Force Drift in Force Mode Dip-Pen Nanolithography

Dip-pen nanolithography (DPN) is a widely employed technique in fabricating micro-and nanopatterns composed of biological molecules or other chemical materials. Force drift, a key factor affecting the force control, therefore the performance of DPN, is commonly happened in DPN. However, the underlying mechanism of force drift is not well understood yet. In this work, based on analyzing the force curve and tapping mode (TM) deflection signals varying with dwell time (i.e., the 'surface delay' period), the force drift during force mode dip-pen nanolithography (FMDPN) was studied in depth. For an open-loop atomic force microscope (AFM) scanner the force drift is about 30% of its preset value on a soft polydimethylsiloxane (PDMS) substrate while it can reach 400% on a rigid silicon wafer during the dwell time of 2 seconds. The creep effect of the scanner in the z direction determines the force drift and the thermal drift of AFM system is negligible in comparison with the preset loading force when the AFM system is stabilized. For a closed-loop scanner the loading force can nearly keep constant on either a soft PDMS substrate or a rigid silicon wafer during the whole dwell time due to the compensation for the creep effect of piezoelectric tube in the z direction of the AFM scanner. This study is helpful for properly employing DPN technique to fabricate micro-and nano-patterned structures on solid substrates.