Experimental evidence of surface copper boride

To validate the crystal structure and elucidate the formation mechanism of the unexpected surface copper boride, a systematic scanning tunneling microscope, X-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, and aberration-corrected scanning transmission electron microscopy investigations were conducted to confirm the structure of copper-rich boride Cu₈B₁₄ after depositing boron on single-crystal Cu(111) surface under ultrahigh vacuum. First-principles calculations with defective surface models further indicate that boron atoms tend to react with Cu atoms near terrace edges or defects, which in turn shapes the intermediate structures of copper boride and leads to the formation of stable Cu-B monolayer via large-scale surface reconstruction eventually.