Liam S. MorrisseyNASA GSFC / Catholic University
Liam S. Morrissey
Doctor of Engineering
Currently working as a postdoc at NASA GSFC, seeking masters and PhD students soon!
About
31
Publications
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163
Citations
Citations since 2017
Publications
Publications (31)
Atomic oxygen (AO) impacts on spacecraft materials represent one of the biggest threats to material performance in low Earth orbit (LEO). However, testing material performance in LEO is difficult and can be cost prohibitive. As a result, research has shown the potential to use the reactive force field (referred to as ReaxFF here) in molecular dynam...
High-energy atomic impacts represent one of the biggest threats to material performance in both the low earth orbit (LEO) and deep space environment. However, while significant test data exists for LEO atomic oxygen (AO) collisions, further research is needed on the effect of high-energy collisions that can potentially occur in deeper space. As suc...
We compare various sputtering simulation methods to experimental results in both the low energy (<1 keV) and high energy (≥1 keV) impact regimes for argon ions impacting a pure copper substrate at normal incidence. Our results indicate that for high energy impacts, both binary collision approximation (BCA) and molecular dynamics methods can be used...
For nearly 40 yr, studies of exosphere formation on airless bodies have been hindered by uncertainties in our understanding of the underlying ion collisional sputtering by the solar wind (SW). These ion impacts on airless bodies play an important role in altering their surface properties and surrounding environment. Much of the collisional sputteri...
We use molecular dynamics (MD) simulations to better explain the movement of atomic hydrogen in amorphous silica and quantify the planetary science implications of these findings. Previous MD simulations had a large range of predicted values and did not agree well with experiment. Our simulations sample atomic motion for a longer duration and consi...
Future exploration efforts of the Moon, Mars, and other bodies are poised to focus heavily on persistent and sustainable survey and research efforts, especially given the recent interest in a long‐term sustainable human presence at the Moon. Key to these efforts understands a number of important processes on the lunar surface for both scientific an...
Future exploration efforts of the Moon, Mars and other bodies are poised to focus heavily on persistent and sustainable survey and research efforts, especially given the recent interest in a long-term sustainable human presence at the Moon. Key to these efforts is understanding a number of important processes on the lunar surface for both scientifi...
Future exploration efforts of the Moon, Mars and other bodies are poised to focus heavily on persistent and sustainable survey and research efforts. This is especially true for the Moon, as additional orbital and surface efforts have been made by a number of countries for the first time and given the recent interest in a long-term sustainable human...
Solar wind (SW) ion irradiation on airless bodies can play an important role in altering their surface properties and surrounding exosphere. Much of the ion sputtering data needed for exosphere studies come from binary collision approximation sputtering models such as TRansport of Ions in Matter and its more recent extension, SDTrimSP. These models...
Reactive molecular dynamics simulations are carried out to investigate solar wind implantation on lunar surface. This study resolves both the chemical reactions and physical interactions of implantation, analyzes the effects from hydroxyl saturation, solar wind reflection, and water molecule sputtering, and quantifies the contribution of solar wind...
While significant research has been conducted on the various mechanisms of hydrogen embrittlement, there remains a lack of quantitative understanding on the effect of atomic hydrogen concentration on mechanical properties. Previous work suggests that an increased hydrogen concentration will degrade both the elastic modulus and yield stress. However...
We have simulated the sodium (Na) exosphere of Mercury to show how the exosphere is affected by the assumed surface binding energy (SBE) of Na in the sputtered component. We constrained ion precipitation onto the surface using distributions for the cusp regions that are consistent with measurements by the MErcury Surface, Space ENvironment, GEochem...
This study considers the importance of the surface binding energy when simulating the yield and energy distribution of sputtered sodium atoms from Mercury's surface by solar wind impacts.
The choice of a proper interatomic potential is critical to obtaining accurate and realistic molecular dynamics results. However, previous studies that have tested the suitability of a potential to predict mechanical properties often do so using elastic constants from a triaxial stress state that ignores Poisson’s effect. While this method is suita...
Molecular Dynamics (MD) was used to determine the accuracy of different force fields on predicting the elastic modulus of single crystal aluminum through nanoindentation tests. In this work, nanoindentation was performed using three different types of force fields (EAM, MEAM and ReaxFF) and the resulting elastic modulus was compared to the value ob...
Uniaxial deformation was performed using molecular dynamics to estimate the mechanical properties of nanocrystalline aluminium. It was observed that the stacking faults and sliding of the grain boundaries affected the mechanical properties. In addition, accumulation of atoms near grain boundaries during deformation hardened the nanocrystalline mate...
Previous research simulating gold nanowires predicts a wide range of elastic moduli and does not agree on the effect of nanowire cross-sectional size on elastic modulus. However, these studies do not use the same potentials, possibly explaining the inconsistencies and relative errors. Many of the previous studies used potentials that were not param...
As opposed to traditional laboratory testing, Molecular Dynamics (MD) offers an atomistic scale method to estimate the mechanical properties of metals. However, there is limited literature that shows the effect of interatomic potentials when determining mechanical properties. Hence, the present research was conducted to investigate the accuracy of...
Molecular dynamics simulations are more frequently being utilised to predict macroscale mechanical properties as a result of atomistic defects. However, the interatomic force field can significantly affect the resulting mechanical properties. While several studies exist which demonstrate the ability of various force fields to predict mechanical pro...
The Tablelands massif in Western Newfoundland is part of a Phanerozoic ophiolite sequence and is a terrestrial site of serpentinization. Similar to other Phanerozoic ophiolite sequences, the Tablelands possess environmental conditions that are conducive to all three established pathways of methanogenesis – abiogenic, microbial, and thermogenic – or...
Molecular dynamics simulations, which take place on the atomistic scale, are now being used to predict the influence of atomistic processes on macro-scale mechanical properties. However, there is a lack of clear understanding on which potential should be used when attempting to obtain these properties. Moreover, many MD studies that do test mechani...
Hydrogen diffusion into the microstructure is a key first step for both hydrogen embrittlement and hydrogen blistering. Previous research has suggested that an increase in voids pre-loading can significantly affect the void growth and failure of samples during loading. However, there is a lack of knowledge on the effect of hydrogen alone on initial...
The effect of porosity on elastic modulus in low-porosity materials is investigated. First, several models used to predict the reduction in elastic modulus due to porosity are compared with a compilation of experimental data to determine their ranges of validity and accuracy. The overlapping solid spheres model is found to be most accurate with the...
We measured CO2, CH4, and N2O gas fluxes from a pool of ultra-basic water discharging from serpentinized rock in Winterhouse Canyon, Gros Morne, Newfoundland. The flux of CH4 released and CO2 sequestered were calculated to be 4.6 × 10⁻⁷ and 1.9 × 10⁻⁵ mol/(m²·min), respectively, whereas N2O concentrations showed little change. The net radiative for...
Present-day serpentinization generates groundwaters with conditions (pH > 11, Eh < -550mV) favorable for the microbial and abiotic production of organic compounds from inorganic precursors. Elevated concentrations of methane, C2-C6 alkanes, acetate, and formate were detected at these sites, but the microbial or abiotic origin of these compounds rem...
Questions
Question (1)
When I plot the Thompson relationship for an incoming ion the peak in the plot (normalized energy distribution vs sputtered atom energy) occurs at approximately half the cohesive energy. This is a known relationship. However, in TRIM tutorial 2 it clearly states that sputtering cannot occur unless the energy of the atom leaving the surface is above the cohesive energy. In the differential and integral plots from TRIM they both agree with this as atoms before this energy are deemed "not sputtered". Therefore, how are studies constantly showing SRIM and Thompson results in agreement?
Second, how can I turn the results from trim (energy of each sputtered atom) into a plot of energy distribution vs sputter atom energy?
