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21 Aug 2000

Volume 77, Issue 8, pp. 1071-1232

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Doping of covalently bound fullerene monolayers: Ag clusters on C60/Si(111)

M. D. R. Taylor, P. Moriarty, B. N. Cotier, M. J. Butcher, P. H. Beton, and V. R. Dhanak

Appl. Phys. Lett. 77, 1144 (2000); http://dx.doi.org/10.1063/1.1289797 (3 pages) | Cited 6 times

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The deposition of silver on a C60 monolayer chemisorbed on Si(111) leads to the formation of nanoscale clusters which, as determined from valence band photoemission measurements, donate minimal charge to the adsorbed fullerene molecules. The low doping level of the C60 monolayer leads to a slow rate of Ag cluster neutralization following the emission of a photoelectron, resulting in a significant shift of the cluster Fermi level and valence band features to higher binding energy. © 2000 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.18.-g Langmuir-Blodgett films on liquids
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Ultrasonic investigation of Pd39Ni10Cu30P21 bulk metallic glass upon crystallization

Li Min Wang, W. H. Wang, R. J. Wang, Z. J. Zhan, D. Y. Dai, L. L. Sun, and W. K. Wang

Appl. Phys. Lett. 77, 1147 (2000); http://dx.doi.org/10.1063/1.1289801 (3 pages) | Cited 35 times

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Acoustic velocities of Pd39Ni10Cu30P21 bulk metallic glass (BMG) are measured by an ultrasonic technique upon annealing. The elastic constants and the Debye temperature are obtained. A large softening of the transverse phonon is exhibited in the as-quenched BMG relative to its crystallized state. Upon crystallization, the shear modulus and the Debye temperature increase by ∼ 30% and ∼ 12%, respectively; however, the density increases by only ∼ 0.6%. Some anomalous acoustic and elastic behaviors are observed near the glass transition temperature and in the supercooled liquid region of the BMG. The anomalies are explained with regard to the structural changes. © 2000 American Institute of Physics.
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61.43.Fs Glasses
62.65.+k Acoustical properties of solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
62.20.D- Elasticity
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
63.50.-x Vibrational states in disordered systems

Er3+ in strong light-confining microcavity

M. Lipson and L. C. Kimerling

Appl. Phys. Lett. 77, 1150 (2000); http://dx.doi.org/10.1063/1.1289800 (3 pages) | Cited 8 times

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Er3+ ions produce a sharp line emission that has small absorption cross section, long radiative lifetime, and is independent of external perturbations. These optical properties of the Er3+ ions limit the pumping efficiency and tunability of the emission line. In this work we present a study in which Er3+ emission was modified by coupling an ensemble of Er3+ ions to a microcavity resonance. The optical response of an optical cavity that consists of an Er2O3 layer confined between Si/SiO2 distributed Bragg reflectors is studied. When the cavity is in resonance with the optical transition of the Er3+ ions, the resonances in the reflectivity spectra split. The results are explained by a standard semiclassical model of atom–photon coupling. © 2000 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Formation of ultrafine nanostructure by crystallization of Zr52Al6Cu14Ni8Fe20 metallic glass

N. Mattern, U. Kühn, J. Neuefeind, and J. Eckert

Appl. Phys. Lett. 77, 1153 (2000); http://dx.doi.org/10.1063/1.1289802 (2 pages) | Cited 6 times

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The short-range order and the crystallization behavior of amorphous Zr52Al6Cu14Ni8Fe20 alloys have been investigated by means of calorimetry and x-ray diffraction. The amorphous structure transforms upon annealing without formation of long-range order. An ultrafine microstructure consisting of about 60 vol % cubic NiZr2 crystal-like clusters with a size of 〈D〉 ≈ 2 nm embedded in a residual amorphous matrix phase forms as a first step of crystallization resulting from high nucleation rate combined with low growth velocity. In a second step growth of the clusters to crystals up to a mean diameter of 〈D〉 ≈ 4–5 nm takes place as a distinct process. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments

Grain-size-dependent thermal conductivity of nanocrystalline yttria-stabilized zirconia films grown by metal-organic chemical vapor deposition

G. Soyez, J. A. Eastman, L. J. Thompson, G.-R. Bai, P. M. Baldo, A. W. McCormick, R. J. DiMelfi, A. A. Elmustafa, M. F. Tambwe, and D. S. Stone

Appl. Phys. Lett. 77, 1155 (2000); http://dx.doi.org/10.1063/1.1289803 (3 pages) | Cited 58 times

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A grain-size-dependent reduction in the room-temperature thermal conductivity of nanocrystalline yttria-stabilized zirconia is reported for the first time. Films were grown by metal-organic chemical vapor deposition with controlled grain sizes from 10 to 100 nm. For grain sizes smaller than approximately 30 nm, a substantial reduction in thermal conductivity was observed, reaching a value of less than one-third the bulk value at the smallest grain sizes measured. The observed behavior is consistent with expectations based on an estimation of the phonon mean-free path in zirconia.© 2000 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Crystallization kinetics of the bulk-glass-forming Pd43Ni10Cu27P20 melt

Jan Schroers, William L. Johnson, and Ralf Busch

Appl. Phys. Lett. 77, 1158 (2000); http://dx.doi.org/10.1063/1.1289033 (3 pages) | Cited 41 times

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The crystallization of undercooled Pd43Ni10Cu27P20 melts is studied under isothermal conditions and at constant heating and cooling rates. Investigations are carried out by fluxing the melt with B2O3 and without any fluxing material. The isothermal experiments allow us to determine the complete time–temperature-transformation diagram with a minimum crystallization time of about 200 s for the fluxed melt and about 130 s for the unfluxed Pd43Ni10Cu27P20 melt. The results of the experiments at constant cooling and heating rates are summarized in a continuous heating and cooling diagram. The critical cooling rate for the fluxed alloy is determined to be 0.09 K/s, whereas the critical heating rate is 6 K/s. For the unfluxed Pd43Ni10 Cu27P20, 0.4 and 9 K/s are found, respectively. This alloy exhibits the most sluggish crystallization kinetics of all metallic systems known so far. © 2000 American Institute of Physics.
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61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)

Thermal wet oxidation of GaP and Al0.4Ga0.6P

J. H. Epple, K. L. Chang, G. W. Pickrell, K. Y. Cheng, and K. C. Hsieh

Appl. Phys. Lett. 77, 1161 (2000); http://dx.doi.org/10.1063/1.1286871 (3 pages)

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Thermal wet oxidations of GaP and Al0.4Ga0.6P at 650 °C for various times have been performed. Comparisons are made on oxidation rates and post oxidation morphology. Transmission electron microscopy shows that when oxidizing GaP, polycrystalline monoclinic GaPO4⋅2H2O forms without noticeable loss of phosphorus. Oxidation for 6 h or more leads to poor morphology resulting in cracks and detachment. A thickness expansion of about 2.5–3 times is noticed as a result of oxidation. In contrast, oxidized Al0.4Ga0.6P exhibits much better morphology without cracks or detachment from the substrate. The oxide has an almost amorphous-like microstructure. The oxidation process shows typical diffusion-limited reaction at long anneals. Preliminary work on the oxidation of AlP indicates that the reaction leads to formation of Al2O3 and possible volatile P2O5 diffusing out of the specimen. Thus, from the structural viewpoint, AlGaP forms a better oxide suitable for device needs. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Ea III-V semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.20.Pm Rate constants, reaction cross sections, and activation energies
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Gh Other heat and thermomechanical treatments
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Acceptor reactivation kinetics in heavily carbon-doped GaAs epitaxial layers

J. Mimila-Arroyo and S. W. Bland

Appl. Phys. Lett. 77, 1164 (2000); http://dx.doi.org/10.1063/1.1289268 (3 pages) | Cited 8 times

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The reactivation kinetics of the acceptor behavior of carbon in GaAs layers has been studied. The reactivation was achieved by ex situ rapid thermal annealing. To follow the carbon reactivation process, a multistage annealing experiment was performed, with changes in the sample carrier concentration monitored at each stage. An analysis of these data indicates that carbon reactivation follows a first-order kinetics process that can be explained by a model which includes the effects of dopant repassivation by hydrogen retrapping during hydrogen out-diffusion, and a dependence of the attempt frequency with the carbon concentration. The reactivation occurs with an activation energy of 1.41 eV. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.05.Ea III-V semiconductors

Observation of resonant tunneling through a quantized state in InP quantum dots in a double-barrier heterostructure

C. V. Reddy, V. Narayanamurti, J. H. Ryou, U. Chowdhury, and R. D. Dupuis

Appl. Phys. Lett. 77, 1167 (2000); http://dx.doi.org/10.1063/1.1289264 (3 pages) | Cited 8 times

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A direct spectroscopic signature associated with the quantized state of the charge carriers in three-dimensionally confined InP quantum dots (QDs) is reported using a ballistic electron emission microscopy (BEEM)/spectroscopy technique. The self-assembled InP QDs are sandwiched in an AlInP double-barrier heterostructure. The excellent nanometer-scale lateral resolution of the BEEM technique is used to investigate the current transport mechanism by the direct injection of electrons into a single quantum dot. The BEEM spectra taken on and off the dot revealed the presence of a localized state at around 0.1±0.02 eV above the ground state. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
73.23.Hk Coulomb blockade; single-electron tunneling

Barrier-width dependence of quantum efficiencies of GaN/AlxGa1−xN multiple quantum wells

Eun-joo Shin, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 77, 1170 (2000); http://dx.doi.org/10.1063/1.1289262 (3 pages) | Cited 11 times

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We present the results of picosecond time-resolved photoluminescence (PL) measurements for a set of 30 Å well GaN/AlxGa1−xN (x ∼ 0.2) multiple-quantum-well (MQW) structures with varying barrier widths LB from 30 to 100 Å, grown by metalorganic chemical-vapor deposition. The PL quantum efficiency and the recombination lifetime of these MQWs were observed to increase monotonously with an increase of the barrier width up to 80 Å. These behaviors were explained by considering two distinct mechanisms that control the radiative recombination efficiencies in MQWs. When the barrier width is below the critical thickness, the nonradiative recombination rate increases with a decrease of the barrier width due to enhanced probabilities of the electron and hole wave functions at the interfaces as well as in the AlGaN barriers. On the other hand, the misfit dislocation density increases as the barrier width approaches the critical thickness, which can result in an enhanced nonradiative interface recombination rate. Our studies here have shown that the optimal GaN/AlGaN (x ∼ 0.2) MQW structures for UV light-emitter applications are those with barrier widths ranging from 40 to 80 Å. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.47.-p Spectroscopy of solid state dynamics

Electrical measurements on p+–p−–p+ homoepitaxial diamond capacitors

Takashi Inushima, Takahiro Matsushita, Rinat F. Mamin, Seishirou Ohya, and Hiromu Shiomi

Appl. Phys. Lett. 77, 1173 (2000); http://dx.doi.org/10.1063/1.1289270 (3 pages) | Cited 3 times

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Conductance versus voltage and capacitance versus voltage (C–V) characteristics are investigated for p+–p−–p+ capacitors over a temperature range of 40–300 K, where the p+ layer is heavily doped homoepitaxial diamond and has impurity-band conduction and the p− layer is slightly doped with valence-band conduction. Above 200 K, the capacitors behave like a semiconductor–insulator–semiconductor diode with interface barrier height of about 0.07 eV. The C–V curve agrees closely with the standard theory of semiconductor–insulator–semiconductor structure and shows formation of the deletion layer at the p+ layer on the interface. The Cole–Cole plot of conductance versus susceptance reveals that there is a virtual trap level in the p− layer which is located about 0.06 eV above the valence band. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
84.32.Tt Capacitors

Growth temperature dependence of transport properties of InAs epilayers grown on GaP

Victor Souw, V. Gopal, E.-H. Chen, E. P. Kvam, M. McElfresh, and J. M. Woodall

Appl. Phys. Lett. 77, 1176 (2000); http://dx.doi.org/10.1063/1.1289269 (3 pages) | Cited 2 times

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Undoped InAs was grown by molecular-beam epitaxy directly on GaP at a set of different substrate temperatures. Transport properties were characterized by means of Hall-effect and resistivity measurements at temperatures between 3 and 300 K. It was observed that samples grown at higher temperatures had lower carrier concentrations, consistent with a decrease of ionized defects. In addition, samples grown at higher temperatures also had higher mobility, consistent with a smaller number of scattering centers. Samples grown at higher temperatures also showed much higher sensitivity of the mobility to the measurement temperature, suggesting a drop in neutral scattering defects. Transmission electron microscopy showed that the samples grown at higher temperatures had a significantly different dislocation microstructure. The observed dislocation microstructure is consistent with the mechanisms proposed for the influence of growth temperature on the variation of carrier concentration and mobility. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
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
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Single-electron tunneling study of two-dimensional gold clusters

Bing Wang, Xudong Xiao, Xianxiang Huang, Ping Sheng, and J. G. Hou

Appl. Phys. Lett. 77, 1179 (2000); http://dx.doi.org/10.1063/1.1289500 (3 pages) | Cited 25 times

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By using scanning tunneling microscopy/spectroscopy, we have studied the current–voltage characteristics of two-dimensional (2D) Au clusters, thermally deposited on self-assembled alkanethiol monolayer. The curves display Coulomb blockade and staircase with asymmetric behavior. The measured zero conductance gap as a function of cluster size is in excellent agreement with classical model calculations, in which the 2D Au island is treated as metallic in the planar direction but nonmetallic in the normal direction. © 2000 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.22.-f Electronic structure of nanoscale materials and related systems
73.61.At Metal and metallic alloys

Quantum confinement in germanium nanocrystals

Y. M. Niquet, G. Allan, C. Delerue, and M. Lannoo

Appl. Phys. Lett. 77, 1182 (2000); http://dx.doi.org/10.1063/1.1289659 (3 pages) | Cited 122 times

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The electronic structure of Ge nanocrystals is studied using a sp3 tight binding description. Analytical laws for the confinement energies, valid over the whole range of sizes, are derived. We validate our results with ab initio calculations in the local density approximation for smaller clusters. Comparing to experimental data, we conclude that, similar to the case of silicon: (a) the blue-green photoluminescence (PL) of Ge nanocrystals comes from defects in the oxide and (b) the size dependent PL in the near infrared probably involves a deep trap in the gap of the nanocrystals. We predict that the radiative lifetimes remain long in spite of the small difference (0.14 eV) between direct and indirect gaps of bulk Ge. © 2000 American Institute of Physics.
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71.55.Cn Elemental semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Hot hole relaxation dynamics in p-GaN

Hong Ye, G. W. Wicks, and P. M. Fauchet

Appl. Phys. Lett. 77, 1185 (2000); http://dx.doi.org/10.1063/1.1289651 (3 pages) | Cited 13 times

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The hot hole relaxation dynamics is studied in a Mg-doped p-type GaN film grown by molecular-beam epitaxy on sapphire. A nondegenerate femtosecond pump-probe technique is used, in which the holes are excited by an infrared pump and the hole dynamics is monitored by a tunable near ultraviolet probe. Complex transients, showing bleaching or induced absorption, are observed. A hot hole energy relaxation time of 0.6 ps has been obtained. Modeling suggests that longitudinal optical phonon emission modified by hot phonon effects is the dominant energy relaxation process. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
63.20.-e Phonons in crystal lattices
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

The effect of back channel hydrogen plasma treatment on the electrical characteristics of amorphous thin film transistors

S. G. Kang, S. C. Bae, and S. Y. Choi

Appl. Phys. Lett. 77, 1188 (2000); http://dx.doi.org/10.1063/1.1289657 (3 pages) | Cited 1 time

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This letter reports that hydrogen plasma treatments on the back channel of thin film transistors are an effective way to improve the off-current characteristics. The effects of the hydrogen plasma treatments on the amorphous Si were checked using current–voltage plotter, atomic force microscopy, and secondary ion mass spectrometry. The surface of the amorphous Si was etched and passivated by the hydrogen radicals at various radio-frequency (rf) powers. The resistance of the modulated back channel increased and the off-current characteristic was improved from 530 to 1.68 pA, which was caused by the increase of roughness and hydrogen contents at back channel as a function of rf power. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
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)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Cy Elemental semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
81.65.Cf Surface cleaning, etching, patterning
81.65.Rv Passivation
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Enhanced blocking temperature in NiO spin valves: Role of cubic spinel ferrite layer between pinned layer and NiO

R. F. C. Farrow, M. J. Carey, R. F. Marks, P. M. Rice, and David J. Smith

Appl. Phys. Lett. 77, 1191 (2000); http://dx.doi.org/10.1063/1.1289660 (3 pages) | Cited 4 times

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We compare the blocking temperature for simple permalloy (80% Ni)/Au/permalloy/NiO spin valves with and without an interfacial, oxidized Fe layer (Fe layer 12 Å thick) inserted at the permalloy/NiO interface. We find a significantly increased blocking temperature and pinning field for spin valves with the interfacial Fe-oxide layer, as a result of moderate (230 °C/1 h) annealing of the Au/permalloy/Fe-oxide/NiO part of the spin valve. High resolution transmission electron microscopy and electron energy loss microanalysis reveal that the Fe-oxide layer is converted to a cubic spinel ferrite (Ni0.8Fe2.2O4) layer by solid state reaction with the NiO. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Gg Ferrimagnetics

Magnetic properties of CoII mesoclusters

Michi Sato, Syozo Takada, Shigemi Kohiki, Tomohiro Babasaki, Hiroyuki Deguchi, Masaoki Oku, and Masanori Mitome

Appl. Phys. Lett. 77, 1194 (2000); http://dx.doi.org/10.1063/1.1289654 (3 pages) | Cited 4 times

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Clusters of cobalt (II) ions dispersed in a mesoporous silicate, prepared by calcination of the MCM-41 molecular sieve soaked in CoCl2 0.01 mol/l aqueous solution, showed no x-ray diffraction peaks except one from the molecular sieve. X-ray photoelectron spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy revealed that the mesoclusters consisted of CoII ions in tetrahedral coordination. We have observed temperature and frequency dependences of the alternating current susceptibility, and no divergent peaks of the nonlinear susceptibility due to superparamagnetism. Spins derived from the field dependent magnetization above the blocking temperature with the Langevin equation fairly agree with those at the cluster surface estimated from the ionic radii of Co2+ and O2−. © 2000 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Procedure for preparing epitaxial Tl-2201 films on single crystal LaAlO3

H. Q. Chen, L.-G. Johansson, and Z. G. Ivanov

Appl. Phys. Lett. 77, 1197 (2000); http://dx.doi.org/10.1063/1.1289065 (3 pages) | Cited 3 times

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Epitaxial Tl-2201 films are prepared by treating precursor films deposited on single crystal LaAlO3 by laser ablation with Tl2O vapor at high temperature. Here, a procedure is described that includes thallization in two separate steps. The first thallization at 720 °C resulted in good epitaxy as well as in smooth morphology. The second thallization at 820 °C resulted in an improvement of the superconducting properties and in film crystallinity without affecting epitaxy or morphology. The films were characterized by x-ray diffraction (ϕ scan, Ω scan, θ–θ scan), and by resistance and susceptibility measurements. The films are tetragonal. In a typical film, the full width at half maximum of the Ω scan of the (0,0,10) reflection was 0.27°. A 5 μm wide bridge patterned in one film had a Tc of 84 K. The critical current density reached 1.4×106 A/cm2 at 77 K and 1.4×107 A/cm2 at 4.2 K. © 2000 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.10.+v Occurrence, potential candidates
74.25.Sv Critical currents
87.64.Bx Electron, neutron and x-ray diffraction and scattering
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties
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Microstructure and dielectric properties of Ba1−xSrxTiO3 films grown on LaAlO3 substrates

Y. Gim, T. Hudson, Y. Fan, C. Kwon, A. T. Findikoglu, B. J. Gibbons, B. H. Park, and Q. X. Jia

Appl. Phys. Lett. 77, 1200 (2000); http://dx.doi.org/10.1063/1.1289272 (3 pages) | Cited 79 times

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We report a systematic study of the microstructure and dielectric properties of barium strontium titanate, Ba1−xSrxTiO3, films grown by laser ablation on LaAlO3 substrates, where x = 0.1–0.9 at an interval of 0.1. X-ray diffraction analysis shows that when x<0.4, the longest unit-cell axis is parallel to the plane of the substrate but perpendicular as x approaches 1. Dielectric constant versus temperature measurements show that the relative dielectric constant has a maximum value and that the peak temperatures corresponding to the maximum relative dielectric constant are about 70 °C higher when x ⩽ 0.4 but similar when x>0.4, compared with the peak temperatures of the bulk Ba1−xSrxTiO3. At room temperature, the dielectric constant and tunability are relatively high when x ⩽ 0.4 but start to decrease rapidly as x increases. © 2000 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
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)

Dielectric and ferroelectric properties of compositionally graded (Pb,La)TiO3 thin films on Pt/Ti/SiO2/Si substrates

Dinghua Bao, Nobuyasu Mizutani, Xi Yao, and Liangying Zhang

Appl. Phys. Lett. 77, 1203 (2000); http://dx.doi.org/10.1063/1.1289260 (3 pages) | Cited 28 times

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Compositionally graded (Pb,La)TiO3 thin films were prepared on platinum-coated silicon substrates by a sol–gel technique. The crystalline orientation and surface morphology of the graded films were closely related to the deposition sequence of the film layer. The dielectric constants, for up-graded and down-graded films annealed at 600 °C for 60 min, were found to be 765 and 374, respectively. The compositionally graded films had large polarization offsets in hysteresis loops when driven by an alternating electric field. The magnitude of polarization offsets displayed a power-law dependence on the electric field, and the direction of the offsets depended on the direction of the composition gradient with respect to the substrate. The offset, 250 μC/cm2 at the driving electric field of 250 kV/cm, was obtained. These results showed that the sol–gel technique was a very promising route for the realization of compositionally graded ferroelectric thin films and the compositionally-graded (Pb,La)TiO3 thin films had excellent dielectric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. © 2000 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis

Electrical domain fixing of photorefractive index gratings in (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystals

Xiaonong Shen, Jianhua Zhao, Ruibo Wang, Zhenxiang Cheng, Shujun Zhang, and Huanchu Chen

Appl. Phys. Lett. 77, 1206 (2000); http://dx.doi.org/10.1063/1.1289492 (3 pages) | Cited 4 times

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Electrical domain fixing in Cu- and Mn-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 (KNSBN) crystals is presented. The relation between the applied field and the revealed grating in single and multidomain crystals is investigated. In multidomain Mn-doped KNSBN, a revealing efficiency of over 233% is obtained. The mechanism of domain fixing in single and multidomain crystal is discussed. © 2000 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
42.79.Dj Gratings
42.40.Eq Holographic optical elements; holographic gratings
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ln Holographic recording materials; optical storage media
42.70.Gi Light-sensitive materials
42.40.Ht Hologram recording and readout methods

Microstructure of (Ba, Sr)TiO3 thin films deposited by physical vapor deposition at 480 °C and its influence on the dielectric properties

Matthew C. Werner, Indrajit Banerjee, Paul C. McIntyre, Noriaki Tani, and Michio Tanimura

Appl. Phys. Lett. 77, 1209 (2000); http://dx.doi.org/10.1063/1.1288155 (3 pages) | Cited 22 times

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The orientation and microstructure of (Ba, Sr)TiO3 (BST) deposited via physical vapor deposition at 480 °C was studied using x-ray diffraction, atomic force microscopy, and transmission electron microscopy. Annealing Pt/BST (previously annealed at 400 °C) at 800 °C in O2 results in grain growth, enhancement of the {100} texture and a 20% increase in the dielectric constant. The 400 °C annealed films become more textured in the {100} orientation as film thickness is increased. Finally, it appears that an interfacial capacitance, rather than the “bulk” dielectric constant limits the total capacitance density of the films. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
61.72.Cc Kinetics of defect formation and annealing
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Influence of oxygen on band alignment at the organic/aluminum interface

R. I. R. Blyth, S. A. Sardar, F. P. Netzer, and M. G. Ramsey

Appl. Phys. Lett. 77, 1212 (2000); http://dx.doi.org/10.1063/1.1289497 (3 pages) | Cited 17 times

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The presence of adventitious oxygen is inevitable when organic/metal interfaces are formed by evaporation in high vacuum (10−6 mbar.). In this letter, we highlight the importance of this oxygen for band alignment, and hence, performance, in organic-based devices. The influence of controlled amounts of oxygen on band alignment in benzene/aluminum model cathode interfaces has been studied using ultraviolet photoemission in ultrahigh vacuum. We show that even small amounts of oxygen significantly lower the aluminum work function with concomitant improvement in band alignment. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Ns Metal-nonmetal contacts

Improvement of charge trapping by hydrogen post-oxidation annealing in gate oxide of 4H–SiC metal–oxide–semiconductor capacitors

Won-ju Cho, Ryoji Kosugi, Kenji Fukuda, Kazuo Arai, and Seiji Suzuki

Appl. Phys. Lett. 77, 1215 (2000); http://dx.doi.org/10.1063/1.1289806 (3 pages) | Cited 7 times

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The effect of hydrogen postoxidation annealing (POA) on the reliability of gate oxide formed in 4H–SiC metal–oxide–semiconductor (MOS) capacitors has been investigated. Argon POA at 1200 °C and hydrogen POA were carried out over a temperature range of 400–1000 °C to improve the properties of 4H–SiC/SiO2 interface and thermal gate oxide. Interface state density Dit decreases as the temperature of hydrogen POA increases and saturates at 800 °C. Additionally, the characteristics of charge trapping in gate oxide against the electron injection was greatly improved by the hydrogen POA above 800 °C. Hence, we can conclude that the hydrogen POA at high temperature is effective for improving the Dit and reliability of gate oxide formed in 4H–SiC MOS devices. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states
81.40.Gh Other heat and thermomechanical treatments
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