Reflection high-energy electron diffraction (RHEED) is a ubiquitous in situ molecular beam epitaxial (MBE) characterization tool. Although RHEED can be a powerful means for crystal surface structure determination, it is often used as a static qualitative surface characterization method at discrete intervals during a growth. A full analysis of RHEED data collected during the entirety of MBE growths is made possible using principle component analysis (PCA) and $k$-means clustering to examine significant boundaries that occur in the temporal clusters grouped from RHEED data and identify statistically significant patterns. This process is applied to data from homoepitaxial $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ growths, heteroepitaxial $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ grown on scandate substrates, $\mathrm{Ba}\mathrm{Sn}{\mathrm{O}}_3$ films grown on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates, and ${\mathrm{LaNiO}}_3$ films grown on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates. This analysis may provide additional insights into the surface evolution and transitions in growth modes at precise times and depths during growth, and that video archival of an entire RHEED image sequence may be able to provide more insight and control overgrowth processes and film quality.

Through systematic control of the Nd concentration, we show that the carrier density of the two-dimensional electron gas (2DEG) in ${\mathrm{SrTiO}}_3/{\mathrm{NdTiO}}_3/{\mathrm{SrTiO}}_3(001)$ can be modulated over a wide range. We also demonstrate that the ${\mathrm{NdTiO}}_3$ in heterojunctions without a ${\mathrm{SrTiO}}_3$ cap is degraded by oxygen absorption from air, resulting in the immobilization of donor electrons that could otherwise contribute to the 2DEG. This system is, thus, an ideal model to understand and control the insulator-to-metal transition in a 2DEG based on both environmental conditions and film-growth processing parameters.