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Advances in the interconnection technology have played a key role in the continued improvement of the integrated circuit (IC) density, performance and cost. Copper (Cu) metallization, dual damascenes processing and integration of copper with low dielectric constant material are key issues in the IC industries. Chemical mechanical planarization of copper (CuCMP) has emerged as an important process for the manufacturing of ICs. Usually, Cu-CMP process consists of several steps such as the removal of surface layer by mechanical action of the pad and the abrasive particles, the dissolution of the abraded particles in the CMP solution, and the protection of the recess areas. The CMP process occurs at the atomic level at the pad/slurry/wafer interface, and hence, slurries and polishing pads play critical role in its successful implementation. The slurry for the Cu-CMP contains chemical components to facilitate the oxidation and removal of excess Cu as well as passivation of the polished surface. During the process, these slurry chemicals also react with the pad. In the present study, investigations were carried out to understand the effect of hydrogen peroxide (H2O2) as an oxidant and benzotriazole (BTA) as an inhibitor on the CMP of Cu. Interaction of these slurry components on copper has been investigated using electrochemical studies, x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). In the presence of 0.1M glycine, Cu removal rate was found to be high in the solution containing 5% H2O2 at pH 2 because of the Cu-glycine complexation reaction. The dissolution rate of the Cu was found to increase due to the formation of highly soluble Cu-glycine complex in the presence of H2O2. Addition of 0.01M BTA in the solution containing 0.1M glycine and 5% H2O2 at pH 2 exhibited a reduction in the Cu removal rate due to the formation of Cu-BTA complex on the surface of the Cu further inhibiting the dissolution. XPS and SIMS investigations revealed the formation of such Cu-glycine complex, which help understand the mechanism of the Cu-oxidant-inhibitor interaction during polishing. Along with the slurry, pads used in the Cu-CMP process have direct influence an overall process. To overcome problems associated with the current pads, new application specific pad (ASP) have been developed in collaboration with PsiloQuest Inc. Using plasma enhanced chemical vapor deposition (PECVD) process; surface of such ASP pads were modified. Plasma treatment of a polymer surface results in the formation of various functional groups and radicals. Post plasma treatment such as chemical reduction or oxidation imparts a more uniform distribution of such functional groups on the surface of the polymer resulting in unique surface properties. The mechanical properties of such coated pad have been investigated using nanoindentation technique in collaboration with Dr. Vaidyanathan’s research group. The surface morphology and the chemistry of the ASP are studied using scanning electron microcopy (SEM), x-ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FTIR) to understand the formation of different chemical species on the surface. It is observed that the mechanical and the chemical properties of the pad top surface are a function of the PECVD coating time. Such PECVD treated pads are found to be hydrophilic and do not require being stored in aqueous medium during the not-in-use period. The metal removal rate using such surface modified polishing pad is found to increase linearly with the PECVD coating time. Overall, this thesis is an attempt to optimize the two most important parameters of the Cu-CMP process viz. slurry and pads for enhanced performance and ultimately reduce the cost of ownership (CoO).

Biomedical implants are commonly made from commercially pure titanium and other metal alloys, which are chosen for their strength and density. To improve the stability and promote bone cell growth into the implant, efforts to bond coatings to metal have been extensively studied. Many coatings used are considered bioactive, which promote the adhesion and growth of the bone cells surrounding the implant [A.1]. Of these, the most commonly investigated coating is a ceramic called hydroxyapatite, which is brittle, leading to flaking and inadequate bone cell growth [A.2]. Alternate bioactive coatings are being examined, including chitosan, the deacetylated form of chitin. Chitin is the second most abundant polymer in nature [A.3] and is found in the exoskeletons of insects and shellfish [A.4]. Chitosan has been proven to have excellent biocompatibility [A.5], be non-toxic [A.3], and promote the adhesion and growth of bone cells [A.6 ? A.7]. In this research, four treatment combinations were developed and tested in an attempt to improve film bonding. These treatment combinations were created using one of two silane molecules, aminopropyltriethoxysilane and triethoxsilylbutyraldehyde, and one of two metal treatments, passivation and piranha treatment. XPS was used to characterize the reaction steps for each of the treatment combinations. A significant decrease in TiO, along with significant increases in SiOx groups, C ? N ? H, and C = O, indicated that the reactions were proceeding as expected. XPS also indicated that, chemically, the chitosan films were not significantly different and were unchanged by the treatment combinations. Following chemical analysis, mechanical testing was performed on the four treatment combinations. No changes to the bulk properties were seen as demonstrated by nano-indentation, further indicating that the four treatment combinations did not change the chemical properties of chitosan. The bulk adhesion of the films was greatly improved for all four treatment combinations, as demonstrated by tensile testing. The highest value from this research, 19.50 ± 1.63 MPa, was significantly higher than the previously published results of 1.6 ? 1.8 MPa [A.10]. Overall, the treatments developed in this study significantly improved the adhesion of the chitosan film on the titanium substrate, without modifying the chemical or structural properties of chitosan. [A.1] Ratner, B. D. and A. S. Hoffman. Biomaterials Science: An Introduction to Materials in Medicine. California: Academic Press, Inc., 1996, Foreword, 1-8. [A.2] S.D. Cook, K.A. Thomas, J.F. Kay. ?Experimental Coating Defect in Hydroxylapatite-Coated Implants.? Clinical Orthopaedics and Related Research, 1992, 265, 280-290. [A.3] A.K. Singla, M. Chawla. ?Chitosan: some pharmaceutical and biological aspects- an update.? Journal of Pharmacy and Pharmacology, 2001, 53, 1047-1067. [A.4] Q. Li, E.T. Dunn, E.W. Grandmaison, M.F.A. Goosen. ?Application and Properties of Chitosan.? Journal of Bioactive and Compatible Polymers, 1992, 7, 370-397. [A.5] M. Prasitsilp, R. Jenwithisuk, K. Kongsuwan, N. Damrongchai, P. Watts. ?Cellular responses to chitosan in vitro: The importance of deacetylation.? Journal of Materials Science: Materials in Medicine, 2000, 11, 773-778. [A.6] R.A.A. Muzzarelli, M. Mattioli-Belmonte, A. Pugnaloni, G. Biagini. ?Biochemistry, histology, and clinical uses of chitins and chitosans in wound healing.? Chitin and Chitinases, ed. P. Jolles, R.A.A. Muzzarelli, Switzerland: Birkhauser Verlag Basel, 1990. [A.7] P. Klokkevold, L. Vandemark, E.B. Kenney, G.W. Bernard. ?Osteogenesis Enhanced by Chitosan (Poly-N-Acetyl Glucosaminoglycan) In Vitro.? Journal of Periodontology, 1996, 67, 1170-1775. [A.8] J.D. Bumgardner, R. Wiser, P.D. Gerard, P. Bergin, B. Chestnutt, M. Marini, V. Ramsey, S.H. Elder, J.A. Gilbert. ?Chitosan: potential use as a bioactive coating for orthopaedic and craniofacial/dental implants.? Journal of Biomaterials Science, Polymer Edition, 2003, 14 (5), 423-438.

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<p>Fabrication of microarrays using sol-gel immobilization has been utilized as an approach to develop high density biosensors. Microarray fabrication using various printing techniques including pin-printing and piezoelectric ink jet printing methods has been demonstrated. However, only limited characterization to understand the encapsulated biomolecule-material interface has been reported. Herein, Chemical characterization using X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) on pin-printed microarrays of sol-gel derived acetylcholinesterase (AChE) microarrays is reported. Furthermore, the <em>in situ</em> fabrication of microarrays following the sol-gel process using piezoelectric ink jet printing methods was explored. Through techniques measuring solution viscosity, surface tension and particle size, important aspects of bio-ink formulation for piezoelectric ink jet printing were identified. Combined, a greater understanding towards the fabrication and characterization of sol-gel derived microarrays was achieved through this exploratory research.</p> / Master of Science (MSc)

Bipolar electrochemistry is an interesting concept for high throughput screening techniques due to the ability to induce gradients in a range of materials and their properties, such as composition, particle size, or dopant levels, among many others. One of the key advantages of the method is the ability to test, create or modify materials without the need for a direct electrical connection. In this thesis, the viability of this method has been explored for a range of possible applications, such as metal recycling, nanoparticle modification and corrosion analysis. In the initial part of the work a process to electrodeposit gradients in metal composition was evaluated, with a view to applying the technique to the extraction and recycling of metals from fly ash. Compositional gradients in the metals under study could be readily obtained from controlled reference solutions, although the spatial resolution of the metals was not sufficient to perform separation. Only copper could be easily deposited from the fly ash solution. Bipolar electrodeposition was also successfully used to modify the particle size across substrates decorated with gold nanoparticles. The approach was demonstrated both for surfaces possessing either a uniform particle density or a gradient in particle density. In the latter case samples with simultaneous, orthogonal gradients in both particle size and density were obtained. A combination of the bipolar approach with rapid image analysis was also evaluated as a method for corrosion screening, using quantitative analysis of gradients in pitting corrosion damage on stainless steels in HCl as a model system. The factors affecting gradient formation and the initiation of corrosion were thoroughly investigated by the use of a scanning droplet cell (SDC) technique and hard x-ray photoelectron spectroscopy (HAXPES). The ability to screen arrays of different materials for corrosion properties was also investigated, and demonstrated for stainless steel and Ti-Al alloys with pre-formed compositional gradients. The technique shows much promise for further studies and for high throughput corrosion screening applications.

This thesis is concerned with furthering our understanding of the basis of visible region photocatalytic activity exhibited by doped TiO2-based materials. A range of experimental techniques including high resolution X-ray photoemission spectroscopy and diffuse reflectance spectroscopy are used to investigate electronic structure and an attempt is made to link these results to the observed photocatalytic activity. Both anionic (N) and cationic (Rh and Sn) dopants are investigated. [See pdf file for full abstract].

<p>A fundamental understanding of heterogeneous catalysis requires analysis of model catalytic surfaces in tandem with complex technical catalysts. This work was divided in three areas, 1- preparation and characterization of model surfaces synthesized by vapor deposition techniques, 2- kinetic evaluation of model catalysts for formic acid decomposition and dry methane reforming, 3- characterization and kinetic evaluation of technical catalysts for the water gas shift reaction.</p> <p>In the first project, model PdZn intermetallic surfaces, a relevant catalyst for propane dehydrogenation, were prepared using an ALD approach. In this work, model surfaces were synthesized by exposing Pd(111) and Pd(100) surfaces to diethylzinc at ca. 10^-6mbar. Several different surface structures were identified by careful control of the deposition temperature of the substrate. Modifications in the adsorption properties of these surfaces towards carbon monoxide and propylene coincided with the structure of the PdZn surface layer. </p> <p>In the second project, formic acid decomposition kinetics were evaluated on model Pt catalysts. Formic acid decomposition was found to be structure-insensitive on Pt(111), Pt(100), and a polycrystalline foil under standard reaction conditions. CO selectivity remained < 1% for conversions <10%. Additionally, inverse Pd-Zr model catalysts were prepared by ALD of zirconium-t-butoxide (ZTB). Depending on treatment conditions, either ZrO_xH_y or ZrO₂ overlayers or Zr as sub-nanometer clusters could be obtained. The activity of the model catalyst surface towards dry reforming of methane if the initial state of the zirconium is metallic. </p> <p>In the third project, Au/Fe₃O₄ heterodimer catalysts were characterized for their thermal stability. In-situ TEM and XPS characterization demonstrates that the gold nanoparticles transform into gold thin films that wet the Fe₃O₄ surface as the reduction of the oxide proceeds. DFT calculations show that the adhesion energy between the Au film is increased on a partially reduced Fe₃O₄ surface. Additionally, Pt/Nb₂CT_x catalysts were characterized and kinetics evaluated for the water gas shift reaction. XPS and TEM characterization indicates that a Pt-Nb surface alloy is formed under moderate reduction temperatures, 350^OC. Water-gas shift reaction kinetics reveal that the alloy-MXene interface exhibit high H₂O activation ability compared to a non-reducible support or bulk niobium carbide. </p>

The main objective for the work described in this PhD thesiswas to formulate a friction model to characterize thefrictional behavior of paper. More specifically, the modelshould explain a phenomenon that is typical for paper grades,viz.: that the level of paper-to-paper friction is dependent onthe direction and the number of previous slides. The modelshould also explain the lubricating effect oflow-molecular-mass lipophilic compounds (LLC) that occur inpaper on paper-to-paper friction. Furthermore, the model shoulddescribe the types of forces that influence paper-to-paperfiction and explain the mechanism by which the LLC decreasepaper-to-paper friction. This thesis consists of a literature review of the basicconcepts of tribology and a summary of the main results andconclusions from four studies on the frictional characteristicsof paper and a study on the friction and adhesion of cellulosesurfaces together with some unpublished material. The purpose of the investigation described in the firstpaper was to explain a phenomenon that is typical for papergrades, viz.: the level of paper-to-paper friction is dependenton the direction and the number of previous slides. Thisbehavior is called“friction hysteresis”by theauthors, and it has its origin in the reorientation of thefibers on the surface of a paper and their alignment relativeto the sliding direction. The second paper describes a study that was aimed atidentifying lubricants that occur natively in paper. Filterpapers were impregnated with model compounds representing woodextractives, i.e. low-molecular-weight lipophilic compounds,which are present in wood, pulp and paper, and thepaper-to-paper friction was determined. The results of thatstudy show that a wood extractive must fulfill severalstructural criteria in order to lubricate a paper surface: Itmust have a hydrophilic group that can attach to the papersurface and a linear hydrocarbon backbone of sufficientlength. Although it is not specifically stated in the second paper,the authors proposed a type of lubrication by which woodextractives decrease paper-to-paper friction that is, ineffect, boundary lubrication. The purpose of the investigationdescribed in the third paper was to clarify whether woodextractives and other low-molecular-mass lipophilic compoundsthat occur in paper can act as boundary lubricants on papersurfaces. The main objective of that study was to investigatethe role of chemical structure of LLC for their orientationrelative to the paper surface, which is an important criterionfor boundary lubrication. Filter papers were impregnated withmagnesium salts of different lipophilic acids, which were usedfor model compounds for the LLC. The deposited layers ofmagnesium salts were characterized by X-ray photoelectronspectroscopy (XPS) and contact angle goniometry and thefriction of the impregnated paper sheets was determined. Theresults show that the degree of lubrication and the resistanceto wear of the layers of a magnesium salt increased withincreasing chain length and increasing degree of linearity ofthe lipophilic acid. Based on the results of that study and ofearlier studies, it is concluded that boundary lubrication isthe type of lubrication by which low-molecular-mass lipophiliccompounds that occur natively in paper decreasepaper-to-paper-friction. In boundary lubrication, surfaces are covered withmonolayers of lubricant molecules that comprise an active headgroup that can attach to the surface, e.g. a carboxyl group,and an inert linear backbone, such as a long saturatedhydrocarbon chain. Such compounds form ordered monolayers onsurfaces, so that the backbone points vertically out of planeof the surface. The friction is then determined by theinteractions between the monolayers, which are weaker than theinteractions between the clean surfaces and this gives a lowerfriction. The fourth paper describes a study on the origin of thedifferences in friction levels between different linerboardsbased on recycled fiber (old corrugated container, OCC). Thesheets were subjected to two extraction stages and analyzedwith respect to surface roughness and their content oflow-molecular-mass lipophilic compounds (LLC). The resultsshowed that a high amount of LLC in the sheets lead to lowfriction, due to lubrication. The fifth paper describes a study that was aimed atdetermining the types of forces that influence the frictionbetween the surfaces of hydrophilic polymers and explaining themechanism by which boundary lubricants decrease the friction.The adhesion and the friction of model systems was measuredwith atomic force microscopy (AFM) using regenerated cellulosefilms and functionalised AFM tips and the effect of fatty acidsand humidity was investigated. The friction significantlyincreased with increasing humidity and that there was a strongcorrelation between the ability of a fatty acid to form ahydrophobic surface and its lubricating performance. Measuredadhesion forces at high humidity were well predicted bytheoretical models that took into account the effect of theLaplace pressure acting in a water meniscus formed aroundcontact regions due to capillary condensation. The resultsindicated that the degree of capillary condensation may beeffectively suppressed by increasing the hydrophobicity of thecontacting surfaces, causing adhesion and friction to decrease.These results suggest that friction between paper surfacesunder ambient conditions is greatly influenced by the degree ofcapillary condensation. Furthermore, lubrication by fatty acidsis achieved by the formation of a vertically oriented,hydrophobic monolayer that can withstand the stresses duringsliding and increase the hydrophobicity of the paper surfaceand thereby suppress capillary condensation. <b>Keywords:</b>Friction, paper-to-paper friction, frictionhysteresis, fibers, orientation, sliding direction, woodextractives, low-molecular-mass lipophilic compounds, boundarylubrication, adhesion, capillary condensation, Laplacepressure, surface forces, JKR theory, gas chromatography-massspectroscopy, X-ray photoelectron spectroscopy, contact angle,atomic force microscopy