No abstract

The mass production technique of gravure contact printing is used to fabricate state‐of‐the art polymer field‐effect transistors (FETs). Using plastic substrates with prepatterned indium tin oxide source and drain contacts as required for display applications, four different layers are sequentially gravure‐printed: the semiconductor poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), two insulator layers, and an Ag gate. A crosslinkable insulator and an Ag ink are developed which are both printable and highly robust. Printing in ambient and using this bottom‐contact/top‐gate geometry, an on/off ratio of >104 and a mobility of 0.04 cm2 V−1 s−1 are achieved. This rivals the best top‐gate polymer FETs fabricated with these materials. Printing using low concentration, low viscosity ink formulations, and different P3HT molecular weights is demonstrated. The printing speed of 40 m min−1 on a flexible polymer substrate demonstrates that very high‐volume, reel‐to‐reel production of organic electronic devices is possible.

We demonstrate a compact, low cost and practical fluorescence detection system for lab-on-a-chip applications. The system comprises a commercially available InGaN light emitting diode (501 nm) as light source, an organic or silicon photodiode detector, absorptive dye coated colour filters and linear and reflective polarisers. An injection moulded polystyrene microfluidic chip is used as the platform for fluorescence immunoassays for cardiac markers myoglobin and CK-MB. The optical limit of detection (LOD) is measured using a TransFluoSphere® suspension at 5.6 × 10(4) beads µl(-1) which can be equated to ∼3 nM fluorescein equivalent concentration. The LOD for the human plasma immunoassays is measured as 1.5 ng ml(-1) for both myoglobin and CK-MB.

We report a new lithographic procedure that enables the patterning of as-received semiconducting polymers and small molecules at the near micron level without causing discernible degradation of the patterned material. The method involves a minimum of processing steps, requires no modification of the active layer, and is compatible with both rigid and flexible substrates. The technique makes use of an intermediate resist layer between the substrate and the active layer, i.e. underneath the active layer, and involves the simultaneous patterning of the resist and active layers in a single expose/develop step. The technique has been successfully applied to the fabrication of flexible ITO-free light-emitting diodes and photodiodes, yielding peak quantum efficiencies of 8.8 cd A 21 and 57% respectively comparable to similar devices fabricated on ITO-coated glass. It is also readily extendible to the patterning on a single substrate of multiple devices incorporating different component materials, e.g. the red, green and blue pixels of a colour display.

HUG 7RXThe lower homologues of the series of 4-n-alkoxy-and 4-n-alkyl-4'-cyanobiphenyls have been prepared and their liquid crystal transition temperatures determined. The trends in the nematic-isotropic liquid (N-I) transition temperatures along the series are compared with observed trends for other homologous series. These results reveal deficiencies in the theoretical treatments That have been proposed to explain trends in N-l transition temperatures in such series. However, the results may be explained by the existence, in the case of the higher homologues, of certain alkyl chain conformations which are especially favourable to the stability of the nematic phase.WE report the nematic-amorphous isotropic liquid (N-I) transition temperatures of the lower members of the homologous series of 4-n-alkyl-and 4-n-alkoxy-4'cyanobiphenyls. These compounds give unexpectedly high values for the N-I transition temperatures compared with those for the higher homo1ogues.l Before discussing the new results, we shall present views on the observed variation in N-I transition temperatures on ascending other homologous series of mesogens.Studies of many homologous series of mesogens have shown that the temperatures for mesophase-mesophase and mesophase-amorphous isotropic liquid transitions show regular trends as the series are ascended.,~~ For series of nematogens, a regular alternation of N-I transition temperatures occurs and when these are plotted against the number of carbons in the terminal alkyl chain, the points lie on two curves. When the alkyl group is directly attached to a ring, the upper curve is for the odd members and the lower curve for the even members. 1471ien the terminal group is an n-alkoxy-group, the reverse situation occurs because the oxygen is geometrically equivalent to a CH, group. A common behaviour for the two separate curves for a series is that both either rise or fall initially and then level out, the alternation becoming less pronounced as the series is ascended. Alternatively, the upper curve may sometimes fall and level out, while the lower curve rises slightly or stays almost level as the series is ascended.At one time, most series gave the types of curve which fall for both odd and even members, the initial slopes being greatest for series involving high N-I transition temperatures. Later,4 series were found for which both curves rise as the chain is lengthened. These series involve rather low N-I transition temperatures, and the quest €or mesogens of low m.p. has increased the number of examples of series giving this type of N-I c ~r v e . ~. 6Attempts have been made to explain the shapes of N-I curves in terms of the effects of increasing chain length on the anisotropy of molecular p~larisability.~ Assuming a rigid, extended zig-zag chain, the axial polarisability is increased about twice as much as the polarisability at