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9 Aug 2004

Volume 85, Issue 6, pp. 855-1088

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1072 (2004); http://dx.doi.org/10.1063/1.1781351 (3 pages)

Liang-Shan Chen, Chao-Hsien Kuo, and Zhen Ye
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Voltage-controlled multiguide directional coupler formed in a planar nematic liquid crystal film

Ming-Shan Tsai, Chie-Tong Kuo, Shuan-Yu Huang, Chia-Chi Shih, and I-Min Jiang

Appl. Phys. Lett. 85, 855 (2004); http://dx.doi.org/10.1063/1.1778468 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2004

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A voltage-controllable multiguide directional coupler is designed with a nematic liquid crystal cell, comprising a grating-like indium-tin-oxide electrode. An incident polarized laser beam can couple into adjacent channels by periodic distribution of the refractive index. This capability is attributed to the reorientation of the periodic liquid crystal caused by the application of a voltage. The coupling variation of the optical power in the transverse direction parallel to the waveguide surface is investigated. This work presents a promising coupling function for potential applications of optical communication devices.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Chirality selection of single-walled carbon nanotubes by laser resonance chirality selection method

Kenzo Maehashi, Yasuhide Ohno, Koichi Inoue, and Kazuhiro Matsumoto

Appl. Phys. Lett. 85, 858 (2004); http://dx.doi.org/10.1063/1.1778471 (3 pages) | Cited 33 times

Online Publication Date: 4 August 2004

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We propose a laser resonance chirality selection method to select single-walled carbon nanotubes (SWNTs) with specific chirality from mass of SWNTs by intense laser irradiation. This technique exploits the multiple Van Hove singularities in the density of states of SWNTs expected for one-dimensional confinement. Absorption of the exciting laser beam can be strongly enhanced for SWNTs with specific chirality when the energy of the incident photon matches the energy of the allowed electronic transitions. As a result of the resonance effect, when the excitation power density of the laser beam increases in an atmosphere of air, at a certain threshold excitation power density, only these SWNTs are oxidized and are removed selectively. With Raman scattering measurements, we have demonstrated that SWNTs with specific chirality are selectively removed after intense laser irradiation.
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61.46.-w Structure of nanoscale materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
61.82.Ms Insulators
78.30.Hv Other nonmetallic inorganics
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Tunable and multiple-wavelengths/temporal output from gain-switched diode laser and a four Bragg-grating Fiber

E. U. Rafailov, I. G. Cormack, F. Floreani, L. Zhang, I. Bennion, and W. Sibbett

Appl. Phys. Lett. 85, 861 (2004); http://dx.doi.org/10.1063/1.1779350 (2 pages) | Cited 2 times

Online Publication Date: 4 August 2004

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We demonstrate spectral narrowing and selective tuning of the picosecond pulse outputs from an injection-seeded, gain-switched diode laser that is simultaneously coupled to four output fibers with different Bragg-grating resonators. A single-, dual-, and triple-wavelength and temporal pulse operation from all four outputs is presented.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.81.Bm Fabrication, cladding, and splicing
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.81.Qb Fiber waveguides, couplers, and arrays

GaSe crystals for broadband terahertz wave detection

Kai Liu, Jingzhou Xu, and X.-C. Zhang

Appl. Phys. Lett. 85, 863 (2004); http://dx.doi.org/10.1063/1.1779959 (3 pages) | Cited 43 times

Online Publication Date: 4 August 2004

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We report experimental results of using GaSe crystals for the broadband detection of terahertz (THz) waves from 100 GHz to 30 THz. In comparison, the THz wave field amplitude measured with a GaSe crystal exceeds that detected by a ZnTe crystal with a comparable detection bandwidth. The central frequency is tunable by varying the angle between the incident THz radiation and the crystal surface normal.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.47.-p Spectroscopy of solid state dynamics

GaInN∕GaN growth optimization for high-power green light-emitting diodes

C. Wetzel, T. Salagaj, T. Detchprohm, P. Li, and J. S. Nelson

Appl. Phys. Lett. 85, 866 (2004); http://dx.doi.org/10.1063/1.1779960 (3 pages) | Cited 36 times

Online Publication Date: 4 August 2004

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Two different approaches to optimize the growth conditions for high-power green light-emitting diodes (LEDs) using Ga1−xInxN∕GaN metalorganic vapor phase epitaxy are discussed. We compare typical results in terms of morphology, photo-, and electroluminescence properties. We find good results for an optimization of the lateral morphological homogeneity of the active region. An extension of growth conditions for the active layers of blue LEDs was misleading. This suggests that different emission processes are involved in blue and green LEDs. We achieve die performances of 2.5 mW at 523 nm (526 nm dominant) for low forward voltages of 3.4 V at a typical drive current of 20 mA.
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81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.60.Fi Electroluminescence

Characteristics of nondegenerate four-wave mixing in electroabsorption modulator

Takashi Mori and Hitoshi Kawaguchi

Appl. Phys. Lett. 85, 869 (2004); http://dx.doi.org/10.1063/1.1779963 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2004

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The characteristics of nondegenerate four-wave mixing (FWM) in an electroabsorption modulator are reported. The input power dependence of FWM intensity agrees well with theoretical results based on third-order nonlinearity over a wide input power range of 16 dB. The detuning characteristics of FWM have a −6 dB∕octave response based on the carrier-density pulsation effect. The experimental results show that a higher reverse voltage brings about a faster carrier recombination. The asymmetricity of positive and negative detuning is the reverse of that of the semiconductor optical amplifier and is explained through a rate equation simulation.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Jq Electro-optical effects

Poling-assisted bleaching of metal-doped nanocomposite glass

Olivier Deparis, Peter G. Kazansky, Amin Abdolvand, Alexander Podlipensky, Gerhard Seifert, and Heinrich Graener

Appl. Phys. Lett. 85, 872 (2004); http://dx.doi.org/10.1063/1.1779966 (3 pages) | Cited 25 times

Online Publication Date: 4 August 2004

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Thermal poling of soda-lime glass which was doped with spherical or ellipsoidal silver nanoparticles has revealed what we believe to be a phenomenon of general interest in the physics of nanocomposite materials: The field-assisted dissolution of metal nanoparticles embedded in glass. Macroscopically, this phenomenon manifested itself as poling-assisted bleaching of the glass in the sense that the glass became more (or even completely) transparent under the anode. The phenomenon is physically interpreted in terms of the ionization of metal nanoclusters followed by the removal of ions from the clusters and their drift in the depth, under the action of the extremely high electric field which is created underneath the anodic surface during poling. The underlying physical mechanism is expected to offer unique opportunities for the control of structural and optical properties of nanocomposite glasses.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
77.22.Ej Polarization and depolarization
61.43.Fs Glasses
64.75.-g Phase equilibria
66.30.H- Self-diffusion and ionic conduction in nonmetals

1.3 to 1.5 μm light emission from InGaAs/GaAs quantum wells

S. M. Wang, Q. X. Zhao, X. D. Wang, Y. Q. Wei, M. Sadeghi, and A. Larsson

Appl. Phys. Lett. 85, 875 (2004); http://dx.doi.org/10.1063/1.1759066 (3 pages) | Cited 7 times

Online Publication Date: 4 August 2004

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We propose using dipole δ-doping across highly strained InGaAs/GaAs quantum wells (QWs) to achieve light emission at wavelengths in the range of 1.3–1.55 μm. For In0.3Ga0.7As/GaAs single QWs, we demonstrate that the photoluminescence (PL) wavelength increases with the doping concentration. With a transition energy reduction as large as 370 meV, PL emission at 1.548 μm at room temperature is realized. Broad area lasers with dipole δ-doping reveal longer lasing wavelengths than those of undoped lasers, although the wavelength redshift is much less than in the PL case. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
42.60.By Design of specific laser systems

Decay mechanisms of a blue organic light emitting diode

S. Y. Ni, X. R. Wang, Y. Z. Wu, H. Y. Chen, W. Q. Zhu, X. Y. Jiang, Z. L. Zhang, and R. G. Sun

Appl. Phys. Lett. 85, 878 (2004); http://dx.doi.org/10.1063/1.1777819 (3 pages) | Cited 9 times

Online Publication Date: 4 August 2004

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A blue organic light-emitting diode employing perylene as light emitting dopant and 9,10-bis(3’5’-diaryl)phenyl anthracene (DPA) as host has been studied for its decay mechanisms. The device structure is ITO(indiumtinoxide)∕CuPc(copperphthalocyanine)∕NPD(α-naphthylphenylbiphenyldiamine)∕DPA:perylene∕Alq3 (8-hydroxy-quinolinealuminum)∕MgAg. In this device, CuPc and NPD are used as hole injection and transporting layers, DPA as a blue host, perylene as a blue emitting dopant, Alq3 as an electron transport layer, MgAg as cathode, respectively. A luminance of 4359 cd∕m2 at 15 V and a current efficiency of 3 cd∕A at 5 V have been achieved. The breakdown of the interfaces in the device is found to be one of the factors for the decay and the decomposition of the light emitter is not significantly studied by current–voltage–luminance, photoluminescence, and electroluminescence measurements. The lifetime is not intrinsic for this type of device.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.-m Photoluminescence, properties and materials

Improvement of signal-to-noise ratio of a subterahertz spectrometer using a continuous-wave multimode laser diode by single-mode fiber optics

O. Morikawa, M. Fujita, and M. Hangyo

Appl. Phys. Lett. 85, 881 (2004); http://dx.doi.org/10.1063/1.1777800 (3 pages) | Cited 6 times

Online Publication Date: 4 August 2004

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The signal-to-noise ratio of the subterahertz spectroscopic system proposed previously, which uses a continuous-wave multimode laser diode and photoconductive antennas, is improved significantly by adopting single-mode fiber optics. The noise estimated from the transmittance measurement of a Si wafer is reduced to about 1∕6 of that obtained by the previous system. The improvement is based on the reduction of the random phase distribution of laser modes with various mode patterns, resulting in the increase of the continuous components in the spectrum.
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42.81.-i Fiber optics
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Planar THz quasioptics

Jianming Dai, S. Coleman, and D. Grischkowsky

Appl. Phys. Lett. 85, 884 (2004); http://dx.doi.org/10.1063/1.1781357 (3 pages) | Cited 9 times

Online Publication Date: 4 August 2004

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Two-dimensional (2D) quasioptical elements are demonstrated as guiding structures in the THz frequency regime. A planar polyethylene lens is incorporated in a parallel metal plate structure and is shown to focus guided THz radiation to a spot comparable to that expected for a three-dimensional (3D) optical element in free space. A 2D double-slit aperture is also demonstrated to diffract the incoming THz beam as expected for 3D. The spatial resolution of the measurement techniques employed is illustrated by the sharpness of the measured diffraction pattern.
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42.79.Bh Lenses, prisms and mirrors
42.79.Gn Optical waveguides and couplers
42.25.Fx Diffraction and scattering

Experimental evidence for index modulation by carrier depletion in SiGe∕Si multiple quantum well structures

A. Lupu, D. Marris, D. Pascal, J.-L. Cercus, A. Cordat, V. Le Thanh, and S. Laval

Appl. Phys. Lett. 85, 887 (2004); http://dx.doi.org/10.1063/1.1781371 (3 pages) | Cited 7 times

Online Publication Date: 4 August 2004

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Experimental results for the refractive index variation obtained by hole depletion in SiGe∕Si multiple quantum wells inserted in a reverse-biased p-i-n junction are reported. The electronic contribution to the index variation is unambiguously separated from the thermal one. Measured refractive index changes around 4.2×10−5 V−1 are in quite good agreement with modeling.
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78.67.De Quantum wells
81.07.St Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Hp Optical processors, correlators, and modulators
85.30.Kk Junction diodes
72.20.Fr Low-field transport and mobility; piezoresistance
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Many-body optical gain of GaInNAs∕GaAs strained quantum-well lasers

Seoung-Hwan Park

Appl. Phys. Lett. 85, 890 (2004); http://dx.doi.org/10.1063/1.1779961 (3 pages) | Cited 10 times

Online Publication Date: 4 August 2004

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Optical properties of strained GaInNAs∕GaAs quantum wells (QWs) are investigated using the multiband effective-mass theory. We also take into account the many-body effects on the optical gain spectrum. It is observed that the transition energy decreases with increasing In or N mole fraction. The theoretical transition energies show very good agreement with the experimental results for several compositions and well widths. The optical gain is shown to increase with increasing compressive or tensile strain. The increase of the transverse electric optical gain is attributed to the fact that the subband energy spacing increases with the strain. On the other hand, the increase of the transverse magnetic optical gain is mainly due to the increases of the optical matrix element. The threshold current density rapidly decreases with increasing well width and begins to saturate near the well width of 80 math. In the case of a QW structure with relatively short cavity length (Lcav=800 μm), it is found that the threshold current density is minimum near 80 math. We see that there is a universal relation governing the dependence of the band-gap renormalization on carrier density and the relation is close to ΔEg∝n2D1∕3.
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42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Experimental demonstration of all-optical 1×2 quantum routing

B. S. Ham

Appl. Phys. Lett. 85, 893 (2004); http://dx.doi.org/10.1063/1.1779968 (3 pages) | Cited 19 times

Online Publication Date: 4 August 2004

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Using a quantum switching technique based on a two-photon coherence swapping, we experimentally demonstrate an all-optical 1×2 quantum routing, where the observed switching time of ∼5 μs is two orders of magnitude faster than the carrier lifetime or the population relaxation time. Owing to the nonabsorption resonance and its enhanced nonlinearity, the observed switching efficiency (intensity ratio of switch-out signal to switch-in signal) is as high as 10%. Such an efficient and fast optical routing method has the potential to hyperterahertz all-optical quantum routers, where semiconductor quantum wells or quantum dots are chosen as the optical medium with a spin dephasing time in the range of picoseconds.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
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Polymer coating on the surface of zirconia nanoparticles by inductively coupled plasma polymerization

Wei He, Zhigang Guo, Yikang Pu, Luting Yan, and Wenjie Si

Appl. Phys. Lett. 85, 896 (2004); http://dx.doi.org/10.1063/1.1778470 (3 pages) | Cited 18 times

Online Publication Date: 4 August 2004

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Polymer coating on the surface of inorganic ceramic nanoparticles is beneficial to decrease agglomeration and improve dispersion in organic solvent in ceramic injection moulding technology. A layer of thin polymer film on zirconia nanoparticles is deposited by inductively coupled ethylene/nitrogen plasma. Transmission electron microscopy photographs indicate the presence of uniform polymer coatings and the thickness of the polymer layer is estimated as several nanometers. The chemical structure of the film is revealed as quasi-polyethylene long hydrocarbon chain by x-ray photoelectron spectroscopy examination.
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82.35.Np Nanoparticles in polymers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
82.35.Gh Polymers on surfaces; adhesion
52.77.Dq Plasma-based ion implantation and deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.46.-w Structure of nanoscale materials
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Modified metal-induced lateral crystallization using amorphous Ge∕Si layered structure

Hiroshi Kanno, Atsushi Kenjo, Taizoh Sadoh, and Masanobu Miyao

Appl. Phys. Lett. 85, 899 (2004); http://dx.doi.org/10.1063/1.1780595 (3 pages) | Cited 9 times

Online Publication Date: 4 August 2004

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Modified metal-induced lateral crystallization (MILC) using a‐Ge∕a‐Si∕Ni∕SiO2 layered structures has been investigated. MILC growth velocity in the a‐Ge∕a‐Si layered structures was enhanced by three times compared with that in the a‐Si single layers. As a result, poly-Si films with large areas (∼10 μm) were obtained in a short time annealing (<5 h) at 550 °C. It is speculated that crystal nucleation in the a‐Ge layers stimulated the bond rearrangement in the a‐Si layers, which enhanced the MILC velocity. This will be a powerful tool for realizing large poly-Si areas on insulating films for future system-in-displays.
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64.70.K- Solid-solid transitions
64.60.Q- Nucleation
68.55.A- Nucleation and growth
61.43.Dq Amorphous semiconductors, metals, and alloys

Quantum-confined Stark effect of GaInNAs(Sb) quantum wells at 1300–1600 nm

Vincenzo Lordi, Homan B. Yuen, Seth R. Bank, and James S. Harris

Appl. Phys. Lett. 85, 902 (2004); http://dx.doi.org/10.1063/1.1777825 (3 pages) | Cited 11 times

Online Publication Date: 4 August 2004

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We report the measurement of electroabsorption spectra from GaInNAs and GaInNAsSb quantum wells grown on GaAs showing quantum-confined Stark effect behavior suitable for optical modulation at 1300 and 1550 nm wavelength, respectively. The high quality of our material is evidenced by sharp exciton resonances with a full width at half maximum <25 meV at 295 K, and peak absorption coefficient of 18 000 cm−1 for GaInNAs and 34 800 cm−1 for GaInNAsSb. Changes in absorption coefficient 10 000 cm−1 with an applied electric field were measured. Device performance from these materials is expected to be comparable to or better than the competing material grown on InP.
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68.65.Fg Quantum wells
78.20.Jq Electro-optical effects
78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Hp Optical processors, correlators, and modulators
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.30.Hv Other nonmetallic inorganics

Infrared dielectric function and phonon modes of Mg-rich cubic MgxZn1−xO (x⩾0.67) thin films on sapphire (0001)

C. Bundesmann, M. Schubert, A. Rahm, D. Spemann, H. Hochmuth, M. Lorenz, and M. Grundmann

Appl. Phys. Lett. 85, 905 (2004); http://dx.doi.org/10.1063/1.1777797 (3 pages) | Cited 12 times

Online Publication Date: 4 August 2004

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Infrared dielectric function spectra and phonon modes of single-phase rocksalt-type MgxZn1−xO thin films with 0.67⩽x⩽1 prepared by pulsed-laser deposition on c-plane sapphire substrates were obtained from infrared spectroscopic ellipsometry (360 cm−1 to 1500 cm−1). A one-mode behavior is found. Phonon mode frequencies, the high-frequency limit of the dielectric function, and phonon mode broadening parameters reflect a considerable and systematic dependence on the Mg content x. X-ray diffraction measurements revealed the single-phase growth and a decreasing lattice constant with increasing x.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
77.22.Ch Permittivity (dielectric function)

Surface-charge polarization effect at an organic and inorganic contact: Case study of tris(8-hydroxyquinolato) aluminum on Si(001)-2×1

Tun-Wen Pi, C.-P. Ouyang, T. C. Yu, H. L. Hsu, J.-F. Wen, and J. Hwang

Appl. Phys. Lett. 85, 908 (2004); http://dx.doi.org/10.1063/1.1777798 (3 pages) | Cited 5 times

Online Publication Date: 4 August 2004

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We have employed synchrotron radiation photoemission to investigate the tris(8-hydroxyquinolato) aluminum (Alq3) molecules adsorbed on an inorganic Si(001)-2×1 surface at room temperature. The surface-related valence states associated with the dimers and backbonds lying a couple of eV below the Fermi level reduce in strength upon Alq3 adsorption, indicating that the organic molecules not only passivate the dangling bonds but also rupture the dimer bonds. The wave function of the surface dangling bonds and of the pyridyl side of an 8-quinolinol ligand overlaps greatly so that charge is polarized toward the organic adlayer, resulting in the appearance of low-energy components in both N 1s and C 1s core-level spectra, which is similar to the case of Mg-doped Alq3. However, the polarization diminishes at greater coverage, in which case both 1s cores behave as in the nominal states.
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71.20.Mq Elemental semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Fr Polymers; organic compounds
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Layer-by-layer photonic crystal with a repeating two-layer sequence

Martin Maldovan

Appl. Phys. Lett. 85, 911 (2004); http://dx.doi.org/10.1063/1.1777799 (3 pages) | Cited 6 times

Online Publication Date: 4 August 2004

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A layer-by-layer periodic dielectric structure with a large complete photonic band gap is presented. This “two-layer (110) diamond” consists of only two constitutive layers with the same pattern, producing a simple stacking sequence suitable for fabrication. The stacking is accomplished by a horizontal translation from layer to layer. The structure possesses a complete 15% photonic band gap for Si∕air (13:1) dielectric contrast. It is a layered structure with the minimum number of different layers necessary to create a three-dimensional photonic crystal. The proposed structure can be assembled by using three different layer-by-layer techniques.
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42.70.Qs Photonic bandgap materials
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ultrafast optical emission of nanodiamond induced by laser excitation

F. L. Zhao, Z. Gong, S. D. Liang, N. S. Xu, S. Z. Deng, J. Chen, and H. Z. Wang

Appl. Phys. Lett. 85, 914 (2004); http://dx.doi.org/10.1063/1.1777803 (3 pages) | Cited 14 times

Online Publication Date: 4 August 2004

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The ultrafast optical emission of nanosized (∼5 nm) crystallites has been detected under the picosecond (ps) laser excitation of 300 nm through ultrafast fluorescence spectroscopy. This optical emission, photoluminescence (PL), induced at a laser wavelength of 300 nm confines blue light. The ultrafast PL spectrum deconvoluted by a Monte Carlo method shows that two fast emission processes with decaytimes of 60 and 350 ps. This type of ultrafast emission has not been observed under the same experimental conditions from the samples of a natural single crystal and an impure natural single crystal diamond. The mechanism responsible for this visible ultrafast emission is proposed by taking into account the effect of surface states and large surface-to-volume ratio of nanoparticles. All of these findings demonstrate the feasibility of using large band-gap nanomaterials to generate ultrafast optical emission at various wavelengths.
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78.47.-p Spectroscopy of solid state dynamics
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
71.20.Mq Elemental semiconductors

Magneto-Seebeck coefficient of a bismuth microwire array in a magnetic field

Y. Hasegawa, Y. Ishikawa, T. Komine, T. E. Huber, A. Suzuki, H. Morita, and H. Shirai

Appl. Phys. Lett. 85, 917 (2004); http://dx.doi.org/10.1063/1.1781390 (3 pages) | Cited 21 times

Online Publication Date: 4 August 2004

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The enhancement of the magneto-Seebeck coefficient of a bismuth microwire array under a magnetic field is measured at temperatures from 45 to 295 K. The measured magneto-Seebeck coefficient exhibits a peak at a certain magnitude of magnetic field, with the peak shifting to higher magnetic fields and becoming broader with increasing temperature. The results show that the magneto-Seebeck coefficient can be improved by approximately 20% by applying an appropriate external magnetic field and temperature. The Boltzmann equation with a relaxation-time approximation is solved numerically to determine the magnetic field and temperature dependences of the magneto-Seebeck coefficient for the bismuth microwire array. The experimental results are compared with calculations, and the two sets of results are shown to be in very good agreement, clarifying the mechanisms contributing to the magneto-Seebeck coefficient for bismuth. The wire array structure is thus suitable for enhancing the thermoelectric properties of materials in a magnetic field.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Gd Galvanomagnetic and other magnetotransport effects

Ultralong coherence times in the purely electronic zero-phonon line emission of single molecules

Alper Kiraz, Moritz Ehrl, Christoph Bräuchle, and Andreas Zumbusch

Appl. Phys. Lett. 85, 920 (2004); http://dx.doi.org/10.1063/1.1779351 (3 pages) | Cited 13 times

Online Publication Date: 4 August 2004

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We report the observation of ultralong coherence times in the purely electronic zero-phonon line emission of single terrylenediimide molecules at 1.4 K. Vibronic excitation and spectrally resolved detection with a scanning Fabry–Perot spectrum analyzer were used to measure a linewidth of 65 MHz. This is within a factor of 1.6 of the transform limit. It therefore indicates that single molecule emission may be suited for applications in linear optics quantum computation. Additionally, it is shown that high-resolution spectra taken with the spectrum analyzer allow for the investigation of fast spectral dynamics in the emission of a single molecule.
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78.55.Kz Solid organic materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
33.50.Dq Fluorescence and phosphorescence spectra
33.70.Jg Line and band widths, shapes, and shifts

Hot hole excitation of EuGa2S4 electroluminescent thin films

Katsu Tanaka and Shinji Okamoto

Appl. Phys. Lett. 85, 923 (2004); http://dx.doi.org/10.1063/1.1779337 (3 pages) | Cited 1 time

Online Publication Date: 4 August 2004

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This letter describes which carrier type (electrons or holes) is dominant for EuGa2S4 thin film electroluminescent (TFEL) excitation. The transient EL wave form was measured on the EuGa2S4 TFEL devices having a single insulating thin film, which emit pure green EL due to the 5d–4f transition of Eu2+ ions. An asymmetric EL wave form was observed under a rectangular applied voltage. The EL occurs at the positively biased side of the EuGa2S4 thin film. This indicates that the green EL occurs because of hot hole excitation. Hot electrons are known to be dominant carriers to excite the luminescent centers in TFEL devices. Hot holes are also effective carriers for TFEL excitation.
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85.60.Jb Light-emitting devices
73.50.Fq High-field and nonlinear effects
78.60.Fi Electroluminescence
72.20.Ht High-field and nonlinear effects
78.66.Nk Insulators

Atomic cracks and (2math×2×math)-R30° reconstruction at 6H-SiC(0001) surface

F. Amy, P. Soukiassian, and C. Brylinski

Appl. Phys. Lett. 85, 926 (2004); http://dx.doi.org/10.1063/1.1774251 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2004

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We investigate the Si-rich 3×3 to Si-terminated math×math phase transition of the 6H-SiC(0001) surface by atom-resolved scanning tunneling microscopy. We find a 2math×2math-R30° reconstruction, coexisting with few 3×3 domains. While a high-quality 3×3 surface preparation is achieved with a very low defect density (<2% of atomic defects), the (2math×2×math)-R30° reconstruction instead exhibits long atomic cracks suggesting important stress relief during the phase transition. A structural model containing 13 Si atoms per unit cell distributed in three layers above the Si terminated bulk SiC substrate is proposed.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
64.70.K- Solid-solid transitions
62.20.M- Structural failure of materials
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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