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18 Jan 2010

Volume 96, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 96, 033101 (2010); http://dx.doi.org/10.1063/1.3291849 (3 pages)

Ferruccio Pisanello, Luigi Martiradonna, Godefroy Leménager, Piernicola Spinicelli, Angela Fiore, Liberato Manna, Jean-Pierre Hermier, Roberto Cingolani, Elisabeth Giacobino, Massimo De Vittorio, and Alberto Bramati
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Room temperature-dipolelike single photon source with a colloidal dot-in-rod

Ferruccio Pisanello, Luigi Martiradonna, Godefroy Leménager, Piernicola Spinicelli, Angela Fiore, Liberato Manna, Jean-Pierre Hermier, Roberto Cingolani, Elisabeth Giacobino, Massimo De Vittorio, and Alberto Bramati

Appl. Phys. Lett. 96, 033101 (2010); http://dx.doi.org/10.1063/1.3291849 (3 pages) | Cited 19 times

Online Publication Date: 19 January 2010

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We propose colloidal CdSe/CdS dots in rods as nonclassical sources for quantum information technology. Such nanoemitters show specific properties such as strongly polarized emission of on-demand single photons at room temperature, dipolelike behavior and mono-exponential recombination rates, making us envision their suitability as sources of single photons with well defined quantum states in quantum cryptography based devices.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
82.70.Dd Colloids
71.35.-y Excitons and related phenomena

The role of dot height in determining exciton lifetimes in shallow InAs/GaAs quantum dots

T. E. J. Campbell-Ricketts, N. A. J. M. Kleemans, R. Nötzel, A. Yu. Silov, and P. M. Koenraad

Appl. Phys. Lett. 96, 033102 (2010); http://dx.doi.org/10.1063/1.3293294 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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The spectral dependence of the photoluminescence recombination lifetime has been measured for individual self-assembled InGaAs/GaAs quantum dots, over the entire emission envelope. The measurements show a rising trend with increasing emission wavelength, increasing from 680 ps at 900 nm to about 1020 ps at 990 nm. Measurements of the out-of-plane diamagnetic coefficients for the dots show almost no correlation with wavelength. As a result, the rising trend in the lifetimes with wavelength is interpreted in terms of the emission energy being predominantly determined by the dot height, with higher dots exhibiting longer lifetimes.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
75.20.Ck Nonmetals
71.35.-y Excitons and related phenomena

Calibrating the atomic balance by carbon nanoclusters

Fengqi Song, Xuefeng Wang, Rebecca C. Powles, Longbing He, Nigel A. Marks, Shifeng Zhao, Jianguo Wan, Zongwen Liu, Jianfeng Zhou, Simon P. Ringer, Min Han, and Guanghou Wang

Appl. Phys. Lett. 96, 033103 (2010); http://dx.doi.org/10.1063/1.3284498 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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Carbon atoms are counted at near atomic-level precision using a scanning transmission electron microscope calibrated by carbon nanocluster mass standards. A linear calibration curve governs the working zone from a few carbon atoms up to 34 000 atoms. This linearity enables adequate averaging of the scattering cross sections, imparting the experiment with near atomic-level precision despite the use of a coarse mass reference. An example of this approach is provided for layer counting of stacked graphene sheets. Suspended graphene sheets with a size below 100 nm are visualized, providing quantitative measurement in a regime inaccessible to optical and scanning probe methods.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
61.48.Gh Structure of graphene
68.37.Ma Scanning transmission electron microscopy (STEM)
68.65.Pq Graphene films

Angle resolved surface enhanced Raman scattering (SERS) on two-dimensional metallic arrays with different hole sizes

C. Y. Chan, J. B. Xu, M. Y. Waye, and H. C. Ong

Appl. Phys. Lett. 96, 033104 (2010); http://dx.doi.org/10.1063/1.3291109 (3 pages) | Cited 11 times

Online Publication Date: 19 January 2010

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The angle resolved surface enhanced Raman scattering (SERS) on two-dimensional Ag hole arrays has been studied as a function of hole size. The Raman enhancement factor has been found to increase with increasing hole size. In particular, by correlating the Raman mappings with the dispersion relations, the enhancement has been attributed to fast surface plasmon polariton radiative decay rate and strong coupling efficiency. Our results indicate that it is possible to optimize the geometry of the arrays to obtain desirable SERS.
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78.30.Er Solid metals and alloys
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Plasmonic resonances and hot spots in Ag octopods

Ivan I. Naumov, Zhiyong Li, and Alexander M. Bratkovsky

Appl. Phys. Lett. 96, 033105 (2010); http://dx.doi.org/10.1063/1.3273859 (3 pages) | Cited 4 times

Online Publication Date: 19 January 2010

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Silver octopod plasmonic nanoparticles have been recently synthesized with a variety of shapes. In the present letter, we demonstrate their versatile optical response using the discrete dipole approximation. There are three major resonances that can be tuned up to a large extent making them especially attractive to use in, e.g., high-performance surface enhanced Raman scattering (SERS) detectors. The excited resonant modes strongly depend on the geometrical parameters of the stars. The field “hot spots” are mostly localized at the surface between the arms and may be both “electric” (important for SERS applications) and “magnetic” in character (potentially identifiable by trapping magnetic nanoparticles in their vicinity). The results are in very good agreement with the data where available and may be used for a “shape spectroscopy” for the nanoparticles.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
75.50.Tt Fine-particle systems; nanocrystalline materials
78.30.-j Infrared and Raman spectra
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Carbon nanotube-Si diode as a detector of mid-infrared illumination

Pang-Leen Ong, William B. Euler, and Igor A. Levitsky

Appl. Phys. Lett. 96, 033106 (2010); http://dx.doi.org/10.1063/1.3279141 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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We report a room temperature mid-infrared photodetector based on a carbon nanotube-silicon heterojunction nanostructure. The observed mid-infrared band (8–12 μm) in the photocurrent spectrum is consistent with the estimated band gap energy of semiconducting multiwall nanotubes (15 to 30 nm diameter). The fast response time (16 ms) and small temperature change ( ∼ 10−8 K) upon infrared light suggest that the photocurrent response is not due to bolometric effect. We determined that the primary mechanism of the photocurrent in this spectral range is associated with photon absorption of semiconducting multiwalled carbon nanotubes followed by charge separation at the interface, their transport, and collection at the external electrodes.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Nonlinear optical and optical limiting properties of graphene families

Miao Feng, Hongbing Zhan, and Yu Chen

Appl. Phys. Lett. 96, 033107 (2010); http://dx.doi.org/10.1063/1.3279148 (3 pages) | Cited 30 times

Online Publication Date: 19 January 2010

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The nonlinear optical (NLO) and optical limiting (OL) properties of graphene families, including graphene oxide nanosheets, graphene nanosheets (GNSs), graphene oxide nanoribbons (GONRs), and graphene nanoribbons (GNRs), were investigated at 532 and 1064 nm using a nanosecond regime. GNSs, GONRs, and GNRs exhibited broadband NLO and OL properties. Reduced graphene samples exhibited stronger NLO and OL responses than their graphene oxide precursors because of their increased crystallinity and conjugation. Nonlinear scattering and two-photon-absorption were found to have strong effects on the NLO and OL responses of the graphene nanostructures.
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78.67.Wj Optical properties of graphene
61.46.-w Structure of nanoscale materials
42.79.-e Optical elements, devices, and systems
78.40.Ri Fullerenes and related materials

On the origin of suppression of free exciton no-phonon emission in ZnO tetrapods

S. L. Chen, S. K. Lee, W. M. Chen, H. X. Dong, L. Sun, Z. H. Chen, and I. A. Buyanova

Appl. Phys. Lett. 96, 033108 (2010); http://dx.doi.org/10.1063/1.3292027 (3 pages) | Cited 5 times

Online Publication Date: 19 January 2010

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Temperature dependent photoluminescence and cathodoluminescence (CL) spectroscopies are employed to investigate free exciton (FX) emissions in ZnO tetrapods. The intensity of the no-phonon line is found to be largely suppressed as compared with longitudinal optical phonon assisted transitions, in sharp contrast to bulk ZnO. From spatially resolved CL studies, this suppression is shown to strongly depend on structural morphology of the ZnO tetrapods and becomes most significant within areas with faceted surfaces. A model based on reabsorption due to multiple internal reflections in the vicinity of the FX resonance is suggested to account for the observed effect.
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71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
63.20.kk Phonon interactions with other quasiparticles
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Anomalously enhanced Raman scattering from longitudinal optical phonons on Ag-nanoparticle-covered GaN and ZnO

C. Y. Liu, M. M. Dvoynenko, M. Y. Lai, T. H. Chan, Y. R. Lee, J.-K. Wang, and Y. L. Wang

Appl. Phys. Lett. 96, 033109 (2010); http://dx.doi.org/10.1063/1.3291041 (3 pages) | Cited 7 times

Online Publication Date: 20 January 2010

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The authors report experimental studies of surface-enhanced Raman scattering (SERS) of wurtzite-type GaN and ZnO crystalline samples covered with Ag-nanoparticles. The longitudinal optical phonons consistently exhibit unusually intense Raman enhancement in comparison with other phonons. The anomaly is interpreted by a proposed model based on a resonant Raman scattering process assisted by metal-induced gap states at the Ag/GaN and Ag/ZnO interfaces. This study suggests that SERS of lattice vibrations in inorganic semiconductors is sensitive to their propagation nature, providing a progressive perspective view on electron-mediated enhanced Raman scattering.
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78.30.-j Infrared and Raman spectra
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Polymer functionalized n-type single wall carbon nanotube photovoltaic devices

Zhongrui Li, Viney Saini, Enkeleda Dervishi, Vasyl P. Kunets, Jianhui Zhang, Yang Xu, Alexandru R. Biris, Gregory J. Salamo, and Alexandru S. Biris

Appl. Phys. Lett. 96, 033110 (2010); http://dx.doi.org/10.1063/1.3284657 (3 pages) | Cited 10 times

Online Publication Date: 20 January 2010

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Photovoltaic conversion was achieved from high-density p-n heterojunctions formed between polymer functionalized n-type single wall carbon nanotubes (SWNTs) and underlying p-type Si substrate. Functionalization of SWNTs by amine-rich polymers results in the evolution of tubes from p-type to n-type, and the polyethylene imine (PEI) functionalized SWNT film can serve as both photogeneration sites and a charge carrier collecting/transport layer. Photoremoval of oxygen adsorbed on the nanotubes prior to PEI functionalization can increase the conversion efficiency of the polymer functionalized n-type SWNT photovoltaic devices.
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88.40.H- Solar cells (photovoltaics)
73.63.Fg Nanotubes
85.35.Kt Nanotube devices
73.61.Ph Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Electronic structure of self-assembled InGaAs/GaAs quantum rings studied by capacitance-voltage spectroscopy

W. Lei, C. Notthoff, A. Lorke, D. Reuter, and A. D. Wieck

Appl. Phys. Lett. 96, 033111 (2010); http://dx.doi.org/10.1063/1.3293445 (3 pages) | Cited 2 times

Online Publication Date: 22 January 2010

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Self-assembled InGaAs quantum rings, embedded in a GaAs matrix, were investigated using magneto-capacitance-voltage spectroscopy. The magnetic-field dispersion of the charging energies exhibits characteristic features for both the first and second electron, which can be attributed to a ground state transition from l = 0 into l = −1, and a ground state transition from l = −1 into l = −2, respectively. Furthermore, using a combination of capacitance-voltage spectroscopy and one-dimensional numerical simulations, the conduction band structure of these InGaAs quantum rings was determined.
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73.21.La Quantum dots
72.20.My Galvanomagnetic and other magnetotransport effects
73.63.Kv Quantum dots

Contrast inversion of the apparent barrier height of Pb thin films in scanning tunneling microscopy

Michael Becker and Richard Berndt

Appl. Phys. Lett. 96, 033112 (2010); http://dx.doi.org/10.1063/1.3291114 (3 pages) | Cited 3 times

Online Publication Date: 22 January 2010

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Scanning tunneling microscopy measurements of the apparent height of the tunneling barrier are analyzed for Pb islands on Ag(111). The apparent barrier height (ABH) significantly varies with the bias voltage. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of the ABH. Using model calculations, these variations are interpreted in terms of the strongly modulated local density of states of thin Pb films, which is caused by quantum well states.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.43.Mn Adsorption kinetics
68.55.-a Thin film structure and morphology
71.20.Gj Other metals and alloys
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.61.At Metal and metallic alloys

Asymmetry in photocurrent enhancement by plasmonic nanoparticle arrays located on the front or on the rear of solar cells

F. J. Beck, S. Mokkapati, A. Polman, and K. R. Catchpole

Appl. Phys. Lett. 96, 033113 (2010); http://dx.doi.org/10.1063/1.3292020 (3 pages) | Cited 42 times

Online Publication Date: 22 January 2010

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We show experimentally that there is asymmetry in photocurrent enhancement by Ag nanoparticle arrays located on the front or on the rear of solar cells. The scattering cross-section calculated for front- and rear-located nanoparticles can differ by up to a factor of 3.7, but the coupling efficiency remains the same. We attribute this to differences in the electric field strength and show that the normalized scattering cross-section of a front-located nanoparticle varies from two to eight depending on the intensity of the driving field. In addition, the scattering cross-section of rear-located particles can be increased fourfold using ultrathin spacer layers.
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88.40.H- Solar cells (photovoltaics)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
79.60.-i Photoemission and photoelectron spectra
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