bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Prediction and Experimental Study of Mechanical Properties for Random and Magnetically Aligned Single-Walled Carbon Nanotube/Epoxy Composites
Authors: Wang Ben , Shankar Ravi , Liang Zhiyong , Wang Zhi , Zhang Chuck , Kramer Leslie
Published: April 2011

Single-walled carbon nanotubes (SWNTs) have exceptional mechanical and functional properties. Many researchers consider SWNTs as the most promising reinforcement for realizing the optimal structural and multifunctional potential of the next generation of high performance nanocomposites. However, due to poor dispersion, weak interfacial bonding and deficient tube orientation, current nanotube-based nanocomposites fail to realize their anticipated properties. A new approach was developed by the authors to use preformed nanotube tube networks (called buckypapers) and a resin infiltration method for producing bulk polymeric nanocomposites with controlled nanostructure and high tube loading. Desired tube alignment in nanocomposites can be achieved by using magnetically aligned carbon nanotube buckypapers, in which SWNTs will tend to align along the direction of applied magnetic field. The mechanical properties of the resultant nanocomposites have been tested. The storage modulus of the magnetically aligned nanocomposites is as high as 47 GPa, which is one of the highest reported values of nanotube-reinforced composites.

In this research, we investigated the influences of tube dispersion, loading and orientation on the mechanical properties of SWNT-reinforced composites. Random and aligned discontinuous reinforcement models of composites were applied to predict the tensile moduli of both individually dispersed SWNT-based and SWNT rope-based nanocomposites. The nanostructural parameters used in the calculation models were determined based on our experimental observations. Comparisons between theoretical estimates and experimental results have shown that the formation of SWNT ropes in the composites has a significant influence on the mechanical properties. The experimental results of the both random and aligned SWNT rope composites are in good agreement with the theoretical predictions.
Defects and Magnetic Properties: The Cr/Fe(001) Interfaces
Authors: Stoeffler D. , Vega A. , Dreyssé H. , Demangeat C.
Published: April 2011

We report self-consistent band-structure calculations for the magnetism of Cr overlayers adsorbed on Fe(001) in order to study the role played by imperfect Fe-Cr interfaces, at the microscopic and macroscopic scales, on the total magnetisation. The surprisingly large reduction of the total magnetisation (≈ - 5 μB/interfacial atom) recently observed in Cr/Fe(001) through in situ magnetometer measurements is shown to be reproduced only when an interchange of one Cr and Fe monolayer at the interface after deposition of the second Cr monolayer occurs.
Nanosecond Structural Transformation of Magnetic thin Films: PtMnSb, Structure and Magnetic Properties
Authors: Kubota Yukiko , Marinero Ernesto E.
Published: April 2011

We report on the phase transformation of amorphous PtMnSb thin films induced by laser annealing in the nanosecond time regime. Structural and magnetic transformations are investigated by TEM, XRD, AFM and in-situ MOKE and VSM. We have established that a minimum laser fluence is required to crystallize the amorphous films and thus, to induce magnetic activity. The transformation kinetics vs number of irradiation pulses reveals that the magnetically active C1b phase is formed via an intermediate phase, namely, tetragonal-PtMn. We have also established that the thin film crystallization induced by the nanosecond laser annealing proceeds via nucleation rather than grain growth. Measurement of the lattice parameter of the C1b-PtMnSb produced by the laser quenching (LQ) indicates an essentially unstrained structure with a =6.17 Å vs a =6.201 Å reported for the bulk. Nevertheless, we observe the generation of large surface undulations upon laser annealing and suggest that this is the mechanism for stress relaxation concomitant with the large volumetric changes involved in the phase transformation. In addition, we observe decrements in saturation moments and Curie temperatures which are attributed to the nanocrystalline nature of the LQ specimens.
Effects of Interface Intermixing on the Magnetoresistance of Spin Valves with Uncoupled Co-Layers
Authors: Willekens M.M.H. , Rijks TH.G.S.M. , Swagten H.J.M. , Jonge W.J.M. De
Published: April 2011

We have studied the effect of an artificially intermixed region grown at the interfaces of Co/Cu spin valves with uncoupled layers. Two different structures are used: exchange-biased spin valves and engineered spin valves in which two layers are antiferromagnetically coupled and a third layer, on top of this system, is not coupled to the other two. It is shown that structural effects, induced by variation of the deposition parameters and by the intermixing can play an important role. Since the present study uses sputtered layers an intrinsic initial intermixing of 4-5Å is already present. For both types of spin valves Gp, ΔG and ΔR/R all show a gradual decrease when the nominal thickness of the total intermixed region is enlarged from 0 to 36Å. Also when the initial degree of intermixing is decreased by sputtering at higher Arpressure, Gp, ΔG and ΔR/R still show a gradual decrease as a function of intermixed layer thickness. Combined with the fact that there is no difference between an intermixed region of thickness t at one Co/Cu interface or intermixed regions of thickness t/2 at two interfaces, this indicates that the electron scattering in the intermixed region is predominantly spin independent, although this region preserves a magnetic moment.
197Au MÖssbauer Study of Au/Fe, Au/Co and Au/Ni Magnetic Multilayers
Authors: Nasu Saburo , Kobayashi Yasuhiro
Published: April 2011

197Au Mössbauer measurements have been performed for Au/Fe, Au/Co and Au/Ni magnetic multilayers. 197Au Mössbauer spectra observed from multilayers consist of at least 4 components having different magnitude of hyperfine fields and isomer shift values those depend on the local environments of the Au probe-atoms in multilayers. Rather large electron spin polarization at Au atoms has been observed in the interface with adjacent ferromagnetic layers, but nearly no magnetic hyperfine field has been observed to the interior of Au layer. It implies that the largest hyperfine field observed is not due to the conduction-electron polarization but induced by the hybridization in the interface with ferromagnetic layer.
Fourier Transform Infrared Spectroscopy of Polymer-Metal Interface Reactions
Authors: Cumpston B. H. , Lu J. P. , Willis B. G. , Jensen K. F.
Published: April 2011

Applications of Fourier transform infrared (FTIR) spectroscopy for probing polymer-metal interfaces are described with examples of polyimide (PI)-metal systems relevant to electronics packaging and poly(phenylene vinylene) (PPV) derivatives used in electroluminescent devices. Emphasis is placed on the detection and interpretation of interfacial reactions that influence performance characteristics (e.g., adhesion, stability, and light emission) of polymer-metal structures. In situ infrared reflection absorption spectroscopy (IRRAS) is used to explore the formation of PI-on-metal interfaces, the hydrolytic stability of such interfaces, and the reactivity of PPV systems when exposed to ultraviolet light and oxygen. Differences between polymer-on-metal and metal-onpolymer interfaces are discussed. Models of the infrared optical processes in the thin film composites are used to distinguish between chemical and optical effects. The FTIR observations are supported by additional spectroscopic characterizations, specifically ex situ X-ray photoelectron spectroscopy (XPS).
The Role of Coupling Agents in Composite Durability
Authors: Macturk K. S. , Schutte C. L. , Schultheisz C. R. , Hunston D. L. , Tarlov M. J.
Published: April 2011

We investigated the role of coupling agents with respect to the relative durability of glass fiber/epoxy matrix composites exposed to water, which degrades both glass fibers and the fiber-matrix interface. Interface chemistry was tailored by coating fibers with mixtures of different coupling agents. Single-fiber fragmentation test results showed little decrease in the strengths of the interface and a slight decrease in fiber strengths upon exposure to water. XPS results showed expected variations in surface composition. Contact angle measurements demonstrated variations in surface hydrophobicity as coupling agent mixtures were changed.
Composition-Structure-Properties Relationship and Durability of Modified Organosilicate Polymeric Composite
Authors: Tchouppina Svetlana V. , Krasil'nikova Larisa N.
Published: April 2011

The present work was aimed at the development of new organosilicate polymeric composite, based on polydimethylphenylsiloxane/polyurethane (PDMPS/PU) miscible blend, filled with silicates and metal oxides. Considerable improvement of mechanical and corrosion-protective properties due to introduction of polyurethane has been observed. Coatings with sufficient thermostability (up to 300°C) have been obtained in the case of 20% polyurethane content, related to amount of binders. The effects coating heat treatment temperature and curing conditions on adhesion of metal/composite interface have been studied. Surface energy characteristics of this coating have been obtained and were correlated with its microstructure, determined from Scanning Electron X-ray Microprobe Analyses. Recently developed composite appeared to show increased durability in atmosphere operation conditions.
Polymer Brush-Lined Membranes for Flow and Filtration Control
Authors: Sevick Edith M. , Bruce Frank A. , Williams David R.M.
Published: April 2011

We describe the flow and filtration control imparted to membranes through the adsorption of polymer brushes onto the interior pores. The brushes exhibit a negative Poisson's ratio, i.e. they swell under shear, and as a result behave as sensors and valves controlling the flow and filtration through the pore. The valve-behavior of brushes adsorbed onto cylindrical pores displays the same constant discharge control but also exhibits a critical shear rate for brush swelling.
Scanning Conduction Microscopy: A Method of Probing Abrasion of Insulating Thin Films on Conducting Substrates
Authors: Dickinson J. T. , Hipps K. W.
Published: April 2011

The use of Scanning Force Microscopy (SFM) to probe wear processes at interfaces is of considerable interest. We present here a simple modification of the SFM which allows us to make highly spatially resolved measurements of conductivity changes produced by abrasion of thin insulating films on metal substrates. The technique is demonstrated on fluorocarbon polymer thin films deposited on stainless steel substrates.
Electroplating of Fluoropolymers using ECR Plasma Deposited TiN as Interlayer
Authors: Weber A. , Dietz A. , Pöckelmann R. , Klages C.-P.
Published: April 2011

A novel low temperature process for titanium nitride (TiN) deposition by means of an electron cyclotron resonance (ECR) plasma CVD process was applied to poly(tetrafluoroethylene) (PTFE). The organometallic compound tetrakis(dimethylamido)titanium (TDMAT) introduced into the downstream region of a nitrogen ECR plasma was used as a precursor for TiN deposition at 100°C.

The thin TiN films (thickness 15-30 nm) act as interlayers to activate the electroless deposition of copper followed by an electroplating process. Prior to the deposition of the interlayer, the samples were treated on a biased susceptor with argon ions to enhance the adhesion of the TiN interlayer. This metallization procedure avoids the use of toxic and pollutive etching agents and yields adherent copper layers on PTFE.

The maximum adhesion of the metal film on PTFE was established to be 13 N/mm2. As shown by atomic force microscopy (AFM), TiN grains were formed on the fluoropolymer surface. Film composition was investigated by secondary ionization mass spectrometry (SIMS).
Adhesion Between Polyimide Films and A12O3 Substrate
Authors: Nakamura Y. , Suzuki Y. , Watanabe Y. , Hirayama S.
Published: April 2011

The adhesive strength of polyimide thin films on an alumina substrate has been studied by the pull test. Polyimide thin films were cured at various temperatures from 300 to 400°C, followed by etching in an oxygen plasma for 3 min. After metallization with chromium and copper, the pull test was carried out. It is found that the adhesive strength increases with an increase of the cure temperature. However the strength deteriorates noticeably at the cure temperature of 400°C. A possible reason for this is the variation of chemical states in the polyimide thin films.
SurfaceSIMS, Secondary Ion Mass Spectrometry Using Oxygen Flooding: A Powerful Tool for Monitoring Surface Metal Contamination on Silicon Wafers
Authors: Smith Stephen P. , Wang Larry , Erickson Jon W. , Chia Victor K. F.
Published: April 2011

Secondary ion mass spectroscopy (SIMS) coupled with oxygen flooding of the silicon surface during analysis provides an analytical technique capable of detecting ≤1010 atoms/cm2 of many surface elemental contaminants. Of particular importance to meet the future needs of the semiconductor industry is the current ability to detect Al and Fe contamination at a level of 2×109 atoms/cm2.
A study of Cleaning Performance and Mechanisms in Dilute SC-1 Processing
Authors: Resnick P. J. , Adkins C. L. J. , Clews P. J. , Thomas E. V. , Korbe N. C.
Published: April 2011

A statistical design of experiments (DOE) approach has been employed to evaluate the effects of megasonic input power, solution chemistry, bath temperature, and immersion time on particle removal in SC-1 chemistries. Megasonic input power was the dominant factor in the response surface model. Substantially diluted chemistries, performed with high megasonic input power and moderate-to-elevated temperatures. were shown to be very effective for small particle removal. Follow-on studies to the original DOE have led to an investigation of ultradilute SC-1 chemistries with megasonic power. These chemistries ranged from 0 to 1000 ppm of NH4OH and H2O2. Post processing light point defect (LPD) counts differ substantially between bare n and p-type Si<100>, and ambient lighting conditions are shown to influence LPD counts on p-type Si<100>. Solution properties such as pH and oxidation potential have been studied, and an investigation of post processing silicon surface properties is underway.
Time-Dependent Dielectric Breakdown in Thin Intrinsic SiO2 Films
Authors: Suehle J. S. , Chaparala P.
Published: April 2011

Time-Dependent Dielectric Breakdown studies were performed on 6.5-, 9-, 15-, 20-, and 22.5- nm thick SiO2 films over a wide range of stress temperatures and electric fields. Very high temperatures (400 °C) were used to accelerate breakdown so that stress tests could be performed at low electric fields close to those used for device operating conditions. The results indicate that the dependence of TDDB on electric field and temperature is different from that reported in earlier studies. Specifically, the electric-field-acceleration parameter is independent of temperature and the thermal activation energy was determined to be between 0.7 and 0.9 eV for stress fields below 7.0 MV/cm.

Failure distributions of high-quality current-generation oxide films are shown to be of single mode and have dispersions that are not sensitive to stress electric field or temperature, unlike distributions observed for oxides examined in earlier studies. These results have implications on the choice of the correct physical model to describe TDDB in thin films. The data also demonstrate for the first time the reliability of silicon dioxide films at very high temperatures.
Valence Band Alignment of Ultra-Thin SiO2/Si Interfaces As Determined By High Resolution X-Ray Photoelectron Spectroscopy
Authors: Alay J. L. , Fukuda M. , Bjorkman C. H. , Nakagawa K. , Sasaki S. , Yokoyama S. , Hirose M.
Published: April 2011

Ultra-thin SiO2/Si(111) interfaces have been studied by high resolution x-ray photoelectron spectroscopy. The deconvolution of the Si 2p core-level peak reveals the presence of the suboxide states Si3+ and Si1+ and the nearly complete absence of Si2+. The energy shifts found in the Si 2p and O is core-level peaks arising from charging effects arc carefully corrected. The valence band density of states for ultra-thin (1.8 - 3.7 nm thick) SiO2 is obtained by subtracting the bulk Si contribution from the measured spcctrum and by taking into account the charging effect of SiO2 and bulk Si. Thus obtained valence band alignment of ultra-thin SiO2/Si(111) interfaces is found to be 4.36 ± 0.10 eV regardless of oxide thickness.
Effects of UV/O3 and SC1 Steps for the HF Last Silicon Wafer Cleaning
Authors: Jeon Hyeongtag , Choi Hyungbok , Cho Y. S. , Ryoo K. K. , Jung S. D.
Published: April 2011

As the size of integrated circuit is scaled down, the importance of Si wafer cleaning has been emphasized. Especially, in the ULSI level device, the cleaning has a great influence on device yields and reliabilities. In this study, we investigate the effects of UV/03 and SCI steps in the HF last cleaning procedures. The UV/O3 and SCI cleaning steps are known to remove the organic contaminants. However, the combination of UV/O3 cleaning step with HF wet chemical solution to remove the metallic impurities has not been studied extensively. We have applied the UV/O3 and SCI steps in the middle of the HF last cleaning procedures and have analyzed Si substrates with TXRF, AFM, I-V, etc. The cleaning splits we applied consist with 4 different types, split 1 (piranha + HF), split 2 (piranha + UV/O3 + HF), split 3 (piranha + SC1 + HF) and split 4 (piranha + UV/O3 + HF repeated 3 times). The contents of metallic impurities were measured with using TXRF and splits 2 and 4 showed low average values of metallic contents. The surface morphologies after each cleaning examined with AFM and the split 3 exhibited rough surface. The electric properties were measured after forming a MOS capacitor with oxide thickness of 250Å. The high leakage current and low breakdown voltage were observed at split 3.
Surface Modification of ZnxCd1-x Te Due to Low Energy Ion Sputtering
Authors: Vijayalakshmi S. , Chen K.-T. , George M. A. , Burger A. , Collins W. E.
Published: April 2011

ZnxCd1-xTe is a widely used substrate for the epitaxial growth of HgCdTe, which is used in infrared detectors. Results of the effect of sputtering of ZnxCd1-xTe single crystals with low energy Ar beam are reported in this paper. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) techniques were used to measure the concentration of Zn in these crystals. Selective sputtering of Zn atoms has been observed from freshly cleaved crystals using XPS studies. Sputtering is a common method of cleaning ZnxCd1-xTe crystals in their device preparation and our studies show that this method of cleaning alters the surface which may introduce lattice mismatch on the surface. Surface morphology before and after cleaving the crystals is studied using Atomic Force Microscopy (AFM).
Conducting AFM: Applications to Semiconductor Surfaces
Authors: Murrell Martin P. , O'Shea Sean J. , Barnes Jack , Welland Mark E. , Sofield Carl J.
Published: April 2011

The use of Conducting Probe Atomic Force Microscopy to give nm scale electronic characterisation of surfaces is reviewed. Local conductance, Kelvin Probe work function measurements, Fowler-Nordheim tunnelling and local C-V characterisation techniques are outlined. The principle results of these and their applications to the semiconductor surface and thin film characterisation are discussed. We present tunnelling data from silicon through varying oxide thickness using conducting AFM and scanning Kelvin Probe measurements from sub micron MOS capacitors. The F-N tunnelling technique has also been used on epitaxial silicon surfaces with atomically flat topography.

The inherent problems associated with quantitative, reproducible measurements are outlined, and the potential applications of the measurements to surface and thin film technology are discussed.
Growth of MonX by Reactive Laser ablation
Authors: Treece Randolph E. , Horwitz James S. , Donovan Edward , Chrisey Douglas B.
Published: April 2011

Control of composition and phase of a series of MoNx thin films has been accomplished by reactive pulsed laser deposition (PLD). Molybdenum foil targets were ablated in a background gas of N2/H2 (10%) at pressures ranging from 40 to 120 mTorr. the MoNx films were deposited simultaneously onto (100) MgO and fused silica substrates. the films were characterized by X-ray diffraction (XRD), temperature-dependent resistivity, and Rutherford backscattering spectroscopy (RBS). the composition, phase, and electronic transport properties were found to depend on N2/H2 pressure, substrate temperature, and substrate orientation. the highest superconducting transition temperature (Tc ) was observed in a hexagonal Mo2N film where Tc (onset) ≈ 8 K. IN general, Tc was observed to correlate most closely with the N/Mo ratio. as the ratio of N/Mo increased above optimal M02N composition, Tc decreased. Films grown on MgO generally had higher N/Mo ratios and hence lower Tc values than films deposited on silic A.
Hyperthermal H Atom Reactions on D/Si(100)
Authors: Buntin Steven A.
Published: April 2011

A photolytic source of H atoms is used to probe abstraction and adsorption reactions on the D/Si(100) monodeuteride surface. Surface H and D coverages are determined for H atom exposures, with incident average kinetic energies of 1.0 and 2.8 eV. the D atom depletion probability per incident H atom is 0.3±0.2 for both kinetic energies, and is likely due to abstraction. these results, together with previous studies, indicate that the rates of depletion of surface D and the uptake of H are nominally independent of H atom kinetic energy over the range of about 0.3 to nearly 3 eV.
In-Situ Transmission Electron Microscopy for Analysis of Ion-Beam-Growth Processes
Authors: Pankov Vladimir V. , Levchuk Nikolai E. , Dostanko Anatoly P.
Published: April 2011

Two types of systems for in situ transmission electron microscopy analysis of ion-beam etching, ion-beam sputtering and ion-beam assisted deposition are reported. their design, operational features and some applications are presented. Radiation-stimulated diffusion in Mo-Si heterostructure, early growth of ion-beam sputtered in-Sn, in-Sn-O, ZnS:Mn films and recrystallization of ln-Sn-O films during vacuum post-annealing are studied.
Evaluation of No-Clean Fluxes for High Reliability Applications
Authors: Pope E. , Watson J. , Kennish D.
Published: April 2011

A series of rosin mildly activated, halide free, low residue fluxes have been evaluated for use with hot bar reflow of Tape Carrier Packages (TCP) to printed circuit boards (PCB). Materials were studied with respect to their wettability, SIR performance, water reflux extractable ionics and residue levels. Ionic levels were measured by FTIR and Ion chromatography. A flux was selected which has demonstrated acceptable performance in 156C/85%RH 10V biased stress testing.
Thin Film Integral Capacitor Fabricated on a Polymer Dielectric for High Density Interconnect (HDI) Applications
Authors: Paik Kyung W. , Lu Toh-Ming
Published: April 2011

The expanding needs of mixed signal applications of thin film MCM technologies which combine analog, digital, power and opto-electric devices require a wide range of integral, thin film, passive components within the MCM structure. There is a need to incorporate these passive elements into the interconnect structure to reduce component count, decrease substrate area and to improve electrical performance. In this study, we investigated advanced material and processing technologies for the in situ formation of capacitor components during the fabrication of multilayer polymer/copper interconnect structures.

Amorphous BaTiO3 film having a dielectric constant of 10 to 40 depending on stoichiometry was deposited on a surface roughness controlled metallized polyimide surface at room temperature using the reactive partial ionized beam (RPIB) technique. Simple metal/insulator/metal(MIM) capacitors were fabricated and characterized. Hundreds of pF capacitance with <10−6 Amp leakage current were obtained depending on the top metal electrode size, dielectric thickness, and stoichiometry of dielectric film. Annealing treatment on dielectric film significantly enhanced the leakage current property. After thermal cycling treatment, it was proved that thin film integral capacitor was reliable enough to be used as a practical MCM application. Process defects control was necessary to improve capacitor yield.
Technique for Measuring Electronic-Based Electro-Optic Coefficients of Ferroelectric Liquid Crystals
Authors: Arnett Kenneth E. , Walba David M. , Drewes Joel A.
Published: April 2011

Among soft organic nonlinear optical materials is a class of recently developed: χ(2)_ enhanced ferroelectric liquid crystals (FLCs). The FLC phase nonlinear susceptibility is enhanced by synthesizing onto the molecules constituting the FLC phase a moiety with an increased hyperpolarizability. The hyperpolarizability of the FLC molecules couples into the permanent, thermodynamically stable, polar order of the FLC phase resulting in a material with an enhanced nonlinear susceptibility. Like other soft organics, the linear and nonlinear optical materials characteristics can be altered by chemical synthesis and mixing.

We report on our technique to evaluate the nonlinear optical properties of χ(2)-enhanced FLCs by measuring their high-frequency electro-optic r-coefficients. The technique is broad-band, readily allowing electro-optic coefficient measurement between 100 KHz and 200 MHz. Although the experimental geometry is not conducive for practical device application, it offers a compromise between ease of fabrication and magnitude of nonlinear response. This technique can also be used to evaluate other organic materials such as poled polymers.
Micro-Raman Study of Sol-Gel Grown Pmn-PT Thin Films
Authors: Ching-Prado E. , Tao R. W. , Guo A. R. , Katiyar R. S. , Bhalla A. S.
Published: April 2011

Thin films of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) were prepared by sol-gel technique and deposited on platinum coated-silicon wafer. The thicknesses of the two films were ∼400 nm and ∼550 nm, respectively. Micro-Raman spectra of the PMN-PT films show strong broad bands centered at 50, 136, 276, 450, 510, 556, and 790 cm−1, which are characteristic of PMN formation. Temperature dependent Raman scattering from 290K to 70K did not show any significant change in the bandwidth of the peaks, meaning thereby that the relaxation times of these phonons are practically temperature independent. The bands are interpreted as due to a break down in the phonon momentum conservation within the Brillouin zone, which is associated with some degree of disorder in the material. As a result, the Raman spectrum is a weighted average of the density of phonon states. Micro-Raman measurements in many different places on the films clearly indicate that they are homogeneous. In addition, the differences found in the Raman spectra of the films, particularly the band at 790 cm−1 is discussed. FT-1R measurements of the PMN-PT films present two broad bands around 260 and 550 cm−1, which are characteristic of perovskite structure and are primarily due to motions of oxygen ions. Also, these bands are compared with those found in PMN single crystal, and with those found in other similar systems, such as PLZT and PSN. SEM and XRD techniques have been used for the structural characterization.
Development of Chromophores Based on the Dicyanomethylene Acceptor Group
Authors: Ermer Susan , Lovejoy Steven M. , Leung Doris S.
Published: April 2011

We have used DCM/polyimide guest-host films for a series of device demonstrations, including demonstrations of high speed, low voltage digital and analog switching. Although useful for such demonstrations, DCM tends to out diffuse at polyimide cure temperatures, motivating the search for related compounds with similar activity, transparency, processibility, and greater thermal stability. We have designed, synthesized, and characterized a series of chromophores with related molecular structures. Like DCM, all of these chromophores share the dicyanomethylene [>C=C(CN)2] acceptor group. Some of these compounds are conventional donor-acceptor chromophores, while others fall into the class of lambda-shaped donor-acceptor-donor (DAD) compounds. An acceptor-donor-acceptor (ADA) chromophore has also been prepared and characterized. The donor-acceptor analog studies utilize a variation on the Knoevenagel condensation reaction used to make DCM, substituting isophorone for 4-pyranone to avoid the formation of mixtures. These reactions lead to the DCI series of compounds. We will describe progress in our investigations of these series of compounds.
Epitaxial Growth of GaN Films Produced by ECR-Assisted MBE
Authors: Moustakas T.D.
Published: April 2011

The epitaxial growth of wurtzite and zincblende GaN on (0001) sapphire and (001) Si by the Electron Cyclotron Resonance-assited Molecular Beam Epitaxy (ECR-MBE) method is discussed. We show that films can be grown in the layer-by-layer mode when growth occurs in Ga-rich regime. Surface roughening mechanisms are addressed. The similarity of photoluminescence data of Mg-doped wurtzite GaN films with those of undoped zincblende GaN films suggests that Mg doping facilitates the formation of stacking faults in the wurtzite structure which are nucleation sites for zincblende domains.
Low-Temperature Growth of High Quality InxGa1−xN by Atomic Layer Epitaxy
Authors: Boutros K.S. , Roberts J.C. , McIntosh F.G. , Piner E.L. , El-Masry N.A. , Bedair S.M.
Published: April 2011

We report on the low temperature epitaxial growth of InxGa1−xN with 0≤x≤0.27 by Atomic Layer Epitaxy (ALE). GaN and InGaN single crystal films have been grown by ALE in the temperature range between 600 and 700 °C using the rotating substrate approach. Films were deposited on sapphire substrates using TMG, EdMIn, and NH3 as precursors. Up to 27% indium content has been achieved in the InGaN films. The FWHM of the (0002) InGaN peak by double crystal X-ray diffraction of these films was as small as 5 minutes. Room-temperature photoluminescence (PL) from these films was dominated by band edge emission between 365 nm and 446 nm. AlGaN/InGaN double heterostructures were grown in a hybrid reactor, in which the AlGaN barrier layers were grown by MOCVD and the InGaN active layer by ALE. The structures showed good crystal quality, and sharp PL emission with peak intensity at 410 nm.
GaN Three Dimensional Nanostructures
Authors: Dmitriev V. , Irvine K. , Zubrilov A. , Tsvetkov D. , Nikolaev V. , Jakobson M. , Nelson D. , Sitnikova A.
Published: April 2011

We report on the growth and characterization of three dimensional nanoscale structures of GaN. GaN dots were grown by metal organic chemical vapor deposition (MOCVD) on 6H-SiC substrates. The actual size of the dots measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) ranged from ∼20 nm to more than 2 μm. The average dot density ranged from 107 to 109 cm−2. The single crystal structure of the dots was verified by reflectance high energy electron diffraction (HEED) and TEM. Cathodoluminescence (CL) and photoluminescence (PL) of the dots were studied at various temperatures and excitation levels. The PL and CL edge peak for the GaN dots exhibited a blue shift as compared with edge peak position for continuous GaN layers grown on SiC.
Electronic Structure of a Nitrogen Vacancy in Cubic Gallium Nitride
Authors: Gubanov V.A. , Wright A.F. , Nelson J.S. , Fong C.Y. , Klein B. M.
Published: April 2011

A nitrogen vacancy in zinc-blende structure gallium nitride (c-GaN) is investigated by the plane-wave pseudopotential (PWPP) and tight binding-linear combination of muffin tin orbitals (TB-LMTO) methods using 32- and 64- atom supercells. The relaxation of the nearest Ga atom to the vacancy site is found to be inward by 0.069 a.u., with a relaxation energy of 0.04 eV/N-atom vacancy. The shell-projected, total and partial densities of states and the charge density maps are obtained to provide detailed information on energy and spatial localization of the N vacancy states.
Electroreflectance from Gallium Nitride Using Second-Harmonic Generation
Authors: Miragliotta Joseph , Wickenden Dennis K.
Published: April 2011

The optical second-harmonic (SH) response of a reverse biased gallium nitride (GaN) film was investigated for SH photon energies near the fundamental absorption edge. With the application of a DC electric field (∼ 100 to 220 kV/cm) along the optical axis of the sample, a strong two-photon resonance was observed in the specular reflected SH signal. This resonance was attributed to electric-field induced SH generation, EFISH, a third-order nonlinear response which arises from an induced polarization that is linearly dependent on the amplitude of the DC field. The EFISH contribution was spectrally localized at the bandedge, demonstrating the potential of SH spectroscopy for analysis of critical points in the band structure of semiconductors.
Light Emission Properties of GaN-Based Double Heterostructures and Quantum Wells
Authors: Loeber D.A.S. , Redwing J.M. , Anderson N.G. , Tischler M.A.
Published: April 2011

Edge emission characteristics of optically pumped GaN-AlGaN double heterostructures and quantum wells are examined. The samples, which were grown by metalorganic vapor phase epitaxy, are photoexcited with light from a pulsed nitrogen laser. The pump light is focused to a narrow stripe on the sample surface, oriented perpendicular to a cleaved edge, and the edge luminescence is collected and analyzed. We first compare emission characteristics of highly excited GaN-AlGaN double heterostructures grown simultaneously on SiC and sapphire substrates. Polarization resolved spectral properties of edge luminescence from both structures is studied as a function of pump intensity and excitation stripe length. Characteristics indicative of stimulated emission are observed, particularly in the sample grown on SiC. We then present results demonstrating laser emission from a GaN-AlGaN separate-confinement quantum-well heterostructure. At high pump intensities, band edge emission from the quantum well exhibits five narrow (∼1 Å) modes which are evenly spaced by 10Å to within the resolution of the spectrometer. This represents the first demonstration of laser action in a GaN-based quantum-well structure.
Laser MBE for Atomically Defined Ceramic Film Growth
Authors: Koinuma H. , Kawasaki M. , Yoshimoto M.
Published: April 2011

Laser MBE is a process especially useful for epitaxial layer-by-layer growth of ceramic thin films directly from sintered ceramic targets. By employing high vacuum MBE conditions, the process has a restriction in the controllability of chemical composition, e.g. nonstoi chiometry in oxides and nitrides, as compared with conventional pulsed laser deposition, but instead gains the possibility of in situ monitoring of surface reaction on an atomic scale by RHEED. Ever since our first success in observing RHEED intensity oscillation for CeO2 film growth on Si(l11), we have verified the molecular layer epitaxy by laser MBE for perovskite oxides (SrTiO3, BaTiO3, SrVO3 ,etc) and infinite-layer cuprates MCuO2 (M= Sr, Ba, Ca) on SrTiO3 substrates as well as for oxide and nitride films on Si substrates. Key factors to design the laser MBE system, operation parameters, and recent experimental results are presented and discussed.
Fs Spectroscopy of Phonon Emission and Absorption for A Cold Plasma in Gallium Arsenide
Authors: Agnesi A. , Cavalleri A. , Malvezzi A.M. , Reali G.C.
Published: April 2011

Degenerate pump and probe measurements on bulk GaAs <100> surfaces with sub-100 fs near infrared laser pulses have been performed in the 0.8 − 3 × 1017 carriers cm-3 excitation range at room temperature. Transient reflectivity data reveal the progressive extinction of the LO-phonon emission channel when the excess excitation energy is decreased. At these wavelengths and for low excitation levels, acoustic phonon absorption from conduction band minimum is observed. Surface recombination rates are deduced from the picosecond evolution of the reflectivity.
Epitaxial Tin Films on Sapphire and Silicon-on-Sapphire by Pulsed Laser Deposition
Authors: Vispute R.D. , Dovidenko K. , Jagannadham K. , Narayan J.
Published: April 2011

We have investigated epitaxial growth of TiN on sapphire and electronic grade silicon-on-sapphire (SOS) by PLD. A pulsed KrF excimer laser was used to ablate the stoichiometric TiN target in the deposition chamber maintained at a base pressure of 3xl0-7 Torr. Epitaxial growth was achieved at deposition temperatures of 500-700°C. The films were characterized by x-ray diffraction technique, Raman spectroscopy, high resolution electron transmission microscopy and four-point-probe electrical resistivity. The x-ray diffraction and TEM results showed that the TiN films deposited on sapphire (0001) and SOS above 500oC were single crystal in nature. The epitaxial relationship for TiN on sapphire was found to be TiN[1 1 1]||Al2O3[0001] and in-plane alignment of TiN[110]||Al2O3[1010]. In case of growth on SOS, epitaxy of TiN on Si was cube-on-cube and is similar to that of TiN grown on bulk Si substrates. Four-point-probe electrical resistivity measurements showed characteristic metallic behavior of these films as a function of temperature with the lowest value of resistivity of about 20-22μΩ-cm at room temperature. This paper describes the fundamental issues related to epitaxy, defect formation and nitride-oxide interfaces. It is also shown that the TiN films on sapphire and SOS have unique characteristics and are promising for metallization in advanced microelectronics.
Femtosecond Laser Deposition of Diamond-Like Carbon Films
Authors: Qian F. , Singh R. K. , Dutta S. , Pronko P.P. , Weber W.H.
Published: April 2011

We have deposited unhydrogenated diamond-like carbon (DLC) films with 100 femtosecond laser pulses, at intensities in the 3x1014 - 6.5x1015 W/cm2 range. Film surface topography, optical property, and bonding structure were examined, respectively, with atomic force microscopy (AFM), spectroscopie ellipsometry (SE) and Raman spectrometry. The femtosecond pulse generated plasma was studied through time-of-flight (TOF) experiment. The most probable kinetic energy of carbon ions was estimated to be in the 300 – 2000 eV range, increasing with laser intensity. In addition, a unique ‘suprathermal’ component with kinetic energy ranging from 4 to 40 keV was observed in the TOF spectrum. This high energy peak is believed to originate from fast ions in a solid density plasma created during the absorption of each femtosecond laser pulse.
Laser Melting and Recrystallization of Bulk Si by Nanosecond UV Laser Pulses
Authors: Garcia C. , Prieto A.C. , Jimenez J. , Sanz L.F.
Published: April 2011

Laser ablation of semiconductors presents an increasing interest for both thin film growth and surface modification. We present herein a study of the damage produced in bulk silicon by nanoseconds UV laser pulses with energy above the melting threshold. This study is carried out with a Raman microprobe. Polarized microRaman was used to reveal the main changes in the melted and recrystallized volume. These changes were observed in the liquid/solid boundaries, where tensile stress due to the induced thermal wave is more important. The morphology of the melted region evidences matter accumulation at such a boundary.
Laser Encapsulation of Metallic Films in SiO2
Authors: Pedraza A. J. , Cao S. , Lowndes D. H. , Allard L. F.
Published: April 2011

Thin films of gold, copper and iron deposited on silica were driven into the substrate by a laser pulse. This transport takes place only when the irradiation is performed at a laser energy density of 0.7 J/cm2 or lower. Cross sectional transmission electron microscopy (TEM) of the irradiated specimens reveals two distinctive stages in the encapsulation process. In the first, the film melts and clusters into small particles and in the second one the particles are driven into the substrate by the laser pulse. The particle size of encapsulated metal varies from 5 to 50 nm. Selected area diffraction of the large particles and lattice fringe images of the smaller particles reveal pure metals, e.g., gold, copper or iron. Titanium films laser irradiated are not encapsulated in silica; instead, these films react with silica forming an amorphous compound. Apparently, one of the conditions required for encapsulation is that the metal should not react with the substrate material. On subsequent irradiation at a laser energy density of 1.5 J/cm2, ablation of silica partially exposes the metallic particles. Strong bonding between a new film deposited after irradiation and the substrate is obtained because these particles anchor the freshly deposited film. Anchoring is clearly revealed by cross sectional TEM. The mechanisms of encapsulation are discussed using results from TEM and adhesion testing.
Laser-Assisted Dry Etching Ablation for Microstructuring of III-V Semiconductors
Authors: Dubowski J.J. , Julier M. , Sproule G.I. , Mason B.
Published: April 2011

Laser-assisted dry etching ablation (LADEA) has been reviewed with an emphasis on its applicability for the microstructuring of III-V semiconductor compounds. The method is based on the application of an excimer laser ( λ= 308 nm) for pulsed heating of a wafer which is placed in a stream of Cl2/He gas. Both the products of chemical reaction and the depth to which a laser-induced reaction takes place depend on laser fluence. This makes possible the ablation of a well defined volume of the material. Little or no structural damage to the surface is observed because ablation is carried out with laser fluences below those required to melt the matrix material. The laser fluence dependence of the etch rate indicates that the process is primarily temperature driven with a characteristic energy for desorption. We have investigated LADEA as a method for in-situ processing of III-V semiconductors and the fabrication of nanostructures. An atomic force microscopy study has shown that atomically smooth surfaces can be obtained if the etch rate is near 1/2 atomic layer per laser pulse. The lateral resolution of LADEA has been found to be at least 20 nm. This, as well as the results of in-situ photoluminescence and Auger electron spectroscopy measurements, indicate that LADEA can be used for the direct (photoresist-free) fabrication of high quality microstructures and, ultimately, for the nanostructuring of III-V semiconductor compounds.
Three-Dimensional Laser Chemical Vapor Deposition of Nickel-Iron Alloys
Authors: Maxwell J.L. , Pegna J. , Deangelis D.A. , Messia D.V.
Published: April 2011

A systematic study of the composition of Ni-Fe steel microstructures grown from iron pentacarbonyl and nickel tetracarbonyl by direct laser-induced pyrolysis is presented. The partial pressures of both precursors were varied from 2 to 40 mbar, resulting in needles of iron, nickel, and iron-nickel alloys. An Ar+ laser was employed at incident powers of 100 to 600 mW. Auger Spectroscopy and a microprobe were used to determine the composition of the needles vs. partial pressure and laser power. Composition was also measured along the length of the rods to determine temperature changes during needle growth. This latter effect is useful in modelling the heat flow mechanisms during 3-dimensional laser CVD, as the threshold decomposition temperatures of Fe(CO)5 and Ni(CO)4 differ and the composition of the rods affects their thermal conductivity. In some iron samples, periodic banded structures were observed along the length of the rods, indicative of periodic melting. Axial deposition rates were also measured relative to laser power density, and rates up to 40 μm/s were achieved. Photolysis in the gas phase was observed for the iron-nickel carbonyl mixture, and was largely eliminated with a high-pass UV filter at 420nm. Additional disassociation of the carbonyl groups produced carbon soot near the reaction zone, but only for high nickel carbonyl concentrations. Convective cooling of the needles during growth was determined to be the primary heat transfer mechanism.
2d Modeling of Laser Induced Plasma Expansion
Authors: Le H.C. , Zeitoun D. , Burtschell Y. , Marine W. , Sentís M. , Dreyus R.W.
Published: April 2011

An axisymmetric two-dimensional modeling of plasma expansion in background gas is carried out to provide a better understanding of pulsed laser deposition (PLD) processes. This model takes into account the plasma plume dynamics just after the laser ablation pulse. It is shown that hydrodynamic behaviour and thermal relaxation of the plasma are strongly dependent on the nature and the pressure of background gas. In good agreement with experimental results backward movement of particles is clearly identified at a late expansion stage (≥ 2 μs).
Diagnostics of Pulsed Plasma Fluxes in Laser Deposition of Thin Films
Authors: Ozegowski M. , Metev S. , Sepold G. , Burmester S.
Published: April 2011

This paper presents the main results of an experimental study of the dependence of some important plasma parameters (plasma flux density, multicharge ion content, degree of ionization, energy distribution of the ions) on some laser parameters (light flux density, wavelength) for two laser types (TEA-CO2- and excimer laser). A special experimental method has been developed for an absolute and simultaneous measurement of the plasma parameters. The results obtained show the possibility to control the parameters of plasma fluxes over the deposition conditions and herewith to control the properties of the deposited films.
Thick-Film Processing of Pb5Ge3O11-Based Ferroelectric Glass-Ceramics
Authors: Cornejo Iván A. , Haun Michael J.
Published: April 2011

Processing techniques were investigated to produce c-axis orientation, or texture, of ferroelectric Pb5Ge3O11-based glass-ceramic compositions during crystallization of amorphous thick-film printed samples from the Pb5Ge3O11-PbTiO3 (PG-PT) and Pb5Ge3O11Pb(Zr1/2Ti1/2)O3 (PG-PZT) systems. In these systems the PG crystallized into a ferroelectric phase, producing a multiple ferroelectric phase composite at low temperatures, PG-PT or PG-PZT. In this way the non-ferroelectric component of traditional ferroelectric glass-ceramics was eliminated.
Pressure-Induced Structural Transformation in Cristobalite Studied by Molecular Dynamic Simulations
Authors: Duffrene Lucas , Kjeffer John
Published: April 2011

The phase transformation between the α- and β-cristobalite modifications of SiO2 were studied using molecular dynamic simulations. The transformation was induced isothermally by control of the pressure within the structure, either through an externally applied constant stress or by changing the simulation box volume. The atomic scale mechanisms of the transformation can best be observed by means of a time-correlation function describing the spatial orientation of the planes containing the Si-O-Si bonds. These planes rotate by 90° over the course of the transition. Both, the bulk modulus, calculated for static structures, as well as the vibrational spectra of the Si-O-Si planes, reflect the softening of acoustic modes in the midst of the transition, which is characteristic of displacive phase transformations. Although the aperiodic shift of atomic positions upon passage of the transformation front could be responsible for a momentary softening of the structure, this is not the only reason, since this behavior persists when maintaining the structure at intermediate densities, which corresponds neither to α-, nor to β- cristobalite.