Electron Holography for Mapping Electric Fields and Charge

The measurement of nanoscale electric fields and mapping of electric charge are important but challenging aspects of nanoscience and nanotechnology. This chapter focuses on electron holography, which is a powerful electron-microscopy interference technique that allows direct access to the phase of an electron wave after it has passed through a thin, electron-transparent object. Measurement of the phase change caused by the object relative to a vacuum reference wave can provide quantitative determination of electrostatic fields and charge within and surrounding the object with high sensitivity and nanoscale resolution. In this chapter, off-axis electron holography is first briefly introduced, and the theoretical background and experimental basis for the technique are outlined. Practical guidelines for carrying out electron holography, as well as requirements for sample preparation are then described. Next, a short, selective overview is given of some applications of the technique to measuring nanoscale electrostatic fields and mapping electric charge. Finally, ongoing problems and prospects for further applications of electron holography are discussed.