Invited Lecture
IN-SITU NANOSCALE WETTABILITY STUDY

Wetting properties of surfaces at high spatial and temporal resolution is an emerging investigation field involving theoretical aspects as well as biotechnological and materials science applications¹. Wettability research using Environmental Scanning Electron Microscope (ESEM) is here reviewed based on two approaches: (a) reflected secondary electrons for analysis^2-3 of bulk sample surfaces down to sub-micron spatial resolution (b) transmitted electrons for analysis^4-6 of low dimensional structures and thin films at nano-scale. We focus on the transmitted-mode using the wet scanning transmission electron microscope (wet-STEM) detector in ESEM.

The quantitative droplet shape and contact angle were provided by fitting Monte-Carlo simulation for transmitted electrons to the wet-STEM experimental results. The dynamics of the initial stages of both film-wise and drop-wise condensation was in-situ studied over self-supported thin liquid films. The role of pinning centers on nanodroplet dynamics was explored as well as the droplet growth and coalescence processes. The corresponding results on delayed coalescence lifetime are compared with other studies on nanodroplets using in-situ transmission electron microscopy (TEM). The results are discussed in relation to possible deviation of nano-scale dynamics from bulk properties in addition to possible e-beam charging effects. These are expected to have an impact on biological processes and nano-scale fluidic applications.

1. "Dynamic study of nanodroplet nucleation and growth using transmitted electrons in ESEM", Z. Barkay, Springer, Lecture notes in nanoscale science and technology, 18, 51-72 (2013)
2. "On universality of scaling law describing roughness of triple line", E. Bormashenko, A. Musin, G. Whyman, Z. Barkay, and M. Zinigrad, Eur. Phys. J. E 38, 2 (2015)
3. "Wettability study of modified silicon dioxide surface using environmental scanning electron microscopy", D. Aronov, G. Rosenman, Z. Barkay, J. Appl. Phys. 101, 084901 (2007)
4. "Wettability study using transmitted electrons in environmental scanning electron microscope", Z. Barkay, Appl. Phys. Lett. 96, 183109 (2010)
5. "Dynamic study of nanodroplet nucleation and growth on self-supported nano-thick liquid films", Z. Barkay, Langmuir 26, 18581 (2010)
6. "In-situ imaging of nano-droplet condensation and coalescence on thin water films", Z. Barkay, Microsc. Microanal. 20, 317 (2014)