Search query: N-Type Conducting CdSe Nanocrystal Solids

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abstract: A bottleneck limiting the widespread application of semiconductor nanocrystal solids is their poor conductivity. We report that the conductivity of thin films of n type CdSe nanocrystals increases by many orders of magnitude as the occupation of the first two electronic shells, 1Se and 1Pe, increases, either by potassium or electrochemical doping. Around half filling of the 1Se shell, a peak in the conductivity is observed, indicating shell to shell transport. Introducing conjugated ligands between nanocrystals increases the conductivities of these states to ~10 2 siemens per centimeter.
author_names: Dong Yu

Congjun Wang

Philippe Guyot-Sionnest
title: n Type Conducting CdSe Nanocrystal Solids
venue: Science
year: 2003

abstract: We present a general synthesis for a family of n type transparent conducting oxide nanocrystals through doping with aliovalent cations. These monodisperse nanocrystals exhibit localized surface plasmon resonances tunable in the mid and near infrared with increasing dopant concentration. We employ a battery of electrical measurements to demonstrate that the plasmonic resonance in isolated particles is consistent with the electronic properties of oxide nanocrystal thin films. Hall and Seebeck measurements show that the particles form degenerately doped n type solids with free electron concentrations in the range of 1019 to 1021 cm 3. These heavily doped oxide nanocrystals are used as the building blocks of conductive, n type thin films with high visible light transparency.
author_names: Benjamin T Diroll

Thomas R Gordon

E Ashley Gaulding

D R Klein

Taejong Paik

Hyeong Jin Yun

E D Goodwin

Divij Damodhar

Cherie R Kagan

Christopher B Murray
title: Synthesis of N Type Plasmonic Oxide Nanocrystals and the Optical and Electrical Characterization of their Transparent Conducting Films
year: 2014

abstract: Electrical 1/f noise is measured in thin films of CdSe, CdSe/CdS, ZnO, HgTe quantum dots and Au nanocrystals. The 1/f noise, normalized per nanoparticle, shows no systematic dependence on the nanoparticle material and the coupling material. However, over 10 orders of magnitude, it correlates well with the nearest neighbor conductance suggesting some universal magnitude of the 1/f noise in these granular conductors. In the hopping regime, the main mechanism of 1/f noise is determined to be mobility fluctuated. In the metallic regime obtained with gold nanoparticle films, the noise drops to a similar level as bulk gold films and with a similar temperature dependence.
author_names: Heng Liu

Emmanuel Lhuillier

Philippe Guyot-Sionnest
title: 1/f noise in semiconductor and metal nanocrystal solids
year: 2014

abstract: The temperature and electrical field dependent conductivity of n type CdSe nanocrystal thin films is investigated. In the low electrical field regime, the conductivity follows sigma approximately exp( (T(/T)(1/2) in the temperature range 10<T<120 K. At high electrical field, the conductivity is strongly field dependent. At 4 K, the conductance increases by 8 orders of magnitude over one decade of bias. At a very high field, conductivity is temperature independent with sigma approximately exp( (E(/E)(1/2) The complete behavior is very well described by variable range hopping with a Coulomb gap.
author_names: Dong Yu

Congjun Wang

Brian L Wehrenberg

Philippe Guyot-Sionnest
title: Variable range hopping conduction in semiconductor nanocrystal solids.
venue: Physical review letters
year: 2004

abstract: Submitted for the MAR05 Meeting of The American Physical Society Electron transport of n type semiconductor nanocrystal thin films DONG YU, CONGJUN WANG, BRIAN WEHRENBERG, PHILIPPE GUYOT SIONNEST, JAMES FRANK INSTITUTE, UNIVERSITY OF CHICAGO TEAM The conductivity of thin films of n type colloidal CdSe nanocrystals increases by up to 12 orders of magnitude as the occupation of the first two electronic shells 1Se and 1Pe increases, either by potassium or electrochemical doping. [D. Yu, C. Wang, P. Guyot Sionnest, Science 300, 1277 (2003) In the low electrical field regime, the conductivity follows s exp( (T /T )1/2) in the temperature range 10K<T<120K. At higher electrical field, the conductivity becomes strongly field dependent. At 4K, the conductance increases by eight orders of magnitude over one decade of bias. At extremely high field conductivity becomes temperature independent, where s exp( (E*/E)1/2) The conduction behavior follows Efros Shklovskii's variable range hopping model with Coulomb gap very well and the parameters determined by experiment agree well with the theoretical prediction. [D. Yu, C. Wang, B. Wehrenberg, P. GuyotSionnest, Phys. Rev. Lett. 92, 216802 (2004) Our current interest is to dope magnetic impurities like Mn2+ inside the NCs. The doped magnetic spins provide strong local magnetic field and large magnetoresistive effect is expected.
author_names: Dong Yu

Congjun Wang

Brian L Wehrenberg

Philippe Guyot-Sionnest
title: Electron transport of n type semiconductor nanocrystal thin films
year: 2005

abstract: Biomolecules labeled with luminescent colloidal semiconductor quantum dots (QDs) have potential for use in numerous applications, including fluoro immunoassays and biological imaging. QD labels exhibit size tunable narrow band luminescent emission and high resistance to photodegradation. They also exhibit efficient Forster energy transfer between neighboring QDs of different sizes and their emission is readily quenched by bound fluorescent dyes. In this paper, we describe preliminary results aimed at defining conditions for the design and preparation of nanoscale QD bio conjugate sensors based on fluorescence quenching. We envision building sensor assemblies that employ quantum dots linked with dye labeled biological receptors that utilize donor acceptor energy transfer between QDs and receptors for conducting recognition based assays. In particular, we report the effects of varying the concentration of energy acceptors bound to nanocrystal surfaces under both soluble and solid phase conditions on quenching phenomena.
author_names: Phan T Tran

Ellen R Goldman

George P Anderson

J Matthew Mauro

Hedi Mattoussi
title: Use of Luminescent CdSe ZnS Nanocrystal Bioconjugates in Quantum Dot Based Nanosensors
year: 2002

abstract: In order to deposit colloidal nanocrystals on different substrates, a large variety of methodologies have been developed, such as dipcoating, spin coating, or spray coating. The deposition of CdSe/CdS core shell nanorods (NRs) with a conventional office printer onto conducting tin doped indium oxide glass surfaces is presented. This involves the preparation of water based inks containing the NRs. To improve the connection between the CdSe/CdS NRs and the underlying substrates, the glass surfaces were modified by means of silanes. Homogeneous films were obtained by consecutively printing several layers of CdSe/CdS NRs.
author_names: Franziska Lubkemann

Ralf Anselmann

Torben Kodanek

Nadja C Bigall
title: Inkjet Printing of Aqueous Photoluminescent CdSe/CdS Nanorods on Solid Substrates
year: 2017

abstract: Al and In doped CdSe nanocrystals were synthesized using a three part core shell synthesis. CdSe core nanocrystals were first prepared, then allowed to react with dopant precursors in the presence of weakly binding ligands, and finally overcoated with an additional shell of CdSe. The addition of Al dopants quickened shell overgrowth and led to more monodisperse nanocrystals while the addition of In dopants produced more polydisperse particles, as seen by absorption spectroscopy. Elemental analysis combined with chemical etching revealed the dopants were inside the particles and solid state 27Al nuclear magnetic resonance (NMR) spectra indicated that the Al impurities were well dispersed. When the Al doped nanocrystals were processed into thin film transistors, enhanced n type transport was observed with a rise in the Fermi level compared to undoped particles.
author_names: Andrew W Wills

Moon-Sung Kang

Katherine M Wentz

Sophia E Hayes

Ayaskanta Sahu

Wayne L Gladfelter

David J Norris
title: Synthesis and characterization of Al and In doped CdSe nanocrystals
year: 2012

abstract: CdSe nanorods (NRs) with an average length of 120 nm were prepared by a solvothermal process and associated to TiO2 nanoparticles (Aeroxide(r) P25) by annealing at 300 degC for 1 h. The content of CdSe NRs in CdSe/TiO2 composites was varied from 0.5 to 5 wt The CdSe/TiO2 heterostructured materials were characterized by XRD, TEM, SEM, XPS, UV visible spectroscopy and Raman spectroscopy. TEM images and XRD patterns show that CdSe NRs with wurtzite structure are associated to TiO2 particles. The UV visible spectra demonstrate that the narrow bandgap of CdSe NRs serves to increase the photoresponse of CdSe/TiO2 composites until 725 nm. The CdSe (2 wt /TiO2 composite exhibits the highest photocatalytic activity for the degradation of rhodamine B in aqueous solution under simulated sunlight or visible light irradiation. The enhancement in photocatalytic activity likely originates from CdSe sensitization of TiO2 and the heterojunction between these materials which facilitates electron transfer from CdSe to TiO2. Due to its high stability (up to ten reuses without any significant loss in activity) the CdSe/TiO2 heterostructured catalysts show high potential for real water decontamination. Introduction The development of efficient photocatalysts to address environmental and energy needs, such as degradation of harmful organic compounds in water and in the air or the conversion of solar energy to chemical energy, for example, via water splitting to produce hydrogen, is the topic of numerous current research projects. Titanium dioxide (TiO2) has been widely inBeilstein J. Nanotechnol. 2017, 8, 2741 2752. 2742 vestigated over the last three decades and has been demonstrated to be of high potential [1,2] However, TiO2 suffers from two main drawbacks. First, due to its wide bandgap (Eg 3.2 and 3.0 eV for anatase and rutile, respectively) TiO2 can only be activated by light with a wavelength of less than 390 nm to trigger the electron hole separation. Second, TiO2 exhibits a low quantum efficiency due to the fast recombination of photogenerated charge carriers (electrons and holes) To address these problems, a number of studies have been devoted to the improvement of light absorption and charge separation by hybridizing TiO2 with narrow bandgap semiconductors, doping with metal or nonmetal elements, association with noble metal particles, or constructing heterojunctions between TiO2 and graphene based materials or carbon nitride (C3N4) acting as electron transport materials [3 5] All of these strategies have the common goal of decreasing the charge carrier recombination rate by increasing the spatial charge separation. The interfacial electron transfer between two semiconductors has gained significant interest because the heterojunction improves both the optical absorption in the visible range and the charge separation yield and thus the charge carrier lifetime [3 8] The photocatalytic activity is enhanced because oxidation of water by holes and reduction of oxygen by electrons are retained at two different sites. Recently, many groups demonstrated that the creation of a heterojunction between TiO2 and CdS, CdSe or alloyed CdSeS nanoparticles allows the optical absorption of TiO2 to be extended into the visible light range and increases the photoconversion efficiency by improving the charge transfer [9 37] CdSe is one of the most commonly used semiconductors due to its narrow bandgap (1.7 eV) and its band energies are located at relatively low potential. Despite the large number of reports describing the sensitization of TiO2 (used in the form of spherical particles, films, wires, tubes, etc. with CdSe nanocrystals (generally quantum dots or spherical nanoclusters) [9 37] very little attention has been devoted to the influence of CdSe crystal morphology on the photocatalytic activity of the CdSe/TiO2 heterostructured photocatalysts. CdSe nanorods (NRs) and wires are of high interest for use as sensitizers for photocatalytic applications due to their high surface area, higher optical absorption cross section (as compared to spherical particles) and easier charge carrier separation [38] Only a couple of reports describe the association of CdSe NRs with TiO2. Luo et al. used chemical vapor deposition to associate CdS, CdSe or CdSeS rods to TiO2 NRs arrays and demonstrated that the CdSeS/TiO2 heterostructure exhibits the highest performances as photoelectrode [39] More recently, small CdSe NRs [40] or type II CdSe/CdSexTe1 x NRs [41] were also used as light harvesters to develop TiO2 based solar cells. Core/shell TiO2/CdSe NRs were also prepared by growing CdSe quantum dots onto TiO2 NRs at high temperature [42] In this paper, we report an investigation on the synthesis of CdSe NR sensitized TiO2 nanoparticles and on the use of these materials for the degradation of rhodamine B (RhB) in aqueous solution. Our results demonstrate that the composite containing 2 wt CdSe NRs exhibits the optimal photocatalytic activity under solar or visible light irradiation. Moreover, the photocatalytic response was maintained after ten cycles in simulated sunlight. A possible mechanism is also discussed. Experimental Chemicals Cadmium acetate (Cd(OAc) 99.995% Sigma) sodium selenite (Na2SeO3, 99% Sigma) diethylenetriamine (99% Sigma) TiO2 nanoparticles (Sigma Aldrich, Aeroxide(r) P25, CAS: 13463 67 7) rhodamine B (RhB, >95% Sigma) tert butanol (t BuOH, >99.5% Sigma) p benzoquinone >98% Sigma) and ethanol >99% anhydrous) were used as received without additional purification. All solutions were prepared using Milli Q water (18.2 MO*cm, Millipore) as the solvent. Synthesis of CdSe nanorods CdSe NRs were synthetized via a solvothermal method according to the protocol described by Li et al. [43] with slight modifications. Briefly, diethylenetriamine (34.3 mL) and water (5.8 mL) were mixed in a reaction flask and the mixture stirred for 5 min. Next, Cd(OAc)2 (0.266 g, 1 mmol) and Na2SeO3 (0.173 g, 1 mmol) were added and the mixture further stirred for 30 min at room temperature to ensure complete dissolution of precursors. Next, the solution was transferred to a teflonlined stainless steel autoclave with 100 mL capacity and heated to 180 degC for 12 h. After cooling to room temperature, the CdSe NRs were recovered by centrifugation (4000 rpm for 15 min) washed with water (5 x 10 mL) then with ethanol (2 x 10 mL) and finally dried at 50 degC for 12 h. Preparation of CdSe/TiO2 composites CdSe/TiO2 composites with a varied content of CdSe NRs (0.5, 1, 2 and 5 wt were prepared. For the CdSe (2 wt /TiO2 composite, commercial Aeroxide(r) P25 TiO2 nanoparticles (250 mg) and CdSe NRs (5 mg) were dispersed by sonication in 5 mL water for 30 min. Next, the mixture was heated to 70 degC to evaporate water. The solid obtained was washed with water (3 x 10 mL) with ethanol (3 x 5 mL) and then calcined under air at 300 degC for 1 h to couple the CdSe NRs with TiO2. CdSe/TiO2 composites with different wt CdSe NRs were prepared using a similar synthetic procedure. Beilstein J. Nanotechnol. 2017, 8, 2741 2752. 2743 Photocatalytic activity measurements The photocatalytic activity of CdSe/TiO2 composites was evaluated by the degradation of RhB in aqueous solution. Sylvania LuxLine FHO T5 neon tubes were used as the simulated solar light source (light intensity 5 mW/cm2) A polycarbonate filter was added for experiments conducted under visible light irradiation (light intensity 10 mW/cm2) In a typical experiment, 50 mg of the CdSe/TiO2 composite were dispersed in 50 mL of aqueous solution of RhB (10 mg/L) in a 70 mL glass flask and the mixture was magnetically stirred in the dark under ambient conditions for 45 min to reach a thorough adsorption desorption equilibrium. After that period, the light was turned on. Aliquots of 2 mL were taken at regular time intervals and centrifuged (4000 rpm for 2 min) to remove the CdSe/TiO2 photocatalyst. The relative concentration of RhB in the solution was determined by comparing its UV visible absorption at 554 nm with that of the starting solution. The mechanism of RhB photodegradation in aqueous solution was investigated through the use of scavengers. t BuOH and p benzoquinone, used as hydroxyl and superoxide scavengers, were used at concentrations of 1 and 10 mM, respectively. Characterization Transmission electron microscopy (TEM) investigations were performed with a JEOL ARM 200F Cold FEG TEM/STEM (point resolution 0.19 nm in TEM mode and 0.078 nm in STEM mode) fitted with a GIF Quatum ER. For each sample, one drop of a dispersed solution was deposited on holey carbon grids and imaged. Scanning electron microscopy (SEM) images were prepared using a JEOL SEM JSM 6490 LV. The crystalline phase of the powders was determined by powder X ray diffraction (XRD) on an X'Pert MPD diffractometer (Panalytical AXS) with a goniometer radius of 240 mm, fixed divergence slit module (1/2deg divergence slit, 0.04 rd Sollers slits) and an X'Celerator as a detector. The samples were placed on a silicon zero background sample holder and the XRD patterns were recorded at room temperature using Cu Ka radiation (l 0.15418 nm) XPS analysis was conducted on a Gammadata Scienta (Uppsala, Sweden) SES 200 2 spectrometer under ultra high vacuum conditions (P 10 9 mbar) For all peak fitting procedures the CASA XPS software (Casa Software Ltd, Teignmouth, UK, http:/www.casaxps.com) was used and the areas of each component were modified according to classical Scofield sensitivity factors. All the optical measurements were performed at room temperature (20 1 degC) under ambient conditions. The absorption spectra of liquid samples were recorded on a Thermo Scientific Evolution 220 UV visible spectrophotometer. Diffuse reflectance spectra (DRS) were recorded on a Shimadzu 2600 UV visible spectrophotometer. BaSO4 powder was used as a standard for baseline measurements and spectra were recorded in a range of 250 1400 nm.
author_names: Fakher Laatar

Hatem Moussa

Halima Alem

Lavinia Balan

Emilien Girot

Ghouti Medjahdi

Hatem Ezzaouia

Raphael Schneider
title: CdSe nanorod TiO 2 nanoparticle heterojunctions with enhanced solar and visible light photocatalytic activity
year: 2017

abstract: A transformative approach is required to meet the demand of economically viable solar cell technology. By making use of recent advances in semiconductor nanocrystal research, we have now developed a one coat solar paint for designing quantum dot solar cells. A binder free paste consisting of CdS, CdSe, and TiO(2) semiconductor nanoparticles was prepared and applied to conducting glass surface and annealed at 473 K. The photoconversion behavior of these semiconductor film electrodes was evaluated in a photoelectrochemical cell consisting of graphene Cu(2)S counter electrode and sulfide/polysulfide redox couple. Open circuit voltage as high as 600 mV and short circuit current of 3.1 mA/cm(2) were obtained with CdS/TiO(2) CdSe/TiO(2) electrodes. A power conversion efficiency exceeding 1% has been obtained for solar cells constructed using the simple conventional paint brush approach under ambient conditions. Whereas further improvements are necessary to develop strategies for large area, all solid state devices, this initial effort to prepare solar paint offers the advantages of simple design and economically viable next generation solar cells.
author_names: Matthew Genovese

Ian Lightcap

Prashant V Kamat
title: Sun believable solar paint. A transformative one step approach for designing nanocrystalline solar cells.
venue: ACS nano
year: 2012