We present a detailed study of the electronic structure and chemical state of high-quality stoichiometric EuO and O-rich Eu 1 O 1+x thin films grown directly on silicon without any buffer layer using hard x-ray photoemission spectroscopy (HAXPES). We determine the EuO oxidation state from a consistent quantitative peak analysis of 4f valence band and 3d core-level spectra. The results prove that nearly ideal, stoichiometric, and homogeneous EuO thin films can be grown on silicon, with a uniform depth distribution of divalent Eu cations. Furthermore, we identify the chemical stability of the EuO/silicon interface from Si 2p core-level photoemission. This work clearly demonstrates the successful integration of high-quality EuO thin films directly on silicon, opening up the pathway for the future incorporation of this functional magnetic oxide into silicon-based spintronic devices.
Nuclear hyperpolarization in the liquid state by dynamic nuclear polarization (DNP) has been of great interest because of its potential use in NMR spectroscopy of small samples of biological and chemical compounds in aqueous media. Liquid state DNP generally requires microwave resonators in order to generate an alternating magnetic field strong enough to saturate electron spins in the solution. As a consequence, the sample size is limited to dimensions of the order of the wavelength, and this restricts the sample volume to less than 100 nL for DNP at 9 T (∼260 GHz). We show here a new approach that overcomes this sample size limitation. Large saturation of electron spins was obtained with a high-power (∼150 W) gyrotron without microwave resonators. Since high power microwaves can cause serious dielectric heating in polar solutions, we designed a planar probe which effectively alleviates dielectric heating. A thin liquid sample of 100 μm of thickness is placed on a block of high thermal conductivity aluminum nitride, with a gold coating that serves both as a ground plane and as a heat sink. A meander or a coil were used for NMR. We performed H DNP at 9.2 T (∼260 GHz) and at room temperature with 10 μL of water, a volume that is more than 100× larger than reported so far. TheH NMR signal is enhanced by a factor of about -10 with 70 W of microwave power. We also demonstrated the liquid state of P DNP in fluorobenzene containing triphenylphosphine and obtained an enhancement of ∼200.
Multilayer approach to the quantitative analysis of x-ray photoelectron spectroscopy results: Applications to ultrathin Si O 2 on Si and to self-assembled monolayers on gold
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