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Abstract Germanium-based oxides such as rutile GeO 2 are garnering attention owing to their wide band gaps and the prospects of ambipolar doping for application in high-power devices. Here, we present the use of germanium tetraisopropoxide (GTIP), a metal-organic chemical precursor, as a source of germanium for the demonstration of hybrid molecular beam epitaxy for germanium-containing compounds. We use Sn 1- x Ge x O 2 and SrSn 1- x Ge x O 3 as model systems to demonstrate our synthesis method. A combination of high-resolution X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy confirms the successful growth of epitaxial rutile Sn 1- x Ge x O 2 on TiO 2 (001) substrates up to x  = 0.54 and coherent perovskite SrSn 1- x Ge x O 3 on GdScO 3 (110) substrates up to x  = 0.16. Characterization and first-principles calculations corroborate that germanium occupies the tin site, as opposed to the strontium site. These findings confirm the viability of the GTIP precursor for the growth of germanium-containing oxides by hybrid molecular beam epitaxy, thus providing a promising route to high-quality perovskite germanate films. 

We investigate the surface electronic structure of SrTiO 3 (STO) films grown by a hybrid molecular beam epitaxy that are both stoichiometric and nonstoichiometric by means of x-ray photoelectron spectroscopy and electron energy loss spectroscopy. Increasing the fraction of the surface that is terminated with an SrO layer is correlated with a decrease in the chemical potential whereby the valence band maximum moves closer to the Fermi level, but without a significant change in the bandgap. Inasmuch as SrO-terminated STO (001) has previously been shown to act as an electron scavenger in which carriers from the bulk are trapped, we argue that the high fraction of SrO in the terminal layer is what lowers the chemical potential in Sr-rich STO. Our experimental results provide important insights into various physical phenomena that can occur on STO (001) surfaces and their effect on bulk electronic properties. 

Hybrid MBE produces epitaxial SrTiO 3 free-standing nanomembranes using remote epitaxy in an adsorption-controlled manner. 

Advances in physical vapor deposition techniques have led to a myriad of quantum materials and technological breakthroughs, affecting all areas of nanoscience and nanotechnology which rely on the innovation in synthesis. Despite this, one area that remains challenging is the synthesis of atomically precise complex metal oxide thin films and heterostructures containing “stubborn” elements that are not only nontrivial to evaporate/sublimate but also hard to oxidize. Here, we report a simple yet atomically controlled synthesis approach that bridges this gap. Using platinum and ruthenium as examples, we show that both the low vapor pressure and the difficulty in oxidizing a “stubborn” element can be addressed by using a solid metal-organic compound with significantly higher vapor pressure and with the added benefits of being in a preoxidized state along with excellent thermal and air stability. We demonstrate the synthesis of high-quality single crystalline, epitaxial Pt, and RuO 2 films, resulting in a record high residual resistivity ratio (=27) in Pt films and low residual resistivity, ∼6 μΩ·cm, in RuO 2 films. We further demonstrate, using SrRuO 3 as an example, the viability of this approach for more complex materials with the same ease and control that has been largely responsible for the success of the molecular beam epitaxy of III-V semiconductors. Our approach is a major step forward in the synthesis science of “stubborn” materials, which have been of significant interest to the materials science and the condensed matter physics community. 

There exists an interplay between antiferrodistortive phase transition and transport in SrTiO 3 via the Hall scattering factor. 

This work reports the quantification of rise in channel temperature due to self-heating in two-terminal SrSnO3 thin film devices under electrical bias. Using pulsed current–voltage (I–V) measurements, thermal resistances of the thin films were determined by extracting the relationship between the channel temperature and the dissipated power. For a 26-nm-thick n-doped SrSnO3 channel with an area of 200 μm2, a thermal resistance of 260.1 ± 24.5 K mm/W was obtained. For a modest dissipated power of 0.5 W/mm, the channel temperature rose to ∼176 °C, a value which increases further at higher power levels. Electro-thermal simulations were performed which showed close agreement between the simulated and experimental I–V characteristics both in the absence and presence of self-heating. The work presented is critical for the development of perovskite-based high-power electronic devices.