No abstract

Smart windows possess the potential to contribute significantly to reducing the world-wide energy consumption in the future. The properties of the thermochromic metal oxide VO2 are closest to the material requirements set by economic considerations for the use as an active layer in thermochromic glazings. We show that the required parameters can be achieved by modifying VO2 on the atomic level, i.e., by simultaneous co-doping with Sr and W on the cation site. In particular, the transition temperature ϑc can be adjusted in the range between 15 and 68 °C by varying W contents, whereas the incorporation of Sr mainly increases the band gap yielding a greyish color of the films. Interestingly, the simultaneous presence of W and Sr enhances both effects. The co-doping leads to values of the luminous transmittance Tlum and the solar transmittance Tsol fulfilling the requirements set by application. The variation of the solar transmittance ΔTsol of the plain thin films on a glass substrate already is larger than 5% for all samples promising that the required value of ΔTsol=10% is achievable by using such thin films as part of an optically engineered multilayer system.

No abstract

Mg doping of thermochromic VO 2 films enhances the optical transmittance and decreases the metal-insulator transition temperature

The ISOLDE resonance ionization laser ion source (RILIS) allows to ionize efficiently and selectively many metallic elements. In recent yield surveys and online experiments with the ISOLDE RILIS we observed 23 (Submitted to Nuclear Instruments and Methods in Physics Research B) IntroductionThe resonance ionization laser ion source (RILIS) [1] provides an efficient, fast and selective way to ionize many metallic elements. The elements ionized with the ISOLDE RILIS were reviewed recently [2,3,4]. In this article we will discuss on-line results, i.e. release curves and yields measured in recent target tests, nuclear spectroscopy experiments and on-line collections.The measured release curves were fitted with the empiric 4-parameter-formula described in [5,6]. Table 1 shows a summary of the release parameters: t r the rise time, t f the fall time of the fast component, t s the fall time of the slow component and α the relative intensity of the fast component. Parameters which had to be fixed to obtain a stable fit are marked in parentheses.The release parameters were used to determine for each radio-isotope the fraction which is released before it decays. The on-line efficiency of the RILIS cannot be easily monitored as in the case of a plasma ion source where the support gas is injected at a well-defined flowrate. Still a rough estimate can be made by scaling the off-line measured efficiency with the laser power available in the on-line run. Also the ion yield of a longlived isotope with known production cross-section gives an indication of the ionization efficiency. Correcting the ion yields for the released fraction and the ionization efficiency allows to deduce the in-target production yield. In some of the following graphs both values are plotted: the ion yield, showing the presently available radioactive ion beam intensity for the user, and the in-target production yield showing the theoretical limit that could be obtained with an ideal target (no decay losses) of the same thickness and dimensions coupled to an ideal ion source (100 % efficiency). The ratio between both curves shows the overall efficiency of the present target and ion source unit.

Ferromagnetic Ni surfaces were investigated on an atomic scale using the perturbed angular correlation spectroscopy probe 111 Cd. A comprehensive set of data for magnetic hyperfine fields (B hf ) at various probe sites is presented. A field variation from 27 T in Ni bulk to the surprisingly large value of 16 T at the adatom position on Ni (111) The knowledge of magnetic properties on an atomic scale on magnetic surfaces and at interfaces of ultrathin magnetic multilayers is becoming increasingly important in both basic research and in the field of applications such as the miniaturization of magnetic devices to smaller and smaller units [1]. In basic research the information on the variation of magnetic properties from atomic layer to atomic layer or even from atom to atom is of fundamental interest. One way to measure magnetic properties on the atomic scale is offered by the use of radioactive probe atoms and the observation of their interaction with the immediate environment. Applying hyperfine-interaction techniques, monolayer-resolved studies are possible [2,3] because of the short range of the hyperfine interaction, where essentially only the nearest neighbors (quantitatively expressed in the coordination number NN) contribute to the interaction. Nuclear methods, in particular, the perturbed angular correlation spectroscopy (PAC), have an extremely high sensitivity. In this technique, only a highly diluted amount of probe atoms (10 24 10 25 of a monolayer) is needed. Therefore, the overall magnetic properties are not disturbed. Among the variety of magnetic interfaces, the surface of a ferromagnetic single crystal in ultrahigh vacuum (UHV) represents one of the most interesting cases. Such a surface offers a variety of different structures, e.g., terraces, steps, kinks, etc. defining the structural surface-layer roughness. Positioning the probe atoms at all sites available allows the coordination number to vary over a broad range. Magnetic properties are expected to vary considerably from structure to structure and a deep insight into the magnetic roughness of a ferromagnetic surface is obtained. In this Letter we show how magnetic properties of probe atoms on low-Miller-index surfaces of Ni(001) and Ni(111) could be measured systematically at a variety of different atomic positions. Including some single results from the literature, we present a full set of data for the coordination-number dependence of a selected magnetic property.Magnetic hyperfine fields (B hf 's) at the nuclei of probe atoms in or on ferromagnetic materials are caused by electronic spin and orbital contributions. Using the nontransition impurity Cd, a member of the 5sp elements, the polarization of the s electrons arising from the hybridization with the valence d electrons of the ferromagnetic host plays the dominant role in generating B hf 's. For transitionelement probe atoms [4,5], additional contributions would have to be taken into account which add to the complexity of the calculations, especially when magnetic properties of the ...

No abstract

Interstitial Fe57m atoms excited in the 14.4 keV Mössbauer state have been created in silicon at 400–800 K as a result of the recoil imparted on these daughter atoms in the β− decay of ion-implanted, substitutional Mn57. Diffusional jumps of the interstitial Fe57m cause a line broadening in their Mössbauer spectra, which is directly proportional to their diffusivity. Thus, the charge-state-dependent diffusivity has been determined in differently doped material.