What is the first compound that nucleates in planar solid silicon–transition-metal binary couple reactions whose members form bulk equilibrium compounds? We propose, for couples annealed at low temperatures, the following simple rule: The first compound nucleated in planar binary reaction couples is the most stable congruently melting compound adjacent to the lowest-temperature eutectic on the bulk equilibrium phase diagram. The predictions of this rule are compared with experimental results.

Polarity-dependent memory switching has been observed in devices of crystalline SnSe and SnSe2 with aluminum contacts. Two types of low-level switching (1 V/1 mA) with reversed polarity dependence can be obtained in suitably formed devices of either material. In addition, a high-level (100 V/10 mA) polarized memory switching can be obtained in either device. The low-level switching appears to involve an electronic process, while the high-level switching is associated with an electrothermally driven mass transport.

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We present a model for solid-state silicide nucleation at the interface of a thin metal film and a silicon substrate, starting with the assumption that compound nucleation in these systems is a kinetically controlled process. We consider the work being done on other systems, such as dendrite nucleation and growth, and snowflake generation, where the processes are kinetically self-limited by the structures that form. We show that the requirements for kinetically self-limited systems can be formally satisfied at the interfaces for silicide forming systems. In particular, in analogy with the selection of metastable shapes for snowflake structures, we would in general expect metastable chemical structures to form at metal-semiconductor interfaces under conditions of large supercooling. We discuss the selection criteria (maximum energy degradation rate), the probable forms of these structures, and the conditions required for their growth. We then discuss an interpretation of phenomenological rules for selection of first-phase nucleation in terms of these structures.

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