NANOTRIBOLOGY (EXPERIMENTAL)
People
Guido Paolicelli
Alberto Rota
Manoj Tripathi
Sergio Valeri
Introduction
Fundamental energy dissipation channels and size dependent effects, resulting from the increasing surface-to-volume ratio, play a crucial role for understanding friction phenomena at the nanoscale. The well-known macroscopic phenomenological laws of tribology may result inadequate to interpret and predict nano-systems response. In particular the contact area plays a crucial role and need to be well controlled in order to define the laws of friction in the nano-scale regime.
Methods
Experimental techniques that can adequately address the peculiarities of nano-scale friction phenomena are limited. Among them the Atomic Force Microscopy (AFM) with lateral force detection, shortly the Friction Force Microscopy (FFM), is the key method. Our laboratory is equipped with an AFM apparatus (Enviroscope by VEECO) able to perform FFM measurements with lateral resolution in the nanometer range, working in a controlled environment from vacuum (P=10-5 Torr) to liquid condition. Moreover, a number of facilities available in the Centre, like surface science preparation and analysis techniques, and the double beam SEM-FIB apparatus, allow the characterization and modification of both the surface and the AFM tips with nanometer accuracy.
Activity
Research line 1) The tribological properties of surfaces can be modified and controlled by changing their morphological characteristics. At the nano-scale the superficial morphological properties can influence friction, adhesion and stiction following different laws with respect to micro/macro-scale. With the aim of contributing to a more general theory of multi-scale friction we have started a research activity addressed to the study of the tribological properties of nano-patterned surfaces. The properties of patterned surfaces, fabricated by means of Focusing Ion Beam (FIB) sculpting (Fig. 1), are investigated using special rounded AFM tips (Fig. 2), modified by FIB as well. First experiments revealed that the presence of nanometric structures on the SiO2-Si(001) induces a hydrophobic character on the surface, which expresses in a decrease of adhesion and coefficient of friction.
Research line 2) Controlled movement and friction response of single nanoclusters on surfaces. Nano and atomic scale FFM experiments present a fundamental limit: the interface between tip apex and substrate cannot be controlled during the measurements and pressure and wear effects, which modify the friction response, are difficult to be addressed separately. A novel approach has been introduced recently and extensively utilized by our group (Fig. 3). The FFM set-up is used to induce detachment and movements of single nano-clusters (Fig. 4) and to evaluate their tribology behaviour through lateral force and energy dissipation measurements. Gold nano-clusters on HOPG have been studied for their particularly low friction coefficient (Fig. 5).
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Fig 1: AFM image of nano-patterns composed by parallel nano-grooves fabricated by means of FIB.
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Fig 1.1: SEM tilted image of a patterns composed by parallel nano-grooves Bfabricated by means of Focused Ion Beam. Advanced analyses by Friction Force Microscopy showed that the coefficient of friction and the adhesion on the patterned area are lower with respect to the pristine surface. This is related to a hydrophobic character assumed by the surface related to the presence of the nano-structures. D. Marchetto et al., Wear 268, 488 (2010).
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Fig 2: FIB-modified Si tip used for tribological tests by AFM: the extended contact area enables to estimate the integrated effect of the nano-structures on the tribological properties of the surface.
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Fig 3: Nanomanipulation : controlled movement and friction response of single nanoclusters on surfaces.
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Fig 4: AFM forced movement of single gold clusters (24 nm diameter) on HOPG. a) initial topographic image. b) manipulation scan: two single clusters are detached and pushed along the slow scan direction. c) final topographic image: cluster on the right has leaved the scan area, cluster on the centre now is sitting on the right upper corner.
G. Paolicelli, M. Rovatti, A. Vanossi, and S. Valeri, Controlling single cluster dynamics at the nanoscale, Appl. Phys. Lett. 95, 143121 (2009).
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Fig 5: Chemically synthesized gold nanoclusters deposited on HOPG. Cluster dimensions: 24 nm and 42 nm in diameter. Detachment energy threshold versus cluster size.
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Publications
Controlled AFM detachments and movement of nano-particles: gold clusters on HOPG at different temperature
M. Tripathi, G. Paolicelli, S. D’Addato and S. Valeri
Nanotechnology accepted for publication.
Sliding onset of nanoclusters: a new AFM based approach
M. Rovatti, G. Paolicelli, A. Vanossi and S. Valeri
Meccanica (Springer Ed.) 46, 597 (2011)
Hydrophobic effect of surface patterning on Si surface
D. Marchetto, A. Rota, L. Calabri, G.C. Gazzadi, C. Menozzi, and S. Valeri
Wear 268, 488 (2010)
Controlling single cluster dynamics at the nanoscale
G. Paolicelli, M. Rovatti, A. Vanossi and S. Valeri
Appl. Phys. Lett. 95, 143121 (2009)
Adhesion detachment and movement of gold nanoclusters induced by dynamic atomic force microscopy
G. Paolicelli, K. Mougin, A. Vanossi, and S. Valeri
J. Phys. Condes. Matter 20, 354011 (2008)
Controlled manipulation of thiol-functionalised gold nanoparticles on Si(100) by dynamic force microscopy
G. Paolicelli, K. Mougin, A. Vanossi, and S. Valeri
Journal of Physics: Conference Series 100, 052008 (2008)
Single cluster AFM manipulation: a specialized tool to explore and control nanotribology effects
G. Paolicelli, M. Rovatti, and S. Valeri in B. Bhushan (ed.) “Scanning Probe Microscopy in Nanoscience and Nanotechnology Vol.2” Springer, Berlin (2011) (Book ID 192663)