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

Abstract

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 200min with a H2O-based overpressure resulting from an Al(OH)3 powder that was thermally cracked at 1200°C. The Al(OH)3 was decomposed into Al2O3 and H2O 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 H2O-based species were. The sapphire substrates were annealed in a Varian Gen II™ MBE system, with H2O beam equivalent pressures (BEPs) of 5×10−6 and 2×10−5Torr, as well as with no H2O flux at all. The AFM images show that the samples annealed with a higher H2O BEP of 2×10−5Torr had noticeably less severe surface scratches than the samples that were annealed with lower H2O BEPs.