S. Kycia

New high temperature furnace for structure refinement by powder diffraction in controlled atmospheres using synchrotron radiation

A low thermal gradient furnace design is described which utilizes Debye–Scherrer geometry for performing high temperature x-ray powder diffraction with synchrotron radiation at medium and high energies (35–100 keV). The furnace has a maximum operating temperature of 1800 K with a variety of atmospheres including oxidizing, inert, and reducing. The capability for sample rotation, to ensure powder averaging, has been built into the design without compromising thermal stability or atmosphere control. The ability to perform high-resolution Rietveld refinement on data obtained at high temperatures has been demonstrated, and data collected on standard Al2O3 powder is presented. Time-resolved data on the orthorhombic to rhombohedral solid state phase transformation of SrCO3 is demonstrated using image plates. Rietveld refinable spectra, collected in as little as 8 s, opens the possibility of performing time-resolved structural refinements of phase transformations.

Local structure of In{sub x}Ga{sub 1-x}As semiconductor alloys by high-energy synchrotron x-ray diffraction

Nearest- and higher-neighbor distances as well as bond length distributions (static and thermal) of the In{sub x}Ga{sub 1-x}As (0{ and displacements. Examination of the Kirkwood model indicates that the standard deviation ({sigma}) of the static disorder on the (In,Ga) sublattice is around 60% of the value on the As sublattice and the (In,Ga) atomic displacements are much more isotropic than those on the As sublattice. The single-crystal diffuse scattering calculated from the Kirkwood model shows that atomic displacements are most strongly correlated along directions.

Time resolved studies of phase transformations using high temperature powder diffraction

A high temperature furnace (up to 1500 °C) has been designed specifically for use with high-energy synchrotron radiation using Debeye-Scherrer transmission geometry. This allows for full bulk sampling and a low thermal gradient (<1 °C/mm) and a controlled environment (inert to oxidizing). Unlike flat plate geometry, the transmission geometry allows for solid-liquid as well as solid-solid phase transitions to be explored. A comparison between image plate and charged-coupled detector (CCD) system will be discussed. The potential is to collect quantifiable powder patterns under a second. Data collected on the tetragonal to cubic transition in the RhTi systems demonstrate the capabilities for performing quantitative time resolved high temperature powder diffraction.

High real-space resolution structure of materials by high-energy x-ray diffraction

Results of high-energy synchrotrons radiation experiments are presented demonstrating the advantages of the atomic Pair Distribution Function technique in determining the structure of materials with high resolution.

Real-Time X-Ray Scattering Study of Surface Dynamics on Au(111) During Ar+ Ion Irradiation

X-ray scattering is used to investigate the surface dynamics on Au(111) during Ar + ion irradiation. During 500 eV Ar + ion irradiation, we observe the three regimes of step retraction, quasi-layer-by-layer removal and three dimensional rough erosion, analagous to molecular beam epitaxy. The quasi-layer-by-layer sputtering regime has been studied to identify similarities and differences in surface evolution during ion irradiation and molecular beam epitaxy. X-ray measurements suggest that 500 eV Ar + ion irradiation does not lead to stable adatom island formation. Also, in contrast to molecular beam epitaxy, adatom detachment and diffusion seems important in describing the surface kinetics during ion irradiation.

High temperature x-ray diffraction in transmission under controlled environment

A compact tube furnace has been developed for high temperature X-ray diffraction studies using high energy synchrotron radiation. The furnace design has a low absorption path in transmission yet allows for a high degree of control of the sample atmosphere and a minimal temperature gradient across the sample. The design allows for a maximum temperature of 1,500 C with a variety of atmospheres including inert, reducing, and oxidizing. Preliminary results obtained at the SRI-CAT 1-ID undulator line (60 keV) at the APS facility and the A2 24 pole wiggler line (45 keV) at CHESS on the Ti{sub 5}Si{sub 3}Z{sub .5} (Z = C, N, O) system will be presented to demonstrate the feasibility of this approach.