ICMCTF2009 Session F3: Characterisation by Electron and Ion Beam Microscopy

Wednesday, April 29, 2009 9:00 AM in Room Sunrise

Wednesday Morning

Start	Invited?	Item
9:00 AM	Invited	F3-5 Characterization of Interfaces Using Scanning Transmission Electron Microscopy Techniques S. Stemmer, J.M. LeBeau (University of California, Santa Barbara) In the first part of this presentation several examples will be presented that demonstrate the utility of advanced scanning transmission electron microscopy (STEM) techniques in determining the atomic scale structure of interfaces between thin films and substrates. We show that interface structures in dissimilar materials systems can be determined directly, without the need for preconceived structure models, using Z-contrast imaging in STEM. Examples will include interfaces between thin dielectric layers and semiconductors, interfaces in complex oxides and metal/semiconductor interfaces. In the second part of the presentation we will discuss the need for a quantitative understanding of the Z-contrast imaging technique and the need for image simulations in the characterization of more complex structures and interfaces. We will present a practical approach for obtaining quantitative Z-contrast images. We compare experiments and image simulations and show that near perfect agreement is achieved.
9:40 AM		F3-7 Thermal Stability of PVD Nitride Multilayer Coatings: Effect of Nitrogen Inter-Diffusion I. Ross, W. Rainforth (University of Sheffield, United Kingdom); P.Eh. Hovsepian (Sheffield Hallam University, United Kingdom) High performance nitride based multilayer PVD coatings show excellent potential for the environmental protection of technologically important light alloys such as gamma titanium aluminide. Previous oxidation studies in air have revealed that uncoated gamma titanium aluminide exhibits a strong affinity for nitrogen. In this study, we report the effect of nitrogen inter-diffusion between the coating and substrate and its impact on the coatings thermal stability. We compare two multilayer coating architectures: CrAlYN/CrN and TiAlYN/CrN deposited on gamma titanium aluminide (Ti-45Al-8Nb-0.17C) via a combined unbalanced magnetron / high power impulse magnetron sputtering technique. Samples of the as-deposited coatings were subjected to isothermal thermal annealing at 750°C - 850°C for times up to 1000 hours in ultra pure argon (300mbar). We have applied advanced transmission electron microscopy, scanning transmission electron microscopy and associated analytical technique s to elucidate the structure of the bulk coating and diffusion layers as a function of annealing time. Site specific cross-sections for transmission electron microscopy were prepared by focused ion beam sectioning. In both the coatings studied, extensive inward nitrogen diffusion from the nitride coating to the near surface region of the substrate was observed at 850°C. The resulting interface region was identified as polycrystalline TiN. The subsequent depletion on Al and Nb from this region results in the formation of an Al₃Nb interlayer between the TiN and the unaffected substrate. An approximate parabolic diffusion rate was observed in each instance. The impact of the TiN diffusion layer on the coating performance and the thermal stability is discussed.
10:00 AM		F3-8 Raman Multi Wavelength and Energy Filtred Tem Study of Diamond-Like Carbon Films Deposited by Femtosecond and Nanosecond Pulsed Laser Ablation A. Sikora (Université Jean Monnet, France); B. Vacher (Ecole Centrale de Lyon, France); A.S. Loir, F. Garrelie, C. Donnet (Université Jean Monnet, France) Diamond-Like Carbon (DLC) films deposited by femtosecond and nanosecond pulsed laser ablation have been investigated using multi wavelength Raman spectroscopy. The a-C films have been deposited at room temperature in high vacuum conditions, by ablating graphite target either with a femtosecond pulsed laser (800 nm, 150 fs, ~5 J/cm², femto-DLC), or with a nanosecond pulsed laser (248 nm, 20 ns, ~40 J/cm², nano-DLC). The thin films have been analyzed by Raman spectroscopy at 3 different wavelengths (325, 488 and 633 nm). This allows the study of the value and dispersion of several parameters such as the G peak position, the D peak position and the I(D)/I(G) ratio. Other parameters are also discussed, including the full width at half maximum of the G peak, the T peak position and the I(T)/I(G) ratio. By coupling Raman with Energy Filtred Transmission Electron Microscopy (EFTEM) performed on thin DLC layers prepared by Focused Ion Beam (FIB), the structure of both films are discussed and compared, depending on the laser used during the ablation process. The degree of disorder, the sp²/sp³ ratio, the sp² clustering and bonding of the two types of thin films are compared. We show that the nano-DLC is more disordered than the femto-DLC. Moreover, the nano-DLC seems to be richer in sp³ bonding. The D band does not appear for the nano-DLC or should be very low. This means that the sp² bonds are more organized as aromatic cycles in the femto-DLC. The comparison of nanosecond and femtosecond pulsed laser ablation on the DLC film structure will thus be highlighted.
10:20 AM	Invited	F3-9 The Stability of Thin Metal Films in Contact with Oxides W. Kaplan, M. Baram (Technion, Israel) Due to the relative interface/surface energies at metal-oxide interfaces, thin metal films on oxide substrates are intrinsically unstable. As a result, thermal annealing will result in the break-up (or dewetting) of thin films, resulting in small droplets if the process is conducted above the melting point of the metal, or in small solid particles if the process is conducted below the melting point of the metal. The process can be kinetically slowed by engineering the relative interface/surface interfaces via equilibrium segregation. Grain boundary grooving of the thin film was thought to be the mechanism for dewetting, but recent experiments have shown that dewetting initiates via the formation of voids at the metal-oxide interface, via vacancy diffusion. These issues will be used for the comparison to the concept of stable equilibrium films at Au-sapphire interfaces. The films were formed using a novel experimental approach, in which thin sputtered films of Au were dewetted on a sapphire substrate which was previously partially wetted with drops of anorthite glass. The process resulted in equilibrated metal particles residing on glass drops and on the sapphire substrate adjacent to the glass drops. Aberration corrected transmission electron microscopy and analytical transmission electron microscopy were used to confirm the existence of the ~1nm thick stable films at the Au-sapphire interfaces, and to explore the degree of order within the film.
11:00 AM		F3-11 Characteristic Analysis of Supporting Precious Metal Nanoparticles on Carbon Nanotubes for Electrocatalysts M. Chen, S.-C. Lu, H.-Y. Chen (Minghsin University of Science and Technology, Taiwan); H.-W. Yu, C.-M. Chen (National Chiao-Tung University, Taiwan) This article introduce an efficient method for achieving high dispersion and loading amount of precious metal nanoparticles on carbon nanotubes supports for electrocatalysts. Pt-Ru nanoparticles with uniform diameter about 4.3/2.5 nm were efficiently disperse and supported on carbon nanotubes (CNTs) by microwave assisted polyol method. Temperature and additives are important factors that affects the reduction rate of metals particle from metal chloride salt. In microwave system, metal chloride salts rapidly dissociate and reduce metal catalyst particles then deposite on the CNTs. An addition of additives in metal chloride salts/ ethylene glycol (EG) solution can efficiently disperse catalyst particles homogeneously on CNTs and enhance the adsorption and reduction metal particles. In this article, the mechanism of supporting precious metal nanoparticles on carbon nanotubes supports for electrocatalysts will also Investigate. The characterization analyses will be determined by SEM, TEM, XRD, XPS, and TGA.
11:20 AM		F3-12 The Effect of Surface Mechanical Attrition Treatment on Phase Transformation in Surface Layer of NiTi Alloy T. Hu, W. Zhang, S. Wu, Y. Xin (City University of Hong Kong); C.W Chu (Southeast University, Taiwan); R.K.Y. Fu (Plasma Technology Limited, Hong Kong); P.K. Chu (City University of Hong Kong, China); K.W. Yeung (City University of Hong Kong); J. Lu (The Hong Kong Polytechnic University, Hong Kong) Surface mechanical attrition treatment (SMAT) is an effective technique to create localized plastic deformation, resulting in grain refinement in the surface layer of metallic materials. In this study, the surface layer of NiTi alloy with martensite as initiate state has been treated with SMAT method. DSC, XRD and TEM were employed to characterize the phase transformation and microstructure features in the deformed surface layer of NiTi alloy. It was found that martensite stabilization and parent B2 phase were introduced after SMAT process. After the occurrence of the first reverse martensitic transformation of B19’→B2, the martensite stabilization vanished. TEM results indicated that the deformed martensite structures and deform-induced dislocations and/or other defects were responsible for the martensite stabilization and parent B2 phase. The decrease of heat of transformation, ΔH, in the first reverse martensitic transformation has also been discussed.