Growth of germanium-silver surface alloys followed by in situ scanning tunneling microscopy: Absence of germanene formation

Abstract

Theoretical studies have shown that new physical properties such as tunable gap opening or quantum spin Hall effect could be expected from group IV graphene analogues (silicene, germanene, stanene). While there have been numerous studies of growth of such Si, Ge, Sn monolayers, the demonstration of their hexagonal organization has been often based on postgrowth characterization and their analogy to graphene has remained controversial. Our realtime scanning tunneling microscopy (STM) observation during Ge deposition on Ag(111) in the [380 K-430 K] temperature range reveals that Ag atoms are involved in all the structures observed before the formation of a second layer, rejecting the possible formation of germanene on this substrate within these experimental conditions. The observation by STM of Ge atomic diffusion shows that easy exchange between Ag and Ge atoms is responsible for the Ge-Ag surface alloying at such temperatures.

Tracing the structural evolution of quasi-freestanding germanene on Ag(111)

“…2 a. According to similar reports of this superstructure, mainly obtained from LEED and STM measurements, the formation can be attributed to a surface alloy 22 , 24 – 28 . Its particular structure will be discussed in “ XPD ”.…”

“…The first experimental study on thin films of epitaxially grown germanium on Ag(111) mainly reported a surface alloy at a coverage of , arranged in a reconstruction 23 , 24 . However, this alloy phase at a layer thickness of germanium is still controversially discussed to form reconstructions of a 25 – 28 , a 29 , a with a Moiré pattern of 30 , or a rectangular 31 . It was also considered as a striped phase (SP) due to tensile strains of the uppermost layer 32 with a long-range order of 26 .…”

Resolving the structure of the striped Ge layer on Ag(111):Ag2Ge surface alloy with alternate fcc and hcp domains

“…This reconstruction was further recognized as a c�√3 × 7� reconstruction and a model of Ge tetramers on top of a Ag(111) plane was proposed for its structure, based on scanning tunneling microscopy (STM) [6]. In contradiction with this model, from real-time STM observations of the growth, we have recently proposed that this latter structure is also a surface alloy with a coverage of 0.6 ± 0.1 ML [7].…”

Unraveling the Highly Complex Nature of Antimony on Pt(111)

“…However, several issues have recently been raised by different authors regarding the successful synthesis of pure layers of these bidimensional materials, especially when they are grown on metal substrates. [12][13][14][15][16][17][18][19] Therefore, further research is necessary to throw light on this present controversy.Among this vast portfolio of 2D materials, antimonene has received a strong amount of interest due to its attractive properties. It has been theoretically predicted to feature a tunable semiconducting band gap, [20,21] a relatively high carrier mobility [22] or quantum spin Hall effect.…”

“…However, several issues have recently been raised by different authors regarding the successful synthesis of pure layers of these bidimensional materials, especially when they are grown on metal substrates. [12][13][14][15][16][17][18][19] Therefore, further research is necessary to throw light on this present controversy.…”