Vibrational spectroscopies using infrared radiation1,2, Raman scattering3, neutrons4, low-energy electrons5 and inelastic electron tunnelling6 are powerful techniques that can analyse bonding arrangements, identify chemical compounds and probe many other important properties of materials. The spatial resolution of these spectroscopies is typically one micrometre or more, although it can reach a few tens of nanometres or even a few ångströms when enhanced by the presence of a sharp metallic tip6,7. If vibrational spectroscopy could be combined with the spatial resolution and flexibility of the transmission electron microscope, it would open up the study of vibrational modes in many different types of nanostructures. Unfortunately, the energy resolution of electron energy loss spectroscopy performed in the electron microscope has until now been too poor to allow such a combination. Recent developments that have improved the attainable energy resolution of electron energy loss spectroscopy in a scanning transmission electron microscope to around ten millielectronvolts now allow vibrational spectroscopy to be carried out in the electron microscope. Here we describe the innovations responsible for the progress, and present examples of applications in inorganic and organic materials, including the detection of hydrogen. We also demonstrate that the vibrational signal has both high- and low-spatial-resolution components, that the first component can be used to map vibrational features at nanometre-level resolution, and that the second component can be used for analysis carried out with the beam positioned just outside the sample—that is, for ‘aloof’ spectroscopy that largely avoids radiation damage.
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We thank A. Howie and J.-C. Idrobo for discussions, W. J. Bowman, J. Bruley, J. H. Butler, V. Domnich, R. A. Haber, Y. Ikuhara, M. R. Libera, D. S. Lowry and V. Nicolosi for provision of samples, J. Mardinly for help with running the instruments, our co-workers at Nion, especially N. J. Bacon, G. J. Corbin, P. J. Cramer, Z. Dellby, R. W. Hayner, P. Hrncirik, P. Phoungphidok, M. C. Sarahan, G. S. Skone, Z. Szilagyi and T. Yoo for help with the construction of the hardware, electronics and software for HERMES, and C. Trevor of Gatan Inc. for an instability-analysing script. We also acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University. Financial support for the purchase of the microscopes was provided by National Science Foundation grants DMR MRI 0821796 (Arizona State University) and DMR MRI-R2 959905 (Rutgers University). Department of Energy grant DE-SC0004954 provided support for P.A.C. and microscopy performed at Arizona State University, and Department of Energy grant DE-SC0005132 provided support for P.E.B., M.J.L. and microscopy performed at Rutgers University. Additional support was provided by the Department of Energy (grant DE-SC0007694), the Natural Sciences and Engineering Council of Canada, the UK Engineering and Physical Research Council (capital equipment grant EP/J021156/1), Arizona State University, Rutgers University and Nion Co.
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Scientific Reports (2017)