Treatment of the stable N-heterocyclic carbene (NHC)
1,3-di-<i>tert</i>-butylimidazolin-2-ylidene
with two equivalents of AlH<sub>3</sub>(NMe<sub>3</sub>) afforded the
structurally unusual ring expanded dialane complex <b>1</b> in 72% yield after sublimation. Complex <b>1</b> has a distorted norbornane-like C<sub>3</sub>N<sub>2</sub>Al<sub>2</sub>
core with two pseudo-tetrahedral Al dihydride sites. Treatment of <b>1</b> with Cp<sub>2</sub>TiCl<sub>2</sub>
as a model for metal thin film precursors produced the hydride-bridged
Ti(III)-Al heterobimetallic complex <b>2</b>
in 45% crystalline yield. Complex <b>1</b>
shows good volatility and thermal stability, subliming at 90-100 °C and 50
mTorr and decomposing in the solid state at ~200 °C. The vapor pressure of <b>1</b> is 0.75 Torr at 120 °C. These
physical properties are promising for a potential atomic layer deposition (ALD)
precursor. Aluminum metal films were deposited by thermal ALD using AlCl<sub>3</sub>
and <b>1</b> as precursors with a growth
rate of ~3.5 Å/cycle after 100 cycles within an ALD window between 120-140 °C.
The films are crystalline aluminum metal by X-ray diffraction (XRD) and X-ray
photoelectron spectroscopy (XPS) analysis showed aluminum metal with 7.0 at.%
C, 3.6 at.% N, and 0.9 at.% Cl impurities. The aluminum metal films had an
electrically discontinuous morphology. Conductive aluminum metal films have
been deposited under similar conditions using a different aluminum hydride
reducing co-reactant, which highlights the impact that small precursor
differences can have on film characteristics.
Investigations into the impact of various substrates and ZnO ultra thin seed layers prepared by atomic layer deposition on growth of ZnO nanowire array