The Effect of Asperity Array Geometry on Friction and Pull-Off Force

Abstract

The friction and pull-off forces between regular asperity arrays with various heights on a silicon wafer and a scanning probe of an atomic force microscope (AFM) were measured. We used two-dimensional periodic asperity arrays. The arrays were created by using a focused ion beam (FIB) to mill patterns on a silicon plate and on a platinum layer deposited on a silicon plate. For both materials, the distance between adjacent peaks was about 240 nm and the groove depth ranged from about 3 to 49 nm. The probe of the AFM was a square flat, 0.7 × 0.7 μm2. For the silicon array, the pull-off force decreased with increasing groove depth and was proportional to the radius of curvature of the asperity. The friction force also decreased with asperity height and was proportional to both the asperity curvature and the pull-off force. For the platinum asperity array, although both the pull-off and friction forces also decreased with groove depth, the friction coefficient (calculated by dividing the friction force by the pull-off force) was about half that of the silicon asperity array.

Tribological properties of bio-mimetic nano-patterned polymeric surfaces on silicon wafer

“…Recent advances in polymer research have brought forth interesting tribological materials such as polymer brushes and nano-composite monolayers [10][11][12], which have promising applicative potential in micro/nanoscale devices. Examples of topographical modification include laser texturing [1], micro-dimple formation [6] and ion-beam roughening of surfaces [8,9]. The topographical modification of surfaces is largely concerned with modifying the local geometry of surfaces in order to imitate the surface topography of 'lotus leaves' that have unique ability to avoid getting wet by the surrounding water (figure 1) [13][14][15].…”

“…Traditionally, silicon is widely used for fabrication of MEMS devices and hence, most of the investigations have been directed towards enhancing its tribological performance [1,2]. In the past, several investigations that were focused on improving the tribological behaviour of silicon, have led to the development of various surface modification techniques such as chemical modification (use of molecular coatings such as Langmuir or self-assembled monolayers (SAMs)) [3][4][5], and topographical modification [1,[6][7][8][9]. Recent advances in polymer research have brought forth interesting tribological materials such as polymer brushes and nano-composite monolayers [10][11][12], which have promising applicative potential in micro/nanoscale devices.…”

Enhanced tribological properties of lotus leaf-like surfaces fabricated by capillary force lithography

“…On a comparative note between various surface modification/fabrication methods mentioned earlier such as laser texturing and ion beam roughening 4,5 and the present topographical patterning, the latter method is simple, cost effective, and less time consuming. As a part of continuing research work, the authors are exploring the replication of other natural surfaces with different polymeric materials to ensure flexibility of the fabrication method, which would provide a wide range of surfaces with superior tribological properties.…”

“…[1][2][3] Motivated by the surface topography of lotus leaf, tribologists have modified/ fabricated surfaces by means of laser texturing, ion beam roughening and fabrication of biomimetic nanopatterns in order to enhance the tribological performance on a micro-/nanoscale. [4][5][6][7][8] Here, the authors report the replication of a real lotus leaf surface by a simple capillarity directed soft lithographic technique and the superior tribological property shown by the surface on a microscale. To the authors' knowledge, this is the first report on creating an artificial surface using a natural template by the process of capillarity directed soft lithography and its investigation in the context of tribology.…”

Unidirectional Feeding of Submillimeter Microparts Along a Sawtooth Surface with Horizontal and Symmetric Vibrations

“…In microparts feeding, to feed along microparts in one direction, the driving force applied to each micropart must vary according to the direction of movement of the micropart. Especially, the movement of microparts smaller than submillimeter can be affected not only inertia but also adhesion which is caused by electrostatic, van der Waal's, intermolecular, and surface tension forces (Ando, 1997). Therefore, we need to derive dynamics including adhesion to evaluate the movement of microparts.…”