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25 May 1998

Volume 72, Issue 21, pp. 2631-2766

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Observation of a highly phase-correlated chirped frequency comb output from a frequency-shifted feedback laser

Koichiro Nakamura, Toshiharu Miyahara, and Hiromasa Ito

Appl. Phys. Lett. 72, 2631 (1998); http://dx.doi.org/10.1063/1.121438 (3 pages) | Cited 9 times

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A laser cavity closed via the first-order diffracted light of an intracavity acousto-optic modulator is referred to as a frequency-shifted feedback laser laser. It has been proven that the laser output consists of a chirped frequency comb evenly spaced at a cavity-free spectral range. In this letter a phase correlation between the chirped comb components is discussed. A homodyne experiment with a Mach–Zehnder interferometer was carried out to examine the problem. It was clarified that the comb components are highly correlated in phase. © 1998 American Institute of Physics.
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42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.25.Fx Diffraction and scattering
07.60.Ly Interferometers
42.60.Fc Modulation, tuning, and mode locking
42.79.Hp Optical processors, correlators, and modulators
42.79.Jq Acousto-optical devices
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials

Continuous-wave emission in the ultraviolet from diatomic excimers in a microdischarge

J. W. Frame, P. C. John, T. A. DeTemple, and J. G. Eden

Appl. Phys. Lett. 72, 2634 (1998); http://dx.doi.org/10.1063/1.121439 (3 pages) | Cited 22 times

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Emission on the I2 (D′→A′), XeI (B2Σ1/2+→X2Σ1/2+) and XeO (2 3Π→1 3Π) bands, peaking in the ultraviolet at 342, 253 and 238 nm, respectively, has been generated on a continuous basis in a microdischarge with a static gas fill. Discharges are produced in Kr/I2, Xe/I2, or Xe/O2 gas mixtures by cylindrical devices 400 μm in diameter and fabricated in silicon. Rare-gas–halide and –oxide microdischarge lamps are attractive ultraviolet or vacuum ultraviolet sources and XeI, in particular, appears to be a potential replacement for Hg resonance line radiation (253.7 nm). © 1998 American Institute of Physics.
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33.20.Lg Ultraviolet spectra
33.20.Ni Vacuum ultraviolet spectra
52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
42.72.Bj Visible and ultraviolet sources
33.50.Dq Fluorescence and phosphorescence spectra

Fused vertical couplers

Bin Liu, Ali Shakouri, Patrick Abraham, Boo-Gyoun Kim, Andrew W. Jackson, and John E. Bowers

Appl. Phys. Lett. 72, 2637 (1998); http://dx.doi.org/10.1063/1.121440 (2 pages) | Cited 20 times

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A vertical directional coupler fabricated using wafer fusion is demonstrated with a very short coupling length of 62 μm. The optical propagation loss introduced by the fused layer is investigated. An excess loss of 1.1 dB/cm at 1.55 μm was measured for waveguides which incorporate a fused junction near the core region. Fused vertical couplers make it possible to realize three-dimensional waveguide structures and compact switching arrays and they solve some of the topology problems of large switch arrays. © 1998 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.86.+b Optical workshop techniques
42.82.Ds Interconnects, including holographic interconnects
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Polarized electroluminescence from smectic mesophase

Hiroaki Tokuhisa, Masanao Era, and Tetsuo Tsutsui

Appl. Phys. Lett. 72, 2639 (1998); http://dx.doi.org/10.1063/1.121441 (3 pages) | Cited 54 times

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Electrically pumped light emission was observed from a smectic mesophase of liquid-crystalline oxadiazole; 2,5-hexyloxybiphenyl–hexyloxyphenyl–oxadiazole (HOBP-OXD), which exhibits high electron transport capability. The light-emitting diode consisted of the HOBP-OXD film, a copper phthalocyanine vacuum deposited film as a hole injection layer, and a tris-(8-hydroxyquinoline) aluminum vacuum deposited film as an electron injection layer. The emission was linearly polarized originating from highly oriented molecular textures in the smectic mesophase with a degree of orientational order of 0.32. © 1998 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
68.15.+e Liquid thin films
78.66.Qn Polymers; organic compounds

Degradation processes at the cathode/organic interface in organic light emitting devices with Mg:Ag cathodes

Hany Aziz, Zoran Popovic, Carl P. Tripp, Nan-Xing Hu, Ah-Mee Hor, and Gu Xu

Appl. Phys. Lett. 72, 2642 (1998); http://dx.doi.org/10.1063/1.121442 (3 pages) | Cited 82 times

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We report electroluminescence degradation studies on tris(8-hydroxyquinoline) aluminum (Alq3)-based organic light emitting devices (OLEDs) with Mg:Ag cathodes in ambient conditions. The nonemissive spots in the OLEDs are studied via optical and fluorescence microscopy and via microscopic infrared spectroscopy. Studies reveal that a majority of the nonemissive spots are caused by the growth of Mg(OH)2 sites at the Alq3/Mg:Ag interface, associated with local degradation of the Alq3 layer. In addition, the growth of elevated cathode bubbles, which also lead to nonemissive spots, is found to be caused by gas evolution from the galvanic corrosion of the Mg/Ag couple as well as from the electrolysis of absorbed moisture. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers
78.55.Kz Solid organic materials
81.65.Kn Corrosion protection
07.60.Pb Conventional optical microscopes

Near-field optical study of InGaN/GaN epitaxial layers and quantum wells

A. Vertikov, M. Kuball, A. V. Nurmikko, Y. Chen, and S.-Y. Wang

Appl. Phys. Lett. 72, 2645 (1998); http://dx.doi.org/10.1063/1.121085 (3 pages) | Cited 22 times

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We have employed near-field scanning optical microscopy to investigate the influence of specific microstructural defects on the optical properties of thin InGaN/GaN epilayers and quantum wells. These defects are empty “pinholes” with a hexahedron cone morphology that are nucleated by threading dislocations from the GaN buffer layer. By correlating atomic force microscopy with spatially and spectrally resolved photoluminescence (PL) on a 100 nm spatial scale, we find that the pinholes have no clearly observable effect on the PL efficiency, at least partly due to the strong carrier localization in the InGaN nonrandom alloy. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
78.55.Cr III-V semiconductors
07.79.Fc Near-field scanning optical microscopes
07.79.Lh Atomic force microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness

Monomolecular layer of squarylium dye J aggregates exhibiting a femtosecond optical response of delocalized excitons

Makoto Furuki, Lyong Sun Pu, Fumio Sasaki, Shyunsuke Kobayashi, and Toshiro Tani

Appl. Phys. Lett. 72, 2648 (1998); http://dx.doi.org/10.1063/1.121086 (3 pages) | Cited 18 times

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We report on the demonstration of the femtosecond nonlinear optical response from a two-dimensional monomolecular layer of squarylium dye J aggregate at 5 °C. The formation of a monomolecular layer Langmuir film was achieved by spreading squarylium dye modified by two propyl and two hexyl groups at the air–water interface, which resulted in a very strong J band (o.d. = 0.3) at 777 nm. The transient absorption spectra in a resonant pump-probe measurement showed a low absorption saturation power (9.7×106 W/cm2) and an ultrafast response (300 fs), which are indicative of exciton delocalization over 18 molecules in this J aggregate, even at 5 °C. © 1998 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.47.-p Spectroscopy of solid state dynamics
78.30.Jw Organic compounds, polymers
68.18.-g Langmuir-Blodgett films on liquids
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Polarization-insensitive four-wave mixing in a semiconductor optical amplifier

A. Mecozzi, G. Contestabile, L. Graziani, F. Martelli, A. D’Ottavi, P. Spano, R. Dall’Ara, and J. Eckner

Appl. Phys. Lett. 72, 2651 (1998); http://dx.doi.org/10.1063/1.121087 (3 pages) | Cited 10 times

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We propose and demonstrate a method to obtain polarization-insensitive four-wave mixing in a semiconductor optical amplifier. The method makes use of two pumps with orthogonal polarization placed at the two sides of the signal spectrum. Unlike a previously proposed scheme, a large bandwidth of the signal does not set a lower limit to the degree of polarization insensitivity obtained. Using a commercially available pig-tailed semiconductor optical amplifier, we have obtained less than 0.4 dB of intensity variation of the conjugate field for arbitrary changes of the signal polarization. © 1998 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors

Phase-matched second harmonic generation in asymmetric double quantum wells

K. L. Vodopyanov, K. O’Neill, G. B. Serapiglia, C. C. Phillips, M. Hopkinson, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 72, 2654 (1998); http://dx.doi.org/10.1063/1.121088 (3 pages) | Cited 13 times

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Efficient ( ∼ 1%) second harmonic generation, resonantly enhanced near λ = 8.6 μm, has been observed in asymmetric double multi-quantum well structures. We used (i) edge-emitting waveguide geometry where the phase matching was achieved by incorporating a separate multiple quantum well region which modifies (via the Kramers–Kronig relation) the dispersion of light and (ii) 45° wedge multi-bounce geometry where the phases of second harmonic waves generated at sequential bounces were synchronized by changing the angle of incidence. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Mechanism for reducing recovery time of optical nonlinearity in semiconductor laser amplifier

Masashi Usami, Munefumi Tsurusawa, and Yuichi Matsushima

Appl. Phys. Lett. 72, 2657 (1998); http://dx.doi.org/10.1063/1.121089 (3 pages) | Cited 23 times

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We propose and demonstrate a novel scheme to reduce the recovery time of optical nonlinearity in a semiconductor laser optical amplifier driven under a loss condition for the signal light pulse. Additional light, which is set at a transparency wavelength in the active layer, promotes stimulated recombination of excess carriers induced by the absorption of the signal light. This scheme excludes any additional carrier transport mechanism and nonradiative recombination and hence generation of heat. The principle of operation is experimentally verified by measuring time-domain transmission variance using a pump–probe method. A drastic reduction of the excess-carrier lifetime to less than 70 ps was confirmed. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Yj Optical parametric oscillators and amplifiers

Polymer electroluminescent devices processed by inkjet printing: I. Polymer light-emitting logo

Jayesh Bharathan and Yang Yang

Appl. Phys. Lett. 72, 2660 (1998); http://dx.doi.org/10.1063/1.121090 (3 pages) | Cited 170 times

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Inkjet printing (IJP) technology is a popular technology for desktop publishing. Since some of the conducting (or conjugated) polymers are solution processable, IJP technology becomes an ideal method for printing polymer light-emitting diodes with high resolution. Unfortunately, the polymer film printed from an inkjet printer usually consists of pin-holes, and this intrinsic character makes it unsuitable for fabricating high quality polymer electronic devices, particularly for devices in the sandwich structure. In this letter, we submit a hybrid structure, which consists of an inkjet printed layer in conjunction with another uniform spin coated polymer layer, as an alternative to the regular inkjet printed structure. The uniform layer serves as a buffer layer to seal the pin-holes and the IJP layer is the layer consisting of the desired pattern, for example the red–green–blue dots for a multicolor display. To demonstrate, we applied this hybrid technology to fabricate efficient and large area polymer light-emitting logos. The use of this concept represents a whole new technology of fabricating polymer electronic devices with lateral patterning capability. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
42.79.Wc Optical coatings
42.86.+b Optical workshop techniques

Modeling the fluorescent lifetime of Y2O3:Eu

R. M. Ranson, E. Evangelou, and C. B. Thomas

Appl. Phys. Lett. 72, 2663 (1998); http://dx.doi.org/10.1063/1.121091 (2 pages) | Cited 16 times

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Phosphor thermography, relying on the temperature dependence of the decay time of photoluminescence from suitable phosphors, provides remote measurement of the temperature of components. Such a phosphor is yttrium oxide doped with europium (Y2O3:Eu). Associated with this phosphor is also a rise time. Demonstrated is that the rise time is also temperature dependent, as a result of known electronic transitions within the Eu ions. For the phosphor Y2O3:Eu (3.4 at.%), the rise time is an activated process in the temperature region between 25 and 850 °C. Faster than the decay time, the rise time offers the opportunity for measurement of higher velocity components. © 1998 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
07.20.Dt Thermometers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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Surface transverse waves on langasite

J. Koskela, S. Lehtonen, V. P. Plessky, and M. M. Salomaa

Appl. Phys. Lett. 72, 2665 (1998); http://dx.doi.org/10.1063/1.121092 (3 pages) | Cited 2 times

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Surface transverse waves (STW) are numerically simulated on langasite. As our method of investigation, we compute the admittance of an infinite synchronous resonator. The resonance and antiresonance frequencies are evaluated as functions of the crystal cut, temperature, and the thickness of the aluminium electrodes. For optimal parameters, we demonstrate a vanishing first-order temperature coefficient at room temperature and find a coupling strength several times stronger than that for Rayleigh waves in ST quartz. In particular, we find that the sensitivity of the resonance frequency to variations in the thickness of the aluminium electrodes is significantly lower in langasite than in ST quartz. © 1998 American Institute of Physics.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.35.Gy Mechanical properties; surface strains
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.90.+k Other topics in dielectrics, piezoelectrics, and ferroelectrics and their properties (restricted to new topics in section 77)
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Observation of chemical shifts of Si 2p level by an x-ray photoelectron spectroscopy system with a laser-plasma x-ray source

Hiroyuki Kondo, Toshihisa Tomie, and Hideaki Shimizu

Appl. Phys. Lett. 72, 2668 (1998); http://dx.doi.org/10.1063/1.121093 (3 pages) | Cited 14 times

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An x-ray photoelectron spectroscopy system with a laser-plasma x-ray source is shown to have energy resolution high enough to observe chemical shifts of Si 2p electrons in SiO2, Si3N4, and pure Si. A boron nitride (BN) plasma x-ray source is produced by irradiation of 100 mJ Q-switched YAG laser pulses. A single line emission at 4.86 nm is selected from the BN plasma by means of carbon foils. Fine spectra are acquired with only 96 laser shots. The results obtained confirm that a laboratory-sized x-ray photoelectron spectroscopy system with submicron spatial resolution and high spectral acquisition speed can be realized. © 1998 American Institute of Physics.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
07.81.+a Electron and ion spectrometers
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Photon emission from Ag and Au clusters in the scanning tunneling microscope

A. Downes and M. E. Welland

Appl. Phys. Lett. 72, 2671 (1998); http://dx.doi.org/10.1063/1.121094 (3 pages) | Cited 14 times

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In principle, chemical information is obtainable from metal surfaces by means of photon emission from the scanning tunneling microscope (STM). However, the photon emission varies significantly with topography and choice of tip. We address the important issue of geometry by studying the emission characteristics of Ag and Au spheres. First, photon maps of Ag clusters, consisting in some cases of just a few atoms, demonstrate that they can be uniquely identified from other nonmetallic particles. Then, the bias at which there is an onset of photon emission for 1 nm Ag and Au clusters is measured and found to be ≈ 3.3 and ≈ 2.1 V, respectively. This allows for the demonstration of the ability of the STM to distinguish different metal particles by their photon emission. The value of the onset bias for each metal can be made almost invariant to sample topography by an appropriate choice of tip; only then is the photon emission related purely to the optical properties of the surface. We envisage a form of chemical microscopy, whereby the bias of emission onset is mapped. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Coupling of GaN- and AlN-like longitudinal optic phonons in Ga1−xAlxN solid solutions

F. Demangeot, J. Groenen, J. Frandon, M. A. Renucci, O. Briot, S. Clur, and R. L. Aulombard

Appl. Phys. Lett. 72, 2674 (1998); http://dx.doi.org/10.1063/1.121095 (3 pages) | Cited 28 times

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Long-wavelength optical phonons of Ga1−xAlxN solid solutions have been identified in a wide compositional range by Raman spectroscopy. The A1 and E1 polar phonon frequencies evolve continuously with x from one-member crystal to the other. The same behavior seems to hold true for the silent B1 mode, which manifests itself by an interference with an unidentified continuum. Coupling of the longitudinal-optic (LO) modes associated with the two types of bonds, via the macroscopic electric field, is treated by a generalization of the dielectric model [D. T. Hon and W. L. Faust, J. Appl. Phys. 1, 241 (1973)]. This approach accounts for the observed frequencies and supports the apparent one-mode behavior of the polar LO phonons. © 1998 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Fs III-V and II-VI semiconductors

The effect of Al3Ti capping layers on electromigration in single-crystal aluminum interconnects

V. T. Srikar and C. V. Thompson

Appl. Phys. Lett. 72, 2677 (1998); http://dx.doi.org/10.1063/1.121096 (3 pages) | Cited 7 times

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Studies of accelerated electromigration were conducted on passivated Al single-crystal interconnects fabricated on oxidized Si, and capped with Al3Ti overlayers. The capping layers were formed by the reaction of the single-crystal Al films with Ti overlayers. The activation energy for electromigration-induced failure was determined to be 0.94±0.05 eV. Previous work on Al single-crystal interconnects without Al3Ti overlayers gave an activation energy of 0.98±0.2 eV and lifetimes of similar magnitude [Y.-C. Joo and C. V. Thompson, J. Appl. Phys. 81, 6062 (1997)]. The similarity of these results suggests that either the rate-limiting mechanism for electromigration-induced failure of single-crystal Al interconnects is not diffusion along the interface of the Al with the surrounding oxide and overlayer, or that, surprisingly, the diffusivity of Al along the Al/Al3Ti interface is approximately the same as, or lower than, the diffusivity of Al along the Al/AlOx interface. © 1998 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Direct observation of the core structures of threading dislocations in GaN

Y. Xin, S. J. Pennycook, N. D. Browning, P. D. Nellist, S. Sivananthan, F. Omnès, B. Beaumont, J. P. Faurie, and P. Gibart

Appl. Phys. Lett. 72, 2680 (1998); http://dx.doi.org/10.1063/1.121097 (3 pages) | Cited 86 times

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Here we present the first direct observation of the atomic structure of threading dislocation cores in hexagonal GaN. Using atomic-resolution Z-contrast imaging, dislocations with edge character are found to exhibit an eight-fold ring core. The central column in the core of a pure edge dislocation has the same configuration as one row of dimers on the {10-10} surface. Following recent theoretical work, it is proposed that edge dislocations do not have deep defect states in the band gap, and do not contribute to cathodoluminescence dislocation contrast. On the other hand, both mixed and pure screw dislocations are found to have a full core, and full screw dislocation cores were calculated to have states in the gap. © 1998 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.55.Eq III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Influence of oxygen plasma treatments on the structural properties of c-Si

N. H. Nickel and I. Sieber

Appl. Phys. Lett. 72, 2683 (1998); http://dx.doi.org/10.1063/1.121098 (3 pages) | Cited 3 times

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The effects of hydrogen and oxygen plasma treatments on the structural properties of n-type c-Si were examined. Specimens were exposed to either an oxygen or a hydrogen electron-cyclotron-resonance plasma in a temperature range of 240–385 °C. Hydrogenations performed at low temperatures (<300 °C) introduced platelets. On the other hand, oxygen plasma treatments did not result in the formation of platelets. Analysis of O and H concentration depth profiles, measured by secondary-ion-mass spectrometry (SIMS), reveal that O and H migrate with a similar diffusion coefficient of Deff ≈ 1012 cm2 s−1. Moreover, the O concentration exceeds the H concentration by roughly a factor of 2.5. This suggests that one H atom and 2–3 O atoms migrate as a cluster. Furthermore, evidence of deep traps for H and O was found from the SIMS depth profiles. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.S- Impurities in crystals
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
71.55.Cn Elemental semiconductors

Low temperature fabrication and properties of sol-gel derived (111) oriented Pb(Zr1−xTix)O3 thin films

Yoon J. Song, Yongfei Zhu, and Seshu B. Desu

Appl. Phys. Lett. 72, 2686 (1998); http://dx.doi.org/10.1063/1.121099 (3 pages) | Cited 44 times

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A novel processing method is developed for preparing sol-gel derived Pb(Zr1−xTix)O3 (x = 0.47) thin films on Pt/Ti/SiO2/Si substrates. Using a modified precursor solution and a rapid heat treatment without pyrolysis, it was possible to obtain highly (111) oriented PZT thin films with high perovskite content at a low annealing temperature of 550 °C. The low temperature processing was assisted by taking advantage of the heterogeneous nucleation of the PZT films, which reduces the activation energy for perovskite phase formation. Using this method, the PZT thin films exhibited better dielectric and ferroelectric properties at 550 °C than those reported by other methods. For example, the PZT films annealed at 550 °C showed a well-saturated hysteresis loop at an applied voltage of 5 V with Pr and Ec of 12 μC/cm2 and 38 kV/cm, and their dielectric constant and dissipation factor at a frequency of 100 kHz were 410 and 0.021, respectively. The leakage current density was lower than 10−8 at an applied electric field of 150 kV/cm. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
77.80.Dj Domain structure; hysteresis
77.22.Ch Permittivity (dielectric function)

Investigation of the interface formation between calcium and tris-(8-hydroxy quinoline) aluminum

V.-E. Choong, M. G. Mason, C. W. Tang, and Yongli Gao

Appl. Phys. Lett. 72, 2689 (1998); http://dx.doi.org/10.1063/1.121100 (3 pages) | Cited 103 times

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X-ray and ultraviolet photoemission spectroscopy investigations reveal strong interactions between Ca and tris-(8-hydroxy quinoline) aluminum (Alq3) during the Ca/Alq3 interface formation. The details of the interaction depend on the direction of the interface formation. For the case of Ca deposited on Alq3, a staged interface reaction is observed. For low Ca coverages (ΘCa ⩽ 4 Å), negatively charged Alq3 radical anions are formed by electron transfer from the Ca. The emergence of new states in the energy gap is observed in the UPS spectra. At higher coverages, the Ca reacts with the phenoxide oxygen resulting in the decomposition of the Alq3 molecule. On the other hand, for the case of Alq3 deposited on Ca, a strong chemical reaction takes place as soon as Alq3 is deposited, and Ca attacks every constituent of Alq3. Finally, no interaction occurs between Alq3 and the Ca substrate if the substrate has been passivated by oxygen prior to the Alq3 deposition. © 1998 American Institute of Physics.
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68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Nonlinearity and scaling behavior in donor-doped lead zirconate titanate piezoceramic

Volkmar Mueller and Q. M. Zhang

Appl. Phys. Lett. 72, 2692 (1998); http://dx.doi.org/10.1063/1.121101 (3 pages) | Cited 28 times

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Two different effective thresholds for the onset of nonlinearity in the dielectric and piezoelectric coefficients of donor-doped lead zirconate titanate (soft PZT) piezoceramics at electric ac fields Ec1 ≈ 100 V/cm and Ec2 ≈ 1 V/cm are found. Both are characterized by a scaling behavior x = x0+A[E−Ec)/Ec]ϕ above the respective threshold, where x is the dielectric or piezoelectric coefficient. The values of the effective exponent ϕ are apparently independent of the particular ceramic system which suggests a universal behavior in soft PZT. We suggest that the nonlinearity is dominated by the dynamics of domain walls in a randomly pinned medium. © 1998 American Institute of Physics.  
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ch Permittivity (dielectric function)

The kinetic glass transition of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass former-supercooled liquids on a long time scale

R. Busch and W. L. Johnson

Appl. Phys. Lett. 72, 2695 (1998); http://dx.doi.org/10.1063/1.121102 (3 pages) | Cited 72 times

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Viscosity and enthalpy relaxation from the amorphous state into the supercooled liquid state was investigated in the bulk metallic glass forming Zr46.75Ti8.25Cu7.5Ni10Be27.5 alloy below the calorimetric glass transition. At different temperatures, the viscosities relax into states that obey the same Vogel–Fulcher–Tammann relation as the data obtained at higher temperatures in the supercooled liquid. Enthalpy recovery experiments after relaxation in the same temperature range show that the enthalpy of the material reaches values that also corresponds to the supercooled liquid state. The glass relaxes into a metastable supercooled liquid state, if it is observed on a long time scale. Equilibration is possible far below the calorimetric glass transition and very likely even below the isentropic temperature. © 1998 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
65.20.-w Thermal properties of liquids
65.40.gd Entropy
66.20.-d Viscosity of liquids; diffusive momentum transport
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Manipulation and writing with Ag nanocrystals on Si(111)-7×7

S. Jay Chey, Lin Huang, and J. H. Weaver

Appl. Phys. Lett. 72, 2698 (1998); http://dx.doi.org/10.1063/1.121103 (3 pages) | Cited 6 times

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Manipulation of Ag nanocrystals derived from up to 200 000 atoms was performed using the tip of a scanning tunneling microscope. By varying the scanning conditions, it was possible to move them laterally on contamination-free Si(111)-7×7 surfaces or to remove them. In both cases, thin Ag tracks were left behind. This demonstrates the concepts of nano patterning and nano painting with metals on clean semiconductor surfaces. © 1998 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
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
81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
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On the feasibility of using ultraviolet/ozone grown oxide as an atomic interdiffusion barrier in Ge/GaAs heterojunctions

K. M. Lui, K. P. Chik, R. W. M. Kwok, W. H. Choy, and I. H. Wilson

Appl. Phys. Lett. 72, 2701 (1998); http://dx.doi.org/10.1063/1.121104 (3 pages)

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A 10 Å ultraviolet/ozone grown oxide was used as an atomic diffusion barrier in a Ge/GaAs heterostructure. Good thermal stability of the oxide layer has been demonstrated by the appearance of dendritic crystallization [K. M. Lui, K. P. Chik, and J. B. Xu, J. Appl. Phys. 81, 7757 (1997)], induced by in situ thermal pulse annealing, of the Ge overlayer. In this work, an abrupt heterointerface was revealed by aligned Rutherford backscattering spectroscopy after annealing and compared with a control with no barrier at the interface where considerable diffusion had taken place. Current–voltage measurement indicated good rectifying properties of the oxide barrier heterojunction. © 1998 American Institute of Physics.
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81.65.Mq Oxidation
68.35.Fx Diffusion; interface formation
81.05.Cy Elemental semiconductors
81.05.Ea III-V semiconductors
72.80.Cw Elemental semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.35.Ct Interface structure and roughness
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