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Room temperature observation of quantum jumps of single molecule into dark states

Description: Fluctuations in the room temperature emission rate from single dye molecules which are excited with the near field scanning optical microscope reveal long (seconds) and short ({approximately} milliseconds) lived dark states.
Date: November 1, 1995
Creator: Ha, T.; Enderle, T.; Ogletree, D.F.; Selvin, P.R.; Weiss, S. & Chemla, D.S.
Partner: UNT Libraries Government Documents Department

Nonlinear optical studies of surfaces

Description: The possibly of using nonlinear optical processes for surface studies has attracted increasing attention in recent years. Optical second harmonic generation (SHG) and sum frequency generation (SFG), in particular, have been well accepted as viable surface probes. They have many advantages over the conventional techniques. By nature, they are highly surface-specific and has a submonolayer sensitivity. As coherent optical processes, they are capable of in-situ probing of surfaces in hostile environment as well as applicable to all interfaces accessible by light. With ultrafast pump laser pulses, they can be employed to study surface dynamic processes with a subpicosecond time resolution. These advantages have opened the door to many exciting research opportunities in surface science and technology. This paper gives a brief overview of this fast-growing new area of research. Optical SHG from a surface was first studied theoretically and experimentally in the sixties. Even the submonolayer surface sensitivity of the process was noticed fairly early. The success was, however, limited because of difficulties in controlling the experimental conditions. It was not until the early 1980`s that the potential of the process for surface analysis was duly recognized. The first surface study by SHG was actually motivated by the then active search for an understanding of the intriguing surface enhanced Raman scattering (SERS). It had been suspected that the enhancement in SERS mainly came from the local-field enhancement due to local plasmon resonances and pointing rod effect on rough metal surfaces. In our view, Raman scattering is a two-photon process and is therefore a nonlinear optical effect.
Date: July 1, 1994
Creator: Shen, Y.R.
Partner: UNT Libraries Government Documents Department

Near-Field Spectroscopy of Selectively Oxidized Vertical Cavity Surface Emitting Lasers

Description: Selectively oxidized vertical cavity surface emitting lasers (VCSELS) have been studied by spectrally resolved near field scanning optical microscopy (NSOM). We have obtained spatially and spectrally resolved images of both subthreshold emission and lasing emission from a selectively oxidized VCSEL operating at a wavelength of 850 nm. Below threshold, highly local high gain regions, emitting local intensity maxima within the active area, were observed; these were found to serve as lasing centers just above threshold. Above threshold, the near field spatial modal distributions of low order transverse modes were identified by spectrally analyzing the emission; these were found to be complex and significantly different from those measured in the far field.
Date: December 9, 1999
Partner: UNT Libraries Government Documents Department

Lithographic measurement of EUV flare in the 0.3-NA Micro ExposureTool optic at the Advanced Light Source

Description: The level of flare present in a 0.3-NA EUV optic (the MET optic) at the Advanced Light Source at Lawrence Berkeley National Laboratory is measured using a lithographic method. Photoresist behavior at high exposure doses makes analysis difficult. Flare measurement analysis under scanning electron microscopy (SEM) and optical microscopy is compared, and optical microscopy is found to be a more reliable technique. In addition, the measured results are compared with predictions based on surface roughness measurement of the MET optical elements. When the fields in the exposure matrix are spaced far enough apart to avoid influence from surrounding fields and the data is corrected for imperfect mask contrast and aerial image proximity effects, the results match predicted values quite well. The amount of flare present in this optic ranges from 4.7% for 2 {micro}m features to 6.8% for 500 nm features.
Date: January 1, 2005
Creator: Cain, Jason P.; Naulleau, Patrick & Spanos, Costas J.
Partner: UNT Libraries Government Documents Department

Microstructural Characterization of Nodular Ductile Iron

Description: The objective of this study is to quantify the graphite particle phase in nodular ductile iron (NDI). This study provides the basis for initializing microstructure in direct numerical simulations, as part of developing microstructure-fracture response models. The work presented here is a subset of a PhD dissertation on spall fracture in NDI. NDI is an ideal material for studying the influence of microstructure on ductile fracture because it contains a readily identifiable second-phase particle population, embedded in a ductile metallic matrix, which serves as primary void nucleation sites. Nucleated voids grow and coalesce under continued tensile loading, as part of the micromechanisms of ductile fracture, and lead to macroscopic failure. For this study, we used 2D optical microscopy and quantitative metallography relationships to characterize the volume fraction, size distribution, nearest-neighbor distance, and other higher-order metrics of the graphite particle phase. We found that the volume fraction was {Phi} = 0.115, the average particle diameter was d{sub avg} = 25.9 {mu}m, the Weibull shape and scaling parameters were {beta} = 1.8 and {eta} = 29.1 {mu}m, respectively, the (first) nearest neighbor distance was L{sub nn} = 32.4 {mu}m, the exponential coefficients for volume fraction fluctuations was A{sub {Phi}} = 1.89 and B{sub {Phi}} = -0.59, respectively. Based on reaching a coefficient-of-variation (COV) of 0.01, the representative volume element (RVE) size was determined to be 8.9L{sub nn} (288 {mu}m).
Date: January 3, 2012
Creator: Springer, H. K.
Partner: UNT Libraries Government Documents Department

MRF Applications: Measurement of Process-dependent Subsurface Damage in Optical Materials using the MRF Wedge Technique

Description: Understanding the behavior of fractures and subsurface damage in the processes used during optic fabrication plays a key role in determining the final quality of the optical surface finish. During the early stages of surface preparation, brittle grinding processes induce fractures at or near an optical surface whose range can extend from depths of a few mm to hundreds of mm depending upon the process and tooling being employed. Controlling the occurrence, structure, and propagation of these sites during subsequent grinding and polishing operations is highly desirable if one wishes to obtain high-quality surfaces that are free of such artifacts. Over the past year, our team has made significant strides in developing a diagnostic technique that combines magnetorheological finishing (MRF) and scanning optical microscopy to measure and characterize subsurface damage in optical materials. The technique takes advantage of the unique nature of MRF to polish a prescribed large-area wedge into the optical surface without propagating existing damage or introducing new damage. The polished wedge is then analyzed to quantify subsurface damage as a function of depth from the original surface. Large-area measurement using scanning optical microscopy provides for improved accuracy and reliability over methods such as the COM ball-dimple technique. Examples of the technique's use will be presented that illustrate the behavior of subsurface damage in fused silica that arises during a variety of intermediate optical fabrication process steps.
Date: November 2, 2005
Creator: Menapace, J A; Davis, P J; Steele, W A; Wong, L L; Suratwala, T I & Miller, P E
Partner: UNT Libraries Government Documents Department

Surface Energy Anisotropy Effects on Pore-Channel Stability:Rayleigh Instabilities in m-Plane Sapphire

Description: Internal, high-aspect-ratio pore channels with their long axes parallel to the m(10{bar 1}0) plane of sapphire were generated through sequential application of photolithography, ion-beam etching and solid-state diffusion bonding. The axial orientation of channels within the m plane was systematically varied to sample a range of bounding-surface crystallographies. The morphologic evolution of these pore channels during anneals at 1700 C was recorded by postanneal optical microscopy. The development and growth of periodic axial variations in the pore channel radius was observed, and ultimately led to the formation of discrete pores. The wavelength and average pore spacing, assumed to reflect the kinetically dominant perturbation wavelength, varied with the in-plane pore channel orientation, as did the time for complete channel breakup. Results are compared to those previously obtained when pore channels were etched into c(0001)-plane sapphire and annealed under similar conditions. The results indicate a strong effect of surface stability on the evolution behavior.
Date: September 7, 2005
Creator: Santala, Melissa K. & Glaeser, Andreas M.
Partner: UNT Libraries Government Documents Department

An image cancellation approach to depth-from-focus

Description: Depth calculation of an object allows computer reconstruction of the surface of the object in three dimensions. Such information provides human operators 3D measurements for visualization, diagnostic and manipulation. It can also provide the necessary coordinates for semi or fully automated operations. This paper describes a microscopic imaging system with computer vision algorithms that can obtain the depth information by making use of the shallow depth of field of microscopic lenses.
Date: March 1, 1995
Creator: Lu, Shin-yee & Graser, M.
Partner: UNT Libraries Government Documents Department

Testing of optical components to assure performance in a high acerage power environment

Description: Evaluation and testing of the optical components used in the Atomic Vapor Laser Isotope Separation (AVLIS) plant is critical for qualification of suppliers, development of new optical multilayer designs and monufacturing processes, and assurance of performance in the production cycle. The range of specifications requires development of specialized test equipment and methods which are not routine or readily available in industry. Specifications are given on material characteristics such as index homogeneity, subsurface damage left after polishing, microscopic surface defects and contamination, coating absorption, and high average power laser damage. The approach to testing these performance characteristics and assuring the quality throughout the production cycle is described.
Date: June 24, 1997
Creator: Chow, R.; Taylor, J.R.; Eickelberg, W.K. & Primdahl, K.A.
Partner: UNT Libraries Government Documents Department

Defect study in fused silica using near field scanning optical microscopy

Description: Surface defects in fused silica have been characterized using Near Field Scanning Optical Microscopy (NSOM). Using total internal reflection of a p- or s- polarized laser beam, optical scattering from defects located on the surface itself as well as in the subsurface layer of polished fused silica has been measured by NSOM. The local scattering intensity has been compared with simultaneously measured surface topography. In addition, surface defects intentionally created on a fused silica surface by nano-indentation have been used to establish a correlation between optical scattering of s- and p- polarized light, surface morphology and the well known subsurface stress-field associated with nano-indentation.
Date: January 21, 1998
Creator: Yan, M.; Wang, L.; Siekhaus, W.; Kozlowski, M.; Yang, J. & Mohideen, U.
Partner: UNT Libraries Government Documents Department

Application of total internal reflection microscopy for laser damage studies on fused silica

Description: Damage studies show that the majority of damage on ultraviolet grade fused silica initiates at the front or rear surface. The grinding and polishing processes used to produce the optical surfaces of transparent optics play a key role in the development of defects which can ultimately initiate damage. These defects can be on or breaking through the surface or can be sub-surface damage. Total Internal Reflection Microscopy has been documented as a tool for revealing both sub-surface and surface defects in transparent materials. Images taken which compare both Total Internal Reflection Microscopy and Atomic Force Microscopy show that the observed defects can be less than one micron in size. Total Internal Reflection Microscopy has the added benefit of being able to observe large areas (1 square millimeter) with sub-micron detection. Both off-line and in-situ systems have been applied in the Lawrence Livermore National Laboratory`s damage laboratory in order to understand defects in the surface and subsurface of polished fused silica. There is a preliminary indication that TIRM quality can be related to the damage resistance. The in-situ microscope is coupled into a 355 run, 7.5 ns, 10 Hz Nd:YAG laser system in order to study damage occurring at localized scatter sites revealed with the Total Internal Reflection Microscopy method. The tests indicate damage initiating at observed artifacts which have many different morphologies and damage behaviors. Some of the scatter sites and damage morphologies revealed have been related back to the finishing process.
Date: December 1997
Creator: Sheehan, L. M.
Partner: UNT Libraries Government Documents Department

Interface Characterization Techniques for 304L Stainless Steel Resistance Upset Welds

Description: In an effort to better characterize and classify austenitic stainless steel resistance upset welds, standard methods have been examined and alternative methods investigated. Optical microscopy yields subjective classification due to deformation obscured bond lines and individual perception. The use of specimen preparations that better reveal grain boundaries aids in substantiating optical information. Electron microscopy techniques produce quantitative information in relation to microstructural constituents. Orientation Imaging Microscopy (OIM) is a relatively new technique for obtaining objective, quantitative information pertaining to weld integrity, i.e., percent grain boundary growth across the interface.
Date: July 26, 1998
Creator: Abeln, T.G.; Kackenko, E.J.; Necker, C.T. & Field, R.D.
Partner: UNT Libraries Government Documents Department

LDRD final report backside localization of open and shorted IC interconnections LDRD Project (FY98 and FY 99)

Description: Two new failure analysis techniques have been developed for backside and front side localization of open and shorted interconnections on ICs. These scanning optical microscopy techniques take advantage of the interactions between IC defects and localized heating using a focused infrared laser ({lambda} = 1,340 nm). Images are produced by monitoring the voltage changes across a constant current supply used to power the IC as the laser beam is scanned across the sample. The methods utilize the Seebeck Effect to localize open interconnections and Thermally-Induced Voltage Alteration (TIVA) to detect shorts. Initial investigations demonstrated the feasibility of TIVA and Seebeck Effect Imaging (SEI). Subsequent improvements have greatly increased the sensitivity of the TIVA/SEI system, reducing the acquisition times by more than 20X and localizing previously unobserved defects. The interaction physics describing the signal generation process and several examples demonstrating the localization of opens and shorts are described. Operational guidelines and limitations are also discussed. The system improvements, non-linear response of IC defects to heating, modeling of laser heating and examples using the improved system for failure analysis are presented.
Date: January 1, 2000
Creator: Cole, E.I. Jr.; Tangyunyong, P.; Benson, D.A. & Barton, D.L.
Partner: UNT Libraries Government Documents Department

Nonlinear optical microscopy for imaging thin films and surfaces

Description: We have used the inherent surface sensitivity of second harmonic generation to develop an instrument for nonlinear optical microscopy of surfaces and interfaces. We have demonstrated the use of several nonlinear optical responses for imaging thin films. The second harmonic response of a thin film of C{sub 60} has been used to image patterned films. Two photon absorption light induced fluorescence has been used to image patterned thin films of Rhodamine 6G. Applications of nonlinear optical microscopy include the imaging of charge injection and photoinduced charge transfer between layers in semiconductor heterojunction devices as well as across membranes in biological systems.
Date: March 1, 1995
Creator: Smilowitz, L.B.; McBranch, D.W. & Robinson, J.M.
Partner: UNT Libraries Government Documents Department

Investigations of Localized Corrosion of Stainless Steel after Exposure to Supercritical CO2

Description: Severe localized corrosion of a 316 stainless steel autoclave occurred during investigating Type H Portland cement stability in 0.16 M CaCl{sub 2} + 0.02 M MgCl{sub 2} + 0.82 M NaCl brine in contact with supercritical CO{sub 2} containing 4% O{sub 2}. The system operated at 85 C and pressure of 29 MPa. However, no corrosion was observed in the same type of autoclave being exposed to the same environment, containing Type H Portland cement cylindrical samples, also operating at pressure of 29 MPa but at 50 C. The operation time for the 85 C autoclave was 53 days (1272 hours) while that for the 50 C autoclave was 66 days (1584 hours). Debris were collected from the base of both autoclaves and analyzed by X-ray diffraction (XRD). Corrosion products were only found in the debris from the 85 C autoclave. The cement samples were analyzed before and after the exposure by X-ray florescence (XRF) methods. Optical microscopy was used to estimate an extent of the 316 stainless steel corrosion degradation.
Date: March 11, 2012
Creator: Ziomek-Moroz, M.; O’Connor, W. & Bullard, S.
Partner: UNT Libraries Government Documents Department

Processing of alumina-niobium interfaces via liquid-film-assistedjoining

Description: Alumina-niobium interfaces were fabricated at 1400 C via solid-state diffusion brazing of a 127-{micro}m-thick niobium foil between alumina blocks. Prior to brazing, some of the alumina mating surfaces, both polished and unpolished, were evaporation-coated with copper films {approx}1.4 {micro}m, {approx}3.0 {micro}m, and {approx}5.5 {micro}m thick to induce liquid-film-assisted joining at the brazing temperature. The effects of copper film thickness and surface roughness on fracture characteristics and ceramic-metal interfacial microstructure were investigated by room-temperature four-point bend tests, optical microscopy, profilometry, and atomic force microscopy. The average strength of bonds between niobium and polished alumina substrates increased with the introduction of copper film interlayers, and the scatter in strength tended to decrease, with an optimum combination of strength and Weibull modulus arising for a copper film thickness of 3.0 {micro}m. The strength characteristics of niobium bonded to unpolished alumina substrates were also improved by liquid-film-assisted joining, but were unaffected by the thickness of the copper interlayers.
Date: February 15, 2005
Creator: McKeown, Joseph T.; Sugar, Joshua D.; Gronsky, Ronald & Glaeser,Andreas M.
Partner: UNT Libraries Government Documents Department

Effects of Impurities on Alumina-Niobium InterfacialMicrostructures

Description: Optical microscopy, scanning electron microscopy, and transmission electron microscopy were employed to examine the interfacial microstructural effects of impurities in alumina substrates used to fabricate alumina-niobium interfaces via liquid-film-assisted joining. Three types of alumina were used: undoped high-purity single-crystal sapphire; a high-purity, high-strength polycrystalline alumina; and a lower-purity, lower-strength polycrystalline alumina. Interfaces formed between niobium and both the sapphire and high-purity polycrystalline alumina were free of detectable levels of impurities. In the lower-purity alumina, niobium silicides were observed at the alumina-niobium interface and on alumina grain boundaries near the interface. These silicides formed in small-grained regions of the alumina and were found to grow from the interface into the alumina along grain boundaries. Smaller silicide precipitates found on grain boundaries are believed to form upon cooling from the bonding temperature.
Date: June 20, 2005
Creator: McKeown, Joseph T.; Sugar, Joshua D.; Gronsky, Ronald & Glaeser,Andreas M.
Partner: UNT Libraries Government Documents Department

Defect reduction in (11-20) a-plane GaN by two step epitaxiallateral overgrowth

Description: We report a two-step growth method to obtain uniformly coalesced epitaxial lateral overgrown a-plane GaN by metal-organic chemical vapor deposition (MOCVD). By obtaining a large wing height to width aspect ratio in the first step followed by enhanced lateral growth in the second step via controlling the growth temperature, we reduced the tilt angle between the advancing Ga-polar and N-polar wings for improved properties. Transmission electron microscopy (TEM) showed that the threading dislocation density in the wing area was 1.0 x 10{sup 8}cm{sup -2}, more than two orders of magnitude lower than that in the window area (4.2 x 10{sup 10} cm{sup -2}). However, a high density of basal stacking faults, 1.2 x 10{sup 4} cm{sup -1}, was still observed in the wing area. Near field scanning optical microscopy (NSOM) at room temperature revealed that the luminescence was mainly from the wing regions with very little contribution from the windows and meeting fronts. These observations suggest that due to significant reduction of threading dislocations radiative recombination is enhanced in the wings.
Date: November 25, 2006
Creator: Ni, X.; Ozgur, U.; Fu, Y.; Biyikii, N.; Morkoc, H. & Liliental-Weber, Z.
Partner: UNT Libraries Government Documents Department

Polishing procedure and surface characterization lead tungstate crystal scintillator Road No. 723 and No. 754

Description: Step by step procedures are given for polishing the scintillator rods. A Strasbaugh spindle polishing machine was used along with visual inspection and hand polishing. Extensive data is given on pre-polish surface characterization, profilometry, microphotography, and interferometry.
Date: May 1, 1996
Creator: Kellam, M
Partner: UNT Libraries Government Documents Department

Microscopical examination of plastic-bonded explosives

Description: Polarized Light Microscopy is a powerful technique for the identification of powdered explosives. The authors apply the technique here to the characterization in bulk of composite, plastic-bonded explosives, typically consisting of 95 w/o explosive particulate and 5 w/o polymeric binder. Mounting and polishing techniques are described, along with attendant issues of mount dyeing and some complications of cleaning very soft samples. The microstructures of PBX 9501 (based on cyclotetramethylene tetranitramine, or HMX), PBX 9502 (based on triaminotrinitrobenzene or TATB), and X-0535 (based on diaminotetrazine dioxide, or TZX) are compared and contrasted. Selected case studies are presented in which development of prominent structural characteristics, such as particle size and crack density, are tracked from the starting powders through formulation and pressing to serviceable, formed articles.
Date: October 1, 1997
Creator: Skidmore, C.B.; Phillips, D.S. & Crane, N.B.
Partner: UNT Libraries Government Documents Department

First Observation of Mechanochromism at the Nanometer Scale

Description: A mechanically-induced color transition (''mechanochromism'') in polydiacetylene thin films has been generated at the nanometer scale using the tips of two different scanning probe microscopes. A blue-to-red chromatic transition in polydiacetylene molecular trilayer films, polymerized from 10,12-pentacosadiynoic acid (poly-PCDA), was found to result from shear forces acting between the tip and the poly-PCDA molecules, as independently observed with near-field scanning optical microscopy and atomic force microscopy (AFM). Red domains were identified by a fluorescence emission signature. Transformed regions as small as 30 nm in width were observed with AFM. The irreversibly transformed domains preferentially grow along the polymer backbone direction. Significant rearrangement of poly-PCDA bilayer segments is observed by AFM in transformed regions. The removal of these segments appears to be a characteristic feature of the transition. To our knowledge, this is the first observation of nanometer-scale mechanochromism in any material.
Date: July 7, 1999
Creator: Carpick, R.W.; Sasaki, D.Y. & Burns, A.R.
Partner: UNT Libraries Government Documents Department


Description: Brookhaven National Laboratory (BNL) investigated the causes of weldability problems and materials failures encountered with the application of Monel (Ni-Cu) 400 as a base material and Stellite 6 (Co-Cr) as the hard-surfacing material when using the oxyacetylene welding process. This work was performed under a cooperative research and development agreement (CRADA) with the Target Rock Division of the Curtiss-Wright Flow Control Corporation. BNL evaluated two heats of Monel 400 material. One of the heats had performed well during manufacturing, producing an acceptable number of ''good'' parts. The second heat had produced some good parts but also exhibited a peculiar type of hardsurfacing/base metal collapse during the welding process. A review of the chemistry on the two heats of material indicated that they both met the chemical requirements for Monel400. During examination of the failed component, linear indications (cracks) were evident on the valve body, both on the circumferential area (top of valve body) and below the hard surfaced weld deposit. independent measurements also indicated that the two heats met the specification requirement for the material. The heat affected zone (HAZ) also contained linear discontinuities. The valve body was welded using the oxyacetylene welding process, a qualified and skilled welder, and had been given a pre-heat of between 1400-1600 F (760-871 C), which is the Target Rock qualified procedure requirement. Both original suppliers performed mechanical testing on their material that indicated the two heats also met the mechanical property requirements of the specification. The BNL investigation into the cause of the differences between these heats of material utilized the following techniques: (1) Heat Treatment of both heats of material; (2) Hardness testing; (3) Optical microscopy; (4) Scanning electron microscope (SEM)/Fractography; and (5) Energy dispersive spectroscopy (EDS). The report concludes that the cause of the failure of the valve body during welding ...
Date: December 1, 2001
Partner: UNT Libraries Government Documents Department

A Taguchi experimental design study of twin-wire electric arc sprayed aluminum coatings

Description: An experimental study was conducted on the twin-wire electric arc spraying of aluminum coatings. This aluminum wire system is being used to fabricate heater tubes that emulate nuclear fuel tubes for use in thermal-hydraulic experiments. Experiments were conducted using a Taguchi fractional-factorial design parametric study. Operating parameters were varied around the typical process parameters in a systematic design of experiments in order to display the range of processing conditions and their effect on the resultant coating. The coatings were characterized by hardness tests, optical metallography, and image analysis. The paper discusses coating qualities with respect to hardness, roughness, deposition efficiency, and microstructure. The study attempts to correlate the features of the coatings with the changes in operating parameters. A numerical model of the process is presented including gas, droplet, and coating dynamics.
Date: August 1, 1992
Creator: Steeper, T. J.; Varacalle, D. J. Jr.; Wilson, G. C.; Johnson, R. W.; Irons, G.; Kratochvil, W. R. et al.
Partner: UNT Libraries Government Documents Department