Hydrogen absorption in thin ZnO films prepared by pulsed laser deposition

ZnO films with thickness of ~80 nm were grown by pulsed laser deposition (PLD) on MgO (1 0 0) single crystal and amorphous fused silica (FS) substrates. Structural studies of ZnO films and a high quality reference ZnO single crystal were performed by slow positron implantation spectroscopy (SPIS). It was found that ZnO films exhibit significantly higher density of defects than the reference ZnO crystal. Moreover, the ZnO film deposited on MgO substrate exhibits higher concentration of defects than the film deposited on amorphous FS substrate most probably due to a dense network of misfit dislocations. The ZnO films and the reference ZnO crystal were subsequently loaded with hydrogen by electrochemical cathodic charging. SPIS characterizations revealed that absorbed hydrogen introduces new defects into Zn

Explaining Africa’s public consumption procyclicality : revisiting old evidence

This paper compiles a novel dataset of time-varying measures of government consumption cyclicality for a panel of 46 African economies between 1960 and 2014. Government consumption has, generally, been highly procyclical over time in this group of countries. However, sample averages hide serious heterogeneity across countries with the majority of them showing procyclical behavior despite some positive signs of graduation from the “procyclicality trap” in a few cases. By means of weighted least squares regressions, we find that more developed African economies tend to have a smaller degree of government consumption procyclicality. Countries with higher social fragmentation and those are more reliant on foreign aid inflows tend to have a more procyclical government consumption policy. Better governance promotes counter- cyclical fiscal policy whileincreased democracy dampens it. Finally, some fiscal rules are important in curbing the procyclical behavior of government consumption.info:eu-repo/semantics/publishedVersio

Central Bank Policies and Income and Wealth Inequality:A Survey

This paper reviews recent research on the relationship between central bank policies and inequality. A new paradigm which integrates sticky-prices, incomplete markets, and heterogeneity among households is emerging, which allows for the joint study of how inequality shapes macroeconomic aggregates and how macroeconomic shocks and policies affect inequality. The new paradigm features multiple distributional channels of monetary policy. Most empirical studies, however, analyze each potential channel of redistribution in isolation. Our review suggests that empirical research on the effects of conventional monetary policy on income and wealth inequality yields mixed findings, although there seems to be a consensus that higher inflation, at least above some threshold, increases inequality. In contrast to common wisdom, conclusions concerning the impact of unconventional monetary policies on inequality are also not clear cut. To better understand policy effects on inequality, future research should focus on the estimation of General Equilibrium models with heterogeneous agents

International demands for austerity: examining the impact of the IMF on the public sector

What effects do International Monetary Fund (IMF) loans have on borrow-ing countries? Even after decades of research, no consensus exists. We offer a straight-forward explanation for the seemingly mixed effects of IMF loans. We argue thatdifferent loans have different effects because of the varied conditions attached to IMFfinancing. To demonstrate this point, we investigate IMF loans with and withoutconditions that require public sector reforms in exchange for financing. We find thatthe addition of a public sector reform condition to a country’s IMF program signifi-cantly reduces government spending on the public sector wage bill. This evidencesuggest that conditions are a key mechanism linking IMF lending to policy outcomes.Although IMF loans with public sector conditions prompt cuts to the wage bill in theshort-term, these cuts do not persist in the longer-term. Borrowers backslide oninternationally mandated spending cuts in response to domestic political pressures

Structural characterization of ZnO thin films grown on various substrates by pulsed laser deposition

ZnO thin films were grown by pulsed laser deposition on three different substrates: sapphire (0 0 0 1), MgO (1 0 0) and fused silica (FS). The structure and morphology of the films were characterized by x-ray diffraction and scanning electron microscopy and defect studies were carried out using slow positron implantation spectroscopy (SPIS). Films deposited on all substrates studied in this work exhibit the wurtzite ZnO structure and are characterized by an average crystallite size of 20–100 nm. However, strong differences in the microstructure of films deposited on various substrates were found. The ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit local epitaxy, i.e. a well-defined relation between film crystallites and the substrate. Domains with different orientation relationships with the substrate were found in both films. On the other hand, the film deposited on the FS substrate exhibits fibre texture with random lateral orientation of crystallites. Extremely high compressive in-plane stress of σ ~ 14 GPa was determined in the film deposited on the MgO substrate, while the film deposited on sapphire is virtually stress-free, and the film deposited on the FS substrate exhibits a tensile in-plane stress of σ ~ 0.9 GPa. SPIS investigations revealed that the concentration of open-volume defects in the ZnO films is substantially higher than that in a bulk ZnO single crystal. Moreover, the ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit a significantly higher density of defects than the film deposited on the amorphous FS substrate

Positronium Formation in Nanostructured Metals

Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-γ annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measures of 3-γ annihilation contribution calculated from single γ-ray and coincidence Doppler broadening spectra were calculated and compared

Positronium Formation in Nanostructured Metals

Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-γ annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measures of 3-γ annihilation contribution calculated from single γ-ray and coincidence Doppler broadening spectra were calculated and compared

Peculiarities of high electric field conduction in p-type diamond

International audienceThe electrical properties of chemical vapour deposited p-type epitaxial diamond layers are studied in high electric field conditions. The quasi-static current-voltage characteristics have been measured using transmission-line pulse method with 100 ns pulses. Reproducible impurity impact ioni-zation avalanche breakdown occurs at a critical electrical field in the range of 100–200 kV cm À1 depending on the acceptor concentration and temperature, leading to complete ionisation of neutral impurities. The current-voltage characteristics exhibit an S-shape with the bi-stable conduction characteristic of impurity impact ionisation. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4946853] Due to their high ionisation energy, dopants in diamond are only partially ionised at room temperature, e.g., less than 0.1% of boron impurities are ionised in a low-doped p-type diamond. As a matter of fact, the temperature range of incomplete ionisation of boron acceptor, i.e., the freeze out region, extends up to about 1000 K. The consequent high re-sistivity severely limits potential applications of diamond as semiconductor. 1,2 In the freeze out regime, the conductivity can be increased by excitation of free carriers bounded to the neutral impurity centres to conduction/valence band by (1) thermal ionisation rising the temperature, (2) optical ionisa-tion with light irradiation of suitable wavelength, and finally (3) impact ionization of neutral centres by the free carriers under a sufficiently high electric field. Under a high electric field, the free carriers can gain enough energy to be able to ionise neutral impurities by inelastic collisions leading to free carrier multiplication. This process results in nonlinear current voltage characteristics.

Effect of oxygen defects on microstructure, optical and vibrational properties of ScN films deposited on MgO substrate from experiment and first principles

We report on the effects of oxygen impurities on the microstructure, surface morphology, optical absorption, and vibrational properties of scandium nitride thin films deposited onto magnesium oxide substrate by reactive magnetron sputtering and under ultrahigh vacuum conditions. Two distinct deposition temperatures of 700 °C and 800 °C were applied to adjust the level of oxygen contamination. The ScN/MgO(0 0 1) thin films have been characterized by various spectroscopic methods, including X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, Raman spectroscopy, and optical microscopy. The ScN films deposited at the lower temperature of the MgO substrate show higher content of defects, stronger disorientation, a larger concentration of twin domains, and suppressed adatom mobility as compared to layers deposited at the higher temperature. An increase by 2% in the amount of accommodated oxygen results in the increase in the direct energy gap of the ScN films by about 0.13 eV, which follows from the increased concentration of the n-type charge carriers incorporated by oxygen impurities. The observed increase in the absorption edge, i.e., enlargement of the optical band gap can be accounted for the Burstein–Moss effect. Experimental Raman spectra reveal coupling between longitudinal optic phonons and electronic states, which can be described by the Fano-type function with the asymmetry parameter increasing with increased content of oxygen defects. The ab initio Raman spectra of ScN with concentrations of oxygen impurities corresponding to the respective experimental values, obtained within density functional theory, demonstrate that incorporated impurities affect significantly the phonon dynamics via modified force constants, including those at atoms beyond the nearest neighbors of defects. The simulated Raman spectra reflect major features of the experimentally determined spectral patterns enabling better insight into the origin of changes experienced by the oxygen-modified ScN/MgO(0 0 1) films.Web of Science615art. no. 15620