We report on the growth of thin layers of Fe 3 O 4 on GaAs and InAs by pulsed laser deposition. It is found that Fe 3 O 4 grows epitaxially on InAs at a temperature of 350°C. X-ray photoelecton spectroscopy ͑XPS͒ studies of the interface show little if any interface reaction resulting in a clean epitaxial interface. In contrast, Fe 3 O 4 grows in columnar fashion on GaAs, oriented with respect to the growth direction but with random orientation in the plane of the substrate. In this case XPS analysis showed much more evidence of interface reactions, which may contribute to the random-in-plane growth.
Gallium oxide films 20 Å in thickness were deposited onto GaAs substrates in ultra high vacuum ͑UHV͒ via e-beam evaporation from a monolithic high-purity source. The substrates were prepared by molecular-beam epitaxy and transferred to the oxide film deposition site in a wholly UHV environment. The Ga 2 O 3Ϫx films were probed by x-ray photoelectron spectroscopy ͑XPS͒. Chemical states were identified and stoichiometry was estimated. Metallic layers were deposited by e-beam evaporation in UHV after XPS analysis as caps and for future work. Film morphology and structure were probed by cross-sectional high-resolution transmission electron microscopy. The films were found to have xр0.3 and a metal/oxide interface roughness Ͻ1 Å.
Na4P2S7–6x
O4.62x
N0.92x
(NaPSON)
glassy solid electrolytes (GSEs) were prepared and tested
for their electrochemical properties and processability into thin
films. The x = 0.2 composition (NaPSON-2) was found
to be highly conducting, non-crystallizable, largely stable against
Na-metal, and supports symmetric cell cycling up to >100 μA
cm–2 without shorting. For these reasons, it was
processed into thin films drawn to 50 μm and tested in symmetric
and asymmetric cells. Measurements of the sodium ion conductivity
using symmetric cells demonstrated that the conductivity of NaPSON-2
was unchanged by film forming. Galvanostatic cycling at 5 μA
cm–2 of a 1.3 mm thick disc of NaPSON-2 showed stability
over 450 h, while cycling a 50 μm thin film of NaPSON-2 showed
a very slow growth in the resistance. Cyclic voltammetry and X-ray
photoelectron spectroscopy of the NaPSON-2 thin film GSE revealed
that it did not react with Na-metal at its surface, but rather in
the bulk of the film, showing S, Na2S, and Na3P reaction products. The source of the surface stability was determined
to be the preferential segregation of trigonally coordinated nitrogen.
These low-cost and easily processed NaPSON GSEs provide a system of
materials that could provide for significantly lower cost higher energy
density grid-scale batteries.
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