bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-electron transistor as an electrometer measuring chemical potential variations
Authors: Wei Y. Y. , Weis J. , v. Klitzing K. , Eberl K.
Published: July 2002

The magnetic field dependence of the chemical potential of an electron system can be measured using a metallic single-electron transistor (SET). To demonstrate the method, a SET made of aluminum was fabricated on top of a GaAs/AlGaAs heterostructure containing a two-dimensional electron system (2DES). A change in the chemical potential of the 2DES causes a change in the contact voltage between the SET leads and the 2DES below the SET island which affects the current flow through the SET island. Tuning a voltage which is externally applied in series to the contact voltage, the change in the intrinsic contact voltage can be compensated to keep the SET current constant. With this tuning voltage, the change of the chemical potential by the magnetic field is directly measured. The method described here is applicable to other materials and other parameters affecting the intrinsic contact voltages.
Ultrathin SiOxNy by rapid thermal heating of silicon in N2 at T=760–1050 °C
Authors: Green M. L. , Sorsch T. , Feldman L. C. , Lennard W. N. , Gusev E. P. , Garfunkel E. , Lu H. C. , Gustafsson T.
Published: July 2002

In this letter, we report on the reaction between Si and N2 in the temperature range of 760–1050 °C, in a rapid thermal processing chamber. Gas phase impurities such as H2O, O2, and H2, which can outgas from the cold walls of the chamber, mediate the Si/N2 reaction, resulting in the formation of SiOxNy. The oxynitridation can be explained by equilibrium chemical thermodynamics, in contrast to the case of oxynitridation using N2O or NO, where the nitrogen is incorporated under nonequilibrium conditions. Using nuclear reaction analysis, we have measured nitrogen contents as high as 2.5×1015 N/cm2 (the equivalent of more than 3 monolayers) in these new dielectrics. They can be reoxidized to form ultrathin (2 to 3 nm) dielectrics.
Stress-engineered spatially selective self-assembly of strained InAs quantum dots on nonplanar patterned GaAs(001) substrates
Authors: Konkar A. , Madhukar A. , Chen P.
Published: July 2002

The lattice-mismatch stress-induced two-dimensional-to-three-dimensional morphology change is combined with interfacet adatom migration to selectively assemble parallel chains of InAs islands on top of [11̄0] oriented stripe mesas of sub-100-nm widths on GaAs(001) substrates. On such mesa stripes, prepared in situ via size-reducing epitaxy, deposition of InAs amounts subcritical for island formation on planar GaAs (001) is shown to allow self-assembly of three, two, and single chains of InAs three-dimensional island quantum dots selectively on the stripe mesa tops for widths decreasing from 100 nm down to 30 nm.
Variation of the relative permittivity of charged dielectrics
Authors: Ong C. K. , Song Z. G. , Oh K. H. , Gong H. , Le Gressus C.
Published: July 2002

The variation of the relative permittivity of charged dielectrics with trapped charge density has been investigated by a time-resolved current method, in conjunction with a mirror image method employing a scanning electron microscope. The calculation is made by a mathematical expression derived from classical electromagnetic theory. It is found that the relative permittivity of the charged area in the polymethylmethacrylate sample increases with the trapped charge density and saturates at a certain value of the trapped charge density. These observations have been discussed by analogy with the dielectric saturation occurring at a high applied external electric field.
Gain of the mode locked p-Ge laser in the low field region
Authors: Hovenier J. N. , Klaassen T. O. , Wenckebach W. Th. , Muravjov A. V. , Pavlov S. G. , Shastin V. N.
Published: July 2002

Following the earlier observation of active mode locking in the high field region of the Voigt configured p-Ge intervalence band laser, presently mode locking in the low field region is also reported. The experimental results on the effective small signal gain for active- as well as for self-mode locked operation are given.
Growing a periodic microstructure on the superconductor crystal surface by electrocrystallization
Authors: Zheng X. G. , Taira M. , Suzuki M. , Xu C. N.
Published: July 2002

A novel microstructure is formed on the single crystal surfaces of the oxide superconductor Ba0.6K0.4BiO3 (BKBO). Micron-sized barium islands periodically grew on the mother crystal during electrocrystallization of BKBO. Experimental analysis suggested the relation of this unusual microstructure to the Liesegang rings well-known for a crystal growth in gels. The present discovery provides a potential technology for fabricating microstructures on substrates of solids.
Deep level traps in the extended tail region of boron-implanted n-type 6H–SiC
Authors: Gong M. , Reddy C. V. , Beling C. D. , Fung S. , Brauer G. , Wirth H. , Skorupa W.
Published: July 2002

Deep traps in the boron extended tail region of ion implanted 6H–SiC pn junctions formed during annealing have been studied using deep level transient spectroscopy. Dramatically high concentrations of ∼1016 cm−3 of the D center have been observed through the unusual appearance of minority peaks in the majority carrier spectra. No evidence is found for any shallow boron acceptor in this region, but an induced hole trap Ih at EV+0.46 eV is found under cold implantation conditions. These results support the picture of the extended tail, rich in boron-vacancy complexes such as the D center, which forms as a result of vacancy enhanced indiffusion. The dominance of the electrically active D center in the depletion layer of the technologically important SiC pn junction diode suggests the need for further research in this area.
The effect of Al3Ti capping layers on electromigration in single-crystal aluminum interconnects
Authors: Srikar V. T. , Thompson C. V.
Published: July 2002

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.
The incorporation of arsenic in GaN by metalorganic chemical vapor deposition
Authors: Li X. , Kim S. , Reuter E. E. , Bishop S. G. , Coleman J. J.
Published: July 2002

We report on the successful incorporation of arsenic (As) in GaN during metalorganic chemical vapor deposition (MOCVD). A characteristic room-temperature luminescence band centered around 2.6 eV (480 nm), similar to the peak position of the As ion-implanted GaN, is found to be related to the As impurity in the MOCVD grown GaN:As films. The arsenic incorporation efficiency as a function of experimental conditions and structure is presented. Temperature- and power-dependent cathodoluminescence measurements have been performed to help establish the nature of the As-related peak.
Effect of film density on boron diffusion in SiO2
Authors: Navi Mitra , Dunham Scott T.
Published: July 2002

Oxides grown at low temperatures exhibit higher density than those grown or annealed at high temperatures. This work investigates the role of oxide density on boron diffusion through thin gate dielectrics. Capacitor structures were fabricated by depositing polycrystalline silicon on top of 54–60 Å oxide films grown at 800 °C in dry O2. A subset of these high density oxides were then annealed at 1100 °C to relax the grown-in stress. Following ion implantation of boron into the polysilicon, the capacitor structures were annealed in an inert ambient at 950 °C to allow boron penetration. Capacitance–voltage measurements revealed that boron penetration was greatly enhanced for the films that saw the high temperature relaxation anneal, leading to the conclusion that boron diffusion in SiO2 is retarded in the presence of excess density.
Long-range ferroelectric interactions in KTaO3/KNbO3 superlattice structures
Authors: Christen H.-M. , Specht E. D. , Norton D. P. , Chisholm M. F. , Boatner L. A.
Published: July 2002

Symmetric superlattice structures consisting of alternating atomic-scale layers of KTaO3 and KNbO3 with variable periodicity were grown on KTaO3 substrates by pulsed laser deposition. The in-plane structure of KNbO3 closely matches that of the KTaO3 substrate, resulting in KTaO3/KNbO3 heterostructures that are uniformly strained in-plane without misfit dislocations. This strain imposes an in-plane KNbO3 lattice spacing identical to that of the KTaO3 substrate for the temperature range 30 °C<T<700 °C, and a tetragonal-to-tetragonal transition is observed whose phase transition temperature Tc depends on the KNbO3 layer thickness. The in-plane strain results in a significant increase in this ferroelectric-paraelectric Tc for superlattices with relatively thick KNbO3 layers (Tc=535 °C for a 17 nm thick layer, as compared to 435 °C for bulk KNbO3) and for K(Nb0.5Ta0.5)O3 random-alloy thin films. As the superlattice period decreases, a reduction of Tc is observed. For superlattices with periodicities of 50 Å or less, the Curie temperature is identical to that of the K(Ta0.5Nb0.5)O3 random-alloy film, indicating significant long-range ferroelectric coupling across the KTaO3 layers.
Perpendicular magnetization and dipolar antiferromagnetism in double layer nanostripe arrays of Fe(110) on W(110)
Authors: Hauschild J. , Gradmann U. , Elmers H. J.
Published: July 2002

Fe(110) nanostripe arrays, consisting of alternating monolayer and double layer stripes, have been grown by step flow on vicinal W(110) substrates. The magnetic easy axis switches from in-plane in the monolayer to perpendicular in the double layer stripes. The data strongly suggest that magnetostatic interactions induce antiferromagnetic order in the double layer nanostripe array. It can be switched into a ferromagnetic arrangement by low external fields.
Polarization switching in a tensile-strained InGaAs/InGaAsP multiple quantum well distributed feedback laser diode
Authors: Mizutani Natsuhiko , Miyazawa Sei-ichi , Nakanishi Masahiro , Majima Masao , Nitta Jun , Sekiguchi Yoshinobu , Nojiri Hidetoshi , Handa Yuichi
Published: July 2002

An inhomogeneously biased distributed feedback (DFB) laser diode (LD) with two electrodes switched its polarization mode by 3 mA change of the bias current, maintaining single longitudinal mode oscillation. In the active layer of the LD, 13 nm thick and 0.6% tensile-strained InGaAs multiple quantum well (MQW) equalized the transverse electric and the transverse magnetic modal optical gain at 1.55 μm. With various grating pitches on the same MQW active layer, polarization switching DFB LDs were realized in the wavelength range as wide as 18 nm. The linewidth characteristics during the polarization switching were confirmed to be narrow due to the small switching current.
Corona discharge: A doping method for polyaniline
Authors: Job Aldo E. , Giacometti José A. , Mattoso Luiz H. C.
Published: July 2002

Corona discharge has been successfully employed to dope thin films of polyaniline coated on poly (ethylene terephthalate) films. Similarly to the conventional doping with aqueous HCl, the process is accompanied by a color change from blue to green and the conductivity can be tuned in the range from 10−10 up to 0.3 S cm−1. This doping method presents several advantages over the conventional one, namely, dry process, use of no chemicals, rapidity and no dopant migration.
Electronic properties of defects introduced in p-type Si1−xGex during ion etching
Authors: Goodman S. A. , Auret F. D. , Mamor M. , Greiner A.
Published: July 2002

We have investigated the electronic properties of defects introduced in boron-doped, strained p-type Si1−xGex (x=0–0.15) during 0.75-keV argon Ar-ion etching, by deep level transient spectroscopy. These defects are compared to those introduced during e-beam deposition of metal contacts and after 5.4-MeV alpha-particle irradiation. Defect HAr1d, detected in p-Si, has similar electronic properties as He2 and Ha15 detected after electron and alpha-particle irradiation, respectively. The variation in activation energy of HAr1d with Ge fraction was studied, and it was found to follow the same change as the band gap of strained Si1−xGex. This defect has a concentration, which decreases sharply from the metal–semiconductor surface. It also has an activation energy, which depends on the Ge content and is pinned to the conduction band.
Direct evidence of impact excitation and spatial profiling of excited Er in light emitting Si diodes
Authors: Coffa Salvatore , Franzò Giorgia , Priolo Francesco , Pacelli Andrea , Lacaita Andrea
Published: July 2002

We provide direct evidence that Er ions incorporated in the depletion layer of a p+–n+ Si junction are efficiently pumped through an impact excitation process with hot carriers. The carriers were accelerated by the electric field present in the depletion layer after being produced by either Zener breakdown of the junction at ∼5 V or by irradiating the diode with an argon laser. Measurements of the electroluminescence yield at 1.54 μm as a function of the reverse bias voltage (and for a constant current through the device) reveal that excitation of Er only occurs at voltages above 1 V, demonstrating that impact is the pumping mechanism. Moreover, we have found that Er ions are only excited within ∼15 nm from the edges of the depletion layer leaving a dark, ∼50 nm thick, region in the central part of the depletion region. Monte Carlo calculations confirmed that only close to the depletion layer edges the energy gained by the carriers in the electric field is high enough to impact excite Er.
Energy level schemes for far-infrared quantum well lasers
Authors: Lyubomirsky I. , Hu Q.
Published: July 2002

We analyze the physics of three-level and four-level systems for optically pumped far-infrared quantum well lasers. The higher complexity of the four-level system offers a great advantage because it gives more flexibility to design the dipole matrix elements and phonon scattering rates to enhance both the gain and emission efficiency. We propose a four-level scheme that is superior in gain and emission efficiency by an order of magnitude over previous designs.
Air-gap amorphous silicon thin film transistors
Authors: Boucinha M. , Chu V. , Conde J. P.
Published: July 2002

Top gate and bottom gate amorphous silicon thin film transistors where the dielectric has been replaced by an air gap have been fabricated on glass substrates using surface micromachining techniques. Bridges were formed by using low density silicon nitride as a sacrificial layer. In bottom gate structures the bridge material was amorphous silicon and in top gate structures it was highly doped n+ microcrystalline silicon. The first working devices show transistor behavior with field effect mobilities between 0.1 and 0.5 cm2 V−1 s−1.
Single-pulse ultraviolet laser-induced surface modification and ablation of polyimide
Authors: Piglmayer K. , Arenholz E. , Ortwein C. , Arnold N. , Bäuerle D.
Published: July 2002

Single-pulse laser ablation of polyimide was investigated by using focused UV-Ar+-laser radiation (λ≈302 nm, 140 ns⩽τl⩽50 ms) and atomic force microscopy. The results clearly demonstrate that the ablation rates do not depend on the total dose only, but depend as well on the duration of the laser pulses, τl. The experimental results can be interpreted almost quantitatively on the basis of a purely thermal model.
Interlayer exchange in (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As semiconducting ferromagnet/nonmagnet/ferromagnet trilayer structures
Authors: Akiba N. , Matsukura F. , Shen A. , Ohno Y. , Ohno H. , Oiwa A. , Katsumoto S. , Iye Y.
Published: July 2002

Magnetic properties of all-semiconductor (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As trilayer structures are studied. The interactions between the two ferromagnetic (Ga,Mn)As layers are investigated by magnetotransport measurements in a number of samples with different GaAs thickness or with different Al content in the intermediary nonmagnetic (Al,Ga)As layer. The results indicate that carriers present in the nonmagnetic layer mediate the coupling between the two ferromagnetic layers.
Strain-induced large low-field magnetoresistance in Pr0.67Sr0.33MnO3 ultrathin films
Authors: Wang H. S. , Li Qi
Published: July 2002

We report magnetoresistance (MR) measurements in very thin Pr0.67Sr0.33MnO3 films (5–15 nm) grown on LaAlO3 (001) substrates. The films are under compressive strain imposed by the lattice mismatch with the substrate. The MR ratio [R(H)−R0]/R0 is ∼92% at H=800 Oe and T=70 K when the magnetic field is applied perpendicular to the film plane and is much smaller when the magnetic field is parallel to the film plane. We suggest that the large low-field MR is due to strain-induced magnetic anisotropy and spin-dependent scattering at domain boundaries.
Electrical field impact on the gas adsorptivity of thin metal oxide films
Authors: Bögner M. , Fuchs A. , Scharnagl K. , Winter R. , Doll T. , Eisele I.
Published: July 2002

A thin semiconducting NiO film is exposed to NO2 at room temperature. This exposure causes a work function change at the surface of the film due to adsorption of the NO2 molecules. It is found that there is a strong dependence of the adsorptivity, i.e., the amount of work function change per unit time, on the magnitude of an electrical field that is applied perpendicular to the film surface. This induced adsorptivity change is known as the electroadsorptive effect. In order to modulate the adsorptivity significantly, the electrical field strength must exceed 104 V/cm. This requirement can be achieved by using hybrid suspended gate field effect transistors with an air gap height below 1 μm.
Modal analysis of guiding structures patterned in a metallic photonic crystal
Authors: Danglot J. , Carbonell J. , Fernandez M. , Vanbésien O. , Lippens D.
Published: July 2002

We present a modal analysis of guiding structures patterned in a two-dimensional metallic photonic crystal. Measurements are carried out on a T-stub structure with various dimensions in the 22–40 GHz frequency band. The pronounced resonances extracted from measured transmissivity spectra are interpreted in terms of multimode propagation phenomena in the T-stub region. Experimental data are assessed by the solution of a suitable form of the 2D Helmholtz equation established for metallic propagation media.
Persistent photoconductivity in Si delta-doped GaAs at low doping concentration
Authors: Chen C. Y. , Thio Tineke , Wang K. L. , Alt K. W. , Sharma P. C.
Published: July 2002

In addition to the persistent photoconductivity (PPC) attributed to DX centers in GaAs delta-doped with Si, a weak PPC (WPPC) with a PPC carrier density independent of Si-doping concentration has been generally reported at ambient atmosphere, but the nature of the deep states responsible has not been elucidated. Here, we present the results of a detailed study of the WPPC in δ-GaAs:Si at low-doping densities, NSi≈1–3×1012 cm−2, and ambient pressure. It is concluded that the WPPC does not arise from DX centers but from another deep defect, which is DX-like in the sense that it can be metastably excited. The presence of two distinct DX-like states is apparent from two separate annealing temperatures of the PPC, Ta≈50 K and Tb≈230 K; to the best of our knowledge, the latter is the highest annealing temperature observed in the AlGaAs:Si system.
Influence of the surface morphology on the yellow and “edge” emissions in wurtzite GaN
Authors: Godlewski M. , Goldys E. M. , Phillips M. R. , Langer R. , Barski A.
Published: July 2002

In this letter we examine an influence of surface morphology on yellow and edge emissions in wurtzite phase GaN. Our cathodoluminescence measurements show that the yellow emission does not correlate with the surface morphology, but simultaneously the “edge” emission shows very strong spatial fluctuations. The observed effect is attributed to granular structures in GaN films and enhancement of the yellow emission in the interface region.
Exciton-phonon scattering in GaAs/AlAs quantum wires
Authors: Gopal A. Venu , Kumar Rajesh , Vengurlekar A. S. , Mélin T. , Laruelle F. , Etienne B.
Published: July 2002

We perform temperature-dependent photoluminescence measurements on a GaAs/AlAs quantum wire array (QWR-A) with a very low disorder. Using these, we deduce the temperature dependence of the homogeneous linewidth of the quasi-one-dimensional exciton to show that exciton scattering rates with optical phonons are enhanced in the QWR-A in comparison with a reference quantum well.
Suppression of the face-centered-cubic-hexagonal-close-packed stacking fault in Co/Cu(111) ultrathin films by pulsed laser deposition
Authors: Zheng M. , Shen J. , Mohan Ch. V. , Ohresser P. , Barthel J. , Kirschner J.
Published: July 2002

The thermal deposition of Co onto Cu(111) results in three-dimensional island growth and a face-centered-cubic-hexagonal-close-packed stacking fault, which hinders a complete antiferromagnetic coupling in Co/Cu(111) superlattices. We report that Co/Cu(111) films can be grown with good layer-by-layer morphology and significantly less stacking faults by pulsed laser deposition. We show that a complete antiferromagnetic coupling can be achieved in the pulsed laser deposited Co/Cu trilayer.
Structural and optical properties of InSb epitaxial films grown on GaAs(100) substrates at low temperature
Authors: Kim T. W. , Bae H. C. , Park H. L.
Published: July 2002

Transmission electron microscopy (TEM) and reflectance measurements were carried out to investigate the structural and the optical properties of the InSb/GaAs heterostructures grown at low temperature (∼290 °C) for the possible use in fabricating CdTe/InSb quantum structures on GaAs substrates. X-ray diffraction measurements showed that the grown InSb layer was an epitaxial film, and TEM measurements indicated that the lattice mismatch between InSb and GaAs generated the formation of plane defects in the InSb epilayer near the InSb/GaAs heterointerface. When a 0.2 μm InSb layer was grown on the GaAs substrate, the InSb layer could be used as a defect-free substrate. Reflectance measurements showed the InSb longitudinal optical phonon. Structural and optical properties of the InSb/GaAs heterostructures were strongly affected by the growth temperature. These results indicate that the InSb buffer layer grown at low temperature, by eliminating the defects due to the lattice mismatch, plays an important role in the growth of CdTe/InSb quantum structures on GaAs substrates.
Magnetic and transport properties of III–V based magnetic semiconductor (GaMn)As: Growth condition dependence
Authors: Shimizu Hiromasa , Hayashi Toshiaki , Nishinaga Tatau , Tanaka Masaaki
Published: July 2002

We have studied growth condition dependence of magnetic and transport properties of magnetic semiconductor (GaMn)As grown by low-temperature molecular-beam epitaxy (LT-MBE). With increasing substrate temperature and decreasing As overpressure during the growth of (Ga1−xMnx)As with x=0.043, the hole concentration increased, the conduction behavior changed from semiconducting to metallic, and the ferromagnetic transition temperature became higher. This is explained by a decrease in the compensation of Mn acceptors by the reduction of excess As related defects in the LT-MBE grown (GaMn)As. Our experimental results indicate that the selection of the MBE growth parameters is very important for better controlling the electronic and magnetic properties of (GaMn)As.
Influence of AlN nucleation layers on growth mode and strain relief of GaN grown on 6H–SiC(0001)
Authors: Waltereit P. , Brandt O. , Trampert A. , Ramsteiner M. , Reiche M. , Qi M. , Ploog K. H.
Published: July 2002

We study the growth mode and strain state of GaN layers grown either directly on 6H–SiC(0001) or on thin (5 nm), coherently strained AlN nucleation layers. Using a combination of structural, optical, and vibrational characterization methods, we show that the 3.4% compressive lattice mismatch strain is fully relieved in the former case, whereas in the latter case a significant amount (0.3%) remains even after 1 μm of growth. This finding is clarified by in situ reflection high-energy electron diffraction and transmission electron microscopy. We demonstrate that the strain state of the GaN layer is determined by its growth mode, which in turn is governed by the degree of wetting of the underlayer rather than by lattice mismatch.
Charge depletion of n+-In0.53Ga0.47As potential wells by background acceptor doping
Authors: Skuras E. , Long A. R. , Vögele B. , Holland M. C. , Stanley C. R. , Johnson E. A. , MacKinnon A.
Published: July 2002

Charge depletion from 20 monolayers of n+-In0.53Ga0.47As, uniformly doped with Si donors and embedded within Be-doped In0.53Ga0.47As, has been studied at 1.2 K by magnetotransport measurements. Electron subband energies and densities associated with the n+-In0.53Ga0.47As potential well prove sensitive to the presence of the acceptors at concentrations up to 3×1016 cm−3. Agreement between the experimental data and the electronic subband structure calculated self-consistently by solving the one-dimensional Schrödinger and Poisson equations is excellent. The results suggest that intentional background acceptor doping could be a useful mechanism for tuning subband fillings and energies in potential wells formed by highly confined donors.
Structural characterization of the low-temperature phase in Sr–Bi–Ta–O films
Authors: Lee Jeong Soo , Kwon Hyun Ja , Jeong Young Woo , Kim Hyun Ha , Hyun S. J. , Noh T. W.
Published: July 2002

The crystal structure and microstructural evolution of Sr–Bi–Ta–O films grown on LaAlO3 substrates were investigated using x-ray diffraction and cross-sectional transmission electron microscopy. It was found that the epitaxial low-temperature phase found in the as-deposited and 650 °C heat-treated films has a fluorite structure (CaF2-type structure) with a face-centered-cubic symmetry. From the electron diffraction patterns for the fluorite phase, {121212} and {100}-type superlattice spots were observed. The epitaxial fluorite phase was gradually encroached upon by polycrystalline layered perovskite SrBi2Ta2O9 grains during heat treatment at 750 °C.
In-plane electro-optic anisotropy of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 thin films grown on (100)-cut LaAlO3
Authors: Lu Yalin , Zheng Jianjun , Croning Golomb Mark , Wang Feiling , Jiang Hua , Zhao Jing
Published: July 2002

Strong electro-optical (EO) anisotropy has been measured in (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 [(1−x)PMN–xPT] single crystalline films epitaxially grown on (100)-cut LaAlO3 substrate, through using an improved dynamic alternating-current ellipsometric null EO detection technique with high accuracy. Large quadratic EO coefficients, which can be as large as 1.38×10−16 (m/V)2 in 0.67PMN–0.33PT film, were obtained in all the used compositions when electric field was applied along {110} directions. The strong EO anisotropy has been explained according to the structural relationship between ferroelectric polarization, input light polarization, and the applied electric field.
Atomic dynamics and defect evolution during oxygen precipitation and oxidation of silicon
Authors: Ramamoorthy M. , Pantelides S. T.
Published: July 2002

We report first-principles calculations in terms of which we propose a unified description of the atomic dynamics that underlie the nucleation and growth of SiO2 precipitates in Si and the oxidation of Si thin films. We identify a mechanism for the observed emission of Si interstitials and show that it eliminates electrically active defects without introducing dangling bonds. The results provide an explanation for the low defect density at the Si–SiO2 interface and suggest a novel family of electrically active interface defects that are akin to the “thermal donors” in Si.
Statistical modeling of pulse height spectrum of gamma-ray spectrometers limited by incomplete charge collection
Authors: Nemirovsky Y.
Published: July 2002

This letter presents an analytic approach to the calculation of the pulse height spectrum, using a statistical model, which simultaneously considers a random point of photon absorption (i.e., nonuniform absorption) and a random drift time for each carrier. The pulse height spectrum of gamma-ray spectrometers is calculated as a function of photon energy, electron and hole mobility-lifetime products and applied electric field. For spectrometers with a uniform electric field the pulse height spectrum is obtained by a single numerical integration of an analytical expression.
Correlation of photoconductivity and structure of microcrystalline silicon thin films with submicron resolution
Authors: Rezek B. , Nebel C. E. , Stutzmann M.
Published: July 2002

Optical beam induced current (OBIC) and atomic force microscopy (AFM) are applied to characterize the optoelectronic properties of microcrystalline silicon (μc-Si) thin films prepared by pulsed interference laser crystallization. The OBIC spatial resolution is about 400 nm, allowing a microscopic detection of μc-Si electronic properties. A correlation of local photoconductivity and microstructure of μc-Si on a submicron scale is presented. There is a surprising resemblance between the AFM profile of a secco etched surface with enhanced grain boundaries and OBIC spatial profiles on an untreated surface. The photocurrent response to a local focused laser beam excitation is dominated by variations in the sample thickness, which is much smaller than the absorption depth of the light used. Fine structure in the photocurrent profile is associated with the granular structure of μc-Si, the size of which is beyond the resolution of OBIC.
Strain relaxation of InxGa1−xAs during lateral oxidation of underlying AlAs layers
Authors: Chavarkar P. , Zhao L. , Keller S. , Fisher A. , Zheng C. , Speck J. S. , Mishra U. K.
Published: July 2002

Strain relaxation of hypercritical thickness InxGa1−xAs layers has been observed during lateral oxidation of underlying AlAs layers. Strain relaxation of InxGa1−xAs layers was studied as a function of indium composition and the AlAs oxidation temperature. It is proposed that the enhanced strain relaxation is due to two factors. The first is enhanced motion of threading dislocations due to stresses generated during the lateral oxidation process. The second is the porous nature of the InxGa1−xAs/Al2O3 interface that minimizes the interaction of threading dislocations with existing misfit dislocation segments. The extent of strain relaxation increases with increasing oxidation temperature, whereas the efficiency of strain relaxation was found to decrease with increasing indium composition.
Atomic structure of Ba0.5Sr0.5TiO3 thin films on LaAlO3
Authors: Gao H.-J. , Chen C. L. , Rafferty B. , Pennycook S. J. , Luo G. P. , Chu C. W.
Published: July 2002

Perovskite barium strontium titanate Ba0.5Sr0.5TiO3(BST) thin films were grown on (001) LaAlO3 (LAO) using pulsed-laser ablation. The microstructures of the as-grown BST films were studied with selected electron diffraction, transmission electron microscopy, and scanning transmission electron microscopy. The BST thin films are oriented with their [001] directions parallel to the 〈102〉 directions of the LAO. Both cross-sectional and plan-view studies show the BST films to be single crystals with smooth surfaces. The interfaces were seen to be atomically sharp by cross-sectional, high-resolution electron microscopy. The density of misfit dislocations was consistent with the 4.3% lattice mismatch, and they were found to be dissociated into partials.
An initiation mechanism of thermal instability of a metal-diamond-vacuum field emission regime
Authors: Xu N. S. , Yu Z. X. , Deng S. Z. , Chen J. , Wu S. S.
Published: July 2002

An analysis is carried out of the physical origin of thermal instability that can trigger a catastrophic vacuum breakdown event in vacuum microelectronic devices based on flat diamond emitters. The temperature rise in a diamond film will enhance internal field emission across metal–diamond interface. This effect can lead to a regenerative process that can initiate a breakdown event at temperature lower than the melting point of an emitter. A set of equations has been developed. These theoretical findings are successfully applied to explain the instability of field emission from the nondoped diamond films.
Controlled growth of a-/b- and c-axis oriented epitaxial SrBi2Ta2O9 ferroelectric thin films
Authors: Moon S. E. , Song T. K. , Back S. B. , Kwun S.-I. , Yoon J.-G. , Lee J. S.
Published: July 2002

Thin films of a-/b- and c-axis oriented SrBi2Ta2O9 (SBT) were epitaxially grown on (110) MgO and (100) MgO substrates, respectively, by a rf magnetron sputtering deposition method. The orthorhombic SBT phase was confirmed by electron probe microanalysis and infrared reflectance spectra. The oriented growth was proved by transmission electron microscopy together with x-ray diffraction. The orientation relationship of the a-/b-axis oriented film with the substrates was determined to be SBT[001]//MgO[001] and SBT[010]//MgO[11̄0](SBT[100]//MgO[11̄0]) from electron diffraction patterns.
Actively mode-locked p-Ge laser in Faraday configuration
Authors: Muravjov A. V. , Withers S. H. , Strijbos R. C. , Pavlov S. G. , Shastin V. N. , Peale R. E.
Published: July 2002

Active mode locking of the far-infrared p-Ge laser has been achieved in the Faraday configuration of electric and magnetic fields applied to the laser crystal. The laser generates 200 ps pulses of 80–110 cm−1 radiation with a laser-cavity roundtrip frequency of 454 MHz. The mechanism of gain modulation by the external rf electric field is based on induced electric-field gradients inside the active crystal and requires less rf power than was found previously for Voigt geometry.
Determination of critical thickness of spin reorientation in metastable magnetic ultrathin films
Authors: Shen J. , Swan A. K. , Wendelken J. F.
Published: July 2002

We investigate the spin reorientation of structurally unstable magnetic ultrathin films (base films) using magnetic capping layers. The capping layers, whose effective anisotropy constant is opposite that of the base films, are grown on the base films with no transformed structure and induce a spin reorientation after exceeding a critical thickness. The critical thickness of the capping layers can be used to deduce the critical thickness as well as the anisotropy constants of the base films. We use Co to cap the well-known Fe/Cu(100) system as an example to demonstrate the proposed approach.
Spectrally resolved luminescence from an InGaAs quantum well induced by an ambient scanning tunneling microscope
Authors: Kemerink M. , Gerritsen J. W. , Koenraad P. M. , van Kempen H. , Wolter J. H.
Published: July 2002

Spectrally resolved scanning tunneling microscope-induced luminescence has been obtained under ambient conditions, i.e., at room temperature, in air, by passivating the sample surface with sulfur. This passivation turned out to be essential to suppress the local anodic oxidation induced by the tunneling current. From the dependence of the luminescence signal on tunneling current and voltage, we find that the passivation solution and post-passivation annealing temperature strongly modify the surface density of states (SDOS). More specifically, we found evidence that, after annealing at 400 °C, no SDOS is left above the bottom of the conduction band. For annealing at 200 °C, the SDOS is found to be extended up to 1.0±0.2 eV above the bottom of the conduction band. In all cases, the passivated (001) surface appears to be completely pinned.
Sensing characteristics of in-plane polarized lead zirconate titanate thin films
Authors: Xu Baomin , Polcawich Ronald G. , Trolier-McKinstry Susan , Ye Yaohong , Cross L. Eric , Bernstein Jonathan J. , Miller Raanan
Published: July 2002

The sensing characteristics of in-plane polarized lead zirconate titanate (PZT) thin films were studied and compared with the through-thickness polarized PZT films. The in-plane polarized PZT films were deposited on ZrO2-passivated silicon substrates and had interdigitated electrode systems on the top surface; hence, they can be polarized in the film plane. This in-plane polarization configuration separates the electrode spacing and film thickness as independent variables; thus, the voltage sensitivity can be increased by using wider electrode spacing even for fixed film thickness. The results show that for films with a thickness of 1 μm the voltage sensitivity of in-plane polarized PZT films can be more than 20 times higher than that of the conventional, through-thickness polarized PZT films which were deposited on Pt-buffered silicon substrates.
Patterned polymer growth on silicon surfaces using microcontact printing and surface-initiated polymerization
Authors: Jeon Noo Li , Choi Insung S. , Whitesides George M. , Kim Namyong Y. , Laibinis Paul E. , Harada Yoshiko , Finnie Krista R. , Girolami Gregory S. , Nuzzo Ralph G.
Published: July 2002

Patterned polymer films were grown on SiO2/Si surfaces by a process starting with microcontact printing (μCP) of octadecyltrichlorosilane (OTS), formation of a monolayer derived from norbornenyl trichlorosilane (Nbn–SiCl3) in areas not protected by OTS, activation of the surfaces derived from Nbn–SiCl3 with a ruthenium catalyst, and surface-initiated ring-opening metathesis polymerization of derivatives of norbornene by the catalytically active ruthenium species. These patterned polymer films were successfully used as reactive ion etching resists. The combination of μCP and surface-initiated polymerization makes possible molecular-level control of polymer composition and thickness in both lateral and vertical directions: the smallest patterned lateral features were 2 μm lines; this width was determined by the features of the stamp used in μCP and is not the intrinsic limit of the method. The thickness of the polymer film was, typically, 5–100 nm and could be controlled by monomer concentration and reaction time.
Interfacial conduction in silica gels containing nanocrystalline copper oxide
Authors: Das D. , Chakravorty D.
Published: July 2002

Nanometer-sized copper particles have been grown within a gel derived glass in the system 60 CuO, 40 SiO2 (mole %). By heat treatment at temperatures in the range of 450–850 °C, copper oxide shells of thickness varying from 1.1 to 1.7 nm have been produced. DC resistivity measurements carried out over the temperature range of 30–300 °C show a drastically reduced activation energy as compared to that of a reference sample with the above composition. This is ascribed to the presence of an interfacial amorphous phase generated by the assembly of nanosized copper oxide particles.
Direct evidence for interaction of magnesium with tris(8-hydroxy-quinoline) aluminum
Authors: He P. , Au Frederick C. K. , Wang Y. M. , Cheng L. F. , Lee C. S. , Lee S. T.
Published: July 2002

The interaction between magnesium (Mg) and tris(8-hydroxy-quinoline) aluminum (Alq3) has been studied using high-resolution electron energy-loss spectroscopy (HREELS). It was found that deposition of magnesium on the Alq3 film gave rise to clear changes in the HREELS spectra. The changes are attributed to the weakly bounded Mg atoms on the Alq3 layer. Interestingly, for a given amount of magnesium (Mg to Al atoms ratio=3) on Alq3 film, remarkable changes were observed in the HREELS spectra when the sample was heated. A loss peak at 81 meV, which was assigned to Mg–O stretch mode, appeared upon annealing and increased in intensity as the annealing temperature increased up to about 360 K. This suggested that the diffusion of Mg atoms into the Alq3 layer and the reaction between Mg and Alq3 molecule occurred at the temperature range investigated. The present work has provided direct evidence for the strong interaction between magnesium and Alq3.
Nanocomposite Nd-rich Nd–Fe–B alloys: Approaching ideal Stoner–Wohlfarth type behavior
Authors: Girt Er. , Krishnan Kannan M. , Thomas G. , Altounian Z.
Published: July 2002

Starting from rapidly quenched NdδFe13.1B(2.05⩽δ⩽147.6) alloys and by appropriate annealing, the microstructure was tailored from strongly interacting Nd2Fe14B grains to magnetically isolated single domain Nd2Fe14B grains embedded in a nonmagnetic Nd-rich matrix (α-Nd and γ-Nd). This change in microstructure was found to have a large effect on coercivity, i.e., coercivity, μ0Hc, increases with an increase of the Nd concentration from 1.25 T in Nd2.05Fe13.1B to 2.75 T in Nd147.6Fe13.1B at 290 K. Using transmission electron microscopy, the Nd2Fe14B grains in Nd147.6Fe13.1B were confirmed to be randomly oriented platelets with the c axis normal to the plate and an average size of 100×40×25 nm. For these randomly oriented, noninteracting, single domain Nd2Fe14B grains, the coercivity was calculated using a Stoner–Wohlfarth model which included the shape anisotropy of the grains. The observed coercivity of Nd2Fe14B in such nanocomposite Nd147.6Fe13.1B alloys is ∼83% of its theoretical value.
Photoluminescence excitation spectroscopy of erbium-doped silicon-rich silicon oxide
Authors: Shin Jung H. , Seo Se-young , Kim Sangsig , Bishop S. G.
Published: July 2002

The 1.54 μm Er3+ photoluminescence excitation (PLE) and photoluminescence (PL) spectra of erbium-doped silicon-rich silicon oxide (SRSO) are investigated. Between 350 and 820 nm, PLE spectra are broad and featureless, and the PL spectra are independent of the excitation wavelengths. The results indicate that in erbium-doped SRSO, the Er3+ luminescence is dominated by a single class of Er sites with a strong coupling to all the carriers in the silicon nanograins.
Barkhausen jumps in a magnetic microstructure
Authors: Puppin Ezio , Ricci Simona , Callegaro Luca
Published: July 2002

The magnetization process in a square dot of permalloy having a size of 20 μm and 80 nm thickness has been investigated with a focused magneto-optical hysteresigraph. With this apparatus, it is possible to measure in a few seconds the hysteresis loop with a signal-to-noise ratio adequate for the observation of Barkhausen jumps also in such a small magnetic sample. From a sequence of 6000 loops, systematic data on the statistical properties of these jumps have been extracted. The observed behavior shows strong deviations with respect to the available data on bulk samples and thin films.
Saturation magnetization and uniaxial magnetocrystalline anisotropy for Co-based binary and Co–Ge–Cr ternary alloys
Authors: Takahashi M. , Shoji H. , Kadowaki S. , Djayaprawira D. D. , Komori Y. , Domon H.
Published: July 2002

In order to develop a magnetic material for high-density magnetic recording media which overcomes the thermal agitation effect, the magnetic properties, such as saturation magnetization and magnetic anisotropy, were evaluated for Co–M (M=Pt, Pd, Ru, Rh, Os, Cr, Ge, Mo, Mn, Re, and Si) binary alloys. Ge addition was found to be effective in maintaining the value of the magnetic anisotropy field of Co. Furthermore, a ternary magnetic alloy of Co–Ge–Cr (85 at. % Co, 10 at. % Ge, 5 at. % Cr) was found to have the following magnetic properties: Kugrain⩾3×106 erg/cm3, Hkgrain≈10 kOe, and 4πMs/Hkgrain<1.0. This magnetic material is a very promising candidate for use in high-density magnetic recording media.
Electronic structure of InNxAs1−x alloys from tight-binding calculations
Authors: Tit Nacir , Dharma-wardana M. W. C.
Published: July 2002

We present tight-binding band-structure calculations for InNxAs1−x alloys as a function of the nitrogen concentration. The high-concentration regime is found to be extremely sensitive to x. The low-concentration region (0<x<0.25) is of technological interest and is examined in detail. Effects of clustering, percolation, and the dependence of the energy gap on the assumed valence-band offsets on the band gap are reported.
Connes duality in pseudo-Riemannian geometry
Authors: Parfionov G. N. , Zapatrin Roman R.
Published: July 2002

The Connes formula giving the dual description for the distance between points of a Riemannian manifold is extended to the Lorentzian case. It resulted that its validity essentially depends on the global structure of space–time. The duality principle classifying space–times is introduced. The algebraic account of the theory is suggested as a framework for quantization along the lines proposed by Connes.
Molecular dynamics in a mixture of 8OCB-d17 and 6OCB showing nematic and reentrant nematic phases: A deuterium nuclear magnetic resonance study
Authors: Dong Ronald Y. , Cheng M.
Published: July 2002

A deuteron NMR study of the molecular dynamics of 4-n-octyloxy-4′-cyanobiphenyl (8OCB) in the mixture of 72 wt % of 8OCB and 28 wt % of 4-n-hexyloxy-4′-cyanobiphenyl is presented. The mixture has the same composition as the one used before (Shen and Dong, 1998) except in the deuteration of the component molecule. The deuteron Zeeman and quadrupolar spin-lattice times and quadrupolar splittings were measured in the nematic, smectic A, and reentrant nematic phases at 15.1 and 46 MHz. The additive potential method was employed to construct the potential of mean torque based on the observed splittings. The spectral density data from the relaxation times were interpreted in terms of the internal conformational motions of the chain decoupled from the molecular small-step rotational diffusion and the order director fluctuations. The latter motion was found to be essential to the fit of experimental results in the nematic phase. The fitting parameters obtained using a global target fitting method are acceptable when compared with those obtained from other deuteron and proton NMR studies of the same mesophases.
Solutions of the spherically symmetric SU(2) Einstein–Yang–Mills equations defined in the far field
Authors: Wasserman Arthur G.
Published: July 2002

It is shown analytically that every static, spherically symmetric solution to the Einstein–Yang–Mills equations with SU(2) gauge group that is defined in the far field has finite ADM mass. Moreover, there can be at most two horizons for such solutions. The three types of solutions possible, Bartnik–McKinnon particle-like solutions, Reissner–Nordström-type solutions, and black hole solutions having only one horizon are distinguished by the behavior of the metric coefficients at the origin.
Theoretical characterization of the structures and properties of phenol-(H2O)2 complexes
Authors: Fang Wei-Hai , Liu Ruo-Zhuang
Published: July 2002

Extensive ab initio calculations at different levels of theory have been performed with the 6-31G(d,p) basis set. Three minimum energy structures of (a), (b), and (c) were found on the ground (S0) and excited (S1) state surfaces of the phenol–(H2O)2 complex, with cyclic structure (a) being the most stable. Experimentally inferred very low frequencies for intermolecular vibrations in S1 were reproduced using the present calculations. The high vibrational mode density resulting from very low frequency vibrations of the structure (b) may be responsible for a broad electronic origin in the spectra of the phenol–(H2O)2 complex. The intermolecular interaction has little influence on the structures of phenol and water, but a significant change is found in the properties upon complexation. The intramolecular vibrations, which have frequencies of the magnitude of the intermolecular vibrations or involve the OH group of phenol, are significantly affected by formation of complex. All of these have been discussed in detail.