Understanding and mitigating nanoscale wear
Mark Lantz, IBM Research GmbH, Switzerland
Tip endurance requirements in emerging probe technologies, such as probe based data storage and lithography, are extremely demanding and have been viewed as one of the major roadblocks for the development of such technologies. In this contribution, this issue is introduced with a discussion of tip wear endurance requirements for a probe based data storage device. Following this, recent experiments to quantify wear of nm-scale sharp silicon tips sliding in contact with a polymer surface with sliding distances up to 1000m are presented . This interface is technically relevant for scanned-probe storage and scanned-probe lithography. The observed deviations from Archard’s wear law can be explained using a new analytic model that captures the crucial aspects of wear physics in a quantitative way. The data and model predict that the wear rates found for sliding silicon tips are prohibitively large.
In the second part of this contribution, strategies for overcoming the wear problem are presented. First the use of alternative tip materials is investigated, namely: monolithic silicon containing diamond like carbon tips (Si-DLC)  and silicon carbide (SiC) terminated silicon tips (see figure 1). Wear tests showing 4-5 order of magnitude improvement in tip life time relative to silicon tips will be presented. Both of these techniques appear very promising for reducing tip wear, but do not address the reciprocal problem of sample wear. Previously, it has been shown that friction can be controlled by high frequency modulation of the tip-surface force. We have investigated the impact of this technique on tip-wear and media-wear of sliding tips on polymer surfaces . We have demonstrated sliding distances of more than 700m without detectable tip-wear for a sharp tip using high frequency modulation. Force modulation appears to be a viable solution for meeting the challenging lifetime requirements to enable scanning probe lithography and data storage. Moreover, the technique can potentially be used with Si-DLC or SiC tips to further enhance tip robustness.
Figure 1. Left panel: monolithic tip made from silicon containing diamond-like carbon (Si-DLC) using a molding process. Right panel: Silicon carbide terminated silicon tip fabricated using carbon implantation into a silicon tip followed by annealing.
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