Dr. Donald Windover

Research Interests

• X-ray reflectometry measurement methods
• High-resolution X-ray diffraction measurement methods
• X-ray wavelength and angle metrology
• Novel X-ray optics development
• Standard Reference Materials development
• Novel X-ray scattering measurement methods development for thin film properties determination

Figure 1 (left): Ceramics Division Parallel Beam Diffractometer (CDPBD) in X-ray reflectometry (XRR) measurement configuration.; Figure 2 (right):  Advanced XRR analysis methods using a Monte Carlo sampling approach for a two-layer model of TiN deposited on a silicon wafer.  The surface layer (t1 – horizontal axis) is poorly refined in the modeling.   The TiN film layer (t2- vertical axis) has a thickness of 19.3 nm +/- 0.23 nm standard uncertainty (k=1).

Figure 3:  International System of Units (SI) –traceable, silicon (220) reflection, 4-bounce, channel-cut X-ray monochromator under construction at NIST.  This optic was used in the certification of SRM 2000 for high resolution X-ray diffraction (HRXRD) calibration.

Postdoctoral Research Opportunities in Diffraction Metrology & Standards

X-ray reflectometry (XRR) is used to characterize the thickness, density, and roughness of thin, nearly-smooth, deposited films, particularly in the microelectronics industry. XRR modeling is essential to interpreting XRR data. In essence, XRR modeling is an inverse problem that often does not lead to a unique solution. As a result, multiple models and parameter refinements often produce contradictory structural information results. NIST is currently developing a first principles assessment of XRR models and implementing Bayesian model comparison. This analysis will also provide parameter uncertainty estimation. This characterization will be applied to microelectronic fabrication line measurements as well as to in-house measurements on NIST’s SI traceable Parallel-Beam Diffractometer. Opportunities exist for both model development (theory and programming of algorithms) and instrumentation (construction, optimization, calibration, and automation of equipment).  For more information...

High-Resolution X-Ray Diffraction (HRXRD) is a powerful technique for characterizing epitaxial crystalline layers as used in many electronic, magnetic, and optical technologies. There are two distinct research areas for HRXRD measurements. One involves quantifying and optimizing the performance of the focusing optics needed for the technique. Another topic is modeling of HRXRD data, which requires dynamical scattering theory to interpret interference effects between epitaxial films and substrates. NIST is interested in first-principles, photon-electron interaction modeling using computational electro-magnetics. NIST is currently producing a Standard Reference Material composed of a SiGe epitaxial layer on a Si substrate designed expressly for HRXRD instrument calibration. Opportunities exist for both model development (theory and programming of algorithms) and for instrumentation (construction, optimization, calibration, and automation of equipment).  For more information...

The production of Standard Reference Materials, which allow for calibration of measurements from powder diffractometers, requires knowledge of the fundamental parameters that determine the observed data. Our goals are to quantify those parameters that contribute to instrument profile functions and to establish baselines for instrument performance. We investigate the use of x-ray powder diffraction for quantifying microstructural parameters through structural analysis using the Rietveld and Fundamental Parameters Approach methods. Our facility, located in temperature-controlled space in the NIST Advanced Measurement Laboratory, is equipped with several NIST-constructed, state-of-the-art, SI-traceable diffractometers of Johansson, Divergent, and Parallel Beam configurations for use in powder diffraction studies. Opportunities exist for both model development (theory and programming of algorithms) and instrumentation (construction, optimization, calibration, and automation of equipment).  For more information...

Awards and Honors

• Karen & Lseter Gerhardt Award for Best Thesis, 2003

• Founders Award of Excellence, 2001

• Walter Eppenstein Good Teaching Award, 1997

• Howard N. Blitman ’50 Graduate Fellowship, 1996

• Frank H. Todd Merit Scholarship, 1991-1993