Curve fitting of extended x-ray absorption fine structure (EXAFS) spectra, transmission electron microscopy (TEM) imaging, and Scherrer analysis of x-ray diffraction (XRD) are compared as methods for determining the mean crystallite size in polydisperse samples of platinum nanoparticles. By applying the techniques to mixtures of pure samples, it is found that EXAFS correctly determines the relative mean sizes of these polydisperse samples, while XRD tends to be weighted more toward the largest crystallites in the sample. Results for TEM are not clear cut, due to polycrystallinity and aggregation, but are consistent with the other results.
In recent years, many investigators have reported visible photoluminescence from structures that consist of Ge or Si nanocrystals embedded in a SiO2 matrix deposited or grown on various substrates. We have developed a rapid technique for studying the through-thickness microstructure of this class of materials via atomic force microscopy (AFM) and, using this technique, we report on the precipitation and growth of Ge crystallites formed via a two-step process of hydrothermal oxidation of Si1−xGexO2 (x=0.15) at 450–500 °C and subsequent chemical reduction in forming gas (85/15: N2/H2; 800 °C). The Ge-particle distributions obtained with this AFM cross-sectional technique are consistent with those previously reported using other techniques. The utility of cross-sectional AFM for the evaluation of nanoscale features in the thickness of a thin film is evaluated.
This project was initiated with an undergraduate student's exploration of two advanced research tools: the scanning electron microscope (SEM) and the atomic force microscope (AFM). A research project was developed to study the application of microscopy to introductory physics instruction. Nine modules covering various aspects of introductory physics were created. Module components included discussions, laboratory experiments and assessments. Four of the nine modules were implemented in various high school classes. Assessments were used to compare student learning with the modules versus standard textbook/lecture techniques. Preliminary results of this study are presented along with recently developed methods created to facilitate implementation of these modules within the high school classroom.
A novel processing procedure for significantly suppressing grain growth in submicrometer alumina compacts has been developed and implemented with the intent of ultimately using the same processing route to control grain size in nanophase alumina compacts. In this study, partially sintered alumina pellets made from 0.5 µm starting powders are altered by the chemical infiltration of Si 3 N 4 . The control and infiltrated pellets are then heated to 1650°C for 4 h. The fully sintered pellets are approximately 97% dense.
Suppressed grain growth is observed in the infiltrated pellets. The average grain size in the control pellets after densification is 4.2 and 1.2 µm in the infiltrated pellets. Depth of infiltration is measured using transmission electron microscopy (TEM) and scanning electron microscopy (SEM).Depending on the specific infiltration conditions used, the outer 15-50% of the infiltrated pellets exhibit a graded microstructure consisting of a region of abnormal grain growth and a region of suppressed grain growth. Abnormal grain growth is visible on the outer surfaces of the infiltrated pellets where a relatively high ratio of Si to N is present. Further into the pellet, after some depletion of the Si source gas has occurred, regions of suppressed grain growth are apparent. Based on these results, an infiltration profile is determined. A mathematical model is developed to describe the infiltration process and to determine optimal infiltration conditions. High-resolution electron microscopy (HREM), energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS) are used to study the infiltrated samples.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.