Atomic force microscopy study of sapphire surfaces annealed with a H ₂O flux from a baffled molecular-beam epitaxy effusion cell loaded with Al(OH) ₃

We present an atomic force microscopy (AFM) study of sapphire surfaces that contain scratches with various severities. The objective was to observe the effects of substrate annealing at 850 °C for 200 min with a H2 O -based overpressure resulting from an Al (OH)3 powder that was thermally cracked at 1200 °C. The Al (OH)3 was decomposed into Al2 O3 and H2 O according to a partial Bayer process in a modified molecular-beam epitaxy (MBE) effusion cell, which was equipped with homemade baffles placed at its outlet. These homemade, simple-to-construct tantalum baffles allow for the selective outfluxing of gaseous species, from those that are solid based. A UTI 100C-model mass spectrometer was used to monitor the species present at the sapphire surface during annealing. Any aluminum-based solid species from the Al (OH)3 were not observed in the mass spectrum, although the H2 O -based species were. The sapphire substrates were annealed in a Varian Gen II MBE system, with H2 O beam equivalent pressures (BEPs) of 5× 10-6 and 2× 10-5 Torr, as well as with no H2 O flux at all. The AFM images show that the samples annealed with a higher H2 O BEP of 2× 10-5 Torr had noticeably less severe surface scratches than the samples that were annealed with lower H2 O BEPs.