Pb. Johnson et Pw. Gilberd, ORDERED GAS-BUBBLE PRECURSORS TO NANOPOROUS LAYER FORMATION IN HELIUM-IMPLANTED METALS, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 127, 1997, pp. 734-737
Nanoporous structures with striking features can be produced in some m
etals by means of high-dose helium implantation. They are characterise
d by nanoscale cavities of uniform size, a high degree of swelling and
metal ''walls'' separating neighbouring cavities which are so thin th
at their width corresponds to a few atom spacings only. These unique s
tructures have considerable potential as substrates for catalytic and
other applications. The nanoporous structures evolve from an earlier s
tage - a gas-bubble superlattice - comprised of small helium bubbles o
f very uniform size (similar to 2 nm diameter) at high concentration (
nearest neighbour distance similar to 4 nm). With increased implantati
on, the bubble array remains ordered as it coarsens. The ordered stage
s are thought to be important in seeding the unique characteristics of
the nanoporous layers. Recent research on bubble ordering and the evo
lution of bubble structure in V, Pt, Cu and Nb is summarised.