ICMCTF2012 Session F1-1: Nanomaterials, Nanofabrication, and Diagnostics

Monday, April 23, 2012 1:30 PM in Room Royal Palm 1-3

Monday Afternoon

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1:30 PM F1-1-1 Diagnostics in Low Pressure Plasmas and Characterisation of Films Properties in HIPIMS Technology
Arutiun Ehiasarian (Sheffield Hallam University, UK)
Plasma diagnostic studies have been instrumental in revealing and understanding the physics behind the high power impulse magnetron sputtering (HIPIMS) discharge and informing the mechanisms of film growth in its environment.

The plasma inside the confinement region has been studied by several methods which are typically not quantitative due to the lack of theory and limited direct access to optical information. Nevertheless, recent fast camera studies showed the existence of drift waves in the sub-MHz region which regulate particle transport. Multi-pin Langmuir probes were used to detect lower hybrid frequency oscillations that promote anomalous transport out of the magnetic confinement. Time-resolved optical emission spectroscopy has been used to study the development of discharge chemistry from gas- to metal- dominated.

The plasma expanding towards the substrate is more accessible. Emissive probes showed high electric fields near the target, which relax as the voltage pulse is switched off resulting in strong confinement and subsequent release of plasma, including metal ions. Energy-resolved mass spectroscopy has shown the effect of gas rarefaction, especially with high sputter yield materials, which extends the region of metal-rich plasma. Plasma chemistry quantitatified by optical absorption spectroscopy is rich in metal ions, which can comprise the majority of total particle flux. Plasma composition is influenced by the peak discharge current and can be tuned precisely. In reactive plasmas, oxygen and nitrogen are dissociated to a very high degree, and affect texture in films.

Ion energy studies by E-MS show negative oxygen ions with energy of several hundred eV – corresponding to the potential on the target. Retarding field analysers show fast evolution of ion energy, reaching high values during the pulse.

The energy of metals is enhanced and conserved at high powers due to gas rarefaction. The energy of gas ions is similarly enhanced and leads to rarefaction.

Film growth is strongly influenced by the chemistry and ion energy in the HIPIMS discharge. High fluxes of dissociated nitrogen to the surface bind arriving Ti adatoms thus effectively lowering their diffusion rate and reducing outdiffusion from 200 surfaces.

Highly ionised metal flux improves coverage of high aspect ratio vias, reduces waviness in interfaces between nanolayers and affects nanocomposite grain size and misorientation.

A number of challenges to remain, mainly connected with the transient stages of the discharge, namely, diagnosing the non-plasma breakdown phase, and obtaining fast quantitative data on plasma chemistry, ion energy and electron temperatures.

2:10 PM F1-1-3 Design of new coating materials for neutron detector applications, the example TM1-xGdxN
Björn Alling (Linköping University, Sweden); Carina Höglund, Richard Hall-Wilton (ESS, Sweden); Lars Hultman (Linköping University, Sweden)

The shortage crisis of 3He has created an urgent need for alternative neutron detectors based on other elements. Solid state based neutron detectors typically demand the applicability of the neutron reactive element in the form of thin films in order to optimise efficiency and usability. 10B and 157Gd are among the most promising isotopes for usage in solid state neutron detectors as well as in purely absorbing, isolating layers due to their high cross section for neutron reactions. The application of these elements implies the need for new coating materials and the optimisation of a series of materials properties for each particular objective. The requirements for either metallic or semiconducting conductivity, corrosion resistance, and mechanical and thermal stability may be met by producing ceramic compounds based on the neutron detecting element, as was made for B4C [1]. In this work we show how theoretical first-principles calculations can be used to guide this materials development with the example of an electrically conductive, oxidation resistant, neutron absorbing coating material based on TM1-xGdxN (TM=Ti, Zr, Hf)[2]. Results show that GdN, prone for oxidation in its pure form, readily mixes with the chemically more inert nitrides ZrN and HfN, possibly as an ordered compound. On the other hand mixing of GdN with TiN is highly unfavourable due to volume mismatch.

[1] B4C thin films for neutron detection, C. Höglund, J. Birch, K. Andersen, T. Bigault, J.-C. Buffet, J. Correa, P. van Esch, B. Guerard, R. Hall-Wilton, J. Jensen, A. Khaplanov, F. Piscitelli, C. Vettier, W. Vollenberg, and L. Hultman, Submitted for publication.

[2] Mixing thermodynamics of TM1−xGdxN (TM=Ti,Zr,Hf) from first principles,

B. Alling, C. Höglund, R. Hall-Wilton, and L. Hultman, Applied Physics Letters, 98, 241911 (2011)

2:30 PM F1-1-4 Hierarchical ZnO Nanorod array Films with Enhanced Photocatalytic Performance
Chi-Jung Chang, Mu-Hsiang Hsu, Chien-Yie Tsay, Chung-Kwei Lin (Feng Chia University, Taiwan)
Hierarchical thin-film photocatalysts exhibiting surface roughness at two length scales were prepared by the consecutive formation of ZnO microstripes and ZnO nanorod-array. At first, polymeric barrier ribs were formed on the substrate by ink-jet printing and UV-curing reaction. ZnO was deposited in the interstice of polymeric ribs by electrochemical deposition. ZnO stripes with microscale roughness were fabricated after removing the ribs. Then. nanoscale roughness was achieved by the growth of ZnO nanorods on the surface. The surface morphology, structural and optical properties were characterized by FESEM, X-ray diffraction, Electron spectroscopy for chemical analysis, UV−vis, and photoluminescence spectroscopy. The final surface comprising hierarchical microstructures and nanostructures not only increases the surface area of the photocatalyst but also helps the diffusion of organic dye during the photodegradation test. The effects of surface texture and surface modification on the photocatalytic properties were investigated. The photodegradation efficiency of the hierarchical thin-film photocatalyst was improved compared with its flat analog. Photocatalytic performance was further enhanced when Ag nanoparticles were deposited on the hierarchical photocatalyst.
3:10 PM F1-1-6 One-step hybrid pulse anodization for nanoporous anodic aluminum oxide synthesis of aluminum thin films sputtered on Si(100) substrate
Chen-Kuei Chung, Ming-Wei Liao, OoiKiat Khor, Hao-Chin Chang (National Cheng Kung University, Taiwan)
Nanoporous anodic aluminum oxide (AAO) fabricated by one-step hybrid pulse anodization from the Al thin films sputtered on Si(100) substrates at various substrate temperatures and deposition times have been investigated. Compared to Al bulk foils, AAO grown on the Si substrates is convenient to further deposit other nanostructured materials. Al thin films with rough surface cause the non-uniform electrical field during anodization process together with poor-ordered nanopore. Also, the limited thickness Al thin film is disadvantageous for proceeding electrochemical polish. Therefore, it is still a challenge for fabricating well-ordered AAO from Al thin film. In this article, Al thin films were deposited at varies substrate temperature of 25~400 °C and deposition time of 40~80 min in order to improve the surface fluctuation. All thickness of the Al thin films were less than 1 μm. The effect of substrate temperature and deposition time on quality of Al thin films was first studied and correlated to AAO performance. The morphology and microstructure of Al films were characterized by atomic force microscope and X-ray diffraction. Anodizing of sputtering Al films was performed in 0.3M oxalic acid at 40 V potential difference by one-step hybrid pulse anodization which differs from conventional direct-current anodization. The pore size distribution of AAO films was examined by scanning electron microscope (SEM) and quantitatively analyzed by image processing of SEM image. The relationship between sputtering parameter, structure, and quality of AAO was discussed and established.
3:30 PM F1-1-7 Nanostructured mesoporous surfaces produced by phase separation in Al-Si thin films
Phil Martin, Avi Bendavid, Karl-Heinz Muller, Lakshman Randeniya (CSIRO Materials Science and Engineering, Australia)

Phase separated Al-Si films were deposited by concurrent deposition of Al using filtered vacuum cathodic arc and Si produced by dc magnetron sputtering deposition. The resulting phase separated films were etched chemically to remove the nanocolumns of Al to produce a SiOx mesoporous structure. The resulting layer had a pore size that was dependent upon the arrival ratio of the Al:Si atoms at the substrate, substrate temperature and negative substrate bias voltage during film growth. Scanning electron microscope images of the etched AlSi films showed that the average diameter of pores could be varied from 2 nm to 11 nm with a well defined size distribution. The results are interpreted using a model to describe the pore size as a function of substrate temperature and particle impingement energy.

3:50 PM F1-1-9 Structural and Electronic Properties of Epitaxial Silicene
Yukiko Yamada-Takamura (JAIST, Japan)

Silicene is an atom-thick, honeycomb sheet of silicon: Si-version of graphene. Silicene is increasingly attracting interests owing to the success of graphene. One of the major differences between these two materials is that silicene is predicted to be more stable in slightly-buckled form with neighboring Si atoms displaced out of plane while graphene is perfectly planar. Silicene may therefore form with a variety of lattice constants related to a different degree of buckling. So far, silicene only exists in the form of epitaxial layer on single-crystalline, metallic substrates, such as silver single crystals and ZrB2 thin films. The relationship between the electronic structure and the atomistic structure of epitaxial silicenes will be discussed in detail.

4:30 PM F1-1-11 Carbon-Nanotube-Templated Metallic Microstructures for MEMS: Preparation and Characterization
Richard Hansen (Brigham Young University, US); Ryan Badger (Utah Valley University, US); David McKenna, Brian Jensen, Richard Vanfleet, Robert Davis, David Allred (Brigham Young University, US)
We discuss a materials breakthrough for MEMS. In contrast with conventional electromechanical devices, whose constituents are chosen from a vast range materials and alloys to optimize fabrication, performance and cost, MEMS have traditionally been made using the same materials and methods as those used in the silicon-based microelectronics industry. In order to make MEMS out of a much richer suite of materials, including metals, semiconductors and ceramics, we have developed a process termed carbon-nanotube-templated microfabrication (CNT-M). In CNT-M we employ patterned, vertically aligned carbon nanotube forests as a three-dimensional microfabrication scaffold to create precise, high-aspect-ratio (~100:1) microstructures. The “as grown,” low density (0.009 g/cc) CNT structures are not useful as mechanical materials because they are extremely fragile, consisting mostly of air. However, when we replace the air spaces between tubes in the forest with a filler material by atomistic deposition, the infiltrated CNT framework becomes a robust microstructure consisting mostly of the filler material. Thus, by patterning the CNT microstructure and limiting the deposition of the filler material, CNT-M allows control over structural features on both the nano and microscales (nanoscale porosity and microscale structure). In the past, we deposited semiconductors (Si and a-C) or dielectrics (SiO2 and SiNx) within the CNT framework by chemical vapor infiltration. But many existing MEMS applications would be benefited, and many contemplated applications such as remotely read (via RF), high-temperature accelerometers would be enabled, by the right metals. We now report on the use of chemical vapor infiltration and electrodeposition to create metallic microstructures composed of tungsten, molybdenum or nickel by CNT-M. These materials are desirable in MEMS applications because of their high conductivity, high melting temperatures, resistance to corrosion, low thermal expansion, and their high Young’s moduli, hardness and yield strength. We will present electrical, mechanical and structural properties of the metal microstructures and discuss deviations from bulk properties.
4:50 PM F1-1-12 Nanocomposite-based wear sensor materials for in-situ process control in cutting applications
Sven Ulrich, Christian Klever, Harald Leiste, Klaus Seemann, Michael Stueber (Karlsruhe Institute of Technology, Germany)
Nano- and microsystem-technologies are doubtlessly the key technologies for future developments of cemented carbides (nanopowder technology), wear-resistant coatings and multifunctional coatings (nanoscale coating design, nanoscale structure, nanoscale interface engineering). An example has been illustrated concerning the design and fabrication of wear-resistant coatings with integrated high-frequency magnetic characteristics. The magnetron sputtered, 1 µm thick TiN/FeCo-multilayer films with 2.6 nm bilayer period and volumetric ratio of 3:1 (TiN:FeCo) are harder than TiN-monolayer films and show a frequency-dependent permeability (about 100) up to 1 GHz. Moreover, enhancement of coating toughness of the multilayer in comparison to the single layers is reasonably anticipated on account of the high FeCo-content (about 25 vol.%), the high interface portion in the 390-layer coatings favoring crack deflection and crack-energy dissipation, and the compressive stress for hindering crack propagation.
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