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RESEARCH PAPERS

# Surface Modification of AFM $Si3N4$ Probes for Adhesion/Friction Reduction and Imaging Improvement

[+] Author and Article Information
Zhenhua Tao

Nanotribology Laboratory for Information Storage and MEMS/NEMS, The Ohio State University, 650 Ackerman Road, Suite 255, Columbus, OH 43202

Bharat Bhushan1

Nanotribology Laboratory for Information Storage and MEMS/NEMS, The Ohio State University, 650 Ackerman Road, Suite 255, Columbus, OH 43202bhushan.2@osu.edu

1

Corresponding author.

J. Tribol 128(4), 865-875 (Jun 02, 2006) (11 pages) doi:10.1115/1.2345411 History: Received January 03, 2006; Revised June 02, 2006

## Abstract

$Si3N4$ probes used for atomic force microscope exhibit large adhesion and friction resulting in artifacts of scanned image. In order to reduce adhesion and friction so as to reduce tip related artifacts, liquid lubricant (Z-TETRAOL) and fluorocarbon polymer (Fluorinert$™$) were applied on the $Si3N4$ probe. A comprehensive investigation of adhesion, friction, and wear of the uncoated/coated tips in both ambient air and various humidity levels as well as the influence of the coatings on the image resolution was performed. Experiments show that the coatings reduce the adhesion and friction of the $Si3N4$ tip, improve the initial image resolution, and exhibit less deterioration as compared to that of uncoated tip after scanning. The image degradation of an uncoated $Si3N4$ probe is also compared with that of an uncoated silicon probe. A probe cantilever deflection model was proposed to correlate the influence of the adhesion and friction with the image distortion.

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## Figures

Figure 1

(a) Chemical structures of Z-TETRAOL and Fluorinert™. (b) SEM images of uncoated/coated probe tips.

Figure 2

(a) Friction force as a function of normal load for uncoated and coated tips. (b) Tip profile (displaced vertically for clarity) and wear volume after 2.4mm(10min) sliding under 100nN for various coated tips. The sliding velocity was 4μm∕s.

Figure 3

(a) Adhesive force and coefficient of friction between (uncoated and/or coated) tip and a Si(100) sample in various humidity levels. (b) Tip profiles and tip wear volume in various humidity levels after sliding for 2.4mm(10min) under 100nN. The sliding velocity is 4μm∕s.

Figure 5

(a) Reaction forces from the sample on a vertical probe. The friction force on the tip is equivalent to a force on the end of cantilever and a torque. The cantilever is simplified to rectangular cross section shape. (b) Surface reaction force and friction force acted on an inclined cantilever when the probe is sliding on a horizontal surface (top) and when the probe is sliding on an inclined asperity (bottom). (c) Influence of coefficient of friction, and surface inclined angle on the AFM servo displacement.

Figure 6

(a) Images obtained by uncoated and various coated tips on a Si(100) surface after ten cycles (85min) scanning. Applied load on tip was 40nN. (b) Adhesion and coefficient of friction between tip and the sample before scanning and after ten cycles (85min) scanning.

Figure 7

(a) SEM image of a Si(100) tip and a Si3N4 tip, (b) tip profiles and the wear volume after 2.4 mm (10 min) sliding on a Si(100) surface under 100nN, (c) initial image and image after ten cycle scan obtained by Si(100) tip and Si3N4 tip. All data about Si(100) tip are from (5).

Figure 4

Images obtained by uncoated and various coated tips on a Si(100) surface. Applied load on tip was 40nN.

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