A holy grail of nanotechnology is to design and build a material with some desirable property by engineering the atomic structure at the nanoscale. A huge impediment to this is the nanostructure problem: the fact that the established quantitative methods for determining atomic structure fail for nano-sized objects. This project addresses this problem with a collaboration of experiment and theory. The experiments utilize the intense beams of x-rays and neutrons available at US national user facilities combined with novel computational approaches for extracting reliable structural information from the data. In addition the local structure of intermediate states will be studied using ultra-fast femtosecond time-resolved electron diffraction, coupled to the same computational infrastructure, allowing us for the first time to probe quantitatively the local structure of excited states of nanoparticles. In this study a number of scientifically and technologically interesting materials will be studied, including quantum-dot nanoparticles and phase-change materials used in writable CD and DVDs. However, the theoretical and methodological developments will be made available to the wider scientific and educational community in the form of freely available software so the methods can be widely applied. In addition to training graduate and undergraduate students in state-of-the-art research, nanotechnology will be taken to the classroom in grades 6-12 and new hands-on nanotechnology modules will be built in collaboration with Everett High School, an inner city Lansing high school. A new curriculum and course content for an AP course will be developed with their active participation. This project is co-supported by the Condensed Matter Physics and Solid State Chemistry programs.
A holy grail of nanotechnology is to design and build a material with desirable properties by engineering the atomic structure at the nanoscale. A huge impediment to this is the nanostructure problem: the fact that the established quantitative methods for determining atomic structure fail for nano-sized objects. This collaborative project addresses this by using novel approaches for analyzing and modeling x-ray and neutron scattering data from nanomaterials. The data will be Fourier transformed to obtain the atomic pair distribution function (PDF) which will be modeled using novel approaches that will be developed such as encoding chemical information as geometrical constraints in the model. The analysis will be extended to electron diffraction data and combined with ultrafast techniques to study local structure quantitatively on femtosecond time-scales. The systems under study include novel electronic and optical materials such as low-dimensional charge-density wave tellurides, quantum-dot nanoparticles and phase change materials that are used in writable CDs and DVDs. The methods developed here will be made available to the broad community of nanotechnology scientists through training and free software. In addition to training graduate and undergraduate students in state-of-the-art research, nanotechnology will be taken to the classroom in grades 6-12 and new hands-on nanotechnology modules will be built in collaboration with Everett High School, an inner city Lansing high school. A new curriculum and course content for an AP course will be developed with their active participation. This project is co-supported by the Condensed Matter Physics and Solid State Chemistry programs.
One of the key elements of nanotechnology is the ability to engineer novel properties in materials by controlling their nanoscale structures. However, quantitatively characterizing the structure on the nanoscale, which ultimately limits our ability to understand and control nanostructure, is a challenging task. This program combines theoretical and experimental expertise to address the nanostructure problem through the development and application of the atomic pair distribution function (PDF) analysis of x-ray, neutron, and electron diffraction data. The PDF method is finding a growing number of applications in the study of nanomaterials, and in bulk crystal with nanoscale disorder, thanks partially to the development made by this group of collaborators. New developments have been made in this program to understand the influence from local structure to the properties of novel materials, such as thermoelectric materials, materials with negative thermal expansion coefficient, and quantum materials containing unusual giant electronic orderings, such as superconductivity and charge density waves. We have developed new methods to understand technologically relevant nanoparticles by extending the PDF method to include information from imaging such as electron microscopy and from small-angle scattering. Local structures of nanoparticles, such as lithium ferrite nanoparticles, superparamagnetc MnAs nanoparticles, have been examined. We have tested the limit of quantitative modeling for systems with tremendous disorders, and have applied powerful geometric modeling methods that allow distorted structures to be refined whilst maintaining the local stereochemistry as a physical constraint. Complex structures, such as hafnia nanosponge and amorphous pharmaceutical molecules, have been examined. We have developed new methods and bridged different techniques. We showed for the first time the explicit relationship between small-angle scattering and the PDF equation. We have also taken steps to integrate the quantitative nanoscale modeling tool to ultrafast electron diffraction (UED) experiment that has recently been developed. We incorporated a new protocol for analyzing structural dynamics from UED by combining the PDF method and the Reverse Monde Carlo technique. These developments have laid the foundation for us to quantitatively evaluate the local structural impacts to the properties of nanomaterials using data obtained from advanced x-ray, neutron, and electron diffraction techniques, with very high spatial and temporal resolutions. Beyond the technological development, the broader impact of the project is community development. Training the future workforce in advanced materials characterization techniques has been one of the core missions of this FRG project. Throughout the program period, there are 6 graduate students, 2 postdoctoral scholars, 4 undergraduate students, 1 high-school teacher, and 1 high school student involved in various parts of the program on the Michigan/New York sites. The FRG collaboration held regular e-meetings where one of the groups in the entire FRG collaboration (Columbia University, Northwestern University, Arizona State University, and Michigan State University) presents their recent results. We have run hands on workshops in-house and held a collaborative group conference to foster interaction between group members and with outside research groups (http://biophysics.asu.edu/workshops/2008_PairDistrFunc/). We have made available to the community free, well documented, user friendly software and online tutorials. Currently, the newest update of the software distribution is through the online portal: www.diffpy.org/.
