TCNQ Physisorption on the Topological Insulator Bi₂Se₃

Abstract

Topological insulators are promising candidates for spintronic applications due to their topologically protected, spin-momentum locked and gapless surface states. The breaking of the time-reversal symmetry after the introduction of magnetic impurities, such as 3d transition metal atoms embedded in two-dimensional molecular networks, could lead to several phenomena interesting for device fabrication. The first step towards the fabrication of metal-organic coordination networks on the surface of a topological insulator is to investigate the adsorption of the pure molecular layer, which is the aim of this study. Here, the effect of the deposition of the electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules on the surface of a prototypical topological insulator, bismuth selenide (Bi Se ), is investigated. Scanning tunneling microscope images at low-temperature reveal the formation of a highly ordered two-dimensional molecular network. The essentially unperturbed electronic structure of the topological insulator observed by photoemission spectroscopy measurements demonstrates a negligible charge transfer between the molecular layer and the substrate. Density functional theory calculations confirm the picture of a weakly interacting adsorbed molecular layer. These results reveal significant potential of TCNQ for the realization of metal-organic coordination networks on the topological insulator surface.

Helium–Surface Interaction and Electronic Corrugation of Bi2Se3(111)

“…Understanding the atom–surface interaction on topological insulators is interesting from a fundamental point of view and may help to obtain a deeper understanding of the interaction with gases and molecules in the physisorption regime. 17,18 For example, as shown recently, the long-range part of the potential can be responsible for band bending effects upon adsorption. 19…”

Spatially Resolved Investigation of Mixed Valence and Insulator-to-Metal Transition in an Organic Salt

“…18 Intramolecular resolution of individual TCNQ molecules shows a characteristic four-arm pattern composed of two symmetric Ulike protrusions and two bulges centered on the dicyanomethylene groups, separated by a central nodal plane, that resembles the lowest unoccupied molecule orbital (LUMO) of free-standing molecules. 19,20 The observation of negative differential resistance (NDR), i.e., the dip below zero in the STS spectrum (Figure 1c), that is characteristic for molecules weakly adsorbed on supporting substrates, further indicates that the electronic structures of TCNQ molecules are wellpreserved on HOPG. 21−23 Nevertheless, the lack of strong chemical interaction does not preclude interfacial charge transfer.…”

Topological Surface State of Bi2Se3 Modified by Physisorption of n‐Alkane

“…These experimental results contradict one another. The interface between TCNQ, a typical electron acceptor, and Bi 2 Se 3 was studied by Pia et al [5] They observed a DP shift to a higher binding energy by ARPES and a shift of the Bi 4 f core-level toward a lower binding energy accompanied by TCNQ deposition by XPS measurements. These results indicate a chemical interaction between the adsorbed TCNQ and Bi 2 Se 3 .…”

“…Recently, several studies have been conducted on TI interfaces with organic molecules for use in TIs in spintronic devices. [3][4][5][6][7][8][9] Caputo et al examined the cobalt phthalocyanine (CoPc)/Bi 2 Se 3 interface [4] and observed a slight shift in the Dirac point (DP) to a higher binding energy by angle-resolved photoemission spectroscopy (ARPES) experiments, indicating charge transfer from CoPc to Bi 2 Se 3 . This indicates that the CoPc/Bi 2 Se 3 interface is a weak chemisorption system.…”

“…reported a topological p‐n junction on the surface of Bi 2‐ x Sb x Te 3‐ y Se y , a three‐dimensional TI fabricated using the electron‐accepting organic molecule F 4 ‐tetracyanoquinodimethane (F 4 ‐TCNQ), and they achieved on‐off switching of the charge flow originating from the TSS, [2] suggesting that electronic functional organic molecules are suitable for TI spintronic devices. Recently, several studies have been conducted on TI interfaces with organic molecules for use in TIs in spintronic devices [3–9] . Caputo et al .…”