An in situ SEM-FIB-based method for contrast enhancement and tomographic reconstruction for structural quantification of porous carbon electrodes.

A new in situ Scanning Electron Microscope-Focused Ion Beam-based method to study porous carbon electrodes involving Pt filling of pores from gaseous precursors has been demonstrated to show drastically improved image contrast between the carbon and porous phases when compared with the Si-resin vacuum-impregnation method. Whereas, the latter method offered up to 20% contrast, the new method offers remarkably higher contrast (42%), which enabled fast semi-automated demarcation of carbon boundaries and subsequent binarization of the images with very high fidelity. Tomographic reconstruction of the porous carbon electrode was then obtained from which several morphological parameters were quantified. The porosity was found to be 72±2%. The axial and radial tortuosites were 1.45±0.04 and 1.43±0.04, respectively. Pore size, which is defined to be the distance from the medial axis of the pore to the nearest solid boundary, was quantified. Average pore size determined from the pore size distribution was 90 nm and the corresponding 1 sigma ranges from 45 to 134 nm. Surface-to-volume ratio of the carbon phase was 46.5 µm(-1). The ratio of total surface area to the total volume of electrode including pores (i.e., specific surface area) was 13 µm(-1).

Electrochemical and electron microscopic characterization of Super-P based cathodes for Li-O2 batteries.

Aprotic rechargeable Li-O2 batteries are currently receiving considerable interest because they can possibly offer significantly higher energy densities than conventional Li-ion batteries. The electrochemical behavior of Li-O2 batteries containing bis(trifluoromethane)sulfonimide lithium salt (LiTFSI)/tetraglyme electrolyte were investigated by galvanostatic cycling and electrochemical impedance spectroscopy measurements. Ex-situ X-ray diffraction and scanning electron microscopy were used to evaluate the formation/dissolution of Li2O2 particles at the cathode side during the operation of Li-O2 cells.

The influence of spatial and temporal averaging on interpretation of HRTEM images of solid-liquid interfaces.

The effects of spatial and temporal averaging on high-resolution transmission electron microscope (HRTEM) images and associated intensity profiles of a solid-liquid Al interface were investigated using atomic coordinates obtained from molecular dynamics simulations. It was found that intensity profiles obtained by spatial averaging across the solid-liquid interface capture the variation in structural features nearly as well as time-averaged intensity profiles. This suggests that adequate spatial averaging of a single HRTEM image can be used to study the contrast from interfaces, and thereby, the structural details, without the need for more time-consuming, computer-intensive time averaged analyses. The limitations of this method are also discussed.

Nanoscale chemical and structural characterization of transient metallic nanowires using aberration-corrected STEM-EELS.

Direct chemical and structural characterization of transient iron-nickel alloy nanowires was performed at subnanometer spatial resolution using probe spherical aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy. Nanowires with diameter less than 2 nm retaining their nominal bulk alloy composition were observed. In some cases, the nanowires were oxidized. Before rupture, a nanojunction as thin as three atoms in width could be imaged. The time-dependent structural analyses revealed the nanowire rupture mechanisms. It is found that the atoms on the {111} planes were the easiest to be removed by electron irradiation and fluctuations between low-energy and high-energy facets were observed. The hitherto unknown rich variety of structural and chemical behavior in alloyed magnetic nanojunctions should be considered for understanding their physical properties.