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This paper describes a capacitive absolute-pressure sensor in which the sealed lead transfer is eliminated. The pick-off capacitance is between a flap or skirt-like extension of the flexible diaphragm that reaches past the sealed cavity, and an electrode patterned on the substrate directly below this extension. The sidewall of the cavity is relatively narrow and flexible. Finite-element analysis is used to explore the relevance of various dimensional parameters and to estimate the sensitivity and temperature coefficients of the device. The device is fabricated from p ++ Si on a glass substrate using the dissolved wafer process with three masking steps. The measurements of fabricated devices with 1 mm radius, 7 µm cavity height, and 8 µm wall thickness show −84 ppm kPa −1 sensitivity at room temperature in touch-mode operation. In non-touch-mode operation the sensitivity is significantly higher. A reference device with similar dimensions shows a less than 22 ppm K −1 temperature coefficient of offset below 150 • C.

In multiphase materials systems involved in coatings, composites or multilayered structures, diffusion treatments often results in the development of intermediate phases at the reaction interfaces. While diffusional growth of phases has received much attention, the initial phase evolution involves a nucleation stage as well. The development of metastable phases during solid state interdiffusion demonstrates that the nucleation reaction can be controlling in some cases. For alloy systems with extensive solubility, intermediate phase nucleation is proceeded by interdiffusional mixing in order to achieve the required supersaturation. This leads to the identification of a critical concentration gradient for the onset of phase nucleation.The concentration gradient and the relative magnitudes of the component diffusivities provide a basis for a phase selection strategy and the application of a kinetic bias to modify the phase selection. For multicomponent alloy systems, the identification of the operative diffusion pathway is central to the control of phase formation. Experimental access to the nucleation stage of reaction is facilitated in thin film multilayer samples where the results from systems with both extensive and limited solubility offer new insight into the phase formation kinetics.

A clear understanding of the factors controlling reproducible composite processing is critical for high temperature application. One approach to obtain stable phase combinations (i.e. compatibility) is to use a controlled interface reaction (in-situ layer design). An effective approach to control the reaction products and diffusion pathway by adding an extra component layer has been practiced and analyzed based upon the relative component fluxes. At the same time, the observed diffusion pathway has been examined in terms of a chemical potential framework, which can provide in assistance interpreting kinetic data in multicomponent systems. While component chemical potential values can increase and decrease through the interdiffusion reaction layers, the total free energy value will be decreased during the interdiffusion reaction. In order to examine the operating principles involved in the synthesis of in-situ composites, model ternary systems including potential materials such as TiAI and SiC have been investigated.

The effect of transition metal substitution for Mo on the phase stability and multi-phase microstructures in the Mo-Si-B ternary system has been examined. The metal-rich portion of the ternary Mo-Si-B system at equilibrium is comprised of thermally stable BCC Mo(ss) phase, a ternary-based Mo5SiB2 (T2 phase), binary-based metal-rich silicides (Mo3Si [the A15 phase] and Mo5Si3 [the T1 phase]) and borides (Mo2B and MoB phases). Systematic alloying with selected transition metals which are substitutional in both Mo(ss) and T2 phases such as Cr, V, Nb, W, Ti and Hf, has been performed to elucidate the roles of the substitution on the stability of the three phase fields of Mo(ss) + T2 + A15 and T2+ T1 + A15. The potential of the alloying effects on the microstructure design and control of the solidification pathways is further detailed.