Oxygen-promoted synthesis of armchair graphene nanoribbons on Cu(111)

We report the systematic investigation of the effects of oxygen on the synthesis of 3 p sub-family armchair graphene nanoribbons(3 p-AGNRs),which revealed a strong catalytic effect with a reduction in the reaction temperature by approximately 180 K without degradation of the AGNRs.Poly(para-phenylene)(3-AGNR)was generated through Ullmann-type coupling of4,4’’-dibromo-p-terphenyl on Cu(111),which was then converted into wider 3 p-AGNRs via lateral fusion.Scanning tunneling microscopy(STM)and X-ray photoelectron spectroscopy demonstrated the formation of different ribbons up to 12-AGNR,which contained regions exhibiting increased STM contrast that we attribute to the intercalation of Br atoms during lateral fusion.

Dynamical evolution of Ge quantum dots on Si(111):From island formation to high temperature decay

Heteroepitaxial growth is a process of profound fundamental importance as well as an avenue to realize nanostructures such as Ge/Si quantum dots(QDs),with appealing properties for applications in opto-and nanoelectronics.However,controlling the Ge/Si QD size,shape,and composition remains a major obstacle to their practical implementation.Here,Ge nanostructures on Si(111)were investigated in situ and in real-time by low energy electron microscopy(LEEM),enabling the observation of the transition from wetting layer formation to 3D island growth and decay.The island size,shape,and distribution depend strongly on the growth temperature.As the deposition temperature increases,the islands become larger and sparser,consistent with Brownian nucleation and capture dynamics.At 550◦C,two distinct Ge/Si nanostructures are formed with bright and dark appearances that correspond to flat,atoll-like and tall,faceted islands,respectively.During annealing,the faceted islands increase in size at the expense of the flat ones,indicating that the faceted islands are thermodynamically more stable.In contrast,triangular islands with uniform morphology are obtained from deposition at 600◦C,suggesting that the growth more closely follows the ideal shape.During annealing,the islands formed at 600◦C initially show no change in morphology and size and then rupture simultaneously,signaling a homogeneous chemical potential of the islands.These observations reveal the role of dynamics and energetics in the evolution of Ge/Si QDs,which can serve as a step towards the precise control over the Ge nanostructure size,shape,composition,and distribution on Si(111).