bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ SEM Observations and Electrical Measurements During the Annealing of Si/Ni Contacts to SiC
Authors: Ervin Matthew H. , Jones Kenneth A. , Derenge Michael A. , Zheleva Tsvetanka S. , Wood Mark C.
Published: June 2019

Nickel (Ni) contacts to n-type silicon carbide (n-SiC) are annealed to ∼950°C in order to achieve their good ohmic properties through the reaction of the Ni with Si from the SiC to form nickel silicides. Unfortunately, the physical contact, and therefore the reliability, is poor. A possible cause is that the silicidation reaction liberates C from the SiC, which then diffuses throughout the contact. The reaction also produces a poor morphology and voids form at the metal-SiC interface. To try to understand the processes that produce the good electrical properties and at the same time improve the physical properties, we studied the reactions of Si/Ni contacts with 1:1 and 1:2 stoichiometric ratios as well as Ni-only contacts on n- and p-type SiC, both visually and electrically in situ using a hot stage and microprobe-equipped scanning electron microscope (SEM). The visual observations of the Ni-only film show that it does not react with the SiC until the temperature reaches 500–550°C. For the n-type SiC, the electrical measurements show a decrease in contact resistivity as the anneal temperature is increased from 500°C to 650°C. Increasing the anneal temperature further increases the resistivity until it begins to drop precipitously as the temperature approaches 950°C and higher. The visual observations of the Si/Ni contacts show that the Si and Ni are reacting at ∼600°C, with phases nucleating and then growing laterally. The electrical measurements for the n-type samples show that the contact resistance initially drops at 100–300°C indicating that there may be reactions, unseen by the SEM, at lower temperatures. The resistance continues to rise and fall over the intervening temperatures but begins to consistently and significantly fall at temperatures above 850°C, and then reaches ohmic values at 900–950°C. Because the silicidation reactions are seen to occur at temperatures far below those required to achieve ohmic properties, it is clear that silicide formation, while it may be necessary, is not sufficient for the formation of Ni-ohmic contacts to n-SiC. In this work, it has been observed that reaction of the Ni with the SiC appears to be necessary for achieving ohmic properties. While this may form a more intimate contact, it is proposed that damaging the SiC surface with this reaction is an important part of ohmic contact formation, possibly through increased current tunneling through interface defect states.
The Effects of Sapphire Surface Treatments and Nitridation on GaN Nucleation Grown using Hydride Vapor Phase Epitaxy
Authors: Dwikusuma F. , Kuech T. F.
Published: June 2019

We have studied the effects of sapphire surface treatments and nitridation on GaN nucleation grown using the hydride vapor phase epitaxy technique. The surface treatments used were airannealing at 1400°C, etching in pure H2SO4 at 250°C, and etching in a 3:1 mixture of H2SO4:H3PO4 solution at 250°C. A nitridation step was carried out using 20% NH3 in N2 gas mixture at 1100°C. GaN nucleation and the early stage s of growth was investigated by short time growth and quench experiments. Atomic force microscopy and double crystal x-ray diffraction were used to examine the sapphire surface morphology, GaN island density, and GaN island structure. A lower density of GaN islands was grown on the air-annealed sapphire compared to the H2SO4-etched and 3:1 H2SO4:H3PO4-etched sapphire. GaN islands grown on the 3:1 H2SO4:H3PO4-etched sapphire had a broad mosaic spread due to preferential growth on surface pits. Sapphire nitridation resulted in a higher GaN island density with a smaller mosaic spread. A high density and uniform nucleation of GaN islands is critical in producing high quality thick GaN films. The H2SO4-etched sapphire and nitridation resulted in a high density of uniform GaN islands.
Effect of Si Layer in The ZnO Thin Films by Pulsed Laser Deposition
Authors: Kang Hong Seong , Kang Jeong Seok , Kim Jae Won , Lee Sang Yeol
Published: June 2019

ZnO thin films and ZnO-Si-ZnO multi-layer thin films have been deposited by pulsed laser deposition (PLD). And then, the films have been annealed at 300°C in oxygen ambient pressure. The optical and structural properties changed by Si layer in ZnO thin film. UV and visible peak position was shifted by Si layer. Electrical properties of the films were improved slightly than ZnO thin film without Si layer. The optical and structural properties of ZnO thin films and ZnOSi-ZnO multi-layer thin films were characterized by PL (Photoluminescence) and XRD(X-ray diffraction method), respectively. Electrical properties were measured by van der Pauw Hall measurements.
Fabrication and Characterizations of ZnO and ZnO:Mn Nanocrystalline Thin Films
Authors: Liu Yichun , Zhao Dongxu , Zhang X.T. , Shen Dezhen , Henderson D.O. , Mu R.
Published: June 2019

This paper provides a brief summary of the structural and optical study of ZnO and ZnO:Mn materials fabricated from simple process: oxidation of ZnS and ZnS:Mn thin films grown by LPMOCVD. Both structural analysis and optical characterization have confirmed the good quality ZnO material formation. XRD results suggest that the fabricated ZnO film is composed of ∼30 nm ZnO nanocrystals with a hexagonal wurtzite structure. Raman spectra show a strong resonant multiphonon effect. In all cases, a UV emission is observed at ∼ 380 nm. A green emission is also observed in the ZnO nanocrystalline film. On the other hand, it is demonstrated that the Mn doping in ZnS film can dramatically affect the luminescence properties of end products: nanocrystalline ZnO thin films. The photoluminescence spectra of the films with an optimized Mn doping concentration only showed the ultraviolet emission, while the green emission was fully quenched. It is argued that the presence of the Mn can effectively passivate the electron and hole trapping sites at the surface and interface of the ZnO nanocrystals.
Electrical Characterization of Defects Introduced in 4H-SiC During High Energy Proton Irradiation and Their Annealing Behavior
Authors: Ahoujja M. , Crocket H. C. , Scott M. B. , Yeo Y.K. , Hengehold R. L.
Published: June 2019

We report on the electrical properties of defects introduced in epitaxial 4H-SiC by 2 MeV protons using deep level transient spectroscopy (DLTS). After proton irradiation with a dose of about 1.5×1014 cm-2, the DLTS measurements were made, and the rate window shows a single broad peak between 280 and 310 K. The intensity of this peak remains unchanged after a thermal anneal at 900°C for 20 min. However, after annealing at or above 1100°C, the peak intensity gradually decreases with anneal temperature up to 1500°C, indicating a decrease in the defect concentration. Because a complete damage recovery of the SiC is not observed even after annealing at 1500°C, we believe a higher temperature annealing is necessary for a complete recovery. Using a curve fit analysis, a set of deep levels of defect centers were found with energy ranging between 567 and 732 meV. These traps do not exhibit a significant change in the trap energy or capture cross-section parameters as a function of anneal temperature, but the decrease in the trap density with increasing anneal temperature demonstrates a damage recovery.
Er doped GaN by Gas Source Molecular Beam Epitaxy on GaN Templates
Authors: Rousseau N. , Briot O. , Ribes V. , Aulombard R.L.
Published: June 2019

Since the work of Favennec et al.[1] it is well known that the quenching of luminescence from rare earth ions decreases with the host band gap. This has led to a large activity with silicon implanted or doped with RE, and then GaAs was used, in hope to realize simple, cheap light emitters. With a band gap of 3.4 eV at room temperature, GaN is even better suited to such applications. As a matter of fact, Steckl et al.[2] have demonstrated a green light emitting device based on Er doped GaN. This resulted in a renewed effort in this direction, but the crystal quality still have to be mastered and the physical phenomenon involved to be understood. In this work, GaN and Er-doped GaN with various Er concentrations were grown by gas source molecular beam epitaxy on high quality GaN templates grown by metalorganic chemical vapour deposition. In order to understand the influence of the Er incorporation on the crystal quality of GaN, Er-doped GaN were grown with a concentration between 0.1% and 5%. High quality undoped GaN were also grown, as a reference material, to show how the smallest amount of Er may affect drastically the structural and optical properties. All the samples were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction. With these measurements, we demonstrate a strong correlation between the Er concentration and the surface roughness and the crystalline quality. This study shows that the activation of the Erbium luminescence is not improved with improving crystal quality. This assumption supports the idea that Er luminescence should be related to defect center in GaN.
Time of Flight of Drifting Electrons and Holes in Stabilized a-Se Film
Authors: Lee Dong-Gil , Park Ji-Koon , Choi Jang-Yong , Kim Jae-Hyung , Nam Sang-Hee
Published: June 2019

Large area, flat panel detectors are being investigated for digital radiogrpahy and fluoroscopy. Theses detectors employ an x-ray conversion layer of photoconductor to detect x-rays. The amorphous selenium layer that is currently being studied for its use as an x-ray photoconductor is not pure a-Se but rather a-Se doped with 0.2-0.5% As and 10-30 ppm Cl, also known as stabilized a-Se. The suitability of the stabilized a-Se is largely determined by its charge on generating, transporting and trapping properties.

In this paper, a conventional time-of-flight measurement was carried out to analyze the transport properties of charge carriers. A laser beam with pulse duration of 5 ns and wavelength of 350 nm was illuminated on the surface of the stabilized a-Se with thickness of 400 μm. The photo response signals of the hole and electron were measured at the applied electric field of 10 V/μm as a function of time. The measured transit times of the hole and electron were about 229.17μs and about 8.73μs at 10 V/μm, respectively. The measured mobility indicated a slight dependence with respect to the applied electric field with a range of 4-10 V/μm. The experimental results showed that the measured mobility of the hole and electron was 0.04584 cm2V-1s-1 and 0.00174 cm2V-1s-1 at the electric field of 10 V/μm.
Novel Oxides for Passivating AlGaN/GaN HEMT and Providing Low Surface State Densities at Oxide/GaN Interface
Authors: Ren F. , Luo B. , Kim J. , Mehandru R. , Gila B. P. , Onstine A. H. , Abernathy C. R. , Pearton S. J. , Fitch R. , Gillespie J. , Jenkins T. , Sewell J. , Via D. , Crespo A. , Irokawa Y.
Published: June 2019

Both MgO and Sc2O3 are shown to provide low interface state densities (in the 1011 eV-1 cm-2 range) on n- and p-GaN, making them useful for surface passivation layers to mitigate current collapse in GaN/AlGaN high electron mobility transistors(HEMTs) and also gate dielectrics for metal-oxide semiconductor(MOS) devices. Clear evidence of inversion has been demonstrated in gate-controlled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high temperature implant activation anneal show a total surface state density of ∼3 × 1012 cm-2. On HEMT structures, both oxides provide effective passivation of surface states and these devices show improved output power. The MgO/GaN diodes and Sc2O3 passivated HEMT are also found to be quite radiation-resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high energy(40MeV) protons.
Effects of Pre-Process Temperature Stressing on AlGaN/GaN HEMT Structures
Authors: Yannuzzi Mark J. , Moser Neil A. , Fitch Robert C. , Jessen Gregg H. , Gillespie James K. , Via Glen D. , Crespo Antonio , Jenkins Thomas J. , Look David C. , Reynolds Donald C.
Published: June 2019

In an effort to investigate the stability of the surface and hetero-interface of AlGaN/GaN HEMTs during high temperature device processing steps, AlGaN/GaN HEMT samples were subjected to temperatures from 650°C to 1150°C for a period of 30 seconds prior to processing. Hall and photoluminescence measurements were performed on samples before and after temperature stressing. The samples annealed at 700°C and 1150°C were then processed, and electrical parametric data were collected during and after processing. Large increases in HEMT Schottky gate diode reverse leakage current are observed at higher pre-process annealing temperatures, while the low-field mobility decreases.
Surface Acoustic Waves And Guided Optical Waves In AlGaN Films
Authors: Bu Gang , Ciplys Daumantas , Shur Michael , Gaska Remis , Fareed Qhalid , Rimeika Romualdas , Yang Jinwei , Khan Asif
Published: June 2019

AlxGa1-xN layers grown by MOCVD on sapphire substrates have been tested using the surface acoustic wave and guided optical wave techniques. Samples with molar fraction of Al up to 0.36 have been investigated. The parameters S11 of single surface acoustic wave transducers and S12 of two-port devices have been measured with the network analyzer. The values of the surface acoustic wave velocity and electromechanical coupling coefficient for the layer-substrate structure have been extracted and calculated using material parameters available from literature. The attenuation of guided optical waves along the propagation track in AlxGa1-xN layers has been measured using the CCD imaging technique. The attenuation dependence on the mode order and layer thickness has been studied. Our results show that the properties of AlxGa1-xN that determine surface acoustic wave and guided optical wave propagation are similar to the properties of GaN films within a relatively wide range of x up to x =0.36.
Cathodoluminescence Study of Gadolinium–Doped Yttrium Oxide Thin Films Deposited By Radio–Frequency Magnetron Sputtering
Authors: Fowlkes J. D. , Rack P. D. , Bansal R. , Fitz–Gerald J.M.
Published: June 2019

A multi–layer gadolinium–doped yttrium oxide thin film was deposited in a combinatorial fashion on a Si (001) substrate using radio–frequency magnetron sputtering. Alternating layers of Y2O3 and Gd were deposited for a total of 9 layers. The film was homogenized in composition by an 850°C 12 hour thermal treatment producing a range of composition from Y1.96Gd0.04O3-Y1.54Gd0.46O3 in a single film. Ultraviolet emission with a peak wavelength at 314-315nm was observed from the gadolinium 8S7/2 - 6P7/2 transition via cathodoluminescence (CL) excitation. The CL–induced intensity was found to be maximum at 9 at% Gd (Y1.82Gd0.18O3) and an optimized electron probe of Vacc = 13 keV was determined for the 1 μm thick thin film. Gadolinium activator saturation was observed for sample current density greater than 0.03 μA/cm2. Non- radiative decay via thermal pathways is suspected for the observed activator saturation.
Large Area 6H- and 4H-SiC Photoconductive Switches
Authors: Doğan S. , Yun F. , Roberts C.B. , Parish J. , Huang D. , Myers R. E. , Smith M. , Saddow S. E , Ganguly B. , Morkoç H.
Published: June 2019

Photoconductive Semiconductor Switches (PCSS) were fabricated in planar structures on high resistivity 4H-SiC and conductive 6H-SiC and tested at DC Bias voltages up to 1000 V. The gap spacing between the electrodes is 1 mm. The average on-state resistance and the ratio of on-state to off-state currents were about 20 Ω and 3×1011 for 4H-SiC, and 60 Ω and 6.6×103 for 6H-SiC, respectively. The typical maximum switch current at 1000 V is about 49 A for 4H-SiC. Photoconductivity pulse widths for all applied voltages were 8-10 ns. The observed performance is due in part to the removal of the surface damage by high temperature H2 etching and surface preparation. Atomic Force Microscopy (AFM) images revealed that very good surface morphology, atomic layer flatness and large step widths were achieved with this surface treatment and these atomically smooth surfaces likely contributed to the excellent switching performance of these devices.
Molecular Dynamics Simulations of Nucleation and Crystallization Processes During Excimer-Laser Annealing of Amorphous Silicon on Glass
Authors: Motooka T. , Munetoh S. , Min Lee Byoung , Nisihira K.
Published: June 2019

We have investigated atomistic processes of nucleation and crystallization in excimer-laser annealed thin Si films on glass based on molecular-dynamics (MD) simulations using the Tersoff potential. MD cells composed of up to approximately 50000 Si atoms were heated to produce melted Si, and then melted Si was quenched under various supercooled conditions with or without a temperature gradient and the corresponding nucleation processes were visualized. Lateral growth of thin Si crystalline films was also simulated by embedding a crystalline nano-particle with various crystal surfaces in melted Si. It has been found that the crystal surfaces become predominantly {111} during the lateral growth processes.
Production of III-V Nanocrystals by Picosecond Pulsed Laser Ablation
Authors: Wu M. H. , Mu R. , Ueda A. , Henderson D. O.
Published: June 2019

In As nanoparticles have been produced by picosecond pulsed laser ablation of bulk targets in the presence of an inert backing gas. Atomic force microscopy measurements show particles ranging in size from one to ten nm. Stoichiometry of the targets, determined by Rutherford backscattering measurements, are typically preserved within ten percent. Optical absorption and raman scattering data help confirm the crystalline, quantum confined nature of the nanoparticles.
Synthesis of Photosensitive Organic-Inorganic Hybrid Polymers via Anhydrous Sol-Gel Process for Integrated Optics
Authors: Luo Xinshi , Zha Congji , Luther-Davies Barry
Published: June 2019

Photosensitive organic-inorganic hybrid polymers were synthesised for integrated optical and optoelectronic devices by a non-hydrous sol-gel process of hydrolysis/condensation of 3-methacryloxypropyltrimethoxysilane (MPS), diphenyldimethoxysilane (DPhDMS), and zirconium isopropoxide (TPZ) with boric acid under anhydrous conditions. The methacryl groups of MPS are UVpolymerizable, which are suitable for low cost fabrication of waveguides with a “UV write/develop” process. The incorporation of DPhDMS and TPZ was found useful in reducing the optical loss and in enhancing the thermostability of the polymer. The refractive index of the hybrid polymer is tuneable from 1.4950 to 1.5360 by variation of the ratio among MPS, DPhDMS and TPZ. Optical characterisation showed that the material has low optical losses at the telecommunications windows (0.16 dB/cm at 1310 nm and 0.4 dB/cm at 1550nm). The hybrid polymer also showed a low birefringence (1.2×10-4), a large thermo-optic (TO) coefficient (-2.77 ×10-4), and an outstanding linearity of dn/dT in a wide range of temperature (from 25 °C to 200 °C). Waveguides forming ability for the hybrid polymer with UV imprinting was also demonstrated.
Temporal Pulse Shaping and Optimization in Ultrafast Laser Ablation of Materials
Authors: Stoian R. , Winkler S. , Hildebrand M. , Boyle M. , Thoss A. , Spyridaki M. , Koudoumas E. , Bulgakova N.M. , Rosenfeld A. , Tzanetakis P. , Fotakis C. , Hertel I.V.
Published: June 2019

The possibility of phase manipulation and temporal tailoring of ultrashort laser pulses enables new opportunities for optimal processing of materials. Phase-manipulated ultrafast laser pulses allow adapting the laser energy delivery rate to the material properties for optimal processing laying the groundwork for adaptive optimization in materials structuring. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show that this can result in lower stress, cleaner structures, and allow for a materialdependent optimization process.
Factors Influencing the Lithium Extraction Rate in Layered Oxide Cathodes of Lithium Ion Cells
Authors: Manthiram A. , Choi J.
Published: June 2019

The lithium extraction rate and the rate capability of layered LiNi0.5–0.5yMn0.5–0.5yCoyO2 with 0 ≤ y ≤ 1 have been investigated, respectively, by chemically extracting lithium with the oxidizer NO2BF4 in acetonitrile medium and electrochemically discharging at various C-rates. Both the chemical lithium extraction rate and the electrochemical rate capability are found to increase with increasing Co content y in LiNi0.5–0.5yMn0.5–0.5yCoyO2. While no clear relationship is seen between electrical conductivity and the rate capability, increasing cation disorder between the lithium and transition metal planes with decreasing Co content is found to decrease the chemical lithium extraction rate and rate capability. The lithium extraction rate also influences the structure (P3 vs O1 vs O3) of the end members Ni0.5–0.5yMn0.5–0.5yCoyO2-δ obtained by extracting all the lithium with 100 % excess NO2BF4 in an acetonitrile medium.
Transient and Steady-State Radionuclide Transport Through Penetrations in Nuclear Waste Containers
Authors: Chambre P. L. , Lee W. W.-L. , Kim C. L. , Pigford T. H.
Published: June 2019

In this paper we analyze the transport of radionuclides through penetrations in nuclear waste containers. Penetrations may result from corrosion or cracks and may occur in the original container material, in degraded or corroded material, or in deposits of corrosion products. We do not consider how these penetrations occur or the characteristics of expected penetrations in waste containers. We are concerned only with the analytical formulation and solutions of equations to predict rates of mass transfer through penetrations of specified size and geometry. Expressions for the diffusive mass transfer rates through apertures are presented. We present numerical illustrations for steady-state mass-transfer rates through a circular hole, including concentration isopleths. The results are extended to multiple holes, including a criterion for hole spacing wherein superposition of single-hole solutions can be used. Results illustrated for holes in thin-walled containers show that significant mass transfer can occur even if a small fraction of the container area is perforated. We also illustrate the case of holes facing a water gap, instead of being in intimate contact with porous rock. In this case the radionuclide flux from many small holes approaches that from a bare waste cylinder.
Evaluation of the Susceptibility of Astm A216 Grade Wca Mild Steel to Stress Corrosion Cracking in Simulated Salt Repositopy Environments
Authors: Pitman S. G.
Published: June 2019

In current conceptual designs, a mild steel (ASTM A?16 Grade WCA) is the relerence container material for use in high level nuclear waste packages intended for emplacement in a salt repository. The resistance of the steel to stress corrosion crackinq (SCC) is being investigated as part of the effort underway to verify the suitability of the material for waste package applications. Static tests (U-bend and bolt-loaded fracture toughness specimens) and dynamic tests (slow strain rate and corrosion fatigue) were conducted on both as-cast and weldment specimens of the material, in both low-Mg and high-Mg halite-saturated brines, in the temperature range of 90 to 200°C. The investigations indicate that the steel is not susceptible to SCC under the test conditions employed.
Materials Interactions Relating to Long-Term Geologic Disposal of Nuclear Waste Glass
Authors: Bibler Ned E. , Jantzen Carol M.
Published: June 2019

In the geologic disposal of nuclear waste glass, the glass will eventually interact with groundwater in the repository system. Interactions can also occur between the glass and other waste package materials that are present. These include the steel canister that holds the glass, the metal overpack over the canister, backfill materials that may be used, and the repository host rock. This review paper systematizes the additional interactions that materials in the waste package will impose on the borosilicate glass waste form-groundwater interactions. The repository geologies reviewed are tuff, salt, basalt, and granite. The interactions emphasized are those appropriate to conditions expected after repository closure, e.g. oxic vs. anoxic conditions. Whenever possible, the effect of radiation from the waste form on the interactions is examined. The interactions are evaluated based on their effect on the release and speciation of various elements including radionuclides from the glass. It is noted when further tests of repository interactions are needed before long-term predictions can be made.
Transport and Reaction Kinetics at the Glass:Solution Interface Region: Results of Repository-Oriented Leaching Experiments
Authors: Abrajano Teofilo A. , Bates John K.
Published: June 2019

Repository-oriented leaching experiments involving Savannah River Laboratory (SRL) 165 type glass under a γ-radiation field (1= 0.2 × 104 R/h) have been performed by the Nevada Nuclear Waste Storage Investigations (NNWSI) project. In this communication, we discuss glass surface analyses obtained by SEM, nuclear resonance profiling, and SIMS together with leachate solution data in relation to a mechanism that couples diffusion, hydrolysis (etching and gelation), and precipitation to qualitatively describe the release of different glass components to the leachant solutions. The release of mobile (e.g., Li) and partly mobile (e.g., B) species is controlled primarily by interdiffusion with water species across the interdiffusion zone. Glass components that are immobile in the interdiffusion zone are released to the solution by etching. For prediction of long-term steady-state concentrations of glass components with low solubility, the relative rates of release from the glass and secondary mineral precipitation must be taken into account.
Effects of Gamma Radiolysis on Waste Package Components
Authors: Lewis Michele A. , Reed Donald T.
Published: June 2019

Preliminary short-term experiments to study the effect of gamma radiation on the waste package materials interactions in the environment of a nuclear waste repository in basalt were completed. Experimental parameters were similar to those expected during the saturated post- closure period of the repository, i.e., a temperature of 200°C and a hydrostatic pressure of ≤70 bar. The test components included various combinations of synthetic groundwater (GR4), low carbon steel coupons, CH4, basalt, and basalt/bentonite mixtures (packing). The tests were run in low carbon steel pressure vessels.

It was found that gamma radiation at a dose rate of 104rad/hr for a duration of one and two months increased the H2 yield in all tests. Increases in the organic carbon yield, the sulfate ion concentration, and the corrosion rate of the coupon were observed in some of the tests. These latter results varied with the combination of waste package components included in the tests. Evidence for the quench effect was observed in tests which included basalt.
Radiation Damage and Its Annealing in Sodium Silica Glass
Authors: Mark T.D. , Ritter W.
Published: June 2019

Annealing of radiation damage in artificial sodium silica glass has been studied by absorption spectroscopy for different radiation sources (fission fragments produced by n,f reactions, alpha decays produced by n, α reactions, and 2 MeV electrons) as a function of annealing time and temperature. The annealing observed can be described best by a single exponential function

A(t) = a exp (− αt)

with an Arrhenius type temperature dependence of the annealing coefficient α

α(T) = α0 exp (− EA/kT)

For the three different radiation sources similar activitation energies EA were deduced from the data. Possible annealing processes are discussed.
Tc Behavior in the Basalt-Synthetic Groundwater System as a Function of Temperature and Initial Oxygen Content
Authors: Wood M. I. , Ames L. L. , Mcgarrah J. E.
Published: June 2019

Experiments have been completed in the basalt-Tc-doped groundwater sys- tem to quantify the mobility of Tc in the waste package and near field envion- ment in a repository located in basalt. The experiments were completed using a batch sorption technique in which 8 rushed basalt and Tc-doped groundwater were reacted at 85, 100, 125 and 150 °C for periods of time up to 118 days. The water to rock ratio was 10:1 ml/g. In another set of experiments, basalt crushed under anoxic conditions and Tc-doped groundwater were reacted at 85°C at different water to rock ratios (10:3, 20:3, 40:3 and 80:3 ml/g).

The rate and percentage of Tc removed from solution increased with increasing temperature and decreasing water to rock ratio. Also, basalt crushed under anoxic conditions removed >87% of Tc from solution at 85°C in 7 days while no Tc was removed from solution with basalt crushed in air at the same temperature after 118 days. These results are consistent with the hypothesis that (1) ferrous iron in basalt phases preferentially consumes oxygen and will not reduce Tcuntil all free oxygen in the system is consumed. Once oxygen is consumed, reduction of Tc is quite rapid. These data indicate that the potential exists in a basalt hydrothermal environment to satisfactorily immobilize Tc. Reliable application of these data will depend on experimental and theoretical estimates of oxygen consumption with time in the waste package environment following repository closure, subsequent saturation and long term hydrothermal reactions.
Radiometric Dating of Ochoan (Permian) Evaporites, Wipp Site, Delaware Basin, New Mexico, Usa
Authors: Brookins Douglas G. , Lambert Steven J.
Published: June 2019

We have attempted radiometric dating of halide-sulfate salts and clay minerals from the Delaware Basin, New Mexico, USA, as part of geochemical study of the stability of the evaporite sequence at the WIPP (Waste Isolation Pilot Plant--a US DOE facility) site. We undertook this dating to determine: (1) primary age of evaporite genesis or time(s) of recrystallization, (2) if previously undated evaporite minerals (leonite, polyhalite, kieserite) give useful data, and (3) if the detrital clay minerals have been radiometrically reset at any time following their incorporation into the evaporite medium. We have shown earlier that polyhalites can indeed be successfully dated by the K-Ar method, and once corrections are applied for admixed halide minerals, dates of 210-230 Ma for the Delaware Basin are obtained. Rb-Sr isochrons from early stage sylvites-polyhalites- anhydrites yield 220 ± 10 Ma, even when some sylvites yield lower K-Ar dates due to l1s of 40Ar*. K-Ar dates on leonites and kieserites are also low due to 40Ar* loss, but their Rb-Sr dates are higher. Detrital clay minerals from the Delaware Basin collectively yield a highly scattered isochron (390 ± 77 Ma), but samples from a local area, such as the WIPP Site, give a much better age of 428 ± 7 Ma. These dates show that the interaction between the clay minerals and the evaporitic brines was insufficient to reset the clay minerals Rb-Sr systematics. In a related study, we note that a dike emplaced into the evaporite at 34 Ma had only very limited effect on the intruded rocks; contact phenomena were all within 2 m of the dike. All of our geochemical (radio-metric and trace element) studies of the WIPP site argue for preservation of the isotopic and chemical integrity of the major minerals for the past 200 Ma.
Spent Fuel as a Waste Form - Data Needs to Allow Long Term Performance Assessment Under Repository Disposal Conditions.
Authors: Oversby V. M.
Published: June 2019

Performance assessment calculations are required for high level waste repositories for a period of 10,000 years under NRC and EPA regulations. In addition, the Siting Guidelines (IOCFR960) require a comparison of sites following site characterization and prior to final site selection to be made over a 100,000 year period. In order to perform the required calculations, a detailed knowledge of the physical and chemical processes that affect waste form performance will be needed for each site. While bounding calculations might be sufficient to show compliance with the requirements of IOCFR60 and 40CFRI91, the site comparison for 100,000 years will need to be based on expected performance under site specific conditions. The only case where detailed knowledge of waste form characteristics in the repository would not be needed would be where radionuclide travel times to the accessible environment can be shown to exceed 100,000 years. This paper will review the factors that affect the release of radionuclides from spemt fuel under repository conditions, summarize our present state of knowledge, and suggest areas where more work is needed in order to support the performance assessment calculations.
Mechanical properties and size effect in nanometric W/Cu multilayers
Authors: Villain P. , Faurie D. , Renault P.-O. , Bourhis E. Le , Goudeau P. , Badawi K.-F.
Published: June 2019

The mechanixcal behavior of W/Cu multilayers with periods ranging from 24 down to 3 nm prepared by ion beam sputtering was analyzed using a method combining X-ray diffraction and tensile testing, and instrumented indentation. Cracks perpendicular to the tensile axis observed by optical microscopy were generated in the films under the largest applied tensile stresses. These cracks may appear in the multilayer while W layers are still in a compressive stress state. Elastic modulus and hardness values were extracted from nano-indentation data. Crack initiation and elastic constants were observed to depend on the period of these multilayers.
Improvement of the Elastic Modulus of Micromachined Structures using Carbon Nanotubes
Authors: Joshi Prasoon , Duarte Nicolás B. , Goyal Abhijat , Gupta Awnish , Tadigadapa Srinivas A. , Eklund Peter C.
Published: June 2019

Microelectromechanical flexural structures have been fabricated using sandwiched multi-layers consisting of bundled singled walled carbon nanotubes(SWNTs) incorporated into silicon nitride (Si3N4) films. The Si3N4-SWNT composite layer was patterned by reactive ion etching followed by release in XeF2 to create freestanding bridge structures. The mechanical stiffness of the micromechanical bridges was monitored via force-displacement (F-D) curves obtained using an Atomic Force Microscope (AFM). Inclusion of SWNTs resulted in an increase in the spring constant of the bridge by as much as 64%, with an average increase of 25%. In a second experiment, micromachined bridges fabricated using dissolved wafer process were coated with debundled SWNTs. The SWNTs suspended in N-methyl-2-pyrrolidinone (NMP) solvent were sprayed locally on each bridge using a piezoelectric print head. Resonance frequency measurements were done in vacuum (∼10-4 Torr) on the bridges after successive SWNT depositions. A 20% increase in the resonance frequency of the bridges was observed. The observed increase in stiffness in the first set of experiments as well as the observed increase in the frequency in the second set of experiments can be attributed to the high axial modulus of elasticity (∼1 TPa) of the carbon nanotubes.
Role of stress on the phase control and dielectric properties of (1-x) BiFeO3 - xBa0.5Sr0.5TiO3 solid solution thin films
Authors: Cho Chin Moo , Hong Hee Bum , Hong Kug Sun
Published: June 2019

Dielectric properties and structure of (1-x) BiFeO3 (BFO) - x Ba0.5Sr0.5TiO3 (BST) (x = 0 ∼1) solid solution thin films were investigated. All films were prepared at 600 oC on (111) oriented Pt / TiO2 / SiO2 / Si substrates by pulsed laser deposition (PLD) technique. Solid solution could be achieved in all composition ranges, evidenced by X-ray diffraction (XRD) and field emission scanning electric microscope (FE-SEM). The intermediate compositions (0.4 = x = 0.8) exhibited a distinct (111) oriented cubic perovskite structure, while rhombohedra symmetry was found in the x < 0.4 range. Dielectric constant and tunability of the (1-x) BFO – x BST films within this composition region (0.4 = x = 0.8) decreased from 1110 to 920 at 1 MHz, and increased from 28.34 % to 32.42 % at 200 kV/cm, respectively, while loss tangent remains constant. A systematic decrease in lattice parameter with BST addition reduced stress due to reduction of lattice parameter mismatch between film and the substrate. In that range, the improvement of the dielectric properties without a degradation of loss tangent is attributed to the presence of the stress relaxation, which was quantitatively confirmed by a surface profiler based on Stoney's equation.
Residual Stresses in TiO2 Anatase Thin Films Deposited on Glass, Sapphire and Si Substrates
Authors: Al-Homoudi Ibrahim A. , Zhang Linfeng , Georgiev D.G. , Naik R. , Naik V.M. , Rimai L. , Simon Ng K.Y. , Baird R.J. , Auner G.W. , Newaz G.
Published: June 2019

Anatase-TiO2 films (thickness 100-1000 nm) were grown on glass, sapphire, and Si(100) substrates using pulsed dc-magnetron reactive sputtering. By measuring the curvature of substrates before and after the thin film deposition, the residual stresses were determined. These results clearly show that the bi-axial stresses are compressive type and decreases with the increasing film thickness. The Raman spectra of these films were measured with two different excitation wavelengths (514 and 785 nm) and the thickness dependent shifts of Eg phonon mode were studied. The dominant 144 cm-1 Eg mode in TiO2 anatase clearly shifts to a higher value by 0.45 to 17.4 cm-1 depending on the type of substrate and the thickness of the film. Maximum shift was seen for the films on glass substrate indicating a higher bi-axial compressive stress in agreement with the curvature measurements. The excitation wavelength dependent shift of Eg mode clearly shows that the bi-axial stress increases along the film depth, being larger at the film/substrate interface.
Stress Analysis of Strained Superlattices.
Authors: Peleshchak R. , Khlyap H.
Published: June 2019

The latest successful development of smart technologies, in particular, molecular-beam epitaxy technique and pulse-laser deposition method, made it possible to manufacture optoelectronic active elements based on semiconductor materials with sufficient mismatch of the lattice parameters. This problem is of special interest for preparing photosensitive devices with strained superlattices. The paper focuses on the analysis of charge carriers behavior in mechanically strained superlattices based on semiconductor materials from A2B6 and A4B6 (ZnSe, ZnTe and PbS) playing an important role in the optoelectronics design. Computational modeling is settled on the solution of one-dimensional Schroedinger equation.
Analysis of film residual stress on a of 4-point bend test for thin film adhesion
Authors: Roham Sassan , Hight Timothy
Published: June 2019

The four-point bend (4PB) test has emerged as a method of choice in semiconductor industry for obtaining bimaterial interface adhesion data. When measuring the interface adhesion using 4PB test, it is essential to obtain a crack through the interface of interest. The deposited films, however, posses intrinsic and extrinsic stresses which affect the ratio between energy release rates for interface cracking and crack penetration. Crack penetration and deflection at a bimaterial interface and the role of residual stress has been broadly studied before. However, the results are based on asymptotic analysis regarding interface between two semi-infinite half spaces, where the results do not directly account for boundary conditions and finite size effects of an actual test specimen. In this paper, we look at the role these residual stresses play on the competition between deflection and penetration energy release rates of a bimaterial interface and the extent of which the previous assumption of two semi-infinite media can be accepted.
Thermomechanical Behavior and Properties of Passivated Pvd and Ecd Cu Thin Films
Authors: Gregoire M. , Kordic S. , Gergaud P. , Thomas O. , Ignat M.
Published: June 2019

The thermomechanical behavior is investigated of SiCN-encapsulated blanket Physical Vapor Deposited (PVD) and Electrochemically Deposited (ECD) Cu films. At lower ECD Cu film thicknesses an anomalous shape and a tail of the stress-temperature curve are observed, which are not caused by impurities at the interfaces, but are correlated to highly textured microstructure. Repeated thermal cycling of up to 400 °C does not markedly change the texture of the films, but a significant texture change takes place with increasing ECD Cu thickness. Thermal cycling induces grain growth for thicker films only. Impurity content and distribution in the PVD films do not change due to cycling.
Elastic behavior of fibre-textured gold films by combining synchrotron X-ray diffraction and in-situ tensile testing
Authors: Faurie D. , Renault P.-O. , Bourhis E. Le , Goudeau P.
Published: June 2019

The elastic behavior of gold thin films deposited onto Kapton substrate has been studied using in-situ tensile tester in a four-circle goniometer at a synchrotron beam line (LURE facility, France). Knowing the stress tensor in the film, the strong {111} fibre texture was taken into account using the Crystallite Group Method (CGM). CGM strain analysis allows predicting a non linear relationship between strain and sin2 Ψ obtained for the thin films due to the strong anisotropy of gold. In contrast, the average of strains in longitudinal and transversal directions varies linearly with sin2 Ψ. The evolution of the slope of these curves as a function of the applied stresses in the film allowed determining the single-crystal elastic constant s44 of thin gold films.
Fiber-optics Low-coherence Integrated Metrology for In-Situ Non-contact Characterization of Wafer Curvature for Wafers Having Non-uniform Substrate and Thin Film Thickness
Authors: Walecki Wojciech J. , Pravdivtsev Alexander , Lai Kevin , Santos Manuel , Mikhaylov Georgy , Mihaylov Mihail , Koo Ann
Published: June 2019

Abstract. We propose novel stress metrology technique for measurement of local values stress tensor components in the coated wafers. New metrology is based on fiber-optic low coherence interferometry and can be applied to study stress not only in semicondiuctor wafers but in wide variety applications spanning from semiconductor to construction industry where measurements of plates covered by thin film encountered in flat panel displayes, solar cells, modern windows.
Novel Single Frequency and Broadly Tunable Laser Sources Developed at Coherent Technologies Inc. for Remote Sensing Applications
Authors: Phillips Mark W.
Published: June 2019

This paper provides an overview of novel single frequency and broadly tunable laser technology being developed at Coherent Technologies, Inc. (CTI) for long-range remote sensing of hard targets and distributed targets from ground based and airborne platforms. In all these applications, the need for high beam quality and efficient high power operation is paramount. For many of the applications, it is also critical to control and measure frequency content of the emitted and collected light to a high degree of accuracy. For example, a sub-kHz linewidth is typically required for velocity and vibration imaging, and sub-MHz linewidth for some differential absorption lidar (DIAL) type measurements.
Laser And Nonlinear Optical Materials For Laser Remote Sensing
Authors: Barnes Norman P.
Published: June 2019

NASA remote sensing missions involving laser systems and their economic impact are coutlined. Potential remote sensing missions include: green house gasses, tropospheric winds, ozone, water vapor, and ice cap thickness. Systems to perform these measurements use lanthanide series lasers and nonlinear devices including second harmonic generators and parametric oscillators. Demands these missions place on the laser and nonlinear optical materials are discussed from a materials point of view. Methods of designing new laser and nonlinear optical materials to meet these demands are presented.
Robust, Efficient, Optical-Damage-Resistant, 200 mJ Nanosecond Ultraviolet Light Source for Satellite-Based Lidar Applications
Authors: Armstrong Darrell J. , Smith Arlee V.
Published: June 2019

Conventional wisdom contends that high-energy nanosecond UV laser sources operate near the optical damage thresholds of their constituent materials. This notion is particularly true for nonlinear frequency converters like optical parametric oscillators, where poor beam quality combined with high intra-cavity fluence leads to catastrophic failure of crystals and optical coatings. The collective disappointment of many researchers supports this contention. However, we're challenging this frustrating paradigm by developing high-energy nanosecondUVsources that are efficient, mechanically robust, and most important, resistant to optical damage. Based on sound design principles developed through numerical modeling and rigorous laboratory testing, our sources generate 8-10 ns 190 mJ pulses at 320 nm with fluences≤ 1 J/cm2. Using the second harmonic of a Q-switched, injection-seeded Nd:YAGlaser as the pump source, we convert the near-IR Nd:YAG fundamental to UV with optical-to-optical efficiency exceeding 21%.
Two MOEMS Microphone Designs for Acoustic Sensing Applications
Authors: Avset Berit S. , Bakke Kari A. H. , Fismen Britta. G. , Johansen Ib-Rune , Rogne Henrik , Sagberg Håkon , Wang Dag T.
Published: June 2019

Two different micro-optical microphones are presented. The first is based on interferometric read-out of a deflecting membrane, based on the Fabry-Perot principle. The sensing device is produced in Silicon by combining standard CMOS and MEMS processing. This ensures that high accuracy alignment and low cost production can be obtained. Optical sensor elements with a ring structure are included on one of the Fabry-Perot surfaces whereas the other surface is an optically transparent membrane. Light from an uncollimated light source such as a semiconductor laser or a LED, will form a ring pattern when transmitted through the membrane.

The other microphone principle presented is based on a diffractive lens. The structure has a metallic ring pattern separated from a reflecting membrane with an air gap. When the air gap is an odd number of quarter wavelengths of the impinging light, these surfaces form a binary phase diffractive lens. By placing a light source and a detector in the focal plane of the lens, the measured intensity will be highly sensitive to the position of the membrane. Similarly to the first microphone this device can be mass produced at low cost using micromachining techniques.

Results from prototype devices will be presented, proving both principles and showing excellent properties compared to expensive commercially available condenser microphones.
Behaviour of underpinning piles due to shield tunnel installation
Authors: Wang Bolin , Wang Xu , Ma Wenjie
Published: June 2019

A laboratory simulation of the number 1 metro line in Lanzhou City, China, was carried out to determine the feasibility of passing through existing bridge projects. The results show that the foundation settlement of the underpinning piles is less than that of the existing piles. A great change in the axial forces on underpinning piles occurs about 10 cm lower than it does on the existing piles. The side friction of the underpinning piles reaches its peak value within the range 20–30 cm. The maximum side friction of an underpinning pile is higher than that of the existing piles. The bearing capacity of the underpinning pile system is larger than that of the existing pile system. In the excavation simulation of a shield tunnel, the axial forces on underpinning piles change in a similar manner as that of the existing piles at excavation depths of 0–20 and 100–120 cm. Negative friction occurs when the depth of excavation is 30 cm, and it reaches a maximum at 20 cm from the tops of the underpinning piles. The neutral point is about 32 cm from the top of the pile body. The load-sharing ratio of the pile cap increases with increases in loading.