Phase separation and applications of amorphous gold-silicon alloys.

摘要

The pursuit of nanoscaled architectures has demanded new synthesis methodologies for creating and organizing metal particles. The challenge still remains to create well-defined structures with a tight control over size and size distribution. This dissertation will describe a method for creating gold-rich nanoparticles through the amorphous phase separation of silicon-rich gold-silicon sputtered alloys. Using this technique, gold-rich nanoparticles, ranging from 2--3 nm in diameter, can be routinely grown with large aeral densities. Both electron microscopy and diffraction studies indicate that Au-rich nanoparticles have an amorphous-like character.; The phase separation process is modelled by a spinodal decomposition mechanism. Calculated fastest growing composition wavelengths are in close agreement with observed average particle-to-particle spacing. Extended anneals close to the eutectic temperature demonstrate the remarkable stability of these particles and suggest that their amorphous character is thermodynamically stable due to their relatively low interfacial energy and high degree of curvature.; Fundamental studies of annealed gold-silicon/silicon multilayers reveal that Au-rich particles act as catalysts for the transformation of amorphous silicon via metal-induced crystallization. Crystalline silicon grains are modelled as tapered nanowires behind Au-rich nanoparticles. It is calculated that particles with a radius less than 1.2 nm are unable to induce crystallization, and these findings are experimentally confirmed by TEM characterization.; Finally, gold-rich nanoparticles are successfully incorporated into metal oxide semiconductor (MOS) structures for use as a charge trapping layer in floating gate devices. From high frequency capacitance measurements, MOS structures containing these particles showed a significant hysteresis as compared to structures without nanoparticles. The difference in behavior is attributed to additional charge storage in either nanoparticle or nanoparticle interface states. For devices operating in the Fowler-Nordheim tunnelling regime, a memory window of 0.6 V can be achieved under a 10 V program. The memory window can be enhanced with further increases of programming voltages and/or write times. This work represents one of the first examples of metal nanoparticles, formed by phase separation, utilized as a floating gate layer for non-volatile memory applications.