Toward condensing stable water meniscus for Dip-pen nanolithography considering ambient condition, surface wettability, and SPM probe structure

Water menisci are molecular transport channels for the Dip-pen Nanolithography (DPN), affecting pattern qualities and imaging resolutions. The feature sizes (volumes, bottom diameters, etc.) of the menisci and the adhesive forces (AF) generated by the menisci are greatly influenced by key operational factors in DPN, including environment humidity (RH), temperature (T), surface contact angle (SCA), tip radius (R), and probe-substrate gap (d). However, there is a lack of researches on the relationships between these DPN parameters and the water meniscus characteristics, posing challenges for controlling the lithography processes. In this work, based on the governing equations derived from force-balance method, infinitesimal method, and Kelvin effect, the impact of the DPN operational factors on the water meniscus characteristics is studied. The lithography efficiencies and resolutions are contradictory. A meniscus with large volume would be condensed with high RH, low T, small SCA, large R, and small d to improve the DPN efficiencies but drop its resolutions. The RH is the most important factor affecting the water meniscus, and the menisci would fail to condense with a large gap d. The temperatures exhibit linear relationships with the water meniscus characteristics. The equivalent SCA is a critical factor in understanding the water meniscus characteristics between two curved surfaces, as it determines the differences between top- and bottom- diameters of meniscus. The RH > 80 %, SCA > 10°, sharp probe and d > 1 nm would reduce lithography stabilities of the DPN processes. The AFs are linearly related to the tip radii and gaps, providing a potential approach to characterize the wear- and contact- status of the probe. This work contributes to providing theoretical references and technical supports for controlling the DPN processes and studying the capillary phenomenon for the probe-based techniques.