Islands And Holes As Measures Of Mass Balance In Growth Of The (√3×√3)R30° Phase Of Ag On Si(111), 2010 Iowa State University
Islands And Holes As Measures Of Mass Balance In Growth Of The (√3×√3)R30° Phase Of Ag On Si(111), Alex Belianinov, Barış Ünal, Ning Lu, Min Ji, Kai-Ming Ho, Cai-Zhuang Wang, Michael C. Tringides, Patricia A. Thiel
It is well known that conversion of Si(111)-(7×7) into the (√3×√3)R30° phase of adsorbed Ag requires a change in the Si density, and causes formation of islands and holes at the surface. By mass balance, the ratio of areas of islands and holes (RIH) should be approximately 1. However, we find that the ratio is significantly higher, depending on preparation conditions. A possible explanation would be that there are different types of (√3×√3)R30° structures. However, neither scanning tunneling microscopy nor density-functional theory (implemented as a genetic algorithm search) supports this explanation. We ...
Giant Raman Enhancement On Nanoporous Gold Film By Conjugating With Nanoparticles For Single-Molecule Detection, 2010 University of Nevada, Las Vegas
Giant Raman Enhancement On Nanoporous Gold Film By Conjugating With Nanoparticles For Single-Molecule Detection, Lihua Qian, Biswajit Das, Yan Li, Zhilin Yang
Electrical and Computer Engineering Faculty Publications
Hot spots have the contradictively geometrical requirements for both the narrowest interstices to provide strong near-field coupling, and sufficient space to allow entrance of the analytes. Herein, a two-step method is employed to create hot spots within hybrid nanostructures, which consist of self-supported nanoporous gold films with the absorbed probes and subsequent nanoparticle conjugates without surface agents or mechanical motion. The molecules confined into 1 nm interstice exhibit 2.9 × 107 times enhancement in Raman scattering compared to pure nanoporous gold. Giant enhancement primarily results from strong near-field coupling between nanopore and nanoparticle, which is theoretically confirmed by finite-difference ...
Microstructural Effects During Chemical Mechanical Planarization Of Copper, 2010 Boise State University
Microstructural Effects During Chemical Mechanical Planarization Of Copper, Patrick J. Andersen, Mariela N. Bentancur, Amy J. Moll, Megan Frary
Materials Science and Engineering Faculty Publications and Presentations
Novel die-stacking schema using through-wafer interconnects require vias to be filled with electroplated Cu, resulting in thick copper films, and requiring an aggressive first-step CMP. This work investigates the effects of microstructure on CMP of copper films, which are not presently well understood. Bulk and local removal rates were investigated for several different microstructures. Surface orientation maps were created and the orientations of individual grains were correlated with topographical data to elucidate local removal behavior. Cu removal depends on the details of the microstructure, and certain microstructures allowed for either faster or more uniform removal of thick Cu films.
Influence Of Y Substitutions On The Magnetism Of Gd5ge4, 2010 Iowa State University
Influence Of Y Substitutions On The Magnetism Of Gd5ge4, Durga Paudyal, Yaroslav Mudryk, Vitalij K. Pecharsky, Sumohan Misra, Gordon J. Miller, Karl A. Gschneidner Jr.
The interrelation between the specific crystallographic positions and their influence on the magnetism of neighboring atoms is examined from first principles electronic structure calculations using the Gd5Ge4 compound as a model system. The predicted preferences of the specific occupations by nonmagnetic yttrium atoms and the resulting magnetism of substituted Gd5Ge4 have been confirmed, respectively, by single crystal x-ray diffraction and magnetization experiments.
Low-Temperature Adsorption Of H2s On Ag(111), 2010 Iowa State University
Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel
H2S forms a rich variety of structures on Ag(111) at low temperature and submonolayer coverage. The molecules decorate step edges, exist as isolated entities on terraces, and aggregate into clusters and islands, under various conditions. One type of island exhibits a (×)R25.3° unit cell. Typically, molecules in the clusters and islands are separated by about 0.4 nm, the same as the S–S separation in crystalline H2S. Density functional theory indicates that hydrogen-bonded clusters contain two types of molecules. One is very similar to an isolated adsorbed H2S molecule, with both ...
Variation Of Growth Morphology With Chemical Composition Of Terraces: Ag On A Twofold Surface Of A Decagonal Al-Cu-Co Quasicrystal, T. Duguet, Barış Ünal, Yong Han, James W. Evans, J. Ledieu, Cynthia J. Jenks, J.-M. Dubois, V. Fournée, Patricia A. Thiel
Growth of Ag thin films on the twofold surface of a decagonal Al-Cu-Co quasicrystal is characterized by scanning tunneling microscopy, at different temperatures, and for coverages ranging from submonolayer to 11 monolayers. From prior work, three types of clean surface terraces are known to exist. By correlation with a bulk structural model, the major difference between them lies in their transition-metal (TM) content, two being aluminum-rich (0 and 15 at. % TM) and one being TM-rich (40–50 at. % TM). The present article focuses on understanding the difference between Ag film morphologies on these terminations, in terms of their chemical content ...
Formation And Coarsening Of Ag(110) Bilayer Islands On Nial(110): Stm Analysis And Atomistic Lattice-Gas Modeling, Yong Han, Barış Ünal, Dapeng Jing, Feili Qin, Cynthia J. Jenks, Da-Jiang Liu, Patricia A. Thiel, James W. Evans
Scanning tunneling microscopy analysis of the initial stages of film growth during deposition of Ag on NiAl(110) reveals facile formation of bilayer Ag(110) islands at temperatures of 130 K and above. Annealing subsequent to deposition at 130 K induces coarsening of the bilayer island distribution. The thermodynamic driving force for bilayer island formation reflects a lower relative surface energy for films of even layer thicknesses. This feature derives from quantum size effects due to electron confinement in the Ag film. The kinetics of island formation and relaxation is controlled by terrace and edge-diffusion barriers, detachment barriers, interlayer diffusion ...
Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, 2010 Iowa State University
Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, Barış Ünal, Alex Belianinov, Patricia A. Thiel, Michael C. Tringides
Ag on Si(111)-7×7 was one of the first systems where height selection of metal islands was attributed to electron confinement, i.e., stabilization of selected heights through a quantum size effect (QSE). However, it has been puzzling how the requisite electron standing waves can form, because the Fermi level EF (along the growth  direction) is within the gap for bulk Ag. With detailed experiments over a wide coverage and temperature range, we show that a large increase of 12% is present in the interlayer spacing within the bilayer islands. This can shift EF below ...
Nanoscale “Quantum” Islands On Metal Substrates: Microscopy Studies And Electronic Structure Analyses, 2010 Iowa State University
Nanoscale “Quantum” Islands On Metal Substrates: Microscopy Studies And Electronic Structure Analyses, Yong Han, Barış Ünal, Dapeng Jing, Patricia A. Thiel, James W. Evans
Confinement of electrons can occur in metal islands or in continuous films grown heteroepitaxially upon a substrate of a different metal or on a metallic alloy. Associated quantum size effects (QSE) can produce a significant height-dependence of the surface free energy for nanoscale thicknesses of up to 10–20 layers. This may suffice to induce height selection during film growth. Scanning STM analysis has revealed remarkable flat-topped or mesa-like island and film morphologies in various systems. We discuss in detail observations of QSE and associated film growth behavior for Pb/Cu(111), Ag/Fe(100), and Cu/fcc-Fe/Cu(100 ...
Periodic Step Arrays On The Aperiodic I-Al-Pd-Mn Quasicrystal Surface At High Temperature, 2010 University of California, Davis
Periodic Step Arrays On The Aperiodic I-Al-Pd-Mn Quasicrystal Surface At High Temperature, Y. Sato, Barış Ünal, Thomas A. Lograsso, Patricia A. Thiel, A. K. Schmid, T. Duden, N. C. Bartelt, K. F. Mccarty
We have observed the configuration and motion of surface steps on the aperiodic icosahedral (i-) Al-Pd-Mn quasicrystal using low-energy electron microscopy and scanning tunneling microscopy. As the quasicrystal is cooled from high temperature, bulk vacancies migrate to the surface causing the surface to be etched. Surprisingly, this etching occurs by two types of steps with different heights moving in different directions with different velocities. The steady-state surface morphology is a uniformly spaced rhomboidal step network. This network requires that the layer stacking near the surface deviates from the bulk quasicrystal stacking.
Excitation-Induced Germanium Quantum Dot Formation On Si (100)-(2×1), 2010 Old Dominion University
Excitation-Induced Germanium Quantum Dot Formation On Si (100)-(2×1), Ali Oguz Er, Hani E. Elsayed-Ali
Physics Faculty Publications
The effect of nanosecond pulsed laser excitation on the self-assembly of Ge quantum dots grown by pulsed laser deposition on Si (100)-(2×1) was studied. In situ reflection high-energy electron diffraction and ex situ atomic force microscopy were used to probe the quantum dot structure and morphology. At room temperature, applying the excitation laser decreased the surface roughness of the grown Ge film. With surface electronic excitation, crystalline Ge quantum dots were formed at 250 °C, a temperature too low for their formation without excitation. At a substrate temperature of 390 °C, electronic excitation during growth was found to ...
The Properties And Structure Of Tin Phosphate Glasses Modified With Other Oxides, 2010 Missouri University of Science and Technology
The Properties And Structure Of Tin Phosphate Glasses Modified With Other Oxides, Jong Wook (Austin) Lim
"The main objective of this research was to evaluate the properties and structures of glasses from the stannous (SnO) phosphate system for possible use in low temperature optical applications. Glasses in the binary xSnO-(100-x)P₂O₅ system (50 ≤ x ≤ 70) were prepared and their thermal and optical properties were evaluated. Differences in glass transition temperatures (Tg) measured here and reported in the literature were explained by differences in the residual water content in the glasses, as determined by infrared spectroscopy. In general, increasing the SnO content of the binary glasses increased the refractive index and the glass transition temperature ...
Controlling Strength And Permeability Of Silica Investment Casting Molds, 2010 Missouri University of Science and Technology
Controlling Strength And Permeability Of Silica Investment Casting Molds, Darryl M. Kline
"Investment casting is a metal casting process in which a ceramic mold is created around a disposable pattern using dip coating. The fine silica flour making up most of the mold gives the benefits of a smooth internal mold surface and high density. The high density allows for investment casting molds to be thinner and lighter than sand-based molds, but gives substantially smaller gaps between particles for air flow. This research focused on the design and improvement of the formulation for making investment casting molds with customizable physical properties. Properties of the molds, specifically flexural strength, permeability, and physical structure ...
Zinc Iron Phosphate Glasses For Enameling Applications, 2010 Missouri University of Science and Technology
Zinc Iron Phosphate Glasses For Enameling Applications, Sagnik Saha
"New compositions of low temperature black glasses were developed that are suitable as frits for enameling soda-lime silicate (S-L-S) glass substrates. Zinc iron phosphate glasses are of interest for this application because they possess dilatometric low softening points (under 600ºC) and have coefficients of thermal expansion that are compatible with S-L-S glass (in the range 90-110x10⁻⁷/ºC). The development of compositions with excellent chemical durability, particularly in acidic conditions, is also desired. Compositional modification were made to the (Na₂O+K₂O)·ZnO·MnO·Fe₂O₃·P₂O₅ glass system using design of experiments. The compositional boundaries used in the design were based ...
Characterization Of Diamond Thin Films And Related Materials, 2010 Missouri University of Science and Technology
Characterization Of Diamond Thin Films And Related Materials, Travis K. Mckindra
"Thin carbon films including sputtered deposited graphite and CO₂ laser-assisted combustion-flame deposited graphite and diamond thin films were characterized using optical and electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Amorphous carbon thin films were deposited by DC magnetron sputtering using Ar/O₂ gases. The film morphology changed with the oxygen content. The deposition rate decreased as the amount of oxygen increased due to oxygen reacting with the growing film. The use of oxygen in the working gas enhanced the crystalline nature of the films. Graphite was deposited on WC substrates by a CO₂ laser-assisted O₂/C₂H₂ combustion-flame method. Two distinct ...
Dependency Of Machinability In Gray Cast Iron On Nitride-Induced Age Strengthening, 2010 Missouri University of Science and Technology
Dependency Of Machinability In Gray Cast Iron On Nitride-Induced Age Strengthening, Jared Teague
"Work of previous researchers has suggested that room temperature age strengthening in gray cast irons improves machinability. Verification and quantification of the machinability improvement is important to industry. Improved machinability will reduce overall manufacturing costs and reduce raw material consumption by decreasing the rate at which tools are replaced. Experimental work was performed to determine a connection between improved machinability in gray cast iron and changes in machining mechanics. An industrial tool wear study verified that age strengthening improved machinability by reducing tool wear to less than one-quarter of the unaged value. Laboratory tests on iron castings from the same ...
Experimental Study On Thermal Treatment Of Used Printed Wiring Boards (Pwbs), 2010 Missouri University of Science and Technology
Experimental Study On Thermal Treatment Of Used Printed Wiring Boards (Pwbs), Xiangjun Zuo
The availability of cheaper and better electronic products as a result of the rapid innovation in technology in past decades has driven the production of e-waste forward. Printed wiring board (PWB) is a component made of one or more layers of insulating material with electrical conductors. The existing processes of recycling PWBs use pyrometallurgical or hydrometallurgical methods, which generate atmospheric pollution. Green recycling has obvious benefits to decrease the amount of PWBs. Green recycling includes two features, 1) little or zero pollution of toxic gases and heavy metals, and 2) efficient (quick and economical) recycling.
The aim of this work ...
Phosphate Post-Treatment Of Cerium-Based Conversion Coatings On Al 2024-T3, 2010 Missouri University of Science and Technology
Phosphate Post-Treatment Of Cerium-Based Conversion Coatings On Al 2024-T3, Daimon K. Heller
"Phosphate post-treatment of cerium-based conversion coatings (CeCCs) on high strength aluminum alloys can significantly improve corrosion resistance. As-deposited CeCCs exhibit corrosion pits and salt tails across the specimen surface after 3 days of exposure, but post-treated CeCCs have withstood 14 days of salt spray exposure without visibly corroding. The morphology, phase, and electrochemical properties of spray deposited CeCCs were affected by post-treatment parameters such as immersion time, solution temperature, and phosphate source. The best performing coatings were post-treated in aqueous orthophosphate solutions for at least 5 min at temperatures of at least 85⁰C. These conditions converted cerium hydroxy/peroxy species ...
Factors Controlling Ductility In Ultrafine Grain Aluminum Alloys Under Monotonic And Cyclic Loading, 2010 Missouri University of Science and Technology
Factors Controlling Ductility In Ultrafine Grain Aluminum Alloys Under Monotonic And Cyclic Loading, Partha Sarathi De
"Ultrafine grained (UFG) Al processed by severe plastic deformation (SPD) methods are characterized by high strength and a limited uniform ductility. Friction stir processing (FSP), an offshoot of friction stir welding has emerged as a new technique to produce UFG alloys. FSP-UFG Al alloys show a distinctly different behavior with higher uniform elongation and improved high cycle fatigue life as compared to other SPD processed variants. The objective of this work was to study the microstructural basis for such mechanical behavior in FSP-UFG Al alloys.
To study the mechanical behavior of FSP Al alloys, a subsize bending fatigue and uniaxial ...
Borate Based Bioactive Glass Scaffolds For Hard And Soft Tissue Engineering, 2010 Missouri University of Science and Technology
Borate Based Bioactive Glass Scaffolds For Hard And Soft Tissue Engineering, Steven B. Jung
"The main objectives of this dissertation were to evaluate bioactive borate glass scaffolds for hard and soft tissue applications and determine the potential toxicity of the borate glasses on the adjacent and systemic tissues. Porous randomly oriented fiber scaffolds composed of bioactive borate glass were implanted in subcutaneous soft tissue sites and in calvaria defects of laboratory rats and no signs of toxicity (necrotic tissue, increase in macrophages or other immune cells) were detected in any of the adjacent tissues (hard or soft). Systemic organs (kidney and liver) of laboratory rats implanted with bioactive borate scaffolds were analyzed for possible ...