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In-situ Electron Microscopy Developments

In-situ electron microscopy techniques are crucial to enable a direct correlation between structure/structural changes and properties of materials

1. In situ mechanical testing in the TEM

We have been developing the combination of in-situ straining experiments using a Hysitron PicoIndenter with a Push-to-Pull device together with automated crystal orientation mapping (ACOM) using a NanoMegas ASTAR system. The straining is monitored in situ using up-STEM on a FEI Tecnai F20 and, at seleted points, orientation maps are acquired during holding segments of the straining series. This enables adirect quantitative analysis of crystallographic changes during mechanical straining with nanometer resolution.

PTP for in-situ straining in the TEM

Fig. 1.1: PTP device for in situ straining of thin-films in the TEM.

 

The total acquisition time of 6 and 12 hoursa for a compelete straining series puts very high demands on the mechanical stability of the microscope and the straining holder. Under displacement controled operation of the Picoindenter, some relaxation of the stage can not be prevented, but the stability is sufficient for a qualitative evaluation of the straining state for the different orientation maps (Fig. 1.2). This approach was used to e.g. follow the grain growth (Fig. 1.3), twining and grain rotation in nanocrystalline gold.

Stress-strain curve

 

Fig. 1.2: Stress-strain curve of the repeated deformation of a nanocrystalline Au film under displacement control. The stress-strain curve shows that the film was initially slightly bend and is first straightening during the deformation, before the 'normal' straining of the film occurs.

 

Grain growth during in-situ straining in ncAu

Fig. 1.3: Anomalous grain growth during in situ straining of ncAu.

 

By operating the PicoIndenter under load control, a much better stability mechanical stability can be achieved, which enables working at reliable straining states. Despite the relatively long data acquisition times, creep is not contributing significantly to the deformation except for the straining states close to failure of the thin film.

In-situ straing under load control

Fig. 1.4: In situ straining under load control and corresponding stress-strain curve with creep contribution during ACOM acquisition.

 

Details of this work have been published and are available at

 

  • A. Kobler, A. Kashiwar, H. Hahn, C. Kübel, "Combination of in-situ straining and ACOM TEM: a novel method for analysis of plastic deformation of nanocrystalline metals", Ultramicroscopy, 2013, 128, 68-81; DOI: 10.1016/j.ultramic.2012.12.019.
  • A. Kobler, C. Brandel, H. Hahn, C. Kübel, "In situ observation of deformation processes in nanocrystalline face-centered cubic metals", Beilstein Journal of Nanotechnology, 2016, 7, 572–580; DOI: 10.3762/bjnano.7.50.

 

2. In situ heating in the TEM

The combination of in situ heating in (S)TEM with automated crystal orientation mapping (ACOM) is a powerful approach to directly image the microstructural evolution and orientation changes of all individual grains of a thin film at the nanoscale as the basis to understand the processes controlling thermally induced grain growth.
In this study, sputter deposited nanocrystalline palladium thin films with ~50 nm thickness were used to study the grain growth and crystallographic development in real space. Mapping the grain orientation and their changes in an area with more than one thousand grains in the initial structure with a resolution of 1.5 nm allowed for a statistically meaningful analysis of grain orientation, grain boundary character, grain rotation and grain boundary migration with temperature. Local analysis showed that a reduction in grain boundary curvature and grain boundary area are driving forces for the grain growth, but they are not sufficient to explain grain growth in nanocrystalline metals. Quadruple and higher order line networks appear to locally stabilize the nano grain network.

In situ heating ncPd 

Fig. 2.1: Thermally induced grain growth in a nanocrystalline palladium thin film at 300 ºC.

 

 

 

3. In situ electrical testing of solid state batteries in the TEM

To better understand the processes during cycling of rechargable batteries, we are developing new preparation and analysis approaches to follow the structural changes in micron sized solid state batteries and half cells in situ. The basic idea is to use FIB preparation to cut a thin cross-section from a solid state battery that is then transferred under (close to) inert conditions onto an electro-contacting TEM holder for in situ analysis using low-dose and low voltage TEM and STEM techniques if needed.

In-situ TEM Characterization of Solid State Batteries

Fig. 5: a) Schematic of a thin film solid state battery with a FIB milling of a thin lamella indicated;
b) schematic and dimensions of a typical TEM lamella based micron sized battery;
c) schematic of the set-up for in-situ analysis of a solid state battery inside the TEM.

 

The materials that have been recently investigated are solid state fluoride ion batteries in caollaboration with Prof. Max Fichtner's group. For a La0.9Ba0.1F2.9/Bi half-cell and for a MgF2/La0.9Ba0.1F2.9/Cu full cell, we have performed the first successful in situ cycling experiments, where we obtained a reasonable I/V charging/discharging curve and imaged some of the structural and compositional changes during cylcing.

I/V curve during charging of a LaBaF/Bi half-cellMorphological changes during cycling of a MgF2/LaBaF/Cu full cell 

Fig. 6: a) I/V curve obtained during in situ charging of a micron sized La0.9Ba0.1F2.9/Bi half-cell with the main peaks corresponding to Bi oxidation and BiF3 formation; b) morphological changes during cycling of a MgF2/La0.9Ba0.1F2.9/Cu full cell with Cu recrystallization, void formation and finally fracture at the interface between eletrode and electrolyte visible.

Details have been published at

  • In situ TEM studies of micron-sized all-solid-state Fluoride Ion Batteries: Preparation, Prospects and Challenges,M. Hammad, V.S.K. Chakravadhanula, M.A. Reddy, C. Rongeat, T. Scherer, H. Hahn, M. Fichtner, C. Kübel, Microscopy Research and Technique, 2016, 79, 615-624; DOI: 10.1002/jemt.22675.

 

4. In situ liquid in the TEM

As part of the development of the in situ liquid experiments in the TEM, we have the possibility to introduce liquids between two SiN membranes using a Protochips Posseidon in situ liquid flow holder along with electrical measurements. On the other hand, nanoparticles can also be generated in liquids inside the TEM induced through electron beam which is critical to differentiate from the actual experiment of interest.

As an example here, here we show the video of electron beam induced growth of Ag nanoparticles in 0.01 M AgNO3 solution.

Fig. 3.1: Beam induced in situ growth of Ag nanoparticles in a solution of 0.01 M AgNO3 solution (4X speed).

 

 

5. In situ mechanical testing in the FIB/SEM

As an easy and cheap solution for in situ straining and bending experiments in the FIB, we have developed the combination of an AFM cantilever with an OmniProbe micromanipulator. For mechanical testing of nanowires, these are attached to both the OmniProbe tip as well as the AFM cantilever. The displacement of the OmniProbe is used to strain or bend the nanowire while the structural changes are manitored by the SEM, while the applied forces can be determined from the displacement of the (calibrated) AFM cantilever.

 

FIB in-situ mechanical testing

Fig. 4.1: In situ mechanical testing using an AFM cantilever and an OmniProbe micromanipulator inside a DualBeam FIB.

Details of this work have been published and are available at

 

  • T. Scherer, S. Zhong, T. Schimmel, "Tensile Testing of Microstructures", G.I.T. Imaging & Microscopy, 1/2011, 44-47.