Description

Octadecanethiol (ODT) is an alkanethiol with a long carbon chain mainly used as a self-assembled monolayer (SAM) for surface modification of a wide range of materials.

Surface passivation

Salihoglu et al. report the effects of an octadecanethiol (ODT) monolayer on type-II InAs/GaSb photodetector. Furthermore, they show the improvement of the dark current density only at 77 K temperature. From a practical point of view, higher temperatures for the detector operation are desired. In particular, the temperature of 225 K obtained by employing a 4-stage thermoelectric Peltier cooler is essential. Hence, Papis-Polakowska et al. present surface passivation of (100) GaSb using self-assembled monolayers of long-chain octadecanethiol. The ODT-based treatment is promising for the passivation of T2SL InAs/GaSb photodetectors[1]. The dark current was reduced at least by one order of magnitude for the T2SL InAs/GaSb detector passivated in 10mM ODT-C2H5OH, but an effective passivation process requires the second step - an encapsulation - to protect the surface for a long time.

Anti-Tarnish Process

When the octadecanethiol molecules are continuously coated on the surface, and the silver oxide and extra octadecanethiol layer are constantly removed by the chemicals in the extra layer remover in the ultrasonic bath, a chemically reacted monomolecular octadecanethiol layer is formed on the silver surface, regardless of the surface shape, morphology, and residual thick oxide layers[2]. With the monomolecular octadecanethiol film, the silver surfaces remained almost in their initial condition after severe sulfurization tests that equated to exposure to the ambient atmosphere for several years. Without a protective film, the color of the silver surfaces changed to deep brown and blue, typical colors of silver sulfide. The closely packed film blocks the H2S or other sulfur ions from contacting the silver surface, protecting it from tarnishing for a very long time.

References

[1] E. Papis-Polakowska. “Surface passivation of (100) GaSb using self-assembled monolayers of long-chain octadecanethiol.” AIP Advances 6 1 (2016): 055206.

[2] Ying, Tony. “An Advanced Anti-Tarnish Process for Silver Coins and Silverware—Monomolecular Octadecanethiol Protective Film.” Tribology Transactions 64 1 (2020): 341–349.