Exploring the Bonding of Large Hydrocarbons on Noble Metals: Diindoperylene on Cu(111), Ag(111), and Au(111)

We present a benchmark study for the adsorption of a large pi-conjugated organic molecule on different noble metal surfaces, which is based on X-ray standing wave (XSW) measurements and density functional theory calculations with van der Waals (vdW) interactions. The bonding distances of diindenoperylene on Cu(111), Ag(111), and Au(111) surfaces (2.51 A, 3.01 A, and 3.10 A, respectively) determined with the normal incidence XSW technique are compared with calculations. Excellent agreement with the experimental data, i.e. deviations less than 0.1 A, is achieved using the Perdew-Burke-Ernzerhof functional with vdW interactions that include the collective response of substrate electrons (PBE+vdW^{surf} method). Noteworthy, the calculations show that the vdW contribution to the adsorption energy increases in the order Au(111) < Ag(111) < Cu(111).Comment: 6 pages, 4 figures, accepted by Phys. Rev.

Pentacene perfluoropentacene bilayers on Au 111 and Cu 111 Impact of organic metal coupling strength on molecular structure formation

As crucial element in organic opto electronic devices, heterostructures are of pivotal importance. In this context, a comprehensive study of the properties on a simplified model system of a donor acceptor D A bilayer structure is presented, using ultraviolet photoelectron spectroscopy UPS , X ray photoelectron spectroscopy XPS , low energy electron diffraction LEED and normal incidence X ray standing wave NIXSW measurements. Pentacene PEN as donor and perfluoropentacene PFP as acceptor material are chosen to produce bilayer structures on Au 111 and Cu 111 by sequential monolayer deposition of the two materials. By comparing the adsorption behavior of PEN PFP bilayers on such weakly and strongly interacting substrates, it is found that i the adsorption distance of the first layer PEN or PFP indicates physisorption on Au 111 , ii the characteristics of the bilayer structure on Au 111 are almost independent of the deposition sequence, and hence, iii in both cases a mixed bilayer is formed on the Au substrate. This is in striking contrast to PFP PEN bilayers on Cu 111 , where strong chemisorption pins PEN molecules to the metal surface and no intermixing is induced by subsequent PFP deposition. The results illustrate the strong tendency of PEN and PFP molecules to mix, which has important implications for the fabrication of PEN PFP heterojunction

Energy level alignment at strongly coupled organic metal interfaces

Energy-level alignment at organic–metal interfaces plays a crucial role for the performance of organic electronic devices. However, reliable models to predict energetics at strongly coupled interfaces are still lacking. We elucidate contact formation of 1,2,5,6,9,10-coronenehexone (COHON) to the (1 1 1)-surfaces of coinage metals by means of ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, the x-ray standing wave technique, and density functional theory calculations. While for low COHON thicknesses, the work-functions of the systems vary considerably, for thicker organic films Fermi-level pinning leads to identical work functions of 5.2 eV for all COHON-covered metals irrespective of the pristine substrate work function and the interfacial interaction strength.Deutsche Forschungsgemeinschafthttps://doi.org/10.13039/501100001659Soochow University-Western University Joint Center for Synchrotron Radiation ResearchCollaborative Innovation Center of Suzhou Nano Science & Technology111 Project of the Chinese State Administration of Foreign Experts AffairsAustrian Science Fundhttps://doi.org/10.13039/501100002428National Key R&D Program of ChinaPeer Reviewe

The Online Shadow of Offline Signals: Which Sellers Get Contacted in Online B2B Marketplaces?

This article extends the understanding of what impels buyers to contact particular sellers in online business-to-business (B2B) marketplaces, which are typically characterized by sparse social structures and concomitant limitations in observing social cues. Integrating an institutional perspective with signaling theory, our core argument is that offline seller characteristics that are visible online—in particular, geographic location and legal status—convey credible signals of seller behavior because they provide buyers with information on sellers’ local institutional quality and the institutionally-induced obligations and controls acting on sellers. Using unique data from a large Italian online B2B marketplace between the fourth quarter of 1999 and July 2001, we find that both sellers’ local institutional quality and their legal statuses affect a buyer’s likelihood of contacting a seller. Moreover, consistent with the idea that a buyer’s own local institutional quality generates a relevant reference point against which sellers are evaluated, we find that a buyer is progressively more likely to contact sellers the higher their local institutional quality relative to the buyer. Jointly, our findings imply that in online B2B marketplaces, signals conveyed by sellers’ geographic locations and legal statuses may constitute substantive sources of competitive heterogeneity and market segmentation