Scanning tranission electron microscopy (STEM) has joined the ultrafast four-dimensional TEM club, researchers at Caltech report (J. Am. Chem. Soc., DOI: 10.1021/ja203821y). The development, which combines 3-D nanoscale spatial resolution of conventional TEM with femtosecond temporal resolution, may enable researchers to probe subtle specimen motions and morphological changes in materials and biological sciences. During the past few years, Ahmed H. Zewail and coworkers have developed laser-based methods for conducting pulsed TEM experiments. The work has led to techniques for shortening by 10 orders of magnitude the timescale for measuring electron energy loss (EEL) spectra, thereby providing time-resolved, element-specific information from a nanoscale region of a TEM specimen. The researchers also demonstrated ultrafast electron tomography. Zewail and Volkan Ortalan have now extended this approach to STEM by integrating femtosecond resolution into a raster-type technique that, for some specimens, can provide chemical and imaging data simultaneously. To demonstrate the technique, they measured ultrafast mechanical motions and shape changes in silver nanowires. The pair also imaged a single gold nanoparticle and measured its EEL spectrum simultaneously, which can’t be done via conventional methods, they say.
