The WASP consortium is conducting an ultra-wide field survey of stars between 8–15 mag from both hemispheres. Our primary science goal is to detect extra-solar ‘hot-Jupiter’-type planets that eclipse (or transit) bright host stars and for which further detailed investigation will be possible. We summarize the design of the SuperWASP instruments and describe the first results from our northern station SW-N, sited in La Palma, Canary Islands. Our second station, which began operations this year, is located at the South African Astronomical Observatory. Between April and September, 2004, SW-N continuously observed ~6.7 million stars. The consortium's custom-written, fully automated data reduction pipeline has been used to process these data, and the information is now stored in the project archive, held by the Leicester database and archive service (LEDAS). We have applied a sophisticated, automated algorithm to identify the low-amplitude (~0.01 mag), brief (~few hours) signatures of transiting exoplanets. In addition, we have assessed each candidate in the light of all available catalogue information in order to reject data artefacts and astrophysical false positive detections. The highest priority candidates are currently being subjected to further observations in order to select the true planets. Once the exoplanets are confirmed, a host of exciting opportunities are open to us. In this paper, we describe two techniques that exploit the transits in order to detect other objects within the same system. The first involves determining precise epochs for a sequence of transit events in order to detect the small timing variations caused by the gravitational pull of other planets in the same system. The second method employs ultra-high precision photometry of the transits to detect the deviations caused by the presence of exoplanetary moons. Both of these techniques are capable of detecting objects the size of terrestrial planets.

Color information is commonly captured by silicon sensor arrays covered by a mosaic of color filters. However, the detection of the colors red, green and blue at different spatial positions of the sensor arrays leads to color aliasing or color moiré effects. This effect inherently limits conventional sensor arrays. In order to overcome this limitation we have realized color sensors based on vertically integrated thin-film structures. The complete color information can be detected at the same position of a sensor array without using optical filters. The sensors consist of a multilayer thin-film system based on amorphous silicon and its alloys. The spectral sensitivity of the sensors can be controlled by the optical and optoelectronic properties of the employed materials and the applied bias voltages. The working principle of the thin-film sensors and the sensor arrays will be presented. For the first time a large area three color sensor array was realized without using optical filters.

The development of electronic paper has been a long-term goal and electrophoretic displays are a promising candidate for this application. Apart from developing the electrophoretic display medium there are important issues to solve regarding the overall system. The importance of the electronic addressing method increases with the demand for arbitrary images or text. We have developed and tested active-matrix backplanes based on amorphous silicon technology, as well as the driver electronics. The electrophoretic ink is combined with the backplane employing polymer MEMS cell structures. This system allows us to display high-resolution images and it is a good test bed for investigating various parameters of the electrophoretic display medium and of the electronics.

The performance of thermally evaporated pentacene TFTs is strongly affected by defects. The influence of the preparation conditions on the level of defects were studied by Photoconductivity (CPM) and Photothermal Deflection Spectroscopy (PDS). CPM and PDS are powerful tools to provide insights in the band structure, the sub band gap absorption, distribution of defects and the ordering of the material. The influence of the preparation conditions on the morphology and the structural properties will be discussed and correlated with experimental data of CPM and PDS. In particularly, the influence of the deposition temperature on the absorption spectra of the polycrystalline films will be addressed. Furthermore, the material analyse will be correlated with the device performance of pentacene TFTs.

Phase-change wax-based printed masks were used to fabricate a-Si:H thin-film transistors (TFTs) in place of conventional lithography. Wax-mask features with a minimum feature size of ∼20 [.proportional]m was achieved using an acoustic-ink-printing process. Bottom-gate TFTs with source-drain contacts overlapping the channel were created using a four-mask process. The TFTs have I-V characteristics comparable to photolithographically patterned devices, with mobility of 0.6-1 cm2/V·s, threshold voltage of 2-3 V, and on/off ratios exceeding 107, for devices with channel lengths below 50[.proportional]m.

The design of a novel spectrometer based on a thin film diode in combination with an electro statically tunable micro machined mirror will be presented. The semi transparent diode is introduced into a standing wave created in front of a reflector to sample the profile of the standing wave. Varying the position of the reflector results in a shift of the phase of the standing waves and thus in a change of the optical generation profile within the detector. The spectral information of the incoming light can be determined by the Fourier transformation of the transient response of the sensor. An analytical optical model will be presented which facilitates the evaluation of different detector concepts. The model will be applied to discuss different device designs regarding the resolution of the spectrometer, the spectral range and the linearity.

Pulsed Excimer-Laser Annealing (ELA) has become an important technology to produce high performance, poly-Si Thin Film Transistors (TFTs) for large area electronics. The much-improved performance of these poly-Si TFTs over the conventional hydrogenated amorphous Si TFTs enables the possibility of building next generation flat panel imagers with higher-level integration and better noise performance. Both the on-glass integration of peripheral driver electronics to reduce the cost of interconnection and the integration of a pixel level amplifier to improve the noise performance of large area imagers have been demonstrated and are discussed in this paper.

Conventional MEMS devices are based on silicon micro-machining and their maximum size is limited by the wafer. In contrast, we are exploring micro-machining for large area applications on substrates such as glass using polymeric materials. Our research is focused on the photopolymer SU-8, and we apply the MEMS fabrication technology to large area image sensors and displays. There are many challenges concerning the materials and processes, since large area compatibility is essential and integration with large area electronics may be required. The adhesion of SU-8 to the underlying layers as well as stress in the SU-8 are important issues and surface treatments have been investigated. Two applications of SU-8 MEMS are discussed to illustrate large area applications:. First, in the fabrication of an X-ray imager, high aspect ratio SU-8 walls form a micro-patterned phosphor screen to increase the image resolution. Second, a similar approach of patterning SU-8 into arrays of micro-cells is applied to an electrophoretic display.

A very large enhancement of the photoconductivity in pentacene transistors at negative gate voltages is observed. The enhancement is attributed to the separation of electron-hole pairs by the gate field and the consequent slow recombination. The ratio of photoconductivity to dark conductivity is approximately independent of mobility, for samples with a wide range of microstructure. The pentacene films were thermally deposited at different deposition rates and temperatures on silicon thermal oxide. The structure and the morphology of the films were studied by x-ray diffraction measurements and atomic force microscopy, and the influence of the deposition temperature on the morphology and structural properties is discussed. The size of the crystals is correlated with the crystalline bulk phase of the material, which increases with the deposition temperature and the film thickness. The mobility of the transistors increases with the size of the crystallites.

Micromachining has potential applications for large area image sensors and displays, but conventional MEMS technology, based on crystalline silicon wafers cannot be used. Instead, large area devices use deposited films on glass substrates. This presents many challenges for MEMS, both as regards materials for micro-machined structures and the integration with large area electronic devices. We are exploring the novel thick photoresist SU-8, as well as plating techniques for the fabrication of large area MEMS. As an example of its application, we have applied this MEMS technology to improve the performance of an amorphous silicon based image sensor array. SU-8 is explored as the structural material for the X-ray conversion screen and as a thick interlayer dielectric for the thin film readout electronics of the imager.

Amorphous silicon large area sensor arrays are in production for x-ray medical imaging. The most common pixel design works very well for many applications but is limited in spatial resolution because the available sensor area (the fill factor) vanishes in small pixels. One solution is a 3-dimensional structure in which the sensor is placed above the active matrix addressing. However, such high fill factor designs have previously introduce cross talk between pixels.

We present data for a design in which the a-Si:H p-i-n photodiode sensor layer has a continuous i-layer and top p+-layer, and a patterned n+-layer contact to the pixel. Arrays of 64 μm and 75μm pitch have been fabricated and are the highest resolution a-Si:H arrays reported to date. The resolution matches the pixel size, and sensitivity has been improved by the high fill factor. Comparison is made between arrays with standard TFTs and TFTs with self-aligned source and drain contacts. Data line capacitance is improved by use of the self-aligned contacts.

Measurements are included on the contact to bias capacitance. The high fill factor design greatly suppresses lateral leakage currents, while retaining ease of processing. Provided illumination levels remain below saturation, the resolution matches expectation for the pixel size.

This paper examines, through the use of Accelerator Mass Spectrometry dating, the database of Lateglacial cultures involved in the recolonisation of northern Europe. The aim is not only to determine the timing of that recolonisation, but also to propose a general model of hunter-gatherer colonisation at a sub-continental scale. The question is addressed of how long the period of abandonment of northern Europe during the Würm/Weichsel glaciation may have lasted, and when it both started and came to an end. A series of questions is asked concerning the processes and mechanics of recolonisation and the sequences for specific areas are examined. AMS radiocarbon dating shows that a two stage process was involved, which has important implications for our analysis of regional settlement patterns and the changing scale of Lateglacial hunting systems. Recolonisation was a dynamic process, integral to, and internally driven by, the social life of Lateglacial hunters. It may have been constrained by environmental and resource factors, which we have emphasised here, but ultimately it was an historical, social process and should be similarily regarded to that of the farmers. By measuring rates of expansion data are provided for use in other studies of hunter-gatherer colonisation.

The development of a large area, high-resolution, a-Si:H x-ray imager is reported. The array has 1536×1920 pixels, a pixel pitch of 127μm, and an area of 19.5×24.4 cm2. Tne array is tailored to the high frame rate and high spatial resolution requirements of diagnostic x-ray imaging. The design of this array is presented and examples of x-ray images are illustrated. Initial Measurements of the sensor capacitance and pixel time constant properties are in good agreement with theoretical expectations. These results indicate that high-resolution arrays of this construction are capable of providing fluoroscopic images at rates of at least 30 frames per second.

Metastable defect creation by illumination and by a forward current in p-i-n devices are compared using CPM and reverse current measurements of the defect density. The data show that the same defects are formed by the two mechanisms, but with different spatial profiles. Numerical modelling shows how the spatial profile influences the reverse bias current.

1H NMR dipolar echo measurements have been performed on a series of samples of phosphorus- and boron-doped a-Si:H. The dipolar echo sequence consists of three rf pulses followed by an echo in the form: (π/2)x - τ1 - (π /4)y - π2- (π /4)y - echo. The echo height is plotted against π2 and the slope yields the dipolar spin-lattice relaxation time (T1D). T1D is a measure of fluctuations in the local dipolar field surrounding each hydrogen atom in a-Si:H, and measurement of this quantity can be employed as a probe of hydrogen motion on a microscopic scale. The T1D measurements of 10-5 B-doped, 10-3 P-doped and undoped a-Si:H are compared to the previously measured T1D of 10-4 B-doped a-Si:H. The T1D values for 10-4B-doped, 10-4 B-doped and undoped a-Si:H are, respectively, 1.7 ms, 11 ms and 22 ms at 300 K. The T1D for 10-3 P-doped is found to be the same as for 10-5 B-doped within experimental error. These trends are similar to the variation of the macroscopic diffusion of hydrogen with respect to various doping levels, but the details of the local motion are very different from those of the macroscopic diffusion.

Hall experiments performed on intrinsic, phosphorus and boron doped a-Si:H and a-SiC:H in the temperature regime 200 K ≤ T ≤400 K are introduced and discussed. The data confirm the double sign anomaly meaning the Hall coefficient is p-type on intrinsic and phosphorus doped a-Si:H and a-SiC:H, and n-type on boron doped a-Si:H. The Hall mobilities, μH, are significantly smaller than the drift mobilities, decreasing with increasing doping and/or carbon content. μH of holes is about half that for electron which indicate that μH scales approximately with 1/Eg where Eg is the tail slope. The presented interpretation of the Hall coefficient, that is introduced to be a function of Hall- and drift-mobility, enables the accurate determination of the carrier density in intrinsic and doped amorphous silicon and alloys from Hall data.

Amorphous silicon imaging arrays with ∼3×105 pixels have recently been developed and x-ray images of low contrast anatomical phantoms have been demonstrated. This paper reports on the linearity of response of these a-Si:H imaging pixels as a function of reverse bias voltage. The fraction of the imaging pixel's full signal range that maintains a linear response has been found to increase with increasing voltage.

Electron transport properties of a-Si:H prepared in a remote hydrogen plasma deposition reactor (RHPD) at TD = 400°C were investigated in the temperature regime 110 K ≤ T ≤ 300 K by time-of-flight and post-transit spectroscopy experiments. Based on these data the conduction-band-tail state distribution was calculated. In the energy range 85 meV ≤ Ec- E ≤ 350 meV below the mobility edge Ec the tail is well described by an exponential distribution with a characteristic energy of ≃ 21 meV. Deeper in the mobility gap (Ec-E > 350 meV) the tail smoothly passes over into the defect density which is approximately six orders of magnitude smaller than at the mobility edge. Comparisons with data deduced on conventionally prepared a-Si:H (RF-, DC-glow discharge) at TD = 230 °C show that electron transport and the conduction band tail of the RHPD material are comparable.

Large area, two-dimensional, amorphous silicon arrays are under development for x-ray imaging applications. Theoretical limits on frame rates imposed by array design and operational requirements are examined. Measurements of image lag as a function of frame rate are reported.

The first page-sized a-Si:H sensor array intended for use as a contact imager is described. The array collects light very efficiently, making it well suited to high speed document input and medical x-ray imaging (by the addition of a phosphor). The array structure, control electronics and imaging properties are discussed. Data is presented from a 13" diagonal array with 512⋗560 pixels of size 0.45 mm, although the technology is capable of higher resolution. The image is read-out using 8 ICs containing 64 voltage sensitive amplifiers. The intrinsic dynamic range of the imaging array is about 105, but is limited to <1000 by the read-out amplifiers. The minimum read-out time of about 25 msec allows real time imaging.