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Micromilling of Metal Alloys with Focused Ion Beam-Fabricated Tools
This work combines focused ion beam sputtering and ultra-precision machining as a first step in fabricating microstructure in metals and alloys. Specifically, {approx}25{micro}m diameter micro-end mills are made from cobalt M42 high-speed steel and C2 micrograin tungsten carbide tool blanks by ion beam sputtering. A 20 keV focused gallium beam defines tool cutting edges having radii of curvature < 0.1{micro}m. Micro-end mills having 2, 4 and 5 cutting edges successfully machine small trenches in 6061-T4 aluminum, brass, 4340 steel and polymethyl methacrylate. Machined trench widths are approximately equal to the tool diameters and surface roughnesses (rms) are {approx}150 nm or less. Microtools are robust and operate for more than 6 hours without fracture. Results from ultra-precision machining aluminum at feed rates as high as 50 mm/minute are included.
Date:
November 5, 1999
Creator:
ADAMS,DAVID P.; VASILE,M.J.; BENAVIDES,GILBERT L. & CAMPBELL,ANN N.
Object Type:
Article
System:
The UNT Digital Library
Observations of Non-Close-Packed Arrangements in Multilayers of Passivated Gold Clusters
The stacking of second and third layers of supercrystals of self-assembled passivated gold nanoparticles has been investigated using transmission electron microscopy. We report for the first time nanoparticles occupying the twofold saddle site in the third layer.
Date:
October 5, 1999
Creator:
AINDOW, M.; Brown, P.; Kiely, C. J.; Wellner, A. & Wilcoxon, Jess P.
Object Type:
Article
System:
The UNT Digital Library
Behavior of W and WSi(x) Contact Metallization on n- and p- Type GaN
Sputter-deposited W-based contacts on p-GaN (N{sub A} {approximately} 10{sup 18} cm{sup {minus}3}) display non-ohmic behavior independent of annealing temperature when measured at 25 C. The transition to ohmic behavior occurs above {approximately} 250 C as more of the acceptors become ionized. The optimum annealing temperature is {approximately} 700 C under these conditions. These contacts are much more thermally stable than the conventional Ni/Au metallization, which shows a severely degraded morphology even at 700 C. W-based contacts may be ohmic as-deposited on very heavily doped n-GaN, and the specific contact resistance improves with annealing up to {approximately} 900 C.
Date:
January 5, 1999
Creator:
Abernathy, C. R.; Cao, X. A.; Cole, M. W.; Eizenberg, M.; Lothian, J. R.; Pearton, S. J. et al.
Object Type:
Article
System:
The UNT Digital Library
Inductively Coupled Plasma Etching of III-Nitrides in Cl(2)/Xe,Cl(2)/Ar and Cl(2)/He
The role of additive noble gases He, Ar and Xe to C&based Inductively Coupled Plasmas for etching of GaN, AIN and InN were examined. The etch rates were a strong function of chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with C12/Xe, while the highest rates for AIN and GaN were obtained with C12/He. Efficient breaking of the 111-nitrogen bond is crucial for attaining high etch rates. The InN etching was dominated by physical sputtering, in contrast to GaN and AIN. In the latter cases, the etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of -80 for InN to GaN and InN to AIN were obtained.
Date:
January 5, 1999
Creator:
Abernathy, C.R.; Cho, H.; Donovan, S.M.; Hahn, Y.B.; Hays, D.C.; Jung, K.B. et al.
Object Type:
Article
System:
The UNT Digital Library
Ion Beam Sputter Fabrication of Micro-Grooving and Micro-Threading Tools
This paper presents techniques for fabricating microscopic, nonplanar features in a variety of materials. Micro-grooving and micro-threading tools having cutting dimensions of 10-30{micro}m are made by focused ion beam sputtering and used in ultra-precision machining. Tool fabrication involves directing a 20 keV gallium beam at polished cylindrical punches made of cobalt M42 high-speed steel or C2 tungsten carbide. This creates cutting edges having radii of curvature less than 0.4 {micro}m, and rake features similar to conventional lathe tools. Clearance for minimizing frictional drag of a tool results from the sputter yield dependence on ion herd target incidence angle. Numerically controlled, ultra-precision machining with micro-grooving tools results in a close matching between tool width and feature size. Microtools controllably machine 13 {micro}m wide, 4 {micro}m deep, helical grooves in polymethyl methacrylate and 6061-T6 Al cylindrical substrates. Micro-grooving tools also fabricate sinusoidal waveform features in polished metal substrates.
Date:
November 5, 1999
Creator:
Adams,David P.; Vasile,M. J. & Krishnan,A. S. M.
Object Type:
Article
System:
The UNT Digital Library
Empirical Calculations of {sup 29}Si NMR Chemical Shielding Tensors: A Partial Charge Model Investigation of Hydrolysis in Organically Modified Alkoxy Silanes
Organically modified alkoxy silanes play an important role in tailoring different properties of silica produced by the sol-gel method. Changes in the size and functionality of the organic group allows control of both physical and chemical properties of the resulting gel, with the kinetics of the polymerization process playing an important role in the design of new siloxane materials. High resolution {sup 29}Si NMR has proven to be valuable tool for monitoring the polymerization reaction, and has been used to investigate a variety of organically modified alkoxy silane systems.
Date:
August 5, 1999
Creator:
Alam, Todd M. & Henry, Marc
Object Type:
Article
System:
The UNT Digital Library
Oral History Interview with Howard L. Patton, January 5, 1999
Access:
Use of this item is restricted to the UNT Community
Interview with Howard L. Patton, a Army WWII veteran from Flora, Illinois. Patton discusses his family background, commissioning into the Army through ROTC, training with anti-air artillery, his marriage, deployment to New Guinea, the assault on Wakde Island, the battle of Leyte, operations at Zamboanga, and the end of the war.
Date:
January 5, 1999
Creator:
Alexander, William J. & Patton, Howard L.
Object Type:
Book
System:
The UNT Digital Library
The Oklahoma Daily (Norman, Okla.), Vol. 83, No. 99, Ed. 1 Friday, February 5, 1999
Student newspaper of the University of Oklahoma in Norman, Oklahoma that includes national, local, and campus news along with advertising.
Date:
February 5, 1999
Creator:
Allam, Heather
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
The Oklahoma Daily (Norman, Okla.), Vol. 83, No. 119, Ed. 1 Friday, March 5, 1999
Student newspaper of the University of Oklahoma in Norman, Oklahoma that includes national, local, and campus news along with advertising.
Date:
March 5, 1999
Creator:
Allam, Heather
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
The Oklahoma Daily (Norman, Okla.), Vol. 83, No. 133, Ed. 1 Monday, April 5, 1999
Student newspaper of the University of Oklahoma in Norman, Oklahoma that includes national, local, and campus news along with advertising.
Date:
April 5, 1999
Creator:
Allam, Heather
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
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
Ensemble: 1999-04-05-African Cultural Festival
An African music festival performed at the UNT College of Music Winspear Hall.
Date:
April 5, 1999
Creator:
Alorwoyie, Gideon Foli
Object Type:
Sound
System:
The UNT Digital Library
High Efficiency Release Targets for Use at ISOL Facilities: Computational Design
This report describes efforts made at the oak Rklge NatiOnrd Laboratory to design high- efficiency-release targets that simultaneously incorporate the short diffusion lengths, high permeabilities, controllable temperatures, and heat-removal properties required for the generation of useful radioactive ion beam (RIB) intensities for nuclear physics and astrophysics research using the isotope separation on-line (ISOL) technique. Short diffusion lengths are achieved either by using thin fibrous target materials or by coating thin layers of selected target material onto low-density carbon fibers such as reticulated-vitreous-carbon fiber (RVCF) or carbon-bonded-carbon fiber (CBCF) to form highly permeable composite target matrices. Computational studies that simulate the generation and removal of primary beam deposited heat from target materials have been conducted to optimize the design of targetheat-sink systems for generating RIBs. The results derived from diffusion release-rate simulation studies for selected targets and thermal analyses of temperature distributions within a prototype targetlheat-sink system subjected to primary ion beam irradiation will be presented in this report.
Date:
October 5, 1999
Creator:
Alton, G. D. & Liu, Y.
Object Type:
Article
System:
The UNT Digital Library
Development of a Model for Maaging Organizational Knowledge
We created three models to represent a comprehensive knowledge model: · Stages of Knowledge Management Model (Forrester) · Expanded Life-Cycle Information Management Model · Organizational Knowledge Management Model. In building a series of models, we started with an attempt to create a graphical model that illustrates the ideas outlined in the Forrester article (Leadership Strategies, Vol. 3, No. 2, November/December 1997). We then expanded and detailed a life-cycle model. Neither of these effectively reflected how to manage the complexities involved in weaving local, enterprise, and global information into an easily navigated resource for end users. We finally began to synthesize these ideas into an Organizational Knowledge Management Model. This model acknowledges the relevance of life-cycle management for different granularities of information collections and places it in the context of the integrating infrastructure needed to assist end users.
Date:
May 5, 1999
Creator:
Ashdown, B. & Smith, K.
Object Type:
Article
System:
The UNT Digital Library
241-Z-361 Sludge Characterization Sampling and Analysis Plan
This sampling and analysis plan (SAP) identifies the type, quantity, and quality of data needed to support characterization of the sludge that remains in Tank 241-2-361. The procedures described in this SAP are based on the results of the 241-2-361 Sludge Characterization Data Quality Objectives (DQO) (BWHC 1999) process for the tank. The primary objectives of this project are to evaluate the contents of Tank 241-2-361 in order to resolve safety and safeguards issues and to assess alternatives for sludge removal and disposal.
Date:
August 5, 1999
Creator:
BANNING, D.L.
Object Type:
Report
System:
The UNT Digital Library
Doped Contacts for High-Longevity Optically Activated, High Gain GaAs Photoconductive Semiconductor Switches
The longevity of high gain GaAs photoconductive semiconductor switches (PCSS) has been extended to over 50 million pulses. This was achieved by improving the ohmic contacts through the incorporation of a doped layer beneath the PCSS contacts which is very effective in the suppression of filament formation and alleviating current crowding to improve the longevity of PCSS. Virtually indefinite, damage-free operation is now possible at much higher current levels than before. The inherent damage-free current capacity of the switch depends on the thickness of the doped layers and is at least 100A for a dopant diffusion depth of 4pm. The contact metal has a different damage mechanism and the threshold for damage ({approximately}40A) is not further improved beyond a dopant diffusion depth of about 2{micro}m. In a diffusion-doped contact switch, the switching performance is not degraded when contact metal erosion occurs. This paper will compare thermal diffusion and epitaxial growth as approaches to doping the contacts. These techniques will be contrasted in terms of the fabrication issues and device characteristics.
Date:
August 5, 1999
Creator:
Baca, A. G.; Brown, D. J.; Donaldson, R. D.; Helgeson, W. D.; Hjalmarson, H. P.; Loubriel, G. M. et al.
Object Type:
Article
System:
The UNT Digital Library
Lifetime studies of Mo/Si and Mo/Be multilayer coatings for extreme ultraviolet lithography
Extreme Ultraviolet Lithography (EUVL) is a candidate for future application by the semiconductor industry in the production of sub-100 nm feature sizes in integrated circuits. Using multilayer reflective coatings optimized at wavelengths ranging from 11 to 14 nm, EUVL represents a potential successor to currently existing optical lithography techniques. In order to assess lifetimes of the multilayer coatings under realistic conditions, a series of radiation stability tests has been performed. In each run a dose of EUV radiation equivalent to several months of lithographic operation was applied to Mo/Si and MO/Be multilayer coatings within a few days. Depending on the residual gas concentration in the vacuum environment, surface deposition of carbon during the exposure lead to losses in the multilayer reflectivity. However, in none of the experimental runs was structural damage within the bulk of the multilayers observed. Mo/Si multilayer coatings recovered their full original reflectivity after removal of the carbon layer by an ozone cleaning method. Auger depth profiling on MO/Be multilayers indicate that carbon penetrated into the Be top layer during illumination with high doses of EUV radiation. Subsequent ozone cleaning fully removed the carbon, but revealed enhanced oxidation of the area illuminated, which led to an irreversible …
Date:
August 5, 1999
Creator:
Bajt, S; Clift, W M; Folta, J A; Gullikson, E M; Klebanoff, L E; Kleineberg, U et al.
Object Type:
Article
System:
The UNT Digital Library
Single top production and top properties at the Tevatron
We summarize recent measurements made at the Tevatron Collider using top event candidates. Cross section and mass measurements are discussed in a separate contribution to these Proceedings. Here we report on studies of the top P<sub>T</sub> distribution in t{anti t} production and studies of single top production. Properties of top decays examined are: BF(t {yields} Wb)/BF(t {yields} Wq), helicity amplitudes of W's from top decays and correlations of t{anti t} decay products. Searches for new physics in rare top decays and a search for a state X {yields} t{anti t} are also reported.
Date:
November 5, 1999
Creator:
Barbaro-Galtieri, Angela
Object Type:
Article
System:
The UNT Digital Library
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
Oregon Wildlife Planning Coordination Project, October 1, 1998 to September 30, 1999 Annual Report.
The intent of the Oregon Wildlife Planning Coordination project is to fund Oregon Department of Fish and Wildlife (ODFW) staff to facilitate wildlife mitigation coordination and planning between Oregon wildlife managers. The primary goal of ODFW wildlife mitigation planning/coordination staff is to foster, facilitate, and manage a statewide cooperative wildlife mitigation planning and implementation effort between the Oregon wildlife managers (the Oregon Wildlife Coalition or OWC) to mitigate for wildlife losses in Oregon caused by the development and operation of the hydropower system.
Date:
October 5, 1999
Creator:
Barnes, Susan P.
Object Type:
Report
System:
The UNT Digital Library
News Bulletin (Castroville, Tex.), Vol. 41, No. 31, Ed. 1 Thursday, August 5, 1999
Weekly newspaper from Castroville, Texas that includes local, state, and national news along with extensive advertising.
Date:
August 5, 1999
Creator:
Barnes, Thomas
Object Type:
Newspaper
System:
The Portal to Texas History
Optimizing Chemical Sensor Array Sizes
Optimal selection of array sensors for a chemical sensing application is a nontrivial task. It is commonly believed that "more is better" when choosing the number of sensors required to achieve good chemical selectivity. However, cost and system complexity issues point towards the choice of small arrays. A quantitative array optimization is carried out to explore the selectivity of arrays of partially-selective chemical sensors as a function of array size. It is shown that modest numbers (dozens) of target analytes are completely distinguished with a range of arrays sizes. However, the array selectivity and the robustness against sensor sensitivity variability are significantly degraded if the array size is increased above a certain number of sensors, so that relatively small arrays provide the best performance. The results also suggest that data analyses for very large arrays of partially-selective sensors will be optimized by separately anal yzing small sensor subsets.
Date:
May 5, 1999
Creator:
Bartholomew, J. W.; Martinez, R. F.; Osbourn, G. C.; Ricco, A. J. & Yelton, W. G.
Object Type:
Article
System:
The UNT Digital Library
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
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