In the process of thin film deposition, we produce layers nanometers to microns thick on a surface in order to impart specific properties not necessarily inherent in the bulk material.

New thin film applications are developing all the time as are the materials required to execute a certain result. In addition to the more common applications such as optical coatings for a lens or mirror, or electronic semiconductor devices, the need for novel or unusual materials to be applied as a thin film is increasing. For example, Intlvac recently provided a thin film coating service to a customer conducting liquid argon physics experiments using direct immersion photomultiplier tubes. In order to detect 128 nm photons produced in a liquid argon reservoir using an off the shelf photomultiplier tube, a wavelength shift of 425 nm is required.

Liquid argon is a popular detection medium for both neutrino and dark matter experiments, due to the high light yield and potential for high-precision pulse shape discrimination. The coating material required for this application was tetraphenyl butadiene (TPB) that could withstand immersion in the liquid bath.

TPB is an organic chemical compound commonly used as an electroluminescent dye. It is also a scintillator material, making it widely used as a wavelength shifter to absorb ultraviolet photons and emit blue photons, making it useful for measurement and research purposes. For this application, tetraphenyl butadiene (TPB) was used to coat photomultiplier tubes (PMTs) used in the detection of vacuum ultraviolet (VUV) photons. Intlvac provided TPB coating for over 120 PMTs enabling the customer to successfully run their PDS system.

Source & Further Reading:

https://www.osti.gov/biblio/1454590

https://www.researchgate.net/publication/45897082_A_Study_of_the_Fluorescence_Response_of_Tetraphenyl-butadiene

https://dspace.mit.edu/handle/1721.1/88416

https://arxiv.org/pdf/1001.4214.pdf