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The ability of the semiconductor industry to continue scaling microelectronic devices to ever smaller dimensions (a trend known as Moore's Law) is limited by quantum mechanical effects: as the thickness of conventional silicon dioxide (SiO₂) gate insulators is reduced to just a few atomic layers, electrons can tunnel directly through the films. Continued device scaling will therefore probably require the replacement of the insulator with high-dielectric-constant (high-k) oxides, to increase its thickness, thus preventing tunnelling currents while retaining the electronic properties of an ultrathin SiO₂ film. Ultimately, such insulators will require an atomically defined interface with silicon without an interfacial SiO₂ layer for optimal performance. Following the first reports of epitaxial growth of AO and ABO₃ compounds on silicon^,,,,, the formation of an atomically abrupt crystalline interface between strontium titanate and silicon …