Big data and deep data in scanning and electron microscopies: deriving functionality from multidimensional data sets

The development of electron and scanning probe microscopies in the second half of the twentieth century has produced spectacular images of the internal structure and composition of matter with nanometer, molecular, and atomic resolution. Largely, this progress was enabled by computer-assisted methods of microscope operation, data acquisition, and analysis. Advances in imaging technology in the beginning of the twenty-first century have opened the proverbial floodgates on the availability of high-veracity information on structure and functionality. From the hardware perspective, high-resolution imaging methods now routinely resolve atomic positions with approximately picometer precision, allowing for quantitative measurements of individual bond lengths and angles. Similarly, functional imaging often leads to multidimensional data sets containing partial or full information on properties of interest, acquired as a function of multiple parameters (time, temperature, or other external stimuli). Here, we review several recent applications of the big and deep data analysis methods to visualize, compress, and translate this multidimensional structural and functional data into physically and chemically relevant information.

Ferromagnetism and nonmetallic transport of thin-film α-FeSi(2): a stabilized metastable material

A metastable phase α-FeSi_{2} was epitaxially stabilized on a silicon substrate using pulsed laser deposition. Nonmetallic and ferromagnetic behaviors are tailored on α-FeSi_{2} (111) thin films, while the bulk material of α-FeSi_{2} is metallic and nonmagnetic. The transport property of the films renders two different conducting states with a strong crossover at 50 K, which is accompanied by the onset of a ferromagnetic transition as well as a substantial magnetoresistance. These experimental results are discussed in terms of the unusual electronic structure of α-FeSi_{2} obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our finding sheds light on achieving ferromagnetic semiconductors through both their structure and doping tailoring, and provides an example of a tailored material with rich functionalities for both basic research and practical applications.

Ferroelectricity in ultrathin BaTiO3 films: probing the size effect by ultraviolet Raman spectroscopy

We demonstrate the dramatic effect of film thickness on the ferroelectric phase transition temperature Tc in strained BaTiO3 films grown on SrTiO3 substrates. Using variable-temperature ultraviolet Raman spectroscopy enables measuring Tc in films as thin as 1.6 nm, and a film thickness variation from 1.6 to 10 nm leads to Tc tuning from 70 to about 925 K. Raman data are consistent with synchrotron x-ray scattering results, which indicate the presence of 180 degrees domains below Tc, and thermodynamic phase-field model calculations of Tc as a function of thickness.

Characterizing the two- and three-dimensional resolution of an improved aberration-corrected STEM

The successful development of third-order aberration correctors in transmission electron microscopy has seen aberration-corrected electron microscopes evolve from specialist projects, custom built at a small number of sites to common instruments in many modern laboratories. Here we describe some initial results illustrating the two- and three-dimensional (3D) performance of an aberration-corrected scanning transmission electron microscope with a prototype improved aberration corrector designed to also minimize fifth-order aberrations and a new, higher brightness gun. We show that atomic columns separated by 0.63 A can be resolved and demonstrate detection of single dopant atoms with 3D sensitivity.

Enhancement of ferroelectricity in strained BaTiO3 thin films

Biaxial compressive strain has been used to markedly enhance the ferroelectric properties of BaTiO3 thin films. This strain, imposed by coherent epitaxy, can result in a ferroelectric transition temperature nearly 500 degrees C higher and a remanent polarization at least 250% higher than bulk BaTiO3 single crystals. This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.