Fabrication of nanoscale alumina on NiAl(1 0 0) with a scanning tunneling microscope

Nanoscale alumina was fabricated on NiAl (1 0 0) surface using a scanning tunneling microscope in an ultrathin vacuum condition. With the tunneling current greater than 0.4 nA and the power (bias voltage × tunneling current) greater than 0.24 nW, Al and pre-adsorbed O atoms were activated to form alumina (with thickness 0.25–1.0 nm) on the surface directly vicinal to the tip; the width and thickness of the grown alumina strips are controllable by the current and bias. With an evidently smaller power and a smaller bias (≦1.0 V), crystalline alumina were grown along direction [0 0 1] or [0 1 0] of NiAl(1 0 0) in the tip-scanned area of either O-chemisorbed or oxidized surfaces, independent of the direction of tip movement. The alumina strips grown through the latter mode have minimal width near 3 nm.