Electron Holography of Nanostructured Materials

Abstract

This chapter contains an overview of the theory and applications of electron holography, a powerful technique that allows the phase shift of a high-energy electron wave that has passed through a thin sample to be measured in the transmission electron microscope (TEM). The recorded phase shift is sensitive to both the magnetic induction and the electrostatic potential within and around the specimen. The chapter begins with the theoretical basis of the off-axis mode of electron holography in the TEM. Selected applications of the technique for the quantitative measurement of magnetic fields and electrostatic potentials in nanoscale materials and devices are then described. The in situ application of external stimuli, including applied voltage, magnetic field, temperature and a gas reaction environment during the acquisition of electron holograms, is discussed. High-resolution electron holography and alternative modes of electron holography are described briefly and possible future developments and applications of the technique are outlined.

High brightness ultrafast transmission electron microscope based on a laser-driven cold-field emission source: principle and applications

“…Proposed by Gabor as a new experimental method to improve the electron microscope resolution [59], electron holography is a fully quantitative technique used to retrieve the electron wave phase recorded in an interference pattern [60]. This pattern originates from the coherent overlap of the sample wave and a reference one.…”

Interferometric methods for mapping static electric and magnetic fields

“…When using a single electron biprism, the interference distance, field of view and fringe spacing are not independent of one another, Fresnel diffraction fringes from the edges of the biprism perturb the image and, more importantly when studying long-range electromagnetic fields, the reference wave is perturbed by the field itself [4]. Applications of electron holography to high-resolution and field mapping have been overwhelming, as testified by several books (e.g., [110][111][112]), book chapters (e.g., [113][114][115]) and review articles (e.g., [116][117][118][119][120][121]).…”

Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source

“…Following the initial suggestion of Gabor in 1948, new techniques such as the off-axis electron holography have started to exploit the high spatial coherence of the electron beam to produce interferograms from which modifications of the phase of the electronic wavepacket can be retrieved [2]. These studies have shown that the phase of the electron wave is a very sensitive probe of the electrostatic field, strain field or magnetic field which allows the quantitative mapping of these observables with nanometer resolution [3,4,5,6]. The brightness of the source, defined as the current per unit area and solid angle, is the figure of merit that must be optimized in order to get the highest spatial coherence or the highest spatial resolution for applications like holography or spatially resolved spectroscopies (in this latter case, the improved energy resolution of the cold FE sources is also very important).…”