Structures and stability of reconstructed BAs surfaces: an ab initio-based approach

We report systematic and comprehensive studies for the surface reconstructions of BAs in various orientations including the (100) as well as (111) and ( 1 ¯ 1 ¯ 1 ¯ ) planes on the basis of density functional calculations. Using surface phase diagrams which are obtained by comparing the calculated adsorption energy with vapor-phase chemical potentials, a conditional interval that makes BAs stable and determine the most stable structure under each condition can be obtained. This can greatly narrow the range of BAs film growth experimental conditions and help us understand the mechanism during the experiment. • First-principles reveal stable BAs surface reconstructions on (100), (111)-As, (111)-B. • State diagrams map BAs stability vs. growth temperature and As pressure. • As 2 vs. As 4 source comparison shows distinct reconstruction behaviors. We report systematic ab initio DFT studies on surface reconstructions of BAs crystals across (100), (111), and (1̅1̅1) orientations. Through surface phase diagrams derived from adsorption energetics and vapor-phase equilibria, we establish thermodynamic stability intervals and identify arsenic-source-dependent reconstructions: For (111), the As-adlayer (2 × 2) dominates under all conditions for both As 2 and As 4 sources. In contrast, (1̅1̅1) exhibits universal As-trimer stability with As 4 , whereas with As 2 it transitions from an As-adlayer below 550 K to trimers above. On (001), c(4 × 4) arsenic dimers prevail universally with As 4 ; with As 2 , c(4 × 4) persists above 1087 K but shifts to a (1 × 2) As-dimer configuration below 886 K. These source-specific reconstructions, coupled with decomposition boundaries (As 2 : 1000–1200 K; As 4 : 820–950 K), drastically reduce experimental trial-and-error for BAs film growth and elucidate epitaxial mechanisms.