of a Dissertation Submitted to the Graduate School of The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

Composite overlay patches are bonded to damaged or undamaged marine structure as a means to improve or restore damage tolerance and load-carrying capacity. While this repair and reinforcement method is currently demonstrated on marine structures around the globe, design and analysis methodologies that account for the high variability in design parameters, material properties, and loading conditions are lagging behind its implementation. In order to optimize patch design and to ensure safe performance during the lifecycle of the patch, a comprehensive understanding of the effects of uncertainty on patch performance is essential. This work demonstrates an approach based on sensitivity analysis to quantify the influence of composite overlay design parameters on structural performance.

Composite patches are bonded to damaged or undamaged aerospace structure as a means to improve or restore damage tolerance and load-carrying capacity. While this repair and reinforcement method is currently demonstrated on structures around the globe, design and analysis methodologies that account for the high variability in design parameters, material properties, and loading conditions are lagging behind its implementation. In order to achieve safe and optimized patch design, a comprehensive understanding of the effects of uncertainty on patch performance is essential. One aspect of patch performance of particular concern is internal damage that is not visible, but could propagate and cause patch and consequentially structural failure. To investigate the damage tolerance of patched structure subjected to low-velocity impact loading and to quantify the effects of uncertainty on performance, a 3D high fidelity finite element model of a patched structure was developed and validated. This model of a metal plate with a composite patch that is adhesively bonded captures multiple damage mechanisms including composite damage, delamination between composite layers, adhesive disbond, and plastic deformation of the metal. Computational simulation with this model is performed to study damage tolerance under low-velocity impact with respect to uncertain input parameters to determine the sensitivity of patch performance relative to these parameters.

Focused ion beam technologies have revolutionized the modern material research, development and production. It has offered new possibilities for materials modification and fabrication with a higher spatial resolution by using helium and neon ions. In recent years, various experimental and numerical simulation approaches have been developed and implemented to broaden the applications of focused ion beam technology. The Monte Carlo (IMC) simulation approach is one of the useful techniques to study the ion-solid interactions which provides crucial quantitative information which cannot be achieved, in some cases, from the experiments. The MC approaches have a number of advantages over analytical calculations. It allows a more rigorous treatment of scattering events, energy distribution of incident ions, recoil target atoms or molecules and secondary electrons as well as their angular distributions. This chapter presents a brief introduction of a Monte Carlo simulator called EnvizION and some simulation results related to focused ion beam induced physical sputtering, Extreme Ultraviolet (IEUV) mask repairs, and sputtering-limiting as well as resolution-limiting effects.

In order to enhance the etch rate of electron-beam-induced etching, we introduce a laser-assisted focused electron-beam-induced etching (LA-FEBIE) process which is a versatile, direct write nanofabrication method that allows nanoscale patterning and editing. The results demonstrate that the titanium electron stimulated etch rate via the XeF2 precursor can be enhanced up to a factor of 6 times with an intermittent pulsed laser assist. The evolution of the etching process is correlated to in situ stage current measurements and scanning electron micrographs as a function of time. The increased etch rate is attributed to photothermally enhanced Ti-F reaction and TiF4 desorption and in some regimes enhanced XeF2 surface diffusion to the reaction zone.

We report on the use of helium ion implantation to independently control the out-of-plane lattice constant in epitaxial La(0.7)Sr(0.3)MnO(3) thin films without changing the in-plane lattice constants. The process is reversible by a vacuum anneal. Resistance and magnetization measurements show that even a small increase in the out-of-plane lattice constant of less than 1% can shift the metal-insulator transition and Curie temperatures by more than 100 °C. Unlike conventional epitaxy-based strain tuning methods which are constrained not only by the Poisson effect but by the limited set of available substrates, the present study shows that strain can be independently and continuously controlled along a single axis. This permits novel control over orbital populations through Jahn-Teller effects, as shown by Monte Carlo simulations on a double-exchange model. The ability to reversibly control a single lattice parameter substantially broadens the phase space for experimental exploration of predictive models and leads to new possibilities for control over materials' functional properties.

In this study, we focus on the resolution limits for quasi 2-D single lines synthesized via focused electron-beam-induced direct-write deposition at 5 and 30 keV in a scanning electron microscope. To understand the relevant proximal broadening effects, the substrates were thicker than the beam penetration depth and we used the MeCpPt(IV)Me-3 precursor under standard gas injection system conditions. It is shown by experiment and simulation how backscatter electron yields increase during the initial growth stages which broaden the single lines consistent with the backscatter range of the deposited material. By this it is shown that the beam diameter together with the evolving backscatter radius of the deposit material determines the achievable line widths even for ultrathin deposit heights in the sub-5-nm regime.

The gas field ion microscope was used to investigate helium and neon ion beam induced etching of nickel as a candidate technique for extreme ultraviolet (EUV) lithography mask editing. No discernable nickel etching was observed for room temperature helium exposures at 16 and 30 keV in the dose range of 1 × 1015–1 × 1018 He+/cm2; however, transmission electron microscopy (TEM) revealed subsurface damage to the underlying Mo-Si multilayer EUV mirror. Subsequently, neon beam induced etching at 30 keV was investigated over a similar dose range and successfully removed the entire 50 nm nickel top absorber film at a dose of ∼3 × 1017 Ne+/cm2. Similarly, TEM revealed subsurface damage in the underlying Mo-Si multilayer. To further understand the helium and neon damage, the authors simulated the ion–solid interactions with our EnvizION Monte-Carlo model, which reasonably correlated the observed damage and bubble formation to the nuclear energy loss and the implanted inert gas concentration, respectively. A critical nuclear energy density loss of ∼80 eV/nm3 and critical implant concentration of ∼2.5 × 1020 atoms/cm3 have been estimated for damage generation in the multilayer structure.

One critical area for EUV lithography is the development of appropriate mask repair strategies. To this end, we have explored etching repair strategies for nickel absorber layers and focused electron beam induced deposition of ruthenium capping layers. Nickel has higher EUV absorption than the standard TaN absorber layer and thus thinner films and improved optical quality can be realized. A thin (2.5 nm) ruthenium film is commonly used as a protective capping layer on the Mo-Si EUV multi-layer mirror which mechanically and chemically protects the multi-layers during standard mask-making procedures. The gas field ion (GFIS) microscope was used to investigate helium and neon ion beam induced etching (IBIE) of nickel as a candidate technique for EUV lithography mask editing. No discernable nickel etching was observed for helium, however transmission electron microscopy (TEM) revealed subsurface damage to the underlying Mo-Si multilayers. Subsequently, neon beam induced etching at 30 keV was investigated and successfully removed the 50 nm nickel absorber film. TEM imaging also revealed subsurface damage in the underlying Mo-Si multilayer. Two damage regimes were apparent, namely: 1) beam induced mixing of the Mo-Si layers and 2) nanobubble formation. Monte Carlo simulations were performed and the observed damage regimes were correlated to: 1) the nuclear energy loss and 2) a critical implant concentration. Electron beam induced deposition (EBID) was explored to deposit ruthenium capping/protective layers. Several ruthenium precursors were screened and so far liquid bis(ethylcyclopentyldienyl) ruthenium(II) was successful. The purity of the as-deposited nanodeposits was estimated to be 10% Ru and 90% C. We demonstrate a new chemically assisted electron beam purification process to remove carbon by-products and show that high-fidelity nanoscale ruthenium repairs can be realized.

The ion beam induced nanoscale synthesis of PtCx (where x ∼ 5) using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPtIVMe3) precursor is investigated by performing Monte Carlo simulations of helium and neon ions. The helium beam leads to more lateral growth relative to the neon beam because of its larger interaction volume. The lateral growth of the nanopillars is dominated by molecules deposited via secondary electrons in both the simulations. Notably, the helium pillars are dominated by SE-I electrons whereas the neon pillars are dominated by SE-II electrons. Using a low precursor residence time of 70 μs, resulting in an equilibrium coverage of ∼4%, the neon simulation has a lower deposition efficiency (3.5%) compared to that of the helium simulation (6.5%). At larger residence time (10 ms) and consequently larger equilibrium coverage (85%) the deposition efficiencies of helium and neon increased to 49% and 21%, respectively; which is dominated by increased lateral growth rates leading to broader pillars. The nanoscale growth is further studied by varying the ion beam diameter at 10 ms precursor residence time. The study shows that total SE yield decreases with increasing beam diameters for both the ion types. However, helium has the larger SE yield as compared to that of neon in both the low and high precursor residence time, and thus pillars are wider in all the simulations studied.

We present an inverse approach for studying hydrogen microstructure in amorphous silicon. The approach consists of generating a prior distribution (of spins/hydrogen) by inverting experimental nuclear magnetic resonance (NMR) data, which is subsequently superimposed on a network of amorphous silicon. The resulting network is then relaxed using a total-energy functional to obtain a stable, low-energy configuration such that the initial spin distribution is minimally perturbed. The efficacy of this approach is demonstrated by generating model configurations that not only have the correct NMR spectra but also satisfy simultaneously experimental structural, electronic and vibrational properties of hydrogenated amorphous silicon.

A three dimensional Monte Carlo simulation program was developed to model physical sputtering and to emulate vias nanomachined by the gas field ion microscope. Experimental and simulation results of focused neon ion beam induced sputtering of copper are presented and compared to previously published experiments. The simulation elucidates the nanostructure evolution during the physical sputtering of high aspect ratio nanoscale features. Quantitative information such as the energy-dependent sputtering yields, dose dependent aspect ratios, and resolution-limiting effects are discussed. Furthermore, the nuclear energy loss and implant concentration beneath the etch front is correlated with the sub-surface damage revealed by transmission electron microscopy at different beam energies.

The ion beam induced nanoscale synthesis of platinum nanowires using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPtIVMe3) precursor is investigated using helium and neon ion beams in the gas field ion microscope. The He+ beam induced deposition resembles material deposited by electron beam induced deposition with very small platinum nanocrystallites suspended in a carbonaceous matrix. The He+ deposited material composition was estimated to be 16% Pt in a matrix of amorphous carbon with a large room-temperature resistivity (∼3.5 × 104–2.2 × 105 μΩ cm) and temperature-dependent transport behavior consistent with a granular material in the weak intergrain tunnel coupling regime. The Ne+ deposited material has comparable composition (17%), however a much lower room-temperature resistivity (∼600–3.0 × 103 μΩ cm) and temperature-dependent electrical behavior representative of strong intergrain coupling. The Ne+ deposited nanostructure has larger platinum nanoparticles and is rationalized via Monte Carlo ion-solid simulations which show that the neon energy density deposited during growth is much larger due to the smaller ion range and is dominated by nuclear stopping relative to helium which has a larger range and is dominated by electronic stopping.