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Ambient pressure CAIT

All versions of CAIT, which are based on alkali ions or electrons, require vacuum conditions, since the respective charge carriers are not macroscopically stable at ambient conditions. Many aspects of charge carrier transport are particularly interesting at ambient pressure and e.g. controllable relative humidity. Therefore, it is rewarding to develop an ambient pressure version of CAIT.

Such an ambient pressure version of CAIT has recently been implemented. The charge carrier source is a plasma ignited by focusing a fs-laser into a gaseous medium. In the first realization the gas medium was plain air. Initially the fs-laser plasma in air consists of oxygen/nitrogen cations and electrons. Subsequently the electrons are converted to oxygen/nitrogen anions.

Subsequent attachment of these oxygen/nitrogen cations or anions (depending on the polarity applied) to the surface of a sample leads to a charging-up of the surface and consequently charge carrier transport inside the sample is induced. The plasma-CAIT approach is calibrated against a sample of known conductivity. Finally, the correct absolute ionic conductivity and activation energy of a sample of interest can be measured.

Figure 1   Current-voltage data for plasma-CAIT of a D263T glass in positive and negative polarity (left) and corresponding Arrhenius plot leading to the same activation energy as an independent K+-CAIT experiment [1].

Over the last two years we have further developed the fs-laser plasma CAIT experiment. A first modification included a housing being built around the CAIT spectrometer. This allows the use of almost any plasma medium which can be ignited by a fs-laser. Right now, we concentrate on hydrogen and deuterium plasma. As a second modification we have implemented the possibility to measure absolute ionic conductivities as demonstrated in ref. [2]

Fig. 2   Left graph: Comparison of the Arrhenius measurement by various CAIT experiments [2]. Right graph: Concentration depth profile in D263T glass after D+ attachment.

Literature:

[1]   J.L. Wiemer, K.-M. Weitzel
Remote access to electrical conductivity by charge attachment from an ambient pressure plasma
Applied Physics Letters, 113, 052902, (2018)

[2]   J.L. Wiemer, S. Mardeck, C. Zülch, K.-M. Weitzel,
Proton and deuteron electrodiffusion in a D263T borosilicate glass by controlled charge attachment from a fs-plasma
Solid state Ionics, 357 115469, (2020)