bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochemical Pattern Etching of Single-Crystalline 3C-SiC
Authors: Mori T. , Hatao K. , Murahara M.
Published: April 2011

A single-crystalline 3C-SiC is very difficult to etch compared with a polycrystalline SiC. Thus, a photochemical pattern etching of the SiC was demonstrated by using Xe2* excimer lamp and ArF or KrF excimer laser. To promote the surface reaction, a Xe2* excimer lamp was employed to produce many radicals on the sample surface; simultaneously, ArF or KrF laser light irradiated the surface via a circuit pattern to dissociate the Si-C bonds. The Si and C reacted with the F and N radicals photo-dissociated from NF3 gas to form SiF4, CFn and CN, which diffused in the reaction cell. As a result, the single-crystalline 3C-SiC was photo-chemically etched effectively. With the NF3 gas of 200Torr, the Xe2* excimer lamp of 7mW/cm2, and the KrF excimer laser of 650mJ/cm2, 20Hz and 10,000shots, the etch depth of 700 Å was successfully achieved.
Low Temperature Chemical Vapor Deposition of Titanium Dioxide Thin Films Using Tetranitratotitanium (IV)
Authors: Gilmer D. C. , Gladfelter W. L. , Colombo D. G. , Taylor C. J. , Roberts J. , Campbell S. A. , Kim H.-S. , Wilk G. D. , Gribelyuk M. A.
Published: April 2011

Crystalline titanium dioxide films were deposited on silicon (100) at temperatures as low as 184°C using the volatile molecular precursor, tetranitratotitanium(IV). Deposition rates in a low pressure chemical vapor deposition (LPCVD) reactor operated at 230 – 500°C with a precursor vessel temperature at 22°C were typically 4 nm/min. The effect of deposition temperature and annealing conditions on morphology are shown. Following post-deposition annealing in oxygen and hydrogen, Pt/TiO2/Si/Al capacitors were fabricated and exhibited dielectric constants in the range of 19 – 30 and leakage current densities as low as 10−8 Amp/cm2.
Formation of Platinum and Palladium Bimetallic Superfine Particles by Ultrasonic Irradiation
Authors: Fujimoto Toshiyuki , Terauchi Shinya , Umehara Hiroyuki , Kojima Isao , Henderson William
Published: April 2011

Pt/Pd bimetallic nanoparticles were prepared by ultrasonic irradiation of aqueous solutions containing salts of both metal ions. Uniform bimetallic particles were found to have a 2.8 nm average diameter and a narrow size distribution. The size was similar to Pt monometallic particles, and the shape was similar to Pd monometallic particles, both prepared by ultrasound in the same way.
The Impact of the Graphite Nanofiber Structure on the Behavior of Supported Nickel
Authors: Park C. , Baker R. T. K.
Published: April 2011

In the current investigation we have used the hydrogenation of ethylene and crotonaldehyde as probe reactions in an attempt to follow any changes in catalytic behavior induced by supporting nickel on different types of graphite nanofiber support materials. The hydrogenation of the α,β-unsaturated aldehyde to the desired product, crotyl alcohol, is a particularly difficult task since there is a strong tendency to hydrogenate both the C=C and C=O in the reactant molecule. This study is designed to compare the catalytic behavior of the metal particles when dispersed on three types of nanofibers, where the orientation of the graphite platelets within the structures is significantly different in each case. The metal crystallites are located in such a manner that the majority of particles are in direct contact with graphite edge regions. For comparison purposes, the same set of hydrogenation reactions were carried out under similar conditions over γ-Al2O3 supported nickel particles.
The Hydrothermal Synthesis and Characterization of New Organically Templated Layered Vanadium Oxides by Methylamine
Authors: Chen Rongji , Zavalij Peter Y. , Stanley Whittingham M.
Published: April 2011

The hydrothermal reaction of vanadium pentoxide with methylamine leads to a series of new layered vanadium oxides by using different acids to adjust the initial pH. The structure of these layered vanadium oxides was established by X-ray single crystal and powder diffraction. The new phases were also characterized by TGA and FTIR. The oxidation state of vanadium was determined. These materials are expected to exhibit catalytic activity and may be of interest as cathode materials for secondary lithium batteries.
Catalytic Decomposition of Perfluorocompounds
Authors: Kanno S. , Ikeda S. , Yamashita H. , Azuhata S. , Irie S. , Tamata S.
Published: April 2011

It is becoming increasingly important to decompose PFCs (Perfluorocompounds), which are powerful greenhouse gases. The process of catalytic decomposition is expected to be effective in operating at lower temperatures if catalysts of high activity and durability are developed. The decomposition activities of PFC with H2O was investigated using several catalysts. It was found that PFC decomposition activity was related to the reactivity of fluorine and the formation of mixed oxides. Using the catalyst we have developed, CF4 was decomposed with conversion above 99.9% over 1988h. Furthermore, another PFC was decomposed over the catalyst. The order of the conversion was CHF3 > CF4 > C2F6. The catalytic decomposition system can use the treatment of PFCs in dry etch process waste gas.
Generating Structural Models of Amorphous Tetrahedral Carbon: Basis set Dependencies
Authors: Schultz Peter A. , Stechel E. B.
Published: April 2011

We present the results of a systematic first-principles investigation of the requirements for developing realistic and reliable structural models for amorphous tetrahedral carbon (a-tC) and relate those structural models to the physical properties of this material. Within a linear combination of atomic orbitals formulation of density functional theory, we show that a large variational flexibility is required to accurately treat the highly defected and strained structures that can exist in a-tC. The average strain in the a-tC lattice is predicted to be roughly twice the strain of having all carbon atoms in three-member rings. A key figure of merit of a structural model, the proportion of three-fold bonded atoms, is shown to triple in going from a minimal basis description of a structure to a high quality basis. The basis-converged calculations agree well with experimental observables, such as the presence of four-member rings, lack of dangling bonds, and a significant gap. The simulations predict a much larger proportion of three-fold atoms than estimated in simple analyses of EELS and neutron scattering experiments. We show that the larger three-fold fraction is indeed consistent with the properties of a-tC, and imply that there are flaws in the simplifying assumptions that go into constructing experimental estimates of coordination numbers. These results highlight the perils of applying highly simplified theoretical models for a-tC before the correct physics has been identified and built into the models.
Hydrogenated Carbon-Nitrogen Films Obtained by Pecvd using Acetylene and Nitrogen as Precursor Gases
Authors: Jacobsohn L. G. , Franceschini D. F. , Freire F. L.
Published: April 2011

Amorphous hydrogenated carbon-nitrogen films were deposited by plasma enhanced chemical vapor deposition (PECVD) using acetylene-nitrogen mixtures. The atomic composition and density of the films were determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERDA). Raman and Infrared spectroscopies monitored their structure. The addition of nitrogen gas to the deposition atmosphere resulted in a decrease in the film deposition rate. The increase of the nitrogen content is accompanied by the reduction of the carbon content. The IR absorption spectra show an increase intensity of the C=N Raman band and the N-H and CsN stretching bands. On the other hand, the IR results show a decrease in the intensity of the C-H stretching band. Raman results suggest an increase with the nitrogen content of the fraction of carbon atoms in a sp2 state of hybridization with the nitrogen content. The internal compressive stress has been measured by the determination of the bending of the substrate; a reduction of up to 50 % has been observed depending on the nitrogen content.
Structural Trends in Amorphous Carbon
Authors: Wang C. Z. , Ho K. M.
Published: April 2011

Amorphous carbon (a-C) structures over a wide range of densities are generated by tight-binding molecular dynamics simulations using the recently developed environment-dependent carbon tight-binding potential. Our simulation results show that the relative concentration of the sp2 and sp3 bondings in the a-C samples changes systematically with the density of the samples. The a-C networks obtained by quenching the low density liquids consist of mostly three-fold coordinated atoms while the diamond-like tetrahedral a-C can be generated by quenching the high density (about 3.0g/cm3) liquid carbon.
High Pressure Solid State Chemistry of A3(VO4)2 Compounds (A: Ca, Sr, Ba)
Authors: Grzechnik Andrzej , McMillan Paul F.
Published: April 2011

The purpose of this study is to explore the potential of high pressure methods for preparation of new series of compounds in the A3(VO4)2 systems (A: Ca, Sr, Ba). In this study, we present our in situ vibrational and X-ray diffraction data on the behavior of the A3(VO4)2 compounds at high pressure and room temperature. Upon compression up to 290 kbar, there is no phase change in Ba3(VO4)2. Sr3(VO4)2 undergoes a first order phase transition to an olivine-like structure at about 150 kbar. In both the ambient pressure and olivine structures of Sr3(VO4)2, oxygen atoms form a hexagonal close packing. The packing in the olivine structure is distorted from this due to loss of 3-fold axis. Ca3(VO4)2 amorphizes at about 100 kbar. The high pressure behavior of the compounds studied here is related to the size of the A(2)2+ cations. Small Ca(2)2+ cations hinder the completion of crystal-to-crystal transformations in Ca3(VO4)2.
Temperature Dependence of the Intervalley Deformation Potential of GaAs/AlAs Superlattices Under Hydrostatic Pressure
Authors: Guha S. , Cai Q. , Chandrasekhar M. , Chandrasekhar H. R. , Kim Hyunjung , Alvarenga A. D. , Vogelgesang R. , Ramdas A. K. , Melloch M. R.
Published: April 2011

We have studied the pressure dependence of the type-I and type-II transitions in (GaAs)m/(AlAs)m superlattices by photoluminescence (PL) spectroscopy. From the study of PL linewidths of the type-I exciton as a function of pressure and temperature, we determine the intervalley deformation potential. Beyond the type-I and type-II crossover, the PL linewidth increases both as a function of pressure and temperature. We find that the electron-phonon deformation potential for Γ-X intervalley scattering varies with temperature.
Electron Transport Properties of La1-xSrxTiO3 Under Hydrostatic Pressure
Authors: Hays Charles C. , Zhou Jianshi , Goodenough John B. , Markert John T.
Published: April 2011

The temperature dependence of the resistance and thermoelectric power under hydrostatic pressure between 10 and 300 K are reported for two compositions, x = 0.044 and x = 0.05, of the narrowband system La1-xSrxTiO3. The application of hydrostatic pressure at room temperature induces a transition from a positive p-type to a negative n-type thermoelectric power for x = 0.044. This behavior is interpreted within a model of itinerant-electron antiferromagnetism in LaTiO3.
Metastable Melting Lines for H2O and the Liquid-Liquid Phase Transition Hypothesis
Authors: Mishima Osamu , Eugene Stanley H.
Published: April 2011

When ice Ih in an emulsion is compressed below 250 K, it melts to supercooled liquid water, avoiding the formation of other crystal phases. Here, we create emulsified high-pressure ices under high pressure and low temperature, and measure their temperature while these ices are decompressed at a constant rate at different temperatures. We detect metastable melting points of high-pressure ices, and identify their melting lines. We find what could be possibly two new ice phases, and discuss the relationship between decompression-induced melting and decompression-induced amorphization. Finally, we discuss briefly the analysis of experimental data and simulation results that are consistent with the hypothesized “second critical point” with temperature and pressure coordinates of approximately 200 K and 100 Mpa.
Radio Frequency Heating Coils for Shock Wave Experiments
Authors: Chen George Q. , Ahrens Thomas J.
Published: April 2011

Radio-frequency eddy current heating of metallic samples in shock wave, ultrasonic and diamond anvil apparatus provides a methodology for obtaining hot samples or hot metallic gaskets (containing a sample) and yet not heating the entire target, ultrasonic assembly or diamond cell. Analysis of a previous design of a radio-frequency (∼0.5 MHz) coil demonstrated that the center of 13 mm diameter shock wave experiment sample discs were underheated and the experimental temperatures achieved resulted from conduction of heat from the overheated sample edges relative to the center of the sample. We show, using the Biot-Savant law, that the ratio of magnetic field in the center to that at the edge of the sample, f, can be maximized to a value of f=1.8, by decreasing the radius of the heater coil, relative to the 13 mm diameter of sample. A simple analysis provides the thermal gradient across the sample thickness. An electric skin depth for iron of ∼1 mm for the 0.45 MHz frequency of the heater power supply of our system is obtained. This leads to a maximum temperature gradient of ∼52 K over the 4 mm thickness of the shock wave sample discs.
Study of the Local Atomic order in Si/C/N Nanopowders by X-ray Photoelectron Spectroscopy
Authors: Gheorghiu-de la Rocque A. , Dufour G. , Bonnefont P. A. , Sénémaud C. , Cauchetier M.
Published: April 2011

A study by X-ray photoelectron spectroscopy (XPS) of the local atomic environment in laser-synthetized Si/C/N nanopowders is presented. The Si 2p, C Is, and N 1s core levels as well as the valence band distribution are investigated. The attention is focused on samples with C/N atomic ratio around 0.6 which exhibit interesting properties concerning annealing treatments. The presence of C-N bonds after 1500°C annealed samples is evidenced.
Rheological behavior of an aluminum nitride nanoparticle suspension in Poly(amic acid)-nmp system
Authors: Chen Xiaohe , Gonsalves Kenneth , Rounds R. S.
Published: April 2011

Preliminary rheological characterizations of aluminum nitride (AIN) nanoparticle suspensions in nonaqueous Newtonian fluid media, NMP and NMP/poly(amic acid) solutions, reveal marked differences in viscoelastic behavior, at relatively low dispersed phase volume fractions. Dynamic mechanical and steady shear measurements provide experimental evidence of the effective interparticle and polymer/particle interactions in a dispersion process of nonoxide nanoparticles for ceramic/polymer nanocomposites. The rheological nature of the nanoparticle suspensions corresponds to interparticle physicochemical interactions that have been previously concluded and discussed.
Surface controlled nanospheres as drug carriers for intravenous and intranasal administration
Authors: Gref R. , Quellec P. , Dellacherie E. , Tobio M. , Alonso M. J.
Published: April 2011

The arival on the market of new therapeutic and antigenic molecules requires the development of appropriate delivery systems. The design of injectable nanoparticulate drug caniers invisible to the mononuclear phagocyte system is a major challenge. Also, overcoming mucosa baniers, such as the nasal one, using biodegradable nanospheres is another strategy still to be explored. These routes of administration require nanoparticulate systems with optimized surface properties. We investigated the ability of polyethylene glycol (PEG)-coated nanospheres made of amphiphilic diblock copolymers to achieve these goals. After an optimization of the nanosphere surface properties, we studied the possibility of entrapping macromolecules within the PEG-coated nanospheres. Results showed that it is possible to encapsulate a model protein, human serum albumin (HSA) within monodisperse nanospheres of a mean diameter of about 200 nm, reaching loadings as high as 9% (w/w). Moreover, these nanospheres showed excellent abilities for the transport of a model antigen, tetanus toxoid (Tr) through the nasal mucosa.
Nanostructured powders: a new class of materials for forming high performance particulate coatings
Authors: Skandan Ganesh
Published: April 2011

Nanostructured powders, with particle sizes in the range 1 to 100 nm, have shown great promise in the forming of advanced films and coatings for a variety of applications including tribological, high surface area supports for catalysts, chemical gas sensors, and optoelectronics. This paper is a summary of two major classes of powder synthesis techniques: (1) precipitation from aqueous salt solutions, and (2) condensation from vapor phase. The solution approach leads to powder particles that are spherical shells consisting of nanograins. The powder is milled with melting point lowering compounds and reagglomerated to make it suitable for thermal spraying. In contrast, the vapor condensation approach yields powder particles that are discrete, and loosely agglomerated. In a variation of the process, the heated clusters or nanoparticles are allowed to sinter on a heated substrate, forming porous or dense coatings. Films/coatings with thicknesses between 0.5 μm and 20.0 μm at rates in excess of 1 μm/min. are formed by thein situdeposition process. The synthesis techniques, powder and coating characteristics, and applications of the technologies, are described in this paper.
A Metastable-atom Deexcitation Spectroscopy (MDS) study on the First Atomic Layer of a Polycrystalline Titanium Surface
Authors: Kurahashi M. , Yamauchi Y.
Published: April 2011

The oxygen adsorption on a polycrystalline titanium surface at room temperature has been studied by MDS in conjunction with UPS and AES. MDS and UPS spectra were measured using a pulsed-dischaxge-type metastable helium atom source which we have newly developed. FRom the analysis of the measured spectra, we found the following about the local density of states (LDOS) of the oxygen-adsorbed titanium surface: (1) With increasing oxygen exposure at 0-2 L, the LDOS on the first atomic layer (SDOS) at 0-1 eV below the Fermi level (EF) decreases more steeply than that of deeper layers. (2) The SDOS at 5–8 eV below EF remains small at 0-2 L, and begins to increase at ca. 2 L while the LDOS of subsurface layer increases first. We discuss the positions of adsorbed oxygen atoms based on these results.
Effect of surface modification on the electrical properties of TiO2 and SnO2 nanopowders
Authors: Chancel Fabienne , Tribout Jérôme , Baraton Marie-Isabelle
Published: April 2011

The surface modification of titania and tin dioxide nanopowders by hexamethyldisilazane and hexamethyldisiloxane grafting has been followed in situ by FT-IR spectroscopy. A grafting mechanism is proposed for both compounds and the formation of new surface species is discussed. Since TiO2 and SnO2 are widely used in chemical gas sensors due to their electrical properties, the respective behaviors of the non-grafted and grafted samples in reducing (CO) environment as well as the humidity effects are compared. Because the transmitted IR energy depends on the concentration of the free carriers, a correlation between the electrical conductivity variation and the perturbation of the IR spectra is attempted.
Oxygen adsorption on tin oxide nanosized powders characterized by FTIR spectrometry and Relation with the sensor properties
Authors: Tribout J. , Chancel F. , Baraton M.-I. , Ferkel H. , Riehemann W.
Published: April 2011

The surfaces of two tin oxide nanosized powders synthesized by laser evaporation and presenting different average grain sizes were studied by Fourier transform infrared spectrometry. The oxygen adsorption onto activated and oxidized surfaces appeared to be dependent upon the grain size. Moreover, the nature of surface acidic sites probed by pyridine was shown to be dependent on the oxidizing treatment. A simultaneous study of the infrared energy variations and the spectrum perturbations when CO and mixtures of CO and O2 were in contact with the SnO2 samples, showed both the formation of CO2 and the CO reducing effect. The need of an oxygen environment for the surface recovery was clearly brought in evidence as well as the importance of the temperature in the CO sensing mechanism.
Radiation Effect on the Viscosity of the Simple B2O3 Glasses
Authors: Barbu A. , Jaskierowicz G.
Published: April 2011

The creep velocity of B203 glass fibers under irradiation with 2.5 MeV electrons at low flux ( around 5 1013 e-cm−2s−1) has been studied versus temperature. As under very high energy heavy ions irradiation (1.6 GeV argon), the viscosity is drastically reduced below 300°C. An important difference between the two kinds of irradiation is the occurrence of a compaction phenomenon at the beginning of electron irradiation experiments. The results can be understood by assuming two totally different mechanisms: a relaxation driven by melting of the glass along the path of the ions for very high energy heavy ion irradiations and a relaxation driven by individual radiation induced points defects for high energy electron irradiations.
Hrtem and Eels Studies of Reacted Materials From Caf2 by Electron Beam Irradiation
Authors: Kogure T. , saiki K. , Konno M. , Kamino T.
Published: April 2011

The change of calcium fluoride (CaF2) by electron beam irradiation has been investigated in TEMs operated at 200 kV. By irradiation fluorine is desorbed rapidly from CaF2 crystal. Although plasmon peaks in EELS spectra suggest the formation of Ca metal, no evidence for the existence of Ca metal is found in electron diffraction pattern or HRTEM images. This is due to perfect topotactic formation of Ca metal from CaF2 with a similar crystal structure and closely similar lattice parameters. Irradiation also forms amorphous material near the edge of Ca/CaF2 and randomly oriented CaO crystallites grow from the amorphous material. This amorphous material is regarded as hydroxide formed through the reaction of Ca and water, considering the residual gas composition and the formation rate of the material.
Thermal Behaviour of Implanted Nitrogen and Accumulated Hydrogen in Titanium
Authors: Soltani-Farshi M. , Baumann H. , Rück D. , Walter G. , Bethge K.
Published: April 2011

The influence of nitrogen ion implantation on the hydrogen accumulation in titanium was investigated as function of sample temperature and ion fluence. 150 keV nitrogen (15N) ions were implanted at different sample temperatures up to 700°C with fluences ranging from 1 × 1017 to 1 × 1018 ions/cm2. The amount of accumulated hydrogen and its depth distribution was measured quantitatively with the 15N depth profiling method. The implanted 15N depth profiles were measured by the reverse reaction 15N(p, αγ)12C at 429 keV. The binary phases of the implanted nitrogen with titanium are detected by grazing incidence x-ray diffraction. The results are compared with those obtained for samples implanted at RT and subsequently thermally treated.
Numerical Modeling and Experimental Measurements of Pulsed Ion Beam Surface Treatment
Authors: Thompson Michael O. , Renk T. J.
Published: April 2011

Pulsed ion beam treatment of materials provides an attractive alternative to pulsed laser processing for near surface modification of semiconductors, metals and polymers. The transfer of energy to the sample occurs by electronic and nuclear stopping over depths extending to several microns depending on ion species and voltage. A numerical code for modeling the melt and solidification behavior of materials under ion beam processing has been developed. The code and parameter extraction procedures were validated experimentally by comparing simulations with experimental measurements of the melt duration in silicon. The sensitivity of the melt behavior to variations in the beam properties was also investigated. The quiescent nature of the melt was confirmed by measurements of the diffusion of arsenic in the melt. These results demonstrate that simulations of the ion beam treatment can quantitatively match experimental results with no adjustable parameters.
Nanocrystal Growth at High Dose Rates in Negative Copper-Ion Implantation Into Insulators
Authors: Kishimoto N. , Gritsyna V. T. , Takeda Y. , Lee C. G. , Umeda N. , Saito T.
Published: April 2011

Nanoparticles of Cu were fabricated by negative-ion implantation, leading to spontaneous formation at high beam fluxes. Negative ions, alleviating surface charging, exhibit significant merits in carrying out low-energy implantation at high dose rates. The kinetic processes were studied by measuring dose-rate dependence of colloid formation and resultant optical properties. Negative-Cu ions of 60 keV were implanted into silica glasses at high-current densities, up to 260 μA/cm2, fixing the total dose at 3.0 × 1016 ions/cm2. Spherical nanocrystals of Cu atoms formed within a narrow region, near the projectile range of Cu ions. Simultaneously, much smaller particles spread out beyond a depleted zone, deeper than the projectile range. The nanocrystal growth and optical properties were greatly dependent on the dose rate and the specimen boundary condition. The growth process is explained by a droplet-model based on surface tension and radiation-induced diffusion. Beam-surface interactions also play an important role in the mass transport from the beam flux to the interior solid.
Advances in Ion and Laser Beam Technology: Achievements of Japanese Government and University Projects
Authors: Yamada Isao
Published: April 2011

This paper reviews recent R&D activity in advanced beam technologies funded by MITI and JST. A large-scale national project known as AMMTRA (Advanced Material-Processing and Machining Technology Research Association) funded by MITI has made a significant contribution to industrial applications of beam processing by developing high density ion and laser beam equipment. A subsequent program, the ACTA (Advanced Chemical Processing Technology Research Association) project involves development of multi-beam deposition systems for metal and dielectric materials formation including several systems which combine ion and laser beams, ion beams and CVD and plasma, and laser beams with sputtering. NEDO Proposal Based Project and JST (The Japan Science and Technology Corporation)-Exploitation and Application Study Project are fundamentally aimed to transfer technology from university to industry. Research in gas cluster ion beam technology is currently being conducted in the following areas: (i) shallow ion implantation for 0.1 μ m PMOS junction formation, (ii) high rate etching and smoothing for Si, diamond, SiC and metal oxide films and (iii) thin film depositions for optical filter and transparent conductive film. The gas cluster ion beam processes are discussed in comparison with traditional ion beam processing methods which are presently limited by available atomic and molecular ion beams.
Photo Modified Growth of GaAs by Chemical Beam Epitaxy
Authors: Jothilingam R. , Farrell T. , Joyce T.B. , Goodhew P.J.
Published: April 2011

We report the photo modified growth of GaAs by chemical beam epitaxy at substrate temperatures in the range 335 to 670°C using triethygallium (TEG) and arsine. A mercury-xenon lamp (electrical power 200 W) provided the irradiation for the photoassisted growth. The growth was monitored in real time by laser reflectometry (LR) using a 670 nm semiconductor laser, and the optically determined growth rate agreed with that obtained from the layer thickness measured by cross sectional transmission electron microscopy. The observed photo-enhancement of the growth rate at low substrate temperatures and inhibition at high substrate temperatures is thermal in origin, consistent with raising the substrate temperature by 10±3°C. Cross sectional transmission electron microscopy showed that the photoassisted layers are essentially free from dislocations
Engineering Dislocation Dynamics in Inx(AlyGa1−y)1−xP Graded Buffers Grown on Gap by Movpe
Authors: Kim A.Y. , Fitzgerald E.A.
Published: April 2011

To engineer high-quality Inx(AlyGa1−y)1−x P/Ga1−xP graded buffers, we have explored the effects of graded buffer design and MOVPE growth conditions on material quality. We demonstrate that surface roughness causes threading dislocation density (TDD) to increase with continued grading: dislocations and roughness interact in a recursive, escalating cycle to form pileups that cause increasing roughness and dislocation nucleation. Experiments show that V/III ratio, temperature, and grading rate can be used to control dislocation dynamics and surface roughness in InxGa1−xP graded buffers. Control of these parameters individually has resulted in x = 0.34 graded buffers with TDD = 5 × 106 cm−2and roughness = 15 nm and a simple optimization has resulted in TDD = 3 × 106 cm −2and roughness = 10 un. Our most recent work has focused on more sophisticated optimization and the incorporation of aluminum for x > 0.20 to keep the graded buffer completely transparent above 545 nm. Given our results, we expect to achieve transparent, device-quality Inx(AlyGa1−y)1−x P/GaP graded buffers with TDD < 106 cm−2
Hydrogenation and Defect Creation in GaAs-Based Devices During High Density Plasma Processing
Authors: Maeda T. , Lee J. W. , Abernathy C. R. , Pearton S. J. , Ren F. , Constantine C. , Shul R. J.
Published: April 2011

The effects of Inductively Coupled Plasma (ICP) and Electron Cyclotron Resonance (ECR) H2 plasmas on GaAs metal semiconductor field effect transistors (MESFETs), high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) have been measured as a function of ion flux, ion energy and process pressure. The chemical effects of hydrogenation have been compared to direct physical bombardment by Ar plasmas under the same conditions. Si dopant passivation in MESFETs and HEMTs and C base-dopant passivation in HBTs produces much larger changes in sheet resistance, breakdown voltage and device gain or transconductance than Ar ion bombardment and suggests that H2-containing plasma chemistries (CH4/H2 for semiconductor etching, SiH4 for dielectric deposition, CHF3 for dielectric etching) should be avoided, or at least the exposure of the surface minimized. In some cases the device degradation is less for higher source power conditions, due to the suppression of cathode dc self-bias and hence ion energy.
Athermal Annealing of Silicon
Authors: Grun J. , Manka C.K. , Hoffman C. A. , Meyer J. R. , Glembocki O. J. , Qadri S. B. , Skelton E. F. , Donnelly D. , Covington B.
Published: April 2011

We experimentally demonstrate the annealing and electrical activation of doped silicon without the direct application of heat as in conventional thermal annealing or pulsed laser annealing. 25 × 25 × 3 mm samples of silicon doped by neutron transmutation were irradiated with a short pulse from a 1.06-micron laser. The few joule laser pulse was focused to mm-diameter surface spot which resulted in high power (∼ 1011W/cm2) capable of launching shocks into the entire sample. In a few instances the entire silicon slab, including regionsfar outside the illuminated spot, was annealed and electrically activated. In the annealed samples electrical activation of donors throughout the slab, measured with a four-point probe, was uniform and comparable to that of thermally annealed control samples. Far-infrared spectroscopy and Hall measurements also showed that the donor species was activated and Raman spectroscopy demonstrated marked improvement in the crystal structure. We conjecture that the annealing was caused by the mechanical energy that was launched into the slab by the laser pulse. Results of experiments on an ion-implanted silicon sample are also discussed.
Evidence of Defect Migration and Clustering in MeV Heavy Ion Damaged Silicon
Authors: Mohapatra Y.N. , Girl P.K.
Published: April 2011

We have studied electrically active defects created by MeV heavy ion implantation in n-silicon. The buried damaged layer, created by implanting Ar’ ions of energy 1.45 MeV and doses in the range 1013-1014 cm−2 at room temperature, is embedded within the depletion layer of a Schottky diode. The defects are characterized using capacitance-voltage (C-V), current-voltage (I-V) and deep level transient spectroscopy (DLTS). Large concentration of electrically active defects are found to occur in a region several microns beyond the ion range or the damage profile predicted by Monte Carlo simulations. The dominance of a single trap in the damaged region is established from hysteresis effect in C-V, space charge limited conduction in forward I-V characteristics and DLTS results. With annealing in the temperature range of 400-600C, the observed changes in defect charge profile indicate that the effective electrical interface moves progressively towards the surface. C-V characteristics have been simulated using model charge profiles which suggest presence of a compensated region and a sharp negatively charged defect profile at a distance much larger than that expected from ion range. Our results constitute experimental evidence of migration and clustering of interstitial related defects, even at room temperature in case of high dose irradiation.
Schottky Barrier Modification Of Low Energy Ar-Ion Bombarded GaAs And Si
Authors: Deenapanray P.N.K. , Auret F.D. , Goodman S.A.
Published: April 2011

Epitaxially grown GaAs (p- and n-type) and n-Si were bombarded with low energy Ar-ions. Current voltage measurements on Schottky barrier diodes fabricated on the sputtered p-GaAs (Sc) and n-Si (Pd) showed that the series resistance and ideality factor were increased as the Arion dose was increased. The respective increase and decrease in barrier heights of Sc/p-GaAs and Pd/n-Si diodes were attributed to the presence of donor-type surface states in the bombarded material. The barrier heights of Au Schottky diodes made on n-GaAs changed nonmonotonically with Ar-ion sputter voltage. Variations of barrier height in the 0-1 kV range were explained by the introduction of donor-type defects. We demonstrated that the introduction of high concentrations of continuous level defects above 1 kV resulted in Fermi level pinning to become the dominant mechanism for controlling the effective barrier of current transport. Our results have shown that Schottky barrier properties could be changed by controlled amounts by varying the bombarding ion dose or sputter voltage.
Electrical Characterization of 1 keV He-, Ne-, and Ar-Ion Bombarded n-Si Using Deep Level Transient Spectroscopy
Authors: Deenapanray P.N.K. , Auret F.D. , Ridgway M.C. , Goodman S.A. , Myburg G.
Published: April 2011

We report on the electrical properties of defects introduced in epitaxially grown n-Si by 1 keV He-, Ne-, and Ar-ion bombardment. Epitaxial layers with different O contents were used in this study. We demonstrate using deep level transient spectroscopy that the low energy ions introduced a family of similarly structured defects (DI) with electronic levels at ∼0.20 eV below the conduction band. The introduction of this set of identical defects was not influenced by the presence of O. Ion bombardment of O-rich Si introduced another family of prominent traps (D2) with levels close to the middle of the band gap. Both sets of defects were thermally stable up to ∼400 °C, and their annealing was accompanied by the introduction of a family of secondary defects (D3). The “D3” defects had levels at ∼0.21 eV below the conduction band and were thermally stable at 650 °C. We have proposed that the “DI”, “D2”, and “D3” defects are higherorder vacancy clusters (larger than the divacancy) or complexes thereof.
Metal Impurity Mapping in Semiconductor Materials Using X-Ray Fluorescence
Authors: McHugo S.A. , Thompson A.C. , Padmore H.
Published: April 2011

We present x-ray fluorescence (XRF) results from studies of metal impurities in silicon. A synchrotron-based XRF microprobe, with μm spatial resolution, was used to detect and map the impurities. The sensitivity of the XRF microprobe was determined for copper and iron in silicon using well-characterized standard samples. We have concluded the system can detect one iron or copper precipitate in silicon with a radius of ≈14nm. This sensitivity pertains to other relevant impurities in silicon, such as, chromium, manganese, cobalt, nickel and gold. Furthermore, we have detected and spatially mapped metal impurity precipitates in silicon, which are undetectable by Energy Dispersive Spectroscopy in a Scanning Electron Microscope. These results exhibit the extraordinary sensitivity of the XRF microprobe for metal impurities in semiconductors.
Phosphorus Passivation of GaAs
Authors: Watkins S.P. , Xu X. , Hu J. , Ares R. , Yeo P. , Harrison D.A. , Thewalt M.L.W. , Bolognesi C.R. , Springthorpe A.J.
Published: April 2011

We have performed a systematic study of the effect of various phosphorus passivation techniques on the room temperature photoluminescence (PL) intensity of undoped GaAs. The effects of passivation by two methods are compared: (1) the P-exchange reaction on exposure to tertiarybutylphosphine (TBP) vapour between 500-620°C, and (2) the growth of thin layers of GaP directly on GaAs. An x-ray diffraction technique was used to estimate the thickness of the passivating layers. Reflectance difference spectroscopy indicated a similar chemical origin for the two passivation methods. Both passivation techniques resulted in strong enhancements in the room temperature PL. PL intensity was observed to increase very rapidly with adsorbed P for both cases saturating at approximately 2 monolayers equivalent GaP coverage.
A Study of Solder Paste Rheology for The Alternative Assembly and Reflow Technology (AART) Process
Authors: Murthy S.T. , Manessis D. , Srihari K. , Westby G.R.
Published: April 2011

Solder paste performance related properties such as stencil print quality, viscosity, thixotropy, and slump resistance are of great importance in the pre-reflow stages of the electronics assembly process. This paper focuses on the study of the rheological behavior of solder paste and its correlation to process performance during the various steps of the Alternative Assembly and Reflow Technology (AART) process. This technology aims to integrate the Printed Circuit board (PCB) assembly process for both through hole and surface mount components. Four solder pastes were considered in this study and their rheological characteristics were identified through flow and oscillation tests. The oscillation tests provided the linear viscoelastic characteristics of solder paste whereas the flow tests revealed information on the yield stress as well as the degree of shear-thinning and thixotropy of the solder paste. Pastes with high elastic properties and yield stress exhibited good hot slump resistance. Furthermore, extensive shear thinning of the paste facilitated the filling of the Plated-Through-Hole (PTH) sites. Recommendations are provided for tailoring the properties of a solder paste to meet the needs of the AART process.
Reliability and Lifing Methodologies for Microelectronic Systems
Authors: Reifsnider Ken
Published: April 2011

Integration of core electronic functions is progressing at a remarkable rate. The high-end computers that we are using now may be available on a single die by the turn of the century. The effect of this, and other advances on semiconductor assembly and packaging has generated the need for integrated component-level electrical thermal, and mechanical models and simulation methods, as described in the Semiconductor Industry Association national Technology Roadmap for Semiconductors. Although corporate and university research and development in the semiconductor area is intense (there are eight major university-based packaging centers around the world, for example), design/development methodologies that consider the combined and interactive effects of mechanical, thermal and chemical conditions on the reliability and durability of integrated components have been slow to develop. However, such methodologies have been developed for applications of complex composite systems in various other technologies where the operating conditions are similar. The present paper will discuss those developments and the possibility of applying that technology to microelectronic systems.
Molecular Modeling as a Tool for Adhesive Performance Understanding
Authors: Iwamoto N. , Pedigo J. , Grieve A. , Li M.
Published: April 2011

As higher levels of reliability are sought, it will become increasingly important to understand the relationship between the adhesive formulation and its bonded substrate. Johnson Matthey has been addressing this need by using molecular modeling to simulate the physical effects of adhesive components on properties such as adhesion, surface spread or bleed, and underfill flow. By using a molecular modeling method as opposed to a continuum calculation, the individual components of an adhesive may be theoretically manipulated without pre-determination of properties or property effects. The potential utility of the technique lies in the prediction or confirmation of property trends when different components or processes are used. Additionally, the molecular scale helps to gain insight of the interfacial contribution to performance.
A Combined Analysis of Moisture Diffusion with Interface Fracture Mechanics on the Interface Delamination in the Plastic IC Packages During Reflow Soldering
Authors: Park Y. B. , Yu Jin
Published: April 2011

The popcorn cracking phenomenon of plastic IC packages during the reflow soldering was investigated by conducting the stress analysis of heat transfer and moisture diffusion. Vapor pressures at delaminated interfaces between the die pad and EMC(Epoxy molding compound) were calculated and mechanistic parameters such as energy release rate, stress intensity factor and phase angle were derived under various loading conditions; thermal, crack face vapor pressure and mixed loadings. It was shown that thermal loading was the main driving force for crack propagation for small cracks lengths, but vapor pressure loading played more significant role as the crack extended.
Maskless, Direct Deposition of Copper onto Aluminum Bond Pads for Flip Chip Applications
Authors: Fang M. , O'Keefe T. , Stroder M. , Shih W. , O'Keefe M. , Strawser R. , Via D.
Published: April 2011

Flip chip interconnection of integrated circuits (IC) for packaging applications such as direct chip attachment use Pb-Sn solders as the connection between the die and the substrate. Underbump metallization is typically used to transition from the non-solderable Al bond pad on the IC to a solderable surface such as copper using traditional blanket metal deposition, photolithography and etching procedures. In this study, we report for the first time the use of a novel process for selectively depositing adherent copper directly onto aluminum thin films, eliminating the need for adhesion promoting transition layers and additional patterning steps. Utilizing copper bearing organic solutions and standard electroless and electrolytic copper plating baths, as-deposited and annealed sputter deposited Al-x%Cu (x = 0 to 2) thin films were coated with metallic copper. An increase in the organically deposited copper nucleation site density was observed with increasing copper concentration in the sputtered aluminum/copper thin films. Preliminary results using focused ion beam microscopy indicated that dissolution of the aluminum oxide surface and subsequent deposition of copper by cementation occurs in the non-conducting organic solution at sub-micron reaction lengths. Qualitative adhesion testing of samples resulted in the majority of films passing the tape test. Demonstration of the process using 50 micron diameter vias in BCB coated flip chip test vehicles from MCNC will be presented.
Effect of Grain Size and Magnetic Switching Volume on Media Noise Due to Intergranular Coupling in CoCrTaPt/Cr Thin Film Media
Authors: Malhotra Sudhir S. , Lal Brij B. , Russak Michael A.
Published: April 2011

In this work the effect of grain size and magnetic switching volume on media noise due to intergranular coupling for CoCrTaPt/Cr thin film media deposited at substrate temperature of 160 and 260°C are investigated. The film deposited at substrate temperature of 260°C showed weaker intergranular interaction and lower media noise compared to the film deposited at 160°C. The magnetic switching volume (V*) is an important consideration for thermal stability and media noise in high density recording media. The magnetic switching volume V* for the film deposited at 160 and 260°C was calculated to be 3.7 x 10-18 and 3.2 x 10-18 cm3 respectively. The magnetic switching volume is correlated to the average Co-alloy grain size, media noise and the interactions between the grains.
Structure of Molecularly -Thin Perfluoropolyether Films on Amorphous Carbon Surfaces
Authors: Tyndall G.W. , Waltman R.J.
Published: April 2011

Surface energies of molecularly-thin, perfluoropolyether (PFPE)-lubricated, amorphous carbon surfaces are presented as a function of the applied PFPE structure and thickness. A framework is developed to aid in the interpretation of the surface energy data. Information regarding the structure of these PFPE films adsorbed on CHx at the monolayer thickness levels is elucidated. Evidence for ordering in these polymer films is presented and interpreted to result from a combination of both, lateral cohesive interactions within the plane of the monolayer, and adhesive interactions between the PFPE monolayer and the underlying substrate.
Crystal Ion-Slicing of Magnetic and Ferroelectric Oxide Films
Authors: Levy M. , Osgood R.M. , Kumar A. , Bakhru H. , Liu R. , Cross E.
Published: April 2011

The epitaxial separation of single-crystal magnetic and ferroelectric oxide films is presented. Ion implantation is used to create a buried damage layer beneath the surface. The high etch-selectivity of this sacrificial layer makes it possible to detach high quality single-crystal films from bulk samples. Magnetic and electrical properties of the films are discussed.
Amorphous Rare Earth-Transition Metal Alloys for Magneto-Optical Storage
Authors: Gambino Richard J.
Published: April 2011

Amorphous alloys of the heavy rare earth elements with cobalt and iron have magnetic and optical properties that make them ideally suited for magneto-optical mass storage media. These materials are used in all commercial erasable (MO) optical disk systems and in optically assisted magnetic storage such as the recordable music minidisk. The important properties of these materials for this application are: 1/ ferrimagnetic exchange with a magnetic compensation point near room temperature, 2/ perpendicular easy axis anisotropy when prepared under suitable conditions as thin films, 3/low media noise as compared to polycrystalline films, 4/low processing temperatures compatible with polymer substrates and 5/thermally stable when cycled repeatedly to the Curie temperature. The magneto-optical Kerr effect that is used to read the information off the disk is large at the 800 nm wavelength used in current devices but low at 400 nm. Since the areal storage density is set by the diffraction limit, improvements in shorter wavelength device performance are needed.
Magnetic and Magneto-Optical Properties of Al Substituted Bi-RIG Particles Dispersed in a Plastic Binder
Authors: Hirano T. , Yoshida K. , Yamazaki Y. , Namikawa T. , Kishi M.
Published: April 2011

Nano-size R2BiAlxFe5-xO12(R: Dy, Gd, Th) particles were prepared with a coprecipitation and annealing method. The coating films of the particles were prepared with a coating technique. The magnetic and magneto-optical properties of the particles and films were investigated. The coercive forceHcof the particles and films was increased and saturation magnetizationMs. dropped with the Al contentx. TheHcof the coating films was about 200 Oe at the compositions of dispersed particles for which theMswas almost zero. These results suggest that the increase was made with magnetic compensation. The BiTb2A10.6Fe4.4O12coating film shows Faraday rotation spectra. The figure of merit of the film is about 0.5 at 520 nm. The coating BiTb2A10.6Fe4.4O12film is one of the candidate materials for a new economical magneto-optical storage medium.