Optical and electronic functionality arising from controlled defect formation in nanoscale complex oxide lateral epitaxy.

Epitaxial crystallization of complex oxides provides the means to create materials with precisely selected composition, strain, and orientation, thereby controlling their functionalities. Extending this control to nanoscale three-dimensional geometries can be accomplished via a three-dimensional analog of oxide solid-phase epitaxy, lateral epitaxial crystallization. The orientation of crystals within laterally crystallized SrTiO3 systematically changes from the orientation of the SrTiO3 substrate. This evolution occurs as a function of lateral crystallization distance, with a rate of approximately 50° µm-1. The mechanism of the rotation is consistent with a steady-state stress of tens of megapascal over a 100-nanometer scale region near the moving amorphous/crystalline interface arising from the amorphous-crystalline density difference. Second harmonic generation and piezoelectric force microscopy reveal that the laterally crystallized SrTiO3 is noncentrosymmetric and develops a switchable piezoelectric response at room temperature, illustrating the potential to use lateral crystallization to control the functionality of complex oxides.

Tilting in coronene layers on Au(111).

Control of molecule adsorption and ordering on metal surfaces is of critical importance for the design and fabrication of molecule-based functional materials. In the present work, the molecule layer structures of coronene on Au(111) and HOPG are studied by combining scanning tunneling microscopy with image analysis techniques to unravel small changes in molecule adsorption geometry. Coronene forms a densely packed layer on Au(111) and HOPG at room temperature, but does not preferentially decorate the herringbone reconstruction. The molecule layer structure is confirmed by histograms of molecule radius and apparent height obtained from STM images using a python based open source code. Annealing at 116 °C initiates a tilting of coronene molecules on Au(111) by about 11 ± 4° which is deduced from statistical image analysis. The structural analysis is combined with an assessment of apparent height modulation with bias voltage to ascertain the reliability of the statistical analysis. Our work illustrates that the combination of advanced image analysis processing and STM images allows one to extract even small changes in a molecule layer structure.