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The transmembrane diffusion of L(+)-ascorbic acid has been studied by means of 1H-n.m.r. spectroscopy using small unilamellar DPPC vesicles as a model system. It is shown that the electro-neutral form of L(+)-ascorbic acid diffuses faster across the membranes than the anionic form by about two orders of magnitude. The diffusion is influenced by a molecular interaction between L(+)-ascorbate and the membrane surface and depends also on the fluidity of the membrane. The calculated permeation coefficients of neutral L(+)-ascorbic acid are between 6 x 10(-10) and 3 x 10(-8) cm s-1 (35-52 degrees C).

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We report on the current status of a project on development and characterization of CD photomasks with 6025 format to be used as reference standards for different type of CD metrology instruments. The project consortium consists of mask suppliers, manufacturers of CD metrology instruments, users of such instruments and calibration laboratories. Different type of CD metrology instrumentation, namely optical CD microscopes, CD-SEM, and AFM will be applied for investigation and measurement of microstructures, additionally supported by AIMS tool. We will describe the basic design criteria of the mask standard and first measurement results gained with different metrology tools on the prototype mask standards.