Orientation of pentacene molecules on SiO2: From a monolayer to the bulk

Abstract

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy is used to study the orientation of pentacene molecules within thin films on SiO2 for thicknesses ranging from monolayers to the bulk (150 nm). The spectra exhibit a strong polarization dependence of the pi* orbitals for all films, which indicates that the pentacene molecules are highly oriented. At all film thicknesses the orientation varies with the rate at which pentacene molecules are deposited, with faster rates favoring a thin film phase with different tilt angles and slower rates leading to a more bulklike orientation. Our NEXAFS results extend previous structural observations to the monolayer regime and to lower deposition rates. The NEXAFS results match crystallographic data if a finite distribution of the molecular orientations is included. Damage to the molecules by hot electrons from soft x-ray irradiation eliminates the splitting between nonequivalent pi* orbitals, indicating a breakup of the pentacene molecule.

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

“…8͒ and inert substrates. 30,31 AFM images of pentacene thin films on LSMO give NEXAFS results a cogent support by images as well as a layer height value. Figure 4 demonstrates AFM images of ͑a͒ bare LSMO, ͑b͒ 1 nm pentacene, and ͑c͒ 20 nm pentacene thin films.…”

Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

“…For example, pentacene possesses a relatively higher mobility in its b-c plane than a-b plane, as shown in Figure 1e [6,7]. Thus, various substrates, metals [8][9][10], native oxide silica [11][12][13][14], and layered materials [6,7,[15][16][17][18], have been chosen for the growth of high quality thin films. In order to optimize the devices performance, it is essential to clarify how the interactions between molecules and substrates affect the growth of organic thin films.…”

Direct imaging and spectral identification of the interfaces in organic semiconductor-ferromagnet heterojunction

“…4(a), we compare the linearly polarized NEXAFS C K-edge spectra taken from Pn(8 nm)/ Cu(0.18 nm) and Pn(8 nm)/Co(0.18 nm) grown on a Sið100Þ=SiO x surface. The characteristic p à -and r à -resonances of the Pn film covered with a Cu layer remain similar to those found in a thick Pn film, 27 whereas they are significantly altered upon the Co deposition. The non-reactive behavior seen in Pn/Cu bilayers is further proved in Fig.…”