The influence of annealing parameters -temperature (Ta) and time (ta) -on the magnetic properties of As-capped (Ga,Mn)As epitaxial thin films have been investigated. The dependence of the transition temperature (TC) on ta marks out two regions. The TC peak behavior, characteristic of the first region, is more pronounced for thick samples, while for the second ('saturated') region the effect of ta is more pronounced for thin samples. A right choice of the passivation medium, growth conditions along with optimal annealing parameters routinely yield TC-values of ∼ 150 K and above, regardless of the thickness of the epilayers.
The superior high temperature oxidation resistance of FeCrAl alloys relies on the formation of a dense and continuous protective aluminium oxide layer on the alloy surface when exposed to high temperatures. Consequently, the aluminium content, i.e. the aluminium concentration at the alloy-oxide layer interface, must exceed a critical level in order to form a protective alumina layer. In the present study the oxidation behaviour of six different FeCrAl alloys with Al concentrations in the range of 1.2-5.0 wt% have been characterised after oxidation at 900 8C for 72 h with respect to oxide layer surface morphology, thickness and composition using scanning electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. The results show that a minimum of 3.2 wt% Al in the FeCrAl alloy is necessary for the formation of a continuous alumina layer. For Al concentrations in the range of 2.0-3.0 wt% a three-layered oxide layer is formed, i.e. an oxide layer consisting of an inner alumina-based layer, an intermediate chromia-based layer and an outer iron oxide-based layer. In contrast, the 1.2 wt% Al FeCrAl alloy is not able to form a protective oxide layer inhibiting extensive oxidation.
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is an important tool for the analysis of bone minerals at implant surfaces. Most studies have been performed with monoatomic primary ion sources such as Ga(+) with poor secondary molecular ion production efficiency and only elemental distributions and minor fragments of bone minerals have been reported. By using cluster ion sources, such as Au(1-3) (+) and Bi(1-3) (+), identification of larger hydroxyapatite species at m/z 485, 541, 597 and 653, identified as Ca(5)P(3)O(12), Ca(6)P(3)O(13), Ca(7)P(3)O(14) and Ca(8)P(3)O(15), respectively, became possible. The ions appear to be fragments of the hydroxyapatite unit cell Ca(10)(PO(4))(6)(OH)(2). Each ion in the series is separated by 55.9 m/z units, corresponding to CaO, and this separation might reflect the columnar nature of the unit cell.
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