bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Assessment of a Repository for Intermediate-Level Radioactive Waste Using the Probabilistic System Assessment Program Mascot
Authors: Sinclair J. E. , Agg P.J.
Published: April 2011

UK Nirex Ltd is planning the deep geological disposal of intermediate- and low-level radioactive wastes. A site close to Sellafield in Cumbria in the north-west of England has been selected for evaluation, and an extensive programme of site characterization is underway. In support of this programme of characterization, and in preparation for presentation of a post-closure radiological safety case, performance assessment using mathematical modelling has been carried out by the Disposal Safety Assessment Team at AEA Technology, on behalf of UK Nirex Ltd. This paper describes recent developments of the assessment models relating to the groundwater pathway for return of radionuclides to the environment.
Processes Controlling Radionuclide Release from Spent Fuel
Authors: Loida A. , Grambow B. , Geckeis H. , Dressler P.
Published: April 2011

Dissolution of spent fuel has been studied in saline, anaerobe, carbonate free solutions. Processes controlling spent fuel dissolution and associated radionuclide release are radiolytically controlled oxidative dissolution, sorption on container, solubility and coprecipitation. Upper limits for oxidative dissolution rates are given by the production rates of oxidative radiolysis products. This limitation leads to a strong decrease in surface area normalized reaction rates with increasing surface to volume ratio (S/V) and imposes geometric constraints on prediction of spent fuel behavior in a repository. Solution concentrations of Am during spent fuel corrosion were about 5 orders of magnitude lower than the solubility of Am(OH)3(s) and are likely controlled by coprecipitation. Pu concentrations may be controlled by Pu(VI) or Pu(IV) (hydr)oxides.
Uranium (iv) Dioxide and Simfuel as Chemical Analogues of Nuclear Spent Fuel Matrix Dissolution. A Comparison of Dissolution Results in a Standard Naci/NaHCO3 Solution
Authors: Bruno Jordi , Casas I. , Cera E. , de Pablo J. , GimÉnez J. , Torrero M. E.
Published: April 2011

We have carried out an experimental comparison study of the dissolution rates of unirradiated UO2 and SIMFUEL pellets and particles (100–300 μm) in a standard NaCI/NaHC03 solution, under oxidizing conditions. We have performed the experiments using batch and flow methodologies. Both methodologies gave similar results, indicating that the overall oxidation/dissolution process is the same in both cases. The results from the experiments indicate that under these conditions the dissolution process is both oxygen and bicarbonate promoted. The dissolution rates we obtained are: R=2.4 ± 0.8 mg U/m2 d for U02 and R= 0.17 ± 0.05 mg U/m2 d for SIMFUEL. The results of the experiments indicate that the dissolution rate under oxic conditions is clearly dependent on the number of U(VI) surface sites which for spent nuclear fuel is a function of the extent of radiolytic oxidation.
Study of Media Effect on Glass Surface
Authors: Shanggeng Luo , Zhaoguang Wu , Delu Liu
Published: April 2011

The present work described the effects of media, such as tuff, zeolite, bentonite and Fe2O3, on the glass surface leached in deionized water or in underground water. Element depletion or enrichment differ in different media system. No crystals were found in the leached glass surfaces layer. But there are pitting corrosion and precipitates on the leached glass surfaces. The amounts, both of them, increase along with the leaching time.
An Evaluation of Hydrogen Evolution from Corrosion of Carbon Steel in Low/Intermediate Level Waste Repositories
Authors: Matsuda Fumio , Wada Ryutaro , Fujiwara Kazuo , Fujiwara Ai
Published: April 2011

As a sequence of studies to evaluate the quantity of gas evolution from low/intermediate level waste repositories,hydrogen gas evoluted from corrosion of carbon steel in simulated repository environment was evaluated by laboratory experiments. The experimental results on the hydrogen gas evolution both in air purging condition simulated oxidizing environment and nitrogen purging condition simulated reducing environment, are summarized as follows.

(1)

Hydrogen gas evolution enough to analyze quantitavely by gas chromatography (>5ppm) has been recognized under almost all test conditions except reducing equilibrium cement water.

(2)

Effects of purging gas (air,nitrogen) on the hydrogen gas evolution and the corrosion rate calculated from weight loss were air purge > nitrogen purge. On the other hand, the contribution ratio of hydrogen evolution reaction in corrosion rate was nitrogen purge > air purge.

(3)

Effects of test solution on the hydrogen evolution rate were as fo11ows.

• Air Purge :

Equilibrium Bentonite Water ≈ Equilibrium Cement Water > Synthetic Sea Watert

• N2 Purge:

Synthetic Sea Water > Equilibrium Bentonite Water >> Equilibrium Cement Water

(4)

No distinct effect of crevice geometry of test specimen on hydrogen evolution rate was recognized. Only under the reducing equilibrium cement water, however, the increase of hydrogen evolution was confirmed after the immersion of several hundred hours.

(5)

Hydrogen evolution rates tended to decrease with testing time except in the reducing equilibrium cement water.

(6)

No distinct difference of hydrogen evolution rate between steels (SPHC, SPCC) was observed.
Exafs Study of (La1-XCex)2Zr207
Authors: Yokoi Hiroto , Matsui Tsuneo , Ohno Hideo , Kobayashi Katsumi
Published: April 2011

The local structures around Zr atoms such as coordination number of oxygen and cations, and the Zr-0 and Zr-Ln (Ln; La, Ce) interatomic distances in the (La1-xCex).2Zr2O7 Pyrochlore compounds (X = 0–0.25), where Ce is a simulation of actinides,were studied by means of extended X-ray absorption fine structure (EXAFS) spectrometry. The local structure determined by EXAFS in this study is discussed in relation to the dissolution behavior of (La1-xCex)2Zr207 (leaching rates of Zr, La and Ce) in an acid solution (pH=1) at 363K reported previously. The difference in the local structure before and after leaching test was also investigated.
Fundamental Study on the Solidification of Radionuclides with Hydrous TiIV Oxide Modified with Either Si or Zr
Authors: Yamazaki Hiromichi , Inoue Yasushi
Published: April 2011

The potentiality of hydrous TiIV-Si oxide (TS) and hydrous TiIV-Zr oxide (TZ) for the selective sorption and immobilization of radioactive Co2+, Eu3+, Th4+ and UO22+ ions has been studied experimentally: The distribution coefficients and sorption capacity for these ions at various conditions in solutions, the structure and the composition of the exchangers in relevant ionic forms at high temperatures, and the leaching rates from the calcined exchangers into water and 0.01M HNO3 solution at room temperature. These results were discussed together with the results previously obtained for Cs+ and St2+, in order to evaluate the performance of TS and TZ as solidification media for radioactive liquid waste. TS takes up these cations more than TZ does in acidic solutions due to the higher acidity of the exchange site. In TZ, transition metal ions show high affinity despite the small distribution coefficients for representative metal ions. The dissolution of Co2+, Eu3+, and Th4+ is very slow from both calcined exchangers due to the crystallization of titanates of these cations. The leaching rates of Cs+, St2+ and UO22+ from calcined TS are much slower than those from TZ, indicating the formation of titanium silicate containing these cations. Based on these results, TS is considered to be superior to TZ in the sorption capacity and fixation capability of various kinds of radionuclides and is considered as a promising material for the solidification of radwaste.
Rietveld Analysis of Phase Separation in Annealed and Leach Tested Cm-Doped Perovskite
Authors: White T. J. , Mitamura H. , Tsuboi T.
Published: April 2011

A quantitative powder X-ray diffraction study was made of actinide doped perovskite of bulk composition Ca0.98919An0.01081Ti0.98919Al0.01081O3 where An corresponded to approximately equimolar proportions of Cm-244 and Pu-240. Sections of this sample accumulated irradiation doses up to 7.51 × 1017 alpha decay events per gram (± g−1). The damaged samples were treated in two ways. First, to establish the critical temperature for structural recovery under the reducing conditions of geological repositories, isochronal annealing was carried out at 600, 800, 1000 and 1100˚C for 12 hours in graphite crucibles. Two groups of perovskites that had previously sustained doses of 4.5 × 1017 and 7.4 × 1017 ± g−1 were tested in this way. For the former group, these conditions resulted in up to 9 weight percent (wt%) of available actinide separating as a fluorite-type dioxide near the perovskite surface. In the latter group, calcium was reduced to the metal which vaporised, leaving an excess of refractory titanium that crystalised as rutile. Second, material which had sustained doses of 1.6–4.0 × 1017 alpha decays per gram was subjected to an MCC-1 leach test for two months at 90˚C using a pH ∼ 2 solution. Under these conditions surficial perovskite dissolved congruently to release calcium into solution while the titanium reprecipitated as anatase. The implications of these results for the ultimate disposal of perovskite-bearing polyphase nuclear waste ceramics are considered.
Improvement of Characteristics of Solidified Radioactive Waste Forms with Polymer-Concrete Layer
Authors: Grebenkov Alexandre J. , Trubnikov Vitaly P. , Verzhynskaja Antonina B. , Nikolajev Victor A. , Kapustina Inna B.
Published: April 2011

Within the framework of the Belarus National Programme, IPEP is performing research on the immobilization of low level radioactive waste after decontamination and remediation of Chernobyl Zone. The goal of the R&D programme is to develop a composite matrix for embedding these wastes using special encapsulation technology and reinforced and hydro-resisting polymer-concrete layer on solidified waste blocks to minimise the amount of cement for conditioning of waste.
Suppression of Ion-Induced Charge Collection by High-Energy B+-Implanted Layer
Authors: Kishimoto T. , Sayama H. , Takai M. , Ohno Y. , Sonoda K. , Nishimura T. , Kinomura A. , Horino Y. , Fujii K.
Published: April 2011

Control of charge carrier collection by high-energy boron-implanted layers has been investigated to clarify the validity of buried well structures against soft errors in dynamic random-access memories (DRAMs) by ion-induced-current measurements using high-energy proton microprobes. A finely focused 1.3 MeV proton beam has been used to irradiate normal to n+p diodes with buried layers fabricated by B+ implantation at 160 — 1000 keV and to doses of 1 × 1012 — 1 × 101 ions/cm2, and reverse-biased at 1 to 5 V. The measured current was induced by carriers generated by ion microprobes. The collection of charge carriers induced by microprobe irradiation could be reduced by a buried layer formed by boron implantation. It was found that the rate of charge collection depended not on the depth but on the implantation dose of the buried layer. The carrier collection efficiency of the n+p diode with twin wells (i.e., a retrograde well) was two thirds of that with a conventional well.
Linear and Nonlinear Optical Properties of Metal Nanocluster-Silica Composites Formed by Sequential Implantation of Ag And Cu
Authors: Zuhr R.A. , Magruder.III R.H. , Anderson T.A. , Osborne D.O.
Published: April 2011

Metal nanocluster-glass composites demonstrate unique optical properties and significant nonlinear response. In this work nanometer dimension metal colloids were formed in silica by sequential implantation of Ag and Cu ions. The Ag and Cu were implanted with relative ratios of Ag to Cu of 9:3,6:6, and 3:9 at a total nominal dose of 12xl016 ions/cm2. TEM techniques were used to examine colloid size and size distributions. The linear optical response was measured from 200 to 900 nm, while the nonlinear optical properties were measured using the z-scan technique at a wavelength of 570 nm. The linear and nonlinear optical properties were found to be dependent upon the ratio of sequentially implanted Ag to Cu and are consistent with effective medium theory.
Diffusion of Implanted Dopants and Isolation Species in III-V Nitrides
Authors: Pearton S.J. , Abernathy C.R. , Vartuli C.B. , Wilson R.G. , Zavada J.M.
Published: April 2011

Twelve different elements used for doping or isolation were implanted into GaN, (and selected species into A1N and InN), and the resulting range parameters were measured by Secondary Ion Mass Spectrometry. For lighter elements such as Be, F and H the agreement between experimental range and range straggle dtermined using a Pearson IV computer fitting routine and those predicted by TRIM 92 calculations was good, but for heavier elements such as Ge and Se the discrepancy can be as much as a factor of two in range. There was little redistribution of any of the investigated species up to 700 °C, except for 2H in A1N and S in GaN. Elements such as F and Be which are generally rapid difiusers in III-V compounds do not display any redistribution in GaN for temperatures up to 800 °C.
Atomic Transport by Ion Beam Mixing in the Radiation Enhanced Diffusion Region
Authors: Jung S. M. , Chang G. S. , Joo J. H. , Woo J. J. , Jang K. S. , Whang C. N.
Published: April 2011

In order to study atomic transport in the radiation enhanced diffusion (RED) region, Pd/Co bilayers were intermixed by 80keV Ar+ in the temperature range from 90 K to 700 K. The critical temperature for the onset of RED was found to be ∼ 400 K, and the transported amount of Pd atoms was found to be always larger than that of Co in the RED region. This result cannot be explained by pre-existing models. Thus we have developed a comprehensive model for atomic transport in the RED region including size effect, damage controlled effect, and cohesive energy effect.
SiCx Layers on Diamond by Si Implantation for Protection Against High Temperature Oxidation
Authors: Kirkpatrick A.R. , Dallek S. , Kosik W.E.
Published: April 2011

Diamond is subject to oxidation if exposed to oxygen while at temperatures above approximately 600°C. A method has been demonstrated for protection of diamond against oxidation by employing Si+ ion implantation to transform a thin surface layer into silicon carbide which exhibits excellent oxidation resistance. Integral SiCx oxidation barrier layers have been formed on diamond using high Si+ dose levels and high temperatures during implantation. SiCx layers have been characterized using Rutherford backscattering, IR spectrophotometry and scanning electron microscopy. The effects of high temperature exposure to oxygen have been examined using various oxidation test procedures including thermogravimetric analysis. SiCx layers capable of providing protection of underlying diamond for periods of several minutes at temperatures beyond 1000°C have been accomplished.
Effect of Titanium Implantation on the Mechanical Properties of Silicon Nitride
Authors: Fujihana T. , Nishimura O. , Yabe K. , Hayashi H. , Iwaki M.
Published: April 2011

A study has been made of the chemical composition and mechanical properties of Ti+-implanted Si3N4 surface layers. Implantation of 48Ti+ was performed with doses ranging from 10 to 1017 ions cm”2 at an energy of 150 keV, and at nearly room temperature. XPS was used to analyze the depth dependence of atomic fraction and chemical bonding states of Ti+-implanted layers. The near-surface hardness was measured by a Vickers hardness tester. The friction and wear properties were measured under unlubricated conditions at room temperature using a pin on disk-plane and a block on wheel-periphery configurations, in which the pin and wheel used were AISI1045 and ASTM Wl-9, respectively. Implanted Ti-atoms formed a gaussian distribution predicted by the range theory. At the average projected range, most of Ti-atoms existed as a metallic state and TiN bonding was also formed. Oxygen and carbon were found near the surface layers. In addition to the surface peak, O-atoms accumulated in front of the average projected range of Ti. Such O-atoms formed bonds of Si-oxides and Ti-oxides. Carbon existed as a graphitic state. With increasing a Ti dose, the near-surface hardness decreased, and the wear rate increased at the running-in stage having the high friction coefficient. The steady wear attributed to the stable friction coefficient appeared after the running-in stage, although such a stable stage was not observed for unimplanted Si3N4. The mechanism for the change in mechanical properties of Si3N4 induced by Ti+-implantation will be discussed in relation to XPS characteristics.
Understanding and Controlling Transient Enhanced Dopant Diffusion in Silicon
Authors: Stolk P.A. , Gossmann H.-J. , Eaglesham D.J. , Jacobson D.C. , Luftman H.S. , Poate J.M.
Published: April 2011

Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during initial annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, we have used B doping marker layers in Si to probe the injection of interstitials from near-surface, non-amorphizing Si implants during annealing. The in-diffusion of interstitials is limited by trapping at impurities and has an activation energy of -3.5 eV. Substitutional C is the dominant trapping center with a binding energy of 2-2.5 eV. The high interstitial supersaturation adjacent to the implant damage drives substitutional B into metastable clusters at concentrations below the B solid solubility limit. Transmission electron microscopy shows that the interstitials driving TED are emitted from {311} defect clusters in the damage region at a rate which also exhibits an activation energy of 3.6 eV. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ∼1019/cm3 prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation.
Boron Enhanced Diffusion Due to High Energy Ion-Implantation and Its Suppression by Using RTA Process
Authors: ONO Atsuki , ABIKO Hitoshi , SAKAI Isarai
Published: April 2011

SIMS measurements revealed that high energy boron-implantation causes transient enhanced diffusion (TED) of a shallow dopant profile due to Si interstitials even for a relatively low dose of ∼2E13cm-2. By systematic analysis, it is found that this anomalous diffusion is most significant in 700∼800°C annealing, and it takes place in the initial stage (less than 30sec for 800°C) of annealing. Moreover, this anomalous diffusion is more considerable than the enhanced diffusion during oxidation (OED) in practical device fabrication processes. It is found that rapid thermal annealing (RTA) at 1000-1100°C is effective for suppressing the transient enhanced diffusion and realizing a shallow channel profile for deep sub-micron devices.
Improving Wettability of PoIyMethylMetiiAcrylate by Ar+ ion Irradiation in Oxygen Environment
Authors: Koh Seok-Keun , Choi Won-Kook , Cho Jun-Sik , Song Seok-Kyun , Jung Hyung-Jin
Published: April 2011

Ion irradiation has been carried out to improve wettability of PMMA to water. The polymer was irradiated by argon and oxygen ions, and amount of ions was changed from 1014 ArVcm2 to 5xl016Ar+/cm2. Ions energies were varied from 0.5 keV to 1.5 keV, and oxygen gas was flowed from 0 seem to 6 scan near the polymer surface during ion irradiation. Wetting angle was reduced from 68 degree to 49 degree with increasing Ar+ ion irradiation, to 43 degree with Ch+ ion irradiation, and dropped to 8 degree with Ar+ ion irradiation with flowing 4 seem oxygen gas near the polymer surface. Recovery of wettability in dry air condition, and maintenance of it in dilute HC1 solution were explained in a view of formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and flowing oxygen near the surface. Reactions among polymer matrix, energetic ions and oxygen gas to form hydrophilic group by energetic ions were discussed in terms of a two-step reaction, in which the first step is the creation of an unstable polymer chain by the ion irradiation and the second step is a reaction between the radicals and the oxygen gas.
Trace Contamination Measurements Using Heavy Ion Backscattering Spectrometry
Authors: Knapp J.A. , Banks J.C. , Brice D.K.
Published: April 2011

Heavy Ion Backscattering Spectrometry (HIBS) is a tool for measuring surface contamination at levels much lower than previously achievable with ion beam analyses. Many areas of materials research and development require very low levels of impurities, with advanced microelectronics as the best example. HIBS uses low-energy, heavy ions for analysis, taking advantage of the increased backscattering yield which can be obtained from high Z ion beams at low energy. Background due to increased yield from the substrate is eliminated by a thin carbon foil as part of the detector, with a thickness chosen to range out ions scattered from the substrate and allow only ions scattered from impurities heavier than the substrate to reach the detector. Our research system, using 150-200 keV N+ beams and a single time-of-flight detector optimized for large solid angle, has achieved a sensitivity ranging from ∼5×1010 atoms/cm2 for Fe to ∼1×109 atoms/cm for Au on Si, without preconcentration. A stand-alone HIBS prototype which we have developed for SEMATECH is expected to reach detection limits of -5×10 atoms/cm for Fe and -1×10 atoms/cm for Au on Si. In this paper we discuss in detail the factors which affect sensitivity for HIBS.
Stebic Revisited
Authors: Brown Paul D. , Humphreys Colin J.
Published: April 2011

We re-examine the technique of Scanning Transmission Electron Beam Induced Conductivity and report on the acquisition of remote contact EBIC images at 200keV showing variations in electrical activity within P-doped CdTe.
High Resolution Tem Study of Diamond Formation on Silicon and Molybdenum Field Emitter Surfaces
Authors: Myers A. F. , Liu J. , Choi W. B. , Wojak G. J. , Hren J. J.
Published: April 2011

Diamond is an attractive material for coating microfabricated metal and semiconductor field emitters, since it enhances the stability and emission characteristics of the emitter. In the present study, polycrystalline diamond thin films were grown on silicon and molybdenum field emitters by microwave plasma chemical vapor deposition, using the bias-enhanced nucleation technique. High resolution transmission electron microscopy (TEM) was used to analyze the morphology of the diamond film and the structure of the diamond/emitter interface. Electron diffraction patterns and high resolution images indicate the presence of a polycrystalline diamond film, as well as a polycrystalline SiC layer between the diamond film and the Si emitter. A carbide interlayer was also found to exist between the diamond and the Mo emitter surface. Parallel electron energy loss spectroscopy confirms the TEM identification of a polycrystalline diamond film.
Microstructural evolution during ion beam assisted Deposition
Authors: Hubler Graham K.
Published: April 2011

The advantages of energetic deposition are low temperature processing, oriented or single crystal films, high phase purity, high density and good adhesion to substrates. The time and spatial scales over which the atoms arrange themselves on a surface are not easy accessed experimentally. Therefore, these advantages are customarily verified by ex-situ examination of films after deposition is complete, which gives little information on atomic scale processes that lead to the listed advantages. The addition of energy to the deposition flux effects surface processes that are otherwise only controllable by changing the substrate temperature. Thus, understanding the mechanisms by which energetic atoms alter surface processes in analogy with thermal effects is of paramount interest for optimization of the deposition parameters. This review summarizes the state of knowledge on the effects of energetic ions on film formation. For high quality, defect free films, the energy must be controlled in the energy region of 5 eV to 30 eV. Below about 5 eV, the energy is ineffective for changing the physical processes, and above about 30 eV, defects are added to the film by displacement damage that cannot anneal out due to low temperature of the deposition. Models for the composition and chemistry of films energetically deposited are progressing well, while models for prediction of the phases that form are almost nonexistent. Molecular dynamics provide the best information, but only a handful of cases have been simulated.
Strain Measurements of Sigec Heteroepitaxial Layers On Si(100) Using Ion Beam Analysis
Authors: Sego S. , Culbertson R. J. , Ye P. , Hearne S. , Xiang J. , Herbots N. , Atzmon Z. , Bair A.E.
Published: April 2011

The strain in SiGeC heteroepitaxial films grown on Si(100) substrates has been quantified using ion channeling. The films were grown both by combined ion beam and molecular beam epitaxy (CIMD) and chemical vapor deposition (CVD). Rutherford backscattering spectrometry (RBS) was used to quantify the Ge concentration as well as the film thickness, nuclear resonance elastic ion scattering was used to quantify the carbon concentration, and ion channeling was utilized to measure film quality. Channeling angular scans across an off normal major axis were used to quantify the strain. Part of the film was removed by using a solution of HF, HN03 and CH3COOH in order to obtain a reliable scan in the substrate. The results indicate that C may be compensating for the strain introduced by Ge.
Directional Sputter Deposition for Semiconductor Applications
Authors: Rossnagel S.M.
Published: April 2011

The deposition of metal and compound films from ions rather than neutrals allows a high degree of control over the incident particle's direction and energy. Metal-rich plasmas have been produced using large magnetrons (30 cm dia., 20 kW) and in-flight ionization of the sputtered atoms by means of a dense, inductively coupled rf plasma. This plasma is generated by a multi-turn antenna inside the chamber located between the cathode and the sample. The nature of the deposition, including the ion-to-neutral ratio and the ion energy are controllable. Relative ionization of the metal has been measured at over 80%. Ion energy is controlled by a negative dc sample bias. Metal films of Cu and AlCu have been deposited on 200 mm Si wafers at room temperature into moderate aspect ratio wafer features with no voids. The features used are trenches and vias of width >3500A, and the technique has also been used to fill 2-level, “dual damascene” features. The films are highly (111) oriented and have low stress and low Ar content. The effects of ion direction as well as resputtering of the film topography are readily observed, and are consistent with computer model predictions. High quality TiN films (40 micro-Ohm-cm, gold colored) have also been deposited at room temperature into trenches and vias for applications as diffusion barriers.
Deposition of Diamond-Like Carbon (DLC) With Picosecond Laser Pulses
Authors: Qian F. , Singh R.K. , Dutta S.K. , Pronko P.P.
Published: April 2011

We have deposited unhydrogenated diamond-like carbon (DLC) thin films by laser ablation of graphite, using a high power Ti: Sapphire solid state laser system. DLC films were deposited onto single crystal silicon substrates at room temperature with picosecond laser pulses, at peak power densities in the 5x1011- 8x1012W/cm2range. A variety of techniques, including scanning and transmission electron microscopy (SEM and TEM), Raman spectroscopy, spectroscopic ellipsometry (SE), and electron energy loss spectroscopy (EELS) have been used to analyze the film quality. Smooth, partially transparent films were produced, distinct from the graphite target. Sp3volume fractions were found to be in the 50 - 60% range, with optical bandgaps ranging from 0. 6 to1. 2 eV, depending on the laser power density.
Tem Observation of the Damages in Heavily Ion-Implanted Fine Si Columns
Authors: Shingubara S. , Sukesako H. , Kawasaki T. , Inoue K. , Matusi Y. , Sakaue H. , Takahagi T. , Horiike Y.
Published: April 2011

Si nanometer structures are promising for exhibiting the quantum size effect at temperatures even as high as a room temperature. The present work investigates by TEM the damages induced by a heavy ion-implantation to the fine Si columns, aim of fabrication of 1-D tunneling PN diode in future. Si columns are fabricated by electron beam lithography and reactive ion etching, followed by thinning by thermal oxidation of Si . Ultra fine Si column with a diameter of 8 nm are successfully formed. TEM lattice image observations for fine Si columns, which are subject to ion-implantation and subsequent annealing, are carried out. In the case of heavy doping of As, as well as BF2, as-doped structure is amorphous, and recrystallization is observed after annealing at 1000 °C for 30 min. Typical damages such as dislocations which are parallel to the {111} planes and Si micro-crystals which are differently oriented from the Si single crystal substrate are observed for Si columns with diameters larger than 40nm. However, it should be noted that no damage is observed for fine Si columns with diameters less than 20nm. It is suggested that defects are diffused out to the surface or the Si/SiO2 interface for ultra fine Si columns during annealing.
Characteristics of Excimer-Laser-Crystallized Polysilicon Films by Line Beam Scanning Method
Authors: Min Jhon Young , Hwan Kim Dong , Chu Hong , Woo Lee Chang , Sam Choi Sang
Published: April 2011

Characteristics of polysilicon films, crystallized by excimer laser annealing, have been investigated. The entire amorphous silicon film of 50 mm X 50 mm has been crystallized by scanning a line shape excimer laser beam, which basically reduces the nonuniformity in the beam overlap region of the 2-dimensional scanning method. The laser beam had a Gaussian profile in the scanning direction, which ensured good crystallization by the reversible transitions between the crystalline and amorphous states and was expected to give step annealing effect The laser energy density and substrate temperature were varied.
Flat-Top Polygonal Temperature Profiles by Laser Beams
Authors: Lu Y.F.
Published: April 2011

A method was proposed to generate flat-top polygonal temperature distributions in substrates from a Gaussian-shaped laser source. The original Gaussian beam is equally and diametrically separated into several portions and is then rearranged so that the each portion has its peak intensity allocated toward outside. This can be realized by a symmetrical multi-facet prism. A mathematical model was derived to calculate the temperature rise induced the rearranged portions of the laser beam. Flat-top polygonal temperature profiles with two, three, four and six corners have been investigated by numerical calculations. It is shown that flat-top polygonal temperature distributions can be obtained by this method if the distance between the peaks of the beam portions is arranged to be certain proportions to the original Gaussian beam. It is also found the shape of the temperature profile is almost with the same size as the original Gaussian beam size and does not depend on the incident laser power and the substrate material.
Hydrogen Ion Beam Processing of Single Crystal Diamond Chips
Authors: Kiyohara Shuji , Miyamoto Iwao
Published: April 2011

In order to apply ion beam etching with hydrogen ions to the ultra-precision processing of diamond tools, hydrogen ion beam etching characteristics of single crystal diamond chips with (100) face were investigated. The etching rate of diamond for 500 eV and 1000 eV hydrogen ions increases with the increase of the ion incidence angle, and eventually reaches a maximum at the ion incidence angle of approximately 50°, then may decrease with the increase of the ion incidence angle. The dependence of the etching rate on the ion incidence angle of hydrogen ions is fairly similar to that obtained with argon ions. Furthermore, the surface roughness of diamond chips before and after hydrogen ion beam etching was evaluated using an atomic force microscope. Consequently, the surface roughness after hydrogen ion beam etching decreases with the increase of the ion incidence angle within range of the ion incidence angle of 60°.
Composition and Structure of Zirconium Nitride Films Produced by Ion Assisted Deposition
Authors: Valizadeh R. , Colligon J.S. , Donnelly S.E. , Faunce C.A. , Park D. , Kheyrandish H.
Published: April 2011

The growth mechanism of ZrNx films produced by reactive ion beam sputtering with or without concurrent low energy ion bombardment of argon or nitrogen has been investigated. The effect of substrate temperature in the range of 300-680K, partial pressure of nitrogen and ion/atom arrival rate on the composition and microstructure of the films have been studied. RBS analysis has confirmed that the nitrogen content varies over wide range 0-60 at. %, depending on the nitrogen/zirconium arrival rate, and the ion assist flux but it is independent of the ion assist energy. TEM analysis shows that the films are non-columnar and polycrystalline with grain sizes l-15nm which depend on the nitrogen content and the deposition temperature.
In-Situ Electron Microscopy Studies of The Behavior of Metal Particles on Ceramic Substrates
Authors: Terry R. , Baker K. , Rodriguez Nelly M.
Published: April 2011

This paper is devoted to a discussion of how the information derived from the application of in-situ transmission electron microscopy can be used to gain a unique insight into the manner by which various factors dictate the morphological characteristics of metal particles on a variety of ceramic substrates. In this context, we have used the technique to examine the influence of the strength of the metal-support interaction on the mode of sintering of small particles, and how the chemical nature of the gas environment can induce significant changes in the shapes of the metal particles in a given system. Attention is also focussed on the wetting behavior of metal particles dispersed on graphite when reacted in oxygen and how this aspect impacts on their subsequent mode of catalytic attack.
Effect of Surface Structure on The Adsorption of CO(II) on ∝-Al2O3: A Glancing Angle Xafs Study
Authors: Towle Steven N. , Bargar John R. , Brown Gordon E. , Parks George A. , Barbee Troy W.
Published: April 2011

Glancing-angle x-ray absorption fine structure (XAFS) spectroscopy has been used to characterize the structure of Co(II) complexes adsorbed from aqueous solution on single crystal ∝-Al2O3 surfaces. The spectra reveal considerable differences in the local structure, as a function of both the crystallographic face and the orientation of the sample with respect to the beam polarization. Data analysis indicates that the predominant mode of Co chemisorption is as a tridentate CoO6 octahedral complex edge-shared with surface Al octahedra. For systems where this method is feasible, it is the technique of choice for characterizing metal ion adsorption complexes.
Electron Microscopy Studies and Image Simulation of the YBa2Cu3O7−x/ BaF2 Interface
Authors: Lee J. L. , Silcox J.
Published: April 2011

Images of the YBa2Cu3OT7−x (YBCO) / BaF2 interface obtained with a scanning transmission electron microscope (STEM) show a relatively wide (∼40 Å) band of contrast at the interface, despite attempts to orient the interface plane parallel to the beam. Simulation of STEM annular dark field (ADF) images of several different interface geometries suggests that strain is the dominant cause of this wide band of contrast at the interface. In particular, it is the dislocations which run normal to the beam direction which make a significant contribution to the width of the contrast band in the case of this YBCO / BaF2 interface. A line scan taken across the interface using energy dispersive X-ray spectrometry (EDX) suggests that there is no significant Ba concentration at the interface, indicating that Z-contrast is not the primary contrast mechanism in these ADF images of the YBCO / BaF2 interface.
Influence of Internal Interfaces on the Dielectric Properties of Ceramic Microwave Resonators
Authors: Davies Peter K.
Published: April 2011

The structures of all the prominent ceramic dielectric resonators have been found to exhibit extensive inhomogeneity. This structural disorder arises from the formation of extended defects, polytype intergrowths or variable degrees of cation order. For the systems involving a cation order-disorder reaction, e.g. ZrTiO4 and Ba(Zn1/3Ta2/3)O3, the formation of internal interfaces can have a pronounced effect on the dielectric properties. In the absence of secondary dopants the lattice strains associated with the interfaces increase the dielectric losses by as much as two orders of magnitude. However, the contributions of the interfaces can apparently be controlled, and perhaps eliminated, by introducing selected dopants that segregate and stabilize the local boundary regions.
Direct Correlation of Transport Properties and Microstructure In Y1Ba2Cu3O7-x Thin Film Grain Boundaries
Authors: Vuchic B. V. , Merkle K. L. , Buchholz D. B. , Chang R. P. H. , Marks L. D.
Published: April 2011

Individual 45° [001] tilt grain boundaries in Y1Ba2Cu3O7-x thin films grown on biepitaxial substrates were studied. The thin films were grown using both pulsed organometallic beam epitaxy (POMBE) and laser ablation. Transport characteristics of the individual grain boundaries were measured including resistance - temperature (R-T) and current - voltage (I-V) dependencies with and without an applied magnetic field. In order to elucidate possible structural origins of the differences in transport behavior, the same grain boundaries which were electrically characterized were subsequently thinned for electron-microscopy analysis. Transmission-electron-microscopy and high-resolution-electron-microscopy were used to structurally characterize the grain boundaries. The macroscopic and microscopic structures of two boundaries, a nominally resistive and a superconducting grain boundary, are compared.
First Principles Calculations for Metal/Ceramic Interfaces
Authors: Finnis M. W. , Kruse C. , SchÖnberger U.
Published: April 2011

We discuss the recent first principles calculations of the properties of interfaces between metals and oxides. This type of calculation is parameter-free, and exploits the density functional theory in the local density approximation to obtain the electronic structure of the system. At the same time the equilibrium atomic structure is sought, which minimises the excess energy of the interface. Up to now calculations of this type have been made for a few model interfaces which are atomically coherent, that is with commensurate lattices. Examples are Ag/MgO and Nb/Al2O3. In these cases it has been possible to predict the structures observed by high resolution electron microscopy. The calculations are actually made in a supercell geometry, in which there are alternating nanolayers of metal and ceramic. Because of the effectiveness of metallic screening in particular, the interfaces between the nanolayers do not interfere much with each other.

Besides the electronic structure of the interface, such calculations have provided values of the ideal work of adhesion. Electrostatic image forces in conjunction with the elementary ionic model provide a simple framework for understanding the results.

An important role of such calculations is to develop intuition about the nature of the bonding, including the effects of charge transfer, which has formerly only been described in an empirical way. It may then be possible to build atomistic models of the metal/ceramic interaction which have a sound physical basis and can be calibrated against ab initio results. Simpler models are necessary if larger systems, including misfit dislocations and other defects, are to be simulated, with a view to understanding the atomic processes of growth and failure. Another area in which ab initio calculations can be expected to contribute is in the chemistry of impurity segregation and its effect at interfaces. Such theoretical tools are a natural partner to the experimental technique of high resolution electron energy loss spectroscopy for studying the local chemical environment at an interface.
Simulation of Segregation to Interfaces in Metal-Oxides
Authors: Battaile C. , Najafabadi R. , Srolovitz D.J.
Published: April 2011

Segregation of isovalent cation impurities to (001) and (011) free surfaces in (Co0.3Ni0.7)O and (Fe0.12Mn0.88)O was investigated using atomistic computer simulations. Impurity concentrations were represented by a mean-field approximation, and equilibrium distributions of impurities were calculated by minimization of the free energy. Surface energy effects were found to dominate segregation behavior, even when in competition with misfit strain energy effects. These Free Energy method predictions compared well with more accurate Monte Carlo simulations, suggesting that the mean-field representation of impurity concentration is satisfactory for this application.
High Resolution Transmission Electron Microscopy of Metallic Film/Laser-Irradiated Alumina Couples.
Authors: Pedraza A. J. , Cao Siqi , Allard L. F. , Lowndes D. H.
Published: April 2011

A near-surface thin layer is melted when single crystal alumina (sapphire) is pulsed laserirradiated in an Ar-4%H2 atmosphere. γ-alumina grows epitaxially from the (0001) face of axalumina (sapphire) during the rapid solidification of this layer that occurs once the laser pulse is over. Cross sectional high resolution transmission electron microscopy (HRTEM) reveals that the interface between unmelted sapphire and γ-alumina is atomistically flat with steps of one to a few close-packed oxygen layers; however, pronounced lattice distortions exist in the resolidified γ-alumina. HRTEM also is used to study the metal-ceramic interface of a copper film deposited on a laser-irradiated alumina substrate. The observed changes of the interfacial structure relative to that of unexposed substrates are correlated with the strong enhancement of film-substrate bonding promoted by laser irradiation. HRTEM shows that a thin amorphous film is produced after irradiation of 99.6% polycrystalline alumina. Formation of a diffuse interface and atomic rearrangements that can take place in metastable phases contribute to enhance the bonding strength of copper to laser-irradiated alumina.
Characterization of the Thin Oxide-Nitride-Oxide (ONO) Structure Using Spectroscopic Ellipsometry
Authors: Asinovsky Leo M. , Zierer Steve
Published: April 2011

Spectroscopic ellipsometry has been used to characterize thin oxide/nitride/oxide (ONO) layer structures. Films were deposited on top of the Si/oxide/polysilicon filmstack using a low-pressure chemical vapor deposition (LPCVD) technique. Different approaches to modeling this structure are compared to select an adequate representation. Analysis of the data for the three-layer-with-abrupt-interfaces ONO model using an effective-medium or Cauchy approximation shows strong correlation of the parameters and ambiguity of the results. A more robust and physically plausible model of the ONO structure as an inhomogeneous oxynitride film with Gaussian distribution of the silicon nitride component is suggested. This interpretation of the ONO structure is supported by the results of Auger electron spectroscopy (AES) and transmission electron microscopy (XTEM).
Use of Quantum-Well Superlattices to Increase the Thermoelectric Figure of Merit: Transport and Optical Studies
Authors: Hicks L. D. , Bi X. X. , Dresselhaus M. S.
Published: April 2011

The thermoelectric figure of merit (ZT) of a material is a measure the usefulness of the material in a thermoelectric device. Presently, the materials with the highest ZT are Bi2Te3 alloys, with ZT ≃ 1. There has been little improvement in ZT for over 30 years. So far, all the materials used in thermoelectric applications have been in bulk form. Recently, however, calculations have shown that it may be possible to increase ZT of some materials through the use of quantum-well superlattices. We have made preliminary measurements on the Bi/PbTe superlattice system using transport and optical techniques to determine whether it is possible to achieve such an increase in ZT.
A New Method for Preparing Ge Nano-Crystallites Embedded in SiNY Matrices
Authors: Chen Kunji , Qu Xuexuan , Huang Xinfan , Li Zhifeng , Feng Duan
Published: April 2011

We report a new method for synthesizing Ge nano-crystallites embedded in SiNy film matrices. On the basis of the effect of the reactant precursors and preferential chemical bonding of Si-N and Ge-Ge, thin films with Ge clusters embedded in SiNy matrices have been prepared in the PECVD system with reactant gases of SiH4, GeH4 and NH3 mixed in the hydrogen plasma. The as-deposited films were then crystallized by Ar ion laser annealing or thermal annealing technique to form nanometer-sized Ge crystallites.

The composition and microstructures of these new type of sample were characterized by infrared absorption spectra, transmission electron microscopy, X-ray diffraction and Raman scattering spectra. The results indicated that the average size of Ge crystallites was estimated to be 2-20 nm depending on the deposition and annealing parameters and can be controlled by a designed manner.
Synthesis, Structural Characterization, and Optical Spectroscopy of Close Packed CdSE Nanocrystallites
Authors: Kagan C. R. , Murray C. B. , Bawendi M. G.
Published: April 2011

We describe a method to synthesize optical quality thin and thick films of close packed CdSe nanocrystallites (quantum dots). The average dot size is tunable from ∼12-150 Å in diameter with ∼3.5% rms size distribution. The identity of each particle and the high monodispersity of the sample are maintained in the films as revealed by small-angle x-ray scattering, transmission electron microscopy, and optical spectroscopy. We use small-angle x-ray diffraction patterns to obtain form factors for the individual dots and to generate radial distribution functions for the densely packed films. We observe the random close packing of dots in the solid state using transmission electron microscopy. Comparing optical spectra of particles close packed in a film with those of nanocrystallites dispersed in alkanes reveals similar optical resonances in absorption while the emission lineshape is modified and its position is red shifted. Differences in film emission are consistent with electronic energy transfer between close packed dots within the inhomogeneous distribution of the sample.
Resonant Raman Scattering in CdSxSe1−x Nanocrystals: Electron-Phonon Coupling
Authors: Silvestri M. , Hwang L.W. , Persans P. , Schroeder J.
Published: April 2011

We report pressure and laser tuned Raman scattering studies on CdSxSei1-x nanocrystals. The electron-phonon coupling strength was determined as a function of pressure beyond the bulk phase transition pressure point. The coupling strength at atmospheric pressure determined from the Stokes shifted photoluminescence and resonant Raman scattering is not drastically smaller than the bulk value as might be expected theoretically. As a function of pressure it also shows no abrupt changes at the bulk phase transition pressure point. These results indicate that deep traps play a critical part in the mechanism of the electron-phonon coupling.