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As a promising class of alternatives to noble metal-based oxygen electrocatalysts, hybrids of metal/metal oxide (M/MO) and N-doped carbon have been widely explored. To address the often-insufficient catalytic activity of single M/MO-embedded N–C systems, researchers have introduced a second M/MO, usually via wet processes. In this work, we leverage the unique capability of atomic layer deposition (ALD) to enable the introduction of a trace amount of ceria throughout a Co/CoOx-embedded N-doped carbon nanostructure in a highly uniform and dispersed manner to maximize heterogeneous interfacial areas and thus catalytically active sites. An optimally prepared catalyst achieves an ORR onset potential of 0.95 V (0.1 M KOH) and an OER potential of 1.53 V at 10 mA cm−2 (1 M KOH) and exhibits excellent cyclic durability. Quasi-operando observations reveal the multifaceted roles of the tiny amount of introduced ceria in facilitating electrocatalytic activity and enhancing durability. The ceria activates reactant adsorbates and transfers the activated intermediates to neighboring CoOx and electronically couples with Co and N species for enhanced catalytic activity. A high concentration of trivalent Ce state is readily and continuously restored during ORR/OER for an uninterrupted activation of reactants, also contributing to a highly stable reaction.

We aim to illuminate how the microscopic properties of a metal surface map to its electric-field noise characteristics. In our system, prolonged heat treatments of a metal film can induce a rise in the magnitude of the electric-field noise generated by the surface of that film. We refer to this heat-induced rise in noise magnitude as a thermal transformation. The underlying physics of this thermal transformation process is explored through a series of heating, milling, and electron treatments performed on a single surface ion trap. Between these treatments, $^{40}$Ca$^+$ ions trapped 70~$\mu$m above the surface of the metal are used as detectors to monitor the electric-field noise at frequencies close to 1~MHz. An Auger spectrometer is used to track changes in the composition of the contaminated metal surface. With these tools we investigate contaminant deposition, chemical reactions, and atomic restructuring as possible drivers of thermal transformations.

Some organic additive manufacturing feedstocks can be cohesive and tend to agglomerate in suspensions, which can lead to significant challenges in formulating solids-loaded fluids, like those used in many additive manufacturing processes. By depositing an ultra-thin, layer of a second material conformally with the surface of the feedstock powder, Atomic Layer Deposition (ALD) can be used to uniquely modify the surface and, thereby, cohesion of the powder material without changing the properties of the bulk material. This paper demonstrates low temperature (

In this report, we demonstrate that a uniform angstrom-level oxide overcoat (either ceria or yttria with a nominal thickness of 0.7–1.5 A) by atomic layer deposition is highly effective not only in enhancing the thermal stability of underlying infiltrated ceria nanoparticles but also in facilitating electrode kinetics. By employing Sr-free electrodes and Cr-free gas environment, we focus on the thermal agglomeration as the major degradation pathway and reveal the close correlation between thermal agglomeration rate of infiltrated nanoparticles and degradation rate of electrode performance in a quantitative manner. We also provide a mechanistic perspective on the beneficial effect of the overcoat in durability and performance of solid oxide fuel cell cathodes.

Herein we report the fabrication of ultralight gold aerogel monoliths with tunable densities and pore structures. Gold nanowires are prepared at the gram scale by substrate-assisted growth with uniform size, ultrathin diameters, high purity, and a high aspect ratio. Freeze-casting of suspensions of these nanowires produces free-standing, monolithic aerogels with tunable densities from 6 to 23 mg/cm3, which to the best of our knowledge represents the lowest density monolithic gold material. We also demonstrate that the pore geometries created during freeze-casting can be systematically tuned across multiple length scales by the selection of different solvents and excipients in the feedstock suspension. The mechanical behavior of porous materials depends on relative density and pore architectures.

In this report, we demonstrate a bimetallic Co/Cu-embedded N-doped carbon structure for trifunctional catalysis of oxygen reduction, oxygen evolution and hydrogen evolution reactions in alkaline media. A hybrid catalyst synthesized through a metal-organic framework-based process (M-NC-CoCu) enables an active trifunctional catalysis due to its multi-faceted favorable characteristics. It is believed that a range of catalytically active sites are formed through the approach including well-dispersed tiny CuCo2O4 phases, a high concentration of pyridinic and graphitic N, and Cu-Ox, Cu-Nx and Co-Nx moieties. In addition, a high-surface-area morphology with a high concentration of sp2 bonding, which is beneficial for facilitated electron conduction, further contributes to the performance as an electrocatalyst.

Three-dimensional (3D) printed, hierarchically porous nickel molybdenum (NiMo) electrocatalysts were synthesized and evaluated in a flow-through configuration for the hydrogen evolution reaction (HER) in 1.0 M KOH(aq) in a simple electrochemical H-cell. 3D NiMo electrodes possess hierarchically porous structures because of the resol-based aerogel precursor, which generates superporous carbon aerogel as a catalyst support. Relative to a traditional planar electrode configuration, the flow-through configuration allowed efficient removal of the hydrogen bubbles from the catalyst surface, especially at high operating current densities, and significantly decreased the overpotentials required for HER. An analytical model that accounted for the electrokinetics of HER as well as the mass transport with or without the flow-through configuration was developed to quantitatively evaluate voltage losses associated with kinetic overpotentials and ohmic resistance due to bubble formation in the porous electrodes. The chemical composition, electrochemical surface area (ECSA), and roughness factor (RF) were also systematically studied to assess the electrocatalytic performance of the 3D printed, hierarchically porous NiMo electrodes. An ECSA of 25163 cm2 was obtained with the highly porous structures, and an average overpotential of 45 mV at 10 mA cm-2 was achieved over 24 h by using the flow-through configuration. The flow-through configuration evaluated in the simple H-cell achieved high electrochemical accessible surface areas for electrochemical reactions and provided useful information for adaption of the porous electrodes in flow cells.

As theoretically hypothesized for several decades in group IV transition metals, we have discovered a dynamically stabilized body-centered cubic (bcc) intermediate state in Zr under uniaxial loading at sub-nanosecond timescales. Under ultrafast shock wave compression, rather than the transformation from alpha-Zr to the more disordered hex-3 equilibrium omega-Zr phase, in its place we find the formation of a previously unobserved nonequilibrium bcc metastable intermediate. We probe the compression-induced phase transition pathway in zirconium using time-resolved sub-picosecond x-ray diffraction analysis at the Linac Coherent Light Source. We also present molecular dynamics simulations using a potential derived from first-principles methods which independently predict this intermediate phase under ultrafast shock conditions. In contrast with experiments on longer timescale (> 10 ns) where the phase diagram alone is an adequate predictor of the crystalline structure of a material, our recent study highlights the importance of metastability and time dependence in the kinetics of phase transformations.

Synthesis of chlorine-free, rare earth oxide aerogels from the lanthanide series was achieved using a modified epoxide-assisted sol-gel method. An ethanolic solution of the hydrated metal nitrate, propylene oxide, and ammonium carbonate was found to gel upon heating to 333 K. Critical point drying of the wet gel in CO2 yielded monolithic aerogels. Most of the aerogels were amorphous as-prepared, but became nano-crystalline after calcination at 923 K in air. The aerogels had high surface areas (up to 150 m2/g), low densities (40–225 mg/cm3), and were photoluminescent.

Boron-doped and defect-engineered graphene aerogels are prepared using triphenyl boron as a boron precursor and subsequent heat treatments. The boron chemistry and concentration in the graphene lat...

Transition metal oxides (TMOs) anchored on a carbon nanostructure have been widely pursued for oxygen reduction reaction (ORR) catalysis. The high ORR activity of TMO/graphene has been often attrib...

The reaction of water and molecular oxygen with stoichiometric uranium dioxide (i.e. UO2) powder at elevated temperature was studied by high-resolution x-ray photoelectron spectroscopy (XPS), infrared (IR) spectroscopy, powder x-ray diffraction (XRD), and scanning electron microscopy (SEM). Oxidation resulting from the dissociative chemisorption of the adsorbing molecules and subsequent incorporation into the oxide lattice was observed and quantified. Molecular oxygen was found to be a stronger oxidation agent than water at elevated temperatures but not at ambient.

Reactive Ti-5Al-5 V-5Cr-3Mo (Ti5553) alloy feedstock powder is used in laser powder-bed fusion (LPBF). Due to the large quantity of powder necessary for LPBF, powder is reused numerous times under oxidizing environments. Transformations to the powder’s native surface oxide may impact the LPBF process and lead to deviations from expected behavior of printed parts. Here, we present a multimodal characterization of new and reused powder by combining X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and transmission electron microscopy (TEM) of focused ion beam (FIB)-prepared cross sections of individual powder particles to understand how the surface oxide composition changes, grows, and becomes hydroxylated and hydrated due to reuse. We show that the native oxide film of Ti5553 powder is a hydroxylated mixed oxide composed of TiO2 and Al2O3 that grows from 5.6 +/- 0.7 nm to 8.3 +/- 1.1 nm due to reuse. Al oxide regions of the surface oxide become more hydroxylated during reuse in comparison to Ti oxide regions. This indicates that an outer oxide of pure TiO2 may enhance recyclability of Ti5553 powder while the presence of Al oxides may decrease recyclability. Further characterization of surface transformations due to recyclability may eliminate unnecessary variation in LPBF.

Auger electron spectroscopy (AES) was used to characterize the oxide scale formed on an ∼0.5 wt. % Ga plutonium metal alloy. Analysis of changes to the characteristic Auger transitions for Pu and O during sputter depth profiles were used in combination with previously measured sputter yields to determine the thickness of the oxide scale and provide insight into its chemistry. From this data, the parabolic kinetics for the Pu-Ga alloy were determined as a function of relative humidity, RH = 14–92%, and oxygen partial pressure, p(O2) = 31–157 Torr, at 25 °C. For each relative humidity investigated, the parabolic rate constant was found to be independent of oxygen partial pressure. Power-law fits to the relative humidity effect on the rate constant was found to have a power of n = 1.265, indicating the diffusion species which rate-limits the reaction isn’t molecular water, which subsequent dissociates at the oxide-metal interface, or hydroxyl from dissociation at the gas-surface interface.

Reflection Electron Energy Loss Spectra (REELS) have been acquired on plutonium δ-Pu-Ga alloys, α-Pu2O3 and PuO2. The position of the peaks attributable to the Pu 6p excitation can be used as ‘fingerprint’ for these species. X-ray Photoelectron Spectroscopy has been used to aid interpretation of the REELS spectra. The band gap of PuO2 was determined from the onset of the energy loss in the REELS spectrum. The REELS data have been evaluated within the dielectric response theory by means of the QUEELS-∊(k, w)-REELS software [Surf. Interface Anal. 36, (2004) 824]. The Energy Loss Function, dielectric function, refractive index and extinction coefficient for these materials have been determined in the ultraviolet and extreme ultraviolet range and are compared to previously reported results. Crown copyright (C) 2021 Published by Elsevier B. V. All rights reserved.

High resolution x-ray photoemission spectroscopy (XPS) was used to characterize the chemical speciation of high purity uranium dioxide (UO2) powder samples following aging for periods of up to one year under controlled conditions with relative humidity ranging from 34% to 98%. A systematic shift to higher uranium oxidation states, and thus an increase in the mean uranium valence, was found to directly correlate with the dose of water received (i.e. the product of exposure time and relative humidity). Exposure duration was found to have a greater impact on sample aging than relative humidity. The sample aged at 98% relative humidity was found to have unique structural differences for exposure time beyond 180 days when observed by scanning electron microscopy (SEM).

The equation of state (EOS) of materials at warm dense conditions poses significant challenges to both theory and experiment. We report a combined computational, modeling, and experimental investigation leveraging new theoretical and experimental capabilities to investigate warm-dense boron nitride (BN). The simulation methodologies include path integral Monte Carlo (PIMC), several density functional theory (DFT) molecular dynamics methods [plane-wave pseudopotential, Fermi operator expansion (FOE), and spectral quadrature (SQ)], activity expansion (actex), and all-electron Green's function Korringa-Kohn-Rostoker (mecca), and compute the pressure and internal energy of BN over a broad range of densities and temperatures. Our experiments were conducted at the Omega laser facility and the Hugoniot response of BN to unprecedented pressures (1200--2650 GPa). The EOSs computed using different methods cross validate one another in the warm-dense matter regime, and the experimental Hugoniot data are in good agreement with our theoretical predictions. By comparing the EOS results from different methods, we assess that the largest discrepancies between theoretical predictions are $\ensuremath{\lesssim}4%$ in pressure and $\ensuremath{\lesssim}3%$ in energy and occur at ${10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, slightly below the peak compression that corresponds to the $K$-shell ionization regime. At these conditions, we find remarkable consistency between the EOS from DFT calculations performed on different platforms and using different exchange-correlation functionals and those from PIMC using free-particle nodes. This provides strong evidence for the accuracy of both PIMC and DFT in the high-pressure, high-temperature regime. Moreover, the recently developed SQ and FOE methods produce EOS data that have significantly smaller statistical error bars than PIMC, and so represent significant advances for efficient computation at high temperatures. The shock Hugoniot predicted by PIMC, actex, and mecca shows a maximum compression ratio of $4.55\ifmmode\pm\else\textpm\fi{}0.05$ for an initial density of $2.26\phantom{\rule{0.28em}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$, higher than the Thomas-Fermi predictions by about 5%. In addition, we construct tabular EOS models that are consistent with the first-principles simulations and the experimental data. Our findings clarify the ionic and electronic structure of BN over a broad range of temperatures and densities and quantify their roles in the EOS and properties of this material. The tabular models may be utilized for future simulations of laser-driven experiments that include BN as a candidate ablator material.

High purity UO 2 powder samples were subjected to accelerated aging under controlled conditions with relative humidity ranging from 34% to 98%. Characterization of the chemical speciation of the products was accomplished using X-ray photoelectron spectroscopy (XPS). A shift to higher uranium oxidation states was found to be directly correlated to increased relative humidity exposure. Additionally, the relative abundance of O 2- , OH - , and H 2 O was found to vary with exposure time. Thus, it is expected that uranium oxide materials exposed to high relative humidity conditions during processing and storage would display a similar increase in average uranium valence.

An oxide layer with a known thickness and chemistry was grown on delta stabilized Pu and sputtered with 1–5 keV Ar+ ions over a range of incident ion angle between 22° and 72°. From the time required to remove the oxide layer, sputter yields of PuO2 were calculated. The sputter yields appear to increase with higher Ar+ ion beam energy in the range of 1–5 keV at an incident sputter ion angle of 42° and were found to increase with a decreasing angle of incidence up to 62°. The degree of oxide reduction induced during the sputter process was found to vary with the incident sputter ion angle.

Thallium bromide (TlBr) crystals subjected to hydrochloric acid (HCl) chemical treatments have been shown to advantageously affect device performance and longevity in TlBr-based room temperature radiation detectors, yet the exact mechanisms of the improvements remain poorly understood. Here, we investigate the influence of several HCl chemical treatments on device-grade TlBr and describe the changes in the composition and electronic structure of the surface. Composition analysis and depth profiles obtained from secondary ion mass spectrometry (SIMS) identify the extent to which each HCl etch condition affects the detector surface region and forms of a graded TlBr/TlBrCl surface heterojunction. Using a combination of X-ray photoemission spectroscopy (XPS) and hybrid density functional calculations, we are able to determine the valence band offsets, band gaps, and conduction band offsets as a function of Cl content over the entire composition range of . This study establishes a strong correlation between device process conditions, surface chemistry, and electronic structure with the goal of further optimizing the long-term stability and radiation response of TlBr-based detectors.

Interaction of short-wavelength free-electron laser (FEL) beams with matter is undoubtedly a subject to extensive investigation in last decade. During the interaction various exotic states of matter, such as warm dense matter, may exist for a split second. Prior to irreversible damage or ablative removal of the target material, complicated electronic processes at the atomic level occur. As energetic photons impact the target, electrons from inner atomic shells are almost instantly photo-ionized, which may, in some special cases, cause bond weakening, even breaking of the covalent bonds, subsequently result to so-called non-thermal melting. The subject of our research is ablative damage to lead tungstate (PbWO4) induced by focused short-wavelength FEL pulses at different photon energies. Post-mortem analysis of complex damage patterns using the Raman spectroscopy, atomic-force (AFM) and Nomarski (DIC) microscopy confirms an existence of non-thermal melting induced by high-energy photons in the ionic monocrystalline target. Results obtained at Linac Coherent Light Source (LCLS), Free-electron in Hamburg (FLASH), and SPring-8 Compact SASE Source (SCSS) are presented in this Paper.

Realization of macroscale three-dimensional isotropic carbons that retain the exceptional electrical and mechanical properties of graphene sheets remains a challenge. Here, a method for fabricating graphene-derived carbons (GDCs) with isotropic properties approaching those of individual graphene sheets is reported. This synthesis scheme relies on direct cross-linking of graphene sheets via the functional groups in graphene oxide to maximize electronic transport and mechanical reinforcement between sheets and the partial restacking of the sheets to increase the material density to about 1 g cm-3. These GDCs exhibit properties 3–6 orders of magnitude higher than previously reported 3D graphene assemblies.

Spectroscopic ellipsometry is combined with scanning electron microscopy and multisample analysis of the measured oxide thickness difference from one sample at two different times during the oxide growth phase or from two separate samples to obtain the optical constants of the oxides. With the obtained thickness and optical constants of the oxides, the optical properties of the substrate material can be uniquely deduced. This methodology has been applied to obtain, the refractive indices and extinction coefficients of delta plutonium (δ-Pu) metal with 0.5 wt. % Ga in the wavelength region from 435 nm to 850 nm, without the influence of surface oxides. The presented methodology can also be applied to metals and semiconductors from surface oxidized samples, even when the oxides do not possess a common set of optical characteristics.Spectroscopic ellipsometry is combined with scanning electron microscopy and multisample analysis of the measured oxide thickness difference from one sample at two different times during the oxide growth phase or from two separate samples to obtain the optical constants of the oxides. With the obtained thickness and optical constants of the oxides, the optical properties of the substrate material can be uniquely deduced. This methodology has been applied to obtain, the refractive indices and extinction coefficients of delta plutonium (δ-Pu) metal with 0.5 wt. % Ga in the wavelength region from 435 nm to 850 nm, without the influence of surface oxides. The presented methodology can also be applied to metals and semiconductors from surface oxidized samples, even when the oxides do not possess a common set of optical characteristics.

Thallium bromide (TlBr) is a material of interest for use in room temperature gamma ray detector applications due to is wide bandgap 2.7 eV and high average atomic number (Tl 81, Br 35). Researchers have achieved energy resolutions of 1.3% at 662 keV, demonstrating the potential of this material system. However, these detectors are known to polarize using conventional configurations, limiting their use. While high quality material is a critical starting point for excellent detector performance, we show that the room temperature stability of planar TlBr gamma spectrometers can be significantly enhanced by treatment with both hydrofluoric and hydrochloric acid. By incorporating F or Cl into the surface of TlBr, current instabilities are eliminated and the longer term current of the detectors remains unchanged. In addition the choice of electrode metal is shown to have a dramatic effect on the long term stability of TlBr detector performance 241Am spectra are also shown to be more stable for extended periods; detectors have been held at 4000 V/cm for 50 days with less than 10% degradation in peak centroid position.

CdZnTe-based gamma detectors require a reduction of electronic noise contributed by apparent device and surface leakage current, especially for advanced readout schemes such as the Co-planar Grid or Pixelated Grid. In this work, we describe a combination of surface treatments and amorphous semiconductor layers that result in a reduction of both apparent device and surface leakage current compared to metal contacts on Br:MeOH etched devices. Characterization by scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), x-ray photoelectron spectroscopy (XPS), current-voltage (IV), and pulse height spectra is performed.

Ring opening metathesis polymerization (ROMP) of cycloolefins is a promising new route for the preparation of polymeric aerogels. The resulting unsaturation in the polymer backbone, however, makes these particular systems susceptible to oxidative degradation under ambient conditions. One method to increase the oxidative stability of these aerogels is to hydrogenate the material. In the present study, hydrogenation of poly(dicyclopentadiene) gels was achieved through thermolysis of para-toluenesulfonyl hydrazide in the presence of tripropylamine followed by solvent exchange and supercritical drying to form the hydrogenated aerogel (H- p DCPD). Aerogels were prepared with varying densities and were characterized by FTIR-ATR, elemental analysis, BET, SEM, XPS, DSC and TGA. The oxidative stability of H- p DCPD aerogels over p DCPD was investigated through thermolysis in the presence of atmospheric oxygen. We report herein the synthesis and characterization of this new material.

We report on the x-ray absorption of Warm Dense Matter experiment at the FLASH Free Electron Laser (FEL) facility at DESY. The FEL beam is used to produce Warm Dense Matter with soft x-ray absorption as the probe of electronic structure. A multilayer-coated parabolic mirror focuses the FEL radiation, to spot sizes as small as 0.3μm in a ∼15fs pulse of containing >10 12 photons at 13.5 nm wavelength, onto a thin sample. Silicon photodiodes measure the transmitted and reflected beams, while spectroscopy provides detailed measurement of the temperature of the sample. The goal is to measure over a range of intensities approaching 10 18 W/cm 2. Experimental results will be presented along with theoretical calculations. A brief report on future FEL efforts will be given. © 2009 SPIE.

We report on experiments aimed at the generation and characterization of solid density plasmas at the free-electron laser FLASH in Hamburg. Aluminum samples were irradiated with XUV pulses at 13.5 nm wavelength (92 eV photon energy). The pulses with duration of a few tens of femtoseconds and pulse energy up to 100 μJ are focused to intensities ranging from 10 13 to 10 17 W/cm 2. We investigate the absorption and temporal evolution of the sample under irradiation by use of XUV spectroscopy. We discuss the origin of saturable absorption, radiative decay, bremsstrahlung and ionic line emission. Our experimental results are in good agreement with hydrodynamic simulations. © 2012 American Institute of Physics.

We have studied a solid-to-plasma transition by irradiating Al foils with the FLASH free electron laser at intensities up to 10(16) W/cm(2). Intense XUV self-emission shows spectral features that are consistent with emission from regions of high density, which go beyond single inner-shell photoionization of solids. Characteristic features of intrashell transitions allowed us to identify Auger heating of the electrons in the conduction band occurring immediately after the absorption of the XUV laser energy as the dominant mechanism. A simple model of a multicharge state inverse Auger effect is proposed to explain the target emission when the conduction band at solid density becomes more atomiclike as energy is transferred from the electrons to the ions. This allows one to determine, independent of plasma simulations, the electron temperature and density just after the decay of crystalline order and to characterize the early time evolution.

Shock compression studies of pressed and confined ultrafine 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) powder were conducted using ultrashort ~300 ps, ~50 GPa shock waves. The recovered decomposition products were characterized using X-ray photoelectron spectroscopy, infrared spectroscopy, and Raman spectroscopy. A substantial amount of shock-related chemistry was observed. Approximately 75% of the nitrogen atoms were liberated as gas-phase species, along with ~33% of the oxygen atoms, as a result of the applied shock. Furthermore, we observe C 1s binding energies suggesting the formation of sp(3) hybridized amorphous carbon. For comparison, a carbon nitride material was also prepared and characterized by thermally pyrolizing TATB. The shock-compressed TATB and the thermally pyrolized TATB are qualitatively different, suggesting that, carbon nitrides, a possible indicator of nitrogen-rich heterocycles precursors, are not a major product class for strongly overdriven shock conditions. These experimental conditions were, however, not detonation conditions, and the possible formation of nitrogen-rich heterocycles in actual detonations still exists.

We report on experiments aimed at the generation and characterization of solid density plasmas at the free-electron laser FLASH in Hamburg. Aluminum samples were irradiated with XUV pulses at 13.5 nm wavelength (92 eV photon energy). The pulses with duration of a few tens of femtoseconds and pulse energy up to 100 µJ are focused to intensities ranging between 1013 and 1017 W/cm2. We investigate the absorption and temporal evolution of the sample under irradiation by use of XUV and optical spectroscopy. We discuss the origin of saturable absorption, radiative decay, bremsstrahlung and atomic and ionic line emission. Our experimental results are in good agreement with simulations.

Application of the linear least squares (LLS) methodology allows for quantitative determination of variation in material composition with depth. LLS fits were applied to decompose and enhance the interpretation of spectra obtained by Auger electron spectroscopy during depth profiles of oxidized plutonium surfaces. By means of the LLS algorithm, chemical state assignments of the Pu P1VV/O45VV, O KLL, and C KLL Auger transitions were determined and the existence of a subsurface oxycarbide layer was identified, with confirmation of the oxide and metal components provided from comparison to previous measurements of standard samples.Application of the linear least squares (LLS) methodology allows for quantitative determination of variation in material composition with depth. LLS fits were applied to decompose and enhance the interpretation of spectra obtained by Auger electron spectroscopy during depth profiles of oxidized plutonium surfaces. By means of the LLS algorithm, chemical state assignments of the Pu P1VV/O45VV, O KLL, and C KLL Auger transitions were determined and the existence of a subsurface oxycarbide layer was identified, with confirmation of the oxide and metal components provided from comparison to previous measurements of standard samples.

The FLASH XUV-free electron laser has been used to irradiate solid samples at intensities of the order 1016 W cm-2 at a wavelength of 13.5 nm. The subsequent time integrated XUV emission was observed with a grating spectrometer. The electron temperature inferred from plasma line ratios was in the range 5-8 eV with electron density in the range 1021-1022 cm-3. These results are consistent with the saturation of absorption through bleaching of the L-edge by intense photo-absorption reported in an earlier publication. © 2009 Elsevier B.V. All rights reserved.

We review development of multimillijoule X-ray lasers and of applications of these new laboratory sources carried out recently at the PALS facility. A backbone of this development is the neon-like zinc laser providing saturated output at 21.2 nm, with up to 10 mJ of energy per pulse. This represents currently the most energetic soft X-ray laboratory source. Recent improvements in its operation include better control of the beam shape, and more complete understanding of the prepulse pumping. The laser at 21.2 nm has been employed for a number of application experiments reviewed in this paper. They include transmission measurements of intense soft X-ray radiation, studies of fundamental processes of soft X-ray ablation, ablation micropatterning, feasibility study of soft X-ray Thomson scattering from dense plasmas, visualization of nanometric transient perturbation of optical surfaces, measurements of ablation rates of foils heated by IR pulses, and studies of 2D plasma hydrodynamics in the regime of sequen...

Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) has been employed for the first time to investigate uranium hydride. The deuterated form of uranium hydride (UD3) was formed on a polycrystalline uranium sample by exposure to high-purity D2 gas at room temperature. The characteristic positive and negative secondary-ion fragments observed from uranium hydride are reported and assigned. Our investigations show that negative-ion fragments provide the most unambiguous method for identification of uranium hydride, through the detection of and fragments. In addition, density functional theory (DFT) calculations are presented which confirm the identity and stability of, and also assign structural geometries to, the ion fragments observed within the SIMS experiment. The DFT calculations show that ions adopt a linear arrangement, whereas positive tri- and tetrahydride ions ( ) adopt structures based on square planar geometries, although negative tri- and tetrahydride ions ( ) adopt structures based on tetr...

Due to its wide band gap (2.68 eV) and high stopping power, thallium bromide (TlBr) is being investigated as a room-temperature semiconductor gamma-ray spectrometer. When cooled to −20°C, performance of better than 1% FWHM at 662 keV has been observed on 5×5×5 mm3 pixelated TlBr detectors. The room-temperature lifetime (under continuous bias) of thick TlBr detectors operated at high fields (∼2000 V/cm) has been limited to weeks or months due to polarization caused by ionic conduction. Previous work has shown that the degradation process is limited to the surface and that surface preparation techniques can extend the lifetime of thin planar TlBr devices at room temperature. In this work, the lifetime and stability of two large 5×5×5 mm3 pixelated TlBr arrays are presented. Detector performance is compared for different surface preparation techniques and improved stability is observed. Additionally, we use depth-sensing techniques to track the depth-dependent photopeak centroids over time and conclude that once surface degradation effects are mitigated, TlBr performance can improve over time at room temperature. The improvement is likely similar to conditioning at −20°C in which the electric field stabilizes and becomes more uniform.

Degradation of room temperature operation of TlBr radiation detectors with time is thought to be due to electromigration of Tl and Br vacancies within the crystal as well as the metal contacts migrating into the TlBr crystal itself due to electrochemical reactions at the metal/TlBr interface. Scanning Auger electron spectroscopy (AES) in combination with sputter depth profiling was used to investigate the metal contact surface/interfacial structure on TlBr devices. Device-grade TlBr was polished and subjected to a 32% HCl etch to remove surface damage and create a TlBr1-xClx surface layer prior to metal contact deposition. Auger compositional depth profiling results reveal non-equilibrium interfacial diffusion after device operation in both air and N2 at ambient temperature. These results improve our understanding of contact/device degradation versus operating environment for further enhancing radiation detector performance.

Transition metal nitrides are of great technological and fundamental importance because of their strength and durability and because of their useful optical, electronic, and magnetic properties. We have evaluated a recently synthesized platinum nitride (PtN) that was shown to have a large bulk modulus, and we propose a structure that is isostructural with pyrite and has the stoichiometry PtN 2 . We have also synthesized a recoverable nitride of iridium under nearly the same conditions of pressure and temperature as PtN 2 . Although it has the same stoichiometry, it exhibits much lower structural symmetry. Preliminary results suggest that the bulk modulus of this material is also very large.