An Anticipatory Model of Cavitation (open access)

An Anticipatory Model of Cavitation

The Anticipatory System (AS) formalism developed by Robert Rosen provides some insight into the problem of embedding intelligent behavior in machines. AS emulates the anticipatory behavior of biological systems. AS bases its behavior on its expectations about the near future and those expectations are modified as the system gains experience. The expectation is based on an internal model that is drawn from an appeal to physical reality. To be adaptive, the model must be able to update itself. To be practical, the model must run faster than real-time. The need for a physical model and the requirement that the model execute at extreme speeds, has held back the application of AS to practical problems. Two recent advances make it possible to consider the use of AS for practical intelligent sensors. First, advances in transducer technology make it possible to obtain previously unavailable data from which a model can be derived. For example, acoustic emissions (AE) can be fed into a Bayesian system identifier that enables the separation of a weak characterizing signal, such as the signature of pump cavitation precursors, from a strong masking signal, such as a pump vibration feature. The second advance is the development of extremely fast, …
Date: April 5, 1999
Creator: Allgood, G. O.; Dress Jr., W. B.; Hylton, J. O. & Kercel, S. W.
Object Type: Article
System: The UNT Digital Library
Material characterization of the clay bonded silicon carbide candle filters and ash formations in the W-APF system after 500 hours of hot gas filtration at AEP. Appendix to Advanced Particle Filter: Technical progress report No. 11, January--March 1993 (open access)

Material characterization of the clay bonded silicon carbide candle filters and ash formations in the W-APF system after 500 hours of hot gas filtration at AEP. Appendix to Advanced Particle Filter: Technical progress report No. 11, January--March 1993

(1) After 500 hours of operation in the pressurized fluidized-bed combustion gas environment, the fibrous outer membrane along the clay bonded silicon carbide Schumacher Dia Schumalith candles remained intact. The fibrous outer membrane did not permit penetration of fines through the filter wall. (2) An approximate 10-15% loss of material strength occurred within the intact candle clay bonded silicon carbide matrix after 500 hours of exposure to the PFBC gas environment. A relatively uniform strength change resulted within the intact candles throughout the vessel (i.e., top to bottom plenums), as well as within the various cluster ring positions (i.e., outer versus inner ring candle filters). A somewhat higher loss of material strength, i.e., 25% was detected in fractured candle segments removed from the W-APF ash hopper. (3) Sulfur which is present in the pressurized fluidized-bed combustion gas system induced phase changes along the surface of the binder which coats the silicon carbide grains in the Schumacher Dia Schumalith candle filter matrix.
Date: April 5, 1993
Creator: Alvin, M. A.
Object Type: Report
System: The UNT Digital Library
Modal study of refractive effects on x-ray laser coherence (open access)

Modal study of refractive effects on x-ray laser coherence

The role of smoothly varying transverse gain and refraction profiles on x-ray laser intensity and coherence is analyzed by modally expanding the electric field within the paraxial approximation. Comparison with a square transverse profile reveals that smooth-edged profiles lead to: (1) a greatly reduced number of guided modes, (2) the continued cancellation of local intensity from a loosely guided mode by resonant free modes, (3) and the absence of extraneous (or anomalous) free mode resonances. These generic spectral properties should enable a considerable simplification in analyzing and optimizing the coherence properties of laboratory soft x-ray lasers. 6 refs., 3 figs.
Date: April 5, 1991
Creator: Amendt, P.; London, R.A. (Lawrence Livermore National Lab., CA (USA)) & Strauss, M. (Israel Atomic Energy Commission, Beersheba (Israel). Nuclear Research Center-Negev)
Object Type: Article
System: The UNT Digital Library
Feature, Event, and Process Screening and Scenario Development for the Yucca Mountain Total System Performance Assessment (open access)

Feature, Event, and Process Screening and Scenario Development for the Yucca Mountain Total System Performance Assessment

Scenario development has two primary purposes in the design and documentation of post-closure performance assessments in a regulatory setting. First, scenario development ensures a sufficiently comprehensive consideration of the possible future states of the system. Second, scenario development identifies the important scenarios that must be considered in quantitative analyses of the total system performance assessment (TSPA). Section 2.0 of this report describes the scenario development process. Steps in the process are described in Section 2.1, and terms introduced in this section are defined in Section 2.2. The electronic database used to document the process is described in Section 3, and Section 4 provides a summary of the current status of the YMP scenario development work. Section 5 contains acknowledgments, and Section 6 contains a list of the references cited.
Date: April 5, 1999
Creator: Barnard, R.; Barr, G.; Burch, P.; Freeze, G.; Rechard, R.; Schenker, A. et al.
Object Type: Article
System: The UNT Digital Library
Growth and Structure of Metallic Barrier Layer and Interconnect Films I: Experiments (open access)

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

We present experimented results directed at understanding the growth and structure of metallic barrier layer and interconnect films. Numerical simulation results associated with this experimental work are presented in an accompanying paper in these proceedings. Here, thin films of Al, Ti, Cu and Ta have been grown by magnetron sputtering onto oxidized Si substrates. Using a specially-constructed substrate holder, the orientation of the substrate with respect to the growth direction was varied from horizontal to vertical. Films were grown at both low and high argon pressure; in the case of Ta, the cathode power was varied as well. The film structure and in particular the surface roughness was measured by X-ray reflectance and also by atomic force microscopy. We find that the surface roughness increases markedly with orientation angle in the case of Ta and Cu films, and in Ti films grown at high argon pressure. At low pressure, however, the Ti film surface roughness remains constant for all substrate orientations. No variation in roughness with either orientation angle or argon pressure was observed in the Al films. These results suggest that, under certain circumstances, shadowing effects and/or grain orientation (i.e., texture) competition during growth can give rise to lower …
Date: April 5, 1999
Creator: Baumann, F.H.; Gilmer, G.H.; O'Sullivan, P.L.; Sapjeta, J.; Torre, J.D. & Windt, D.L.
Object Type: Article
System: The UNT Digital Library
Epitaxial Growth of Yb<sub>2</sub>O<sub>3</sub> Buffer Layers on Biaxially Textured-Ni (100) Substrates by Sol-Gel Process (open access)

Epitaxial Growth of Yb<sub>2</sub>O<sub>3</sub> Buffer Layers on Biaxially Textured-Ni (100) Substrates by Sol-Gel Process

In order to develop an alternative buffer layer architecture using the sol-gel process to produce YBCO (YBa2Cu307+) coated conductors, Yb203 has been chosen as the candidate material. Buffer layers of fi03 were epitaxkdly grown on biaxially textured-Ni (100) substrates by the sol gel process for the first time. The ~03 precursor solution was prepared from an alkoxide sol-gel route in 2-xnetho~ethanol and was deposited on textured-Ni (100) substrates by either spin coating or dip coating methods. The amorphous film was then processed at 1160oC under flowing (96%)MH2(4%) gas mixture for one hour. The fi03 iihn exhibited a strong c-axis orientation on the Ni (100) substrates. The phi and omega scans indicated good in plane and out of plane orientations. The X-ray (222) pde figure showed a cube-on-cube epitaxy. High current YBCO films were grown on the Y&03 sol-gel buffered-Ni substrates.
Date: April 5, 1999
Creator: Beach, D. B.; Chirayil, T. G.; Christen, D. K.; Feenstra, R.; Goyal, A.; Kroeger, D. M. et al.
Object Type: Article
System: The UNT Digital Library
Transformation as a Design Process and Runtime Architecture for High Integrity Software (open access)

Transformation as a Design Process and Runtime Architecture for High Integrity Software

We have discussed two aspects of creating high integrity software that greatly benefit from the availability of transformation technology, which in this case is manifest by the requirement for a sophisticated backtracking parser. First, because of the potential for correctly manipulating programs via small changes, an automated non-procedural transformation system can be a valuable tool for constructing high assurance software. Second, modeling the processing of translating data into information as a, perhaps, context-dependent grammar leads to an efficient, compact implementation. From a practical perspective, the transformation process should begin in the domain language in which a problem is initially expressed. Thus in order for a transformation system to be practical it must be flexible with respect to domain-specific languages. We have argued that transformation applied to specification results in a highly reliable system. We also attempted to briefly demonstrate that transformation technology applied to the runtime environment will result in a safe and secure system. We thus believe that the sophisticated multi-lookahead backtracking parsing technology is central to the task of being in a position to demonstrate the existence of HIS.
Date: April 5, 1999
Creator: Bespalko, Stephen J. & Winter, Victor L.
Object Type: Article
System: The UNT Digital Library
Closed-form approach to checking frame design (open access)

Closed-form approach to checking frame design

This brief report contains calculations of deflections and stresses of the support frame on the XMM project. The goal is to provide an independent view of structural integrity of the frame utilizing a noncomputer approach to design based on elementary closed form solutions and approximate models of mechanical and structural behavior. It is recognized that full confidence can only be assured when computer generated results pertaining to the critical areas and features of the integrating structure can be enveloped by the bracketing solutions. Although the computer solutions have come from the three independent sources, this report utilizes the numerical values from the LLNL studies represented by the computer runs and analysis of the critical elements of the frame. Since the frame geometry, deformation patterns, and the nature of loading are highly complex, this study is restricted to simplified models of selected areas of the structure which can be handled by the conventional formulas and reasonable approximations. This report contains some comments related to material properties, stress concentration, and elements of fracture mechanics directly applicable to frame analysis and design. Such topics and parameters fall usually outside the finite element modeling, but they can have a crucial influence on the mechanical …
Date: April 5, 1995
Creator: Blake, A.
Object Type: Report
System: The UNT Digital Library
Strain and Texture in Al-Interconnect Wires Measured by X-Ray Microbeam Diffraction (open access)

Strain and Texture in Al-Interconnect Wires Measured by X-Ray Microbeam Diffraction

The local strain and texture in Al interconnect wires have been investigated using white and monochromatic x-ray microbeams on the MHATTCAT undulator beam line at the Advanced Photon Source. Intergrain and intragrain orientations were obtained with ~0.01 degree sensitivity using white beam measurements on wide Al pads (~100 Mu-m) and thin (2 Mu-m) Al wires. Orientation changes of up to 1 degree were found within individual grains of the (111) textured Al interconnects. Deviatoric strain measurements indicate small intragranular strain variations, but intergranular strain variations were found to be quite large.
Date: April 5, 1999
Creator: Budai, J. D.; Chung, J.-S.; Ice, G. E.; Larson, B. C.; Lowe, W. P.; Tamura, N. et al.
Object Type: Article
System: The UNT Digital Library
MAGNETIZATION REVERSAL IN MELT-QUENCHED NdFeB. (open access)

MAGNETIZATION REVERSAL IN MELT-QUENCHED NdFeB.

Melt-quenched NdFeB is an important modern permanent magnet material. However there still remains doubt as to the magnetization reversal mechanism which controls coercivity in material prepared by this processing route. To investigate this problem a new technique based on measurements of reversible magnetization along recoil curves has been used. The technique identifies the presence of free domain walls during magnetic reversal. For this study samples of isotropic (MQI), hot pressed (MQII) and die upset (MQIII) melt-quenched NdFeB were examined. The results indicate that in MQI free domain walls are not present during reversal and the reversal mechanism is most likely incoherent rotation of some form. Free domain walls are also not present during reversal in the majority of grains of MQII, even though initial magnetization measurements indicate that the grain size is large enough to support them. In MQIII free domain walls are present during reversal. These results are attributed to the reduced domain wall nucleation field in MQIII compared with MQII and the increased dipolar interactions in MQIII.
Date: April 5, 1999
Creator: CREW,D.C.
Object Type: Article
System: The UNT Digital Library
Increasing Waterflood Reserves in the Wilmington Oil Field through Improved Reservoir Characterization and Reservoir Management (open access)

Increasing Waterflood Reserves in the Wilmington Oil Field through Improved Reservoir Characterization and Reservoir Management

This project used advanced reservoir characterization tools, including the pulsed acoustic cased-hole logging tool, geologic three-dimensional (3-D) modeling software, and commercially available reservoir management software to identify sands with remaining high oil saturation following waterflood. Production from the identified high oil saturated sands was stimulated by recompleting existing production and injection wells in these sands using conventional means as well as a short radius redrill candidate.
Date: April 5, 1999
Creator: Clarke, D.; Koerner, R.; D., Moos; Nguyen, J.; Phillips, C.; Tagbor, K. et al.
Object Type: Report
System: The UNT Digital Library
Laser Field Imaging Through Fourier Transform Heterodyne (open access)

Laser Field Imaging Through Fourier Transform Heterodyne

The authors present a detection process capable of directly imaging the transverse amplitude, phase, and Doppler shift of coherent electromagnetic fields. Based on coherent detection principles governing conventional heterodyned RADAR/LADAR systems, Fourier Transform Heterodyne incorporates transverse spatial encoding of the reference local oscillator for image capture. Appropriate selection of spatial encoding functions allows image retrieval by way of classic Fourier manipulations. Of practical interest: (1) imaging may be accomplished with a single element detector/sensor requiring no additional scanning or moving components, (2) as detection is governed by heterodyne principles, near quantum limited performance is achievable, (3) a wide variety of appropriate spatial encoding functions exist that may be adaptively configured in real-time for applications requiring optimal detection, and (4) the concept is general with the applicable electromagnetic spectrum encompassing the RF through optical.
Date: April 5, 1999
Creator: Cooke, Bradly J.; Laubscher, Bryan E.; Olivas, Nicholas L.; Galbraith, Amy E.; Strauss, Charlie E. & Grubler, Andrew C.
Object Type: Article
System: The UNT Digital Library
Analysis and System Design Framework for Infrared Spatial Heterodyne Spectrometers (open access)

Analysis and System Design Framework for Infrared Spatial Heterodyne Spectrometers

The authors present a preliminary analysis and design framework developed for the evaluation and optimization of infrared, Imaging Spatial Heterodyne Spectrometer (SHS) electro-optic systems. Commensurate with conventional interferometric spectrometers, SHS modeling requires an integrated analysis environment for rigorous evaluation of system error propagation due to detection process, detection noise, system motion, retrieval algorithm and calibration algorithm. The analysis tools provide for optimization of critical system parameters and components including : (1) optical aperture, f-number, and spectral transmission, (2) SHS interferometer grating and Littrow parameters, and (3) image plane requirements as well as cold shield, optical filtering, and focal-plane dimensions, pixel dimensions and quantum efficiency, (4) SHS spatial and temporal sampling parameters, and (5) retrieval and calibration algorithm issues.
Date: April 5, 1999
Creator: Cooke, Bradly J.; Smith, Barham W.; Laubscher, Bryan E.; Villeneuve, Pierre V. & Briles, Scott D.
Object Type: Article
System: The UNT Digital Library
Magnetization reversal in melt-quenched NdFeB (open access)

Magnetization reversal in melt-quenched NdFeB

Melt-quenched NdFeB is an important modern permanent magnet material. However, there still remains doubt as to the magnetization reversal mechanism which controls coercivity in material prepared by this processing route. To investigate this problem a new technique based on measurements of reversible magnetization along recoil curves has been used. The technique identifies the presence of free domain walls during magnetic reversal. For this study samples of isotropic (MQI), hot pressed (MQII) and die upset (MQIII) melt-quenched NdFeB were examined. The results indicate that in MQI free domain walls are not present during reversal and the reversal mechanism is most likely incoherent rotation of some form. Free domain walls are also not present during reversal in the majority of grains of MQII, even though initial magnetization measurements indicate that the grain size is large enough to support them. In MQIII free domain walls are present during reversal. These results are attributed to the reduced domain wall nucleation field in MQIII compared with MQII and the increased dipolar interactions in MQIII.
Date: April 5, 1999
Creator: Crew, D.C.
Object Type: Article
System: The UNT Digital Library
Chemical Detection Based on Adsorption-Induced and Photo-Induced Stresses in MEMS Devices (open access)

Chemical Detection Based on Adsorption-Induced and Photo-Induced Stresses in MEMS Devices

Recently there has been an increasing demand to perform real-time in-situ chemical detection of hazardous materials, contraband chemicals, and explosive chemicals. Currently, real-time chemical detection requires rather large analytical instrumentation that are expensive and complicated to use. The advent of inexpensive mass produced MEMS (micro-electromechanical systems) devices opened-up new possibilities for chemical detection. For example, microcantilevers were found to respond to chemical stimuli by undergoing changes in their bending and resonance frequency even when a small number of molecules adsorb on their surface. In our present studies, we extended this concept by studying changes in both the adsorption-induced stress and photo-induced stress as target chemicals adsorb on the surface of microcantilevers. For example, microcantilevers that have adsorbed molecules will undergo photo-induced bending that depends on the number of absorbed molecules on the surface. However, microcantilevers that have undergone photo-induced bending will adsorb molecules on their surfaces in a distinctly different way. Depending on the photon wavelength and microcantilever material, the microcantilever can be made to bend by expanding or contracting the irradiated surface. This is important in cases where the photo-induced stresses can be used to counter any adsorption-induced stresses and increase the dynamic range. Coating the surface of the …
Date: April 5, 1999
Creator: Datskos, P. G.
Object Type: Article
System: The UNT Digital Library
Detection of Infrared Photons Using the Electronic Stress in Metal-Semiconductor Interfaces (open access)

Detection of Infrared Photons Using the Electronic Stress in Metal-Semiconductor Interfaces

It is well known that the work function of metals decreases when they are placed in a nonpolar liquid. A similar decrease occurs when the metal is placed into contact with a semiconductor forming a Schottky barrier. We report on a new method for detecting photons using the stress caused by photo-electrons emitted from a metal film surface in contact with a semiconductor microstructure. The photoelectrons diffuse into the microstructure and produce an electronic stress. The photon detection results from the measurement of the photo-induced bending of the microstructure. Internal photoemission has been used in the past to detect photons, however, in those cases the detection was accomplished by measuring the current due to photoelectrons and not due to electronic stress. Small changes in position (displacement) of microstructures are routinely measured in atomic force microscopy (AFM) where atomic imaging of surfaces relies on the measurement of small changes (&lt; l0{sup -9} m) in the bending of microcantilevers. In the present work we studied the photon response of Si microcantilevers coated with a thin film of Pt. The Si microcantilevers were 500 nm thick and had a 30 nm layer of Pt. Photons with sufficient energies produce electrons from the platinum-silicon …
Date: April 5, 1999
Creator: Datskos, P. G.; Datskou, I.; Egert, C. M. & Rjic, S.
Object Type: Article
System: The UNT Digital Library
Ultra-Responsive Thermal Sensors for the Detection of Explosives Using Calorimetric Spectroscopy (CalSpec) (open access)

Ultra-Responsive Thermal Sensors for the Detection of Explosives Using Calorimetric Spectroscopy (CalSpec)

We have developed a novel chemical detection technique based on infrared micro-calorimetric spectroscopy that can be used to identify the presence of trace amounts of very low vapor pressure target compounds. Unlike numerous recently developed low-cost sensor approaches, the selectivity is derived from the unique differential temperature spectrum and does not require the questionable reliability of highly selective coatings to achieve the required specificity. This is accomplished by obtaining the infrared micro-calorimetric absorption spectrum of a small number of molecules absorbed on the surface of a thermal detector after illumination through a scanning monochromator. We have obtained infrared micro-calorimetric spectra for explosives such as TNT over the wavelength region 2.5 to 14.5 Mu-m. Thus both sophisticated and relatively crude explosive compounds and components are detectable with these ultra-sensitive thermal-mechanical micro-structures. In addition to the above mentioned spectroscopy technique and associated data, the development of these advanced thermal detectors is also presented in detail.
Date: April 5, 1999
Creator: Datskos, P. G.; Datskou, I.; Marlar, T. A. & Rajic, S.
Object Type: Article
System: The UNT Digital Library
Using emissivity-corrected thermal maps to locate deep structural defects in concrete bridge decks (open access)

Using emissivity-corrected thermal maps to locate deep structural defects in concrete bridge decks

Dual-band infrared (DBIR) thermal imaging is a promising, non-contact, nondestructive evaluation tool to evaluate the amount of deteriorated concrete on asphalt-covered bridge decks. We conducted proof-of-principle demonstrations to characterize defects in concrete structures which could be detected with DBIR thermal imaging. We constructed two identical concrete slabs with synthetic delaminations, e.g., 1/8-in. thick styrofoam squares, implanted just above the 2-in.-deep steel reinforcement bars. We covered one of the slabs with a 2-in. layer of asphalt. We mounted the DBIR cameras on a tower platform, to simulate the optics needed to conduct bridge-deck inspections from a moving vehicle. We detected 4-in. implants embedded in concrete and 9-in. implants embedded in asphalt-covered concrete. The midday (above-ambient) and predawn (below-ambient) delamination-site temperatures correlated with the implant sizes. Using DBIR image ratios, we enhanced thermal-contrast and removed emissivity-noise, e.g., from concrete compositional variations and clutter. Using the LLNL/VIEW code, we removed the asphalt thermal-gradient mask, to depict the 4-in. deep, 9-in. square, concrete implant size. We plan to image bridge deck defects, from a moving vehicle, for accurate estimations of the amount of deteriorated concrete impairing the deck integrity. Potential longterm benefits are affordable and reliable rehabilitation for asphalt-covered decks.
Date: April 5, 1995
Creator: Del Grande, N. K. & Durbin, P. F.
Object Type: Article
System: The UNT Digital Library
Chloromethyl chlorosulfate as a voltage delay inhibitor in lithium cells (open access)

Chloromethyl chlorosulfate as a voltage delay inhibitor in lithium cells

Chloromethyl chlorosulfate (CMCS) is used as a passive film growth inhibitor in electrochemical cells to minimize voltage delay and low-voltage discharge. Film growth on lithium anodes is significantly diminished when CMCS is added to SOCl{sub 2} and SO{sub 2}Cl{sub 2} electrolytes of lithium batteries. The CMCS also has the effect of extending the shelf-life of Li/SOCl{sub 2} and Li/SO{sub 2}Cl{sub 2} batteries.
Date: April 5, 1991
Creator: Delnick, F. M.
Object Type: Patent
System: The UNT Digital Library
Demonstration, testing, and evaluation of in situ heating of soil. Final report, Volume 2, Appendices A to E (open access)

Demonstration, testing, and evaluation of in situ heating of soil. Final report, Volume 2, Appendices A to E

This is a final report presented in two volumes. Volume I contains the technical report and Volume II contains appendices with background information and data. In this project approximately 300 cubic yards of clayey soil containing a low concentration plume of volatile organic chemicals was heated in situ by the application of electrical energy. It was shown that as a result of heating the effective permeability of soil to air flow was increased such that in situ soil vapor extraction could be performed. The initial permeability of soil was so low that the soil gas flow rate was immeasurably small even at high vacuum levels. It was demonstrated that the mass flow rate of the volatile organic chemicals was enhanced in the recovered soil gas as a result of heating. When scaled up, this process can be used for the environmental clean up and restoration of DOE sites contaminated with VOC`s and other organic chemicals. Although it may be applied to many types of soil formations, it is particularly attractive for low permeability clayey soil where conventional in situ venting techniques are limited by air flow.
Date: April 5, 1996
Creator: Dev, H.; Enk, J.; Jones, D. & Sabato, W.
Object Type: Report
System: The UNT Digital Library
Demonstration, testing, and evaluation of in situ heating of soil. Volume 1, Final report (open access)

Demonstration, testing, and evaluation of in situ heating of soil. Volume 1, Final report

This document is a final reports in two volumes. Volume I contains the technical report and Volume II contains appendices with background information and data. In this project approximately 300 cubic yards of clayey soil containing a low concentration plume of volatile organic chemicals was heated in situ by the application of electrical energy. It was shown that as a result of heating the effective permeability of soil to air flow was increased such that in situ soil vapor extraction could be performed. The initial permeability of soil was so low that the soil gas flow rate was immeasurably small even at high vacuum levels. It was demonstrated that the mass flow rate of the volatile organic chemicals was enhanced in the recovered soil gas as a result of heating.
Date: April 5, 1996
Creator: Dev, H.; Enk, J.; Jones, D. & Sabato, W.
Object Type: Report
System: The UNT Digital Library
Acceptance test report for the 241-AN-107 caustic addition mixer pump data logger (open access)

Acceptance test report for the 241-AN-107 caustic addition mixer pump data logger

The Acceptance Test Procedure for the 241-AN-107 Caustic Addition Mixer Pump Data logger, WHC-SD-WM-ATP-149, was started on September 25, 1995, and completed November 13, 1995. K.G. Carothers of Tank Waste Remediation Engineering requested the test procedure and ICF Kaiser Control Systems Engineering group wrote the test procedure and executed it at the 305 building in 300 area and at the 241-AN Tank Farm in 200 East area. The purpose of this report is to document that the Caustic addition Mixer Pump Data logger, functioned as intended as installed at 241-AN-107 tank farm.
Date: April 5, 1996
Creator: Dowell, J. L.
Object Type: Report
System: The UNT Digital Library
Z-Contrast STEM Imaging and EELS of CdSe Nanocrystals: Towards the Analysis of Individual Nanocrystal Surfaces (open access)

Z-Contrast STEM Imaging and EELS of CdSe Nanocrystals: Towards the Analysis of Individual Nanocrystal Surfaces

We have applied Atomic Number Contract Scanning Transmission Electron Microscopy (Z-Contrast STEM) and STEM/EELS (Electron Energy Loss Spectroscopy) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. Unlike the case of conventional phase-contrast High Resolution TEM, Z-Contrast images are direct projections of the atomic structure. Hence they can be interpreted without the need for sophisticated image simulation and the image intensity is a direct measure of the thickness of a nanocrystal. Our thickness measurements are in agreement with the predicted faceted shape of these nanocrystals. Our unique 1.3A resolution STEM has successfully resolve3d the sublattice structure of these CdSe nanocrystals. In [010] projection (the polar axis in the image plane) we can distinguish Se atom columns from Cd columns. Consequently we can study the effects of lattice polarity on the nanocrystal morphology. Furthermore, since the STEM technique does not rely on diffraction, it is superbly suited to the study of non-periodic detail, such as the surface structure of the nanocrystals. EELS measurements on individual nanocrystals indicate a significant amount (equivalet to 0.5-1 surface monolayers) of oxygen on the nanocrystals, despite processing in an inert atmosphere. Spatially resolved measurements at 7A resolution suggest a surface oxide layer. …
Date: April 5, 1999
Creator: Erwin, M.; Kadavanich, A. V.; Kippeny, T.; Pennycook, S. J. & Rosenthal, S. J.
Object Type: Article
System: The UNT Digital Library
Self-Diffusion Along Step-Bottoms on Pt(111) (open access)

Self-Diffusion Along Step-Bottoms on Pt(111)

First-principles total energies of periodic vicinals are used to estimate barriers for Pt-adatom diffusion along straight and kinked steps on Pt(111), and around a corner where straight steps intersect. In all cases studied, hopping diffusion has a lower barrier than concerted substitution. In conflict with simulations of dendritic Pt island formation on Pt(111), hopping from a corner site to a step whose riser is a (111)-micro facet is predicted to be more facile than to one whose riser is a (100).
Date: April 5, 1999
Creator: Feibelman, Peter J.
Object Type: Article
System: The UNT Digital Library