Interface Structure and Evolution of Dinaphthothienothiophene (DNTT) Films on Noble Metal Substrates

Abstract

The latter characteristic is particularly important since charge carrier mobility and transport properties of crystalline π-conjugated molecular materials are typically strongly anisotropic, [5] which underlines the importance of a precise structural control of OSC films at the contact interfaces.Among the newly synthesized OSCs, dinaphthothienothiophene (DNTT) has received particular attention because it combines a remarkably high charge carrier mobility [6,7] with distinct chemical robustness, [8,9] hence making it superior to previous OSC benchmark systems based on pentacene (PEN) or rubrene. [10][11][12] DNTT is a planar polycyclic hydrocarbon (PAH) with similar shape and intermolecular interaction as PEN [13] and likewise adopts a layered crystal structure. In the (001) planes, which are the typical surface planes in DNTT crystals, the molecules are uprightly oriented and exhibit a face-on-edge herringbone packing arrangement. [6] Despite their structural similarity, both the materials exhibit, however, different growth characteristics. For example, a notable dewetting was found upon growth of DNTT films on SiO 2 and other dielectrics as well as on graphite substrates, [14] while smoother PEN films are formed on these substrates. [15,16] On the other hand, PEN (as well as many other PAH) films that are deposited onto crystalline metal substrates reveal a distinct dewetting and island formation beyond the first monolayer (ML), [17][18][19] which is attributed to the structural misfit between the flat-lying chemisorbed molecules in the seed layer and the herringbone motif in the bulk crystal structure. [20] Despite their importance for device applications, interfaces between DNTT and metals are hardly studied so far. The only exception is the previous work of Hasegawa et al. who studied the initial stage of DNTT film growth on Au(111) and reported a transition from an initially diluted phase into a densely packed adlayer which comprises a mixture of flat-lying and inclined molecules. [21] While this growth scenario is of particular interest, as it would allow adjusting the interface structure to the crystal bulk phase, no clear evidence for such a tilting was given and also the structure of thicker films was not analyzed. A similar mechanism has been identified before for the growth of PEN Dinaphthothienothiophene (DNTT) is a promising new organic semiconductor which combines high charge carrier mobility with chemical robustness. Although the properties of organic electronic devices are largely determined by the interfaces with electrodes, the interface between DNTT and metals is hardly studied so far. Here, the interface structures of DNTT on Ag(111) and multilayers are examined and they are compared with films grown on polycrystalline and (111) surfaces of silver and gold. In the seedlayer regime, two different interface structures formed by exclusively flatlying molecules and a herringbone arrangement are identified for increased coverages. Combining low energy electron diffraction, scanning tunneling micro...

Fabrication of Highly Oriented Multilayer Films of Picene and DNTT on Their Bulklike Monolayer

“…From the AFM image shown in Figure 3c, the surface of the DNTT crystal island is rather rough. These results are consistent with the recent work of Dreher et al 16…”

Titanylphthalocyanine Films on Ag(111): An Epitaxial Metal/Organic Heterosystem with an Exceptional Smooth Surface

“…Most interestingly, however, this effect saturates at a covering level of 80% for temperatures above 350 K, which is in close agreement with our AFM covering analysis, indicating that dewetting and island formation does not further proceed with growth temperature. This behavior differs significantly from the growth of most planar π-conjugated molecules, such as PEN, perfluoropentacene (PFP), perylene, or dinaphthothienothiophene (DNTT), ,− where a distinct dewetting and island formation hampers the fabrication of smooth molecular films covering the metal surface.…”

Blurred Electrode for Low Contact Resistance in Coplanar Organic Transistors

“…Based on the energy band theory, the orientation of OSC molecules on the substrate has been confirmed to affect the interface dipoles and overlapping of molecular orbitals, which will actually affect their energy levels, such as the highest occupied molecular orbital (HOMO) and the work function (WF). − Therefore, the gradually changed orientation of the DNTT molecules along and across the contact edge will cause a gradual shift of work function and the HOMO levels. In other words, the synergistically guided hybrid crystal on the transition region induces continuously distributed states inside the gap, which can not only lower the contact injection barrier but also be favorable for the carriers traveling to the channel after injected .…”