F16CuPc Films Research Articles

Growth and Electrical Transport Properties of Organic Semiconductor Thin Films

Hexadecafluorophthalocyanine (F16CuPc) and Cobalt phthalocyanone (CoPc) thin films of different thickness (20-200nm) have been grown by Molecular Beam Epitaxy (MBE) using different deposition rate (0.2 – 1.0 Å/s). For nanowire type growth lower deposition rate and for films of smooth surface higher deposition rate are found suitable. Charge transport (J~V) of CoPc and F16CuPc films is governed by bulk-limited processes with a bias dependent crossover from Ohmic to trap-free space-charge-limited conduction. The mobility (μ) values at 300 K were found 4.5 and 5.5 cm2 V−1 s−1 for CoPc and F16CuPc films respectively. Mechanism of reverse rectification behavior of an organic heterojunction comprising of CoPc and F16CuPc is explained by Kelvin Probe measurement.

Electronic properties of the interface between hexadecafluoro copper phthalocyanine and unsubstituted copper phthalocyanine films

The formation of an interface during the deposition of unsubstituted copper phthalocyanine (CuPc) films on the surface of hexadecafluoro copper phthalocyanine (F16-CuPc) films is studied. An incident low-energy electron beam with energies from 0 to 25 eV is used to test the surface under study according to the very-low-energy electron-diffraction technique (VLEED) in the mode of total current spectroscopy. For F16-CuPc films, the structure of the maxima in the total current spectra and its main differences from the structure of the maxima for the CuPc film are determined in the energy range from 5 to 15 eV above the Fermi level. The differences in the structure of vacant electron orbitals for CuPc and F16-CuPc are also revealed using density functional theory calculations. As a result of an analysis of variations in the intensities of the total current spectra of the CuPc and F16-CuPc films, it is assumed that an intermediate layer up to 1 nm thick appears during the formation of an interface between these films, which is characterized by a spread of the features in the total current spectrum. The height, width, and change in the work function are determined for the studied F16-CuPc/NuPc interface barrier. A decrease in the level of vacuum by 0.7 eV occurs in the boundary region, which corresponds to electron density transfer from the CuPc film toward the F16-CuPc substrate.

Tuning of C60 energy levels using orientation-controlled phthalocyanine films

The interface electronic structure of C60/CuPc and C60 heterojunctions on SiO2 and highly oriented pyrolytic graphite has been studied using ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and synchrotron based photoelectron spectroscopy. Fermi level pinned to the negative integer charge transfer state of C60 molecules on the standing CuPc film has been observed, while nearly vacuum-level alignment is observed for C60 on the lying CuPc film. We also found small vacuum-level shifts for C60 on both standing and lying F16CuPc films, which can be attributed to the rearrangement of underlying F16CuPc molecules. With the use of orientation-controlled CuPc and F16CuPc thin films, C60 highest occupied molecular orbital energy levels relative to the substrate Fermi level can be tuned from 1.9 eV for C60 on the standing CuPc film to 1.0 eV on the standing F16CuPc film.

The influence of orientations and external electric field on charge carrier mobilities in CuPc and F16CuPc films on highly ordered pyrolytic graphite and octane-1-thiol terminated Au(111) substrates

The lying-down and standing-up CuPc and F(16)CuPc films on HOPG (highly ordered pyrolytic graphite) and C8-SAM/Au(111) (octane-1-thiol terminated Au(111)) substrates are investigated by using a hybrid strategy combing the molecular dynamic (MD) simulations with density functional theory (DFT) calculations, in order to understand the influence of packing orientation on charge carrier mobilities. On the basis of the periodic slab model and consistent-valence force field, MD simulations show the populations of various packing configurations and radial distribution of intermolecular distance in the films at room temperature. It is also demonstrated that the external electric field (parallel or perpendicular to the substrate) perturbs the intermolecular distances in CuPc and F(16)CuPc films, especially for the slipped edge-to-face stackings. DFT calculations are then used to evaluate two key charge-transfer parameters, reorganization energy and transfer integral. An electrostatics embedding model is employed to approximately consider the external electrostatics contributions to reorganization energy. The thermal-averaged mobility is consequently estimated by taking account of both electronic structures of charge-hopping pairs and dynamic fluctuations in film morphologies under various experimental conditions. It is found that CuPc has smaller reorganization energy and larger hole (electron) mobilities than F(16)CuPc. Under the external electric field of 10(4)-10(7) V cm(-1), both hole and electron mobilities of CuPc and F(16)CuPc films would decrease to 1-3 orders of magnitude. CuPc (F(16)CuPc) films show substantial orientation dependence of mobilities on the ratio of standing-up versus lying-down orientations falling in the range of 10-1000.

Supramolecular Assembly of a 2D Binary Network of Pentacene and Phthalocyanine on Cu(100)

A crystalline nanoporous molecular network was tailored by supramolecular assembly of pentacene and F16CuPc on Cu(100). The structure and self-assembly mechanisms of the pure and binary layers were analyzed by STM. F16CuPc films and mixed layers of pentacene/F16CuPc in a ratio of 2:1 show two enantiomorphic chiral domains with high structural order in contrast to pentacene which exhibits no long-range order in pure films. A model of the epitaxial relationship on Cu(100) is given, which suggests C-F...H bonding as a possible driving force for the bimolecular self-assembly in addition to the still strong interaction between the substrate and the organic bilayer.

Langmuir−Blodgett Monolayer as an Efficient p-Conducting Channel of Ambipolar Organic Transistors and a Template for n-Type Molecular Alignment

The Langmuir-Blodgett (LB) technique was used to deposit a monolayer on the gate insulator to identify the role of the monolayer in the organic transistors. Ambipolar transistors were obtained on the basis of the CuPc LB monolayer and F16CuPc films. The results proved that a single molecular layer is enough to show field-effect performance. Moreover, the preorganized LB monolayer led to the alignment of subsequent molecules deposited on it through intermolecular pi-pi interactions.

Weak Epitaxy Growth of Copper Hexadecafluorophthalocyanine (F16CuPc) on p-Sexiphenyl Monolayer Film

Weak epitaxy growth (WEG) behavior and mechanism of copper hexadecafluorophthalocyanine (F16CuPc) on p-sexiphenyl (p-6P) monolayer film were investigated by atomic force microscopy (AFM), selected area electron diffraction (SEAD), and wide-angle X-ray diffraction (WAXD). High-quality F16CuPc films with high order, large size, and molecular-level smoothness were obtained successfully by WEG method. It was identified that there exists incommensurate epitaxial relation between highly oriented F16CuPc and p-6P films. The geometrical channels of p-6P monolayer surface induce the nucleation and growth of F16CuPc molecules. Two kinds of in-plane structures, referred to as "phase I" and "phase II", coexist in the initial few molecular layers. As thin-film thickness increases, the distance of (001) plane diminishes and phase I disappears. Furthermore, coalescence, dislocation, and high-angle grain boundary between F16CuPc neighboring domains were observed by high-resolution AFM.

Molecular Orientation and Electromagnetic Properties of Perhydrogenated and Perfluorinated Copper Phthalocyanine Thin Films

X-ray diffraction (XRD) data shows lattice planes with a spacing of 12.8 Å for copper phthalocyanine (CuPc) thin films. Comparison between the XRD patterns of CuPc powder and thin films suggests that the molecules are oriented along the (100) lattice plane nearly perpendicular to the substrate. The XRD data of the perfluorinated phthalocyanine (F16CuPc) thin film indicate a similar structure to that of CuPc, but with a wider lattice spacing of 14.6 Å. Angular variations of the line position (g-value) of ESR spectra reveal tilt angles of 39 and 34° for the CuPc and F16CuPc thin films, respectively, and the same deviation angle of 24°. This indicates a cone-shaped orientation of CuPc and F16CuPc with similar tilt and deviation angles. The ESR linewidths of both films show angular variation, indicating one-dimensional spin-chain interactions in both the CuPc and F16CuPc thin films. Organic thin-film transistors (OTFTs) with CuPc and F16CuPc films are tested for their suitability as channel layers. The OTFTs with a CuPc film exhibit conduction with holes as carriers, and have a field-effect mobility of 2.6 ×10-5 cm2 V-1 s-1 and an on/off ratio of 10 in the accumulation mode. The OTFTs with F16CuPc films exhibit conduction with electrons as carriers (n-type), and have a field-effect mobility of 2.0 ×10-4 cm2 V-1 s-1 and an on/off ratio of 2.4 ×104 in the accumulation mode.

Thickness-Dependent Structural Transitions in Fluorinated Copper-phthalocyanine (F16CuPc) Films

The detailed structure of F16CuPc films on SiO2 has been determined by means of in situ grazing incidence X-ray diffraction from the first monolayer to thicker films. In contrast to films of the homologous H16CuPc molecule, the F16CuPc films exhibit the same structure independently from the deposition temperature. The films show a thickness-dependent polymorphism manifested in the in-plane crystal structure, which implies large differences in the molecular tilt within the cofacial stacking of the molecules.

Self-organization of phthalocyanines on Al2O3 (1120) in aligned and ordered films

We studied the self-organization process of F16CuPc films (20–30 ML) on stepped Al2O3 (1120) substrates. X-ray diffraction measurements revealed a highly ordered layered structure with the molecules in a nearly upright configuration. The morphology, investigated by atomic force microscopy, consisted of long (several microns) and narrow (20–100 nm) needlelike terraces unidirectionally aligned along one of the main crystallographic directions of the Al2O3 (1120) surface. High resolution atomic force microscopy images revealed in-plane molecular order with the molecular stacking direction parallel to the needlelike terraces. Such anisotropic morphology is the result of a self-organization process of F16CuPc in elongated crystallites driven to a preferential orientation by the interaction with the substrate. Spectroscopic ellipsometry showed that these films exhibit anisotropic optical properties correlated with the molecular arrangement.

Structure, morphology, and optical properties of thin films of F16CuPc grown on silicon dioxide

Abstract Thin films of hexadecafluorophthalocyanine (F16CuPc) were grown by organic molecular beam deposition (OMBD) under ultra high vacuum (UHV) conditions on oxidized Si(0 0 1) substrates. The film thicknesses ranged from 120 to 450 A and the substrate temperature was varied from −150 to 300 °C. X-ray diffraction and atomic force microscopy (AFM) were used to characterize the structure and morphology of the layers. Spectroscopic ellipsometry was employed to determine the dielectric properties and to locate characteristic transitions between 1.4 and 3.7 eV. The correlation of the electronic properties with the molecular packing in the films is discussed. The results are compared to the case of F16CuPc films grown on stepped sapphire surfaces, which differ in their lateral ordering behavior.

Electronic structure, diffusion, and p-doping at the Au/F16CuPc interface

Interfaces formed by evaporating Au on copper hexadecafluorophthalocyanine (F16CuPc) and F16CuPc on Au are studied via ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy. The energy position of the molecular levels is found to depend on the deposition sequence. The Au-on-F16CuPc interface exhibits a lower hole injection barrier than the F16CuPc-on-Au interface. This behavior is attributed to the diffusion of Au into the organic matrix at the Au-on-top interface, in which they behave as acceptors. Band bending consistent with p doping, i.e., upward away from the metal interface, is observed in Au-doped F16CuPc films. Current–voltage measurements on Au/F16CuPc/Au sandwich structures show a higher electron injection barrier at the top Au electrode contact than at the bottom electrode contact, also consistent with p-type doping F16CuPc by Au.