2, University of Tennessee, Knoxville, Knoxville, Tennessee, United States
3, Drexel University, Philadelphia, Pennsylvania, United States
Manipulation and control of the matter at the atomic level is one of the ultimate goals in nanoscience. As device elements continue to shrink, and new device concepts such as oxide electronics are being proposed based on unique materials properties, it is vitally important to be able to manipulate a wide range of materials at atomic scale. We have recently demonstrated atomic-level sculpting of 3d crystalline oxide nanostructures from metastable amorphous precursor in a scanning transmission electron microscope (STEM) . SrTiO3 nanowires were fabricated epitaxially from the crystalline substrate following the beam path, producing crystalline structures as small as 1-2 nm and the process can be observed in situ with atomic resolution. The details of the process led us to conclude that the relevant energy transfer is knock-on in nature, rather than associated with local heating. High localization associated with this process allowed us to fabricate arbitrary shaped structures via control of the position and scan speed of the electron beam.
We have explored the utility of this approach beyond STO/STO structures. Similar processes can be indiced ar Si/amorphous Si interfaces . The growth behavior and the resulting feature shape are well described by modeling using a two-temperature approach. The growth is strongly affected by the presence of SiO2 at the crystalline-amorphous interface. For linear trajectories of the electron beam, the growth rate appears to depend on crystallographic direction.
We have further investigated using beam-induced growth to create heterostructures, where BaTiO3 features were grown on SrTiO3 substrate. Due to substantial lattice mismatch, the beam-induced features exhibit island-type growth with 2-unit-cell-thick pseudomorphic layer. The STEM probe has nm-scale size in beam direction, resulting in localization of the electron beam impact on a similar scale. The prospects for creating functional heterostructures with this approach, as well as its unique utility for uncovering atomic-scale structure property relationships, will also be discussed.
* Research supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Division of Materials Sciences and Engineering, and by ORNL's Laboratory Directed Research and Development Fund. A portion of this research was conducted at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.
 Stephen Jesse et al., Small, 11 5895 (2015)
 Nan Jiang et al., MRS Bulletin, 42 , 653 (2017).