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Stoichiometry and Deposition Temperature Dependence of the Microstructural and Electrical Properties of Barium Strontium Titanate Thin Films

Description: Barium Strontium Titanate (BST) was deposited on Pt/ZrO2 / SiO2/Si substrates using liquid source metal organic chemical vapor deposition. A stoichiometry series was deposited with various GrII/Ti ratios (0.658 to 1.022) and a temperature series was deposited at 550 to 700°C. The thin films were characterized using transmission electron microscopy. Both series of samples contained cubic perovskite BST and an amorphous phase. The grain size increased and the volume fraction of amorphous phase decreased with increasing deposition temperature. The electrical and microstructural properties improved as the GrII/Ti ratio approached 1 and deteriorated beyond 1. This research demonstrates that BST thin films are a strong candidate for future MOS transistor gate insulator applications.
Date: May 1998
Creator: Pena, Piedad
Partner: UNT Libraries
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Mechanical Properties of Materials with Nanometer Scale Microstructures

Description: We have been engaged in research on the mechanical properties of materials with nanometer-scale microstructural dimensions. Our attention has been focused on studying the mechanical properties of thin films and interfaces and very small volumes of material. Because the dimensions of thin film samples are small (typically 1 mm in thickness, or less), specialized mechanical testing techniques based on nanoindentation, microbeam bending and dynamic vibration of micromachined structures have been developed and used. Here we report briefly on some of the results we have obtained over the past three years. We also give a summary of all of the dissertations, talks and publications completed on this grant during the past 15 years.
Date: October 31, 2004
Creator: Nix, William D.
Partner: UNT Libraries Government Documents Department
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Role of Microstructural Phenomena in Magnetic Thin Films. Final Report

Description: Over the period of the program we systematically varied microstructural features of magnetic thin films in an attempt to better identify the role which each feature plays in determining selected extrinsic magnetic properties. This report summarizes the results.
Date: April 30, 2001
Creator: Laughlin, D. E. & Lambeth, D. N.
Partner: UNT Libraries Government Documents Department
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Characterization of Boron Nitride Thin Films on Silicon (100) Wafer.

Description: Cubic boron nitride (cBN) thin films offer attractive mechanical and electrical properties. The synthesis of cBN films have been deposited using both physical and chemical vapor deposition methods, which generate internal residual, stresses that result in delamination of the film from substrates. Boron nitride films were deposited using electron beam evaporation without bias voltage and nitrogen bombardment (to reduce stresses) were characterize using FTIR, XRD, SEM, EDS, TEM, and AFM techniques. In addition, a pin-on-disk tribological test was used to measure coefficient of friction. Results indicated that samples deposited at 400°C contained higher cubic phase of BN compared to those films deposited at room temperature. A BN film containing cubic phase deposited at 400°C for 2 hours showed 0.1 friction coefficient.
Date: August 2007
Creator: Maranon, Walter
Partner: UNT Libraries
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Thin film adhesion by nanoindentation-induced superlayers. Final report

Description: This work has analyzed the key variables of indentation tip radius, contact radius, delamination radius, residual stress and superlayer/film/interlayer properties on nanoindentation measurements of adhesion. The goal to connect practical works of adhesion for very thin films to true works of adhesion has been achieved. A review of this work titled ''Interfacial toughness measurements of thin metal films,'' which has been submitted to Acta Materialia, is included.
Date: June 2001
Creator: Gerberich, William W. & Volinsky, A. A.
Partner: UNT Libraries Government Documents Department
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Stress Evolution Behavior in CoCrPt Alloy Thin Films with varying Pt Concentration

Description: CoCrPt alloy thin film is one of the most promising candidates for ultrahigh density magnetic recording media. One of interesting issues for an application of ferromagnetic thin film to high density magnetic recording media is to investigate growth stress, since stress inevitably generated during thin film fabrication drastically alters magnetic properties as well as mechanical properties due to film fracture and buckling [1]. However, sufficient studies have not been addressed on in situ experimental investigation on stress evolution during film growth of magnetic thin film and its correlation with directly observed film growth structure. We have investigated in situ stress evolution of 400-{angstrom} (Co{sub 82}Cr{sub 18}){sub 100-x}Pt{sub x}/1100-{angstrom} Ti alloy films with varying Pt concentration by means of an ultrahigh vacuum (UHV) chamber equipped with a highly sensitive optical deflection-detecting system [2]. Interestingly enough, the stress evolution patterns during the film deposition are remarkably changed with varying the Pt concentration. CoCrPt alloy films with lower Pt concentration (6 {le} x {le} 13) grow through compressive, tensile, and again compressive stress during film deposition, while CoCrPt alloy films with higher Pt concentration (21 {le} x {le} 28) develop with compressive and relaxed compressive stress without tensile stress generation. In situ stress-evolution behavior for 400-{angstrom} (Co{sub 82}Cr{sub 18}){sub 100-x}Pt{sub x}/1100-{angstrom} Ti alloy films with the Pt concentrations of (a) 6, (b) 13, (c) 21, and (d) 28 at.% are demonstrated in Fig.1. Here, the positive slope corresponds to tensile stress, while the negative slope implies compressive stress. The microstructural studies at the stress transition region reveal that film growth structure plays a major role in considerable change of stress evolution pattern in CoCrPt alloy films with the increase of Pt concentration.
Date: November 1, 2007
Creator: Im, M.-Y.; Jeong, J.-R. & Shin, S.-C.
Partner: UNT Libraries Government Documents Department
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Effect of Underlayer on Coalescence of Silver Islands Grown Byfiltered Cathodic Arc Deposition

Description: For low-emissivity application on window glass, coalescenceof thin film silver islands is crucial for high transmittance in thevisible andhigh reflectance in the infrared. It is well known that theenergy of ions arriving at the substrate (kinetics) as wells as the typeof underlayer (thermodynamics) affect the nucleation and growth mode.Little is known about coalescence of silver islands synthesized byenergetic condensation, e.g., by filtered cathodic vacuum arc deposition.In this work, the effect of the underlayer on nucleation and growth ofsilver films deposited by filtered cathodic vacuum arc was investigatedby transmission electron microscopy (TEM) and atomic force microscopy(AFM). The results are compared with data obtained on magnetron sputteredfilms. It was found that uncoated and titanium-oxide-coated glass requiremore silver to achieve the same low value of sheet resistance than silveron zinc-oxide-coated glass. This can be associated with the energy ofinteraction between surface and silver atoms. Silver films made bycathodic arc deposition show an earlier onset of island coalescence andformation of short links. It was found that silver islands in energeticdeposition exhibit a reduced aspect ratio compared to evaporation andsputtering. A nominal 0.1 nm niobium underlayer increases the nucleationdensity and promotes coalescence of silver islands, however, a 0.2 nmlayer did not show these features, indicating the need for furtherstudies.
Date: March 1, 2003
Creator: Byon, Eungsun & Anders, Andre
Partner: UNT Libraries Government Documents Department
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Experimental characterization and mitigation of specimen charging on thin films with one conducting layer

Description: Specimen charging may be one of the most significant factors that contribute to the high variability generally low quality of images in cryo-electron microscopy. Understanding the nature of specimen charging can help in devising methods to reduce or even avoid its effects and thus improve the rate of data collection as well as the quality of the data. We describe a series of experiments that help to characterize the charging phenomenon which has been termed the Berriman effect. The pattern of buildup and disappearance of the charge pattern have led to several suggestions for how to alleviate the effect. Experiments are described that demonstrate the feasible of such charge mitigation.
Date: April 4, 2003
Creator: Downing, Kenneth H.; McCartney, M.R. & Glaeser, Robert M.
Partner: UNT Libraries Government Documents Department
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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
Partner: UNT Libraries
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The Effect of Average Grain Size on Polycrystalline Diamond Films

Description: The work function of hydrogen-terminated, polycrystalline diamond was studied using ultraviolet photoelectron spectroscopy. Polycrystalline diamond films were deposited onto molybdenum substrates by electrophoresis for grain sizes ranging from 0.3 to 108 microns. The work function and electron affinity were measured using 21.2 eV photons from a helium plasma source. The films were characterized by x-ray photoelectron spectroscopy to determine elemental composition and the sp2/sp3 carbon fraction. The percentage of (111) diamond was determined by x-ray diffraction, and scanning electron microscopy was performed to determine average grain size. The measured work function has a maximum of 5.1 eV at 0.3 microns, and decreases to 3.2 eV at approximately 4 microns. Then the work function increases with increasing grain size to 4.0 eV at 15 microns and then asymptotically approaches the 4.8 eV work function of single crystal diamond at 108 microns. These results are consistent with a 3-component model in which the work function is controlled by single-crystal (111) diamond at larger grain sizes, graphitic carbon at smaller grain sizes, and by the electron affinity for the intervening grain sizes.
Date: May 2002
Creator: Abbott, Patrick Roland
Partner: UNT Libraries
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Thin Films As a Platform for Understanding the Conversion Mechanism of FeF2 Cathodes in Lithium-Ion Microbatteries

Description: Conversion material electrodes such as FeF2 possess the potential to deliver transformative improvements in lithium ion battery performance because they permit a reversible change of more than one Li-ion per 3d metal cation. They outperform current state of the art intercalation cathodes such as LiCoO2, which have volumetric and gravimetric energy densities that are intrinsically limited by single electron transfer. Current studies focus on composite electrodes that are formed by mixing with carbon (FeF2-C), wherein the carbon is expected to act as a binder to support the matrix and facilitate electronic conduction. These binders complicate the understanding of the electrode-electrolyte interface (SEI) passivation layer growth, of Li agglomeration, of ion and electron transport, and of the basic phase transformation processes under electrochemical cycling. This research uses thin-films as a model platform for obtaining basic understanding to the structural and chemical foundations of the phase conversion processes. Thin film cathodes are free of the binders used in nanocomposite structures and may potentially provide direct basic insight to the evolution of the SEI passivation layer, electron and ion transport, and the electrochemical behavior of true complex phases. The present work consisted of three main tasks (1) Development of optimized processes to deposit FeF2 and LiPON thin-films with the required phase purity and microstructure; (2) Understanding their electron and ion transport properties and; (3) Obtaining insight to the correlation between structure and capacity in thin-film microbatteries with FeF2 thin-film cathode and LiPON thin-film solid electrolyte. Optimized pulsed laser deposition (PLD) growth produced polycrystalline FeF2 films with excellent phase purity and P42/mnm crystallographic symmetry. A schematic band diagram was deduced using a combination of UPS, XPS and UV-Vis spectroscopies. Room temperature Hall measurements reveal that as-deposited FeF2 is n-type with an electron mobility of 0.33 cm2/V.s and a resistivity was 0.255 Ω.cm. The LiPON …
Date: August 2015
Creator: Santos-Ortiz, Reinaldo
Partner: UNT Libraries
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Reactivity of Oxide Surfaces and Metal-Oxide Interfaces: Effects of Water Vapor Pressure on Ultrathin Aluminum Oxide Films, and Studies of Platinum Growth Modes on Ultrathin Oxide Films and Their Effects on Adhesion

Description: The reactivity of oxide surfaces and metal-oxide interfaces play an important role in many technological applications such as corrosion, heterogeneous catalysis, and microelectronics. The focus of this research was (1) understanding the effects of water vapor exposure of ultrathin aluminum oxide films under non-ultrahigh vacuum conditions (>10-9 Torr) and (2) characterization of Pt growth modes on ultrathin Ta silicate and silicon dioxide films and the effects of growth modes on adhesion of a Cu overlayer. These studies were conducted with X-ray photoelectron spectroscopy (XPS). Ni3Al(110) was oxidized (10-6 Torr O2, 800K) followed by annealing (1100K). The data indicate that the annealed oxide film is composed of NiO, Al2O3 and an intermediate phase denoted here as "AlOx". Upon exposure of the oxide film at ambient temperature to increasing water vapor pressure (10-6 - 5 Torr), a shift in both the O(1s) and Al(2p)oxide peak maxima to lower binding energies is observed. In contrast, exposure of Al2O3/Al(polycrystalline) to water vapor under the same conditions results in a high binding energy shoulder in the O(1s) spectra which indicates hydroxylation. Spectral decomposition provides further insight into the difference in reactivity between the two oxide films. The corresponding trends of the O(1s)/Ni0(2p3/2) and Al(2p)/Ni0(2p3/2) spectral intensity ratios suggest conformal changes of the oxide film on Ni3Al(110). The growth behavior of sputter deposited Pt at ~300K on Ta silicate and SiO2 ultrathin films formed on Si(100) was investigated. The XPS data show that Pt deposition results in uniform growth or "wetting" on Ta silicate and 2-D cluster growth on SiO2. Electroless Cu deposition on ~11 monolayers (ML) Pt/Ta silicate film results in an adherent Cu film which passed the Scotch tape test. In contrast, electroless Cu deposition on ~11ML Pt/SiO2 results in a non-adherent Cu film due to weak Pt/SiO2 interaction.
Date: May 2004
Creator: Garza, Michelle
Partner: UNT Libraries
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Applications of Passive Thin Films

Description: The physical properties of thin films affect the performance and durability of nearly every solar energy conversion device. Familiar examples of thin films for solar applications are optical materials and protective coatings. Optimized optical properties are key to cost-effective photothermal conversion where individual components must have high absorptance, reflectance, or transmittance. The protection of sensitive substrates from corrosion and/or erosion is essential to ensure adequate component and system lifetime. Such substrates range from photovoltaic materials operating near room temperature to turbine blade structural alloys in hostile environments at very high temperatures (>1,000 degrees C). Although much has been written on particular categories of thin-film materials for solar energy (for example, absorbers for receiver surfaces), to date no one has provided an overview of the spectrum of applications for passive thin films in solar energy. This work is such an overview and also reviews the material state of the art as described in the current literature. Active thin film devices such as photovoltaics and thermoeleetrics are not discussed.
Date: May 1, 1979
Creator: Call, P. J.
Partner: UNT Libraries Government Documents Department
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High spatial resolution grain orientation and strain mapping in thin films using polychromatic submicron X-ray diffraction

Description: The availability of high brilliance synchrotron sources, coupled with recent progress in achromatic focusing optics and large area 2D detector technology, have allowed us to develop an X-ray synchrotron technique capable of mapping orientation and strain/stress in polycrystalline thin films with submicron spatial resolution. To demonstrate the capabilities of this instrument, we have employed it to study the microstructure of aluminum thin film structures at the granular and subgranular level. Owing to the relatively low absorption of X-rays in materials, this technique can be used to study passivated samples, an important advantage over most electron probes given the very different mechanical behavior of buried and unpassivated materials.
Date: March 26, 2002
Creator: Tamura, N.; MacDowell, A. A.; Celestre, R. S.; Padmore, H. A.; Valek, B. C.; Bravman, J. C. et al.
Partner: UNT Libraries Government Documents Department
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Analysis of Order Formation in Block Copolymer Thin Films UsingResonant Soft X-Ray Scattering

Description: The lateral order of poly(styrene-block-isoprene) copolymer(PS-b-PI) thin films is characterized by the emerging technique ofresonant soft X-ray scattering (RSOXS) at the carbon K edge and comparedto ordering in bulk samples of the same materials measured usingconventional small-angle X-ray scattering. We show resonance using theoryand experiment that the loss of scattering intensity expected with adecrease in sample volume in the case of thin films can be overcome bytuning X-rays to the pi* resonance of PS or PI. Using RSOXS, we study themicrophase ordering of cylinder- and phere-forming PS-b-PI thin films andcompare these results to position space data obtained by atomic forcemicroscopy. Our ability to examine large sample areas (~;9000 mu m2) byRSOXS enables unambiguous identification of the lateral lattice structurein the thin films. In the case of the sphere-forming copolymer thin film,where the spheres are hexagonally arranged, the average sphere-to-spherespacing is between the bulk (body-centered cubic) nearest neighbor andbulk unit cell spacings. In the case of the cylinder-forming copolymerthin film, the cylinder-to-cylinder spacing is within experimental errorof that obtained in the bulk.
Date: November 27, 2006
Creator: Virgili, Justin M.; Tao, Yuefei; Kortright, Jeffrey B.; Balsara,Nitash P. & Segalman, Rachel A.
Partner: UNT Libraries Government Documents Department
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Reliability of materials in MEMS : residual stress and adhesion in a micro power generation system.

Description: The reliability of thin film systems is important to the continued development of microelectronic and micro-electro-mechanical systems (MEMS). The reliability of these systems is often tied to the ability of the films to remain adhered to its substrate. By measuring the amount of energy to separate the film from the substrate, researchers can predicts film lifetimes. Recent work has resulted in several different testing techniques to measure this energy including spontaneous buckling, indentation induced delamination and four point bending. This report focuses on developing quantifiable adhesion measurements for multiple thin film systems used in MEMS and other thin film systems of interest to Sandia programs. First, methods of accurately assessing interfacial toughness using stressed overlayer methods are demonstrated using both the W/Si and Au/Si systems. For systems where fracture only occurs along the interface, such as Au/Si, the calculated fracture energies between different tests are identical if the energy put into the system is kept near the needed strain energy to cause delamination. When the energy in the system is greater than needed to cause delamination, calculated adhesion energies can increase by a factor of three due to plastic deformation. Dependence of calculated adhesion energies on applied energy in the system was also shown when comparisons of four point bending and stressed overlayer test methods were completed on Pt/Si systems. The fracture energies of Pt/Ti/SiO{sub 2} were studied using four-point bending and compressive overlayers. Varying the thickness of the Ti film from 2 to 17 nm in a Pt/Ti/SiO{sub 2} system, both test methods showed an increase of adhesion energy until the nominal Ti thickness was 12nm. Then the adhesion energy began to decrease. While the trends in toughness are similar, the magnitude of the toughness values measured between the test methods is not the same, demonstrating the difficulty in …
Date: September 1, 2007
Creator: Moody, Neville Reid; Kennedy, Marian S. (Washington State University, Pullman, WA) & Bahr, David F. (Washington State University, Pullman, WA)
Partner: UNT Libraries Government Documents Department
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Failure by fracture and fatigue in 'NANO' and 'BIO'materials

Description: The behavior of nanostructured materials/small-volumestructures and biologi-cal/bio-implantable materials, so-called "nano"and "bio" materials, is currently much in vogue in materials science. Oneaspect of this field, which to date has received only limited attention,is their fracture and fatigue properties. In this paper, we examine twotopics in this area, namely the premature fatigue failure ofsilicon-based micron-scale structures for microelectromechanical systems(MEMS), and the fracture properties of mineralized tissue, specificallyhuman bone.
Date: December 19, 2003
Creator: Ritchie, R. O.; Muhlstein, C. L. & Nalla, R. K.
Partner: UNT Libraries Government Documents Department
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Advances in Photovoltaics at NREL

Description: This paper discusses the critical strategic research and development issues in the development of next-generation photovoltaic technologies, emphasizing thin-film technologies that are believed to ultimately lead to lower production costs. The critical research and development issues for each technology are identified. An attempt is made to identify the strengths and weaknesses of the different technologies, and to identify opportunities for fundamental research activities suited to advance the introduction of improved photovoltaic modules.
Date: September 9, 1999
Creator: von Roedern, Bolko
Partner: UNT Libraries Government Documents Department
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Low Temperature Polymeric Precursor Derived Zinc Oxide Thin Films

Description: Zinc oxide (ZnO) is a versatile environmentally benign II-VI direct wide band gap semiconductor with several technologically plausible applications such as transparent conducting oxide in flat panel and flexible displays. Hence, ZnO thin films have to be processed below the glass transition temperatures of polymeric substrates used in flexible displays. ZnO thin films were synthesized via aqueous polymeric precursor process by different metallic salt routes using ethylene glycol, glycerol, citric acid, and ethylene diamine tetraacetic acid (EDTA) as chelating agents. ZnO thin films, derived from ethylene glycol based polymeric precursor, exhibit flower-like morphology whereas thin films derived of other precursors illustrate crack free nanocrystalline films. ZnO thin films on sapphire substrates show an increase in preferential orientation along the (002) plane with increase in annealing temperature. The polymeric precursors have also been used in fabricating maskless patterned ZnO thin films in a single step using the commercial Maskless Mesoscale Materials Deposition system.
Date: December 2006
Creator: Choppali, Uma
Partner: UNT Libraries
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