ICMCTF2010 Session D3: Carbon and Nitrogen-Containing Nanostructured Composite and Nanolaminated Films

Friday, April 30, 2010 8:00 AM in Room Pacific Salon 3
Friday Morning

Time Period FrM Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF2010 Schedule

Start Invited? Item
8:00 AM Invited D3-1 Optical and Electronic Properties of Carbon- and Nitrogen-Based Nanostructured Inorganic Thin Films
Andreas Schuler (Ecole Polytechnique Federal de Lausanne (EPFL), Switzerland)
Nanostructuring carbon- and nitrogen based inorganic films result in novel fascinating optical and electronic properties. Such films are deposited by vacuum processes such as reactive magnetron cosputtering or combined physical vapor deposition (PVD) and plasma assisted chemical vapor deposition (PECVD). Already during film preparation, useful information on the optical properties can instantaneously be obtained by in-situ measurements such as laser reflectometry during film preparation. Complementary ex-situ techniques such as spectrophotometry or spectroscopic ellipsometry allow a precise optical characterisation in a wide spectral range. While nanolaminated films can be treated as multilayered interference stack, the dielectric function of nanocomposite films can be described within the framework of effective medium theories taking into account finite grain size effects. The superiority of the Ping Sheng theory with respect to the theories of Maxwell Garnett and Bruggeman can clearly be demonstrated. The optical properties of nanostructured films are closely related to their electronic properties. A powerful tool for the characterization of the latter is in-situ photoelectron spectroscopy. Due to the high surface sensitivity of the technique it is preferable to work with in-situ sample transfer between the preparation chamber and the UHV photoelectron spectrometer, thus avoiding any exposure of the sample surface to air. X-ray photoelectron spectroscopy (XPS) allows quantifying atom concentrations, identifying compounds by comparing chemical shifts of the involved core levels, and studies of characteristic electron energy losses and final state screening effects. Ultraviolet photoelectron spectroscopy (UPS) allows characterizing experimentally the valence band, yields spectra which can be compared to band structure calculations, and provides important information on the density of states of conduction electrons at the Fermi edge. The small dimensions occurring in nanostructured films give rise to one-electron charging effects which are a typical feature of embedded metallic nanocrystals. Examples for carbon- and nitrogen- based nanostructured inorganic materials include thin films based on a-C:H/Ti, a Si:C:H/Ti, and Ti Al N. Potential optical applications include selective absorber coatings for solar collectors and architectural solar control glazing.
8:40 AM Invited D3-3 Development of TiVCr-Based High Entropy Alloy Coatings
Fuh-Sheng Shieu, Ruei-Sung Yu, Du-Cheng Tsai (National Chung Hsing University, Taiwan)
High entropy alloys have emerged as a new class of multifunctional materials over the years. Unlike conventional alloys with only one or two major components, high entropy alloys usually contain more than three principal elements of approximately equal fraction. One of the distinct characteristics of the high entropy alloys is that thermodynamiclly the Gibbs free energy decreases with increasing temperature due to maximal mixing entropy. Mechanical properties, e. g., tensile strength, of the alloys tend to increase or remain stable at high temperature. The crystal structure of the alloys also exhibits a simple form, such as body-centered cubic, face-centered cubic, and hexagonal closed-packed. Research on the properties and microstructure of TiVCr-based high entropy alloy films prepared by magnetron sputtering was carried out in this study. Attempt is made to correlate among deposition parameters, microstructure, and mechanical properties of the TiVCr-based high entropy alloy films.
9:20 AM D3-5 Non-Uniform Elastic Deformation of MAX Phases
Caroline Humphrey, Howard Stone, William Clegg (University of Cambridge, United Kingdom); Matt Tucker (Rutherford Appleton Laboratory, United Kingdom)
In many layered structures, such as MAX phases, elastic deformation normal to the plane of the layers occurs more easily than deformation parallel to the layers due to the M-A bonds being much weaker than the M-X bonds in these structures. Such ideas are consistent with simulations and it has been suggested that this might explain why basal slip in MAX phases is very easy. However, there are no experimental measurements of the relative deformation of the individual atom layers when the material is compressed in the direction perpendicular to the layers. To examine this, the relative movement of the individual layers in 211 MAX phases (Ti2AlC, Ta2AlC and Cr2AlC) under hydrostatic compression to 20 GPa was measured. Time-of-flight neutron diffraction data was collected from samples hydrostatically compressed using a Paris-Edinburgh cell with a deuterated methanol-ethanol mixture acting as a pressure medium and a lead pellet as the pressure marker. Full-profile Rietveld refinement of the patterns was carried out to obtain the changes in the lattice parameters and the change in position of the layers of the M atoms within the unit cell. It has been found that in Ti2AlC that the Ti-Al layers do not appear substantially more compliant than the Ti-C layers so that the deformation of the unit cell, in Ti2AlC at least, appears almost uniform.
9:40 AM D3-6 Properties of Thin MAX Phase Films Produced by Ion-Beam-Assisted Deposition
Reza Valizadeh, Valdmir Vishnyakov, John Colligon (Manchester Metropolitan University, United Kingdom)

Thin films of MAX phase alloys, which are multilayer materials with chemical composition Mn+1AXn, where M is a transition metal, A is an element from the A group in the periodic table and X is either C or N. These materials were first reported by Nowotny et al (1,2) and are stable at high temperatures but are relatively easy to machine. A remaining problem is to produce thin films of these materials at temperatures low enough to preserve the properties of the substrates. Hence, in the present study thin films of around 1µm thickness of Crn+1AlCn, MAX phases have been produced using a dual ion beam system at substrate temperatures ranging from 300 to 750 K and ion beam assistance was used to mediate the film growth. Substrates used were silicon, silica, sapphire and steel. The areas of the component species were adjusted to maintain film composition under various deposition conditions. Some films were later annealed in vacuum at temperatures up to 1150 K. Material chemical composition was determined by Energy- and Wave-Dispersive X-Ray Spectroscopy (EDX and WDX). Chemical bonding was probed by X-Ray Photoelectron Spectroscopy (XPS) and micro-Raman. Structural analysis was conducted by X-Ray Diffraction (XRD) and cross- sectional Transmission Electron Microscopy (TEM). Mechanical properties have been determined by nano-indentation and tribological properties have been measured by nano-scratch testing.

The fully developed MAX phase is known to have a precisely layered atomic structure (3,4,5). As-grown films already exhibit some ordering which increases with the substrate temperature and is influenced by ion assistance at low bombarding ion energies which leads to more uniform local chemical bonding. Sample annealing reinforces this trend. Most films show good crack resistance during nano-scratch testing. The mechanical properties depend on deposition and annealing conditions and possibly can be explained on the basis of nanostructural hardening associated with the transition from the disordered state to a layered atomic arrangement.

10:00 AM D3-7 Tilting of Self-Organized Layered Arrays of Encapsulated Metal Nanoparticles in C:Ni Nanocomposite Films by Means of Hyerpthermal Ion Deposition
Gintautas Abrasonis (Forschungszentrum Dresden-Rossendorf, Germany & University of Sydney, Ausralia); Thomas Oates (Linköping University, Sweden); Gyorgy J. Kovacs, Jorg Grenzer (Forschungszentrum Dresden-Rossendorf, Germany); Per Persson (Linköping University, Sweden); Karl H. Heinig, Andrius Martinavicius, Nicole Jeutter, Carsten Baethz (Forschungszentrum Dresden-Rossendorf, Germany); Marc Tucker, Marcela M.M. Bilek (University of Sydney, Australia); Wolfhard Moller (Forschungszentrum Dresden-Rossendorf, Germany)
Self-organization at the nanoscale is a key issue in modern material science as it promises a potential route to commercially scalable production of functional nanomaterials. Here we present the growth-structure study of self-organized layered arrays of carbon encapsulated Ni nanoparticles grown by means of pulsed filtered cathodic vacuum arc deposition. Influence of the oblique ion incidence and Ni content on the film morphology is investigated. The film morphology has been determined by transmission electron microscopy (TEM) and grazing incidence small angle x-ray scattering (GISAXS) while C/Ni ratio was determined by means of nuclear reaction analysis. The C:Ni films with the Ni content in the range of ~6-50 at.% are considered. The results show that for the perpendicular incoming depositing ion incidence the C:Ni film structure consists of alternating self-organized nickel carbide and carbon layer oriented parallel to the film surface. However, for the oblique ion incidence the layered structure tilts in relation to the surface. The tilting angle and periodicity strongly depends on the deposition angle as well as on the Ni content. Combined TEM and GISAXS analysis shows that the film cross-section can be described by two density modulation waves advancing with the growing film surface – one towards the incoming ions, another one with the weaker amplitude moving in roughly perpendicular direction. The results are discussed on the basis of the interplay between thermodynamically driven phase separation and energetic ion induced ballistic effects. Such structures show significant anisotropy which can be considered for tribological, optical, magnetic or magnetotransport applications.
10:20 AM D3-8 Nano Composite TiNiC-Coatings for Low Friction and Low Contact Resistance
Benny André, Erik Lewin, Ulf Jansson, Urban Wiklund (Uppsala University, Sweden)

Materials in electrical connectors should have low inherent resistivity and should be able to give a low contact resistance. It is also good if the friction against its mating surface is low for easy connection, and in case the contact is a sliding contact. Today, many electrical contacts have a surface made of noble metals such as gold or silver and in most of these cases both mating surfaces are made of the same material. The choice of noble metals is based on their ability to provide low contact resistance through a combination of softness that gives a large contact area, a low resistivity and a good oxidation resistance. The drawbacks with connectors coated with noble metal are their low wear resistance, high friction and the cost. In many cases there is also problem with cold welding of the surfaces giving low contact resistance but extreme forces for separation.

In this work carbon based nanocomposite coatings in the Ti-Ni-C system are considered as alternative coatings for electrical contacts. These have previously shown promising tribological performance, due to an ability to provide free carbon in the contact, but so far their combined tribological and electrical properties have not been studied in detail.

Nine different nanocomposite coatings with different compositions were deposited on copper cylinders with 20 μm nickel as an interlayer using sputtering. The tests where performed by having two cylinders, 10mm in diameter, sliding reciprocally in a crossed cylinder geometry. One cylinder was coated with nanocomposite coating and the other one by a thick silver layer. Since only one of the mating surfaces has a nanocomposite on top the contact area, determined by the hardness of the softest material and the load, will stay virtually the same as in the case of a silver-silver contact. This eliminates influences from contact area differences on the results. A load of 40N was applied and a current of 3A was fed through the contact to simulate a high current connector. The frequency of the sliding was 1 Hz and the amplidude was 1 mm. During the test the evolution of contact resistance and the coefficient of friction was measured and after the test the surfaces where closely investigated in SEM. The results show that the coatings give low contact resistance and coefficient of friction. The tests also show how the different amounts of carbon, dictated by the Ti to Ni ratio, influences the contact resistance, coefficient of friction and wear. Contact resistances as low as 100 micro Ohm was measured for the best coatings.

10:40 AM D3-9 Nanometer-Thick Protective Films for Miniature Applications Deposited Using Reactive Magnetron Sputtering
Chrysostomos Tsotsos, Kyriaki Polychronopoulou (University of Cyprus); Nicholaos Demas, Ryan Meschewski (University of Illinois at Urbana-Champaign); Claus Rebholz (University of Cyprus); Andreas Polycarpou (University of Illinois at Urbana-Champaign)

TiN, TiC and TiCN thin films with thicknesses below <100 nm were deposited using reactive magnetron sputtering on Si-wafer substrates. A PCS300 magnetron sputtering deposition unit developed by the Assembly Systems and Special Machinery department of Robert Bosch GmbH in Stuttgart Germany was used for the coating experiments. Different analytical techniques were used, such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) for crystalline phases, exact thin film thickness/surface topography and roughness evaluation, respectively. The XRD spectra demonstrated the formation of TiN, TiC and TiCN phases at the different films investigated with different preferred orientations. Cross sectional SEM images showed a thickness of about 85 nm. Laser acoustic waves (LAWAVE) technique was used to confirm the elastic modulus of the films, which was found to be between 100 and 240 GPa. Since miniature devices, such as MEMS and storage disks is the ultimate application of this work, nanomechanical properties of the thin films were also explored. Nanotribological performance was investigated using nanoscratch technique. Coefficient of friction in the nanoscale was found to be in the 0.08-0.1 range.

11:00 AM D3-10 Magnetron Sputtered Ti3SiC2 as Ohmic Contact to SiC
Kristina Buchholt (Linköping University, Sweden); Reza Ghandi (KTH – Royal Institute of Technology, Sweden); Per Eklund (Linköping University, Sweden); Martin Domeij, Carl Mikael Zetterling (KTH – Royal Institute of Technology, Sweden); Lars Hultman, Anita Lloyd Spetz (Linköping University, Sweden)

SiC is a promising semiconductor material for power and sensor applications and for high temperature operation in harsh and corrosive environments due to its large bandgap, thermal conductivity, and chemical inertness. The formation of high quality ohmic contacts to SiC is very important to device performance and is an issue remaining to be satisfactorily solved. Ti3SiC2, which is a member of the MAX-phase family, form at the interface between SiC and Ti-containing contacts when annealed at high temperature [1] . Ti3SiC2 is thermally and electrically conductive like a metal, while simultaneously displaying ceramic properties such as high decomposition temperature and low thermal expansion [2, 3] . We propose that epitaxially grown Ti3SiC2 layers may give low resistance ohmic contacts to SiC.

We have grown Ti3SiC2 films on n-type and p-type 4H-SiC through magnetron co-sputtering from three separate targets at a temperature of 850 °C and investigated the ohmic contact properties of these films. The films have been characterized with X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM), confirming the successful growth of Ti3SiC2 with a stacked plate-like structure, which follows the structure of the 8° off axis cut SiC substrates closely. The sheet resistance of the Ti3SiC2 films is ~1 Ω/cm2. Since patterning methods are essential for processing ohmic contacts, different methods for patterning the Ti3SiC2 were investigated, including wet chemical etching as well as dry etching methods, where Inductively Coupled Plasma (ICP) show the most promising results and was employed to pattern TLM structures for measuring the specific contact resistivity of the material.

[1] Pécz, B., et al., /Ti_3 SiC_2 formed in annealed Al/Ti contacts to p-type SiC./ Applied Surface Science, 2003. *206*(1-4): p. 8-11.

[2] Barsoum, M.W. and T. El-Raghy, /The Max Phases: Unique New Carbide and Nitride Materials./ American Scientist, 2001. *89*: p. 334-343.

[3] Eklund, P., et al., /The Mn + 1AXn phases: Materials science and thin-film processing./ Thin Solid Films. *Published online, Corrected Proof*.

Time Period FrM Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF2010 Schedule