  The recent emergence of topological insulators (TI) has spurred intensive
efforts to grow TI thin films on various substrates. However, little is known
about how robust the topological surface states (TSS) are against disorders and
other detrimental effects originating from the substrates. Here, we report
observation of a well-defined TSS on Bi2Se3 films grown on amorphous SiO2
(a-SiO2) substrates and a large gating effect on these films using the
underneath doped-Si substrate as the back gate. The films on a-SiO2 were
composed of c-axis ordered but random in-plane domains. However, despite the
in-plane randomness induced by the amorphous substrate, the transport
properties of these films were superior to those of similar films grown on
single-crystalline Si(111) substrates, which are structurally better matched
but chemically reactive with the films. This work sheds light on the importance
of chemical compatibility, compared to lattice matching, for the growth of TI
thin films, and also demonstrates that the technologically-important and
gatable a-SiO2/Si substrate is a promising platform for TI films.
