Giulio Pozzi

Electron interferometry and interference electron microscopy

A state-of-the-art review of electron interferometry and interference electron microscopy is given. The various types of interferometry device, interferometers and interference microscopes, which have been proposed and/or constructed are reviewed and commented upon. The electron biprism, by far the most successful interferometry device, is treated in some detail from both the experimental and theoretical (geometric and wave optics) points of view. The applications of electron interferometry are presented with particular reference to off-axis electron holography. Finally the future perspectives are indicated.

ELECTRON HOLOGRAPHY OF LONG-RANGE ELECTRIC AND MAGNETIC FIELDS

The influence of the perturbed reference wave in electron holography is considered for the case of static electromagnetic microfields, whose extension around the observed specimen cannot be neglected. These microfields are called ‘‘long‐range’’ to distinguish them from the ‘‘short‐range’’ ones, whose extension is strictly limited within the object wave and hence do not perturb the reference wave. Optical reconstructions of experimental holograms of simple electrostatic or magnetic long‐range fields have been modeled and simulated. The results indicate that perturbation effects must be taken into account when long‐range microfields are investigated by electron holography; it is also shown that their influence can be minimized by increasing the interference distance between the object and reference wave.

Observation of electrostatic fields by electron holography: The case of reverse-biased p-n junctions

Abstract The technique of electron holography is applied to the investigation of microelectric fields such as those associated with reverse-biased p-n junctions. Suitable electron-optical conditions were adopted in order to minimize the effect of the electrostatic fringing field on the reference wave. The electron holograms were optically processed by the method of differential interferometry.

Electron holography in the study of the electrostatic fields : the case of charged microtips

Abstract The use of electron holography has been tested to map the electrostatic field around a charged microtip. Theoretical and experimental results show that whenever a modulated reference wave is used the equiphase lines observed in the final maps are not directly or simply related to the potential distribution. A set of double-exposure holograms has been used to circumvent the limited brightness and coherence of the field emission gun so as to obtain a larger useful field.

Electron holography of long-range electrostatic fields

Publisher Summary This chapter presents a discussion on electron holography of long-range electrostatic fields. The chapter discusses the fundamental theoretical considerations underlying the observation of electric fields. The basic tool—that is, the phase-object approximation (POA)—is applied to the case of the electron biprism to obtain its transmission function and to analyze its effect on the image wave function within an interferometric or holographic setup. The chapter presents the basic principles of holographic recording and processing, with the modifications introduced by the long-range behavior of a particular class of electric fields—namely, the perturbation of the reference wave. Although the main emphasis is on image electron holography by means of an electron biprism, Fresnel holography using a single crystal film as an amplitude beam splitter is described in brief as this method can be carried out even if the microscope is not equipped with a field emission gun. The case of charged dielectric spheres is treated and charged microtips are analyzed. The electrostatic Aharonov–Bohm effect is reviewed in brief and it is shown how nonlocal quantum effects can arise with a particular configuration of electrostatic fields.

Mapping of microelectric and magnetic fields with double‐exposure electron holography

The double‐exposure electron holographic technique has been put into practical use for the first time. By this method an accurate recording of the distribution of electric and magnetic fields can be directly obtained by the electron microscope without resorting to sophisticated optical manipulation of the holograms. Problems concerning the operative definition of the contour maps are discussed. Experimental results are presented.

Electron holographic tomography for mapping the three-dimensional distribution of electrostatic potential in III-V semiconductor nanowires

Electron holographic tomography (EHT), the combination of off-axis electron holography with electron tomography, is a technique, which can be applied to the quantitative 3-dimensional (3D) mapping of electrostatic potential at the nanoscale. Here, we show the results obtained in the EHT investigation of GaAs and GaAs-AlGaAs core-shell nanowires grown by Au-catalysed metalorganic vapor phase epitaxy. The unique ability of EHT of disentangling the materials mean inner potential (MIP) from the specimen projected thickness allows reconstruction of the nanowire 3D morphology and inner compositional structure as well as the measurement of the MIP.

Nanofabrication and the realization of Feynman’s two-slit experiment

Two nanosized slits are opened by focused ion beam milling in a membrane to observe, with a transmission electron microscope, electron interference fringes. Then, on the same sample, one of the slits is closed by focused ion beam induced deposition and the corresponding transmitted intensity is recorded. The comparison between the two measurements provides an impressive experimental evidence of the probability amplitude of quantum mechanics following step by step the original idea proposed by Feynman [The Feynman Lectures on Physics (Addison-Wesley, Reading, MA, 1966), Vol. 3, Chap. 1].

Interferometry using convergent electron diffracted beams plus an electron biprism (CBED + EBI)

Abstract A method of interferometry which interferes convergent electron beams by means of an electron biprism, CBED + EBI, is presented. The method requires an electron biprism which is placed below the specimen and in between any two or more convergent beams. The biprism compensates the convergent beams deviation angle by means of an applied potential. When overlaid the diffracted beams interfere to produce an interferogram. Theoretical and practical descriptions of the CBED + EBI method are presented, as well as some of its special features such as its ability to interfere high spatial frequency beams, to produce high contrast fringes and to measure the electron beams coherency.

Young’s double-slit interference experiment with electrons

In this short Note we report a method for producing samples containing two nano-sized slits suitable for demonstrating to undergraduate and graduate students the double-slit electron interference experiment in a conventional transmission electron microscope.