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7 Aug 2000

Volume 77, Issue 6, pp. 767-915

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Luminescence properties of GaN and Al0.14Ga0.86N/GaN superlattice doped with europium

H. J. Lozykowski, W. M. Jadwisienczak, J. Han, and I. G. Brown

Appl. Phys. Lett. 77, 767 (2000); http://dx.doi.org/10.1063/1.1306645 (3 pages) | Cited 38 times

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We report the observation of visible photoluminescence and cathodoluminescence of Eu3+ ions implanted in GaN and Al0.14Ga0.86N/GaN superlattice. The sharp characteristic emission lines corresponding to Eu3+ intra-4f6-shell transitions are resolved and observed over the temperature range of 7–330 K. The luminescence shows dominant transitions 5D0→7F1,2,3 and weaker 5D0→7F4,5,6 and 5D1→7F1. The luminescence emission is very weakly temperature dependent. The intensity of Eu3+ emission from Al0.14Ga0.86N/GaN superlattice annealed in N2 is ∼58% stronger than from Eu3+ in the GaN layer. The Al0.14Ga0.86N/GaN superlattice and GaN epilayers may be suitable as a material for visible optoelectronic devices. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Eq III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Submicrometer resolution Yablonovite templates fabricated by x-ray lithography

C. Cuisin, A. Chelnokov, J.-M. Lourtioz, D. Decanini, and Y. Chen

Appl. Phys. Lett. 77, 770 (2000); http://dx.doi.org/10.1063/1.1306646 (3 pages) | Cited 14 times

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We report the fabrication and optical characterization of diamond-like photonic structures with 1.3 μm lattice constants. In analogy with the first Yablonovite obtained by a mechanical drilling of a dielectric material, the structures are fabricated in poly(methylmethacrylate) resist using three consecutive exposures to an x-ray beam through a triangular lattice of holes. Up to six crystal periods are obtained in a 6.2-μm-thick resist. The measured reflection and transmission spectra show well contrasted photonic gaps in agreement with numerical simulations. This demonstrates the good optical quality of the structures that can be used as porous templates for transferring the diamond-like pattern to high-refractive-index dielectrics or metals. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers
42.70.Jk Polymers and organics

Room-temperature gain and differential gain characteristics of self-assembled InGaAs/GaAs quantum dots for 1.1–1.3 μm semiconductor lasers

Nobuaki Hatori, Mitsuru Sugawara, Kohki Mukai, Yoshiaki Nakata, and Hiroshi Ishikawa

Appl. Phys. Lett. 77, 773 (2000); http://dx.doi.org/10.1063/1.1306662 (3 pages) | Cited 25 times

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This letter presents an explanation of the optical gain and differential gain of two types of self-assembled quantum dots in the laser active region, which shows 1.16 and 1.31 μm spontaneous emission from the ground state at room temperature. The gain spectrum was measured using the Hakki–Paoli method up to the lasing threshold. The maximum optical gain of the ground state was found to be 150–400 cm−1 and the differential gain to be 3×10−15–1×10−16 cm2, which agrees quite well with the calculation, taking into account both homogeneous broadening and inhomogeneous broadening. Our results will be a guide to the design of laser structures. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Determination of the band offset and the characteristic interdiffusion length in quantum-well lasers using a capacitance–voltage technique

J. Arias, I. Esquivias, E. C. Larkins, S. Bürkner, S. Weisser, and J. Rosenzweig

Appl. Phys. Lett. 77, 776 (2000); http://dx.doi.org/10.1063/1.1306660 (3 pages) | Cited 4 times

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In this work, a capacitance–voltage (C–V) technique, based on a combination of measured and simulated C–V characteristics, was applied to characterize In0.35Ga0.65As/GaAs multiquantum-well laser structures at room temperature. A theoretical model, including the self-consistent solution of Poisson and Schrödinger equations, was developed to simulate the C–V characteristics and the carrier concentration profiles. Measured C–V carrier concentration profiles were used to obtain the average impurity concentration in active regions. The comparison between experimental and simulated results was used to determine the conduction band offset, yielding ΔEc/ΔEg ≈ 0.8. In the case of samples with postgrowth quantum-well intermixing, this technique was applied to extract the characteristic interdiffusion length. © 2000 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.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.Ey III-V semiconductors

Oxide and hydrogen capped ultrasmall blue luminescent Si nanoparticles

Gennadiy Belomoin, Joel Therrien, and Munir Nayfeh

Appl. Phys. Lett. 77, 779 (2000); http://dx.doi.org/10.1063/1.1306659 (3 pages) | Cited 83 times

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We dispersed electrochemical etched silicon into a colloid of ultrasmall ultrabright Si nanoparticles. Direct imaging using transmission electron microscopy shows particles of ∼1 nm in diameter, and infrared and electron photospectroscopy show that they are passivated with hydrogen. Under 350 nm excitation, the luminescence is dominated by an extremely strong blue band at 390 nm. We replace hydrogen by a high-quality ultrathin surface oxide cap by self-limiting oxidation in H2O2. Upon capping, the excitation efficiency drops, but only by a factor of 2, to an efficiency still two-fold larger than that of fluorescein. Although of slightly lower brightness, capped Si particles have superior biocompatability, an important property for biosensing applications. © 2000 American Institute of Physics.
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78.66.Vs Fine-particle systems
61.46.-w Structure of nanoscale materials
78.55.Ap Elemental semiconductors
81.65.Rv Passivation
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
81.65.Mq Oxidation
87.64.K- Spectroscopy

Ultrabroadband AIGaAs/CaF2 semiconductor saturable absorber mirrors

S. Schön, M. Haiml, and U. Keller

Appl. Phys. Lett. 77, 782 (2000); http://dx.doi.org/10.1063/1.1306917 (3 pages) | Cited 8 times

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Ultrabroadband semiconductor saturable absorber mirrors (SESAMs) are required to support self-starting sub-10-fs-pulse generation with Ti:sapphire lasers. Conventional AlxGa1−xAs/AlAs SESAMs are limited by the reflection bandwidth of about 60 nm of the bottom Bragg mirror. In this letter, we demonstrate a GaAs saturable absorber which is epitaxially grown on CaF2 using molecular-beam epitaxy. Even though the difference of the thermal expansion coefficient is very large, we were able to demonstrate good modulation depth with small nonsaturable losses. This is interesting for ultrabroadband SESAMs because the large refractive-index difference between CaF2 and AlxGa1−xAs results in very broadband AlxGa1−xAs/CaF2 Bragg mirrors extending over about a 400-nm-wide reflection bandwidth for a center wavelength of 850 nm. © 2000 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors

Designing finite-height two-dimensional photonic crystal waveguides

T. Søndergaard, A. Bjarklev, M. Kristensen, J. Erland, and J. Broeng

Appl. Phys. Lett. 77, 785 (2000); http://dx.doi.org/10.1063/1.1306915 (3 pages) | Cited 9 times

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Guidelines for designing planar waveguides based on introducing line-defects in two-dimensional photonic-crystal slabs are obtained by comparing calculations on two-dimensional structures with dispersion relations for the media above and below the slab. © 2000 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Tunable piezoelectric semiconductor laser controlled by the carrier injection level

V. Ortiz, N. T. Pelekanos, Guido Mula, and Le Si Dang

Appl. Phys. Lett. 77, 788 (2000); http://dx.doi.org/10.1063/1.1306908 (3 pages) | Cited 2 times

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We propose a tunable laser diode based on a piezoelectric heterostructure. The tuning mechanism consists of modulating the gain spectrum during lasing by the quantum-confined Stark effect. The modulating electric field is produced by carrier separation in the active region, and its amplitude depends on the injected carrier density. In a proof-of-principle photopumped experiment, we were able to generate a space-charge field of 20 kV/cm which shifted the lasing wavelength by more than 3 nm in the 800 nm spectral region. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
77.22.Jp Dielectric breakdown and space-charge effects
78.20.Jq Electro-optical effects

Photoresponsivity of ultraviolet detectors based on InxAlyGa1−x−yN quaternary alloys

T. N. Oder, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 77, 791 (2000); http://dx.doi.org/10.1063/1.1306540 (3 pages) | Cited 17 times

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We describe the growth, fabrication, and characterization of an ultraviolet (UV) photoconductive detector based on InxAlyGa1−x−yN quaternary alloy that is lattice matched to GaN. The detector consisted of 0.1 μm InxAlyGa1−x−yN alloy grown on 0.5–1.0 μm GaN epilayer by metalorganic chemical vapor deposition. With varying indium concentration, the cut-off wavelength of the InxAlyGa1−x−yN detectors could be varied to the deep UV range. The most important and intriguing result is that the responsivity of the InxAlyGa1−x−yN quaternary alloy exceeded that of AlGaN alloy of a comparable cutoff wavelength by a factor of five. This makes the nitride quaternary alloy very important material for solar blind UV detectors applications particularly in the deep UV range where Al rich AlGaN alloys have problems with low quantum efficiency and cracks due in part to lattice mismatch with GaN. The advantages of InxAlyGa1−x−yN quaternary over AlGaN ternary alloys for UV detector applications are also discussed. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
42.79.Pw Imaging detectors and sensors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Finite-source dye-diffusion thermal transfer for doping and color integration of organic light-emitting devices

Chung-chih Wu, Cheng-chung Yang, Hsin-hua Chang, Chieh-Wei Chen, and Cheng-Chung Lee

Appl. Phys. Lett. 77, 794 (2000); http://dx.doi.org/10.1063/1.1306293 (3 pages) | Cited 9 times

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An effective process of performing controllable doping of polymer films in organic light-emitting devices is reported. In this approach, a film to be doped is brought into direct contact with a dye-dispersed polymer donor film to permit direct dye-diffusion thermal transfer. Theoretical and experimental studies indicate that this doping process can be modeled by Fick’s diffusion theory and that a desired dopant distribution may be obtained in a single transfer step by adjusting the diffusion conditions. Doped-polymer light-emitting devices made by this process exhibited the same device characteristics as those by the conventional blending process. Along with patterned color donor plates, we also demonstrated multicolor devices of arbitrary patterns over large areas with a single thermal transfer step. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
66.30.J- Diffusion of impurities
85.60.Pg Display systems
78.66.Qn Polymers; organic compounds

Organic–inorganic hybrid electroluminescence device fabricated by conjugated polymer and ZnS:Mn

Xiaohui Yang and Xurong Xu

Appl. Phys. Lett. 77, 797 (2000); http://dx.doi.org/10.1063/1.1306390 (3 pages) | Cited 17 times

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An organic–inorganic hybrid device was fabricated. The architecture of the hybrid device consisted of two layers sandwiched between two injecting electrodes, one of which was a conjugated polymer layer and the other was an inorganic material layer. Emission from both the organic and inorganic layers was observed, but the mechanisms of luminescence for the layers were different. Our primary results suggest the possibility of integrating different types of luminescence into one device structure. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Hf II-VI semiconductors
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
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Charged species profiles in oxygen plasma

S. V. Berezhnoj, C. B. Shin, U. Buddemeier, and I. Kaganovich

Appl. Phys. Lett. 77, 800 (2000); http://dx.doi.org/10.1063/1.1306637 (3 pages) | Cited 25 times

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The charged species profiles have been studied in oxygen plasma of asymmetrically driven capacitively coupled rf discharge. The electron (ne), negative (n), and positive (p) ion densities have been measured by Langmuir probe in a wide range of pressures (3–30 Pa) and interelectrode distances (2–10 cm). At small powers (ne<1015 m−3) it was obtained that the electronegativity is high (n/ne ∼ 10) and the electron density profile is flat in plasma bulk. The negative ion density profile is nearly flat in the ion–ion core, where n≫ne, and falls off towards the plasma-sheath boundary with n ≈ 0 with the spatial scale πmath, determined by the negative ion diffusion coefficient Dn and detachment frequency γd. As the pressure decreases, this spatial scale exceeds half of the interelectrode distance and the negative ion density profile tends to a parabolic one. The obtained spatial distributions of charged particles are compared with the results of self-consistent modeling by use of a fluid approach for ions, and kinetic equation for electrons. Numerical simulation results agree well with both theory predictions and measurement data. © 2000 American Institute of Physics.
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52.25.-b Plasma properties
52.65.Kj Magnetohydrodynamic and fluid equation
52.80.Pi High-frequency and RF discharges
52.70.Ds Electric and magnetic measurements
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Correlation between N 1s core level x-ray photoelectron and x-ray absorption spectra of amorphous carbon nitride films

C. Quirós, J. Gómez-García, F. J. Palomares, L. Soriano, E. Elizalde, and J. M. Sanz

Appl. Phys. Lett. 77, 803 (2000); http://dx.doi.org/10.1063/1.1306636 (3 pages) | Cited 15 times

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This work presents a comparative analysis of the N 1s core level spectra, as measured by x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS), of amorphous CNx films which gives evidence of the existing correlation between the different components that constitute the respective spectra. After annealing, the contribution of XPS at 399.3 eV and the components of XAS at 399.6 and 400.8 eV are clearly enhanced. They are assigned to sp2 with two neighbors and to sp states of nitrogen. In addition, the XPS component at 401.3 eV is related to the XAS feature at 402.0 eV and has been assigned to sp2 nitrogen bonded to three carbon neighbors. © 2000 American Institute of Physics.
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71.55.Jv Disordered structures; amorphous and glassy solids
79.60.Ht Disordered structures
79.60.Dp Adsorbed layers and thin films
78.70.Dm X-ray absorption spectra
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.-a Thin film structure and morphology
61.43.Er Other amorphous solids

Second-harmonic imaging of semiconductor quantum dots

John Erland, Sergey I. Bozhevolnyi, Kjeld Pedersen, Jacob R. Jensen, and Jørn M. Hvam

Appl. Phys. Lett. 77, 806 (2000); http://dx.doi.org/10.1063/1.1306634 (3 pages) | Cited 6 times

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Resonant second-harmonic generation is observed at room temperature in reflection from self-assembled InAlGaAs quantum dots grown on a GaAs (001) substrate. The detected second-harmonic signal peaks at a pump wavelength of ∼ 885 nm corresponding to the quantum-dot photoluminescence maximum. In addition, the second-harmonic spectrum exhibits another smaller but well-pronounced peak at 765 nm not found in the linear experiments. We attribute this peak to the generation of second-harmonic radiation in the AlGaAs spacer layer enhanced by the local symmetry at the quantum-dot interface. We further observe that second-harmonic images of the quantum-dot surface structure show wavelength-dependent spatial variations. Imaging at different wavelength is used to demonstrate second-harmonic generation from the semiconductor quantum dots. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.60.Pb Conventional optical microscopes

Self-assembled zinc blende GaN quantum dots grown by molecular-beam epitaxy

E. Martinez-Guerrero, C. Adelmann, F. Chabuel, J. Simon, N. T. Pelekanos, Guido Mula, B. Daudin, G. Feuillet, and H. Mariette

Appl. Phys. Lett. 77, 809 (2000); http://dx.doi.org/10.1063/1.1306633 (3 pages) | Cited 38 times

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Zinc blende (ZB) GaN quantum dots have been grown by plasma-assisted molecular-beam epitaxy on AlN buffer layers using 3C-SiC(001) substrates. The two- to three-dimensional growth mode transition is studied by following the evolution of the reflection high-energy electron diffraction pattern. ZB GaN island layers are further examined by atomic force microscopy and transmission electron microscopy, extracting a mean island height of 1.6 nm and a mean diameter of 13 nm at a density of 1.3×1011 cm−2. Embedded ZB GaN quantum dots show strong ultraviolet photoluminescence without any thermal quenching up to room temperature. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Photoluminescence up-conversion in InAs/GaAs self-assembled quantum dots

P. P. Paskov, P. O. Holtz, B. Monemar, J. M. Garcia, W. V. Schoenfeld, and P. M. Petroff

Appl. Phys. Lett. 77, 812 (2000); http://dx.doi.org/10.1063/1.1306653 (3 pages) | Cited 35 times

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We report up-converted photoluminescence in a structure with InAs quantum dots embedded in GaAs. An efficient emission from the GaAs barrier is observed with resonant excitation of both the dots and the wetting layer. The intensity of the up-converted luminescence is found to increase superlinearly with the excitation density. The results suggest that the observed effect is due to a two-step two-photon absorption process involving quantum dot states. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Performance enhancement of metal-hydride switchable mirrors using Pd/AlOx composite cap layers

A. T. M. van Gogh, S. J. van der Molen, J. W. J. Kerssemakers, N. J. Koeman, and R. Griessen

Appl. Phys. Lett. 77, 815 (2000); http://dx.doi.org/10.1063/1.1306643 (3 pages) | Cited 22 times

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A drastic improvement of the optical properties and lifetime of switchable mirrors is obtained by placing a thin AlOx buffer layer between the Pd cap layer and the optically active, rare earth layer. The buffer layer lowers the minimum necessary Pd thickness to ∼1 nm, resulting in a ≈20% increase of the maximum transmittance. The optimal Pd and Al layer thicknesses are determined for the YHx and LaHx system using a powerful combination of optical and matrix film techniques. The AlOx buffer is shown to be superior to the native oxide layers YOx and LaOx. The buffer layer is essential for lanthanum, which is a particularly vulnerable, but fundamentally very important material. Using this composite cap layer, we have been able to switch LaHx films several times. © 2000 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings
78.66.Bz Metals and metallic alloys
81.65.Kn Corrosion protection
72.60.+g Mixed conductivity and conductivity transitions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Temperature variation of near-infrared emission from Cr4+ in aluminate glass for broadband telecommunication

Setsuhisa Tanabe and Xian Feng

Appl. Phys. Lett. 77, 818 (2000); http://dx.doi.org/10.1063/1.1306644 (3 pages) | Cited 31 times

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Temperature dependence of fluorescence spectra of Cr4+ in an aluminate glass in the range of 1.2–1.6 μm was investigated from 15 to 300 K. The emission spectra were broadband centered at about 1.3 μm, wider than 200 nm width. The emission intensity drastically increased with decreasing temperature and that of 15 K was 20 times larger than that of 300 K. The bandwidth and mean energy of the emission band changed very slightly with temperature. The emission of Cr4+ in the glass fiber is expected as a tunable laser source and a broadband amplifier for the wavelength-division-multiplexed telecommunication. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
42.70.Hj Laser materials
42.70.Ce Glasses, quartz
42.55.Rz Doped-insulator lasers and other solid state lasers

Effects of tensile and compressive strain on the luminescence properties of AlInGaN/InGaN quantum well structures

M. E. Aumer, S. F. LeBoeuf, S. M. Bedair, M. Smith, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 77, 821 (2000); http://dx.doi.org/10.1063/1.1306648 (3 pages) | Cited 36 times

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We report on the luminescence properties of AlInGaN/In0.08Ga0.92N quantum wells (QWs) subjected to a variable amount of lattice mismatch induced strain, including wells with zero strain, compressive strain, and tensile strain. The primary peak emission energy of a 3 nm In0.08Ga0.92N QW was redshifted by 236 meV as the stress in the well was changed from −0.86% (compressive) to 0.25% (tensile). It was also found that the photoluminescence intensity of quantum wells decreased with increasing strain. A lattice matched 9 nm QW exhibited a luminescence intensity that is three times greater than its highly strained counterpart. The potential applications of this strain engineering will be discussed. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Photoluminescence of disordered ABO3 perovskites

P. S. Pizani, E. R. Leite, F. M. Pontes, E. C. Paris, J. H. Rangel, E. J. H. Lee, E. Longo, P. Delega, and J. A. Varela

Appl. Phys. Lett. 77, 824 (2000); http://dx.doi.org/10.1063/1.1306663 (3 pages) | Cited 79 times

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Intense photoluminescence in highly disordered (amorphous) BaTiO3, PbTiO3, and SrTiO3 prepared by the polymeric precursor method was observed at room temperature. The emission band maxima from the three materials are in the visible region and depend on the exciting wavelength. The origin of the photoluminescence was not exactly identified. However, the line shape indicates that confinement effects are not probable. The experimental results indicate that it could be related to the disordered perovskite structure. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
61.43.Er Other amorphous solids
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Nonlinear optical studies of 3-methyl-4-methoxy-4′-nitrostilbene single-crystal films

Shida Tan, Achintya K. Bhowmik, Sunil Sodah, and Mrinal Thakur

Appl. Phys. Lett. 77, 827 (2000); http://dx.doi.org/10.1063/1.1306664 (3 pages) | Cited 2 times

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We report the second-order optical measurement of single-crystal thin-films of 3-methyl-4-methoxy-4′-nitrostilbene by transverse second-harmonic generation (SHG) technique. Phase mismatch was negligible in the measurements since the thickness of the films was less than the coherence length. Detailed polarization selective measurements were used to determine the magnitudes of the tensor elements of second-order susceptibility. The values of d coefficients at the fundamental wavelength of 1064 nm were measured to be d33 = 195±10 pm/V and d24 = 75±5 pm/V. Both type I and type II phase-matched propagation directions were identified in the crystal and the type II phase matching direction lies parallel to the film. The results show that these films are promising for applications such as phase-matched SHG in waveguides. © 2000 American Institute of Physics.
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42.70.Mp Nonlinear optical crystals
42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds

Plasma-induced alignment of carbon nanotubes

Chris Bower, Wei Zhu, Sungho Jin, and Otto Zhou

Appl. Phys. Lett. 77, 830 (2000); http://dx.doi.org/10.1063/1.1306658 (3 pages) | Cited 243 times

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Uniform films of well-aligned carbon nanotubes have been grown using microwave plasma-enhanced chemical vapor deposition. It is shown that nanotubes can be grown on contoured surfaces and aligned in a direction always perpendicular to the local substrate surface. The alignment is primarily induced by the electrical self-bias field imposed on the substrate surface from the plasma environment. It is found that switching the plasma source off effectively turns the alignment mechanism off, leading to a smooth transition between the plasma-grown straight nanotubes and the thermally grown “curly” nanotubes. The nanotubes grow at a surprisingly high rate of ∼100 nm/s in our plasma process, which may be important for large-scale commercial production of nanotubes. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Reversible photoquenching of luminescence in conjugated polymers

S. V. Frolov

Appl. Phys. Lett. 77, 833 (2000); http://dx.doi.org/10.1063/1.1306661 (3 pages) | Cited 1 time

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Photoluminescence in thin films of poly(p-phenylene vinylene) derivatives is studied using a two-beam excitation technique. It is demonstrated that excited state absorption leads to the reversible quenching of steady-state luminescence. Measurements of ultrafast exciton dynamics show that this quenching is due to exciton depletion by photogenerated metastable quenching centers. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
71.20.Rv Polymers and organic compounds
71.35.Gg Exciton-mediated interactions

Near-field surface photovoltage

R. Shikler and Y. Rosenwaks

Appl. Phys. Lett. 77, 836 (2000); http://dx.doi.org/10.1063/1.1306916 (3 pages) | Cited 1 time

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A phenomenon called near-field surface photovoltage is presented. It is based on inducing photovoltage only at a semiconductor space-charge region using near-field illumination. The photovoltage is obtained by measuring the contact potential difference between an optical near-field force sensor and a semiconductor surface under illumination. It is shown that the near-field illumination induces photovoltage at the surface which is principally different from photovoltage induced by far-field illumination. The mechanisms that govern the different far-field and near-field photovoltage response are discussed. © 2000 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
73.20.At Surface states, band structure, electron density of states

Atomic-layer expulsion in nanoindentations on an ionic single crystal

P. F. M. Terán Arce, G. Andreu Riera, P. Gorostiza, and F. Sanz

Appl. Phys. Lett. 77, 839 (2000); http://dx.doi.org/10.1063/1.1306909 (3 pages) | Cited 11 times

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Utilizing atomic-force microscopy, we have performed and characterized nanoindentations on a MgO(100) surface with depths varying between one monatomic layer and tens of nm. Our results show that plastic deformation is indicated by discrete events in the indentation curve which are associated with the number of atomic layers being expelled by the tip penetrating the surface. An estimation of the energy required to expel MgO ions from a monatomic deep cavity correlates well with our data. The critical shear strength was evaluated and lies in the same order of magnitude as the theoretical value. © 2000 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.F- Deformation and plasticity
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