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Abstract
This paper describes friction experiments and pull‐off force measurements using atomic force microscopy (AFM), between a nonfunctionalized silicon probe and a 2.5 µm diameter CH3 and COOH terminated thiol self‐assembled monolayer pattern. The pattern is microcontact printed onto a gold‐coated silicon wafer, in air, at room temperature, with a relative humidity around 30%, and used to examine probe‐monolayer interactions. Atomic force microscopy imaging reveals that the patterns have been successfully reproduced on the substrate surface. We obtained force values of (8.67±2.60) · 10−9 N, (2.68±1.09) · 10−8 N, and (4.60±0.24) · 10−8 N for CH3 terminated alkyl‐thiol, COOH terminated thiol, and gold substrate respectively. Normalizing these values with the tip radius we obtained (0.87±0.27) N/m for CH3 terminated alkyl‐thiol, (2.68±1.10) N/m for COOH terminated thiol, and (4.60±2.50) N/m for bare gold. These interactions are discussed in terms of the chemical affinity between the probe and the substrate.
This work has been supported by the Spanish government MEC (Ministerio de Educación y Ciencia) through the projects PCI 76/03‐04, HF2005‐0055, NAN2004‐09415‐C05‐01 and TEC2005‐07996‐C02‐021MIC. The authors wish to acknowledge Dr. E. Martínez from Nanotechnology Platform of Barcelona Science Park for her helpful and insightful comments concerning this subject.
