counted antimony donor implants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, M., E-mail: msingh@sandia.gov; Luhman, D. R.; Lilly, M. P.

2016-02-08

Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors in 100 nm × 150 nm windows straddling quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular Coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

Electrostatically defined silicon quantum dots with counted antimony donor implants

NASA Astrophysics Data System (ADS)

Singh, M.; Pacheco, J. L.; Perry, D.; Garratt, E.; Ten Eyck, G.; Bishop, N. C.; Wendt, J. R.; Manginell, R. P.; Dominguez, J.; Pluym, T.; Luhman, D. R.; Bielejec, E.; Lilly, M. P.; Carroll, M. S.

2016-02-01

Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors in 100 nm × 150 nm windows straddling quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular Coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

Organic molecules as tools to control the growth, surface structure, and redox activity of colloidal quantum dots.

PubMed

Weiss, Emily A

2013-11-19

In order to achieve efficient and reliable technology that can harness solar energy, the behavior of electrons and energy at interfaces between different types or phases of materials must be understood. Conversion of light to chemical or electrical potential in condensed phase systems requires gradients in free energy that allow the movement of energy or charge carriers and facilitate redox reactions and dissociation of photoexcited states (excitons) into free charge carriers. Such free energy gradients are present at interfaces between solid and liquid phases or between inorganic and organic materials. Nanostructured materials have a higher density of these interfaces than bulk materials. Nanostructured materials, however, have a structural and chemical complexity that does not exist in bulk materials, which presents a difficult challenge: to lower or eliminate energy barriers to electron and energy flux that inevitably result from forcing different materials to meet in a spatial region of atomic dimensions. Chemical functionalization of nanostructured materials is perhaps the most versatile and powerful strategy for controlling the potential energy landscape of their interfaces and for minimizing losses in energy conversion efficiency due to interfacial structural and electronic defects. Colloidal quantum dots are semiconductor nanocrystals synthesized with wet-chemical methods and coated in organic molecules. Chemists can use these model systems to study the effects of chemical functionalization of nanoscale organic/inorganic interfaces on the optical and electronic properties of a nanostructured material, and the behavior of electrons and energy at interfaces. The optical and electronic properties of colloidal quantum dots have an intense sensitivity to their surface chemistry, and their organic adlayers make them dispersible in solvent. This allows researchers to use high signal-to-noise solution-phase spectroscopy to study processes at interfaces. In this Account, I describe the varied roles of organic molecules in controlling the structure and properties of colloidal quantum dots. Molecules serve as surfactant that determines the mechanism and rate of nucleation and growth and the final size and surface structure of a quantum dot. Anionic surfactant in the reaction mixture allows precise control over the size of the quantum dot core but also drives cation enrichment and structural disordering of the quantum dot surface. Molecules serve as chemisorbed ligands that dictate the energetic distribution of surface states. These states can then serve as thermodynamic traps for excitonic charge carriers or couple to delocalized states of the quantum dot core to change the confinement energy of excitonic carriers. Ligands, therefore, in some cases, dramatically shift the ground state absorption and photoluminescence spectra of quantum dots. Molecules also act as protective layers that determine the probability of redox processes between quantum dots and other molecules. How much the ligand shell insulates the quantum dot from electron exchange with a molecular redox partner depends less on the length or degree of conjugation of the native ligand and more on the density and packing structure of the adlayer and the size and adsorption mode of the molecular redox partner. Control of quantum dot properties in these examples demonstrates that nanoscale interfaces, while complex, can be rationally designed to enhance or specify the functionality of a nanostructured system.

Andreev molecules in semiconductor nanowire double quantum dots.

PubMed

Su, Zhaoen; Tacla, Alexandre B; Hocevar, Moïra; Car, Diana; Plissard, Sébastien R; Bakkers, Erik P A M; Daley, Andrew J; Pekker, David; Frolov, Sergey M

2017-09-19

Chains of quantum dots coupled to superconductors are promising for the realization of the Kitaev model of a topological superconductor. While individual superconducting quantum dots have been explored, control of longer chains requires understanding of interdot coupling. Here, double quantum dots are defined by gate voltages in indium antimonide nanowires. High transparency superconducting niobium titanium nitride contacts are made to each of the dots in order to induce superconductivity, as well as probe electron transport. Andreev bound states induced on each of dots hybridize to define Andreev molecular states. The evolution of these states is studied as a function of charge parity on the dots, and in magnetic field. The experiments are found in agreement with a numerical model.Quantum dots in a nanowire are one possible approach to creating a solid-state quantum simulator. Here, the authors demonstrate the coupling of electronic states in a double quantum dot to form Andreev molecule states; a potential building block for longer chains suitable for quantum simulation.

Diffuse optical tomography for breast cancer imaging guided by computed tomography: A feasibility study.

PubMed

Baikejiang, Reheman; Zhang, Wei; Li, Changqing

2017-01-01

Diffuse optical tomography (DOT) has attracted attentions in the last two decades due to its intrinsic sensitivity in imaging chromophores of tissues such as hemoglobin, water, and lipid. However, DOT has not been clinically accepted yet due to its low spatial resolution caused by strong optical scattering in tissues. Structural guidance provided by an anatomical imaging modality enhances the DOT imaging substantially. Here, we propose a computed tomography (CT) guided multispectral DOT imaging system for breast cancer imaging. To validate its feasibility, we have built a prototype DOT imaging system which consists of a laser at the wavelength of 650 nm and an electron multiplying charge coupled device (EMCCD) camera. We have validated the CT guided DOT reconstruction algorithms with numerical simulations and phantom experiments, in which different imaging setup parameters, such as projection number of measurements and width of measurement patch, have been investigated. Our results indicate that an air-cooling EMCCD camera is good enough for the transmission mode DOT imaging. We have also found that measurements at six angular projections are sufficient for DOT to reconstruct the optical targets with 2 and 4 times absorption contrast when the CT guidance is applied. Finally, we have described our future research plan on integration of a multispectral DOT imaging system into a breast CT scanner.

Proceedings of the 8th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology

NASA Astrophysics Data System (ADS)

Ishioka, Sachio; Fujikawa, Kazuo

2006-06-01

Preface -- Committees -- Opening address / H. Fukuyama -- Welcoming address / N. Osakabe -- Special lecture. Albert Einstein: opportunity and perception / C. N. Yang -- Quantum information and entanglement. Quantum optics with single atoms and photons / H. J. Kimble. Quantum information system experiments using a single photon source / Y. Yamamoto. Quantum communication and quantum computation with entangled photons / A. Zeilinger. High-fidelity quantum teleportation and a quantum teleportation network for continuous variables / N. Takei, A. Furusawa. Long lived entangled states / H. Häffner ... [et al.]. Quantum non-locality using tripartite entanglement with non-orthogonal states / J. V. Corbett, D. Home. Quantum entanglement and wedge product / H Heydari. Analysis of the generation of photon pairs in periodically poled lithium niobate / J. Söderholm ... [et al.]. Generation of entangled photons in a semiconductor and violation of Bell's inequality / G. Oohata, R. Shimizu, K. Edamatsu -- Quantum computing. Decoherence of a Josephson junction flux qubit / Y. Nakamura ... [et al.]. Spectroscopic analysis of a candidate two-qubit silicon quantum computer in the microwave regime / J. Gorman, D. G. Hasko, D. A. Williams. Berry phase detection in charge-coupled flux-qubits and the effect of decoherence / H. Nakano ... [et al.]. Locally observable conditions for the successful implementation of entangling multi-qubit quantum gates / H. F. Hofmann, R. Okamoto, S. Takeuchi. State control in flux qubit circuits: manipulating optical selection rules of microwave-assisted transitions in three-level artificial atoms / Y.-X. Liu ... [et al.]. The effect of local structure and non-uniformity on decoherence-free states of charge qubits / T. Tanamoto, S. Fujita. Entanglement-assisted estimation of quantum channels / A. Fujiwara. Superconducting quantum bit with ferromagnetic [symbol]-Junction / T. Yamashita, S. Takahashi, S. Maekawa. Generation of macroscopic Greenberger-Horne-Zeilinger states in Josephson systems / T. Fujii, M. Nishida, N. Hatakenaka -- Quantum-dot systems. Tunable tunnel and exchange couplings in double quantum dots / S. Tarucha, T. Hatano, M. Stopa. Coherent transport through quantum dots / S. Katsumoto ... [et al.]. Electrically pumped single-photon sources towards 1.3 [symbol]m / X. Xu ... [et al.]. Aharonov-Bohm-type effects in antidot arrays and their decoherence / M. Kato ... [et al.]. Nonequilibrium Kondo dot connected to ferromagnetic leads / Y. Utsumi ... [et al.]. Full counting-statistics in a single-electron transistor in the presence of strong quantum fluctuations / Y. Utsumi -- Anomalous Hall effect and Spin-Hall effect. Geometry and the anomalous Hall effect in ferromagnets / N. P. Ong, W.-L. Lee. Control of spin chirality, Berry phase, and anomalous Hall effect / Y. Tokura, Y. Taguchi. Quantum geometry and Hall effect in ferromagnets and semiconductors / N. Nagaosa. Spin-Hall effect in a semiconductor two-dimensional hole gas with strong spin-orbit coupling / J. Wunderlich ... [et al.]. Intrinsic spin Hall effect in semiconductors / S. Murakami -- Spin related phenomena. Theory of spin transfer phenomena in magnetic metals and semiconductors / A. S. Núñez, A. H. MacDonald. Spin filters of semiconductor nanostructures / T. Dietl, G. Grabecki, J. Wróbel. Experimental study on current-driven domain wall motion / T. Ono ... [et al.]. Magnetization reversal of ferromagnetic nano-dot by non local spin injection / Y. Otani, T. Kimura. Theory of current-driven domain wall dynamics / G. Tatara ... [et al.]. Magnetic impurity states and ferromagnetic interaction in diluted magnetic semiconductors / M. Ichimura ... [et al.]. Geometrical effect on spin current in magnetic nano-structures / M. Ichimura, S. Takahashi, S. Maekawa. Ferromagnetism in anatase TiO[symbol] codoped with Co and Nb / T. Hitosugi ... [et al.] -- Superconductivity in nano-systems. Nonlinear quantum effects in nanosuperconductors / C. Carballeira ... [et al.]. Coalescence and rearrangement of vortices in mesoscopic superconductors / A. Kanda ... [et al.]. Superconductivity in topologically nontrivial spaces / M. Hayashi ... [et al.]. DC-SQUID ratchet using atomic point contact / Y. Ootuka, H. Miyazaki, A. Kanda. Superconducting wire network under spatially modulated magnetic field / H. Sano ... [et al.]. Simple and stable control of mechanical break junction for the study of superconducting atomic point contact / H. Miyazaki ... [et al.]. Critical currents in quasiperiodic pinning arrays: one-dimensional chains and Penrose lattices / V. R. Misko, S. Savel'ev, F. Nori. Macroscopic quantum tunneling in high-Tc superconductor Josephson junctions / S. Kawabata -- Novel properties of carbon nanotubes. Carbon nanotubes and unique transport properties: importance of symmetry and channel number / T. Ando. Optical processes in single-walled carbon nanotubes threaded by a magnetic flux / J. Kono ... [et al.]. Non-equilibrium transport through a single-walled carbon nanotube with highly transparent coupling to reservoirs / P. Recher, N. Y. Kim, Y. Yamamoto -- Novel properties of nano-systems. Transport properties in low dimensional artificial lattice of gold nano-particles / S. Saito ... [et al.]. First principles study of dihydride-chain structures on H-terminated Si(100) surface / Y. Suwa ... [et al.]. Electrical property of Ag nanowires fabricated on hydrogen-terminated Si(100) surface / M. Fujimori, S. Heike, T. Hashizume. Effect of environment on ionization of excited atoms embedded in a solid-state cavity / M. Ando ... [et al.]. Development of universal virtual spectroscope for optoelectronics research: first principles software replacing dielectric constant measurements / T. Hamada ... [et al.]. Quantum Nernst effect / H Nakamura, N. Hatano, R. Shirasaki -- Precise measurements. Quantum phenomena visualized using electron waves / A. Tonomura. An optical lattice clock: ultrastable atomic clock with engineered perturbation / H. Katori ... [et al.]. Development of Mach-Zehnder interferometer and "coherent beam steering" technique for cold neutron / K. Taketani ... [et al.]. Surface potential measurement by atomic force microscopy using a quartz resonator / S. Heike, T. Hashizume -- Fundamental Problems in quantum physics. Berry's phases and topological properties in the Born-Oppenheimer approximation / K. Fujikawa. Self-trapping of Bose-Einstein condensates by oscillating interactions / H. Saito, M. Ueda. Spinor solitons in Bose-Einstein condensates - atomic spin transport / J. Ieda. Spin decoherence in a gravitational field / H. Terashima, M. Ueda. Berry's phase of atoms with different sign of the g-factor in a conical rotating magnetic field observed by a time-domain atom interferometer / A. Morinaga ... [et al.] -- List of participants.

Interplay of coupling and superradiant emission in the optical response of a double quantum dot

NASA Astrophysics Data System (ADS)

Sitek, Anna; Machnikowski, Paweł

2009-09-01

We study theoretically the optical response of a double quantum dot structure to an ultrafast optical excitation. We show that the interplay of a specific type of coupling between the dots and their collective interaction with the radiative environment leads to very characteristic features in the time-resolved luminescence as well as in the absorption spectrum of the system. For a sufficiently strong coupling, these effects survive even if the transition energy mismatch between the two dots exceeds by far the emission linewidth.