Development of novel electron microscopy techniques to extract obscured information on material properties

July 31, 2017, National Institute for Materials Science
Development of novel electron microscopy techniques to extract obscured information on material properties
Diagrams illustrating the working principle of the four-point probe technique using a spectroscopic microscope. Credit: National Institute for Materials Science

NIMS researchers Bo Da (researcher at the RCAMC and the CMI2, MaDIS) and Hideki Yoshikawa (leader of the Surface Chemical Analysis Group) and a research group led by Shigeo Tanuma (NIMS Special Researcher), Kazuhito Tsukakoshi (MANA Principal Investigator, NIMS), Kazuyuki Watanabe (Professor, Tokyo University of Science) and Zejun Ding (Professor, University of Science and Technology of China) jointly developed versatile spectroscopic microscopy techniques capable of simultaneously measuring a nano-thin film at a wide range of electron energy levels, from almost zero energy to high energy, using a microscope employing electron beams. The group also demonstrated the effectiveness of the technique.

Conventional methods of measuring nano-thin films require great care because they require changing the level of a monochromatic incident and readjusting the electron optical system while measuring the electron microscope image. We addressed this issue using a creative approach. We developed a new measurement technique using secondary electrons―which are generated in a substrate material and have a wide energy distribution―as a virtual white electron probe. To reduce this technique to practice, we needed to completely eliminate background signals from secondary electrons. We adopted the four-point probe method used in astronomy to accurately detect weak signals captured by telescopes. This method enabled us to simultaneously measure the electron transmittance of graphene at a wide range of energy levels between almost zero and 600 . We then confirmed that the measured values matched well with theoretical values. This study reports for the first time that information on the properties of a material ―specifically, the electron transmittance of nano-thin films―can be extracted from secondary electron signals.

Measurement of the transmittance characteristics of a material using visible light of various energy levels is analogous to identifying the color of the material. Similarly, measurement of the electron transmittance of a nano-thin film using electrons of various energy levels is analogous to identifying the color of a localized area of the film using a more narrowly focused "eye" (electrons). It is difficult to quickly determine the quality (e.g., color) of nano-thin films at specific target sites, as the film itself is normally difficult to locate. Accordingly, techniques such as the one developed in this study will be very valuable in research on new nano-thin films in which the qualitative consistency of the film across a large area needs to be ensured.

Explore further: Graphene specimen support technique for low voltage STEM imaging

More information: Bo Da et al. Virtual substrate method for nanomaterials characterization, Nature Communications (2017). DOI: 10.1038/ncomms15629

Related Stories

Device design allows ten-fold increase in spin currents

June 8, 2017

An electron carries electrical charge and spin that gives rise to a magnetic moment and can therefore interact with external magnetic fields. Conventional electronics are based on the charge of the electron. The emerging ...

Changing semiconductor properties at room temperature

October 28, 2016

It's a small change that makes a big difference. Researchers have developed a method that uses a one-degree change in temperature to alter the color of light that a semiconductor emits. The method, which uses a thin-film ...

Recommended for you

Optical nanoscope images quantum dots

January 23, 2018

Physicists have developed a technique based on optical microscopy that can be used to create images of atoms on the nanoscale. In particular, the new method allows the imaging of quantum dots in a semiconductor chip. Together ...

Quantum dot ring lasers emit colored light

January 22, 2018

Researchers have designed a new type of laser called a quantum dot ring laser that emits red, orange, and green light. The different colors are emitted from different parts of the quantum dot—red from the core, green from ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.