Stephen Taller

Profile Information
Dr. Stephen Taller
Oak Ridge National Laboratory
Alvin M. Weinberg Fellow
CV File

Dr. Stephen Taller joined ORNL in 2020 as an Alvin M. Weinberg Fellow in the Nuclear Energy and Fuel Cycle Division. Prior to joining ORNL, he was a postdoctoral fellow at the University of Michigan and completed a Ph.D. in Nuclear Engineering and Radiological Sciences at the University of Michigan in 2020. Stephen Taller has extensive experience in designing, conducting, and analyzing experiments to study radiation damage effects in neutron irradiated and ion irradiated materials, primarily using transmission electron microscopy. 

Research Interests

  • Radiation effects in metals, alloys, and ceramics
  • Microstructural characterization of metals and alloys
  • Ion irradiation as a surrogate for neutron irradiation
  • Advanced alloy development for nuclear applications
  • Advanced manufacturing methods for nuclear technology
  • Optimizing the nuclear structural materials development cycle
Austenitic stainless steels, dislocation loops, Ferritic Martensitic Steels, Helium, Helium Effects, In Situ Ion Irradiation, ion beam analysis, Ion Beam Irradiation, Irradiated Microstructure, Nickel Alloys, Post-Irradiation Examination, Radiation Induced Segregation, Transmission Electron Microscopy (TEM), Void Swelling, Voids
"A methodology for customizing implantation profiles of light ions using a single thin foil energy degrader" Stephen Taller, Fabian Naab, Gary Was, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms Vol. 478 2020 274-283 Link
A method was developed to quantify the spatial distribution and implantation depth of energy-degraded light ions with a thin foil rotating energy degrader for use during multiple ion beam irradiation. The methodology covers three physical phenomena: ions passing through the thin foil, ions travelling through the vacuum to the target, and ion implantation into the target, and accounts for the distribution of ions both in depth and in plane. The processes of energy straggling and scattering were calculated using SRIM. The effects of raster-scanning, and the geometry of the system were implemented in scripts handling the SRIM output files. Elastic backscattering (EBS) using 2.38 MeV H+ protons was used to measure the helium depth profiles after implantation with and without thin foil energy degradation. Defect analysis with transmission electron microscopy confirmed the implantation profiles measured with EBS and calculated with SRIM.
"Application of NSUF Capabilities Towards Understanding the Emulation of High Dose Neutron Irradiations with Ion Beams" Kevin Field, Stephen Taller, Christopher Ulmer, Zhijie Jiao, Tarik Saleh, Arthur Motta, Gary Was, Transactions of the American Nuclear Society Vol. 116 2017 Link
"Emulation of fast reactor irradiated T91 using dual ion beam irradiation" Stephen Taller, Zhijie Jiao, Kevin Field, Gary Was, Journal of Nuclear Materials Vol. 527 2019 Link
Dual ion irradiations using 5 MeV defocused Fe2+ ions and co-injected He2+ ions were conducted on a ferritic-martensitic steel alloy, T91, in the temperature range of 406 °C–570 °C over a damage range of 14.6–35 dpa followed by characterization of the microstructure using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Dislocation loops were observed to increase in diameter and decrease in density with temperature until only network dislocations were observed at the highest temperatures of 520 °C and 570 °C. Swelling exhibited the expected bell-shaped trend with temperature following the number density of cavities, peaking at 460 °C and with a bimodal size distribution except at 520 °C and 570 °C. Nickel- and silicon-rich clusters formed under dual ion irradiations near the surface at all but the highest temperatures of 520 °C and 570 °C. Very little Cr and Si segregation was observed at lath boundaries while Ni enriched at all temperatures examined. Segregation of Cr and Ni appeared to saturate by 17 dpa, while Si enriched up to 35 dpa. The dislocation and cavity microstructures of dual ion irradiated T91 and T91 irradiated in the BOR-60 fast reactor matched extremely well using a temperature shift of +60–70 °C. However, segregation to grain boundaries and formation of nickel-silicon rich clusters were minimal in the dual ion irradiated T91 and less than that in T91 irradiated in the BOR-60 fast reactor.
"Microchemical evolution of irradiated additive-manufactured HT9" Pengyuan Xiu, Caleb Massey, T.M. Kelsey Green, Stephen Taller, dieter Isheim, Niyanth Sridharan, JNM Vol. 559 2022 Link
"Microstructure evolution of T91 irradiated in the BOR60 fast reactor" Zhijie Jiao, Stephen Taller, Kevin Field, G. Yeli, M.P. Moody, Gary Was, Journal of Nuclear Materials Vol. 504 2018 122-134 Link
"Multiple ion beam irradiation for the study of radiation damage in materials" Stephen Taller, David Woodley, Elizabeth Getto, Anthony Monterrosa, Zhijie Jiao, Ovidiu Toader, Fabian Naab, Thomas Kubley, Shyam Dwaraknath, Gary Was, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms Vol. 412 2017 1-10 Link
The effects of transmutation produced helium and hydrogen must be included in ion irradiation experiments to emulate the microstructure of reactor irradiated materials. Descriptions of the criteria and systems necessary for multiple ion beam irradiation are presented and validated experimentally. A calculation methodology was developed to quantify the spatial distribution, implantation depth and amount of energy-degraded and implanted light ions when using a thin foil rotating energy degrader during multi-ion beam irradiation. A dual ion implantation using 1.34 MeV Fe+ ions and energy-degraded D+ ions was conducted on single crystal silicon to benchmark the dosimetry used for multi-ion beam irradiations. Secondary Ion Mass Spectroscopy (SIMS) analysis showed good agreement with calculations of the peak implantation depth and the total amount of iron and deuterium implanted. The results establish the capability to quantify the ion fluence from both heavy ion beams and energy-degraded light ion beams for the purpose of using multi-ion beam irradiations to emulate reactor irradiated microstructures.
"Resolution of the carbon contamination problem in ion irradiation experiments" Stephen Taller, Gary Was, Zhijie Jiao, Anthony Monterrosa, David Woodley, Dylan Jennings, Thomas Kubley, Fabian Naab, Ovidiu Toader, Ethan Uberseder, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms Vol. 412 2017 58-65 Link
The widely experienced problem of carbon uptake in samples during ion irradiation was systematically investigated to identify the source of carbon and to develop mitigation techniques. Possible sources of carbon included carbon ions or neutrals incorporated into the ion beam, hydrocarbons in the vacuum system, and carbon species on the sample and fixture surfaces. Secondary ion mass spectrometry, atom probe tomography, elastic backscattering spectrometry, and principally, nuclear reaction analysis, were used to profile carbon in a variety of substrates prior to and following irradiation with Fe2+ ions at high temperature. Ion irradiation of high purity Si and Ni, and also of alloy 800H coated with a thin film of alumina eliminated the ion beam as the source of carbon. Hydrocarbons in the vacuum and/or on the sample and fixtures was the source of the carbon that became incorporated into the samples during irradiation. Plasma cleaning of the sample and sample stage, and incorporation of a liquid nitrogen cold trap both individually and especially in combination, completely eliminated the uptake of carbon during heavy ion irradiation. While less convenient, coating the sample with a thin film of alumina was also effective in eliminating carbon incorporation.
"Solute segregation and precipitation across damage rates in dual-ion–irradiated T91 steel" Stephen Taller, Valentin Pauly, Zhijie Jiao, Rigel Hanbury, Gary Was, JNM Vol. 563 2022 Link
"Technical Aspects of Delivering Simultaneous Dual and Triple Ion Beams to a Target at the Michigan Ion Beam Laboratory " Ovidiu Toader, Gary Was, Fabian Naab, Ethan Uberseder, Thomas Kubley, Stephen Taller, Physics Procedia Vol. 90 2017 385-390 Link
The Michigan Ion Beam Laboratory (MIBL) at the University of Michigan in Ann Arbor, Michigan, USA, plays a significant role in supporting the mission of the U.S. DOE Office of Nuclear Energy. MIBL is a charter laboratory of the NSUF (National Scientific User Facility – US DoE) and hosts users worldwide. The laboratory has evolved from a single accelerator laboratory to a highly versatile facility with three accelerators (3 MV Tandem, a 400 kV Ion Implanter and a 1.7 MV Tandem), seven beam lines and five target chambers that together, provide unique capabilities to capture the extreme environment experienced by materials in reactor systems. This capability now includes simultaneous multiple (dual, triple) ion irradiations, an irradiation accelerated corrosion cell, and soon, in-situ dual beam irradiation in a transmission electron microscope (TEM) for the study of radiation damage coupled with injection of transmutation elements. The two beam lines that will connect to the 300 kV FEI Tecnai G2 F30 microscope are expected to be operational by the end of 2017. Multiple simultaneous ion beam experiments involving light and heavy ions are already in progress. This paper will outline the current equipment and will focus on the new capability of running dual and triple ion beam experiments.
"Understanding bubble and void nucleation in dual ion irradiated T91 steel using single parameter experiments" Stephen Taller, Gary Was, Acta Materialia Vol. 198 2020 47-60 Link
Ferritic-martensitic steels are attractive candidates for structural materials in next generation nuclear reactor systems due to their resistance to radiation induced swelling. Cavity and dislocation loop evolution was characterized in dual ion irradiated T91 steel in three separate irradiation campaigns examining single parameter dependencies of temperature, helium co-injection rate, and damage rate. Irradiations resulted in bimodal cavity size distributions across nearly all ranges of experimental parameters. It was determined that irradiation temperature and helium co-injection rate are stronger influences on bubble stability and the transition from bubbles to voids than is the irradiation damage rate. At low helium injection rates all helium is in vacancy clusters that evolve into bubbles or voids. At high helium injection rates, bubbles become saturated with helium resulting in accumulation of helium at other traps such as dislocation loops. At intermediate levels of He that should aid in the nucleation of bubbles and enhance swelling, the high density of sinks in the F-M microstructure suppresses bubble nucleation and therefore, the onset of swelling. At high enough temperatures, helium is only in bubbles as other strong helium traps, such as dislocation loops, did not form. The mechanism of bubble to void transition was found to shift from being driven by the accumulation of helium to the critical bubble at low damage rates to being driven by spontaneous formation by stochastic vacancy fluctuation at high damage rates.
"Application of NSUF Capabilities Towards Understanding the Emulation of High Dose Neutron Irradiations with Ion Beams" Kevin Field, Zhijie Jiao, Tarik Saleh, Stephen Taller, Gary Was, 2017 ANS Annual Meeting [unknown]
"Technical Aspects of Delivering Simultaneous Dual and Triple Ion Beams to a Target at the Michigan Ion Beam Laboratory" Stephen Taller, Ovidiu Toader, Gary Was, Conference on the Application of Accelerators in Research and Industry, CAARI 2016 October 30-6, (2016)
NSUF Articles:
RTE 1st Call Awards Announced - Projects total approximately $1.4 million These projects will continue to advance the understanding of irradiation effects in nuclear fuels and materials in support of the mission of the DOE-NE. Friday, February 8, 2019 - Calls and Awards
Department of Energy Nuclear Science User Facilities Awards 29 Rapid Turnaround Experiment Proposals - Awarded projects total nearly $1.14M in access awards Tuesday, June 8, 2021 - News Release, Calls and Awards