Microscopy Research

"Development of Low Energy Holography Electron Microscope."
Tsumoru Shintake, Hidehito Adaniya, Masao Yamashita, Martin Philip Cheung.
KENBIKYO - The Japanese Society of Microscopy (2017) 52: 51-54.

"Development of a SEM-based low-energy in-line electron holography microscope for individual particle imaging".
Hidehito Adaniya, Martin Cheung, Cathal Cassidy, Masao Yamashita, Tsumoru Shintake.
Ultramicroscopy (2018) 188:31-40.  doi: 10.1016/j.ultramic.2018.03.002.

Prof. Dennis Gabor invented holography in the 1940’s. His original purpose was to the cure spherical aberration problems in electron microscopes.  However, due to technical problems like insufficient beam quality, his original idea was not realized. After the invention of optical lasers in the 1960’s, holography was realized and widely utilized for three-dimensional image recording, high-precision geometrical measurement, and compressed data recording. Prof. Dennis Gabor was awarded the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method”.

In our research, we take up the challenge of realizing his original idea using today’s advanced electron microscopy technology and numerical data analyzing capability.

Our equipment uses a high-performance SEM column as a coherent electron source. We place a cryo-sample on a rotatable stage at target position. First, we inspect the sample in SEM mode, then we cut the sample into thin membranes using FIB: Focused Ion Beam tool. We then put the electron beam on the membrane sample and take a diffraction from downstream using a two-dimensional electron detector. Using numerical processing, the electron phase is recovered, and the real image is reconstructed through back-Fourier transformation. 

This microscopy will be applicable to the following the research areas in bio-science, physics and technology.
(1) DNA and virus imaging, (2) Protein structure determination using two-dimensional protein crystals, (3) Membrane protein analysis using micron-sized crystals, (4) Ice embedded single bio-particle imaging, (5) Carbon nanotube, fullerene and various kinds of nano-particles. 

"Improved sample dispersion in cryo-EM using “perpetually-hydrated” graphene oxide flakes".
Martin Cheung, Hidehito Adaniya, Cathal Cassidy, Masao Yamashita, Kun-Lung Li, Seita Taba, Tsumoru Shintake.
Journal of Structural Biology (2018) 1: 75-79.  doi: 10.1016/j.jsb.2018.07.008.

"Graphene specimen support technique for low voltage STEM imaging".
Masao Yamashita, Matthew Ryan Leyden, Hidehito Adaniya, Martin Philip Cheung, Teruhisa Hirai, Yabing Qi, Tsumoru Shintake.
Microscopy (2017) 66 4:261-271.  doi:  10.1093/jmicro/dfx014.

"Determination of the mean inner potential of cadmium telluride via electron holography".
Cathal Cassidy, Ankur Dhar, Tsumoru Shintake.
Applied Physics Letters (2017) 110(163503).  doi: 10.1063/1.4981809.

"Electron holography studies of CdTe"
Cathal Cassidy, Tsumoru Shintake
Grant-In-Aid for Scientific Research (C), KAKENHI-PROJECT-18K04247, 2018-04-01 - 2021-03-31.

Electron holography allows quantitative measurement of the amplitude and phase of the electron wave which passes through a specimen, to atomic resolution.  Measurement of electron wave amplitude and phase in turn enable quantitative mapping of electric and magnetic fields in the specimen.  This is of particular relevance for semiconductor devices, where atomic scale structures and defects can have a macroscopic effect on the electrical performance of the device.

In this project, as a target material we focus on the detector-grade single crystal CdTe and devices.  CdTe has been used for many years in niche gamma-ray astronomy applications, but today is also attracting a lot of attention for mainstream medical imaging technology.  A global leading manufacturer of CdTe detector devices (Acrorad Ltd) is located in Okinawa prefecture, close to OIST.

This project has 4 defined phases.  Firstly, we explore strategies to optimize electron-transparent lamella preparation for this rather brittle semiconductor material.  This includes exploration of cryo-FIB, and in situ treatment to control surface layers.   Secondly, we establish simulation environments to compute the expected electron wave propagation and scattering in the material, as a function of electron beam and specimen parameters like beam tilt and specimen thickness.  Thirdly, we work on optimizing the experimental settings to obtain best-case spatial and phase (voltage) resolution.  Fourthly, we apply our framework to the study of the electric field distributions at structural defects and junctions, at mesoscale and atomic scale.

PhD Student Project:  Mr. Ankur Dhar

Electron holography is a popular microscopy technique that allows for the visualization of electromagnetic fields within and without of materials. It has made possible the detection of many unique phenomena, such as the Aharonov-Bohm effect and magnetic skyrmions. Here at OIST, I am working on designing electron holography experiments that will image magnetic monopole-like excitations in a type of spin system known as spin ice. These monopole analogs have been indirectly detected, but holography presents a good chance to image them directly. To realize this experiment, I am taking measurements of larger scale approximations of spin ice monopoles made from single domain magnetic structures, as well as simulating the spin ice experiment with finite element methods. All of this work comes together to build understanding of the technical requirements that will ultimately be necessary to observe monopoles in spin ice directly.