Scanning Tunneling Microscope and Photoemission Spectroscopy Investigations of Bismuth on Epitaxial Graphene on SiC(0001)

Abstract

The initial growth of bismuth (Bi) on epitaxial graphene (EG) on SiC(0001) at low deposition rates has been investigated using low temperature scanning tunneling microscopy (LT-STM) and synchrotron-based photoemission spectroscopy (PES). PES measurements reveal an islanding growth mode of Bi on EG due to weak interfacial interactions. LT-STM measurements show that Bi forms onedimensional (1D) 4-monolayer-thick nanoribbons on EG with the orientation relationship of Bi(011̅ 2) ∥ EG(0001) and Bi⟨112̅ 0⟩ aligned well with EG⟨112̅ 0⟩. Scanning tunneling spectroscopy (STS) results reveal the semiconducting nature of such Bi nanoribbons. ■ INTRODUCTIONBismuth (Bi) is a group-V semimetal with a charge carrier concentration far less than normal metals, having small effective electron mass and long Fermi wavelength (∼40 nm at room temperature). 1−3 Because of quantum and finite size effects, Bi nanostructures exhibit interesting physical properties, such as semimetal to semiconductor transition, 4−6 high thermoelectric efficiency, 7 and superconductivity. 8 Additionally, strong spin− orbit coupling on Bi surfaces results in a significant and anisotropic splitting of the surface-state bands, indicating possible applications in spintronics. 9,10 Details of structural and electronic properties of low-index surfaces of bulk Bi can be found in the review by Hofmann. 1 As the electronic properties of Bi nanostructures depend significantly on their structural properties, there have been numerous investigations on their growth. For example, on highly ordered pyrolitic graphite (HOPG), Bi forms islands with striped surface features at a preferred height and with the orientation relationship Bi(011̅ 2) ∥ HOPG(0001) as well as with a preference for Bi⟨112̅ 0⟩ ∥ HOPG⟨101̅ 0⟩. 11−15 Graphene, a single layer of graphite, has attracted great interest in both academia and industry due to its superlative electronic properties 16−19 such as high charge carrier mobility even at high charge carrier concentration at room temperature (RT) 20 and long spin relaxation length up to micrometer scale at RT. 21 Epitaxial graphene (EG) on SiC 22−24 has been proposed as a possible platform for the development of graphene-based electronics. 23−27 There are numerous investigations of adsorbates on graphene, 28−34 for instance, atomic hole doping of EG by simple atomic adsorbates. 29 ARPES measurements have shown that Bi is able to shift the Dirac point toward the Fermi level (E F ), i.e., reducing the n-type doping from the substrate, 29 even though density functional theory (DFT) calculations reveal that the isolated Bi atom is weakly physisorbed on EG. 35 Therefore, understanding the interactions between adsorbates and graphene in real space at atomic level is very important for fundamental understanding and possible applications.In this work, the structural and electronic properties of Bi thin films on EG are systematically investigated using low temperature scanning tunneling microscopy (LT-STM) and synchrotron-based photoemission spectroscopy (PES...

Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene

“…2(c) . In triangular islands, the Bi-Bi distance is about 1.6 nm, which is very close to × a = 1.57 nm {a = 4.54 Å, which is the lattice constant along the [11–20] direction of Bi nanoribbon 22 }. The black solid line in Fig.…”

“…The 1D linear structure appears (green dashed line) in accompany with a Bi-Bi nearest neighbors distance of around 1.8 nm, reflecting a characteristic 1D growth mode at low coverage. Notably, the Bi-Bi distance of 1.8 nm is almost four times the lattice spacing along the [11–20] direction of Bi nanoribbon 22 . At 0.039 ML, 2D triangular islands (indicated by red and white dashed lines) are observed and linear structures are still detected, as presented in Fig.…”

Bi ultra-thin crystalline films on InAs(1 1 1)A and B substrates: a combined core-level and valence-band angle-resolved and dichroic photoemission study

“…[6]). Along this line many investigations of the changes with respect to bulkBi of the electronic structure of Bi thin films deposited on semiconductors, e.g.Si(1 1 1) [7,8], SiC(0 0 0 1) [9], and highly-oriented pyrolytic graphite [10], have been performed. Such studies on Bi thin films are also of importance for a better understanding of the physical properties of topological insulators [1,3,[11][12][13]] (see also [14] review).…”

Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

“…For example, pentacene possesses a relatively higher mobility in its b-c plane than a-b plane, as shown in Figure 1e [6,7]. Thus, various substrates, metals [8][9][10], native oxide silica [11][12][13][14], and layered materials [6,7,[15][16][17][18], have been chosen for the growth of high quality thin films. In order to optimize the devices performance, it is essential to clarify how the interactions between molecules and substrates affect the growth of organic thin films.…”