In this work we present a new microfabricated nanochannel device for in situ liquid TEM based on wafer bonding (Fig.1a). A schematic depiction of the chip cross section is presented in Fig.1b. The cell system was fabricated with a new direct bonding technique linking the adhesion properties of Silicon Rich Nitride (SiNx)/Stoichiometric Silicon Nitride (Si₃N₄) within atomic layer deposition (ALD) of Al₂O₃ tuned for this application to provide low temperature bonding. The liquid vessel is designed with multiple nanochannels on a suspended membrane area, with tunable liquid layer thickness ~100 nm and silicon nitride windows ~ 50 nm. The channel design of the system improves the control of the top and bottom membrane bulging compared to commercial liquid cell devices and is hence expected to improve the area with high spatial resolution achievable in liquid TEM imaging.  Our nanofluidic system together with a custom-made flow holder will give further control of liquid conditions dynamically varying experimental conditions.

The liquid cell was first tested by optical fluorescence microscopy using a solution of 10 nm quantum dots (QD) and as depicted in Fig.2. Flow and diffusive motion of the QDs could be followed. In a Tecnai TEM at 200 kV, a solution of 30 mM HAuCl₄ was sealed in the channel with epoxy glue and upon TEM irradiation gold particles in average size between 5 and 15 nm were nucleated along the channels (Fig.3a). Sometimes rocking particle motion was observed, confirming their enclosure within the liquid layer (Fig.3b). In our design membranes are inner bending on each other and plastically deformed due to the extremely high (>12 bar) capillary force. Thus, a thin layer of water < 100 nm is trapped among the membranes. In contrast with other  recent liquid vessels ^[1], our nanofluidic system points toward higher resolution since liquid thickness  [2], biomineralization synthesis ^[3] , liquid phase displacement and in liquid holography.

References

1.                  Tanase, M. et al. Microsc. Microanal. 21, 1629–1638 (2015).

2.                  Nielsen, M. H. et al. Microsc. Microanal. 20, 425–436 (2014).

3.                  Smeets, P. J. M., Cho, K. R., Kempen, R. G. E., Sommerdijk, N. a J. M. & De Yoreo, J. J. Nat. Mater. 1–6 (2015). doi:10.1038/nmat4193

Figures:

Fig.1 – a) Nanofluidic device croos section after microfabrication. On the side of the membranes inlet and outlet are visible. b) Zoom in of the imaging area. Nanochannels ( white ) and bonded Silicon Nitride regions ( purple ) are visible. Scale bar 50 μm.

Fig. 2 – Fluorescent 10 nm quantum dots inside the channels. The quantum dot is moving along the channel a) and b). Time btw. images is 2 sec. Scale bar 20 μm.

Fig. 3 – a) Gold particles nucleated in thin liquid layer. Scale bar 15 nm b) Single gold nanoparticle in liquid rocking along is x-y axis. Imaged were obtained using a TECNAI T20 200kV using respectively a beam current of 2.1 nA and an electron dose of 2.5 e/nm2*s. Time btw. images is 1 s for each pictures. Scale bar 5 nm

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