Sub-wavelength coherent diffractive imaging using a tabletop high harmonic light source
Visible microscopes can produce crisp images with a spatial resolution on order of the illuminating wavelength, because of the availability of near-perfect lenses in this region of the spectrum. Extreme ultraviolet (EUV) and soft X-ray (SXR) light has wavelengths 10-100 times shorter than visible light: thus, it should be possible to design a powerful microscope that can image structures that are too small or too opaque to be seen with visible light. However, EUV/SXR lenses are very lossy and imperfect, limiting the advantage of using shorter wavelengths, and blurring the resulting images to >8 times the theoretical limit. Fortunately, new techniques pioneered by STROBE scientists Kapteyn, Murnane and Miao make it possible to build lensless microscopes illuminated by coherent laser-like beams — a capability that is revolutionizing X-ray imaging worldwide. Very recently, the Kapteyn-Murnane group at CU Boulder used tabletop EUV beams at a wavelength of 13nm to achieve sub-wavelength spatial resolution imaging at short wavelengths for the first time – essentially demonstrating the first near-perfect X-ray microscope. Moreover, because the EUV source produces exceedingly short, femtosecond (~10-15 sec), bursts of light, it can now be used to make stroboscopic movies to observe how the nanoworld functions. STROBE graduate student Dennis Gardner received the American Physical Society Division of Laser Science Thesis Award for this work.
Deciphering chemical order/disorder and material properties at the single-atom level
The precise location of atoms, together with the direction and strength of their bonds to one another, determine the mechanical, catalytic, optical, electronic and magnetic properties of many materials. The STROBE deputy director (John Miao) led an interdisciplinary team (including STROBE members from UCLA, UC Berkeley and LBNL) that determined the 3D coordinates of 6,569 iron and 16,627 platinum atoms in a model iron-platinum nanoparticle system, with 22 picometer precision. The measured atomic positions and chemical species have been used as direct input to quantum mechanical calculations to correlate crystal defects and chemical order/disorder with material properties at the single-atom level. This work also solved a puzzle as to why the magnetic strength of the iron-platinum nanoparticle was not as high as expected – the atomic positions were optimal only in a small region of the nanoparticle. This work makes significant advances in characterization capabilities and expands our fundamental understanding of structure-property relationships, which is anticipated to find broad applications in physics, chemistry, materials science, nanoscience and nanotechnology.