Evan J. Musterman

Piezoresponse force microscopy (PFM) techniques, which probe nanoscale electromechanical coupling, are often difficult to interpret. For ferroelectric mixed conductors useful for computation elements, this becomes more difficult due to non-piezoelectric electromechanical effects. The measured PFM signal can have tip-local and nonlocal contributions associated with multiple coupling mechanisms, and it is often unclear what material property is truly being probed. Here, using antimony sulfide (Sb2S3) as a model system, an emerging phase change material for optical and electrical memory and computation elements, we show that the PFM signal can be separated into a fast, capacitive contribution, and a slow, ionic contribution whose time-domain characteristics match well with diffusion-controlled kinetics. This ionic contribution, rather than ferroelectric switching, leads to electromechanical hysteresis in Sb2S3, with no clearly measurable ferroelectric switching effects. Uniquely, electromechanical behavior has a very clear spatial contrast that is decoupled from surface topography, showing that the signal arises from surface charging that reflects bulk-like properties and allowing a self-consistent interpretation in terms of dielectric behavior. This protocol establishes a clear interpretation of a non-piezoelectric signal, often mischaracterized as an indication of the ferroelectric state. Additionally, because all electromechanical experiments show a strong, low-frequency electric relaxation in crystalline Sb2S3 while the response of glassy Sb2S3 is static, we conclude that the crystalline phase of Sb2S3 is a mixed conductor, while the amorphous phase remains strictly insulating.

Schematic of electrode evolution at the mesoscale: a porous structure with Zn–Mn shell-like domains forms around undissolved MnO ₂ after ∼400 hours of cycling, hindering ion transport and causing capacity fade in aqueous Zn/MnO ₂ batteries.

Single crystals fabricated in glass by localized heating can develop uniquely deformed lattices stabilized by the surrounding amorphous medium. The development of lattice curvature appears to be intrinsic to the crystal growth process in some systems, while the result of the locally changing crystallography in others. In this work, a model laser‐fabricated rotating lattice Sb₂S₃ crystal grown in stoichiometric glass is used to demonstrate fabrication of novel macroperiodic metastructures that utilize intrinsic lattice curvature superimposed with subtle crystallographic influences. The limited availability of slip systems drives the lattice curvature magnitude to vary with crystal growth direction, maximizing for lattices aligned with the predominant Burgers vector along with corresponding increases in dislocation density. Misaligned lattice orientations form smaller secondary lattice curvatures arising from misaligned Burgers vectors with further elastic contributions. Over extended crystal growth, these secondary components align the lattice to rotate about either the or crystal axes forming repeating metastructures of lattice orientation with periodicity 20–160 microns in length. The mechanistic approach used in this work may be expanded to other systems with known slip systems to better understand and design macroperiodic metastructures.

Laser heating is well-established to impart optical functionality into glass by local modification and crystallization. In this paper, we demonstrate electron beam heating in scanning and transmission microscopes as an alternative for the local crystallization of Sb₂S₃ in Sb-S-I glasses as a model system. Governed by different absorption physics, the electron beam expands morphological control of crystal cross section relative to laser, producing nanoscale (∼50 nm) single crystal architectures. We also report the effects of accelerating voltage and probe current and characterize the curved lattice of crystals formed in glass with electron diffraction techniques.

Atomic arrangements systemically deviating from the classic definition of single crystal lattice have been known in spherulites for over a century. However, their unusual curved lattice could not be exploited for useful applications due to their uncontrolled orientations and lattice curvatures. Heating of glass with focused laser, electron, or X‐ray beam has yielded well‐defined conditions for forming single crystal architectures. Furthermore, by controlling the conditions of irradiation and confinement by glass matrix for a given system, desired lattice curvature (rotations and twists) can be reproducibly introduced into these crystals. Here, we review several examples of laser‐fabricated crystals with curved lattices in glass using a common coordinate system, which helps to establish correlations between processing parameters and lattice curvature. The mechanisms of lattice deformations are discussed along with potential methods to control the orientation of the initially formed seeds that determine the lattice orientations of the end product. The recent developments of laser‐fabrication of single crystal architectures in glass with controlled heating profile appear promising for engineering the curvature of their lattices.