Senior Research Associate

Department of Chemical Engineering
Doherty Hall Room 3101
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-5662 (lab)
412-268-9537 (office)
412-268-7139 (fax)

Several investigations of the tribological properties of various crystalline materials have shown that friction forces between single crystals are anisotropic with respect to either the shearing direction or the lattice orientation. Recently, the combined use of an ultra-high vacuum tribometer and a number of surface science techniques has enabled us to start to explore the anisotropic tribological properties of Ni(100) and Pd(100) surfaces.

Measurements made by systematic variation of the crystallographic orientation of the Ni(100) surfaces have revealed that the friction coefficient is anisotropic with respect to lattice orientation (Fig. 1). The minimum static friction coefficient (µ) occurred when the two clean Ni(100) surfaces were misoriented by q ~ 45° (µ= 2.5±1), while for other angles the static friction was much higher, µ= 8.6±2.5 (Ref. 1). This effect of misorientation is also observed for Pd(100) surfaces (Ref. 2).

In all the systems described above, the friction anisotropy is measured under conditions of plastic deformation rather than elastic contact. However, recent molecular dynamics simulations and some experiments have shown that the friction force disappears at small loads, i.e., when the contact is elastic and no deformation is observed. In order to verify this possibility, we are planning to measure the friction coefficient between a pair of Si(100) surfaces under elastic contact.

Figure 1: FCC lattice unit cell with the (100) surface exposed at the top. The four (111) slip planes are shown in the bulk of the unit cell and project out to the (100) surface. The <110> shearing direction is marked as 0°. When the two surfaces are aligned, shearing occurs along the 0° direction for both and friction is high. When the two surfaces are misaligned by 45° the friction is low. Under these conditions the shearing occurs along the 0° direction for one crystal and along the 45° for the other.

Using my previous experience in carbon-based thin films (Ref. 3-6) I am also collaborating in a research program of the laboratory that studies the physico-chemical properties of lubricant films deposited on freshly sputtered amorphous carbon overcoats of data storage disks.

• J.S. Ko, A.J. Gellman, "Friction Anisotropy at Ni(100)/Ni(1000) Interfaces" Langmuir; 2000, 16(22), 8343-8351.
• "Friction Anisotropy at Pd(100)/Pd(1000) Interfaces", in preparation.
• E. Broitman, N. Hellgren, J. Neidhardt, I. Brunell, L. Hultman "Electrical properties of carbon nitride thin films: role of morphology and hydrogen content" Journal of Electronic Materials; 2002, 31(9), L11-L15.
• E. Broitman, N. Hellgren, O. Wanstrand, M.P. Johansson, T. Berlind, H. Sjöström, J.-E Sundgren, M. Larsson, L. Hultman, "Mechanical and tribological properties of CNx films deposited by reactive magnetron sputtering" Wear; 2001, 248(1-2),55-64.
• E. Broitman, W. Macdonald, N. Hellgren, G. Radnoczi, Z. Czigany, A. Wennerberg, M. Jacobsson, L. Hultman, "Carbon nitride films on orthopedic substrates" Diamond and Related Materials; 2000, 9(12), 1984-1991.
• E. Broitman, W.T. Zheng, H. Sjöström, I. Ivanov,J.E. Greene, J.-E. Sundgren, "Stress development during deposition of CNx thin films" Applied Physics Letters; 1998, 72(20), 2532-2534.

• A. Zocco, A. Perrone, E. Broitman, Zs. Czigany, L. Hultman, M. Anderle, N. Laidani, "Mechanical and tribological properties of CNX films deposited by reactive pulsed laser ablation" Diamond and Related Materials; 2002, 11(1), 98-104.
• N. Hellgren, N. Lin, E. Broitman, V. Serin, S.E. Grillo, R. Twesten, I. Petrov, C. Colliex, L. Hultman, J.-E Sundgren, "Thermal stability of carbon nitride thin films" Journal of Materials Research; 2001, 16(11), 3188-3201.
• H. De Rosa, G. Cardus, E. Broitman, R. Zimmerman, "Structural properties of AlSn thin films deposited by magnetron sputtering" Journal of Materials Science Letters; 2001), 20(14), 1365-1367.
• N. Hellgren, M.P. Johansson, E. Broitman, L. Hultman, J.-E. Sundgren, "Anisotropies in magnetron sputtered carbon nitride thin films" Applied Physics Letters; 2001, 78(18), 2703-2705.
• S.E. Grillo, N. Hellgren, V. Serin, E. Broitman, C. Colliex, L. Hultman, Y. Kihn, "Monitoring the structural and chemical properties of CNX thin films during in situ annealing in a TEM" European Physical Journal: Applied Physics; 2001), 13(2), 97-105.
• N. Hellgren, M.P. Johansson, E. Broitman, P. Sandstrom, L. Hultman, J.-E. Sundgren, "Effect of chemical sputtering on the growth and structural evolution of magnetron sputtered CNX thin films" Thin Solid Films; 2001), 382(1,2), 146-152.
• E. Broitman, N. Hellgren, K. Jarrendahl, M.P. Johansson, S. Olafsson, G. Radnoczi, J.-E Sundgren, L. Hultman, "Electrical and optical properties of CNX(0<x<0.25) films deposited by reactive magnetron sputtering" Journal of Applied Physics; 2001, 89(2), 1184-1190.
• N. Hellgren, M.P. Johansson, B. Hjorvarsson, E. Broitman, M. Ostblom, B. Liedberg, L. Hultman, J.-E. Sundgren, "Growth, structure, and mechanical properties of CNxHy films deposited by dc magnetron sputtering in N2/Ar/H2 discharges" Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films; 2000, 18(5), 2349-2358.
• W.T. Zheng, W.X. Yu, H.B. Li, Y.M. Wang, P.J. Cao, Z.S. Jin, E. Broitman, J.-E. Sundgren, "Chemical bonding, structure, and hardness of carbon nitride thin films" Diamond and Related Materials; 2000, 9(9-10), 1790-1794.
• N. Hellgren, K. Macak, E. Broitman, M.P. Johansson, L. Hultman, J.-E. Sundgren, "Influence of plasma parameters on the growth and properties of magnetron sputtered CNX thin films" Journal of Applied Physics; 2000, 88(1), 524-532.
• M. P. Johansson, N. Hellgren, T. Berlind, E. Broitman, L. Hultman, J.-E. Sundgren, "Growth of CNX/BN:C multilayer films by magnetron sputtering" Thin Solid Films; 2000, 360(1,2), 17-23.
• K. Suenaga, M. P. Johansson, N. Hellgren, E. Broitman, C. Colliex, L. Hultman, J.-E. Sundgren, "Carbon nitride nanotubulite - densely-packed and well-aligned tubular nanostructures", Chemical Physics Letters; 1999, 300(5,6), 695-700.
• M. P. Johansson, E. Broitman, L. Hultman, J.-E. Sundgren, "Role of nitrogen in the formation of hard and elastic CNX thin films by reactive magnetron sputtering", Physical Review B: Condensed Matter and Materials Physics; 1999, 59(7), 5162-5169.
• M.P. Johansson, E. Broitman, N. Hellgren, L. Hutman, J.-E. Sundgren, "HREM studies of magnetron sputtered leek-like CNX films" Electron Microscopy 1998, Proceedings of the International Congress on Electron Microscopy, 14th, Cancun, Mex., Aug. 31-Sept. 4; 1998, 3, 89-90.
• E. Broitman, R. Zimmerman, "Ion-plated discontinuous thin film strain gauges" Thin Solid Films; 1998, 317(1,2), 440-442.
• D. Boffelli, E. Broitman, R. Zimmerman, "Resistance adjustment in RuO2-based thick film strain-gauges by laser irradiation" Journal of Materials Science Letters; 1997, 16(24), 1983-1985.
• W.T.Zheng, E.Broitman, H.Sjostrom, K.Z.Xing, S.W.Guo, I.Ivanov, L.Hultman, J.-E.Sundgren, "Reactive magnetron sputtering of CNX thin films at different substrate bias" Thin Solid Films; 1997, 308-309, 223-227.
• E. Broitman, P. Alonso, R. Aragon, R. Zimmerman, "High sensitivity strain gauge sensors" Advances in Materials Science & Technology; 1996, 1(1), 13-16.
• R. Aragon, P. Alonso, E. Broitman, M.I. Pascuet, R. Zimmerman, "Piezoresistivity of cermet thin solid films" Anales de la Asociacion Quimica Argentina; 1996, 83(6), 373-377.
• E. Broitman, R. Zimmerman, "Influence of deposition parameters on the microstructure of ion-plated films", AIP Conference Proceedings (Surfaces, Vacuum, and Their Applications); 1996, 378, 356-359.
• W.T. Zheng, H. Sjostrom, I. Ivanov, K.Z. Xing, E. Broitman, W.R. Salaneck, J.E. Greene, J.-E.Sundgren, "Reactive magnetron sputter deposited CNX: effects of N2 pressure and growth temperature on film composition, bonding, and microstructure", Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films; 1996, 14(5), 2696-2701.
• E. Broitman, P. Alonso, R. Zimmerman, "Deviations from Matthiessen's rule in continuous metal films", Thin Solid Films; 1996, 277(1-2), 192-195.
• W.J. Varhue, M. Massimo, J.M. Carrulli, V. Baranauskas, E.Adams, E.Broitman, "Deposition of yttrium sesquioxide by plasma enhanced organometallic chemical vapor deposition using an electron cyclotron resonance source", Journal of Vacuum Science & Technology, A: Vacuum, Surfaces, and Films; 1993, 11(4, Pt. 2), 1870-4.
• R. Zimmerman, E. Broitman, S. Harriague, S. Terlisky, "Order twins in (111)-evaporated thin films of copper-gold (CuAu) I", Thin Solid Films; 1990, 191(2), 275-82.
• R. Zimmerman, E. Broitman, D. Latorre, "The growth of single-crystal films of silver on rock salt by ion plating", Thin Solid Films; 1988, 165(1), L101-L105.