1. RESEARCH PROPOSAL STUDY OF LAYERED MoS 2, WITH MoTe 2, AND MoSe 2 Warren Courtney University of Waterloo March 29, 2006

2. Background  Numerous studies have looked at the tribology of multi-layered dry lubricants, for myriad reasons (ref 1, 2, 3, 8)  Studies have also been done on the orientation of molecules in the lubricating layers to determine the effects. Dramatic increase in friction can occur when molecules align (ref 9)  This study proposes looking at a nano-structured material composed of layers of MoS 2, MoTe 2, and MoSe 2 in which the material are deemed to have similar properties but different crystal structures which should reduce friction by not allowing co- incidence structure.

3. Nanoscale friction  Graph of atomic force microscopy probe moving across a smooth surface of NaCl (monet.unibas.ch/gue/uhvafm/tribo.html)  Proposed mechanism based on Tomlinson’s model of atomic friction ( www.nanoscience.de/group_r/theory/) the sample surface

4. physics web.org/articles/world/18/2/9 Phononic friction  As surfaces pass over one another the theory of friction indicates that attachments are made and broken between materials resulting in the production of phonons  It should be more difficult for multilayer materials to pass over one another since there are more ways for the atoms to move and interact and create heat and phonons  Such "phononic" friction is particularly great when the surface atoms are equally spaced, and when they are aligned with the counter face atoms upon which they are sliding.

5. ref4 Lince, R. L. and Frantz, P.P. Structure of MoS 2  Structure of MoS 2 Strong bonds within layers and very weak bonds between layers  Similar structures are proposed for MoSe 2 and MoTe 2 However the structure are altered due the size differences in the dichalcogenes

6. www.webelements.com Crystal Structures Analogous to Molybdenum Disulphide  Prototypical structure: 

7. Geike, T. Popov, v. L. ref 1 Multilayer graphite structure Friction is reduced each time a new layer starts to move relative to the others

8. Sandia National Laboratories Nano-tractor to measure very low frictional forces This image obtained using a scanning electron microscope shows a "nano- tractor" that can measure ultra low frictional forces as it creeps along a surface. In the centre of the device is a tangential-force actuation plate, flanked by two electrostatic "clamps" that respond to an applied voltage.

9. Hu, J. J., Bultman, J. E., Zabinski, J. S. ref 7 Preparation of Nanolayered Molybendum Dichalcogenides  High purity films can be created by laser ablation using an excimer laser UV radiation at 248 nm wavelength, 20 ns duration 50 Hz.  Characteristics and composition of the layers will be determined with x-ray photoelectric spectroscopy  Samples for testing will consist of layers of MoS 2 with MoSe 2 ; MoS 2 with MoTe 2 ; MoSe 2 with MoTe 2 ; and MoS 2 alone as a standard for comparison

10. CSM Instruments SA Testing of Multilayer Molybdenum Dichalcogenides  Initial testing will be performed at the nanoscale using the nanotractor shown previously  Should result show promise a further set of testing will be conduced in a nitrogen purged pin on disc tribometer

11. Environmental Testing  Further test comparisons will be made after 200 hours conditioning in environments containing air at relative humidity of 15%, 25%, 50%, and 75% relative humidity in air at 35 o C; testing will be performed in the conditioning environment

12. References 1.Geike, T., Popov, V. L. Tribology International 39 (2006) pp 437-443, Multi-layer models of friction between solids 2.Lince, J. R. Tribology Letters, Vol 17, No. 3, October 2004, Tribology of co-saputtered nanocomposite Au/MoS 2 solid lubricant films over a wide contact stress range. 3.Popov, V. L., Psakhie, S. G., Tribology International 39 (2006) pp 426-430, Physical nature and properties of dynamic surface layers in friction 4.Lince, J. R., Frantz, P. P., Tribology Letters, Vol 9, No. 3-4, 2000, Anistropic oxidation of MoS 2 crystallites studied by angle- resolved X-ray photoelectron spectroscopy 5.Hu, J. J., Zabinski, J. S., Tribology Letters, Vol. 18, No. 2, February 2005, Nanotribology and lubrication mechanisms of inorganic fullerene-like MoS 2 nanoparticles investigated using lateral force microscopy (LFM) 6.Tagawa, M. Muromoto, M., et al Tribology Letters, Vol. 18, No. 4, April 2005, Hyperthermal atomic oxygen interaction with MoS 2 lubricants and relevance to space environmental effects in low earth orbit – effects on friction coefficient and wear life 7.Hu. J. J., Bultman, J. E., Zabinski, J. S., Tribology Letters, Vol. 18, No. 1 January, 2006, Microstructure and lubrication mechanism of multilayered MoS 2 /Sb 2 O 3 thin films 8.Editorial Popov V. L. Tribology International 39, (2006), pp 369, Development of surface topography in friction processes 9.www. nanoscience.de/group_r/theory/ 10.physicsweb.org/articles/world/18/2/9 11.Monet.unibas.ch/gue/uhvafm/tribo.html