bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Stability of a-SiNx:H Films
Authors: Kudoyargva V.Kh. , Aivazov A. A. , Budaguan B. G. , Filatova I. V.
Published: March 2011

The investigations of thermal stability of a-SiNx:H films (x≤0.4) have xbeen performed bv both IR spectroscopy and DTA techniques. The properties of samples with x≤0.06 were attentively considered because in this case the nitrogen may be treated as an impurity in a-Si:H. It has been shown that controlled nitrogen doping (up to 0.5 Pa NH3) can be used as an effective technique for thermostabilization of a-Si:H properties.
Prolonged Storage of Electrons in Monos-Structures
Authors: Maslovsky Vladimir M. , Simanovich Ellen V.
Published: March 2011

The transient process of the accumulation of charge in the Silicon Nitride by applying a positive voltage pulse to MONOS structure is investigated with the help of the experimental and theoretical methods (monopolar injection of electrons). The mathematical model of charge carriers transport in an amorphous nitride thin films in MONOS structures at the high electric fields has been developed. The essential peculiarity of this modelis that the injected carriers from the contact are captured by a quasi - continuous spectrum of states that there are traps, having an exponential distribution of densityin the nitride band gap and by the monoenergetic positively charged deep centers. The positive traps are made by the negative correlation energy defects. These defects are formed by the weak quasi- hydrogenous bonds Si-H-Si the changes of ones in consequences of a migration of hydrogen stipulate for the degradation processes in the nitride. It is established that the quasi - distributed traps are answered for the prolonged relaxation of current in the external circuit when t≫Tg in which the exponent α of function J∼t-α is determined by the parameter of the energy distribution of traps and by the applied voltage on the structure that is in agreement with experimental results and corresponds to the dispersive transport of carriers.
The Effects of Silicon Source Gas on PECVD SiO2 Properties
Authors: Burns James A. , Gleason Edward F.
Published: March 2011

Silicon dioxide was plasma-deposited at 300C using either the reaction of silane and nitrous oxide or the reaction of tetraethylorthosilicate with oxygen. The structural and electronic properties of films produced by both reactions were studied as functions of post-deposition heat treatments. The former reaction produced films which were more dense and less conductive than the latter. A model was developed to determine the amount and location of charge in the deposited films. The charge was found to be dependent on the reaction and the post-deposition anneal.
Hydrogen in RF Reactive Magnetron Sputtered Silicon Nitride Films
Authors: Lin Chi-Hsien , Wachtman J. B. , Sigel G. H. , Pfeffer R. L. , Monahan T. P. , Lareau R. T.
Published: March 2011

ABSTRACT: Silicon nitride films (a-SixN1−x:H) have been prepared by rf reactive magnetron sputtering from a silicon target in a mixture gas of Ar, N2, and H2. The effects of the presence of hydrogen gas have been related to the refractive index, deposition rate, etch rate, and the Si-H and N-H bonding in the films. Hydrogen contents were measured by a quadrupole secondary ion mass spectrometer (SIMS) using deuterium implanted samples as reference standards. The deuterium implanted samples were annealed at 900°C for various periods of time to study the diffusion behavior of deuterium and hydrogen in a Si-rich and a nearly stoichiometric silicon nitride film.
Study of SiF4-N2-H2 Plasmas for the Deposition of Fluorinated Silicon Nitride Films
Authors: Cicala G. , Bruno G. , Capezzuto P. , Losurdo M.
Published: March 2011

Radiofrequency glow discharges, operating under various conditions, have been used to deposit hydrogenated and fluorinated silicon nitride (a-Si,N:H,F) from SiF4-N2-H2 gas mixtures. The effect of the feeding mixture composition has been investigated in order to establish the optimum deposition conditions for stable silicon nitride. High H2-dilution of the feeding mixture has been found to produce transparent (Eg>5.6eV) and stoichiometric (N/Si=1.3) films.
Interaction of Atonic Hydrogen with Ion Bombardment Induced Defects at Si/SiO2 Interfaces
Authors: Kar S. , Ashok S.
Published: March 2011

Electrically active traps were induced in the Si-SiO2 interfacial region by silicon ion bombardment. A Kaufman source was used to introduce 400 eV hydrogen ions into the oxide and the interface. The interaction of the hydrogen species with the traps was monitored by a comprehensive set of electrical measurements of the metal-oxide-silicon [MOS] structures.
Paramagnetic Defect Analysis in UV Lamp Induced Chemical Vapour Deposited a-SiO2 Films
Authors: Debauche C. , Licoppe C. , Flicstein J. , Devine R. A. B.
Published: March 2011

An electron spin resonance study has been carried out on a-SiO2 films deposited from SiH4 and N2O gases using UV lamp induced chemical vapour deposition. Deposition pressures have been varied from 5 torr to 30 torr whilst the substrate temperature was maintained at 240°C. Bridging nitrogen (O3≡Si-N-Si≡O3) and oxygen-vacancy center defects are observed in small quantities (≈ 1016cm−3) whilst over coordinated N defects are observed in concentrations up to 1018 cm−3 dependent upon the deposition pressure. The concentration of these defects can be dramatically reduced either by depositing the a-SiO2 at high pressures (≈ 30 torr) or by post-deposition annealing at ≈ 600°C. Comparison with data on films produced by plasma enhanced chemical vapour deposition demonstrates that the mode of incorporation of nitrogen into the network depends critically upon the chemical species in the deposition reactor.
Charge Trapping Properties of Thin Plasma Nitrided Oxides Induced by Nitrogen and Hydrogen Incorporation
Authors: Plossu C. , Seigneur F. , Balland B. , Piot B. , Straboni A.
Published: March 2011

In this work, we report the effects of an ammonia plasma nitridation on the charge trapping properties of thin SiO2 films in correlation with their nitrogen and hydrogen contents. Electron traps characteristics were determined by die avalanche injection technique. Hydrogen contents were measured by Elastic Recoil Detection analysis (ERDA). Nitrogen depth profiles were obtained with Auger spectroscopy. It is shown that the bulk electron trapping properties are essentially controlled by the specificity of hydrogen and nitrogen incorporation in the SiO2 films during the ammonia plasma process. For short nitridation times, an increase of hydrogen related electron trap densities is observed in good agreement with hydrogen ERDA measurements. However hydrogen concentration never exceeds 3 at% and can be scaled down by a short time post-nitridation anneal in oxygen, to a level comparable indeed inferior to that of a non-nitrided oxide. For heavy nitridation, an additional electron trap is detected which could be associated to the presence of nitrogen in the bulk of SiO2.
Energy-Filtered Electron Diffraction from Silica Thin Films
Authors: Qin L. C. , Hobbs L. W.
Published: March 2011

Energy filtering has been applied to electron diffraction patterns to obtain electron scattering intensity data of single energy collected using a scanning transmission electron microscope. For amorphous materials, the technique permits reconstruction of radial distribution functions from elastically scattered electron intensity data; amorphous silica thin films have been analyzed in the present experiments. The radial distribution functions are characterized in terms of interatomic distances and are compared to neutron scattering results in the form of total correlation functions.
Plasma Deposited Oxynitride Films: Structural and Electrical Characterization
Authors: Scaglione S. , Mariucci L. , Mattacchini A. , Pecora A. , Fortunato G.
Published: March 2011

In the present work structural and electrical properties of thin films, deposited by PECVD from He-diluted S1H4+NH3+N2O gas mixtures, have been studied. Film compositions have been analyzed by NRA, RBS and hydrogen content has been determinated by ERDA while Infrared spectroscopy has been used to evaluate the local bonding configurations. Electrical properties have been measured in metal-insulator-metal structures by I-V ramp. From the results obtained, the oxynitride films show suitable properties for application as gate insulator in amorphous silicon thin film transistor.
Accelerated Degradation Mechanisms in Amorphous Silicon Thin Film Transistors
Authors: Chung I. J. , Oh C. H. , Kim W. Y. , Hwang J. R. , Kim Y. S. , Park J. S. , Lee S. K. , Han M. K.
Published: March 2011

The accelerated degradation phenomena in amorphous silicon thin film transistors due to both electrical stress and visible light illumination under the elevated temperature have been investigated systematically as a function of gate bias, light intensity, and stress time. It has been found that, in case of electrical stress, the threshold voltage shifts of a-Si TFT's may be attributed to the defect creation process at the early stage, while the charge trapping phenomena may be dominant when the illumination periods exceed about 2 hours. It has been also observed that the degradation in the device characteristics of a-Si TFT's is accelerated due to multiple stress effects, where the defect creation mechanism may be more responsible for the degradation rather than the charge trapping mechanism.
Low-Dielectric-Constant Interlayer Insulation for Multilevel Metallization
Authors: Maeda Masahiko
Published: March 2011

SiBN ternary and SiOBN quaternary films prepared by rf-plasma and/or ECR-plasma CVD have been proposed, and this paper evaluates the relationship between film structure and dielectric constant as well as the other film properties. The SiBN films contain Si-N and B-N bonds, and the dielectric constant of the SiBN films reduces with increasing proportion of B-N bonds in the films. The SiBN films are less hygroscopic than BN films and they are therefore more stable. For the SiOBN films, the effects of oxygen doping on the dielectric constant and on breakdown strength are discussed in terms of the film composition and bonding configuration. The dielectric constant decreases with increasing oxygen atomic ratio and reaches a minimum when the amount of oxygen is equal to the amount of silicon. The effectiveness of this low-dielectric-constant material as an interlay-er is confirmed in actual VLSIs with planarized two-level metallization using the SiBN interlayer.
Charge Trapping Centers in Ferroelectric Ceramics
Authors: Seager C. H. , Warren W. L. , Tuttle B. A. , Nasby R. D. , Dimos D.
Published: March 2011

Electron paramagnetic resonance (EPR), photo-thermal deflection spectroscopy (PDS), and electrical measurements have been used to characterize as-received and UV-lluminated lead lanthanum zirconate titanate (PLZT) and PZT ceramics. Following optical illumination we observe the activation of positively charged Pb+3 and negatively charged Ti+3 ions, as well as an increased broad absorption peak around 2.6 eV. The spatial distribution of the induced absorption correlates well with the location of the absorbed UV, suggesting that photo-produced carrier pairs are trapped at Ti+4 and Pb+2 producing the observed paramagnetism. The Ti+3 EPR spectra were successfully fit using the crystal field parameters derived from the PDS spectra. Preliminary results suggest that these charged paramagnetic ions can influence the electrical properties of PZT thin films. We investigated the effects of UV light and dc bias sequences by polarization-electric field (PE) measurements and find that the coercive fields are dependent on the sign of the applied bias during UV exposure. It is reasonable to expect that Pb+3 and/or Ti+3 ions act as the charge trapping sites which cause the threshold voltage shifts in the PE loop.
Physical and Electrical Properties of Tantalum Oxide Thin Films Deposited by Low Pressure Chemical Vapor Deposition
Authors: Hitchens William R. , Krusell Wilbur C. , Dobkin Daniel M.
Published: March 2011

Ta2O5 films suitable for DRAM use have been deposited on silicon, polysilicon, and SiO2 by LP-CVD from Ta (OC2H5)5 and O2. Uniformity, reproducibility, and conformality are excellent. Annealed films are polycrystalline, and their surfaces are characterized by 2 nm high, 1 mgr;m diameter nucleation centers surrounded by circular crystallization fronts. The electrical properties of annealed films are dominated by a SiO2-rich layer which forms between the Ta2O5 and the silicon or polysilicon substrate.
Low Temperature Tantalum Pentoxide Thin Films
Authors: Kwon Kee-Won , Kang Chang-Seok , Park Tai-su , Sun Yong-Bin , Sandler Neal , Tribula Dana
Published: March 2011

Ta2O5 films of high reliability and low leakage current density were obtained by low temperature deposition and subsequent high temperature oxygen anneal. At higher temperatures than 410°C, growth was governed by the formation of radicals in gas phase and oxidation on the surface, while at lower temperatures by the dissociation of reactant on the surface of substrates. As a result, the films deposited at lower temperatures had undensified structures, and contained more carbon that might be a leakage current source in Ta2O5 film. During post-deposition heat treatment in 800°C oxidating ambient, carbon was removed away and silicon was diffused from the substrate into the Ta2O5 film efficiently for its as-grown porous structure. After oxygen anneal, low temperature films get denser and are crystallized to mixed phase of orthorhombic and hexagonal Ta2O5, while high temperature films crystallized to orthorhombic single phase. Ta2O5 capacitor with low temperature films showed superior leakage characteristics applicable to sub-half micron memory devices.
Interactions in and Interfacial Structure of Annealed Co / a-Si3N4 Studied by Hrtem
Authors: Nguyen Tai D. , Nguyen Tue , Ho Herbert L. , Gronsky Ronald
Published: March 2011

Interactions between Co and a-Si3N4 films during Rapid Thermal Anneal (RTA) in N2 and Ar ambients, and during vacuum anneal, have been studied using plan-view and cross-sectional Transmission Electron Microscopy (TEM). Annealing in the temperature range 600–1000°C reveals agglomeration of the 12.5 nm Co layer and partial exposure of the nitride layer to the surface. Morphological damage of the Co/Si3N4 interface, and diffusion of Co into the nitride layer and possibly to the Si substrate, were observed after high temperature anneals. Phases of Co and CoSi2 were identified from the plan-view electron diffaction patterns. The Co/Si3N4 interaction seems to occur at lower temperature when annealed in vacuum. The microstructures and morphology of the layers and interfaces are presented. The mechanism for the diffusion of Co into the nitride layer is proposed.
Radiation Hardening of Simox Buried Oxide by Nitridation
Authors: Karulkar Pramod C. , Wyatt P. W.
Published: March 2011

Radiation hardening of SIMOX buried oxides by nitridation is demonstrated in this paper. Bare SIMOX oxide substrates, obtained by selective reactive ion etching of the top silicon film, were nitrided by annealing in ammonia at a high temperature. Al-Si thin film capacitors were fabricated on the SIMOX oxide and also on concurrently processed dry thermal oxides of similar thickness. Radiation hardness was tested by C-V measurements before and after the exposure to x-rays in an ARACOR x-ray source. SIMOX oxides were found to be inherently more resistant to radiation damage than the thermal oxides. Nitridation improved the radiation hardness of SIMOX oxides similarly to that of thermal oxides. Reoxidation nearly reversed the radiation hardening effect of nitridation in these thick (> 300 nm) oxides. For example, the following shifts in the flat band voltage were obtained when the capacitors were biased with ±5 V on the Al-Si dots and exposed to 100 krad (SiO2): -24 V for SIMOX oxide, -14.2 V for nitrided SIMOX oxide, and -22.8 V for reoxidized nitrided SIMOX oxide.
Influence of Hydrogen Plasma Treatment Upon Native Oxides Plasma Grown on INP
Authors: Belyakova E. D. , Belyakov S. V. , Berman L. S. , Gorelenok A. T. , Karimov I. N. , Karzhavin R. V. , Mokina I. A. , Shmidt N. M.
Published: March 2011

Investigations of plasma grown native oxides on indium phosphide carried out recently [1,2] have shown that these oxides exhibit properties which are promising to be used in MIS structures on InP, due to their stable composition which includes [InxPyOz]n polyphosphate phase mainly and due to reduced density of interface states (Nss<1011 eV−1 cm−2). It has been shown also that MIS structures with plasma native oxides exhibit C-V characteristics shifted towards positive values of voltage bias. The flat band shift is assigned to a negative charge injected into oxide film during plasma oxidation. The presence of this negative charge in plasma grown native oxides on InP may cause instability of electric properties of MIS structures [2].

The aim of this work was to make an attempt to influence upon negative effective oxide charge density by means of hydrogen plasma treatment.
Fast Photoluminescence Decay in a-SiNx:H Films
Authors: Palsule C. , Gangopadhyay S. , Yi S. , Shen J. M. , Naseem H. A. , Kizzar S. , Goh Freddy H. C.
Published: March 2011

We have used a fast analog technique (100 ps resolution) to study photoluminescence (PL) decay in a-SiNx:H films in nanosecond (0.1–50 ns) range. Films prepared using RF glow discharge of NF3 and pure SiH4 were used for these measurements. The PL decays in the films were studied as a function of nitrogen content for 0≤x≤0.13. When the PL decay measured at 25 K is fitted with I (t) = ao +Σai exp (-t/Ti), where ao, ai and ti, are fitting parameters, we get three distinct lifetimes with t1 = 0.8 ± 0.2 ns, T2 = 3.5 ± 0.5 ns and T3 = 14.0 ± 3.0 ns. We find that these lifetimes do not change with nitrogen content but their relative contributions to the PL decay change with nitrogen content. We have also studied the effect of temperature and excitation energy on the PL decays at different emission energies. We suggest an excitonic origin to these three recombination processes.
Determination of Atomic Velocity Distributions Using Transient Absorption Measurements
Authors: Macler Michel , Fajardo Mario E.
Published: March 2011

Results of experiments on Al, Li, and Na atomic beams produced by laser ablation using XeCI excimer laser pulses (I∼107 to l08 W/cm2) are presented. Plume emission spectra showed that further than ∼5 mm from the targets most of the excited ablated species are in neutral, atomic form. Transient absorption measurements permitted the detection of ground state atoms with different flight times, at fixed distances from the target. The resulting time of flight (TOF) distributions were converted into velocity and kinetic energy (KE) distributions.

The measured fluxes of fast atoms always increased with ablation laser intensity. The velocity distributions could not be fitted to Maxwell-Boltzmann (MB), or MB plus stream velocity type distributions. For Al plumes, comparison of velocity distributions measured at various distances from the target surface indicates that Al atoms are produced within ∼100 nsec following the leading edge of the ablation laser pulse, implying that there is a one-to-one mapping of the initial velocities to the distances traveled by the atoms after ∼1 μsec. This result should encourage efforts to develop a method of velocity selection of laser ablated metal atoms based on the spatial separation of the various velocity components along the direction of travel.
Collision Enhanced Decomposition of Microclusters Ablated from Si Surface by Excimer Laser Irradiation in Gas Environment
Authors: Kasuya A. , Nishina Y.
Published: March 2011

Laser vaporization processes in Si are analyzed in vacuum and in inert gas environment by space/time resolved optical spectrometry. The results show significant increases in the intensity of luminescence emitted from laser-vaporized plume in gas pressures up to 5 Torr in Ar and 20 Torr in Xe. The intensity then decreases with further increase in the pressure. The observed results are interpreted that collisions of inert gas atoms with a vaporized Si cluster enhances its fragmentation leading to ejection of electronically excited Si atoms and ions. The decomposition process of highly charged clusters are discussed in terms of electrostatic Coulomb effect.
Evolution and Dynamics of Excimer Laser Vaporized YBa2Cu3O7−δ
Authors: Dye R. C. , Brainard R. , Foltyn S. R. , Muenchausen R. E. , Wu X. D. , Nogar N. S.
Published: March 2011

Pulsed laser deposition of thin films is a technology whose fundamental processes are often poorly understood. Because of the difficulty of monitoring in real time either the ablation process itself (the laser-solid interaction), or thin film growth (plume-substrate interaction), studies have largely relied on diagnostic studies of the ablated plume and the resulting film to infer details about other steps in the process. Information gained from this approach has helped improve the production of high-temperature superconducting thin films.

We have studied plume dynamics during the in-situ pulsed laser deposition of YBa2Cu3O7−δ thin films. The 248 and 308 nm lines of an excimer laser were used to generate a plume from a bulk YBa2Cu3O7−δ target. Both fast intensified CCD imaging and spectral diagnostics were used to monitor plume dynamics. Variations in the plume distribution as a function of processing gas, pressure, fluence, energy, and spot size were monitored by film composition and spectral-and time-resolved imaging.
Ablation, Melting, and Smoothing of Polycrystalline Alumina by Pulsed Excimer Laser Radiation
Authors: Lowndes Douglas H. , Desilva M. , Godbole M. J. , Pedraza A. J. , Geohegan D. B.
Published: March 2011

The effects of pulsed XeCl (308 nm) laser radiation on polycrystalline Al2O3 (alumina, 99.6% pure) and single-crystal Al2O3 (sapphire) are studied as a function of laser fluence. No laser etching ofeither material is detected below a threshold fluence value, which is much lower for alumina than for sapphire. Above this threshold, laser etching of both materials is observed following a number of incubation (induction) pulses. This number is much larger for sapphire than for alumina but decreases with increasing fluence for both materials. Laser etching rates for the two materials are similar at high fluences and after the incubation period. Scanning electron microscope images show that alumina melts and flows under repeated irradiation at fluences ≥0.7 J/cm2. Atomic force microscopy and surface profilometry reveal significant smoothing of the as-received polycrystalline alumina surface after repeated irradiations at moderate fluences (∼1−3 J/cm2). Ion probe measurements for alumina in vacuum confirm the incubation behavior, and reveal that at fixed fluence the (positive) charge collected per pulse saturates after a sufficient number of pulses, as does the etch-plume velocity. The results are interpreted in terms of laser-generation of a sufficient concentration of absorption centers before efficient ablation/etching of these wide bandgap materials can occur.
Laser Assisted Seeding for Electroless Plating on Insulators
Authors: Schrott A.G. , Braren B. , O'sullivan E.J.M. , Saraf R.F.
Published: March 2011

Excimer laser pulses with wavelengths of 248 and 308 nm were used to selectively seed Pd on SiO2 surfaces, making them suitable for electroless plating. This novel seeding process for insulating materials is accomplished with the sample immersed in the seeding solution, and occurs only on the areas of the substrate that are illuminated (through the liquid) by the laser light. The Pd content of the seeded samples increased with the number of pulses, but was rather independent of repetition rate. The deposition rate showed a dependence with wavelength consistent with a defect driven mechanism for electron excitation through the band gap of SiO2. These electrons then reduce the Pd ions in the solution in contact with the surface.
Direct Patterning of Quartz Substrates by Laser Ablation Using VUV Anti-Stokes Raman Pulses
Authors: Sugioka K. , Wada S. , Tashiro H. , Toyoda K. , Sakai T. , Takai H. , Moriwaki H. , Nakamura A.
Published: March 2011

High speed microfabrication of quartz substrates by laser ablation using vacuum ultraviolet (VUV) laser beams is described. The VUV light is generated by anti-Stokes stimulated Raman scattering of fourth harmonics of Q-switched Nd:YAG laser. The well-defined patterns with a cross-sectional profile of rectangular shape are formed by using a contact mask. The role of short wavelength components of the VUV laser beams in the process is discussed.
Fast-Iccd Photography and Gated Photon Counting Measurements of Blackbody Emission from Particulates Generated in The KrF-Laser Ablation of BN and YBCO
Authors: Geohegan David B.
Published: March 2011

Fast intensified CCD photography and gated photon counting following KrF-laser irradiation of YBCO and BN targets reveal the first observations of very weak emission from slow-moving ejecta up to 2 cm from the target and times extending to ∼1.5 ms. Time-of-flight velocities inferred from the emission measurements indicate velocities (v ˜ (0.45−1.2) x 104 cm s−1) comparable to those measured for the large particles which often accompany the pulsed laser deposition process. Gated photon counting is employed to obtain temporally resolved spectra of this weak emission. The spectral shape is characteristic of blackbody emission, which shifts to longer wavelengths as the particles cool during flight in vacuum. Estimates of the temperature of the particles are made based on the emissivity of a perfect blackbody and range from 2200 K to 3200 K for both BN and YBCO when irradiated at Φ248 = 3.5 J cm−2 and 1.5 J cm−2, respectively. The temperature decrease of the particles in vacuum is compared to a radiative cooling model which gives estimates of the initial surface temperature and radii of the particles.
Epitaxial Growth of TiN on GaAs(100) by Pulsed Laser Deposition
Authors: Zheleva Tsvetanka S. , Jagannadham K. , Kumar A. , Narayan J.
Published: March 2011

Epitaxial growth of TiN films on GaAs(100) by pulsed laser deposition has been studied. Excimer KrF laser (λ=248 nm, τ=30 ns) has been used for deposition of TiN films in a chamber maintained at vacuum of ≤ 10−6 torr. The microstructure of TiN films has been characterized by x-ray diffraction and transmission electron microscopy (TEM). Cross-sectional high resolution TEM showed a smooth unreacted interface between the single crystalline TiN film and GaAs. The predominant epitaxial relationship was found to be [110]TiN//[010]GaAs, (220)TiN//(040)GaAs at a substrate temperature of 350°C. Modelling of epitaxial growth showed that the interfacial energy is an important term responsible for 45° rotation of the TiN unit cell with respect to that of GaAs. The high strain energy associated with the coherent epilayer is reduced by domain epitaxial growth. These films were characterized using high-resolution TEM techniques, and experimental results were rationalized by thin film growth modeling.
Structural and Electro-Optic Properties of Laser-Ablated Ferroelectric Bi4Ti3O12 Thin Films
Authors: Jo William , Cho Hag-Ju , Noh Tae Won , Cho Yun Seok , Kwun Suk-Il
Published: March 2011

Ferroelectric Bi4Ti3O12 thin films have been deposited using second harmonics of a Q-switched Nd:YAG laser. Various single crystal substrates, including SrTiO3(100), SrTiO3(110). MgO(100), and MgO(110), were used. Structural and electro-optic properties of the films were investigated using XRD, x-ray pole figure, and linear birefringence measurements. It is found that substrate kinds and their surface orientations are important growth parameters which determine crystal axis orientation and electro-optic properties of the Bi4Ti3O12 thin films.
Crack Development in Pulsed Laser-Deposited Pzt Thin Films
Authors: Lee H. M. , Chuang T. J. , Chiang C. K. , Cook L. P. , Schenck P. K.
Published: March 2011

The development of cracks in a PZT thin film prepared by pulsed laser deposition on an unheated Pt-coated silicon substrate, and subsequently crystallized by post-deposition annealing, was investigated as a function of film thickness. As deposited, the film was amorphous. The film was heated at 600°C to produce predominantly ferroelectric crystalline PZT. Spacing, width and morphology of cracks in the film followed a regular progression in which crack area decreased with decreasing film thickness. Data on area shrinkage, as deduced from crack area, were fit equally well as either a linear or a parabolic function of film thickness. It is suggested that crystallization-induced stresses rather than thermal-gradient related stresses, were dominant in the formation of the cracks, and that these stresses were modified by interaction with the substrate.
Laser Ablation of Pzt Films for use in Bimorph Actuator Structures
Authors: Frantti Johannes , Moilanen H. , Leppävuori S. , Uusimäki A.
Published: March 2011

Laser ablation has been used to produce piezoelectric films for use in a low voltage cantilever bimorph actuator structure. Nd doped lead zirconium titanate (PZT) films were deposited by a pulsed Q-switched Nd:YAG laser (wavelength 1064 nm) on to unheated silver-coated oxidised silicon substrates at a distance of 30 mm between substrate and target. Growth rates were typically 20 Å/s. The as-deposited PZT films were amorphous but contained small microcrystalline pyrochlore and perovskite regions. Optimisation of the annealing conditions resulted in perovskite as the main phase (T=750°C, t=2 h). A special fabrication technique (PbO covered PZT) was used to minimise film defects mainly caused by large particles.

In order to improve the density of the film and deposition rates of the ablated PZT film, ablations using an XeCl excimer laser (wavelength 308 nm) under the influence of a static magnetic field were also studied. The decreased particle size in the deposited films showed that the surface quality of the films fabricated by the excimer laser was better than that of films deposited by the Nd:YAG laser. Films were studied using EDS, XRD and also micro-Raman spectrometry.

Bimorph cantilever element structures were realised using Nd:YAG laser ablation. DC bending characteristics of these low voltage cantilever bimorphs were measured as a function of voltage using a Michelson interferometer. Displacements in the order of microns were obtained from a 15 mm x 4 mm x 80 �ement with a driving voltage level of 10 V.
Modulated Reflectance Spectroscopy of CdTe-Cd1−xMnxTe Multiple Quantum Wells and Superlattices Grown by Pulsed Laser Evaporation and Epitaxy
Authors: Labrie D. , Dubowski J.J.
Published: March 2011

Piezoreflectance and photoreflectance spectroscopies have been used to investigate the electronic properties of CdTe-Cd1-xMnxTe (x − 0.10) multiple quantum well and superlattice structures grown by Pulsed Laser Evaporation and Epitaxy (PLEE). The structures with the CdTe well widths from 54Å to 245Å have been investigated. The spectra exhibit a series of signatures which are attributed to free exciton transitions occuring between the heavy-hole and light-hole bands and the upper electron subbands within the CdTe well layers. The spectra indicate that the PLEE grown structures are of an excellent quality typical of the best currently available material.
Pulsed Laser Deposition of High Quality ZnO Thin Films
Authors: Amirhaghi S. , Craciun V. , Beech F. , Vickers M. , Tarling S. , Barnes P. , Boyd I. W.
Published: March 2011

Thin films of ZnO have been grown on silicon and glass substrates by the pulsed laser deposition method. The effects of the oxygen partial pressure, substrate temperature and laser wavelength on the structural and optical properties of the films have been studied. The KrF excimer laser (at 248 nm) was found to produce better quality thin films than the frequency doubled Nd:YAG laser (532 nm). Layers produced at substrate temperatures as low as 300°C were c-axis oriented with a FWHM value for the 002 XRD reflection less than 0.2° and exhibited optical transmission higher than 80% in the visible region.
Microstructure and Properties of CoSi2 Thin Films on (100) Silicon by Laser Physical Vapor Deposition
Authors: Tiwari P. , Chowdhury R. , Narayan J.
Published: March 2011

Laser physical vapor deposition (LPVD) has been used to deposit thin CoSi2 films on (001)silicon at different substrate temperatures ranging from room temperature to 600°C. Particulate-free silicide thin films were characterized by X-ray diffraction, Rutherford backscattering, and high resolution transmission electron microscopy. We have found that films deposited at 200°C and below are amorphous; 400°C deposited films are polycrystalline whereas films deposited at 600°C are of epitaxial nature. The Effect of subsequent annealing on resistivity of room-temperature deposited thin films has been investigated. The resistivity value decreases to less than 15 μΩcm after annealing making these films suitable for microelectronics applications. The correlation between microstructure and properties of these films are discussed.
Ybco Encapsulation by Diamond Like Carbon Films Deposited by Laser Ablation Technique
Authors: Ganapathi L. , Giles S. , Rao Rama
Published: March 2011

We have investigated the deposition and superconducting properties of YBCO thin films on single crystal LaAlO3, MgO and polycrystalline alumina substrates followed by the DLC (diamond like carbon) encapsulation [1]. DLC films were deposited at pressures ranging from high vacuum to 100 mT He. Substrate temperature was varied from 21°C to greater than 100°C. The process compatibility of Laser ablation technique for depositing both the materials was found convenient to sequentially depositYBCO and DLC films from high purity stoichiometric targets. Epitaxial YBCO films on (100) LaAlO3, (Tc−zero = 89K) and (100) MgO (Tc−zero = 85K) substrates showed identical superconducting transitions before and after encapsulation by a DLC layer. The encapsulated films showed no degradation due to acid treatment or aging over a period of 45 days. Similar results were obtained for YBCO films on polycrystallinealumina substrate. A buffer layer of YSZ was essential to obtain good superconductingproperties on alumina substrate. A 200 nm thick YSZ provided the barrier necessary for minimizing the interface reaction between Al2O3 and YBCO. Typically a Tce = 86 K was obtained for these films. These films were textured with c-axis perpendicular to the substrate surface. Likewise, there was no degradation of superconducting properties of these films after deposition of the DLC films or chemical attack by dilute HNO3.
Structure and Properties of a-C:N Films Prepared by Pulsed Excimer Laser Deposition
Authors: Xiong Fulin , Chang R. P. H. , White C. W.
Published: March 2011

We present results on the synthesis of a-C:N films deposited by pulsed excimer laser ablation of graphite in a nitrogen gas ambient. Analysis with RBS and forward recoil spectrometry show that the films are hydrogen-free and nitrogen can be incorporated upto 40% by varying the nitrogen gas pressure. Electron microscopy has identified these films to be amorphous. Raman spectroscopy, infrared spectroscopy, and electron energy loss spectroscopy have revealed carbon-nitrogen bonding structures. Compared to a-diamond films prepared by the same technique, the C:N films still possess the properties of high mechanical hardness, chemically inertness and good wear resistance, but incorporation of nitrogen into the films generally degrades their diamond-like properties. The results suggest that nitrogen doping effect is resulted in the films under the present process, instead of carbon-nitrogen compound formation.
Polymerization of Isobutylene Initiated by Laser Vaporization of Metal Targets
Authors: Vann Walter , Daly George M. , El-shall M. Samy
Published: March 2011

A novel technique involving the initiation of polymerization using laser vaporization of metal targets is being explored. In the experiment, metal ions such as Ti+, Zr+, Ag+ are generated in the gas phase by pulsed laser vaporization/ionization of a metal target using the second harmonic of a Nd:YAG laser (532 nm). The ions are pulled toward a monomer liquid(isobutylene which can only be polymerized by cationic mechanisms) by applyingappropriate electric fields across the reaction chamber. Under different experimentalconditions (temperature, pressure of a carrier gas, laser energy, electric field strength, reaction time) different polymeric products (viscous liquids or solids) were obtained with average molecular weights ranging from 200 to greater than 106. Full characterization of these materials is currently in progress. This technique could lead to a powerful approach for the synthesis of a wide variety of polymeric materials with unique properties such as stability, strength and photo and electrical conductivity.
Strong Polarity and Bond Characterization of Nanostructured Silicon Nitride Solids
Authors: Zhang Lide , Mo Chimei , Wang Tao , Xie Cunyi
Published: March 2011

Nanostructured silicon nitride solids (NANO–SSNS) were investigated by x–ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and dielectric measurements. It is found that the dielectric constant of NANO–SSNS depends strongly on the measuring frequency, f. When f<100Hz, at room temperature it is forty times as much as that of conventional Si3N4. ESR measurements show that a large number of unbinding electrons exist in interfaces. This suggests that the NANO–SSNS possess strong polarity. The study on the bond properties indicates that a large number of unsaturated and dangling bonds exist in interfaces of NANO–SSNS.
Synthesis of Transition Metal Clusters and Their Catalytic and Optical Properties
Authors: Wilcoxon J. P. , Martino A. , Baughmann R.L. , Klavetter E. , Sylwester A.P.
Published: March 2011

Metal Clusters may be synthesized in the interior of surfactant aggregates called inverse micelles. These nanosize chemical reactors permit the controlled growth of several types of metal clusters. We describe this process for the formation of Au, Ag, Pd, Pt and Ir clusters and cluster alloys. Two size-control strategies are described: 1)variation of micelle size by alteration of the surfacant and/or solvent combination used, and 2) judicious use of micelle interactions or phase behavior. Using these two methods size control in the range of 1-100 nm is possible. The optical properties of metal clusters of gold, silver, and gold/silver alloys are described and the surface plasmon resonances are shown to have dramatic blue shifts and extensive line broadening with decreasing size in the range of 10-1 nm. In the case of gold clusters, the distinct resonancein the visible disappears for sizes less than 2.0 nm and new features appear in the UV. The optical spectra of alloys of gold and silver are shown to differ dramatically from their homoatomic counterparts of the same average size. We use electron and X-ray diffraction to determine the phase structure of the metal clusters and small angle X-ray scattering, neutron scattering, light scattering and TEM to characterize the average size and size distributions of these clusters. Finally, we describe measurements of the catalytic activity of Pd clusters and demonstrate a dramatic increase in hydrogenation activity on the size range of 2-10 nm.
Nmr Study of Cluster-Assembled Nanophase Copper
Authors: Suits B. H. , Meng M. , Siegel R. W. , Liao Y. X.
Published: March 2011

63Cu and 65Cu NMR spectra from cluster-assembled nanophase copper with an average grain size between 5 and 10nm show a broadened peak, at the normal Knight-shifted frequency for copper metal, which arises from only the central 1/2 to -1/2 transition. A very broad background is observed on either side of that peak. Some samples exhibit a second broad peak at a position normally associated with non-metallic copper. Pulsed NMR measurements of the central peak show that virtually all the copper signals are significantly broadened and have a spin-spin relaxation time longer than larger grained copper samples. Line shape measurements, using spin echoes, as a function of delay between rf excitation and measurement show there are a number of copper sites with longer relaxation times which have a significantly larger broadening. Those sites are tentatively identified as being at or near a grain boundary or free surface. A small orientation effect is observed indicating an anisotropy within the samples. An isochronal anneal of one sample showed significant, but not complete, line narrowing after an anneal at 450°C consistent with other nanophase metals which show grain growth above 40-50% of the melting temperature.
Surface Structure - Catalytic Function in Nanophase Gold Catalysts
Authors: Sze Chien , Gulari Erdogan , Demczyk B.G.
Published: March 2011

Catalysts consisting of ultra-fine gold particles supported on iron oxide have been synthesized by the coprecipitation method. Subsequent to preparation, each sample was heat treated in air at four different temperatures, ranging from 473 K to 773 K. Steady state carbon monoxide oxidation was carried out over each sample. Upon extended reaction, catalyst deactivation took place over three of the catalysts whose respective surface compositions (e.g., gold to iron atomic ratio) were altered appreciably from their initial state. Surface structure analyses performed on all the unreacted catalysts have revealed variations in physical properties (e.g., degree of crystallinity and particle size). In addition, lattice parameters of gold were observed to increase up to 20 % from the bulk value. In contrast, XPS showed both gold and iron to be in essentially the same chemical states for all catalysts, irrespective of heat treatment temperatures. The importance of surface sensitive parameters to catalytic function are discussed.
Excess Thermodynamic Properties of Nanophase Titanium Dioxide Prepared by Chemical and Physical Methods
Authors: Terwilliger Chrysanthe D. , Chiang Yet-Ming
Published: March 2011

The excess enthalpy and excess heat capacity of nanophase TiO2 prepared by a chemically-derived process and by inert gas condensation have been measured using differential scanning calorimetry. In comparison to the chemically-derived samples, the excess enthalpy of the inert gas condensed samples is significantly larger, perhaps due to the presence of intragranular planar defects that accomm oate oxygen deficiency. Significant extraneous contributions from planar defects, lattice strain, phase transformation, oxidation, or sintering have been ruled out for the chemically-derived samples. A grain boundary enthalpy of 13-1.6 J/m2 in the temperature range 600-1000°C is obtained from scanning measurements. However, the data also indicate a grain size and/or temperature dependence of the grain boundary enthalpy.
Effect of Porosity on Properties of Nanocrystalline Materials
Authors: El-Sherik A.M. , Erb U. , Krstic V. , Szpunar B. , Aus M.J. , Palumbo G. , Aust K.T.
Published: March 2011

This paper discusses the effects residual porosity may have on some properties of nanocrystalline materials. The two examples considered here are Young's modulus and saturation magnetization. It will be shown that the large variations observed for these properties may be explained, at least in part, on the basis of the residual porosity in thematerials which may vary considerably depending on the production techniques used to synthesize nanostructured materials.
Structure of CoxAg100-x and Its Relation to GMR
Authors: Xiao John Q. , Samuel J. , Chien C. L.
Published: March 2011

We have studied the structure of the Co-Ag granular system across the entire composition range, as well as the annealed samples, using transmission electron microscopy (TEM) and x-ray diffraction. GMR, as much as 80% at 5K and 25% at room temperature, have been observed. The absolute values of the resistivity (ρ) and the change of the resistivity (δρ) as functions of the magnetic Co concentration and the annealing temperature have been determined. A linear relation between δρ and I/rco, where rco is Co particle size, has been found. This result suggests that the magnetic scattering at the interfaces is crucial to GMR.
Crystallization Process of Fe73.5Cu1Nb3Si13.5B9
Authors: Nakabayasiii H. , Doi M. , Matsui M. , Doyama M.
Published: March 2011

To clarify the relation between high magnetic permeability and magnetic phases of Fe73.5Cu1Nb3Si13.5B9 ribbons, the process of precipitation was investigated by using the Xray diffraction, DTA, VSM and the Mössbauer spectra at various annealing temperatures. The volume fraction of each magnetic phase was estimated. The sample annealed at 853K which shows maximum permeability is composed of partially ordered Fe3Si(70%), Fe(B) solid solution(10%) and amorphous(20%) phases. The relative permeability of the sample annealed below 853K increases with increasing the volume fraction of both of the Fe3Si partially ordered and the Fe(B) solid solution phases. The relationship between tile permeability and the volume fraction is interpreted by the random anisotropy model.
Nanophase Molecular Antiferromagnets
Authors: Papaefthymiou Georgia C.
Published: March 2011

Nanometer-sized molecular complexes of superexchange-coupled iron ions with iron nuclearity n < 10 exhibit short-range intramolecular magnetic ordering and ‘particlelike’ superparamagnetism in their low temperature Mössbauer spectra. A comparative study of the magnetic properties of ca 10 Å diameter iron-oxo phases obtained through controlled hydrolytic polymerization of iron in non-aqueous solvents is presented. The magnetic anisotropy energy constant, K, which is proportional to the observed blocking temperature, TB, and the sharpness of the superparamagnetic transition depend critically on the iron oxidation state and degree of 3d-electron delocalization. Representative examples of mixed-valent iron complexes containing oxo-bridged, octahedrally coordinated iron with primarily either Fe(III) or Fe(II) character are discussed.
Real-Space Imaging of Nanoscale Electrodeposited Ceramic Superlattices in the Scanning Tunneling Microscope
Authors: Golden Teresa D. , Raffaelle Ryne P. , Phillips Richard J. , Switzer Jay A.
Published: March 2011

We have imaged fractured cross-sections of electrodeposited ceramic oxides based on the TI-Pb-O system using a scanning tunneling microscope. The goal of this work is to measure both the modulation wavelength and compositional profile of the superlattices by mapping out the electronic properties in real space on a nanometer scale. Fourier analysis was done on STM images of all superlattices to yield the modulation wavelength. The modulation wavelength from STM was then compared with those obtained, by Faraday calculation and x-ray diffraction. The STM can be used to design “better” superlattices. We have found that the composition profile in superlattices deposited by modulating the potential was more square than in superlattices deposited by modulating the current.
Superhard Nanocomposite of Nitride Superlattices by Opposed-Cathode Unbalanced Magnetron Sputtering
Authors: Chu X. , Wong M. S. , Sproul W. D. , Barnett S. A.
Published: March 2011

Nanocomposite films of polycrystalline nitride superlattices with nanometer grain size were deposited onto tool steel substrates by a one-step process using an opposed-cathode high-rate reactive unbalanced magnetron sputtering system. The superlattices are composed of alternating thin layers of different nitrides such as TiN/NbN and TiN/VN. The thicknesses of two neighboring layers were between 3 and 150 nm and were determined by the rotating speed of the substrate holder and the sputtering rate of the individual layer material. The films exhibited exceptional hardness as high as 5200 kgf/mm2 for TiN/NbN superlattice and 5 100 kgf/mm2 for TiN/VN superlattice. The hardnesses of the superlattice coatings were strongly dependent on several deposition parameters such as the superlattice period, the nitrogen partial pressure, and the substrate bias voltage. One of the possible mechanisms for the hardness enhancement is the effect of nanophase materials, which were created mainly by the influence of the artificially layered-structure and the low energy ion bombardment during film growth.