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Nanojoule Adsorption Calorimetry (NAC) is a modern technique for measuring adsorption enthalpies of molecules or atoms on well-defined substrates, such as thin metal or oxide single crystals and organic thin films. Similar to previous adsorption calorimeters by Černy, King and Campbell, NAC relies on the direct measurement of tiny temperature changes induced by adsorption utilizing pyroelectric detectors. Thus, its scope extends beyond that of conventional methods such as temperature-programmed desorption (TPD), which require reversible adsorption and cannot be used if thermal decomposition occurs at a lower temperature than desorption. The apparatus is optimized for investigating well-defined metal-organic interfaces, which are models for interfaces in organic electronic devices. Specifically, this contribution covers the challenges in the nanojoule and picomole regimes as well as first proof of concept measurements. These basic studies aim at interfaces between low-work function metals (Calcium) and π-conjugated semiconducting organic thin films (PTCDA) playing an important role in the above-mentioned devices. |
