Control of Unipolar/Ambipolar Transport in Single‐Molecule Transistors through Interface Engineering

Abstract

To realize single‐molecule field‐effect transistors, a crucial test for evaluating the integrity of single‐molecule electronics into conventional circuit architectures, remains elusive. Though interfacial effect is widely accepted to be crucially important in electronic devices, rare reports have studied fine control of the interface in single‐molecule transistors. Through molecular engineering, different numbers of methylene groups are incorporated between the diketopyrrolopyrrole (DPP) kernel and anchor groups (AMn‐DPP, n = 0−3), and how the molecule–electrode interface affects the performance of single‐molecule transistors is investigated. Both experimental and theoretical data demonstrate that p‐type charge transport dominates in AM0‐DPP and AM1‐DPP single‐molecule transistors, while AM2‐DPP and AM3‐DPP systems exhibit ambipolar field‐effect behaviors, which is attributed to the HOMO‐pinning effect in AM0‐DPP and AM1‐DPP molecular junctions. Theoretical calculations show that the parity of the methylene number results in two different connection symmetries between the DPP kernel and graphene electrodes, and thus different electronic interactions, leading to different relative molecular energy‐level alignments form those of isolated molecules, which has never been reported before. These results provide crucial information for precise control of the interfaces in molecular junctions, new insight into building multifunctional graphene–organic hybrid electronic devices, and the design of functional organic materials.

Van der Waals Heterostructures by Design: From 1D and 2D to 3D

“…Graphene has attracted considerable interest as a potential contact material for 2D semiconductors due to its gate-tunable work function, 107 which allows graphene to be used as a band-matching contact for either p-or n-type 2D semiconductors, as demonstrated in prototypes of graphene-contacted WSe 2 transistors. 108 Later, MoS 2 transistors with graphene contacts were proved to exhibit zero barrier height and linear output curve even at cryogenic temperatures (Figure 5H), thus achieving significantly improved performance compared with previous MoS 2 FETs in terms of on-current and apparent two-terminal mobility.…”

Single‐Molecule Electrochemical Transistors

“…Besides metal contacts, carbon-based electrodes, for example graphene, have also been used in SMECTs. [82,83] Inherited from the unique properties of the graphene, the transmission curve of the single-molecule junctions shows an antiresonance feature, and the minima located around the Fermi level corresponds to the Dirac point of the graphene. Therefore, the ambipolar behavior can be realized in SMECTs with graphene contacts, regardless of the HOMO-LUMO gap of the functional molecules.…”

Molecule‐Based Transistors: From Macroscale to Single Molecule.

“…Through molecular engineering, different amounts of methylene were added between the diketopyrrolopyrrole (DPP) functional center and the anchor group (AMN‐DPP, n=0–3) to control the interfacial coupling between the molecular functional center and the electrodes (Figures 13c and 13d). When there are 0 or 1 methylene groups, HOMO‐pinning effect occurs in molecular junctions; and when there are 2 or 3 methylene groups, there is an ambipolar field effect across the devices [79] …”

“…When there are 0 or 1 methylene groups, HOMO-pinning effect occurs in molecular junctions; and when there are 2 or 3 methylene groups, there is an ambipolar field effect across the devices. [79] Generalized single-molecule FETs can also be realized by directly designing functional molecules and further introduce other ways such as light stimulation to adjust the conductance of single-molecule junctions. For example, through molecular engineering, a stable single-molecule junction can be formed by covalently assembling single diarylethene molecule with photoisomerization function to nano-gapped graphene electrodes.…”