bluuebunny/crossref_metadata_2025 huggingface dataset:
Composition Analysis of RF Plasma-Deposited Amorphous Silicon Oxynitride Thin Films by Spectroscopic Phase-Modulated Ellipsometry
Authors: Campmany J. , Andujar J. L. , Canillas A. , Costa J. , Bertran E.
Published: March 2011

Thin films of highly transparent amorphous silicon oxynitride (a-SiOx Ny:H) were prepared by rf glow discharge decomposition of SiH4,NH3 and N2O gases, in a PECVD reactor provided with an in situ phase-modulated ellipsometer. The ratio [N2O]/ ([N2O] + [NH3]) was varied from 0 to 1 in a dilution with 5% of SiH4, keeping constant the total gas flow rate. From spectroscopic ellipsometric measurements, performed in the range 1.5–5.0 eV, the refractive index of the films was calculated applying the Bruggeman effective medium theory. The structural model used considers a three-component mixture layer, composed of void, silicon dioxide (glass) and silicon nitride (pyrolitic), on a c-Si substrate. The x and y composition parameters were calculated from the fitted relative volume fraction of each constituent, ranging from a-SiO2 N0:H to a-SiO0N1.33:H, which are in fair agreement with those obtained from XPS measurements. These results, along with data of FTIR spectra of the films show a clear correlation between the void fraction and the bonded hydrogen content of the films.
Comparison of the Density and Distribution of Traps Generated by High Voltage Stress in Silicon Oxide and Silicon Oxynitrides
Authors: Richardson J. T. , Dumin D. J. , Lo G. Q. , Kwong D. L. , Gross B. J. , Sodini C. G.
Published: March 2011

A technique has been developed to determine the density and distribution of spatially deep traps throughout an insulator. These traps were created and charged by a high voltage stressing pulse and allowed to discharge upon the removal of the pulse. During the transient following pulse removal, the currents were measured. A correlation from current to trap densities and from time of decay to location within the dielectric has been made. This method has been applied to gauge the differences between nitrided dielectrics and thermal oxides. We have found initial trap levels, before stressing, to be lower in silicon oxide devices than silicon oxynitride devices. However, trap levels increased faster in thermal oxides as the stress increased, and became larger than the levels found in nitrided oxides. Nitrided devices tended to resist additional trap formation. Current-voltage measurements have shown that nitrides developed higher leakage currents as the stress was increased than did thermal oxides.
A Thermodynamic Model for the Hydrogen Incorporation in PECVD Silicon Oxynitrides Thin Layers
Authors: Cros Y. , Viscaïno S. , Arnold Bik W. M. , Habraken F. H. P. M.
Published: March 2011

In the PECVD SixNyHzOw the hydrogen is principally incorporated as N-H bonds. For O/(O+N) below 0.4, the %H is constant at 25%; from 0.4 to 1, it decreases to 4%. We show that a chemical ordered model is likely to describe the hydrogen incorporation in the amorphous network while a random bond model fails.
Instability in Amorphous Silicon Dioxide/Amorphous Silicon Structures
Authors: Fortunato G. , Mariucci L.
Published: March 2011

Amorphous insulator/amorphous silicon structures show, under bias-stress conditions, a drift of the electrical characteristics. In the present work, in order to discriminate the main source of instability in amorphous silicon dioxide/amorphous silicon Thin-Film Transistors, the determination of both threshold voltage and flat-band voltage has been performed after bias-stressing the devices with different gate voltages and at different temperatures. Flat-band voltage was determined by the space-charge photomodulation technique. From the close correlation observed between the two quantities, we conclude that the predominant instability mechanism is represented by change in the gate insulator charge at and near the insulator/semiconductor interface. Time evolution of the threshold voltage shifts has been investigated as a function of stress bias and temperature. The data are explained in terms of a new model based on the dispersive charge injection (hopping of electrons via localised states) into the first 2–3 nm of the gate insulator adjacent to die semiconductor layer (transitional region). Possible origin of the transitional region can be related to the reduction of the gate insulator induced by activated hydrogen, as suggested by photoemission experiments performed with synchrotron radiation on SiO2 bombarded with low energy (100 eV) H-ions.
FT-IR, Sims and Electrical Characterization of Si3N4 Thin Films Obtained from C.V.D. Assisted by In-Situ Electrical Discharge
Authors: Balland B. , Bureau J. C. , Plossu C. , Botton R.
Published: March 2011

An original process has been developed enabling the fabrication of CVD insulating (Si3N4) thin films, by means of an in-situ activation of the reactions at T < 400°C and under P=1 to 2 torr. Mono-Si substrates were nitrided using a mixture of argon containing SiH4 and NH3·O2 has also been added to the reaction gases. The activation was performed by a DC electrical discharge. The substrate was not used as an electrode and was placed parallel to the discharge current. This configuration minimized the contamination of the films during their formation. The obtained layers have been analyzed using FT-IR and SIMS.

M.I.S. structures have been realized, and the flat-band shift ΔVFB and the interface state density Nit have been extracted from the high and low frequency C-V characteristics. The values of the flat-band shift depend on the discharge domain and decrease with temperature. Good electrical characteristics are obtained for thin films formed at low temperature.
In Situ Investigation of Amorphous Silicon / Silicon Nitride Interfaces by Infrared Ellipsometry
Authors: Shirai H. , Drévillon B. , Ossikovski R.
Published: March 2011

A detailed in situ study, by Infrared Phase Modulated Ellipsometry (IRPME), of interfaces between amorphous silicon (a-Si:H) and silicon nitride (a-SiNx) is presented. A behaviour compatible with a sharp interface is observed when a-SiNx is deposited on top of a-Si:H, the underlayer material being very weakly influenced by the deposition of the overlayer. In contrast a graded transition is observed when a-SiNx is deposited first. In the latter case, the IR measurements directly reveal a nitrogen incorporation in the first monolayers of a-Si:H together with an increase of intensity of the SiH bonds at the interface.
Fluorinated Gate Oxide Films Utilized in Polysilicon Thin Film Transistors
Authors: Kouvatsos Dimitrios N. , Kung Ji-Ho , Hatalis Miltiadis K. , Jaccodine Ralph J.
Published: March 2011

Silicon dioxide films have been grown on polysilicon films at low temperatures in dry ambients by utilizing NF3 - enhanced oxidation, which affords markedly enhanced oxidation kinetics. This facilitates thin film transistor applications, for which low thermal budget processing is essential. The grown oxide films are thicker than corresponding oxides grown on (100) single crystal silicon. Thin film transistors having a polysilicon self-aligned gate structure were fabricated on polycrystalline silicon. The gate oxide films were thermally grown by NF3 -enhanced oxidation at 650°C or 800°C. Electrical characterization of the TFTs having 800°C gate oxides showed on/off current ratios up to 5×107, effective electron mobilities (μneff) of 26 to 38 cm2/Vsec, threshold voltage (VT) values of 0±0.7 V and subthreshold swing (S) values as low as 0.3 V/dec. The devices were stable under dc electrical stressing at a field of 3 MV/cm. Further, the source to drain current activation energy was determined as a function of the gate voltage. The 650°C gate oxide TFTs exhibited on/off current ratio of 105, VT of 3.5 V, Uneffof10 cm2/V.sec and S of 0.7 V/dec.
Properties of Oxide-Nitride-Oxide Stacked Films for Gate Insulation in Active Matrix Displays
Authors: Waechter D. , Billard T. , Gogna P.
Published: March 2011

Oxide-nitride-oxide (ONO) stacked films deposited by plasma enhanced chemical vapor deposition (PECVD) have been studied for use as the gate dielectric in active matrix displays. Good electrical properties were obtained for cadmium selenide thin film transistors (TFTs) with either ONO or single layer SiO2 gate insulation. However, the dielectric strength was up to twice as large for the ONO films. This improvement was observed with both Al and Cr electrodes.

The individual oxide layers had compressive stress, while the individual nitride layers had tensile stress. When combined in an ONO structure, a net tensile stress of relatively low magnitude was obtained. Index of refraction and infrared absorption measurements indicated that the oxide films were oxygen deficient. Hydrogen incorporation was present for both the oxide and nitride films.
Amorphous Sol-Gel Insulating Films
Authors: Brinker C. Jeffrey , Warren William L. , Logan Monica N. , Ashley Carol S.
Published: March 2011

The porosity of sol-gel thin films may be tailored for specific applications through control of the size and structure of inorganic polymers within the coating sol, the extent of polymer reaction and interpenetration during film formation, and the magnitude of the capillary pressure exerted during the final stage of drying. By maximizing the capillary pressure and avoiding excessive condensation, dense insulating films may be prepared as passivation layers on silicon substrates. Such films can exhibit excellent dielectric integrity, viz., low interface trap densities and insulating properties approaching those of thermally grown SiO2. Alternatively, through exploitation of the scaling relationship of mass and density of fractal objects, silica films can be prepared that show a variation in porosity (7–29 %) and refractive index (1.42 ndash;1.31) desired for applications in sensors, membranes, and photonics.
Electron Holographic Characterization of Ferroelectric Thin Films
Authors: Zhang Xiao , Joy David C.
Published: March 2011

In this paper we will present recent experimental results, using electron holography and electron interferometry, of studies of ferroelectric domain walls in BaTiO3 thin films. Unlike conventional TEM diffraction contrast imaging of ferroelectrics, the new technique that we have developed not only allows direct visualization of ferroelectric domain walls and electrostatic field distributions in the vicinity of the domain wall, but also enables quantitative measurement of domain wall width and local polarization. We have measured 90° domain wall width to be between 20 to 50 Å for a BaTiO3 thin specimen. The variation of polarization across the domain wall will be shown to be close to that predicted by the Zhirnov model. The value of the measured spontaneous polarization is about 1.5×10−5 C/cm2, which is closed to the bulk macroscopically measured value.
Influence of Surface Preparation Prior to Thermal Nitridation on the Electrical Characteristics of Silicon Nitride Films Deposited on Polycrystalline Silicon Films
Authors: Mathews Viju K. , Thakur Randhir P.S. , Ditali Akram , Fazan Pierre C.
Published: March 2011

Rapid thermal nitridation of the polycrystalline silicon film prior to the deposition of the silicon nitride dielectric film has been shown to be very effective in improving the dielectric characteristics for thin films. The changes at the polysilicon-silicon nitride interface has been further investigated using an in-situ clean process. This pre-treatment reduces the oxygen levels at the interface and improves the time dependent dielectric breakdown. The leakage current increases slightly due to the thinning of the silicon dioxide film at the interface.
Electrical Properties and Film Structures of (BaxSr1−x)TiO3 Thin Films by RF Sputtering
Authors: Makita T. , Horikawa T. , Kuroki H. , Kataoka M. , Tanimura J. , Mikami N. , Sato K. , Nunoshita M.
Published: March 2011

Thin films of (BaxSrj-x)TiO3 (BST) deposited by RF sputtering have been studied for the application to the capacitor material of dynamic random access memory (DRAM). The effects of film structures on the dielectric constant and the leakage current were investigated. The films deposited at 550–600°C consist of granular grains, and the films deposited above 650°C contain columnar grains. The dielectric constant is related to the grain size in the direction of thickness. The leakage current increases as the film structure changes from granular to columnar. The low leakage current (less than 10−8 A/cm2 at +2 and -2 V) and the small value of equivalent SiO2 thickness (0.9 nm) were attained in the (Ba065Sr035) TiO3 thin films.
Properties of Buried SiO2 Films in Simox Structures
Authors: Revesz A. G. , Brown G. A. , Hughes H. L.
Published: March 2011

Implantation of 1.8×1018O+/cm2 into silicon results in a buried oxide (BOX) layer, nominally 400 nm thick. The as-implanted BOX has ∼1020 cm−3 dangling bonds, ∼1020cm−3 reactive sites for interaction with H (D); the dielectric properties are ill-defined, and, similarly to densified or ion-bombarded silica glass, the SiO2 network contains an increased proportion of high energy Si-O bonds, i.e. it is “strained”. After annealing above 1300°C the properties approach those of thermally grown SiO2, the dangling Si bonds are eliminated, the D-uptake decreases, the Si/SiO2 interfaces become sharper, and the dispersed silicon agglomerates into clusters of various kind. However, the properties of BOX are still significantly different from those of thermally grown SiO2 films as shown by pronounced electron trapping, large concentration of different hole traps, decreased etch rate in HF, increased D-uptake and E' center generation rate, as well as by increased bulk conduction and the presence of localized conducting defects. These phenomena are likely to be related to some oxygen deficiency, e.g. O3SiO3 groups, as oxygen treatments reduce, but not completely eliminate, the difference between BOX and thermal oxide.
Properties of Ultrathin Amorphous Silicon Nitride Films on III V Semiconductors
Authors: Huang L.J. , Kwok R. W. M. , Lau W. M. , Tang H. T. , Lennard W. N. , Mitchell I. V. , Schultz Peter J. , Landheer D.
Published: March 2011

Properties of ultrathin (— lOnm) silicon nitride films on single crystal Si, InP and GaAs have been studied using Raman spectroscopy, medium energy ion scattering (MEIS), variable-energy positron annihilation spectroscopy and x-ray photoelectron spectroscopy (XPS). The silicon nitride films were prepared by remote microwave plasma chemical vapour deposition (RPCVD). The results showed that oxidation of the film due to air exposure was restricted to the near surface with an oxygen penetration depth no greater than 2 nm. The residual stress in the as-grown films was substrate-dependent. For films on Si (100), the film induced residual stress was compressive with a value of 0.5GPa. Annealing at 500°C for 60 minutes resulted in a complete release of the residual stress. Vacuum annealing at a temperature below 500° C also led to changes of the electrical properties in the films but not the substrate.
Advanced Dielectrics for Passivation of INSB
Authors: Barbour J. C. , Casalnuovo S. A. , Kurtz S. R.
Published: March 2011

A combination of Electron Cyclotron Resonance (ECR) plasma, electrochemical, and chemical growth process were examined to synthesize dielectric surface passivation layers on InSb. The material properties of ECR-grown SiOxNyon InSb at temperatures from 30°C to 250°C were investigated. Composition analysis was done using Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD). The electrical quality of the passivation layer was characterized with capacitance-voltage (C-V) measurements on metal-insulator-semiconductor structures over the frequency range from 1 kHz to 1 MHz. Sulfided layers, Si3ON2on InSb, and sulfided layers capped with S3ON2all exhibited good C-V properties consistent with interface state densities on the order of 1011/cm2-eV, and flatband voltages of magnitude less than 1 V. The difference in adhesion of Si3N4on InSb and the adhesion of Si3ON2on InSb was described in terms of the strength of the bonding at the dielectric-InSb interface. This work is the first to demonstrate passivation of an InSb surface with high-quality ECR silicon oxynitrides grown at room temperature.
Features of Plasma Grown Native Oxides on Indium Phosphide
Authors: Belyakova E. D. , Belyakov S. V. , Berman L. S. , Gorelenok A. T. , Karimov I. N. , Karzhavin R. V. , Mikoushkin V. M. , Mokina I. A. , Sysoev S. E. , Shmidt N. M.
Published: March 2011

Ellipsometry and XPS investigations of RF plasma grown native oxide and C-V measurements of its interface were performed.

Strong dependence of the composition of the plasma grown native oxides and electric properties of MIS structures on the time of plasma treatment has been observed. The greater the content of stable polyphosphate phase of [InxPyOz] is in the native oxide composition, the better parameters of its interface with InP (NS 11 cm−2 eV−1 and the hysteresis of C-V characteristics≤0.2 V) and the lesser C-V drift after treatment may be achieved. Plasma oxidation results in creating a negative effective oxide charge density.
Electronic Structure of Defects in Amorphous Silicon Nitride
Authors: Robertson John
Published: March 2011

The paper reviews the electronic properties of defects in amorphous silicon nitride (a-Si3N4) and the hydrogenated alloys a-SiNx:H. The main defects in a-Si3N4 are the Si and N dangling bonds (DBs). The Si DB forms a sp3 state near midgap, while the N DB forms a highly localized pπ level just above the valence band edge. The behaviour of the alloys changes near x ≈ 1.1, the percolation threshold of Si-Si bonds. In the Si-rich alloys, both band edges are Si-like, only Si DBs are seen and their density is controlled by equilibration with weak Si-Si bonds. The x>1.1 alloys behave like silicon nitride; the valence band changes towards N pπ-like, both Si and N DBs can arise, the Si DB can have a high density and prefers to be in its charged diamagnetic configurations.
Spectroscopic Investigations of the Ablation Plume of Several Inorganic Materials
Authors: Rosenfeld A. , Mitzner R. , Konig R.
Published: March 2011

Time resolved absorption spectroscopic investigations of the KrF laser ablation of MgO-ceramics and sapphire on atmospheric conditions were carried out with a time resolution of about 5 ns and a two-dimensional space resolution of less than 100 μm. The time delay between the ablation pulse and the broad band probe pulse was varied from 10 ns up to 10 μs.

Absolute particle densities of the species were determined in dependence on the time delay and on the distance to the surface. The spatial and temporal behaviour of the particles in the ablation plume near the surface was found to be strongly affected both by air atmosphere and the reaction dynamic in the plasma zone. In the case of sapphire the time evolution of the densities of Al, Al+ and AlO species are discussed in comparison to measurements on vacuum conditions.
Mechanisms of Excimer Laser Ablation of Wide Band-Gap Materials: the Role of Defects in Single Crystal MgO
Authors: Dickinson J. T. , Jensen L. C. , Webb R. L. , Dawes M. L. , Langford S. C.
Published: March 2011

Laser ablation has important applications in surface modification, materials analysis, and thin film deposition. We have been examining the details of processes that lead to the emission and formation of particles (atomic/molecular ground state neutrals, excited neutrals, tions, electrons) when wide band gap materials are irradiated with pulsed UV laser light. Etching and deposition of wide bandgap materials is of particular interest due to their excellent insulating and optical properties. Our studies bear directly on achieving control of emission intensities and particle characteristics for use in film deposition and materials analysis. In model wide bandgap materials such as single crystal alkali halides and MgO (nominally transparent materials), exposure to repeated pulses of 248 nm excimer laser radiation of a few J/cm2 results in substantial interaction including extensive biaxial deformation and cleavage. Significant surface heating also occurs, consistent with strong free-carrier/laser interactions. We present strong evidence that achieving intense emission of atomic, molecular, and ionic particles actually depends on point defect production by laser-induced deformation and fracture. Defect production via dislocation motion yields orders of magnitude increases in laser vaporization of these wide bandgap materials, including cluster ion formation. The dependence of the laser-material interaction on dislocation density and mobility, as well as point defect density, suggests several novel strategies for the enhancing the ablative response or preventing laser damage.
Vacuum Ultraviolet Laser Ablation of Teflon (PTFE)
Authors: Herman Peter R. , Chen Boyi , Moore David J.
Published: March 2011

Vacuum-ultraviolet laser ablation of Teflon is reviewed. The 157 nm irradiation of Teflon produces clean ablation sites well suited to micromachining applications in the electronics and medical fields. At 193 nm, etching profiles are poorly defined, showing swelling characteristics commonly produced by longer wavelength lasers. Comprehensive new 193 nm ablation data are presented showing the first evidence of incubation effects for Teflon. A computer model was developed to include ablation, swelling and incubation processes. The computer results satisfactorily model the experimental data over a large fluence range of 0.6 to 13 J/cm2 with three adjustable parameters.
Excimer Laser Induced Electrical Conductivity in Polymers
Authors: Phillips H. M. , Feurer T. , Callahan D. L. , Sauerbrey R.
Published: March 2011

The electrical conductivity of high temperature polymers (i.e. polyimide) has been changedpermanently from 10−17 Ω−1 cm−1 to 10 Ω−1 cm−1 by excimer laser irradiation. The conduction mechanism is found to be phonon assisted variable range hopping between small (∼10 nm) carbon clusters that form a macroscopic percolation cluster. The critical concentration of carbon clusters is found to be Pc = 0.24 ± 0.02 and the critical exponent of the insulator-conductor transition is t = 1.97 ± 0.25.
Buffer Gas Effects on the Ablation Rates of Copper Using a Pico-Second Pulsed Nd:YAG Laser
Authors: Mao X.L. , Chan W.T. , Russo R.E.
Published: March 2011

Copper samples were ablated by a pico-second pulsed Nd:YAG laser in Ar and He gases under different pressures. At 1064 nm, the change of ablation rate of copper in He gas from lx10−5 to 760 torr is smaller than that in Ar gas. A model for the development of a plasma above the target surface is presented based on inverse Bremsstrahlung absorption between fast electrons and the gas medium. Ionization rate of the buffer gas versus pressure was estimated using the model, and a good correlation was found with the ablation rate.
Laser-Induced Surface Activation of Aluminum Oxide for Electroless Deposition
Authors: Pedraza A.J. , Godbole M.I. , Desilva M.J. , Lowndes D.H.
Published: March 2011

A new process for writing a copper pattern into alumina or sapphire substrates is presented. This process employs in sequence ultraviolet laser irradiation and electroless deposition of copper. The laser irradiation activates the substrate and copper is deposited in the activated region when the substrate is immersed in the electroless solution. The laser-activation can be performed months in advance to the deposition.

A small amount of metallic aluminum is left on the surface of laser irradiated alumina substrates. The presence of this metallic aluminum appears to play a very important role in the laser surface activation process. In addition to aluminum cluster formation there must be other activation centers that promote copper deposition in laser treated alumina substrates. These catalytic centers are much weaker that the aluminum clusters and have been tentatively identified as surface defects.
Surface Modification of Aluminum Nitride and of Aluminum by Excimer Laser
Authors: Pedraza A.J. , Zhang J.-Y. , Esrom H.
Published: March 2011

A new technique for selective metallization of aluminum nitride (AIN) has been previously reported (1). It involves the use of an excimer laser to activate the AIN surface followed by electroless plating (Cu,Ni,Au) of the irradiated areas. The mechanism of decomposition of ALN is accompanied by ablation and the formation of an Al film on the substrate surface. Ablation rates are reported here as a function of fluence and number of pulses for three different wavelengths λ = 193 nm (ArF), λ = 248 (KrF) and λ = 351 nm (XeF).

The effect of laser wavelength on the ablation rate is discussed. The ablation rates for Al were zlso measured and are compared with the AIN ablation rates. A numerical thermal model is used to analyze the mechanisms of laser ablation of both materials. The evaporation kinetics are incorporated into the model. The Clausius-Clapeyron approximation is used to make a self-consistent calculation of boiling and decomposition temperatures.
Pulsed Laser Deposition and Atomic Scale Characterization of Perovskite Oxide Films
Authors: Koinuma H. , Yoshimoto M. , Kawasaki M. , Ohkubo H. , Kanda N. , Gong J.P.
Published: March 2011

Perovskite oxide films inclusive of high Tc cuprates were fabricated by pulsedlaser deposition (PLD) under both conventional Po2(0.01∼1Torr) and high vacuum(≤10−6 Torr) conditions and their surface morphology, crystal quality, and conductivity were evaluated. Under optimized conventional PLD conditions, we obtained high quality YBa2Cu3O7−δ (YBCO) films that showed clear energy gaps and atomically flat surface image in the small area (4x4nm) STM/STS measurements. AFM and SEM ana!yscs on wider film surfaces (∼1x1μm), however, revealed granular structure of about 250nm grains with their root mean square roughness of 5nm.

Under high vacuum PLD, i.e. laser MBE conditions, not only epitaxial but also two dimensional growth has been verified for such films as SrTiO3−x, SrVO3−y, and (AE)CuO2−z(AE=alkaline earth metal) by the RHEED observation of fine streak patterns and intensity oscillations. AFM demonstrated atomically flat surfaces of these films. Oxgen or nitric oxide pressure at the laser MBE growth gave crucial effects on the electrical conductivity of SrTiO3−x. and predominant crystal phase of SrCuO2−z.

Insulating BaTiO3 films with atomically flat surfaces could be fabricated by both conventional and high vacuum PLD conditions. RBS channeling measurements revealed very high epitaxial quality (χmin−2%) of our SrTiO3 and BaTiO3 films. The factors controlling the surface morphology and electrical properties of perovskite oxide epitaxial films,are discussed.
Low Teperature Synthesis of Silicon Oxide and Oxynitride Films by Reactive Laser Ablation
Authors: Fogaassy E. , Fuchs C. , Slaoui A. , De unamumo S. , Stoquert J.-P. , Marine W. , Lans B.
Published: March 2011

Silicon oxide and oxynitride films are deposited, at low temperature (≤ 450°C) by pulsed ArF excimer laser ablation from silicon, silicon monoxide, fused silica and silicon nitride targets, performed under vacuum and in oxygen atmosphere. We investigate in this paper the specific influence of laser fluence, target materials, substrate temtperature and oxygen pressure on the composition and final properties of SiOxNy grown layers. The synthesis of good quality SiO2 films is demonstratedx. By contrast, the preparation of stoichiometric Si7N4 layers by laser ablation has to be optimized.
Vacuum Ultraviolet Spectroscopy Study of Excimer Lasergfenerated Plasmas: Spatial Distribution of Plasma
Authors: Chrise D.B. , Mehbnan G. , Horwit J.S. , Burkhalte P.G. , Newman D.A. , Leuchtner R.E.
Published: March 2011

Emission spectra from 1200 Å to 3500 Å have been measured for laser-generated plasmas produced by the focused output (1−4 J/cm2)of a Kr-F excimer.laser onto solid targets of single and multicomponent materials (e.g., Al, Y2O3, BaO, Cu, and YBa2Cu3O7−δ). We have measured the spatial distribution and fluence dependence of the plasma emission. The emission spectra indicated that very large density gradients from the large opacity at the target surface were present. In general, the spectra were dominated by excited neutrals and singly and doubly ionized species. Plasma emission spectra from Al have been analyzed in more detail to derive plasma temperature and density. A plasma temperature of 2 eV and an electronic density of ∼1018/cm3 at 2 J/cm2 was estimated from the relative line intensities. Spatial variation of the total vacuum ultraviolet emission provided evidence for laser absorptionin the ablated material.
Pulsed Laser Deposition of Thin Silicon Nitride Films
Authors: Xu Xiangqun , Seki Kanekazu , Chen Naiqun , Okabe Hideo , Frye Joan M. , Halpern Joshua B.
Published: March 2011

ABSTRACTPulsed laser deposition of compressed Si3N4 powder has been used to grow thin SiNx films on a variety of substrates at substrate temperatures ranging from room temperature to 350°C. Film composition was analyzed by Auger electron spectroscopy. The SiN0.33 films have a band gap of 5.60 eV as measured by UV absorption. The FT-IR spectrum shows an absorption characteristic of Si-N. The Si/N ratio in the deposited films corresponding to various substrate temperatures has also been determined.
Preparation of PbTiO3-Pb(Mg0.5W0.5)O3 Thin Films Using Pulsed Laser Deposition
Authors: Lee B. W. , Lee H. M. , Cook L. P. , Schenck P. K. , Paul A. , Wong-ng W. , Chiang C. K. , Brody P. S. , Rod B. J. , Bennett K. W.
Published: March 2011

Thepreparation of modified lead titanate (0.PbTiO3-Pb(Mg0.5W0.5)O3) thin films by pulsed excimer laser deposition on Pt-coated Si substrates has been studied. Films were prepared with substrate temperatures of 300–650°C, and ambient oxygen pressures of 2.7–4OPa. Phase formation and morphology of the films varied according to deposition conditions. At 650°C, 40Pa, well-crystallized perovskite single phase films were obtained. Most films were ferroelectric and showed preferred orientation which could be correlated with the texture of the underlying platinum. The effect of preferred orientation on the dielectric properties of the films is discussed.
Kinetics of Photodeposition of Superconducting Films
Authors: Chen C. H. , Phillips R. C. , Morrison P. W.
Published: March 2011

Kinetics of photodeposition of superconducting films was studied by using real time in-situ monitoring of gas phase species with mass spectrometry and thin-film properties by Fourier Transform Infrared (FTIR) spectrometry. A mass spectrometer was used to study wavelength and power dependent desorbed atoms and molecules during laser ablation process. FTIR was used to monitor the surface properties of thin film. Real time surface temperatures can be easily obtained by FTIR. By combinging mass spectrometry and FTIR, an optimum condition of making high-quality superconducting film can possibly be found.
Photoluminescence Study of Reproduction of Energy Levels in Cdte Films Grown by Pulsed Laser Evaporation and Epitaxy
Authors: Wrobel J. M. , Moffitt C. E. , Dubowski J. J.
Published: March 2011

A comparison between the electronic energy structure of a target material and epitaxial films obtained from this material by pulsed laser evaporation and epitaxy is presented in the paper. Targets with various impurity concentrations were used in this experiment, and the epitaxial growth took place at various substrate temperatures. Studies of photoluminescence spectra included temperature and power dependencies of spectral features associated with the impurities. Properties of donor-acceptor pair recombination served for the analysis of the differences in the impurity concentration in the layers and the source material.
Epitaxial ZnS, ZnSe and ZnS-ZnSe Superlattices Grown on (001)GaAs By Pulsed-Laser Ablation
Authors: McCamy J. W. , Lowndes Douglas H. , Budai J. D. , Jellison G. E. , Hermant I. P. , Kimt S.
Published: March 2011

Pulsed KrF (248nm) laser ablation of polycrystalline ZnS and ZnSe targets has been used to grow high quality, fully epitaxial ZnS and ZnSe thin films on (001) GaAs. Photoluminescence measurements of the ZnS thin films show strong edge emission, while ZnSe thin films show free excitonic as well as donor and acceptor peaks. By alternately ablating each target, strained layer superlattices of the form (ZnSe)m–(ZnS)n were grown with as many as 65 periods of compositional modulation. A ZnSxSe1–x structure also was fabricated which simultaneously incorporated both continuously graded and abrupt compositional changes.
Laser Ablation of CuInSe2 and CuIn/GaSe2 Alloys for Solar Cell Applications
Authors: hill Arthur E. , Leppåvuori Seppo , Tomlinson Robert D. , Pilkington Richard D. , Levoska Juhani , Ahmed Ejaz , Frantt Johannes
Published: March 2011

Copper indium diselenide (CIS) is one of the most promising materials proposed for use in the next generation of solar cells. A successful technique to deposit thin films of this material, which would maximise the advantage offered by its exceptionally high absorption coefficient and radiation resistance, has proved to be elusive. Dissociation of the source material during the physical deposition of these thin films has forced commercial production to adopt a binary (Cu/In) deposition route with a subsequent selenisation stage. This has proved to be a major difficulty; selenisation has introduced its own problems of non-uniformity and toxicity. Laser ablation is especially suited to the deposition of multi-component films in that the initial composition is conserved.

Single crystal and polycrystalline targets of CIS were laser ablated using an XeCl excimer laser. The films were analysed using EDAX, XRD, RBS and Raman spectroscopy. Results from EDAX and RBS measurements indicated that the composition of the source material had largely been maintained in the films. This suggests that laser ablation could prove to be a significant technique in the preparation of complex ternary semiconductor thin films for solar cell applications which would allow the full potential of these materials to be realised in device production.
Preferentially Oriented Cubic Boron Nitride Films Grown on Si (001) Substrates by Ion Assisted Pulsed Laser Deposition
Authors: Ballal A. K. , Salamanca-riba L. , Doll G. L. , Taylor C. A. , Clarke R.
Published: March 2011

Preferentially oriented and extremely adherent cubic boron nitride films have been obtained using ion-assisted pulsed laser deposition on (001) Si substrates. The films were ∼ 1800 Å thick, optically transparent and formed an antireflective coating on the Si substrate. Infrared transmittance spectra showed a strong absorption peak at 1080 cm−1, indicating sp3 bonded film. Cross-sectional and plan-view transmission electron microscopy indicate that the cubic boron nitride films are polycrystalline having cubic zinc-blende crystal structure and a lattice constant of 3.62 Å. A preferred texture is observed with the [110] axis of cubic boron nitride parallel to [001] axis of silicon.
Deposition and Modification of Tantalum Carbide Coatings on Graphite by Laser Interactions
Authors: Veligdan James , Branch D. , Vanier P.E. , Barletta R.E.
Published: March 2011

Graphite surfaces can be hardened and protected from erosion by hydrogen at high temperatures by refractory metal carbide coatings, which are usually prepared by chemical vapor deposition (CVD) or chemical vapor reaction (CVR) methods. These techniques rely on heating the substrate to a temperature where a volatile metal halide decomposes and reacts with either a hydrocarbon gas or with carbon from the substrate. For CVR techniques, deposition temperatures must be in excess of 2000° C in order to achieve favorable deposition kinetics. In an effort to lower the bulk substrate deposition temperature, the use of laser interactions with both the substrate and the metal halide deposition gas has been employed. Initial testing involved the use of a CO2 laser to heat the surface of a graphite substrate and a KrF excimer laser to accomplish a photodecomposition of TaCI5 gas near the substrate. The results of preliminary experiments using these techniques are described.
Hydrodynamic Modeling of Laser Ablation
Authors: Mancini R.C.
Published: March 2011

We present a hydrodynamic model to simulate laser ablation. The model conisistently takes into account the main physical phenomena involved in laser ablation: heating, thermal conduction, hydrodynamics and atomic kinetics. It computes the ionization balance, plasma formation and expansion, and the attenuation of the laser light as it travels through the plasma. Preliminary results are presented.
Stress Transients Generated by Excimer-Laser Irradiation of Polyimide
Authors: Zweig A. D. , Venugopalan V. , Deutsch T. F.
Published: March 2011

We measure the stress transients resulting from pulsed excimer laser irradiation of polyimide at 351, 308, 248 and 193 nm, using thin (9 μm) piezoelectric PVDF (polyvinylidene fluoride) films. We find that fluences between 3·10−3 and 102 J/cm2 generate peak stresses between 104 and 109 Pa. Further, the results show three ranges of fluence where different physical mechanisms mediate the stress generation. In the lowest range of fluence, subsurface thermal decomposition (for λ = 351 and 308 nm) and photodecomposition (for λ = 248 and 193 nm) govern the generation of the observed stresses. At higher fluences we identify two regimes, independent of laser wavelength, where the gas dynamic expansion of the ablation products and plasma formation and expansion, are responsible for the generated stresses.
Dynamics of Laser Ablation and Vaporization of Lead Zirconate Titanate: Target Effects
Authors: Leuchtner R.E. , Horwitz J.S. , Chrisey D.B.
Published: March 2011

Using the pulsed laser deposition (PLD) technique to prepare PbZrxTi(1−x)03 (PZT) films from stoichiometric targets, it has been found that the Pb content of the films is very sensitive to, among other parameters, the phase of the ablation target. In an effort to better understand PZT film growth, a time-of-flight quadrupole mass spectrometer (TOF/QMS) was used to obtain the temporal and mass profiles of material ejected from two different solid targets with a nominal composition of PbZr0.54Ti0.46O3over a laser fluence range of 0.2 to 2.0 J/cm2. The ablation targets were made from either a compressed mixture of oxides or a fully reacted PZT solid. The composition of the plume varied significantly depending upon the phase of the target and the laser fluence. In general, two distinct ejection processes were identified and the TOF profiles observed could be characterized as either thermal vaporization (fluence ≤ 0.3 J/cm2), ablation, with a highly forward directed ejection pattern normal to the target surface, or a combination of the two processes (fluences ≥ 0.3 J/cm2). The thermal vaporization (or low energy) component of the ejected species were modeled using a Maxwell-Boltzmann distribution. The fully reacted target yielded atomic species which had higher translational temperatures (about 100–700K) than the corresponding components of the pressed oxide target. The translational temperatures ranged from about 1000–6500K, depending upon the species and the laser fluence. Both targets showed distinctly different behavior as a function of laser fluence with regard to the production of PbO: the PbO/Pb ratio from the pressed oxide target was roughly constant while the PbO/Pb ratio from the fully reacted target decreased significantly with increased laser fluence. It is postulated that PbO plays an important role in the incorporation of Pb into the film during film growth.
Ultra Fine Particle Films by Gas Deposition Method
Authors: Oda Masaaki , Katsu Isao , Tsuneizumi Michitaka , Fuchita Eiji , Kashu Seiichiro , Hayashi Chikara
Published: March 2011

Ultra fine particles(UFP) of organic and inorganic materials can be formed by the gas evaporation method(gas condensation method). In the gas deposition method, particles formed by the gas evaporation method in an evaporation chamber are carried to another chamber (a deposition chamber) through a pipe. Particles are accelerated in the pipe with a gas flow and come out of a nozzle located in the deposition chamber which is being evacuated down to less than 10 torr and deposited on a substrate to form UFP films. The final speed of the particles depends on the pressure difference between the evaporation chamber and the deposition chamber. The particles speed exceeds 500m/s and adhesion strengths of the films reach 50OKgf/cm2 as well as vacuum deposition films in the condition that the pressure of the evaporation chamber is at 4 atms. Patterns of spots and lines with 50μm size and also wider films can be formed on a substrate without a masking system. The process is effective for repairing electric connecting lines or producing electrodes and condensers on an industrial scale.
Production of Silicon Powder by Square-Wave Modulated Rf Silane Plasma
Authors: Costa J. , Sardin G. , Campmany J. , AndÚjar J.L. , Canillas A. , Bertran E.
Published: March 2011

Silicon powder has been produced by means of square-wave modulated rf silane plasma. The plasma conditions were: 30°C of reaction chamber temperature, 70 Pa of pressure, 80 W of rf power and 0. 1 Hz of square-wave modulation frequency. The gas flow rate was varied from 5 to 90 sccm.

The distribution and size of the powder grains were determined by transmission electron microscopy. The compositional and microstructural analysis of the powder was performed by FTIR spectroscopy. This analysis has revealed the dominant presence of SiH2 groups (2100 cm−1), in a highly polymeric form (850 and 890 cm−1), as well as the existence of an absorption band (1000-1100 cm−1) associated with oxidation of the powder.

These results have shown the great influence of the flow rate, through the gas residence time, on the composition and microstructure of silicon powder.
Atom-Probe Microanalysis of Metallic Nanostructured Materials
Authors: Mackenzie Ross A.D. , Cerezo Alfred , Conyers James S. , Petford-Long Amanda K. , Subrandu Sybren J. , Smith George D. W.
Published: March 2011

Atom-probe techniques have been used to characterise nanostructured metallic materials prepared by thermal evaporation and by sputtering. Multilayer samples of Fe-Cr have been prepared by sputter deposition and analysed using the Oxford position-sensitive atom probe. This has made it possible to observe the quality of interfaces in the material, and also accurately determine local compositions at each layer within the multilayer stack. Preliminary experiments aimed at producing dual phase nanocrystalline films by thermal evaporator deposition are also reported.
Nanocrystalline Ni-Mo Alloys Prepared by Mechanical Alloying for Applications in Catalysis
Authors: Schulz R. , Dignard-Bailey L , Trudeau M.L , Huot J.Y. , Yan Z.H.
Published: March 2011

Amorphous and nanocrystalline Nil-xMox alloys have been prepared by mechanical alloying of pure Ni and Mo elemental powders in an atmosphere containing various amounts of oxygen. Metastable fcc solid solutions are formed when the Mo content is less than 30 at.%. The amorphization of the supersaturated solid solution occurs when the Mo concentration exceeds 30 at.%. The electrocatalytic properties of the nanocrystalline alloys for the hydrogen evolution reaction in alkaline solutions have been investigated. High electrocatalytic activity is found when the average crystal size is below 10 nm and when the supersaturated solid solution contains some oxygen.
Nanocomposites: Retrospecr and Prospect
Authors: Roy Rustum
Published: March 2011

In this paper we make clear distinctions from the terms nanophase, nanocrystalline and deal only with nanocomposites defined as an interacting mixture of two phases, one of which is in the nanometer size range in at least one dimension. The author's origins of development of the idea that nanocomposites are a virtually infinite class of new materials are described.

Then we refer to the results of our extensive studies of nanocomposites derived by solution-solgel techniques to illustrate the properties of such materials in the area of chemical and thermal reactivity.

Finally it is pointed out that in the last few years nanocomposite materials have become a major part of new materials synthesis all over the world for applications ranging from mechanical to optical, to magnetic to dielectric.
Sintering of Coated Powders. I. Silica-Ytfria System
Authors: Giesche Herbert
Published: March 2011

Silica particles were produced by the well known “Stbber” process. The silica core size as well as the coating thickness could be varied by the reaction conditions. Respectively, yttria core particles or coatings on silica nuclei were synthesized by the ureadecomposition method, previously described in general by Matijevic or Akinc et al.

The (silica or yttria) core size (86 to 400 nm) as well as the coating thickness (monolayer to 100 nm) was varied systematically. Green compacts of about 50 to over 60 % thD. were produced either by sedimentation, centrifugation, or pressure filtration of well dispersed slurries.

The results demonstrated the enhanced densification of coated powders. A two step shrinkage process was observed for some of the samples. TEM micrographs and X-ray analysis exemplify the microstucture and phase development during sintering.
Structural Investigation of Sol-Gel-Derived Hybrid Siloxane-Oxide Materials Using 29Si MAS-NMR Spectroscopy
Authors: Babonneau F. , Bois L. , Livage J. , Dire S.
Published: March 2011

Hybrid siloxane-oxide systems were prepared by sol-gel techniques. Siloxane precursors are either monomeric species, dimethyldiethoxysilane, or OH-terminated polydimethylsiloxanes. The oxide component is introduced via metallic alkoxides, M(OR)n (M=Si, Ti, Zr). Transparent materials from flexible to brittle gels, can be obtained over a large M/siloxane range. The structure of the various systems was investigated by 29Si MAS-NMR. The signals due to the difunctional Si units, (CH3)2SiO, depend strongly on the nature of M and on the M/siloxane ratio. Structural models are proposed, ranging from single phase systems with highly interconnected siloxane and oxide units, to nanocomposites made of polysiloxane chains crosslinked with oxide-based particles.
Textured Coatings from Colloidal Suspensions of Faceted Oxide Microcrystals
Authors: Steadman Gregg.W. , Brewster J. R. , Budai J. D. , Boatner L. A.
Published: March 2011

The morphological properties of cubic, faceted MgO microcrystals have been exploited in the formation of textured coatings. Coatings exhibiting a <100> “fiber” texture were formed by centrifugal sedimentation of colloidal suspensions onto a flat substrate. A decrease in the degree of preferred orientation in the coatings with increasing areal coverage of the particles was quantified for several particle-size distributions by using x-ray diffraction. Novel methods for the deposition of particles exhibiting an in-plane preferred orientation in addition to fiber texture have been investigated.