bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Defects in Laser Annealed GaAs
Authors: Fletcher John , Narayan J. , Lowndes D. H.
Published: March 2011

The nature and depth distributions of residual damage in ion implanted and pulsed ruby laser annealed GaAs have been studied using both plan-view and cross-section transmission electron microscopy (TEM) specimens for high dose (1.0 × 1015 cm−2) Zn+, Se+ and Mg+ implants. It was found that laser energy densities above 0.36 J/cm2 were required to remove the implantation damage, this threshold energy density giving good agreement with that indicated by electrical activation measurements. Laser induced surface degradation of the GaAs was present even for energy densities as low as 0.25 J/cm2, and more severe damage, with the introduction of dislocations near the surface, was present for energy densities above 0.8 J/cm2. The use of thin SiO2 layers for encapsulation during laser annealing was found to substantially reduce this surface degradation.
Scanning Cathodoluminescence Microscopy of Polycrystalline GaAs
Authors: Salerno Jack P. , Gale Ronald P. , Fan John C. C. , Vaughan John
Published: March 2011

Scanning cathodoluminescence microscopy (SCM) has been used for nondestructive characterization of the optoelectronic properties of heavily Zn-doped, Bridgman-grown polycrystalline GaAs. Grain boundaries can either show no cathodoluminescence contrast, appear as dark lines, or appear slightly brighter than the surrounding matrix. Boundaries with similar surface morphologies can show different contrast. Spectral analysis data indicate that many of the observed features are due to local variations in impurity concentration.
Ion Channeling Techniques for Defect and Surface Studies
Authors: Appleton B. R.
Published: March 2011

The channeling and blocking phenomena are well enough understood that they can be combined with ion scattering or ion induced reactions to investigate defects and surface structures. A brief review is given of the origins of these phenomena, of associated concepts which are useful for defect and surface analysis, and of experimental constraints and requirements. Applications to selected problems are used to illustrate the advantages and limitations of these techniques.
Density Functional Theory of Interplane Cohesion in Graphite and Graphite Intercalation Compounds
Authors: Divincenzo D.P. , Mele E.J.
Published: March 2011

We employ density functional theory to study structural energies in pure graphite, Li-graphite, and K-graphite. Qualitative agreement with experiment is obtained for the carbon plane binding energy, lattice constants, compressibilities, and in-plane alkali-alkali potentials.
Change of C–C Bond Length in Layers of Graphite Upon Charge Transfer
Authors: Kertesz Miklos , Vonderviszt Ferenc , Hoffman Roald
Published: March 2011

Tight binding crystal orbital calculations on infinite layers of graphite have been performed for charge transfer (q) values ranging from −0.15 to +0.15 e/carbon atom. The rC-C carbon-carbon bond lengths have been optimized at several q values. The change of the calculated rC-C values as a function of q fits very well with the experimentally observed variations of the C-C bond lengths of both acceptor and donor compounds of intercalated graphite. The asymmetry of the variation of rC-c with respect to the sign of the charge transfer is related to the slightly antibonding nature (at the level of second neighbor interactions) of the π-electrons around the Fermi level of pristine graphite, similar to those in polyacetylene.
C-Axis Resistivity Of Some Stage 1 Donor Compounds
Authors: Fischer J.E. , Fuerst C.D. , Kim H.J.
Published: March 2011

Temperature-dependent c-axis resistivity measurements on LiC6, KC8, RbC8, CsC8 with and without substitutional boron in the starting material, and KHgC4 are presented. The overall behavior is metallic except for the MC8 compounds below 50-100K where Pc increases with decreasing T. This effect appears to be an intrinsic property of stage 1 materials with commensurate 2×2 superlattices.
Superconductivity and Intralayer Structure in Potassium Amalgam-Gic
Authors: Timp G. , Elman B.S. , Dresselhaus M.S. , Tedrow P.
Published: March 2011

We report on the structural, lattice and electronic properties of stage 1,2,3 potassium-amalgam GIG and the relation of these properties to the observed superconducting transition temperature. The ultramicrostructure of the intercalant domains is investigated using lattice fringe imaging. Our observation of macroscopic (√3×√3),(2×2) and (√3×2) domains is consistent with the basal plane zonefolded phenomena observed in the Raman spectra. Shubnikovde Haas measurements of the Fermi surface show high frequency (>1000 T) oscillations in stage 2, identified with the intercalant band.
Susceptibility of Magnetic Graphite-CoCl2Intercalation Compounds
Authors: Elahy M , Dresselhaus G.
Published: March 2011

Precise measurements of the temperature dependence of the magnetic susceptibility for stage 2 and 5 graphite-CoCl2intercalation compounds are reported. Comparison of the experimental results with theoretical calculations based on a two-dimensional planar model show agreement with theory, suggesting that graphite intercalation compounds represent ideal two-dimensional magnetic systems.
Metal Chloride-Graphite Compounds as Cathode and Anode Materials For Batteries
Authors: Flandrois Serge , Baron Francis
Published: March 2011

Graphite intercalation compounds can be used as electrode materials in batteries owing to the high electronic conductivity of carbon layers and the easy diffusion of ions between the layers. Moreover intercalation has the beneficial effect of impeding some parasitic reactions detrimental to good electrode reversibility. After a brief review of recent proposals, emphasis is given to transition metal chlorides. It is shown that, besides the nickel chloride-graphite compound proposed two years ago as a cathode material for alkaline batteries, other metal chlorides intercalated into graphite are excellent cathode or anode materials.
Staging Transitions In Li-Graphite : Phonon Spectra Of Dilute Stage 1
Authors: Woo K.C. , Mertwoy H. , Fischer J.E. , Kamitakahara W.A. , Robinson D.S.
Published: March 2011

First-order transitions to dilute stage one from stages 2,3 and 4 and from mixed stage 1+2 are observed in Li-graphite as predicted by Safran. The upper phase boundary is asymmetric in concentration and is sharply peaked about x ∼ 0.4. The phonons in the dilute stage 1 have energies between those of LiC6 and graphite. Unlike the stage 2 compounds, the compressibility does not scale in a simple way with intercalant density.
Single-Crystal X-Ray Scattering Study of Superstructures and Phase Transitions in Graphite-Hno3 and Graphite-Br2 Intercalation Compounds
Authors: Moret R. , Comes R. , Furdin G. , Fuzellier H. , Rousseaux F.
Published: March 2011

In α-C5n-HNO3 the condensation of the room-temperature liquid-like diffuse ring associated with the disorder-order transition around 250 K is studied and the low-temperature. superstructure is examined.

It is found that β-C8n-HNO3 exhibits an in-plane incommensurate order at room temperature.

Two types of graphite-Br2 are found. Low-temperature phase transitions in C8Br are observed at T1 ≍ 277 K and T2 ≍ 297 K. The room-temperature structure of C14Br is reexamined. Special attention is given to diffuse scattering and incommensurability.
Lattice Dynamical Model for Graphite-Bromine Intercalation Compounds
Authors: Al-Jishi R. , Dresselhaus G.
Published: March 2011

A Born-von Kármán lattice dynamical model for the graphite Br2 intercalation compounds is presented. The low frequency bromine branches are calculated using a commensurate (√3 × √13)R(30°, 13.9°) unit cell with two Br2 molecules/unit cell. In-plane zone folding is used to calculate the high frequency graphitic modes at the Brillouin zone center.
Mixed Phonon Mode In C24Rb
Authors: Funahashi Satoru , Kondow Tamotsu , Iizumi Masashi
Published: March 2011

The [001] L-mode phonon excitations of C24Rb were studied by neutron inelastic scattering in the region where the phonon dispersion curve of the acoustic branch anticrosses the transverse Einstein oscillation level. The interaction between the longitudinal collective mode and the transverse Einstein mode could be observed only in the temperature region where the rubidium atoms form an ordered structure. The mechanism of the interactions between the transverse and longitudinal modes is discussed in relation to the symmetry of the atomic position of rubidium.
NMR Spectroscopy of Synthetic Metals: Intercalated Graphite
Authors: Resing H. A. , Moran M. J. , Miller Gerald Ray , Banks L. G. , Poranski C. F. , Weber D. C.
Published: March 2011

NMR techniques have been used in graphite intercalation systems for chemical analysis and for determinations of structure, molecular dynamics, exchange kinetics, conductivity and electron concentration. Salient results will be presented. We have been most interested in understanding the reaction

3AsF5 + 2Cn ⇋ 2CnAsF6 + AsF3 (1)

for which a single, extremely narrow 19F NMR line is observed when AsF5 reacts with graphite. In contrast, when the reaction

NO2AsF6(in CH3NO2) + Cn→NO2 ↑ + CnAsF6 (2)

is carried out, followed by addition of the stoichicmetric amount of AsF3, separate spectra for the AsF6 (a broad doublet) and lor AsF3 (a sharp 1:2:1 triplet) are observed, indicating that these two species do not exchange fluorine atoms, and suggesting that eq. (1) is not reversible. The AsF3 triplet gives an order parameter for the molecular thrae fold axis with respect to the graphite c-axis. The carbon-13 spectrum for a fifth stage intercalate of HNO3 shows the 2:2:1 triplet expected if each kind of layer Is resolved.
13C NMR Chemical Shifts of Oriented Cesium-Graphite Intercalation Compounds
Authors: Dominguez D.D. , Resing H.A. , Poranski C.F. , Murday J.S.
Published: March 2011

The 13C NMR lines of the stage I cesium graphite compound are broad (ca. 600 Hz) at all orientations, reflecting immobile Cs intercalation; in terms of an axial pattern the principal values are δ11 = 95 ± 5 and δ┴6 = 130 ± 6 ppm. For third and fourth stage compounds the bounding layers give a relatively sharp (60–100 Hz) pair of lines at all orientations, thus demonstrating axially symmetric shift tensors: δ11 = 66 and 56 ppm; δ┴ = 159 and 149 ppm, respectively. These well defined axial tensors reflect atomic motions in the incommensurate Cs layer; the pair of lines may arise from the two classes of carbons - those above carbons in a subsequent layer and those above hexagon centers. Lines of inner layers are sharpest for special orientations →c II →B0 and →c ┴ →B0.
Disorder in Staging of Potassium Graphite: Fractional Stage 3/2 and STAGE 7
Authors: Fuerst C.D. , Koch T.C. , Fischer J.E. , Axe J.D. , Hastings J.B. , McWhan D.B.
Published: March 2011

At high pressure KC8undergoes a staging transition to a mixture of stages 1 and 3/2 at 15 kbar and stages 1 and 2 at 19 kbar. The width of the new peaks are not resolution limited but show a pronounced and non-monotonic variation with Q. This broadening is the result of a finite concentration of staging defects which can be simply modeled by stochastic disordering of an appropriately chosen two component layer sequence. This same analysis has also been used to explain deviations from the Bragg locations in KC84.
A Study of the Electrical and Mechanical Properties of Alkali Metal Intercalated Graphite Fibers
Authors: Dominguez D.D. , Lakshmanan J.L. , Barbano E.F. , Murday J.S.
Published: March 2011

Individual graphite fibers (TP 4104B and GY-70) were intercalated with alkali metals using the two-zone vapor transport method commonly used to prepare alkali metal intercalated graphite. The progress of the reaction was followed in situ by measuring the electrical resistances of the fibers as the temperature difference (ΔT) between the fiber and the metal was decreased stepwise. These measurements showed that the ease and extent of intercalation are related to fiber graphitization. Without exposure to air, the temperature dependence of the resistances of the intercalated fibers were also measured from −196°C to 400°C. The measurements showed that the intercalated fibers have a metallic dependence on temperature. Tensile strength measurements on the intercalated fibers showed that intercalation of the heavy alkali metals is deleterious.
Optical Reflectance Studies of the Stage 1 and 2 Potassiummercurographitides in the Energy Range 0.16-5.8 eV
Authors: Heinz R.E. , Eklund P.C.
Published: March 2011

Reflectance spectra of the stage 1 and 2 compounds of graphite intercalated with Hg-K amalgam are reported for the range (0.2-5.8eV). A Kramers-Kronig analysis was performed on the spectra to determine the dielectric function ∊1(ω) and ∊2(ω). The intraband and interband contributions to ∊(ω) have been separated to determine the plasma frequency and free carrier lifetime.
Optical Reflectance Studies of Stage 1-6 Graphite-Fecl3Intercalation Compounds
Authors: Smith D. S. , Eklund P. C.
Published: March 2011

Results of Optical Reflectance measurements on stage 1-6 graphite-FeCl3intercalation compounds are reported. The frequency dependences of the dielectric constants(∊1, ∊2) are determined. The contributions from free carrier and interband absorption are separated to determine important material parameters.
Lead Zirconate Titanate Films Produced by Pulsed Laser Deposition
Authors: Saenger K. L. , Roy R. A. , Etzold K. F. , Cuomo J. J.
Published: March 2011

The synthesis of ferroelectric lead zirconate titanate (PZT) films by pulsed laser deposition at 248 nm is described. This study has focused on producing thin (≲ 0.6μm) PZT films on bare and platinum coated MgO < 100 > substrates. Deposition was in an oxygen gas ambient (30 mTorr) at temperatures typically ∼ 525 °C. Rutherford Backscattering Spectroscopy (RBS) was used to evaluate film composition. Film lead content was found to decrease both with increasing laser fluence, and increasing substrate temperature. Film microstructure was evaluated by x-ray diffraction. Electrical measurements were made on the films before and after annealing to determine the dielectric constant and polarization. Properties after annealing were substantially improved, with dielectric permittivity values comparable to bulk PZT.
Lead Zirconate-Titanate Thin Films Prepared by the Laser Ablation Technique
Authors: Chiang C. K. , Cook L. P. , Schenck P. K. , Brody P. S. , Benedetto J. M.
Published: March 2011

Lead zirconate-titanate (PZT) thin films were prepared by the laser ablation technique. The PZT (Zr/Ti=53/47) target was irradiated using a focused q-switched Nd:YAG laser (15 ns, 100 mJ at 1.064 μ;m). The as-deposited films were amorphous as indicated by X-ray powder patterns, but crystallized readily with brief annealing above 650°C. The dielectric constant and the resistivity of the crystallized films were studied using a parallel-plate type capacitor structure.
Ferroelectric Film Synthesis, Past and Present: A Select Review
Authors: Roy R. A. , Etzold K. F. , Cuomo J. J.
Published: March 2011

A review of the history of ferroelectric (FE) thin film synthesis is given covering the period of the 1960's to the present. Early methods, materials and applications are discussed. An assessment of the recent upsurge in activity takes note of current targeted applications, including nonvolatile memory, piezoelectric actuators, capacitors, and electro-optic devices. Focus is placed on similarities and differences in the most common film deposition processes. Comparison of microstructure and composition variation seen in films deposited by sputtering, laser ablation, and solution deposition is made. More detailed understanding of process-microstructure relations is stressed as necessary for film property control. Also discussed are the roles of substrate interactions and interface layers in thin film growth.
Preparation and Characterization of Sol-Gel Derived PbTiO3 Thin Layers on GaAs
Authors: Schwartz R. W. , Xu Z. , Payne D. A. , DeTemple T. A. , Bradley M. A.
Published: March 2011

PbTiO3 thin layers were deposited onto GaAs by sol-gel processing. The GaAs substrates were encapsulated with Si3N4 or SiO2 to minimize diffusion problems. Gel layers were heat treated to 350°C for removal of organic species and for the densification of the amorphous gel structure. Rapid thermal processing at 600°C was used to crystallize PbTiO3 into the perovskite structure. SIMS analysis determined limited diffusion of Ga and As into PbTiO3. The fine grain microstructure contained domains.
Grain-Oriented Lithium Niobate Thin-Layers Prepared by Sol-Gel Methods
Authors: Hagberg Daniel S. , Payne D. A.
Published: March 2011

Thin-layers of lithium niobate were deposited on polycrystalline platinum and (001) sapphire. Preferred orientation was observed by x-ray diffraction measurements, and confirmed by x-ray rocking curve studies. The orientation was [006] LiNbO3 with [111] Pt and [001] Al2O3. Dielectric data are reported for grain oriented LiNbO3 as a function of frequency for layer thicknesses from 0.15 to 0.70 μm.
Plasma Etching of PLT Thin Films and Bulk PLZT Using Fluorine- and Chlorine-Based Gases
Authors: Poor M. R. , Hurd A. M. , Fleddermann C. B. , Wu A. Y.
Published: March 2011

Potential applications for ferroelectric thin films include both electronic and optoelectronic devices. In order to integrate a large number of devices on a single ceramic film or to incorporate ceramic devices with silicon-based integrated circuits, suitable film patterning techniques must be developed. In this study, the use of plasma etching for device patterning of PLT thin films has been explored using a dc hollow cathode discharge with HCl and CF4 etching gases. At room temperature, no etching of material is discernable. As the substrate temperature is increased, however, relatively rapid etching takes place. Etch rates for PLT thin films as high as 6500 Å/hour were measured. Etching occurred in both chlorinated and fluorinated plasmas, but at considerably different rates. The etch rate is enhanced by a factor of six by using a combination of HCl and CF4 in the plasma. After etching, the stoichiometry of the film, measured by energy dispersive spectroscopy (EDS), varied greatly with changes in substrate temperature. Although the removal rate for each element is different, all traces of lead, titanium, and lanthanum can be removed from the substrate over a wide range of plasma etching conditions.
Physical Characterization of Thin Films of Lithium Niobate Deposited on Silicon Substrates
Authors: Baumann Robert C. , Rost Timothy A. , Rabson Thomas A.
Published: March 2011

Thin films (.1-.6 μm) of LiNbO3 have been deposited on silicon substrates by reactive rf sputtering. Under optimized deposition conditions the resulting thin films of LiNbO3 were optically transparent, adhered well to the silicon substrates, and were found to be polycrystalline and uniaxial with the c axis oriented normal to the silicon surface. Optical microscopy and scanning electron microscopy were used to examine film morphology. Both methods indicated that the films were smooth and contained no gross irregularities. The ratio of oxygen to niobium in these films was measured by Rutherford backscattering to be approximately 3 to 1. Auger electron spectroscopy depth profiling revealed that the films had the expected ratio of Li, Nb, and O. This information, together with Bragg x-ray diffraction data, indicates that the thin films deposited on silicon were stoichiometric, crystalline LiNbO3.
Computer Simulation Study of the Effect of Defects on Switching in Ferroelectric Thin Films
Authors: Pugh Robert D. , Sabochick Michael J. , Luke Theodore E.
Published: March 2011

A new computational method for simulating the dynamics of switching in ferroelectric materials is presented. The new method is shown to be more realistic for dynamic simulations and computationally more efficient than the traditional Monte Carlo method. The method is used to investigate the effect of polar defects on switching behavior. The results are in qualitative agreement with experimental observations of fatigue.
PbTiO3 Thin Films by Chemical Beam Deposition
Authors: Kingon A.I. , Hsieh K.Y. , King L.L.H. , Rou S.H. , Bachmann K.J. , Davis R.F.
Published: March 2011

The feasibility of chemical beam deposition of PbTiO3 thin films is demonstrated. The method utilizes chemical (molecular) beams of metalorganic precursors in a high vacuum chamber. Pyrolysis reactions of the metalorganics at the substrate surface are facilitated by presence of active oxygen from an ozone source. Fine grained, smooth polycrystalline PbTiO3 films have been deposited at substrate temperatures as low as 325°C.
Plasma Assisted Low Temperature OMVPE of GaAs Utilizing Trimethylgallium and Trimethylarsenic Feedstock Gases
Authors: Pihlstrom B. G. , Thompson L. R. , Asher S. , Collins G. J.
Published: March 2011

A spatially confined disk shaped hydrogen plasma is used for plasma assisted organometallic vapor phase epitaxy (PAOMVPE) of GaAs at substrate temperatures from 245–430°C. Feedstock gases, trimethylgallium (TMGa) and trimethylarsenic (TMAs), are introduced downstream from the disk shaped plasma in the near afterglow. Dissociation of the organometallics is dominated by VUV photons and metastable species energy transfer reactions rather than non-selective electron impact. At the temperatures employed no thermal CVD occurs. An Arrhenius plot of the growth rate shows a low activation of 3 Kcal/mole for surface mobility. The transitional temperature from amorphous to homoepitaxial growth (300°C) is determined via electron diffraction patterns from deposited films versus substrate temperature. Increases in the feedstock gas V-III ratio resulted in decreases in absolute carbon concentration in the deposited films.
Anisotropic ArF Laser-Assisted Cl2 Etching of GaAs
Authors: Tejedor Paloma , Briones Fernado
Published: March 2011

ArF laser etching of n-GaAs (100) in Cl2 gas ambient has been investigated as a function of laser fluency and the main thermodynamical parameters of the process (pressure, temperature and gas phase composition). Experimental results indicate that GaAs laser etching in the presence of Cl2 occurs by a combination of thermally and photochemically initiated reaction steps. The etch rate was found to be kinetically controlled by the surface reaction between photogenerated CI adatoms and GaAs, with an activation energy of 6.3 Kcal/mol. Vertical etch profiles with smooth bottom surfaces were obtained at substrate temperatures above 150°C, low Cl2 partial pressures (≤ 1.5 m Torr), and low laser fluences (≤ 25 mJ/cm2) for etch masks parallel to the | 01 1 | direction.
Novel Process for Ceramic Epitaxy Using Laser Mbe
Authors: Yoshimoto Mamoru , Nagata Hirotoshi , Tsukahara Tadashi , Gonda Satoshi , Koinuma Hideomi
Published: March 2011

An ArF excimer laser MBE system specially designed for the deposition of ceramic thin films was used to construct atomi-cally defined epitaxial SrCuO2−x films. According to XPS analysis, Cu valence was evaluated to be 2+ in the film as-grown in the presence of 10−7 Torr NO2, but it was less than 2+ in the film prepared in the presence of 10−7Torr 02. In situ XPS depth analysis of as-grown SrCuO2−x film on SrTiO3 substrate revealed the band profile at the interface of the film and substarte. Ceramic superlattices composed of metallic SrCuO2−x (3∼8nm thick) and insulative SrTiO3 (8nm thick) were prepared by sequential heteroepitaxial growth.
Growth and Properties of Ceramic thin Films Processed by In-Situ Laser Deposition Technique
Authors: Kanetkar S. M. , Sharan S. , Tiwari P. , Matera J. , Narayan J.
Published: March 2011

Good quality ceramic thin films of yttria-stabilized zirconia (YSZ), MgO, BN and TiN were grown on single crystal silicon with (100) orientation using in-situ pulsed laser physical vapor deposition (LPVD) technique.Laser deposition parameters were optimized and the resulting thin films were characterized by X-ray diffraction ,Rutherford backscattering spectrometry and transmission electron microscopy (plan and cross section). All the films were found to be polycrystalline with a texture. The absence of interfacial reaction and smooth interface on the atomic scale are the main features observed in these oxides and nitrides thin films on Si (100) substrate.
Ductility Enhancement and Mechanical Properties of Ibad Ceramic thin films
Authors: Hirvonen J. K. , Tetreault T. G. , Parker G. , McHargue C. J.
Published: March 2011

Thin ceramic films (A12O3 ZrO2, Si3N4, and BN) have been prepared by ion beam assisted deposition (IBAD) and their mechanical properties examined. The films exhibit extreme ductility and adhesion, with the former property possibly attributed to the very fine grained, quasi-amorphous grain structure noted for low temperature IBAD coatings.
Effects of Excimer Laser Ablation on the Surface of Hexagonal Boron Nitride
Authors: Doll G. L. , Perry T. A. , Sell J. A.
Published: March 2011

The laser-induced changes in the hexagonal boron nitride targets that are used in the deposition of pulsed laser-deposited cubic boron nitride films are examined. Although the structure of the hexagonal boron nitride in the irradiated areas is unaltered, the surface morphology changes considerably. Boron-rich spheroids were found to cover the irradiated area. Their origin is consistent with the hydrodynamic sputtering of the hexagonal boron nitride targets, and a liberation of nitrogen atoms to the gas phase.
High-Energy Low-Dose Implanted Silicon Annealed by Transient RTA
Authors: BÁrsony IstvÁn , Heideman Jean-Luc , Middelhoek Jan , Wallinga Hans
Published: March 2011

Transient RTA performed in the sub-second time range has been applied for low-thermal-budget post-implantation anneal of low-dose, high-energy P and B implanted wafers. This very rapid thermal step not only accomplished full activation and minimum profile motion but was also effective in reducing the resident damage-associated lifetime problems compared to conventional annealing. The generation lifetime and velocity depth-profiling used for process characterization shed light on the role of metallic impurities in the high-energy B and P implanted samples during the fast-quenching operations in determining the electrical behavior.
Ion-Irradiation Study of the “Exotic” Mineral Neptunite: LiNa2K(Fe,Mg,Mn)2Ti2Si8O24
Authors: Eby Ray K. , Wang L. M. , Arnold G. W. , Ewing R. C.
Published: March 2011

Single crystals of the silicate neptunite were irradiated with 600 keV Ar2+ and 1.5 MeV Kr+ and analysed by transmission electron microscopy. Amorphization was observed in a surface layer several hundred angstroms thick following Ar2+ irradiations up to 5.0×l013 Ar/cm2, yet the Ar2+ ions travelled an average of 1/2 μm in depth. The microstructure of the amorphous surface layer depends on the ion fluence, but the amorphous layer thickness remained constant. At the highest fluence, a narrow region below the amorphous layer shows a brittle-to-ductile strain transition, due to tensional volume-expansion of the adjacent ductile amorphous layer. With 1.5 MeV Kr1+, amorphization of the electron transparent region was completed after a fluence of 1.7×l014 Kr+/cm2, and no further damage was observed up to 5.1×1015 Kr+/cm2. However, following a low fluence of 2.0×1011 Kr+/cm2, a single crystal of neptunite became a polycrystalline aggregate (grain size 10 nm) within 7 days of room temperature aging.
Molecular Beam Induced Dissociative Chemisorption at Surfaces
Authors: Madix Robert J.
Published: March 2011

The application of supersonic nozzle beams to the study of the dynamics of gas-surface scattering is discussed. Examples are chosen to illustrate the use of such beam sources in synthesizing surface compounds otherwise unaccessible under normal ambient conditions in ultrahigh vacuum and the role of trapping and direct collisional activation in adsorption on surfaces.
Implantation Doping and Stimulated Emission of Er3+ in LinbO3:Ti Optical Waveguides
Authors: Buchal Ch. , Brinkmann R. , Sohler W. , Suche H.
Published: March 2011

We have implanted Nd and Er ions into x- and z-cut LiNbC3 single crystals and investigated the recrystallization of the host and the rare earth solubility and diffusion. The diffusion is substitutional, fastest parallel to c-axis and characterized by an activation energy of 3.6 eV. Optical fluorescence experiments of Er3+ in a waveguide configuration show stimulated emission and amplification at 1.53, 1.55 and 1.56 μm wavelength.
Electrical and Optical Properties of Si+ and P+ Implanted InP:Fe
Authors: Shen Honglie , Yang Genqing , Zhou Zuyao , Xia Guanqun , Zou Shichang
Published: March 2011

Dual implantations of Si+ and P+ into InP:Fe were performed both at 200°C and room temperature. Si+ ions were implanted by 150keV with doses ranging from 5×1013 /cm2 to 1×1015 /cm2, while P+ ions were implanted by 110keV. 160keV and 180keV with doses ranging from 1×l013 /cm2 to 1×1015 /cm2. Hall measurements and photoluminescence spectra were used to characterize the silicon nitride encapsulated annealed samples. It was found that enhanced activation can be obtained by Si+ and P+ dual implantations. The optimal condition for dual implantations is that the atomic distribution of implanted P overlaps that of implanted si with the same implant dose. For a dose of 5×l014 /cm2, the highest activation for dual implants is 70% while the activation for single implant is 40% after annealing at 750°C for 15 minutes. PL spectrum measurement was carried out at temperatures from 11K to 100K. A broad band at about 1.26eV was found in Si+ implanted samples, of which the intensity increased with increasing of the Si dose and decreased with increasing of the co-implant P+ dose. The temperature dependence of the broad band showed that it is a complex (Vp-Sip) related band. All these results indicate that silicon is an amphoteric species in InP.
On the Amorphization of Silicon by Light Ion Implantation: Ion Flux and Substrate Temperature Effects
Authors: Claverie A. , Roumili A. , Gessinn N. , Beauvillain J.
Published: March 2011

In this work, we have observed by cross-sectional electron microscopy (XTEM) and high resolution electron microscopy (HREM) the kinetics of silicon amorphization during nitrogen and helium bombardments for various dose rates and substrate temperatures. It is shown that the progression of the cla interfaces can be accurately described by the “Critical Damage Energy Density” (CDED) model for both ions at 100°K. At this temperature however, dose rate effects are unimportant. When increasing the substrate temperature up to 300°K, the amorphization efficiency is lowered. At 300°K dose rate effects are important and we show that for higher dose rates, the efficiency of the amorphization process is improved. In this case, the amorphous layers created by helium implantation are situated in the near surface region in apparent contradiction with damage calculations. The present experimental study demonstrates the competition which exists between the generation rate of point defects and the anihilation rate of these defects. Therefore, it is shown that the position of the a-layers created by light ion implantation at room temperature can be predicted by using a three-dimensional damage energy calculation.
In Situ

Study of the Effects of Heavy-Ion Irradiation on Co-Evaporated Cosi2 Films
Authors: Allen Charles W. , Smith David A.
Published: March 2011

The in situ ion irradiation capability of Argonne’s HVEM-Tandem User Facility has been employed to study effects of 1.5 MeV Kr+ irradiation and 300 kV electron irradiation on the crystallization of as-deposited and of partially crystallized 40 nm thick films of CoSi2. Ion fluxes ranged from 8.5×1014 to 6.8×1015 m−2s−1 for which beam heating effects may be neglected. The maximum electron flux at 300 kV was 0.8×1023 m−2S−1. The maximum temperature at which crystalline CoSi2 is amorphized by the ion irradiation of flux = 6.8×1015 m−2s−1 is between 250 and 280 K. At higher temperatures amorphous material crystallizes by growth of any preexisting crystals and by classical nucleation and growth, with radial growth rates which are proportional to ion flux. The average degree of transformation per ion is 4×10−26 m3 per ion. Thermally induced crystallization of as-deposited films occurs above approximately 420 K. For ion doses at least as low as 3.4×1016 m−2 ion irradiation at 300 K promotes thermal crystallization at 450 K, by virtue of enhanced apparent nucleation and at large doses, by enhanced growth rate.
CoSi2Precipitate Coarsening During Formation of Buried Epitaxial Cosi2Layers By Ion Beam Synthesis
Authors: Jebasinski R. , Mantl S. , Radermacher K. , Fichtner P. , Jăger W. , Buchal Ch.
Published: March 2011

The coarsening of CoSi2precipitates and the microstructural evolution of (111) Si implanted with 200 keV Co+ions at 350°C and fluences of 1×1016cm−2and 6×1016cm−2were investigated as a function of depth, annealing temperature and annealing time using Rutherford Backscattering Spectroscopy (RBS) and Transmission Electron Microscopy (TEM). After annealing cross-section TEM micrographs show a layered array of platelet-shaped precipitates with preferred facets on {111} planes. The fraction of Co-atoms, that were redistributed during the different annealing temperatures and times, has been used to determine an activation energy for the precipitate coarsening. By applying the Meechan-Brinkman and the change-of-slope methods, we obtained activation energies in the range of 3.2 – 3.6 eV.
Laser-Target Interactions and its Effect on Surface Morphology of Laser Deposited thin films
Authors: Singh R. K. , Bhattacharya D. , Narayan J.
Published: March 2011

The laser-target interactions during pulsed laser evaporation (PLE) of materials have been investigated in detail. Sub-surface temperatures have been calculated to be higher than the surface temperatures during planar surface evaporation of the target material. While the evaporating surface is being cooled due to the latent heat of vaporization, sub-surface superheating occurs due to the finite absorption depth of the laser beam. Detailed computer simulations have been carried out to understand the evaporation characteristics of different targets (Si, YBa2Cu3O7 ) as a function of laser and target variables. For silicon targets irradiated with 25 nanosecond laser pulses (energy density of 10J/cm2, absorption coefficient of 105 cm−1), the sub-surface temperatures were found to be more than 2000°C above the surface evaporation temperatures. The sub-surface superheating increased with increasing energy density and absorption depth. This internal superheating effects may lead to volume evaporation of the target where a solid material in form of particles may be ejected from the target surface. Based on the above understanding, parameters required to reduce the particle density in PLE films are predicted.
Selective Surface Modification of a Fluorocarbon Resin Into Hydrophilic Material Using an Excimer Laser
Authors: Okoshi M. , Murahara M. , Toyoda K.
Published: March 2011

Selective surface modification of fluorocarbon resin has been demonstrated by using an ArF excimer laser beam and an ammonia complex which was made from NH3 and B2H6 gases. The fluorocarbon resin was set in the atmosphere of NH3 gas. NH3 molecules which were adsorbed on the surface reacted quickly with the B2H6 molecules, and an ammonia complex was produced. As a result, the complex was adsorbed on the surface. The resin surface was selectively irradiated by ArF laser beam. The complex and C-F bonds of this resin were excited by the laser beam, and the surface was selectively modified to be hydrophilic property. The modified samples were evaluated by XPS analysis, measuring the contact angles of the water and the SEM image on the surface.
Excimer-Laser-Assisted Etching of Gallium Arsenide: The Effect of Substrate Temperature
Authors: Berman Michael R.
Published: March 2011

The excimer-laser-assisted etching of GaAs in Cl2 at 308 nm has been studied as a function of substrate temperature in the range of 23 to 150°C. Rectangular channels were etched into (100)-oriented, undoped GaAs wafers. The fluence from the xenon chloride excimer laser at the GaAs surface was 175 mJ/cm2. At temperatures below 75°C, the etch rate was independent of substrate temperature and the etch rate increased with Cl2 pressure from 0.4 to 2.0 Torr. At substrate temperatures above 75°C, the etch rate increased with increasing substrate temperatures and was independent of Cl2 pressure. Analysis of the temperature dependence of the total etch rate above 75°C according to an Arrhenius expression gave an activation energy of 11.8 kcal/mol, which is consistent with the enthalpy of vaporization of GaCl3. The onset of the temperature dependent region coincides with the melting point of GaCl3.
Laser Ablation Synthesis of Ceramic Powders
Authors: Fahrenholtz W. G. , Foltyn S. R. , Ott K. C. , Chadwick M. , Smith D. M.
Published: March 2011

A pulsed excimer laser was used to ablate aluminum metal into an oxygen-containing atmosphere. The resulting fine powder was collected on a 0.1 μm filter and analyzed to determine structure and composition. Using a combination of TEM, EELS, and thermal analysis techniques, the product was found to be amorphous aluminum oxide, Al2O3. The morphology of the powders was investigated using SEM, TEM, and surface area measurements. The resulting powder was crystallized and examined by x-ray diffraction.
Plasma Dynamics During Pulsed Laser Evaporation of High TcSuperconductors
Authors: Singh Rajiv K. , Neifeld R. , Narayan J.
Published: March 2011

We have theoretically and experimentally investigated the dynamics of the evaporated material generated by nanosecond excimer laser irradiation of YBa2Cu3O7targets in vacuum. The velocity distribution and the ionization of the plasma were determined by the ion time of flight measurements. The excimer laser ablated species possessed very high velocities (> 106cm/sec) which increased non-linearly with energy density. The ionization/ volume of the evaporated material exhibited a weak dependence on energy density, thereby suggesting the role of nonthermal mechanisms in the ionization process. These experimental results have been correlated with the theoretical model analyzing the plasma dynamics during pulsed laser evaporation of materials. A new modification to the earlier theoretical model is developed which accurately predicts the terminal velocities and the effect of ionization on these velocities. Various factors including, evaporation rates, degree of ionization, and laser wavelength which affect the plasma velocities will also be discussed.
Photoemission Study of Low-Fluence, Non-Thermal Laser Damage of UHV-Cleaved Gallium Arsenide (110)
Authors: Goldenberg S. S. , Long J. P. , Kabler M. N.
Published: March 2011

The pulsed-laser induced photochemical production of metallic Ga islands on the surface of GaAs cleaved, irradiated, and studied in ultrahigh vacuum (UHV) is documented through photoelectron spectroscopy and subsequent scanning electron microscopy. Ga islands are detected for laser fluences as low as 1 mJ/cm2, far below those previously reported for modification of GaAs, and for which the temperature rise is negligible.
Structure-Process-Property Relations in Excimer Laser Surface Processed Ti-6Al-4V Alloy
Authors: Jervis T. R. , Zocco T. G. , Steele J. H.
Published: March 2011

Excimer laser processing results in very rapid solidification of metal surfaces. In addition to mixing or segregation processes, rapid heat treatment can result in phase transformations which yield beneficial surface properties. We have investigated the effect of pulsed excimer laser radiation on the microstructure and surface hardness of Ti-6A1-4V. This material undergoes a well defined martensite transformation during rapid quenching from temperatures in the β phase field. The depth of the transformed layer is thus a marker for the temperature profile during processing. We find that the depth of the transformed layer agrees well with a simple 1-D calculation of heat flow following the laser pulse. As measured by the nanoindenter, we find that the surface martensite is softer than the mechanically polished alloy. Multiple pulse processing at high fluences results in an increase in surface hardness, but at a depth much less than that of the martensite, suggesting an independent mechanism.
Threshold Fluence UV Laser Ablation of Single Crystal Bi2Sr2Ca1Cu2O8: Product Population and Kinetic Energy Distributions of Ejected Ionic Species
Authors: Wiedeman Lawrence , Sook Kim Hyun , Helvajian Henry
Published: March 2011

We have conducted an experiment which measures the product population and kinetic energy (KE) distributions from the UV laser induced decomposition of crystalline Bi2Sr2Ca1Cu2O8. We have measured these distributions at two laser wavelengths 248, 351. At a third wavelength (355 nm) we have measured the photoejected mass spectra from both a single crystal Bi2Sr2Ca1Cu2O8 sample and a polycrystalline Bi2Sr2Ca2Cu3O10 sample. For all the experiments, the laser fluence is maintained near the threshold for ion formation. The laser fluences are well below the level for instigating a laser induced above surface plasma. Our results show that the ejected products are not the consequence of a laser surface evaporation process. We measure a wavelength dependence in the ejected species population distribution and the ejected kinetic energy distribution (< KE > = 5 ± 1 eV.2eV FWHM) is indicative of an electronic excitation process. The measured ion mass spectra show atomic, diatomic (e.g. Sr2+), and oxide (e.g. SrO+, CaO+) species with lesser quantities of the complex oxides (e.g. S2O+). Distinctly absent from the mass spectra are the oxide compounds BiO+, CuO+, and the atomic species O+. Furthermore, the mass spectrum shows that at 248 nm laser excitation, the Bi+ species is the abundant photopro-duct. However, for both the 351 nm and 355 nm excitations, the Sr+ and SrO+ ions are measured as more abundant. Also, comparing the 355 nm laser excitation of the single and polycrystalline samples, there is very little difference in the photoejected species mass spectrum.
In Situ Observations of Beam-Induced Effects During High-Resolution Electron Microscopy
Authors: Smith David J. , Lu Ping , McCartney M. R. , Sharma R.
Published: March 2011

A variety of electron-beam-induced effects, including oxidation, reduction and surface rearrangements are observed to occur at surfaces of oxides, fluorides and compound semiconductors during electron irradiation within the electron microscope. The extent and type of surface modifications observed are shown to depend upon the irradiation level, the residual microscope vacuum and the specimen temperature. For example, ex situ annealing of compound semiconductors leads to different end-products compared with in situ irradiation, thus showing that residual gas components can have a strong influence on the surface reactions. Electron irradiation of rutile during annealing at high temperature under ultrahigh vacuum conditions caused the rapid development of well-facetted holes without the usual intermediary phase seen at room temperature in conventional vacuum.
Angular and Energy Distributions of RH Atoms Desorbed in an Excited State from Ion-Bombarded Rh{100}
Authors: Maboudian Roya , El-Maazawi M. , Postawa Z. , Winograd N.
Published: March 2011

Multiphoton resonance ionization spectroscopy has been used to determine the polar-angle and the kinetic-energy distributions of rhodium atoms desorbed from ion-bombarded Rh{100} surface in the fine-structure components of the a 4Fj (J=9/2 and 7/2) ground-state multiplet. The peak in the energy distribution of the metastable level (4F7/2 with excitation energy of 0.2 eV) is found to occur roughly at the same value as the ground-state (4F9/2) distribution but decays more gradually at higher energies. The measured spectra have been used to investigate the dependence of the excitation probability on the takeoff angle (θ) as well as the emission velocity (v). It is shown that the excitation probability depends strongly on these parameters, approaching an exponential dependence on l/[v cos(θ)] at higher velocities (> 5×l05cm/sec).
Sputtering of Molecules From ZnS, CdS, and FeS2
Authors: Nikzad S. , Calaway W. F. , Pellin M. J. , Young C. E. , Gruen D. M.
Published: March 2011

It has been the general consensus in the sputtering community that molecules are sputtered from a clean metal surface in much smaller quantities than atoms. Some of the existing models further suggest that the sputter yield of molecules should be even lower from a compound than from a pure metal when the constituents of the molecule do not reside on neighboring sites in the solid.

In our experiments, neutral species sputtered from single crystals of ZnS, CdS, and FeS2by a 3 keV Ar+beam have been observed by laser photo-ionization followed by time-of-flight mass spectrometry. While the atomic metal (Fe, Zn, Cd) and S2were the predominant species observed, substantial amounts of S, FeS, Zn2, ZnS, Cd2, and CdS were also detected. The experimental results demonstrate that molecules represent a larger fraction of the sputtered yield than was previously believed from secondary ion mass spectrometry experiments. In addition, our data suggest that the sputtered molecules are not necessarily formed from adjacent atoms in the solid. The applicability of various sputtering models will be discussed in the light of these results.
Phase Separation During Film Deposition
Authors: Atzmon M. , Adams C. D. , Cheng Y.-T. , Srolovitz D. J.
Published: March 2011

We report a study of the microstructure and surface morphology of co-deposited Al-Ge films. At 200 °C and above, the terminal solid solutions are obtained, whereas at lower temperatures, metastable amorphous or crystalline phases coexist with the Al-rich terminal phase. For film thickness below 200 nm, lateral phase separation is observed with surface grooving which reflects the bulk microstructure. Analysis of the data with a model for the diffusion process shows that the results are consistent with a surface diffusion mechanism. For thicker films, there is a transition into a layered microstructure in which Al segregates to the surface. This transition is explained in terms of the surface and interfacial energies of the phases.
The Nucleation and Growth of Polycrystalline Silicon Carbide
Authors: Sheldon Brian W. , Besmann Theodore M.
Published: March 2011

Silicon carbide was deposited from methyltrichlorosilane onto polished polycrystalline SiC substrates at reduced pressure, and the resultant surface morphology was characterized by analyzing the angular spectrum of scattered light which was generated with a He-Ne laser. Light-scattering analyses incorporating specific nucleation and growth models were developed. With these methods, it was possible to analyze the angular scattering spectra and directly measure the nucleation and growth rates. These results were verified by using image analysis to quantify the number and size distribution of surface features that were observed with scanning electron microscopy. The nucleation and growth rates that were obtained by fitting the models to the image-analysis results were in good agreement with the rates obtained from the light-scattering.
Thermal Spike Model of Ion-Induced Grain Growth
Authors: Alexander Dale E. , Was Gary S.
Published: March 2011

A thermal spike model has been developed to describe the phenomenon of ion irradiation-induced grain growth in metal alloy thin films. In single phase films where the driving force for grain growth is the reduction of grain boundary curvature, the model shows that ion-induced grain boundary mobility, Mion, is proportional to the quantity FD2/ΔHcoh3, where FD is the ion and recoil energy deposited in nuclear interactions and ΔHcoh is the cohesive energy of the element or alloy. Experimental grain growth results from ion irradiated coevaporated binary alloy films compare favorably with model predictions.