Joshua B. Halpern - Research

EMAIL: jhalpern at howard dot edu
SNAIL MAIL: J.B. Halpern, Chemistry, Howard University, Washington, DC 20059, USA

Nanowire growth and characterization - Since 1999 the Howard group (Halpern, Harris, He) has been growing various nanowires, mostly by a catalyst free method.  Principally, we have grown GaN, InN, and SiC.  We have been collaborating with others at Johns Hopkins, Michigan State University and the University of Maryland.  Publications include

  1. "Biphasic GaN nanowires: Growth mechanism and properties" J.B. Halpern, A. Bello, J. Gilcrease, G.L. Harris and M. He, Microelectronics Journal, 40(2) 316-318 (2009).
  2. "Electron transport in zinc-blende wurtzite biphasic gallium nitride nanowires and GaNFETs". B W Jacobs, V M Ayres, R E Stallcup, A Hartman, M A Tupta, A D Baczewski, M A Crimp, J B Halpern, M He and H C Shaw. Nanotechnology 18(47) 475710 (2007).
  3. "Electronic and Structural Characteristics of Zinc-Blende Wurtzite Biphasic Homostructure GaN Nanowires", B.W. Jacobs, V.M. Ayres, M.P. Petkov, J.B. Halpern, MaoQe He, A.D. Baczewski, K. McElroy, M.A. Crimp, J. Zhang, H.C. Shaw. Nano Letters, 7(5), 1435-1438 (2007)
  4. "Investigations of heavy ion irradiation of gallium nitride nanowires and nanocircuits", V.M. Ayres, B.W. Jacobs, M.E. Englund, E.H. Carey, M.A. Crimp, R.M. Ronningen, A.F. Zeller, J.B. Halpern, M.-Q. He, G.L. Harris D. Liu, H.C. Shaw and M.P. Petkov. Diamonds and Related Materials, 15, 1117-1121, (2005).
  5. "Growth of GaN Nanowires by Direct Reaction of Ga with NH3", M.Q. He, P.Z. Zhou, S. N. Mohammad, G.L. Harris, J.B. Halpern, R. Jacobs, W.L. Sarney and L. Salamanca-Riba. Journal of Crystal Growth, 231, 357-365 (2001).
  6. "Structural Characterization of GaN Nanowires Fabricated via Direct Reaction of Ga vapor and Ammonia." R.N. Jacobs, L. Salamanica Riba, M. He, G.L. Harris, P. Zhou, S.M. Mohammad and J.B. Halpern. Materials Research Society Symposium Proceedings (2001), 675(Nanotubes, Fullerenes, Nanostructured and Disordered Carbon), W9.4.1-W9.4.5
  7. "Growth of Large-Scale Nanotubes and Nanowires by Direct Reaction of Ga with NH3", M. He, I. Minus, P. Zhou, S.N. Mohammad, J.B. Halpern, R. Jacobs, W.I. Sarney, L. Salamance-Riba and R. Vispute. Applied Physics Letters 77 3731 (200).

This is an outgrowth of earlier work on pulsed laser deposition of nitride semiconductors, done with colleagues at the University of Maryland

  1. "Heteroepitaxy of ZnO on GaN and Its Implications for Fabrication of Hybrid Optoelectronic Devices." R.D. Vispute, V. Talyansky, S. Choopun. R.P. Sharma, T. Venkatesan, M. He, X. Tang, J.B. Halpern, M.G. Spencer,.X. Li, L.G. Salamanca-Riba, A.A. Iliadis, and K.A. Jones,. Applied Physics Letters, 73, 348-350 (1998).
  2. "Pulsed Laser Deposition of Highly Crystalline GaN Films on Sapphire", R.D. Vispute, V. Talyansky, S. Choopun, R. Enck, T. Dahmas, S.B Ogale, RP. Sharma, T. Venkatesan, Y.X. Li, L.G. Salamanca-Riba, A.A. Iliadis, M. He, X. Tang, J.B. Halpern, M.G. Spencer, , M.A. Khan, K.A. Jones, V Bel'kov, V. Botnaryuk, I. Diakonu, L. Fedorov and Y. Zhilyaev. Materials Research Society Symposium Proceedings, 482, 343-348 (1998).
  3. "Preparation of Oxygen Free AlN Thin Films by Pulsed Laser Desorption", M. He, N. Cheng, P. Zhou, H. Okabe and J.B. Halpern. Journal of Vacuum Science A19, 2372 (1998).
  4. "Pulsed Laser Desorption of Silicon Nitride", X. Xu, J.M. Frye, H. Okabe and J.B. Halpern. Proceedings of the Materials Research Society, 285, 331 (1993).

Atmospheric chemistry of the outer planets:  For over thirty years, our group has studied the atmospheric chemistry of the outer planets, their moons and comets.  This work continues at Howard, in collaboration with Dr. Askar Fahr who has joined our group from NIST.  Recent publications include

  1. "Hydrogen Migration and Vinylidene Pathway for Formation of Methane in the 193 nm Photodissociation of Propene: CH3CH=CH2 and CD3CD=CD2”, Y-L Zhao, A.H. Laufer, J.B. Halpern, and A. Fahr. J. Phys. Chem. A, 111 (34), 8330 -8335 (2007).
  2. "Pressure and Temperature Dependence of the Reaction of Vinyl Radical with Ethylene", H. Ismail, C.F. Goldsmith, P.R. Abel, P.-T. Howe, A. Fahr, J.B. Halpern, L.E. Jusinski, Y. Georgievskii, C.A. Taatjes, W.H. Green. J. Phys. Chem. A 111(29); 6843-6851. (2007)
  3. "Calculational and Experimental Investigations of the Pressure Effects on Radical-Radical Cross Combination Reactions: C2H5 + C2H3", A. Fahr, J.B. Halpern, and D.C. Tardy. J. Phys. Chem. 111(29); 6600-6609, (2007).
  4. "Kinetics of the reaction of vinyl radicals with NO: Ab initio theory, master equation predictions, and laser absorption measurements", F. Striebel, L. E. Jusinski, A. Fahr, J.B. Halpern, S.J. Klippenstein, C.A. Taatjes, Physical Chemistry Chemical Physics, 2216-2223, (2004) .
  5. "Vinyl Radical Visible Spectroscopy and Excited State Dynamics", M. Shahu, C-Y. Yang, C.D. Pibel, A. McIlroy, C.A. Taatjes and J.B. Halpern. Journal of Chemical Physics, 116, 8343 (2002).
  6. "Vibrational Spectroscopy of a Transient Species Through Time-resolved Fourier Transform Infrared Emission Spectroscopy: The Vinyl Radical", L. Letendre, D-K Liu, C.D. Pibel, J.B. Halpern and H-L Dai, Journal of Chemical Physics, 112, 9209-9212 (2000).
  7. "Collisional Effects on Angular Momentum Orientation in Acetylene: II. Disorientational by Rotationally and Multiple Inelastic Collisions," A.D. Rudert, J.B. Halpern, J. Martin, W.B. Gao and H. Zacharias, Journal of Chemical Physics 112, 9749-9758, (2000).
  8. "Collisional Effects on Angular Momentum Orientation in Acetylene: I. Preparation, Detection and Single Collision Transfer". A.D. Rudert, J.B. Halpern, J. Martin, W.B. Gao and H. Zacharias. Journal of Chemical Physics 111 9549 (2000).
  9. "Reaction Rates of the CN Radicals with CH Unsaturated Hydrocarbons: Relations Between Reaction Rates and Molecular Lengths." T. Ochimizua, K. Seki, M. Yagi, M. He, J.B. Halpern and H. Okabe. Chemical Physics Letters 313, 451-55 (1999).
  10. "Rotational State-to-State Rate Constants and Pressure Broadening Coefficients for He-C2H2 Collisions: Theory and Experiment". T.G.A. Heihmen, R. Moszynski, P.E.S. Wormer, A. v.d. Avoird, A.D. Rudert, J.B. Halpern, J. Martin, W.B. Gao and H. Zacharias. Journal of Chemical Physics 111, 2519 (1999).
  11. "Comment on Anisotropic Translational Cooling: Velocity Dependence of Collisional Alignment in a Seeded Supersonic Expansion". C. Pibel and J.B. Halpern. Journal of Physical Chemistry 103, 4421 (1999).
  12. "The Vinyl Radical (A 2A" <-- X 2A' ) Spectrum Between 530 and 415 nm Measured by Cavity Ring Down Spectroscopy", C.D. Pibel, A. McIlroy, C.A. Tatjes, S. Alfred, K. Patrick and J.B. Halpern. Journal of Chemical Physics 110, 1841 (1999).

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