The simultaneous formati on of single domain(3×3)and multi domai n(√7×√7)R(±19.1°)germa nene phases on Al(111)surface in thesub-monolayer range was studied using seanning tunneling microscopy(STM...The simultaneous formati on of single domain(3×3)and multi domai n(√7×√7)R(±19.1°)germa nene phases on Al(111)surface in thesub-monolayer range was studied using seanning tunneling microscopy(STM)and density functional theory(DFT)based simulations.Experimental results revealed that both germa nene phases nu cleate and grow in dependently from each other and regardless of Al substratetemperature within significantly expanded range Ts=27-200℃.Our results unambiguously showed that STM images with hexagonalcontrast yield correct-resolved structure for both germanene phases,while honeycomb contrast is a result of an artificial tip-induced STM resolution.First-principles calculations suggested atomic models with strongly buckled germanene(2×2)/Al(111)(3×3)and(√3×√3)R30°/Al(111)(√7×√7)R(±19.1°)with one of eight and one of six Ge atoms protruding upward respectively,that consistently describe the experimentally observed STM images both for single and multi domai n surface phases.According to the DFT based simulati ons both germa nene(2×2)and(√3×√3)R30°superstructures have a stretched lattice strain with respect to the ideal free-standing germa nene by 6.2%and 13.9%,respectively.Hence,numerous small domains separated by domain boundaries in the(√3×√3)R30°/Al(111)(√7×√7)R(±19.1°)germanenephase tend to reduce the surface energy and prevent the formation of extended single domains,in contrast to the(2×2)/Al(111)(3×3)phase.However,our experimental results showed that the nucleation and growth of germa nene on Al(111)surface yield strong modifications of Alsurface even at room temperature(RT),which may be contributed to the formation of Al-Ge alloy due to Ge surface solid-states reactivitythat was ignored in recent studies.It is already evident from our present findings that the role of Al atoms in the formation of(3×3)and(√7×√7)R(±19.1°)germa nene phases is worthy to be carefully studied in the future,which could be an important knowledge for large-quantityfabrication of germanene on aluminum.展开更多
文摘The simultaneous formati on of single domain(3×3)and multi domai n(√7×√7)R(±19.1°)germa nene phases on Al(111)surface in thesub-monolayer range was studied using seanning tunneling microscopy(STM)and density functional theory(DFT)based simulations.Experimental results revealed that both germa nene phases nu cleate and grow in dependently from each other and regardless of Al substratetemperature within significantly expanded range Ts=27-200℃.Our results unambiguously showed that STM images with hexagonalcontrast yield correct-resolved structure for both germanene phases,while honeycomb contrast is a result of an artificial tip-induced STM resolution.First-principles calculations suggested atomic models with strongly buckled germanene(2×2)/Al(111)(3×3)and(√3×√3)R30°/Al(111)(√7×√7)R(±19.1°)with one of eight and one of six Ge atoms protruding upward respectively,that consistently describe the experimentally observed STM images both for single and multi domai n surface phases.According to the DFT based simulati ons both germa nene(2×2)and(√3×√3)R30°superstructures have a stretched lattice strain with respect to the ideal free-standing germa nene by 6.2%and 13.9%,respectively.Hence,numerous small domains separated by domain boundaries in the(√3×√3)R30°/Al(111)(√7×√7)R(±19.1°)germanenephase tend to reduce the surface energy and prevent the formation of extended single domains,in contrast to the(2×2)/Al(111)(3×3)phase.However,our experimental results showed that the nucleation and growth of germa nene on Al(111)surface yield strong modifications of Alsurface even at room temperature(RT),which may be contributed to the formation of Al-Ge alloy due to Ge surface solid-states reactivitythat was ignored in recent studies.It is already evident from our present findings that the role of Al atoms in the formation of(3×3)and(√7×√7)R(±19.1°)germa nene phases is worthy to be carefully studied in the future,which could be an important knowledge for large-quantityfabrication of germanene on aluminum.
