National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

Moderate doping leads to high performance of semiconductor/insulator polymer blend transistors

Abstract: Polymer transistors are being intensively developed for next-generation flexible electronics. Blends comprising a small amount of semiconducting polymer mixed into an insulating polymer matrix have simultaneously shown superior performance and environmental stability in organic field-effect transistors compared with the neat semiconductor. Here we show that such blends actually perform very poorly in the undoped state, and that mobility and on/off ratio are improved dramatically upon moderate doping. Structural investigations show that these blend layers feature nanometre-scale semiconductor domains and a vertical composition gradient. This particular morphology enables a quasi three-dimensional spatial distribution of semiconductor pathways within the insulating matrix, in which charge accumulation and depletion via a gate bias is substantially different from neat semiconductor, and where high on-current and low off-current are simultaneously realized in the stable doped state. Adding only 5 wt% of a semiconducting polymer to a polystyrene matrix, we realized an environmentally stable inverter with gain up to 60.

The theory of grain boundary segregation in terms of surface adsorption analogues

Abstract: The theory of equilibrium solute segregation at solid/solid interfaces can be approached usefully from classical surface/gas adsorption isotherms of varying complexity and encompassing both chemisorption and physisorption behavior. Thus, the McLean segregation theory, the simplest type of behavior, is the counterpart of the Langmuir theory for solid/gas adsorption. Assuming strong pair interactions between segregate neighbors, the McLean theory can be adapted to a more complex form, the analogue of the Fowler isotherm, in which adsorbate clustering or protoprecipitation occurs. Again, multilayer segregation is possible, which can be rationalized by " BET " adsorption analogue behavior. Recent developments show how isotherms may be extended to multicomponent systems, assuming interactions between elements and segregants, with important implications in the behavior of embrittlement-prone engineering steels. The mass action equilibrium approach for surface adsorptive reactions is extended here to grain boundaries and tested on the limited number of isotherms available. This may prove to be a useful analytical procedure, giving a rapid insight into the nature of the segregation process, such as adsorbate interactions and variations in adsorption potential among the various sites.

Production of Multiple Beam Fringes from Photographic Scatterers

Abstract: A method is described for the production of interference fringes equivalent to those produced by a series of linearly arranged pinholes without actually constructing such pinholes. Exposures of varying duration are recorded on a photographic plate which is successively displaced with respect to a laser speckle pattern. The Fourier transform of the pattern produced by these multiple exposures is then obtained optically by illuminating the plate with a converging spherical wave. The fringes observed are similar to those occurring in multiple beam hologram interferometry and to the lobes produced by one dimensional antenna arrays.