Materials Science & Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2792
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Item Characterizing the effect of atomic layer deposited coatings for the prevention of glass alteration in museum collections(2019) Hiebert, Miriam; Phaneuf, Raymond J; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Glass alteration in museum collections poses a serious problem for museum conservators and collections managers. There are currently few options available to slow or stop the progression of glass alteration. This thesis work has focused on assessing the potential use of atomic layer deposited (ALD) amorphous metal oxide coatings on glass as a potential solution to this problem. A modified ASTM accelerated aging method was used to age the glass samples within a time frame that could be reasonably studied, and the spatially-averaged alteration responses of the glass types chosen for this thesis were determined. The effect of applied ALD coatings on the alteration experienced by glass samples that had been subjected to accelerated aging was assessed. It was found that while TiO2 ALD films did not have a significant effect on the degree of alteration experienced, Al2O3 ALD coatings resulted in a significant decrease in the alteration response measured. The success of these coatings was limited, however, by the presence of coating defects, which expand significantly on the surface of the glass samples as a result of the accelerated aging method used. These defects stem from both the formation of pinholes in the coating during the ALD process, and cracking or buckling of the coatings due to mismatches in the coefficients of thermal expansion between the glass and the coating. Methods of mitigation for the formation of these defects and resulting coating loss were investigated. In addition to the efficacy of the ALD coatings, the appropriateness of this method for the treatment of museum objects was assessed. This included investigations of the impact on the appearance of the object imparted by the coatings. Al2O3 ALD coatings were found to have a minimal effect on the perceived color of the glass samples. In addition, the reversibility of the treatment was examined, and it was found that Al2O3 ALD are able to be removed quickly and safely from glass sample surfaces using mild alkali etchant solutions.Item ATOMIC LAYER DEPOSITION OF LEAD ZIRCONATE-TITANATE AND OTHER LEAD-BASED PEROVSKITES(2019) Strnad, Nicholas Anthony; Phaneuf, Raymond J; Polcawich, Ronald G; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lead-based perovskites, especially lead zirconate-titanate (PbZrxTi1-xO3, or PZT), have been of great technological interest since they were discovered in the early 1950s to exhibit large electronic polarization. Atomic layer deposition (ALD) is a thin-film growth technique capable of uniformly coating high aspect-ratio structures due to the self-limited nature of the precursor chemisorption steps in the deposition sequence. In this thesis, a suite of related processes to grow lead-based perovskites by ALD are presented. First, a new process to grow ferroelectric lead titanate (PbTiO3, or PTO) by ALD using lead bis(3-N,N-dimethyl-2-methyl-2-propanoxide) [Pb(DMAMP)2] and tetrakis dimethylamino titanium [TDMAT] as the lead and titanium cation precursors, respectively, is discussed. A 360-nm thick PTO film grown by ALD displayed a maximum polarization of 48 µC/cm2 and remanent polarization of ±30 µC/cm2. Second, a new process (similar to the ALD PTO process) to grow PZT by ALD is demonstrated by partial substitution of TDMAT with either tetrakis dimethylamino zirconium or zirconium tert-butoxide. The 200 nm-thick ALD PZT films exhibited a maximum polarization of 50 µC/cm2 and zero-field dielectric constant of 545 with leakage current density < 0.7 µA/cm2. Third, a new ALD process for antiferroelectric lead hafnate (PbHfO3, or PHO) is presented along with electrical characterization showing a field-induced antiferroelectric to ferroelectric phase transition with applications for capacitive energy storage. Finally, ALD lead hafnate-titanate (PbHfxTi1-xO3, or PHT), considered to be an isomorph of PZT, is demonstrated by combining the process for PTO and PHO. The thin-film PHT grown by ALD is shown to have electronic properties that rival PZT grown at compositions near the morphotropic phase boundary (MPB). The processes for both ALD PZT and PHT are shown to yield films with promising properties for microelectromechanical systems (MEMS) actuators and may help to dramatically increase the areal work density of such devices.Item Atomic Layer Deposition of Ru and RuO2: New Process Development, Fabrication of Heterostructured Nanoelectrodes, and Applications in Energy Storage(2013) Gregorczyk, Keith E.; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to fabricate heterostructured nanomaterials with each layer of the structure having some specific function, i.e. energy storage, charge collection, etc., has recently attracted great interest. Of the techniques capable of this type of process, atomic layer deposition (ALD) remains unique due to its monolayer thickness control, extreme conformality, and wide variety of available materials. This work aims at using ALD to fabricate fully integrated heterostructured nanomaterials. To that end, two ALD processes, using a new and novel precursor, bis(2,6,6-trimethyl-cyclohexadienyl)ruthenium, were developed for Ru and RuO2 showing stable growth rates of 0.5 Å/cycle and 0.4 Å/cycle respectively. Both process are discussed and compared to similar processes reported in the literature. The Ru process is shown to have significantly lower nucleation while the RuO2 is the first fully characterized ALD process known. Using the fully developed RuO2 ALD process, thin film batteries were fabricated and tested in standard coin cell configurations. These cells showed high first cycle gravimetric capacities of ~1400 mAh/g, which significantly degraded after ~40 cycles. Rate performance was also studied and showed a decrease in 1st cycle capacity as a function of increased rate. These results represent the first reports of any RuO2 battery studied beyond 3 cycles. To understand the degradation mechanisms witnessed in the thin film studies in-situ TEM experiments were conducted. Single crystal RuO2 nanowires were grown using a vapor transport method. These nanowires were cycled inside a TEM using Li2O as an electrolyte and showed a ~95% volume expansion after lithiation, ~26% of which was irreversible. Furthermore, a chemical irreversibility was also witnessed, where the reaction products Ru and Li2O remain even after full delithiation. With these mechanisms in mind heterostructured nanowires were fabricated in an attempt to improve the cycling performance. Core/shell TiN/RuO2 and MWCNT/RuO2 structures were fabricating using the ALD process developed in this work. While the TiN/RuO2 structures did not show improved cycling performance due to connection issues, the MWCNT/RuO2 structure showed a stable areal capacity of ~600 μAh/cm2 after ~20 cycles and were easily cycled 100 times.Item EXPLOITING PROCESS SYNERGY BETWEEN ANODIC ALUMINUM OXIDE NANOTEMPLATES AND ATOMIC LAYER DEPOSITION: FROM THIN FILMS TO 3D NANO-ELECTRONIC DEVICES(2011) Banerjee, Parag; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Self-assembled, 3D nanoporous templates present an opportunity to develop devices which are lithography-free, massively scalable and hence, highly manufacturable. Self-limited deposition processes on the other hand, allow functional thin films to be deposited inside such templates with precision and unprecedented conformality. Taken together, the combination of both processes provides a powerful `toolbox' to enable many modern nano devices. In this work, I will present data in three parts. First, I will demonstrate the capabilities of Atomic Layer Deposition (ALD), a self-limited thin film deposition technique in preparing nanoalloyed Al-doped ZnO (AZO) thin films. These films are visibly transparent and electrically conducting. Structure-property relationships are established that highlight the power of ALD to tailor film compositions at the nanoscale. Next, I will use ALD ZnO films in conjunction with aged, ALD V2O5 films to form pn junctions which show rectification with an Ion/Ioff as high as 598. While, the ZnO is a well known n-type semiconductor, the discovery of p-type conductivity in aged V2O5 is surprising and is found to be due to the protonic (H+) conductivity of intercalated H2O in V2O5. Thus, we demonstrate a mixed electronic-ionic pn junction for the first time. Finally, I combine the material set of the pn junction with self-assembled, anodic aluminum oxide (AAO) 3D nanoporous templates to create 3D nanotubular pn junctions. The pn junctions are built inside pores which are only 90nm wide and up to 2μm deep and show rectification with Ion/Ioff of 16.7. Process development and integrations strategies will be discussed that allow for large scale manufacturing of such devices a real possibility.