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We have fabricated organic light emitting diodes (OLEDs) based on poly(p-phenylenevinylene) (PPV) and poly(methacrylic acid) (PMA), including an isolating layer composed of montmorillonite. We show that the single clay layer influences the behavior of the devices, lowering current densities and increasing light output in comparison with pure polymer systems. The subnanometer positioning of this isolating barrier within the active medium with respect to both electrodes, which is easily controlled by the deposition sequence, plays a key role for the electrooptical properties of the diodes.

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%675$&7For the first time at ITU electrochemical quartz crystal micro-balance has been used for the investigation of UO 2 thin film oxidation. The combination of cyclic voltammetry with nanogram weight change measurements in-situ has shown at least two steps in the initial stages of UO 2 dissolution under oxidising conditions relevant to spent fuel storage.,1752'8&7,21Direct storage of spent nuclear fuel in a repository is being considered as one of the options in storage of nuclear waste. It is expected after 1000 years of storage groundwater may penetrate through the engineered barriers to make contact with the fuel pellets through ruptures in the cladding. In the radiation field the penetrating groundwater will undergo radiolysis. Hydrogen peroxide is a major radiolysis product and oxidant of UO 2 . Therefore studies have been initiated to measure the influence of H 2 O 2 on the dissolution behaviour of UO 2 . In presence of H 2 O 2 the formation of a surface layer on the UO 2 was observed [1,2]. This layer was investigated by impedance spectroscopy and cathodic sweep voltammetry. Both techniques show an increase of the layer thickness with time, although the thickness values differed by one order of magnitude. To clarify this discrepancy, additional information about the corrosion process such as the mass change is needed. A highly sensitive method to study mass changes is the quartz crystal microbalance (QCM) and is an excellent tool to determine in-situ corrosion rates and inhibition effects. Mass changes in the sub-nanogram range can be detected. On the other side, the total mass, which can be used with the QCM, is restricted; here to some 100 µg. Therefore only thin films of UO 2 can be investigated.(;3(5,0(17$/ '(7$,/6Microgravimetric measurements were carried out with the Model 430 electrochemical quartz crystal microbalance (QCM) from CH Instruments. This is a complete system including an electrochemical call, an oscillator and the potentiostat. The system is controlled by a computer running the CHI software.The frequency difference of the working crystal and the reference crystal is measured. This measured frequency shift is converted in to a mass variation relying on the Sauerbrey equation [3].The diameter of the quartz crystal is 13.7 mm in the centre the crystal is coated with gold (diameter 5 mm). Usually the gold covers the whole oscillating area of the crystal. Mass changes that appear outside this area have only a very little effect on the frequency shift (< 1%). UO 2 is sputter-deposited on the crystal using a stencil to achieve a homogeneous layer covering the Mat. Res. Soc. Symp. Proc. Vol. 807