Disordering of an Organic Overlayer on a Metal Surface Upon Cooling

Abstract

Inverse melting or disordering, in which the disordered phase forms upon cooling, is known for a few cases in bulk systems under high pressure. We show that inverse disordering also occurs in two dimensions: For a monolayer of 1,4,5,8-naphthalene-tetracarboxylic dianhydride on Ag(111), a completely reversible order-disorder transition appears upon cooling. The transition is driven by strongly anisotropic interactions within the layer versus with the metal substrate. Spectroscopic data reveal changes in the electronic structure of the system corresponding to a strengthening of the interface bonding at low temperatures. We demonstrate that the delicate, temperature-dependent balance between the vertical and lateral forces is the key to understanding this unconventional phase transition.

Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional

“…7 shows our results and UPS data of Ref. 141. Compared to the experimental results, OT-RSH correctly depicts the pinned LUMO, the HOMO resonance, and places the HOMO-1 where UPS shows a shoulder, already around 3.5 eV below E F .…”

“…Similar to PTCDA on Ag(111), it also features a LUMO peak at E F , as evidenced in UPS measurements. [140][141][142] We relax the NTCDA-Ag(111) geometry with the PBE + vdW surf method 122 as implemented in VASP, using 3 layers of Ag(111) and a 4 × 4 surface unit cell as the substrate. The level alignment calculations are carried out using a 4 × 4 × 1 k-mesh (2 × 2 × 1 for the Fock exchange contribution).…”

Substrate-mediated band-dispersion of adsorbate molecular states

“…The strength of the molecule-substrate interaction, and thereby the magnitude of the substrate-enhanced band width of the LUMO, clearly depends on the vertical distance between the molecule and the substrate. In view of several investigations on very similar systems, such as PTCDA/Ag(111) 33,34 and NTCDA/Ag(111) 35 , a reduction of this vertical bonding distance can be achieved by lowering the substrate temperature and is accompanied by an energy shift of the LUMO towards larger binding energies. Figure 4 shows energy distribution curves of PTCDA/Ag(110) recorded in the (1 10) direction at k ¼ 1.45 Å À 1 and thus at the binding energy minimum of the LUMO measured at sample temperatures of 300 K (top), 45 K (middle) and 10 K (bottom).…”

“…The ARPES data for NTCDA/Ag(110) was recorded at beamline 9 Å of the Hiroshima Synchrotron Radiation Centre using photons with circular polarization and a photon energy hv ¼ 36 eV. The beamline is equipped with a 6-axes manipulator (i-GONIO, R-Dec Co.) and a Scienta R4000 photoelectron analyser enabling photoemission measurements with an energy resolution better than 10 meV at a base pressure of 4 Â 10 À 11 mbar 35,38,44,45 .…”

Interplay of local and global interfacial electronic structure of a strongly coupled dipolar organic semiconductor

“…More commonly though, organic thin film growth can be rather complex [15], and mechanisms of establishing the interfacial electronic structure must be inferred somewhat indirectly.…”