In this study, atomic layer deposition (ALD) of nanoscale boron oxide (B2O3) films on Si using BCl3/H2O precursors at room temperature was investigated using in situ x-ray photoelectron spectroscopy (XPS). B2O3 thin films are of considerable interest in ultra-shallow Si doping applications, including high aspect ratio FinFET structures, where film conformality and precise thickness control are crucial. ALD is therefore of particular interest for such applications. XPS data demonstrate that initial BCl3 exposures on Si at room temperature are self-limiting and are accompanied by partial B-Cl dissociation and Cl-Si formation. H2O exposures >1.7 × 108 Langmuir at room temperature removed Cl from B sites, but failed to remove Cl from the Cl-Si species. ALD-type growth of B2O3 was observed with an average growth rate of ∼2.5 Å/cycle and without further increase in the Cl content. The initial Cl contamination was due to Cl-Si bond formation at the interface, without Cl incorporation into the oxide film. The role of Cl in the inhibition of oxide film growth was further investigated by the reactions of BCl3/O2 on SiO2 at room temperature and 650 K. BCl3/O2 precursors exhibit negligible B2O3 growth at room temperature. At 650 K, B2O3 growth was observed with a decreasing growth rate per BCl3/O2 cycle, corresponding to an increase in the Cl:B atomic ratio. These data indicate that room temperature ALD using BCl3/H2O precursors is a potential route toward the formation of uniform B2O3 films for shallow Si doping applications, but that Cl-Si formation significantly impacts initial oxide nucleation and growth.

The direct epitaxial growth of multilayer BN by atomic layer deposition is of critical significance for two dimensional device applications. To date, however, epitaxial growth has only been reported on graphene or on transition metal surfaces. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) demonstrate layer-by-layer BN epitaxy on a monolayer of RuO2(110) formed on a Ru(0001) substrate. Growth was accomplished with BCl3/NH3 cycles at 600 K substrate temperature and subsequent annealing in ultrahigh vacuum. This yielded stoichiometric BN layers, Cl impurities levels of ≲1 at. %, and an average BN film thickness linearly proportional to the number of BCl3/NH3 cycles. XPS data indicate negligible charge transfer or band bending for the BN/RuO2 interface. LEED data indicate a 30° rotation between the coincident BN and oxide lattices. The atomic layer epitaxy of BN on an oxide surface suggests new routes to the direct growth and integration of graphene and BN with industrially important substrates, including Si(100).

The deposition of boron oxide (B 2 O 3 ) films on Si and SiO 2 substrates by atomic layer deposition (ALD) is of growing interest in microelectronics for shallow doping of high aspect ratio transistor structures. B 2 O 3 , however, forms volatile boric acid (H 3 BO 3 ) upon ambient exposure, requiring a passivation barrier, for which BN was investigated as a possible candidate. Here, the authors demonstrate in situ deposition of BN by sequential BCl 3 /NH 3 reactions at 600 K on two different oxidized boron substrates: (a) B 2 O 3 deposited using BCl 3 /H 2 O ALD on Si at 300 K ("B 2 O 3 /Si") and (b) a boron-silicon oxide formed by sequential BCl 3 /O 2 reactions at 650 K on SiO 2 followed by annealing to 1000 K ("B-Si-oxide"). X-ray photoelectron spectroscopy (XPS) data demonstrate layer-by-layer growth of BN on B 2 O 3 /Si with an average growth rate of ∼1.4 Å/cycle, accompanied by some B 2 O 3 removal during the first BN cycle. In contrast, continuous BN growth was observed on B-Si-oxide without any reaction with the substrate. XPS data also indicate that the oxide/nitride heterostructures are stable upon annealing in ultrahigh vacuum to >1000 K. XPS data, after the exposure of these heterostructures to ambient, indicate a small amount of BN oxidation at the surface NH x species, with no observable hydroxylation of the underlying oxide films. These results demonstrate that BN films, as thin as 13 Å, are potential candidates for passivating boron oxide films prepared for shallow doping applications.

The feasibility of a site-selective hydration strategy that enables site-selective atomic layer deposition (ALD) is investigated among four rutile TiO 2 facets [( 110), ( 100), ( 101) and ( 001)] and their most prevalent step edges. First-principles simulations of asymmetric slab models were utilized to create accurate representations of pristine terrace and step edge sites. The adsorption free energies for molecular and dissociative adsorption of H 2 O were calculated to evaluate this strategy as a viable route to step edge selectivity. We predict that selective hydroxylation is possible on the 110 and 001 step edges and further computationally evaluate three metalorganic ALD precursors for their compatibility with the selective hydration strategy. Experimental evidence for delayed nucleation of ALD on rutile (001), (110), and (100) TiO 2 single crystals corroborates predictions of the dehydration of the surface and suggests the possibility of site-selective ALD.

Solid-state electrolytes (SSEs) are of significant interest for their promise as lithium ion conducting materials but are prone to degradation due to lithium carbonate formation on the surface upon exposure to atmosphere, adversely impacting Li ion conduction. In situ x-ray photoelectron spectroscopy monitored changes in the composition of the SSE Li garnet [Li6.5La3Zr1.5Ta0.5O12 (LLZTaO)] upon annealing in ultrahigh vacuum (UHV) and upon Ar+ ion sputtering. Trends in core level spectra demonstrate that binding energy (BE) calibration of the Li 1s at 56.4 eV yields a more consistent interpretation of results than the more commonly used standard of the adventitious C 1s at 284.8 eV. Annealing one ambient-exposed sample to >1000 K in UHV effectively reduced surface carbonate and oxygen, leaving significant amounts of carbon in lower oxidation states. A second ambient-exposed sample was subjected to 3 keV Ar+ ion sputtering at 500 K in UHV, which eliminated all surface carbon and reduced the O 1s intensity and BE. These methods present alternative approaches to lithium carbonate removal than heating or polishing in inert atmospheres and are compatible with fundamental surface science studies. In particular, the data show that sputtering at mildly elevated temperatures yields facile elimination of carbonate and other forms of surface carbon. This is in contrast to annealing in either UHV or noble gas environments, which result in carbonate reduction, but with significant remnant coverages of other forms of carbon.