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MODELING AND THE SPUTTER DEPOSITION OF COATINGS ONTO SPHERICAL CAPSULES

Description: The sputter deposition of coatings onto capsules of polymer and oxide shells as well as solid metal spheres is accomplished using a chambered substrate platform. Oxides and metal coatings are sputter deposited through a screen-aperture array onto a 0.3-1.2 mm diameter, solid spheres and hollow shells. Each shell is contained within its own individual chamber within a larger array. Ultrasonic vibration is the method used to produce a random bounce of each capsule within each chamber, in order to produce a coating with uniform thickness. Characterization of thin aluminum-oxide coated, platinum solid spheres and thicker copper-gold layer coated, hollow capsules (of both glass and polymer) show that uniform coatings can be produced using a screen-aperture chambered, substrate platform. Potential advantages of this approach compared to open-bounce pans include improved sample yield and reduced surface roughness from debris minimization. A process model for the coating growth on the capsules is developed to assess selection of the screen aperture based on the effects of sputter deposition parameters and the coating materials.
Date: September 19, 2006
Creator: Jankowski, A F & Hayes, J P
Partner: UNT Libraries Government Documents Department

Deposition of field emissions cathodes over large areas

Description: Field emission cathodes (FECs) with characteristics of cold emission, low voltage operation, high current density and microscopic size meet the requirements for an electron source for use in vacuum microelectronics. Deposition efforts have focused on evaporation techniques, as electron beam, to produce the size and shape of cathode required for efficient operation. After two decades of development, the convention for FEC synthesis involves coating with very high tolerances for thickness uniformity using a planetary substrate fixture and a long source-to-substrate distance. A further reduction in the operating voltage results by increasing the density of emitters through a reduction of cathode size and spacing. In addition, the objective of scaling the substrate size from small to large areas has compounded the manufacturing requirements to a point beyond that which is obtainable through modifications to the conventional FEC deposition process. We have been successful in a new alternative approach to design, assemble and operate a system that enables FEC synthesis over large areas through the control of deposition source divergence and step-and-repeat substrate handling.
Date: April 3, 1997
Creator: Jankowski, A.F. & Hayes, J.P.
Partner: UNT Libraries Government Documents Department

Chemical bonding in hard boron-nitride multilayers

Description: The oxides and nitrides of boron show great potential for use as hard, wear resistant materials. However, large intrinsic stresses and poor adhesion often accompany the hard coatings as found for the cubic boron-nitride phase. These effects may be moderated for use of a layered structure. Alternate stiff layers of boron and compliant layers of nitride are formed by modulating the sputter gas composition during deposition of boron target. The B/BN thin films are characterized with transmission electronic microscope to evaluate the microstructure, nanoindentation to measure hardness and ex-ray absorption spectroscopy to determine chemical bonding. The effects of layer pair spacing on chemical bonding and hardness are evaluated for the B/BN films.
Date: June 1, 1997
Creator: Jankowski, A.F. & Hayes, J.P.
Partner: UNT Libraries Government Documents Department

Reactive sputter deposition of yttria-stabilized zirconia

Description: Yttria-stabilized zirconia (YSZ) films are synthesized using reactive de magnetron sputter deposition. A homogeneous alloy of Zr-Y is synthesized and processed into a planar magnetron target which is reactively sputtered with an Argon-Oxygen gas mixture to form Zr-Y-0 films. The sputtering conditions of gas flow, gas pressure, deposition rate and substrate temperature are determined in order to produce the cubic phase of zirconia as verified with x-ray diffraction. A higher rate of deposition is achievable when the sputtering mode of the Zr-Y alloy target is metallic as opposed to oxide. The Zr-Y composition of the planar magnetron target is designed for optimium oxygen-ion conductivity in the YSZ films, at elevated temperature for potential use in solid-oxide fuel cells. The oxygen concentration of the as-deposited films is measured using Auger electron spectroscopy and found to principally vary as a function of the sputter deposition rate. A fuel cell is produced with the reactive deposition process using Pt electrodes from which the growth morphology of the YSZ layer is characterized using scanning electron microscopy.
Date: May 1, 1995
Creator: Jankowski, A.F. & Hayes, J.P.
Partner: UNT Libraries Government Documents Department

Activation Energy for Grain Growth in Aluminum Coatings

Description: To produce a specific grain size in metallic coatings requires precise control of the time at temperature during the deposition process. Aluminum coatings are deposited using electron-beam evaporation onto heated substrate surfaces. The grain size of the coating is determined upon examination of the microstructure in plan view and cross-section. Ideal grain growth is observed over the entire experimental range of temperature examined from 413 to 843 K. A transition in the activation energy for grain growth from 0.7 to 3.8 eV {center_dot} atom{sup -1} is observed as the temperature increases from <526 K to >588 K. The transition is indicative of the dominant mechanism for grain growth shifting with increasing temperature from grain boundary to lattice diffusion.
Date: October 14, 2004
Creator: Jankowski, A F; Ferreira, J L & Hayes, J P
Partner: UNT Libraries Government Documents Department

The Thermal Stability of Nanocrystalline Au-Cu Alloys

Description: Grain refinement to the nanocrystalline scale is known to enhance physical properties as strength and surface hardness. For the case of Au-Cu alloys, development of the pulsed electroplating has led to the functional control of nanocrystalline grain size in the as-deposited condition. The thermal aging of Au-Cu electrodeposits is now investigated to assess the stability of the nanocrystalline grain structure and the difference between two diffusion mechanisms. The mobility of grain boundaries, dominant at low temperatures, leads to coarsening of grain size whereas at high temperature the process of bulk diffusion dominates. Although the kinetics of bulk diffusion are slow below 500 K at 10{sup -20} cm{sup 2} {center_dot} sec, the kinetics of grain boundary diffusion are faster at 10{sup -16} cm{sup 2} {center_dot} sec. The diffusivity values indicate that the grain boundaries of the as-deposited nanocrystalline Au-Cu are mobile and sensitive to low-temperature anneal treatments affecting the grain size, hence the strength of the material.
Date: February 15, 2006
Creator: Jankowski, A F; Saw, C K & Hayes, J P
Partner: UNT Libraries Government Documents Department

THERMAL STABILITY AND MECHANICAL BEHAVIOR OF ULTRA-FINE BCC TA AND V COATINGS

Description: Ultra-refined microstructures of both tantalum (Ta) and vanadium (V) are produced using electron-beam evaporation and magnetron sputtering deposition. The thermal stability of the micron-to-submicron grain size foils is examined to quantify the kinetics and activation energy of diffusion, as well as identify the temperature transition in dominant mechanism from grain boundary to lattice diffusion. The activation energies for boundary diffusion in Ta and V determined from grain growth are 0.3 and 0.2 eV{center_dot}atom{sup -1}, respectively, versus lattice diffusion values of 4.3 and 3.2 eV{center_dot}atom{sup -1}, respectively. The mechanical behavior, as characterized by strength and hardness, is found to inversely scale with square-root grain size according to the Hall-Petch relationship. The strength of Ta and V increases two-fold from 400 MPa, as the grain size decreases from 2 to 0.75 {micro}m.
Date: November 3, 2006
Creator: Jankowski, A F; Go, J & Hayes, J P
Partner: UNT Libraries Government Documents Department

Reactive sputter deposition of boron nitride

Description: The preparation of fully dense, boron targets for use in planar magnetron sources has lead to the synthesis of Boron Nitride (BN) films by reactive rf sputtering. The deposition parameters of gas pressure, flow and composition are varied along with substrate temperature and applied bias. The films are characterized for composition using Auger electron spectroscopy, for chemical bonding using Raman spectroscopy and for crystalline structure using transmission electron microscopy. The deposition conditions are established which lead to the growth of crystalline BN phases. In particular, the growth of an adherent cubic BN coating requires 400--500 C substrate heating and an applied {minus}300 V dc bias.
Date: October 1, 1995
Creator: Jankowski, A.F.; Hayes, J.P.; McKernan, M.A. & Makowiecki, D.M.
Partner: UNT Libraries Government Documents Department

Eutectic bonding of a Ti sputter coated, carbon aerogel wafer to a Ni foil

Description: The formation of high energy density, storage devices is achievable using composite material systems. Alternate layering of carbon aerogel wafers and Ni foils with rnicroporous separators is a prospective composite for capacitor applications. An inherent problem exists to form a physical bond between Ni and the porous carbon wafer. The bonding process must be limited to temperatures less than 1000{degrees}C, at which point the aerogel begins to degrade. The advantage of a low temperature eutectic in the Ni-Ti alloy system solves this problem. Ti, a carbide former, is readily adherent as a sputter deposited thin film onto the carbon wafer. A vacuum bonding process is then used to join the Ni foil and Ti coating through eutectic phase formation. The parameters required for successfld bonding are described along with a structural characterization of the Ni foil-carbon aerogel wafer interface.
Date: June 1, 1994
Creator: Jankowski, A.F.; Hayes, J.P. & Kanna, R.L.
Partner: UNT Libraries Government Documents Department

Formation of cubic boron-nitride by the reactive sputter deposition of boron

Description: Boron-nitride films are synthesized by RF magnetron sputtering boron targets where the deposition parameters of gas pressure, flow and composition are varied along with substrate temperature and applied bias. The films are analyzed using Auger electron spectroscopy, transmission electron microscopy, nanoindentation, Raman spectroscopy and x-ray absorption spectroscopy. These techniques provide characterization of film composition, crystalline structure, hardness and chemical bonding, respectively. Reactive, rf-sputtering process parameters are established which lead to the growth of crystalline BN phases. The deposition of stable and adherent boron nitride coatings consisting of the cubic phase requires 400 `C substrate heating and the application of a 300 V negative bias.
Date: March 1, 1997
Creator: Jankowski, A.F.; Hayes, J.P.; Makowiecki, D.W. & McKeman, M.A.
Partner: UNT Libraries Government Documents Department

Near-edge x-ray absorption fine structure examination of chemical bonding in sputter deposited boron and boron-nitride films

Description: Near-edge x-ray absorption fine structure (NEXAFS) is used to examine the chemical bonding in boron and boron-nitride films sputter deposited from a fully-dense, pure boron target. Reactive sputtering is used to prepare the boron-nitride and multilayered films. Although the process of sputter deposition often produces films that lack long range order, NEXAFS reveals the distinguishing features of sp{sup 2} and sp{sup 3} hybridization that are associated with different crystalline structures. The sensitivity of NEXAFS to local order further provides details in bonding modifications that exist in these films.
Date: May 1, 1996
Creator: Jankowski, A.F.; Hayes, J.P. & Suthreland, D.G.J.
Partner: UNT Libraries Government Documents Department

Field-emission cathode micro-electro-mechanical system technology for sensors, diagnostics, and microelectronics

Description: We have investigated field-emission devices for applications in sensors, diagnostics, and micro-electronics. Field-emission devices micromachined from silicon and molybdenum have been fabricated and tested. Experimental results have shown that the presence of nitrogen gas molecules for pressures up to 1 mtorr has only a moderate impact on device emission performance, and has no long term effect on device operation. These results demonstrate that field-emission cathodes can potentially be used in sensors applications where gas ionization by election impact is desirable, or other applications in which the field-emission device is exposed to less than ideal vacuum conditions.
Date: March 30, 1998
Creator: Morse, J.D.; Koo, J.C.; Graff, R.T.; Jankowski, A.F. & Hayes, J.P.
Partner: UNT Libraries Government Documents Department

NANOCRYSTALLINE GROWTH AND GRAIN-SIZE EFFECTS IN AU-CU ELECTRODEPOSITS

Description: The processing-structure-property relationship is investigated for electrodeposited foils of the gold-copper alloy system. A model is presented that relates the deposition process parameters to the nanocrystalline grain size. An activation energy of 1.52 eV {center_dot} atom{sup -1} for growth is determined for a long pulse (>10 msec) mode, and is 0.16 eV {center_dot} atom{sup -1} for short pulses (<5 msec). The affect of nanocrystalline grain size on the mechanical properties is assessed using indentation measurements. A Hall-Petch type variation of the Vickers microhardness with nanocrystalline grain size (>6 nm) is observed for Au-Cu samples with 1-12 wt.% Cu as tested in cross-section. The hardness increases three-fold from a rule-of-mixtures value <1 GPa to a maximum of 2.9 GPa.
Date: February 25, 2005
Creator: Jankowski, A F; Saw, C K; Harper, J F; Vallier, R F; Ferreira, J L & Hayes, J P
Partner: UNT Libraries Government Documents Department

ACTIVATION ENERGY FOR GRAIN GROWTH IN BISMUTH COATINGS

Description: The knowledge of both activation energy and diffusion coefficient is needed for a predictive processing of grain size in coatings. However, for metals as Bismuth there is insufficient information available in the literature for these parameters. To determine these values, a method is adopted wherein an examination of the grain size is conducted for coatings deposited isothermally. The exponent for grain growth with time is determined, thereby enabling quantification of the activation energy and diffusion coefficient. Bismuth coatings that range from 10 {micro}m to 1 mm thick are deposited using electron-beam evaporation onto temperature-controlled substrate surfaces of glass and lithium fluoride. The grain size of each coating is measured upon examination of the microstructure in cross-section using the intercept method. Ideal grain growth is observed over the experimental range of deposition temperatures examined from 317 to 491 K. The activation energy (Q) for grain growth in bismuth is fit as 0.47 eV {center_dot} atom{sup -1} with a diffusion coefficient (D{sub 0}) of 3.3 x 10{sup -4} cm{sup 2} {center_dot} sec{sup -1}.
Date: September 9, 2005
Creator: Jankowski, A F; Hayes, J P; Smith, R F; Reed, B W; Kumar, M & Colvin, J D
Partner: UNT Libraries Government Documents Department

Properties of boron/boron-nitride multilayers

Description: Boron-Nitride films are of interest for their high hardness and wear resistance. Large intrinsic stresses and poor adhesion which often accompany high hardness materials can be moderated through the use of a layered structure. Alternate layers of boron (B) and boron-nitride (BN) are formed by modulating the composition of the sputter gas during deposition from a pure B target. The thin films are characterized with TEM to evaluate the microstructure and with nanoindentation to determine hardness. Layer pair spacing and continuity effects on hardness are evaluated for the B/BN films.
Date: June 1, 1996
Creator: Jankowski, A. F.; Wall, M. A.; Hayes, J. P. & Alexander, K. B.
Partner: UNT Libraries Government Documents Department

Resistance behavior of Cr-Si-O thin films

Description: Thin coatings of Cr-Si-O are assessed for use as a resistor. The submicron thick films are sputter deposited using a (l-x)Ar-(x)O{sub 2} working gas. Several compacts of metal and oxide powders are commercially prepared for use as the sputter targets. The deposition process yields film compositions which range from 2 to 30 at.% Cr and 20 to 45 at.% Si as measured using Rutherford backscattering. A broad range of resistivities from 10{sup 1} to 10{sup 14}{Omega} cm are found as measured through the film thickness between metal pads deposited onto the Cr-Si-O surface. The film structure and morphology are characterized using transmission electron microscopy from which the resistance behavior can be correlated to the distribution of metallic particles. Thermal aging reveals the metastability of the Cr- Si-O film morphology and resistance behavior.
Date: October 23, 1996
Creator: Jankowski, A.F.; Hayes, J.P.; Musket, R.; Cosandey, F.; Gorla, C.E.; Besser, R.S. et al.
Partner: UNT Libraries Government Documents Department

Fabrication of x-ray spiral masks by laser ablation.

Description: The manipulation of x-rays by phase structures is becoming more common through devices such as compound refractive lenses, blazed zone-plates and other structures. A spiral phase modulation structure can be used to condition an x-ray beam to produce an x-ray vortex. An x-ray beam in this form can be used as the first step towards a self-collimating beam. Also it can be used as a controllable pathological feature in studies of x-ray phase retrieval. The authors describe the microfabrication of a spiral phase modulation structure by excimer laser ablation. A multi-step fabrication using 15 separate chrome-on-quartz mask patterns is used to create a 16 step spiral staircase structure approximating the desired spiral ramp. The results of simulations and initial experimental results are presented.
Date: July 2, 2002
Creator: Peele, A. G.; Nugent, K. A.; McMahon, P. J.; Paterson, D.; Tran, C. Q.; Mancuso, A. et al.
Partner: UNT Libraries Government Documents Department