We describe a technique for efficient, quantitative, standardless elemental mapping using a high-angle annular detector in a scanning transmission electron microscope (STEM) to collect elastically scattered electrons. With a single crystal specimen, contrast due to thickness variations, diffraction, and channelling effects can be avoided, so that the resulting image contrast quantitatively reflects variations in impurity concentration. We compare a number of simple analytical approximations to the elastic scattering cross sections and show that a standardless analysis is possible over a wide range of atomic number and inner detector angle to an absolute accuracy of better than 20%.

The compositional dependence of the lattice parameter in Ge1-ySny alloys has been determined from combined X-ray diffraction and Rutherford Backscattering (RBS) measurements of a large set of epitaxial films with compositions in the 0 < y < 0.14 range. In view of contradictory prior results, a critical analysis of this method has been carried out, with emphasis on nonlinear elasticity corrections and systematic errors in popular RBS simulation codes. The approach followed is validated by showing that measurements of Ge1-xSix films yield a bowing parameter θGeSi =−0.0253(30) Å, in excellent agreement with the classic work by Dismukes. When the same methodology is applied to Ge1-ySny alloy films, it is found that the bowing parameter θGeSn is zero within experimental error, so that the system follows Vegard's law. This is in qualitative agreement with ab initio theory, but the value of the experimental bowing parameter is significantly smaller than the theoretical prediction. Possible reasons for this discrepancy are discussed in detail.

The absence of a Mn local moment was observed in Mn-doped amorphous silicon ͑a-Mn x Si 1−x ͒ films. The magnetic susceptibility obeys the Curie-Weiss law for a wide range of x ͑5 ϫ 10 −3 up to 0.175͒ but with extremely small moment. Magnetization measurements suggest that this behavior occurs because only a small percentage of Mn ͑Mn 2+ states with J = S =5/ 2͒ contribute to the magnetization. Thus, the magnetic moments are quenched for the majority of Mn atoms, contrary to the general belief of the existence of a localized Mn moment in Si. X-ray absorption spectroscopy suggests that the quenching of Mn moments is attributed to the formation of an itinerant but Anderson-localized impurity band, forming at x as low as 5 ϫ 10 −3 .

The first stage of epitaxial growth of Au on Ag(lll) has been studied by MeV ion scattering. The monolayer-by-monolayer (Frank-van der Merwe) growth mode for this system is confirmed by measurements of (1) the Ag surface peak, (2) the Au-Au shadowing effect, and (3) the Ag Auger intensity.PACS numbers: 68.55.+ b, 68.48.+ f, 79.20.Fv Epitaxial growth of thin films has been divided into three categories: (1) the Volmer-Weber mode, in which the surface energy of the film material is large compared with that of the substrate, i.e., Au on NaCl; (2) the Frank-van der Merwe mode in which the surface energy of the film is less than or comparable to that of the substrate and there is low strain energy in the film, and (3) the Stranski-Krastanov mode in which the surface energy of the film is less than or comparable to that of the substrate but there is a high strain energy in the film. 1 The Frankvan der Merwe mode is characterized as layerby-layer growth (as opposed to three-dimensional island formation) and is generally applicable in cases of autoepitaxy (i.e., Si on Si) or in cases of "almost autoepitaxy" (i.e., metal A on metal B with a close match in lattice constant). The initial stages of growth in this mode are necessarily studied by the surface-science techniques of lowor medium-energy electron diffraction (LEED or MEED) and Auger analysis.In this Letter we describe the first systematic study of Au epitaxial growth on a Ag(lll) surface using high-energy ion scattering. We show that the growth mode in this system is clearly of a Frank-van der Merwe type (as expected) and that ion scattering techniques are particularly suited to these studies.Experiments were carried out in an UHV system equipped with LEED and Auger apparatus and a Au deposition source. 2 The UHV system is directly coupled to a Van de Graaf accelerator so that high-energy ion scattering experiments can be performed in situ. Prior to Au deposition, the bulk Ag(lll) samples were cleaned via sputtering and annealing. They showed essentially no trace impurities either in the Auger scan or in the ion scattering spectra; the LEED pattern displayed a sharp, well-defined (lxl) pattern. The magnitude of the surface peak in the normal (111) direction and the off-normal (110) direction was in good agreement with calculations assuming a "bulklike" surface. Analyses of this data indicated that both horizontal and vertical displacements of the surface atoms in the clean Ag surface are <0.1 A, in good agreement with LEED analyses. 3 Au deposition was monitored primarily through the ion scattering spectra, although Auger spectra were checked following Au deposition to affirm that light impurity contamination was negligible. Measurements and evaporation were done with the substrate at room temperature and at 140 °K.The first indication of epitaxy in the scattering experiments is the reduction of the substrate surface peak (SP). 4 For a clean crystal the SP results from the interaction of the aligned ion beam with the first monolayer(s) of the single crystal soli...

Technology (CRESMET), and an evaluator for several NSF projects. His first research strand concentrates on the relationship between educational policy and STEM education. His second research strand focuses on studying STEM classroom interactions and subsequent effects on student understanding. He is a codeveloper of the Reformed Teaching Observation Protocol (RTOP) and his work has been cited more than 1800 times and his publications have been published in multiple peer-reviewed journals such as Science is professor in the Materials Science Program in the Fulton School of Engineering at Arizona State University. He teaches in the areas of introductory materials engineering, polymers and composites, and capstone design. His research interests include evaluating conceptual knowledge, misconceptions and technologies to promote conceptual change. He has co-developed a Materials Concept Inventory and a Chemistry Concept Inventory for assessing conceptual knowledge and change for introductory materials science and chemistry classes. He is currently conducting research on an NSF faculty development program based on evidence-based teaching practices. The overall goal is to develop disciplinary communities of practice across the college of engineering. The approach is being promoted through semester-long faculty workshops and then through a semester of supported implementation of faculty classroom innovations. Changes in faculty beliefs and classroom practice should positively impact student performance and retention.