2:00 – 2:15
Luis Stand
(Melcher’s Research Group)
Dept. of Materials Science & Engineering
2:20 – 2:35
Growth and Characterization of Potassium
Strontium Iodide: A New High Light Yield
Scintillator with 2.4% Energy Resolution
Brett Lewis
(Rack’s Research Group)
Dept. of Materials Science & Engineering
Electron Stimulated Purification of Platinum
Nanostructures Grown Via Focused Electron
A new ternary metal halide scintillator, potassium strontium iodide, activated with divalent europium
(KSr
2
I
5
:Eu) has been discovered at SMRC. This material has a monoclinic crystal structure with a density of 4.39 g/cm 3 . Differential scanning calorimetry indicates a congruent melting point of
470°C and suggests that this compound has no solid-solid phase transitions. As is the case with most metal halides, the material is hygroscopic, and it has some internal radioactivity due to the presence of 40 K. Single crystals of KSr
2
I
5
doped with 4% Eu 2+ were grown in evacuated quartz ampoules via the Bridgman technique. The x-ray excited emission spectrum consisted of a single peak at ~445 nm due to the 5d-4f transition in Eu 2+ .
The measured light yield is ~94,000 photons/MeV with an energy resolution of 2.4% at 662 keV. The crystal has an excellent proportionality response over a wide range of energies from 14 keV to 1275 keV.
Beam Induced Deposition
Electron Beam Induced Deposition (EBID) is a direct write mode capable of fabricating highly precise nanoscale structures by employing a scanning electron beam to disassociate adsorbed precursor molecules which subsequently condense on a substrate. The major drawback of the EBID process is that high purity metallic deposition is rarely achieved due to the incomplete dissociation of the precursor molecule by the electron beam during deposition. Thus, purification strategies for nanoscale EBID deposits has been a critically important research area as EBID is poised to impact many nanoscale science and technology applications. To this end, our recent work has been focused on the post-deposition purification of
EBID structures. In this presentation we demonstrate the purification of Platinum–carbon nanostructures deposited via EBID from
MeCpPt(IV)Me
3
during a post-deposition electron exposure treatment in a localized oxygen ambient at room temperature. Time-dependent studies demonstrate that the process occurs from the top-down.
Electron beam energy and current studies demonstrate that the process is controlled by a confluence of the electron energy loss and oxygen concentration. Furthermore, the experimental results are modeled as a
2 nd order reaction which is dependent on both the electron energy loss density and the oxygen concentration. In addition to purification, the post-deposition electron stimulated oxygen purification process enhances the resolution of the EBID process due to the isotropic carbon removal from the as-deposited materials which produces highfidelity shape retention.
2:40 – 2:55
Shuying Chen
(Liaw’s Research Group)
Dept. of Materials Science & Engineering
The Characteristic of Serrated flow
Serration behavior is related to the erratic deformation avalanche after the yield process during deformation. On the stress-strain curve, the serrated behavior is associated with the strain/stress burst. In fact, as a universal phenomenon, serration behavior is ubiquitous in many structural materials, such as carbon steels, Al-Mg alloys, nano-materials, amorphous materials, magnetic functional materials, and high-entropy alloys. Because of their unique and universal properties, many researchers focus on this field of study to understand what causes the unordinary serration behaviors and affects the serration characteristics, which is the necessary prerequisite to reveal the mechanisms of plastic deformation and investigate the structural evolution during deformation.