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Very long single- and few-walled boron nitride nanotubes via the pressurized vapor/condenser method

Description: Boron nitride nanotubes (BNNTs) are desired for their exceptional mechanical, electronic, thermal, structural, textural, optical, and quantum properties. A new method for producing long, small-diameter, single- and few-walled, boron nitride nanotubes (BNNTs) in macroscopic quantities is reported. The pressurized vapor/condenser (PVC) method produces, without catalysts, highly crystalline, very long, small-diameter, BNNTs. Palm-sized, cotton-like masses of BNNT raw material were grown by this technique and spun directly into centimeters-long yarn. Nanotube lengths were observed to be 100 times that of those grown by the most closely related method. Self-assembly and growth models for these long BNNTs are discussed.
Date: November 1, 2009
Creator: Michael W. Smith, Kevin Jordan, Cheol Park, Jae-Woo Kim, Peter Lillehei, Roy Crooks, Joycelyn Harrison
Partner: UNT Libraries Government Documents Department


Description: Graphite is oxidized by O{sub 2}{sup +} AsF{sub 6}{sup -} and by OsF{sub 6} to give first-stage graphite salts C{sub 8}{sup +} MF{sub 6}{sup -} and S{sub 2}O{sub 6}F{sub 2} oxidizes both graphite and boron nitride to yield the salts C{sub 12}{sup +} SO{sub 3}F{sup -} and (BN){sub 4}{sup +} SO{sub 3}F{sup -}, the latter being the first example of a first-stage boron nitride salt.
Date: December 1, 1977
Creator: Bartlett, Neil; Biagioni, R.N.; McQuillan, B.W.; Robertson, A.S. & Thompson, A.C
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

Preparation of diamond-like carbon and boron nitirde films by high-intensity pulsed ion beam deposition

Description: Intense ion beams (300-keV C{sup +}, O{sup +}, and H{sup +}, 20--30 kA, 50 to 400-ns pulsewidth, up to 0.3-Hz repetition rate) were used to prepare diamond-like carbon (DLC) and boron nitride (BN) films. Deposition rates of up to 25{plus_minus}5 nm/pulse were obtained with instantaneous rates exceeding 1 mm/s. Most films were uniform, light brown, translucent, and nonporous with some micron-size particulates. Raman and parallel electron energy loss spectroscopy indicated the presence of DLC. The films possessed favorable electron field-emission characteristics desirable for cold-cathode displays. Transmission electron microscopy (TEM) and transmission electron diffraction (TED) revealed that the C films contained diamond crystals with 25 to 125-nm grain size. BN films were composed of hexagonal, cubic and wurtzite phases.
Date: May 1, 1995
Creator: Rej, D.J.; Davis, H.A. & Remnev, G.E.
Partner: UNT Libraries Government Documents Department

Anisotropic Hexagonal Boron Nitride Nanomaterials - Synthesis and Applications

Description: Boron nitride (BN) is a synthetic binary compound located between III and V group elements in the Periodic Table. However, its properties, in terms of polymorphism and mechanical characteristics, are rather close to those of carbon compared with other III-V compounds, such as gallium nitride. BN crystallizes into a layered or a tetrahedrally linked structure, like those of graphite and diamond, respectively, depending on the conditions of its preparation, especially the pressure applied. Such correspondence between BN and carbon readily can be understood from their isoelectronic structures [1, 2]. On the other hand, in contrast to graphite, layered BN is transparent and is an insulator. This material has attracted great interest because, similar to carbon, it exists in various polymorphic forms exhibiting very different properties; however, these forms do not correspond strictly to those of carbon. Crystallographically, BN is classified into four polymorphic forms: Hexagonal BN (h-BN) (Figure 1(b)); rhombohedral BN (r-BN); cubic BN (c-BN); and wurtzite BN (w-BN). BN does not occur in nature. In 1842, Balmain [3] obtained BN as a reaction product between molten boric oxide and potassium cyanide under atmospheric pressure. Thereafter, many methods for its synthesis were reported. h-BN and r-BN are formed under ambient pressure. c-BN is synthesized from h-BN under high pressure at high temperature while w-BN is prepared from h-BN under high pressure at room temperature [1]. Each BN layer consists of stacks of hexagonal plate-like units of boron and nitrogen atoms linked by SP{sup 2} hybridized orbits and held together mainly by Van der Waals force (Fig 1(b)). The hexagonal polymorph has two-layered repeating units: AA'AA'... that differ from those in graphite: ABAB... (Figure 1(a)). Within the layers of h-BN there is coincidence between the same phases of the hexagons, although the boron atoms and nitrogen atoms are alternatively located along ...
Date: August 1, 2008
Creator: Han,W.Q.
Partner: UNT Libraries Government Documents Department

Melting and spheroidization of hexagonal boron nitride in a microwave-powered, atmospheric pressure nitrogen plasma `

Description: We have developed a method for producing spherically-shaped, hexagonal phase boron nitride (hBN) particles of controlled diameter in the 10-100 micron size range. Specifically, platelet-shaped hBN particles are passed as an aerosol through a microwave-generated, atmospheric pressure, nitrogen plasma. In the plasma, agglomerates formed by collisions between input hBN particles, melt and forms spheres. We postulate that this unprecedented process takes place in the unique environment of a plasma containing a high N-atom concentration, because in such an environment the decomposition temperature can be raised above the melting temperature. Indeed, given the following relationship [1]: BN{sub (condensed)} {leftrightarrow} B{sub (gas)} + N{sub (gas)}. Standard equilibrium thermodynamics indicate that the decomposition temperature of hBN is increased in the presence of high concentrations of N atoms. We postulate that in our plasma system the N atom concentration is high enough to raise the decomposition temperature above the (undetermined) melting temperature. Keywords Microwave plasma, boron nitride, melting, spherical, thermodynamics, integrated circuit package.
Date: January 1, 2001
Creator: Gleiman, S. S. (Seth S.) & Phillips, J. (Jonathan)
Partner: UNT Libraries Government Documents Department

Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

Description: Studies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.
Date: May 1, 1996
Creator: Kiggans, J.O.: Tiegs, T.N. & Kimrey, H.D.
Partner: UNT Libraries Government Documents Department

Boron nitrides synthesized directly from the elements at high pressures and temperatures

Description: We use angle-resolved synchrotron x-ray diffraction, laser sample heating, and diamond-anvil cells to follow in-situ chemical reactions directly between elemental boron and nitrogen. The structures of the solid reaction products vary with pressure. Below 10 GPa, hexagonal BN is the product; cubic or wurzite BN form at higher pressures. Under nitrogen-rich conditions, another hexagonal allotrope occurs which seems to be a new highly transparent, low density h`-BN. No direct reactions occur at ambient temperature even at pressures as high as 50 GPa, implying that a large activation barrier limits the kinetics of these exothermic processes. Laser heating overcomes the large kinetic activation barrier and initiates spontaneous, self-sustaining exothermic reactions even at moderate pressures.
Date: November 1, 1996
Creator: Nicol, M.; Yoo, C.S.; Akella, J. & Cynn, H.
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

Corrosion resistance of inconel 690 to borax, boric acid, and boron nitride at 1100{degrees}C

Description: Significant general and localized corrosion was observed on Inconel 690 coupons following exposure to borax, boric acid and boron nitride at 1100{degrees}C. Severe localized attack at and below the melt line was observed on coupons exposed to borax. An intergranular attack at and below the melt line was observed on coupons exposed to borax. An intergranular attack (IGA) of the Inconel 690 was also observed. Severe internal void formation and IGA (30 mils penetration after 3 days) was observed in the coupon exposed to boric acid. Both borax and boric acid remove the protective chromium oxide; however, this layer can be reestablished by heating the Inconel 690 to 975 {degrees}C in air for several hours. Inconel 690 in direct contact with boron nitride resulted in the formation of a thick chromium borate layer, a general corrosion rate of 50 to 90 mils per year, and internal void formation of 1 mil per day.
Date: December 12, 1996
Creator: Imrich, K. J.
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

Mechanical response of cross-ply Si{sub 3}N{sub 4}/BN fibrous monoliths under uniaxial and biaxial loadings

Description: Mechanical properties of hot-pressed Si{sub 3}N{sub 4}/BN fibrous monoliths (FMs) were evaluated under ambient conditions in four-point and biaxial flexure modes. Effects of cell orientation, 0{degree}/90{degree} and {+-}45{degree}, on elastic modulus and fracture strength of the FMs were investigated. Fracture surfaces were examined by scanning electron microscopy.
Date: March 1, 2000
Creator: Singh, D.; Cruse, T. A.; Hermanson, D. J.; Goretta, K. C.; Zok, F. W. & McNulty, J. C.
Partner: UNT Libraries Government Documents Department

Nitrogen implantation effects on the chemical bonding and hardness of boron and boron nitride coatings

Description: Boron nitride (BN) coatings are deposited by the reactive sputtering of fully dense, boron (B) targets utilizing an argon-nitrogen (Ar-N{sub 2}) reactive gas mixture. Near-edge x-ray absorption fine structure analysis reveals features of chemical bonding in the B 1s photoabsorption spectrum. Hardness is measured at the film surface using nanoindentation. The BN coatings prepared at low, sputter gas pressure with substrate heating are found to have bonding characteristic of a defected hexagonal phase. The coatings are subjected to post-deposition nitrogen (N{sup +} and N{sub 2}{sup +}) implantation at different energies and current densities. The changes in film hardness attributed to the implantation can be correlated to changes observed in the B 1s NEXAFS spectra.
Date: February 8, 1999
Creator: Anders, S; Felter, T; Hayes, J; Jankowski, A F; Patterson, R; Poker, D et al.
Partner: UNT Libraries Government Documents Department

High-temperature compressive deformation of Si{sub 3}N{sub 4}/BN fibrous monoliths.

Description: Fibrous monolithic Si{sub 3}N{sub 4}/BN ({approx}85 vol.% Si{sub 3}N{sub 4}/15 vol.% BN) and monolithic Si{sub 3}N{sub 4} ceramics were compressed at a nearly constant strain rate ({var_epsilon}) at 1200-1400 C in N{sub 2}. The {var_epsilon} range was {approx}1 x 10{sup {minus}6} to 5 x 10{sup {minus}6} s{sup {minus}1}; the stress ({sigma}) range was 37-202 MPa. The Si{sub 3}N{sub 4} and the unidirectional fibrous monoliths that were oriented with the long axis of the Si{sub 3}N{sub 4} cells parallel to the compression direction exhibited plasticity at 1300 and 1400 C, with {var_epsilon} {proportional_to} {sigma}. A 0/90{degree} cross-ply Si{sub 3}N{sub 4}/BN laminate also exhibited significant plasticity, but it was weaker than the above-mentioned ceramics. The unidirectional fibrous monoliths that were compressed perpendicular to the cell direction fractured at {approx}50 MPa in all tests. A {+-}45{degree} laminate tested at 1300 C fractured at a stress of {approx}40 MPa. Low fracture stress correlated with shear through BN layers.
Date: February 4, 1999
Creator: Routbort, J. L.
Partner: UNT Libraries Government Documents Department

Nanohardness and chemical bonding of Boron Nitride films

Description: Boron-nitride (BN) films are deposited by the reactive sputter deposition of fully dense, boron targets utilizing a planar magnetron source and an argon-nitrogen working gas mixture. Near-edge x-ray absorption fine structure analysis reveals distinguishing features of chemical bonding within the boron is photoabsorption cross-section. The hardness of the BN film surface is measured using nanoindentation. The sputter deposition conditions as well as the post-deposition treatments of annealing and nitrogen-ion implantation effect the chemical bonding and the film hardness. A model is proposed to quantify the film hardness using the relative peak intensities of the p*-resonances to the boron 1s spectra.
Date: July 8, 1998
Creator: Jankowski, A F
Partner: UNT Libraries Government Documents Department

X-ray absorption study of pulsed laser deposited boron nitride films

Description: B and N K-edge x-ray absorption spectroscopy measurements have been performed on three BN thin films grown on Si substrates using ion- assisted pulsed laser deposition. Comparison of the films` spectra to those of several single-phase BN powder standards shows that the films consist primarily of sp{sup 2} bonds. Other features in the films`s spectra suggest the presence of secondary phases, possibly cubic or rhombohedral BN. Films grown at higher deposition rates and higher ion-beam voltages are found to be more disordered, in agreement with previous work.
Date: February 2, 1994
Creator: Chaiken, A.; Terminello, L. J.; Wong, J.; Doll, G. L. & Sato, T.
Partner: UNT Libraries Government Documents Department

Nucleation and Growth of Cubic Boron Nitride Films Produced by Ion-Assisted Pulsed Laser Deposition

Description: We are studying the boron nitride system using a pulsed excimer laser to ablate from hexagonal BN (cBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (25--800C) Si (100) surfaces and are using a broad-beam ion source operated with Ar and N{sub 2} source gases to produce BN films with a high percentage of sp{sup 3}-bonded cBN. In order to optimize growth and nucleation of cBN films, parametric studies of the growth parameters have been performed. The best films to date show >85% sp{sup 3}-bonded BN as determined from Fourier-transform infrared (FTIR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 30--40 mn. We find from both the FTIR and TEM analyses that the cBN content in these films evolves with growth time. Initially, the films are deposited as hBN and the cBN nucleates on this hBN underlayer. Importantly, the position of the cBN IR phonon also changes with growth time. Initially this mode appears near 1130 cm{sup {minus}1} and the position decreases with growth time to a constant value of 1085 cm{sup {minus}1}. Since in bulk cBN this IR mode appears at 1065 cm{sup {minus}1}, a large compressive stress induced by the ion bombardment is suggested. In addition, we report on the variation in cBN percentage with temperature.
Date: December 31, 1993
Creator: Friedmann, T. A.; Medlin, D. L.; Mirkarimi, P. B.; McCarty, K. F.; Klaus, E. J.; Boehme, D. R. et al.
Partner: UNT Libraries Government Documents Department

Effects of ambient conditions on the adhesion of cubic boron nitride films on silicon substrates

Description: Effect of environmental conditions on cubic boron nitride (cBN) film adhesion to silicon substrates was studied. cBN films were deposited onto (100)-oriented silicon substrates by ion-assisted pulsed laser deposition. Irradiating ions were mixtures of nitrogen with argon, krypton, and xenon. Under room-ambient conditions, the films delaminated in the following time order: N/Xe, N/Kr, and N/Ar. cBN films deposited using N/Xe ion-assisted deposition were exposed to four environmental conditions for several weeks: a 1-mTorr vacuum, high humidity, dry oxygen, and dry nitrogen. Films exposed to the humid environment delaminated whereas those stored under vacuum or in dry gases did not. Films stored in dry nitrogen were removed after nearly two weeks and placed in the high-humidity chamber; these films subsequently delaminated within 14 hours.
Date: August 1, 1994
Creator: Cardinale, G. F.; Howitt, D. G.; Mirkarimi, P. B.; McCarty, K. F.; Klaus, E. J. & Medlin, D. L.
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

Optimum conditions for composites fiber coating by chemical vapor infiltration

Description: A combined analytical and numerical method is employed to optimize process conditions for composites fiber coating by chemical vapor infiltration (CVI). For a first-order deposition reaction, the optimum pressure yielding the maximum deposition rate at a preform center is obtained in closed form and is found to depend only on the activation energy of the deposition reaction, the characteristic pore size, and properties of the reactant and product gases. It does not depend on the preform specific surface area, effective diffusivity or preform thickness, nor on the gas-phase yield of the deposition reaction. Further, this optimum pressure is unaltered by the additional constraint of a prescribed deposition uniformity. Optimum temperatures are obtained using an analytical expression for the optimum value along with numerical solutions to the governing transport equations. These solutions account for both diffusive and advective transport, as well as both ordinary and Knudsen diffusion. Sample calculations are presented for coating preform fibers with boron nitride.
Date: April 1997
Creator: Griffiths, S. K. & Nilson, R. H.
Partner: UNT Libraries Government Documents Department

Minerals of the earth's deep interior

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The project addresses the major geophysical issue of the nature of the seismic velocity and density discontinuity at 670 km depth (the boundary between upper and lower mantle with temperature about 1,900 K and pressure about 23 GPa). A phase change at this depth would represent a relatively small barrier to mantle convection through the discontinuity, but compositional change would inhibit thermal convection throughout the mantle. To address this problem the authors measured equation of state parameters in mantle minerals as functions of high P-T using single crystal x-ray diffraction with a unique, new diamond-anvil cell (DAC) at simultaneous high temperature and pressure. Single-crystal diffraction improves absolute accuracy in lattice constants over those from powder diffraction by a factor of 5 to 10. The authors have measured equations of state of orthoenstatite MgSiO{sub 3} and hexagonal boron nitride hBN.
Date: November 1, 1998
Creator: Schiferl, D.; Zhao, Y. & Shankland, T.J.
Partner: UNT Libraries Government Documents Department

X-ray photoemission electron microscopy for the study of semiconductor materials

Description: Photoemission Electron Microscopy (PEEM) using X-rays is a novel combination of two established materials analysis techniques--PEEM using UV light, and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. This combination allows the study of elemental composition and bonding structure of the sample by NEXAFS spectroscopy with a high spatial resolution given by the microscope. A simple, two lens, 10 kV operation voltage PEEM has been used at the Stanford Synchrotron Radiation Laboratory and at the Advanced Light Source (ALS) in Berkeley to study various problems including materials of interest for the semiconductor industry. In the present paper the authors give a short overview over the method and the instrument which was used, and describe in detail a number of applications. These applications include the study of the different phases of titanium disilicide, various phases of boron nitride, and the analysis of small particles. A brief outlook is given on possible new fields of application of the PEEM technique, and the development of new PEEM instruments.
Date: March 1998
Creator: Anders, S.; Stammler, T.; Padmore, H.; Terminello, L. J.; Jankowski, A. F.; Stohr, J. et al.
Partner: UNT Libraries Government Documents Department

An X-ray photoelectron spectroscopic study of the B-N-Ti system

Description: Composite nitrides (such as BN, TiN) are widely used in various industrial applications because of their extreme wear and corrosion resistance, thermal and electrical properties. In order to obtain composite materials with these optimal properties, it is important to elucidate whether any chemical reactions occur at nitride/metal interfaces, e.g., those involving BN-Ti/TiN. Materials of interest include the deposition by PVD of Ti and TiN on BN substrates. Some of these systems were then subjected to varying degrees of physical and thermal alteration. Detailed X-ray photoelectron spectroscopy (XPS) has therefore been rendered of these interfaces using cross-sectional display and sputter etching. Resulting structural and morphological features have been investigated with transmission electron microscopy (TEM) and X-ray diffraction (XRD). Diffusion of the nitridation, oxynitride formation and interfacial growth are of general interest.
Date: March 1, 1997
Creator: Seal, S.; Barr, T.L.; Sobczak, N.; Benko, E. & Morgiel, J.
Partner: UNT Libraries Government Documents Department