434
12 Localized or Spatially Selective Electrodeposition Methods
studies of electrodeposition apply very similar setups [30], though X-ray microscopy
has a lower resolution.
If the phenomenon of interest is the nucleation, a lateral view of the working electrode is to be observed. In this case, one of the Si 3 N 4 windows (usually the bottom
one) is covered with a continuous but thin and electron-transparent conducting layer.
The counter and the reference electrodes are outside the observation windows. This
makes the cell asymmetrical, which is generally unfavourable for the current uniformity; nevertheless, this is a necessary compromise for the undisturbed observation by
using an electron beam. Although the direction of the electric current corresponding
to the electrochemical process is determined by the relative position of the anode and
the cathode, it can be regarded as if the current were perpendicular to the substrate,
at least at the length scale of the nuclei being deposited. It is to be noted that this
geometry is not used in thin-layer cells of macroscopic dimensions. The transmission
electron images thus obtained make it possible to describe the population of nucleating grains during electrodeposition processes. Studies utilizing this arrangement
will be dealt with in Sect. 12.2.2.
Another typical goal during in situ TEM studies is the observations of either the
phase boundary or the propagation of the front during layer/grain growth. For such
purposes, well-separated electrode strips are pre-manufactured on the bottom plate of
the electron-transparent cell. These electrodes do not have to be electron transparent
since the newly emerging phase at their edge will be the target of the observation, and
the transparency change as compared to the neighbouring solution will provide the
detection signal. Although the pre-manufactured electrodes are typically pure gold
strips, their modification (e.g., by electroplating) can make them suitable for reference electrode. Plating Cu in a Cu
2+ -containing solution and Ag/AgCl in chloridecontaining solution provides a reference electrode of the first and second kind, respectively. For short-term observation in the absence of any potential-determining reactions, the bare Au strips themselves can serve as a quasi-reference electrode. The
direction of the current related to the electrochemical process is in the plane of the
thin liquid layer entrapped between the TEM observation windows. Sect. 12.2.3 will
deal with studies where this geometry was used.
Regardless of the electrode arrangement, an unbeatable advantage of the in situ
TEM observation is the high imaging rate combined with a large lateral resolution. As
compared to optical imaging, an ultrafast camera is capable of an image recording
rate several orders of magnitude higher than the normal video rate (which is 30
frame/second). However, the detection limit of the optical devices is about half a
micrometre, and there is no opportunity to image nanoscale objects even as a whole,
not to mention their subtle details. Scanning probe techniques are capable of imaging
surfaces down to the atomic resolution, but this is accompanied with a slow recording
rate like 2–3 image/minute. In situ TEM observation covers an intermediate regime,
making it possible to obtain a few tens or hundreds of images per second with a
resolution at the nanometre scale. The lateral resolution is still less than that for standalone solid crystalline samples, which is due to the irregular scattering background
of the surrounding liquid and the cell windows. At the same time, construction of
reconstructed diffraction images of nanoscale segments of the electrode surface is
12 Localized or Spatially Selective Electrodeposition Methods
studies of electrodeposition apply very similar setups [30], though X-ray microscopy
has a lower resolution.
If the phenomenon of interest is the nucleation, a lateral view of the working electrode is to be observed. In this case, one of the Si 3 N 4 windows (usually the bottom
one) is covered with a continuous but thin and electron-transparent conducting layer.
The counter and the reference electrodes are outside the observation windows. This
makes the cell asymmetrical, which is generally unfavourable for the current uniformity; nevertheless, this is a necessary compromise for the undisturbed observation by
using an electron beam. Although the direction of the electric current corresponding
to the electrochemical process is determined by the relative position of the anode and
the cathode, it can be regarded as if the current were perpendicular to the substrate,
at least at the length scale of the nuclei being deposited. It is to be noted that this
geometry is not used in thin-layer cells of macroscopic dimensions. The transmission
electron images thus obtained make it possible to describe the population of nucleating grains during electrodeposition processes. Studies utilizing this arrangement
will be dealt with in Sect. 12.2.2.
Another typical goal during in situ TEM studies is the observations of either the
phase boundary or the propagation of the front during layer/grain growth. For such
purposes, well-separated electrode strips are pre-manufactured on the bottom plate of
the electron-transparent cell. These electrodes do not have to be electron transparent
since the newly emerging phase at their edge will be the target of the observation, and
the transparency change as compared to the neighbouring solution will provide the
detection signal. Although the pre-manufactured electrodes are typically pure gold
strips, their modification (e.g., by electroplating) can make them suitable for reference electrode. Plating Cu in a Cu
2+ -containing solution and Ag/AgCl in chloridecontaining solution provides a reference electrode of the first and second kind, respectively. For short-term observation in the absence of any potential-determining reactions, the bare Au strips themselves can serve as a quasi-reference electrode. The
direction of the current related to the electrochemical process is in the plane of the
thin liquid layer entrapped between the TEM observation windows. Sect. 12.2.3 will
deal with studies where this geometry was used.
Regardless of the electrode arrangement, an unbeatable advantage of the in situ
TEM observation is the high imaging rate combined with a large lateral resolution. As
compared to optical imaging, an ultrafast camera is capable of an image recording
rate several orders of magnitude higher than the normal video rate (which is 30
frame/second). However, the detection limit of the optical devices is about half a
micrometre, and there is no opportunity to image nanoscale objects even as a whole,
not to mention their subtle details. Scanning probe techniques are capable of imaging
surfaces down to the atomic resolution, but this is accompanied with a slow recording
rate like 2–3 image/minute. In situ TEM observation covers an intermediate regime,
making it possible to obtain a few tens or hundreds of images per second with a
resolution at the nanometre scale. The lateral resolution is still less than that for standalone solid crystalline samples, which is due to the irregular scattering background
of the surrounding liquid and the cell windows. At the same time, construction of
reconstructed diffraction images of nanoscale segments of the electrode surface is