ICMCTF2003 Session TS2: Self-Organization and Surface Response Effects in Thin Film Technology

Tuesday, April 29, 2003 1:30 PM in Room Royal Palm 1-3

Tuesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	TS2-1 Exact Positioning and Perfect Alignment of Semiconductor Quantum Dots and Nanotubes O. Schmidt, H. Heidemeyer, C. Deneke, R. Zapf-Gottwick (Max-Planck-Institut Für Festkoerperforschung, Germany) Dense arrays of perfectly ordered quantum dots (QDs) and lateral quantum dot molecules (QDMs) are fabricated on GaAs(001) and Si(001) substartes. This result is achieved by growing the QDs and QDMs on patterned surfaces decorated with periodoc 2D hole arrays. The ability to control the exact position of self- assembled QDs opens the door for new visionary single QD devices. Furthermore, we release strained semiconductor bilayers from their surface to fabricate individual rolled-up micro- and nanotubes at well-defined positions. We control the diameter of these tubes from the nano- to micrometer range by simply changing the layer thicknesses and built-in strain. Our experimental results are excellently described by existing theory. We present a straight GaInP microtube of more than 2 mm length and a length to diameter ratio of about 2000. Possible applications of this new technology are discussed.
2:10 PM		TS2-3 Self-Oganized Nanostructure Formation in SiGe Films C. Teichert, S. Abermann, C. Hofer (University of Leoben, Austria); T. Bobek, S. Facsko (RWTH Aachen, Germany); K. Lyutovich (University of Stuttgart, Germany); H. Kurz (RWTH Aachen, Germany); E. Kasper (University of Stuttgart, Germany) The ongoing trend towards miniaturization in high-technology applications calls for efficient ways to fabricate large-area nanostructured film surfaces. Spontaneous pattern formation during heteroepitaxial growth is an elegant route towards this goal [1]. This will be demonstrated for SiGe films grown on vicinal Si(001) substrates. In this system, the growth front undergoes a series of strain-relief mechanisms that include the formation of {105}-faceted three-dimensional crystallites and the evolution of a dislocation network. By tuning substrate miscut and film thickness or growing superlattices a variety of patterns with different symmetries can be obtained. Recently, it has been demonstrated that ion erosion of compound semiconductors may also result in well ordered surface patterns [2]. On the technological most relevant silicon surfaces this method failed so far. However, by bombarding self-organized SiGe films the nanopatterns can indeed be transformed into the Si substrate. The details of the pattern transition and its dependence on ion energy are discussed in the framework of current theories of ion bombardment induced pattern formation. Research supported by the FWF, Austria (No. P14009-TPH). [1] C. Teichert, Phys. Rep. 365, 335 (2002) [2] S. Facsko, et al. Science 285, 1551 (1999); F. Frost, et al., Phys. Rev. Lett. 85, 4116 (2000) .
2:30 PM		TS2-4 Novel Self-organized Nanostructures in Metastable Transition Metal Nitride Layers Formed Using High-Flux, Low-Energy Ion Irradiation During Growth I. Petrov (Frederick Seitz Materials Research Laboratory\University of Illinois); T.-Y. Lee, C.-S. Shin, Y.-W. Kim, N. Hellgren, J.-G. Wen (University of Illinois); J. Patscheider (EMPA, Switzerland); J.E. Greene (University of Illinois) We use high-flux, low-energy ion irradiation during low-temperature growth to control the kinetic pathways of phase separation in metastable transition-metal nitride layers in order to produce novel nanostructures composed of self-organized nanolamellae in δ-TaN_x or nanocolumns in Ti_1-xCe_xN. Coherent δ-TaN(111)/γ-Ta₂N(0002) nanolamellae form spontaneously in reactively-sputter-deposited TaN_x layers when using ion energy E_i ~ 50 - 65 eV with an ion-to-metal flux ratio J_i/J_Me ~ 11; at lower E_i the films are phase-pure metastable δ-TaN_x. The nanolayers are coherent platelets of alternating metastable cubic δ-TaN_x and thermodynamically-stable hexagonal γ-Ta₂N phases which are lattice-matched along their hexagonal closed-packed δ-TaN(111) and γ-Ta₂N(0002) planes. The formation of γ-Ta₂N nanolamellae is attributed to ion-irradiation-induced ordering of N vacancies within the (111) N planes of δ-TaN that causes hexagonal stacking of the closed-packed Ta planes. The nanolamellar TaN layers exhibit superhardness values (H = 40-45 GPa). During reactive sputter-deposition of metastable Ti_1-xCe_xN alloys, we observe nanophase films with x>0.1. Under conditions of low ion-irradiation, i.e. grounded or floating substrates, the nanostructure consists of equiaxed grains which forms due to continuous renucleation induced by CeN segregation. This is analogous to the nanostructure to the one observed in crystalline/amorphous nanocomposites, e.g. TiN/Si₃N₄. In contradistinction, a novel nanocolumnar structure forms when the alloys are grown under intense ion-irradiation with J_i/J_Me ~ 15 and E_i = 45 eV. The intense ion mixing in the near surface area allows sufficient adatom mobility to form local TiN- and CeN-rich areas that propagate along the growth direction.
2:50 PM		TS2-5 Effects of the Sb₂Te₃ Crystallization-induced Layer on Crystallization Behaviors and Properties of Phase Change Optical Disk W.-H. Wang, L.-C. Chung, C.-T. Kuo (National Chiao Tung University, Taiwan, ROC) The conventional phase-change optical disk is generally fabricated by the sputtering process, which has a drawback of requiring an initialization process to change the as-deposited recording layer in the disk from amorphous to crystalline phases, before the disk can be used for reading or writing. In order to develop an initialization-free process, the Sb2Te3 alloy was used as target to deposit an additional layer below or above the recording Ge₂Sb₂Te₅ layer to study its effect on crystallization behaviors of the recording layer. The results show that the upper Sb-Te layer has no significant effect on crystallization behavior of the recording layer. The effect of the additional Sb-Te lower layer is essentially to reduce the activation energy of crystallization of Ge₂Sb₂Te₅ recording layer by inducing nucleation from (110) plane of Sb-Te crystals. This is taking the advantage that the crystallization temperature of Sb-Te crystal is about 85°C below that of Ge₂Sb₂Te₅ crystal, in addition to a lower lattice mismatch and the same crystal structure between two crystals. From the Johnson-Mehl-Avrami kinetic analyses of amorphous-crystalline transformation, it indicates that the Avrami exponent (n) of the rate equation is an increasing function of Sb-Te lower layer thickness. At the Sb-Te lower layer thickness of 15 nm or higher, the n values are greater than 2.5, signifying a desired nucleation controlling process. However, at higher Sb-Te thickness, the electrical signal modulation (m) of the disk can be reduced to an unacceptable lower value. In other words, the results depict that the Sb-Te-assisted disks with Sb-Te lower layer thickness between 13 and 20 nm show the best combination of reflectivity and modulation. The results also indicate that the crystallization time of the Sb-Te-assisted disks is below 70 ns, which is much lower than 100 ns for commercial disks, implying a higher writing speed is possible. The most important advantage of this process is that the Sb-Te-assisted disks are required no initialization process for Sb-Te lower layer thickness between 13 and 20 nm, because the as-deposited disks can be directly written and erased.
3:10 PM		TS2-6 Thin Films Formation and Self-Organization during Friction Under Current Collection Conditions I.S. Gershman, N.A. Bushe (All-Russian Railway Research Institute, Russia) The thin films are forming on the surface during friction with the composition and properties that are significantly different from the same characteristics of the base materials of the tribo-couples. It is shown basing on the analysis of entropy balance that wear intensity of non-equilibrium surface films (dissipative structures) is lower that the same characteristic of equilibrium surface films. The conclusion is proved by the data for the ‘copper-graphite’ electric sliding contact. Dissipative structures do not depend on initial conditions and are stable in a wide range of friction parameters. Thus the development of wear resistant materials should be based on the surface films studies. The investigations of the copper contact wires friction surfaces are performed and the mechanisms of the self-organization at different currents are determined; the leading role of carbon is shown. Finally a novel material is developed on the natural graphite matrix for current collectors applications. The self-organization of the developed material starts at lower currents compare to the traditional materials. The wear resistance and arc-resistance of the developed material is superior to the majority of traditional materials besides mechanical and conductive properties of the material are lower. It is shown for stable conditions that the wear intensity drops due to entropy production decrease. An analytical equation is derived for current lubricating effect basing on Prigogine theorem. This equation is experimentally proved for different current collecting materials. It is shown that current lubricating effect is typical for dissipative surface structures. The process of self-organization starts with dissipative structures formation when the system passes the bifurcation point. It is shown using excessive entropy production as the Lapunov function that an instability is possible for tribo-system with current collection when the contact resistance decrease vs. current growth. This is also proved by experimental data.
3:30 PM	Invited	TS2-7 Formation of Stable Nanostructures in Superhard Coatings by Self-Organization due to Spinodal Phase Segregation S. Veprek (Technical University Munich, Germany) Super- (H_v ~~ 40 - 70 GPa) and ultrahard (H_v ≥70 GPa in the range of diamond) nanocomposites which are prepared according to the generic design principle [1] under conditions of a strong thermodynamically driven segregation show not only a high hardness combined with a high elastic recovery limit and high resistance against cracks for-mation [2] but also a high thermal stability up to ≥ 1100°C [3] and a high tensile strength of 10 - 40 GPa that is approaching the ideal decohesion strength of flaw-free materials [4]. The absence of built-in defects can be understood in terms of a self-organization of the nanostructure during the growth. I shall summarize the experimental results from our work as well as from published papers of other authors which show that such a phase segrega-tion has many features that are characteristic of spinodal decomposition. A relatively small increase of hardness during the recrystallization of (TiZr)N [5,6] and (TiZr)C [5] coatings was reported and attributed to spinodal decomposition but this idea was not further substantiated and elaborated. I shall discuss the thermodynamic and kinetic parameters controlling the spi-nodal decomposition and the dependence of the crystallite size of the formed nanostructure on the properties of the phases. This will explain the discrepancies found in the recent published papers on the relatively low hardness enhancement (e. g. [7]) or its complete absence [8] in "Ti-Si-N" coatings prepared by different deposition techniques under conditions when the spinodal decomposition is thermodynamically or kinetically hindered. Furthermore, I shall also explain the recent findings that superhardness of 40-50 GPa can be obtained in nanocom-posites even if the crystallite size is larger than 10-20 nm. [1] S. Veprek and S. Reiprich, Thin Solid Films 268 (1995) 64. [2] S. Veprek and A. S. Argon, J. Vac. Sci. Technol. B 20 (2002) 650. [3] H.-D. Männling, D. S. Patil, K. Moto et al., Suf. Coat. Technol. 146-147 (2001) 263. [4] S. Veprek, S. Mukherjee, P. Karvankova, et al., J. Vac. Sci. Technol., 2003 (submit-ted) [5] O. Knotek and A. Barimani, Thin Solid Films 174 (189) 51 [6] R. A. Andrievski, I. A. Anisimova and V. P. Anisimov, Thin Solid Films 205 (1991) 171 [7] [J. Patscheider, T. Zehnder and M. Diserens, Surf. Coat. Technol. 146-147 (2001) 201. [8] W. J. Meng, X. D. Zhang, B. Shi et al., J. Mater. Res. 17 (2002) 2628.
4:10 PM		TS2-9 Nano-Crystaline FAD (Filtered Arc Deposited) TiAlN PVD Coatings for High-Speed Machining Application G.S. Fox-Rabinovich, G.C. Weatherly (McMaster University, Canada); A.I. Dodonov (VIT Company, Russia); A.I. Kovalev (Surface Phenomena Researches Group Physical Metallurgy Institute CNIICHERMET, Russia); L.S. Shuster (Ufa Aircraft Technology University, Russia); S.C. Veldhuis, G.K. Dosbaeva (McMaster University, Canada); D.L. Wainstein (Surface Phenomena Researches Group Physical Metallurgy Institute CNIICHERMET, Russia); M.S. Migranov (Ufa Air Craft Technological University, Russia) The main advantage of FAD (filtered arc deposition) technique is a significant grain refinement that leads to the formation of nano-crystalline (grain size around 60-80 nm) PVD coatings. This improves the wear resistance of FAD TiAlN coating during high-speed machining when cutting tool oxidation wear predominates. A study of the surface structure characteristics of the FAD TiAlN coatings using SEM, EDS, TEM, AES, and SIMS was performed. The microhardness of the coatings and their adhesion to the substrate were measured. The microstructure of the chips was analyzed. The compression of the chips as well as shear angle was measured. The friction parameter on the rake surface of tools was determined in- situ. It was shown that the major cause of the high wear resistance of the FAD coatings during high-speed machining is the formation of a thin protective oxide film (tribo-ceramic) on the cutting tool surface. The grain size refinement of the coatings promotes the formation of a protective alumina film. Tribo-ceramics that form at the surface of nano-crystalline FAD TiAlN coating during high-speed cutting mainly consist of alumina-like protective thin films whereas the films forming on the surface of TiAlN commercial coatings with coarser grains consist only of non-protective titania. The formation of the protective alumina films significantly improves coated tools friction and wear performance. The tendency of the workpiece material to adhere is reduced and considerably more heat is dissipated via chip removal. This is a major cause of the enhanced wear resistance of the FAD coatings. Tribo-oxidation during cutting is a typical process of the self-organization of TiAlN coatings that results in a quasi-stabilization of cutting tool wear. The self-organization and friction control for coated cutting tools is considered basing on a non-equilibrium thermodynamic approach.
4:30 PM		TS2-10 Surface Response Effects in Diesel Motors M. Kopnarski, H. Oechsner (IFOS, Technical University Kaiserslautern, Germany); B. Kehrwald, A. Gervé (IAVF Antriebstechnik AG, Germany) Friction and wear strongly influence the properties of surfaces which get in contact during the tribological process. Tribomutation effects in thin layers at the tribostressed surfaces can be characterized by corresponding surface analytical methods. As an example, it will be shown by AES sputter depth profiling that the chemical composition of the gusset area in private car diesel motors varies characteristically with the working conditions during the running-in period of bench tests. The gusset is a circular zone of the cylinder wall at the top dead center of the piston motion and is subjected to an increased wear rate. High load conditions during 2 hours of running-in result in the self-organizing formation of thin surface layers which lead to significant lower wear rates than those measured for other running-in procedures. Interestingly the beneficial effect of this some nm thick layers is well preserved even after 145 or 300h total running time. A simple model to understand this behaviour will be presented.
4:50 PM		TS2-11 Improvement of 'Duplex' PVD Coatings for HSS Cutting Tools by Ion Mixing G.S. Fox-Rabinovich, G.C. Weatherly (McMaster University, Canada); A.I. Kovalev (Surface Phenomena Researches Group, Physical Metallurgy Institute, CNIICHERMET, Russia); S.N. Korshunov (Russian Research Center "Kurchatov Institute", Russia); V.N. Scvortsov (All-Russian Scientific and Research Institute for Machinery, Russia); L.S. Shuster (Ufa Aircraft Technology University, Russia); G.K. Dosbaeva (McMaster University, Canada); D.L. Wainstain (Surface Phenomena Researches Group, Physical Metallurgy Institute, CNIICHERMET, Russia) The paper considers some ways to improve 'duplex' coatings for cutting tool applications. These coatings were formed by diffusion saturation with nitrogen (ion nitriding) followed by the application of a (Ti,Cr)N hard PVD coating. The coating includes an additional ion mixed layer applied to the previously nitrided surface of HSS prior to hard PVD coating deposition. Such multi-layered coatings significantly increase (by 3.0-4.0 times) the wear resistance of cutting tools compared to 'duplex' coatings. Three transition metals (Ti, Zr, W) and Al were studied in combination with three non-metallic elements (N, C, O), ion mixed into the substrate surface, to compare the effects on the HSS cutting tool life with the 'duplex' coating. The highest wear resistance after the triple surface treatment is achieved when titanium together with nitrogen are used to modify the surface by ion mixing. The surface of the ion mixed layer before and after cutting was investigated using AES and SIMS methods. The friction parameter of the modified layer was studied vs. temperature. The improved ability of the ion mixed layer to accommodate the forces of cutting by elastic deformation was shown using nano-indentation tests. Ion mixing produces a thin surface layer with an amorphous-like structure that promotes quasi-stabilization of the wear process as a result of a self-organization mechanism. In this case the friction control implies a prevention of the non-linear irreversible processes with intensive entropy production that leads to stability loss and deep surface damage. This is beneficial for the prolongation of a stable wear stage, considerably enhancing the tool life.