David L. Gil

Certification of NIST Standard Reference Material 640d

The National Institute of Standards and Technology (NIST) certifies a variety of standard reference materials (SRM) to address specific aspects of instrument performance for divergent beam diffractometers. This paper describes SRM 640d, the fifth generation of this powder diffraction SRM, which is certified with respect to the lattice parameter. It consists of approximately 7.5 g silicon powder specially prepared to produce strain-free particles in a size range between 1 and 10 μ m to eliminate size-broadening effects. It is typically used for calibrating powder diffractometers for the line position and line shape. A NIST built diffractometer, incorporating many advanced design features, was used to certify the lattice parameter of the silicon powder measured at 22.5 °C. Both type A, statistical, and type B, systematic, errors have been assigned to yield a certified value for the lattice parameter of a =0.543 159±0.000 020 nm.

The Application of the Fundamental Parameters Approach as Implemented in TOPAS to Divergent Beam Powder Diffraction Data

The fundamental parameters approach (FPA) as implemented in TOPAS is investigated for analyses of conventional X-ray powder diffraction (XRPD) data. The FPA involves the convolution of a series of models, each one constituting an individual contribution to the geometric portion of the instrument profile function (IPF). Parameters within each model are refined by least squares to yield a presumably accurate description of the experiment. If one wishes to interrogate the functionality of said models, a diffractometer wherein the uncertainties in optical character are minimized is required. To this end, a diffractometer was built at NIST which featured conventional divergent beam optics in conjunction with a well aligned, stiff, and accurate goniometer assembly. Initial results indicated that the detector arm was flexing; this problem has been addressed with the fabrication and installation of a new arm and counterweight assembly. Data collected from NIST Standard Reference Material (SRM) 660a, lanthanum hexaboride, are analyzed using the FPA method to yield conclusions on the validity of the models with respect to shape and position of the diffraction profiles.

NIST High Resolution X‐Ray Diffraction Standard Reference Material: SRM 2000

NIST recently released a standard reference material (SRM) for the calibration of high resolution X‐ray diffraction (HRXRD) instruments. HRXRD is extensively used in the characterization of lattice distortion in thin single, epitaxial crystal layers on single‐crystal wafer substrates. Currently, there is a great need for improved accuracy and transferability for the measurement of strain fields in these epitaxial thin films. This implies an essential need for the calibration of HRXRD instruments to allow measurement intercomparison for both research and manufacturing communities. This first HRXRD SRM release provides certified measurements of diffraction features for a silicon reference substrate, Si (220) in transmission and Si (004) in reflection, allowing for calibration of either monochromator wavelength or goniometer angles. The SRM also provides information on the surface‐to‐crystal‐plane misalignment, which allows calibration of sample holders and sample alignment hardware. This calibration should ...

D-91 CHARACTERIZING X-RAY MIRRORS IN RECIPROCAL SPACE: RESULTS FROM THE NIST X-RAY OPTICS EVALUATION DOUBLE-CRYSTAL DIFFRACTOMETER

In the last decade, multilayer x-ray optics have rapidly become ubiquitous on laboratory instruments. Parabolic graded multilayers, in particular, decrease beam divergence and so can dramatically increase the intensity of the source for many experiments. Although the spatial profiles produced by these multilayers have been studied by simulation methods and by observing the beam, their energy/divergence characteristics are less well-known. A study using a single-axis diffraction experiment has shown that for high-accuracy lattice parameter determination these effects must be taken into account.[1]