Electronic structure and molecular orientation of pentacene thin films on ferromagneticLa0.7Sr0.3MnO3

Abstract

Pentacene thin films deposited on a ferromagnetic electrode, La 0.7 Sr 0.3 MnO 3 ͑LSMO͒, have been studied using near-edge x-ray absorption fine structure ͑NEXAFS͒, ultraviolet photoemission spectroscopy ͑UPS͒, and atomic force microscopy ͑AFM͒. Here we present electronic structure and molecular orientation of pentacene thin film on LSMO. No evidence related to covalent bonding or significant charge transfer between pentacene and LSMO has been found in the NEXAFS or UPS results. UPS measurements suggest that the vertical ionization potential of pentacene on LSMO is 4.9 eV. Our results extracted from NEXAFS indicate that molecular long axis of pentacene stands on the LSMO substrate surface with a tilt angle of about 22°Ϯ 2°b etween the main molecular axis and the substrate surface normal. AFM images show the terracelike crystalline grain formed by stacking pentacene crystalline layers and a rough crystal-layer spacing of 14-15 Å. Findings deduced from UPS, NEXAFS, and AFM consistently demonstrate that pentacene stands on LSMO with a tilt angle.

Energy level alignment in Au/pentacene/PTCDA trilayer stacks

“…The decrease in WF upon pentacene deposition is attributed to charge transfer from pentacene molecules to the gold substrate causing pentacene cations to be formed and the Fermi level is pinned to the E ICT+ of the pentacene molecules. The IP and WF values are in line with those previously reported [21,22], where a standing geometry for the pentacene molecules at weakly-interacting interfaces was found.…”

“…For example, physisorption of pentacene molecules on a non-metallic surface such as SiO 2 which is used as gate dielectric in transistors leads to a standing orientation. Other examples of substrates which induce standing orientation in pentacene molecules are polycrystalline Cu [26], LSMO [21], PEDOT: PSS [16] and C 60 [22].…”

Pentacene thin films on ferromagnetic oxide: Growth mechanism and spintronic devices

“…40 C, in the latter because desorption started to play a significant role. From the Arrhenius plot in Figure 4(a), we extracted E N ¼ 0.65 6 0.05 eV for 40 T 60 C. This energy scale is confirmed by ultra-violet photoemission spectroscopy measurements of a 0.4 eV energy dipole between pentacene and LSMO, 27 which is low if compared to the 1 eV found for pentacene deposited on Co. 33,34 The E N value for pentacene on LSMO can be compared with the nucleation energy found for pentacene grown on SiO 2 over the same temperature range: E N ¼ 0.78 6 0.05 eV was found for a growth rate of 0.007 nm/s, 35 which is similar to the one used in the present experiment. At higher growth rates (0.03 nm/s) P i à m¼2 E m þ i à E D ¼ 1.13 6 0.04 eV and i* ¼ 3 were reported, 36 hence E N ¼ 0.23 6 0.01 eV.…”

Conditions for the growth of smooth La0.7Sr0.3MnO3 thin films by pulsed electron ablation

“…Although the commercial application of this and other manganites is still strongly questioned by their relatively low Curie temperature (about 350-370K) [11], they represent an excellent tool for unravelling most basic and important effects in spintronic systems involving organic semiconductors [8,12,13]. Such application advances nevertheless extremely tough requirements to the sharpness of all the involved interfaces, and hence to the smoothness of all the components surfaces.…”