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Full-Text Articles in Physics

Dynamic Arrest And Glass Formation Induced By Self-Aggregation Of Icosahedral Clusters In Zr1−Xcux Alloys, S. G. Hao, Cai-Zhuang Wang, M. Z. Li, Ralph E. Napolitano, Kai-Ming Ho Aug 2011

Dynamic Arrest And Glass Formation Induced By Self-Aggregation Of Icosahedral Clusters In Zr1−Xcux Alloys, S. G. Hao, Cai-Zhuang Wang, M. Z. Li, Ralph E. Napolitano, Kai-Ming Ho

Materials Science and Engineering Publications

Using ab initio molecular dynamics simulations, we find direct evidence that icosahedral clusters have a strong tendency to aggregate in Zr1−xCux liquids. Remarkably, the dynamic arrest effect is much more significant in aggregated icosahedral clusters than in nonaggregated ones by a factor of 2 or more. Simulations using a lattice model demonstrate that the dynamic arrest effect resulting from the aggregation of icosahedral clusters may be a fundamental characteristic of the glass transition. Our studies provide an atomistic structural mechanism for dynamic arrest and glass formation.


Soft Holographic Interference Lithography Microlens For Enhanced Organic Light Emitting Diode Light Extraction, Joong Mok Park, Zhengqing Gan, Wai Y. Leung, Rui Liu, Zhuo Ye, Kristen P. Constant, Joseph Shinar, Ruth Shinar, Kai-Ming Ho Jul 2011

Soft Holographic Interference Lithography Microlens For Enhanced Organic Light Emitting Diode Light Extraction, Joong Mok Park, Zhengqing Gan, Wai Y. Leung, Rui Liu, Zhuo Ye, Kristen P. Constant, Joseph Shinar, Ruth Shinar, Kai-Ming Ho

Materials Science and Engineering Publications

Very uniform 2 μm-pitch square microlens arrays (μLAs), embossed on the blank glass side of an indium-tin-oxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by ~100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the ...


Fabrication Of Submicron Metallic Grids With Interference And Phase-Mask Holography, Joong Mok Park, Tae Geun Kim, Kristen P. Constant, Kai-Ming Ho Jan 2011

Fabrication Of Submicron Metallic Grids With Interference And Phase-Mask Holography, Joong Mok Park, Tae Geun Kim, Kristen P. Constant, Kai-Ming Ho

Materials Science and Engineering Publications

Complex, submicron Cu metallic mesh nanostructures are made by electrochemical deposition using polymer templates made from photoresist. The polymer templates are fabricated with photoresist using two-beam interference holography and phase mask holography with three diffracted beams. Freestanding metallic mesh structures are made in two separate electrodepositions with perpendicular photoresist grating templates. Cu mesh square nanostructures having large (52.6%) open areas are also made by single electrodeposition with a photoresist template made with a phase mask. These structures have potential as electrodes in photonic devices.


Far-From-Equilibrium Film Growth On Alloy Surfaces: Ni And Al On Nial(110), Yong Han, Dapeng Jing, Baris Unal, Patricia A. Thiel, James W. Evans Jan 2011

Far-From-Equilibrium Film Growth On Alloy Surfaces: Ni And Al On Nial(110), Yong Han, Dapeng Jing, Baris Unal, Patricia A. Thiel, James W. Evans

Chemistry Publications

STM analysis reveals diverse nonequilibrium island structures formed by deposition of Ni and Al on NiAl(110) at around 300 K. Epitaxial growth in this complex alloy system is described by multisite lattice-gas modeling incorporating DFT energetics for adatoms both at adsorption sites and transition states. This approach accounts for multiple adsorption sites and diffusion paths, and accurately describes diffusion and detachment kinetics for a vast number of step-edge configurations. This is key for realistic description of island growth shapes, structure, and partial alloy ordering.


Destabilization Of Ag Nanoislands On Ag(100) By Adsorbed Sulfur, Mingmin Shen, Selena M. Russell, Da-Jiang Liu, Patricia A. Thiel Jan 2011

Destabilization Of Ag Nanoislands On Ag(100) By Adsorbed Sulfur, Mingmin Shen, Selena M. Russell, Da-Jiang Liu, Patricia A. Thiel

Chemistry Publications

Sulfur accelerates coarsening of Ag nanoislands on Ag(100) at 300 K, and this effect is enhanced with increasing sulfur coverage over a range spanning a few hundredths of a monolayer, to nearly 0.25 monolayers. We propose that acceleration of coarsening in this system is tied to the formation of AgS2 clusters primarily at step edges. These clusters can transport Ag more efficiently than can Ag adatoms (due to a lower diffusion barrier and comparable formation energy). The mobility of isolated sulfur on Ag(100) is very low so that formation of the complex is kinetically limited at ...


Fe-Fe Adatom Interaction And Growth Morphology On Graphene, Xiaojie Liu, Cai-Zhuang Wang, Myron Hupalo, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, Michael C. Tringides Jan 2011

Fe-Fe Adatom Interaction And Growth Morphology On Graphene, Xiaojie Liu, Cai-Zhuang Wang, Myron Hupalo, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, Michael C. Tringides

Chemistry Publications

The nucleation and growth of Fe on graphene is highly unusual. A constantly increasing island density indicates the presence of strong, predominantly repulsive, adatom interactions. We study these interactions by first-principles calculations to identify their origin. We find that the interactions consist of a short-range attraction and longer-range repulsion. We show that electric dipole-dipole interaction can contribute only part of the repulsive force (∼30%) between Fe adatoms, and the repulsion due to the elastic interaction is small. We suggest that the dominant contribution to the repulsive energy would originate from the indirect (or RKKY) interactions mediated through the delocalized electrons ...


Comment On “Origin Of Friction Anisotropy On A Quasicrystal Surface”, K. Mclaughlin, D. Rabson, Patricia A. Thiel Jan 2011

Comment On “Origin Of Friction Anisotropy On A Quasicrystal Surface”, K. Mclaughlin, D. Rabson, Patricia A. Thiel

Chemistry Publications

A Comment on the Letter by Aleksander E. Filippov, Andrea Vanossi, and Michael Urbakh, Phys. Rev. Lett. 104 074302 (2010). The authors of the Letter offer a Reply.


In Situ Observation Of Antisite Defect Formation During Crystal Growth, Matthew J. Kramer, Mikhail I. Mendelev, Ralph E. Napolitano Dec 2010

In Situ Observation Of Antisite Defect Formation During Crystal Growth, Matthew J. Kramer, Mikhail I. Mendelev, Ralph E. Napolitano

Materials Science and Engineering Publications

In situ x-ray diffraction (XRD) coupled with molecular dynamics (MD) simulations have been used to quantify antisite defect trapping during crystallization. Rietveld refinement of the XRD data revealed a marked lattice distortion which involves an a axis expansion and a c axis contraction of the stable C11b phase. The observed lattice response is proportional in magnitude to the growth rate, suggesting that the behavior is associated with the kinetic trapping of lattice defects. MD simulations demonstrate that this lattice response is due to incorporation of 1% to 2% antisite defects during growth.


From Initial To Late Stages Of Epitaxial Thin Film Growth: Stm Analysis And Atomistic Or Coarsegrained Modeling, James W. Evans, Yong Han, Barış Ünal, Maozhi Li, K. J. Caspersen, Dapeng Jing, Anthony R. Layson, C. R. Stoldt, T. Duguet, Patricia A. Thiel Aug 2010

From Initial To Late Stages Of Epitaxial Thin Film Growth: Stm Analysis And Atomistic Or Coarsegrained Modeling, James W. Evans, Yong Han, Barış Ünal, Maozhi Li, K. J. Caspersen, Dapeng Jing, Anthony R. Layson, C. R. Stoldt, T. Duguet, Patricia A. Thiel

Chemistry Conference Papers, Posters and Presentations

Epitaxial thin film growth by vapor deposition or molecular beam epitaxy under ultra‐high vacuum conditions generally occurs in two stages: (i) nucleation and growth of well‐separated islands on the substrate; (ii) subsequent formation of a thicker continuous film with possible kinetic roughening. For homoepitaxial growth, two‐dimensional (2D) monolayer islands are formed during submonolayer deposition. Typically, the presence of a step‐edge barrier inhibits downward transport and leads to the formation of mounds (multilayer stacks of 2D islands) during multilayer growth. For heteroepitaxial growth, islands formed in the initial stages of deposition sometimes have a 2D monolayer structure ...


Thermodynamic Limits Of Crystallization And The Prediction Of Glass Formation Tendency, Yongxin Yao, Ralph E. Napolitano, Cai-Zhuang Wang, Kai-Ming Ho Jun 2010

Thermodynamic Limits Of Crystallization And The Prediction Of Glass Formation Tendency, Yongxin Yao, Ralph E. Napolitano, Cai-Zhuang Wang, Kai-Ming Ho

Materials Science and Engineering Publications

We have calculated the T0 curves for several Al-rare-earth binary alloys to assess the importance of the transport-based resistance to crystallization in the overall glass formation process and the general effectiveness of thermodynamic prediction of glass-forming ability. Our results show that the experimentally observed glass-forming compositions for Al-(Ce, Gd, Ho, Nd, Y, Dy) alloys strongly correlate with the composition range bounded by the T0curves associated with the relevant crystalline phases. This indicates that sluggish material transport, together with the tendency for clustering and other types of ordering at medium-range scale, is a key factor governing glass formation in these ...


Semicrystalline Woodpile Photonic Crystals Without Complicated Alignment Via Soft Lithography, Jae-Hwang Lee, Ping Kuang, Wai Y. Leung, Yong-Sung Kim, Joong Mok Park, Henry Kang, Kristen P. Constant, Kai-Ming Ho Jan 2010

Semicrystalline Woodpile Photonic Crystals Without Complicated Alignment Via Soft Lithography, Jae-Hwang Lee, Ping Kuang, Wai Y. Leung, Yong-Sung Kim, Joong Mok Park, Henry Kang, Kristen P. Constant, Kai-Ming Ho

Materials Science and Engineering Publications

We report the fabrication and characterization of woodpile photonic crystals with up to 12 layers through titania nanoparticle infiltration of a polymer template made by soft lithography. Because the complicated alignment in the conventional layer-by-layer fabrication associated with diamondlike symmetry is replaced by a simple 90° alignment, the fabricatedphotonic crystal has semicrystalline phase. However, the crystal performs similarly to a perfectly aligned crystal for the light propagation integrated from the surface normal to 30° at the main photonic band gap.


Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel Jan 2010

Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

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 Jan 2010

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

Chemistry Publications

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 ...


Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, Barış Ünal, Alex Belianinov, Patricia A. Thiel, Michael C. Tringides Jan 2010

Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, Barış Ünal, Alex Belianinov, Patricia A. Thiel, Michael C. Tringides

Chemistry Publications

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 [111] 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, Yong Han, Barış Ünal, Dapeng Jing, Patricia A. Thiel, James W. Evans Jan 2010

Nanoscale “Quantum” Islands On Metal Substrates: Microscopy Studies And Electronic Structure Analyses, Yong Han, Barış Ünal, Dapeng Jing, Patricia A. Thiel, James W. Evans

Chemistry Publications

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, Y. Sato, Barış Ünal, Thomas A. Lograsso, Patricia A. Thiel, A. K. Schmid, T. Duden, N. C. Bartelt, K. F. Mccarty Jan 2010

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

Chemistry Publications

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.


Adsorbate-Enhanced Transport Of Metals On Metal Surfaces: Oxygen And Sulfur On Coinage Metals, Patricia A. Thiel, Mingmin Shen, Da-Jiang Liu, James W. Evans Jan 2010

Adsorbate-Enhanced Transport Of Metals On Metal Surfaces: Oxygen And Sulfur On Coinage Metals, Patricia A. Thiel, Mingmin Shen, Da-Jiang Liu, James W. Evans

Chemistry Publications

Coarsening (i.e., ripening) of single-atom-high, metal homoepitaxial islands provides a useful window on the mechanism and kinetics of mass transport at metal surfaces. This article focuses on this type of coarsening on the surfaces of coinage metals (Cu, Ag, Au), both clean and with an adsorbed chalcogen (O, S) present. For the clean surfaces, three aspects are summarized: (1) the balance between the two major mechanisms—Ostwald ripening (the most commonly anticipated mechanism) and Smoluchowski ripening—and how that balance depends on island size; (2) the nature of the mass transport agents, which are metal adatoms in almost all ...


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 Jan 2010

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

Chemistry Publications

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 ...


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 Jan 2010

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

Chemistry Publications

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 ...


Spectrally Narrowed Edge Emission From Leaky Waveguide Modes In Organic Light-Emitting Diodes, Zhengqing Gan, Yun Tian, David W. Lynch, Ji-Hun Kang, Q-Han Park, Joseph Shinar Jan 2009

Spectrally Narrowed Edge Emission From Leaky Waveguide Modes In Organic Light-Emitting Diodes, Zhengqing Gan, Yun Tian, David W. Lynch, Ji-Hun Kang, Q-Han Park, Joseph Shinar

Physics and Astronomy Publications

A dramatic spectral line narrowing of the edge emission at room temperature from tris(quinolinolate) Al (Alq3), N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (NPD), 4,4′-bis(2,2′-diphenyl-vinyl)-,1′-biphenyl (DPVBi), and some guest-host small molecular organic light-emitting diodes(OLEDs), fabricated on indium tin oxide (ITO)-coated glass, is described. In all but the DPVBi OLEDs, the narrowed emission band emerges above a threshold thickness of the emitting layer, and narrows down to a full width at half maximum of only 5–10 nm. The results demonstrate that this narrowed emission is due ...


Twofold Surface Of The Decagonal Al-Cu-Co Quasicrystal, T. Duguet, Barış Ünal, M. C. De Weerd, J. Ledieu, R. A. Ribeiro, Paul C. Canfield, S. Deloudi, W. Steurer, Cynthia J. Jenks, J.-M. Dubois, V. Fournée, Patricia A. Thiel Jan 2009

Twofold Surface Of The Decagonal Al-Cu-Co Quasicrystal, T. Duguet, Barış Ünal, M. C. De Weerd, J. Ledieu, R. A. Ribeiro, Paul C. Canfield, S. Deloudi, W. Steurer, Cynthia J. Jenks, J.-M. Dubois, V. Fournée, Patricia A. Thiel

Chemistry Publications

We have investigated the atomic structure of the twofold surface of the decagonal Al-Cu-Co quasicrystal using scanning tunneling microscopy and low-energy electron diffraction. We have found that most of the surface features can be interpreted using the bulk-structure model proposed by Deloudi and Steurer (S. Deloudi, Ph.D. thesis, ETH, Zürich, 2008). The surface consists of terraces separated by steps of various heights. Step heights and steps sequences match with the thickness and the stacking sequence of blocks of layers separated by gaps in the model. These blocks of layers define possible surface terminations consisting of periodic atomic rows which ...


Energetics Of Nonequilibrium Solidification In Al-Sm, Shihuai Zhou, Ralph E. Napolitano Nov 2008

Energetics Of Nonequilibrium Solidification In Al-Sm, Shihuai Zhou, Ralph E. Napolitano

Materials Science and Engineering Publications

Solution-based thermodynamic modeling, aided by first-principles calculations, is employed here to examine phase transformations in the Al-Sm binary system which may give rise to product phases that are metastable or have a composition that deviates substantially from equilibrium. In addition to describing the pure undercooled Al liquid with a two-state model that accounts for structural ordering, thermodynamic descriptions of the fcc phase, and intermediate compounds (Al4Sm-β, Al11Sm3-α, Al3Sm-δ, and Al2Sm-σ) are reanalyzed using special quasirandom structure and first-principles calculations. The possible phase compositions are presented over a range of temperatures using a “Baker-Cahn” analysis of the energetics of solidification and ...


Polarized Thermal Radiation By Layer-By-Layer Metallic Emitters With Sub-Wavelength Grating, Jae-Hwang Lee, Wai Y. Leung, Tae Guen Kim, Kristen P. Constant, Kai-Ming Ho Jun 2008

Polarized Thermal Radiation By Layer-By-Layer Metallic Emitters With Sub-Wavelength Grating, Jae-Hwang Lee, Wai Y. Leung, Tae Guen Kim, Kristen P. Constant, Kai-Ming Ho

Materials Science and Engineering Publications

Metallic thermal emitters consisting of two layers of differently structured nickel gratings on a homogeneous nickel layer are fabricated by soft lithography and studied for polarized thermal radiation. A thermal emitter in combination with a sub-wavelength grating shows a high extinction ratio, with a maximum value close to 5, in a wide mid-infrared range from 3.2 to 7.8 µm, as well as high emissivity up to 0.65 at a wavelength of 3.7µm. All measurements show good agreement with theoretical predictions. Numerical simulations reveal that a high electric field exists within the localized air space surrounded by ...


Spectrally Narrowed Edge Emission From Organic Light-Emitting Diodes, Yun Tian, Zhengqing Gan, Zhaoqun Zhou, David W. Lynch, Joseph Shinar, Ji-Hun Kang, Q-Han Park Oct 2007

Spectrally Narrowed Edge Emission From Organic Light-Emitting Diodes, Yun Tian, Zhengqing Gan, Zhaoqun Zhou, David W. Lynch, Joseph Shinar, Ji-Hun Kang, Q-Han Park

Physics and Astronomy Publications

A dramatic spectrally narrowed edge emission (SNEE) from small molecular organic light-emitting diodes at room temperature, with a full width at half maximum of 5–10nm, is described. The results show that this emission is due to irregular waveguide modes that leak from the indium tin oxide anode to the glass substrate at a grazing angle. Measurements of variable stripe length devices exhibit an apparent weak optical gain, but there is no observable threshold bias associated with this SNEE. Hence this apparent “optical gain” is suspected to result from misalignment of the propagating leaky waveguide mode and the collecting optics.


Layer-By-Layer Photonic Crystal Fabricated By Low-Temperature Atomic Layer Deposition, Jae-Hwang Lee, Wai Y. Leung, Jinho Ahn, Tasho Lee, In-Sung Park, Kristen P. Constant, Kai-Ming Ho Jan 2007

Layer-By-Layer Photonic Crystal Fabricated By Low-Temperature Atomic Layer Deposition, Jae-Hwang Lee, Wai Y. Leung, Jinho Ahn, Tasho Lee, In-Sung Park, Kristen P. Constant, Kai-Ming Ho

Materials Science and Engineering Publications

Layer-by-layer three-dimensional photonic crystals are fabricated by low-temperature atomic layer deposition of titanium dioxide on a polymer template created by soft lithography. With a highly conformal layer of titanium dioxide, a significantly enhanced photonic band gap effect appears at 3.1μm in transmittance and reflectance. From optical investigations of systematically shifted structures, the robust nature of the photonic band gap with respect to structural fluctuations is confirmed experimentally. With angle-resolved Fourier-transform spectroscopy, the authors also demonstrate that the fabricatedphotonic crystal can be a diffraction-free device as the photonic band gap exists over the diffracting regime.


Three-Dimensional Metallic Photonic Crystals Fabricated By Soft Lithography For Midinfrared Applications, Jae-Hwang Lee, Chang-Hwan Kim, Yong-Sung Kim, Kai-Ming Ho, Kristen P. Constant, Cha-Hwan Oh Jan 2006

Three-Dimensional Metallic Photonic Crystals Fabricated By Soft Lithography For Midinfrared Applications, Jae-Hwang Lee, Chang-Hwan Kim, Yong-Sung Kim, Kai-Ming Ho, Kristen P. Constant, Cha-Hwan Oh

Materials Science and Engineering Publications

We present an efficient method of fabricating freestanding three-dimensional metallic photonic crystals using soft lithography. Low cost and ease of fabrication are achieved through gold sputter deposition on a freestanding woodpile polymer template. We compare experimental results to theoretical calculations for tetragonal and face-centered-tetragonal structures as a function of the number of layers. The photonic crystals behave like full metallic structures with a photonic band edge at a wavelength of 3.5μm. The rejection rates of the structures are about 10dB/layer.


Tribological Properties Of Quasicrystals: Effect Of Aperiodic Versus Periodic Surface Order, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel Jan 2006

Tribological Properties Of Quasicrystals: Effect Of Aperiodic Versus Periodic Surface Order, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel

Chemistry Publications

We investigated the nanoscale tribological properties of a decagonal quasicrystal using a combination of atomic force microscopy and scanning tunneling microscopy in ultrahigh vacuum. This combination permitted a variety of in situ measurements, including atomic-scale structure, friction and adhesion force, tip-sample current, and topography. We found that thiol-passivated tips can be used for reproducible studies of the tip-quasicrystal contact while nonpassivated probes adhere irreversibly to the clean quasicrystalline surface causing permanent modifications. The most remarkable results were obtained on the twofold surface of the Al-Ni-Co decagonal quasicrystal where atoms are arranged periodically along the tenfold axis and aperiodically in the ...


Photonic Bandgaps Of Conformally Coated Structures, Rana Biswas, Jinho Ahn, Taoho Lee, Jae-Hwang Lee, Yong-Sung Kim, Chang-Hwan Kim, Wai Y. Leung, Cha-Hwan Oh, Kristen P. Constant, Kai-Ming Ho Dec 2005

Photonic Bandgaps Of Conformally Coated Structures, Rana Biswas, Jinho Ahn, Taoho Lee, Jae-Hwang Lee, Yong-Sung Kim, Chang-Hwan Kim, Wai Y. Leung, Cha-Hwan Oh, Kristen P. Constant, Kai-Ming Ho

Materials Science and Engineering Publications

Polymeric molds of the layer-by-layer photonic crystal can be economically synthesized with a microtransfer molding technique. The refractive indices of these molds are low, preventing formation of a photonic bandgap. We find that such molds can be conformally coated with higher-index material. Photonic band calculations find structures in which conformally coated layer-by-layer molds have complete bandgaps for both titania and silicon coatings. Large stop bands exist in the 001 stacking direction. Feasibility of experimental conformal coating of the molds has been demonstrated with a titania-coated polyurethane mold, which shows optical features in agreement with simulations of reflection and transmission.


Elastic And Inelastic Deformations Of Ethylene-Passivated Tenfold Decagonal Al-Ni-Co Quasicrystal Surfaces, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel Jan 2005

Elastic And Inelastic Deformations Of Ethylene-Passivated Tenfold Decagonal Al-Ni-Co Quasicrystal Surfaces, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel

Chemistry Publications

The adhesion and friction force properties between a tenfold Al‐Ni‐Co decagonal quasicrystal and a titanium nitride (TiN)-coated tip were investigated using an atomic force microscope in ultrahigh vacuum. To suppress the strong chemical adhesion found in the clean quasicrystal surfaces, the sample was exposed to ethylene that formed a protective passivating layer. We show that the deformation mechanism of the tip-substrate junction changes from elastic to inelastic at a threshold pressure of 3.8 to 4.0 GPa. Images of the indentation marks left above the threshold pressure indicate the absence of new steps, and indicate that ...


Temperature Dependence Of Island Growth Shapes During Submonolayer Deposition Of Ag On Ag(111), Eric Cox, Maozhi Li, Po-Wen Chung, C. Ghosh, T. S. Rahman, Cynthia J. Jenks, James W. Evans, Patricia A. Thiel Jan 2005

Temperature Dependence Of Island Growth Shapes During Submonolayer Deposition Of Ag On Ag(111), Eric Cox, Maozhi Li, Po-Wen Chung, C. Ghosh, T. S. Rahman, Cynthia J. Jenks, James W. Evans, Patricia A. Thiel

Chemistry Publications

Growth shapes of Ag islands formed on Ag(111) during submonolayer deposition at different temperatures were studied with scanning tunneling microscopy, and analyzed via kinetic Monte Carlo simulation of a suitable atomistic lattice-gas model. Distinct shape transitions can be observed, from dendrites with triangular envelopes at low temperatures (below 140 K) to more isotropic fat fractal islands at intermediate temperatures, and then to distorted hexagonal shapes with longer Bsteps and shorter A steps at higher temperatures (above 170 K). In contrast, the equilibrium island shapes in this system are almost perfect hexagons displaying a near-sixfold symmetry. Modeling reveals that the ...