Phase-shifting electron holography for accurate measurement of potential distributions in organic and inorganic semiconductors

Abstract

Phase-shifting electron holography (PS-EH) is an interference transmission electron microscopy technique that accurately visualizes potential distributions in functional materials, such as semiconductors. In this paper, we briefly introduce the features of the PS-EH that overcome some of the issues facing the conventional EH based on Fourier transformation. Then, we present a high-precision PS-EH technique with multiple electron biprisms and a sample preparation technique using a cryo-focused-ion-beam, which are important techniques for the accurate phase measurement of semiconductors. We present several applications of PS-EH to demonstrate the potential in organic and inorganic semiconductors and then discuss the differences by comparing them with previous reports on the conventional EH. We show that in situ biasing PS-EH was able to observe not only electric potential distribution but also electric field and charge density at a GaAs p-n junction and clarify how local band structures, depletion layer widths, and space charges changed depending on the biasing conditions. Moreover, the PS-EH clearly visualized the local potential distributions of two-dimensional electron gas (2DEG) layers formed at AlGaN/GaN interfaces with different Al compositions. We also report the results of our PS-EH application for organic electroluminescence (OEL) multilayers and point out the significant potential changes in the layers. The proposed PS-EH enables more precise phase measurement compared to the conventional EH, and our findings introduced in this paper will contribute to the future research and development of high-performance semiconductor materials and devices.

Single-particle cryo-EM: alternative schemes to improve dose efficiency

“…better than the fringe spacing (Vö lkl & Lichte, 1990;Yamamoto et al, 2010Yamamoto et al, , 2021. It is essential to have fine interference fringes for high spatial resolution.…”

“…This approach takes a series of holograms with interference fringes shifted every image by a beam-tilt, allowing for the retrieval of both the amplitude and phase information of the objective wave from the periodically changing fringe intensity (Ru et al, 1994). It is unnecessary to filter the signal in Fourier space, since phaseshifting electron holography is able to obtain high-resolution phase images without the loss of fringe contrast (Yamamoto et al, 2021).…”

Direct visualization of electric potential distribution in organic light emitting diode by phase-shifting electron holography

“…Our group previously demonstrated the feasibility of visualizing the inner potential distribution in an OLED consisting of five layers. 20) However, because of the complex five-layer structure, the built-in potential profile was difficult to interpret. In this letter, we prepared two-layered OLED model samples with p-type and n-type organic layers for PS-EH to interpret the built-in potential profile compared with previous reports.…”