bluuebunny/crossref_metadata_2025 huggingface dataset:
Canted Magnetic Moments at the Gd (0001) Surface
Authors: Li Dongqi , Zhang Jiandi , Dowben P. A. , Garrison K. , Johnson P. D. , Tang H. , Walker T.G. , Hopster H. , Scott J.C. , Weiler D. , Pappas D. P.
Published: September 2012

With spin polarized electron spectroscopies, we have investigated ordered Gd (0001) films deposited on W (110). The photoemission features of the gadolinium 5d surface state, the 4f levels, and the background exhibit considerable spin polarization along the same direction in the plane of the film, indicative of ferromagnetic coupling between the surface and the bulk. The 4f spin polarized photoemission data provides strong evidence that the surface 4f polarization differs from the bulk 4f polarization for Gd (000l). Our temperature dependent measurements with spin polarized secondary electron spectroscopy conclusively establishes that the surface of clean Gd (0001) possesses a perpendicular polarization component which persists to an enhanced surface Curie temperature. SMall amounts of contamination at the surface result in the disappearance of the perpendicular component and, therefore, a more perfect ferromagnetic coupling between the surface and the bulk.
In-Situ Magneto-Optical Kerr Effect of Epitaxial GD (0001)
Authors: Chappert C. , Weiler D. , Tang H. , Scott J.C. , Hopster H. , Pappas D.P.
Published: September 2012

We have characterized magnetization loops of epitaxially grown Gd (0001) films on W (110) in the temperature range 145≤T≤300K. This was accomplished by measuring magneto-optical Kerr loops in UHV, in the transverse geometry, using a 2×10-4 deg sensitivity differential detector and He-Ne laser light.

Films grown in the Stranski-Krastanov (SK) Mode (growth temperature 400°C) and films grown in a Frank-van-der-Merwe (FM) like Mode (growth temperature 20°C) behave significantly differently. While the room temperature grown films (FM) show square hysteresis behavior only after an annealing cycle to at least 300°C, the higher growth temperature (SK) leads to highly remanent films in the as grown state.

The hysteresis behavior of these films is most important in conjunction with recently reported spin-polarized photoemission results, which showed that the growth temperature and therefore the film morphology has a strong influence on the surface magnetic reconstruction of Gd (0001) [1].
Growth, Structure and magnetism of Cobalt-Platinum Ultrathin Films and Sandwiches
Authors: Deville J.P. , Barbier A. , Boeglin C. , Carriere B.
Published: September 2012

Cobalt-platinum alloys and multilayers are now well known for their potentialities in Magneto-optical recording Media. The growth of ultrathin layers and sandwiches is thought to be useful to find the relationship between the structural and magnetic properties at an atomic level. Low Energy Electron Diffraction (LEED) and Auger spectroscopy (AES) are used here to study the crystallography and the growth modes of Pt on Co (0001) surfaces. Co/Pt/Co sandwiches are also built and investigated by the same Methods. At room temperature we show the evidence of a good epitaxy of platinum on the Co (0001) surface leading to the possibility of obtaining ordered Co/Pt/Co sandwiches. Annealings at moderate temperatures lead to an epitaxial alloy formation. Auger results show that alloying indeed induces a magnetic moment on platinum atoms. This could explain the magnetic properties already observed in CO/Pt (111) Multilayers.
Spin Polarized Electron Spectroscopies of 3d and 4f Systems
Authors: Hopster H.
Published: September 2012

Recent results from spin polarized electron spectroscopie studies of surfaces and ultrathin films are presented. The Magnetic coupling of 3d transition Metals (Cr,Mn) to the Fe (100) surface is studied by spin polarized electron energy loss spectroscopy. The first atomic layer of Cr and mn aligns antiparallel to the Fe. For larger thicknesses we find evidence for layer-by-layer antiferromagnetic order. In the range of 1–6 atomic layers the behavior is more complex with the surface of the Cr films showing preferential ferromagnetic alignment while the mn surface aligns antiparallel to the Fe substrate.

Secondary electrons from Gd (0001) surfaces are shown to be highly spin polarized. However, no enhancement mechanism at low kinetic energy as in the 3d transition metals is observed indicating the absence of strongly spin dependent inelastic scattering in Gd. Temperature dependent spin polarized 4f photoemis-sion results show almost complete polarization demonstrating ferromagnetic surface coupling. However, a perpendicular surface magnetization component is found indicating surface spin canting. A large enhancement of the surface Curie temperature is also present.
Calculations of Bulk and Surface Magnetic Polaritons in Modulated Antiferromagnetic / Non-Magnetic Superlattices
Authors: Lacy Fred , Carter Ernest L. , Richardson Steven L.
Published: September 2012

Recent advances in molecular beam epitaxy have renewed research on the physics of artificially structured magnetic superlattices. In particular, there has been much theoretical research on the propagation of magnetic spin waves or magnetic polaritons in magnetic superlattices.1 In this work, we have studied the effect of modulating both the period of an antiferromagnetic/non-Magnetic semi-infinite superlattice and the relative thickness of its individual layers to see how the dispersion relationships co (k) for bulk and surface magnetic polaritons are effected. We have also calculated the effect of an external magnetic field on (u (k) and our calculation goes beyond the magnetostatic approximation by taking retardation effects into account.
Electrical and Optical Properties of Co Alloyed β-FeSi2 Formed by Ion Beam Synthesis
Authors: Panknin D. , Henrion W. , Wieser E. , Voelskow M. , Skorupa W. , Völise H.
Published: September 2012

By subsequent implantation of iron and cobalt into silicon buried layers of semiconductinβ-(Fe1−xCox)Si2 are formed. The band gap energy as well as the spreading resistance decrease with increasing cobalt content. The microstructure of the sulicide layers is characterized by XTFM images.
On the Interface Structure of Buried CoSi2/Si(001) Layers and their Respective Schottky Barrier Heights
Authors: Wemer P. , Jäger W. , Schüppen A.
Published: September 2012

This paper describes a high-resolution transmission electron microscope (HRTEM) study of the morphology and the atomic structure of CoSi2/Si(001) interfaces of continuous buried sulicide layers. These layers were produced by high-dose Co+ ion implantation and subsequent rapid thermal annealing. Planar interface regions of high perfection with domains of different atomic interface structure, and interface steps, frequently with I 111)I facets, were observed. There were significant differences in the interface structure between the upper and lower interfaces. Measuring Schottky barrier heights (SBH's) revealed different values for the upper (0.67eV) and lower (0.78eV) CoSi2/n-Si(001) interfaces. Possible correlations between the atomic interface structures and the resulting electronic properties are discussed.
Growth of Buried CoSi2 Layers in Si(100) by Molecular Beam Allotaxy
Authors: Mantl S. , Bay H.L. , Michel I. , Mesters S. , Trinkaus H.
Published: September 2012

Buried single crystalline CoSi2 layers in Si(100) have been grown using molecular beam allotaxy. In this paper, we investigated the diffusive interaction of two buried silicide precipitate layers, one with a small Co peak concentration of 10 at% and another one with 26 at%. Annealing causes first local coarsening in each layer, and then dissolution of the thinner precipitate layer. The accumulation of the Co atoms at the thicker layer is described by a simple model for the diffusional redistribution.
Fractals in Porous Media: From Pore to Field Scale
Authors: Sahimi Muhammad , Rassamdana Hossein , Mehrabi Alireza
Published: September 2012

Two applications of fractal concepts to problems involving porous media are discussed. One of them occurs at the pore level and involves the formation of large molecular aggregates as the result of injecting a fluid into an oil reservoir, or because of compositional changes in the oil. Formation of such aggregates and their precipitation on the pore surfaces cause severe problems for enhanced recovery of oil, and also many processes which use porous catalysts. We argue that these molecular structures are similar to diffusion-limited cluster-cluster aggregates, and small-angle neutron scattering data support our argument. The second application involves field-scale distributions of the porosity and permeability of oil reservoirs. We show that, contrary to the recent assertions that such distributions are described by fractional Brownian motion or fractional Gaussian noise with positive correlations (persistence), they are described by Lévy distributions withnegativecorrelations (anti-persistence).
Slow Relaxation in Polymeric Glasses by Two-Dimensional NMR
Authors: Jones Alan A. , Inglefield P. T. , Chin Y. H. , Zhang C.
Published: September 2012

A variety of relaxation and recovery experiments on polymeric glasses indicate a complex response in either the time or frequency domain1. The behavior is far from that seen in simple liquids where relaxation can be characterized in terms of exponential decay and a single time constant or rate. A variety of more complicated mathematical functions have been employed in an attempt to match the observed relaxation behavior of polymeric glassesl. One of the more successful mathematical forms is the stretched exponential correlation2 function which can be used to characterize experimental observations obtained from mechanical, dielectric, thermodynamic and spectroscopic investigations3.
Two-Length-Scale Structure in Some Computer-Generated Aggregates Grown by Diffusion-Limited Aggregation
Authors: Schmidt Paul W. , Pipitone Giuseppe , Floriano M. A. , Caponetri E. , Triolo R.
Published: September 2012

The properties of some aggregates “grown” on a computer by diffusion-limited aggregation have been investigated. Calculations showed that the intensity of the small-angle x-ray and neutron scattering from the aggregates was proportional to q−D for qL ≫ 1, where D > 0, L is a length that characterizes the large-scale structure of the aggregate, q = 4πλ−1 sin(θ/2), γ is the wavelength, and θ is the scattering angle. The magnitude of the exponent D was appreciably smaller than the fractal dimensions that many simulations have shown to be typical of the mass fractal aggregates grown by diffusion-limited aggregation. The calculations suggest that the aggregates have structure on two different characteristic-length scales.
A Theory for Growing Interfaces in Laplacian Fields: A Many-Body Formulation and Statistical Analysis
Authors: Blumenfeld Raphael
Published: September 2012

I formulate a theory for the growth of an interface in a Laplacian field. The problem is mapped to a many-body system and the process is shown to be Hamiltonian. The corresponding set of dynamical equations is analysed and surface effects are introduced as a term in the Hamiltonian that gives rise to a repulsion between the quasi-particles and the interface. The theory accommodates anisotropic surface effects. The underlying Hamiltonian allows a statistical-mechanical analysis of the limit distribution of the quasi-particles. Noise can be naturally incorporated in this formalism. Finally the distribution of the particles is translated into the statistics of the interface, which leads to predictions on the morphology. The main thrust of this approach is in finding a statistical mechanical approach to this nonequilibrium process.
From Facets to Fractals - Growth Morphologies in Molecular Crystals of Carbon Tetrabromide (Cbr4) and Fullerene C60
Authors: Xiao Rong-Fu
Published: September 2012

We have experimentally studied the growth morphologies of carbon tetrabromide CBr4 and fullerene C60crystals in their orientationally disordered solid phases. Very rich growth morphologies have been observed from these crystals, ranging from facets to dendrites and to fractals. In the vapor growth of CBr4crystals, we found that the growth morphologies depend not only on temperature and supersaturation, but also sensitively on the total pressure of the inert gas in the growth chamber. With increasing total pressure, under otherwise the same growth conditions, crystals with initially smooth surfaces evolve into dendritic structures. For fullerene C60, the growth morphologies from solution are mainly fractals with strong anisotropy in the individual crystals. The growth morphologies from vapor are normally faceted and the growth proceeds via a layer-by-layer mode.
Reail Space Renormalization Group for Self Organized Criticality in Sandpile Models
Authors: Zapperi S. , Vespignanit A. , Pietronero L.
Published: September 2012

We have introduced a new renormalization group approach that allows us to describe the critical stationary state of sandpile models (Phys. Rev. Lett. 72, 1690 (1994)). We define a characterization of the phase space in order to study the evolution of the dynamics under a change of scale. We obtain a non trivial actractive fixed point for the parameters of the model that clarifys the self organized critical nature of these models. We are able to compute the values of the critical exponents and the results are in good agreement with computer simulations. The method can be naturally extended to several other problems with non equilibrium stationary state.
Ion Beam Modification of Cluster-Covered Silicon Surfaces
Authors: Gulko O. V. , Zinke-Allmang M. T.
Published: September 2012

Clusters of independently tailored areal density and size distribution were grown on semiconductor surfaces in ultra-high vacuum and used as masks for selective ion beam modification. First studies were undertaken to characterize the vertical interface between areas exposed to low energy ion beams and areas covered by clusters (crystalline silicon). Selective etching was employed to create a patterned surface as a substrate for heteroepitaxial growth of thick Ge layers to test defect density reduction due to finite size growth areas. The quality of the overlayers is discussed.
Formation and Characteristics of CoSi2 Layers Synthesized by Mevva Implantation
Authors: Wong S. P. , Peng Qicai , Cheung W. Y. , Guo W. S. , Xu J. B. , Wilson I. H. , Hark S. K. , Morton R. , Lau S. S.
Published: September 2012

Ion beam synthesis of CoSi2 layers in Si by MEVVA (Metal Vapor Vacuum Arc) implantation has been performed under various conditions. The formation and characteristics of these CoSi2 layers have been studied by XTEM, RBS, AFM, X-ray diffraction, ellipsometry, electrical and Hall effect measurements. It was found that a higher substrate temperature during implantation results in an as-implanted Co distribution closer to the surface and hence the formation of a shallower CoSi2 layer after annealing. Buried CoSi2 layers of good crystal quality and low resistivity CoSi2 can be formed by MEVVA implantation and annealing under appropriate conditions. A strong temperature dependence of the Hall coefficient showing a large peak at around 100K was observed for the CoSi2 layers formed in p-type Si substrates but not in n-type substrates. The properties and their dependence on the processing conditions, in particular, the substrate temperature during implantation, are presented and discussed.
Plasma Doping and Plasma-Less Doping of Semiconductor
Authors: Mizuno Bunji , Takase Michihiko , Nakayama Ichiro , Ogura Mototsugu
Published: September 2012

New doping processes which can alternate the ion implantation to achieve the ultra shallow junction are reviewed. Mainly two ways have been proposed. One uses plasma and the other uses vapor phase reaction. 0.17μm Surface Channel (SC) - PMOSFET's have been successfully fabricated by especially plasma doping method.
Range and Damage Distribution in Cluster Ion Implantation
Authors: Yamada I. , Matsuo J. , Jones E. C. , Takeuchi D. , Aoki T. , Goto K. , Sugii T.
Published: September 2012

Cluster ion implantation is an attractive alternative to conventional ion implantation, particularly for shallow junction formation. It is easy to obtain high-current ion beams with low equivalent energy using cluster ion beams. The implanted boron distribution in 5keV B10H14 implanted Si is markedly shallower than that in 5keV BF2 ion implanted Si. The implanted depth is less than 0.04 μm, indicating that cluster ion implantation is capable of forming shallow junctions. The sheet resistance of 3keV B10H14 implanted samples falls below 500 Ω/sq after annealing at 1000°C for 10s. Shallow implantation can be realized by a high energy cluster beam without space-charge problems in the incident beam. Defect formation, resulting from local energy deposition and multiple collisions, is unique for cluster ions. The thickness of the damaged layer formed by cluster ion bombardment increases with the size of the cluster, if implant energy and ion dose remain constant. This is one of the nonlinear “cluster effects,” which may allow some control over the implant damage distributions that accompany implanted ions, and which have been shown to have a great effect on dopant redistribution during annealing
Electrical Resistivity of Copper Films by Partially Ionized Beam Deposition
Authors: Han S. , Yoon K. H. , Kim K. H. , Jang H. G. , Choi S. C. , Jung H. J. , Koh S. K.
Published: September 2012

Copper films on Si(100) were prepared by partially ionized beam at 0 kV and 3 kV acceleration voltages in order to investigate effects of ion energy on electrical property with thickness. X-ray diffraction(XRD) pattern analysis was used to investigate crystallinity of the copper films, microstructure by Scanning electron microscope(SEM) and surface roughness by atomic force microscopy(AFM). The crystallinity of the copper films grown at the 3 kV was more (111) textured than that at the 0 kW. The copper films grown at the both condiitions had nearly same grain size below a thickness of 1000 Å. The 1800 Å Cu film grown at the 3 kV was 3 times rough than that at the 0 kV. The resistivity of copper films increased due to surface and grain boundary scattering, and the change of resistivity was discussed in terms of surface roughness, grain size and film density assisted by average depositing energy.
Charge State Defect Engineering of Silicon During Ion Implantation
Authors: Brown R. A. , Ravi J. , Erokhin Y. , Rozgonyi G. A. , White C. W.
Published: September 2012

The effects of in situ interventions which alter defect interactions during implantation, and thereby affect the final damage state, have been investigated. Specifically, we examined the effects of internal electric fields and charge carrier injection on damage accumulation in silicon. In the first part of this work, we implanted H or He ions into diode structures which were either reverse or forward biased during implantation. In the second part, we implanted B or Si ions into plain silicon wafers whilst illuminating them with UV light. In each case, the overall effect is one of damage reduction. Both the electric field and charge carrier injection effects may be understood as resulting from changes in defect interactions caused in part by changes to the charge state of defects formed during implantation.
Modeling of Extended Defects in Silicon
Authors: Law M. E. , Jones K. S. , Earles S. K. , Lilak A. D. , Xu J-W.
Published: September 2012

Transient Enhanced Diffusion (TED) is one of the biggest modeling challenges present in predicting scaled technologies. Damage from implantation of dopant ions changes the diffusivities of the dopants and precipitates to form complex extended defects. Developing a quantitative model for the extended defect behavior during short time, low temperature anneals is a key to explaining TED. This paper reviews some of the modeling developments over the last several years, and discusses some of the challenges that remain to be addressed. Two examples of models compared to experimental work are presented and discussed.
He Implanted Channel Waveguides of New Design for Efficient Blue Laser Light Generation
Authors: Beckers L. , Bauer St. , Buchal Ch. , Fluck D. , Pliska T. , Günter P.
Published: September 2012

We present a new mask design and implantation scheme, which uses one single ion implantation step of 2 MeV He ions at a dose of 7–1014 to 3–1015 He/cm2 to form channel waveguides in single crystalline KNbO3. The special processing of the photoresist mask enables the formation of channel waveguides with a trapezoidal-shaped cross section, providing for the first time simultaneous confinement of both TE and TM modes in a permanent KNbO3 channel waveguide. 2.6 mW second-harmonic blue light at 441 nm was generated in a 5.8 mm long guide for a fundamental power of approx. 200 mW.
Identification of Hydrophilic Group Formation on Polymer Surface During Ar+ Ion Irradiation in O2 Environment
Authors: Cho Jun-Sik , Choi Won-Kook , Kim Sung-Ryong , Jung Hyung-Jin , Koh Seok-Keun
Published: September 2012

Ar+ ion irradiation on low density polyethylene (LDPE), and polystyrene (PS) was performed in an O2 environment in order to improve wettability of polymers to water and to identify the formation of hydrophilic groups originated from chemical reactions on the surface of polymers. Doses of a broad Ar+ ion beam of 1 keV energy were changed from 5 × 1015 to 1 × 1017 /cm2 and the rate of the oxygen gas flowing near the sample surface was varied from 0 to 7 mi/min. The contact angle of polymers was not reduced much by Ar+ ion irradiation without oxygen gas. However, it dropped largely to a minimum of 35 ° and 26 ° for At+ ion irradiation in the presence of flowing oxygen gas on LDPE and PS, respectively. From x-ray photoelectron spectroscopy analysis, it was observed that hydrophilic groups were formed on the surface of polymers through an ion-assisted chemical reaction between the ion-induced unstable chains and oxygen. The newly formed hydrophilic group was identified as -(C=O)- bond and -(C=O)-O- bond. The contact angle of polymer was greatly dependent on the hydrophilic group formed on the surface.
Plasma and Ion Beam Tools for Enhanced Battery Electrode Performance
Authors: Anders A. , Kong F. , Chen Y. , Monteiro O. R. , McLarnon F. R. , Brown I. G.
Published: September 2012

Plasma and ion beam methods such as gas and metal ion implantation, plasma immersion ion implantation (PIII), and metal plasma immersion ion implantation and deposition (MePIIID) are introduced as powerful tools to modify the properties of battery electrodes. Three kinds of rechargeable electrochemical cells have been investigated: the lead-acid cell, the nickel alkaline-electrolyte cell, and the lithium cell. It was experimentally shown that (i) metal ion implantation of Ti, V, Cr, Ni, and W into lead and lead-antimony electrodes reduced the corrosion current by more than one order of magnitude, (ii) cobalt ion implantation into nickel electrodes enhanced the interconversion of Ni(OH)2 to NiOOH and the associated cycle life, (iii) nitrogen-PIII resulted in the formation of a nitrided lithium layer on lithium which stabilized the surface against corrosion, (iv) MePIIID with a tungsten plasma reduced the pitting corrosion of aluminum, a current collector for a lithium battery.
Carbon Nitride Films Formed using Sputtering and Negative Carbon Ion Sources
Authors: Murzin I. H. , Tompa G. S. , Wei J. , Muratov V. , Fischer T. E. , Yakovlev V.
Published: September 2012

We report the results of using sputtering and negative carbon ion sources to prepare thin films of carbon nitride. In this work, we compare the structural, tribological, and optical properties of the carbon nitride films that were prepared by two different ion assisted techniques. In the first approach we used a magnetron gun to sputter deposit carbon in a nitrogen atmosphere. The second method utilized a beam of negatively charged carbon ions of 1 to 5 μA/cm2 current density impinging the substrate simultaneously with a positive nitrogen ion beam produced by a Kaufman source. We were able to synthesize microscopically smooth coatings with the carbon to nitrogen ratio of 1 : 0.47. These films possess wear rates lower than 5×10−7 mm3/Nm and friction coefficients in the range of 0.16 to 0.6. Raman spectroscopy revealed that the magnetron sputtered films are more structurally disordered than those formed with the negative carbon ion gun. FTIR showed the presence of the C≡N stretching mode in both types of films. Finally, spectroscopic ellipsometry produced films with dielectric constants as low as 2.3 in the photon energy range from 1.2 to 5 eV.
Dose Rate Effects During Damage Accumulation in Silicon
Authors: Caturla M.-J. , Rubia T. Diaz de la
Published: September 2012

We combine molecular dynamics and Monte Carlo simulations to study damage accumulation and dose rate effects during irradiation of Silicon. We obtain the initial stage of the damage produced by heavy and light ions using classical molecular dynamics simulations. While heavy ions like As or Pt induce amorphization by single ion impact, light ions like B only produce point defects or small clusters of defects. The amorphous pockets generated by heavy ions are stable below room temperature and recrystallize at temperatures below the threshold for recrystallization of a planar amorphous-crystalline interface. The damage accumulation during light ion irradiation is simulated using a Monte Carlo model for defect diffusion. In this approach, we study the damage in the lattice as a function of dose and dose rate. A strong reduction in the total number of defects left in the lattice is observed for lower dose rates.
HRLEED and STM Study of Misoriented Si (100) with and without a Te Overlayer
Authors: Yala Salima , Montano Pedro A.
Published: September 2012

The growth of high quality Te on misoriented Si(100) is important as an intermediate phase for epitaxial growth of CdTe. The misorientation angle plays a key role in the growth quality of CdTe/Si(100); this incited our curiosity to investigate the effect of the misorientation angle on the topography of the surface structure of Si(100). Our main goal is to show the relation between the misorientation angle, the terrace width and the step height distributions. HRLEED ( High Resolution Low Energy Electron Diffraction ) provides information in reciprocal space while STM gives real space topographic images of the surface structure. STM and HRLEED measurements were performed on Si(100) with misorientation angle υ= 0.5°, 1.5° and 8° towards the ]110] direction and υ= 4° towards the ]130] direction. Except for the 8° misorientation in which case a regular step array with diatomic step height was observed, for the other misorientations the terrace width was variable. The average terrace width decreased with increasing misorientation angle. A mixture of diatomic and monatomic step heights was observed on the 0.5° and 1.5° misoriented Si(100) samples. It proves that one can not assume purely monatomic step height for low misorientation angles. Our results do not agree with the belief that at low miscut angle A and B terraces are equal and that as the misorientation angle increases the B terrace tends to be wider than the A terrace. In fact, pairing of terraces was not observed at all. Te was deposited at a substrate temperature of 200 C. We observed a significant reduction in the terrace widths for all miscut angles.
Microstructural Studies of Co Silicide Layers Formed on SiGe and SiGeC
Authors: Jin S. , Bender H. , Donaton R.A. , Maex K. , Vantomme A. , Langouche G. , Amour A.St. , Sturm J.C.
Published: September 2012

Transmission electron microscopy is used to investigate the structural development as a function of the annealing temperature of Co-silicides prepared on SiGe and SiGeC. The transition temperature from Co(SiGe) into Co(SiGe)2 is higher for SiGeC than for SiGe.
Monitoring of Dopant Activation in Sub-Surface P-Type Si Using the Surface Charge Profiling (SCP) Method
Authors: Roman P. , Staffa J. , Fakhouri S. , Ruzyllo J. , Kamieniecki E.
Published: September 2012

In this study the SCP (Surface Charge Profiling) method, based on non-contact, small-signal ac-SPV measurement is used to study thermal activation of boron in the near surface region of p-type Si wafers. Boron tends to form pairs with impurities such as hydrogen, iron and copper in the near surface region of Si substrates which render it inactive. During device processing, activation of boron may take place resulting in uncontrolled variations in active boron concentration in the near surface region.

In this work, both boron doped, polished CZ wafers and wafers with boron doped epitaxial layers are studied. In the former case, the concentration of active boron in the near surface region was initially up to an order of magnitude less than the bulk concentration determined from four-probe measurements, but increased with the temperature of an anneal in ambient air and approached the bulk value. In contrast, the wafers with epitaxial layers showed no consistent variations of surface dopant concentration with temperature. These results confirmed previous findings that the near surface region of the polished wafers is contaminated with metals introduced during polishing operations. The SCP method was found to be very effective in monitoring variations in active boron concentration in the near-surface region.
Box Model of Radionuclide Dispersion and Radiation Risk
Estimation for Population in Case of Radioactivity Release from Nuclear
Submarine #601 Dumped in the Kara Sea
Authors: Yefimov E. I. , Pankratov D. V. , Ignatiev S. V.
Published: September 2012

A relatively simple model is suggested for radionuclide dispersion and
assessment of additional population dose and radiation risk for radionuclide
release from the nuclear submanne (NS) #601 with Pb-Bi coolant that was
dumped in the Kara Sea.
Glass-Ceramic Waste Forms for Immobilizing
Plutonium
Authors: O'Holleran T. P. , Johnson S. G. , Frank S. M. , Meyer M. K. , Noy M. , Wood E. L. , Knecht D. A. , Vinjamuri K. , Staples B. A.
Published: September 2012

Results are reported on several new glass and glass-ceramic waste
formulations for plutonium disposition. The approach proposed involves
employing existing calcined high level waste (HLW) present at the Idaho
Chemical Processing Plant (ICPP) as an additive to: 1) aid in the formation
of a durable waste form and 2) decrease the attractiveness level of the
plutonium from a proliferation viewpoint. The plutonium, PuO2,
loadings employed were 15 wt% (glass) and 17 wt% (glass-ceramic). Results in
the form of x-ray diffraction patterns, microstructure and durability tests
are presented on cerium surrogate and plutonium loaded waste forms using
simulated calcined HLW and demonstrate that durable phases, zirconia and
zirconolite, contain essentially all the plutonium.
Direct Conversion of Halogen-Containing Wastes to Borosilicate
Glass
Authors: Forsberg C. W. , Beahm E. C. , Rudolph J. C.
Published: September 2012

Glass has become a preferred waste form worldwide for radioactive wastes;
however, there are limitations. Halogen-containing wastes can not be
converted to glass because halogens (chlorides, fluorides, etc.) form
poor-quality waste glasses. Furthermore, halides in glass melters often form
second phases that create operating problems. A new waste vitrification
process, the Glass Material Oxidation and Dissolution System (GMODS),
removes these limitations by converting halogen-containing wastes into
borosilicate glass and a secondary, clean, sodium-halide stream.
Comparison of the Corrosion Behavior of Tank 51 Sludge-Based
Glass and a Nonradioactive Homologue Glass
Authors: Nuñez L. , Ebert W. L. , Wolf S. F. , Bates J. K.
Published: September 2012

We are characterizing the corrosion behavior of the radioactive glass that
was made with sludge from Tank 51 at the Defense Waste Processing Facility
(DWPF) and a nonradioactive glass having the same composition, except for
the absence of radionuclides. Static dissolution tests are being conducted
in a tuff groundwater solution at glass surface area/solution volume ratios
(S/V) of 2000 and 20,000 m−1. These tests are being conducted to
assess the relationship between the behavior of this glass in a 7-day
Product Consistency Test and in long-term tests, to assess the effects of
radionuclides on the glass corrosion behavior, and to measure the
disposition of radionuclides that are released as the radioactive glass
corrodes. The radioactive glass reacts slower than the nonradioactive glass
through the longest test durations completed to date, which are 140 days for
tests at 2000 m−1 and about 400 days for tests at 20,000
m−1. This is probably because radiolysis results in lower
solution pH values being maintained in tests with the radioactive glass.
Rate-affecting alteration phases that had formed within one year in tests
with other glasses having compositions similar to the Tank 51 glass have not
yet formed in tests with either glass.
An Electrodeless Melter for Vitrification of Nuclear
Waste
Authors: Freidberg J. P. , Shajii A. J. , Wenzel K. W. , Lierzer J. R.
Published: September 2012

This paper describes a new concept for a high-temperature, electrodeless
melter for vitrifying radioactive wastes. Based on the principles of
induction heating, it circumvents a number of difficulties associated with
existing technology. The melter can operate at higher temperatures
(1500–2000°C vs 1150°C), allowing for a higher quality, more durable glass
which reduces the long-term leaching rate. Higher processing temperatures
also enable conversion from borosilicate to high-silica glass which can
accommodate 2 to 3 times as much radioactive waste, potentially halving the
ultimate required long-term disposal space. Finally, with high temperatures,
conversion of nuclear waste into ceramics can also be considered. This too
leads to higher waste loading and the reduction of repository space. The
melter is toroidal, linked by an iron core transformer that allows efficient
electrical operation even at 60 Hz. One-dimensional electrical and thermal
analyses are presented.
The Incorporation of Cerium in Zirconolite
Authors: Begg B. D. , Vance E. R.
Published: September 2012

Zirconolite (CaZrTi2O7) is the primary
actinide-bearing Synroc phase for the immobilisation of high-level nuclear
waste. Using X-ray absorption spectroscopy and microanalysis we have
investigated the incorporation of cerium, as a simulant for plutonium, on
both zirconolite's Ca and Zr sites under a range of redox conditions. The Ce
valence state was found to vary between Ce3+ and Ce4+
depending on the both the sintering atmosphere and temperature. The
existence of alternative charge compensation schemes, predominantly cation
vacancies, in addition to those used in the sample design was inferred in
many of the zirconolites and will be discussed in detail.
Spent Fuel Reaction: the Behavior of the ε-Phase Over 3.1
Years
Authors: Finn P. A. , Hoh J. C. , Wolf S. F. , Surchik M. T. , Buck E. C. , Bates J. K.
Published: September 2012

The release fractions of the five elements in the ε-phase (99Tc,
97Mo, Ru, Rh, and Pd) as well as that of 238U are
reported for the reaction of two oxide fuels (ATM-103 and ATM-106) in
unsaturated tests under oxidizing conditions. The 99Tc release
fractions provide a lower limit for the magnitude of the spent fuel
reaction. The 99Tc release fractions indicate that a surface
reaction might be the rate controlling mechanism for fuel reaction under
unsaturated conditions and the oxidant is possibly
H2O2, a product of alpha radiolysis of water.
Dissolution of Unirradiated UO2 Fuel Under Oxidizing
Conditions: Evaluation of Solubility (Steady State) Limiting Factors
(EQ3/6)
Authors: Ollila K.
Published: September 2012

The solubility behavior of unirradiated UO2 pellets was studied
under oxic, air-saturated conditions in deionized water, in
NaHCO3 solutions and in two types of synthetic groundwater
(25°C). The Allard groundwater represents natural fresh groundwater
conditions at great depths in granite bedrock and bentonite groundwater
simulates the effects of bentonite on granitic fresh groundwater. The
release of uranium was measured during static batch dissolution experiments
of long duration (6 years). A comparison was made with the theoretical
solubility data calculated with the geochemical code, EQ3/6, in order to
evaluate solubility (steady state) limiting factors. Various hypotheses for
redox control (redox potential of the bulk solution or redox potential at
the surface) were tested in the modeling calculations.

The measured concentrations for uranium at steady-state in deionized water
were equal to the solubility of schoepite (PO2 = 0.2 atm). In
NaHCO3 solutions with lower carbonate concentrations (0.98 –
1.96 mmol/1) and in Allard groundwater they were close to the calculated
solubilities of U at the U3O7/U3O8 redox potential. In bentonite
groundwater, the results suggest the formation of a secondary phase with a
lower solubility. Only uranium oxide with a crystal structure of uraninite
(UO2 - U3O7) was identified in all
waters, when analyzing particulate material in the solutions after contact
with UO2 pellets.
The Kinetics of Spinel Crystallization from a High-Level Waste
Glass
Authors: Reynolds J. G. , Hrma P.
Published: September 2012

The kinetics of spinel crystallization from a molten high-iron simulated
high-level nuclear waste glass was studied using isothermal heat treatments.
Optical microscopy with image analysis was used to measure volume fraction
of spinel as a function of heat treatment time and temperature. The
Johnson-Mehl-Avrami equation was fitted to data to determine kinetic
coefficients for spinel crystallization. The liquidus temperature and Avrami
number are TL = 1337K and n = 1.5.
Solubility of Sn(IV) Oxide in Dilute NaClO4 Solution
at Ambient Temperature
Authors: Amaya Takayuki , Chiba Tamotsu , Suzuki Kazunori , Oda Chie , Yoshikawa Hideki , Yui Mikazu
Published: September 2012

The solubility of Sn(IV) oxide was determined in a dilute NaClO4
solution with pH 2 through 12 at ambient temperature. Both oversaturation
and undersaturation experiments were carried out in an inert gas glovebox
where the concentration of the oxygen and carbon dioxide were less than 1
ppm. The solubility of Sn(IV) oxide was 3×10-8 mol/1 at neutral
pH, and increased at pH >7.5. Equilibrium constants of soluble reactions
were calculated from the experimental data, using curve fitting method.

The study suggests that the solubility of Sn(IV) oxide would be higher than
that provisionally used in current safety assessments of HLW disposal
sites.
Plutonium Solubility and Speciation to be Applied to the Separation of Hydrothermal Waste Treatment Effluent
Authors: Neu M. P. , Reilly S. D. , Runde W. H.
Published: September 2012

One of the most complex problems concerning nuclear waste management and the restoration of plutonium production sites is the treatment and disposition of mixed and TRU wastes. Hydrothermal oxidation, which has been shown to be effective in oxidizing a wide variety of organic material to CO2, water, salts and other nonhazardous oxides, is a promising new technology for the treatment and volume reduction of actinide-containing waste. Information on the speciation and solubility of plutonium under process effluent conditions will facilitate the development of separation techniques for removing it from the treated solutions. Such a strongly oxidizing environment will generate plutonium(VT); and upon the destruction of organics, hydrothermal reactor solutions will contain carbonate. We are investigating the solubility and speciation of the plutonium(VI) carbonate system as a function of ionic strength (0.1 to 5.0 M). Formation constants for the tris- and biscarbonato complexes of plutonium(IV) were determined to be, log β130= 17.7 and log β120= 13.6, respectively, by spectrophotometry. These formation constants indicate that PuO2CO3(aq)is the plutonium (VI) carbonate solution species with the largest relevant stability range. We prepared and characterized the corresponding solid using XRD, EXAFS, and diffuse reflectance, and initiated solubility experiments in 0.1, 0.2, 0.5, 1,2, and 5 M NaCl at 22±1°C under 100% CO2. Data collected thus far yield the solubility products, log Kspmol2/kg2= -12.9 (0.1 m NaCl), -12.4 (0.2 m NaCl), -12.5 (0.5 m NaCl), -12.3 (1 m NaCl), -12.2 (2 m NaCl), -12.3 (5 m NaCl).
Chlorine-36 Investigations of Groundwater Infiltration in the
Exploratory Studies Facility at Yucca Mountain, Nevada
Authors: Levy Schön S. , Fabryka-Martin June T. , Dixon Paul R. , Liu Beiling , Turin H. J. , Wolfsberg Andrew V.
Published: September 2012

Chlorine-36, including the natural cosmogenic component and the component
produced during atmospheric nuclear testing in the 1950's and 1960's (bomb
pulse), is being used as an isotopie tracer for groundwater infiltration
studies at Yucca Mountain, a potential nuclear waste repository. Rock
samples have been collected systematically in the Exploratory Studies
Facility (ESF), and samples were also collected from fractures, faults, and
breccia zones. Isotopie ratios indicative of bomb-pulse components in the
water (36Cl/Cl values > 1250 × 10-15), signifying
less than 40-yr travel times from the surface, have been detected at a few
locations within the Topopah Spring Tuff, the candidate host rock for the
repository. The specific features associated with the high
36Cl/Cl values are predominantly cooling joints and syngenetic
breccias, but most of the sites are in the general vicinity of faults. The
non-bomb pulse samples have 36Cl/Cl values interpreted to
indicate groundwater travel times of at least a few thousand to possibly
several hundred thousand years. Preliminary numerical solute-travel
experiments using the FEHM (Finite Element Heat and Mass transfer) code
demonstrate consistency between these interpreted ages and the observed
36Cl/Cl values but do not validate the interpretations.
Immobilization and Recovery of Thorium, A Neptunium Surrogate,
using Phase-Separated Glasses
Authors: Meaker T. F. , Karraker D. , Tosten M. , Pareizs J. M. , Ramsey W. G.
Published: September 2012

The Savannah River Site has the majority of the United States' supply of
neptunium currently stored in an acid solution in one of their canyon
facilities. A program is being developed that could be utilized to ship this
material, as glass, to Oak Ridge National Laboratory where the Np could be
leached from the glass, purified by ion exchange and made into target
material for the production of Pu-238. Ion exchange purification dictates no
material be in the leachate making the isolation of the Np difficult. We
have developed a process using thorium as a surrogate for Np that could
immobilize the Np into a soda borosilicate glass for shipment. To achieve
recovery of the Np, the glass can be phase separated prior to leaching with
nitric acid. Phase separation would produces a Np-rich sodium-borate phase
and a Si-rich phase similar to a Vycor® glass. The nitric acid selectively
attacks the sodium-borate phase allowing high Np recovery in a solution that
contains only sodium and boron. These can be easily separated from Np by ion
exchange. Essentially all of the silicon which would interfere with ion
exchange by precipitation is retained in the Vycor®-type phase. This
technology may also be applied to other actinides stored in relatively pure
solutions.

This paper will report the optimization of variables for maximizing Th (a Np
surrogate) recovery while minimizing Si release. Th solubility in glass,
heat treatment conditions and leaching parameters will be discussed.
Transmission Electron Microscopy (TEM) with energy dispersive spectroscopy
(EDS) data will be included to show phase separation after heat
treatment.
High-Temperature Optical Properties of Thin-Film Vanadium Oxides – VO2 and V2O3
Authors: Thomas Michael S. , DeNatale Jeff F. , Hood Patrick J.
Published: September 2012

Thin-film vanadium dioxide (VO2) and vanadium sesquioxide (V2O3) undergo shear phase transformations at 340K and 120K, respectively. The electrical and infrared optical properties of these materials are dramatically impacted by this phase transformation. Below the phase transition temperature, both VO2 and V2O3 are “poor” electrical insulators and have minimal absorption in the infrared spectral region. Above the phase transition temperature, both VO2 and V2O3 are poor conductors and are opaque in the infrared. The infrared thermochromic properties of these materials make them interesting candidates for several optical applications.

Utilization of either VO2 or V2O3 necessitates an accurate knowledge of the optical properties both above and below the phase transition temperature. This paper reports on some recent infrared ellipsometric measurements on the optical properties of these materials above the transition temperature. These measurements found that both are strongly dispersive through the 3–12 micron spectral region. In addition, the temperature dependence of the optical properties of VO2 above the transition temperature can be related to the film morphology and stoichiometry.
Numerical Modeling of Nonlinear Beam Propagation Phenomena
Authors: Swartzlander G. A. , Deykoon A. M. , Jackson D. W. , Law C. T.
Published: September 2012

A user-friendly beam propagation program has been developed for use over the worldwide- web to aid the optical limiting community in modeling the transmission of light through nonlinear refractive and absorptive media having local intensity-dependent or nonlocal fluencedependent mechanisms.
Non-Linear Light Scattering in a Two Component Medium Optical Limiting Application
Authors: Joudrier V. , Fabre J C. , Bourdon P. , Hache F. , Flytzanis C
Published: September 2012

The first experimental investigation of an optical limiting device based on a suspension of spherical particles in a surrounding liquid is presented. The expected property is the non-linear light scattering based on a refractive index mismatch between the two components that appears at high intensity. Several experiments performed at 532 nm with nanosecond laser pulses provide good indication that such non-linear scattering is observed.
Modeling the Effects of Solvation on the Structure and Properties of Optical Limiting Materials Using Ab Initio Quantum Chemistry
Authors: Day P. N. , Wang Z. , Pachter R.
Published: September 2012

he Effective Fragment Potential (EFP) model of solvation can now be extended beyond aqueous systems due to the development of transferable exchange repulsion potentials. EFPs for methanol and chloroform have been developed, and calculations with these new EFPs agree well with full ab initio calculations. Ab initio calculations have been carried out on zinc tetraphenyl-octobromyl-porphyrin both with and without the EFP solvation model. While the aqueous calculation, which had its geometry optimized, gave good results, the single-point calculations carried out with the two new solvent models indicate the need for geometry optimization.
Effect of AlGaN/GaN Strained Layer Superlattice Period on InGaN MQW Laser Diodes
Authors: Hansen Monica , Abare Amber C. , Kozodoy Peter , Katona Thomas M. , Craven Michael D. , Speck Jim S. , Mishra Umesh K. , Coldren Larry A. , DenBaars Steven P.
Published: September 2012

AlGaN/GaN strained layer superlattices have been employed in the cladding layers of InGaN multi-quantum well laser diodes grown by metalorganic chemical vapor deposition (MOCVD). Superlattices have been investigated for strain relief of the cladding layer, as well as an enhanced hole concentration, which is more than ten times the value obtained for bulk AlGaN films. Laser diodes with strained layer superlattices as cladding layers were shown to have superior structural and electrical properties compared to laser diodes with bulk AlGaN cladding layers. As the period of the strained layer superlattices is decreased, the threshold voltage, as well as the threshold current density, is decreased. The resistance to vertical conduction through p-type superlattices with increasing superlattice period is not offset by the increase in hole concentration for increasing superlattice spacing, resulting in higher voltages.