Nanotribology and MEMS

http://content.stockpr.com/amedica/db/265/827/pdf/paperg.pdf

Orthopedic applications of silicon nitride ceramics.

Understanding friction1,2,3,4 and wear5,6,7,8,9,10,11 at the nanoscale is important for many applications that involve nanoscale components sliding on a surface, such as nanolithography, nanometrology and nanomanufacturing Defects, cracks and other phenomena that influence material strength and wear at macroscopic scales are less important at the nanoscale, which is why nanowires can, for example, show higher strengths than bulk samples12 The contact area between the materials must also be described differently at the nanoscale13 Diamond-like carbon is routinely used as a surface coating in applications that require low friction and wear because it is resistant to wear at the macroscale14,15,16,17,18,19,20, but there has been considerable debate about the wear mechanisms of diamond-like carbon at the nanoscale because it is difficult to fabricate diamond-like carbon structures with nanoscale fidelity Here, we demonstrate the batch fabrication of ultrasharp diamond-like carbon tips that contain significant amounts of silicon on silicon microcantilevers for use in atomic force microscopy This material is known to possess low friction in humid conditions, and we find that, at the nanoscale, it is three orders of magnitude more wear-resistant than silicon under ambient conditions A wear rate of one atom per micrometre of sliding on SiO2 is demonstrated We find that the classical wear law of Archard21 does not hold at the nanoscale; instead, atom-by-atom attrition7,8 dominates the wear mechanisms at these length scales We estimate that the effective energy barrier for the removal of a single atom is ∼1 eV, with an effective activation volume of ∼1 × 10−28 m3 Ultrasharp scanning probe microscope tips made of diamond-like carbon that contains silicon and oxygen demonstrate very high levels of wear resistance

https://alliance.seas.upenn.edu/~carpickg/dynamic/wordpress/wp-content/uploads/2014/01/Bhaskaran_NatNano_2010.pdf

Ultralow nanoscale wear through atom-by-atom attrition in silicon-containing diamond-like carbon

The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients.

/pdf/critical-length-scale-controls-adhesive-wear-mechanisms-t9vsgwetb7.pdf

Critical length scale controls adhesive wear mechanisms

Atomic force microscopy (AFM) is a powerful tool for studying tribology (adhesion, friction, and lubrication) at the nanoscale and is emerging as a critical tool for nanomanufacturing However, nanoscale wear is a key limitation of conventional AFM probes that are made of silicon and silicon nitride (SiNx) Here we present a method for systematically quantifying tip wear, which consists of sequential contact-mode AFM scans on ultrananocrystalline diamond surfaces with intermittent measurements of the tip properties using blind reconstruction, adhesion force measurements, and transmission electron microscopy (TEM) We demonstrate direct measurement of volume loss over the wear test and agreement between blind reconstruction and TEM imaging The geometries of various types of tips were monitored over a scanning distance of approximately 100 mm The results show multiple failure mechanisms for different materials, including nanoscale fracture of a monolithic Si tip upon initial engagement with the surface, film failure of a SiNx-coated Si tip, and gradual, progressive wear of monolithic SiNx tips consistent with atom-by-atom attrition Overall, the method provides a quantitative and systematic process for examining tip degradation and nanoscale wear, and the experimental results illustrate the multiple mechanisms that may lead to tip failure

Method for Characterizing Nanoscale Wear of Atomic Force Microscope Tips

Nanometer scale single asperity tribochemical wear of silicon nitride was examined by measuring the wear of atomic force microscope tips translated against a variety of substrates in aqueous solutions. We show that the chemical nature of the substrate plays an important role: significant wear was observed only when the substrate surface is populated with appropriate metal-hydroxide bonds. Mica and calcite substrates, whose water-exposed cleavage surfaces lack these bonds, produced little if any tip wear. As a function of contact force FN and scan duration t, the length of the tips in this work decreases approximately as (FNt)0.5. We propose that pressure-induced intermediate states involving hydroxyl groups form on both the tip and the substrate; chemical reactions subsequently form transient bridging chemical bonds that are responsible for tip wear.

https://public.wsu.edu/~jtd/publications/MawSi3N4TipWearJAP02.pdf

W. Maw

Papers

Single asperity tribochemical wear of silicon nitride studied by atomic force microscopy