Christian Schlepuetz Seminar

The past couple of years have marked the centennial anniversary of x-ray crystallography - a field of research that has seen a tremendous growth ever since its birth. Rather than going out of fashion eventually, it has helped to push the boundaries of our understanding of matter and materials steadily further. New x-ray techniques are continuously added to our set of available research tools, while established methods of crystallograpy are reaching new frontiers by taking advantage of the latest instrumentation developments.
The exploration of reciprocal space has taken a leap in terms of speed, accuracy, reliability, and the obtainable level of detail with the advent of modern single-photon-counting x-ray area detectors featuring high frame rates and zero readout noise. Each detector image represents a 2-dimensional slice through reciprocal space, and a single diffractometer scan extends this to a stack of slices probing a 3-dimensional volume. This allows for the rapid characterization of large volumes of reciprocal space, revealing all of the structural phases and their orientations present in a sample. The method is particularly powerful if not all the constituent phases and the corresponding locations of their diffraction signals are known, and aids in the discovery of unexpected phenomena or crystal structures.
In this talk, Christian gave a basic tutorial on how to navigate in reciprocal space and showed how to use a Pilatus 100K pixel detector to collect large volume data sets, which could then be processed to yield 3-dimensional reciprocal space maps (RSMs), high-quality powder diffraction data, or simultaneous measurements of pole figures for a whole range of 2-theta values. The capabilities of this approach were then highlighted using several topical research examples: The detailed investigation of the domain structure of multiferroic bismuth ferrite (BiFeO3) thin films and its phase transitions with temperature and film thickness was only possible due to the rapid collection of many RSMs, including those around the half-order film Bragg Peaks, which contain sensitive information about the oxygen octahedra rotation patterns in this material. Iron oxide (Fe2O3), as another example, is an attractive material for the photoelectrochemical (PEC) oxidation of water, particularly when it is heteroepitaxially grown on the facets of indium tin oxide (ITO) nanowires to form a core-shell structure with a large catalytic surface area, long optical absoption paths, and short charge transfer pathways. Simultaneous pole figure measurements of the ITO and Fe2O3 diffraction signals help to reveal the epitaxial relationship at the interface between the ITO nanowire facets and the Fe2O3 layer and provide information which can ultimately be used to guide the design and optimization of future PEC devices.

Engineering Open House 2014

UIUC AVS had a booth "Peeps in Spaaaaace" at Engineering Open House on Mar. 14-15, 2014.

Vacuums are more than your trusty Hoover! They are used in a wide variety of industries and can be used to illustrate many important physical concepts, such as pressure, phase changes, and acoustics. Have you ever wondered what would happen to a balloon in a vacuum? Could you hear an explosion in space? What happens to fire in the vacuum of space? Can you get a fireball in space? How can you get ice to crystallize at room temperature? What happens when you put Peeps and shaving cream in a vacuum?

Thank you to all who helped to man the booth!

Jasprit Singh Seminar

Professor Jasprit Singh from the Department of Electrical Engineering and Computer Science at the University of Michigan, Ann-Arbor, discussed how technology can be used to bring harmony to our lives. In today’s age of “knowledge abundance” a key challenge is to bring harmony between knowledge and action. Our modern age may be called the age of mindfulness where lack of mindfulness is reflected in the gap between resources, knowledge and action. Human consumption has never been higher but more than a third of human actions worldwide are taken to undo our previous actions. This represents the “Carnot efficiency” of modern life. The obesity crisis, the environmental crisis as well as global economic crisis are not primarily due to a lack of knowledge or resources but due to our inability to act on what we know and want.
What role can technology play to harmonize what we know, what we want and what we do? What kinds of sensors and devices are needed for making this happen? In this talk I will describe some of the potential roles technology can play in acting as a “mentor” in our life. In particular I will describe our work on mobile “mentor platforms” and describe the potential role of new materials and sensors that could be integrated in mobile or wearable devices.

Peter Voorhees Seminar

Professor Voorhees of Northwestern University’s Department of Materials Science came to the University of Illinois Champaign-Urbana to discuss his research into vapor-liquid-solid nanowire growth. Faculty and students, alike learned new techniques and analysis methods. His group used video-rate lattice-resolved environmental transmission electron microscopy to show in-situ the nanowire growth interface during growth. He found that, due to the nanowire geometry, a single twin boundary is located at the nanowire center. This twin acts as a preferential nucleation site from which the nanowire grows. He also discussed a model that he used to demonstrate the manner in which the catalyst droplet becomes unstable and compared the predictions of this simulation to experimental observations.

Mark Hersam Seminar

Carbon nanomaterials have attracted significant attention due to their potential to improve applications such as transistors, transparent conductors, solar cells, batteries, and biosensors. In the seminar, Prof. Hersam highlight his latest efforts to develop strategies for purifying, functionalizing, and assembling carbon nanomaterials into functional devices. For example, he and his team has recently developed and commercialized a scalable technique for sorting surfactant-encapsulated single-walled carbon nanotubes (SWCNTs) by their physical and electronic structure using density gradient ultracentrifugation (DGU). The resulting monodisperse SWCNTs enhance the performance of thin film transistors, infrared optoelectronic devices, photovoltaics, catalysts, and transparent conductors. The DGU technique also enables multi-walled carbon nanotubes to be sorted by the number of walls and solution phase graphene to be sorted by thickness, thus expanding the suite of monodisperse carbon nanomaterials. By extending their DGU efforts to carbon nanotubes and graphene dispersed in biocompatible polymers (e.g., DNA, Pluronics, Tetronics, etc.), new opportunities have emerged for monodisperse carbon nanomaterials in biomedical applications. In addition to these solution-phase approaches, the seminar also discussed vacuum compatible methods for functionalizing the surfaces of carbon nanomaterials. For example, a suite of perylene-based molecules form highly ordered self-assembled monolayers (SAMs) on graphene via gas-phase deposition in ultra-high vacuum. Due to their noncovalent bonding, these SAMs preserve the superlative electronic properties of the underlying graphene while providing uniform and tailorable chemical functionality. In this manner, disparate materials (e.g., high-k gate dielectrics) can be seamlessly integrated with graphene, thus enabling the fabrication of capacitors, transistors, and related electronic/excitonic devices. Alternatively, via aryl diazaonium chemistry, functional polymers can be covalently grafted to graphene. In addition to presenting opportunities for graphene-based chemical and biological sensing, covalent grafting allows local tuning of the electronic properties of the underlying graphene.

Fermilab 2012

The operation of the Tevatron, the world’s second largest particle accelerator, at Fermilab was a coalition of efforts by numerous physics, material scientists, and engineers from diverse backgrounds ranging from particle physics, to polymer science and superconductivity. In our trip to the accelerator, measuring 1 kilometer in diameter, the AVS group had a chance visit many of the sites along its perimeter, while talking the primary actors involved in continuing the legacy left by the discovery of the bottom Omega baryon. Amongst the various sites seen, the group had an opportunity to tour within the DZero detector!

James Coleman Seminar

Semiconductor quantum dot lasers have been extensively studied for applications in future lightwave telecommunications systems. Prof. Coleman described the growth, processing and characteristics of quantum dot and nanostructure lasers that exhibit interesting and potentially important effects arising from reduction of the active medium to the quantum regime (<50 nm) in all three dimensions. The motivation for quantum dots in lasers was outlined along with methods for forming self-assembled and patterned quantum dots. The resultant laser characteristics was presented. Prof. Coleman introduced a novel inverted quantum dot structure or nanopore laser, containing three dimensional quantization formed from an engineered periodicity.