bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecule and Charge Carrier Diffusion in Optical and Electro-Optical Devices
Authors: Katz H. E. , Dhar L. , Hale A. , Schnoes M. , Schilling M. L. , Bao Z , Dodabalapur A.
Published: April 2011

Many organic-based optical components are based on refractive index modulation or contrast as the origin of their activity. These range from passive components such as waveguides, to active components that include electro-optic switches, photorefractive information processing elements, and holographic storage media. Common to the materials used in these applications is the need for charge and/or molecular migration in their preparation or utilization. This paper focuses on some of these migration effects, with special attention paid to a new class of photopolymers being designed for high density digital holographic data storage applications.
Biomimetic Preparation of ha Precursors at 37°C in Urea- and Enzyme Urease-Containing Synthetic Body Fluids
Authors: Bayraktar D , Tas A C.
Published: April 2011

An important inorganic phase of synthetic bone applications, calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2), was prepared as a single-phase and sub-micron bioceramic powder. Carbonated HA precursors were synthesized from calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts dissolved in “synthetic body fluid” (SBF) solutions, containing urea (H2NCONH2) and enzyme urease, under the biomimetic conditions of 37°C andpH 7.4, by using a novel chemical precipitation technique.
Borrowing Ideas from Nature: Peptide Specific Binding to Gallium Arsenide
Authors: Whaley Sandra R. , Belcher Angela M.
Published: April 2011

Biological systems have a unique ability to control crystal structure, phase, orientation and nanostructural regularity of inorganic materials. An example is seen with the control of crystallographic phase and orientation of calcium carbonate with the polyanionic proteins isolated from shells of the marine gastropod abalone. We are currently investigating the principles of natural biological molecular recognition in materials and developing new methods to pattern useful non-biological electronic and magnetic materials on new length scales. A peptide combinatorial approach has been employed to identify proteins that select for and specifically bind to inorganic structures such as semiconductor wafers, nanoparticles and quantum confined structures. This approach utilizes the inherent self-organizing, highly selective properties of biologically derived molecules. We are currently investigating peptide recognition and interaction with III-V and II-VI semiconductor materials, magnetic materials, calcium carbonates and phosphates. We have selected peptides that can specifically bind and discriminate between zinc-blende III-V semiconductor surfaces. These peptides show crystal face specificity and are being used to organize nanoparticle heterostructures. Long term potential application of these materials would include opto-electronic devices such as light emitting displays, optical detectors, lasers, and nanometer scale computer components.
Proteins From Oyster Shell: Biomineralization Regulators and Commercial Polymer Analogs
Authors: Wheeler A. P. , Sikes C. S.
Published: April 2011

Molluscan shell is a composite made up of μm-sized CaCO3 crystals and an organic phase (matrix). This report outlines our studies on the structure and activities of matrix proteins isolated from the inner calcite layer of shell of the Eastern oyster, including their cellular origin and structure and their relationship to the crystalline mineral phase. In addition, we present results of the synthesis and commercialization of polypeptide polymers which are based on the structure and activities of the oyster proteins. Extracted shell proteins are polyanionic and range in size from relatively small soluble forms to those which are crosslinked and insoluble. The soluble forms are capable of adsorbing to calcite in vitro and in the process changing its growth habit and acting as threshold growth inhibitors. Their function in vivo is not understood, but they may serve to control shell crystal morphology. The insoluble protein forms gels readily and may serve to provide resiliency to the shell and, from in vitro and in situ observations, appears to serve as a site for nucleation of crystals. However, from studies in vitro, these gels do not lower the energy of activation for nucleation, as previously expected. Matrix protein aggregates are identifiable by AFM on the surface of crystals, but as such do not serve as nucleation sites for new crystal growth. If the aggregates are removed, then ectopic crystal growth proceeds readily revealing orientation of the underlying crystals. All the matrix proteins contain domains rich in aspartic acid, are heavily phosphorylated, crossreact in antibody studies and may belong to a limited number of gene families with individuals modified post-synthesis. The proteins are made by a specialized group of cells located primarily some distance from the growing edge of the shell and appear to be assembled into sheets soon after secretion. Soluble anti-scalants and crosslinked insoluble water absorbents have been developed based on the structure and activity of the matrix proteins. These are primarily poly(aspartates) which can be made in large scale via thermal polycondensation of aspartic acid. The soluble forms are commercially used as biodegradable water treatment chemicals among other applications.
Learning From Biological Systems: Novel Routes to Biomimetic Synthesis of Ordered Silica Structures
Authors: Chal Jennifer N. , Shimizu Katsuhiko , Zhou Yan , Christiansen Sean C. , Chmelka Bradley F. , Deming Timothy J. , Stucky Galen D. , Morse Daniel E.
Published: April 2011

Biological systems have evolved mechanisms that precisely control inorganic structures on both the micro- and nanoscale, operating at ambient pressures and temperatures. In both the calcium carbonate, calcium phosphate and silicon dioxide utilizing organisms, proteins and polysaccharides have been found to play integral roles in the organization of these biominerals[1–3]. The organic constituents generally have been thought to act as direct templates or modulators for the deposition of the particular mineral. We have explored the synthesis and structural control of silica by the marine sponge, Tethya aurantia. Needles of amorphous silica comprise the skeletal system of this organism, representing 75% of the dry weight of the organism. These glassy needles, called spicules, are 2 mm in length and 30 μn in width[4,5]. We have characterized the structure, genetics and functions of the proteins that form an occluded axial filament within each silica spicule. Based on our discovery, a unique structure-directing catalytic mechanism exhibited by these protein filaments, and the structural determinants responsible for the catalytic activity, we have designed novel block copolypeptides that catalyze and spatially direct he condensation of silicon alkoxides to form organized silica structures ranging from transparent spheres to lath-like structures at ambient pressure, low temperature and neutral pH.
Removal Pathway of Bioactive Glass Resorption Products from the Body
Authors: Lai W. , Ducheyne P. , Garino J. , Flaitz C. M.
Published: April 2011

We traced and quantified the silicon released from bioactive glass (BG) granules in vivo (45S5, 300–355 μm). 1500 mg of BG granules were implanted in the paraspinal muscle of 7 four kg rabbits. Blood samples and 24-hour urine samples were obtained over a 24 week period. Local muscle tissue as well as the following organs were harvested for chemical and histological analyses: brain, heart, kidney, liver, lung, lymph nodes, spleen, and thymus. Flame atomic absorption spectrophotometry was used to measure the concentration of elemental silicon in all the samples after digestion. Tissues and fluids from a sham group of 7 rabbits (underwent surgical procedure but received no implants) were obtained in a similar manner.

The urinary silicon of the implanted group was significantly higher than in the control group. From the data, the calculated average excretion rate was approximately 2.4 mg/day, and as such, 100 percent of the implanted silicon was excreted in 19 weeks. No elevated concentrations of silicon were found at the implant site or in the other organs after 24 weeks. Histological appearance of all major organs was normal for all animals in the study.

The concentrations of silicon measured in the urine were well below saturation and since no significant increase in silicon was found in the kidney or in the other organs, the increased silicon excretion rate was within the physiological capacity of rabbits. Therefore, it can be concluded that the resorbed silica gel is harmlessly excreted in soluble form through the urine.
Investigation of the Transport Mechanism in Doped La-Based Manganite Thin Films by Traveling Wave Method
Authors: Wang L. , Huang S. , Yin J. , Huang X. , Xu J. , Liu Z. , Chen K.
Published: April 2011

The traveling wave (TW) method has been utilized to investigate the transport mechanism in paramagnetic-insulator state of La0.75Sr0.11Ca0.14MnO3 films. The drift mobility of the films increased from 2.5 × 10−2 cm2/Vs at 310 K to about 9.2 × 10−2 cm2/Vs at 400 K. The Arrhenius behaviors of the conductivity and drift mobility indicate that the transport process in manganites above the Curie temperature is dominated by the thermally assisted hopping of small polarons.
Properties of the Ferrimagnetic Double-Perovskites A2FeReO6 (A=Ba and Ca)
Authors: Prellier W. , Smolyaninova V. , Biswas A. , Galley C. , Greene R.L. , Ramesha K. , Gopalakrishnan J.
Published: April 2011

We have synthesized ceramics of A2FeReO6 double-perovskites A2FeReO6 (A=Ba, Ca). Structural characterizations indicate a cubic structure with a=8.0854(1) Å for Ba2FeReO6 and a distorted monoclinic symmetry with a=5.396(1) Å, b=5.522(1) Å, c=7.688(2) Å and β=90.4° for Ca2FeReO6. The barium compound is metallic from 5K to 385K, i.e. no metal-insulator transition has been seen up to 385K, and the calcium compound is semiconducting from 5K to 385K. Magnetization measurements show a ferrimagnetic behavior for both materials, with Tc =315 K for Ba2FeReO6 and above 385K for Ca2FeReO6. At 5K we observed, only for Ba2FeReO6, a negative magnetoresistance of 10% in a magnetic field of 5T. Electrical, magnetic and thermal properties are discussed and compared to those of the analogous compounds Sr2Fe(Mo,Re)O6 recently studied.
The Effects of Substrate-Induced Strains on the Charge-Ordering Transition in Nd0.5Sr0.5MnO3 Thin Films
Authors: Prellier W. , Biswas Amlan , Rajeswari M. , Venkatesan T. , Greene R.L.
Published: April 2011

We report the growth and characterization of Nd0.5Sr0.5MnO3 thin films deposited by the Pulsed Laser Deposition (PLD) technique on [100]-oriented LaAlO3 substrates. X-ray diffraction (XRD) studies show that the films are [101]-oriented, with a strained and quasi-relaxed component, the latter increasing with film thickness. A post-annealing under oxygen leads to a quasi-relaxed film with a metallic behavior. We also observe that transport properties are strongly dependent on the thickness of the films. Variable temperature XRD down to 100 K suggests that this is caused by substrate-induced strain on the films.
A-Site Ordered, Perovskite-Like Manganites Grown by PLD or Laser-MBE: Their Growth, Structural and Physical Characterization
Authors: Mercey B. , Haghiri-Gosnet A.M. , Lecoeur Ph. , Chippaux D. , Raveau B. , Salvador P.A.
Published: April 2011

Using both a “classical” pulsed laser deposition process and a laser-MBE process, superlattices in the Pr0.5Sr0.5MnO3 system were grown from PrMnO3 and SrMnO3 targets. A-site ordering of perovskite-like manganite was achieved using both deposition processes. However the electric and magnetic properties of the superlattices are shown to be strongly dependent on the growth process.
The Oxygen Mobility and Catalytic Activity of LaMO3±δ(M=Cr, Mn, Co) Phases
Authors: Koudriashov I.A. , Borovskikh L.V. , Mazo G.N. , Scheurell S. , Kemnitz E.
Published: April 2011

The activity of LaMO3, where M=Cr, Mn, Co, perovskite-type complex oxides in oxygen diffusion and catalytic processes was investigated. For sample preparation freeze-drying technique was used and dynamic thermal isotope exchange method was used to study exchange reaction between18O from the gas phase and16O from the samples synthesized, and to investigate the methane catalytic oxidation reaction. The results obtained allowed to indicate temperature intervals of different types of reaction taking place and that LaCrO3is far less active in mentioned reactions than LaCoO3and LaMnO3.
Growth and Magnetic Properties of La0.65Pb0.35MnO3 Films
Authors: Xu Q. L. , Liu M. T. , Liu Y. , Borca C. N. , Dulli H. , Dowben P. A. , Liou S. H.
Published: April 2011

We have successfully grown La0.65PbO.35MnO3 thin films by a RF magnetron sputtering method onto (100) LaAlO3 single crystal substrates. X-ray diffraction measurements are consistent with a (100) cubic orientation of the films. The fourfold symmetry showed by LEED(Low Energy Electron Diffraction) patterns indicate that the films have surface order. STM(Scanning Tunneling Microscopy) measurements indicate that the surface of the films were smooth, with approximate 5 nm roughness. XPS (X-ray Photoemission Spectroscopy) shows that the surface defect density in the films is comparatively low. The bulk magnetization of the films at 6K in 1 T magnetic field reached 77 emu/g and a Curie temperature near 354 K, close to maximum resistivity. A negative magnetoresistance of 47% was observed at 320K in 5.5 T magnetic field.
Magnetically Tuned Superconducting Filters
Authors: Oates D. E. , Anderson A. C. , Dionne G. F.
Published: April 2011

We have demonstrated magnetically tunable superconducting filters consisting of microwave circuits coupled to ferrite substrates in monolithic structures using both niobium at 4 K and YBCO at 77 K. A three-pole 1% bandwidth filter with 10-GHz center frequency, 1-dB insertion loss, and greater than 10% tunability has been demonstrated. Operation of the ferrite in the partially magnetized state prevents degradation of the surface resistance of the superconductor. This technology has the potential for compact, light weight, multipole filters with very low insertion loss, <0.5 dB, and very rapid tunability, <1 µs, due to the low inductance of the magnetic circuits. We also discuss the use of lightly coupled ferroelectric films to introduce trimming of the individual resonators in the magnetically tuned filters. The materials issues that limit performance and means to improve present performance are discussed.
Frequency Agile Microwave Applications Using (Ba,Sr)TiO3/Y3Fe5O12 Multilayer Grown by Pulsed Laser Deposition
Authors: Kim W.J. , Chang W. , Qadri S.B. , Wu H.D. , Pond J.M. , Kirchoefer S.W. , Newman H.S. , Chrisey D.B. , Horwitz J.S.
Published: April 2011

(Ba,Sr)TiO3 (BST) thin films have been deposited by pulsed laser deposition (PLD) onto single crystal Y3Fe5O12 (YIG) substrates with/without an MgO buffer layer. The structure and microwave properties of BST films have been investigated as function of substrate orientation and O2 deposition pressures (5-800m Torr). The orientation of BST film is varies with the deposition conditions. The dielectric constant, loss tangent, and change in dielectric constant with an applied electric field have been measured at room temperature using interdigitated capacitors at 0.1 – 20 GHz. Polycrystalline BST films have a high tunability (∼40%) with a dc bias field of 67kV/cm and a dielectric Q (=l/tanδ) between 30 and 40, while (001) oriented BST films have a lower tunability (∼20%) but higher dielectric Q (∼50). A coplanar waveguide transmission line was fabricated from a (001) oriented BST film on (111)YIG which exhibited a 17° differential phase shift with an applied dc bias of 21 kV/cm. An equivalent differential phase shift was achieved with a magnetic field of 160Guass.
Effect of the Oxygen Partial Pressure on the Microstructure and Properties of Barium Strontium Titanate Thin Films Synthesized by Pulsed Laser Deposition
Authors: Fountzoulas C.G. , Hubbard C. W. , Ngo Eric H. , Kleinmeyer J. D. , Demaree J. D. , Joshi P. C. , Cole M. W.
Published: April 2011

Barium strontium titanate (BSTO) films were synthesized by the pulsed laser deposition technique (PLD) on silicon substrates at room temperature. The BSTO film synthesis took place at constant laser energy, 500 mJ, and partial oxygen pressure of 3, 15, 30, 45, 100 mTorr. All films were post annealed at 750 °C in a tube furnace in an oxygen atmosphere. The microstructure, crystallinity and lattice constant of the BSTO films were studied with the aid of scanning electron microscopy (SEM), photon tunneling microscopy (PTM) and Glancing Angle X-ray Diffraction analysis (GAXRD). The hardness and modulus of elasticity of the films were studied with the aid of a nanohardness indenter. The film stoichiometry was determined with the aid of Rutherford Back Scattering (RBS). The results of this research will be combined with the results of our previous work [1] on the effect of substrate temperature on the microstructure and mechanical properties of the BSTO films in order to construct a structural zone model (SZM) of the BSTO films synthesized by PLD.
Nanocrystalline Thin Films for Tunable High Q UHF/VHF Devices
Authors: Win Winston N. , Park Jin-Young , Walser Rodger M.
Published: April 2011

Recent studies indicate that reactively sputtered FeCrTaN nanocrystalline thin films have many of the properties [large magnetization (4πMs), anisotropy (Han), and resistivity (ρ)] required for application in high Q (>1000), magnetically tunable devices operating in the VHF/UHF (∼50 MHz to 500 MHz) frequency range. These films had thickness (d) of ∼0.1 -µm, but film thickness of ∼1-µm may be required for many devices. Although most previous research has shown that the magnetic properties of sputtered films are significantly deteriorated when d∼1-µm, there are recent reports that those of reactively sputtered nanocrystalline films of similar alloys (FeTaN, CoAl/SiO) are independent of thickness to d≈1-2-µm. Accordingly, this work investigated the possibility of reactively sputtering FeCrTa alloys in O/N gas mixtures to obtain films with device quality properties, that are independent of thickness to 1-2µm. The correlations between their magnetic and electrical properties, and their nano-heterogeneous microstructure, were studied to determine optimum reactive gas mixtures and sputtering parameters. Cross-section TEM studies were conducted to investigate the origins of the thickness independent properties, and the unexpected increases in anisotropy.
Broadband Determination of Microwave Permittivity and Loss in Tunable Dielectric Thin Film Materials
Authors: Booth James C. , Vale Leila R. , Ono Ronald H.
Published: April 2011

We demonstrate a new method for determining the frequency-dependent dielectric properties of thin-film materials at microwave frequencies using coplanar waveguide (CPW) transmission line measurements. The technique makes use of the complex propagation constant determined from multiline thru-reflect-line (TRL) calibrations for CPW transmission lines to determine the distributed capacitance and conductance per unit length. By analyzing data from CPW transmission lines of different geometries, we are able to determine the complex permittivity of the dielectric thin film under study as a function of frequency from 1 to 40 GHz. By performing these measurements under an applied bias voltage, we are able in addition to determine the tuning and figure of merit that are of interest for voltage-tunable dielectric materials over the frequency range 1 to 26.5 GHz. We demonstrate this technique with measurements of the permittivity, loss tangent, tuning, and figure of merit for a 0.4 µm film of Ba0.5Sr0.5TiO3 at room temperature.
What Does Self-Diffusion Tell Us about Ultra Shallow Junctions?
Authors: Ural Ant , Koh Serene , Griffin P. B. , Plummer J. D.
Published: April 2011

Understanding the coupling between native point defects and dopants at high concentrations in silicon will be key to ultra shallow junction formation in silicon technology. Other effects, such as transient enhanced diffusion (TED) will become less important. In this paper, we first describe how thermodynamic properties of the two native point defects in silicon, namely vacancies and self-interstitials, have been obtained by studying self-diffusion in isotopically enriched structures. We then discuss what this tells us about dopant diffusion. In particular, we show that the diffusion of high concentration shallow dopant profiles is determined by the competition between the flux of mobile dopants and those of the native point defects. These fluxes are proportional to the interstitial or vacancy components of dopant and self-diffusion, respectively. This is why understanding the microscopic mechanisms of silicon self-diffusion is important in predicting and modeling the diffusion of ultra shallow dopant profiles. As an example, we show experimental data and simulation fits of how these coupling effects play a role in the annealing of shallow BF2 ion implantation profiles. We conclude that relatively low temperature furnace cycles following high temperature rapid thermal anneals (RTA) have a significant effect on the minimum junction depth that can be achieved.
Ion Implantation Effect on Dislocation Propagation in Pseudomorphically Strained P/P+ Silicon
Authors: Feichtinger Petra , Poust Ben , Fukuto Hiroaki , Sandhu Rajinder , Goorsky Mark S. , Oster Dwain , Rickborn Steve F. , Moreland Jim
Published: April 2011

We studied damage evolution and the influence on defect interactions as a function of Si self implantation dose in p/p+ silicon wafers. Highly boron doped 150 mm diameter silicon substrate wafers with a 2.5 μm thick nominally un-doped epitaxial layer (p/p+) were employed. Due to the misfit strain, misfit dislocations formed during the epitaxial growth process around the wafer edges. This localized dislocation distribution was utilized to study the role of the implant on both the nucleation and growth of the misfit dislocation segments. Triple axis x-ray diffraction was used to determine changes to the strain in the layer due to both the implant and to subsequent annealing. Double axis x-ray topography combined with rapid thermal annealing was used to measure the nucleation and extension of the misfit dislocation segments after annealing. For the lower implantation dose (1012 cm−2) samples, the velocity of dislocations was reduced measurably and the density of newly formed misfit dislocations also decreased significantly relative to regions that received no ion implantation. A higher implantation dose reduced the nucleation and glide velocity further such that neither glide nor nucleation of new segments was detected. SIMS measurements confirmed that the interfacial lattice parameter grading was not appreciably different after an anneal step for the lower implant dose sample, but was measurable for the higher dose sample. In the latter case, transient point defect enhanced diffusion of boron was responsible for the grading. However, the lack of grading in the low dose sample indicates that interfacial grading did not significantly impede dislocation kinetics. This comparison indicates that it is the excess point defects that are produced during implantation that retard both the nucleation and extension of misfit dislocation segments.
The Impact of Point Defects on Stress-Induced Dislocation Generation in Silicon
Authors: Loiko Konstantin V. , Nallapati Giri , Jarreau Keith M. , Ekbote Shashank S. , Hensley Roy A. , Simpson Dale , Harrington Thomas E. , Frensley William R. , Peidous Igor V.
Published: April 2011

Factors responsible for the onset of dislocation generation in the fields of localized high stresses have been studied in LOCOS-isolated test structures by means of preferential etching, junction leakage analysis, and computer simulation. A strong correlation between densities of stacking faults and dislocations was observed in the experiments. Defect distributions also correlated to leakage currents. 2D simulations of stresses, interstitial injection, and stacking fault growth during field oxidation showed that maximum resolved shear stress in the structures did not exceed the critical level for dislocation generation and that the agglomeration of silicon interstitial atoms did not play a notable role in dislocation nucleation. Dislocation and stacking fault formation was attributed to surface mechanical damage introduced during plasma processing.
Phosphorus / Silicon Interstitial Annealing After Ion Implantation
Authors: Keys P. H. , Brindos R. , Krishnamoorthy V. , Puga-Lambers M. , Jones K. S. , Law M. E.
Published: April 2011

The release of interstitials from extended defects after ion implantation acts as a driving force behind transient enhanced diffusion (TED). Implantation of Si+ ions into regions of phosphorus-doped silicon provides experimental insight into the interaction of silicon interstitials and dopant atoms during primary damage annealing. The presence of phosphorus influences the morphology of secondary defects during initial nucleation. Transmission electron microscopy (TEM) is used to differentiate between defect types and quantify the interstitials trapped in extended defects. This analysis reveals that phosphorus results in a reduction of interstitials trapped in observable extended defects. The interstitial flux released from the implanted region is also affected by the phosphorus doping. This phenomenon is closely studied using secondary ion mass spectrometry (SIMS) to monitor diffusion enhancements of dopant layers. Shifts in diffused dopant profiles are correlated with the different morphologies of the extended defects and the decay of the silicon interstitial supersaturation. This correlation is used to understand the interaction of excess silicon interstitials with phosphorus atoms.
Molybdenum as a Gate Electrode for Deep Sub-Micron CMOS Technology
Authors: Ranade Pushkar , Yeo Yee-Chia , Lu Qiang , Takeuchi Hideki , King Tsu-Jae , Hu Chenming
Published: April 2011

Molybdenum has several properties that make it attractive as a CMOS gate electrode material. The high melting point (∼2610°C) and low coefficient of thermal expansion (5×10−6/°C, at 20 °C) are well suited to withstand the thermal processing budgets normally encountered in a CMOS fabrication process. Mo is among the most conductive refractory metals and provides a significant reduction in gate resistance as compared with doped polysilicon. Mo is also stable in contact with SiO2 at elevated temperatures. In order to minimize short-channel effects in bulk CMOS devices, the gate electrodes must have work functions that correspond to Ec (NMOS) and Ev (PMOS) in Si. This would normally require the use of two metals with work functions differing by about 1V on the same wafer and introduce complexities associated with selective deposition and/or etching. In this paper, the dependence of the work function of Mo on deposition and annealing conditions is investigated. Preliminary results indicate that the work function of Mo can be varied over the range of 4.0-5.0V by a combination of suitable post-deposition implantation and annealing schemes. Mo is thus a promising candidate to replace polysilicon gates in deep sub-micron CMOS technology. Processing sequences which might allow the work function of Mo to be stabilized on either end of the Si energy band gap are explored.
Investigation on C54 nucleation and growth by micro-Raman imaging
Authors: Privitera Stefania , Meinardi Francesco , Quilici Simona , Via Francesco La , Spinella Corrado , Grimaldi Maria Grazia , Rimini Emanuele
Published: April 2011

The processes of nucleation and growth of the C54 TiSi2 phase into the C49 phase in thin films have been studied by electrical measurements and micro-Raman spectroscopy. The Raman spectra have been acquired scanning large silicide areas (100×50 μm2) in step of 0.5 μm. Images showing the evolution of the C54 grains during the transition have been obtained for temperatures between 680 and 720 °C and the transformed fraction, the density and the size distribution of the C54 grains have been measured as a function of the temperature and the annealing time. The activation energies for the nucleation rate and the growth velocity have been determined obtaining values of 4.9 ± 0.7 eV and 4.5 ± 0.9 eV, respectively.
Performance of Polishing Slurries containing Silica Particles grown by Sol-Gel Method
Authors: Bae Sun Hyuk , So Jae-Hyun , Yang Seung-Man , Kim Do Hyun
Published: April 2011

Silica slurry used as abrasives in wafer polishing process is made by dispersing silica particles in an alkali solution. Since commercially available colloidal or fumed silica particles need some modifications to be directly used as abrasive slurry due to their small sizes, irregular shapes or broad size distribution, we have prepared silica abrasives by particle growth of fumed silica or colloidal silica as seeds by sol-gel method. Silica slurries prepared by this step-wise growth from commercial seeds were tested using one-armed polisher for the comparison with commercial slurries and showed the performance comparable to commercial slurries. Microstructures of polishing slurries were investigated using transmission electron microscopy and ARES rheometer. From the result, stability of the slurry was found to be more important than the primary particle sizes for the polishing performance.
Superparamagnetic Behavior of Granular Co-C Films Consisting of Nanocrystalline Cobalt Encapsulated in Carbon
Authors: Wang Hao , Wong S.P. , Cheung W.Y. , Ke N. , Chiah M.F. , Wen G.H. , Zhang X.X.
Published: April 2011

Nanocomposite Co-C thin films of about 15 nm thick were prepared by pulsed filtered vacuum arc deposition. The films were characterized by x-ray photoelectron spectroscopy, non-Rutherford backscattering spectrometry, x-ray diffraction, magnetic force microscopy and magnetic measurements. The as-deposited films were amorphous. After annealing at 350°C for one hour in vacuum (< 10−3 Pa), the films were found to consist of nanocrystalline Co grains encapsulated in carbon. The superparamagnetism of the annealed Co36C64 film was demonstrated by the measurement of DC susceptibility and magnetic hysteresis using a SQUID magnetometer. The superparamagnetic relaxation blocking temperature was marked to be about 12K by the peak of the zero-field-cooled magnetization under a field of 100 Oe. The magnetic properties of these annealed granular Co-C films transform from superparamagnetism to ferromagnetism when the Co concentration increases.
Manufacturability of Gmr Heads: 10Gb/in2 and Beyond
Authors: Sahu S. , Chen Jian , Talghader V. , Cool S. , Mao S.
Published: April 2011

Consistency of spin-valve stack deposition, both wafer-to-wafer and within a wafer, is key to the manufacturability of GMR heads. For typical GMR heads, film thicknesses are now in the range of 5Å-150Å and process control is becoming a challenge.

This paper discusses the importance of characterizing the thickness and uniformity of each material in the spin-valve stack within the context of single layer sheet films. For this study, single layer sheet films and full multilayer spin-valve stacks were deposited in a multi-target cluster tool. The sheet resistance and thickness of the single layer sheet films were measured using a 4-point probe and ellipsometry, respectively. Results were then correlated to the sheet resistance and magnetic performance (i.e., GMR ratio, exchange field, and magneto-static coupling field) of the full spin-valve stacks with a synthetic antiferromagnet as the pinned layer. The 1σ < 2% uniformity, wafer-to-wafer and within wafer, realized for the full stacks is a strong indicator of a manufacturable process.

Model calculations of the sheet resistance and GMR were carried out to provide theoretical understanding of the film thickness dependence. The calculated results are well correlated with the experimental measurements. The model is based on band structures and implicitly includes the momentum-dependent reflection and transmission coefficients at the interfaces.

Results from both experiments and calculations show that process control and repeatability (both within a wafer and from wafer to wafer) are crucial to the spin-valve manufacturability, offering a critical challenge to the disc drive industry as it heads into the next generation of GMR heads.
Residual Stresses and Magnetoelastic Coupling in Ultrathin Fe Films Deposited on GaAs(001)
Authors: Gergaud P. , Lallaizon C. , Putero M. , Lépine B. , Thomas O. , Guivarc'h A.
Published: April 2011

The growing interest in the behavior of magnetic thin films on semiconductor substrates is due in part to their potential application in spin-sensitive heterostructure devices. High-quality epitaxial Fe(001) thin films can be grown on GaAs(001) substrates because of the small lattice parameter mismatch (−1.4%). Magnetic measurements performed on Fe films thinner than 3 nm have shown that such films exhibit an in-plane uniaxial magnetic anisotropy although an ideal bcc Fe(001) film should have fourfold symmetry. The source of this uniaxial component remains an open question and one of the mechanisms which may contribute to this is the epitaxial strain, through magnetoelastic coupling. Very small strains anisotropies are able to modify the magnetic anisotropy of iron thin films. Moreover the sign and magnitude of the magnetoelastic coupling seem to depend on the film thickness or film strain [1]. In this study, the strain tensor components in two Fe thin films (1.7 and 3.0 nm thick) has been measured by XRD. The magnetic free energy has been derived, using the strain tensor components.
Work Function Study of Polycrystalline Metals using a UHV Scanning Kelvin Probe
Authors: Petermann U. , Baikie I.D. , Lägel B. , Dirscherl K.M.
Published: April 2011

We have undertaken a study of high work function (φ) surfaces as part of an ongoing project searching for efficient target materials for use in Hyperthermal Surface Ionisation (HSI), a new mass spectroscopy ionisation technique. HSI relies on high work function surfaces for the production of positive ions. Polycrystalline metals as Re, W, Mo and Pt are particularly interesting materials in this respect as oxidation substantially increases their φ. We present and discuss the following experimental evidence: a) the magnitude and sign of φ changes in terms of adsorbate induced dipoles, b) the effect of molecular hydrogen exposure on the clean surface, and c) the effect of subsequent oxygen exposure.

Using a novel UHV Scanning Kelvin Probe we have followed the oxidation kinetics of polycrystalline metals at different temperatures and examined the effects of oxidation, flash annealing and sputter-anneal cleaning cycles via high-resolution φ topographies. Our results indicate in particular Re as a suitable HSI target material exhibiting a φ increase of 1050 meV at 300 K increasing to 2050 meV at 900 K. Sputter-cleaned surfaces exhibit a dramatic change in the second oxidation phase.

We have also examined φ changes associated with N2O and CO2 on Tungsten and Molybdenum. We observe that atomic oxygen gives similar results to O2 but has a much lower initial sticking coefficient. We report that CO2 actually lowers the φ for substrate temperatures under 650 K, the peak work function changes occurs at 850 K and is approximately 1/3 the height of the O2 or O peak.
Observation of Long-Range Orientational Ordering in Metal Films Evaporated at Oblique Incidence onto Glass
Authors: Everitt David L. , Zhu X. D. , Miller William J. , Abbott Nicholas L.
Published: April 2011

We studied long-range orientational ordering in polycrystalline Au films (10 nm - 30 nm) that are evaporated at oblique incidence onto a glass substrate at room temperature. By measuring the averaged optical second-harmonic response from the films over a 6-mm diameter region, we observed a transition from the expected in-plane mirror symmetry at 10 nm to a surprising three-fold in-plane rotational symmetry at 30 nm. X-ray pole figure analysis performed on these films showed the strong <111> fiber texture typical of fcc films, but with a restricted, three-fold symmetric, distribution of crystallite orientations about the fiber axis.
Alignment of InAs Quantum Dots on GaAs Using the Manipulation of Strain Fields
Authors: Kim Kwang Moo , Park Young Ju , Park Young Min , Nah Jong Bum , Hyon Chan Kyeong , Kim Eun Kyu , Park Jung Ho
Published: April 2011

We fabricated InAs self-assembled quantum dots (QDs) on strained layer using molecular beam epitaxy. The strained layer consisted of InAs/GaAs superlattice(SL) and GaAs barrier layer on (001) GaAs substrate. Through controlling thickness of the strained layer, we formed two-dimensional alignments of QDs on misfit dislocation arrays along <110> directions made by strained layer. The increase of the strained layer thickness resulted in a stronger alignment of QDs, which were observed by atomic force microscopy studies. The aligned QDs were confirmed to confine carriers well and have different size distributions by photoluminescence measurement.
On Kinetically vs. Energetically Driven Growth Instabilities in Solid and Vapor Phase Epitaxy
Authors: Aziz Michael J.
Published: April 2011

A stress-induced kinetically-driven morphological instability is of general applicability to driven systems. The effect of stress on the reaction mobility for incorporation into the growing solid couples to stress variations along a perturbed planar growth front, resulting in amplification or decay of the perturbation depending on the sign of the stress. Experimentally we studied a model system in which stress is applied externally to a chemically pure substance, permitting us to isolate the effect of strain from any possible effects of composition, and found that the new kinetically-driven effect dominates the behavior for solid phase epitaxial growth (SPEG) of Si(001). A linear stability analysis of a sinusoidally perturbed planar growth front, incorporating both the kinetically and the energetically driven effects, has been performed. Stability maps are developed, indicating parameter ranges under which the morphological evolution is dominated by the energetically-driven instability, the kinetically-driven instability, and the kinetically-driven stabilization. Numerical values of the key dimensionless parameters for SPEG and for SiGe/Si(001) Molecular Beam Epitaxy (MBE) are very similar in cases where they are known, indicating that the kinetically-driven effect may be important in determining morphological evolution related to quantum dot formation in MBE as well
Structure and Optical Properties of Si/InAs/Si Layers Grown by MBE on Si Substrate at Different Temperatures
Authors: Zakharov N.D. , Werner P. , Gösele U. , Heitz R. , Bimberg D. , Ledentsov N.N. , Ustinov V.M. , Volovik B.V. , Alferov ZH.I. , Polyakov N.K. , Petrov V.N. , Egorov V.A. , Cirlin G.E.
Published: April 2011

Epitaxial Si/InAs/Si heterostructure grown on (001) Si substrate by molecular beam epitaxy (MBE) and annealed at 800°C, and 880°C were investigated by High Resolution Transmission Electron Microscopy (HRTEM). Extensive interdiffusion at 800°C leads to the formation of an InAs solid solution as well as InAs-enriched regions with extensions of ∼6nm, which exhibit two kinds of ordering. The ordering of InAs molecules occurred, respectively, in {110} planes inclined and parallel to the [001] growth direction. It is attributed to the energy gain from the reduced number of mixed Si-As and Si-In bonds. The sample grown at 800°C shows photoluminescence in the 1.3.µm region, which is tentatively attributed to the recombination of excitons localised in the ordered regions
Metalorganic Molecular Beam Epitaxy of Magnesium Oxide on Silicon
Authors: Niu F. , Hoerman B.H. , Wessels B.W.
Published: April 2011

Epitaxial cubic MgO thin films were deposited on single crystal Si (001) substrates by metalorganic molecular beam epitaxy (MOMBE) using the solid precursor magnesium acetylacetonate as the source and an RF excited oxygen plasma as the oxidant. The growth process involved initial formation of an epitaxial β-SiC interlayer followed by direct deposition of a MgO overlayer. The film structure was characterized by X-ray diffraction as well as conventional and high-resolution transmission electron microscopy. Both the MgO overlayer and β-SiC interlayer had an epitaxial relationship such that MgO (001) (or SiC (001)) // Si (001) and MgO [110] (or SiC [110])// Si [110]. No evidence of an amorphous layer was observed at either the MgO/SiC or SiC/Si interface. Dielectric properties of the epitaxial MgO thin films on Si (001) were evaluated from capacitance-voltage (C-V) characteristic of metal-oxide-semiconductor (MOS) structures. The C-V measurements indicated an interface trap density at midgap as low as 1011 to 1012 cm−2 eV−1 and fixed oxide charge of the order of 1011/ cm2, respectively. These results indicate that epitaxial MgO deposited by MOMBE has potential as a gate insulator.
Real Time Observations of Dislocation-Mediated Plasticity in the Epitaxial AI (011)/Si(100) Thin Film System
Authors: Stach Eric A. , Dahmen U. , Nix W.D.
Published: April 2011

Despite numerous theoretical and experimental studies of strain relaxation in metal films on silicon substrates, the exact mechanisms by which dislocations mediate plasticity in these structures are not well understood. To elucidate these mechanisms, we present results from in-situ transmission electron microscopy annealing of thin aluminum films grown on Si (100). As a model system, we have chosen to focus on aluminum films which contain two (011) epitaxial variants with respect to the silicon substrate. In this paper we discuss our observations of the glide and climb behavior of dislocations in these structures during thermal cycling. These observations give qualitative insight into the mechanisms by which dislocation motion accommodates thermally induced strains in thin metal films.
Thickness Dependent Tetragonal Relaxation of Iron in Epitaxial Fe/Pd Multilayer Films
Authors: Steffl T. , Rellinghaus B. , Mühlbauer H. , Müller CH. , Herper H. , Dumpich G.
Published: April 2011

We have prepared (Fe(001)/Pd(001)) multilayers onto Pd-buffered sapphire substrates. Structural investigations utilizing HRTEM, RHEED and XRD show that the films grow epitaxially for up to 32 bilayers. Whereas the Fe lattice is found to assume the lateral (in-plane) lattice spacing of the underlying Pd layers, the out-of-plane lattice parameter along the [001] growth direction of the film is successively reduced with increasing Fe layer thickness. This outof-plane lattice relaxation even survives a subsequent growth of Pd onto the Fe. Thus, by varying the Fe layer thickness we have control of the atomic volume of Fe. Magnetization measurements reveal that the magnetic moment of Fe is as high as 2.7 µB per atom when the atomic volume is larger than Vat(Fe) ≥ 11.7 Å3 and is reduced to 2.2 µB per atom for Vat(Fe) ≤ 11.1 Å3.
Insulator/GaN Heterostructures of Low Interfacial Density of States
Authors: Hong M. , Ng H. M. , Kwo J. , Kortan A. R. , Baillargeon J. N. , Anselm K. A. , Mannaerts J. P. , Cho A. Y. , Lee C. M. , Chyi J. I. , Lay T. S. , Ren F. , Abernathy C. R. , Pearton S. J.
Published: April 2011

A review is given on insulators (oxides and nitrides) which have been deposited on GaN to form metal-insulator (oxides and nitrides)-semiconductor (MOS or MIS) diodes with a low interfacial density of states (Dit). These insulators include AlN, SiO2, Si3N4, SiO2/Ga2O3, and Ga2O3(Gd2O3). Techniques for depositing these insulators and methods for cleaning GaN surfaces prior to the insulator deposition are discussed. Recent progress on GaN MOSFET's (with SiO2/Ga2O3, and Ga2O3(Gd2O3) as gate dielectrics) and MISFET's (with AlN as a gate dielectric) is also reviewed. When exposed to room air, GaN surface is not as robust as previously thought. Therefore, preparation of a clean GaN surface for deposition of oxides and nitrides is necessary to achieve a low Dit. By heating GaN samples in UHV to clean the surfaces followed by deposition of Ga2O3(Gd2O3) and SiO2, we have achieved a low Ditwith negligible hysteretic loops in the capacitance-voltage curves
Present Status of III-Nitride Based Photodetectors
Authors: Monroy Eva , Calle Fernando , Pau José Luis , Muñoz Elías , Omnès Franck , Beaumont Bernard , Gibart Pierre
Published: April 2011

This paper describes the characteristics of a variety of AlGaN-based photodetectors (photoconductors, metal-semiconductor-metal photodiodes, Schottky photodiodes and p-i-n photodiodes), grown on sapphire by metalorganic vapor phase epitaxy. The features that determine their performance are analyzed. Results using other substrates (epitaxial lateral overgrown GaN, Si) are also presented.
Effect of Interface Manipulation for MBE Growth of AlN on 6H-SiC
Authors: Naniwae Koichi , Hartman Jeff , Petrich Chris , Davis Robert F. , Nemanich Robert J.
Published: April 2011

AlN layers were grown on 6H-SiC(0001) by molecular beam epitaxy using ammonia as the nitrogen source. Clean (√3×√3)R30° SiC surfaces was prepared by in-situ annealing alone and also by in situ annealing consisted of followed by Si deposition and subsequent annealing. The surface morphology of the AlN films observed by AFM was significantly changed by the nucleation procedure. When the AlN growth was initiated with Al flux exposure on a SiC surface prepared by thermal annealing, the surface roughness of the AlN was significantly reduced. Two-dimensional growth of AlN was observed with reflection high-energy electron diffraction from the very beginning. Atomically flat AlN surfaces with a RMS-roughness of ∼0.3 nm were obtained. On the other hand, when film growth was initiated with an ammonia flux exposure on a Si rich SiC surface, a high density of bumps was observed. The bumps seemed to originate from SiNx formation at the heteroepitaxial interface. It was found that control of the Si composition and the V/III ratio at the growth interface is crucial for the AlN film quality.
Arsenic Incorporation in Gallium Nitride grown by Metalorganic Chemical Vapor Deposition using Dimethylhydrazine and Tertiarybutylarsenic
Authors: Kellermann S. , Yu K. M. , Haller E. E. , Bourret-Courchesne E. D.
Published: April 2011

MOCVD growth of As-doped GaN using dimethylhydrazine, triethylgallium and tertiarybutylarsenic has been investigated. A maximum doping concentration of 4.0 × 1019cm−3 at growth temperatures between 600°C and 800°C was obtained. At 1000°C the As doping level dropped below the SIMS detection limit of ∼1.0 × 1017cm−3. The As incorporation depended only weakly on variations of the V/III molar flow ratio between 11 and 61. Raising the As/V molar flow ratio from 0.01 to 0.06 increased the As concentration which then decreased by further increase to 0.11. Different morphologies of the layers were found depending on the growth conditions. A surfactant-like behavior of As was observed leading to smooth GaN films grown on top of the As-doped GaN layer. Two characteristic luminescence peaks at 3.31 eV and 3.425 eV were found for samples doped with As below 900°C. These spectral features are believed to originate at extended lateral defects - presumably stacking faults.