The proposal seeks funds to acquire a cryogenically-cooled, double-crystal, x-ray monochromator system for usage by the HPCAT synchrotron consortium at the Advanced Photon Sources (APS), Argonne National Laboratory. Acquisition of the state-of-the-art monochromator will enable us to harness the full capacity of the new, powerful, canted undulator source which is scheduled for installation this Fall according to the APS x-ray source upgrade program. By handling the 5-10 times higher heat load from the upgraded undulator and preserving the source size, stability, and coherence, the proposed new monochromator system will improve the spatial and temporal resolutions of high-pressure x-ray diffraction, spectroscopy and imaging experiments by one to two orders of magnitude and will double the effective user beam time. Such unprecedented advance in high-pressure synchrotron technology will greatly enhance high-pressure physics research in areas of superconductivity, ferroelectricity, colossal magnetoresistivity, phonon dynamics, Fermi-surface nesting, d-electron spin pairing, f-electron delocalization, and insulator-metal transition, and chemistry research in areas of high-pressure syntheses and characterizations of novel nitrides, hydrides, oxides, molecular compounds, crystal amorphization, bonding changes, and photochemistry. The progresses in fundamental research, in turn, impact on the applied sciences, ranging from the understanding the Earth's and planetary deep interiors to the creations of novel and technologically important materials. The timely upgrade of the world-class high-pressure synchrotron consortium is essential for the U.S. high-pressure research and education community, and benefits students and postdoctoral researchers who are the dominant users of the consortium facility.
Pressure is a fundamental environment that alters all states of matter. In the currently accessible pressure range of 300 gigapascals (that is three million times the pressure of the Earth's atmosphere at sea level), ordinary materials transform to novel forms that may possess extremely useful properties for modern technological applications. Realization of the enormous potential in science and technology, however, relies upon the advancement of instrumentation for probing these properties under the extreme pressures. We propose to acquire a state-of-the-art high-pressure x-ray instrument, namely a monochromator assembly, that can harness the full capacity of the powerful x-ray source at the newly upgraded HPCAT facility. The proposed instrument will provide atomic-scale clarity and millionth-of-a-second time resolution for investigation of a wide range of pressure-induced phenomena. It will lead to unprecedented advances in high-pressure materials research in physics, chemistry and Earth sciences. The deep secrets hidden under the extreme pressures and temperatures in the Earth's and planetary interiors will be unraveled. Technologically useful materials will be discovered in the vast, unexplored, high-pressure regime, and recovered for usage at ordinary conditions. The timely upgrade of the world-leading high-pressure consortium facility is essential for the U.S. high-pressure research and education community, especially for the benefits of students and postdoctoral researchers who are the main users of the facility.
A new type of monochromator assembly has been designed to match the new canted undulators at the HPCAT beamlines at the nation's most brilliant high energy x-ray source, the Advanced Photon Source. The assembly has been successfully installed and commissioned in November 2011. The high-pressure synchrotron research at the HPCAT beamline facility has impacted an exceedingly broad scientific frontier. With the acquisition of the new monochromator assembly, together with the undulator source upgrade, we have greatly enhanced the current available capabilities. Meanwhile, several new techniques have been being developed for the next generation exploration. (a) Enhancing time resolved high-pressure studies. With the order of the magnitude increase in flux benefitted from the new acquisition, together with the newly available advanced detectors, high-pressure x-ray diffraction can now be performed at sub-milisecond level, a three-orders-of-magnitude improvement compared to the situation before the acquisition of the monochromators. We have further developed the matching dynamic loading devices and pulsed laser heating techniques for fast (de)compression and rapid or modulated heating, which are now widely used for studies on phase transition kinetics, materials metastability, high pressure melting, and precise thermal equations of state. This area is now moving out from its infancy stage and growing very rapidly, largely benefitted from the new acquisition of the monochromator assembly. (b) Megabar high-pressure spectroscopy. Our previous limiting factor to achieve a small (1-2 microns) beam was the beam distortion from a water-cooled diamond monochromator. This has now overcome with the newly installed monochromator assembly. By pressure-tuning materials over a wide range, we are ble to study fundamental properties of the electron gas, strongly correlated electron systems, high-energy electronic excitations and phonons in energy and momentum space at multimegabar pressures. The results will have important implications for a variety of materials problem applications as well as providing basic information for understanding the deep interior of the Earth and other planets. The enabled megabar high-pressure spectroscopy, together with the high depth resolution, provides the best spatial resolution with superior signal/noise ratio through depth collimation, thus advancing the national user facility to the next level of cutting edge. (c) High-pressure micron to sub-micron probes. It took three decades to reduce the x-ray beam size from 50 microns to the current 5 microns in high-pressure research. This one order of magnitude reduction has proven to be tremendously significant, and is responsible for many breakthroughs in high-pressure science using synchrotron. The new monochromator minimizes the distortion caused by the high heat load of the undulator source, and allows for one order of magnitude reduction to a beam size of 0.1-1 microns in the end station 16ID-E at HPCAT. Although we have not finished the upgrade, the acquisition of the monochromators has prepared us to provide the highest spatial resolution among high-pressure beamlines in the world, and will allow users to probe small sample sizes for possibly reaching ultrahigh static pressures, to investigate grain-to-grain interactions with sub-micron resolution in all three dimensions, to map the grain boundary, phase boundary, chemical ordering, local stress/strain and structure evolution within the individual grains, and to study nanoscale single crystals. (d) Quality performance, reliability, and low-maintenance are the major characteristics of the instrument. Besides the above enabling techniques with its minimum beam distortion and excellent stability, the monochromator assembly greatly enhances the daily operation at the HPCAT user facility. Users benefit greatly from the larger energy range, super stability, and operation reproducibility, enabling new research areas, minimizing the down-time for checking and realigning the beamline and the sample position, and greatly increasing the quality and efficiency in beamline experiments. The high reproducibility will also allow for timely switching techniques, thus obtaining complementary data from the same sample at the same extreme conditions.
