arXiv subjects

Daniel S. Gianola

Publications and source records attributed to Daniel S. Gianola.

23 records · Page 2Linked to original sources

arXiv2020

Electron Backscattered Diffraction using a New Monolithic Direct Detector: High Resolution and Fast Acquisition

A monolithic active pixel sensor based direct detector that is optimized for the primary beam energies in scanning electron microscopes is implemented for electron back-scattered diffraction (EBSD) applications. The high detection efficiency of the detector and its large array of pixels allow sensitive and accurate detection of Kikuchi bands arising from primary electron beam excitation energies of 4 keV to 28 keV, with the optimal contrast occurring in the range of 8-16 keV. The diffraction pattern acquisition speed is substantially improved via a sparse sampling mode, resulting from the acquisition of a reduced number of pixels on the detector. Standard inpainting algorithms are implemented to effectively estimate the information in the skipped regions in the acquired diffraction pattern. For EBSD mapping, a speed as high as 5988 scan points per second is demonstrated, with a tolerable fraction of indexed points and accuracy. The collective capabilities spanning from high angular resolution EBSD pattern to high speed pattern acquisition are achieved on the same detector, facilitating simultaneous detection modalities that enable a multitude of advanced EBSD applications, including lattice strain mapping, structural refinement, low-dose characterization, 3D-EBSD and dynamic in situ EBSD.

cond-mat.mtrl-sci↗

arXiv2019

Flexible Conductive Composites with Programmed Electrical Anisotropy Using Acoustophoresis

3D printing mechanically flexible composite materials with high electrical conductivity is currently hindered by the need to use high loading of conductive filler, which severely limits flexibility. Here, microstructural patterning of composite materials via acoustophoresis imparts these materials with high conductivity and flexibility simultaneously, filling a technology gap in the field. Acoustophoresis patterns filler particles into highly efficient percolated networks which utilize up to 97\% of the particles in the composite, whereas the inefficient stochastic networks of conventional dispersed-fiber composites utilize $<5$\%. These patterned materials have conductivity an order of magnitude higher than conventional composites made with the same ink, reaching 48\% the conductivity of bulk silver within the assembled silver-particle networks (at 2.6v\% loading). They also have low particle loading so that they're flexible, withstanding $>$500 bending cycles without losses in conductivity and changing conductivity only $5$\% within cycles on average (for 2.6v\% composites). In contrast, conventional unpatterned composites with the same conductivity require such high loading that they're prohibitively brittle. Finally, modulating the shape of the applied acoustic fields allows control over the anisotropy of the conductive networks and produces materials which are either 2-D conductive, 1-D conductive, or insulating, all using the same nozzle and ink.

physics.app-ph↗

arXiv2019

New techniques for imaging and identifying defects in electron microscopy

Defects in crystalline materials control the properties of materials, and their characterization focuses our strategies to optimize performance. Electron microscopy has served as the backbone of our understanding of defect structure and their interactions owing to beneficial spatial resolution and contrast mechanisms that enable direct imaging of defects. These defects reside in complex microstructures and chemical environments, demanding a combination of experimental approaches for full defect characterization. In this article, we describe recent progress and trends in methods for examining defects using scanning electron microscopy platforms, where several emerging approaches offer attractive benefits, for instance in correlative microscopy across length scales and in situ studies of defect dynamics.

cond-mat.mtrl-sci↗

arXiv2014

Robust Scaling of Strength and Elastic Constants and Universal Cooperativity in Disordered Colloidal Micropillars

We study the uniaxial compressive behavior of disordered colloidal free-standing micropillars composed of a bidisperse mixture of 3 and 6 um polystyrene particles. Mechanical annealing of confined pillars enables variation of the packing fraction across the phase space of colloidal glasses. The measured normalized strengths and elastic moduli of the annealed freestanding micropillars span almost three orders-of-magnitude despite similar plastic morphology governed by shear banding. We measure a robust correlation between ultimate strengths and elastic constants that is invariant to relative humidity, implying a critical strain of $\sim$0.01 that is strikingly similar to that observed in metallic glasses (MGs) [W.L. Johnson, K. Samwer, Phys. Rev. Lett. 95, 195501, 2005] and suggestive of a universal mode of cooperative plastic deformation. We estimate the characteristic strain of the underlying cooperative plastic event by considering the energy necessary to create an Eshelby-like ellipsoidal inclusion in an elastic matrix. We find that the characteristic strain is similar to that found in experiments and simulations of other disordered solids with distinct bonding and particle sizes, suggesting a universal criterion for the elastic to plastic transition in glassy materials with the capacity for finite plastic flow.

cond-mat.soft↗

arXiv2010

Extremely Low Drift in Amorphous Phase Change Nanowire Materials

Time-dependent drift of resistance and threshold voltage in phase change memory (PCM) devices is of concern as it leads to data loss. Electrical drift in amorphous chalcogenides has been argued to be either due to electronic or stress relaxation mechanisms. Here we show that drift in amorphized Ge2Sb2Te5 nanowires with exposed surfaces is extremely low in comparison to thin-film devices. However, drift in stressed nanowires embedded under dielectric films is comparable to thin-films. Our results shows that drift in PCM is due to stress relaxation and will help in understanding and controlling drift in PCM devices.

cond-mat.mtrl-sci↗