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The electronic properties of hematite were investigated by means of synchrotron radiation photoemission (SR-PES) and X-ray absorption spectroscopy (XAS). Hematite samples were exposed to trimethyl aluminum (TMA) pulses, a widely used Al-precursor for the atomic layer deposition (ALD) of Al2O3. SR-PES and XAS showed that the electronic properties of hematite were modified by the interaction with TMA. In particular, the hybridization of O 2p states with Fe 3d and Fe 4s4p changed upon TMA pulses due to electron inclusion as polarons. The change of hybridization correlates with an enhancement of the photocurrent density due to water oxidation for the hematite electrodes. Such an enhancement has been associated with an improvement in charge carrier transport. Our findings open new perspectives for the understanding and utilization of electrode modifications by very thin ALD films and show that the interactions between metal precursors and substrates seem to be important factors in defining their electronic and photoelectrocatalytic properties.
Iron oxide and magnesium-doped iron oxide films were grown by atomic layer deposition in the temperature range of 350–500 ◦C from ferrocene, (dimethylaminomethyl)ferrocene, magnesiumβ-diketonate, and ozone. Phase composition of the films depended on the deposition temperature, as magnetite and/or maghemite tended to form instead of hematite upon lowering the temperature. Iron oxide layers were also mixed with magnesium oxide by alternate deposition of MgO and Fe2O3 which also favored the formation of magnetite or maghemite structure prior to hematite. Scanning electron microscopy implied the smoothening of the films after doping with magnesium oxide. Magnetometry was used to study the effects of temperature and doping levels on the magnetic properties of
the films.
Ru films were grown by atomic layer deposition in the temperature range of 275-350 degrees C using (ethylcyclopentadienyl)(pyrrolyl)ruthenium and air or oxygen as precursors on HF-etched Si, SiO(2), ZrO(2), and TiN substrates. Conformal growth was examined on three-dimensional silicon substrates with 20: 1 aspect ratio. ZrO(2) promoted the nucleation of Ru most efficiently compared to other substrates, but the films roughened quickly on ZrO(2) with increasing film thickness. The minimum number of cycles required to form continuous and conductive metal layers could be decreased by increasing the length of the oxygen pulse. In order to obtain well-conducting Ru films growth to thicknesses of at least 8-10 nm on any surface was necessary. Resistivities in the ranges of 30-60 and 14-16 mu Omega . cm were achieved for 4-6 and 10-15 nm thick films, respectively. Delamination became an issue in the Ru films grown to thicknesses about 10 nm and higher.