Evaluation of alternatives to paraffin for antirelaxation coatings

Abstract

Paraffin wax is currently used as an antirelaxation coating in alkali metal vapor cells since it prevents spin depolarization of alkali atoms. However, the performance of paraffin decreases rapidly above 80 °C due to degradation; thus, the inability to operate at higher temperatures motivates a search for alternatives. Here, the authors use first-principles density functional theory to study rubidium (Rb) atom interactions with paraffin, along with potential alternative coating materials such as pristine and hydrogenated graphene, molybdenum disulfide, and the hydrogen-terminated silicon (111) surface. The authors’ results are in close agreement with experiments that find an adsorption energy of 0.1 eV for Rb on paraffin. The authors also find that Rb adsorbs strongly on graphene, MoS2, and silicon surfaces, but that Rb has a low adsorption energy on hydrogenated graphene, which may be suitable as an antirelaxation coating. The authors link adsorption behavior to the charge-transfer-induced ionic bonding between Rb and the underlying material. In paraffin and hydrogenated graphene, charge transfer is avoided, leading to low Rb adsorption energies for these materials.

Effect of Preparation Processes on Structural Thermal Stability and Collision Energy Dissipation of Common Antirelaxation Coatings on Quartz Substrates

“…5–8 factors were successfully monitored in AMFM mode to obtain the panoramic viscoelastic data at 100 °C under an air atmosphere, whereas the paraffin coatings could not be monitored at the temperature of 100 °C. This is consistent with the report on the difference in heat resistance between OTS coating (170 °C) and paraffin coating (80 °C) in the vapor cell . Within the OTS concentration groups of 4 and 5 mM, the real energy dissipation of the coating with majority silylation times (15, 20, 23, 60, 77 min) showed a decreasing trend with temperature rising below 50 °C, while that with the small part times changed minimally (26, 33 min).…”

“…This range is at least 1 order of magnitude greater than that of paraffins (dotriacontane/hexatriacontane). This great disparity is similar to the difference in collision numbers between alkali metal atoms and paraffin-coated cells (∼10 4 times) and those coated with OTS (∼2100 times) . Specifically, the OTS coatings prepared at No.…”

“…This is consistent with the report on the difference in heat resistance between OTS coating (170 °C) and paraffin coating (80 °C) in the vapor cell. 12 Within the OTS concentration groups of 4 and 5 mM, the real energy dissipation of the coating with majority silylation times (15, 20, 23, 60, 77 min) showed a decreasing trend with temperature rising below 50 °C, while that with the small part times changed minimally (26, 33 min). Within the 6 mM concentration group, the real energy dissipation of coatings silanized for 8, 9, 10, and 40 min showed insignificant thermal change below 55 °C, whereas that of coatings silanized for 7 and 20 min fluctuated greatly.…”

“…The earliest antirelaxation coating material utilized paraffin with low absorption energy. , Despite being below its degradation temperature (58–62 °C), the morphology, polarity, and partial charge distribution of paraffin undergo significant changes with temperature due to its poor thermal stability, thus limiting its applications. In contrast, octadecyltrichlorosilane (OTS) exhibits high thermal stability (170 °C) and holds promise as an antirelaxation coating material. , It is worth noting that although both ends are long-chain hydrocarbons, the maximum polarization lifetime from an OTS coating is only ∼2100 bounces, less than ∼10 4 bounces from paraffin coating .…”

A comprehensive study of the effects of different factors on anti-relaxation properties of octadecyltrichlorosilane-coated rubidium vapor cells

“…Paraffins belong to the alkane family. The number of bounces of paraffin coatings and alkene coatings can be up to 10 4 and 10 6 , respectively [25,26]. Paraffins and alkenes form coatings on the inner wall of cells by physical adsorption.…”