bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and mechanical characterization of ultrashort nanocantilevers
Authors: Nilsson S. G. , Sarwe E.-L. , Montelius L.
Published: August 2003

Three aspects on nanocantilevers are presented in this letter. First, we present the fabrication process of 2 μm long freestanding chromium cantilevers with width 150 nm, and thickness 50 nm. Second, a measurement scheme using an atomic force microscope operating in contact mode was employed to study the mechanical properties along the length of the cantilevers. Third, we have investigated extremely large deflections on these nanoscale cantilevers demonstrating their high ductility. The spring constants calculated from the experimental data are smaller than expected from classical mechanics calculations, but show good agreement with previously reported calculations for largely deflected beams.
Energetics of variant conversion in ferromagnetic shape memory alloys by external magnetic fields
Authors: Steuwer Axel , Mori Tsutomu , Kato Hiroyuki , Wada Taishi
Published: August 2003

Using energetics, we examine the occurrence of large strains, so-called giant magnetostriction, in ferromagnetic shape memory alloys by the application of an external magnetic field. It is claimed that these strains originate from the conversion of one martensite variant to another. In this article, we attempt to show that magnetic work cannot supply the work required for the conversion of martensite variants in most cases. It is also pointed out that the latter work dissipates, while most of the magnetic work is conserved, as indicated by almost hysteresis-free magnetization curves. Therefore, simple energy conservation arguments rule out the suggested variant conversion mechanism not only quantitatively, but also qualitatively. A possible explanation for the occurrence of large strains is offered.
Harmonic content and time variation of electron energy distributions in high-plasma-density, low-pressure inductively coupled discharges
Authors: Vasenkov Alex V. , Kushner Mark J.
Published: August 2003

Plasma kinetics models which are commonly used to model rf discharges often produce electron energy distributions (EEDs) averaged over the rf cycle. In doing so, the time dynamics of the EEDs are lost. In this article we describe a technique to recover these time dynamics by using an “on-the-fly” (OTF) Monte Carlo method. The OTF method directly computes the harmonic content of the EEDs using Fourier transform techniques during advancement of the trajectories of pseudoelectrons. The OTF method was incorporated into a two-dimensional plasma equipment model to investigate the harmonic content of the EEDs and their time dependencies in inductively coupled low-pressure (⩽10 mTorr) and low-frequency (⩽16 MHz) plasmas sustained in Ar. The computational results demonstrated that the second harmonic dominates the time dynamics of the EEDs, and that this harmonic content mostly occurs at higher energies. The harmonic content at low energies is significant only in the electromagnetic skin layer. We also found that the time evolution of the second harmonic of the EED involves the simultaneous transit of several pulses in energy and space. These pulses are attributed to the nonlinear Lorentz force resulting from the rf magnetic field.
Atomic force acoustic microscopy methods to determine thin-film elastic properties
Authors: Hurley D. C. , Shen K. , Jennett N. M. , Turner J. A.
Published: August 2003

We discuss atomic force acoustic microscopy (AFAM) methods to determine quantitative values for the elastic properties of thin films. The AFAM approach measures the frequencies of an AFM cantilever’s first two flexural resonances while in contact with a material. The indentation modulus M of an unknown or test material can be obtained by comparing the resonant spectrum of the test material to that of a reference material. We examined a niobium film (d=280±30 nm) with AFAM using two separate reference materials and two different cantilever geometries. Data were analyzed by two methods: an analytical model based on conventional beam dynamics, and a finite element method that accommodated variable cantilever cross section and viscous damping. AFAM values of M varied significantly depending on the specific experimental configuration and analysis technique. By averaging values obtained with both reference materials, very good agreement (5–10 % difference) with values determined by other methods was achieved. These results provide insight into using AFAM methods to attain reliable, accurate measurements of elastic properties on the nanoscale.
Formation of nanosized Fe–Co alloys in α−Al2O3 crystals by ion implantation
Authors: Hayashi N. , Sakamoto I. , Wakabayashi H. , Toriyama T. , Honda S.
Published: August 2003

Nanometer-sized Fe–Co composite clusters in α−Al2O3 matrices were synthesized by sequential implantation of Fe and Co ions with the projectiles’ energy at 100 keV. The synthesized clusters were shown to have bcc structure by the measurement of glancing angle x-ray diffraction. We have observed an apparent change in the internal magnetic field of the Fe–Co composite clusters with changing Co concentration, which exhibits the maximum at a concentration around 25 at. % Co as revealed by conversion electron Mössbauer spectroscopy. The magnetoresistance ratio of the granules was observed to increase with the Co addition to the Fe nanoclusters. The results provide clear evidences on the alloy formation of Fe–Co nanoclusters in α−Al2O3 layers synthesized by ion implantation.
Electric field in phthalocyanine/perylene heterojunction solar cells studied by electroabsorption and photocurrent measurements
Authors: Hiromitsu Ichiro , Murakami Yohei , Ito Takashi
Published: August 2003

The electric-field distribution in Au/Zn-phthalocyanine(ZnPc)/3,4,9,10-perylene-tetracarboxylbis-benzimidazole(PTCBI)/In/Al heterojunction solar cells is studied by electroabsorption and photocurrent measurements. In the PTCBI surface region near the PTCBI/In interface, a large anomalous electric field exists which is nearly bias independent and does not contribute to the photocurrent generation. This anomalous electric field exists only for the PTCBI-film thickness ⩾35 nm. The electric fields in the bulk of the PTCBI and ZnPc layers are responsible for the photocurrent generation. The bulk electric field in the PTCBI layer changes its sign at a forward bias, Vbias, of 0.3 V, while that in the ZnPc layer disappears for Vbias⩾0.5 V. The latter may indicate that holes are hardly trapped in the ZnPc layer.
Spectroscopic ellipsometry study of a self-organized Ge dot layer
Authors: Gallas B. , Rivory J.
Published: August 2003

We report on the determination of the dielectric function of a Ge dot layer obtained by epitaxial growth on Si(001) in the presence of Sb as surfactant and capped by Si. After growth, spectroscopic ellipsometry reveals a SiGe alloy containing Ge rich regions. After etching the Si cap, the dielectric function of the Ge rich regions exhibits critical points located at 2.92, 3.65, and 4.25 eV. It is shown that this dielectric function does not correspond either to an alloy or to bulk Ge, and is affected by confinement.
Effects of having two populations of defects growing in the cavity of a semiconductor laser
Authors: Lam S. K. K. , Mallard R. E. , Cassidy Daniel T.
Published: August 2003

In this study, we show the effects of the growth of two noninteracting populations of defects in the cavity of a semiconductor laser diode, induced by accelerated lifetesting. The development of one type of defect is considered to give rise to a particular failure mode or mechanism. Using a multicomponent model, we demonstrate that the evolution of the threshold current as a function of time is strongly affected by the operating temperature. We describe the progression of the degradation in terms of different thermal activation energies associated with each of the different failure modes. This observation explains why a common shape of the aging curve is seldom observed from one experiment to another and why it is difficult to have one universal threshold-aging model that everyone agrees on. In addition, the study offers insight on the estimation of the lifetime of a semiconductor laser diode.
Spectroscopy of silicon dioxide films grown under negative corona stress
Authors: Prasad Ila , Chandorkar A. N.
Published: August 2003

Silicon dioxide films were grown in oxygen ambient under negative corona stress at low temperatures (400–450 °C). Fourier transform infrared spectra of these films show a peak at 935 cm−1 along with the conventional transverse optic mode peaks around 1074, 800, and 456 cm−1. A broad shoulder at 1150 cm−1 was also observed. The extra peak is attributed to the presence of SiO42− ions and could be the outcome of incomplete oxidation at the surface. The films indicated properties similar to a fully relaxed thermally grown silicon dioxide film with a contradictory nature. The results of these experiments can be comprehensively explained only by assuming the presence of some mixed phase of SiO2.
In situ
monitoring of the growth and characterization of (PrMnO3)n(SrMnO3)n superlattices
Authors: Mercey B. , Salvador P. A. , Lecoeur Ph. , Prellier W. , Hervieu M. , Simon Ch. , Chippaux D. , Haghiri-Gosnet A. M. , Raveau B.
Published: August 2003

Superlattices having the general formula (PrMnO3)n(SrMnO3)n were grown from PrMnO3 and SrMnO3 ceramic targets by pulsed laser deposition (PLD) in low pressures (laser-MBE) and were compared to those grown in standard pressures (“classical”-PLD). For the laser-MBE grown films, the growth was monitored and the thickness of each deposited layer was controlled in situ at the level of one unit cell using reflection high energy electron diffraction. Perfectly ordered stacks of PrMnO3 and SrMnO3 layers were thusly grown. The transport and magnetic properties of the laser-MBE superlattices differ from similar superlattices grown in a “classical” PLD system. The different physical behaviors are explained by the combination of two factors, the roughness of the interfaces between the different layers and the oxygen deficiency, both of which are larger in the films grown using classical-PLD. X-ray and electron diffraction, as well as high-resolution electron microscopy, were used to characterize the structures of the laser-MBE superlattices. The valence of the manganese cations was probed by x-ray photoelectron spectroscopy and the results support the idea that the oxygen deficiency is larger in films grown in the classical-PLD system. This difference arises because pure molecular oxygen is used as the oxidizer in classical-PLD, whereas a mixture of molecular oxygen and ozone is used as the oxidizer in the laser-MBE system.
Prevention of tissue damage by water jet during cavitation
Authors: Palanker Daniel , Vankov Alexander , Miller Jason , Friedman Menahem , Strauss Moshe
Published: August 2003

Cavitation bubbles accompany explosive vaporization of water following pulsed energy deposition in liquid media. Bubbles collapsing at the tip of a surgical endoprobe produce a powerful and damaging water jet propagating forward in the axial direction of the probe. We studied interaction of such jet with tissue using fast flash photography and modeled the flow dynamics using a two-dimensional Rayleigh-type hydrodynamic simulation. Maximal velocity of the jet generated at pulse energies of up to 1 mJ was about 80 m/s. The jet can produce tissue damage at a distance exceeding the radius of the cavitation bubble by a factor of 4. We demonstrate that formation of this flow and associated tissue damage can be prevented by application of the concave endoprobes that slow down the propagation of the back boundary of the bubble. Similar effect can be achieved by positioning an obstacle to the flow, such as a ring behind the tip.
Photon force analysis for a spherical particle near a substrate illuminated by a tightly focused laser beam
Authors: Inami Wataru , Kawata Yoshimasa
Published: August 2003

We present an analysis of the radiation force acting on a spherical particle near a substrate that is illuminated by a tightly focused laser beam. The particle may be trapped at multiple positions due to multiscattering between the particle and the substrate. The particle is attracted to the substrate when the two are very close to each other, because the multiscattering produces a high-intensity region on the substrate surface. In many instances we found that a precise control of the focal position was necessary in order to scan the particle on the substrate surface. On the basis of the results of our analysis, we also compare the potentials of radiation forces on the particle with and without a substrate.
Epitaxial growth and magnetic properties of EuO on (001) Si by molecular-beam epitaxy
Authors: Lettieri J. , Vaithyanathan V. , Eah S. K. , Stephens J. , Sih V. , Awschalom D. D. , Levy J. , Schlom D. G.
Published: August 2003

Epitaxial (001) EuO thin films have been grown on (001) Si utilizing an intermediate, epitaxial SrO buffer layer by molecular-beam epitaxy. Four-circle x-ray diffraction reveals nearly phase-pure samples. Magnetic measurements indicate that the EuO layer is ferromagnetic, with a transition temperature (68 K) close to the bulk value and a saturation magnetic moment of 4.7 Bohr magnetons per Eu atom. The magneto-optic Kerr effect observed is also comparable to bulk EuO. Such heterostructures have potential as a means to inject spin-polarized electrons into silicon for use in spintronics applications.
Electrically induced luminescence quenching in p+-type and anodically oxidized n-type wet porous silicon
Authors: Gelloz B. , Bsiesy A. , Herino R.
Published: August 2003

Electrically induced photoluminescence (PL) quenching from reverse-biased p+-type porous silicon (PS) and forward biased oxidized n-type PS, as well as their dynamics, have been investigated. The two systems exhibit common properties. The energy selectivity of the PL quenching by the applied potential is much lower than with nonoxidized n-type PS. The PL quenching time is independent of the emission energy. It is governed by carrier injection into PS and is limited by the Helmoltz capacitance at the electrolyte–PS interface and the electrolyte resistivity. The PL recovery time is longer than the quenching time and increases as the emission energy decreases. It is limited by the transparency of the energy barrier (due to oxide in the case of oxidized n-type PS and the depletion region in the case of p+-type PS) at the PS–substrate interface. It is shown that electron storage into PS is possible for time in excess of several seconds depending on parameters such as the oxidation level, the PS thickness, and the electrolyte resistivity.
Theory of local distortion in ErO6 cluster: Spontaneous symmetry reduction in lanthanoid octahedrons
Authors: Ishii Masashi , Komukai Yasuo
Published: August 2003

Molecular orbital calculations for an ErO6 cluster predicted a stable C4v pseudo-octahedron with an Er displacement of ∼0.1 Å from the center of the octahedron with an Er–O bond length of 2.27 Å. In this particular configuration, the hybridization balance of O 2p–Er 6s with O 2p–Er 5d minimizes electron transfer from the O anion to the Er cation, thereby strengthening the Er–O ionic bond. Excessive O 2p–Er 5d hybridization due to π-bond formation is found in the shorter Er–O bond range, while insufficient hybridization caused by a weak σ-bond is obtained in the longer Er–O bond range. Though spontaneous reduction of symmetry has also been confirmed in other LO6 (L=65Tb–71Lu) systems, the stablest pseudo-octahedron is obtained for ErO6.
Copper-induced dielectric breakdown in silicon oxide deposited by plasma-enhanced chemical vapor deposition using trimethoxysilane
Authors: Takeda Ken-ichi , Ryuzaki Daisuke , Mine Toshiyuki , Hinode Kenji , Yoneyama Ryo
Published: August 2003

The barrier mechanism against copper-ion diffusion in silicon-oxide films deposited by plasma-enhanced chemical vapor deposition (PECVD) using trimethoxysilane (TMS) and nitrous oxide (N2O) chemistry (PE-TMS oxide) was studied. It was found that the flow ratio of TMS gas to N2O gas during deposition strongly affects a time-dependent dielectric-breakdown lifetime of PE-TMS oxide with a copper electrode as well as other PE-TMS oxide film properties such as electrical properties (leakage current and dielectric constant), a physical property (atomic composition), and chemical properties (chemical bonding states and wet-etching rate). The dielectric-breakdown lifetime of PE-TMS oxide film with a copper anode is a maximum at a source-gas ratio ranging from 1.7% to 3.3%. On the other hand, leakage current density, wet-etch rate, and dielectric-breakdown lifetime of PE-TMS oxide film with an aluminum electrode are degraded by increasing the source-gas flow ratio (0.83% to 12%). These results suggest that two types of degradation mode exist in the dielectric breakdown of PE-TMS oxide with a copper electrode. Namely, at low flow ratio (<1.7%), copper-induced degradation is dominant, but at high flow ratio (>3.3%), the dielectric degradation is probably not caused by copper contamination but by low-quality dielectric material. The dielectric-breakdown lifetimes of a PE-TMS oxide film (flow ratio: 3.3%) with a copper anode show an Arrhenius-type temperature dependence. That is, the activation energy of the dielectric-breakdown lifetime depends on the applied electric field and decreases from 1.8 to 0.55 eV when the applied field is increased from 0 to 5 MV/cm. As a simple kinetic model of the copper injection reaction at the anode surface, a thermally activated reaction process between two energy states—copper atom state on the anode surface and copper ion state in the dielectric material—is proposed.
Carrier migration in structures with InAs quantum dots
Authors: Popescu Dan P. , Eliseev Peter G. , Stintz Andreas , Malloy Kevin J.
Published: August 2003

A spectrally and spatially resolved investigation of emission from InAs/GaInAs quantum dots is performed using confocal photoluminescence. Structures investigated included a single layer of InAs dots embedded in a Ga0.85In0.15As quantum well and InAs dots embedded directly in GaAs. Excitation is performed at different wavelengths to provide selective excitation of either the quantum well or both the well and GaAs barrier. No noticeable lateral migration is observed under 900 nm wavelength pumping generating carriers only inside the quantum well. This is an indication that the diffusion of excess carriers is strongly suppressed by capture into dots. When GaAs surrounding material is also excited, the migration of excitation power occurs over 1.65 μm at the ground state of the quantum dots and 1.2 μm at the first-excited state. Saturation of the ground, first-, and second-excited state bands, when the carriers are generated only in quantum well, is also studied.
Electron emission of carbon nitride films and mechanism for the nitrogen-lowered threshold in cold cathode
Authors: Zheng W. T. , Li J. J. , Wang X. , Li X. T. , Jin Z. S. , Tay B. K. , Sun Chang Q.
Published: August 2003

Carbon nitride films have been deposited by rf reactive magnetron sputtered graphite carbon in an N2 discharge. The process parameters, viz., nitrogen partial pressure (PN2), substrate temperature (Ts), and substrate bias (Vb) were varied in order to investigate their influence on the field emission properties. The effective work function for carbon nitride films determined using the Fowler–Nordheim equation is in the range of 0.01–0.1 eV. Insight is presented into the nitrogen-lowered threshold of cold cathode electron emission of carbon from the perspective of nitride tetrahedron bond formation. The involvement of nonbonding (lone pair) and lone-pair-induced antibonding (dipole) states is suggested to be responsible for lowering the work function and hence the electron emission threshold. It is found that the substrate temperature of 200 °C, floating potential at the substrate, and nitrogen partial pressure of 0.3 Pa are favorable to promote the reaction that lowers the work function.
Detection of weak-order phase transitions in ferromagnets by ac resistometry
Authors: Khovailo V. V. , Abe T. , Takagi T.
Published: August 2003

It is shown that ac resistometry can serve as an effective tool for the detection of phase transitions, such as spin reorientation or premartensitic phase transitions, which generally are not disclosed by dc resistivity measurement. Measurement of temperature dependence of impedance, Z(T), allows one to unmask the anomaly, corresponding to a weak-order phase transition. The appearance of such an anomaly is accounted for by a change in the effective permeability μ of a sample upon the phase transition. Moreover, frequency dependence of μ makes it possible to use the frequency of the applied ac current as an adjusting parameter in order to make this anomaly more pronounced. The applicability of this method is tested for the rare earth Gd and Heusler alloy Ni2MnGa.
Improving images from a near-field scanning microwave microscope using a hybrid probe
Authors: Kim Jooyoung , Kim Myungsick , Kim Hyun , Song Doohee , Lee Kiejin , Friedman Barry
Published: August 2003

We fabricated a near-field scanning microwave microscope (NSMM) using a hybrid tip combining a reduced length of the tapered part with a small apex. In order to understand the function of the probe, we fabricated three different tips using a conventional chemical etching technique and observed three different NSMM images for patterned Cr films on glass substrates. These probe tips were coupled to a high-quality dielectric resonator at an operating frequency f=4.46 GHz. By using the hybrid tip, we demonstrated an improved, high-contrast NSMM image of lambda phage DNA on a glass substrate.
Current–voltage characteristics of diversely disulfide terminated λ-deoxyribonucleic acid molecules
Authors: Hartzell B. , McCord B. , Asare D. , Chen H. , Heremans J. J. , Soghomonian V.
Published: August 2003

Current–voltage characteristics were obtained at room temperature on duplex λ-deoxyribonucleic acid (DNA) molecules labeled with disulfide end groups in two configurations: Either the disulfide groups were attached to the 3′ ends of opposite DNA strands, or on the same strand at one 3′ end and at one 5′ end. In the latter configuration, only one strand is attached and contacted to the two Au electrodes utilized in the measurement. The current–voltage characteristics of both configurations are linear and do not reveal significant differences. The disulfide end groups in either configuration thus provide an equivalent contact. Moreover, the strand contacted at both ends by disulfide groups is not preferred for charge transport which, hence, involves the complete double-helical structure.
Effects of sheet resistance and contact shading on the characterization of solar cells by open-circuit voltage measurements
Authors: Harder N.-P. , Sproul A. B. , Brammer T. , Aberle A. G.
Published: August 2003

The measurement of the open-circuit voltage (Voc) as a function of the illumination intensity (Suns–Voc) is a useful tool for characterizing solar cells, giving a characteristic curve with virtually no influence from series resistance. In particular, Suns–Voc measurements allow the extraction of the diode properties without a complete contacting scheme, such as for test structures in research or for quality control between processing steps during production. In this article, we show by means of resistive network calculations, that the combination of contact shading and high sheet resistance can cause severe deviations of the measured Suns–Voc curve from that measured without contact shading or with only negligible sheet resistance. These deviations bear the danger of an erroneous assessment of the fundamental diode properties. For sheet resistances typical for thin layers of doped hydrogenated amorphous Si even the shadow of the tip of a needle-shaped contacting probe can be sufficient to cause a distorted Suns–Voc curve. Results of experiments performed on a microcrystalline p–i–n Si thin-film solar cell with an amorphous n layer are presented and qualitatively explained within the framework of a resistive network model. A “rule of thumb” is presented, which allows an estimate to be made of the impact of contact shading and sheet resistance on Voc measurements for arbitrary solar cells and contact area sizes.
Method for hybrid recording with single layer CoTbAg medium
Authors: Lie C. T. , Kuo P. C. , Shen C. L.
Published: August 2003

This work presents a hybrid-recording disk with a single layer CoTbAg recording medium. Co69.48−xTb30.52Agx films with x=0–25.68 at. % are fabricated on glass and naturally oxidized silicon wafer substrate by dc magnetron sputtering. The effects of Ag content on the magnetic properties and the microstructure of the film are investigated. The transmission electron microscope diffraction pattern indicates that all the films are amorphous. The saturation magnetization of the Co67.23Tb30.52Ag2.25 film is about 310 emu/cm3; perpendicular remanence is about 255 emu/cm3, and the perpendicular coercivity is about 3100 Oe at room temperature. The saturation magnetization and perpendicular coercivity decrease rapidly as temperature increases from room temperature to 200 °C. The compensation temperature Tcomp of this film is about 225 °C. This film is a promising candidate for hybrid recording media applications.
Slab-thickness dependent band gap size of two-dimensional photonic crystals with triangular-arrayed dielectric or magnetic rods
Authors: Hong Chin-Yih , Drikis I. , Yang S. Y. , Horng H. E. , Yang H. C.
Published: August 2003

The band structures of two-dimensional photonic crystals are investigated numerically. The examined photonic crystal has a substrate-slab-cover architecture, wherein the rods in the slab are either dielectric or magnetic and are arrayed triangularly. The material used for the substrate, the cover and the surrounding medium in the slab is the same. It was found that the bandgap size of zodd modes initially becomes larger as slab thickness increases, reaching a maximum value, after which, the band gap size reduces. A similar behavior for the slab thickness-dependent band gap size was also observed for slabs containing rods with higher magnetic permeability and lower dielectric permeability, except that there was a shift toward lower values for the band gap size. A detailed discussion on the influence of the magnetic permeability of rods on the band gap size of zodd modes is also given.
Continuous index of refraction measurements to 20 GPa in Z-cut sapphire
Authors: Hayes D. B. , Hall C. A. , Asay J. R. , Knudson M. D.
Published: August 2003

Isentropic compression experiments (ICE) on Sandia National Laboratories’ Z Accelerator are used to make continuous measurements of the index of refraction in single crystal Z-cut sapphire as the longitudinal stress is gradually increased to 20 GPa (uniaxial strain of about ∼3.9%). A planar, ramp compression wave, generated by a large magnetic field, propagates through a planar copper base plate. Part of the rear surface of the base plate is a free surface and part is covered with a sapphire window. Comparisons are made of velocity histories measured simultaneously at the free surface and at the copper/sapphire interface using a velocity interferometer system for any reflector (VISAR). This is sufficient to determine the index of refraction of the sapphire continuously as a function of density. Perturbations to the compression waves caused by interactions with the free surface and with the sapphire are accounted for by backward or forward solutions to the equations of motion. The effect of the unsteady nature of the compression wave in sapphire on the interferometry measurements is also taken into account. Results validate the interpretation of VISAR measurements on continuous loading experiments performed with optical windows. The measured index of refraction of sapphire agrees with previous studies validating this experimental technique and showing that it is useful for studying other materials for which index of refraction data do not exist. In addition, measured compression isentropes for copper and sapphire compare favorably with existing theoretical models.
High resolution-high energy x-ray photoelectron spectroscopy using third-generation synchrotron radiation source, and its application to Si-high k insulator systems
Authors: Kobayashi K. , Yabashi M. , Takata Y. , Tokushima T. , Shin S. , Tamasaku K. , Miwa D. , Ishikawa T. , Nohira H. , Hattori T. , Sugita Y. , Nakatsuka O. , Sakai A. , Zaima S.
Published: August 2003

High-resolution x-ray photoelectron spectroscopy (XPS) at 6 keV photon energy has been realized utilizing high-flux-density x rays from the third generation high-energy synchrotron radiation facility, SPring-8. The method has been applied to analysis of high-k HfO2/interlayer/Si complementary metal–oxide–semiconductor gate-dielectric structures. With the high energy resolution and high throughput of our system, chemical-state differences were observed in the Si 1s, Hf 3d, and O 1s peaks for as-deposited and annealed samples. The results revealed that a SiOxNy interlayer is more effective in controlling the interface structure than SiO2. Our results show the wide applicability of high resolution XPS with hard x rays from a synchrotron source.
Thermal bias operation in electro-optic polymer modulators
Authors: Park Suntak , Ju Jung Jin , Do Jung Yun , Park Seung Koo , Lee Myung-Hyun
Published: August 2003

An electro-optic polymer Mach–Zender modulator based on thermal biasing is proposed and demonstrated. The bias point of the modulator is controlled through the thermo-optic effect. Biasing is achieved by thermally changing the optical path length of one arm of the Mach–Zender interferometer. Tuning of bias points is realized by applying an electrical power of only 14 mW. It is verified that this approach is stable and substantially dc-drift free.
On the propagation of acoustic waves in quasi-two-dimensional conductors in a quantizing magnetic field
Authors: Kirichenko O. V. , Peschansky V. G. , Galbova O. , Ivanovski G. , Krstovska D.
Published: August 2003

The damping of acoustic waves propagating perpendicular to the layers of a quasi-two-dimensional conductor is analyzed for the case of low temperatures, at which the energy quantization of the conduction electrons leads to an oscillatory dependence of the acoustic damping coefficient on the inverse magnetic field. The acoustic damping decrement is found for different orientations of the magnetic field with respect to the layers. It is shown that that a layered conductor is most transparent for an acoustic wave in the case when the magnetic field is perpendicular to the layers.
Evidence of the Meyer–Neldel rule in InGaAsN alloys and the problem of determining trap capture cross sections
Authors: Johnston Steven W. , Crandall Richard S. , Yelon Arthur
Published: August 2003

Deep-level transient spectroscopy measurements have been performed on the quaternary semiconductor InGaAsN. A series of as-grown and annealed metalorganic chemical-vapor-deposited and molecular-beam-epitaxy samples with varying composition were studied. We observed a deep hole trap with activation energy ranging between 0.5 and 0.8 eV in all samples. The data clearly obey the Meyer–Neldel rule (MNR) with an isokinetic temperature of 350 K. We show that great care must be used in extracting capture cross sections (σ) from materials that obey the MNR. In fact, we argue that it is probably not possible to determine σ from the detrapping rate alone. One must measure both trapping and detrapping rates.
Improvement in retention time of metal–ferroelectric–metal– insulator–semiconductor structures using MgO doped Ba0.7Sr0.3TiO3 insulator layer
Authors: Tseng T. Y. , Lee S. Y.
Published: August 2003

We report the results of the fabrication and characterization of Pt/Bi3.35La0.85Ti3O12 (BLT)/LaNiO3 (LNO)/Ba0.7Sr0.3TiO3 (BST)/Si metal–ferroelectric–metal–insulator–semiconductor (MFMIS) structures for ferroelectric memory field effect transistor applications. The BLT films were deposited on LNO/BST/Si using the metalorganic decomposition method and annealed by rapid thermal annealing (RTA) process at 600 °C for 3 min. The ratio of remanent polarization to saturation polarization (Pr/Ps) increases with reducing area ratio, AF/AI. A large memory window of 3.1 V can be obtained for a small AF/AI ratio. By the utilization of 5 mol % MgO doped BST insulator layer, LNO bottom electrode layer for BLT, and small area ratio, AF/AI=1/12 in the MFMIS structure, large Pr/Ps ratio in BLT film and low leakage current and good capacitance matching of the ferroelectric and the insulator in the MFMIS structures have been achieved and, hence, long data retention time >106 s has been obtained in this study. Experimental results demonstrate the significant progress in increase of the retention time of these structures, which make them attractive for practical ferroelectric memory field effect transistor applications.
Photoluminescence in tensile-strained Si type-II quantum wells on bulk single-crystal SiGe substrates
Authors: Sheng S. R. , Rowell N. L. , McAlister S. P.
Published: August 2003

Near-band edge photoluminescence (PL) in high-quality tensile-strained Si type-II quantum wells (QWs) with varying well width grown on bulk crystal SiGe substrates by using ultrahigh vacuum chemical vapor deposition has been studied. In contrast to the blueshifts observed in the PL lines of Si1−xGex QWs on Si, the PL lines of Si QWs exhibit redshifts with increasing excitation density. The PL from the SiGe substrate shows no such shift. The excitation-induced PL redshifts decrease as the well width decreases, and are essentially independent of temperature up to 15 K. The rapid thermal annealing (RTA) was found to improve the crystal quality of the samples. RTA enhances the integrated PL intensity, results in narrowing and blueshifting of PL bands at a given excitation density, and reduces the exponent in the excitation power dependence as well as the amount of excitation-induced PL redshifting. Possible mechanisms for the observed excitation-induced PL redshifts were examined, including band bending, band filling, and binding of excitons to impurities.
Slow electromagnetic pulse propagation through a narrow transmission band in a coaxial photonic crystal
Authors: Munday J. N. , Robertson W. M.
Published: August 2003

We demonstrate the slow group-velocity propagation of electromagnetic pulses through a narrow transmission band of a simple coaxial photonic crystal. The narrow transmission band was formed by creating a defect in a periodic coaxial cable filter which resulted in a narrow-frequency passband within an otherwise forbidden band stop region. Strong normal dispersion within this region causes the group velocity of the pulse to be slowed well below the speed of light and below the expected propagation speed in a coaxial cable. This phenomenon is essentially similar to the much-studied slow light propagation observed in atomic vapors through regions of strong dispersion. The simplicity with which this phenomenon can be observed in a one-dimensional coaxial photonic crystal makes this a versatile experiment for such studies. Group velocities of 0.30c, where c is the speed of light in a vacuum, were observed.
Atomic arrangement at the AlN/Si (111) interface
Authors: Liu R. , Ponce F. A. , Dadgar A. , Krost A.
Published: August 2003

High-quality GaN epilayers have been grown on Si (111) substrates by metalorganic vapor phase epitaxy using a low-temperature AlN nucleation layer. The atomic arrangement at the epilayer/substrate interface has been investigated by high-resolution electron microscopy. A crystallographically abrupt interface is observed along most of the epilayer, indicating that the AlN/Si interface is thermodynamically stable and of high crystalline quality. Lattice images at the interface show a periodic array of misfit dislocations. The lattice images have been analyzed in detail in order to obtain information about the atomic arrangement, and interface bonding models are proposed.
Investigation of radiative recombination from Mn-related states in Ga1−xMnxAs
Authors: Teran F. J. , Zhao L. X. , Patanè A. , Campion R. P. , Foxon C. T. , Eaves L. , Gallagher B. L.
Published: August 2003

We show that the incorporation of a Ga1−xMnxAs layer with x=1% in the intrinsic region of a p–i–n diode produces an intense electroluminescence signal due to electronic transitions that involve holes bound to Mn-related states. The intensity of the electroluminescence signal is weakly affected by the temperature over the range of 5–290 K, thus indicating that the Mn-related hole states act as efficient sites for radiative recombination even at room temperature, despite the strong disorder in the Ga1−xMnxAs at relatively high values of x.
Photochromic effect in magnesium-doped α-Al2O3 single crystals
Authors: Tardı́o M. , Ramı́rez R. , González R. , Chen Y. , Kokta M. R.
Published: August 2003

A reversible photochromic effect was investigated in Mg-doped α-Al2O3 single crystals oxidized at elevated temperatures. Alternate illumination with blue and UV light at T⩽210 K results in reversible disappearance and reappearance of a gray-purple coloration, respectively. The coloration can also be fully rejuvenated by warming the crystal to T⩾215 K.
Low tunnel magnetoresistance dependence versus bias voltage in double barrier magnetic tunnel junction
Authors: Colis S. , Gieres G. , Bär L. , Wecker J.
Published: August 2003

We report on the magnetic and transport properties of [IrMn8/CoFe1.5]/AlOx1.2/[CoFe1/NiFe5/CoFe1]/AlOx1.2/[CoFe1.5/IrMn8] (nanometer) double magnetic tunnel junctions (DMTJs) deposited by magnetron sputtering and patterned using optical lithography. The tunnel magnetoresistance (TMR) versus the bias voltage presents a symmetric characteristic, which indicates a good and similar quality of both AlOx barriers. The junctions show a resistance-area product about 35 kΩ μm2, a high TMR at room temperature of 49.5%, and a high bias voltage at which the TMR signal is decreased to half of its maximum value, V1/2DMTJ=1.33 V. Both hard magnetic layers are rigid in negative field up to 51.5 kA/m, while the coercive field of the soft layer is around 1.1 kA/m. The large difference of coercive fields, combined with the large TMR and V1/2, makes these systems very promising for spin electronic devices.
Surface plasmon resonance on microaperture vertical-cavity surface-emitting laser with metal grating
Authors: Shinada Satoshi , Hashizume Jiro , Koyama Fumio
Published: August 2003

We proposed a microaperture vertical-cavity surface-emitting laser (VCSEL) with metal grating for the enhancement of optical near-field induced by surface plasmon resonance. We carried out the two-dimensional modeling on the near-field intensity at a microaperture surrounded by a grating in a silver film. An increase in throughput through the microaperture was obtained by the control of a surface plasmon mode, which is strongly dependent on some structural parameters of the grating, such as the period and the depth of a grating, and so on. We also fabricated a microaperture VCSEL with concentric circular grating, exhibiting a large enhancement in peak intensity. The intensity is eight times larger than that of a single-aperture device without grating.
Spin-dependent transmission in waveguides with periodically modulated strength of the spin-orbit interaction
Authors: Wang X. F. , Vasilopoulos P.
Published: August 2003

The electron transmission T is evaluated through waveguides, in which the strength of the spin-orbit interaction α is varied periodically, using the transfer-matrix technique. It is shown that T exhibits a spin-transistor action, as a function of α or of the length of one of the two subunits of the unit cell, provided only one mode is allowed to propagate in the waveguide. A similar but not periodic behavior occurs as a function of the incident electron energy. A transparent formula for T through one unit is obtained and helps explain its periodic behavior. The structure considered is a good candidate for the establishment of a realistic spin transistor.
Generation of coherent gigahertz acoustic phonons in AlGaN/GaN microwave field-effect transistors
Authors: Song Jung-Hoon , Zhang Qiang , Patterson W. , Nurmikko A. V. , Uren M. J. , Hilton K. P. , Balmer R. S. , Martin T.
Published: August 2003

We apply an optical probing technique on AlGaN/GaN field-effect transistors to demonstrate that coherent gigahertz phonons are generated copiously under large signal operation. The phonon generation originates from time varying electron screening of the piezoelectric polarization fields in the active region, and may provide a nondiffusive means of energy dissipation for high power devices.
Improved performance and stability of organic light-emitting devices with silicon oxy-nitride buffer layer
Authors: Poon C. O. , Wong F. L. , Tong S. W. , Zhang R. Q. , Lee C. S. , Lee S. T.
Published: August 2003

The use of silicon oxy-nitride (SiOxNy) as an anode buffer layer in organic light-emitting devices (OLEDs) with a configuration of indium tin oxide (ITO)/SiOxNy/α-naphtylphenyliphenyl diamine (NPB)/8-hydroxyquinoline aluminum/Mg:Ag has been studied. With a SiOxNy buffer layer several angstroms thick, the device efficiency increased from 3.0 to 3.8 cd/A. The buffer layer also protected the ITO surface from contamination due to air exposure. Upon exposing the cleaned ITO substrate to air for one day before device fabrication, the device current efficiency and turn-on voltage degraded to 2.1 cd/A and 4.3 V, respectively, from 3 cd/A and 3.3 V for the device fabricated on an as-cleaned ITO surface. In contrast, devices prepared on air-exposed SiOxNy/ITO surface had almost the same current efficiency (3.85 cd/A) and turn on voltage (3.7 V) comparing to devices (3.8 cd/A and 3.7 V) fabricated on freshly prepared SiOxNy/ITO surface. The results suggested that SiOxNy is a promising anode buffer layer for OLEDs, for both efficiency and stability enhancements.
Retrieval of the complex permittivity of spherical nanoparticles in a liquid host material from a spectral surface plasmon resonance measurement
Authors: Saarinen Jarkko J. , Vartiainen Erik M. , Peiponen Kai-Erik
Published: August 2003

A method for obtaining the complex permittivity of a Maxwell Garnett liquid with the aid of spectral surface plasmon resonance spectroscopy is presented. The Maxwell Garnett liquid is assumed to consist of small absorbing spherical inclusions in a host liquid. It is shown that the permittivity of the inclusions can be calculated if the optical constants of the host liquid are known. It is believed that such a method will gain increasing importance in the analysis of biological reactions.
Demonstration of finite-aperture tapered unstable resonator lasers
Authors: Bedford Robert , Schillgalies Marc , Fallahi Mahmoud
Published: August 2003

In this letter, we report experimental results of semiconductor lasers that incorporate a mirror with finite lateral extent at the output of a semiconductor tapered laser in InAlGaAs/InGaAsP/InP. We directly compare the “finite-aperture” tapered unstable resonator laser to that of the conventional “infinite-aperture” tapered laser. Using the finite aperture, we show the differential quantum efficiency is increased by 40%. Additionally, the beam is coupled out of the laser cavity using a grating, allowing for a quasicircular, low-divergence beam with no external optics.
Fiber-coupled erbium microlasers on a chip
Authors: Yang Lan , Armani D. K. , Vahala K. J.
Published: August 2003

An erbium-doped, toroid-shaped microlaser fabricated on a silicon chip is described and characterized. Erbium-doped sol-gel films are applied to the surface of a silica toroidal microresonator to create the microcavity lasers. Highly confined whispering gallery modes make possible single-mode and ultralow threshold microlasers.
Effect of rapid thermal annealing on strain in ultrathin strained silicon on insulator layers
Authors: Drake T. S. , Chléirigh C. Nı́ , Lee M. L. , Pitera A. J. , Fitzgerald E. A. , Antoniadis D. A. , Anjum D. H. , Li J. , Hull R. , Klymko N. , Hoyt J. L.
Published: August 2003

The fabrication of ultrathin strained silicon directly on insulator is demonstrated and the thermal stability of these films is investigated. Ultrathin (∼13 nm) strained silicon on insulator layers were fabricated by epitaxial growth of strained silicon on relaxed SiGe, wafer bonding, and an etch-back technique employing two etch-stop layers for improved across wafer thickness uniformity. Using 325 nm Raman spectroscopy, no strain relaxation is observed following rapid thermal annealing of these layers to temperatures as high as 950 °C. The thermal stability of these films is promising for the future fabrication of enhanced performance strained Si ultrathin body and double-gate metal-oxide-semiconductor field-effect transistors.
Phase-coherent multicolor femtosecond pulse generation
Authors: Kobayashi Yohei , Takada Hideyuki , Kakehata Masayuki , Torizuka Kenji
Published: August 2003

We achieved phase-coherent multicolor femtosecond pulse generation by optical phase locking among the pump and its subharmonic signal and idler pulses in an optical parametric oscillator. The ability for coherent superposition of the multicolor pulses is demonstrated in a time-domain measurement. Clear interferometric fringes between two sum-frequency pulses, corresponding to phase stability among the subharmonics, were observed with phase locking.
Structure and bulk modulus of M2AlC (M=Ti, V, and Cr)
Authors: Sun Zhimei , Ahuja Rajeev , Li Sa , Schneider Jochen M.
Published: August 2003

We have performed theoretical studies of the bulk modulus of M2AlC, where M=Ti, V, Cr by means of ab initio total energy calculations using the projector augmented wave methods. Our estimated equilibrium volume and the lattice parameters (c/a) agree well (within ±2% and ±0.06%, respectively) with experimental data. The bulk modulus of M2AlC increases as Ti is substituted with V and Cr by 19% and 36%, respectively. This can be understood since the substitution of Ti by V and Cr is associated with an extensive increase in the M–Al and M–C bond energy.
Synthesis of iron-based bulk metallic glasses as nonferromagnetic amorphous steel alloys
Authors: Ponnambalam V. , Poon S. Joseph , Shiflet Gary J. , Keppens Veerle M. , Taylor R. , Petculescu G.
Published: August 2003

Iron-based amorphous metals are investigated as nonferromagnetic amorphous steel alloys with magnetic transition temperatures well below ambient temperatures. Rod-shaped amorphous samples with diameters reaching 4 mm are obtained using injection casting. Amorphous steel alloys are designed by considering atomistic factors that enhance the stability of the amorphous phase, coupled with the realization of low-lying liquidus temperatures. The present alloys are found to exhibit superior mechanical strengths. In particular, the elastic moduli are comparable to those reported for super austenitic steels.
Design of a channel drop filter in a two-dimensional triangular photonic crystal
Authors: Qiu Min , Jaskorzynska Bozena
Published: August 2003

A design of a channel drop filter in a two-dimensional photonic crystal with a triangular lattice of air holes is presented. The requirement of the accidental degeneracy of the frequency is achieved by tuning the radii of the air holes in the cavity system. In contrast to the other designs proposed, the present one does not involve either inclusion of additional materials or an extra small feature size.