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3 Oct 2011

Volume 99, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 141901 (2011); http://dx.doi.org/10.1063/1.3644948 (3 pages)

G. Kozlowski, P. Zaumseil, M. A. Schubert, Y. Yamamoto, J. Bauer, J. Matejova, T. Schulli, B. Tillack, and T. Schroeder
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Large-area transparent conductive few-layer graphene electrode in GaN-based ultra-violet light-emitting diodes

Byung-Jae Kim, Chongmin Lee, Younghun Jung, Kwang Hyeon Baik, Michael A. Mastro, Jennifer K. Hite, Charles R. Eddy, Jr., and Jihyun Kim

Appl. Phys. Lett. 99, 143101 (2011); http://dx.doi.org/10.1063/1.3644496 (3 pages) | Cited 15 times

Online Publication Date: 4 October 2011

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We report on the development of a large-area few-layer graphene (FLG)—based transparent conductive electrode as a current spreading layer for GaN-based ultraviolet (UV) light-emitting diodes (LEDs). Large-area FLG was deposited on Cu using the chemical vapor deposition (CVD) method and subsequently transferred to the surface of the UV LED. UV light at a peak of 372 nm was emitted through the FLG-based transparent conductive electrode. The current spreading effects of FLG were clearly evident in both the optical images of electroluminescence (EL) and current-voltage (I-V) characteristics. Degradation of the FLG-based transparent conductive electrode could be induced by high power operation. Our results indicate that a large-area FLG-based electrode on GaN offers excellent current spreading and ultra-violet transparency properties when compared to the standard optoelectronic indium tin oxide (ITO) contact layer.
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85.60.Jb Light-emitting devices
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.60.Fi Electroluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Metal induced crystallization mechanism of the metal catalyzed growth of silicon wire-like crystals

Andrey Sarikov

Appl. Phys. Lett. 99, 143102 (2011); http://dx.doi.org/10.1063/1.3644981 (3 pages) | Cited 1 time

Online Publication Date: 4 October 2011

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A thermodynamic mechanism explaining the universal role of metal catalyst in the transformation of Si in the crystalline state and the preferential growth of Si wire-like crystals in the vapor-liquid-solid and relative processes is proposed based on the mechanism of the metal induced crystallization of amorphous Si. It includes metal stimulated crystallization of disordered Si formed on the catalyst and substrate surfaces and the wire-like crystal sidewalls, driven by the chemical potential difference of Si in the disordered and crystalline states. Obtained results have general nature and are applicable to the metal catalyzed wire-like crystal growth in different metal/semiconductor systems.
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64.70.kg Semiconductors
65.40.G- Other thermodynamical quantities
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.05.Cy Elemental semiconductors

Angle-resolved cathodoluminescence spectroscopy

Toon Coenen, Ernst Jan R. Vesseur, and Albert Polman

Appl. Phys. Lett. 99, 143103 (2011); http://dx.doi.org/10.1063/1.3644985 (3 pages) | Cited 9 times

Online Publication Date: 4 October 2011

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We present a cathodoluminescence spectroscopy technique which combines deep subwavelength excitation resolution with angle-resolved detection capabilities. The cathodoluminescence emission is collected by a paraboloid mirror (effective NA = 0.96) and is projected onto a 2D CCD array. The azimuthal and polar emission pattern is directly deduced from the image. As proof of principle, we use the technique to measure the angular distribution of transition radiation from a single crystalline gold surface under 30 keV electron irradiation. We find that the experiment matches very well with theory, illustrating the potential of this technique for the characterization of photonic structures with deep subwavelength dimensions.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.80.Fe Electron and positron radiation effects
61.82.Bg Metals and alloys

Control of dense carbon nanotube arrays via hierarchical multilayer catalyst

C. Fisher, Z. J. Han, I. Levchenko, and K. Ostrikov

Appl. Phys. Lett. 99, 143104 (2011); http://dx.doi.org/10.1063/1.3645625 (3 pages) | Cited 3 times

Online Publication Date: 4 October 2011

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Effective control of dense, high-quality carbon nanotube arrays using hierarchical multilayer catalyst patterns is demonstrated. Scanning/transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and numerical simulations show that by changing the secondary and tertiary layers one can control the properties of the nanotube arrays. The arrays with the highest surface density of vertically aligned nanotubes are produced using a hierarchical stack of iron nanoparticles and alumina and silica layers differing in thickness by one order of magnitude from one another. The results are explained in terms of the catalyst structure effect on carbon diffusivity.
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81.16.Hc Catalytic methods
61.46.Fg Nanotubes
78.67.Ch Nanotubes
81.07.De Nanotubes
78.30.Na Fullerenes and related materials
68.35.Fx Diffusion; interface formation

Nitrogen flux induced GaN nanostructure nucleation at misfit dislocations on Al2O3(0001)

Manoj Kesaria and S. M. Shivaprasad

Appl. Phys. Lett. 99, 143105 (2011); http://dx.doi.org/10.1063/1.3646391 (3 pages) | Cited 4 times

Online Publication Date: 4 October 2011

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The work demonstrates the dominant role of nitrogen flux rate on GaN nanostructure formation on bare Al2O3(0001). In nitrogen rich conditions, wurtzite c-oriented GaN nanowall honeycomb network is formed as strain relaxation pathway of nucleation at edge dislocations. A specific nitrogen flux rate in a plasma assisted molecular beam epitaxy growth is necessary for fixed Ga flux and substrate temperature to form columnar self assembled nanostructures. It is argued that kinetically hindering diffusion of Ga adatoms and the low sticking coefficient of r and m planes of nanowalls promote 1-dimension nanocolumn formation at screw dislocations formed at the GaN-Sapphire interface.
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61.46.-w Structure of nanoscale materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.Ct Interface structure and roughness
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors

Field emission from hydrogen titanate nanotubes

Indrani Chakraborty, Sriparna Chatterjee, and Pushan Ayyub

Appl. Phys. Lett. 99, 143106 (2011); http://dx.doi.org/10.1063/1.3646401 (3 pages)

Online Publication Date: 4 October 2011

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Hydrothermally synthesized hydrogen titanate (H2Ti3O7) nanotube meshes and arrays exhibit excellent field emission characteristics. The turn-on field is as low as 1.4 V μm−1 for the mesh and 2.6 V μm−1 for the array, while the electric field corresponding to an emission current density of 10 μA cm−2 is 2 V μm−1 (mesh) and 3.8 V μm−1 (array). The H2Ti3O7 nanotube mesh has one of the lowest reported turn-on voltages and highest enhancement factors. The emission current also shows good long term stability. We attribute the efficient field emission to the presence of mid-gap states arising from the negative surface charge on the H2Ti3O7 nanotubes.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Fg Nanotubes
81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing

Penetration depth in near-field radiative heat transfer between metamaterials

Soumyadipta Basu and Mathieu Francoeur

Appl. Phys. Lett. 99, 143107 (2011); http://dx.doi.org/10.1063/1.3646466 (3 pages) | Cited 4 times

Online Publication Date: 4 October 2011

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In this letter, we investigate the penetration depth in near-field radiative heat transfer between metamaterials when surface polaritons are excited at both electrical and magnetic resonances. The analyses show that based on the optical properties of the metamaterial, two different penetration depths can be defined corresponding to electrical and magnetic resonances. Depending upon the scattering rate of the metamaterial, it is possible to selectively enhance or reduce the penetration depth of near-field thermal radiation at electric and magnetic resonances. The results obtained from this study will benefit applications of metamaterials in near-field energy harvesting.
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44.40.+a Thermal radiation
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
42.70.-a Optical materials

Reproducible electrochemical etching of silver probes with a radius of curvature of 20 nm for tip-enhanced Raman applications

J. S. Lloyd, A. Williams, R. H. Rickman, A. McCowen, and P. R. Dunstan

Appl. Phys. Lett. 99, 143108 (2011); http://dx.doi.org/10.1063/1.3646106 (3 pages)

Online Publication Date: 5 October 2011

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The performance of tip-enhanced Raman spectroscopy (TERS) largely depends on probe optimisation. An electrochemical etch using nitric acid and ethanol produces sharp silver probes with radius of curvature between 20 and 60 nm. Optimisation also identified controllable tapers; rough or smooth. Boundary element method simulations comparing the response to 532 nm excitation of silver and gold probes reveal no discernable field enhancement at the gold apex, but strong localised enhancement is observed at the silver apex. The motivation for employing this method of etching silver probes can also be seen in the signal enhancement observed in preliminary TERS data presented.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
02.60.Pn Numerical optimization

Spectroscopy of mechanical dissipation in micro-mechanical membranes

Andreas Jöckel, Matthew T. Rakher, Maria Korppi, Stephan Camerer, David Hunger, Matthias Mader, and Philipp Treutlein

Appl. Phys. Lett. 99, 143109 (2011); http://dx.doi.org/10.1063/1.3646914 (3 pages) | Cited 5 times

Online Publication Date: 5 October 2011

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We measure the frequency dependence of the mechanical quality factor (Q) of SiN membrane oscillators and observe a resonant variation of Q by more than two orders of magnitude. The frequency of the fundamental mechanical mode is tuned reversibly by up to 40% through local heating with a laser. Several distinct resonances in Q are observed that can be explained by coupling to membrane frame modes. Away from the resonances, the background Q is independent of frequency and temperature in the measured range.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.30.Ng Oscillators, pulse generators, and function generators

Effects of electrical contacts on the photoconductive gain of nanowire photodetectors

Hongsik Park, Jin Ho Kim, Roderic Beresford, and Jimmy Xu

Appl. Phys. Lett. 99, 143110 (2011); http://dx.doi.org/10.1063/1.3647559 (3 pages) | Cited 1 time

Online Publication Date: 6 October 2011

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The mechanism of the photoconductive gains of nanowire (NW) photodetectors has not been clearly explained yet, although it is generally thought to be the result of a long excess carrier lifetime due to a large trap density. Here, we demonstrate that the photoconductive gain of a Bi2S3 NW photodetector can be contributed by optical modulation of the electrical injection through contacts. We propose a quantitative model to explain the results based on a model of metal-nanowire contacts. The study shows that optically generated excess carriers can modify the barrier structure at the metal-nanowire interface and thereby increase photoconductivity.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

High efficiency resonance-based spectrum filters with tunable transmission bandwidth fabricated using nanoimprint lithography

Alex F. Kaplan, Ting Xu, and L. Jay Guo

Appl. Phys. Lett. 99, 143111 (2011); http://dx.doi.org/10.1063/1.3647633 (3 pages) | Cited 6 times

Online Publication Date: 6 October 2011

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We propose a nanostructured color filter based on a metallic resonant waveguide structure capable of extremely high transmission efficiency. As an experimental demonstration, a blue and a red device were fabricated over a large area using nanoimprint lithography. Achieving transmission as high as 90% with a variable transmission bandwidth, these devices exhibit desirable features for numerous color filter applications.
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42.79.Gn Optical waveguides and couplers
42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography

Nitrogen deep accepters in ZnO nanowires induced by ammonia plasma

Rui Huang, Shuigang Xu, Wenhao Guo, Lin Wang, Jie Song, Tsz-Wai Ng, Jianan Huang, Shuit-Tong Lee, Shengwang Du, and Ning Wang

Appl. Phys. Lett. 99, 143112 (2011); http://dx.doi.org/10.1063/1.3647773 (3 pages) | Cited 5 times

Online Publication Date: 6 October 2011

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Nitrogen doping in ZnO nanowires was achieved through ammonia plasma treatment followed by thermal annealing. The strong dependence of the red light emission from the nanowires excited by 2.4 eV on the nitrogen concentration, suggests that the red light emission originates from nitrogen related defects. The mechanism responsible for the red light emission is in good agreement with the deep-acceptor model of nitrogen defects, clarifying that nitrogen atoms caused deep accepters in ZnO nanowires. Based on this model, the enhanced green emission from defects in nitrogen-doped samples (excited by 325 nm line) can be well explained by the increase of the concentration of activated oxygen vacancies resulting from the compensation of nitrogen deep acceptors.
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61.72.uj III-V and II-VI semiconductors
78.67.Uh Nanowires
81.07.Gf Nanowires
78.55.Et II-VI semiconductors
78.55.Hx Other solid inorganic materials
61.72.jd Vacancies

In-situ observation of 〈110〉 oriented Ge nanowire growth and associated collector droplet behavior

Miroslav Kolíbal, Tomáš Vystavěl, Libor Novák, Jindřich Mach, and Tomáš Šikola

Appl. Phys. Lett. 99, 143113 (2011); http://dx.doi.org/10.1063/1.3647774 (3 pages) | Cited 2 times

Online Publication Date: 6 October 2011

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Using in-situ microscopy, we show that germanium nanowires can be grown by a vapor-liquid-solid process in 〈110〉 directions both on Ge(100) and Ge(111) substrates if very low supersaturation in the collector droplet is ensured. This can be provided if thermal evaporation is utilized. Such a behavior is also in agreement with earlier chemical vapor deposition experiments, where 〈110〉 oriented wires were obtained for very small wire diameters only. Our conclusions are supported by in-situ observations of nanowire kinking towards 〈111〉 direction occurring more frequently at higher evaporation rates.
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81.07.Gf Nanowires
81.05.Cy Elemental semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Tunable two-dimensional molecular dipole dot arrays on graphite

Tian Chao Niu, Yu Li Huang, Jia Tao Sun, Satoshi Kera, Nobuo Ueno, Andrew Thye Shen Wee, and Wei Chen

Appl. Phys. Lett. 99, 143114 (2011); http://dx.doi.org/10.1063/1.3647563 (3 pages) | Cited 3 times

Online Publication Date: 7 October 2011

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We report the construction of two dimensional molecular dipole dot arrays with tunable dipole density via self-assembly of binary molecular system of dipolar molecule of chloroaluminium phthalocyanine (ClAlPc) with copper hexadecafluorophthalocyanine (F16CuPc) on graphite surface, as revealed by in situ low-temperature scanning tunneling microscopy experiments. The formation of multiple intermolecular C−H…F−C hydrogen bondings between the periphery F atoms on F16CuPc and H atoms on neighboring ClAlPc molecules can ensure structural rigidity and stability for potential applications in molecular nanodevices.
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81.07.Nb Molecular nanostructures
85.65.+h Molecular electronic devices
36.20.Hb Configuration (bonds, dimensions)

Stress evolution during the oxidation of silicon nanowires in the sub-10 nm diameter regime

Byung-Hyun Kim, Mauludi Ariesto Pamungkas, Mina Park, Gyubong Kim, Kwang-Ryeol Lee, and Yong-Chae Chung

Appl. Phys. Lett. 99, 143115 (2011); http://dx.doi.org/10.1063/1.3643038 (3 pages) | Cited 4 times

Online Publication Date: 7 October 2011

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Using a reactive molecular dynamics simulation, the oxidation of Si nanowires (Si-NWs) with diameters of 5, 10, and 20 nm was investigated. The compressive stress at the interface between the oxide and the Si core decreased with increasing curvature in the sub-10 nm regime of the diameter, in contrast to the theory of self-limiting oxidation where rigid mechanical constraint of the Si core was assumed. The Si core of the thinner Si-NW was deformed more with surface oxidation, resulting in a lower compressive stress at the interface. These results explain the experimental observation of full oxidation of very thin Si-NWs.
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81.65.Mq Oxidation
62.20.F- Deformation and plasticity
62.23.Hj Nanowires
81.16.Pr Micro- and nano-oxidation
81.40.Lm Deformation, plasticity, and creep

Theoretical analysis and modeling of light trapping in high efficicency GaAs nanowire array solar cells

Long Wen, Zhifei Zhao, Xinhua Li, Yanfen Shen, Haoming Guo, and Yuqi Wang

Appl. Phys. Lett. 99, 143116 (2011); http://dx.doi.org/10.1063/1.3647847 (3 pages) | Cited 15 times

Online Publication Date: 7 October 2011

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A rigorous analysis and design of efficient light trapping for Gallium arsenide nanowire array (NWA) solar cells is presented. The influence of the geometric parameters on the optical absorption of NWA has been thoroughly analyzed by using finite-difference time-domain simulations. It is found that the NWA have superior absorption characteristic over thin-film due to the combined effects of intrinsic anti-reflection and efficient excitation of resonant modes. Optimized optical designs are obtained by maximizing the ultimate photocurrent under AM1.5G illumination. The photogeneration profiles under optimized conditions are incorporated into electrical modeling, in which the core-shell NWA solar cells exhibit 22.3% efficiency.
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88.40.jm Thin film III-V and II-VI based solar cells
88.40.hj Efficiency and performance of solar cells
02.70.Bf Finite-difference methods
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.07.Gf Nanowires
81.05.Ea III-V semiconductors

Subwavelength slow-light waveguides based on a plasmonic analogue of electromagnetically induced transparency

Yin Huang, Changjun Min, and Georgios Veronis

Appl. Phys. Lett. 99, 143117 (2011); http://dx.doi.org/10.1063/1.3647951 (3 pages) | Cited 12 times

Online Publication Date: 7 October 2011

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We introduce a plasmonic waveguide system, based on a plasmonic analogue of electromagnetically induced transparency, which supports a subwavelength slow-light mode, and exhibits a small group velocity dispersion. The system consists of a periodic array of two metal-dielectric-metal (MDM) stub resonators side-coupled to a MDM waveguide. Decreasing the frequency spacing between the two resonances increases the slowdown factor and decreases the bandwidth of the slow-light band. We also show that there is a trade-off between the slowdown factor and the propagation length of the slow-light mode.
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42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Ferromagnetic and antiferromagnetic spin-wave dispersions in a dipole-exchange coupled bi-component magnonic crystal

V. L. Zhang, H. S. Lim, C. S. Lin, Z. K. Wang, S. C. Ng, M. H. Kuok, S. Jain, A. O. Adeyeye, and M. G. Cottam

Appl. Phys. Lett. 99, 143118 (2011); http://dx.doi.org/10.1063/1.3647952 (3 pages) | Cited 3 times

Online Publication Date: 7 October 2011

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The magnon dispersion relations of the ferromagnetic and antiferromagnetic phases in a dipole-exchange coupled one-dimensional magnonic crystal comprising alternating cobalt and Permalloy nanostripes have been mapped by Brillouin spectroscopy. To elucidate the magnetization dynamics at the interfaces between stripes, the experimental data are analyzed based on a macroscopic theory under Hoffmann-type boundary conditions. Good agreement is obtained between theory and experiment for both the ferromagnetic and antiferromagnetic phases. Results suggest the existence of strong exchange coupling across the cobalt-Permalloy interfaces, comparable with the exchange coupling within each component material.
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75.30.Ds Spin waves
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
75.78.-n Magnetization dynamics

Graphene nano-ribbon formation through hydrogen-induced unzipping of carbon nanotubes

L. Tsetseris and S. T. Pantelides

Appl. Phys. Lett. 99, 143119 (2011); http://dx.doi.org/10.1063/1.3648105 (3 pages) | Cited 8 times

Online Publication Date: 7 October 2011

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Longitudinal unzipping of carbon nanotubes (CNTs) can create graphene nano-ribbons (GNRs) with predetermined width. Experiments have used thus far an oxidative-induced unzipping approach that produces residual oxygen impurities. Here, we employ results of first-principles calculations to demonstrate an alternative scenario of GNR formation. We show that hydrogen loading at open CNT ends leads to successive C–C bond breaking and opening of CNTs to GNRs with edge morphologies that depend on CNT chirality. We also show that re-zipping of partially open CNTs can lead to new type of materials, for example, CNTs with lines of oxygen inter-carbon bridges.
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81.05.ue Graphene
61.48.Gh Structure of graphene
81.16.-c Methods of micro- and nanofabrication and processing
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.07.De Nanotubes
68.35.bp Fullerenes

Keeping gallium metal to liquid state under the freezing point by using silica nanoparticles

Lingfei Cao, Hyunseo Park, Gjergj Dodbiba, Kenji Ono, Chiharu Tokoro, and Toyohisa Fujita

Appl. Phys. Lett. 99, 143120 (2011); http://dx.doi.org/10.1063/1.3645596 (3 pages) | Cited 1 time

Online Publication Date: 7 October 2011

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Gallium metal under the freezing point was observed to maintain its liquid state by dispersing silica nanoparticles of a given particle size and concentration. Though the freezing point of pure gallium is 302.9 K, the liquid gallium maintained its supercooling state at 276-277 K for more than 400 days by dispersing 1.0 wt. % of silica nanoparticles (10 nm in size). Extended x-ray absorption fine structure analysis shows that the supercooled gallium liquid has a β-Ga-like feature, and the nearest neighboring atom distance is 0.1 Å larger than that of pure liquid gallium. This method opens the way to use liquid gallium as a promising fluid carrier in energy conversion devices.
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64.70.D- Solid-liquid transitions
61.25.Mv Liquid metals and alloys
78.70.Dm X-ray absorption spectra
82.70.Dd Colloids

Log-normal distribution of single molecule fluorescence bursts in micro/nano-fluidic channels

Lazar L. Kish, Jun Kameoka, Claes G. Granqvist, and Laszlo B. Kish

Appl. Phys. Lett. 99, 143121 (2011); http://dx.doi.org/10.1063/1.3648118 (3 pages) | Cited 4 times

Online Publication Date: 7 October 2011

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The width and shape of photon burst histograms pose significant limitations to the identification of single molecules in micro/nano-fluidic channels, and the nature of these histograms is not fully understood. To reach a deeper understanding, we performed computer simulations based on a Gaussian beam intensity profile with various fluidic channel diameters and assuming (1) a deterministic (noise-free) case, (2) photon emission/absorption noise, and (3) photon noise with diffusion. Photon noise in narrow channels yields a Gaussian burst distribution while additional strong diffusion produces skewed histograms. We use the fluctuating residence time picture [J. Söderlund et al., Phys. Rev. Lett. 80, 2386 (1998)] and conclude that the skewness of the photon number distribution is caused by the longitudinal diffusive component of the motion of the molecules as they traverse the laser beam. In the case of strong diffusion in narrow channels, this effect leads to a log-normal distribution. We show that the same effect can transform the separate peaks of the photon burst histograms of multiple molecule mixtures into a single log-normal shape.
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87.15.Vv Diffusion
02.50.-r Probability theory, stochastic processes, and statistics
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Substrate-mediated electron tunneling through molecule-electrode interfaces

Jia-Tao Sun, Lan Chen, Yuan Ping Feng, and Andrew Thye Shen Wee

Appl. Phys. Lett. 99, 143122 (2011); http://dx.doi.org/10.1063/1.3650248 (3 pages) | Cited 2 times

Online Publication Date: 7 October 2011

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Electron tunneling properties at the molecule-electrode interfaces formed by coronene molecules adsorbed on Ag(111) and highly oriented pyrolytic graphite surfaces are investigated by scanning tunneling microscopy and first-principles calculations. Experimentally, the coronene molecules display significant variation in the electronic density of states at the molecular centers on different substrates. An analysis of the electronic structures for both systems by first-principles calculations based on density functional theory reveals that substrate dependent molecular image contrast is ascribed to the resonant tunneling process mediated by geometrically different substrates. Possible consequences for electron transport are briefly discussed.
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73.40.Gk Tunneling
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
82.45.-h Electrochemistry and electrophoresis
71.20.Rv Polymers and organic compounds

Room temperature photoluminescence of high density (In,Ga)As/GaP quantum dots

T. Nguyen Thanh, C. Robert, C. Cornet, M. Perrin, J. M. Jancu, N. Bertru, J. Even, N. Chevalier, H. Folliot, O. Durand, and A. Le Corre

Appl. Phys. Lett. 99, 143123 (2011); http://dx.doi.org/10.1063/1.3646911 (3 pages) | Cited 7 times

Online Publication Date: 7 October 2011

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We report on the achievement of high density (In,Ga)As self-assembled quantum dots on GaP substrate with a good homogeneity. Good structural and electronic properties have been achieved, as revealed by room temperature photoluminescence measurements and by comparison to both InAs/GaAs and InAs/InP materials reference systems. This is supported by atomistic calculations where the indium incorporation in InGaAs/GaP quantum structures is found to enhance both the type-I bandlineup and direct bandgap properties. The photoluminescence temperature dependence of the bandgap evidences the quantum confinement effects. Our results provide a valid framework to implement silicon optical devices based on InGaAs/GaP nanostructures.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
73.21.La Quantum dots
81.07.Ta Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
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