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Effect of Substrate Support on Dynamic Graphene/Metal Electrical Contacts

Description: This article investigates the stability of dynamic electrical contacts at a graphene/metal interface using atomic force microscopy (AFM), under static conditions with variable normal loads and under sliding conditions with variable speeds.
Date: March 22, 2018
Creator: Lee, Jihyung; Hu, Xiaoli; Voevodin, Andrey A.; Martini, Ashlie & Berman, Diana
Partner: UNT College of Engineering

The wetting behavior of NiAl and NiPtAl on polycrystalline alumina

Description: In order to understand the beneficial effect of Pt on the adherence of thermally grown alumina scales, sessile drop experiments were performed to study the wetting of poly-crystalline alumina by nickel-aluminum alloys with or without platinum addition where the amount of Pt ranged from 2.4 to 10 at.%. Subsequent interfacial structure was evaluated using atomic force microscopy. Platinum addition enhances the wettability of NiAl alloys on alumina, reduces the oxide/alloy interface energy and increases the interfacial mass transport rates.
Date: July 1, 2007
Creator: Saiz, Eduardo; Gauffier, Antoine; Saiz, Eduardo; Tomsia, Antoni P. & Hou, Peggy Y.
Partner: UNT Libraries Government Documents Department

Reactivity of Ozone with Solid Potassium Iodide Investigated by Atomic Force Microscopy

Description: The reaction of ozone with the (100) plane of solid potassium iodide (KI) was investigated using atomic force microscopy (AFM). The reaction forming potassium iodate (KIO{sub 3}) initiates at step edges prior to reacting on the flat terraces. Small domains of KIO{sub 3}, initially 3.8 {angstrom} in height are formed on the top of step edges. Following reaction at the step edge, domains of KIO{sub 3} are formed across the terraces. With prolonged exposure to ozone, KIO{sub 3} domains nucleate further growth until the surface is evenly covered with KIO{sub 3} particles that are 4-6 nm in height, at which point the surface is passivated and the reaction terminates.
Date: April 14, 2008
Creator: Mulleregan, Alice; Brown, Matthew A.; Ashby, Paul D.; Ogletree, D. Frank; Salmeron, Miquel & Hemminger, John C.
Partner: UNT Libraries Government Documents Department

An atomic force microcopy study of the mechanical and electricalproperties of monolayer films of molecules with aromatic end groups

Description: The effect of intermolecular {pi}-{pi} stacking on the electrical and mechanical properties of monolayer films molecules containing aromatic groups was studied using atomic force microscopy. Two types of aromatic molecules, (4-mercaptophenyl) anthrylacetylene (MPAA) and (4-mercaptophenyl)-phenylacetylene (MPPA) were used as model systems with different {pi}-{pi} stacking strength. Monolayer films of these molecules on Au(111) surfaces exhibited conductivities differing by more than one order of magnitude, MPAA being the most conductive and MPPA the least conductive. The response to compressive loads by the AFM tip was also found to be very different for both molecules. In MPAA films distinct molecular conductivity changes are observed upon mechanical perturbation. This effect however was not observed on the MPPA film, where intermolecular {pi}-{pi} interactions are likely weaker.
Date: September 6, 2007
Creator: Fang, Liang; Park, J.Y.; Ma, H.; Jen, A.K.-Y. & Salmeron, M.
Partner: UNT Libraries Government Documents Department

Probing deviations from traditional colloid filtration theory by atomic forces microscopy.

Description: Colloid transport through saturated media is an integral component of predicting the fate and transport of groundwater contaminants. Developing sound predictive capabilities and establishing effective methodologies for remediation relies heavily on our ability to understand the pertinent physical and chemical mechanisms. Traditionally, colloid transport through saturated media has been described by classical colloid filtration theory (CFT), which predicts an exponential decrease in colloid concentration with travel distance. Furthermore, colloid stability as determined by Derjaguin-Landau-Veney-Overbeek (DLVO) theory predicts permanent attachment of unstable particles in a primary energy minimum. However, recent studies show significant deviations from these traditional theories. Deposition in the secondary energy minimum has been suggested as a mechanism by which observed deviations can occur. This work investigates the existence of the secondary energy minimum as predicted by DLVO theory using direct force measurements obtained by Atomic Forces Microscopy. Interaction energy as a function of separation distance between a colloid and a quartz surface in electrolyte solutions of varying ionic strength are obtained. Preliminary force measurements show promise and necessary modifications to the current experimental methodology have been identified. Stringent surface cleaning procedures and the use of high-purity water for all injectant solutions is necessary for the most accurate and precise measurements. Comparisons between direct physical measurements by Atomic Forces Microscopy with theoretical calculations and existing experimental findings will allow the evaluation of the existence or absence of a secondary energy minimum.
Date: December 1, 2005
Creator: Reno, Marissa Devan
Partner: UNT Libraries Government Documents Department

Nanostructured Arrays Formed by Finely Focused Ion Beams

Description: Amorphous, polycrystalline, and single crystal nanometer dimension particles can be formed in a variety of substrates by ion implantation and subsequent annealing. Such composite colloidal materials exhibit unique optical properties that could be useful in optical devices, switches, and waveguides. However colloids formed by blanket implantation are not uniform in size due to the nonuniform density of the implant, resulting in diminution of the size dependent optical properties. The object of the present work is to form more uniform size particles arranged in a 2-dimensional lattice by using a finely focused ion beam to implant identical ion doses only into nanometer size regions located at each point of a rectangular lattice. Initial work is being done with a 30 keV Ga beam implanted into Si. Results of particle formation as a function of implant conditions as analyzed by Rutherford backscattering, x-ray analysis, atomic force microscopy, and both scanning and transmission electron microscopy will be presented and discussed.
Date: November 30, 1998
Creator: Budai, J.D.; Datsos, P.G.; Feldman, L.C.; Heinig, K.-H.; Meldrum, A.; Strobel, M. et al.
Partner: UNT Libraries Government Documents Department

Growth and Structure of Metallic Barrier Layer and Interconnect Films I: Experiments

Description: We present experimented results directed at understanding the growth and structure of metallic barrier layer and interconnect films. Numerical simulation results associated with this experimental work are presented in an accompanying paper in these proceedings. Here, thin films of Al, Ti, Cu and Ta have been grown by magnetron sputtering onto oxidized Si substrates. Using a specially-constructed substrate holder, the orientation of the substrate with respect to the growth direction was varied from horizontal to vertical. Films were grown at both low and high argon pressure; in the case of Ta, the cathode power was varied as well. The film structure and in particular the surface roughness was measured by X-ray reflectance and also by atomic force microscopy. We find that the surface roughness increases markedly with orientation angle in the case of Ta and Cu films, and in Ti films grown at high argon pressure. At low pressure, however, the Ti film surface roughness remains constant for all substrate orientations. No variation in roughness with either orientation angle or argon pressure was observed in the Al films. These results suggest that, under certain circumstances, shadowing effects and/or grain orientation (i.e., texture) competition during growth can give rise to lower density, more porous (and thus more rough) films, particularly at large orientation angles, as on sidewalls in sub-micron trenches.
Date: April 5, 1999
Creator: Baumann, F.H.; Gilmer, G.H.; O'Sullivan, P.L.; Sapjeta, J.; Torre, J.D. & Windt, D.L.
Partner: UNT Libraries Government Documents Department

MATERIALS WITH COMPLEX ELECTRONIC/ATOMIC STRUCTURES

Description: We explored both experimentally and theoretically the behavior of materials at stresses close to their theoretical strength. This involves the preparation of ultra fine scale structures by a variety of fabrication methods. In the past year work has concentrated on wire drawing of in situ composites such as Cu-Ag and Cu-Nb. Materials were also fabricated by melting alloys in glass and drawing them into filaments at high temperatures by a method known as Taylor wire technique. Cu-Ag microwires have been drawn by this technique to produce wires 10 {micro}m in diameter that consist of nanoscale grains of supersaturated solid solution. Organogels formed from novel organic gelators containing cholesterol tethered to squaraine dyes or trans-stilbene derivatives have been studied from several different perspectives. The two types of molecules are active toward several organic liquids, gelling in some cases at w/w percentages as low as 0.1. While relatively robust, acroscopically dry gels are formed in several cases, studies with a variety of probes indicate that much of the solvent may exist in domains that are essentially liquid-like in terms of their microenvironment. The gels have been imaged by atomic force microscopy and conventional and fluorescence microscopy, monitoring both the gelator fluorescence in the case of the stilbene-cholesterol gels and, the fluorescence of solutes dissolved in the solvent. Remarkably, our findings show that several of the gels are composed of similarly appearing fibrous structures visible at the nano-, micro-, and macroscale.
Date: September 1, 2000
Creator: PARKIN, D. M.; CHEN, L. & AL, ET
Partner: UNT Libraries Government Documents Department

Orthoclase surface structure dissolution measured in situ by x-ray reflectivity and atomic force microscopy.

Description: Orthoclase (001) surface topography and interface structure were measured during dissolution by using in situ atomic force microscopy (AFM) and synchrotrons X-ray reflectivity at pH 1.1-12.9 and T = 25-84 C. Terrace roughening at low pH and step motion at high pH were the main phenomena observed, and dissolution rates were measured precisely. Contrasting dissolution mechanisms are inferred for low- and high-pH conditions. These observations clarify differences in alkali feldspar dissolution mechanisms as a function of pH, demonstrate a new in situ method for measuring face-specific dissolution rates on single crystals, and improve the fundamental basis for understanding alkali feldspar weathering processes.
Date: November 28, 2000
Creator: Sturchio, N. C.; Fenter, P.; Cheng, L. & Teng, H.
Partner: UNT Libraries Government Documents Department

Mechanistic study of dielectric chemical mechanical polishing by spectral and scaling analysis of atomic force microscope images

Description: Thermal oxide and PETEOS oxide surfaces, polished on an IPEC 472 with different combinations of polish pad, slurry, and polishing conditions, were studied with ex situ atomic force microscopy. The post polish surfaces were analyzed qualitatively by visual inspection and quantitatively by spectral and scaling analyses. Spectral and scaling analyses gave consistent interpretations of morphology evolution. Polishing with either a fixed abrasive pad or alumina-based slurry occurred via a mechanism for which asperities are removed and recesses are filled. A sputtering-type mechanism may contribute to material removal when polishing with silica- or ceria-based slurries.
Date: December 22, 1999
Creator: Verhoff, M.L.
Partner: UNT Libraries Government Documents Department

Identification and Characterization of a Human DNA Double-Strand Break Repair Complex

Description: The authors have used atomic force microscopy (AFM) to characterize the assembly and structure of the macromolecular assemblies involved in DNA repair. They have demonstrated using AFM that the DNA-dependent protein kinase can play a structural role in the repair of DNA double-strand breaks (DSBs) by physically holding DNA ends together. They have extended these studies to include other DNA damage response proteins, these efforts have resulted in important and novel findings regarding the ATM protein. Specifically, the work has demonstrated, for the first time, that the ATM protein binds with specificity to a DNA end. This finding is the first to implicate the ATM protein in the detection of DNA damage by direct physical interaction with DSBs.
Date: July 12, 1999
Creator: Chen, D.J. & Cary, R.B.
Partner: UNT Libraries Government Documents Department

Periodic arrays of pinning centers in thin vanadium films.

Description: Commensurability effects between the superconducting flux line lattice and a square lattice (period d=1{micro}m and diameter D=0.4{micro}m) of submicron holes in 1500 {angstrom} vanadium films were studied by atomic force microscopy, DC magnetization, AC susceptibility, magnetoresistivity and I-V measurements. Peaks in the magnetization and critical current at matching fields are found to depend nonlinearly upon the value of external AC field or current, as well as the inferred symmetry of the flux line lattice.
Date: July 13, 1997
Creator: Brueck, S. R. J.; Chung, K.; Crabtree, G.; DeLong, L. E.; Hesketh, P. J.; Ilic, B. et al.
Partner: UNT Libraries Government Documents Department

Interfacial phenomena on selected cathode materials

Description: We have carried out a series of surface studies of selected cathode materials. Instrumental techniques such as Raman microscopy, surface enhanced Raman spectroscopy (SERS), and atomic force microscopy were used to investigate the cathode surfaces. The goal of this study was to identify detrimental processes which occur at the electrode/electrolyte interface and can lead to electrode degradation and failure during cycling and/or storage at elevated temperatures.
Date: June 22, 2001
Creator: Kostecki, Robert; Matsuo, Yoshiaki & McLarnon, Frank
Partner: UNT Libraries Government Documents Department

A Single Step Lapping and Polishing Process for Achieving Surfaces of Compound Semiconductors with Atomic Flatness using a Sub-micron Agglomerate-free Alumina Slurry

Description: A novel approach for a single step lapping and final polishing of III-V and II-VI compounds using agglomerate-free alumina slurries has been developed. The agglomerate-free nature of the sub-micron slurry leads to removal rates comparable to conventional slurries (with larger particles of tens of microns) used for semiconductor lapping. Surfaces with minimal surface damage and extremely low surface roughness have been obtained using the sub-micron slurries and a soft pad. Strategies for post polishing surface cleaning have been discussed. The new methodology has been experimented on GaSb, InAs, GaAs, InP, InSb, CdTe, GaInSb, GaInAs, AlGaAsSb, GaInAsSb and HgCdTe. Selected results of surface analyses of GaSb and GaInSb using atomic force microscopy will be presented.
Date: August 29, 2002
Creator: Dutta, P.S.; Rajagopalan, G.; Gutmann, J.J.; Keller, D. & Sweet, L.
Partner: UNT Libraries Government Documents Department

Subsurface damage assessment with atomic force microscopy

Description: The performance of transparent optics in high fluence applications is often dominated by inhomogeneities in the first few hundred nanometers of material. Defects undetectable with optical methods can cause catastrophic failures when used in critical applications where high strength, chemical or mechanical resistance or extreme smoothness is required. Not only are these defects substantially smaller than the wavelength of visible light, they are often concealed below a layer of glass-like material deposited during the polishing process. In high quality glass, the chemical and material properties of the outermost layer are modified by the grinding, lapping and polishing processes used in fabrication. Each succeeding step in a process is designed to remote damage from the previous operation. However, any force against the surface, no matter how slight will leave evidence of this damage. These processes invariably create dislocations, cracks and plastic deformation in the subsurface region.
Date: April 16, 1999
Creator: Carr, J W; Fearon, E; Hutcheon, I D & Summers, L J
Partner: UNT Libraries Government Documents Department

Characterization of piesoelectric ZnO thin films and the fabrication of piezoelectric micro-cantilevers

Description: In Atomic Force Microscopy (AFM), a microcantilever is raster scanned across the surface of a sample in order to obtain a topographical image of the sample's surface. In a traditional, optical AFM, the sample rests on a bulk piezoelectric tube and a control loop is used to control the tip-sample separation by actuating the piezo-tube. This method has several disadvantages--the most noticeable one being that response time of the piezo-tube is rather long which leads to slow imaging speeds. One possible solution aimed at improving the speed of imaging is to incorporate a thin piezoelectric film on top of the cantilever beam. This design not only improves the speed of imaging because the piezoelectric film replaces the piezo-tube as an actuator, but the film can also act as a sensor. In addition, the piezoelectric film can excite the cantilever beam near its resonance frequency. This project aims to fabricate piezoelectric microcantilevers for use in the AFM. Prior to fabricating the cantilevers and also part of this project, a systematic study was performed to examine the effects of deposition conditions on the quality of piezoelectric ZnO thin films deposited by RF sputtering. These results will be presented. The deposition parameters that produced the highest quality ZnO film were used in the fabrication of the piezoelectric cantilevers. Unfortunately, the fabricated cantilevers warped due to the intrinsic stress of the ZnO film and were therefore not usable in the AFM. The complete fabrication process will be detailed, the results will be discussed and reasons for the warping will be examined.
Date: August 1, 2005
Creator: Johnson, Raegan Lynn
Partner: UNT Libraries Government Documents Department

SEISMIC AND ROCK PHYSICS DIAGNOSTICS OF MULTISCALE RESERVOIR TEXTURES

Description: As part of our study on ''Relationships between seismic properties and rock microstructure'', we have studied (1) How to quantify elastic properties of clay minerals using Atomic Force Acoustic Microscopy. We show how bulk modulus of clay can be measured using atomic force acoustic microscopy (AFAM) (2) We have successfully measured elastic properties of unconsolidated sediments in an effort to quantify attributes for detection of overpressures from seismic (3) We have initiated efforts for velocity upscaling to quantify long-wavelength and short-wavelength velocity behavior and the scale-dependent dispersion caused by sediment variability in different depositional environments.
Date: May 1, 2002
Creator: Mavko, Gary
Partner: UNT Libraries Government Documents Department

Observation of Localized Corrosion of Ni-Based Alloys Using Coupled Orientation Imaging Microscopy and Atomic Force Microscopy

Description: We present a method for assessing the relative vulnerabilities of distinct classes of grain boundaries to localized corrosion. Orientation imaging microscopy provides a spatial map which identifies and classifies grain boundaries at a metal surface. Once the microstructure of a region of a sample surface has been characterized, a sample can be exposed to repeated cycles of exposure to a corrosive environment alternating with topographic measurement by an atomic force microscope in the same region in which the microstructure had been mapped. When this procedure is applied to Ni and Ni-based alloys, we observe enhanced attack at random grain boundaries relative to special boundaries and twins in a variety of environments.
Date: November 24, 1999
Creator: Bedrossian, P. J.
Partner: UNT Libraries Government Documents Department

Nanoscale investigation of polarization retention loss in ferroelectric thin films via scanning force microscopy.

Description: Scanning force microscopy (SFM) was applied to direct nanoscale investigation of the mechanism of retention loss in ferroelectric thin films. Experiments were conducted by performing local polarization reversal within an individual grain with subsequent imaging of a resulting domain structure at various time intervals. A conductive SFM tip was used for domain switching and imaging in the SFM piezoresponse mode.
Date: February 12, 1998
Creator: Aggarwal, S.; Auciello, O.; Gruverman, A.; Prakash, S. A.; Ramesh, R. & Tokumoto, H.
Partner: UNT Libraries Government Documents Department

A Chemical Approach to 3-D Lithographic Patterning of Si and GeNanocrystals

Description: Ion implantation into silica followed by thermal annealingis an established growth method for Si and Ge nanocrystals. Wedemonstrate that growth of Group IV semiconductor nanocrystals can besuppressed by co-implantation of oxygen prior to annealing. For Sinanocrystals, at low Si/O dose ratios, oxygen co-implantation leads to areduction of the average nanocrystal size and a blue-shift of thephotoluminescence emission energy. For both Si and Ge nanocrystals, atlarger Si/O or Ge/O dose ratios, the implanted specie is oxidized andnanocrystals do not form. This chemical deactivation was utilized toachieve patterned growth of Si and Ge nanocrystals. Si was implanted intoa thin SiO2 film on a Si substrate followed by oxygen implantationthrough an electron beam lithographically defined stencil mask. Thermalannealing of the co-implanted structure yields two-dimensionallypatterned growth of Si nanocrystals under the masked regions. We applieda previously developed process to obtain exposed nanocrystals byselective HF etching of the silica matrix to these patterned structures.Atomic force microscopy (AFM) of etched structures revealed that exposednanocrystals are not laterally displaced from their original positionsduring the etching process. Therefore, this process provides a means ofachieving patterned structures of exposed nanocrystals. The possibilitiesfor scaling this chemical-based lithography process to smaller featuresand for extending it to 3-D patterning is discussed.
Date: December 12, 2005
Creator: Sharp, I. D.; Xu, Q.; Yi, D. O.; Liao, C. Y.; Ager, J. W., III; Beeman, J. W. et al.
Partner: UNT Libraries Government Documents Department