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Amorphization and De-vitrification in Immiscible Copper-Niobium Alloy Thin Films

Description: While amorphous phases have been reported in immiscible alloy systems, there is still some controversy regarding the reason for the stabilization of these unusual amorphous phases. Direct evidence of nanoscale phase separation within the amorphous phase forming in immiscible Cu-Nb alloy thin films using 3D atom probe tomography has been presented. This evidence clearly indicates that the nanoscale phase separation is responsible for the stabilization of the amorphous phase in such immiscible systems since it substantially reduces the free energy of the undercooled liquid (or amorphous) phase, below that of the competing supersaturated crystalline phases. The devitrification of the immiscible Cu-Nb thin film of composition Cu-45% Nb has been studied in detail with the discussion on the mechanism of phase transformation. The initial phase separation in the amorphous condition seems to play a vital role in the crystallization of the thin film. Detailed analysis has been done using X-ray diffraction, transmission electron microscopy and 3D atom probe tomography.
Date: May 2007
Creator: Puthucode Balakrishnan, Anantharamakrishnan

Determination of Wear in Polymers Using Multiple Scratch Test.

Description: Wear is an important phenomenon that occurs in all the polymer applications in one form or the other. However, important links between materials properties and wear remain illusive. Thus optimization of material properties requires proper understanding of polymer properties. Studies to date have typically lacked systematic approach to all polymers and wear test developed are specific to some polymer classes. In this thesis, different classes of polymers are selected and an attempt is made to use multiple scratch test to define wear and to create a universal test procedure that can be employed to most of the polymers. In each of the materials studied, the scratch penetration depth s reaches a constant value after certain number of scratches depending upon the polymer and its properties. Variations in test parameters like load and speed are also studied in detail to understand the behavior of polymers and under different conditions. Apart from polystyrene, all the other polymers studied under multiple scratch test reached asymptotes at different scratch numbers.
Date: August 2004
Creator: Damarla, Gowrisankar

Development of a Novel Grease Resistant Functional Coatings for Paper-based Packaging and Assessment of Application by Flexographic Press

Description: Recent commercial developments have created a need for alternative materials and methods for imparting oil/grease resistance to paper and/or paperboard used in packaging. The performance of a novel grease resistant functional coating comprised of polyvinyl alcohol (PVA), sodium tetraborate pentahydrate (borate) and acetonedicarboxylic acid (ACDA) and the application of said coating by means of flexographic press is presented herein. Application criteria is developed, testing procedures described, and performance assessment of the developed coating materials are made. SEM images along with contact angle data suggest that coating performance is probably attributable to decreased mean pore size in conjunction with a slightly increased surface contact angle facilitated by crosslinking of PVA molecules by both borate ions and ACDA.
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Date: August 2004
Creator: Brown, Robert W.

Evaluation of hydrogen trapping in HfO2 high-κ dielectric thin films.

Description: Hafnium based high-κ dielectrics are considered potential candidates to replace SiO2 or SiON as the gate dielectric in complementary metal oxide semiconductor (CMOS) devices. Hydrogen is one of the most significant elements in semiconductor technology because of its pervasiveness in various deposition and optimization processes of electronic structures. Therefore, it is important to understand the properties and behavior of hydrogen in semiconductors with the final aim of controlling and using hydrogen to improve electronic performance of electronic structures. Trap transformations under annealing treatments in hydrogen ambient normally involve passivation of traps at thermal SiO2/Si interfaces by hydrogen. High-κ dielectric films are believed to exhibit significantly higher charge trapping affinity than SiO2. In this thesis, study of hydrogen trapping in alternate gate dielectric candidates such as HfO2 during annealing in hydrogen ambient is presented. Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) were used to characterize these thin dielectric materials. It was demonstrated that hydrogen trapping in bulk HfO2 is significantly reduced for pre-oxidized HfO2 prior to forming gas anneals. This strong dependence on oxygen pre-processing is believed to be due to oxygen vacancies/deficiencies and hydrogen-carbon impurity complexes that originate from organic precursors used in chemical vapor depositions (CVD) of these dielectrics.
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Date: August 2006
Creator: Ukirde, Vaishali

Indentation induced deformation in metallic materials.

Description: Nanoindentation has brought in many features of research over the past decade. This novel technique is capable of producing insights into the small ranges of deformation. This special point has brought a lot of focus in understanding the deformation behavior under the indenter. Nickel, iron, tungsten and copper-niobium alloy system were considered for a surface deformation study. All the samples exhibited a spectrum of residual deformation. The change in behavior with indentation and the materials responses to deformation at low and high loads is addressed in this study. A study on indenter geometry, which has a huge influence on the contact area and subsequently the hardness and modulus value, has been attempted. Deformation mechanisms that govern the plastic flow in materials at low loads of indentation and their sensitivity to the rate of strain imparted has been studied. A transition to elastic, plastic kind of a tendency to an elasto-plastic tendency was seen with an increase in the strain rate. All samples exhibited the same kind of behavior and a special focus is drawn in comparing the FCC nickel with BCC tungsten and iron where the persistence of the elastic, plastic response was addressed. However there is no absolute reason for the inconsistencies in the mechanical properties observed in preliminary testing, more insights can be provided with advanced microscopy techniques where the study can be focused more to understand the deformation behavior under the indenter. These experiments demonstrate that there is a wealth of information in the initial stages of indentation and has led to much more insights into the incipient stages of plasticity.
Date: December 2005
Creator: Vadlakonda, Suman

Investigation of growth kinetics of self-assembling monolayers by means of contact angle, optical ellipsometry, angle-resolved XPS and IR spectroscopy.

Description: Absorption of octadecanethiol and p-nitrobenzenethiol onto gold surfaces from ethanol solutions has been studied by means of contact angle, optical ellipsometry, angle-resolved XPS (ARXPS), and with grazing angle total reflection FTIR. Growth of the monolayers from dilute solutions has been monitored and Langmuir isotherm adsorption curves were fitted to experimental data. A saturated film is formed within approximately 5h after immersion in solutions of concentrations ranging from 0.0005mM to 0.01mM. We found, that the final density of monolayer depends on the concentration of the solution.
Date: August 2004
Creator: Jakubowicz, Agnieszka

A magnetorheological study of single-walled and multi-walled carbon nanotube dispersions in mineral oil and epoxy resin.

Description: Single wall carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were dispersed in mineral oil and epoxy resin. The magnetorheological properties of these dispersions were studied using a parallel plate rheometer. Strain sweeps, frequency sweeps, magneto sweeps and steady shear tests were conducted in various magnetic fields. G', G", h* and ty increased with increasing magnetic field, which was partially attributed to the increasing degree of the alignment of nanotubes in a stronger magnetic field. The SWNT/mo dispersions exhibited more pronounced magnetic field dependence than SWNT/ep and MWNT/mo counterparts due to their much lower viscosity. The alignment of SWNTs in mineral oil increased with rising nanotube concentration up to 2.5vol% but were significantly restricted at 6.41vol% due to nanotube flocculation.
Date: May 2005
Creator: Yang, Zhengtao

Micro and nano composites composed of a polymer matrix and a metal disperse phase.

Description: Low density polyethylene (LDPE) and Hytrel (a thermoplastic elastomer) were used as polymeric matrices in polymer + metal composites. The concentration of micrometric (Al, Ag and Ni) as well as nanometric particles (Al and Ag) was varied from 0 to 10 %. Composites were prepared by blending followed by injection molding. The resulting samples were analyzed by scanning electron microscopy (SEM) and focused ion beam (FIB) in order to determine their microstructure. Certain mechanical properties of the composites were also determined. Static and dynamic friction was measured. The scratch resistance of the specimens was determined. A study of the wear mechanisms in the samples was performed. The Al micro- and nanoparticles as well as Ni microparticles are well dispersed throughout the material while Ag micro and nanoparticles tend to form agglomerates. Generally the presence of microcomposites affects negatively the mechanical properties. For the nanoparticles, composites with a higher elastic modulus than that of the neat materials are achievable. For both micro- and nanocomposites it is feasible to lower the friction values with respective to the neat polymers. The addition of metal particles to polymers also improves the scratch resistance of the composites, particularly so for microcomposites. The inclusion of Ag and Ni particles causes an increase in the wear loss volume while Al can reduce the wear for both polymeric matrices.
Date: December 2007
Creator: Olea Mejia, Oscar Fernando

Modified epoxy coatings on mild steel: A study of tribology and surface energy.

Description: A commercial epoxy was modified by adding fluorinated poly (aryl ether ketone) and in turn metal micro powders (Ni, Al, Zn, and Ag) and coated on mild steel. Two curing agents were used; triethylenetetramine (curing temperatures: 30 oC and 70 oC) and hexamethylenediamine (curing temperature: 80 oC). Variation in tribological properties (dynamic friction and wear) and surface energies with varying metal powders and curing agents was evaluated. When cured at 30 oC, friction and wear decreased significantly due to phase separation reaction being favored but increased when cured at 70 oC and 80 oC due to cross linking reaction being favored. There was a significant decrease in surface energies with the addition of modifiers.
Date: August 2009
Creator: Dutta, Madhuri

Morphological properties of poly (ethylene terephthalate) (PET) nanocomposites in relation to fracture toughness.

Description: The effect of incorporation of montmorillonite layered silicate (MLS) on poly (ethylene terephthalate) (PET) matrix was investigated. MLS was added in varying concentration of 1 to 5 weight percent in the PET matrix. DSC and polarized optical microscopy were used to determine the crystallization effects of MLS addition. Non isothermal crystallization kinetics showed that the melting temperature and crystallization temperature decrease as the MLS percent increases. This delayed crystallization along with the irregular spherulitic shape indicates hindered crystallization in the presence of MLS platelets. The influence of this morphology was related with the fracture toughness of PET nanocomposites using essential work of fracture coupled with the infra red (IR) thermography. Both the essential as well as non essential work of fracture decreased on addition of MLS with nanocomposite showing reduced toughness.
Date: August 2005
Creator: Pendse, Siddhi

Orientation, Microstructure and Pile-Up Effects on Nanoindentation Measurements of FCC and BCC Metals

Description: This study deals with crystal orientation effect along with the effects of microstructure on the pile-ups which affect the nanoindentation measurements. Two metal classes, face centered cubic (FCC) and body centered cubic (BCC, are dealt with in the present study. The objective of this study was to find out the degree of inaccuracy induced in nanoindentation measurements by the inherent pile-ups and sink-ins. Also, it was the intention to find out how the formation of pile-ups is dependant upon the crystal structure and orientation of the plane of indentation. Nanoindentation, Nanovision, scanning electron microscopy, electron dispersive spectroscopy and electron backscattered diffraction techniques were used to determine the sample composition and crystal orientation. Surface topographical features like indentation pile-ups and sink-ins were measured and the effect of crystal orientation on them was studied. The results show that pile-up formation is not a random phenomenon, but is quite characteristic of the material. It depends on the type of stress imposed by a specific indenter, the depth of penetration, the microstructure and orientation of the plane of indentation. Pile-ups are formed along specific directions on a plane and this formation as well as the pile-up height and the contact radii with the indenter is dependant on the aforesaid parameters. These pile-ups affect the mechanical properties like elastic modulus and hardness measurements which are pivotal variables for specific applications in micro and nano scale devices.
Date: May 2008
Creator: Srivastava, Ashish Kumar

Polyethylene-layered double hydroxide and montmorillonite nanocomposites: Thermal, mechanical and flame retardance properties.

Description: The effect of incorporation two clays; layered double hydroxides (LDH) and montmorillonite layered silicates (MLS) in linear low density polyethylene (PE) matrix was investigated. MLS and LDH were added of 5, 15, 30 and 60 weight percent in the PE and compounded using a Brabender. Ground pellets were subsequently compression molded. Dispersion of the clays was analyzed using optical microscopy, SEM and XRD. Both the layered clays were immiscible with the PE matrix and agglomerates formed with increased clay concentration. The thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Both clays served as nucleation enhancers increasing recrystallization temperatures in the composites. Flame retarding properties were determined by using the flammability HVUL-94 system. LDH indicated better flame retarding properties than MLS for PE. The char structure was analyzed by environmental scanning electron microscopy. Mechanical properties were studied by tensile testing and Vickers microhardness testing apparatus.
Date: May 2008
Creator: Kosuri, Divya

Processing, Structure, and Tribological Property Interrelationships in Sputtered Nanocrystalline ZnO Coatings

Description: Solid lubricant coatings with controlled microstructures are good candidates in providing lubricity in moving mechanical assembly applications, such as orthopedics and bearing steels. Nanocrystalline ZnO coatings with a layered wurtzite crystal structure have the potential to function as a lubricious material by its defective structure which is controlled by sputter deposition. The interrelationships between sputtered ZnO, its nanocrystalline structure and its lubricity will be discussed in this thesis. The nanocrystalline ZnO coatings were deposited on silicon substrates and Ti alloys by RF magnetron sputtering with different substrate adhesion layers, direct current biases, and temperatures. X-ray diffraction identified that the ZnO (0002) preferred orientation was necessary to achieve low sliding friction and wear along with substrate biasing. In addition, other analyses such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were utilized to study the solid lubrication mechanisms responsible for low friction and wear.
Date: August 2009
Creator: Tu, Wei-Lun

Saturation and foaming of thermoplastic nanocomposites using supercritical CO2.

Description: Polystyrene (PS) nanocomposite foams were prepared using supercritical fluid (SCF) CO2 as a solvent and blowing agent. PS was first in-situ polymerized with a range of concentrations of montmorillonite layered silicate (MLS). The polymerized samples were then compression molded into 1 to 2mm thick laminates. The laminates were foamed in a batch supercritical CO2 process at various temperatures and pressures from 60°-85°C and 7.6-12MPa. The resulting foams were analyzed by scanning electron microscopy to determine effect of MLS on cellular morphology. Differential scanning calorimetry was used to determine the impact of nanocomposite microstructure on glass transition of the foamed polymer. X-ray diffraction spectra suggested that the PS/MLS composite had an intercalated structure at both the 1% and 3% mixtures, and that the intercalation may be enhanced by the foaming process.
Date: May 2005
Creator: Strauss, William C.

Study of Conductance Quantization by Cross-Wire Junction

Description: The thesis studied quantized conductance in nanocontacts formed between two thin gold wires with one of the wires coated by alkainthiol self assembly monolayers (SAM), by using the cross-wire junction. Using the Lorenz force as the driving force, we can bring the two wires in contact in a controlled manner. We observed conductance with steps of 2e2 / h. The conductance plateaus last several seconds. The stability of the junction is attributed to the fact that the coating of SAM improves the stability and capability of the formed contact.
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Date: May 2004
Creator: Zheng, Tao

Study of lead sorption on magnetite at high temperatures.

Description: Lead's uptake on magnetite has been quantitatively evaluated in the present study at a temperature of 200°C and pH of 8.5 with lead concentrations ranging from 5 ppm to175 ppm by equilibrium adsorption isotherms. The pH independent sorption behavior suggested lead sorption due to pH independent permanent charge through weak electrostatic, non-specific attraction where cations are sorbed on the cation exchange sites. The permanent negative charge could be a consequence of lead substitution which is supported by increase in the lattice parameter values from the X-ray diffraction (XRD) results. Differential scanning calorimetry (DSC/TGA) results showed an increase of exothermic (magnetite to maghemite transformation) peak indicating substitution of lead ions due to which there is retardation in the phase transformation. Presence of outer sphere complexes and physical sorption is further supported by Fourier transformed infrared spectroscopy (FTIR). None of the results suggested chemisorption of lead on magnetite.
Date: December 2006
Creator: Paliwal, Vaishali

Supercritical CO2 foamed biodegradable polymer blends of polycaprolactone and Mater-Bi.

Description: Supercritical CO2 foam processing of biopolymers represents a green processing route to environmentally friendly media and packaging foams. Mater-Bi, a multiconstituent biopolymer of polyester, starch and vegetable oils has shown much promise for biodegradation. The polymer, however, is not foamable with CO2 so blended with another polymer which is. Polycaprolactone is a biopolymer with potential of 4000% change in volume with CO2. Thus we investigate blends of Mater-Bi (MB) and polycaprolactone (PCL) foamed in supercritical CO2 using the batch process. Characterization of the foamed and unfoamed samples were done using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Micrographs of the samples from the SEM revealed that the cell size of the foams reduced and increased with increase in MB concentration and increase in the foaming temperature respectively. Mechanical tests; tensile, compression, shear and impact were performed on the foamed samples. It was noted that between the 20-25% wt. MB, there was an improvement in the mechanical properties. This suggests that at these compositions, there is a high interaction between PCL and MB at the molecular level compared to other compositions. The results indicate that green processing of polymer blends is viable.
Date: December 2007
Creator: Ogunsona, Emmanuel Olusegun

Supercritical Silylation and Stability of Silyl Groups

Description: Methylsilsesquioxane (MSQ) and organosilicate glass (OSG) are the materials under this study because they exhibit the dielectric constant values necessary for future IC technology requirements. Obtaining a low-k dielectric value is critical for the IC industry in order to cope time delay and cross talking issues. These materials exhibit attractive dielectric value, but there are problems replacing conventional SiO2, because of their chemical, mechanical and electrical instability after plasma processing. Several techniques have been suggested to mitigate process damage but supercritical silylation offers a rapid single repair step solution to this problem. Different ash and etch damaged samples were employed in this study to optimize an effective method to repair the low-k dielectric material and seal the surface pores via supercritical fluid processing with various trialkylchlorosilanes. Fourier transform infrared spectroscopy (FTIR), contact angle, capacitance- voltage measurements, and x-ray photoemission spectroscopy, dynamic secondary ion mass spectroscopy (DSIMS), characterized the films. The hydrophobicity and dielectric constant after exposure to elevated temperatures and ambient conditions were monitored and shown to be stable. The samples were treated with a series of silylating agents of the form R3-Si-Cl where R is an alkyl groups (e.g. ethyl, propyl, isopropyl). Reactivity with the surface hydroxyls was inversely proportional to the length of the alkyl group, perhaps due to steric effects. Contact angle measurements revealed that heating the films in ambient diminished hydrophobicity. Depth and surface profiling using (DSIMS) and (XPS) were utilized to develop a model for surface coverage.
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Date: May 2006
Creator: Nerusu, Pawan Kumar

Surface Engineering and Characterization of Laser Deposited Metallic Biomaterials

Description: Novel net shaping technique Laser Engineered Net shaping™ (LENS) laser based manufacturing solution (Sandia Corp., Albuquerque, NM); Laser can be used to deposit orthopedic implant alloys. Ti-35Nb-7Zr-5Ta (TNZT) alloy system was deposited using LENS. The corrosion resistance being an important prerequisite was tested electrochemically and was found that the LENS deposited TNZT was better than conventionally used Ti-6Al-4V in 0.1N HCl and a simulated body solution. A detailed analysis of the corrosion product exhibited the presence of complex oxides which are responsible for the excellent corrosion resistance. In addition, the in vitro tests done on LENS deposited TNZT showed that they have excellent biocompatibility. In order to improve the wear resistance of the TNZT system boride reinforcements were carried out in the matrix using LENS processing. The tribological response of the metal matrix composites was studied under different conditions and compared with Ti-6Al-4V. Usage of Si3N4 balls as a counterpart in the wear studies showed that there is boride pullout resulting in third body abrasive wear with higher coefficient of friction (COF). Using 440C stainless steel balls drastically improved the COF of as deposited TNZT+2B and seemed to eliminate the effect of “three body abrasive wear,” and also exhibited superior wear resistance than Ti-6Al-4V.
Date: May 2007
Creator: Samuel, Sonia

Wettability of Silicon, Silicon Dioxide, and Organosilicate Glass

Description: Wetting of a substance has been widely investigated since it has many applications to many different fields. Wetting principles can be applied to better select cleans for front end of line (FEOL) and back end of line (BEOL) cleaning processes. These principles can also be used to help determine processes that best repel water from a semiconductor device. It is known that the value of the dielectric constant in an insulator increases when water is absorbed. These contact angle experiments will determine which processes can eliminate water absorption. Wetting is measured by the contact angle between a solid and a liquid. It is known that roughness plays a crucial role on the wetting of a substance. Different surface groups also affect the wetting of a surface. In this work, it was investigated how wetting was affected by different solid surfaces with different chemistries and different roughness. Four different materials were used: silicon; thermally grown silicon dioxide on silicon; chemically vapor deposited (CVD) silicon dioxide on silicon made from tetraethyl orthosilicate (TEOS); and organosilicate glass (OSG) on silicon. The contact angle of each of the samples was measured using a goniometer. The roughness of the samples was measured by atomic force microscopy (AFM). The chemistry of each of the samples were characterized by using X-ray photoelectron spectroscopy (XPS) and grazing angle total attenuated total reflection Fourier transform infrared spectroscopy (FTIR/GATR). Also, the contact angle was measured at the micro scale by using an environmental scanning electron microscope (ESEM).
Date: December 2009
Creator: Martinez, Nelson