  Titanium-island formation on graphene as a function of defect density is
investigated. When depositing titanium on pristine graphene, titanium atoms
cluster and form islands with an average diameter of about 10nm and an average
height of a few atomic layers. We show that if defects are introduced in the
graphene by ion bombardment, the mobility of the deposited titanium atoms is
reduced and the average diameter of the islands decreases to 5nm with
monoatomic height. This results in an optimized coverage for hydrogen storage
applications since the actual titanium surface available per unit graphene area
is significantly increased.
