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1 Aug 2005

Volume 87, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 054101 (2005); http://dx.doi.org/10.1063/1.2006209 (3 pages)

Xiuqin Chen, S. Yang, M Hasegawa, K. Kawabe, and S. Motojima
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THz parallel plate photonic waveguides

Adam Bingham, Yuguang Zhao, and D. Grischkowsky

Appl. Phys. Lett. 87, 051101 (2005); http://dx.doi.org/10.1063/1.1997273 (3 pages) | Cited 28 times

Online Publication Date: 26 July 2005

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We have observed narrowband transmission or rejection in the frequency spectra of THz pulses transmitted through air-spaced parallel plate photonic waveguides. These waveguides have one of the metal plates covered by a silicon plate with a metallic photonic band gap (PBG) surface precisely fabricated by lithographic techniques. We use two different PBG surface types: an array of metallic cylindrical pillars, and an array of metallic cylindrical holes. With the inversion of the PBG structures from cylinders to holes, the output spectra changes from narrow bandpass to narrow band-reject filtering. These photonic waveguides show extremely sharp spectral responses in regions as large as 1 THz, with stop bands or transmission bands having contrasts of as much as 90 dB.
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84.40.Az Waveguides, transmission lines, striplines
42.70.Qs Photonic bandgap materials

Enhancement of third-harmonic generation in a polymer-dispersed liquid-crystal grating

Przemyslaw P. Markowicz, Vincent K. S. Hsiao, Hanifi Tiryaki, Alexander N. Cartwright, Paras N. Prasad, Ksenia Dolgaleva, Nick N. Lepeshkin, and Robert W. Boyd

Appl. Phys. Lett. 87, 051102 (2005); http://dx.doi.org/10.1063/1.1999849 (3 pages) | Cited 7 times

Online Publication Date: 27 July 2005

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We report the observation of significant enhancement of one-step third-harmonic generation in a one-dimensional photonic crystal pumped by a near-infrared laser beam tuned to the low-frequency edge of the first photonic band gap. The third-harmonic phase matching can be controlled by changing the angle of incidence of the fundamental radiation, allowing tunability of the third-harmonic wavelength. The observed phenomenon was modeled theoretically using the transfer-matrix method. The enhancement is attributed to the combined action of phase-matching between the pump and harmonic waves and pump-field localization within the photonic crystal.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Df Liquid crystals
61.30.Vx Polymer liquid crystals
42.79.Dj Gratings
42.70.Jk Polymers and organics
42.70.Qs Photonic bandgap materials

Short wavelength intersubband emission from InAs/AlSb quantum cascade structures

D. Barate, R. Teissier, Y. Wang, and A. N. Baranov

Appl. Phys. Lett. 87, 051103 (2005); http://dx.doi.org/10.1063/1.2007854 (3 pages) | Cited 15 times

Online Publication Date: 28 July 2005

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The InAs/AlSb material system is a promising candidate for the development of short wavelength quantum cascade lasers because of the large conduction band offset of 2.1 eV. In this letter, we present a study of room temperature electroluminescence of InAs/AlSb quantum cascade structures as a function of the emission wavelength. Intersubband emission with a transition energy of 500 meV (λ = 2.5 μm) has been obtained.
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78.67.De Quantum wells
78.60.Fi Electroluminescence
73.21.Fg Quantum wells

Identification of longitudinal optical modes by hyper-Raman scattering in noncentrosymmetric ceramics

Holger Hellwig

Appl. Phys. Lett. 87, 051104 (2005); http://dx.doi.org/10.1063/1.2009824 (3 pages) | Cited 4 times

Online Publication Date: 28 July 2005

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Hyper-Raman scattering has been applied to ceramic samples of noncentrosymmetric lead zirconate titanate (PZT5H). The intense second-harmonic signal was blocked by using a holographic notch filter. Based on comparison with conventional Raman spectra taken under the same conditions, LO mode frequencies could be derived directly from the hyper-Raman spectra. The assignment of LO mode frequencies based on hyper-Raman spectra provides the possibility to measure LO-TO splitting in noncentrosymmetric ceramics, for which conventional Raman measurements alone provide only limited information.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.30.Hv Other nonmetallic inorganics
77.80.-e Ferroelectricity and antiferroelectricity
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Electrical control of polariton coupling in intersubband microcavities

Aji A. Anappara, Alessandro Tredicucci, Giorgio Biasiol, and Lucia Sorba

Appl. Phys. Lett. 87, 051105 (2005); http://dx.doi.org/10.1063/1.2006976 (3 pages) | Cited 27 times

Online Publication Date: 28 July 2005

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We demonstrate the external control of the coupling between the intersubband transition and the photonic mode of a GaAs/AlGaAs microcavity with multiple quantum wells embedded. By electrical gating, the charge density in the wells can be lowered, thereby quenching the intersubband polaritons and reverting the system to uncoupled excitations. The angle-dependent reflectance measurements are in good agreement with theoretical calculations performed in the transfer matrix formalism. The experiment shows the prospects offered by intersubband microcavities through manipulation of the system ground state.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.21.Fg Quantum wells
78.67.De Quantum wells

Optical vibration sensor fabricated by femtosecond laser micromachining

Masanao Kamata, Minoru Obara, Rafael R. Gattass, Loren R. Cerami, and Eric Mazur

Appl. Phys. Lett. 87, 051106 (2005); http://dx.doi.org/10.1063/1.2008362 (3 pages) | Cited 17 times

Online Publication Date: 29 July 2005

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We fabricated an optical vibration sensor using a high-repetition rate femtosecond laser oscillator. The sensor consists of a single straight waveguide written across a series of three pieces of glass. The central piece is mounted on a suspended beam to make it sensitive to mechanical vibration, acceleration, or external forces. Displacement of the central piece is detected by measuring the change in optical transmission through the waveguide. The resulting sensor is small, simple, and requires no alignment. The sensor has a linear response over the frequency range 20 Hz–2 kHz, can detect accelerations as small as 0.01 m/s2, and is nearly temperature independent.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.-h Mechanical instruments and equipment
42.86.+b Optical workshop techniques
42.62.-b Laser applications
06.30.Gv Velocity, acceleration, and rotation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Vertically oriented GaN-based air-gap distributed Bragg reflector structure fabricated using band-gap-selective photoelectrochemical etching

R. Sharma, E. D. Haberer, C. Meier, E. L. Hu, and S. Nakamura

Appl. Phys. Lett. 87, 051107 (2005); http://dx.doi.org/10.1063/1.2008380 (3 pages) | Cited 23 times

Online Publication Date: 29 July 2005

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A three-period vertically oriented GaN-based air-gap distributed Bragg reflector structure was fabricated using band-gap-selective photoelectrochemical (PEC) etching. The epitaxial structure consisted of an Al0.08Ga0.92N/(In0.04Ga0.96N/In0.07Ga0.93N) superlattice structure, wherein the InGaN layers served as sacrificial layers during PEC etching. Microreflectance measurements yielded an average enhancement in the reflected signal of ∼ 12-fold over the wavelength range of 550–650 nm, when compared with the signal from a dry-etched GaN surface.
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42.82.Gw Other integrated-optical elements and systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Bh Lenses, prisms and mirrors
81.65.Cf Surface cleaning, etching, patterning
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Cubic nitridation layers on sapphire substrate and their role in polarity selection of ZnO films

Y. Wang, X. L. Du, Z. X. Mei, Z. Q. Zeng, M. J. Ying, H. T. Yuan, J. F. Jia, Q. K. Xue, and Z. Zhang

Appl. Phys. Lett. 87, 051901 (2005); http://dx.doi.org/10.1063/1.2001138 (3 pages) | Cited 18 times

Online Publication Date: 25 July 2005

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Well-defined cubic AlN ultrathin layers formed by nitridation of Al2O3 (0001) substrate at various temperatures were observed by high-resolution transmission electron microscopy. The polarity of the AlN layers strongly depends on the substrate pretreatment and nitridation temperature. The structure of the AlN layers plays a key role in polarity selection of subsequent ZnO films, and both Zn-polar and O-polar ZnO films could be steadily obtained by control of the cubic AlN layers.
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81.05.Dz II-VI semiconductors
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)

First-principles elastic stiffness of LaPO4 monazite

Jingyang Wang, Yanchun Zhou, and Zhijun Lin

Appl. Phys. Lett. 87, 051902 (2005); http://dx.doi.org/10.1063/1.2005392 (3 pages) | Cited 34 times

Online Publication Date: 25 July 2005

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In this letter, the full set of elastic coefficients of LaPO4 monazite is presented based on the first-principles plane-wave pseudopotential total energy method. Mechanical parameters (bulk modulus, shear modulus, Young’s moduli, and Poisson’s ratio) are also presented and compared with experimental results for polycrystalline monazite. The responses of electronic structure and chemical bonds to a series of {010}⟨001⟩ shear strains are examined in order to study the mechanism of low shear strain resistance. The results show that small shear moduli originate from the inhomogeneous strengths of atomic bonds. For example, the weak La–O bonds accommodate the shear strain locally, while the PO4 tetrahedra are almost rigid. The theoretical elastic stiffness may be useful to understand the deformation mechanisms of LaPO4 monazite.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Role of step edges in oxygen vacancy transport into SrTiO3(001)

X. D. Zhu, Y. Y. Fei, H. B. Lu, and G. Z. Yang

Appl. Phys. Lett. 87, 051903 (2005); http://dx.doi.org/10.1063/1.2005398 (3 pages) | Cited 8 times

Online Publication Date: 25 July 2005

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Using a combination of oblique-incidence optical reflectivity difference and specular reflection high energy electron diffraction techniques, we studied vacuum annealing of pulsed-laser deposited Nb-doped SrTiO3 monolayers on SrTiO3(100) near 730 °C. In oxygen-free ambient, the as-grown monolayers are oxygen deficient. The excess oxygen vacancies in the monolayers are reduced by vacancy diffusion into the bulk. We found that the reduction rate is characterized by an activation energy E = 1.0 eV. More interestingly, the pre-exponential factor decreases significantly as the annealing time interval increases between two successive monolayer depositions. We propose that the indiffusion of excess surface oxygen vacancies takes place at step edges, and the Oswald ripening governs the density of the latter during vacuum annealing.
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66.30.Lw Diffusion of other defects
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
68.35.Fx Diffusion; interface formation

Formation of ZrTiCuNiBe bulk metallic glass by shock-wave quenching

C. Yang, R. P. Liu, Z. J. Zhan, L. L. Sun, J. Zhang, Z. Z. Gong, and W. K. Wang

Appl. Phys. Lett. 87, 051904 (2005); http://dx.doi.org/10.1063/1.2005367 (3 pages) | Cited 10 times

Online Publication Date: 25 July 2005

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Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) was prepared by shock-wave quenching. Differences in property, structure, and thermal stability were found between the BMGs prepared by the shock-wave quenching and water quenching. The glass transition temperature of the shock-wave-quenched BMG is about 13 K higher than that of the water-quenched one. Although the density of the shock-wave-quenched BMG is decreased, the acoustic velocities in it are increased. Shock-wave quenching is possibly a promising method for preparing BMG.
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81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
62.50.-p High-pressure effects in solids and liquids
81.40.Gh Other heat and thermomechanical treatments

Plasticity-improved Zr–Cu–Al bulk metallic glass matrix composites containing martensite phase

Y. F. Sun, B. C. Wei, Y. R. Wang, W. H. Li, T. L. Cheung, and C. H. Shek

Appl. Phys. Lett. 87, 051905 (2005); http://dx.doi.org/10.1063/1.2006218 (3 pages) | Cited 49 times

Online Publication Date: 25 July 2005

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Zr48.5Cu46.5Al5 bulk metallic glass matrix composites with diameters of 3 and 4 mm were produced through water-cooled copper mold casting. Micrometer-sized bcc based B2 structured CuZr phase containing martensite plate, together with some densely distributed nanocrystalline Zr2Cu and plate-like Cu10Zr7 compound, was found embedded in a glassy matrix. The microstructure formation strongly depends on the composition and cooling rate. Room temperature compression tests reveal significant strain hardening and plastic strains of 7.7% and 6.4% before failure are obtained for the 3-mm- and 4-mm-diam samples, respectively. The formation of the martensite phase is proposed to contribute to the strain hardening and plastic deformation of the materials.
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81.05.Pj Glass-based composites, vitroceramics
81.05.Bx Metals, semimetals, and alloys
61.43.Fs Glasses
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
81.20.-n Methods of materials synthesis and materials processing
81.30.Fb Solidification
61.66.Dk Alloys

Probing a molecular interface in a functioning organic diode

Young Jong Lee, So-Jung Park, Andre J. Gesquiere, and Paul F. Barbara

Appl. Phys. Lett. 87, 051906 (2005); http://dx.doi.org/10.1063/1.2006975 (3 pages) | Cited 4 times

Online Publication Date: 25 July 2005

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The effect of hole-polaron charging at a hole-injection/hole-transport interface within a functioning organic diode was investigated by single molecule spectroscopy and associated modeling. Efficient quenching of both singlet and triplet excitons by hole polarons is observed at high forward bias due to a buildup of interfacial polaron density. Additionally, for some diodes, an unexpected quenching process was observed at reverse bias, which is ascribed to hole charging of the interface due to the leakage current.
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85.60.Jb Light-emitting devices

Cracking diamond anvil cells by compressed nanographite sheets near the contact edge

Bin Zhang and Wanlin Guo

Appl. Phys. Lett. 87, 051907 (2005); http://dx.doi.org/10.1063/1.2001161 (3 pages) | Cited 9 times

Online Publication Date: 26 July 2005

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Uniformly cold-compressed nanographite sheets in diamond anvil cells (DAC) are found to transform from soft into hard phase at about 17 GPa using molecular dynamics simulations. The hard phase can reach the compressive strength of about 150 GPa. Finite element analyses show that high stress concentrations occur along the boundary of interface on the diamond-anvil culets contacted with the nanographite sheets. The concentrated compressive stress can exceed the strength of diamond in a ring region with the width about 0.2 μm, when the average pressure in the graphite sample is 17 GPa as in [ W. L. Mao et al., Science 302, 425 (2003) ]. Within the narrow ring, superhard carbon phase can be formed from the nanographite sheets, which leads to cracking of the DAC near the contact edge.
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81.05.U- Carbon/carbon-based materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
64.70.Nd Structural transitions in nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.46.-w Structure of nanoscale materials

Optimizing boron junctions through point defect and stress engineering using carbon and germanium co-implants

Victor Moroz, Yong-Seog Oh, Dipu Pramanik, Houda Graoui, and Majeed A. Foad

Appl. Phys. Lett. 87, 051908 (2005); http://dx.doi.org/10.1063/1.2001163 (3 pages) | Cited 15 times

Online Publication Date: 26 July 2005

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We report the fabrication of p+/n junctions using Ge+, C+, and B+ co-implantation and a spike anneal. The best junction exhibits a depth of 26 nm, vertical abruptness of 3 nm/decade, and sheet resistance of 520 Ohm/square. The junction location is defined by where the boron concentration drops to 1018 cm−3. These junctions are close to the International Technology Roadmap specifications for the 65 nm technology node and are achieved by careful engineering of amorphization, stresses, and point defects. Advanced simulation of boron diffusion is used to understand and optimize the process window. The simulations show that the optimum process completely suppresses the transient-enhanced diffusion of boron and the formation of boron-interstitial clusters. This increases the boron solubility to 20% above the equilibrium solid-state solubility.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing

Hydrothermal growth and photoluminescence property of textured CdWO4 scintillator films

H. M. Shang, Y. Wang, M. Bliss, and G. Z. Cao

Appl. Phys. Lett. 87, 051909 (2005); http://dx.doi.org/10.1063/1.2001133 (3 pages) | Cited 3 times

Online Publication Date: 26 July 2005

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Cadmium tungstate (CWO) films on glass substrate have been first prepared by hydrothermal method at temperatures ranging from 120 to 180 °C from cadmium nitrite and tungstic acid in hydrogen peroxide solution. Crack free and dense CWO films with textured structure and thickness up to 8 μm were formed at 150 and 180 °C as revealed by x-ray diffraction (XRD) and scanning electron microscopy (SEM) studied. Photoluminescence (PL) measurements revealed that highly textured CWO thick films possess better PL property. The growth mechanism and preferred orientation or textured structure as well as the relations between textured structure and PL property have been discussed.
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78.55.Hx Other solid inorganic materials
81.10.Dn Growth from solutions
68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
29.40.Mc Scintillation detectors

Grain size effect on the semiconductor-metal phase transition characteristics of magnetron-sputtered VO2 thin films

D. Brassard, S. Fourmaux, M. Jean-Jacques, J. C. Kieffer, and M. A. El Khakani

Appl. Phys. Lett. 87, 051910 (2005); http://dx.doi.org/10.1063/1.2001139 (3 pages) | Cited 59 times

Online Publication Date: 26 July 2005

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Single-phase vanadium dioxide (VO2) thin films have been grown on Si3N4/Si substrates by means of a well-controlled magnetron sputtering process. The deposited VO2 films were found to exhibit a semiconductor-to-metal transition (SMT) at ∼ 69 °C with a resistivity change as high as 3.2 decades. A direct and clear-cut correlation is established between the SMT characteristics (both amplitude and abruptness of the transition) of the VO2 films and their crystallite size.
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81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
73.61.Le Other inorganic semiconductors
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
64.70.K- Solid-solid transitions

The origin of n-type conductivity in undoped In2O3

Takumi Tomita, Kazuyoshi Yamashita, Yoshinori Hayafuji, and Hirohiko Adachi

Appl. Phys. Lett. 87, 051911 (2005); http://dx.doi.org/10.1063/1.2001741 (3 pages) | Cited 22 times

Online Publication Date: 26 July 2005

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This study explores the origin of the native donor in undoped In2O3. The electronic structure of various point defects in In2O3 clusters is studied using the first-principles molecular orbital calculation. The results show that an oxygen vacancy cannot act as a native donor, because the defect level formed is much lower than the bottom of the conduction band. However, interstitial indium can generate a shallow donor level, close to the conduction band, and an even shallower donor level is formed when it associates with an oxygen vacancy. It is concluded that the origin of the native donor in undoped In2O3 is interstitial indium, but also that the existence of an oxygen vacancy is absolutely essential for carrier generation.
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71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters
72.80.Jc Other crystalline inorganic semiconductors
71.15.-m Methods of electronic structure calculations

Characterization of in-grown stacking faults in 4H–SiC (0001) epitaxial layers and its impacts on high-voltage Schottky barrier diodes

H. Fujiwara, T. Kimoto, T. Tojo, and H. Matsunami

Appl. Phys. Lett. 87, 051912 (2005); http://dx.doi.org/10.1063/1.1997277 (3 pages) | Cited 37 times

Online Publication Date: 27 July 2005

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The density, shape and structure of in-grown stacking faults in 4H–SiC (0001) epitaxial layers have been characterized by cathodeluminescence, photoluminescence and high-resolution transmission electron microscopy. These analyses indicate that in-grown stacking faults are of 8H structure, and are generated mostly near the epilayer/substrate interface during chemical vapor deposition. The impact of the stacking faults on the performance of 4H–SiC (0001) Schottky barrier diodes has been investigated. It is revealed that the stacking faults cause the lowering of Schottky barrier height as well as the decrease of breakdown voltage.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.72.Nn Stacking faults and other planar or extended defects
85.30.Kk Junction diodes
78.66.Li Other semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Hx Other solid inorganic materials

Bonding of nitrogen in dilute InAsN and high In-content GaInAsN

J. Wagner, K. Köhler, P. Ganser, and M. Maier

Appl. Phys. Lett. 87, 051913 (2005); http://dx.doi.org/10.1063/1.2005389 (3 pages) | Cited 15 times

Online Publication Date: 27 July 2005

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Dilute InAs1−yNy and high In-content Ga1−xInxAs1−yNy layers with y ⩽ 0.012 and x ≥ 0.92 were grown by rf-nitrogen plasma source molecular-beam epitaxy on InP substrates using a metamorphic GaInAs buffer layer. The bonding of nitrogen in these alloys was analyzed by Raman spectroscopy, showing that nitrogen is incorporated in dilute InAsN as isolated NAs for a nitrogen content of y = 0.005; two additional nitrogen-related modes were found to appear at higher nitrogen contents (y = 0.012), possibly due to the formation of higher-order di-nitrogen In–N complexes. The addition of a small amount of Ga to the InAsN ([Ga] ⩽ 8%) was found to lead to an almost complete change from pure In–N bonding to a preferential bonding of the substitutional nitrogen to at least one Ga neighbor. Further, the effect of nitrogen incorporation on the higher-lying E1 and E1+Δ1 interband transitions of InAsN has been studied by spectroscopic ellipsometry, revealing a high-energy shift of both interband transitions with increasing nitrogen content at a rate similar to that reported for dilute GaAsN [ J. Wagner et al., Appl. Phys. Lett. 77, 3592 (2000) ].
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61.72.S- Impurities in crystals
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Early-stage suppression of Cu (001) oxidation

J. A. Eastman, P. H. Fuoss, L. E. Rehn, P. M. Baldo, G.-W. Zhou, D. D. Fong, and L. J. Thompson

Appl. Phys. Lett. 87, 051914 (2005); http://dx.doi.org/10.1063/1.2005396 (3 pages) | Cited 16 times

Online Publication Date: 27 July 2005

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In situ synchrotron x-ray studies of the early-stage oxidation behavior of Cu (001) reveal that for Cu2O nanoislands, the Cu–Cu2O equilibrium phase boundary is shifted to larger oxygen partial pressure (pO2) by many orders of magnitude relative to bulk Cu2O. Real-time scattering measurements find that an ordered surface structure appears with increasing pO2, followed by the nucleation of epitaxial Cu2O nanoislands. By adjusting the pO2, it is possible to reversibly grow or shrink these islands and accurately determine the equilibrium phase boundary. These observations provide insight into the general stability of oxide nanoclusters grown by various techniques.
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81.65.Mq Oxidation
68.43.Fg Adsorbate structure (binding sites, geometry)
61.46.-w Structure of nanoscale materials
64.60.Q- Nucleation
68.55.A- Nucleation and growth

Influence of self-trapped states on the fluorescence intermittency of single molecules

Jörg Schuster, Frank Cichos, and Christian von Borczyskowski

Appl. Phys. Lett. 87, 051915 (2005); http://dx.doi.org/10.1063/1.2006217 (3 pages) | Cited 32 times

Online Publication Date: 27 July 2005

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We present data on photoinduced fluorescence intermittency of single terrylene molecules embedded in polymer films. Intermittency statistics follow power laws on time scales from tens of milliseconds to tens of seconds. Power law exponents vary with the polarity of the medium while the probability of long dark periods is drastically increased in the more polar matrix. Our experiments support a picture, which assumes a molecule charged by photoexcitation and coupled to a broad manifold of (charged) self-trapped states stabilized by the dielectric response of the surrounding matrix. This model is able to explain long living dark states both for semiconductor nanoparticles and fluorescent dye molecules making use of a unique microscopic description. It also takes into account a competitive photoinduced irreversible bleaching of the molecular state.
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78.55.Kz Solid organic materials
33.50.Dq Fluorescence and phosphorescence spectra
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Photon correlation studies of single GaN quantum dots

Charles Santori, Stephan Götzinger, Yoshihisa Yamamoto, Satoshi Kako, Katsuyuki Hoshino, and Yasuhiko Arakawa

Appl. Phys. Lett. 87, 051916 (2005); http://dx.doi.org/10.1063/1.2006987 (3 pages) | Cited 27 times

Online Publication Date: 27 July 2005

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We present measurements of the second-order coherence function on emission from single GaN quantum dots. In some cases a large degree of photon antibunching is observed, demonstrating isolation of a single quantum system. For a selected quantum dot, we study the dependence of photon antibunching on excitation power and temperature. Using pulsed excitation, we demonstrate an ultraviolet triggered single-photon source operating at a wavelength of 358 nm.
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78.67.Hc Quantum dots
42.50.Dv Quantum state engineering and measurements
42.72.Bj Visible and ultraviolet sources

Mechanical stability of a flexible ferroelectric liquid crystal display with a periodic array of columnar spacers

Dong-Woo Kim, Chang-Jae Yu, Yong-Woon Lim, Jun-Hee Na, and Sin-Doo Lee

Appl. Phys. Lett. 87, 051917 (2005); http://dx.doi.org/10.1063/1.2007856 (3 pages) | Cited 19 times

Online Publication Date: 28 July 2005

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We report on a high-speed flexible display based on a deformed helix ferroelectric liquid crystal (DHFLC) in a vertically aligned configuration. The mechanical stability of the flexible DHFLC display was achieved using a periodic array of columnar spacers formed directly on the top side of in-plane electrodes by the photolithography technique. Several unique features of display performances such as flexibility, uniform alignment, fast response, and gray scale capability were obtained. The switching time was found to be a few hundred microseconds.
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42.79.Kr Display devices, liquid-crystal devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.60.Pg Display systems

Reversal of doping-induced energy level shift: Au on Cs-doped tris(8-hydroxyquinoline) aluminum

Huanjun Ding and Yongli Gao

Appl. Phys. Lett. 87, 051918 (2005); http://dx.doi.org/10.1063/1.2007858 (3 pages) | Cited 9 times

Online Publication Date: 28 July 2005

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We investigated the electronic structure of the interface formed by depositing Au on Cs-doped tris(8-hydroxyquinoline) aluminum (Alq) film using ultraviolet and x-ray photoemission spectroscopy. The initial Au deposition quenches the Alq gap state caused by Cs doping. Further Au depositions gradually shift the energy levels opposite to that induced by Cs doping, especially the highest occupied molecular orbital that shows approximately full recovery to the pristine Alq position. However, the recovery is only partial for the other levels, most noticeably the C 1s core level.
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73.20.At Surface states, band structure, electron density of states
71.20.Rv Polymers and organic compounds
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Ns Metal-nonmetal contacts
61.72.up Other materials
68.35.Ct Interface structure and roughness
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