Recent Advances in Mechatronics - Ryszard Jabonski et al (Eds) Episode 2 Part 5 pdf

544 S.A. Chizhik, Z. Rymuza, V.V. Chikunov, T.A. Kuznetsova, D. Jarzabek Rotation tribometry consists in rotational movement of a micro- or nanoindentor The movement radius can be adjusted and decreased down to tens of nanometers Here, the area of the contact area–friction area overlapping on the sample approaches 100% The analysis of the friction area is carried out by the SPM method, The method enables one to study the phenomena of local change in a material as a result of tribochemical reactions on the contact spots Friction of the silicon tip with a radius of 40 nm over the silicon surface was studied, when the latter is protected by a monomolecular polymeric layer of thickness of nm A 100 cycles of tip sliding were performed with an external load, whose value changes to several micronewtons The rotation radius R of the tip relative to the chosen point on the sample was changed from several micrometers to 20 nm The analysis of the friction zone by the SPM method showed substantial differences in the changes in the friction zone depending on the rotation radius of the indentor For a greater rotation radius, the abrasive wear of protective coating to a depth equal to the coating thickness is revealed For small rotation radius, beginning from 50 nm, where the contact and friction areas are comparable, a negative wear is seen (Fig 4), i.e., an additional material arises on the friction area An image of lateral forces shows high contrast (Fig 4d) in the limits of the areas with a rotation radius of 50 nm, which is indicative of a chemical change in the material The thickness of the layer changed is about nm (Fig 4b) These changes can be explained by the mechanochemical reaction of silicon oxidation that is due to high temperatures and shearing reactions in the friction zone (a) (b) Micro- and nanoscale testing of tribomechanical properties of surfaces  (c) 545 (d) Fig Rotation tribometry: 3D image of the friction zone, the left and right zones correspond to R = 200 nm and 50 nm (a); 2D image of topography (b); image of the lateral forces (c); topography profile along the trajectory shown in b) (d) Conclusions A set of nanotribometry techniques and examples of their use for studies of the MEMS surfaces is presented It is shown that a combined application of lateral force, oscillation, and rotation tribometry techniques can characterize the friction surfaces on micro- and nanoscale most fully References [1] B Bhushan “Handbook on Micro- and Nanotribology” CRC Press, New York, 1995 [2] E Meyer, H Heinzelmann, P Grütter e.a., Thin Solid Films 181 (1989) 527 [3] S A Chizhik, H.-S Ahn, V V Chikunov, A A Suslov, Scanning Probe Microscopy (2004) 119 Novel design of silicon microstructure for evaluating mechanical properties of thin films under quasi axial tensile conditions D Denkiewicz, Z Rymuza Institute of Micromechanics and Photonics, Faculty of Mechatronics, Warsaw University of Technology, ul Św A Boboli 8, Warsaw, 02-525, Poland Abstract A new testing method to estimate mechanical properties of e.g metallic thin films supported by a MEMS structure as a lever mechanism is developed The MEMS support structure is chosen for coupling microspecimen with measuring macro-devices The thin films microspecimens were designed in two shapes The first one provides information about the Young’s modulus from the tensile test, whereas the second used to the buckling test gives a value of the Kirchoff’s modulus Poisson’s ratio can be estimated analytically A FEM model was prepared to confirm the obtained analytical results Introduction The analysis of existing test methods follows that values of the mechanical parameters are dependent from a particular measuring device Moreover, there is not possibility to carry the microspecimens between different measuring devices The distinguishing feature of the proposed solution is possibility to standardize the measuring method; to realize the tests with the specimen it is possible to combine of the designed MEMS structure with many existing measuring systems (especially nanoindentation devices) The results of tests will provide an objective estimation of mechanical properties: Young’s modulus, Kirchoff’s modulus, Poisson’s ratio, and fracture strain Novel design of silicon microstructure for evaluating mechanical properties of thin 547 Structure configuration A silicon chip has been designed utilizing the knowledge of MEMS devices microfabrication process (Fig.1) Fig Overview of chip etched in silicon substrate The chip was designed to fulfil two fundamental functions: the silicon chip is a supporting frame preventing specimens against destroy and realizes an executive mechanism (a lever mechanism) to perform tensile test uniaxially on the specimen; the substrate with the chips is convenient to manipulate into a working area Typical lever mechanism described by Parszewski [1] consists of four links connected by joins (Fig.2) Fig Executive mechanism and cross section of silicon chip Element connected with link and support is the microspecimen In this example the mechanism of driving link (a winch) is extended by rigid link Link is a loading lever It transfers an external vertical force P to the elements of mechanism to move them The driving link is connected flexible to connecting link and sway beam Rotary movement of the driving link is changed to linear movement of the connecting link The equal lengths of the winch and the sway beam assure a parallel displace- 548 D. Denkiewicz, Z. Rymuza ment of the connecting link in relation to support The tensile force RH acting on the microspecimen is quasi axial Testing method The elaborated test algorithm bases on an energy balance of the mechanism The energy accumulated in the lever mechanism is shared between joins and tensile element The energy of the joins deformation can be measured experimentally after the lever mechanism will be released; the test element will rupture Fig represents relationship between the external force P and its displacement for two variants of scheme: first, original, when specimen is present and second - without specimen Hence, one is able to estimate participation of the spring energy accumulated in the specimen as E EB = E P − EWO (1) where: EEB is the work of external force P equivalent to a spring energy of the deformed element 6, EP - work of external force P at original configuration, EWO - work of external force P at the second configuration Fig Energy balance of the lever mechanism The right side values of the equation (1) will be found experimentally Knowledge of the articulated quadrangle mechanical characteristic gives a possibility to prepare the final graph of the accumulated energy in the test element (Fig 5) Since, the simple calculation can be made to estimate the tensile forces RH and the strain of the specimen The strain is proportional to displacement of the connecting link Novel design of silicon microstructure for evaluating mechanical properties of thin 549 Fig Graphical representation of tensile force RH versus displacement of connecting link The presented procedure is typical for estimation of the Young’s modulus of the elongated elements Fig shows the specimens of two different shapes that will be used to perform the tests The first one (a) is a typical uniaxial test specimen, whereas the second (b) serves to make a buckling tests according to theorem described by Timoshenko and Gere [2] Fig Shape of specimens will have used for (a) tensile and (b) buckling tests Verification of the analytical model of the microstructure was carried out with FEM model (ANSYS) The results of theoretical and FEM models were converged It confirms the correctness of the received solution Fabrication process The fabrication process has some advantages: it is possible to change kind of the evaporated metals, the evaporated metals are protected by the oxide masks against the etching processes (except HF oxide mask remover), and the specimens are released at the end of the fabrication process The assumed dimensions of uniaxial test specimen are: ~2 µm wide,