Piezoresponse force microscopy is used to study the velocity of the polarization domain wall in ultrathin ferroelectric barium titanate (BTO) films grown on strontium titanate (STO) substrates by molecular beam epitaxy. The electric field due to the cone of the atomic force microscope tip is demonstrated as the dominant electric field for domain expansion in thin films at lateral distances greater than about one tip diameter away from the tip. The velocity of the domain wall under the applied electric field by the tip in BTO for thin films (less than 40 nm) followed an expanding process given by Merz’s law. The material constants in a fit of the data to Merz’s law for very thin films are reported as about 4.2 KV/cm for the activation field, $$E_{\mathrm{a}}$$ E a , and 0.05 nm/s for the limiting velocity, $$v_{\infty }$$ v ∞ . These material constants showed a dependence on the level of strain in the films, but no fundamental dependence on thickness.

The band offsets for the β-(Al 0.21 Ga 0.79 ) 2 O 3 /β-Ga 2 O 3 (010) heterojunction have been experimentally measured by X-ray photoelectron spectroscopy. High-quality β-(Al 0.21 Ga 0.79 ) 2 O 3 films were grown by metal−organic chemical vapor deposition for characterization. The indirect band gap of β-(Al 0.21 Ga 0.79 ) 2 O 3 was determined by optical transmission to be 4.69 ± 0.03 eV with a direct transition of 5.37 ± 0.03 eV, while β-Ga 2 O 3 was confirmed to have an indirect band gap of 4.52 ± 0.03 eV with a direct transition of 4.94 ± 0.03 eV. The resulting band alignment at the heterojunction was determined to be of type II with the valence and conduction band edges of β-(Al 0.21 Ga 0.79 ) 2 O 3 being −0.26 ± 0.08 and 0.43 ± 0.08 eV, respectively, above those of β-Ga 2 O 3 (010). These values can now be used to help better design and predict the performance of β-(Al x Ga 1−x ) 2 O 3 heterojunctionbased devices.

The compositional and optical properties of an aluminum‐based transition‐metal alloy system (Au–Ag–Al) as an advanced material for photonic applications are investigated. The system is fabricated by sequentially evaporating thin layers of gold, silver, and aluminum. The thickness of Al is varied to reflect different percentages in the alloyed films. Alloying of the metals is confirmed from the shifts in the electronic binding energy of the pure elements through X‐ray photoelectron spectroscopy. The current–voltage measurements demonstrate good ohmic conductivity in the films and the optical properties are obtained by standard absorption and z‐scan techniques. Plasmonic peaks are observed in the alloyed system related to the participating metals. The thermal nonlinear optical response is conducted in the continuous wave (CW) regime. The films show large values for the thermo‐optical coefficient (∂n/∂T) which results in high values (≈10−3 cm2 W−1) for the third‐order nonlinear coefficient (n2them). A discussion of these values and their impact on the application of thin alloyed metals is presented.

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