Coverage dependence of the structure of tetracene on Ag(110)

Abstract

The ordered adsorption structures of tetracene on Ag(110) have been studied by low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At a low coverage, as calibrated with LEED, both p(4 × 4) and c(8 × 4) ordered structures are simultaneously formed on an Ag(110) surface at room temperature. STM images suggest the molecular plane is parallel to the Ag surface with its long molecular axis aligned along the [001] azimuth. DFT optimization reveals a separation of 0.3 nm between the molecular plane and substrate surface while the center of the tetracene molecule is on the long bridge site. Increasing coverage slightly, a structure is formed while the adsorbed molecules maintain the flat-lying geometry with adjacent molecules alternating their height relative to the surface.

Exploring the Adsorption Mechanism of Tetracene on Ag(110) by STM and Dispersion-Corrected DFT

“…In addition, tetracene can also be packed with varying manners depending on the film thickness, for instance, the long molecular axis of tetracene can be aligned along either the [001] or [1][2][3][4][5][6][7][8][9][10] symmetry direction of Ag(110). In special, it was demonstrated that neighboring tetracene molecules were imaged with alternating bright and dim area in STM with high molecular coverage in dense packing in our previous work [16], which was originally assigned to the adsorption height difference induced by the delicate balance between the molecule-substrate and intermolecular interaction, as pointed out by conventional density functional theory (DFT) calculations. However, it has been realized afterwards that, however, the commonly used exchange-correlation functions for electrons, either local density approximation (LDA) or extensions thereof, gradient approximation (GGA) fail to describe the long-range electron correlations (or electron dispersion force) [26,27], namely, the Van der Waals (vdW) interaction, which is found to play a core role in determining the structure and properties of noncovalent or weak bonding molecular network [28].…”

“…STM experiments were performed in an ultrahigh-vacuum (UHV) variable temperature STM system (VT-STM, Omicron, Berlin, Germany) with a base pressure better than 5.0 × 10 −10 mbar, details can be found elsewhere [16,33]. The clean Ag(110) surface (Mateck) was obtained by cycles of argon sputtering (1200 V at beginning and 800 eV in the end) and post annealing to around 573 K, while the cleanliness was double checked by low energy electron diffraction (LEED), core level photoelectron spectroscopy (Specs 100 spectrometer, Berlin, Germany) and STM measurements (Omicron VT-STM).…”

“…Attributed to the rapid and expanding development of DFT, especially the introduction of van der Waals interaction correction [26][27][28], noncovalent forces such as hydrogen bonding and vdW interactions can be much more accurately described in supramolecular architectures, molecular crystals, adsorbates and solids nowadays [29][30][31][32]. Based on these considerations, the lack of vdW interaction description in the tetracene/Ag(110) adsorption complex might give unreliable explanation to STM observations in the previous work [16]. Therefore, it becomes meaningful to reinvestigate the tetracene molecular network formed on the Ag(110) surface via the dispersion-corrected DFT approach, which might shed new insights onto understanding the adsorption mechanism behind such interesting arrangement of tetracene molecules.…”

“…In particular, tetracene has been proven to be an appealing candidate due to its low-cost processability, high stability, and appropriate band gap [1,10]. Therefore, considerable investigations have been paid to the preparation of tetracene film on solid substrates [11][12][13][14][15][16][17][18][19][20][21][22]. For example, the adsorption of tetracene molecules on the silver substrate has been exploited in literature via scanning tunneling microscopy (STM) [23,24], ultraviolet photoemission spectroscopy (UPS) [25] and so on.…”

Ordered structures of pentacene on Cu(110)

“…Thus, the moleculesurface and molecule-molecule interactions are expected to be weak ͑van der Waals type͒ and mainly through their cloud. 10,11 Ordered structures have also been observed for submonolayer amounts of pentacene on both Au͑110͒ ͑Ref. The ͑110͒ surfaces of noble metals have received special attention in this respect.…”