Thin nanocrystalline ceramic membranes of ion conductive materials are very promising for a number of applications ranging from oxygen sensors to fuel cells. Owing to its high ionic conductivity compared to many alternative oxygenconducting materials, [1,2] heavily doped cerium dioxide (for instance Ce 0.8 Gd 0.2 O 1.9 ) is particularly attractive for these applications. Undoped oxygen deficient CeO 2±x is a mixed ionic±electronic conductor with predominantly electronic n-type conductivity. The defect equilibrium in undoped CeO 2 has been relatively well studied [3±7] and therefore the undoped material constitutes a good model system. The slow chemical reaction between CeO 2 and Si [8,9] might also permit applications of CeO 2 -based films and membranes integrated in Sibased microelectromechanical systems (MEMS). Thin membranes are usually prepared from thin substratesupported films by local substrate removal. This substrate removal (ªmembrane releaseº) is accompanied by a change in the macroscopic and microscopic stresses that may cause the membranes to disintegrate. In addition, inhomogeneity of oxygen concentration results in a variation of the lattice parameters and ªchemically inducedº mechanical stresses.[10±13]Thus chemical [3,4] and mechanical properties of nanocrystalline CeO 2 -based electrolytes are interdependent. The present work reports on mechanical and chemical processes occurring in undoped nanocrystalline CeO 2 membranes due to the order±disorder transition of oxygen vacancies. For the present study, 1.5 ± 0.2 lm thick CeO 2 films were deposited by radio frequency (RF) magnetron plasma sputtering on Si. Two oxygen/argon sputtering gas ratios, 1:1 (henceforth referred to as films A) and 1:5 (henceforth referred to as films B), were used. Post-deposition annealing allowed the mechanical stress, lattice cell size, and the optical properties of the films to reach constant values. As-deposited films A and B were under a compressive stress of 1.5±2 GPa. Post-deposition annealing decreased the stress to ± 150 MPa for films A and to 0±200 MPa for films B. The X-ray diffraction (XRD) patterns of films A and B were consistent with the standard pattern of cubic CeO 2[14] with a preferred orientation of (111) (Figs. 1a,b). The lattice parameter calculated from the position of the peaks is 5.44(4) ± 0.01 and 5.41(3) ± 0.01 for films A and B, respectively. From the known relationship between the lattice expansion and oxygen stoichiometry [15] one can deduce the mean oxygen content in films A, CeO 1.94 ± 0.02 , and of films B, CeO 2.00 ± 0.02 . The differences in stoichiometry were too small to be detected by energy-dispersive X-ray fluorescence spectroscopy (EDS) ) WAXD patterns of the CeO 2 membranes A and B, respectively, indicating that CeO 2 remained close to the cubic phase after substrate removal. Due to the low angular resolution of the WAXD measurements calculation of small differences in lattice parameters is not possible.

CdTe/CdS solar cells were subjected to heat stress at 200 °C in the dark under different environments (in N2 and in air), and under illumination (in N2). We postulate that two independent mechanisms can explain degradation phenomena in these cells: i) Excessive Cu doping of CdS: Accumulation of Cu in the CdS with stress, in the presence of Cl, will increase the photoconductivity of CdS. With limited amounts of Cu in CdS, this does NOT affect the photovoltaic behavior, but explains the crossover of light/dark current–voltage (J–V) curves. Overdoping of CdS with Cu can be detrimental to cell performance by creating deep acceptor states, acting as recombination centers, and compensating donor states. Under illumination, the barrier to Cu cations at the cell junction is reduced, and, therefore, Cu accumulation in the CdS is enhanced. Recovery of light‐stress induced degradation in CdTe/CdS cells in the dark is explained by dissociation of the acceptor defects. ii) Back contact barrier: Oxidation of the CdTe back surface in O2/H2O‐containing environment to form an insulating oxide results in a back‐contact barrier. This barrier is expressed by a rollover in the J–V curve. Humidity is an important factor in air‐induced degradation, as it accelerates the oxide formation. Heat treatment in the dark in inert atmosphere can stabilize the cells against certain causes of degradation, by completing the back contact anneal.

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Photosystem 1 and 2 and antioxidant enzyme activities were determined in wheat (Triticum aestivum L. cv. Sonalika) leaves. Seedlings from both control seeds and seeds soaked in solutions like dithiothreitol, thioglycollic acid and thiourea were subjected to water stress induced by polyethylene glycol. Photosystem 1 and 2 activities were less inhibited by water stress due to seed soaking with sulphydryl compounds. The changes in activities of antioxidant enzymes induced by water stress were higher in seedlings from thiol-pretreated seeds than from water-soaked seeds.

The electrodeposition of ZnTe films on an ITO-coated glass substrate in a bath containing M/10 ZnCl 2 , M/2000 TeCl 4 and M/3.3 KI dissolved in ethylene glycol is described. Cyclic voltammetry in the dark and under illumination was used to identify the potential for ZnTe deposition. It is shown that cubic ZnTe can be grown at −0.95 V. Film characterization by x-ray diffraction and scanning electron microscopy is also discussed.