Fabrication, characterization, and mechanism of vertically aligned titanium nitride nanowires

Titanium nitride (TiN) nanowires have been grown on single crystal magnesium oxide (MgO) substrates using a bottom-up pulsed laser deposition method where Ti–N based gaseous reactants in the laser plume supersaturate the catalytic gold (Au) liquid located on the substrate surfaces. Growth of TiN continues as long as the dissolution rate of material into the catalyst matches the extrusion of solid material at the liquid/solid interface. This bottom-up approach gives rise to a one-dimensional TiN nanowire structure (length: 200–300 nm and diameter: 20–30 nm) capped with a catalytic Au seed. The ascent of Au nanodots to the top of TiN nanowires can be explained based on breaking of weaker bonds and formation of stronger bonds. From strength point of view, these bonds are listed here in order of decreasing strength as follows: Ti–O (672 kJ/mol) > Ti–N (496 kJ/mol) > Au–N (416 kJ/mol) > Au–O (221 kJ/mol). The TiN nanowires were provided vertical alignment by selecting a plane of the substrate that provides the least lattice mismatching to the (1 1 1) plane of TiN which has lower surface energy than its other planes: (1 0 0) or (1 1 0).