Abstract:High-resolution scanning
tunneling microscopy (STM) is a promising
method for characterizing organic semiconductors to obtain a deep
understanding of organic semiconductor physics. However, organic films
on conductive single-crystal substrates, which are required for STM,
usually present different growth behaviors than the films on inert
substrates such as SiO2. Here, we reported a simple modification
method for modulating the organic semiconductor film growth on the
highly oriented pyrolytic graphite (HOPG) a… Show more
“…2e ). The thickness-dependent surface domain ordering may originate from the dipolar screening of the internal electrostatic field in RPP by the substrate, or from the presence of substrate-induced strain, as both effects become increasingly stronger closer to the substrate 30 , 31 . Importantly, a higher degree of surface crystalline order was observed for RPP on G compared to Au, which is attributed to the high-quality van der Waals interface formed between RPP and G. Fig.…”
Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (~50 fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm2V−1s−1 between 1.7 to 200 K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.
“…2e ). The thickness-dependent surface domain ordering may originate from the dipolar screening of the internal electrostatic field in RPP by the substrate, or from the presence of substrate-induced strain, as both effects become increasingly stronger closer to the substrate 30 , 31 . Importantly, a higher degree of surface crystalline order was observed for RPP on G compared to Au, which is attributed to the high-quality van der Waals interface formed between RPP and G. Fig.…”
Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (~50 fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm2V−1s−1 between 1.7 to 200 K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.
“…The film growth scenario observed in this study parallels with the cases of pentacene on inert substrates such as SiO 2 , [39] Al 2 O 3 , [47] highly oriented pyrolytic graphite, [34] and self-assembled monolayer-modified metal substrate. [48] In these cases, the intramolecular interaction between pentacene dominates monolayer-substrate interaction which favors the thermodynamically most stable (001) orientated film. [49] In our case, it is expected that the atomically smooth surface of copper substrate was covered by a monolayer of -COOH groups after the specific anneal-treatment.…”
Controlling the alignment and packing structure of organic molecules on solid substrate surfaces at molecule level is essential to develop high-performance organic thin film (OTF) devices. Pentacene, which is a typical p-type semiconductor material usually adopts lying-down geometry on metal substrates owning to π–d coupling between pentacene and metal substrates. However, in this study, we found that pentacene molecules can be adsorbed on an anneal-treated Cu (111) surface with their long axis perpendicular to substrate surface. Highly ordered single-layer pentacene film with stand-up molecular geometry was achieved on this substrate. It was found that the functionalization of Cu surface with C = O groups due to annealing treatment should be accounted for standing-up geometry of pentacene on Cu substrate. This observation shed light on the tuning of the alignment and packing structure of organic molecules.
“…Interestingly, the multilayer signal sets in at an unusually high ion dose (four times higher than found previously for the planar PAH homologue hexabenzocoronene C 42 H 18 ). This might be an indicator that, for higher submonolayer coverages, the structure of the rubrene film changes similar to what is seen for pentacene where a planar to tilted herringbone packing transition has been discussed . For further analysis, we will use 1 ML = 1.8 × 10 14 ions cm −2 based on the multilayer signal onset and the termination of the T p shift.…”
Section: Binding Energies and Frequency Factors For Various 60 C‐atommentioning
A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases.
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