Papers

ICMCTF2005 Session F3: Advanced Characterization of Thin Films

Friday, May 6, 2005 8:30 AM in Room Royal Palm 4-6

Friday Morning

Start	Invited?	Item
8:30 AM		F3-1 Beating the Minimum Thermal Conductivity with W/Alumina Nanolaminates D.G. Cahill (University of Illinois at Urbana-Champaign) The thermal conductance of interfaces is a key factor in controlling thermal conduction in nanostructured materials, composites, and individual nanostructures. We have recently advanced the state-of-the-art of time-domain-thermoreflectance (TDTR) measurements of thermal transport and are using TDTR to study heat transport across individual interfaces with extremely high and low thermal conductance; and heat transport in nanoscale W/alumina multilayers that circumvent the lower-limits for homogeneous materials imposed by the minimum thermal conductivity. The 3 µm spatial resolution of our TDTR measurements also enables rapid high-resolution imaging of the thermal conductivity of complex microstructures and combinatorial samples.
9:10 AM		F3-3 Nanostructural Evolution of Interface Engineered Cr/Ti Multilayers N. Ghafoor, J. Birch, P. Persson (Linköping University, Sweden); F. Eriksson (Columbia Astrophysics Laboratory); F. Schäfers (BESSY GmbH, Germany) Normal-incidence soft x-ray multilayer mirrors require deposition of consecutive layers with no roughness accumulation over several hundred layers with individual thicknesses of 0.5-1 nm and interface widths <0.4 nm. Thus a detailed understanding of the growth process is needed. We have grown Cr/Ti multilayers, a new combination of metals with potential as highly reflective soft x-ray optics at the Ti-2p absorption edge, E=452 eV (λ=2.741 nm), by ion-assisted magnetron sputter deposition. A binary collision model was used to estimate the ion energy window where adatom mobility is promoted while kinetic mixing of the interfaces is suppressed. For Cr/Ti, this ion-energy window was found to be between 21 eV to 51 eV. By modulating the fluxes as well as energies during growth of each layer, we engineered the interfaces for minimal accumulated roughness, improved interface flatness and reduced intermixing. The optimal conditions produced a near-normal soft x-ray reflectivity of 2.1% for a multilayer with N=100 bilayers and a bilayer period of λ=1.379 nm . The nano-structural evolution with increasing number of bilayers (N=[20-200]), bilayer thicknesses (λ=[1.379 - 7.22] nm), and different ion energies was investigated by a combination of hard- and soft x-ray reflectivity as well as cross-sectional transmission electron microscopy. A transition from amorphous to crystalline layers is observed with increasing layer thicknesses and an increased accumulated roughness is evident as λ as well as N increases. An experimental analysis of roughness correlation with varying growth conditions is in good agreement with the estimated energy-window.
9:30 AM		F3-4 Sputter Deposition of Cr Films on Tilted Substrates: the Role of Flux Angular Distribution S.Yu. Grachev (Netherlands Institute of Metals Research, Netherlands); G.C.A.M. Janssen (TU Delft, Netherlands) In a typical industrial sputter deposition reactor, coatings are deposited onto a substrate, which is subjected to a complicated rotation. This rotation is meant to insure a homogeneous coverage of parts being coated. In addition to this, the mentioned rotation redistributes the angular distribution of the flux arriving at a coated surface. An anisotropy in the flux distribution as well as flux directed under shallow angles can affect properties of thin films dramatically. We report on stress and microstructure observations in Cr films produced by sputter-deposition on tilted substrates. We deposited Cr films onto 45° tilted substrates at Ar pressures of 1.5x10^-3 and 6.3x10^-3 mbar. Films in a thickness range of 50 nm to 4.5 µm were produced at 50-100°C. The tilt angles of the films columnar structure and of the (110) crystallographic texture depended on Ar pressure. At low Ar pressure columns grew under highest tilt angle of 43°, which is close to the average angle of the arriving flux. This is in contradiction with the 'tangent rule', which predicts the tilt of ~26°. The tilt of the (110) biaxial texture is much smaller and tends to the normal as thickness increases. The tensile stress in deposited films evolved with thickness according to a power law with exponents of 0.42 and 0.57 for the two mentioned pressures. We discuss these results in terms of the flux angular and energy distribution, both of which are altered by the pressure. The flux angular distribution was experimentally measured with the use of a diaphragm in front of the sample. The distribution was highly anisotropic and reflected the elongated geometry of the Cr target.
9:50 AM		F3-5 Characterization of a γ''-FeN Coating by Electron Microscopies V. Demange, Tran Huu Loi, P. Weisbecker, E. Bauer-Grosse (Ecole des Mines, France) We were interested to characterize films of γ''-FeN not only by X-ray diffraction (XRD), but also by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Samples were obtained by dc magnetron sputtering of an iron target in N₂ atmosphere at high pressure. The XRD technique indicates that films are constituted of a single phase, i.e. the γ''-FeN phase. SEM and TEM show the presence of a strong <111> texture in the coatings. Films are constituted of triangular sections rods perpendicular to the substrate. These rods present {111} twins defects. We also frequently observe occurrence of supplementary diffraction spots on electron diffraction patterns of some rods. Intensity of these spots is less important that the one of the γ''-FeN phase spots. These weak spots also lie at half the distance between two consecutives spots of the γ''-FeN phase. These two facts suggest that these additional spots correspond to a superstructure of the γ''-FeN. This new phase is face-centered cubic and its lattice parameter is twice those of γ''-FeN, i.e. a = 0.871 nm. Darkfield experiments performed with both fundamental and superstructure spots indicate that the new phase is rather located on surface of rods and form nanodomains. In order to construct structural models of this new phase, microanalysis by electron dispersion spectroscopy and electron energy loss spectroscopy are under progress.
10:10 AM		F3-6 Electronic States and Physical Properties of Hexagonal β-Nb₂N and δ'-NbN Nitrides R. Sanjines (SB-EPFL, Switzerland); M. Benkahoul (IPMC-SB-EPFL, Switzerland); D. Music (RWTH-Aachen, Germany); F. Levy (IPMC-SB-EPFL, Switzerland) The electronic structure of hexagonal β-Nb₂N and δ'-NbN, and fcc-NbN, grown by magnetron sputtering, have been investigated by X-ray photoemission spectroscopy and ellipsometric measurements. The valence band VB)energy distribution curves (EDC) of these nitrides significantly differ from each other. While the strongly hybridized N2p-Nb4d of β-Nb₂N originate a featureless peak centered at 6 eV below the Fermi level, those of the δ'-NbN are characterized by two narrow peaks centered at 5 eV and 6.5 eV. Striking changes are also observed in the EDC's near the Fermi level, these features are associated with the nearly metallic Nb4d states. These trends are in good agreement with theoretical density of states (DOS) obtained by means of ab initio calculations. The dielectrical function of these nitrides reveals structures near the screened plasma edge which correlate well with their associated electronic structure. The dielectric function spectra can be used in the phase identification of the hexagonal and fcc phases. The chemical shift of core levels is interpreted in terms of changes in the charge distribution providing indication of the degree of ionicity and covalency of the bonding. Comparing hexagonal and fcc structures, both β-Nb₂N and δ'-NbN are more covalent that the cubic NbN. The prominent covalent bonding in these hexagonal nitrides can be related to their higher hardness values compared to that of the cubic phase.
10:30 AM		F3-7 Characterization by Optical Emission Spectroscopy a PVD Process to Produce AlN Layers F. Sandoval, U. Figueroa (ITESM-CEM, Mexico); O. Salas, J. Oseguera (ITESM, Mexico); A. Ricard (Universite Paul Sabatier, France) Optical emission spectroscopy (OES) is an important tool to understand the mechanisms of plasma excitation and control the plasma process. AlN layers were produced on Al substrates by a PVD process with a non balanced magnetron. OES was used to characterize the plasma during deposition of the layers. The main spectral lines, from UV to IR, related to the plasma process parameters, were identified. This information associated with the plasma density, measured by a Langmuir probe, was used to describe some mechanisms of plasma excitation and was related to structural of the AlN layers.
10:50 AM		F3-8 Texture Development during Growth of Ti_1-xAl_xN Thin Films Studied by In-Situ X-Ray Diffraction M. Beckers, N. Schell, R.M.S. Martins, A. Mücklich, W. Möller (Forschungszentrum Rossendorf, Germany) Ti_1-xAl_xN coatings are used for a vast variety of applications. For each of them, controlling the microstructure is crucial because it determines performance and lifetime. Thus, literature on the relationship between deposition parameters, microstructure, and performance of Ti_1-xAl_xN coatings is large. However, little is known regarding the atomistic mechanisms for these observed relationships. Our approach for understanding is in-situ x-ray diffraction during the growth of Ti_1-xAl_xN films using a deposition chamber installed at the Rossendorf beam line BM20 at the European Synchrotron Radiation Facility in Grenoble, France. All films were deposited by reactive co-sputtering from Ti and Al targets; one series at constant x = 0.06 varying substrate temperature, bias voltage, and nitrogen partial pressure and thus growth rate. In another series, x was varied from 0 to 0.73 while keeping all other parameters constant. Values of x < 0.15 and high deposition rates lead to a typical cross-over behavior between initial (002) and final (111) preferred orientation (PO). Reducing the deposition rate leads to (002) PO practically independent of film thickness and substrate temperature. Yet, suppressing collisionally-induced atomic N on the sample surface by applying a positive bias voltage, brings back a (111) preferred orientation. Those observations are consistent with the atomistic model proposed by Gall et al¹. Keeping the deposition rates low, (111) PO can also be induced by increasing x above 0.15, which in the presence of atomic N can be explained by its higher adatom mobility. Increasing x towards the AlN segregation threshold at x = 0.60 leads to extremely hard nano-composite Ti_1-xAl_xN/AlN, and pushing x further to 0.73 leads to highly stressed AlN with an a-axis off-plane PO. ¹ D. Gall, S. Kodambaka, M. A. Wall, I. Petrov, and J. E. Greene, J. Appl. Phys. 93, 9086 (2003).
11:10 AM		F3-9 Plasmonic Excitation and Detection using an Integrated Detector in Semiconductors. D.T. Wei (Wei and Associates); A. Scherer (California Institute of Technology) A laser light incident on a nanoscale thin layer of gold, silver or a number of other metal deposit on a planar substrate will excite electrons to a strong, collective oscillation called a surface plasmon effect. A surface plasmon's unit is an electron excited into oscillation of a natural frequency inherent to the film deposit by an external energy source. The energy source could be a beam of light of limited cross section. Thus, the electron is in resonance at the photon frequency of incident light conditioned to a certain incidenece angle and a certain surface topography. At the resonance peak, the photon frequency is tuned to the surface plasma frequency of the film and its material. A state of surface plasmon resonance is thus reached when a dense population of the electrons, not just some individual ones, over a surface skin of certain area and depth. This collection of electrons is resonant to an ubiquitous frequency and has a relaxation time. The scale of relaxation time, corresponds to spectral width, in turn informs the average life time of resonant surface plasmons. To help exciting surface plasmons, a grating or a prism is often used to serve as an input coupler. Conventionally, light emission from surface plasmons, its intensity and its time of relaxation are frequently sensed by a remote detector as recorded data. However, if we put the detector, the input coupler, and the plasmon material together into a functional block, we are a step closer to watch how surface electrons play their roles in the plasmon history, from excitation to peak to decay. When a semiconductor substrate is used as a platform for such a block, it is even a step closer in getting surface plasmons connected to the electronics in research and industry. In this paper, several novel coupling and detecting schemes for surface plasmons are explored in details.
11:30 AM		F3-10 TEM Obxervations of the (100) Silicon Surface Treated by an Ultra Short Bias-Enhanced Nucleation Procedure for MPCVD Diamond Genesis I.H. Choi, F. Herbst, J.Ch Arnault, S. Barrat, E. Bauer-Grosse (Ecole des Mines, France) A thinned area of (100) silicon submitted to a Bias-Enhanced Nucleation (BEN) treatment into a Microwave Plasma assisted Chemical Vapour Deposition (MPCVD) reactor has been examined by conventional transmission electron microscopy (TEM). The BEN treatment is generally used to enhance both the diamond nucleation and the diamond nuclei orientation with respect to the Si substrate. It is shown that a very short time (120 secondes) of BEN is enough to modify the substrate surface which is partly covered with SiC and diamond crystals. Rings electron diffraction patterns indicate that Si is slightly etched and both SiC and n-diamond are formed. Furthermore, some SiC crystals can be oriented nearly epitaxially with respect to the Si lattice. TEM images show the presence of already well-facetted isolated diamond crystals. They can reach 200 nm in size and present planar defects.
11:50 AM		F3-11 Synthesis and Characterization of Polymer/Carbon Nanotube Composites. E. Titus, N. Ali, J. Gracio (University of Aveiro, Portugal); B.P. Ramesh (Trinity College, Ireland); P.K. Tyagi, A. Misra, D.S. Misra (Indian Institute of Technology, India) Carbon nanotubes (CNTs) and conducting polymers are both interesting material for their unique electrochemical and mechanical properties. In the case of carbon nanotubes, it is their high surface area and electrical conductivity that makes them attractive, particularly in terms of their fast response times. In contrast, the redox chemistry of conducting polymers enables them to achieve large charge storage capacities and dimensional changes in response to potential, though this benefit comes at the expense of response times. Our work has been aimed at merging the desirable properties of carbon nanotubes with those of conducting polymers in composite films comprising these two materials. The growth of CNTs was performed in our laboratory using Microwave Plasma Chemical Vapor Deposition (MPCVD) technique. The composites of carbon nanotubes, with various polymers were prepared as thin films by spin coating. Different conjugated polymers having different conductivities and CNTs prepared under different growth parameters were used to exploit their extra-ordinary properties. The resulting films with different compositions were characterized using TEM, ESCA, UV-VIS spectroscopy, Raman and FTIR spectroscopy. The dc electrical conductivity of the films was measured at different temperatures.
12:10 PM		F3-12 A Study of Defect Evolution in Microwave Plasma Treated Al-Films H. Wulff, A. Quade, M. Quaas (University of Greifswald, Germany) Low temperature plasma processing of solid surfaces is essentially affected by energetic and thermal quantities. We report on the influence of a microwave induced plasma (SLAN) on the defect structure of Al films. The defect formation process was activated in a 2.45 GHz microwave discharge under different plasma parameters as microwave power and gas type.The Al-films were investigated with grazing incidence x-ray diffractometry (GIXD). Lattice defects in the thin Al-films influence the x-ray data. From shifting and broadening of x-ray line profiles concentrations of vacancies, dislocation densities, and domain sizes in the films were calculated. The defect structure evolution is mainly manifested in the diffraction angle. That means changing in the local atomic ordering of Al-films during plasma treatment result predominantly in a change in its molar volume and is related to changes in film stress. The stored energy in the films induced by microwave plasma was calculated using the energy of individual vacancies and dislocations and from the fraction of atoms associated with grain boundaries.