ICMCTF2000 Session F3-2: Surface and Thin Film Analysis
Monday, April 10, 2000 1:30 PM in San Diego
F3-2-1 Surface Effects in Single Crystal Tribology
A.J. Gellman, J.S. Ko (Carnegie Mellon University)
Atomic scale influences on the macroscopic tribological properties of surfaces are being explored through studies of friction between single crystalline and quasicrystalline surfaces prepared and characterized under ultra-high vacuum conditions. Our experiment allows us to make friction measurements between pairs of well prepared and very highly characterized surfaces to be brought into contact under an applied load and then sheared at constant velocity. One simple set of measurements has explored the frictional properties of single grain quasicrystals. Quasicrystals are materials have very complex, aperiodic structures with five-fold rotational symmetry axes and claims have been made that they exhibit anomalously low frictional properties. Under vacuum conditions Al70Pd21Mn9 quasicrystal surfaces have been cleaned prior to making friction measurements. While these yield coefficients of friction for perfectly clean surfaces that are significantly lower than those observed with clean metal surfaces they are higher than those measured with quasicrystals in air. Controlled oxidation of the Al70Pd21Mn9 quasicrystal surfaces has been shown to lower friction coefficients and be in part the source of the low friction measured in air. Additional and more complex measurements have explored the frictional anisotropy between single crystal Ni(100) surfaces as they are rotated with respect to one another. The effects on friction of the relative crystallographic orientation of pairs of Ni(100) crystals has been measured for clean surface and surfaces covered with monolayers of adsorbed sulfur atoms and layers of adsorbed ethanol. The role of the adsorbed films is to change the orientations of the surface lattices independent of the orientations of the bulk lattices. These experiments probe the relative importance of surface lattice versus bulk lattice orientation in determining friction between metal crystals. Finally, we have explored the effects of adsorbed films on the friction between metal surfaces. These show evidence for the layering of molecular films in sliding contacts and for the effects of layering on friction.
F3-2-3 Structural and Quantitative Analysis of Nitrided Stainless Steel Coatings Deposited by DC-magnetron Sputtering
G. Terwagne, J. Colaux (Facultés Universitaires Notre-Dame de la Paix, Belgium); G.A. Collins (Australian Nuclear Science & Technology Organisation - ANSTO, Australia); F. Bodart (Facultés Universitaires Notre-Dame de la Paix, Belgium)
Recently a phase, known as 'S phase', based on an alloy of austenic stainless steel and nitrogen, has shown potential for simultaneously improving wear and corrosion resistance. Stainless steel coatings were deposited on low carbon steel and mono-crystalline silicon substrates by DC-magnetron sputtering in a reactive atmosphere of nitrogen. The total mass flow of argon and nitrogen was kept constant (20 sccm) for all depositions and the nitrogen mass flow was varied between 0 and 10 sccm with increments of 1 sccm while argon mass flow was decreased for the same amount. @paragraph@The elemental composition of coatings and the deposition rates were studied by Rutherford backscattering (RBS), by X-ray emission induced by charge particles (PIXE) and by nuclear reactions (NRA). The nitrogen content is found to increase with increasing mass flow up to saturation value of 45 atomic percent. @paragraph@A structural analysis by means of conversion electron Mössbauer spectroscopy (CEMS) and grazing incidence X-ray diffraction (GXRD) was also performed. The results indicate that the lattice expands as the nitrogen mass flow increases and that this expansion is caused by the incorporation of nitrogen into interstitial sites. Moreover, the presence of the so-called S-phase is detected. The latter is probably due to nitrogen in solid solution at vacancies in the stainless steel. This phase is particularly interesting for industrial applications because it increases the resistance to wear without compromising the corrosion resistance of the steel.
F3-2-4 Characterization of Transparent Aluminium Oxide and Indium Tin Oxide Layers on Polymer Substrates.
B.M. Henry, A.G. Erlat (Department of Materials, University of Oxford, United Kingdom); C.R.M. Grovenor (University of Oxford, United Kingdom); G.A.D. Briggs (Oxford University, United Kingdom); Y. Tsukahara, T. Miyamoto (Toppan Printing Company, Japan)
The microstructural and gas barrier properties of transparent metal oxide layers deposited on plastic substrates are of great importance to the food packaging and the flat panel display industries. The deposited ceramic layer can be tailored to offer many properties including transparency, microwave compatibility and conductivity, in addition to alleviating health and environmental concerns. It is apparent, nevertheless, that the reasonable gas barrier properties of these oxide films are controlled by defects such as nano-scale pores. The influence of film composition and thickness on the microstructural integrity and thus the barrier properties has not been fully established. For this aim a comprehensive microstructural understanding of the barrier coating is of major importance. In this study oxide layers, including aluminium oxide and indium tin oxide, on PET has been characterized using a variety of analytical techniques, including transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The microstructure of the barrier layers has been correlated with measurements of the oxygen and water permeation of the composites.
F3-2-5 Digital Film X-Ray Diffraction and X-Ray Reflectivity Analysis of Coatings and Thin Films
S.L. Lee (US Army Armament Research, Development, and Engineering Center, Benét Labs); D. Windover (Benet Laboratories)
Two-dimensional high-resolution digital film applications in X-ray diffraction (XRD) and X-ray reflectivity (XRR) were explored. XRD and XRR analyses were performed using digital film detector complemented by conventional one-dimensional solid state detector and radiation from a conventional X-ray tube. In this paper, we studied the chemistry, phase, and texture of surfaces of several 120?m Cr and Ta coatings on steel for wear and erosion applications, retained austenite and martinsite contents for metallurgical applications, and thickness, density1, and interface of 50nmTaOX thin films on silicon for electronic applications. Conventional XRD scans give 2? pattern for the 'hkl' reflections, and the pole figures give ?-? crystalline orientation, where ? and ? represent, respectively, specimen rotation and tilt. Digital film detector using a grazing incidence X-ray beam, gives fast, simultaneous, multiple 2? scans at various tilts, and ?-? digital image without specimen tilt. Conventional XRD complemented by digital films, give a complete and more accurate chemistry, phase, and structure information of crystalline solids. This is shown from the determination of the ratio of alpha to beta phase tantalum contents integrated over the Debye ring. In X-ray reflectivity, Kiessig interference fringes give information on thin film and multi-layer thickness, surface and interface roughness, porosity, and electron density. Digital film XRR provides the additional capability of two-dimensional digital Kiessig interference fringe image. The technique can be used for rapid determination of thin film thickness and screening for surface and interface uniformity of thin films. @footnote 1@1 D. Windover and S.L. Lee, Advances in X-ray Analysis 42, 1999, in press.
F3-2-6 Thickness Dependent Properties of Thin Polycrystalline Polymer Films for Multilayer Interconnect Applications
H.K. Kim, F.G. Shi (University of California, Irvine); B. Zhao, M. Brongo (Conexant Systems Inc.)
As thinner and thinner polymer films are being employed in many technological applications, an investigation of their thickness-dependent properties becomes necessary. Thickness dependent electrical, thermal, dielectrical, and optical properties of a low-dielectric constant (low-k) on-wafer polymer thin film are investigated for various temperatures. The investigation involves the use of glancing angle x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), ellipsometer, and Filmetrics F20. All of the properties are found to be strongly dependent on film thickness. Theoretical models are proposed for describing the experimental observations.
F3-2-7 Optical and Electrical Properties of Transparent Conductive ITO Thin Films Deposited by Sol-gel Process
M.J. Alam, D.C. Cameron (Dublin City University, Ireland)
The optical and electrical properties of ITO films are found to be sensitive to preparation conditions. The sol-gel method is an attractive one due to the ability to coat on large areas and easy control of the doping level without using expensive and complicated equipment when compared with other methods. In general, the sol-gel process uses metal alkoxides as raw materials, but it is expensive to obtain indium and tin alkoxides, therefore we prepared ITO thin films from the sol-gel process using metal salts as raw materials and organic solvents. The films have been deposited onto glass substrates from a starting solution prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. ITO thin films containing 0-20 mol % SnO@sub2@ were successfully prepared by heat-treatment at above 400@super0@ C. The resistivity of ITO films has been minimised by optimizing the amount of tin doping. @Paragraph@ The electrical, optical and structural properties of ITO thin films were investigated. The thickness of ITO film was measured by ellipsometer. The electrical resistivity was measured by using four-point probe method. The ITO thin films containing 10 mol % SnO@sub2@ showed the minimum resistivity of 1.5 X10-3 ohm-cm. Transmittance of ITO thin films were measured by a UV-vis spectrometer. The ITO film has high transmittance above 80 % over the wavelength range 400 to 900 nm and has an absorption edge at 280 nm. This is high enough for applying ITO thin film as transparent electrodes. Grazing incidence X-ray diffraction showed that the sol-gel films heat treated up to 700@super0@ C are polycrystalline with a cubic structure. XPS analysis has shown that Sn was incorporated into the In@sub2@O@sub3@ structure substitutionally.
F3-2-8 Characterisation by X-ray Absorption Spectroscopy of Thin Films Prepared by Ion Beam Induced CVD
A.R. González-Elipe, A Caballero, J.P. Espinós, F Yubero, J.P. Holgado, J Morales (CSIC-Univ. Sevilla, Spain)
X-ray absorption spectroscopy (XAS) has been widely used to study many different types of compounds and materials in gas, solid or liquid forms. This technique presents an obvious interest when the materials to be investigated have a poor crystallographic order or are amorphous. Depending on the deposition method and type of material, it is very often found that many thin films do not have a well-crystallised structure. In these cases XAS can be an interesting alternative for their structural characterisation. @paragraph@This paper wants to give a general overview of the possibilities of this technique to study thin films and of the problems that may be encountered for its systematic use as a tool of thin film characterisation. Thus, it is recognised that a versatile and simple collection method of XAS spectra for thin films is the so called "conversion electron yield" (CEY) detection. The information depth provided by this method depends on the element to be investigated and on the type of constituent material of the film. From the calibration curves obtained for a series of oxide materials it can be concluded that thickness around 100 nm are typical for this type of analysis with oxide materials. @paragraph@The possibilities of the XAS methodology for thin film characterisation are illustrated with a series of examples of nitrogen implanted layers and oxide thin films prepared by Ion Beam Induced CVD. This method consists of the bombardment of a suitable substrate with accelerated oxygen ions in the presence of a volatile precursor. As an effect of the ion bombardment, structural effects such as amorphisation, preferential growth of certain crystallographic planes, etc. can be induced in the films. The chosen examples illustrate the possibilities of XAS for a structural and chemical characterisation of the layers as an alternative and/or complement to the conventional X-ray diffraction technique (XRD). The advantages of using an approach based on these two techniques are clearly illustrated with the presented examples
F3-2-10 CuO Doped SnO@sub 2@ Thin Films as H@sub 2@S Gas Sensor
A. Khanna, R. Kumar (Guru Nanak Dev University, India)
Thin films of SnO@sub 2@ doped with CuO were grown on alumina substrates by reactive evaporation technique in an oxygen atmosphere of 4x10@super -4@ Torr, while the substrates were heated to a temperature of 200@super o@C during the deposition process. The growth rate used was in the range 10-15 Å s@super -1@. The films grown were annealed in oxygen flowing conditions at 700@super o@C for 8 hours. The electrical properties of these films were studied by two probe method in the temperature range of 100 to 250@super o@C. On exposing the CuO-SnO@sub 2@ thin films to H@sub 2@S-air mixture, it is observed that the resistance decreases by several thousand times. The response time was typically about 3 minutes. This very large and fast change in the resistance of CuO-SnO@sub 2@ films shows that these materials can be used for highly sensitive and fast detection of H@sub 2@S gas. The unique surface state of CuO-SnO@sub 2@ was investigated by SEM in relation to its properties to H@sub 2@S. The SEM studies show that CuO particles are dispersed in a SnO@sub 2@ matrix and interact electronically with it to form p-n junctions. This electronic interaction causes the film to have high resistance in air. On exposure to H@sub 2@S gas CuO is converted to CuS, a metallic conductor, in the process destroying the p-n junctions and decreasing the film resistance. Thus the outstanding chemical action of CuO towards H@sub 2@S is responsible for the large change in the resistance of these films. On removal of H@sub 2@S gas, CuS converts back to CuO when heated in air at the operating temperature of about 200@super o@C and returns the films to high resistance state in about 15 minutes.
F3-2-11 Aging Effect and Effective Surface Modification of SiO@sub2@ Xerogel Film for Intermetal Dielectric Application
H.H. Park, J.H. Kim, H.R. Kim (Yonsei University, Korea)
Low density SiO@sub2@xerogel film prepared by two-step procedure is a novel material of lower dielectric constant compared to conventional SiO@sub2@film by chemical vapor deposition. Theoretically, dielectric constant depends on porosity, for example, dielectric constant of a film with 50% porosity is about 2.5. Therefore, a major issue of xerogel film is the porosity due to its inherent porous nature.@@In SiO@sub2@xerogel film prepared by ambient pressure drying, it is very important to avoid shrinkage and crack by capillary force during drying. The aging step can increase mechanical properties due to the condensation to form Si-O-Si bonds and the neck growth by dissolution/prerecipitation in SiO@sub2@xerogel film. Through the surface modification, surface bonding of -OH was modified with hydrophobic -CH@sub3@of trichloromethylsilane. Surface modification can reduce condensation and we could obtain porous microstructure by spring-back effect. Therefore, aging parameters and the degree of surface modification could control the porosity of SiO@sub2@xerogel thin film prepared using a sol-gel technique. In this work, we have studied the microstructural changes and properties of SiO@sub2@xerogel films by varying aging solution and controlling surface modification.
F3-2-12 Analysis of CrN Coatings by Raman Spectroscopy
C. Moura, L. Cunha (Universidade do Minho, Portugal)
Raman spectroscopy can be used as an internal probe in the analysis of thin films. The elementary excitations used in Raman scattering are sensible to chemical characteristics and to the structure of the thin film. The orientation of the sample and the presence of surface defects could be observed by this non-destructive technique. The relative orientation of the polarized radiation, the incident and the scattered one, related with the crystallographic axes of the material can give an information about the preferential orientation on crystal growing. The presence of an amorphous phase in CrN coatings can also be detected using Raman spectroscopy. The residual coating stress is closed related to the presence of defects in coating. In the Raman spectra the defects produce a modification in the vibrational frequency, but the spectral shape of the peak is preserve. In fact, if we are in the presence of a compressive stress, as is the case of CrN coatings, we observe a shift in the position of the peak to higher frequency. The CrN coatings were deposited onto steel substrates by RF and DC magnetron sputtering. Raman scattering measurements were performed, at room temperature, using a Jobin-Yvon triple monochromator coupled with photomultiplier (PM) and a charge coupled device (CCD). An Ar+ laser operating at 488 nm and 514.5 nm was used as a light source.