University of Illinois Frederick Seitz Materials Research Laboratory Dislocation-Driven Surface Dynamics on Solids Sanjay V. Khare 1, Suneel Kodambaka, Wacek Swiech, Kenji Ohmori, Ivan Petrov, & Joe Greene Dept. of Materials Science and Frederick Seitz Materials Research Laboratory University of Illinois at Urbana-Champaign Funded by US-DOE through grant DEFG02-91ER45439 Frederick Seitz Materials Research Laboratory 1 1 Department of Physics and Astronomy University of Toledo

University of Illinois Frederick Seitz Materials Research Laboratory Dislocations in solids Bulk dislocation dynamics have been extensively studied. Surface-terminated dislocations affect nanostructural and interfacial stability, crystal growth kinetics, mechanical, chemical, & electronic properties of solids. Very little is known concerning the effects of dislocations on surface dynamics. 250 Å Brune, Giovannini, Bromann, & K. Kern Nature 394, 451 (1998) Teng, Dove, Orme, & J.J. De Yoreo Science 282, 724 (1998) Spila, Desjardins, D’Arcy-Gall, Twesten, & J.E. Greene, JAP 93, 1918 (2003) SiGe/Si Ag/Pt KDP

University of Illinois Frederick Seitz Materials Research Laboratory * K.F. McCarty & N.C. Bartelt: Phys. Rev. Lett. 90, (2003); Surf. Sci. 527, L203 (2003); Surf. Sci. 540, 157 (2003); Journal of Crystal Growth 270, 691 (2004). Develop fundamental understanding of the effect of dislocations on surface dynamics Model system: TiN Use LEEM to investigate surface morphological evolution kinetics as a function of: annealing time temperature & N 2 partial pressure. * Objectives

University of Illinois Frederick Seitz Materials Research Laboratory S. Kodambaka, N. Israeli, J. Bareño, W. Święch, K. Ohmori, I. Petrov, & J.E. Greene, Surf. Sci. 560, 53 (2004). 2D TiN(111) island decay: detachment-limited kinetics + highly permeable steps = 5x10 -8 Torr T = 1550 K 2.8±0.3 eV TiN/TiN(111)

University of Illinois Frederick Seitz Materials Research Laboratory TiN/TiN(111) Spirals field of view: 2.5  m t real = 90 s t movie = 9 s T = 1688 K ~ 0.5T m = 5x10 -8 Torr Observed during annealing in the absence of deposition/evaporation NOT BCF spirals

University of Illinois Frederick Seitz Materials Research Laboratory near-equilibrium* shape-preserving periodic absenceapplied stress net mass change by deposition/evaporation. absence of applied stress & net mass change by deposition/evaporation. t = 0 s15 s 31 s47 s *S. Kodambaka, V. Petrova, S.V. Khare, D.D. Johnson, I. Petrov, & J.E. Greene, Phys. Rev. Lett. 88, (2002).  = 47 s TiN(111) spiral step growth T = 1688 K

University of Illinois Frederick Seitz Materials Research Laboratory TiN/TiN(111) = 5x10 -8 Torr field of view 5.6  m t real = 650 s t movie = 13 s Spirals grow with a constant  & 2D island areas decrease at a constant rate T = 1670 K T = 1690 K

University of Illinois Frederick Seitz Materials Research Laboratory TiN(111) spirals: E growth = 4.6±0.2 eV C = ±0.6 s -1 2D TiN(111) islands*: E decay = 3.1±0.2 eV C = ±0.6 s -1 = 5x10 -8 Torr TiN/TiN(111) *S. Kodambaka, N. Israeli, J. Bareño, W. Święch, K. Ohmori, I. Petrov, & J.E. Greene, Surf. Sci. 560, 53 (2004). TiN(111) spiral step kinetics is different from that of 2D islands.

University of Illinois Frederick Seitz Materials Research Laboratory TiN/TiN(111) 2D island decay: E a = 2.8 eV Spiral step growth: E d = 4.6 eV Ti or TiN desorption*: E evaporation ~ 8-10 eV E a << E d << E evaporation * D. Gall, S. Kodambaka, M.A. Wall, I. Petrov, & J.E. Greene, J. Appl. Phys. 93, 9086 (2003). Spiral nucleation and growth MUST be due to bulk mass transport !! Proposed mechanism: driving force: bulk dislocation line energy minimization  surface spiral step formation via bulk point defect transport dislocation cores emit/absorb point defects at a constant thermally- activated rate. S. Kodambaka, S.V. Khare, W. Święch, K. Ohmori, I. Petrov, & J.E. Greene, Nature 429, 49 (2004). Modeling dislocation-driven spiral growth

University of Illinois Frederick Seitz Materials Research Laboratory Modeling dislocation-driven spiral growth At steady state: B.C.s: R(T) - thermally-activated point defect emission/absorption rate C - point defect concentration (1/Å 2 ) D s - surface diffusivity (Å 2 /s) k s - attachment/detachment rate (Å/s)  - area/TiN (Å 2 ) Step velocity:  constant growth rate dA/dt r core r loop S. Kodambaka, S.V. Khare, W. Święch, K. Ohmori, I. Petrov, & J.E. Greene, Nature 429, 49 (2004).

University of Illinois Frederick Seitz Materials Research Laboratory  is a thermally-activated constant A o : area outside of which R is negligible  : area/TiN (Å 2 )  : spiral angular velocity (rad/s) R(T): thermally-activated point defect emission/absorption rate  Total surface flux = R/A o 1 rotation  1 ML in 2  /  sec Modeling dislocation-driven spiral growth

University of Illinois Frederick Seitz Materials Research Laboratory  decreases monotonically with annealing time field of view 5.6  m T = 1725 K = 5x10 -8 Torr d  /dt ~ /s 2 at 1725 K TiN/TiN(111)  vs. t

University of Illinois Frederick Seitz Materials Research Laboratory 2D TiN(111) island & spiral step kinetics are independent of N 2 partial pressure 5x x10 -7 vacuum 5x10 -7 vacuum 1  m T = 1670 K TiN/TiN(111)  vs. pN 2

University of Illinois Frederick Seitz Materials Research Laboratory E spiral is independent of N 2 pressure & sample history 4.5±0.4 eV at 5x10 -8 Torr 4.6±0.2 eV in vacuum TiN/TiN(111)

University of Illinois Frederick Seitz Materials Research Laboratory Investigated the nucleation & growth kinetics of TiN(111) spiral steps using HT-LEEM. Spiral growth is qualitatively & quantitatively different from 2D island coarsening/decay. Spiral growth is localized BCF growth/etch spirals. Angular velocity: *decreases with time irrespective of N 2 pressure. *does not vary significantly with spiral geometry. *thermally-activated with a constant energy barrier (~ 4.5 eV), independent of the sample history & N 2 pressure. Conclusions

University of Illinois Frederick Seitz Materials Research Laboratory LEEM – Modes of Operation Bright Field LEEM Dark Field LEEM Photoemission (PEEM)Mirror microscopy (MEM)

University of Illinois Frederick Seitz Materials Research Laboratory 2D TiN(111) island decay ALL islands in the cone decay at nearly same rates  mass is not conserved locally T = 1285 o C T = 1320 o C T = 1350 o CT = 1380 o C

University of Illinois Frederick Seitz Materials Research Laboratory Modeling decay kinetics of islands in a cone N. Israeli and D. Kandel, PRB 60, 5946 (1999). r1r1 r2r2 r3r3 Fitting variables: Surface diffusivity D s Attachment/detachment rate K d Step permeability p Rate of bulk transport K bulk Step-step interaction g Solve 2D steady-state diffusion eqn.: B.C.s: adatom fluxes at island step edges Derive general relation for dA i /dt Compare calculated r vs. t with expt.l data

University of Illinois Frederick Seitz Materials Research Laboratory 2D TiN island dynamics studies 2D island coarsening kinetics (Ostwald ripening) TataTata Surf. Sci. 526, 85 (2003). Island shape fluctuation analysis PRL 88, (2002). Equilibrium island shape R  110  R  100   100   110  Surf. Sci. 513, 468 (2002). 2D island coalescence kinetics 50 Å Surf. Sci. 540, L611 (2003).

University of Illinois Frederick Seitz Materials Research Laboratory K bulk /K d = 2.5 & p = 0 p/K d = 2000 & K bulk = 0 High g, p = 0 & K bulk = 0 TiN/TiN(111) T = 1350 o C o LEEM data calculation 2D TiN(111) islands decay kinetics detachment-limited + highly permeable steps OR bulk diffusion

University of Illinois Frederick Seitz Materials Research Laboratory TiN/TiN(111) T = 1670 K = 5x10 -8 Torr field of view 5.6  m t real = 650 s t movie = 13 s Spirals grow with a constant  & 2D island areas decrease at a constant rate

University of Illinois Frederick Seitz Materials Research Laboratory TiN/TiN(111)  vs. spiral geometry field of view 5.6  m  (10 -2 rad/s) 5x < Spiral step velocities do not vary significantly with local environment 1650 K 1675 K