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CHARACTERIZATION OF COPPER ELECTRODEPOSITION IN LIQUID PHASE ELECTRON MICROSCOPY

This application presents the Liquid-phase Transmission Electron Microscopy (LPTEM) technique, which integrates integrates liquid flow capabilities within microfabricated liquid cells, providing the means to study different processes in solution with sub-nanometer spatial resolution and sub-microsecond temporal resolution. Using this technique, it is now possible to visually study topics ranging from material science to life science.

There are several key advantages of this technique including: 

  • Control over liquid environment in a micro or nanoscale space
  • Study dynamic processes in the liquid phase with nanoscale spatial resolution
  • Determine the chemical composition in-situ
  • Obtain electronic structure information

We kindly thank DENSsolutions for this collaboration, and for sharing the results obtained with their system.
For information about DENSsolutions:www.denssolutions.com

Materials and Methods

Liquid cell
The Stream Nano-Cell is a an advanced flow cell for controlling liquid environment within the microscope.

Sample holder
The in situ TEM Sample Holder provides the platform for connecting the pressure-based flow controller to the Nano-Cell.

Microfluidic flow controller
The Flow EZ is the most advanced flow controller for pressure-based fluid control. It can becombined with a Flow Unit to control pressure or flow rate. It can be used without a PC.

Flow sensor
The Flow Unit is a flow sensor that allows real time flow rate measurement.

A-I-O software
Fluigent All-in-One (A-i-O) software is a tool for real-time control of pressures and flow rates.

TEM
FEI Titan 80-300.

Liquid sample
CuSO4 (20 mM) and KH2PO4 (10 mM) mixed aqueous solution.

RESULTS

I. Control of the liquid flow and thickness within the
microfluidic chamber

To demonstrate the high level of liquid control within the microfluidic chamber, the electrolyte was flowed into the window area and subsequently evacuated using the system described in the “Materials & Methods” part of the application note. […]

Figure 2. HAADF-STEM images of the window area of a liquid biasing Nano-Cell at different environmental conditions:
(a) no liquid, (b) completely filled with liquid, (c) half evacuated and (d) no liquid.

II. Growth and morphology evolution of Cu dendrites

After flowing the electrolyte, cyclic voltammetry technique was used to study the electrodeposition of Cu. To do so, the electrolyte was injected using a flow rate of 1,7 µL/min, and voltage ranging from -0,70 V to 0,30 V was applied to the Pt electrode. Figure 3 shows a time series HAADF-STEM images illustrating the growth and etching process of Cu dendrites. We can directly observe the growth and morphology evolution of Cu dendrites. […]

Figure 3. Time series of HAADF-STEM images illustrating the growth and etching process of Cu dendrites on the Pt
electrode by employing cyclic voltammetry scanning. In the experiments, incident electron flux was set ~50 e nm-2s-1,
and the liquid flow rate was 1.7 μL/min.

III. Microstructure and chemical composition analysis

Next, SAED analysis was performed. As a dry or thin liquid state is required for electron diffraction, the liquid is pushed out from the microfluidic chamber. Figure 4 a-d shows TEM images of (a) the Pt electrode and (c) the Cu dendrites on the electrode, and (b, d) the corresponding SAED patterns in the liquid phase. The polycrystalline nature of Pt electrode is confirmed by the SAED pattern (Figure 4 a, b). After the electrodeposition, the diffraction rings for polycrystal were resolved. The indication of 220 diffraction means at least a lattice resolution of ~1.28 Å or better can be obtained in the liquid thickness of ~100 nm.

Finally, the chemical composition of the obtained depositions are directly analyzed in the liquid phase. EDX elemental analysis (point, line, or area analysis) is conveniently performed. Figure 4e shows the HAADF-STEM EDX elemental mapping, displaying the spatial distribution of the Cu dendrites and the Pt electrode in the electrolyte, thus confirming the great functioning of this analysis.

Figure 4. TEM images of (a) the Pt electrode and (c) the Cu dendrites on the electrode, and (b, d) the corresponding SAED patterns in the liquid phase. (e) HAADF-STEM EDX elemental mapping, showing the spatial distribution of the Cu dendrites and the Pt electrode in the electrolyte.

 

Conclusion

We have demonstrated the use of a complete experimental system consisting in a TEM, advanced sample holder and flow cell, and high precision pressure-based flow controllers for the observation and characterization of copper electrodeposition in liquid phase transmission electron microscopy. The fundamental innovation of this design is the controlled flow. In fact, this design ensures that the liquid is forced to flow between the chips and across the imaging area, as this is the only route for the liquid to reach the outlet. By contrast, other commercially available and in-house fabricated liquid cells have a large volume which relies on diffusion to bring reactants to the viewing area. By directly interfacing the inlet tubing to the microfluidic channel on the chip, the direction and speed of the flow can be precisely controlled. Accordingly, the reactants are driven to the imaging area directly, and the cell can be flushed of reacted species. Finally, this configuration ensures that all the exiting liquid has experienced the same environment and temperature conditions. To the best of our knowledge, no other system either commercially available or custom-built, has employed a dual-chip configuration with on-chip channel.

References

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