'World's best microscope' up and running

By Mike Nagle

- Last updated on GMT

Related tags Electron Atom

The world's most powerful transmission electron microscope has been
turned on in the US, with single-atom resolution bringing within
reach the ability to analyse chemicals simply by looking at them.

The Transmission Electron Aberration-corrected Microscope (TEAM 0.5) has been installed at the Lawrence Berkeley National Laboratory, having been developed in collaboration with the US Department of Energy (DOE), the University of Illinois and two microscopy firms: the FEI Company and Germany's CEOS. Traditionally TEM and scanning TEM microscopes have suffered from somewhat limited resolution that stopped frustratingly short of allowing researchers to study materials accurately at the atomic level. This latest development has managed to reach a resolution of 0.5 Angstroms (A) (0.05nm) or one quarter of the diameter of a carbon atom. The increased resolution of the TEAM microscope should enable scientists in all disciplines to characterise atomic scale structure and chemistry more accurately than ever before. The director of the TEAM Project, Uli Dahmen, explained that the microscope is the world's best thanks to the equipments resolution, improved contrast and low signal-to-noise ratio. "[It] brings us within reach of meeting the great challenge posed by the famous physicist Richard Feynman in 1959: the ability to analyse any chemical substance simply by looking to see where the atoms are.​. "It's because the signal-to-noise ratio is so good that you can adjust focus atom by atom, with enough sensitivity to obtain information about the three-dimensional atomic structure of a single nanoparticle,"​ said Dahmen. To achieve such a its resolution, TEAM 0.5 uses technical advances that have only recently become possible, including ultra-stable electronics, improved aberration correctors, and an extremely bright electron source. Spherical aberration is caused by the shape of a lens and degrades images, making points of light look like disks, and correcting it can make dramatic improvements to image resolution. In this case, a series of multipole magnetic lenses of varying geometries shapes the electron beam. "Correcting spherical aberration in an electron microscope has long been possible in theory,"​ says Dahmen. "But only recently has it become practical."​ This is because today's stable electronics reduce drift and fast computers allow continuous adjustments in real time. According to Dahmen, although corrector technology has even become available commercially "no off-the-shelf corrector can match TEAM 0.5's ability to compensate even higher-order aberrations."​ Aberration correction is also essential for another advanced feature of TEAM 0.5: its ability to maintain high resolution with lower electron beam energies. "Low-energy electrons have longer wavelengths, so they are harder to focus,"​ Dahmen explained. "Aberration correction allows better than one-angstrom resolution with excellent contrast even at 80 kilovolts. This is important when you don't want to damage the sample with a high-energy beam -- in biological studies, for example." ​ In preliminary tests at the FEI Company, the microscope was able to resolve individual atoms in samples of two gold crystals connected by a 'nanobridge' only a few dozen atoms wide. From one exposure to the next, researchers were able to see individual gold atoms changing positions. Living the dream ​ TEAM 0.5 will become available to outside users by October, 2008 but the team are already working on enhancements. In order to resolve the position of individual atoms in a structure, images must be taken at different angles, from which the computer reconstructs a 3-D tomograph of the sample, as in a CAT scan. To make this possible a system capable of tilting and rotating the sample, and moving it in all directions under the electron beam, is also being developed at NCEM. Much smaller than sample stages now in use, the new TEAM stage will be housed entirely inside the microscope column. Manipulating the sample by such methods as minute piezoelectric 'crawlers' that change shape when electricity is applied, the new stage will be able to control and reproduce the sample's position and attitude with an accuracy of less than a billionth of a meter. Installation of the new stage must await the next phase of the TEAM Project: the TEAM I microscope, due to be set up at NCEM early in 2009. TEAM I will also correct chromatic aberration in the image beam, which has never been accomplished before. Chromatic aberration results when a lens refracts light or electrons of different wavelengths at different angles. "Correcting chromatic aberration is harder and takes more space,"​ explained Dahmen. The collaborative effort on the TEAM Project will "open the door to other ambitious developments around the world,"​ he concluded. Indeed, the team already have competition. Last February, Jeol said it was developing a competing S/TEM microscope system in collaboration with Dr Takayanagi of the Tokyo Institute of Technology that would 'soon' exceed the TEAM project goals of 0.5A resolution and sub-angstrom 3D imaging capability

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