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29 Sep 2008

Volume 93, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 132101 (2008); http://dx.doi.org/10.1063/1.2988720 (3 pages)

Yueh-Nan Chen and Lukas Gilz
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Low noise superconducting single photon detectors on silicon

S. N. Dorenbos, E. M. Reiger, U. Perinetti, V. Zwiller, T. Zijlstra, and T. M. Klapwijk

Appl. Phys. Lett. 93, 131101 (2008); http://dx.doi.org/10.1063/1.2990646 (3 pages) | Cited 30 times

Online Publication Date: 29 September 2008

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We have fabricated superconducting nanowire single photon detectors made of NbTiN on a silicon substrate. This type of material reduces the dark count rate by a factor of 10 compared to identical NbN detectors, enabling single photon detection with unprecedented signal to noise ratio: we report a noise equivalent power of 10−19 W Hz−1/2 at 4.2 K. The compatibility of our superconducting device with silicon enables its integration with complex structures.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Three photon absorption in silicon for 2300–3300 nm

Shaul Pearl, Nir Rotenberg, and Henry M. van Driel

Appl. Phys. Lett. 93, 131102 (2008); http://dx.doi.org/10.1063/1.2991446 (3 pages) | Cited 12 times

Online Publication Date: 29 September 2008

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We measure the spectral dependence of the degenerate three photon absorption coefficient, γ, for a Si [100] wafer using 200 fs pulses in the range 2300–3300 nm, i.e., photon energy between half and one-third the indirect band gap. For pulses linearly polarized along the [001] crystal axis γ increases from a value of near 0 cm3/GW2 at 3300 nm to a peak value of 0.035 cm3/GW2 at 2700 nm before decreasing with shorter wavelength; this is consistent with the dispersion expected from allowed-allowed-allowed transitions. At 2600 nm the γ value is ∼ 30% larger for light polarized along [011] than along [001].
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
71.20.Mq Elemental semiconductors
78.47.-p Spectroscopy of solid state dynamics

Transverse mode competition effects on the dynamics of gain-switched vertical-cavity surface-emitting lasers

A. Valle, M. Arizaleta, H. Thienpont, K. Panajotov, and M. Sciamanna

Appl. Phys. Lett. 93, 131103 (2008); http://dx.doi.org/10.1063/1.2992630 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2008

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An experimental analysis of the nonlinear dynamics of a multi-transverse-mode vertical-cavity surface-emitting laser (VCSEL) when subject to a high-frequency current modulation is performed. Regular periodic dynamics—with periods equal to the modulation period or twice the modulation period—and irregular pulsating dynamics are obtained. Our results show that the irregular pulsating dynamics in multimode VCSELs subject to large-signal current modulation is due to the competition between different transverse modes.
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42.55.Px Semiconductor lasers; laser diodes

InAs–GaSb laser: Prospects for efficient terahertz emission

L. D. Shvartsman and B. Laikhtman

Appl. Phys. Lett. 93, 131104 (2008); http://dx.doi.org/10.1063/1.2993232 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2008

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We suggest to use InAs/GaSb coupled quantum wells for terahertz lasing. In these heterostructures terahertz lasing is based not on intersubband but on interband transitions. Crucial advantages of this design in comparison with intersubband lasers are (i) a large value of the interband dipole matrix element and (ii) easier maintenance of population inversion. These advantages lead to a gain of two orders of magnitude higher than that for intersubband lasing. Even higher gain can be obtained in special design InAs/GaSb W-structures where a hybridization gap of 1–3 THz is formed and optical density of states is singular.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Generation of tunable Fourier-transform-limited terahertz pulses in 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate crystals

Jinjun Liu and Frédéric Merkt

Appl. Phys. Lett. 93, 131105 (2008); http://dx.doi.org/10.1063/1.2977490 (3 pages)

Online Publication Date: 1 October 2008

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We report difference-frequency generation (DFG) of widely tunable, pulsed, Fourier-transform-limited terahertz radiation (bandwidth of ∼ 10 MHz, peak power up to ∼ 400 μW) from pulse-amplified near-infrared (λ ∼ 800 nm) laser radiation using a crystal of the organic salt 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST) cut along the b axis to fulfill the phase-matching condition. The broad tunability and narrow bandwidth of the terahertz radiation generated by DFG in DAST are illustrated by a single scan of the terahertz spectrum of H2O from 0.1 to 11 THz, and a recording of the absorption spectrum of a pure rotational transition of HF near 5 THz.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Fc Modulation, tuning, and mode locking
78.70.Gq Microwave and radio-frequency interactions

Direct probe of the built-in electric field of Mg-doped a-plane wurtzite InN surfaces with time-resolved electric-field-induced second harmonic generation

Y.-M. Chang, Y.-L. Hong, and S. Gwo

Appl. Phys. Lett. 93, 131106 (2008); http://dx.doi.org/10.1063/1.2979238 (3 pages) | Cited 6 times

Online Publication Date: 2 October 2008

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The exceptionally large electron affinity of InN causes the pinning of surface Fermi level well above the conduction band minimum. This unique electronic property leads to the electron accumulation at InN surfaces and a large built-in electric field in the topmost few nanometers of InN surfaces. In this letter, we demonstrate that this surface electric field can be unambiguously determined and monitored in a-plane wurtzite InN surface via time-resolved electric-field-induced second harmonic generation. This finding makes it possible to directly probe and characterize the surface electronic properties of Mg-doped InN with an all-optical technique in ambient environment.
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73.20.At Surface states, band structure, electron density of states
73.25.+i Surface conductivity and carrier phenomena
78.47.D- Time resolved spectroscopy (>1 psec)
78.20.Jq Electro-optical effects
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.47.N- High resolution nonlinear optical spectroscopy

InSbN alloys prepared by two-step ion implantation for infrared photodetection

D. H. Zhang, W. Liu, Y. Wang, X. Z. Chen, J. H. Li, Z. M. Huang, and Sam S. Y. Zhang

Appl. Phys. Lett. 93, 131107 (2008); http://dx.doi.org/10.1063/1.2990756 (3 pages) | Cited 11 times

Online Publication Date: 2 October 2008

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InSbN alloys are fabricated by two-step nitrogen ion implantation into InSb (111) wafers. X-ray photoelectron spectroscopy indicates that most of the implanted nitrogen ions substitute Sb to form In–N bonds. The percentage of the In–N bonds is found to decrease with the increase in the implanted nitrogen. Such alloys can effectively detect long wavelength infrared radiation and the absorption peak energies can be controlled by monitoring the implanted nitrogen dose. The measured peak wavelengths are consistent with the band gaps of the alloys calculated using a ten-band k⋅p model.
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61.72.uj III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Influence of the material parameters on quantum cascade devices

E. Benveniste, A. Vasanelli, A. Delteil, J. Devenson, R. Teissier, A. Baranov, A. M. Andrews, G. Strasser, I. Sagnes, and C. Sirtori

Appl. Phys. Lett. 93, 131108 (2008); http://dx.doi.org/10.1063/1.2991447 (3 pages) | Cited 8 times

Online Publication Date: 2 October 2008

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An experimental investigation on the influence of the material systems on the optical properties of quantum cascade structures is presented. Three electroluminescent quantum cascade devices have been grown using GaAs/AlGaAs, GaInAs/AlInAs, and InAs/AlSb heterostructures. The devices emit at 10 μm and are based on a similar bandstructure design. Our results verify that the optical quantum efficiency has the predicted dependence on the electron effective mass. We also demonstrate that the shape of the electroluminescence spectra is independent from the particular material parameters and mainly depends on the tunnel coupling between the injector state and the upper state of the radiative transition.
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85.60.Jb Light-emitting devices

Amplified dispersive Fourier-transform imaging for ultrafast displacement sensing and barcode reading

Keisuke Goda, Kevin K. Tsia, and Bahram Jalali

Appl. Phys. Lett. 93, 131109 (2008); http://dx.doi.org/10.1063/1.2992064 (3 pages) | Cited 13 times

Online Publication Date: 2 October 2008

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Dispersive Fourier transformation is a powerful technique in which the spectrum of an optical pulse is mapped into a time-domain waveform using chromatic dispersion. It replaces a diffraction grating and detector array with a dispersive fiber and single photodetector. This simplifies the system and, more importantly, enables fast real-time measurements. Here we describe a novel ultrafast barcode reader and displacement sensor that employs internally amplified dispersive Fourier transformation. This technique amplifies and simultaneously maps the spectrally encoded barcode into a temporal waveform. It achieves a record acquisition speed of 25 MHz—four orders of magnitude faster than the current state of the art.
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42.30.Kq Fourier optics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Dj Gratings

Optical excitation and characterization of gigahertz acoustic resonances in optical fiber tapers

Myeong Soo Kang, André Brenn, Gustavo S. Wiederhecker, and Philip St.J. Russell

Appl. Phys. Lett. 93, 131110 (2008); http://dx.doi.org/10.1063/1.2995863 (3 pages) | Cited 4 times

Online Publication Date: 2 October 2008

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Transverse acoustic resonances at gigahertz frequencies are excited by electrostriction in the few-micrometer-thick waists of low-loss optical fiber tapers of up to 40 cm long. A pump-probe technique is used in which the resonances are excited by a train of optical pulses and probed in a Sagnac interferometer. Strong radially symmetric acoustic resonances are observed and the dependence of their frequencies on taper thickness is investigated. Such easily reconfigurable acousto-optic interactions may have applications in the high-frequency mode locking of fiber lasers.
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42.81.Cn Fiber testing and measurement of fiber parameters
42.81.Dp Propagation, scattering, and losses; solitons
07.60.Ly Interferometers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Supercollimation in photonic crystals composed of silicon rods

Ta-Ming Shih, André Kurs, Marcus Dahlem, Gale Petrich, Marin Soljačić, Erich Ippen, Leslie Kolodziejski, Katherine Hall, and Morris Kesler

Appl. Phys. Lett. 93, 131111 (2008); http://dx.doi.org/10.1063/1.2992198 (3 pages) | Cited 3 times

Online Publication Date: 3 October 2008

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Supercollimation is the propagation of light without diffraction using the properties of photonic crystals. We present the first experimental demonstration of supercollimation in a planar photonic crystal composed of nanoscale rods. Supercollimation was observed over distances of up to 1000 lattice periods.
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42.82.-m Integrated optics
42.70.Qs Photonic bandgap materials

Gigahertz modulation of tunable terahertz radiation from photomixers driven at telecom wavelengths

M. Martin, J. Mangeney, P. Crozat, Y. Chassagneux, R. Colombelli, N. Zerounian, L. Vivien, and K. Blary

Appl. Phys. Lett. 93, 131112 (2008); http://dx.doi.org/10.1063/1.2993352 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2008

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Here, we report the gigahertz-rate modulation of a tunable terahertz carrier. Terahertz radiation, tunable from 300 GHz to 1.2 THz, is generated by mixing two telecom lasers with an offset frequency in an ultrafast In0.53Ga0.47As photoconductive device coupled to a broadband antenna. The microwave modulation applied to the telecom lasers is directly transferred to the terahertz carrier. A maximum modulation rate of 20 GHz has been achieved, and the bandwidth is independent of the carrier frequency.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.Ba Antennas: theory, components and accessories
85.60.Bt Optoelectronic device characterization, design, and modeling

12 W peak-power 10 ps duration optical pulse generation by gain switching of a single-transverse-mode GaInN blue laser diode

Shunsuke Kono, Tomoyuki Oki, Takao Miyajima, Masao Ikeda, and Hiroyuki Yokoyama

Appl. Phys. Lett. 93, 131113 (2008); http://dx.doi.org/10.1063/1.2996025 (3 pages) | Cited 16 times

Online Publication Date: 3 October 2008

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We have generated optical pulses at 405 nm from a single-transverse-mode GaInN blue laser diode under intensive gain-switching operation with a minimum pulse duration of less than 8 ps. The maximum optical peak power was as high as 12 W with a pulse width of 10 ps. The peak power obtained is the highest value for optical pulses ever generated from a single transverse-mode GaInN laser diode.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Px Semiconductor lasers; laser diodes

Near-ultraviolet excitable orange-yellow Sr3(Al2O5)Cl2:Eu2+ phosphor for potential application in light-emitting diodes

Yu-Sheng Tang, Shu-Fen Hu, Wei-Chih Ke, Chun Che Lin, Nitin C. Bagkar, and Ru-Shi Liu

Appl. Phys. Lett. 93, 131114 (2008); http://dx.doi.org/10.1063/1.2996278 (3 pages) | Cited 28 times

Online Publication Date: 3 October 2008

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Sr3(Al2O5)Cl2 phosphor doped with Eu2+ was prepared by a soli-state reaction. This phosphor emits a broad orange-yellow luminescence with a peak wavelength of 620 nm and a full width at half maximum of about 175 nm under near-ultraviolet (NUV) excitation at ∼ 400 nm. Yellow light-emitting diodes (LEDs) for general lighting were fabricated by combining Sr3(Al2O5)Cl2:Eu2+ phosphor with an NUV chip. The phosphor-converted LEDs had a color temperature of about 2300 K and their color rendering index was 74.
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78.55.Hx Other solid inorganic materials
85.60.Jb Light-emitting devices

Reduction in dark current using resonant tunneling barriers in quantum dots-in-a-well long wavelength infrared photodetector

A. V. Barve, S. Y. Shah, J. Shao, T. E. Vandervelde, R. V. Shenoi, W.-Y. Jang, and S. Krishna

Appl. Phys. Lett. 93, 131115 (2008); http://dx.doi.org/10.1063/1.2996410 (3 pages) | Cited 6 times

Online Publication Date: 3 October 2008

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We report the use of resonant tunneling (RT) assisted barriers to reduce the dark current in quantum dots-in-a-well (DWELL) infrared photodetectors. Designed RT barriers allow energy-selective extraction of photoexcited carriers while blocking a continuum of energies. Over two orders of magnitude reduction in the dark current in the RT-DWELL device over a control sample without RT-DWELL at 77 K has been demonstrated. Specific detectivity (D*) of 3.6×109 cm Hz1/2 W−1 at 77 K at λpeak = 11 μm with a conversion efficiency of 5.3% was obtained in the RT-DWELL device. D* for the RT-DWELL device is five times higher than that of the control sample.
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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
72.40.+w Photoconduction and photovoltaic effects

High quality ultraviolet AlGaN/GaN multiple quantum wells with atomic layer deposition grown AlGaN barriers

Zhen-Yu Li, Ming-Hua Lo, C. T. Hung, Shih-Wei Chen, Tien-Chang Lu, Hao-Chung Kuo, and Shing-Chung Wang

Appl. Phys. Lett. 93, 131116 (2008); http://dx.doi.org/10.1063/1.2996566 (3 pages)

Online Publication Date: 3 October 2008

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Low dislocation density ultraviolet (UV) AlGaN/GaN multiple quantum well (MQW) structure was grown using atomic layer deposition (ALD) technique. The AlGaN/GaN MQW grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers formed by ALD grown AlN/GaN superlattices. The as-grown sample showed smooth surface morphology with a root-mean-square roughness value of only 0.35 nm, and no surface cracks were found. The dislocation density was estimated to be as low as 3.3×107 cm−2. X-ray and transmission electron microscope data showed the MQW had sharp interfaces with good periodicity. The sample had an UV photoluminescence emission at 334 nm (3.71 eV) with a very narrow linewidth of 47 meV at 13 K. The cathodoluminescence image revealed a fairly uniform luminescence pattern at room temperature. The AlGaN/GaN MQW grown by ALD technique should be useful for providing high crystalline quality for fabrication of various optical devices.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.67.De Quantum wells
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Suppression of the subband parasitic peak by 1 nm i-AlN interlayer in AlGaN deep ultraviolet light-emitting diodes

J. C. Zhang, Y. H. Zhu, T. Egawa, S. Sumiya, M. Miyoshi, and M. Tanaka

Appl. Phys. Lett. 93, 131117 (2008); http://dx.doi.org/10.1063/1.2996580 (3 pages) | Cited 5 times

Online Publication Date: 3 October 2008

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The origin and suppression of the subband parasitic peak in AlGaN deep ultraviolet light-emitting diodes have been studied. The parasitic peak is clarified to come from a p-AlGaN cladding layer and to be related to Mg dopants. By using 1 nm i-AlN as an interlayer between the active region and the p-AlGaN cladding layer, this peak is suppressed efficiently. The devices with such an interlayer show improved output power by a factor of 4 at injection current density of 20 A/cm2, except that the series resistance and turn-on voltage are slightly increased.
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85.60.Jb Light-emitting devices
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Plasma-liquid electrochemistry: Rapid synthesis of colloidal metal nanoparticles by microplasma reduction of aqueous cations

Carolyn Richmonds and R. Mohan Sankaran

Appl. Phys. Lett. 93, 131501 (2008); http://dx.doi.org/10.1063/1.2988283 (3 pages) | Cited 35 times

Online Publication Date: 1 October 2008

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We demonstrate operation of an aqueous electrochemical cell with an atmospheric-pressure microplasma cathode and a solid metal anode for the rapid production of colloidal metal nanoparticles. Microplasmas are miniaturized versions of low-pressure glow discharges that operate nonthermally at high pressures ( ∼ 1 atm) and contain energetic electrons. Aqueous metal cations are directly reduced by electrons in the microplasma without the presence of a solid cathode or chemical reducing agents. Kinetic studies performed by UV-visible absorbance spectroscopy suggest that particle nucleation and growth are coupled to redox reactions initiated in the electrochemical cell through plasma-liquid interactions.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.45.Fk Electrodes
82.70.Dd Colloids
82.80.Dx Analytical methods involving electronic spectroscopy
62.50.-p High-pressure effects in solids and liquids
82.30.-b Specific chemical reactions; reaction mechanisms

Direct measurements of the energy flux due to chemical reactions at the surface of a silicon sample interacting with a SF6 plasma

R. Dussart, A. L. Thomann, L. E. Pichon, L. Bedra, N. Semmar, P. Lefaucheux, J. Mathias, and Y. Tessier

Appl. Phys. Lett. 93, 131502 (2008); http://dx.doi.org/10.1063/1.2995988 (3 pages) | Cited 10 times

Online Publication Date: 2 October 2008

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Energy exchanges due to chemical reactions between a silicon surface and a SF6 plasma were directly measured using a heat flux microsensor (HFM). The energy flux evolution was compared with those obtained when only few reactions occur at the surface to show the part of chemical reactions. At 800 W, the measured energy flux due to chemical reactions is estimated at about 7 W cm−2 against 0.4 W cm−2 for ion bombardment and other contributions. Time evolution of the HFM signal is also studied. The molar enthalpy of the reaction giving SiF4 molecules was evaluated and is consistent with values given in literature.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.60.Cx Enthalpies of combustion, reaction, and formation

Absolute atomic oxygen density profiles in the discharge core of a microscale atmospheric pressure plasma jet

Nikolas Knake, Kari Niemi, Stephan Reuter, Volker Schulz-von der Gathen, and Jörg Winter

Appl. Phys. Lett. 93, 131503 (2008); http://dx.doi.org/10.1063/1.2995983 (3 pages) | Cited 24 times

Online Publication Date: 3 October 2008

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The micro atmospheric pressure plasma jet is an rf driven (13.56 MHz, ∼ 20 W) capacitively coupled discharge producing a homogeneous plasma at ambient pressure when fed with a gas flow of helium (1.4 slm) containing small admixtures of oxygen ( ∼ 0.5%). The design provides excellent optical access to the plasma core. Ground state atomic oxygen densities up to 3×1016 cm−3 are measured spatially resolved in the discharge core by absolutely calibrated two-photon absorption laser-induced fluorescence spectroscopy. The atomic oxygen density builds up over the first 8 mm of the discharge channel before saturating at a maximum level. The absolute value increases linearly with applied power.
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52.80.Pi High-frequency and RF discharges
52.75.-d Plasma devices
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Experimental studies of the internal Goos–Hänchen shift for self-collimated beams in two-dimensional microwave photonic crystals

Aaron Matthews and Yuri Kivshar

Appl. Phys. Lett. 93, 131901 (2008); http://dx.doi.org/10.1063/1.2980033 (3 pages) | Cited 5 times

Online Publication Date: 29 September 2008

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We study experimentally the Goos–Hänchen effect observed at the reflection of a self-collimated beam from the surface of a two-dimensional photonic crystal and describe a method for controlling the beam reflection through surface engineering. The microwave photonic crystal, fabricated from alumina rods, allows control of the output position of a reflected beam undergoing an internal Goos–Hänchen shift by changing the rod diameter at the reflection surface. The experimental data are in good agreement with the results of the finite-difference time-domain numerical calculations.
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42.70.Qs Photonic bandgap materials
42.79.Ag Apertures, collimators
02.70.Bf Finite-difference methods

Evaluation of growth rate equations of three-dimensional grains using large-scale Monte Carlo simulation

Hao Wang and Guoquan Liu

Appl. Phys. Lett. 93, 131902 (2008); http://dx.doi.org/10.1063/1.2983746 (3 pages) | Cited 7 times

Online Publication Date: 29 September 2008

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Three-dimensional normal grain growth process was simulated in scale of 300×300×300 on the basis of Monte Carlo–Potts model to study topology-dependent growth rate equations for individual grains. The results show that those growth rate equations solely dependent on the grain face number (f) are not applicable for grains with face number f<8; however, Glazier’s equation [ J. A. Glazier, Phys. Rev. Lett. 70, 2170 (1993) ], MacPherson–Srolovitz’s topology-dependent equation [ R. D. MacPherson and D. J. Srolovitz, Nature (London) 446, 1053 (2007) ], and Yu–Liu’s equation [ G. Q. Liu and H. B. Yu, Chin. Sci. Bull. 41, 2000 (1996) ] describe the simulation data well for grains with face number f>8.
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61.72.-y Defects and impurities in crystals; microstructure
02.50.Ng Distribution theory and Monte Carlo studies

Submicrometer periodic patterns fixed by photopolymerization of dissipative structures

A. Hoischen, S. A. Benning, and H.-S. Kitzerow

Appl. Phys. Lett. 93, 131903 (2008); http://dx.doi.org/10.1063/1.2990762 (3 pages) | Cited 4 times

Online Publication Date: 29 September 2008

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In photoreactive liquid crystals, spontaneous pattern formation can be used to fabricate phase gratings or polymer films with a periodic surface modulation. Typically, the periodicity of such structures is comparable to the sample thickness, and thus in the range between several micrometers and about 100 μm. Here, attempts to create and to investigate smaller structures are presented. For a chevron pattern, periodicities as small as 800 nm could be detected.
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42.70.Df Liquid crystals
42.70.Gi Light-sensitive materials
42.70.Jk Polymers and organics
82.35.-x Polymers: properties; reactions; polymerization
42.79.Dj Gratings

Toward the existence of ultrafast diffusion paths in Cu with a gradient microstructure: Room temperature diffusion of Ni

Z. B. Wang, K. Lu, G. Wilde, and S. Divinski

Appl. Phys. Lett. 93, 131904 (2008); http://dx.doi.org/10.1063/1.2992628 (3 pages) | Cited 2 times

Online Publication Date: 29 September 2008

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Room temperature diffusion of 63Ni in Cu with a gradient microstructure prepared by surface mechanical attrition treatment (SMAT) was investigated by applying the radiotracer technique. The results reveal significant penetration of Ni into the nanostructured layer. The relevant diffusivity is higher than that along the conventional high-angle grain boundaries by about six orders of magnitude. This behavior is associated with a higher energy state of internal interfaces produced via plastic deformation. The diffusivity in the top surface layer is somewhat smaller than that in the subsurface layer. This fact is related to nanotwin formation in the former during SMAT.
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66.30.Pa Diffusion in nanoscale solids
66.30.J- Diffusion of impurities
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep
61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals

Measurement of the optical absorption spectra of epitaxial graphene from terahertz to visible

Jahan M. Dawlaty, Shriram Shivaraman, Jared Strait, Paul George, Mvs Chandrashekhar, Farhan Rana, Michael G. Spencer, Dmitry Veksler, and Yunqing Chen

Appl. Phys. Lett. 93, 131905 (2008); http://dx.doi.org/10.1063/1.2990753 (3 pages) | Cited 48 times

Online Publication Date: 30 September 2008

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We present experimental results on the optical absorption spectra of epitaxial graphene from the visible to the terahertz frequency range. In the terahertz range, the absorption is dominated by intraband processes with a frequency dependence similar to the Drude model. In the near-IR range, the absorption is due to interband processes and the measured optical conductivity is close to the theoretical value of e2/4ℏ. We extract values for the carrier densities, the number of carbon atom layers, and the intraband scattering times from the measurements.
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78.70.Gq Microwave and radio-frequency interactions
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
78.40.Ri Fullerenes and related materials
78.66.Tr Fullerenes and related materials
78.30.Na Fullerenes and related materials
73.61.Wp Fullerenes and related materials
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