Erik Jonsson School of Engineering and Computer Science
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Browsing Erik Jonsson School of Engineering and Computer Science by Author "0000 0001 3758 9240 (Walker, AV)"
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Item Partially Fluorinated Oxo-Alkoxide Tungsten(VI) Complexes as Precursors for Deposition of WOx Nanomaterials(Royal Society of Chemistry) Bonsu, R. O.; Kim, H.; O'Donohue, C.; Korotkov, R. Y.; McClain, K. R.; Abboud, K. A.; Ellsworth, Ashley A.; Walker, Amy V.; Anderson, T. J.; McElwee-White, L.; 0000 0001 3758 9240 (Walker, AV)The partially fluorinated oxo-alkoxide tungsten(VI) complexes WO(OR) 4 [4; R = C(CH3)2CF3, 5; R = C(CH3)(CF3)2] have been synthesized as precursors for chemical vapour deposition (CVD) of WOx nanocrystalline material. Complexes 4 and 5 were prepared by salt metathesis between sodium salts of the fluoroalkoxides and WOCl4. Crystallographic structure analysis allows comparison of the bonding in 4 and 5 as the fluorine content of the fluoroalkoxide ligands is varied. Screening of 5 as a CVD precursor by mass spectrometry and thermogravimetric analysis was followed by deposition of WOx nanorods.Item Photochemical CVD of Ru on Functionalized Self-Assembled Monolayers from Organometallic Precursors(American Institute of Physics Inc, 2018-08-20) Johnson, K. R.; Rodriguez, Paul Arevalo; Brewer, C. R.; Brannaka, J. A.; Shi, Zhiwei; Yang, Jing; Salazar, Brian; McElwee-White, L.; Walker, Amy V.; 0000 0001 3758 9240 (Walker, AV); 0000-0003-3079-7367 (Salazar, B); Rodriguez, Paul Arevalo; Shi, Zhiwei; Yang, Jing; Salazar, Brian; Walker, Amy V.Chemical vapor deposition (CVD) is an attractive technique for the metallization of organic thin films because it is selective and the thickness of the deposited film can easily be controlled. However, thermal CVD processes often require high temperatures which are generally incompatible with organic films. In this paper, we perform proof-of-concept studies of photochemical CVD to metallize organic thin films. In this method, a precursor undergoes photolytic decomposition to generate thermally labile intermediates prior to adsorption on the sample. Three readily available Ru precursors, CpRu(CO)₂Me, (η³-allyl)Ru(CO)₃Br, and (COT)Ru(CO)₃, were employed to investigate the role of precursor quantum yield, ligand chemistry, and the Ru oxidation state on the deposition. To investigate the role of the substrate chemistry on deposition, carboxylic acid-, hydroxyl-, and methyl-terminated self-assembled monolayers were used. The data indicate that moderate quantum yields for ligand loss (φ ≥ 0.4) are required for ruthenium deposition, and the deposition is wavelength dependent. Second, anionic polyhapto ligands such as cyclopentadienyl and allyl are more difficult to remove than carbonyls, halides, and alkyls. Third, in contrast to the atomic layer deposition, acid-base reactions between the precursor and the substrate are more effective for deposition than nucleophilic reactions. Finally, the data suggest that selective deposition can be achieved on organic thin films by judicious choice of precursor and functional groups present on the substrate. These studies thus provide guidelines for the rational design of new precursors specifically for selective photochemical CVD on organic substrates.Item Room Temperature Atomic Layerlike Deposition of ZnS on Organic Thin Films: Role of Substrate Functional Groups and Precursors(AVS Science and Technology Society) Shi, Z.; Walker, Amy V.; 0000 0001 3758 9240 (Walker, AV)The room temperature atomic layerlike deposition (ALLD) of ZnS on functionalized self-assembled monolayers (SAMs) was investigated, using diethyl zinc (DEZ) and in situ generated H₂S as reactants. Depositions on SAMs with three different terminal groups, -CH₃, -OH, and -COOH, were studied. It was found that the reaction of DEZ with the SAM terminal group is critical in determining the film growth rate. Little or no deposition is observed on -CH₃ terminated SAMs because DEZ does not react with the methyl terminal group. ZnS does deposit on both -OH and -COOH terminated SAMs, but the grow rate on -COOH terminated SAMs is ∼10% lower per cycle than on -OH terminated SAMs. DEZ reacts with the hydroxyl group on -OH terminated SAMs, while on -COOH terminated SAMs it reacts with both the hydroxyl and carbonyl bonds of the terminal groups. The carbonyl reaction is found to lead to the formation of ketones rather than deposition of ZnS, lowering the growth rate on -COOH terminated SAMs. SIMS spectra show that both -OH and -COOH terminated SAMs are covered by the deposited ZnS layer after five ALLD cycles. In contrast to ZnO ALLD where the composition of the film differs for the first few layers on -COOH and -OH terminated SAMs, the deposited film composition is the same for both -COOH and -OH terminated SAMs. The deposited film is found to be Zn-rich, suggesting that the reaction of H₂S with the Zn-surface adduct may be incomplete.Item Toward Understanding Weak Matrix Effects in TOF SIMS(American Vacuum Society) Gelb, Lev D.; Walker, Amy V.; 0000 0001 3758 9240 (Walker, AV); 0000-0003-0291-5098 (Gelb, LD); Gelb, Lev D.; Walker, Amy V.Chemical imaging methods, including imaging mass spectrometry, are increasingly used for the analysis of samples ranging from biological tissues to electronic devices. A barrier to wider adoption of imaging mass spectrometry is the presence of matrix effects which complicate quantitative analysis. Interactions between an analyte molecule and its surroundings (the "matrix") can substantially alter both the yield and type of ions observed. Furthermore, such "intrinsic" effects can be confused with nonlinear response due to detector saturation and other instrument-related complications. As a result, quantitative analyses of time-of-flight secondary ion mass spectrometry (TOF SIMS) data that attempt to account for matrix effects are rare. The authors discuss analysis of such data using maximum a posteriori reconstruction based on physically motivated models, and present progress toward the quantitative extraction of chemical concentration profiles and component spectra in the presence of matrix effects, using mixed self- assembled alkanethiolate monolayers as a test system. The authors demonstrate that the incorporation of matrix effects to lowest order using a series-expansion approach is an effective strategy and that doing so provides improved quantitative performance in measuring surface compositions and can also yield information about interactions between species during the SIMS process. Published by the AVS.