bluuebunny/crossref_metadata_2025 huggingface dataset:
Photorefractive Conjugated Polymer-Liquid Crystal Composites
Authors: Wasielewski M. R. , Yoon B. A. , Fuller M. , Wiederrecht G. P. , Niemczyk M. P. , Svec W. A.
Published: April 2011

A new mechanism for space-charge field formation in photorefractive liquid crystal composites containing poly(2,5-bis(2′-ethylhexyloxy)-l,4-phenylenevinylene) (BEH-PPV) and the electron acceptor N,N′-dioctyl-1,4:5,8-naphthalenediimide, NI, is observed. Using asymmetric energy transfer (beam coupling) measurements that are diagnostic for the photorefractive effect, the direction of beam coupling as a function of grating fringe spacing inverts at a spacing of 5.5 μm. We show that the inversion is due to a change in the dominant mechanism for space-charge field formation. At small fringe spacings, the space-charge field is formed by ion diffusion in which the photogenerated anion is the more mobile species. At larger fringe spacings, the polarity of the space charge field inverts due to dominance of a charge transport mechanism in which photogenerated holes are the most mobile species due to hole migration along the BEH-PPV chains coupled with interchain hole hopping. Control experiments are presented, which use composites that can access only one of the two charge transport mechanisms. The results show that charge migration over long distances leading to enhanced photorefractive effects can be obtained using conjugated polymers dissolved in liquid crystals.
Investigation of Optical Limiting Mechanism in Multiwalled Carbon Nanotubes
Authors: Sun X. , Xiong Y. N. , Chen P. , Lin J. Y. , Ji W. , Lim J. H. , Yang S. , Hagan D. J. , Stryland E. W. Van
Published: April 2011

We report an investigation into the mechanism responsible for the optical limiting behavior in multiwalled carbon nanotubes. We conducted energy-dependent transmission measurements, picosecond time-resolved pump-probe, and nonlinear scattering experiments at 532-nm wavelength on multiwalled carbon nanotube suspension. For comparison, C60-toluene solution and carbon black suspension were also studied in the same experiments. The similarities that we observed between the multiwalled carbon nanotubes and carbon black suspension suggest that nonlinear scattering, which is known to be responsible for the limiting action in carbon black suspension, should play an important role in the limiting effect in multiwalled carbon nanotubes.
Control of Location and Carrier-Interaction of Erbium Using Erbium-Doped Si/SiO2 Superlattice
Authors: Han Hak-Seung , Lee Won-Hee , Shin Jung H.
Published: April 2011

The effect of controlling the interaction between the erbium atoms and the carriers of the host matrix is investigated using erbium doped Si/SiO2 superlattices. Based on the previous finding that controlling the location of the erbium atoms by doping only the SiO2 layers improves both the Er3+ photoluminescence intensities and the temperature quenching of the Er3+ luminescence, we identify controlling the interaction between erbium atoms and the carriers in the Si layer to be the key point. We demonstrate that by further isolating the erbium atoms from the Si layers by depositing thin buffer layers of pure SiO2 improves the Er3+ photoluminescence by several orders of magnitude while still allowing efficient excitation by carriers to dominate. Finally, we demonstrate that efficient waveguides can be fabricated using such erbium doped Si/SiO2 superlattices.
Experimental Study and Modeling of Nonlinear Scattering in Polymer Dispersed Liquid Crystals
Authors: Pacilli M. , Sebbah P. , Sixou P. , Vanneste C. , Guillard H.
Published: April 2011

We investigate the optical limiting capabilities of composite materials consisting of nematic liquid crystal inclusions within a polymer matrix in the millisecond and CW regime. Preparation of the composite has been optimized to decrease the operation voltage. Clear evidence of light induced reorientation is observed. A numerical model is proposed to describe multiple linear and nonlinear light scattering in the time domain in this medium. Numerical simulations are compared to experiment and confirm promising limiting characteristics of such materials.
Design, Synthesis and Characterization of New Bimechanistic Optical Power Limiters Based on Reverse Saturable and Two-photon Absorption
Authors: Spangler C. W. , Elandaloussi E. H. , Ozer B. , Ashworth K. , Madrigal L. , Reeves B.
Published: April 2011

During the past five years there has been considerable progress in the design of organic materials for optical power limiting (OPL) applications. One of the more promising and widely studied material approaches involves reverse saturable absorption (RSA) from various excited states. We have recently been examining the efficacy of utilizing highly absorbing photogenerated charge states for RSA. Both polaronic radical cations and bipolaronic dications are possible candidates for this mode of optical limiting. Equally intriguing are new approaches to designing chromophores with large two-photon absorption (TPA) cross-sections. For some pulse durations the effective two-photon cross-section for bis-(diphenylamino)diphenylpolyenes, and dendrimers based on these repeat units, are extraordinaryly large, indicative of excited state absorption. In this presentation we will discuss the possibility of combining these two optical limiting mechanistic paradigms in single structures, which may then be considered as bimechanistic optical power limiters.
Optical Limiting With Neutral Nickel Dithiolene Complexes
Authors: Tan W. L. , Ji W. , Zuo J. L. , Bai J. F. , You X. Z. , Lim J. H. , Yang S. S. , Hagan D. J. , Stryland E. W. Van
Published: April 2011

We report an investigation of optical-limiting behavior in two neutral nickel complexes with multi-sulfur 1,2 dithiolene ligands, [Ni(medt)2] I (medt = 5,6-dihydro-6-methyl-1,4-dithiin-2,3- dithiolate) and [Ni(phdt)2] 2 (phdt = 5,6-dihydro-5-phenyl-l,4-dithiin-2,3-dithiolate) in benzene solution. The fluence-dependent transmission of the complexes was observed with nanosecond and picosecond laser pulses at 532-nm wavelength. The limiting thresholds of the complexes were ˜0.3 J/cm2, when measured with the picosecond pulses. Both picosecond time-resolved pump-probe and Z-scan measurement revealed that the limiting effects should originate from excited-state absorption and refraction. The transparency window (400˜900 nm), observed in the linear absorption spectra of the complexes, indicated that their limiting response should cover a wider range than those of fullerenes and phthalocyanines.
Photo-Induced Effects in Mn4+:YAG. Observation of Unusually Efficient Excited State Absorption and a Long–Lived Metastable State
Authors: Han Yanong , Spangler Lee H. , Hutcheson Ralph , Equall Randy W.
Published: April 2011

The Mn4+ ion has the same d3 electron configuration as Cr3+, but is less stable and can transform to other valence states. Both ions are known to occupy several sites in garnet hosts, giving rise to rather complicated optical spectra and photo-induced phenomena. Here, the spectra of the transient, photo-induced absorption and the emission of Mn4+,:YAG are analyzed over a broad wavelength region (from 450 to 1200nm) and over a wide range of time scales (from ns to minutes). Very large amplitude and extremely broadband excited state absorption are observed. Additionally, a long lifetime, photo-induced species was detected that is likely formed via charge transfer. The demonstrated behavior of this material shows it has potential applications for optical limiting and optical storage.
Optical Limiters: Spatial, Temporal, and Bio-Optical Effects
Authors: Hollins R C , McEwan K J , Till S J , Lund D J , Zuclich J A
Published: April 2011

This paper examines the goals which a nonlinear limiter must achieve in order to protect an eye against injury by a pulsed laser. The shape and temporal structure of the image presented to the retina are discussed. New bio-optical data describing retinal injury thresholds for largeimage sources are used to estimate the ocular hazard. The issues and trade-offs surrounding the incorporation of a limiter into an optical system are examined, and the suitability of different materials for an effective low-loss limiter are compared.
A Novel Method For Solution Deposition of Hydroxyapatite on to Three Dimensionally Porous Metallic Surfaces: Peri-Apatite Ha
Authors: Zitelli Joseph P. , Higham Paul
Published: April 2011

A method for applying HA coatings to metallic surfaces, without the use of high temperature plasma spraying, has been developed. The HA coating is precipitated in an aqueous solution under conditions similar to those occurring in the body during bone formation. This surface mineralization process results in a coating which is highly crystalline and 100% HA. Processing and characterization experimentation and results are included in the paper.

The coating method has the ability to penetrate macroporous (> 100 micron pores) metal structures and coat the undersides and interior surfaces of the areas designed for bone ingrowth on orthopedic devices used for joint replacements. This ability to coat all around a surface is the basis for the name Peri-Apatite HA. Electron microscopy is presented illustrating the coverage and morphology of the coating.

The Peri-Apatite HA coating is currently used on both knee joint replacement and hip joint replacement implants.
Apatite Formation on Electrochemically Treated Titanium
Authors: Tsuru K. , Takemoto S. , Hayakawa S. , Osaka A.
Published: April 2011

Apatite formation on artificial materials in a body environment is the prerequisite condition for showing bioactivity i.e. bone-bonding ability. A specific hydrated silica or titania gel has the ability of apatite deposition in body environment. We electrochemically prepared such a bioactive titanium oxide layer on titanium(Ti) with a cell consisting of Ti as the working electrode, Pt as the counter one, Ag/AgCl as the reference one, and an aqueous solution of 0.1 mol/L Ca(NO3)2 as the electrolyte solution. Ti was kept at 9.5V for 1 hour for oxidation(denoted as Ca9.5). Ti was subject to cathodic polarization at −3.0V for 10 min(Ca-3.0).: calcium ions were expected to be adsorbed on its surface. On treatment Ca9.5–3.0 Ti was first oxidated at 9.5V for 1 hour and subsequently kept at −3.0V for 10 min. The specimens of Ca9.5–3.0 and Ca-3.0 were found so bioactive as to deposit apatite within 12 hours and 1 day, respectively, in a simulated body fluid(Kokubo solution) whereas those due to Ca9.5 could not deposit apatite within 7 days. Calcium hydroxide and calcium carbonate detected on the bioactive surface caused no harmful effects on spontaneous deposition of apatite in the fluid.
Template-Mediated Biomineralization of Hemozoin
Authors: Wright David W. , Ziegler James
Published: April 2011

A critical target for the development of new antimalarial treatments is the detoxification pathway of free heme released during the catabolism of host hemoglobin in the digestive vacuole of the malaria parasite Plasmodium falciparum. We have synthesized and examined two peptide dendrimers (BNT I and II) based on the tandem repeat motif of HRP II from P. falciparum for their abilities to both bind heme substrates and to form the critical detoxification polymer hemozoin. Each substrate was capable of binding significant amounts of the natural substrate Fe(III)PPIX along with other substrates such as Zn(II)PPIX and the metal free PPIX. Further, it was shown that the dendrimeric BNT I and II were capable of supporting the aggregation of hemozoin and that this process could be inhibited by the known antimalarial drug, chloroquine.
Importance of Electrostatic Interactions Between Calcite Surfaces and Proteins
Authors: Rodripuez-Navarro Aleiandro , Messier Russell , Jimenez-Lopez Concepcion , Garcia-Ruiz Juan Manuel
Published: April 2011

We have studied the electrostatic interactions of proteins with the calcite surfaces during its subsequent nucleation and growth on a surface. In doing so, a model system of four globular proteins (lysozyme, ribonuclease, myoglobin and α-lactalbumin), having the same size and conformation, but differing in surface properties (i.e. surface charge) was used. Depending on the nature of the charge on the protein, its morphological effect on calcite growth (inhibition of specific crystal faces) varies, with this effect becoming more pronounced as the protein is more negatively charged. To study how the adsorption of proteins affects the growth of calcite along different crystal directions, calcite plates cut with different crystallographic orientations (i.e. (001), (104), (100) and (110)) were used as substrates. The overgrowing calcite crystals show the same orientation as the substrate. The nucleation density also varies with the crystallographic orientation of the calcite substrates, increasing in accordance with the sequence: (110), (100) and (001). Finally, to study how the protein itself controls the orientation of crystals, we used amorphous substrates (glass). After incubation on the glass substrates with negatively charged proteins, an oriented nucleation of the calcite crystals was induced.
Spectroscopic Studies of Manganese Doped LaGaO3 Crystals
Authors: Noginov M. A. , Noginova N. , Loutts G. B. , Babalola K. , Rakhimov R. R.
Published: April 2011

We have grown Mn:LaGaO3 crystals (Mn=0.5%, 2%, 10%, and 50%) and studied their properties with the methods of optical and EPR spectroscopy. We have found Mn2+, Mn4+, and Mn5+ ions in low doped crystals (Mn=0.5% and 2%) and Mn3+ ions in crystals with higher Mn concentrations (10% and 50%). The formation of Mn3+ valence state in Mn:LaGaO3 is discussed.
Giant 1/f Noise in Low-Tc CMR Manganites: Evidence of the Percolation Threshold
Authors: Podzorov V. , Uehara M. , Gershenson M. E. , Koo T. Y. , Cheong S-W.
Published: April 2011

We observed a dramatic peak in the 1/f noise at the metal-insulator transition (MIT) in low-Tc, manganites. This many-orders-of-magnitude noise enhancement is observed for both polycrystalline and single-crystal samples of La5/8−y. Pry, Ca3/8MnO3 (y = 0.35 – 0.4) and Pr1−xCaxMnO3 (x = 0.35 – 0.5). This observation strongly suggests that the microscopic phase separation in the low-Tc, manganites causes formation of a percolation network, and that the observed MIT is a percolation threshold. It is shown that the scale of phase separation in polycrystalline samples is much smaller than that in single crystals.
Spectroscopic Studies of Inhomogeneous Electronic Phases in Colossal Magnetoresistance and Charge-Ordering Compounds
Authors: Cooper S. L. , Liu H. L. , Yoon S. , Cheong S-W. , Fisk Z.
Published: April 2011

Infrared reflectance and Raman spectroscopy measurements have been performed through the metal-semiconductor (or -semimetal) transitions of various “colossal magnetoresistance” and charge-ordering materials, including EuB6 and the manganese perovskites. As described in this paper, our results demonstrate that these systems have phase regions characterized by electronic inhomogeneity of various types, including: (1) pure spin polarons, which form in a narrow temperature range above Tc in the “colossal magnetoresistance” system EuB6; (2) magnetoelastic polarons, and an inhomogeneous ferromagnetic phase comprised of both metallic and insulating regions, in the “colossal magnetoresistance” regime of La1−x(Sr,Ca)xMnO3 (x < 0.5); and (3) phase separation behavior involving coexisting ferromagnetic and antiferromagnetic domains in the intermediatetemperature (CO) phase of the charge-ordering system Bi1−xCaxMnO3 (x > 0.5).
Critical Phenomena at the Antiferromagnetic Transition in MnO
Authors: Woodfield B.F. , Shapiro J.L. , Stevens R. , Boerio-Goates J. , Wilson M.L.
Published: April 2011

The specific heat of a polycrystalline sample of MnO was measured from T ≈ 1 K to T ≈ 400 K using two different experimental apparatuses at zero applied pressure. Features revealed by the data include a hyperfine contribution due to the Mn nuclei, a T2 temperature dependence at low temperatures due to the type-II antiferromagnetic magnon contribution, and a sharp but well defined antiferromagnetic transition (TN = 117.7095 K) that is clearly second order in nature. The critical exponent, α, deduced from the transition is consistent with a two dimensional Ising model. The specific heat of MnO is also compared with recent results on the type-A antiferromagnet LaMnO3.
Tunnel Type Magnetoresistance in Electron Beam Deposited Films of Compositions (Co0.5Fe0.5)x(Al2O3)(100-x) (7 ≤ x ≤ 52)
Authors: Khan H.R. , Vovk A. Ya , Kravets A.F. , Shipil O.V. , Pogoriliy A.N.
Published: April 2011

A series of 400 nm thick metal-insulator films of compositions (Co50Fe50)x(Al2O3(100-x) (7 ≤ x ≤ 52; x is in vol.%) are deposited on glass substrates using dual electron beam evaporation technique. The films are nanocrystalline with crystallite sizes of 1-3 nm. Resistivity of the films varies as a function of (I/T)0.5 showing a tunneling type behaviour. The films show isotropic and negative magnetoresistance (GMR). A film of composition (Co50Fe50)82.5(Al2O3)17.5 show maximum tunneling magnetoresistance (TMR) of 7.2% at room temperature and in a magnetic field of 8.2 kOe.
Structure and Magnetism of Nanocrystalline KδMnO2
Authors: Stroud R.M. , Carpenter E. , Browning V.M. , Long J.W. , Swider K.E. , Rolison D.R.
Published: April 2011

The structure and magnetic properties of sol-gel-synthesized, nanocrystalline KσMnO2 were investigated. The nanoparticles were determined by x-ray diffraction and high-resolution transmission electron microscopy to be single-crystal rods of the cryptomelane phase of MnO2, with a typical particle size of 6 nm × 20 nm. The field and temperature dependence of the magnetization indicates superparamagnetic behavior, with a blocking temperature of 15K. The dependence of the magnetic properties on particle size, surface layers and mixed valency is discussed.
Discovery of a High Spin Freezing Temperature and Control of a Spin-Glass State in Mg1.5FeTi0.5O4 Spinel Films
Authors: Muraoka Y. , Tabata H. , Kawai T.
Published: April 2011

A spin-glass state up to 210 K has been found in (Mg,Fe){Mg,Fe,Ti)2O4 spinel ferrite thin films formed on α-Al2O3(0001) substrates. The long-time relaxation of the magnetization in zero-field-cooled operation, which is characteristic feature of the spin-glass state, has been observed below 210 K. We have also achieved the change of magnetic state in the film from spin-glass to ferrimagnet over a wide temperature range below 160 K by means of light-irradiation. The amount of spin-melt on light-irradiation is calculated to be 41 % at 10 K and 26 % at 100 K.
Deposition and Electrical Characterization of Dielectric/Ferromagnetic Heterostructure
Authors: Wu T. , Ogale S.B. , Garrison J.E. , Nagaraj B. , Chen Z. , Ramesh R. , Venkatesan T.
Published: April 2011

We grow Pb(Zr,Ti)O3 (001)/La1−xCaxMnO3 (001) hetereostructure epitaxially on Nb doped STO substrate using pulsed laser ablation. A field effect device configuration is formed with the manganite as the channel and the Nb:STO substrate as the gate. Channel resistance modulation by the gate pulsing is studied both with and without magnetic field. We not only find a remarkably large electroresistance effect of 76% at 4× 105V/ cm, but also the complimentarity of this ER effect with the widely studied CMR effect. The large size of this effect and the complimentarity of ER and MR effects strongly suggest a percolative phase separated picture of manganites.
Epitaxial Pb(Zr0.52Ti0.48)O3/La0.7(Pb,Sr)0.3MnO3 Ferroelectric/CMR Memory Optimized for Room Temperature Operation
Authors: Lundström Daniel , Yilbar Jan , Khartsev S.I. , Grishin Alex , Okuyama Masanori
Published: April 2011

Epitaxial ferroelectric/colossal magnetoresistive PbZr0.52Ti0.48O3/La0.7(Pb,Sr)0.3MnO3 (PZT/LPSMO) thin film heterostructures have been grown onto SrTiO3 single crystals by KrF pulsed laser deposition technique to fabricate nonvolatile magnetosensitive memory. Colossal magnetoresisitivity (CMR) in LPSMO film has been tailored to room temperature by compositional control to get the maximum temperature coefficient of resistivity of 7.3 %K−1 @ 295 K and maximim magnetoresistivity of 27% @ 7 kOe and 300 K. The main processing parameters have been optimized to preserve CMR performance in LPSMO film after deposition of the top ferroelectric layer. Vertical Au/PZT/LPSMO/STO capacitor cell possesses very high dielectric permittivity about 1500 and rather low loss of 5% at 1 kHz, saturation polarization of 40.4 µC/cm2, remnant polarization of 20.6 µC/cm2, coercive field of 22.8 kV/cm, and no visible fatigue after 1.33.108 reversals. Three top contact metals: Au, Pt, and Ta, deposited at room temperature, have been examined. As compared with Ta, Pt and Au top contacts show superior performance regarding to combined properties: high remnant and saturation polarization, low loss and no fatigue while top Ta contacts have been found to be more efficient to reduce leakage in ferroelectric film.
Synthesis and Properties of Epitaxial Thin Films of c-axis Oriented Metastable Four-Layered Hexagonal BaRuO3
Authors: Lee M. K. , Eom C. B. , Tian W. , Pan X. Q. , Smoak M. C. , Tsui F. , Krajewski J. J.
Published: April 2011

We have grown epitaxial thin films of metastable four-layered hexagonal (4H) BaRuO3 on (111) SrTiO3 by 90° off-axis sputtering techniques. X-ray diffraction and transmission electron microscopy experiments reveal that the films are single crystals of c-axis 4H structures with an inplane epitaxial arrangement of BaRuO3 [2110] // SrTiO3 [110]. Smooth multilayer growth has been observed in these films with a step height equaling the size of half unit cell. In-plane resistivity of the films is metallic, with a room temperature value of about 810µΩ-cm and slightly curved temperature dependence. Their magnetic susceptibility is paramagnetic. The metastable layered compounds can be very useful for understanding new solid-state phenomena and novel device applications.
Growth and Characterization of Epitaxial Thin Heterostructures of Ferromagnetic/Antiferromagnetic SrRuO3/Sr2YRuO6
Authors: Price R.A. , Lee M.K. , Eom C.B. , Wu X.W. , Rzchowski M.S.
Published: April 2011

We have grown epitaxial thin films of antiferromagnetic ruthenate Sr2YRuO6 on miscut (001) SrTiO3 by 90° off-axis sputtering. Sr2YRuO6 is a unique material that allows us to grow epitaxial ferromagnetic/antiferromagnetic heterostructures. Antiferromagnetic Sr2YRuO6 has the same pseudo-cubic perovskite crystal structure as the ferromagnetic conductive oxide SrRuO3. The Sr2YRuO6 perovskite crystal structure has Y and pentavalent Ru located on the octahedral sites and the pseudo-cubic lattice parameter of 4.08Å. The Neel temperature of bulk Sr2YRuO6 is known to be 26K. Four-circle X-ray diffraction analysis revealed the Sr2YRuO6 films are purely (110) normal to the substrate with two 90° domains in the plane. We have also grown epitaxial heterostructures of SrRuO3/Sr2YRuO6. These bilayers permit detailed studies of the magnetic exchange bias phenomena at these interfaces, including the role of uncompensated spins thought to arise from interface roughness. Magnetization measurements on the SrRuO3/Sr2YRuO6 heterostructures show a shifting of the hysteresis loop, indicating exchange bias. Such exchange-biased interfaces are important for electrode pinning in magnetic tunnel junctions.
Substituted Barium Hexaferrite Films for Planar Integrated Phase Shifters
Authors: Oliver S.A. , Yoon S.D. , Kozulin I. , Shi P. , Zuo X. , Vittoria C.
Published: April 2011

Thick films of scandium-substituted BaScxFe12−xO19 (x=0, 0.4, 0.6) were deposited by pulsed laser ablation deposition onto A-plane (1120) sapphire (Al2O3) substrates to yield highly oriented films having the crystallographic c-axis ([0001]) in the film plane. Selected films were characterized by x-ray diffraction, electron microscopy, magnetometry and torque magnetometry measurements. These structural and magnetic measurements show that dense films have excellent in-plane uniaxial anisotropies and good square loop behaviors. Such films will be useful for planar latched phase shifters that can be integrated into microwave integrated circuits.
Properties of Zr-Substituted (Ba,Sr)TiO3 Thin Films for Integrated Capacitors
Authors: Stauf G. T. , Chen P. S. , Paw W. , Roeder J. F. , Ayguavives T. , Maria J.-P. , Kingon A. I.
Published: April 2011

There has been significant interest recently in use of BaSrTiO3 (BST) thin films for integrated capacitors; these devices have benefits for high frequency operations, particularly when high levels of charge or energy storage are required. We discuss the electrical properties of BST thin films grown by metalorganic chemical vapor deposition (MOCVD) which make them suitable for these applications, as well as the impact of processing conditions such as growth temperature on specific film properties. We have also examined addition of Zr in amounts ranging up to 20% to the BST films. X-Ray diffraction indicates that the Zr is incorporated into the BST lattice. Voltage withstanding capability, leakage and dielectric constant of the thin films have been measured as functions of deposition temperature and Zr content. Addition of Zr to BST films increases breakdown voltages by as much as a factor of two, to approximately 2 MV/cm, raising their energy storage density values to levels approaching 30 J/cc. Charge storage densities of above 60 fF/µm2were also obtained.
Pulsed Laser Deposited Na0.5K0.5NbO3 Thin Films
Authors: Cho Choong-Rae , Grishin Alex , Moon Byung-Moo
Published: April 2011

Na0.5K0.5NbO3 films have been grown onto polycrystalline Pt80Ir20 substrates at two different regimes: high (∼ 400 mTorr) and low (∼ 10 mTorr) oxygen pressure. Films grown at high oxygen pressure have been found to be single phase and highly c-axis oriented. The concept of discriminated thermalization has been developed to explain the dynamics of the laser ablation process and to find reliable pulsed laser deposition (PLD) processing conditions. The phenomenon of self assembling of Na0.5K0.5NbO3 films along [001] direction has been observed. On the other hand, films grown at low oxygen pressure have been found to be mixed phase of ferroelectric Na0.5K0.5 NbO3 and paraelectric potassium niobates. Superparaelectric behavior has been observed in these films: 5% tunability at electric field of 100 kV/cm, losses as low as 0.003 and excellent stability to the temperature and frequency changes.
Dielectric Properties of Ba1−xSxTiO3 Films Grown on LaAlO3 Substrates
Authors: Gim Y. , Hudson T. , Fan Y. , Findikoglu A. T. , Kwon C. , Gibbons B. J. , Jia Q. X.
Published: April 2011

We report the crystal structures and dielectric properties of barium strontium titanate, Ba1−xSrxTiO3 (BST), films deposited on LaAlO3 substrates using pulsed laser deposition, where x = 0.1 to 0.9 at an interval of 0.1. We have found that when x < 0.4 the c-axis is parallel to the plane of the substrate but normal as x approaches 1. Temperature-dependent capacitance measurements at 1 MHz show that the capacitance has a peak and that the peak temperature decreases with increasing x. We have found that the peak temperatures of the films are about 70 °C higher than those of bulk BSTs when x < 0.4. From room-temperature capacitance (C) vs applied voltage (V) measurements, we have found that the C-V curves of the BST films exhibit hysteresis except for x = 0.9 and that the peak voltage at which the capacitance becomes maximum decreases with increasing x. At room temperature, the Ba0.6Sr0.4 TiO3 film exhibits the largest capacitance tunability (≈ 37%) with an applied electric field of 40 kV/cm.
Tunable Photonic Crystals
Authors: Figotin A. , Godin Yu.A. , Vitebsky I.
Published: April 2011

Photonic crystals are spatially periodic dielectric structures usually composed of two different components. We consider a photonic crystal formed by a periodic array of voids in an optically dense homogeneous substance as shown in Fig. 1. The electromagnetic (EM) spectrum of a photonic crystal with a given geometry is determined by the refractive indices of its constitutive components.
Permittivity and Microstructure of (Ba,Sr)TiO3 Films: Temperature and Electric Field Response
Authors: Boikov Yu.A. , Claeson T. , Ivanov Z. , Olsson E.
Published: April 2011

Epitaxial heterostructures (001)(Y,Nd)Ba2Cu3O7-δ∥(100)SrTiO3∥(001)(Nd,Y)Ba2Cu3O7-δ,(100)SrRuO3∥(100)Ba0.8Sr0.2TiO3∥(100)SrRuO3, (100)SrRuO3∥(100)SrTiO3∥(100)SrRuO3 and (100)SrTiO3∥(001)YBa2Cu3O7-δ have been grown by laser ablation. There was only a small difference of the dielectric permittivity, in the temperature range 180-300K, between a bulk single crystal and an epitaxial (100)SrTiO3 layer inserted between either high-Tc superconducting or SrRuO3 electrodes. At T<1 50K, on the other hand, the response of the dielectric permittivity of the SrTiO3 layer on temperature or electric field depended to a large extent upon the materials used as bottom and top electrodes in the heterostructures. The temperature dependence of the dielectric permittivity for the SrTiO3 layer in (100)SrRuO3∥(100)SrTiO3∥(100)SrRuO3 was well extrapolated by a Curie-Weiss relation in the range of T=80-300K, with about the same Curie constant (C0=7.5 × 104 K) and Curie temperature (TCurie=21K) as in a bulk single crystal. At temperatures higher the phase transition point (65 K), the electric field response of the permittivity of the SrTiO3 layer between high-TC superconducting or metallic oxide electrodes was well extrapolated by the same relation used for a bulk single crystal. The smallest loss factor, tanδ, was measured for the capacitance (100)SrRuO3∥(100)SrTiO3∥(100)SrRuO3 (T ≈ 50-300K, f=100kHz). The measured conductance G for the SrTiO3 layer in the (001)(Y,Nd)Ba2Cu3O7-δ heterostructure fitted well the relation InG∼-(ED/kT), with ED=0.08-0.09 eV in a temperature range close to 300K. Pronounced hysteresis was observed in the temperature dependence of the dielectric permittivity for the (100)Ba0.8Sr0.2TiO3 layer at temperatures close to the phase transition point, like in the case of a bulk single crystal. The permittivity of the (100)Ba0.8Sr0.2TiO3 layer decreased more than 50% when an electric field of 2.5×106V/m (T ≈ 300K, f=100 kHz ) was applied.
Soft-Mode Phonons in SrTiO3 Thin Films Studied by Far-Infrared Ellipsometry and Raman Scattering
Authors: Sirenko A. A. , Bernhard C. , Golnik A. , Akimov I. A. , Clark A. M. , Hao J.-H. , Xi X. X.
Published: April 2011

We report the experimental studies of the vibrational spectra of SrTiO3 films with the thickness of 1 µm grown by pulsed laser deposition. Fourier-transform infrared ellipsometry between 30 and 700 cm−1 and electric field-induced Raman scattering have been utilized for investigation of the phonon behavior. These results can be used for comparison with the low-frequency measurements of the static dielectric constant. In the films, the soft mode reveals hardening compared to that in bulk crystals. This observation is in agreement with the Lyddane-Sachs-Teller formalism.
Microwave Dielectric Tuning and Losses in Epitaxial Lift-Off Thin Films of Strontium Titanate
Authors: Rogers Charles T. , Dalberth Mark J. , Price John C.
Published: April 2011

We report on the complex dielectric response function for SrTiO3 (STO) thin films that have been removed from the original growth substrate via an epitaxial lift-off process. We measured the dielectric response as a function of frequency (10 kHz to above 2 GHz), as a function of temperature (4 K to 300 K), and as a function of applied electric field (between +/− 10 V/µm). The dielectric properties are well described by a model based on a dilute set of thermally activated two-level dipoles in a matrix of bulk STO. Activation energies for the dipoles are found to cluster around two central values near 50 meV and 100 meV. Attempt frequencies are generally around 10 THz. Assuming that the dipole moment of a typical two-level system is equal to that of a unit cell of polarized bulk STO, we find that a volume fraction of roughly 4% of a typical film is involved in the dipole response.
Ba1−xSrxTiO3 Thin Film Sputter-Growth Processes and Electrical Property Relationships for High Frequency Devices
Authors: Im Jaemo , Auciello O. , Streiffer S.K. , Baumann P.K. , Eastman J.A. , Kaufman D.Y. , Krauss A.R. , Li Jianxing
Published: April 2011

Precise control of Ba1−xSrxTiO3 (BST) film composition is critical for the production of high-quality BST thin films. Specifically, it is known that nonstoichiometry greatly affects the electrical properties of BST film capacitors. We are investigating the compositionmicrostructure- electrical property relationships of polycrystalline BST films produced by magnetron sputter-deposition using a single target with a Ba/Sr ratio of 50/50 and a (Ba+Sr)/Ti ratio of 1.0. It was determined that the (Ba+Sr)/Ti ratios of these BST films could be adjusted from 0.73 to 0.98 by changing the total (Ar+O2) process pressure, while the O2/Ar ratio did not strongly affect the metal ion composition. The crystalline quality as well as the measured dielectric constant, dielectric tunability, and electrical breakdown voltage of BST films have been found to be strongly dependent on the composition of the BST films, especially the (Ba+Sr)/Ti ratio. We discuss the impact of BST film composition control, through film deposition and process parameters, on the electrical properties of BST capacitors for high frequency devices.
Boron Activation During Solid Phase Epitaxial Regrowth
Authors: Lindfors C. D. , Jones K. S. , Law M. E. , Downey D. F. , Murto R. W.
Published: April 2011

To continue scaling dimensions of transistors, higher dopant concentration levels are needed for ultra-shallow contacts. Therefore studies of dopant activation have been performed in preamorphized silicon wafers with various boron implant conditions to determine the maximum achievable dopant concentrations after Solid Phase Epitaxial Regrowth (SPER) alone. In the first experiment a silicon piece was preamorphized with a 30 keV, 1×1015 cm−2 and 90 keV, 1×1015 cm−2 Si+ implant followed by a 30 keV, 1×1015 cm−2 B+ implant. Solid phase epitaxial regrowth at 500 °C indicates that boron can be activated at low temperatures. Ultra Low Energy (ULE) implants were studied in the second experiment. Silicon wafers were implanted with 2.5 keV, 1×1015 cm−2 Si+ to amorphize and then B+ was implanted at 0.5 keV in the dose range of 1×1015 to 9×1015 cm−2. Samples were annealed in the temperature range of 500 to 650 °C. High concentrations of boron make it difficult to fully regrow amorphous layers and thus yield marginal electrical properties. Much of the boron remains inactive, particularly at the higher dose implants. In both experiments Variable Angle Spectroscopic Ellipsometry (VASE) is used to measure amorphous layer thickness and Hall effect measures active boron dose. For the first experiment, Secondary Ion Mass Spectrometry (SIMS) data compares chemical dose to active dose during the regrowth process. Sheet resistance data is obtained from a four point probe for the ULE implant experiment.
Effects of Nonmelt Laser Annealing on a 5keV Boron Implant in Silicon
Authors: Earles Susan , Law Mark , Jones Kevin , Brindos Rich , Talwar omit
Published: April 2011

To investigate the effects of ramp rate on the transient enhanced diffusion of boron in silicon, laser thermal processing (LTP) in the nonmelt regime has been investigated. A nonmelt laser anneal has been performed on a 5 keV, 1e15 boron implant. The implant energy of 5keV was chosen to simplify analysis. A rapid thermal anneal (RTA) at 1000°C and furnace anneals at 750 °C were used to show the effect of post annealing on the LTPd samples. Results show the sheet resistance drops by up to a factor of two for samples receiving the nonmelt LTP and the RTA compared with the samples just receiving the RTA. An increase in the hall mobility was also observed for the samples receiving the LTP. The nonmelt LTP was also shown to strongly affect the extended defect density. During post anneals, a higher density of smaller defects evolved in the samples receiving the LTP.
Self-Interstitial clusters in silicon
Authors: Souza M. M. De , Chichkine M. P. , Narayanan E. M. Sankara
Published: April 2011

In this paper we propose structural models of self-interstitial clusters in silicon using the empirical potential method. Novel, fully co-ordinated compact clusters based on the hexagonal interstitial up to size four have been proposed. The energetics of their formation indicates that energy minimisation occurs due to elimination of dangling bonds. While the conventional dangling bond model yields an exponential decrease in the formation energy with size, we observe stable defects for sizes in multiples of four. The energy barrier required for a transition from compact model to the dangling bond chain model can possibly explain the experimentally observed energy barrier for sizes greater than eight.
SSRM and SCM Observation of Enhanced Lateral As- and BF2-diffusion Induced by Nitride Spacers
Authors: Eyben P. , Duhayon N. , Stuer C. , Wolf I. De , Rooyackers R. , Clarysse T. , Vandervorst W. , Badenes G.
Published: April 2011

State-of-the-art semiconductor devices require an accurate control of the complete twodimensional dopant distribution. The routine use of process simulators to predict the envisaged distributions and their resulting accuracy, is strongly linked to the physical models contained in these programs as well as their calibration. Whereas SIMS and SRP have been used extensively for the calibration of 1D-profiles, calibration of 2D-profiles has been very limited.

In this work, we report some results obtained with the 2D-profiling techniques SSRM (Scanning Spreading Resistance Microscopy) and SCM (Scanning Capacitance Microscopy ) for the study of two-dimensional effects on diffusion. In particular, we discuss the role of the nitride spacer on the lateral diffusion of arsenic and boron. Using series of transistors with different nitride spacers with or without TEOS-liners, a strong dependence between the lateral diffusion and the nitride spacer thickness can be observed using SSRM and SCM. The process flow eliminates the possible contribution of Transient enhanced diffusion (TED) as a dominant mechanism. At the same time an enhancement of the lateral stress underneath the spacers has been observed with CBED and Raman, suggesting a correlation between the lateral diffusion and the nitride spacers. The enhanced diffusion of As and B is strongly linked to the spacer size whereby the differences in enhancement suggest that the proximity of the dopants to the stress field field region is an important parameter.
Increasing the Lateral Resolution of Scanning Spreading Resistance Microscopy
Authors: Kline R.J. , Richards J.F. , Russell P.E.
Published: April 2011

This paper discusses problems inherent to scanning spreading resistance microscopy (SSRM) and ways to correct them to increase the resolution of two-dimensional dopant profiling. Specifically this paper looks into issues related to the probe-silicon contact and the damaged surface layer created by the sample preparation technique. Degradation of the measured dopant profile was observed when the probe scanned over the nitride spacers. Attempts to reduce the required contact pressures to increase the lifetime and effectiveness of the probes are addressed. The force required for SSRM was successfully reduced after the damage layer was partially removed by isotropic etching.
Dopant Diffusion in Silicon Substrate during Oxynitride Process
Authors: Aoki Nobutoshi , Yaegashi Toshitake , Takeuchi Yuji , Fujiwara Makoto , Kusunoki Naoki , Sato Tsutomu , Mizushima Ichiro , Tsunashima Yoshitaka , Hazama Hiroaki , Aritome Seiichi , Shirota Riichiro , Shimizu Takashi
Published: April 2011

We found an anomalous behavior of dopant diffusion in Si substrate during the oxynitride process. SIMS measurements showed a notably enhanced diffusion during the NO and N2O oxynitride process. The considerably enhanced diffusion was also observed in re-oxidation of oxynitride film grown by the NO annealing or NH3 nitridation of a SiO2 film. In order to simulate the enhanced diffusion, an enhancement coefficient was introduced, showing that the simulation results are in reasonable agreement with the experimental ones. We applied the diffusion model to the simulations of MOSFETs fabricated under various conditions of the oxynitride process. The device characteristics of MOSFETs were successfully reproduced by adopting a suitable dependence of nitrogen concentration CN on the surface recombination rate of interstitial Si at the oxynitride/Si substrate interface.
Cryo-Implantation Technology for Controlling Defects and impurity out diffusion
Authors: Murakoshi Atsushi , Suguro Kyoichi , Iwase Masao , Tomita Mitsuhiro , Okumura Katsuya
Published: April 2011

We propose a novel process module by using cryo-implantation and rapid thermal annealing (RTA). Boron or arsenic ions were implanted into a 8 inch (100) Si substrate which was cooled by using liquid nitrogen. The substrate temperature was controlled to be below at -160°C during ion implantation. It was found that an amorphous layer was formed by boron or arsenic implantation and the amorphous layer was completely recovered to a single crystal after annealing at 900°C for 30sec. No dislocation was observed in the implanted layer. It was also found that the thermal diffusion of boron was suppressed by cryo-implantation. PN junction depth was found to be about 10-20% shallower than that of room temperature implantation. These results suggest that transient enhanced diffusion of boron can be reduced by suppressing vacancy migration toward the surface during implantation. Cryo-implantation was found to be very effective in reducing defects and PN junction leakage was successfully reduced by one order of magnitude as compared with room temperature implantation.
Quantitative Measurement of Interstitial Flux and Surface Super-saturation during Oxidation of Silicon
Authors: Carroll M. S. , Sturm J. C.
Published: April 2011

During the oxidation of silicon, interstitials are generated at the oxidizing surface and diffuse into the silicon. Boron diffusion was used to map the local interstitial super-saturation, the ratio of interstitial concentration to the equilibrium concentration of interstitials I/I*, versus depth above buried Si0.795Ge0.2C0.005 layers during oxidation. The average interstitial supersaturation at the silicon surface, extrapolated from the depth profiles, is measured as, ∼24 and ∼11.5 for 750°C and 850°C respectively. Using the measured interstitial concentration at the surface, the silicon interstitial injection into the silicon is calculated for oxidation at 750°C and 850°C. Finally, it is found that the surface boundary condition remains fixed over an interstitial injection rate ranging over 4 orders of magnitude.
Understanding and Modeling Ramp Rate Effects on Shallow Junction Formation
Authors: Chakravarthi Srinvasan , Gencer Alp H. , Dunham Scott T. , Downey Daniel F.
Published: April 2011

In summary, we find it is possible to model the extent of diffusion during spike anneals with varying ramp rates by considering the full thermal cycle. These models allow the optimization of RTP ammealing cycles considering the trade-offs between junction depth and sheet resistance. For example, with 1050°C spike anneals, the active dose (and thus sheet conductivity) varies approximately linearly with junction depth. However, faster ramp rates allow the use of higher spike temperatures, with associated higher activation and reduced sheet resistance for the same junction depth.

Work at Bosten University and the University of Washington was supported by the Semiconductor Research Corporation. We would like to thank Eric Perozziello for details and discussion regarding their experimental results.
Boron Diffusion Mechanism in Silicon Oxide Using AB Initio Methods
Authors: Zubkov V. , Senosiain J. P. , Aronowitz S. , Sukharev V. , Musgrave C. B.
Published: April 2011

Density functional theory was employed to explore the diffusion mechanism of boron in amorphous silicon oxide. The oxide was modeled with clusters of various sizes, and both neutral boron atoms and cations were considered. Three stable structures were found where B (or B+) was inserted into oxide: one in which B (or B+) is divalent and two in which B (or B+) is trivalent. Boron diffusion through silicon oxide proceeds as a sequence of B hops from one inserted position to another. For neutral boron the rate limiting step is B hop from one of trivalent structures to a divalent one with activation energies (Ea) in the range of 2.0-3.1 eV, depending on the model cluster. In the case of a cation the rate-limiting step is the B+ hop over the O atom in a divalent structure Si-B+-O-Si with calculated Ea of 2.4-2.8 eV. Experimental activation energies for B diffusion in silicon oxide are in the 2.3 - 4.2 eV range. Our results suggest that both neutral and cation boron can participate in B diffusion in oxide.
A Study of Boron Clustering Transients and Mechanisms in Doped Silicon
Authors: Lilak Aaron D. , Krishnamoorthy Viswanath , Vieira David , Law Mark , Jones Kevin
Published: April 2011

The ion implantation of boron remains the most practical means of forming shallow and ultra-shallow p+/n junctions in silicon. A high conductive junction requires both a large density of dopant atoms and electrical activation amongst these. While it is possible to simply higher doses of boron at lower energies, the potential benefits of the changes are often muted by the electrical deactivation of the boron was occurs through a clustering process. Therefore, it is important to do understanding of the kinetics and transients involved in these proces.

It has been shown that ion implanted boron clusters with interst residual from the implantation process. These clusters are immobile, fractionally or totally electrically inactive, and very thermally state study a series of experiments were conducted in order to investigate processes. In addition to this, a means of utilizing X-ray Diffractio to correlate electrical activity to the rocking curve has been development
Clusters and Planar Defects in Boron Implanted Silicon an X-Ray Diffuse Scattering Study
Authors: Kegel I. , Sztucki M. , Metzger T. H. , Lubbert D. , Arthur J. , Patel J.R.
Published: April 2011

In a grazing incidence x-ray diffuse scattering study of defects in boron implanted and annealed silicon we have discovered narrow rods of intensity along [111] directions. These diffuse rods of intensity arise from stacking faults formed in the early stages of annealing in the range around 1000°C. From the width of the stacking fault induced rods we can estimate their size, while the integrated intensity is a measure of the total stacking fault area in the implanted layer. Surprisingly we find that these faults initially grow in size and density and after reaching a maximum begin to dissolve and ultimately are totally annihilated. The intensity rods are distinct from the point defect or point defect cluster scattering in the tails of the Bragg peaks referred to as Huang Scattering. From the nature of the q dependence of the diffuse scattering in the Bragg tails we find unequivocal evidence for the presence of clusters in our annealed samples. The average effective size seems remarkably independent of annealing temperature. These observations will be discussed in the context of the enhanced diffusion of boron over its bulk value.