Papers

ICMCTF2008 Session F2: In Situ Characterization

Friday, May 2, 2008 8:00 AM in Room Sunrise

Friday Morning

Start	Invited?	Item
8:00 AM		F2-1 In-Situ XRD Studies of Thin Film and Nanostructure Growth M.I. Richard, T.U. Schulli, G. Renaud (CEA Grenoble, France); E Wintersberger (University of Linz, Austria); V. Favre-Nicolin (CEA Grenoble, France); V. Holy (Charles University Prague, Czech Republic); G. Bauer (University of Linz, Austria) An overview will be presented on x-ray diffraction and x-ray scattering methods suitable for in-situ growth studies of films and nanostructures. In particular, recent advances achieved by employing dedicated beamlines at synchrotron sources with attached growth facilities like molecular beam epitaxy will be reviewed. At such beamlines, apart from composition and strain, also the transition from tow-dimensional to three-dimensional growth modes , encountered in particular in strained layer epitaxy, can be studied in detail. In-situ grazing incidence small angle scattering studies give valuable insight into size and shape and positional correlation of such nanostructures on surfaces.
8:40 AM		F2-3 Measurement of Strain Evolution in Polycrystalline Films During Thermal Processing A.P. Paulikas, B.W. Veal, J. Elam, M.J. Pellin (Argonne National Laboratory) We have developed a technique, using x-ray synchrotron radiation, to measure biaxial in-plane strains in polycrystalline films. An adaptation of the well known sin² ψ method, this technique acquires, in a single exposure, the elliptically distorted Debye-Scherrer diffraction pattern from a stressed film. Analysis of the elliptical distortion yields the biaxial strain. In-plane biaxial strains were measured in film samples of SnO₂, TiO₂, ZrO₂ and In₂O₃, as samples were heated in air to 1100°C. The samples, deposited on Si substrates, were prepared using the ALD (atomic layer deposition) technique. The SnO₂ and TiO₂ samples were amorphous as deposited but converted to fine-grained polycrystalline films with heating. At crystallization, the SnO₂ showed an in-plane tensile strain that relaxed to near-zero at about 900°C, when heated with a 200°C/hr temperature ramp. With cooling, the sample showed a small and systematic increase in tensile strain, a consequence of the coefficient of thermal expansion (CTE) difference between film and substrate. The ZrO₂ and In₂O₃ films, which were crystalline as deposited, showed large compressive strains following deposition. With heating, the compressive strains initially increased, reflecting the CTE difference between films and substrate. At higher temperatures (T > 600 C for ZrO₂ and T > 300°C for In₂O₃), the strains were relieved by plastic flow in the films. With cooling from 1100°C, and with subsequent thermal cycling to 1100°C, the in-plane strains were tensile, reflecting the high temperature strain relieved condition and the CTE difference on cooldown. The ZrO₂ film, as deposited, contained a mixture of monoclinic and tetragonal phases. As the sample was heated, the tetragonal phase converted to the monoclinic phase, the stable low temperature form.
9:00 AM		F2-4 Small Signal Frequency Response Studies for Plasma Electrolytic Oxidation A.L. Yerokhin (University of Sheffield, United Kingdom); E.V. Parfenov (Ufa State Aviation Technical University, Russia); A. Matthews (University of Sheffield, United Kingdom) Plasma enhanced electrochemical treatments are widely recognised as more efficient than electrochemical ones. However, their large-scale application is still restricted, mainly due to limitations in the process control and automation. This problem can be resolved if the frequency response (FR) of the system is known and can be used for the process characterisation. Our previous work has shown the effectiveness of the large signal mode for FR studies of plasma electrolytic oxidation (PEO) of aluminium¹. This research is dedicated to the FR measurements in the small signal mode corresponding to small deviation of voltage and current at large DC values. The study was carried out during PEO of Al at DC voltages varied from 450 to 600V. The FR obtained is a complex frequency dependent conductivity of the PEO electrolyser; this complex number is represented by a modulus and a phase angle. Under potentiostatic conditions, the modulus evolution strongly correlates with the average current value; therefore, it bears insufficient amount of new information. The FR phase angle measured within this study was never obtained before. Depending on the frequency, it varies between 0 and 70 deg (capacitive). One of the most notable features of this characteristic is low values at 500-5000 Hz when microdischarges appear during PEO. The other feature is a correlation with the coating growth. As a result, a new type of PEO process characterisation was developed and shown to be effective for the microdischarge and surface properties estimation during the treatment. ¹E.V.Parfenov, A.L.Yerokhin, A.Matthews, Surface and Coating Technology 201(2007)8661.
9:20 AM		F2-5 In-Situ Scanning Electron Microscopy Based Micro-/Nanomechanical Testing J. Michler (Swiss Federal Institute for Materials Testing and Research (EMPA), Switzerland) Macroscopically, mechanical properties are dominated by a statistical distribution of defects with characteristic length scales like size and distribution of flaws in brittle fracture or dislocation interdistance in metal plasticity. As dimensions like film thickness or external device extensions are scaled down to the characteristic length, material properties become controlled by geometrical constraints. The understanding of these physical size effects is on the one hand a prerequisite for efficient materials processing and high reliability of devices ranging from the sub-mm range in case of MEMS or thin wafer applications to nanoelectromechanical systems or nanowires for sensor and electronic applications. On the other hand new electronic or optical properties of materials may be achieved as mechanical strains can be increased up to several percent in a device at nanometer scale without material failure. Electron microscopy based micromechanical testing allow to manipulate small samples under vision control and to observe mechanical deformation or fracture events in-situ. The presentation will give a broad overview on in-situ SEM based indentation, tensile, compression, bending and vibrational experiments and associated focussed ion beam machining of test samples, nanomanipulation of samples and image processing techniques. The potential of the technique will be illustrated by several case studies: -buckling, fracture strength and plastic deformation of semiconductor micro -pillars loaded in uniaxial compression -shear band formation in amorphous metals during nanoindentation -Youngs modulus and strength of semiconductor nanowires -Youngs modulus and strength of metal nanowires and metal nanotubes -deformation mechanisms in ultrathin multilayer hard coatings.
10:00 AM		F2-7 Cathodoluminescence Study of Phase Transformation Processes in κ- and γ-Alumina Coatings Caused by Heat Treatment G. Pozina, D.H. Trinh, L. Hultman, H. Högberg (Linköping University, Sweden); H. Blomqvist, M. Collin, I. Reineck (Sandvik Tooling AB, Sweden) Aluminium oxide coatings are recognized in the metal cutting industry for their beneficial material properties such as high hardness, wear resistance, low solubility in steel, and thermal and chemical stability. The present interest is focused on metastable κ- and γ-phases which for certain wear applications have superior properties compared to the stable α-phase. Transformation due to heat treatment of κ- and γ-alumina to the stable α-Al₂O₃ may induce cracks in the coatings. From this point of view control over phase stability and quick identification of the phases are required. In this work we have shown that room temperature cathodoluminescence (CL) is a very powerful method in characterization of phase transformation processes in alumina coatings. The samples were κ- and γ-Al₂O₃ films with a thickness of 2-4 µm commercially grown on cemented carbide substrates covered by 7 µm thick TiCN layer. Annealing and in-situ XRD measurements have been done at temperatures between 900 and 1100°C, i.e. below and above the phase transition point in order to study samples both with fully transformed alumina and with mixed alumina phases. Results of XRD analysis have been compared with CL measurements to confirm that the spectral modification after annealing is caused by phase transformation. After samples have been heated above 1000°C the CL spectra were transformed completely. Annealed samples, both γ-Al₂O₃ and κ-Al₂O₃, show similar CL spectra consisting of few bands. The strongest peak is centered at 4.2 eV. Band at 3.8 eV is related to the well-known for α-Al₂O₃ 1B-1A transition of an F⁺ center, which is an oxygen-ion vacancy trapping one electron. The emission band at 4.2 eV is due to divalent impurities such as calcium or magnesium taking place of Al³⁺ site and building F_cat centers. Since it is clear from XRD analysis that annealing leads to phase transformation of γ- and κ-alumina to the stable α-phase, we can attribute the CL spectra of annealed samples to α-alumina.
10:20 AM		F2-8 Thermal Stability and Surface Morphological Evolution of Transition-Metal Nitrides S. Kodambaka (University of California Los Angeles); V. Petrova, J. Bareno (University of Illinois, Urbana); S.V. Khare (The University of Toledo); K. Ohmori, W. Swiech, I. Petrov, J.E. Greene (University of Illinois, Urbana) B1 NaCl-structure transition-metal nitrides are widely used as hard wear-resistant coatings on cutting tools, as diffusion-barrier layers in microelectronics, as corrosion-resistant coatings on mechanical components, and as scratch-resistant layers on optics and architectural glass. Thermal and chemical stability of these materials depend sensitively on the surface and interfacial morphologies. Hence, understanding the morphological evolution of transition-metal nitride thin film surfaces is essential for improving the performance of transition-metal nitride coatings in all the above applications. As a first step, we choose TiN as a model system and studied the dynamics of (001) and (111) surfaces during annealing. Using in situ high-temperature scanning tunneling microscopy (STM) and low-energy electron microscopy (LEEM), we follow the kinetics of two-dimensional (2D) TiN island Ostwald ripening, surface step nucleation and growth, step fluctuations, and island shape evolutin on both (001) and (111) TiN terraces. We obtain time-resolved STM and video rate LEEM measurments of 2D TiN island sizes and shapes as a function of annealing temperatures betwen 1000 and 1750 K. From the data, in combination with continuum models, we determine the rate-limiting mechanisms governing morphological evolution of TiN surfaces and extract surface and bulk mass transport parameters and step energies. We expect that our studies, which are general and applicable to other material systems, provide valuable insights into the thermal stability of transition-metal nitride thin films. *work done at University of Illinois.