We discuss contrast formation in a propagating x-ray beam. We consider the validity conditions for linear relations based on the transport-of-intensity equation (TIE) and on contrast transfer functions (CTFs). From a single diffracted image, we recover the thickness of a homogeneous object which has substantial absorption and a phase-shift of --0.37 radian.

Phase singularities are a ubiquitous feature of waves of all forms and represent a fundamental aspect of wave topology. An optical vortex phase singularity occurs when there is a spiral phase ramp about a point phase singularity. We report an experimental observation of an optical vortex in a field consisting of 9-keV x-ray photons. The vortex is created with an x-ray optical structure that imparts a spiral phase distribution to the incident wave field and is observed by use of diffraction about a wire to create a division-of-wave-front interferometer.

We demonstrate here a new method to control the location of cells on surfaces in two dimensions, which can be applied to a number of biomedical applications including diagnostic tests and tissue engineered medical devices. Two-dimensional control over cell attachment is achieved by generation of a spatially controlled surface chemistry that allows control over protein adsorption, a process which mediates cell attachment. Here, we describe the deposition of thin allylamine plasma polymer coatings on silicon wafer and perfluorinated poly(ethylene-co-propylene) substrates, followed by grafting of a protein resistant layer of poly(ethylene oxide). Spatially controlled patterning of the surface chemistry was achieved in a fast, one-step procedure by nanometer thickness controlled laser ablation using a 248 nm excimer laser. X-ray photoelectron spectroscopy and atomic force microscopy were used to confirm the production of surface chemistry patterns with a resolution of approximately 1 µm, which is significantly below the dimensions of a single mammalian cell. Subsequent adsorption of the extracellular matrix proteins collagen I and fibronectin followed by cell culture experiments using bovine corneal epithelial cells confirmed that cell attachment is controlled by the surface chemistry pattern. The method is an effective tool for use in a number of in vitro and in vivo applications.

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This paper describes a novel technique for bonding polymeric-microfluidic devices using microwave energy and a conductive polymer (polyaniline). The bonding is achieved by patterning the polyaniline features at the polymer joint interface by filling of milled microchannels. The absorbed electromagnetic energy is then converted into heat, facilitating the localized microwave bonding of two polymethylmethacrylate (PMMA) substrates. A coaxial open-ended probe was used to study the dielectric properties at 2.45 GHz of the PMMA and polyaniline at a range of temperatures up to 120 • C. The measurements confirm a difference in the dielectric loss factor of the PMMA substrate and the polyaniline, which means that differential heating using microwaves is possible. Microfluidic channels of 200 µm and 400 µm widths were sealed using a microwave power of 300 W for 15 s. The results of the interface evaluations and leak test show that strong bonding is formed at the polymer interface, and there is no fluid leak up to a pressure of 1.18 MPa. Temperature field of microwave heating was found by using direct measurement techniques. A numerical simulation was also conducted by using the finite-element method, which confirmed and validated the experimental results. These results also indicate that no global deformation of the PMMA substrate occurred during the bonding process.

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The ablation characteristics of the SU-8 photoresist (spun on Si wafers) under 248 KrF excimer pulsed laser radiation have been studied. The variation of etch rate with fluence has been investigated in the range 0.05-3.01 J cm −2 . The threshold fluence for ablation of SU-8 is measured to be about 0.05 J cm −2 . The etch rate of SU-8 is found to be higher than that of polyimide (previously reported) under similar conditions. We have investigated the effects of different prebake temperatures (90, 110, 120 and 200 • C) on ablation characteristics, which are found to be similar for all temperatures. The effect of increasing the number of laser shots (from 10 to 10 000) has been examined at different fluences in order to understand the etch-rate variation near the 'end of film' stage of ablation. The results of our analysis using scanning electron microscopy, profilometry and optical microscopy reveal the very smooth morphology of the etched surfaces with no significant debris, no noticeable damage to underlying silicon and the gradual build-up of a carbonaceous film outside and around the etch pits. We find SU-8 very suitable for excimer ablation lithography and have demonstrated this by patterning a gear structure in an SU-8 resist layer with an aspect ratio of 4.5. For the first time, we have shown that the laser micromachining technique has the potential to cleanly remove SU-8 after electroplating a microstructure with copper.

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