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This work investigates the bubble dynamics during pool boiling from isolated cavities on a horizontal silicon substrate with three surface coatings, silicon oxide, Perfluorodecyltrichlorosilane, and silica nanoparticles. The experiments were conducted with FC-72 under various superheat degrees. In the case of vertical coalescence, coalescences at the boundary between the departed bubble and the subsequent nucleated bubble were observed and analyzed. Vertical coalescence appears with lower superheat degrees on Perfluorodecyltrichlorosilane coated surfaces due to the faster initial bubble growth than on the other surfaces. However, the vertical coalescence has a limited effect on the bubble departure diameter, which is nearly kept constant at around 0.6 mm. In the case of horizontal coalescence, bubbles growing on the silica nanoparticles coated surface are able to coalesce for small cavity spacing with lower superheat degree than other surfaces. Coalescing bubbles from cavities spaced 0.50 mm apart can detach just after coalescence, while for a shorter spacing of 0.25 mm, bubbles remain attached to the surface and further growth is needed for their detachment. Based on the analysis of energy removal per unit of area, the optimal heat transfer performance may be achieved when the cavities spacing is approximate to the single bubble departure diameter. [ABSTRACT FROM AUTHOR]

We present a new type of DNA switch, based on the Holliday junction, that uses a combination of binding and conformational switching to enable specific label-free detection of DNA and RNA. We show that a single RNA oligonucleotide species can be detected in a complex mixture of extracted cellular RNA and demonstrate that by exploiting different aspects of the switch characteristics we can achieve 30-fold discrimination between single-nucleotide mismatches in a DNA oligonucleotide.

The development of a new test chip is presented, containing structures for the direct measurement of stress in metallic interconnect layers associated with silicon integrated circuit technology. The rotation of the structures provides a simple method of differentiating between tensile and compressive stress. This test chip design has been used to fabricate working structures allowing the study of stresses in aluminum layers before and after sample sintering. The results are presented together with the design, fabrication, and measurement considerations that have arisen during the research. The problems experienced in removing the sacrificial layer material, necessary to release the structures, are discussed along with potential solutions. The sensor structure is suitable for fabrication within a CMOS facility and its inherent scalability makes it potentially suitable for in-line testing of state-of-the-art processes. Index Terms--Interconnect, integrated circuit reliability, metallisation, reliability, stress.

Etch selectivity between layers is an important parameter in the fabrication of microelectronics and microsystems. This is particularly true in the case of isotropic gas/vapour etching methods used to release free standing structures through the selective etching of sacrificial layers. Commonly used structural materials have been reported to be largely inert when exposed to a given vapour etchant, indicating high selectivity when measured against typical sacrificial layers. However, there is growing evidence that these structural layers are actually etched at an enhanced rate if they are located in the proximity of the sacrificial layer being removed. Hence, removal rates given in the literature, which have resulted from measurements of layers that have been etched in isolation, can no longer be trusted to characterize critical etch processes in device fabrication. In this paper, a test structure is reported that enables a far more appropriate determination of the etch selectivity between sacrificial and structural materials. The method is demonstrated with the two most common vapour etch processes. Firstly, the XeF2 vapour etch of a polysilicon sacrificial layer located above a silicon nitride structural layer, and secondly, the HF vapour etch of silicon dioxide placed above a silicon nitride structural layer. Both test structure datasets are presented. The polysilicon and silicon nitride layers, etched with XeF2 show a selectivity of 5:4. The silicon dioxide and silicon nitride layers etched with HF, show a selectivity of 6:1 to 8:1. [ABSTRACT FROM AUTHOR]

A unique microfluidics approach for functional hydrogel patterning with multilayered heterogeneous structures is presented. Prepolymer solution droplets with differentiated sodium acrylate concentrations are dispensed/printed in a wetting‐controlled "two‐parallel plate" (TPP, like a Hele‐Shaw Cell) system. The gelation within the system enables hydrogel bilayer structures with reconfigurable 3D deformations driven by in‐plane and through‐thickness heterogeneity under stimuli‐responsive mask‐less swelling/deswelling. The cooperation between swelling mismatch of functional groups results in a higher complexity of 3D reconfiguration in responding to discrete levels of stimulation inputs. This facile patterning technology with an in‐built ionic hierarchy can be scaled up/down with advanced transducing functionalities in various fields. [ABSTRACT FROM AUTHOR]

Contact angle dynamics of droplets deposited on a structured surface were studied in this work and the effects of substrate microstructure and temperature were investigated. Microstructures consisting of uniformly-sized, cubic micropillars with varying pillar spacings were constructed by microfabrication. Droplets (of the order of tens of microlitres in volume) were deposited on these surfaces and dynamic contact angles were observed using various techniques. Advancing and receding contact angles were measured using tilting of the surfaces or by injection and aspiration of fluid from a horizontal droplet by syringe. Droplets on these surfaces appeared to be mainly in the Wenzel state. Contact angle hysteresis was obtained as a function of pillar spacing or, equivalently, surface roughness. Depinning force was deduced and a linear dependence on maximal three phase contact line was found. The techniques of tilting the surface on which the droplet was deposited and uniformly increasing and reducing the volume of the droplet via the syringe both gave the same contact angle hysteresis for a given micropillar spacing. The effect of temperature was then assessed using a heated tilting plate. Contact angle hysteresis was found to increase with temperature. Further work to elucidate mechanisms governing this dependence will be undertaken. [ABSTRACT FROM AUTHOR]