Micromachined Fabry−Pérot Interferometer with Embedded Nanochannels for Nanoscale Fluid Dynamics

Abstract

We describe a microfabricated Fabry-Pérot interferometer with nanochannels of various heights between 6 and 20 nm embedded in its cavity. By multiple beam interferometry, the device enables the study of liquid behavior in the nanochannels without using fluorescent substances. During filling studies of ethanol and water, an intriguing filling mode for partially wetting water was observed, tentatively attributed to the entrapment of a large amount of gas inside the channels.

Capillarity-driven dynamics of water–alcohol mixtures in nanofluidic channels

“…Two batches of nanochannels were fabricated with average thickness of d = 6 and 16 nm, respectively. The manufacturing process as well as the characterization of the channels has been described in (van Delft et al 2007). The typical roughness of the channel walls was determined to &1 nm (root means square) by atomic force microscopy (AFM).…”

“…The experiments are based on measuring the optical transmission through this device, which displays a series of distinct transmission peaks, using an optical microscope (Zeiss Axioskop) equipped with a digital video camera (PCO Pixelfly). Monochromatic light was generated from a white light fiber laser source (Fianium) (compared to the previously used Xe arc lamp (van Delft et al 2007), this source offers superior intensity and stability over time) and a grating monochromator (Newport). From the position of these peaks, we determine the thickness of the nanochannel.…”

“…For a fixed wavelength, this shift gives rise to a variation of the transmitted intensity, which allows a precise localization of the meniscus position even for the very thin channels of this study. More details of the optical setup and the methods can be found in (Heuberger 2001;Becker and Mugele 2005;van Delft et al 2007). Figure 2 shows a series of video snapshots obtained during filling with water.…”

“…To this end, several groups investigated the spontaneous filling of hydrophilic nanochannels driven by capillarity (Tas and Haneveld et al 2004;Han and Mondin et al 2006;Thamdrup et al 2007;van Delft and Eijkel et al 2007;Haneveld et al 2008;Mortensen and Kristensen 2008). The general finding of all those experiments is that the filling dynamics of typically pure simple fluids follows the classical Lucas-Washburn law (Lucas 1918;Washburn 1921), in which the meniscus advances proportional to the square root of time.…”

Measuring concentration fields in microfluidic channels in situ with a Fabry–Perot interferometer

“…[26][27][28] To our knowledge, only one refractometry method, consisting of a Fabry-Perot interferometer with a monochromator, is able to resolve spatial refractive index profiles in a fluidic system. 29 This technique is optimized for measurements in nanofluidic channels and not immediately applicable to measuring evolving concentration profiles in microfluidic channels.…”