bluuebunny/crossref_metadata_2025 huggingface dataset:
Osteointegration of Calcium Phosphate Ceramics in Humans And Animals
Authors: Frayssinet Patrick , Schwartz Claude , Mathona Didier , Rouquet Nicole
Published: April 2011

Calcium phosphate ceramics are bioactive, osteoconductive materials used as guides for bone regeneration. We were able to carry out a histological study of ceramics implanted in large mammals and humans. An identical sequence of events apparently occurred at the contact of the ceramics. The osteoblasts differentiated preferentially in close proximity to the ceramic surface in animals. The early stage lasted longer in humans and was characterized by the presence of a monolayer of multinucleated cells containing TRAP+ (tartrate resistant acid phosphatase activity) granules at the surface of the ceramic. The loose connective tissue invading the pores contained almost exclusively fibroblast-like cells with TRAP+ nucleus. Differentiation of the osteogenic cells around the ceramic is diffuse in humans and not always related to the material surface. Ceramics become embedded in immature bone both in humans and animals. The immature bone and the ceramics are then remodeled and progressively replaced by layered bone. The degradation of the ceramic occurs preferentially at the grain boundaries and the grains released are phagocytosed by the macrophages when below a critical size and degraded in the low pH compartments of the cell. In conclusion: the integration of calcium phosphate ceramics is comparable in animals and man. Although in the cases studied the ceramics were unable to induce osteogenic differentiation, they did favor the differentiation of pre-determined osteogenic cells.
Bioactive Hydroxyapatite-Polysulfone Composite for Tissue Replacement
Authors: Chua B , Wang M
Published: April 2011

A new composite material consisting of hydroxyapatite (HA) and polysulfone (PSU) was produced and evaluated for potential medical applications. The HA/PSU composite containing up to 40vol% of particulate HA was manufactured via a standardised procedure which included drying, compounding, and injection or compression moulding. Defect-free composite samples (bars, discs and dumbbell specimens) could be obtained by injection moulding. Thick composite plates suitable for making fatigue specimens were compression moulded. Both compounded materials and moulded parts were assessed using various techniques. It was found that HA particles were well dispersed in the PSU matrix. Thermogravimetric analysis verified the amount of HA in the composite. Density close to the theoretical value could be achieved for the composite, indicating a void-free structure. Differential scanning calorimetry results indicated that the glass transition temperature of the polymer matrix was not significantly affected by the incorporation of HA. Rheological analysis revealed that PSU and the composite exhibited pseudoplastic flow behaviour at processing temperatures. It was shown that the hardness and modulus of the composite were increased with an increase in HA volume percentage.
Preparation of Hydroxyapatite/Collagen Composites Using Biomimetic Process and their Biocompatibility
Authors: Kikuchi Masanori , Tanaka Junzo , ltoh Soichiro , lchinose Shizuko , Koyama Yoshihisa , Takakuda Kazuo , Nagaoka Katsuyoshi , Tanaka Shigeo
Published: April 2011

Nanocomposites of hydroxyapatite (HAp) and collagen (Col) were prepared by a biomimetic coprecipitation method under controlled pH and temperature. Transmission electron micrographs showed that the c-axis of HAp nanocrystals aligned along collagen by a self- rganization mechanism; a very similar alignment to bone's structure was found in the sample prepared at nearbiological conditions, i.e. pH8–9 and 40'C, which consisted of fibers with length of 20μm. From the material scientific point of view, therefore, osteoblasts may control the chemical condition in a small area around the cells to pH 8–9 as well as supply raw materials of bone, hydroxyapaite and collagen, at the initial state of osteogenesis. The biocompatibility of the composites was examined by animal tests using beagles. The composites were absorbed and new bone was formed as rapidly as a bone remodeling process. The HAp/Col composites prepared by biomimetic process were expected to be applicable as filler materials changing to new bone instead of autograft.
Fabrication and Characterization of Calcium Phosphate / Porous Silicon / Silicon Structures Doped with Platinum Antitumor Compounds
Authors: Coffer Jeffery L. , Li Xin , John John St. , Pinizzotto Russell F. , Chen Yandong , Newey Jon , Canham Leigh T.
Published: April 2011

A process has been developed which permits the encapsulation of an established class of platinum anticancer drugs such as cis-Platin (cis-diammine-dichloroplatinum (II)) within synthetic biocompatible calcium phosphate films that are electrochemically-grown on porous Si/Si substrates. These platinum complex-doped hydroxyapatite / porous Si / Si materials have been characterized by scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (XEDS), and secondary ion mass spectrometry (SIMS). Upon immersion of these structures into aqueous media, the desired platinum species can be released into the surrounding environment. This study also focuses on the influence of initial platinum concentration for a given complex in the deposition process on the rate and resultant amount of platinum complex that can be delivered to the surroundings in vitro. Both inductively-coupled plasma (ICP) spectroscopy and uv-visible absorption spectrometry have been employed to monitor the release of the encapsulated drug from the calcium phosphate layers.
Atomic Displacement Parameters of Carbonate Apatites from Powder Neutron Diffraction Data
Authors: Leventouri Th. , Moghaddam H. Y. , Papanearchou N. , Bunaciu C. E. , Levinson R. L. , Martinez O.
Published: April 2011

We present a comparison between detailed structural parameters of a low temperature synthetic carbonate hydroxyapatite, a hydroxyapatite, and a natural carbonate fluorapatite from Rietveld refinements of neutron powder diffraction data. The observed modifications in the crystallographic parameters of the synthetic carbonate apatite are consistent with the carbonate substitution on the mirror plane of the tetrahedral site as in the case of the natural carbonate apatite.
Nano-Mechanical Properties Across Dentin-Enamel Junction of Adult Human Incisors
Authors: Fong H. , Sarikaya M. , White S. N , Snead M. L.
Published: April 2011

The structure and mechanical properties of the dentin-enamel junction (DEJ) in human teeth play a critical role in transferring stress from hard enamel to soft dentin efficiently in order to preserve the longevity of this functionally gradient biocomposite. In this investigation, nano-hardness and elastic modulus of incisor teeth were studied across the dentin-enamel junction. It was found that, over a length scale of between 15 to 25 μm, there were decreasing trends in the values of both hardness and elastic modulus across the DEJ zone profiling from enamel to dentin. Images obtained, using atomic force and scanning electron microscopy techniques, from polished surfaces of cross-sectioned teeth samples showed an interpenetrating microstructure of enamel and dentin at the DEJ zone. These results suggest that the nano-mechanical property profiles across the DEJ were due to a continuous variation in the relative amount of enamel and dentin. These characteristics of the DEJ zone could be significant for describing the structural and mechanical coupling of the two structures. By increasing the interfacial contact area across the two mineralized tissues, stresses are dissipated into the softer dentin, thus reducing interfacial stress concentrations at the DEJ. This promotes effective load transfer from the hard enamel to soft dentin.
Tem Observance and Analysis of the (000l), l=2n+l, Forbidden Reflections in Synthetic and Biological Hydroxyapatites
Authors: Reyes-Gasga J. , Reyes-Reyes M. , García-García R.
Published: April 2011

The systematic appearance of (000l), l=2n+1, forbidden reflections in the electron diffraction patterns of hydroxyapatite, both synthetic and natural (human tooth enamel), is discussed. Structural disorder, double diffraction, and modulated structures and are discussed as possible causes. Structural disorder and modulated structure could be responsible for the rupture of the reported symmetry, in which oxygen and hydrogen perform an important role.
Lattice Distortions and Domain Structure in Epitaxial Manganite Thin Films
Authors: Suzuki Y. , Wu Yan , Rüdiger U. , Yu J. , Kent A.D. , Nath T.K. , Eom C.B.
Published: April 2011

Lattice distortions, be they in the form of chemical and hydrostatic pressure in bulk or lattice mismatch between film and substrate, have significant effects on the transport as well as the magnetic properties of colossal magnetoresistance (CMR) materials. We summarize here our results on tensilely and compressively strained La0.7Sr0.3MnO3 (LSMO) thin films that indicate the important role of lattice distortions due to the lattice mismatch between the film and substrate. The strain due to lattice distortions can be used to tune the magnetic domain structure, magnetization, magnetic anisotropy and magnetotransport of LSMO thin films.
Strain-Induced Magnetic Properties of Pr0.67Sr0.33MnO3 Thin Films
Authors: Wu X. W. , Rzchowski M. S. , Wang H. S. , Li Qi
Published: April 2011

We report the temperature dependence of the magnetic anisotropy in both compressive and tensile strained films of Pr0.67Sr0.33MnO3 (PSMO). Compressive strain induced by growth on LaAlO3 (LAO) substrates results in a spontaneous out-of-plane magnetization, while tensile strain (grown on SrTiO3) results in in-plane magnetization. The coefficient of linear proportionality between the magnetic anisotropy energy and the tetragonal strain for both compressive and tensile strained PSMO films is larger than that found previously in strained La0.67Ca0.33MnO3 films. From the data, we estimate a 20 unit cell magnetic domain wall width for PSMO / LAO. Scattering from such a narrow domain wall could produce a potentially significant contribution to the resistivity.
Magnetic Measurements on Stressed and Stress Relieved La0.66Ca0.33MnO3 Thin Films
Authors: Habermeier H.-U. , Praus R. B. , Gross G. M. , Razavi F. S.
Published: April 2011

In general, epitaxially grown thin films are biaxially stressed if the lattice mismatch of substrate and film is below 2%. We have used epitaxial strain as an extrinsic source of tensile stress exerted to La0.66Ca0.33 MnO3 thin films deposited on SrTiO3 single crystal substrates. The average stress in the film is a function of film thickness and post deposition annealing. Thickness variation and annealing procedures have been used to explore the stress dependence of the characterisics of magnetization curves of the stressed films. It could be shown that the inflection point of the magnetization curve which determines the transition from Blochwall movements to rotations of the magnetization vector and the Rayleigh constant of the virgin magnetization curve are correlated with the stress of the films in analogy to results obtained for plastically deformed single crystals of conventional ferromagnetic metals.
Conductivity and NMR Study of LaGa1−xMnxO3 Single Crystals
Authors: Noginova N. , Loutts G. , Mattix L. , Babalola K. , Arthur E.
Published: April 2011

Electrical conductivity and magnetic relaxation has been studied in single crystals of Mn doped LaGaO3 with doping concentrations of 0%, 0.5%, 2%, 10% and 50%. The resistivity of the crystals strongly depends on temperature and can be described with the hopping model. Both activation energy and resistivity coefficient grow significantly with decrease in Mn ion concentrations. Dramatic changes are observed in 71Ga NMR spin-lattice relaxation times.
Spin/Orbital Modulation in Perovskite Manganite Superlattices
Authors: Izumi M. , Manako T. , Kawasaki M. , Tokura Y.
Published: April 2011

A systematic study is presented for structural characterization and physical properties of two kinds of perovskite oxide superlattices composed of ferromagnetic (FM) and antiferromagnetic (AF) layers. Spin ordering structures is modulated in FM La0.6Sr0.4MnO3/G-type AF La0.6Sr0.4FeO3 superlattices, whereas, ordering structures both in spin and orbital are modulated in La0.6Sr0.4MnO3/A-type AF La0.45Sr0.55MnO3 along the growth directions. Large magnetoresistance subsists down to low temperature in La0.6Sr0.4MnO3/La0.6Sr0.4 Fe3 (F/G) superlattices as a result of recovery of ferromagnetism, which is once suppressed by spin frustration at the interface between FM and G-type AF layers. In contrast, the constituent layers in the La0.6Sr0.4MnO3/La0.45Sr0.55MnO3 (F/A) superlattices appear to keep their ground states due to the absence of spin frustration at the interface. Magnetoresistance is pronounced in this type of superlattices at low temperatures when the AF layer is very thin, indicating restoration of the electronic coupling between the neighboring FM layers which are otherwise decoupled by intervening A-type AF spin ordering and dx2−y2 orbital ordering in La0.45Sr0.55MnO3 layers.
Magnetotransport and Interface Magnetism in Manganite Heterostructures: Implications for Spin Polarized Tunneling
Authors: Jo Moon-Ho , Mathur N.D. , Evetts J.E. , Blamire M.G.
Published: April 2011

The electronic and magnetic structure at surfaces and interfaces in mixed valence manganites is an active area of research. To study localized properties of interface magnetism in heterostructures we have conducted both current in-plane and current perpendicular-plane measurements in multilayers and trilayer tunnel junctions, respectively. Initial study of the transport in multilayers, consisting of alternating La0.7Ca0.3MnO3 and SrTiO3 with different layer thickness provided information on vertical inhomogeniety in the manganite layers and disordered interfaces. Issues of lattice mismatched strain, structural inhomogeniety were addressed. Trilayer tunnel junctions have been fabricated with the aim of correlating tunneling magnetoresistance to the interface magnetism deduced from multilayer measurements. We describe devices incorporating a novel barrier material which have yielded single domain switchings and very high TMR values above 77 K.
Phase Equilibrium Diagrams of the Binary Systems LaMnO3-SrMnO3 and LaMnO3-CaMnO3
Authors: Majewski Peter , Epple Lars , Schluckwerder Heike , Aldinger Fritz
Published: April 2011

The quasi binary systems LaMnO3 – SrMnO3 and LaMnO3 – CaMnO3 have been studied. Both systems show a miscibility gap below about 1400°C in air. This phenomenon causes the decomposition of single phase (La,Sr)MnO3−x and (La,Ca)MnO3−x solid solution with intermediate La:Sr or La:Ca ratios into La rich SrMnO3−x or CaMnO3−x and Sr or Ca rich LaMnO3−x at lower temperatures. At 1400°C a structure transformation of (La,Sr)MnO3 from orthorhombic to rombohedral has not been observed and the structure of La0.7Sr0.3MnO3 has been determined to be orthorhombic with a = 0.54927 ± 0.0009 nm, b = 0.54582 ± 0.0009 nm, and c = 0.76772 ± 0.0034 nm.
Enhancement of the CMR Effect Near Room Temperature by Defects and Structural Transitions in La1−x−yCaxSryMnO3
Authors: Kolesnik S. , Dabrowski B. , Bukowski Z. , Mais J.
Published: April 2011

We have studied magnetoresistance of a series of La1−xSrxMnO3 and La1−x−yCaxSryMnO3 samples, for which structural and ferromagnetic transformation temperatures are in close proximity. On cooling in zero magnetic field, we observe a rapid increase of resistivity just above TC for La1−xSrxMnO3 samples with x < 0.1425 and x ≤ 0.1725 due to the O*-O' and R-O* - structural phase transformations, respectively. This increase is followed by a rapid decrease due to the ferromagnetic transition. The applied magnetic field significantly shifts the ferromagnetic transition to higher temperatures and suppresses the structure-related resistivity increase. We show that a combination of structural and ferromagnetic transitions gives rise to an enhancement of the negative magnetoresistance due to strong spin-lattice coupling. By choosing a proper composition, the enhancement can be optimized to appear in relatively low magnetic fields. A proper selection of Sr and Ca contents in La1−x−yCaxSryMnO3 and preparation conditions leads to an enhancement of the magnetoresistance effect at room temperature.
Epitaxial La0.7(Pb1−xSrx)0.3MnO3 Thin CMR Film Room Temperature Bolometer
Authors: Lisauskas A. , Khartsev S.I. , Grishin A.M.
Published: April 2011

Using pulsed laser deposition technique we fabricated films of a continuous series of solid solutions La0.7(Pb1−xSrx)0.3MnO3, which undergo metal-to-insulator phase transition close and above room temperature. The optimal composition for uncooled bolometer applications was found at x = 0.37 with maximum of TCR = 7.4 %K−1@ 295 K. Room temperature bolometer demonstrator has been built and tested. Relatively low excess noise (magnitude γ/n of 3·10−21 cm−3) and high TCR enabled achievement of high signal-to-noise ratio of 8·106 √-Hz/K. The observed frequency dispersion of bolometer response has been ascribed to three relaxation mechanisms of the heat transfer: from film thermistor to substrate, from substrate to thermostat, and heat transfer via leads. For fabricated bolometer heat transfer from substrate to thermostat was found to be the slowest one with a time constant of 0.5 s (correspondent substrate-to-thermostat thermal conductance is G = 3·10−3 W/K). Bolometer performance test yields the responsivity ℜ = 0.6 V/W, detectivity D = 9·106 cm√Hz/W and noise equivalent power NEP of 3·10−8 W/√Hz at 30 Hz frame frequency. Further improvement of bolometer thermal isolation using the micromachining technique is believed to achieve the responsivity about 4·103 V/W and detectivity higher than 109 cm√Hz/W@30 Hz.
Ferromagnetic Resonance in Single Crystal Bismuth Iron Garnet Films
Authors: Denysenkov V. , Jalali-Roudsar A. , Adachi N. , Khartsev S. , Grishin A. , Okuda T.
Published: April 2011

Among other magneto-optic materials bismuth substituted yttrium iron garnet (BixY1−x)3 Fe5O12 has the highest Faraday rotation effect in visible region. Completely substituted bismuth iron garnet Bi3Fe5O12 (BIG) films have been grown by pulsed laser deposition technique onto (111) (NdGd)3(ScGa)5O12 single crystal with lattice constant of 12.623 Å. X-ray diffraction proves epitaxial film quality. VSM measurements yield the saturation magnetization 4πMs, = 1100 G and coercive field is about 50 Oe. Ferromagnetic resonance (FMR) method reveals perpendicular magnetic anisotropy in fabricated films. Angular measurements of FMR give the constants of uniaxial and cubic anisotropy in BIG film: Ku = 5.9×104 erg/cm3 and K1= - 6.95×103 erg/cm3. The Faraday rotation has been found to reach - 7.8 deg/µm at 630 nm.
Bismuth Pyrochlore Films for Dielectric Applications
Authors: Ren Wei , Thayer Ryan , Randall Clive A. , Shrout Thomas R. , Trolier-McKinstry Susan
Published: April 2011

Bismuth pyrochlore ceramics have modest temperature coefficients of capacitance, good microwave properties, and can be prepared at relatively modest temperatures (∼900 – 1100 °C). This work focuses on the preparation and characterization of thin films in this family for the first time. A sol-gel procedure using bismuth acetate in acetic acid and pyridine, in combination with zinc acetate dihydrate and niobium ethoxide in 2-methoxyethanol was developed. The solution chemistry was adjusted to prepare (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 and Bi2(Zn1/3Nb2/3)2O7 films. Solutions were spin-coated onto platinized Si substrates and crystallized by rapid thermal annealing. In both cases, crystallization occurred by 550 °C into the cubic pyrochlore structure. (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films remained in the cubic phase up to crystallization temperatures of 750 °C, while the structure of the Bi2(Zn1/3Nb2/3)2O7 thin films is dependent of the firing temperature: cubic below 650 °C and orthorhombic above 750 °C. A mixture of cubic and orthorhombic structures is found at 700 °C. The resulting BZN films are dense, uniform, and smooth (rms roughness of < 5 nm). Cubic bismuth zinc niobate films show dielectric constants up to 150, a negative temperature coefficient of capacitance, TCC, (∼ - 400 ppm/°C), tan δ < 0.01, and a field tunable dielectric constant. Orthorhombic films showed smaller dielectric constants (∼80), low tan δ (< 0.01), positive TCC, and field independent dielectric constants. TCC could be adjusted to new 0 ppm/°C using a mixture of orthorhombic and cubic material.
Microstructure of YBCO and YBCO/SrTiO3/YBCO PLD Thin Films on Sapphire for Microwave Applications
Authors: Lorenz M. , Hochmuth H. , Natusch D. , Thärigen T. , Svetchnikov V. L. , Zandbergen H. W. , Schäfer C. , Kästner G. , Hesse D.
Published: April 2011

A large-area pulsed laser deposition process for high-quality YBa2Cu3O7−δ (YBCO) thin films on both sides of R-plane sapphire substrates with CeO2 buffer layer is used routinely to optimize planar microwave filters for satellite and mobile communication systems. With the experience of more than 700 double-sided 3-inch diam. YBCO:Ag films a high degree of reproducibility of jc values above 3.5 MA/cm2 and of state of the art R5 values is reached. TEM cross sections of the large-area and double-sided PLD-YBCO:Ag thin films on R-plane sapphire with CeO2 buffer layers show typical defects like stress modulation, stacking faults, a-axis oriented grains, precipitates and interdiffusion layers. YBCO films on SrTiO3 / YBCO* / CeO2 film systems on R-plane sapphire wafers have more growth defects compared to bare CeO2 buffers on sapphire but show as microwave resonators encouraging electrical tunability.
MOCVD Growth and Characterization of (BaxSr1−x)Ti1+yO3+z Thin Films for High Frequency Devices
Authors: Baumann P.K. , Kaufman D.Y. , Streiffer S.K. , IM J. , Auciello O. , Erck R.A. , Giumarra J. , Zebrowski J. , Baldo P. , McCormick A.
Published: April 2011

We have investigated the structural and electrical characteristics of (BaxSr1−x)Ti1+yO3+z (BST) thin films. The BST thin films were deposited at 650°C on platinized silicon with good thickness and composition uniformity using a large area, vertical liquid-delivery metalorganic chemical vapor deposition (MOCVD) system. The (Ba+Sr)/Ti ratio of the BST films was varied from 0.96 to 1.05 at a fixed Ba/Sr ratio of 70/30, as determined using x-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). Patterned Pt top electrodes were deposited onto the BST films at 350°C through a shadow mask using electron beam evaporation. Annealing the entire capacitor structure in air at 700°C after deposition of top electrodes resulted in a substantial reduction of the dielectric loss. Useful dielectric tunability as high as 2.3:1 was measured.
Microstructural Architecture of (Ba,Sr)TiO3 Thin Films for Tunable Microwave Applications
Authors: Chang Wontae , Horwitz James S. , Kim Won-Jeong , Gilmore Charles M. , Pond Jeffrey M. , Kirchoefer Steven W. , Chrisey Douglas B.
Published: April 2011

BaxSr1−xTiO3 (BST, x=0.5 and 0.6) thin films have been deposited onto (100) MgO single crystal substrates by pulsed laser deposition (PLD). The room temperature capacitance and dielectric quality factor (Q=1/tanδ have been measured as a function of electric field (≤ 100 kV/cm) at microwave frequencies (1 to 20 GHz) using silver interdigitated electrodes deposited on top of the BST film. It has been observed that the dielectric constant of the film and its change with electric field are closely related to film phase (amorphous to crystalline phase) and film strain which affects the ionic polarization of the film. Amorphous BST films show high dielectric Q (> 100) with low dielectric constant (∼30–200) and low dielectric tuning (< 1%), presumably due to small ionic polarization. Crystalline films have a higher dielectric constant (∼1000–3000) and a higher dielectric tuning (∼ 65%) but a lower dielectric Q (∼20). As an optimal microstructure of the film for tunable microwave applications, strain-relieved large-grained (∼5000 Å) randomly oriented polycrystalline films were deposited using a thin amorphous buffer layer of BST (∼50 Å). Very large grains (size up to a few microns) were observed in BST films prepared using a thicker amorphous buffer layer (∼500 Å). We will present results on how careful control of microstructure can lead to films with optimal dielectric properties for the tunable microwave devices.
Role of SrRuO3 Buffer Layers in Enhancing Dielectric Properties of Ba0.5Sr0.5TiO3 Tunable Capacitors
Authors: Park S.J. , Sok J. , Lee E.H. , Lee J.S.
Published: April 2011

BaM0.5Sr0.5TiO3 (BST) is a first candidate material for the development of voltage-tunable microwave devices, such as, filter, phase-shifter and VCO. In this work, crystal structures and dielectric properties of BST film are investigated with and without SrRuO3(SRO) buffer layers. BST and SRO thin films are sequentially prepared by pulsed laser deposition and Au/Ti metal electrodes are fabricated by a DC magnetron sputtering system. The capacitance of the capacitors has been measured as a function of bias voltages at room temperature using a low frequency LCR meter. For the high frequency characteristics (∼2GHz), a microstrip resonator with ∼2GHz resonance frequency and the center coupling design is fabricated. Using flip-chip BST capacitor attached at the position of the center coupling on the microstrip resonator, Its dielectric loss and tunability were obtained. The microwave loss was obviously enhanced in the film with SRO buffer layer..
Strain Tuned Magnetic Properties of Epitaxial Cobalt Ferrite Thin Films
Authors: Hu G. , Choi J.H. , Eom C.B. , Suzuki Y.
Published: April 2011

Epitaxial cobalt ferrite thin films have been fabricated on bare MgO substrates and compared to those grown on CoCr2O4 buffered MgAl2O4. Various structural characterizations, including x-ray diffraction, Rutherford backscattering spectroscopy and transmission electron microscopy, demonstrate excellent crystallinity of the films. Films grown under tension exhibit magnetic properties dominated by the stress anisotropy. In (110) oriented films grown on CoCr2O4 buffered MgAl2O4, post deposition annealing switched the in-plane easy and hard directions completely while no such behavior is observed in cobalt ferrite films grown on MgO. The anomalous behaviors observed in as-grown films and films after annealing can be explained in terms of lattice distortion and cation redistribution.
Local Optical Probes of Microwave Dielectric Dispersion in Ferroelectric Thin Films
Authors: Hubert Charles , Levy Jeremy , Cukauskas E. J. , Kirchoefer Steven W. , Pond Jeffrey M. , DeSisto William J.
Published: April 2011

The soft-mode contribution to the dielectric response of Ba0.5Sr0.5TiO3 ferroelectric thin films is measured locally at microwave frequencies using time-resolved confocal scanning optical microscopy. Optical measurements performed on an ensemble of nanometer-scale regions show a well-defined phase shift between the paraelectric and ferroelectric response at 2-4 GHz. Application of a static electric field produces large local variations in the phase of the ferroelectric response. These variations are attributed to the growth of a-axis ferroelectric nanodomains whose size-dependent relaxation frequencies lead to strong dielectric dispersion at mesoscopic scales. The in-plane paraelectric response is believed to arise from the surrounding c-axis matrix and non-polar regions, and shows negligible dispersion. These results provide a direct view of the soft-mode mechanisms of microwave dielectric loss in ferroelectric thin films.
RF-Magnetron Sputtered Strontium Titanate: Structure, Processing and Property Relationships
Authors: Gibbons B.J. , Fan Y. , Findikoglu A.T. , Reagor D.W. , Jia Q.X.
Published: April 2011

The low frequency dielectric properties of epitaxial SrTiO3 thin films deposited on LaAlO3 are presented. The films were deposited using radio-frequency magnetron sputtering from stoichiometric targets in an Ar/O2 atmosphere. For the first time, the effects of in situ ozone annealing during the early stages of deposition were explored. X-ray diffraction results indicated that the ozone treatment resulted in more symmetric and sharper diffraction peaks (2 Θ- FWHM decreased from 0.17° to 0.10°). In addition, the peaks for the ozone treated samples were shifted in 2 Θ towards values approaching the bulk value. Rutherford backscattering measurements showed Sr/Ti ratios of 1:1 for these samples, indicating these peak shifts are not due to compositional variations. The dielectric constant of the ozone treated samples increased from 275 at room temperature to 1175 at 22 K (measured at 100 kHz). The effective loss tangent of the device remained between 1 × 10−4 and 1 × 10−3 down to 100 K, where it began to increase. The tunability was also measured. The ozone treated sample showed tunability of 46%, 43% and 38% at 22 K, 40 K and 60 K, respectively. Finally, similar measurements were completed at 1 MHz, indicating a minimal dependence of these properties on frequencies in this range.
Materials Issues in the Application of Ferromagnetic Films in Tunable High Q VHF/UHF Devices
Authors: Walser R.M. , Valanju A. P. , Win W.
Published: April 2011

Thin ferromagnetic films have narrow ferromagnetic resonance bandwidths, and large RF permeabilities that are attractive for tunable high Q device applications. They can also be processed at low temperatures and integrated with most RF and microwave materials. At VHF/UHF frequencies, where discrete devices can be realized, magnetic loss tangents (Q−1) less than 10−3 can be obtained, if the effects of spin resonance and eddy current losses are reduced. The material figure of merit requires a tradeoff of the permeability, and Q. The highest FOM is obtained by maximizing the magnetization, anisotropy, resistivity, and minimizing the magnetic loss. This paper discusses the interplay of these properties, and the fill factor and magnetic bias required for tunable inductors with Q>1000 in the ∼50-500 MHz range. The most promising candidates for these applications are shown to be reactively sputtered nanocrystalline films. The large resistivity, magnetization, and thickness of these films can be used to attain large film permeances, and increased shape anisotropy fields from patterned film objects. The latter eliminates the need for using a large bias magnet to achieve Q's ∼1000 at VHF/UHF operating frequencies.
Study of Vacancy and Impurity Complexes in Si Solid-Phase Epitaxial Crystallization with Positron Annihilation Spectroscopy
Authors: Chen Claudine M. , Rassiga Stefano , Weber Marc H. , Petkov Mihail P. , Lynn Kelvin G. , Atwater Harry A.
Published: April 2011

We investigate the residual vacancy defect species after crystallization of amorphous Si (a-Si) by solid phase epitaxy (SPE). To this end, we correlate the total and electronically-active doping concentrations measured by secondary mass spectrometry and spreading resistance analysis, and data from positron annihilation spectroscopy (PAS), which is sensitive to openvolume defects. Float-zone silicon substrates were implanted with boron, phosphorus and both phosphorus and boron ions to create nonuniform doping profiles at degenerate doping levels, after an amorphization step by 29Si+ ions. Samples were vacuum annealed at 600°C to induce SPE, and the SPE rate was measured by time-resolved reflectivity. PAS was used for identification of the impurity-defect complexes. Momentum-resolved PAS measurements enable the detection of phosphorus-vacancy (P-V) and oxygen-vacancy (O-V) complexes.
Atomistic Modeling of Complex Silicon Processing Scenarios
Authors: Jaraiz Martin , Castrillo Pedro , Pinacho Ruth , Pelaz Lourdes , Barbolla Juan , Gilmer George H. , Rafferty Conor S.
Published: April 2011

The level of sophistication reached by today's Si device fabrication technologies has called for new modeling and simulation schemes, capable of handling the wide variety of interaction mechanisms that govern the complex phenomena that can occur at the atomic level. The kinetic Monte Carlo (KMC) technique seems particularly apt for this task. It takes as input basic materials parameters, derived from ab-initio calculations or from experiments, and is capable of carrying out a detailed simulation up to the dimensions and time scales of current ULSI Si device manufacture. In addition, it can accommodate and efficiently simulate complex interactions between multiple dopant and defect types. We explain the approach and show examples of application in both materials processing and device fabrication. Finally, we present the use of some artificial intelligence techniques (namely, genetic algorithms) that look most promising as methodologies that can easy and efficiently be employed to build the extensive KMC parameter database.
Monte Carlo Analysis of the Evolution from Point to Extended Interstitial Type Defects in Crystalline Silicon
Authors: Magna Antonino La , Coffa Salvatore , Libertino Sebania
Published: April 2011

We present a Lattice Kinetic Monte Carlo study of the atomic evolution leading to {311} defects formation upon annealing of a damaged Si-crystal. Self-interstitial (I) agglomeration is modeled by using local interaction and considering the energetic cost to under/over coordinate the Si atoms belonging to an I-complex. The static properties of the I aggregates as derived by molecular dynamics calculations, in the two extreme regimes of very small and very large clusters, have been mapped in the model. The typical evolution of an excess of Si ions is characterized by three distinct stages: (1) the formation of clusters consisting of few interstitials in a over-coordination state, (2) their redistribution in larger agglomerates containing a few of these small I clusters all preserving their original structure, (3) a transition leading to Is rearrangement along the ≪110> chains, which are the structural units of {311} defects. The duration of the preliminary stages critically depends on temperature and density of the added atoms.
The Application of Solid Source Diffusion in the Vertical Replacement-Gate (VRG) MOSFET
Authors: Oh Sang-Hyun , Hergenrother J.M. , Monroe Don , Nigam T. , Klemens F.P. , Kornblit A. , Mansfield W.M. , Baumann F.H. , Gossmann H.J. , King C.A. , Kleiman R.N. , Vuong H-H. , Weber G.R. , Rafferty C.S.
Published: April 2011

We discuss the first use of solid source diffusion (SSD) to form shallow, self-aligned SDEs in a novel device known as the Vertical Replacement-Gate (VRG) MOSFET. This is the only MOSFET ever built that combines 1) a gate length controlled precisely through a deposited film thickness, independently of lithography and etch, and 2) a high-quality gate oxide grown on a single-crystal Si channel. The use of SSD in this novel geometry allows us to transform the precise gate length control afforded by the VRG process into precise, lithography-independent channel length control. In the VRG-nMOS process, silicon nitride offset spacers separate the phosphosilicate glass (PSG) SSD dopant sources from the polysilicon gate. These offset spacers, whose critical dimensions are also controlled by film thicknesses, allow us to precisely tune the gate-source and gate-drain overlaps in order to optimize the capacitance/series resistance tradeoff. These parasitic overlap capacitances have precluded the high-frequency operation of many previous vertical MOSFETs. In this paper, we discuss the SIMS and sheet resistance characterization of shallow phosphorus junctions formed in one-dimensional SSD experiments. We will also discuss the scanning capacitance characterization of two-dimensional doping profiles of VRG-nMOSFETs with gate lengths down to 50 nm.
Low Energy Implantation of Boron with Decaborane Ions
Authors: Albano Maria A. , Babaram Vijay , Poate John M. , Sosnowski Marek , Jacobson Dale C.
Published: April 2011

Formation of p-type shallow junctions for future generations of Si devices will require ion implantation of B at very low energies (< 1 keV). An alternative to implantation of monomer ions at very low energy is implantation of large molecular ions at a higher energy. In an ion beam of decaborane (B10H14) each of the B atoms carries only 9% of the ion kinetic energy. We have examined ionization properties of decaborane and built an experimental ion source and an implantation apparatus with magnetic mass analysis. Analyzed decaborane ion beams with energies from 2 to 10 keV and beam currents of several microamperes were obtained. Si samples were implanted with decaborane ions and the implanted dose measured by current integration was compared with B content obtained by nuclear reaction analysis. Experiments with electrostatic beam deflection show that the large ions survive the transport in the implanter environment and that neutralization is negligible. During implantation, the retained B dose is reduced in comparison with the nominal implanted dose due to sputtering. Dose loss is greater at 200 eV compared to 500 eV. The properties of decaborane ion beams and the prospects of using them for shallow implantation of B into Si are discussed.
Furnace and Rta Injection of Point Defects into CVD-Grown B Doped Si and SiGe
Authors: Bonar Janet M. , Mcgregor Barry M. , Cowern Nick E. B. , Dan Aihua , Cooke Graham A. , Willoughby Arthur F. W.
Published: April 2011

The diffusion of B in Si and SiGe under the influence of point defect injection by Rapid Thermal Anneal (RTA) and conventional furnace anneal is studied in this work. B-doped regions in SiGe and Si were grown by LPCVD, and point defects were injected by RTA or furnace annealing bare, Si3N4 or SiO2 + Si3N4 covered samples in an oxygen atmosphere. Self-interstitial defects will be injected into bare Si while vacancy defects will be injected into Si3N4 covered samples, and inert annealing will occur in SiO2 + Si3N4 covered samples. The annealed and asgrown profiles were determined using SIMS analysis, and the diffusivities extracted by direct comparison of the profiles. Both interstitials and vacancies were injected during furnace annealing of SiGe, as demonstrated by the respective enhancement and retardation of the B diffusion. Enhanced B diffusion in SiGe was observed even for 5 s RTA at 1000°C, with an enhancement factor of ∼2.5. The B in Si diffusivity enhancement for interstitial injection by RTA oxidation was found to be a factor of ∼3 compared to inert anneals, close to the factor for SiGe.
The Source of Transient Enhanced Diffusion in Sub-keV Implanted Boron in Crystalline Silicon
Authors: Napolitani E. , Carnera A. , Privitera V. , Schroer E. , Mannino G. , Priolo F. , Moffatt S.
Published: April 2011

The transient enhanced diffusion (TED) during activation annealing of ultra low energy implanted boron (0.5 keV & 1 keV, 1×1013/cm2 & 1×1014/cm2) in silicon is investigated in detail. Annealing in the temperature range from 450°C to 750°C is either performed directly after implantation or after the removal of a surface layer before annealing. The kinetics revealed two regimes of enhanced diffusion ruled by different decay constants and different activation energies. The dependence of these two processes on implantation energy and annealing temperature is described and explained from the microscopical point of view. The annealings performed after surface layer removal, revealed that the defects responsible for the faster diffusion are located deeper than the defects responsible for the slower process.
An Analytical Model for Field-Enhanced Diffusion of Ionized Impurities in Highly Doped Si
Authors: Sokolovskii Bogdan S. , Monastyrskii Liubomyr S. , Kovtun Roman M.
Published: April 2011

An expression for concentration dependence of diffusion coefficient of ionized impurity in semiconductors which is derived which is valid for the whole range of carrier degeneracy under the condition that the impurity concentration greatly exceeds the intrinsic carrier density. Due to reduction of impurity field screening by mobile carriers at degenerate conditions the diffusion coefficient is shown to be a monotonously increasing function of impurity concentration. It is proved that taking band gap narrowing into account results in a reduction of the diffusion coefficient in comparison with the case of unperturbed band structure. In addition, a decreasing concentration dependence of the diffusion coefficient can be realized at relatively low impurity concentrations.
The Effect of Carbon/Self-Interstitial Clusters on Carbon Diffusion in Silicon Modeled by Kinetic Monte Carlo Simulations
Authors: Pinachoa R. , Jaraíz M. , Gossmann H. J. , Gilmer G. H. , Benton J. L. , Werner P.
Published: April 2011

A new model for carbon diffusion in silicon that explains carbon diffusion during annealing at 850°C and 900°C in superlattice carbon structures grown by MBE is implemented using the Monte Carlo atomistic simulator DADOS. Carbon concentrations in the delta layers are 2×1020 cm−3, exceeding by far the solid solubility. The simple kick-out mechanism which incorporates the well established values of the product of diffusivity and equilibrium concentrations of intrinsic point defects and in-diffusion experiments of carbon in silicon does not explain the observed C diffusion profiles. A more detailed analysis of the experiments shows that, in order to fit them, a more unstable Ci is required. Therefore, we include the formation of clusters in the simulations. The formation of carbon/Si self-interstitial clusters promotes the premature break-up of Ci and the increase of the Si self-interstitial concentration in the carbon rich regions and, consequently, provides a better fit to the experiments. The low solubility of carbon in silicon at the annealing temperatures explains why these clusters are formed, even under conditions where the self-interstitial concentration is below the equilibrium value.
Amorphous Mixed TiO2 and SiO2 Films on Si(100) by Chemical Vapor Deposition
Authors: Smith Ryan C. , Taylor Charles J. , Roberts Jeffrey , Hoilien Noel , Campbell Stephen A. , Gladfelter Wayne L.
Published: April 2011

Amorphous thin films of composition TixSi1-xO2 have been grown by low pressure chemical vapor deposition on silicon (100) substrates using Si(O-Et)4 and either Ti(O-iPr)4 or anhydrous Ti(NO3)4 as the sources of SiO2 and TiO2, respectively. The substrate temperature was varied between 300 and 535°C, and the precursor flow rates ranged from 5 to 100 sccm. Under these conditions growth rates ranging from 0.6 to 90.0 nm/min were observed. As-deposited films were amorphous to X-rays and SEM micrographs showed smooth, featureless film surfaces. Cross-sectional TEM showed no compositional inhomogeneity. RBS revealed that x (from the formula TixSi1-xO2) was dependent upon the choice of TiO2 precursor. For films grown using TTIP-TEOS x could be varied by systematic variation of the deposition conditions. For the case of TN-TEOS x remained close to 0.5 under all conditions studied. One explanation is the existence of a specific chemical reaction between TN and TEOS prior to film deposition. TEOS was mixed with a CCl4 solution of TN at room temperature to produce an amorphous white powder (Ti/Si = 1.09) and 1HNMR of the CCl4 solution indicated resonances attributable to ethyl nitrate.
Low Temperature Nitridatio of SiO2 Films using a Catalytic-CVD System
Authors: Izumi Akira , Sato Hidekazu , Matsumura Hideki
Published: April 2011

This paper reports a procedure for low-temperature nitridation of silicon dioxide (SiO2) surfaces using species produced by catalytic decomposition of NH3 on heated tungsten in catalytic chemical vapor deposition (Cat-CVD) system. The surface of SiO2/Si(100) was nitrided at temperatures as low as 200°C. X-ray photoelectron spectroscopy measurements revealed that incorporated N atoms are bound to Si atoms and O atoms and located top-surface of SiO2.
A Model of Chemical Mechanical Polishing
Authors: Paul Ed
Published: April 2011

A generic model is presented which explains the dependence of chemical mechanical polishing rates on the concentration of reacting chemicals and abrasives in the slurry. The predictions of this model are compared to data from the literature for tungsten CMP.
Multi-Level Damascene Process Development: Aluminum CMP
Authors: Hansen David A. , Moloney Gerry , Reyes Alex
Published: April 2011

The purpose of this work was to investigate integration of aluminum multi-level damascene devices with the CMP module. Traditionally aluminum is used in the Metal-1 level of device manufacturing and Reverse Ion Etching (RIE) is used to remove the aluminum over layer. However for <0.25-µproportional]m device rules RIE is not a method of choice due to incomplete removal of the over layer leaving stringers that cause shorting, as well as poor With-In Wafer NonUniformity (WIWNU). The result is loss of device yield and process problems for BEOL modules. Integrating aluminum device wafers into the CMP module has its own drawbacks such as immature consumables, i.e., slurry and polishing pads, as well as ease of scratching the soft aluminum interconnect structures. Hence the basis of this work is to highlight the main issues that impede the integration of the aluminum CMP process. Specifically we investigated the origin of deep aluminum scratches and the effect of not completely removing the residue barrier material, which can cause shorting and poor electrical performance. It is argued in this work that the observed deep scratches in the aluminum material are due to the polished debris emanating from the titanium glue layer. Recommendations are made to help to reduce this effect by design modification to the die layout on the patterned wafer and using electrical testing methods to help ascertain the minimum Over Polishing (OP) time required in order to ensure maximum die yield.
Interfacial Fluid Pressure and Its Effects on SiO2 Chemical Mechanical Polishing
Authors: Zhou C. , Shan L. , Hight J. R. , Ng S.H. , Paszkowski A. J. , Tichy J. , Danyluk S.
Published: April 2011

In this paper, the experimental results of interfacial fluid pressure and friction measurements during polishing are presented, as well as their dependence on some major process variables. Under simulated conditions, a sub-ambient fluid pressure was observed, and its magnitude was of the same order of magnitude as the applied polishing load. Since this fluid pressure is non-uniformly distributed, the contact stress, obtained by combining the effects of both applied load and the fluid pressure, is not uniform across the wafer and will result in non-uniform material removal. The mechanism of the presence of the fluid pressure was investigated, and an analytical model was developed to predict the magnitude and distribution of this fluid pressure. The effects of the sub-ambient fluid pressure on material removal rate and profile were tested with thermally grown silicon dioxide on 100mm diameter, P-type (100), single crystal silicon wafers. The polishing experiments show the effect of sub-ambient fluid pressure on polishing rate and profile.
Smoothing Thin Films with Gas-Cluster Ion Beams
Authors: Fenner D.B. , Hautala J. , Allen L.P. , Greer J.A. , Skinner W.J. , Budnick J.I.
Published: April 2011

Thin-film magnetic sensor and memory devices in future generations may benefit from a processing tool for final-step etching and smoothing of surfaces to nearly an atomic scale. Gas-cluster ion-beam (GCIB) systems make possible improved surface sputtering and processing for many types of materials. We propose application of GCIB processing as a key smoothing step in thin-film magnetic-materials technology, especially spin-valve GMR. Results of argon GCIB etching and smoothing of surfaces of alumina, silicon, permalloy and tantalum films are reported. No accumulating roughness or damage is observed. The distinct scratches and tracks seen in atomic-force microscopy of CMP-processed surfaces, are removed almost entirely by subsequent GCIB processing. The technique primarily reduces high spatial-frequency roughness and renders the topographic surface elevations more nearly gaussian (randomly distributed).