Al2O3 Ultra-Thin Films Deposited by PEALD for Rubidium Optically Pumped Atomic Magnetometers with On-Chip Photodiode

Abstract

This communication shows the recipe for plasma-enhanced atomic layer deposition (PEALD) Al2O3 ultra-thin films with thicknesses below 40 nm. Al2O3 ultra-thin films were deposited by PEALD to improve the rubidium optically pumped atomic magnetometers’ (OPMs) cell lifetime. This requirement is due to the consumption of the alkali metal (rubidium) inside the vapor cells. Moreover, as a silicon wafer was used, an on-chip photodiode was already integrated into the fabrication of the OPM. The ALD parameters were achieved with a GPC close to 1.2 Å/cycle and the ALD window threshold at 250 °C. The PEALD Al2O3 ultra-thin films showed a refractive index of 1.55 at 795 nm (tuned to the D1 transition of rubidium for spin-polarization of the atoms). The EDS chemical elemental analysis showed an atomic percentage of 58.65% for oxygen (O) and 41.35% for aluminum (Al), with a mass percentage of 45.69% for O and 54.31% for Al. A sensitive XPS surface elemental composition confirmed the formation of the PEALD Al2O3 ultra-thin film with an Al 2s peak at 119.2 eV, Al 2p peak at 74.4 eV, and was oxygen rich. The SEM analysis presented a non-uniformity of around 3%. Finally, the rubidium consumption in the coated OPM was monitored. Therefore, PEALD Al2O3 ultra-thin films were deposited while controlling their optical refractive index, crystalline properties, void fraction, surface roughness and thickness uniformity (on OPM volume 1 mm × 1 mm × 0.180 mm cavity etched by RIE), as well as the chemical composition for improving the rubidium OPM lifetime.

Hydrogen Production from the Carbon Dioxide Sorption-Enhanced Steam Reforming of Biogas Over a Ni-Based Hybrid Material with a Calcium Oxide Sorbent

“…Among these, the peaks at binding energies of 67.4 and 68.0 eV were due to Al metal, and the oxide peak at binding energy of 73.6 eV was assigned to Al 2 O 3 . The fitting curves coincided well with the raw data of the Al 2p and C 1s spectrum. − In Figure e, a deconvoluted Ca 2p peak at a binding energy of 347.7 eV is seen, which is attributed to CaO having a Ca 2+ valence state. − The deconvoluted peak at binding energy 531.1 eV represents the lattice oxygen species O 2– , which was evident from the spectrum for the peak O 1s in Figure f. , …”