Rapid synthesis of dual-element isotope-enriched α − Mo O 3 crystals by reactive vapor transport

In this work, we develop a rapid reactive vapor transport technique to efficiently utilize limited isotopically pure precursors, particularly gaseous ¹⁸O₂, and synthesize mm-scale, high-quality isotope-enriched crystals within few-minute growth durations. We unlock this capability by using metallic molybdenum precursors with high source temperatures (9000.16em0ex^∘C) and total pressures (~1 atm) to maximize precursor efficiency and yield. Subsequently, we grow α-MoO₃ single crystals with high and uniform enrichment levels of ⁹⁸Mo and ¹⁸O isotopes in several different permutations. As probed by Raman spectroscopy, modest and significant phonon energy redshifts occur following ⁹⁸Mo and ¹⁸O enrichment, respectively. By demonstrating control over both molybdenum and oxygen isotopic enrichments, we establish a powerful tool to advance nanophotonics and thermal management goals using α-MoO₃. This work is motivated by the possibility to enhance and engineer lattice vibrational mode phenomena including thermal conduction and hyperbolic phonon polariton dispersion---with particular interest in comparing the effects of light and heavy element enrichment.