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Posted: Sep 29, 2010
Development of high performance electron source for world's highest resolution in electron microscope
(Nanowerk News) Dr. Jie Tang (Group Leader) and Dr. Han Zhang (Researcher) of the 1D Nanomaterials Group, Exploratory Materials Research Laboratory for Reliability and Safety, National Institute for Materials Science, have succeeded in establishing a surface cleaning and crystal control technology for lanthanum hexaboride (LaB6) nanowires and are able to set a goal of practical applications of LaB6 nanowires, which is expected to significantly improve the performance of electron microscopes.
In current electron microscopes, the electrons which are emitted from the tip of a needle-shaped tungsten (W) wire are accelerated by a high voltage, and enlarged images are obtained by an electron beam utilizing this phenomenon. In aiming at higher resolution while further extending the life of the electron source, the development of a more suitable structure for this purpose is highly demanded utilizing field emission type devices in which electrons are extracted directly from the electron source by an applied voltage. A representative example of these materials is LaB6.
NIMS, in joint research with the University of North Carolina at Chapel Hill (US), had previously succeeded in fabricating LaB6 nanowires and established this process as a technology. This is a process (chemical vapor deposition: CVD) in which the nanowire is grown naturally under a special environment. In order to achieve practical applications using the nanowire as an electron source, stabilization of its properties is essential. For this, cleaning of the surface and control of the surface structure, and particularly the crystal plane, is necessary.
In this work, Dr. Tang collaborators succeeded in cleaning the nanowire surface by field evaporation. This process made it possible to remove impurities and it is indispensible for high brightness emission from the electron source. By optimizing the CVD process, the NIMS researchers also succeeded in controlling the crystal orientation and crystal plane of a nanowire produced by natural growth. The establishment of this technology makes it possible to obtain the optimum crystal plane for using the LaB6 nanowire as an electron source.
As a result of this development, it is now possible for the practical application of a field emission electron source which greatly exceeds the conventional performance. When using an LaB6 field emission electron source in an electron microscope, the performance of measurement and analysis with such electron microscopes can be improved by greatly, and clearer images and improvement in capability for element identification will be possible. In addition to improvement of the performance of electron beam lithographic devices, medical X-ray equipment, and similar technologies, dramatic improvements in the level of nanotechnology research are also expected. In the future, NIMS plans to promote practical applications and commercialization through joint research and development with industrial partners.
These results were obtained as part of the development project "Development of Next-Generation Electron Microscope Using Nanostructure-Controlled LaB6" (Team Leader: Jie Tang) in the Fundamental Technology Development Program of the Japan Science and Technology Corporation's (JST) Industrial Innovation Acceleration Program, "Development of Technologies and Systems for Advanced Measurement and Analysis." The results of this development are published in the US scientific journal, Nano Letters, on September 8.