Key insights into the behaviour of materials can be gained by observing their structure during phase transitions or when they undergo lattice distortion. Laser pulses on the femtosecond time scale can be used to induce disorder in a "pump-probe" experiment with the subsequent transients being probed stroboscopically using femtosecond pulses of visible light 1 ,
The availability of third-generation synchrotrons and ultimately X-ray free-electron lasers 1 is driving the development of many new methods of microscopy. Among these techniques, coherent diffractive imaging (CDI) is one of the most promising, offering nanometre-scale imaging of non-crystallographic samples. Image reconstruction from a single diffraction pattern has hitherto been possible only for small, isolated samples, presenting a fundamental limitation on the CDI method. Here we report on a form of imaging we term 'keyhole' CDI, which can reconstruct objects of arbitrary size. We demonstrate the technique using visible light and X-rays, with the latter producing images of part of an extended object with a detectorlimited resolution of better than 20 nm. Combining the improved resolution of modern X-ray optics with the wavelength-limited resolution of CDI, the method paves the way for detailed imaging of a single quantum dot or of a small virus within a complex host environment.
Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga+), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised sample preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology.
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