Keywords: Nanochannels, capillarity, viscosit

Elwenspoek, M.C.

Haneveld, J.

Jansen, H.V.

Tas, N.R.

English

Jansen, Henricus V.

Tas, Niels Roelof

Elwenspoek, Michael Curt

NARCIS 

Fabrication and capillary filling of sub-10nm nanochannels

University of Twente Research Information

Fabrication and Capillary Filling of sub-10nm Nanochannels  J. Haneveld, N.R. Tas, H.V. Jansen, M. Elwenspoek Transducers Science and Technology group, Mesa+ Research Institute, University of Twente,  P.O. Box 217, 7500 AE Enschede, The Netherlands Email address corresponding author: j.haneveld@utwente.nl  NanoNed-Nanofluidics.  Keywords: Nanochannels, capillarity, viscosity   Planar nanochannels fabricated by silicon based technology can provide an attractive configuration for fundamental studies like of filling kinetics,1,2 diffusion and molecular separation processes. Channel with at least one dimension below 10 nm are extremely interesting as model system to study the dynamics of confined liquids. Accurate measurement of confinement induced viscosity changes have been done using the Surfaces Forces Apparatus (SFA).3,4 Nanochannels with well defined sub-10 nm dimensions could offer a relative simple experimental alternative for these dynamic measurements.  To fabricate well-defined sub-10 nm nanochannels we used a silicon oxide spacer layer which can be grown accurately at the nanometer scale, and patterned and removed selectively from the silicon substrate. The channel height has to be corrected for the native oxide that re-grows on the bottom of the etched trenches during cleaning: see eq. (1). channel spacer nativeoxide0.54d d d= −  (1) Fig. 1 shows a photograph of fabricated chips. Capillary filling was successfully observed in channels between 5 and 47 nm in height. Fig. 2 shows the measured position of the moving meniscus versus the square root of time for filling with water. Qualitatively the filling follows the classical Washburn law, quantitatively the filling is slower than expected, as is represented by a correction factor C (Fig. 3). Various possible explanations for the observed slower than expected filling have been considered. The most likely cause is an ordering or layering effect due to the liquid-wall interaction, and the associated local increase in viscosity. In a first approximation, assuming a completely solidified layer of water molecules next to the channel walls, this layer would have a thickness of 0.9 ± 0.3 nm. This is in accordance with the generally accepted view that in water the influence of the wall extends only a few monolayers into the liquid.          References 1. N.R. Tas, J. Haneveld, H.V. Jansen, M. Elwenspoek and A. van den Berg, Appl. Phys. Lett., 2004, 85, 3274-3276. 2. A. Han, G. Mondin, N.G. Hegelbach, N.F. de Rooij and U. Staufer, J. Coll. Interf. Sc., 2006, 293, 151-157. 3. D.Y.C. Chan and R.G. Horn, J. Chem. Phys., 1985, 83, 5311-5324. 4. J.N. Israelachvili, J. Coll. Interf. Sc., 1986, 110, 263-271. Fig. 3 Dimensionless constant C for filling with water. A value larger than 1 indicates a slower than expected filling. Fig. 2 Measured position of the moving water meniscus vs. square root of time. Fig. 1 Photograph of fabricated chips. Arrays of 1 cm long nanochannels are connected to powder blasted access holes through RIE etched microchannels.  

Fabrication and capillary filling of sub-10nm nanochannels

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University of Twente Research Information