Ion Implantation

We investigate terahertz time-domain spectroscopy (THz-TDS) as a non-destructive and non-contact technique for depth profiling of dopants in semiconductors. THz temporal waveforms transmitted through silicon-ion-implanted semi-insulating gallium arsenide substrates, as-implanted or post-annealed by rapid thermal annealing, were analyzed by assuming a multi-layered Gaussian refractive index profile in the ∼sub-micrometer-thick implantation region. The implantation energy and dosages in this work were 200 KeV, 1014, 5 × 1014, and 1015 ions/cm2, respectively. The average values of real (n) and imaginary (κ) parts of refractive indices of an as-implanted sample in the depth range of 0–800 nm are 5.8 and 0.7, respectively, at 0.5 THz and are 6.2 and 0.2, respectively, at 1 THz. On the other hand, the refractive index profile of the post-annealed samples displays a prominent Gaussian-like form, and peak refractive indices (n ∼ 25 and κ ∼ 32.7 at 0.5 THz and n, κ ∼17 at 1 THz) were found t...

One of the strategies which have been defended to reduce fouling during heat treatment in the dairy industry is to modify the surface properties of the stainless steel used in heat exchangers, in order to decrease its appetence for milk deposits. Previous studies performed in our laboratory on fouling caused by milk components on several stainless steel materials with different surface modification techniques showed the importance of specific surface properties on the type of deposit formed. One of those properties was the surface energy. In the present study, several surfaces with specific surface energies and similar surface composition were obtained by one of the most promising modification technique tested before, reactive sputtering, and were used as fouling supports in contact with a milk simulating solution under constant conditions of temperature, pH, calcium concentration and hydrodynamics. The aim of these new experiments was to quantify deposition and removal parameters, based on the influence of surface energy on the type of deposit formed. A new dependence relation between the amount of deposit formed and the remaining deposit after cleaning with water and the surface energy of the surface, more precisely its - parameter, was found.

Reducing fouling in heat exchangers during treatment of milk products is one of the great challenges in the dairy industry. One approach to mitigate fouling is to alter the surface characteristics of the heat exchangers making them less prone to protein adsorption. On this background the European project MODSTEEL was established to study the use of new modified stainless steel surfaces to control fouling of milk components. This part of the project focuses on the adsorption of β-lactoglobulin (β-Lg) from a whey protein solution on unmodified and modified 316 2R stainless steel surfaces by in situ ellipsometry under welldefined flow conditions, in the turbulent regime. The effects of temperature, flow rate and surface modification, including SiF 3 + and MoS 2 ion implantation, DLC (Diamond-Like Carbon) sputtering, and DLC-PlasmaCVD (Chemical Vapour Deposition), were investigated. The amount of protein adsorbed is discussed in relation to the thermal stability of β-Lg, surface properties and hydrodynamic conditions.

Fouling of heat exchangers in dairy industries is still quite a severe problem both technically and economically. Altering the surface properties of the heating surfaces would be a way of solving this issue. Modified steel surfaces were tested in an Alfa Laval V2 plate heat exchanger throughout dairy product sterilization. The behavior was analyzed for 8 different surfacetreatments, such as coatings (Diamond Like Carbon [DLC], Silica, SiOX, Ni-P-PTFE, Excalibur®, Xylan®) and ion implantation (SiF+, MoS2). All fouling and cleaning experiments were carried out in standard and well-controlled operating conditions. After fouling, no significant difference could be seen between all the modified steels and the reference by statistical variance analysis. Cleaning efficiency of Ni-PPTFE appeared significantly the best. It could be suggested that the free surface energy plays a predominant role and the roughness a minor role in the level of fouling and cleaning efficiency.

One of the strategies which have been defended to reduce fouling during heat treatment in the dairy industry is to modify the surface properties of the stainless steel used in heat exchangers, in order to decrease its appetence for milk deposits. Previous studies performed in our laboratory on fouling caused by milk components on several stainless steel materials with different surface modification techniques showed the importance of specific surface properties on the type of deposit formed. One of those properties was the surface energy. In the present study, several surfaces with specific surface energies and similar surface composition were obtained by one of the most promising modification technique tested before, reactive sputtering, and were used as fouling supports in contact with a milk simulating solution under constant conditions of temperature, pH, calcium concentration and hydrodynamics. The aim of these new experiments was to quantify deposition and removal parameters, based on the influence of surface energy on the type of deposit formed. A new dependence relation between the amount of deposit formed and the remaining deposit after cleaning with water and the surface energy of the surface, more precisely its - parameter, was found.

In order to reduce the fouling caused by milk during heat treatment, it is important to know more about the deposition process of calcium phosphate, one of the main components of milk fouling, on stainless steel surfaces. The fouling behaviour of calcium phosphate is controlled by several factors related to both the fouling solution properties and the surface characteristics. The present work is focused on the influence of two of these factors: 1) the size and size distribution of the calcium phosphate aggregates formed in solution upon heating and 2) the surface tension values of the deposition surface. It was possible to conclude that maximum deposit build up occurs at the temperature corresponding to the formation, in the bulk, of amorphous sphere-like calcium phosphate particles of about 0.1mm diameter and considering the surface effect, the maximum deposition is obtained on those surfaces having higher surface tension values.

Reducing fouling in heat exchangers during treatment of milk products is one of the great challenges in the dairy industry. One approach to mitigate fouling is to alter the surface characteristics of the heat exchangers making them less prone to protein adsorption. On this background the European project MODSTEEL was established to study the use of new modified stainless steel surfaces to control fouling of milk components. This part of the project focuses on the adsorption of b-lactoglobulin (b-Lg) from a whey protein solution on unmodified and modified 316 2R stainless steel surfaces by in situ ellipsometry under well-defined flow conditions, in the turbulent regime. The effects of temperature, flow rate and surface modification, including SiF3+ and MoS2 ion implantation, DLC (Diamond-Like Carbon) sputtering, and DLC-PlasmaCVD (Chemical Vapour Deposition), were investigated. The amount of protein adsorbed is discussed in relation to the thermal stability of b-Lg, surface propertie...

The structural and morphological characteristics of visible-light-emitting
porous Si layers produced by anodic and stain etching of single-crystal Si substrates are compared using transmission electron microscopy and atomic force microscopy ( AFM) . AFM of conventionally anodized, laterally anodized and stain-etched Si layers show that the layers have a fractal-type surface morphology. The anodized layers are rougher than the stain-etched films. At higher magnification 10 nm sized hillocks are visible on the surface. Transmission electron diffraction patterns indicate an amorphous structure with no evidence for the presence of crystalline Si in
the near-surface regions of the porous Si layers.

The paper concerns an important problem which is connected with the inclusion of some impurities in the deposited metal film. It was found that appearance of contaminants in the film is induced mainly by water vapor remnants inside the vacuum chamber. The paper presents information on changes in the gas composition during and between arc-discharges, which is of primary importance for the selection of appropriate experimental conditions.

We have conducted a study of the material and infrared-luminescence properties of Er-implanted GaN thin films as a function of annealing. The GaN films, grown by metal-organic chemical-vapor deposition, were coimplanted with Er and O ions. After implantation, the films were furnace annealed at temperatures up to 1,100°C. Following each annealing stage, the samples were examined by photoluminescence (PL) measurements and secondary ion-mass spectrometry (SIMS) analysis. In the as-implanted samples, no PL signal near 1,540 nm could be detected with either above-bandgap or below-bandgap excitation. Only after annealing at temperatures above 900°C was the 1,540-nm luminescence detectable. Annealing at higher temperatures resulted first in an increase and then a decrease in the PL-signal intensities. The SIMS data showed that large concentrations of Al, O, and C atoms entered into the GaN films with high-temperature annealing. The stoichiometric changes in the GaN appear responsible for the changes in the Er-related luminescence.

We have conducted a study of the material and infrared-luminescence properties of Er-implanted GaN thin films as a function of annealing. The GaN films, grown by metal-organic chemical-vapor deposition, were coimplanted with Er and O ions. After implantation, the films were furnace annealed at temperatures up to 1,100°C. Following each annealing stage, the samples were examined by photoluminescence (PL) measurements and secondary ion-mass spectrometry (SIMS) analysis. In the as-implanted samples, no PL signal near 1,540 nm could be detected with either above-bandgap or below-bandgap excitation. Only after annealing at temperatures above 900°C was the 1,540-nm luminescence detectable. Annealing at higher temperatures resulted first in an increase and then a decrease in the PL-signal intensities. The SIMS data showed that large concentrations of Al, O, and C atoms entered into the GaN films with high-temperature annealing. The stoichiometric changes in the GaN appear responsible for the changes in the Er-related luminescence.

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The high quality of crystal growth and advanced fabrication technology of silicon carbide (SiC) in power electronics enables the control of optically active defects in SiC, such as silicon vacancies (V Si ). In this paper, V Si are generated in hexagonal SiC (4H) samples through ion implantation of nitrogen or (and) aluminum, respectively the n-and p-type dopants for SiC. The presence of silicon vacancies within the samples is studied using cathodoluminescence at 80K. For 4H-SiC samples, the ZPL (zero phonon line) of the V1 center of V Si is more intense than the one for the V1 center before annealing. The opposite is true after 900 • C annealing. ZPLs of the divacancy defect (V C V Si ) are also visible after annealing.

Europa's surface is chemically altered by radiolysis from energetic charged particle bombardment. It has been suggested that hydrated sulfiu-ic acid (H2SOpnH20) is a major surface species and is part of a radiolytic sulfur cycle, where a dynamic equilibrium exists between continuous production and destruction of sulfur polymers S , , sulfur dioxide S02, hydrogen sulfide H2S, and H2S04.nH20. We measured the rate of sulfate anion production for cyclo-octal sulfur grains in frozen water at temperatures, energies, and dose rates appropriate for Europa using energetic electrons. The measured rate is %*e(SO?-) =fSulk (r~/r)~Gl molecules (100 eV)-', wherefsdh is the sulfur weight fraction, r is the grain radius, ro = 50 pm, p = 1.9, and GI = 0.4 k 0.1. Equilibrium column densities N are derived for Europa's surface and follow the ordering N(H2SO4) >> N(S) > N(S02) > N i z S ) . The lifetime of a sulfur atom on Europa's surface for radiolysis to H2S04 is T(-S) = 120(r/r0)~ years. Rapid radiolytic processing hides the identity of the original source of the sulfurous material, but Iogenic plasma ion implantation and an acidic or salty ocean are candidate sources. Sulfate salts, if present, would be decomposed in < 3800 years and be rapidly assimilated into the sulfur cycle.

In this paper an analytical approach for estimation of maximal continuance of manufacturing of integrated circuit elements by dopant diffusion and ion implantation has been introduced. We analyzed influence of parameters of considered technological processes on the value of it's maximal continuance.

Silicon samples that have been ion implanted with boron at energies below 3 keV have been athermally annealed. The annealing process has been characterized using secondary ion mass spectrometry and infrared absorption spectroscopy. The athermally annealed samples show activation comparable to that for thermally annealed samples, but with much less boron diffusion. The activation in the athermally annealed samples is shown to be much higher than would be achieved by recrystallization of the amorphous layer.

Silicon defect and nanocrystal related white and red electroluminescences (EL) of Si-rich SiO 2 based on metal-oxidesemiconductor (MOS) diode using transparent electrode contact are reported. The 500nm-thick Si-rich SiO 2 film on ntype Si substrate is synthesized using multi-recipe Si-ion-implantation or plasma enhanced chemical vapor deposition (PECVD). After 1100 o C annealing for 3 hrs, the PL of Si-ion-implanted sample at 415 nm and 455 nm contributed by the weak-oxygen bond and neutral oxygen vacancy defects is observed. The white-light EL spectrum was observed at reverse bias, which originates from the tunneling and recombination intermediate state of SiO 2 :Si + at a threshold current and voltage of 1.56 mA and 9.6 V, respectively. The maximum EL power of 110 nW is obtained at biased voltage of 25 V. The linear relationship between the optical power and injection current with a corresponding slope of 2.16 W/A is obtained. The 4-nm nanocrystallite silicon (nc-Si) is precipitated in the 240nm-thick PECVD grown silicon-rich SiO 2 film annealed at 1100 o C for 30 min with Indium-tin-oxide (ITO) of 0.8 mm in diameter, which contributes PL at 760 nm. The peak wavelength of the EL spectra coincides well with the PL. The threshold current and voltage are 86 V and 1.08 A, respectively. The power-current (P-I) slope is determined as 697 W/A. The carrier injection mechanism is dominated by Fowler-Nordheim(F-N) tunneling.

Results are presented that have been obtained while operating the graphite hollow cathode duoplasmatron ion source in dual mode under constant discharge current. This dual mode operation enabled us to obtain the mass and emission spectra simultaneously. In mass spectra C3 is the main feature but C4 and C5 are also prominent, whereas in emission spectra C2 is also there and its presence shows that it is in an excited state rather than in an ionic state. These facts provide evidence that C3 is produced due to the regeneration of a soot forming sequence and leave it in ionic state. C3 is a stable molecule and the only dominant species among the carbon clusters that survives in a regenerative sooting environment at high-pressure discharges.

The plasma physics of dielectric barrier discharges (DBD) for carrying out ion implantation in insulators is investigated. A hollow cathode DBD excited by high-voltage pulses is suitable for ion bombardment of the surfaces of insulating tubing, porous material, particles and sheets. Plasma immersion ion implantation of insulating surfaces is useful for many applications in medicine and engineering. The ion bombardment of glass is useful for cleaning and surface modification. The ion implantation of polymers creates radicals that are able to bind molecules to their surfaces for applications in medical procedures and diagnostics. A wire diagnostic probe and optical emission spectroscopy are used for experimental work. A theory based on mutual capacitance is developed to convert data from the probe to give implanted charge as a function of pressure, voltage and pulse duration. We find the operating conditions that allow for charge to be implanted and those that achieve the highest impl...

Dans la realisation de nouveaux composants innovants de la spintronique, de grands espoirs sont places sur les semi-conducteurs magnetiques dilues (DMS). L’enjeu technologique est de developper des materiaux ayant a la fois des proprietes semi-conductrices et ferromagnetiques. Le but de ce travail est de realiser une etude nanostructurale et magnetique detaillee du systeme Fe :SiC candidat prometteur pour devenir un semi-conducteur magnetique dilue a temperature ambiante. Cependant les proprietes magnetiques du materiau (6H-SiC) implante avec des metaux de transitions (MT) dependent fortement de sa microstructure (concentration et nature du dopant, precipitation du dopant…). Afin d’apprehender l’ensemble des proprietes nanostructurales et magnetiques, nous avons etudie le systeme Fe :SiC a l’echelle de l’atome en utilisant la sonde atomique tomographique (SAT) couplee a la spectrometrie Mossbauer 57Fe. Des monocristaux 6H-SiC (0001) de type p et n (~10+18/cm3) ont ete multi-implante...

Semiconductors have large second-order nonlinearities, e.g. GaAs [d 14 ~170 pmV -1 at 2 µm] has a d 2 /n 3 figure-of-merit around 10 times larger than LiNbO 3 . GaAs has a mature fabrication technology with the potential for direct integration with laser diode pump sources. Phase-matching problematic with no natural birefringence in cubic semiconductors. Quasi-phase-matching using Quantum Well Intermixing.

For applications in energy harvesting, environmentally friendly cooling, and as power sources in remote or portable applications, it is desired to enhance the efficiency of thermoelectric materials. One strategy consists of reducing the thermal conductivity while increasing or retaining the thermoelectric power factor. An approach to achieve this is doping to enhance the Seebeck coefficient and electrical conductivity, while simultaneously introducing defects in the materials to increase phonon scattering. Here, we use Mg ion implantation to induce defects in epitaxial ScN (111) films. The films were implanted with Mg + ions with different concentration profiles along the thickness of the film, incorporating 0.35 to 2.2 at.% of Mg in ScN. Implantation at high temperature (600 ˚C), with few defects due to the temperature, does not substantially affect the thermal conductivity compared to a reference ScN. Samples implanted at room temperature, in contrast, exhibited a reduction of the thermal conductivity by a factor of three. The sample doped with 2.2 at.% Mg also showed an increased power factor after implantation. This study thus shows the effect of ioninduced defects on thermal conductivity of ScN films. High-temperature implantation allows the defects to be annealed out during implantation, while the defects are retained for roomtemperature implanted samples, allowing for a drastic reduction in thermal conductivity.

The origin of the formation of multishell fullerenes ͑carbon onions͒ produced by carbon ion-implantations performed at high-temperature into silver is discussed on the basis of high-resolution transmission electron microscopy observations. For low carbon fluences, one observes the formation inside the silver matrix of poorly organized carbon nanostructures the shape of which is roughly spherical. They progressively evolve towards perfect onionlike structures when the implanted carbon fluence increases. The catalytic effect of silver, which lowers the graphitization temperature of the carbon, the irradiation-induced displacements of the carbon atoms, and the effect of the temperature are proposed to be the key mechanisms that control the formation of the onionlike structures observed in such experiments.

The Standards Committee of the Society for Luminescence Microscopy and Spectroscopy (SLMS) circulated doped zircon crystals as a standard for comparison of cathodoluminescence (CL) emission spectra obtained at different laboratories. Eleven laboratories have submitted spectra acquired from this standard. The crystals are synthetic zircons doped with 1.4 wt.% of Dy 2 o 3 .

We have achieved 1 . 6 m -c m resistivity using ion implantation that has little negative effect on MOS devices. Extremely low loss and cross coupling of 6.3 and -79 dB/cm (10pm gap) at 20GHz are measured with lpm Al, respectively, which is due to implant induced trap with -Ips carrier lifetime and stable to 400OC.

The process of ion implantation often involves vacancy generation and migration. The vacancy generation and migration near a monocrystalline silicon surface during three kinds of energetic Si35 cluster ion implantations were investigated by molecular dynamics simulations in the present work. The patterns of vacancy generation and migration, as well as the implantation-induced amorphous structure, were analyzed according to radial distribution function, Wigner–Seitz cell, and identify diamond structure analytical methods. A lot of vacancies rapidly generate and migrate in primary directions and form an amorphous structure in the first two picoseconds. The cluster with higher incident kinetic energy can induce the generation and migration of more vacancies and a deeper amorphous structure. Moreover, boundaries have a loading–unloading effect, where interstitial atoms load into the boundary, which then acts as a source, emitting interstitial atoms to the target and inducing the generat...

A study of structure and surface morphology together with magnetic properties of Mn-implanted rutile-type TiO2 single crystals is performed. Homogenous thin films of about 100 nm with different MnxTi1−xO2 (x=0.03; 0.05 and 0.07) chemical formula were obtained. The Mn ion implanted surface exhibited a dense microstructure with a nano grain size. The dependence of c/a axial ratio on manganese content suggests

The presence of radiation-induced defects and the high temperature of implantation are breeding grounds for helium (He) to accumulate and form He-induced defects (bubbles, blisters, craters, and cavities) in silicon carbide (SiC). In this work, the influence of He-induced defects on the migration of strontium (Sr) implanted into SiC was investigated. Sr-ions of 360 keV were implanted into polycrystalline SiC to a fluence of 2 × 1016 Sr-ions/cm2 at 600°C (Sr-SiC). Some of the Sr-SiC samples were then co-implanted with He-ions of 21.5 keV to a fluence of 1 × 1017 He-ions/cm2 at 350°C (Sr + He-SiC). The Sr-SiC and Sr + He-SiC samples were annealed for 5 h at 1,000°C. The as-implanted and annealed samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Rutherford backscattered spectrometry (RBS). Implantation of Sr retained some defects in SiC, while co-implantation of He resulted in...

Shallow subsurface layers of gold nanoclusters were formed in polymethylmethacrylate (PMMA) polymer by very low energy (49 eV) gold ion implantation. The ion implantation process was modeled by computer simulation and accurately predicted the layer depth and width. Transmission electron microscopy (TEM) was used to image the buried layer and individual nanoclusters; the layer width was ∼6–8 nm and the cluster diameter was ∼5–6 nm. Surface plasmon resonance (SPR) absorption effects were observed by UV-visible spectroscopy. The TEM and SPR results were related to prior measurements of electrical conductivity of Au-doped PMMA, and excellent consistency was found with a model of electrical conductivity in which either at low implantation dose the individual nanoclusters are separated and do not physically touch each other, or at higher implantation dose the nanoclusters touch each other to form a random resistor network (percolation model).

PMMA (polymethylmethacrylate) was ion implanted with gold at very low energy and over a range of different doses using a filtered cathodic arc metal plasma system. A nanometer scale conducting layer was formed, fully buried below the polymer surface at low implantation dose, and evolving to include a gold surface layer as the dose was increased. Depth profiles of the implanted material were calculated using the Dynamic TRIM computer simulation program. The electrical conductivity of the gold-implanted PMMA was measured in situ as a function of dose. Samples formed at a number of different doses were subsequently characterized by Rutherford backscattering spectrometry, and test patterns were formed on the polymer by electron beam lithography. Lithographic patterns were imaged by atomic force microscopy and demonstrated that the contrast properties of the lithography were well maintained in the surface-modified PMMA.

We have investigated the structure of disordered gold-polymer thin films using small angle x-ray scattering and compared the results with the predictions of a theoretical model based on two approaches—a structure form factor approach and the generalized Porod law. The films are formed of polymer-embedded gold nanoclusters and were fabricated by very low energy gold ion implantation into polymethylmethacrylate (PMMA). The composite films span (with dose variation) the transition from electrically insulating to electrically conducting regimes, a range of interest fundamentally and technologically. We find excellent agreement with theory and show that the PMMA-Au films have monodispersive or polydispersive characteristics depending on the implanted ion dose.

This study investigates the fretting wear behavior of diamond-like carbon (DLC) films deposited by plasma-based ion implantation (PBII) and filtered cathodic vacuum arc (FCVA) and that of diamond films deposited by plasma chemical vapor deposition (CVD) and diamond films treated by CF4 (tetrafluoromethane) plasma. The friction properties and surface structural changes of the DLC and diamond films are observed microscopically by varying vibration amplitudes and friction environments. Raman spectroscopy was used to analyze fretting wear behavior and failure mechanisms. The PBII-DLC and FCVA-DLC films showed an opposite dependence of friction behavior on amplitude due to their different indentation hardness and ID/IG values. However, only the friction of the PBII-DLC film can be improved under PAO lubrication conditions. Both CVD diamond and fluorinated diamond films showed good wear resistance under both dry and PAO conditions. In particular, the fluorinated diamond film surface exhibits microscopic changes under dry and PAO-lubricated conditions due to changes in the surface structure. Consequently, the fluorinated diamond film demonstrates minimal wear and a lower friction coefficient in response to small vibrations under both dry and PAO-lubricated conditions than the untreated diamond film.

In this paper negative temperature coefficient of the 6H-SiC diode breakdown voltage is considered. It is shown that the temperature dependence of the breakdown voltage value can be explained in terms of recharging of deep centers in the space charge region of the diode. Experiments made with boron doped 6H-SiC diodes are in good agreement with calculation.

4H-and 6H-SiC small samples were implanted by keV Al + ions at room temperature and annealed in an induction heating furnace, at the center of the susceptor, for different temperatures and times in the range 1600-1800°C and 5-60 min, respectively. The implanted layers were amorphous but the SiC crystalline structures were recovered after annealing, as measured by Rutherford Back-Scattering analyses in Channeling geometry. Al + electrical activation determined by sheet resistance and Hall effect measurements increases with the annealing temperature or time, on both polytypes. When whole SiC wafers were annealed in the same induction heating furnace, sheet resistance mapping systematically presented a radial gradient from the center to the periphery of the wafer. The measured linear dependence between sheet resistance and temperature allowed us to rebuild the radial temperature gradient at the crucible-susceptor furnace during the annealing process.

Intermediate band silicon solar cells have been fabricated by Titanium ion implantation and laser annealing. A two-layer heterogeneous system, formed by the implanted layer and by the unimplanted substrate is obtained. In this work we present electrical characterization results which evidence the formation of the intermediate band on silicon when ion implantation dose is beyond the Mott limit. Clear differences have been observed between samples implanted with doses under or over the Mott limit. Samples implanted under the Mott limit have capacitance values much lower than the non-implanted ones as corresponds to a highly doped semiconductor Schottky junction. However, when the Mott limit is surpassed the samples have much higher capacitance, revealing that the intermediate band is formed. The capacitance increase is due to the big amount of charge trapped at the intermediate band, even at low temperatures. Titanium deep levels have been measured by Admittance Spectroscopy. These deep levels are located at energies which vary from 0.20 to 0.28 eV bellow the conduction band for implantation doses in the range 10 13 -10 14 at/cm 2 . For doses over the Mott limit the implanted atoms become non recombinant. Admittance measurements are the first experimental demonstration the Intermediate Band is formation. Capacitance voltage transient technique measurements prove that the fabricated devices consist of two-layers, in which the implanted layer and the substrate behave as an n + /n junction.

The lunar meteorite Dhofar 1436 is dominated by solar wind type noble gases. Solar argon is equilibrated with “parentless” 40Ar commonly known as lunar orphan argon. Ar‐Ar isochron analyses determined the lunar trapped 40Ar/36Ar ratio to 2.51 ± 0.04, yielding a corrected plateau age of 4.1 ± 0.1 Ga, consistent with the lunar Late Heavy Bombardment period. Lunar trapped and radiogenic argon components are all released at high temperatures (1200–1400 °C). Surprisingly, solar noble gases and lunar trapped argon can largely be released by crushing. Initial crushing steps mainly release elementally fractionated solar wind gases, while in advanced crushing steps, cosmogenic components dominate. Cosmogenic noble gases indicate irradiation at the lunar surface; they are less fractionated than solar wind species. We favor a scenario in which both solar and a large fraction of cosmogenic gases were acquired before the 4.1 Ga event, which caused shock metamorphism and formation of the regolith...

Because of their high degree of structural order, high mechanical strength, and small diameter ( -1 pm), benzene-derived graphite fibers provide an excellent host material for a structural analysis of both the intercalation and ion-implantation processes in graphite. Using the c-axis lat- tice imaging technique, with a high-resolution electron microscope, we observe well-staged inter- calated regions in this fiber matrix. With regard to ion implantation, we find a distribution in the density of lattice defects with depth from the fiber surface. Ion implantation is also found to in- crease the graphite interlayer spacing. This information is correlated with electrical properties of these fibers.

The goal of this NEUP-IRP project is to develop a fuel concept based on an advanced ceramic coating for Zr-alloy cladding. The coated cladding must exhibit demonstrably improved performance compared to conventional Zr-alloy clad in the following respects: During normal service, the ceramic coating should decrease cladding oxidation and hydrogen pickup (the latter leads to hydriding and embrittlement). During a reactor transient (e.g., a loss of coolant accident), the ceramic coating must minimize or at least significantly delay oxidation of the Zr-alloy cladding, thus reducing the amount of hydrogen generated and the oxygen ingress into the cladding. The specific objectives of this project are as follows: To produce durable ceramic coatings on Zr-alloy clad using two possible routes: (i) MAX phase ceramic coatings or similar nitride or carbide coatings; and (ii) graded interface architecture (multilayer) ceramic coatings, using, for instance, an oxide such as yttria-stabilized zirconia (YSZ) as the outer protective layer. To characterize the structural and physical properties of the coated clad samples produced in 1. above, especially the corrosion properties under simulated normal and transient reactor operating conditions. To perform computational analyses to assess the effects of such coatings on fuel performance and reactor neutronics, and to perform fuel cycle analyses to assess the economic viability of modifying conventional Zr-alloy cladding with ceramic coatings. This project meets a number of the goals outlined in the NEUP-IRP call for proposals, including: Improve the fuel/cladding system through innovative designs (e.g. coatings/liners for zirconiumbased cladding) Reduce or eliminate hydrogen generation Increase resistance to bulk steam oxidation Achievement of our goals and objectives, as defined above, will lead to safer light-water reactor (LWR) nuclear fuel assemblies, due to improved cladding properties and built-in accident resistance, as well as the possibilities for enhanced fuel/clad system performance and longevity. Below, we summarize the most significant highlights of this project. Note that figures, tables, equations, etc., are numbered separately for each section.

We measure the crossover from diffusive to ballistic transport as a function of frequency in dc contacted high-mobility two-dimensional electron gas structures in GaAs/ AlGaAs heterostructures at GHz frequencies. By systematically measuring samples of varying mobility we demonstrate that the crossover frequency scales with mobility as predicted by the Drude model. We find the ohmic contact impedance to be real and independent of frequency for samples with mobility higher than 500 000 cm 2 / V s, while there is a significant capacitive component in parallel with the contact resistance for lower mobility samples.

We measure the crossover from diffusive to ballistic transport as a function of frequency in dc contacted high-mobility two-dimensional electron gas structures in GaAs/ AlGaAs heterostructures at GHz frequencies. By systematically measuring samples of varying mobility we demonstrate that the crossover frequency scales with mobility as predicted by the Drude model. We find the ohmic contact impedance to be real and independent of frequency for samples with mobility higher than 500 000 cm 2 / V s, while there is a significant capacitive component in parallel with the contact resistance for lower mobility samples.

Bioinert metals are used for medical implants and in some industrial applications. This study was performed to detect and analyze peculiarities that appear in the temperature distributions during quasi-static tensile testing of bioinert alloys. These alloys include VT1-0 titanium, Zr-1%Nb and Ti-45%Nb in both coarse-grain (CG) and ultrafine-grain (UFG) states. The crystal structure, as well as the crystal domain and grain sizes of these alloys in the UFG state, may be different from the CG versions and identifying the thermal signatures that occur during their deformation and fracture is of interest, as it may lead to an understanding of physical processes that occur during loading. By comparing the surface temperature distributions of specimens undergoing deformation under tensile loading to the distributions at maximum temperatures it was found that the observed differences depend on the alloy type, the alloy structural state and the thermal properties of structural defects in the...

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We studied the rearran gement of ion-implanted hydrogen in <100 > oriented n-type silicon wafers upon annealing and its effect on the crystal damage . The silicon samples were implanted with 42 keV protons to a dose of 2 x 1016 H /cm2 and subsequently vacuum annealed at temperatures r anging from 200 °C to 500 °C . The evolution of the H-concentration and the crystal damage depth profiles during the heat treatments were investigated through the combined use of elastic recoil detection (ERD) analysis, secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectroscopy (RBS) in channeling mode . The obtained results reveal information about the damage accumulation caused by the thermally induced rearrangement o f