ICMCTF2000 Session B1-2(B): Sputter Techniques and Nano-Structures Thin Films

Monday, April 10, 2000 1:30 PM in Room Golden West/2

Monday Afternoon

Start	Invited?	Item
1:30 PM		B1-2(B)-1 High-temperature Properties of Nanocomposite TiB_xN_y and TiB_xC_y Coatings P.H. Mayrhofer, C. Mitterer (University of Leoben, Austria) In this work, high-temperature investigations on nanocomposite TiB_xN_y and TiB_xC_y coatings were performed to determine their thermal stability. All coatings investigated were prepared by means of unbalanced DC magnetron co-sputtering using a segmented TiN/TiB₂ or TiC/TiB₂ target, respectively. The recovery and recrystallization behavior were characterized by means of stress measurements during thermal annealing and differential scanning calorimetry (DSC). The total enthalpy change during the DSC measurement can be attributed to grain growth of the nanocrystalline phases. The grain size of the coatings was monitored using scanning electron microscopy (SEM) before and after the DSC measurements. The observed grain sizes after the temperature treatment are in excellent agreement with the grain sizes calculated from the exothermic peaks of the DSC measurements. Grain growth occurred for TiB_xN_y and TiB_xC_y films during heating up to 1400°C from approximately 2 to 30 nm and 2 to 4 nm, respectively. Recovery effects of the coatings investigated show a pronounced dependence on the plasma conditions during film growth as well as on their chemical composition. The oxidation behavior has been studied using thermogravimetric analysis (TGA) in an argon-oxygen atmosphere. Compared to the recovery effects and recrystallization the oxidation behavior is mainly affected by the chemical composition of the nanocomposite coatings.
1:50 PM		B1-2(B)-2 Nanocomposite TiC / a-C:H Hard Coatings Deposited by Reactive PVD T. Zehnder, J. Patscheider (EMPA Dübendorf, Switzerland) Nanocomposite hard coatings have become an important issue in thin film technology. Motivated by the works on nc-TiN/a-Si₃N₄, the possibilities to deposit nanocrystalline titanium carbide with amorphous hydrogenated carbon by the use of PVD was examined. Coatings were deposited by reactive unbalanced magnetron sputtering using a titanium target and acetylene at temperatures around 150°C. The full compositional range between a-C:H and metallic titanium could be synthesized. At sufficiently high ion energy coatings were obtained with a marked hardness increase up to 35 GPa at a C:Ti ratio of 1.5. As evidenced from XPS, XRD and Raman data the films consist, at conditions of maximal hardness, of nanocrystalline titanium carbide surrounded by amorphous carbon. Low friction values of 0.25 were obtained from pin-on-disk measurements for the coatings of maximal hardness. The compositional range between amorphous hydrogenated carbon and titanium carbide, where the hardness increase is observed, is the same as the one found in other nanocrystalline-amorphous nanocomposite systems. The results will be compared to other nanocomposite thin film materials..
2:10 PM	Invited	B1-2(B)-3 Present and Possible Future Applications of Superhard Nanocomposite Coatings P. Holubar, M. Jilek, M. Sima (SHM Ltd., Czech Republic) Recent investigations into the multicomponent (TiAlSi)N (trade mark MARWIN) and (TiB)N coatings revealed that their nanostructure, properties and deposition conditions needed for their preparation are in agreement with the known generic concept for the design of novel superhard nanocomposites. All coatings were developed on a production scale plasma PVD & CVD equipment. Their characterization was done in a collaboration with University institutions. Depending on the composition and deposition conditions the hardness of the coatings is controlled in the range between 35 and 70 GPa or higher. However, for the majority of applications the highest hardness is not the primary goal. More important is the appropriate combination of high hardness with other properties, such as fracture toughness, oxidation resistance, adhesion etc. The effect of these properties on the resulting utility value of the coated tools will be discussed with respect to the presently available cutting tools made of cemented carbide and coated with the nanocomposites. Presently, dry milling, drilling and possibly turning are the most important applications of such coated tools. In view of the fairly fast transition from the initial development of these coatings towards their industrial production many further applications are expected. Therefore, future possibilities will be discussed as well.
2:50 PM		B1-2(B)-5 Advanced Nanocrystalline Thin Film Coating in Systems Ti-Si-C-N, Ti-Si-B-N, Ti-AI-B-N. E.A. Levashov, D.V. Shtansky, A.N. Sheveiko (Moscow Steel and Alloys Institute, Russia); J.J. Moore (Colorado School of Mines) This study represents the new approach to deposit nanocrystalline multicomponent thin films by magnetron sputtering of multiphase composite targets. The composite targets were synthesized from an exothermal mixture of reactant powders by means of Self-Propagating High-Temperature Synthesis method. The films were deposited by reactive bias sputtering either in an atmosphere of argon or in a mixture of argon and nitrogen on the HSS and stainless steel substrates with thickness about 3-4 m micron. The effects of the subs trate temperatures, bias voltages and nitrogen partial pressures on the structure and elemental compositions of the films were studied. The deposited films were characterized with using Auger electron spectroscopy, X-ray diffraction, Transmission electron microscopy using selected area electron diffraction and high-resolution techniques. It has been shown the introduction of the silicon and aluminum into the coating composition on the titanium carbonitride and diboride based (through the composite target) provides the fixing single-phase nanocrystalline films structure. The crystalline, nanocrystalline and amorphous structure is formed in Ti-Si-C-N a films depending on a ratio of elements. Two-phase nanocrystalline structure is formed in Ti-B-N-Al films. The effects of deposition parameters on the composition, structure, stoichio metry, and microhardness of the films were studied. The dependencies between microhardness, grain size, and stoichiometry of the basic phase were studied. It was shown the films with the size of crystallites about several nanometers, minimum amount of amorphous phase constituent, stoichiometric composition of the crystalline phases , and dense low-defective structure has the best mechanical properties.
3:30 PM		B1-2(B)-7 Composition and Nanostructure of 80 to 100 Gpa Ultrahard Nanocomposites nc-TiN/a-SiN_x/a-& nc-TiSi₂ S. Veprek, A. Niederhofer, K. Moto, T. Bolom, P. Nesladek (Technical University Munich, Germany) 3 to 20 micron thick multiphase nanocomposites nc-TiN/a-SiN_x/a- & nc-TiSi₂ coatings were deposited on steel substrate by means of plasma CVD. The load independent Vickers microhardness of 80 to 105 GPa was measured by the load-depth sensing technique for applied loads between 30 and ≥100 mN and verified by measuring the size of the remining plastic indentation in SEM. We verified that the small biaxial compressive stress of ≤ 0.5 GPa does not falsify the hardness data. The samples were analyzed by means of XRD, EDX, XPS, optical and scanning electron microscopy (SEM) and Energy Recoil Detection (ERD). The results of this complex analysis provide a consistent picture of the nature of the grain boundaries which determines the hardness in the whole range of silicon content between about 3 and 20 at. %: At a high discharge current density of ≥ 2.5 mA/cm² the a-Si₃N₄ forms the grain boundaries and the nanocomposites are superhard (40–50 GPa) as we reported earlier. At a lower current density of ≤ 1 mA/cm² a mixture of TiSi₂ and SiN_x (nearly Si₃N₄) is formed. With increasing Si-content the amount of a-TiSi₂ in the grain boundaries of the TiN nanocrystals increases, and above 10 at. % of Si about 3 nm small TiSi₂ nanocrystals precipitate. The hardness depends critically and in a complex way on the Si₃N₄ content and the TiSi₂/Si₃N₄ ratio: The ultrahardness of ≥ 80 GPa is achieved when the surface of the TiN nanocrystals is covered with about one monolayer of Si₃N₄. Under these conditions the ultrahardness of 80 ≥ 100 GPa depends on the amount of a- &- nc-TiSi₂.
3:50 PM		B1-2(B)-8 Preparation and Characterization of AlN/ZrN and AlN/TiN Nanolaminate Coatings M.S. Wong (National Dong Hwa University, ROC); G.Y. Hsiao, S.Y. Yang (National Dong Hwa University, Taiwan, ROC) The processing, microstructure and properties of AlN/ZrN and AlN/TiN nanolaminate coatings were studied. Advanced ion-assisted, high-rate, reactive dc and pulse-dc magnetron sputtering technique was used to deposit the nitride coatings onto Si, glass slide and stainless steel substrates. The thickness of the nanolaminate coating is about 2 µm and the unit bilayer thickness is 1-10 nm. It was found that under a critical thickness about ~2 nm for the AlN layer the AlN/TiN nanolaminates exhibit a highly textured [111] oriented superlattice structure and an enhancement in film hardness up to 45 GPa. X-ray diffraction and TEM studies indicate that in the highly [111] textured multilayered films, AlN has transformed into a nano-stabilized cubic NaCl-form from its normal hexagonal phase. However, in the case of AlN/ZrN prepared under the growth conditions comparable to those for AlN/TiN, no highly-textured structure, no stabilization of cubic AlN phase and no hardness enhancement was observed. The results indicate that the lattice structure and lattice match in AlN-containing nanolaminate coatings are important for formation of the metastable cubic AlN phase and the other interesting properties associated with the formation of the ordered microstructure.
4:10 PM		B1-2(B)-9 Structure and Morphology of Mixtures and Composites of Bichalcogenides with Metals, Hard Materials and Polymers E. Bergmann, A. Rozen (Geneva School of Engineering, Switzerland) Coatings were prepared by sputtering from 1 - 4 targets. The target materials were various mixtures of molybdenum disulfide, niobium diselenide, nickel, tin, gold, h-BN and Teflon. Thick (3 - 6 microns) and thin coatings were deposited onto polished high speed steel samples, in most cases on top of a TiN or c-MoTiN layer deposited in the same run. Chemical composition was determined by EDX. In some cases the measurements were verified against WDX, GDOS and RBS measurements. The structure of the coatings was determined by DRX and varies from amorphous to microcrystalline. The morphology was determined by SEM and AFM. Some metal- bichalcogenide coatings are nanocomposites of metal inclusions in a bichalcogenide matrix. Others appear to be simple amorphous mixtures of the constituting elements. In one case we were able to demonstrate the first submicrocomposite coatings. The structure can be varied in a wide range using different compositions. The structure does relate well to the mechanical properties which were measured by nano-depth-sensing with differential load. The coatings display a wide range of hardnesses , elastic moduli and fracture toughness. It appears, that the microhardness can be explained by a Hall-Petch relationship.
4:30 PM		B1-2(B)-10 Deposition of Polycrystalline AlN Thin Films by Coherent Magnetron Sputtering at Room Temperature A.K. Chu, C.H. Chao, F.Z. Lee (National Sun Yat-sen University, Taiwan); H.L. Huang (Chinese Military Academy, Taiwan) In recent years, aluminum nitride (AlN) has attracted a great deal of attention due to its excellent electrical, optical and mechanical properties. The applications of the material have been extended from acoustic wave devices ¹, photonic devices to anti-wear coatings. In this article, polycrystalline AlN thin films with smooth surface are reactively deposited on negatively biased ² Al thin film on glass and Si substrates in room temperature by the long-throat coherent magnetron sputtering. The influences of the target-to-substrate distance and negative bias voltage on the microstructure of the AlN thin films are investigated. The microstructures of the deposited films are examined by X-ray diffractometric measurement (XRD), electron diffraction analysis and transmission electron microscopy (TEM). In our long-throat sputtering system, the sputtered particles can be completely thermalized and reach the substrate by diffusion. The deposited AlN films are amorphous when the target is far from the substrate for a bias voltage up to -320 V. When the target-to-substrate distance is decreased to 17 cm a preferred (002) orientation of AlN films is observed at a bias voltage of -240V. Further increasing the bias voltage to -320 V, the peaks of (002) and (101) planes vanish, and the weak peak of (001) plane appears. The diameter of the (002) AlN granular crystals on glass and Si substrates is about 11 nm. Additionally, the deposited polycrystalline AlN films have specular reflectance and no voids can be observed. The maximum surface roughness is 17.2 ± 6.1 nm with a film thickness of 570 nm. This low temperature thin film processing technique is useful for applications where the thickness uniformity of the deposited films and the step coverage are required and the substrate cannot be heated to high temperature. ¹ Stokes et al, IEEE Trans. on Microwave Theory and Technique, 41, (6), 1075 (1993). ² Lee et al, Thin Solid Films, 271, 50 (1995).
4:50 PM		B1-2(B)-11 Pd/Ag Membranes for Hydrogen Purification via Unbalanced Magnetron Sputtering J. O'Brien, R.D. Arnell, R. Hughes (University of Salford, United Kingdom) The present investigation looks at hydrogen permeation through Pd-23%Ag membranes. Pd-23%Ag is utilised as the permeation medium as it is resistant to hydrogen embrittlement at permeator operating temperatures. The dense, thick-walled Pd/Ag membranes currently in operation are expensive due to the cost of the raw materials used. The aim here is to produce composite components consisting of thin film permeators deposited onto porous supports. As hydrogen permeation rate relates inversely to permeator thickness, thin film permeators also offer greatly increased rates of permeation. Substrates investigated are porous stainless steel, porous alpha and gamma alumina, and porous Vycor glass. Initial Pd/Ag coatings have shown some success, however problems found included: pinholes through the coating thickness; coating stresses caused by substrate/coating thermal mismatch; and poor adhesion to ceramic substrates. In addition, the original pore size of the stainless steel tubes was too large to coat with a thin layer of Pd/Ag without modification to the substrate. A number of alternative approaches have been investigated to optimise the permeator performance. One method includes grading the coatings from ceramic-to-metal, another method involves the use of multilayers to decrease initial substrate pore size and to reduce pinholes in the main permeator film. In addition, other permeator materials have been investigated in conjunction with Pd/Ag. Furthermore, stainless steel substrates have been subjected to mechanical treatments to remove the surface layers of the substrate and leave pores with a reduced external diameter. The coating technique employed is unbalanced magnetron sputtering. Preliminary findings are presented here.