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4 Feb 2013

Volume 102, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 102, 053102 (2013); http://dx.doi.org/10.1063/1.4789442 (5 pages)

P. H. Kim, C. Doolin, B. D. Hauer, A. J. R. MacDonald, M. R. Freeman, P. E. Barclay, and J. P. Davis
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Near-field radiative heat transfer between doped silicon nanowire arrays

Soumyadipta Basu and Liping Wang

Appl. Phys. Lett. 102, 053101 (2013); http://dx.doi.org/10.1063/1.4790143 (4 pages)

Online Publication Date: 4 February 2013

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In this letter, we investigate the near-field radiative heat transfer between two doped silicon nanowire arrays separated by a vacuum gap. Using effective medium theory and fluctuational electrodynamics, the radiative heat transfer is calculated for the silicon nanowire arrays with different filling fractions at different vacuum gaps. The energy transfer increases as the nanowire array becomes less dense due to enhancement in channels available for heat transfer. To further understand the impact of filling fraction to the total heat transfer, the dispersion relation of coupled surface plasmon polaritons is calculated inside the vacuum gap by considering temperature-dependent dielectric functions for the doped silicon nanowires. When the filling fraction is 0.5, the radiative heat transfer at a vacuum gap of 20 nm between the nanowire arrays is almost three times of that between two doped silicon plates. Results from this study will facilitate the application of doped silicon nanowires for energy harvesting and thermal management.
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81.05.Cy Elemental semiconductors
81.07.Gf Nanowires
44.40.+a Thermal radiation
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.22.Lp Collective excitations

Nanoscale torsional optomechanics

P. H. Kim, C. Doolin, B. D. Hauer, A. J. R. MacDonald, M. R. Freeman, P. E. Barclay, and J. P. Davis

Appl. Phys. Lett. 102, 053102 (2013); http://dx.doi.org/10.1063/1.4789442 (5 pages) | Cited 1 time

Online Publication Date: 4 February 2013

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Optomechanical transduction is demonstrated for nanoscale torsional resonators evanescently coupled to optical microdisk whispering gallery mode resonators. The on-chip, integrated devices are measured using a fully fiber-based system, including a tapered and dimpled optical fiber probe. With a thermomechanically calibrated optomechanical noise floor down to 7 fm/math, these devices open the door for a wide range of physical measurements involving extremely small torques, as little as 4×10−20N·m.
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42.82.Fv Hybrid systems
42.81.Wg Other fiber-optical devices

Homogeneous and stable p-type doping of graphene by MeV electron beam-stimulated hybridization with ZnO thin films

Wooseok Song, Yooseok Kim, Sung Hwan Kim, Soo Youn Kim, Myoung-Jun Cha, Inkyung Song, Dae Sung Jung, Cheolho Jeon, Taekyung Lim, Sumi Lee, Sanghyun Ju, Won Chel Choi, Min Wook Jung, Ki-Seok An, and Chong-Yun Park

Appl. Phys. Lett. 102, 053103 (2013); http://dx.doi.org/10.1063/1.4790161 (5 pages)

Online Publication Date: 4 February 2013

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In this work, we demonstrate a unique and facile methodology for the homogenous and stable p-type doping of graphene by hybridization with ZnO thin films fabricated by MeV electron beam irradiation (MEBI) under ambient conditions. The formation of the ZnO/graphene hybrid nanostructure was attributed to MEBI-stimulated dissociation of zinc acetate dihydrate and a subsequent oxidation process. A ZnO thin film with an ultra-flat surface and uniform thickness was formed on graphene. We found that homogeneous and stable p-type doping was achieved by charge transfer from the graphene to the ZnO film.
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61.72.up Other materials
68.55.jd Thickness
61.80.Fe Electron and positron radiation effects
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Mq Oxidation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Influence of nanoscale geometry on the dynamics of wicking into a rough surface

Chang Quan Lai, Trong Thi Mai, H. Zheng, P. S. Lee, K. C. Leong, Chengkuo Lee, and W. K. Choi

Appl. Phys. Lett. 102, 053104 (2013); http://dx.doi.org/10.1063/1.4790183 (4 pages)

Online Publication Date: 4 February 2013

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The dynamics of imbibition into the roughness of a surface was investigated with hexagonal arrays of anisotropic nanofins fabricated with interference lithography and metal assisted chemical etching. It was found that viscous drag caused by the nanofins is similar to that caused by open nano-channels of equal length and height containing the same volume of liquid. In addition, the energy dissipated by form drag for a given driving pressure was determined to be directly proportional to the volume of fluid between nanofin planes that are flat and normal to the imbibition direction.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
66.20.-d Viscosity of liquids; diffusive momentum transport
47.56.+r Flows through porous media

Significantly enhanced thermoelectric properties of ultralong double-walled carbon nanotube bundle

Tingting Miao, Weigang Ma, Xing Zhang, Jinquan Wei, and Jialin Sun

Appl. Phys. Lett. 102, 053105 (2013); http://dx.doi.org/10.1063/1.4790190 (5 pages)

Online Publication Date: 4 February 2013

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A T-type method is developed to comprehensively evaluate the thermoelectric properties of materials. The thermoelectric properties, including thermal conductivity, thermopower, and electrical conductivity of an ultralong double-walled carbon nanotube bundle are studied from 240 K to 340 K by applying the T-type method. The determined figure of merit achieves 10−3 which is significantly larger than that reported for carbon nanotubes samples. The bundle consists of thousands of nanotubes aligned along the long axis with low levels of impurities, and the thermal conductivity is significantly reduced compared to that of individual double-walled nanotube, while the electrical conductivity is superior to most of the carbon nanotubes samples.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.Fg Nanotubes
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
71.55.Ht Other nonmetals

Ultrafast modulation of near-field heat transfer with tunable metamaterials

Longji Cui, Yong Huang, Ju Wang, and Ke-Yong Zhu

Appl. Phys. Lett. 102, 053106 (2013); http://dx.doi.org/10.1063/1.4790292 (5 pages) | Cited 1 time

Online Publication Date: 4 February 2013

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We propose a mechanism of active near-field heat transfer modulation relying on externally tunable metamaterials. A large modulation effect is observed and can be explained by the coupling of surface modes, which is dramatically varied in the presence of controllable magnetoelectric coupling in metamaterials. We finally discuss how a practical picosecond-scale thermal modulator can be made. This modulator allows manipulating nanoscale heat flux in an ultrafast and noncontact (by optical means) manner.
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44.40.+a Thermal radiation
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
75.85.+t Magnetoelectric effects, multiferroics

Collective charge transport in semiconductor-metal hybrid nanocomposite

Tuhin Shuvra Basu, Siddhartha Ghosh, Stanislaw Gierlotka, and Mallar Ray

Appl. Phys. Lett. 102, 053107 (2013); http://dx.doi.org/10.1063/1.4790300 (5 pages)

Online Publication Date: 4 February 2013

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Collective charge transport through a hybrid nanocomposite made of Ag nanoparticles (NPs) embedded in ultra-small Si quantum dot (QD) matrix exhibits unexpected and fascinating characteristics. Metallic inclusion (10 wt. % of Ag NPs) in the Si QD matrix affects six orders of magnitude increase in current. In the semiconductor-metal hybrid, three different charge transport mechanisms—quantum tunneling through insulating barriers, variable range hoping, and simple thermally activated conduction dominate in three different temperature regimes that are influenced by bias voltage. We show that there is a cross-over from one transport mechanism to the other and determine the voltage dependent cross-over temperatures.
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73.40.Ns Metal-nonmetal contacts
73.63.Bd Nanocrystalline materials
73.63.Kv Quantum dots
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
73.40.Gk Tunneling

Size-dependence of Raman scattering from graphene quantum dots: Interplay between shape and thickness

Sung Kim, Dong Hee Shin, Chang Oh Kim, Soo Seok Kang, Soong Sin Joo, Suk-Ho Choi, Sung Won Hwang, and Cheolsoo Sone

Appl. Phys. Lett. 102, 053108 (2013); http://dx.doi.org/10.1063/1.4790641 (3 pages)

Online Publication Date: 4 February 2013

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Raman-scattering behaviors have been studied in graphene quantum dots (GQDs) by varying their average size (d) from 5 to 35 nm. The peak frequencies of D and 2D bands are almost irrespective of d, and the intensity of the D band is larger than that of the G band over almost full range of d. These results suggest that GQDs are defective, possibly resulting from the dominant contributions from the edge states at the periphery of GQDs. The G band shows a maximum peak frequency at d = ∼17 nm, whilst the full-width half maximum of the G band and the peak-intensity ratio of the D to G bands are minimized at d = ∼17 nm. Since the average thickness of GQDs (t) is proportional to d, t can act as a factor affecting the d-dependent Raman-scattering behaviors, but they cannot be explained solely by the t variation. We propose that the abrupt changes in the Raman-scattering behaviors of GQDs at d = ∼17 nm originate from size-dependent edge-state variation of GQDs at d = ∼17 nm as d increases.
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78.67.Wj Optical properties of graphene
78.30.Na Fullerenes and related materials

Kinetics of multiexciton complex in GaAs quantum dots on Si

N. Accanto, S. Minari, L. Cavigli, S. Bietti, G. Isella, A. Vinattieri, S. Sanguinetti, and M. Gurioli

Appl. Phys. Lett. 102, 053109 (2013); http://dx.doi.org/10.1063/1.4790148 (5 pages)

Online Publication Date: 5 February 2013

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We study the multiexciton properties of GaAs quantum dots self aggregated on Si substrates. Sequential emission of two photons radiative cascade is observed both in continuous wave and in time resolved measurements. Polarization resolved measurements, with high spectral resolution, allow us to attribute the observed photon cascade to positively charged biexciton. Our results highlight the possibility of obtaining systems showing quantum correlations on a Si based device.
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71.35.-y Excitons and related phenomena
73.21.La Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
78.47.jd Time resolved luminescence

Electro-optical and lasing properties of hybrid quantum dot/quantum well material system for reconfigurable photonic devices

Jiri Thoma, Baolai Liang, Liam Lewis, Stephen P. Hegarty, Guillaume Huyet, and Diana L. Huffaker

Appl. Phys. Lett. 102, 053110 (2013); http://dx.doi.org/10.1063/1.4791565 (4 pages)

Online Publication Date: 5 February 2013

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We characterize the electro-optical and lasing properties of a hybrid material consisting of multiple InAs quantum dot (QD) layers together with an InGaAs quantum well (QW) grown on a GaAs substrate. Over 40 nm Stark shift of the InGaAs QW leading to 9 dB extinction ratio was demonstrated. Lasing operation at the QD first excited state transition of 1070 nm was achieved and together with < 10 ps absorption recovery the system shows promise for high-speed mode-locked lasers and electro-modulated lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Hj Laser materials
78.20.Jq Electro-optical effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift

Electrodynamic control of the nanofiber alignment during electrospinning

Christian Grasl, Matthias M. L. Arras, Martin Stoiber, Helga Bergmeister, and Heinrich Schima

Appl. Phys. Lett. 102, 053111 (2013); http://dx.doi.org/10.1063/1.4790632 (4 pages)

Online Publication Date: 5 February 2013

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A technique is presented to electrospin straight and aligned fibers on a stationary featureless target. Two parallel rotatable plate-like auxiliary electrodes were applied with a time-varying square wave potential. Thereby, the electrospinning jet was periodically deflected between the electrodes, which led to an aligned fiber-deposition. Straight fibers were deposited at a potential difference of 11 kV and a switching frequency of 40 Hz between the auxiliary electrodes. With this setup, freely adjustable orientations can be achieved regardless of the targets design or its movement.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Reactive self-heating model of aluminum spherical nanoparticles

Karen S Martirosyan and M. Zyskin

Appl. Phys. Lett. 102, 053112 (2013); http://dx.doi.org/10.1063/1.4790823 (4 pages)

Online Publication Date: 6 February 2013

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Aluminum-oxygen reaction is important in highly energetic and high pressure generating systems. Recent experiments with nanostructured thermites suggest that oxidation of aluminum nanoparticles occurs in a few microseconds. Such rapid reaction cannot be explained by a conventional diffusion-based mechanism. We present a rapid oxidation model of a spherical aluminum nanoparticle, using Cabrera-Mott moving boundary mechanism, and taking self-heating into account. In our model, electric potential solves the nonlinear Poisson equation. In contrast with the Coulomb potential, a “double-layer” type solution for the potential and self-heating leads to enhanced oxidation rates. At maximal reaction temperature of 2000 °C, our model predicts overall oxidation time scale in microseconds range, in agreement with the experimental evidence.
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81.16.Pr Micro- and nano-oxidation
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
02.30.Jr Partial differential equations
02.60.Lj Ordinary and partial differential equations; boundary value problems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Fluorescence quenching due to sliver nanoparticles covered by graphene and hydrogen-terminated graphene

Cheng-Wen Huang, Hsing-Ying Lin, Chen-Han Huang, Kai-Hong Lo, Yu-Chung Chang, Chih-Yi Liu, Chen-Hao Wu, Yonhua Tzeng, and Hsiang-Chen Chui

Appl. Phys. Lett. 102, 053113 (2013); http://dx.doi.org/10.1063/1.4790825 (4 pages)

Online Publication Date: 6 February 2013

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Fluorescence quenching effects on graphene or hydrogen-terminated graphene covered sliver nanoparticles are studied and the results are explained with energy transfer models. The fluorescence signal of R6G is suppressed by the graphene flakes via Förster resonance energy transfer and by the silver nanoparticles via surface energy transfer. The relative fluorescence intensities of R6G are reduced to 28% and 69% on the single-atom-thick graphene flake and the hydrogen-terminated graphene covered silver film, respectively. The mechanism of the quenching effect is illustrated by the energy diagram of electron transition.
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78.55.Hx Other solid inorganic materials
78.67.Wj Optical properties of graphene

Channel access resistance effects on charge carrier mobility and low-frequency noise in a polymethyl methacrylate passivated SnO2 nanowire field-effect transistors

Min-Kyu Joo, Junghwan Huh, Mireille Mouis, So Jeong Park, Dae-Young Jeon, Doyoung Jang, Jong-Heun Lee, Gyu-Tae Kim, and Gérard Ghibaudo

Appl. Phys. Lett. 102, 053114 (2013); http://dx.doi.org/10.1063/1.4788708 (5 pages)

Online Publication Date: 6 February 2013

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Channel access resistance (Rsd) effects on the charge carrier mobility (μ) and low-frequency noise (LFN) in a polymethyl-methacrylate (PMMA) passivated tin-oxide nanowire (SnO2-NW) field effect-transistor were investigated. To this end, the Y function method was employed for direct electrical parameters extraction without Rsd influence. Numerical simulation was used to evaluate gate-to-channel capacitance (Cgc) accounting for the electrostatic gate coupling effects through PMMA passivation layer. Furthermore, LFN measurements were carried out to study the SnO2/dielectrics interface. The carrier number fluctuation (CNF) noise model was found appropriate to interpret LFN data provided Rsd influence is included.
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85.30.Tv Field effect devices
81.65.Rv Passivation

Enhanced InAs nanopillar electrical transport by in-situ passivation

A. Lin, J. N. Shapiro, A. C. Scofield, B. L. Liang, and D. L. Huffaker

Appl. Phys. Lett. 102, 053115 (2013); http://dx.doi.org/10.1063/1.4791592 (4 pages)

Online Publication Date: 6 February 2013

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We investigate the effects of in-situ passivation on the electrical transport of InAs nanopillars (NPs) grown on InAs (111)B substrates via selective-area epitaxy. Before passivation, the transport properties of InAs NPs, studied by single-NP field-effect transistors, are highly dependent on NP dimensions. With diameters ranging from 70 nm to 200 nm, we find significant differences in resistivity and extracted field-effect mobility (μeff). Growing a 6 nm InP shell for in-situ passivation significantly enhances these transport properties of InAs channel with diameter-independent μeff as high as 6900 cm2/V s. Such heterostructures have the potential as future high electron mobility transistors.
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72.80.Ey III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
81.65.Rv Passivation

Electronic screening in stacked graphene flakes revealed by scanning tunneling microscopy

Xiaofeng Feng and Miquel Salmeron

Appl. Phys. Lett. 102, 053116 (2013); http://dx.doi.org/10.1063/1.4790382 (4 pages)

Online Publication Date: 6 February 2013

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Electronic doping and screening effects in stacked graphene flakes on Ru and Cu substrates have been observed using scanning tunneling microscopy (STM). The screening affects the apparent STM height of each flake in successive layers reflecting the density of states near the Fermi level and thus the doping level. It is revealed in this way that the strong doping of the first graphene layer on Ru(0001) is attenuated in the second one, and almost eliminated in the third and fourth layers. Similar effect is also observed in graphene flakes on Cu(111). In contrast, the strong doping effect is suppressed immediately by a water layer intercalated between the graphene and Ru.
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73.22.Pr Electronic structure of graphene
61.72.up Other materials

GaN quantum-dots integrated in the gate dielectric of metal-oxide-semiconductor structures for charge-storage applications

P. Dimitrakis, P. Normand, C. Bonafos, E. Papadomanolaki, and E. Iliopoulos

Appl. Phys. Lett. 102, 053117 (2013); http://dx.doi.org/10.1063/1.4790439 (4 pages)

Online Publication Date: 6 February 2013

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Gallium nitride quantum dots (QDs) were investigated as discrete charge storage nodes embedded in the gate dielectric of metal-oxide-semiconductor (MOS) capacitors. The GaN QDs were formed on top of 3.5 nm-thick SiO2/n-Si(001) substrates by radiofrequency plasma-assisted molecular beam deposition. The MOS structures were studied by transmission electron microscopy. Deposition dose was determined as a critical process parameter to obtain two dimensional arrays of discrete QDs. The memory window width, programming speed, and charge retention time were evaluated for GaN QD devices with different deposition doses. All devices showed enhanced electron trapping leading to significant memory windows. Charge retention measurements, at room temperature, revealed that the sample with the lowest concentration of QDs exhibits a low charge loss with a significant extrapolated programming window after 10 yrs. The present study not only demonstrates GaN QD embedded SiO2 structures fabricated by a fully complementary metal oxide semiconductor compatible method but also points out that these structures are promising for the realization of nanofloating gate non-volatile memory devices.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits

Nanoparticles charge response from electrostatic force microscopy

A. Mottaghizadeh, P. L. Lang, L. M. Cui, J. Lesueur, J. Li, D. N. Zheng, V. Rebuttini, N. Pinna, A. Zimmers, and H. Aubin

Appl. Phys. Lett. 102, 053118 (2013); http://dx.doi.org/10.1063/1.4790587 (4 pages)

Online Publication Date: 6 February 2013

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Electrostatic force microscopy (EFM) allows measurement of tiny changes in tip-sample capacitance. When nanoobjects are studied by EFM, they only contribute a very small fraction of the total capacitance between the tip and the sample. We show that the analysis of 3D maps of the EFM signal allows extracting the contribution of the nanomaterial to the total capacitance. This opens the way to applications of EFM as a measure of the dielectric coefficient of electrically insulating nanomaterials or the quantum capacitance of conducting nanomaterials. We apply this method to study the charge response of magnetite, Fe3O4, nanoparticles.
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07.79.Pk Magnetic force microscopes
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
77.22.Ch Permittivity (dielectric function)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Shell-thickness-dependent photoinduced electron transfer from CuInS2/ZnS quantum dots to TiO2 films

Jianhui Sun, Jialong Zhao, and Yasuaki Masumoto

Appl. Phys. Lett. 102, 053119 (2013); http://dx.doi.org/10.1063/1.4790603 (4 pages)

Online Publication Date: 6 February 2013

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We demonstrate the electron transfer (ET) processes from CuInS2/ZnS core/shell quantum dots (QDs) into porous anatase TiO2 films by time-resolved photoluminescence spectroscopy. The rate and efficiency of ET can be controlled by changing the core diameter and the shell thickness. It is found that the ET rates decrease exponentially at the decay constants of 1.1 and 1.4 nm–1 with increasing ZnS shell thickness for core diameters of 2.5 and 4.0 nm, respectively, in agreement with the electron tunneling model. This shows that optimized ET efficiency and QD stability can be realized by controlling the shell thickness.
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78.47.jd Time resolved luminescence
73.40.Gk Tunneling
78.55.Hx Other solid inorganic materials
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