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Langmuir

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

Xinxin He, Xiaoya Liu, Jun Tang, Haifeng Dong, Yasuhiro Sugawara, Yan Jun Li, Zongmin Ma, Jun Liu

Published Aug 31, 2023• 3 citations
Publisher

Abstract

Paraffin and octadecyltrichlorosilane (OTS) coatings can alleviate collisions between alkali-metal atoms and cell walls and then prolong the atomic spin-polarization lifetime. The surface structure and collision effects of these antirelaxation coatings, as well as the methods to avoid antirelaxation invalidity, have been the focus of researchers. This study investigated the thermolability of coating surface structure and the collision interactions between alkali metal atoms and coatings, considering the influence of various coating preparation factors, where this collision interaction is indirectly analyzed by measuring the collision energy dissipation between an atomic force microscopy (AFM) probe and the atoms on the coating surface. We found that appropriate evaporation time, carbochain length, and postannealing process can enhance the thermostability of the paraffin coating and eliminate its morphological defects. Furthermore, the OTS/water concentration, the soaking time, and the type of solvent have different levels of influence on the cluster formation and the thermostability of the OTS coatings. Moreover, the antirelaxation performance of coatings has been shown to be characterized by counting the energy dissipated when the AFM probe collides with the antirelaxation coating, replacing the conventional light-atom interaction- based method for measuring the relaxation characteristics, but requiring specific coating preparation factors to be maintained.

DOI
10.1021/acs.langmuir.3c01480

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Paraffin and octadecyltrichlorosilane (OTS) coatings can alleviate collisions between alkali-metal atoms and cell walls and then prolong the atomic spin-polarization lifetime. The surface structure and collision effects of these antirelaxation coatings, as well as the methods to avoid antirelaxation invalidity, have been the focus of researchers. This study investigated the thermolability of coating surface structure and the collision interactions between alkali metal atoms and coatings, considering the influence of various coating preparation factors, where this collision interaction is indirectly analyzed by measuring the collision energy dissipation between an atomic force microscopy (AFM) probe and the atoms on the coating surface. We found that appropriate evaporation time, carbochain length, and postannealing process can enhance the thermostability of the paraffin coating and eliminate its morphological defects. Furthermore, the OTS/water concentration, the soaking time, and the type of solvent have different levels of influence on the cluster formation and the thermostability of the OTS coatings. Moreover, the antirelaxation performance of coatings has been shown to be characterized by counting the energy dissipated when the AFM probe collides with the antirelaxation coating, replacing the conventional light-atom interaction- based method for measuring the relaxation characteristics, but requiring specific coating preparation factors to be maintained.
Abstract This research explores the desorption mechanism and thermal stability of octadecyltrichlorosilane (OTS, CH 3 (CH 2 ) 17 SiCl 3 ) coating on quartz slides and in alkali‐metal vapour cells. The morphological thermal‐changes, energy dissipation diversity, and anti‐relaxation characteristic of OTS coatings before and after exposure to Cs atoms by Fourier transform infrared spectroscopy, water contact angle measurement, atomic force microscopy imaging, collision energy dissipation analysis, and free induction decay of Cs atoms are measured systematically. The results show that the OTS coatings exhibit the best thermal stability under the specific process conditions, and the homogeneous and dense structure makes the adsorption of alkali‐metal atoms more stable, which effectively reduces surface energy dissipation and prolongs the relaxation time of Cs atoms. The study provides certain reference for efficient anti‐relaxation coating fabrication and coated cell application.
Abstract Anti-relaxation surface coatings can reduce collisions between alkali-metal atoms and cell walls, thereby prolonging the spin-polarization lifetime of alkali-metal atoms. This phenomenon can considerably improve the performance of quantum sensors. Researchers have focused on the surface topography and composition of anti-relaxation coatings in alkali-metal vapor cells and on methods that provide an increase in the relaxation time of alkali metals. We proposed a novel method to characterise the coating performance of alkali-metal cells by directly measuring the energy dissipation during collisions between the anti-relaxation coating surface and atoms in the cell. We found that the interactions between alkali-metal atoms and the anti-relaxation coating resemble elastic collisions, which can be indirectly characterised by the energy dissipation during interactions between an atomic force microscopy tip and atoms. In addition, we confirmed that the energy dissipation between collisions is positively correlated with the relaxation characteristics of alkali metals at various temperatures. This discovery is of great significance as it can be utilised to characterise the anti-relaxation coating performance of alkali-metal cells by directly analysing the energy dissipation of anti-relaxation coatings instead of measuring the relaxation time.
Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10 000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials.
Abstract Anti-relaxation coatings play an important role in enhancing the polarization lifetime of polarized alkali-metal atoms. In this study, octadecyltrichlorosilane (OTS) was coated in spherical rubidium vapor cells fabricated using borosilicate glass with two stems as anti-relaxation coatings. An orthogonal experiment method was employed to obtain the optimal conditions. The results showed that OTS concentration is the dominant factor in the number of bounces, followed by the soaking time and molar ratio/(H2O:OTS). The optimal parameters were 6 mM of OTS, 6:1 of molar ratio/(H2O:OTS), and 80 min of soaking time. The number of bounces can be up to 200. Atomic force microscope images showed that the number and coverage ratio of clusters on the anti-relaxation coating fabricated by the optimized parameters are significantly less than the number and coverage ratio of clusters formed by other conditions. This means that the clusters in the coatings significantly affect the anti-relaxation performance. In addition, five OTS-coated cells were fabricated by A3B3C5 combination. However, the variability from cell to cell using the exact same preparation procedure can be up to 43.6%. The variability may be caused by the different aging times of the OTS solution. Because only one beaker of OTS solution was prepared, the OTS solution was pumped into the cells in sequence, not at the same time.
Surface relaxation rates differ for spin-polarized alkali atoms interacting with monolayer or bilayer octadecyltrichlorosilane (OTS) coatings. The morphology and composition of Rb vapor-exposed films of OTS have been studied with atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). On OTS monolayers, numerous small (<500 nm wide) Rb containing islands nucleate at the boundaries of the ∼1–2 μm wide organic domains. On OTS bilayers, singular large (∼3 μm wide) Rb containing islands were found. Alkali island formation mediated by surface structure could affect the antirelaxation behavior of organic coatings used in atomic magnetometer cells.
Antirelaxation surface coatings allow long spin relaxation times in alkali-metal cells without buffer gas, enabling faster diffusion of the alkali atoms throughout the cell and giving larger signals due to narrower optical linewidths. Effective coatings were previously unavailable for operation at temperatures above 80 °C. We demonstrate that octadecyltrichlorosilane (OTS) can allow potassium or rubidium atoms to experience hundreds of collisions with the cell surface before depolarizing, and that an OTS coating remains effective up to about 170 °C for both potassium and rubidium. We consider the experimental concerns of operating without buffer gas and with minimal quenching gas at high vapor density, studying the stricter need for effective quenching of excited atoms and deriving the optical rotation signal shape for atoms with resolved hyperfine structure in the spin-temperature regime. As an example of a high-temperature application of antirelaxation coated alkali vapor cells, we operate a spin-exchange relaxation-free atomic magnetometer with sensitivity of 6 fT/Hz and magnetic linewidth as narrow as 2 Hz.