Search

• Deep-ultraviolet (DUV) laser source for laboratory-based photoemission microscopy. • Intense, narrowband, and tunable output from 192 nm to 210 nm (6.5 eV to 5.9 eV). • Characterize space charge effects at 80 MHz repetition rate in PEEM measurements. • High DUV flux allows high resolution studies of wide bandgap semiconductors. Photoemission electron microscopy (PEEM) is a unique and powerful tool for studying the electronic properties of materials and surfaces. However, it requires intense and well-controlled light sources with photon energies ranging from the UV to soft X-rays for achieving high spatial resolution and image contrast. Traditionally, many PEEMs were installed at synchrotron light sources to access intense and tunable soft X-rays. More recently, the maturation of solid-state lasers has opened a new avenue for laboratory-based PEEMs using laser-based UV light at lower photon energies. Here, we report on the characteristics of a laser-based UV light source that was recently integrated with a PEEM instrument. The system consists of a high repetition rate, tunable wavelength laser coupled to a harmonics generation module, which generates deep-UV radiation from 192 nm to 210 nm. We comment on the spectral characteristics and overall laser system stability, as well as on the effects of space charge within the PEEM microscope at high UV laser fluxes. Further, we show an example of imaging on gallium nitride, where the higher UV photon energy and flux of the laser provides considerably improved image quality, compared to a conventional light source. These results demonstrate the capabilities of laser-based UV light sources for advancing laboratory-based PEEMs. [ABSTRACT FROM AUTHOR]

The cortisol awakening response (CAR) is often assessed in the saliva and considered to be representative of serum cortisol. However, free cortisol is rapidly converted into cortisone as it passes from the serum into the saliva. Because of this enzymatic conversion, the salivary cortisone awakening response (EAR) may be more closely related to serum cortisol dynamics than the salivary CAR. Therefore, the purpose of this study was to measure the EAR and CAR in saliva and compare it to the serum CAR. Male participants (n = 12) had an intravenous catheter placed for serial serum sampling and completed two overnight laboratory sessions, wherein participants slept in the laboratory and saliva and serum samples were collected every 15 min after volitional awakening the following morning. Serum was assayed for total cortisol and saliva for cortisol and cortisone. The CAR and EAR was assessed in saliva and the CAR in serum via mixed-effects growth models and common awakening response indices (area under the curve [AUC] relative to the ground [AUC G ] and relative to the increase [AUC I ], and change scores [Δ]). There was a distinct rise in salivary cortisone following awakening demonstrating the presence of a discernable EAR (β Quadratic = −41.18, [95%CI = −68.90 to −13.46], p < 0.004, Conditional R2 = 0.641). Two EAR indices (AUC G : p < 0.001 and AUC I : p = 0.030) were associated with the corresponding serum CAR indices. We demonstrate for the first time a distinct cortisone awakening response. The results suggest the EAR may be more closely related to serum cortisol dynamics during the post-awakening period, and thus, may be a biomarker of interest in addition to the CAR for assessing hypothalamic-pituitary-adrenal axis functioning. • This is one of the first studies to explicity test for and demonstrate the presence of a cortisone awakening response. • The cortisone awakening response is associated with blood-based cortisol awakening response. • Researchers should consider cortisone as an alternative hormone for assessing salivary awakening responses. [ABSTRACT FROM AUTHOR]

A dry process for selective etching of nanocrystalline diamond thin films has been developed as an alternative to plasma etching. This process relies on subjecting masked diamond films to a controlled oxygen atmosphere at temperatures of 700–800 °C to controllably etch both vertically through the film and laterally underneath the mask. SiO 2 , SiN x , and Al 2 O 3 films constitute viable mask materials for this process, provided that the underlying diamond film is fully outgassed before mask deposition and diamond etching. As expected, etching occurred more rapidly at higher temperatures. The etch rate was higher in the lateral direction than the vertical direction, which has been attributed to accelerated etching along disordered grain boundaries and the underlying nucleation layer. Similar activation energies (136–140 kJ/mol) were obtained for both lateral and vertical etching from 700 to 800 °C. Using the dry etch process developed in this research, diamond films can be removed from exposed features and undercut masked regions at a controlled rate, as indicated by microscopy and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Key experiments in three developing dioxygen activation and oxo transfer projects are described. First, the Pt–oxo complex, K7Na9PtIV(O)(OH2)(PW9O34)2 (KNa1) is further addressed and its first reactivity is noted (oxo transfer under Ar at ambient temperature to PPh3 forming O=PPh3 with nearly quantitative selectivity). Second, an unusually reactive catalyst for aerobic oxygenation of sulfides to sulfoxides (TBANO3 in the presence of TBA4Fe(H2O)PW11O39 in acetonitrile solvent) is reported and its stoichiometry is established to be the desired atom-efficient dioxygenase one (RSR+(1/2)O2→RS(O)R). Third, a crystalline microporous solid (metal organic framework material) capable of catalyzing air-based oxidations is described. Reaction of the bis(triesterified)hexavanadate unit terminating in two carboxylate functions, [(n-C4H9)4N]2[V6O13{(CH2O)3CNHCH2(4-C6H4COOH)}2] reacts with Co(NO3)2·6H2O and 4,4′-bipyridine to form a ladder-like microporous polymer, characterized by X-ray crystallography, that catalyzes the air-based oxidation of a representative thiol, n-PrSH, cleanly to the corresponding disulfide, PrSSPr. The esterified hexavanadate units are the catalysts, and there is no reaction in the absence of the microporous material. [Copyright &y& Elsevier]

The cortisol awakening response (CAR) describes the increase in cortisol within the first 30–60 min after waking from nocturnal sleep, and is a common biomarker used within psychoneuroendocrinology, but the effect of sleep on the CAR is currently unclear. A previous study suggested that reported discrepancies may be due to other lifestyle behaviors such as physical activity; given the role of the CAR in energy regulation and preparation for the day, it is theoretically plausible that activity level would influence the CAR. However, no study has yet utilized objective monitoring of day-to-day sleep and physical activity to investigate potential effects on the CAR. This study aimed to test the hypotheses that either sleep duration or sleep quality would interact with the prior 24 h′ physical activity to predict the CAR on the following morning. Salivary samples were collected from 85 young adults (mean = 19.1 years, SD = 1.89) immediately after waking from nocturnal sleep and again 30 min after waking; two complete and consecutive days were used. Participants wore accelerometers (ActiGraph, wGT3X-BT) throughout this phase of a larger study, which provided objective measures of sleep duration, number of awakenings, and amount of physical activity. Mixed-effects models with post-hoc regions of significance decompositions tested the hypothesized interaction effects. Results demonstrated a significant interaction between prior day sleep duration and physical activity predicting the next day CAR, wherein short sleep duration and high levels of physical activity resulted in an augmented CAR. Although more sleep clearly predicted a smaller next day CAR in main effect, this study provides additional support that sleep duration effects are also moderated by prior day physical activity. Both behavioral factors should be considered when assessing the CAR and the association between the CAR other psychoneuroendocrine outcomes. • The interaction of objectively measured previous day sleep duration and physical activity predicts the CAR. • The interaction of physical activity and sleep quality, as assessed by the number of awakenings, does not predict the CAR. • Short sleep durations coupled with high levels of physical activity was related to an augmented CAR. • Future investigations of the CAR should consider the effect of physical activity when investigating sleep parameters. [ABSTRACT FROM AUTHOR]

Abstract: An AlGaN/GaN HEMT was irradiated with 5MeV protons at a dose up to 2×1015/cm2. Photoluminescence spectra measured at 5K indicated that GaN lattice was severely damaged by collisions with high energy protons although distinct near band-edge features were still observable. An I DS–V DS measurement showed that the current level was decreased by 43% after proton irradiation, and an I GS–V GS measurement suggested that damage at the metal-contact/AlGaN interface was minimal. Transistor operation was found to be resistant to proton irradiation, which was partially attributed to a self-healing mechanism in proximity to the AlGaN/GaN interface. [Copyright &y& Elsevier]

Optical, electrical, and mass spectrometry experiments were carried out on solution grown GaN crystals to detect and identify the impurities incorporated in faces of different polarity at different growth condition. Selective etching, photoluminescence and cathodoluminescence imaging indicate that Mg acceptors incorporate preferentially in GaN nitrogen polar face. Larger incorporation of Mg was observed on crystals grown at lower temperatures. Capacitance–voltage measurements verified p-type conductivity due to an excess of Mg acceptors on N-polar face of the GaN crystals. These results suggest that epitaxial layers deposited from liquid phase may be the best approach to produce p-type conducting layers with high hole concentration and low defect density. [ABSTRACT FROM AUTHOR]

Studies of diamond material for thermal management are reported for a nominally 1-µm thick layer grown on silicon. Thickness of the diamond is measured using spectroscopic ellipsometry. Spectra are consistently modeled using a diamond layer taking into account surface roughness and requiring an interlayer of nominally silicon carbide. The presence of the interlayer is confirmed by transmission electron microscopy. Thermal conductivity is determined based on a heater which is microfabricated followed by back etching to produce a supported diamond membrane. Micro-Raman mapping of the diamond phonon is used to estimate temperature rise under known drive conditions of the resistive heater. Consistent values are obtained for thermal conductivity based on straightforward analytical calculation using phonon shift to estimate temperature and finite element simulations which take both temperature rise and thermal stress into account. [ABSTRACT FROM AUTHOR]

The in-plane thermal conductivity of polycrystalline diamond near its nucleation site, which is a key parameter to an efficient integration of diamond in modern high power AlGaN/GaN high electron mobility devices, has been studied. By controlling the lateral grain size evolution through the diamond growth conditions it has been possible to increase the in-plane thermal conductivity of the polycrystalline diamond film for a given thickness. Besides, the in-plane thermal conductivity has been found strongly inhomogeneous across the diamond films, being also possible to control this inhomogeneity by the growth conditions. The experimental results has been explained through a combined effect of the phonon mean free path confinement due the grain size and the quality of the grain/grain interfaces, showing that both effects evolve with the grain expansion and are dependant on the diamond growth conditions. This analysis shows how the thermal transport in the near nucleation region of polycrystalline diamond can be controlled, which ultimately opens the door to create ultra-thin layers with a engineered thermal conductivity, ranging from a few W/m K to a few hundreds of W/m K. [ABSTRACT FROM AUTHOR]

In situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques are applied to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Determination of the extent of reduction under negative bias on the working electrode and the extent of oxidation are determined after pulse voltammetry to quiescence. While the ionic liquid undergoes full oxidation, it undergoes only partial reduction, likely due to transport issues on the timescale of the experiment. Nearest neighbor Fe-O distances in the fully oxidized state match well to expected values for similarly coordinated solids, but reduction does not result in an extension of the Fe-O bond length, as would be expected from comparisons to the solid phase. Instead, little change in bond length is observed. We suggest that this may be due to a more complex interaction between the monodentate ligands of the metal center anion and the surrounding charge cloud, rather than straightforward electrostatics between the metal center and the nearest neighbor grouping. [ABSTRACT FROM AUTHOR]

A pair of redox flow batteries containing polyoxometalates was tested as part of an ongoing program in stationary energy storage. The iron-containing dimer, (SiFe3W9(OH)3O34)2(OH)311-, cycled between (SiFe3W9(OH)3O34)2(OH)311-/(SiFe3W9(OH)3O34)2(OH)314-and (SiFe3W9(OH)3O34)2(OH)317-/(SiFe3W9(OH)3O34)2(OH)314- for the positive and negative electrode, respectively. This compound demonstrated a coulombic efficiency of 83% after 20 cycles with an electrochemical yield (measured discharge capacity as a percentage of theoretical capacity) of 55%. Cyclic voltammetry on the Lindqvist ion, cis-V2W4O194-, showed quasi-reversible vanadium electrochemistry, but tungsten reduction was mostly irreversible. In a flow cell configuration, cis-V2W4O194-had a coulombic efficiency of 45% (for a two-electron process) and an electrochemical yield of 16% after 20 cycles. The poor performance of cis-V2W4O194-was attributed primarily to its higher charge density. Collectively, the results showed that both polyoxometalate size and charge density are both important parameters to consider in battery material performance. [ABSTRACT FROM AUTHOR]

To improve the durability and ion selectivity of a hydrocarbon membrane for vanadium redox flow batteries (VRFBs) a polymer was rationally designed with an external hydrophobic shell and internal hydrophilic core. The polymer was designed to prevent hydrophilic polymer chain aggregation by functionalizing the external polymer shell with hydrophobic side chains and attaching acid moieties onto the polymer backbone. The hydrophobic shell is the result of pentafluorobenzoyl functionalization on the pendent aryl rings in a Diels Alder poly(phenylene) backbone. The internal polymer chain contains sulfonic acid moieties to impart hydrophilic character. The physical and electrochemical characteristics of the membrane were systematically studied and compared with widely used Nafion-212. The synthesized membranes were found to be superior to Nafion-212 not only in terms of lower vanadium ion permeability (4.25 × 10−8 vs. Nafion-212: 6.0 × 10−6 cm2 min −1) but also higher VRFB performance (EE = 89% and vs. Nafion-212: 85.5% at 40 mA/cm2). The membrane showed over three times higher capacity retention than Nafion-212 (0.075% vs. 0.25% capacity loss per cycle respectively) and excellent ex situ and in situ chemical stability. • Unique polymer design of an external hydrophobic shell and internal hydrophilic core. •50x higher proton/vanadium transport selectivity relative to Nafion-212. •Durable in 1.5 M VO 2 + for 60 days and 800 cycles in vanadium flow battery testing. [ABSTRACT FROM AUTHOR]

Highlights: [•] Copper ionic liquid displayed partially reversible plating and stripping. [•] Ionic liquid reference electrode was evaluated with ferrocene and cobaltocene. [•] Strongly coordinating ligands suppressed copper dendrite formation. [•] Anions influenced copper particle size and morphology. [ABSTRACT FROM AUTHOR]

Abstract: A redox flow battery utilizing two, three-electron polyoxometalate redox couples (SiVV 3WVI 9O40 7–/SiVIV 3WVI 9O40 10− and SiVIV 3WVI 9O40 10−/SiVIV 3WV 3WVI 6O40 13−) was investigated for use in stationary storage in either aqueous or non-aqueous conditions. The aqueous battery had coulombic efficiencies greater than 95% with relatively low capacity fading over 100 cycles. Infrared studies showed there was no decomposition of the compound under these conditions. The non-aqueous analog had a higher operating voltage but at the expense of coulombic efficiency. The spontaneous formation of these clusters by self-assembly facilitates recovery of the battery after being subjected to reversed polarity. Polyoxometalates offer a new approach to stationary storage materials because they are capable of undergoing multi-electron reactions and are stable over a wide range of pH values and temperatures. [Copyright &y& Elsevier]

Abstract: Five new copper(II)-based ionic liquids and three crystalline compounds have been synthesized in order to further understand the role of the anion in determining their physicochemical properties. Materials were prepared with combinations of three different anions (2-ethylhexanoate (EHN), tetrafluoroborate (BF4), and triflate (OTf)) and six-coordinate Cu(II) cations. The complexes that contain at least one BF4 anion consistently displayed both the highest specific conductivity and electrochemical reversibility. The presence of one OTf anion (in combination with one EHN or BF4) facilitates the formation of crystalline materials. Single crystal X-ray diffraction studies were completed on two of the mixed anion compounds. The results show that both ethanolamine (EA) and diethanolamine (DEA) chelate to the Cu(II) centers in a highly distorted tetragonal geometry. The properties of the ionic liquid with the overall lowest viscosity and highest conductivity and electrochemical reversibility (Cu{NH2CH2CH2OH}6(BF4)2, 4) were studied as a function of temperature. The viscosity decreases with increasing temperature, but at 45°C (over three hours) there is a loss of two EA ligands to form a more viscous four-coordinate complex. Cyclic voltammetry of 4 reveals a quasi-reversible Cu(II)/Cu(I) reduction wave that shifts to more positive potentials with increasing temperature. [Copyright &y& Elsevier]

Abstract: In this study, the electrochemical behavior and the electrocatalytic properties towards the reduction of hydrogen peroxide, dioxygen and nitrate are compared for the two mixed sandwich-type complexes Ni2Fe2P4 and Ni2Fe2As4. In media of pH 3, Ni2Fe2P4 displayed two waves corresponding to the reduction of the two FeIII centers within the complex followed by four WVI based-waves. Compared to Ni2Fe2P4, Ni2Fe2As4 displayed only one Fe-based wave and three W-waves. In other words, the two FeIII waves and the first two WVI waves observed for Ni2Fe2P4 merge into one Fe-based wave and one W-wave in Ni2Fe2As4. This is probably related to a slight difference in acidity between the two complexes. In other words, Ni2Fe2P4 is slightly more basic than Ni2Fe2As4. This difference in acidity is also reflected in the position of the potentials. Compared to Ni2Fe2P4, the peak potentials of Ni2Fe2As4 are slightly shifted towards positive values, and the shift is more pronounced for the W-based waves than for the Fe-waves. The remarkable stability of the two complexes (roughly from pH 0 to 7) permitted to evaluate their catalytic behavior towards H2O2, O2 and . For the electrocatalytic reduction of H2O2, it is noticed that Ni2Fe2As4 is more efficient than Ni2Fe2P4. However, for O2 and it is observed that Ni2Fe2P4 is more efficient than Ni2Fe2As4. [ABSTRACT FROM AUTHOR]