Dr. Xinguo Hong [Stony Brook Univ., USA]

Title: High-energy X-ray microfocusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

Time: 9:30 - 10:30 AM, Monday, February 22, 2016

Place: Conference Room 201, HPSTAR (Shanghai)

Host: Dr. Ho-Kwang Mao

Abstract:

High-energy synchrotron radiation can be especially valuable for providing structural information covering short-to-medium range atomic order in crystals but this requires obtaining data covering a large Q range, where Q = (4psinq)/l is the scattering wave vector. The atomic pair distribution function (PDF) method using high-energy X-ray or neutron diffraction is a powerful tool for studying crystalline, disordered, and nanocrytalline materials.

As the refractive index of most materials is close to unity in the X-ray range, focusing X-rays is challenging. In this talk, I will present our recent development of micro-focusingoptics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10-15 µm) has been achieved at energies of 66 and 81 keV.

PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. We have observed direct experimental evidence of a transition in compressional mechanism for n-Au at ~20 GPa, i.e., from deformation dominated by nucleation and motion of lattice dislocations (dislocation-mediated) to a prominent grain boundary mediated response to external pressure. The internal microstructure inside the nanoparticle (nanocrystallinity) plays a critical role for the macro-mechanical properties of nano-Au.

Biography of the Speaker:

Dr. Xinguo Hong is a senior X-ray DAC beamline scientist of Mineral Physics Institute, Stony Brook University, USA. Dr. Hong's research interests are:

-  Synchrotron X-ray measurement of X-ray micro- diffraction, absorption, scattering, fluorescence, tomography. Time-resolve X-ray diffraction and absorption experiments

-  Synchrotron X-ray technologies: high-energy X-ray focusing, X-ray diffraction, High pressure pair-distribution function (HP-PDF), HP-XAFS, etc.

-  Diamond anvil cell high pressure techniques

-  Laser-heating high temperature technique

-  Stress and strain under high pressure

-  High pressure spectroscopy measurements

-  High pressure/high temperature phase transformation, structure and electronic properties

-  Crystal growth and high pressure synthesis

-  Nano materials, energy materials and superhard materials

-  Behavior of minerals under high pressure and temperature

-  Development of novel techniques in X-ray scattering as combined with structural biology, including advanced bio-SAXS/WAXS applications to macromolecular dynamics and/or trapping of intermediate states of reactions, time resolved SAXS/WAXS, envelope based phasing, laser triggered conformational change, etc.