bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Thermal Annealing of III–V Compound Materials
Authors: Kuzuhara M. , Kohzu H. , Takayama Y.
Published: March 2011

Rapid thermal process utilizing radiation from halogen lamps has been used to post-anneal ion-implanted GaAs. Annealing conditions for Si implants in GaAs are discussed from the view point of applying this technique to GaAs MESFET fabrication. Also, the properties of S and Mg implants in GaAs followed by rapid thermal annealing are comparatively studied with the results after conventional furnace annealing. High electrical activation and minimized implant diffusion for both low and high dose implants are the principal features of this technique. The fabricated MESFET showed much higher transconductance without any anomalous characteristics, indicating this technique to be a promising alternative to conventional furnace annealing.
Solid Solubility of Sb and Te Implanted GaAs Following Solid Phase Annealing
Authors: Johnson S.T. , Orrman-Rossiter K.G. , Williams J.S.
Published: March 2011

High dose antimony and tellurium implanted (100) GaAs wafers have been annealed in the solid phase under various time/temperature conditions using a conventional furnace, a rapid incoherent light source and a continuous wave CW Argon ion laser. The samples were capped with RF sputtered SiO2 prior to annealing and analysed using 2MeV He++ ion channeling to determine the solid solubility of the implanted ions. Results indicate that the Te is more soluble than Sb; highest solubilities measured were 6 × 1020cm−3 for Te and 1.3 × 1020cm−3 for Sb.
Raman Scattering and Luminescence Study of Rapid Annealing and Laser Irradiation Effects in Ion Implanted InP
Authors: Kirillov D. , Merz J.L.
Published: March 2011

Raman scattering and luminescence spectroscopic techniques were applied to the study of ion implantation of InP and its annealing by a lamp, oven, or laser beam. It was found that both characterization techniques give important information on surface layer transformation during implantation and annealing.
Raman Vibrational Study of Pulsed Laser Annealing of Implanted GaAs
Authors: Sapriel J. , Nissim Y.I.
Published: March 2011

The lattice reconstruction produced by a pulsed laser irradiation in heavily damaged GaAs layers is studied. Spatially resolved Raman measurements are used to characterize the crystalline quality after the annealing cycle produced by a O-switched Ruby laser or by a picosecond pulsed Nd-YAG laser. The continuous evolution in the Raman spectra is usèd to follow the crystal recovery as a function of the irradiation parameters.
Growth of Nickel Silicides on Silicon by Short Duration Incoherent Light Exposure
Authors: Larsen A. Nylandsted , Chevallier J. , Sørensen G.
Published: March 2011

Short duration, incoherent light from a xenon lamp has been used to grow nickel silicides on silicon single crystals from evaporated nickel films. The formation of these silicides was studied by Rutherford Backscattering Spectrometry, channeling, sheet resistivity, and transmission electron microscopy as function of induced temperature (550– 775°C), exposure time (8– 25 sec), and silicon orientation (>111<, >110<, and >100<). Epitaxial NiSi2 films were formed for temperatures above ˜675°C whereas polycrystalline NiSi films were formed below this temperature.
Laser-Induced Synthesis of Thin GeSe2 Films
Authors: Antoniadis C. , Joliet M.C. , Andrew R. , Laude L.D. , Wautelet M.
Published: March 2011

Thin films of GeSe2 are synthesized by laser irradiation of Ge-Se sandwiches, with 2Se:IGe atomic proportion. The synthesized free-standing films are demonstrated to have the monoclinic crystal structure of GeSe2. Moreover, they exhibit a preferential orientation, with the c-axis perpendicular to the plane of the film. Films synthesized on glass substrate are characterized by an indirect optical energy gap of 2.3 eV, in agreement with published data on GeSe2. The melting point of Ge is not attained in the case of films on glass substrate.
Laser-Solid Interactions: Localization of Momentum and of Energy
Authors: Van Vechten J. A.
Published: March 2011

Mechanisms are discussed by which sufficient momentum and energy may be localized on individual atoms, ions or molecules to account for photoablation in different regimes. In order of increasing excitation intensity, these include the roles of: “recoilless emission” (as in Bragg scattering and the Mössbauer effect) during Auger recombination of a core exciton, particularly in the Knotek-Feibelman effect; the metastable binding of multiple holes earlier proposed by Feibelman, particularly in the data of Itoh and coworkers; the change in the equilibrium interatomic spacing concomitant with excitation of a Frenkel exciton (localized broken bond), particularly in the ablative photodecomposition reported by Srinivasan and co-workers; the interaction of virtual excitons with real excitons in a strongly polarized solid, e.g. one subject to laser annealing pulses; and the interaction of ions with surface plasmons, particularly in the laser sputtering data of Hanabusa et al. A connection is made to rapid annealing and to sub-threshold defect formation. Further support is noted for the bose condensation model of pulsed laser annealing.
Measurement of Ultrafast Melting and Regrowth Velocities in Pulsed Laser Heated Silicon
Authors: Bucksbaum Philip H. , Bokor Jeffrey
Published: March 2011

Direct measurements of the liquid/solid interface veiocity have been made during both melt-in and regrowth for puised (20 psec) ultraviolet lasei irradiation or crystailine silicon. The regrowth velocity was 25 m/sec, independent or laser fluence. Regrowtn velocities of 50 to 100 m/sec are expected from heat diffusion calculations which neglect undercooling, whereas the inclusion of an appropriate undercooling curve brings the calculation into good agreement with the data. Tne liquid films produced were up to 40 nm thick and were fully amorphized on resoliaificaion.
Oscillation in the Interlayer Coupling of Fe Films Across Cr Films Measured by Means of Light Scattering from Spin Waves and M(H)-Curves
Authors: Demokritov S. , Wolf J.A. , GrÜnberg P. , Zinn W.
Published: March 2011

By means of light scattering from spin waves and magnetooptical Kerr measurements we investigated the exchange interaction of two Fe films across a Cr film as a function of the Cr thickness dCr.

Using good quality epitaxial samples with a special wedge geometry of the interspacer we observed up to four full periods of the long range oscillations of the exchange, including its ferromagnetic parts. At room temperatures the damping of the oscillations does not follow the d-2Crpendence predicted by zero-temperature RKKY-type theory.

After a special e-beam treatment of the samples a short-range oscillation with a period around a lattice constant of Cr are discovered. The value of coupling in the maximum in this case shows considerable temperature dependence.

The analysis of domain patterns and M(H) curves reveals the existence of a noncollinear interaction, which causes a configuration where the magnetizations of two Fe films are perpendicular to each other.
Magnetism and Magnetoresistance of Multilayers with Two Magnetic Components. I. Cu-Based Films
Authors: Yamamoto H. , Okuyama T. , Dohnomae H. , Shinjo T.
Published: March 2011

Magnetoresistance (MR) properties were studied in Cu/Co/Cu/Ni80Fe20 system, and a large MR ratio was observed in weak external fields. In the course of field sweeping, these two magnetic components (Co and Ni(Fe)) are oriented antiparallel, because of the difference of coercive forces, and then the resistivity is greatly enhanced. The MR ratio was observed to be 10% at 300K, and 32% at 20K, respectively, in a multilayer \Cu(55Å)/ Co(25Å)/Cu(55Å)/Ni80Fe20(25Å)] ×15.
NMR Study on the Nanostructure of Co/X multilayers
Authors: Jonge W. J. M. De , Gronckel H. A. M. De , Kopinga K. , Panissod P. , Broeder F. J. A. Den
Published: March 2011

The nanostructure and local strain of \111] FCC Co/Cu and Co/Ni multilayers is studied by means of nuclear magnetic resonance. The atomic topology of the interface can be deduced from the NMR spectrum, the local strains from the shift in the hyperfine fields. The results show that the Co/Cu interface is a mixed monolayer and that the Co layers, including the interface, have uniform (tensile) strain inversely proportional to the Co thickness (within experimental error) with the proportionality constant depending on the Cu thickness. In Co/Ni the interface consists of two mixed layers and the Co layers have uniform compressive strain inversely proportional to the Co thickness.
Magnetoresistance of Magnetically Uncoupled Multilayered Structures
Authors: Zhang Shufeng , Levy Peter M.
Published: March 2011

The magnetoresistive effect first observed in Fe/Cr and other antiferromagnetically coupled metallic multilayered structure, has also been observed, albeit somewhat attenuated, in structures where the magnetic layers are not coupled. We explain the magnetoresistive effect in these systems that are nominally uncoupled, and we provide a new interpretation for the magnetoresistance of Co/Cu, Fe/Cr and Co/Ru by considering these multilayered structures to consist of, not only ferro and antiferromagnetically aligned layers, but also mixtures of the two which have zero magnetization.
The Effect of Spin Dependent Scattering from Impurities on Giant Magnetoresistance and Thermal Conductivity in Fe/Cr Multilayers
Authors: Johnson B.L. , Camley R.E.
Published: March 2011

Recent experiments have tested the assumption that a spin-dependent asymmetry in scattering is responsible for the giant magnetoresistance (GMR) in Fe/Cr multilayers by introducing additional impurities (with different spin-dependent scattering asymmetries) at the interfaces. This paper presents a theoretical calculation based on a Boltzmann transport equation approach which is appropriate for these new experiments. We find that when impurities (Mn, V) are introduced which have a spin-dependent scattering asymmetry similar to that of Cr in Fe the GMR is not substantially changed. When impurities (Al, Ir) with a spin-dependent scattering asymmetry opposite to that of Cr in Fe are introduced there is a rapid degredation of the GMR. Our results are compared with experiment and good agreement is found provided that the magnitude of the scattering asymmetry in Al is reduced somewhat from low-temperature published values. It is argued that thermal effects could indeed provide such a reduction. We also point out that the thermal conductivity should undergo changes with magnetic field in these structures, since the thermal conductivity also depends upon electron mobility.
Anisotropy Energies and Critical Behavior of Ultrathin Ni(111) Films Grown on Smooth and Rough W(110) (invited)
Authors: Li Yi , Baberschke K.
Published: March 2011

6 to 80 Å thin Ni(111) films were prepared on smooth and rough W(110) substrates in UHV and characterized by LEED and Auger spectroscopies. The measurements of the magnetic properties were carried out in situ by ferromagnetic resonance at 9 GHz between 300 and 600 K. We found that the effective anisotropies, which consist of surface, crystal, and stress induced anisotropy, increase with decreasing film thickness and temperature. The roughness of the substrate results in the drastic decrease of the effective anisotropy. This is attributed to the change of the surface structure and the stress within the Ni films. Furthermore we found that the Curie temperature Tc and the critical exponent β of Ni films on the smooth and rough substrates show no change.
Magnetization and Curie Temperature of Ferromagnetic Ultrathin Films: The Influence of Magnetic Anisotropy and Dipolar Interactions (invited)
Authors: Bruno P.
Published: March 2011

Theoretical investigations of the magnetization and Curie temperature of ferromagnetic ultrathin films in the presence of magnetic anisotropy and long-range dipolar interactions are presented. The Curie temperature of fcc (001) cobalt ultrathin films is calculated and compared with experimental results on Co/Cu (001) films. The influence of an external magnetic field, and the surface gradient of the magnetization are also discussed.
Surface, Interface and Thin-Film Magnetism: An Overview
Authors: Falicov L. M.
Published: March 2011

A brief review of the state of the art in the field of surface, interface and thin-film magnetism is presented.
Morphology and Magnetic Phase Transitions of Monolayer-Range Fe Films on Au(001)
Authors: Liew Y.-F. , Wang G.-C.
Published: March 2011

We have studied the morphology and magnetic phase transitions of monolayer-range Fe films on a reconstructed Au(001) surface using the combination of High-Resolution Low-Energy Electron Diffraction (HRLEED) and Surface Magneto-Optic Kerr Effect (SMOKE) techniques. Through the measurement of energy dependent angular profiles of the specularly diffracted beam, we discovered a simple method to determine not only the interfacial spacings (Fe-Au and Fe-Fe) but also to detect the build up of the second layer. For a one-level (2-D) Fe films with coverage of ∼ 0.6 monolayer (ML) perpendicular magnetization was observed. For a 1 ML equivalent 3-D film both perpendicular and in-plane magnetization were observed. The magnetic phase transitions of these magnetic islands showed finite size broadening effect. The perpendicular saturation magnetization decreases with temperature above 100°C but never vanishes and the magnetization curve has no hysteresis loop above ∼ 120°C. The implication of superparamagnetism is discussed.
Magnetic and Structural Characteristics of Multi-layered Films Composed of Fe and Si Ultra-thin Layers
Authors: Kubota K. , Nagakubo M. , Naoe M.
Published: March 2011

Fe and Si layers were deposited alternately by using ion beam sputtering apparatus and the relationship between crystal structure and soft magnetic properties of these multi-layered films have been investigated in detail. The clear periodicity of multi-layered films was confirmed even at the thicknesses of Fe and Si layers δFe and δSi as small as 8.5 Å.

The saturation magnetization 4πMs for all Fe layers decreased with decrease of δFe and δSi, and the coercivity Hc of these films took minimum of 1.0 Oe at δFe of 8.5 Å.

Such a significant decrease of 4TEMs may be attributed to the formation of nonmagnetic regions at both side of each Fe layers. The thickness of these nonmagnetic regions may be estimated at approximately 1.5 Å from the measured value of 4flMs. This thickness seems to be very small because it is almost equal to that of one monolayer of bcc α-Fe. The low Hc of the films with δFe and δSi of 8.5 Å may be due to the formation of ultra-fine crystallites in Fe layer by insertion of amorphous Si layer and the direct magnetostatic interaction among Fe layers.
Magnetic Properties of Sputtered Ni/Al Multilayers
Authors: Tsang E. , Cates J. C. , Tan M. , Waknis A. , Alexander C. , Parker M.R. , Barnard J.A.
Published: March 2011

Magnetic properties of sputtered Ni/Al multilayers have been investigated by vibrating sample magnetometry and ferromagnetic resonance. In these compositionally modulated films (CMFs) the Al ‘spacer’ layer thickness was fixed at 3.5 nm while the total Ni content of each film was held constant at 308 nm. The thickness of the individual Ni layers was varied from 4.8 to 154 nm. The CMFs showed a variety of magnetic characteristics which were dependent on the thickness of the Ni layers. CMFs with Ni layer thickness 30 nm and above showed clear evidence of perpendicular anisotropy. This anisotropy is characterized by low-remanence perpendicular hysteresis loops of the type commonly found in CoCr alloy films. As the Ni layer thickness diminishes the perpendicular anisotropy decreases and is eventually lost. Simultaneously, the CMFs show increasing in-plane remanence, rising to a peak squareness of greater than 0.5 at a Ni layer thickness of 11 nm. As the Ni thickness continues to decrease, the remanence again declines. At Ni thicknesses of a few nm the CMFs become quasi-superparamagnetic. These CMFs do not show a monotonic reduction in saturation magnetization, Ms, with decreasing Ni layer thickness. Instead, both Ms and the coercivity, Hc, pass through a maximum in the region of 40–80 nm Ni layer thickness. FMR measurements were also made on these films. A plot of the effective anisotropy field produces data of a similar form to the Ms versus Ni layer thickness plot, again with a clear maximum. The FMR data also reveals interesting resonances in the films exhibiting perpendicular anisotropy. The presence of satellite resonances adjacent to the principal resonance peaks seems to suggest, in structural terms, a two-phase system as the basis of the observed anisotropy.
MÖssbauer Measurements of Interfacial Magnetism of MBE Grown FE(100)/AG(100) Multilayers
Authors: Tang H. , Wieczorek M.D. , Keavney D.J. , Storm D.F. , Gutierrez C.J. , Qiu Z.Q. , Walker J.C.
Published: March 2011

Multilayers of Fe(100)/Ag(100) were grown by MBE and analyzed with in situ RHEED and MÖssbauer spectroscopy. These films had a constant Ag layer thickness of 40 monolayers (ML) and varying Fe layer thicknesses of 3, 6, and 9 ML. Using MÖssbauer spectroscopy the presence of three Fe sites was inferred. From considerations of the hyperflne parameters and the relative intensities of the sextets, we assign one site to the bulk, and one to each interface: Fe on Ag and Ag on Fe. We believe that one explanation of this is differing tetragonal distortions at the two interfaces. Consequently, another series of films was grown in an attempt to distinguish these sites. These films were essentially identical to the 9 ML film above, but the Fe layers were composed of 56Fe, with a 2 ML 57Fe probe layer effused at the bulk and at each interface in turn. At this point 57Fe MÖssbauer spectroscopy was used to determine the hyperfine field and its temperature dependence for each of the three sites.
Preparation and Magnetism of CuO/A12O3 and CuO/MgO Artificial Superstructured Films
Authors: Sohma Mitsugu , Kawaguchi Kenji
Published: March 2011

Three kinds of copper oxide (CuO) films, that is, CuO mono-layer films (MLFs), CuO/A12O3 artificial superstructured films (ASFs) and CuO/MgO ASFs were prepared by a reactive vapor deposition method. Magnetic susceptibility of the MLFs is almost constant against temperature and the Neel temperature (TN) is a little lower than that of bulk CuO. There is paramagnetic contribution proportional to the number of the interfaces for both kinds of ASFs. It is considered to be caused by imperfect -Cu-O-Cu- antiferromagnetic superexchange interactions located in the vicinity of interfaces.
Magnetic Anisotropy of Crystalline Defects
Authors: Clemens B.M. , White R.L. , Nix W.D. , Bain J.A.
Published: March 2011

We consider the anisotropies due to coherency strains and the inilioliogcliotis stratlus associated with misfit dislocations, both of which give rise to anisotropy through maguctostrictive coupling. Coherency strains can give rise to anl apparent surface anisotrnpy due to the decrease in coherency strain with the film thickness. This anisotropy is comparable in magnitude to that observed experimentally for Fe [110] epitaxial thiut films on W [110]. The strain field associated with misfit dislocations produces a. surface anisotropy which is also comparable in magnitude to experimentally observed anisotropies. Dislocatioms along the inplane [001] and [110] directions both produce the same preferred direction of maguctization orientation.
The Perpendicular Magnetic Anisotropy and Structure of Sputtered Ag/Co, Pd/Co, and AgPd/Co Multilayered Films
Authors: Yamaguchi Akira , Soe We-Hyo , Yamamoto Ryoichi , Kobayashi Masonobu
Published: March 2011

The structural and magnetic properties of sputtered Ag/Co, Pd/Co, and AgPd/Co multilayered films were investigated. When substrate temperature during deposition (Ts) was set at room temperature, the easy magnetization axis of the Pd/Co films with Co thickness less than 7Å was normal to the film plane and that of the Ag/Co films was parallel. AgPd/Co multilayered films showed a transition of the preferred direction of magnetic moment from lying in the film plane towards lying along the film normal when increasing the Pd concentration above 81 at%. Moreover, an anomalous reduction of the saturation magnetization was found. The perpendicular magnetic anisotropy of Pd/Co films with low Ts increased with decreasing the thickness of Co layer. However, the Pd/Co films with high Ts showed opposite tendency.
Spin Polarized Photoemission Studies of Surfaces and Thin Films
Authors: Johnson Peter D. , Brookes N.B. , Chang Y.
Published: March 2011

Spin polarized photoemission is used to study the magnetic states associated with the clean iron (001) surface. These studies reveal evidence for a minority spin surface state in agreement with a first principles calculation. Studies of the same surface with silver and chromium epitaxial overlayers reveal evidence for interface states derived from this state found on the clean surface. In the case of the silver overlayer the binding energy of the new state is found to be dependent on the layer by layer thickness of the overlayer. With chromium overlayers the binding energy for the same interface state does not show the same thickness dependence. However a second interface state is observed immediately below the Fermi level. These changes in the interfacial electronic structure have implications for any modelling of magnetic coupling in multilayers dependent on the magnetic properties of the interface.
Epitaxial Rare-Earth Superlattices and Films
Authors: Salamon M.B. , Beach R.S. , Borchers J.A. , Erwin R. W. , Flynn C.P. , Matheny A. , Rhyne J.J. , Tsui F.
Published: March 2011

Epitaxial growth of rare-earth superlattices is demonstrated to have opened important new areas of research on magnetic materials. The propagation magnetic order through non-magnetic elements, including its range and anisotropy, has been studied. The importance of magnetostriction in determining the phase diagram is demonstrated by the changes induced by epitaxial clamping. The crystallinity of epitaxial superlattices provides the opportunity to study interfacial magnetism by conventional x-ray and neutron scattering methods.
Preparation, Characterization And Activity Of Molecular Sieve Material As Base Catalysts.
Authors: Corma Avelino
Published: March 2011

There are a series of reactions such as isomerization, alkylation, dimerization of olefins, condensation, etc, which are catalyzed by bases. Solid base catalysts are competitive with respect to solid acid catalyst for carrying out reactions which can be catalyzed by either acids or bases. Solid bases can successfuly catalyze transformations of organic substrates containing heteroatoms, such as N, O, and S. Solid acids, which can also catalyze these reactions, often are poisoned by those substrates. Moreover, in some cases, such as olefin and alkyne isomerizations, it is possible by using bases to achieve stereochemical control. This has impulsed researches to look for very strong solid base catalysts, i.e., superbasic solids, such as supported alkaline metals. These, while active at moderate temperatures, present a major drawback derived from their relatively low stability and frequent catalyst regenerations. However, there are a significant number of interesting reactions which can also be catalyzed by bases with medium strength. In this case, the use of a very strong base catalyst can be disadvantageous because it can also catalyze other, non desired, more demanding reactions, with the corresponding decrease in selectivity to the desired product. Furthermore, in some processes, it can become more critical to adequately control the acid-base pairs than to achieve a very strong type of basic sites.
Zeolite Crystal Layers Coupled To Piezoelectric Sensors: Molecular Recognition Demces
Authors: Yan Yongan , Bein Thomas
Published: March 2011

Microporous zeolite crystals were successfully coupled onto the gold electrodes of quartz crystal microbalances (QCM). A self-assembled monolayer of thiol-alkoxysilane coupling agent on the gold surface was used as the Interfacial layer to promote adhesion of the zeolite crystals to the QCM. The resulting, densely packed single layers of zeolite crystals were stable to at least 625 K. Transient sorption behavior of organic vapor pulses, dynamic vapor sorption isotherms and nitrogen sorption isotherms at liquid nitrogen temperature were examined to characterize the zeolite-coated QCMs. Depending on the type of zeolite coating, the resonance frequency response to vapor pulses could be increased up to 500-fold compared to the bare QCM. The regular micropores (0.3–0.8 nm) of the QCM-attached zeolite crystals were found to control molecular access into the extensive intrazeolite volume. Selectivity of the frequency response in excess of 100:1 toward molecules of different size and/or shape could be demonstrated. An additional recognition mechanism based upon intrazeolite diffusion rates was also established.
Formation And Characterization Of Sulfide Clusters In Molecular Sieve Zeolite Materials
Authors: Winterer Markus , Iton Lennox E. , Johnson Stanley A. , Maroni Victor A.
Published: March 2011

The incorporation of molybdenum into the faujasite pore system via reaction of MoCl5 with H-Y zeolite results in dealumination of the zeolite framework and formation of MoO3 species. These species are readily sulfided by H2S, but MoS2 clusters are not produced. A sulfur-bridged dimeric molybdenum cluster, of proposed composition HO-Mo-(S)3-Mo-OH, is formed, which can strongly chemisorb CO. Sulfidation of niobium in this manner is not readily accomplished.
Directing Effect Of Fluoride In The Synthesis Of Molecular Sieves With New Characteristics And Of The First Twenty-Membered Ring Microporous Solid
Authors: Kessler Henri
Published: March 2011

The directing effect of fluoride anions in the synthesis of molecular sieves seems to be related to the strength of its interaction with the framework. For example, whereas F is bridging 2 Al atoms of a four-membered ring in AlPO4-5 containing tetrapropylammonium fluoride and in an new triclinic morpholine-containing chabazite-like AlPO4, it is found in double four-rings in three other phases which were synthesized recently. Firstly in the tetragonal all-silica AST-type octadecasil (space group I4/m, a = 9.194(2)Å c = 13.396(4)Å) which was obtained in the presence of quinuclidine and HF. Secondly in two novel cubic microporous gallophosphates which are formed selectively in the presence of hydrofluoric acid. One has the structure type LTA (space group Fm3c, a = 24.0354(1)Å) and crystallizes with di-n-propylamine as a template, and the other shows a novel structure type (space group Fm3c, a = 51.84Å) with a 3-dimensional 20-membered ring channel system. This is the largest membered ring ever reported for a synthetic material.
Systematic Preparation Of Polyoxometalate Pillared Layered Double Hydroxides Via Direct Aqueous Reaction
Authors: Wang Jiandang , Tian Ying , Wang Ren-Chain , Colón Jorge L. , Clearfield Abraham
Published: March 2011

The series of layered double hydroxides, MgnAl(OH)2n+2X (n = 2–5, X = NO3− or Cl−) and NinAl(OH) 2n+2X (n = 2–4, X = NO3− or Cl−), were pillared with polyoxometalate ions of the Keggin structure, ranging from [PW12O40]3− to [PV4W8O40]7−, in aqueous solution. Full exchange of the Keggin ions into the layers is achieved as evidenced by X-ray powder diffraction, infrared spectroscopy, elemental analysis and thermogravimetric analysis. Also, partial exchange was observed for Ni5Al(OH)12NO3 The key factor that effects these reactions is the pre-swelling step. Thus, when the layered double hydroxides are thoroughly wet either by preparing wet solids or by soaking the dried products for an extended period, pillaring reactions proceed with great ease. Relations can be extracted between the water content and the separation between the layers, as well as between layer charge density and the charge of the Keggin ion. The pillared layered double hydroxides were found generally to have interlayer distances ranging from 11.0 to 13.5 Å, which is smaller than the numerical sum of the Keggin ion diameter and the ideal thickness of the hydroxide layer. This fact and the low crystallinity are attributed to strong interaction between the basic layered double hydroxides and the acidic Keggin ions. A more crystalline phase with the expected 14.5 Å interlayer spacing was also obtained as a mixture with the lower spaced products.
Preparation of Montmorillonite-p-Aminoazobenzene Intercalation Compounds and Their Photochemical Behavior
Authors: Ogawa Makoto , Fujii Keiko , Kuroda Kazuyuki , Kato Chuzo
Published: March 2011

Homoionic-montmorillonite-p-aminoazobenzene intercalation compounds were prepared by novel solid-solid reactions at room temperature. When Na-, Ca- and Ni-montmorillonites were used as host materials, the absorption maxima of p-aminoazobenzene changed considerably upon intercalation, causing the difficulty of studying photochemical behavior of the intercalated dyes. The n-dodecylammonium-montmorillonite-p-aminoazobenzene intercalation compound gave an absorption spectrum similar to that observed for p-aminoazobenzene dissolved in benzene. The intercalated paminoazobenzene in the interlayer space of n-dodecylammoniummontmorillonite exhibited reversible cis-trans photoisomerization by irradiation of UV light.
Raman Microprobe Analysis of Simox Structures Implanted With Screen Oxide
Authors: Perez-Rodriguez A. , Morante J. R. , Martin E. , Jimenez J. , Margail J. , Papon M. A.
Published: March 2011

The analysis of SIMOX structures obtained by doing the implantation with different thicknesses of thermal oxide (screen oxide) has been perfomed by Raman scattering, and the results have been correlated with those previously obtained by TEM. The use of a microRaman system on low angle bevelled sample has allowed to directly observe the different regions in the structures, corroborating the structural differences observed by TEM as a function of the screen oxide thickness. For as implanted structures, strong non homogeneous strain and disorder effects are observed in the top Si layers. After the High Temperature Anneal (HTA) process, crystalline quality of the structures is improved. The analysis of the spectra obtained at different excitation powers points out the dependence of the thermal effects of the spectra on the structural features of the scattering volume, as the dislocation density in the annealed layers. This dependence allows the assesment of the crystalline quality of these structures to be made.
Localized Crystallinity Measurement of Single-Crystal Ge on Insulator by Raman Polarization
Authors: Kato K. , Takai M.
Published: March 2011

Agglomeration has occurred during zone-melting to obtain single-crystal germanium layers because of insufficient wettability between germanium and silicon-dioxide. The agglomeration could be suppressed by controlling the capping layer thickness, germanium layer thickness, and the island shape. A rotation of crystal orientation was found in the stripe shape island, which was presumably caused by the stress relieving within an island.
Picosecond Photocarrier Lifetimes in Ion-Irradiated Amorphous and Crystalline Silicon
Authors: Stolk P. A. , Calcagnile L. , Roorda S. , van Linden H. B. , Heuvell Van den , Saris F. W.
Published: March 2011

Crystalline silicon (c-Si) and structurally relaxed amorphous silicon (a-Si) were implanted with 1 MeV Si+ at liquid nitrogen temperature. The photocarrier lifetime τ in the implanted samples was determined with sub-picosecond resolution through pump-probe reflectivity measurements. At low damage levels (i.e. <1014 ions/cm2), τ decreases with increasing ion dose in both materials, indicating a build up of trapping and recombination centers. The dominant centers in c-Si appear to be related to simple defects. The generation rate of electrically active defects is found to be the same in relaxed a-Si and c-Si, which suggests that the structural defects formed in a-Si strongly resemble the simple defects in c-Si. For ion doses > 1014 /cm2, τ saturates at a level of 0.8 ps for both materials. Strikingly, the saturation sets in far below the dose needed to amorphize (>1015 /cm2). The defect density in a-Si at saturation is estimated to be ≈1.6 at.%.
Evolution of Buried Oxide “Pipe” Defects Upon Implantation Through Particles in Simox Material
Authors: El-Ghor M. K. , Joyner K. A. , Hosack H. H.
Published: March 2011

We have investigated the effect of the presence of oxide particles on the surface of silicon wafers during high energy, high dose implantation of oxygen into silicon. It was found that for single implants with doses of 1.5 × 1018/cm2 or 1.8 × 1018/cm2, such particles produce a non-continuous buried oxide layer in the as-implanted condition as well as after annealing. Etching results showed that no defects, which formed etchable paths through the buried oxide, were produced for particles with diameters 0.43 um or below for the lower dose and 0.53 um for the higher dose.
The Detailed Variation of Boron and Fluorine Profiles with Tilt and Rotation Angles for BF2+ ION Implantation in (100) Silicon
Authors: Gupta Puneet , Park Changhae , Klein Kevin , Yang Shyh-horng , Morris Steve , Do Vu , Tasch Al , Simonton Robert , Lux Gayle
Published: March 2011

Over 250 boron and over 250 fluorine profiles have been obtained from BF2+ implants over a wide range of implant energies, doses, tilt angles, and rotation angles. A detailed study has been conducted on the boron and fluorine profile variations with the tilt and rotation angles over the available range of energies and doses. Channeling through a few low index axial and planar channels in (100) silicon has been found to account for the observed profile variations with implant angle. Tilt and rotation angle combinations which minimize channeling and ensure process uniformity have been deduced.
Sb Implantation in Si1–xGex/Si(100) Structures
Authors: Atzmon Z. , Eizenberg M. , Revesz P. , Mayer J. W. , Schäffler F.
Published: March 2011

Solid phase epitaxial regrowth of Sb implanted strained Si1−x Gex alloy layers is reported. Two sets of Si1–xGex alloys with compositions of x=0.08 and x=0.18, MBE grown on (100)Si substrates, were implanted at room temperature with Sb− ions at energies of 200 and 100 keV, respectively, and a dose of 1015cm−2. These alloys were heat-treated in a rapid thermal annealing system at temperatures of 525, 550 and 575°C for durations between 5 and 600 sec. The study of the solid phase epitaxial regrowth was performed by Rutherford backscattering in the channeling mode. The measurements show a significant difference in the regrowth mechanism between the two alloys. For the Si0.92Ge0.00 alloy a fast regrowth process (faster than for Sb implanted Si or Si implanted SiGe layers) occured with an activation energy of 2.92±0.2eV. For the Si0.02Ge0.10 alloy the regrowth took place in two steps: a) a very fast initial process over a short distance, b) a regrowth process of the majority of the amorphous layer.
Diffusion and Phase Formation During Combined Heating and Sputter Etching
Authors: Harper J. M. E. , Hong Q. Z. , Motakef S. , Kelly R.
Published: March 2011

Sputter etching normally removes material with an overall composition equal to the target composition. At room temperature, this steady-state removal process is usually quickly established by the formation of an altered surface layer which compensates for preferential sputtering, together with an altered subsurface layer which reflects the existence of bombardment-induced Gibbsian segregation (GS). At elevated temperature, ordinary GS, diffusion and the presence of compound phases may strongly affect the development of the steady-state condition. In this paper, we describe two cases in which diffusion and GS become significant processes during sputter etching of a compound material AxB1−x on an underlying substrate of B atoms. In the first case, diffusion is dominated by the substrate species. This case is demonstrated by the sputtering of TiSi2 on (100) Si by 300 eV Ar+. At room temperature, normal sputtering of the TiSi2 layer occurs. At elevated temperature (500–700°C), however, Si diffuses from the substrate to the surface, where it undergoes GS. This allows the development of a steady-state highly selective sputtering of Si atoms, accompanied by movement of the TiSi2 layer into the substrate. In the second case, diffusion is dominated by the non-substrate species. This case is demonstrated by CoSi2, for which the development of steady-state etching occurs in two distinct stages which are strongly temperature-dependent. In this material, Co is the dominant diffusing species, and it is unclear whether or not Si GS occurs. What is clear, however, is that Ar+ bombardment at 500–600°C leads to partial decomposition of the CoSi2 layer and diffusion of Co towards the substrate Si, where new CoSi2 is formed. The combination of sputter etching and elevated temperature is shown to be a controllable environment for compound phase formation at a buried interface.
Silicide Formation in High-Dose Fe-Implanted Silicon
Authors: Tan Z. , Namavar F. , Heald S. M. , Budnick J. I. , Sanchez F. H.
Published: March 2011

We have studied the silicide formation in Fe-implanted Si(100), with 1×1017-1×1018 Fe/cm2, using extended x-ray-absorption fine structure (EXAFS), x-ray diffraction and Rutherford backscattering spectrometry (RBS) methods. In the samples as-implanted at 350 °C, no silicide was observed at doses below 3×1017 Fe/cm2. At 5×1017 Fe/cm2, both α-FeSi2 and (β-FeSi2 form but α-FeSi2 appears to be the majority phase. As the dose increases to 7×1017 and above, ordered FeSi forms, but implantation damage is severe and a large number of Fe atoms are in very disordered environments. In addition to FeSi, Fe5Si3 was also observed in the 1×1018 Fe/cm2 sample. Upon post-implantation annealing at 700 °C or 900 °C, single phase P-FeSi2 was obtained independent of the dosage.
Phase Formation of Platinum Silicides Formed by Ion Implantation
Authors: Kalkhoran Nader M. , Namavar F. , Perry D. , Cortesi E.
Published: March 2011

We have studied the formation of platinum silicide layers by ion implantation and annealing, and have determined the dependence of platinum silicide phase formation on ion implantation conditions and substrate orientation. The results indicate that in most cases, the ion implanted layer consists of PtSi phase. However, depending on the implantation and annealing conditions and substrate orientation, other phases, including Pt2Si, Pt3Si, and Pt12Si5, as well as Si and Pt microcrystals, also form.
Study of Amorphization Process in Silicon Irradiated by Different Ions Using In Situ Stress-Measurement and TEM Techniques
Authors: Yuan Jianzhong , Verner Igor V. , Maksimov Sergei K. , Corbett James W.
Published: March 2011

Detailed measurements of the stresses induced by implantation of ions of different types, such as light ions: boron and nitrogen, and heavy ions: argon, krypton and xenon, were carried out in situ on thin silicon films. The measurement were made for keV energy of ions, for a wide range of doses and for different values of the dose rate. Experimental results indicate that the ion-beam-induced transformation in silicon is dose-rate dependent for light ions, as well as for heavy ions. The last conclusion contradicts the classical ideas of amorphization of elemental semiconductors by heavy ions that are based on the concepts of a heterogeneous mechanism of formation of the amorphous state during implantation. Heavy-ion implantation behaves similarly with light-ion implantation at a higher sample temperature. A comparison TEM investigation with stress measurement was made. The results indicate that i) the ion-beam-induced deformation correlates with structural changes and ii) both homogeneous and heterogeneous mechanisms are involved in the structural changes. The results are discussed in terms of non-equilibrium phase transitions in silicon under irradiation.
Erbium-defect interactions in silica films implanted with MeV Er ions
Authors: Polman A. , Jacobson D. C. , Poate J. M.
Published: March 2011

The effect of ion implantation damage on energy transfer processes in Er-doped silica films prepared by MeV ion implantation is studied, using measurements of the luminescence decay of Er3+(4ƒ11) at 1.535 μm. Silica films implanted with Er and annealed at 900°C show a luminescence lifetime of 14.1 ms. Subsequent irradiation with MeV C, Si, or Ge ions at fluences as low as 1011 ions/cm2 decreases the lifetime, which eventually saturates at 6.6–7.8 ms for fluences larger than 1014 ions/cm2. The fluence required to saturate and the lifetime at saturation depend on the ion used. These results are interpreted in terms of non-radiative energy transfer processes caused by irradiation-induced defects in the silica. The ion damage effects are mainly caused by the electronic component of the energy loss along the ion trajectories.
Formation of Au Colloid Particles in Silica Glass by Ion Implantation.
Authors: Fukumi K. , Chayahara A. , Adachi M. , Kadono K. , Sakaguchi T. , Miya M. , Horino Y. , Kitamura N. , Hayakawa J. , Yamashita H. , Fujii K. , Satou M.
Published: March 2011

Formation of Au colloid particles and their optical property have been investigated in silica glasses implanted with Au+ ions at an acceleration energy of 1.5MeV and fluence levels of 1016-1017 ions/cm2. The Au colloid particles are formed in the as-implanted glasses. It is inferred that the average radius of Au colloid particles depends on the fluence level, although the fluence level does not affect the distribution of Au atomic concentration. The heat-treatment little affects the Au atomic distribution. The Au colloid particles grow to 4.3nm in average radius during heat treatment. It is revealed that the large nonlinear optical property of the Au+ -ion-implanted silica glass is attributed to the high concentration of the Au colloid particles in the narrow region.
Dynamic Redistribution of Excess Charge During Photoemission in an Electron Bombarded Glass-Ceramic
Authors: Carroll D. L. , Doering D. L. , Blais B. S.
Published: March 2011

We have measured the energy distribution of excess charge trapped by an electron irradiated mica-glass ceramic, Macor™. Photoelectron emission as a function of incident wavelength shows two distinctly different contributions to the measured density of electron trap states. First, there is a broad continuum of binding states which extends well above the Fermi level. This results in spontaneous electron emission which depletes the excess charge in these states rapidly at room temperature and more slowly at 170K. The free decay of charge emission can be described semiclassically. Second, localized trap states appear as peaks on the continuum distribution which occur at 2.7 and 3.1 eV. These correspond to two thermionic emission peaks which occur during heating at 550K and 595K respectively. Photoemission at high intensities using the 458, 488, and 514 nm wavelengths of an argon ion laser and the 632 nm wavelength of a He-Ne laser greatly enhances the depletion of excess charge from the sample. The laser-induced emission intensity is initially high and drops rapidly, followed by a more gradual decrease. The initial intensity measures the population of electrons with binding energies less than the photon energy. The later emission is related to the repopulation of these states by the dynamic redistribution of electrons from deeper states. This behavior may lead to a model for the mechanism of electron redistribution in charged insulating materials.
The Role of Ballistic, Electronic, and Thermal Processes in Electron Irradiation Damage of Maximum Valence Transition Metal Oxide Surfaces
Authors: Buckett M. I. , Marks L. D.
Published: March 2011

Surface-initiated radiation damage processes in a number of the maximum valence transition metal oxides - TiO2, V2O5, WO3, MoO3, Ta2O5, Al2O3, and Nb2O5 - have been investigated by in-situ high resolution electron microscopy under UHV conditions and at incident energies ranging from 3 keV to 300 keV. The relative contributions of ballistic, electronic, and thermal effects are evaluated by a comparison of the observed structural changes and damage rates - made under various experimental conditions of incident electron energy and flux - to theoretical predictions based on thermodynamic and available energy criteria.
The Behavior of Intersttitals in Irradiated Graphite
Authors: Pedraza D. F.
Published: March 2011

A computer model is developed to simulate the behavior of self-interstitials with particular attention to clustering. Owing to the layer structure of graphite, atomistic simulations can be performed using a large parallelepipedic supercell containing a few layers. In particular, interstitial clustering is studied here using a supercell that contains two basal planes only. Frenkel pairs are randomly produced. Interstitials are placed at sites between the crystal planes while vacancies are distributed in the two crystal planes. The size of the computational cell is 20000 atoms and periodic boundary conditions are used in two dimensions. Vacancies are assumed immobile whereas interstitials are given a certain mobility.

Two point defect sinks are considered, direct recombination of Frenkel pairs and interstitial clusters. The clusters are assumed to be mobile up to a certain size where they are presumed to become loop nuclei. Clusters can shrink by emission of singly bonded interstitials or by recombination of a peripheral interstitial with a neighboring vacancy. The conditions under which interstitial clustering occurs are reported. It is shown that when clustering occurs the cluster size population gradually shifts towards the largest size cluster. The implications of the present results for irradiation growth and irradiation-induced amorphization are discussed.
In Situ Transmission Electron Microscope Studies of Ion Irradiation-Induced and Irradiation-Enhanced Phase Changes
Authors: Allen Charles W.
Published: March 2011

Motivated at least initially by materials needs for nuclear reactor development, extensive irradiation effects studies employing transmission electron microscopes (TEM) have been performed for several decades, involving irradiation-induced and irradiation-enhanced microstructural changes, including phase transformations such as precipitation, dissolution, crystallization, amorphization, and order-disorder phenomena. From the introduction of commercial high voltage electron microscopes (HVEM) in the mid-1960s, studies of electron irradiation effects have constituted a major aspect of HVEM application in materials science. For irradiation effects studies two additional developments have had particularly significant impact; (1) the development of TEM specimen holders in which specimen temperature can be controlled in the range 10–2200 K and (2) the interfacing of ion accelerators which allows in situ TEM studies of irradiation effects and the ion beam modification of materials within this broad temperature range. This paper treats several aspects of in situ studies of electron and ion beam-induced and enhanced phase changes and presents two case studies involving in situ experiments performed in an HVEM to illustrate the strategies of such an approach of the materials research of irradiation effects.