Final Report Summary - NANOSCULPTURE (Exploration of strains in synthetic nanocrystals)
The overall goal of the "nanosculpture" grant was to explore the structure and properties of nanocrystals by the new method of coherent X-ray Diffraction (CXD). To do this we put together a team of postdocs and students to learn how to grow (bottom-up) and sculpt (top-down) the samples in the clean-rooms of the new London Centre for Nanotechnology. The samples were measured first at the Advanced Photon Source in Chicago, then at the Diamond Light Source in the UK. We analysed the structures of a wide range of nanocrystals and established the general principles underlying their nanocrystal structure. This used the language of nanoscale strain caused by the surface structure of the crystals. This was all summarised in a review article [27] and numerous public presentations, such as the Morris Fine Lecture at Northwestern University (see attachment).
One notable result resulted from an investigation of gold nanocrystals before and after they were dosed with propyl thiol molecules. Prior to our study, such molecules were believed to form simple close-packed self-assembled monolayers on the gold surface. A distinct change in the pattern of internal strain was detected in the crystals. Through our theoretical principles of nanocrystal structure and subsequent modelling, we could assign the pattern of changes to a change in differential surface stress caused by the thiol. Since the differential was large, it has to be attributed to a new kind of surface structure, possibly an intermixed gold-sulphur structure on the spherical regions of the nanocrystal surface morphology [22].
Along the way, we discovered a new non-uniqueness of the solution to CXD inversion problems in the general case. This has major consequences for the widespread applicability of the coherence-based methods and explains why "strong phase" objects are hard to invert, for example. To get around this, we developed a new method called GPER, which was used to watch the mecahical breakdown of fabricated silicon nanowires [34].
A major overall goal of the grant was to transfer the knowledge of coherence-based imaging from the USA to Europe. We arranged a long-term collaboration with the APS facility in Chicago where one of our postdocs was based. In this way, we developed a new coherence-based imaging method called X-ray ptychography. We started at the APS under our long-term collaborative arrangements, then moved to Diamond. We used the method to illustrate one of its major new applications, the measurement of X-ray optical wavefronts. This was applied to examine the focus of a new MLL focussing device [32], as well as more conventional mirror focussing systems.
We did the first optical pump, X-ray probe measurements of vibration modes in nanocrystals. This used the new capabilities of the first hard X-ray Free Electron Laser (XFEL) at Stanford. We saw the two expected "breathing modes" of the cylindrical shaped nanocrystals and then, using CDI, saw an additional shear mode in the patterns of strain within the crystal. This new work has been well received and was published in Science [33].
One notable result resulted from an investigation of gold nanocrystals before and after they were dosed with propyl thiol molecules. Prior to our study, such molecules were believed to form simple close-packed self-assembled monolayers on the gold surface. A distinct change in the pattern of internal strain was detected in the crystals. Through our theoretical principles of nanocrystal structure and subsequent modelling, we could assign the pattern of changes to a change in differential surface stress caused by the thiol. Since the differential was large, it has to be attributed to a new kind of surface structure, possibly an intermixed gold-sulphur structure on the spherical regions of the nanocrystal surface morphology [22].
Along the way, we discovered a new non-uniqueness of the solution to CXD inversion problems in the general case. This has major consequences for the widespread applicability of the coherence-based methods and explains why "strong phase" objects are hard to invert, for example. To get around this, we developed a new method called GPER, which was used to watch the mecahical breakdown of fabricated silicon nanowires [34].
A major overall goal of the grant was to transfer the knowledge of coherence-based imaging from the USA to Europe. We arranged a long-term collaboration with the APS facility in Chicago where one of our postdocs was based. In this way, we developed a new coherence-based imaging method called X-ray ptychography. We started at the APS under our long-term collaborative arrangements, then moved to Diamond. We used the method to illustrate one of its major new applications, the measurement of X-ray optical wavefronts. This was applied to examine the focus of a new MLL focussing device [32], as well as more conventional mirror focussing systems.
We did the first optical pump, X-ray probe measurements of vibration modes in nanocrystals. This used the new capabilities of the first hard X-ray Free Electron Laser (XFEL) at Stanford. We saw the two expected "breathing modes" of the cylindrical shaped nanocrystals and then, using CDI, saw an additional shear mode in the patterns of strain within the crystal. This new work has been well received and was published in Science [33].