Chemically vapor deposited Si nanowires nucleated by self-assembled Ti islands on patterned and unpatterned Si substrates

When Ti is deposited on Si in the 600–700°C temperature range, the lattice mismatch between the Ti-containing deposit and the Si substrate causes TiSix nanoislands to form. The nanoislands grow when annealed at temperatures above 800°C. When the nanoislands (either unannealed or annealed) are exposed to a Si-containing precursor gas, the Ti catalyzes the decomposition of the gas, allowing one-dimensional nanowires to grow. If oxide-patterned Si substrates are used, the Ti islands form selectively on the exposed Si and are preferentially positioned near the pattern edges. The subsequently grown Si nanowires are, therefore, positioned with respect to the larger lithographically formed pattern. Exposing the wires to an ion beam after deposition promotes the parallel alignment of nanowires.