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Full-Text Articles in Physics

Optical Absorption Properties Of Ge2–44 And P-Doped Ge Nanoparticles, Wei Qin, Wen-Cai Lu, Li-Zhen Zhao, Kai-Ming Ho, Cai-Zhuang Wang Dec 2017

Optical Absorption Properties Of Ge2–44 And P-Doped Ge Nanoparticles, Wei Qin, Wen-Cai Lu, Li-Zhen Zhao, Kai-Ming Ho, Cai-Zhuang Wang

Ames Laboratory Accepted Manuscripts

The optical absorption properties of non-crystalline and crystalline Ge nanoparticles with the sizes from ∼2.5 to 15 Å have been studied at the B3LYP/6-31G level using time-dependent density functional theory. Hydrogen passivation and phosphorus doping on some selected Ge nanoparticles were also calculated. With the increase of cluster size, the optical absorption spectra of the non-crystalline Ge nanoparticles change from many peaks to a continuous broad band and at the same time exhibit a systematic red-shift. Doping phosphorus also causes the absorption spectra to shift toward the lower energy region for both non-crystalline and crystalline Ge nanoparticles. The ...


High-Speed 3d Shape Measurement With Fiber Interference, Beiwen Li, Pan Ou, Song Zhang Aug 2014

High-Speed 3d Shape Measurement With Fiber Interference, Beiwen Li, Pan Ou, Song Zhang

Mechanical Engineering Conference Presentations, Papers, and Proceedings

This paper presents a miniaturized fringe projection system that only uses two fibers to potentially achieve superfast (e.g., MHz to GHz) 3D shape measurement speeds. The proposed method uses two optical fibers that carry the same wavelength of laser light with polarization and phase information properly modulated to generate high-quality sinusoidal fringe patterns through interference. The high-speed phase shifting is achieved by employing a high-speed Lithium Niobate (LN) electrooptic phase modulator. Since only two optical fibers are used to generate sinusoidal patterns, the system has a great potential of miniaturization for applications where the sensor size is critical (e ...


Metal-Nanowall Grating Transparent Electrodes: Achieving High Optical Transmittance At High Incident Angles With Minimal Diffraction, Ping Kuang, Joong Mok Park, Geyuan Liu, Zhuo Ye, Wai Y. Leung, Sumit Chaudhary, David W. Lynch, Kai-Ming Ho, Kristen P. Constant Jan 2013

Metal-Nanowall Grating Transparent Electrodes: Achieving High Optical Transmittance At High Incident Angles With Minimal Diffraction, Ping Kuang, Joong Mok Park, Geyuan Liu, Zhuo Ye, Wai Y. Leung, Sumit Chaudhary, David W. Lynch, Kai-Ming Ho, Kristen P. Constant

Materials Science and Engineering Publications

A novel architecture has been employed to fabricate transparent electrodes with high conductivity and high optical transmittance at high incident angles. Soft lithography is used to fabricate polymer grating patterns onto which thin metallic films are deposited. Etching removes excess metal leaving tall walls of metal. Polymer encapsulation of the structure both protects the metal and minimizes diffraction. Transmission is dependent upon the height of the walls and encapsulation and varies from 60% to 80% for structures with heights of 1400 nm to 300 nm. In encapsulated structures, very little distortion is visible (either parallel to or perpendicular to standing ...


Photonic Crystal: Energy-Related Applications, Zhuo Ye, Joong Mok Park, Kristen P. Constant, Tae Guen Kim, Kai-Ming Ho Jun 2012

Photonic Crystal: Energy-Related Applications, Zhuo Ye, Joong Mok Park, Kristen P. Constant, Tae Guen Kim, Kai-Ming Ho

Materials Science and Engineering Publications

We review recent work on photonic-crystal fabrication using soft-lithography techniques. We consider applications of the resulting structures in energy-related areas such as lighting and solar-energy harvesting. In general, our aim is to introduce the reader to the concepts of photonic crystals, describe their history, development, and fabrication techniques and discuss a selection of energy-related applications.


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.


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.


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 ...


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.


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.


Diffracted Moiré Fringes As Analysis And Alignment Tools For Multilayer Fabrication In Soft Lithography, Jae-Hwang Lee, Chang-Hwan Kim, Yong-Sung Kim, Kai-Ming Ho, Kristen P. Constant, Wai Y. Leung, Cha-Hwan Oh Jan 2005

Diffracted Moiré Fringes As Analysis And Alignment Tools For Multilayer Fabrication In Soft Lithography, Jae-Hwang Lee, Chang-Hwan Kim, Yong-Sung Kim, Kai-Ming Ho, Kristen P. Constant, Wai Y. Leung, Cha-Hwan Oh

Materials Science and Engineering Publications

We studied the first-order diffractedmoiré fringes of transparent multilayered structures comprised of irregularly deformed periodic patterns. By a comparison study of the diffractedmoiré fringe pattern and detailed microscopy of the structure, we show that the diffractedmoiré fringe can be used as a nondestructive tool to analyze the alignment of multilayered structures. We demonstrate the alignment method for the case of layer-by-layer microstructures using soft lithography. The alignment method yields high contrast of fringes even when the materials being aligned have very weak contrasts. The imaging method of diffractedmoiré fringes is a versatile visual tool for the microfabrication of transparent deformable ...


Fabrication Of Photonic Band Gap Crystal Using Microtransfer Molded Templates, Wai Y. Leung, Henry Kang, Kristen P. Constant, D. Cann, Chang-Hwan Kim, Rana Biswas, M. M. Sigalas, Kai-Ming Ho Jan 2003

Fabrication Of Photonic Band Gap Crystal Using Microtransfer Molded Templates, Wai Y. Leung, Henry Kang, Kristen P. Constant, D. Cann, Chang-Hwan Kim, Rana Biswas, M. M. Sigalas, Kai-Ming Ho

Materials Science and Engineering Publications

We have proposed and demonstrated an economical technique to fabricate a three-dimensional layer-by-layer photonic band gapstructure in the infrared wavelengths. An organic polymer template structure, an inverse layer-by-layer photonic crystalstructure, is assembled using the microtransfer molding technique. This template is infiltrated with sol-gel or nanoparticle titanium oxide slurry, then later removed by heat treatment at a temperature range of 550–800 °C. This method can be extended to fabricatephotonic crystals operating at optical and ultraviolet frequencies.


Structural Characterization Of Thin Film Photonic Crystals, G. Subramania, Rana Biswas, Kristen P. Constant, M. M. Sigalas, Kai-Ming Ho May 2001

Structural Characterization Of Thin Film Photonic Crystals, G. Subramania, Rana Biswas, Kristen P. Constant, M. M. Sigalas, Kai-Ming Ho

Materials Science and Engineering Publications

We quantitatively analyze the structure of thin film inverse-opal photonic crystals composed of ordered arrays of air pores in a background of titania. Ordering of the sphere template and introduction of the titania background were performed simultaneously in the thin film photonic crystals. Nondestructive optical measurements of backfilling with high refractive index liquids, angle-resolved reflectivity, and optical spectroscopy were combined with band-structure calculations. The analysis reveals a thin film photonic crystal structure with a very high filling fraction (92–94 %) of air and a substantial compression along the c axis (∼22–25%).


Optical Photonic Crystals Fabricated From Colloidal Systems, G. Subramania, Kristen P. Constant, Rana Biswas, M. M. Sigalas, Kai-Ming Ho Jun 1999

Optical Photonic Crystals Fabricated From Colloidal Systems, G. Subramania, Kristen P. Constant, Rana Biswas, M. M. Sigalas, Kai-Ming Ho

Materials Science and Engineering Publications

Photonic crystals of close-packed arrays of air spheres in a dielectric background of titania have been fabricated with a ceramic technique. Unlike previous methods, ordering of the spheres and the formation of the titania network are performed simultaneously. The photonic crystals exhibit a reflectance peak and a uniform color at the position of the first stop band. The wavelength of the reflectance peak scales very well with the sphere size.


Electromodulation Spectroscopy Of Excitons In Simple Cubic Tlcl And Tlbr, John Frederick Mcclelland, David W. Lynch Mar 1979

Electromodulation Spectroscopy Of Excitons In Simple Cubic Tlcl And Tlbr, John Frederick Mcclelland, David W. Lynch

Physics and Astronomy Publications

Transmission and electromodulated transmission spectra have been measured in the direct Wannier exciton region for TlCl and TlBr. The spectra were obtained at a sample temperature between 5 and 6 K for a range of applíed electric fields. The data have been reduced to obtain the electric-field-induced changes in the dielectric function and compared in detail to the calculations of Blossey. The experimental results support the trends predicted by the calculations.


Piezoreflectance Of Dilute Α-Phase Ag-In Alloys, Charles E. Morris, David W. Lynch Jun 1969

Piezoreflectance Of Dilute Α-Phase Ag-In Alloys, Charles E. Morris, David W. Lynch

Physics and Astronomy Publications

The fractional change in reflectivity due to strain ΔRR of evaporated film samples of four silver-indium alloys was measured in the energy range 2.5-4.5 eV. The films had indium concentrations of 0.4, 1.6, 3.3, and 5.0 at.%. A Kramers-Kronig inversion of ΔRR yielded the change, due to strain, of the phase shift of the reflected electric field. The strain-induced changes of the real and imaginary parts of the complex dielectric constant, Δε1 and Δε2, were calculated. Interpretation of the structure in Δε2 of silver and the four alloys yielded the following conclusions. (a) The ...


Optical Properties Of Agcl, Agbr, T1c1, And T1br Under Hydrostatic Pressure, A. D. Brothers, David W. Lynch Apr 1969

Optical Properties Of Agcl, Agbr, T1c1, And T1br Under Hydrostatic Pressure, A. D. Brothers, David W. Lynch

Physics and Astronomy Publications

The pressure shifts of the optical absorption edges in four thallium and silver halides at 10°K were determined to be, in units of 10−6 eV/atm, -1.5 (AgCl), -1.9 (AgBr), -18 (TlCl), and -16 (TlBr). The pressure shifts of the first exciton peaks in thin evaporated films of these salts were measured at 80°K. In the same units these are 6.2 (AgCl), 6.4 and 5.6 (AgBr doublet), -13.9 (TlCl), and -13.4 (TlBr). The similarity of the pressure coefficients of the absorption edge in the two silver halides is evidence that ...


Optical Properties Of Dilute Ag-In Alloys, R. M. Morgan, David W. Lynch Aug 1968

Optical Properties Of Dilute Ag-In Alloys, R. M. Morgan, David W. Lynch

Physics and Astronomy Publications

The optical constants of silver and five dilute silver-indium alloys (<5% In) were determined from reflectance and transmittance measurements in the spectral region between 3.35 and 4.28 eV on vacuum-evaporated films. The data are consistent with the assumption that the onset of interband absorption in silver arises primarily from direct interband transitions from the d band near L3 to the Fermi surface, but with a small, though not insignificant, contribution due to direct transitions from the conduction band near L2′ to the conduction band near L1. The changes in the complex dielectric constant induced by alloying were interpreted to indicate a shift of the L3→EF transition to higher energy and a shift of the L2′→L1 transition to lower energy. Because contributions to the dielectric constant of the two transitions overlap and because of the limited energy range investigated, no firm estimates of the magnitudes of the shifts could be made, but it seems clear that the L2′−L1 energy gap decreases as indium is added to silver. The strength of the interband absorption in the alloys at energies below that of the edge in silver appeared to be too strong to be accounted for by indirect transitions. Alloying-induced changes in the energy-loss function showed that the relatively undamped plasma resonance in silver near 3.8 eV becomes strongly damped as indium is added. The increase in damping was attributed partly to a decrease in the conduction-electron relaxation time, and partly to the shift of interband transitions so that they occur at the plasma energy. Data from measurements on films cooled to liquid-helium temperature showed some sharpening of structure in the complex dielectric constant and of the peak in the loss function.


Infrared Absorption In Mg2ge, L. A. Lott, David W. Lynch Jan 1966

Infrared Absorption In Mg2ge, L. A. Lott, David W. Lynch

Physics and Astronomy Publications

Optical-absorption measurements on n- and p-type Mg2Ge single crystals were made at wavelengths between 1.5 and 25 μ at temperatures between 4.2 and 300°K. The absorption edge in p-type crystals arises from allowed indirect transitions. The energy gap is 0.570 eV at 0°K and the phonon involved has an energy of 0.025 eV. At higher temperatures the temperature dependence of the energy gap is -1.8×10−4 eV/deg. At longer wavelengths p-type crystals exhibit absorption bands interpreted as being caused by transitions between three valence bands at the center of the Brillouin ...


Infrared Reflectivities Of Magnesium Silicide, Germanide, And Stannide, D. Mcwilliams, David W. Lynch Jun 1963

Infrared Reflectivities Of Magnesium Silicide, Germanide, And Stannide, D. Mcwilliams, David W. Lynch

Physics and Astronomy Publications

The room-temperature reflection spectra of Mg2Si, Mg2Ge, and Mg2Sn have been measured at wave-lengths between 20 and 50μ. Reststrahl reflectivity peaks were observed at 36 and 45 μ for Mg2Si and Mg2Ge, respectively, and a rising reflectivity in Mg2Sn is estimated to peak at about 54 μ. The occurrence of peaks indicates that these compounds are partly ionic. The reflection spectra are more like those of the alkali halides than those of the III-V semiconducting compounds. If a simple damped harmonic oscillator is used to describe the reststrahl mode, the three Mg compounds have the same force constant for this ...


Color Centers In Additively Colored Csbr, David W. Lynch Sep 1962

Color Centers In Additively Colored Csbr, David W. Lynch

Physics and Astronomy Publications

Color centers have been studied in CsBr single crystals additively colored with potassium or cesium. More than ten absorption bands were produced, most of which had previously been found in crystals colored by ionizing radiation. All bands produced by irradiation at or above liquid nitrogen temperature appear to arise from trapped electrons. The most prominent bands in the additively colored crystals are the F band at 642 mμ (liquid nitrogen temperature) and a band at 243 mμ which appears to be due to an impurity. Optically bleaching the F band at 200°K produces bands analogous to the M and ...