Structure determination of proteins and other macromolecules has historically required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. We applied serial femtosecond crystallography (SFX) using an x-ray free-electron laser (XFEL) to obtain high-resolution structural information from microcrystals (less than 1 micrometer by 1 micrometer by 3 micrometers) of the well-characterized model protein lysozyme. The agreement with synchrotron data demonstrates the immediate relevance of SFX for analyzing the structure of the large group of difficult-to-crystallize molecules.

We showed how intermetallic formation reactions can be studied under rapid heating ͑10 6 -10 7 K s −1 ͒ using x-ray microdiffraction with temporal resolution on microsecond time scales. Rapid heating was achieved by initiating an exothermic reaction in multilayer foils comprising alternating nanoscale layers of elemental metals. The reaction occurred in a front ϳ100 m wide which propagated across the foil at ϳ1-10 m s −1 . By using synchrotron x-rays focused to a small spot ͑60 m diameter͒ and a fast pixel-array detector, we were able to track the evolution of phases in the reaction front during the initial heating transient, which occurred in approximately 1 ms, through cooling over a period of hundreds of milliseconds. In Al/Ni multilayer foils, the first phases to form were an Al-rich liquid and the cubic intermetallic AlNi ͑which likely formed by nucleation from the liquid͒. In foils of overall composition AlNi, this is the stable intermetallic and the only phase to form. In foils of composition Al 3 Ni 2 , during cooling we observed a peritectic reaction between AlNi and the remaining liquid to form Al 3 Ni 2 , which is the stable phase at room temperature and the final product of the reaction. This is in contrast to the sequence of phases under slow heating, where we observed formation of nonequilibrium Al 9 N 2 first and do not observe formation of a liquid phase or the AlNi intermetallic. We also observed formation of an amorphous phase ͑along with crystalline ZrNi͒ during rapid heating of Zr/Ni multilayers, but in this system the temperature of the reaction front never reached the lowest liquidus temperature on the Zr-Ni phase diagram. This implies that the amorphous phase we observed was not a liquid arising from melting of a crystalline phase. We suggest instead that a Zr-rich amorphous solid formed due to solid-state interdiffusion, which then transformed to a supercooled liquid when the temperature exceeded the glass transition temperature. Formation of the supercooled liquid presumably facilitated continued rapid intermixing, which may be necessary to sustain a self-propagating reaction front in this system.

We have used self-propagating exothermic reactions in Al/Ni multilayers as a means to explore the effect of rapid heating on phase transformations. Using time-resolved synchrotron x-ray microdiffraction with an extremely fast detector, we were able to examine the reaction sequence in detail at heating rates of ϳ10 6 K s −1. We observed that the intermediate phases formed during the self-propagating reactions are different from those formed at lower heating rates, even though the final phases are the same. In situ characterization is essential, as other means of studying self-propagating reactions ͑such as quenching the reaction followed by ex situ analysis͒ provide different-and potentially misleading-results.

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The production of high-performance carbon nanotube (CNT) materials demands understanding of the growth behavior of individual CNTs as well as collective effects among CNTs. We demonstrate the first use of grazing incidence small-angle X-ray scattering to monitor in real time the synthesis of CNT films by chemical vapor deposition. We use a custom-built cold-wall reactor along with a high-speed pixel array detector resulting in a time resolution of 10 msec. Quantitative models applied to time-resolved X-ray scattering patterns reveal that the Fe catalyst film first rapidly dewets into well-defined hemispherical particles during heating in a reducing atmosphere, and then the particles coarsen slowly upon continued annealing. After introduction of the carbon source, the initial CNT diameter distribution closely matches that of the catalyst particles. However, significant changes in CNT diameter can occur quickly during the subsequent CNT self-organization process. Correlation of time-resolved orientation data to X-ray scattering intensity and height kinetics suggests that the rate of self-organization is driven by both the CNT growth rate and density, and vertical CNT growth begins abruptly when CNT alignment reaches a critical threshold. The dynamics of CNT size evolution and self-organization vary according to the catalyst annealing conditions and substrate temperature. Knowledge of these intrinsically rapid processes is vital to improve control of CNT structure and to enable efficient manufacturing of high-density arrays of long, straight CNTs.