Search

The study addresses the stability of point defects in SrTiO3 (STO) during thin film processing using electron paramagnetic resonance (EPR) spectroscopy. In particular, the intensity of the Fe3+VO EPR signal is monitored after various steps during the growth of STO films on STO substrates. Controlled O2 and vacuum heat treatments are also performed to clarify the fundamental mechanisms responsible for the effects of different processing steps. Comparison of results from film fabrication with those obtained during exposure to the control ambient shows that the presence of oxygen in the pretreatment growth atmosphere decreases the amount of the Fe3+VO complex, but exposure to the low pressure environment of the growth chamber returns the signal to the original intensity. These results are consistent with accepted theories of oxygen vacancy diffusion. However, an unexpected decrease in the oxygen vacancy related signal is also observed during vacuum treatment of an as-received sample. Furthermore, the decrease occurs over the same temperature range as seen for an O2 anneal. The difference between the O2 and vacuum treatments is revealed in postannealing photoinduced EPR and resistivity measurements, which indicate that vacancy related centers change charge state during the O2 anneal and are not removed by oxygen. The effect of the vacuum treatment, though different from that of oxygen, is not yet clear as no charge state changes were induced after exposure to visible or ultraviolet radiation, but the conductivity of the samples changed. [ABSTRACT FROM AUTHOR]

The stability of point defects in SrTi[O.sub.3] (STO) during thin film processing is addressed by using electron paramagnetic resonance (EPR) spectroscopy. The results have shown that oxygen treatment has altered the electrical charge state of the vacancy, while exposure to vacuum causes different changes, either conversion to a different charge state or creation of the vacancy.

Crops that grow on soils with higher fertility often have higher yields and higher tissue nutrient concentrations. Whether this is the case for all crops, and which soil and management factors, or combinations mostly affect yields and food nutrient concentrations however, is poorly understood. Here, the main aim was to evaluate effects of soil and management factors on crop yields and food nutrient concentrations in (i) grain, fruit and tuber crops, and (ii) between high and low soil fertility areas. Total elemental concentrations of Mg, P, S, K, Ca, Fe, Zn, Mn and Cu were measured using a portable X-Ray Fluorescence Spectrometer (pXRF) in maize grain (Zea mays; Teso South, Kenya: n = 31; Kapchorwa, Uganda n = 30), cassava tuber (Manihot esculenta; Teso South: n = 27), and matooke fruit (Musa acuminata; Kapchorwa, n = 54). Soil properties measured were eCEC, total N and C, pH, texture, and total elemental content. Farm management variables (fertilisation, distance to household, and crop diversity) were collected. Canonical Correspondence Analyses (CCA) with permutation rank tests identified driving factors of alterations in nutrient concentrations. Maize grain had higher correlations with soil factors (CCA > 80%), than cassava tuber (76%) or matooke fruit (39%). In contrast, corresponding correlations to management factors were much lower (8-39%). The main soil properties affecting food nutrients were organic matter and texture. Surprisingly, pH did not play an important role. A positive association of crop diversity with nutrient concentration and yield in lower fertility areas was observed. Considering, food nutrient composition, apart from yield, as response variables in agronomic trials (e.g. fertilisation or soil improvement strategies), would contribute towards discounting the notion that crops growing on fertile soils always produce healthy and high quality foods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)