  4d transition metal oxides have emerged as promising materials for numerous
applications including high mobility electronics. SrNbO$_{3}$ is one such
candidate material, serving as a good donor material in interfacial oxide
systems and exhibiting high electron mobility in ultrathin films. However, its
synthesis is challenging due to the metastable nature of the d$^{1}$ Nb$^{4+}$
cation and the limitations in the delivery of refractory Nb. To date, films
have been grown primarily by pulsed laser deposition (PLD), but development of
a means to grow and stabilize the material via molecular beam epitaxy (MBE)
would enable studies of interfacial phenomena and multilayer structures that
may be challenging by PLD. To that end, SrNbO$_{3}$ thin films were grown using
hybrid MBE for the first time using a tris(diethalamido)(tert-butylimido)
niobium precursor for Nb and an elemental Sr source on GdScO$_{3}$ substrates.
Varying thicknesses of insulating SrHfO$_{3}$ capping layers were deposited
using a hafnium tert-butoxide precursor for Hf on top of SrNbO$_{3}$ films to
preserve the metastable surface. Grown films were transferred in vacuo for
X-ray photoelectron spectroscopy to quantify elemental composition, density of
states at the Fermi energy, and Nb oxidation state. Ex situ studies by X-ray
absorption near edge spectra illustrates the SrHfO$_{3}$ capping plays an
important role in preserving the Nb 4d$^{1}$ metastable charge state in
atmospheric conditions.
