The electronic nature of metal-semiconductor contacts is a fundamental issue in the understanding of semiconductor device physics, because such contacts control charge injection, and therefore play a major role in determining the electron/hole population in the semiconductor itself. This role is particularly important for organic semiconductors as they are generally used in their pristine, undoped form. Here, we review our progress in the understanding of the energy level line-up in finished, blue-emitting, polyfluorene-based light-emitting diodes, which exploit LiF and CsF thin films in combination with Ca and Al to obtain cathodes with low injection barriers. We have used electroabsorption measurements, as they allow the noninvasive determination of the built-in potential when changing the cathode. This provides precious experimental information on the alteration of the polymer/cathode interfacial energy level line-up. The latter is found to depend strongly on the electrode work function. Thus, the Schottky–Mott model for the energy level alignment is found to be a better first-order approximation than those models where strong pinning or large interface dipoles determine the alignment (e.g., Bardeen model), except for electrodes that extensively react with the polymer, and introduce deep gap states. In addition, we show results that validate the approximation of rigid tilting of polymer energy levels with bias (for biases for which no significant injection of carriers occurs). To investigate further the consequences of the electronic line-up on device operation, we complemented the electroabsorption measurements with characterization of the emissive and transport properties of the light-emitting diodes, and confirmed that the cathodic barrier lowering in CsF/Ca/Al and LiF/Ca/Al electrodes leads to the best improvements in electron injection. We found that luminance and overall current are greatly affected by the barrier-reducing cathodes, indicating a truly bipolar transport, with comparable electron and hole currents. We also found significant indications of CsF/Ca/Al cathodes strongly reacting with the polymer, which is suggestive of CsF dissociation and diffusion in the bulk of the polymer.

The demand for increased information storage densities has pushed silicon technology to its limits and led to a focus on research on novel materials and device structures, such as magnetoresistive random access memory and carbon nanotube field-effect transistors, for ultra-large-scale integrated memory. Electromechanical devices are suitable for memory applications because of their excellent 'ON-OFF' ratios and fast switching characteristics, but they involve larger cells and more complex fabrication processes than silicon-based arrangements. Nanoelectromechanical devices based on carbon nanotubes have been reported previously, but it is still not possible to control the number and spatial location of nanotubes over large areas with the precision needed for the production of integrated circuits. Here we report a novel nanoelectromechanical switched capacitor structure based on vertically aligned multiwalled carbon nanotubes in which the mechanical movement of a nanotube relative to a carbon nanotube based capacitor defines 'ON' and 'OFF' states. The carbon nanotubes are grown with controlled dimensions at pre-defined locations on a silicon substrate in a process that could be made compatible with existing silicon technology, and the vertical orientation allows for a significant decrease in cell area over conventional devices. We have written data to the structure and it should be possible to read data with standard dynamic random access memory sensing circuitry. Simulations suggest that the use of high-k dielectrics in the capacitors will increase the capacitance to the levels needed for dynamic random access memory applications.

Carbon nanotubes are used as the smallest possible scattering element for diffracting light in a highly controlled manner to produce a 2D image. An array of carbon nanotubes is elegantly patterned to produce a high resolution hologram. In response to incident light on the hologram, a high contrast and wide field of view CAMBRIDGE image is produced.

Arrays of parallel connected coaxial multiwall‐carbon‐nanotube–amorphous‐silicon solar cells are fabricated. In this configuration, orthogonalization of the directions of light absorption and charge‐carrier collection is realized. Under simulated solar illumination (AM 1.5 G), the short‐circuit current of our carbon‐nanotube enhanced solar cell is ∼25% higher than that of the planar cell.

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