Pentacene Structure Research Articles

Template Driven Self-Assembly of the Pentacene Structure on the Si(553)-Pb Surface

Template Driven Self-Assembly of the Pentacene Structure on the Si(553)-Pb Surface

Dynamics of Frenkel Excitons in Pentacene.

The dispersion relation for noninteracting excitons and the influence of perturbative corrections are examined in the case of pentacene structure. The values of exchange integrals are determined by nonlinear fits to the experimental dispersion data, obtained by the inelastic electron scattering reported in recent experiments. We obtain theoretical dispersion curves along four different directions in the Brillouin zone which possess the same periodicity as the experimental data. We also show that perturbative corrections are negligible since the exciton gap in the dispersion relation is huge in comparison to the exchange integrals.

Organic Electronics: 1 GHz Pentacene Diode Rectifiers Enabled by Controlled Film Deposition on SAM‐Treated Au Anodes (Adv. Electron. Mater. 2/2016)

A gigahertz-operable pentacene rectifier enabled by controlled film formation using a self-assembled monolayer (SAM) is demonstrated by Kang et al. in article number 1500282. Pentacene deposited on SAM-treated Au forms an ordered structure, thereby exhibiting much improved electrical characteristics, in contrast with a disordered pentacene structure on bare Au. Moreover, SAM treatment lowers the charge injection barrier, which further improves the device performance.

Composite Fluorescent Nanoparticles for Biomedical Imaging

In the rapidly expanding field of biomedical imaging, there is a need for nontoxic, photostable, and nonquenching fluorophores for fluorescent imaging. We have successfully encapsulated a new, extremely hydrophobic, pentacene-based fluorescent dye within polymeric nanoparticles (NPs) or nanocarriers (NCs) via the Flash NanoPrecipitation (FNP) process. Nanoparticles and dye-loaded micelles were formulated by FNP and characterized by dynamic light scattering, fluorescence spectroscopy, UV-VIS absorbance spectroscopy, and confocal microscopy. These fluorescent particles were loaded from less than 1% to 78% by weight core loading and the fluorescence maximum was found to be at 2.3 wt.%. The particles were also stably formed at 2.3% core loading from 20 up to 250 nm in diameter with per-particle fluorescence scaling linearly with the NC core volume. The major absorption peaks are at 458, 575, and 625 nm, and the major emission peaks at 635 and 695 nm. In solution, the Et-TP5 dye displays a strong concentration-dependent ratio of the emission intensities of the first two emission peaks, whereas in the nanoparticle core the spectrum is independent of concentration over the entire concentration range. A model of the fluorescence quenching was consistent with Förster resonant energy transfer as the cause of the quenching observed for Et-TP5. The Förster radius calculated from the absorption and emission spectra of Et-TP5 is 4.1 nm, whereas the average dye spacing in the particles at the maximum fluorescence is 3.9 nm. We have successfully encapsulated Et-TP5, a pentacene derivative dye previously only used in light-emitting diode applications, within NCs via the FNP process. The extreme hydrophobicity of the dye keeps it encapsulated in the NC core, its extended pentacene structure gives it relatively long wavelength emission at 695 nm, and the pentacene structure, without oxygen or nitrogen atoms in its core, makes it highly resistant to photobleaching. Its bulky side groups minimize self-quenching and localization within the nanoparticle core prevents interaction of the dye with biological surfaces, or molecules in diagnostic assays. Loading of dye in the NP core allows 25 times more dye to be delivered than if it were conjugated onto the nanocarrier surface. The utility of the dye for quantifying nanoparticle binding is demonstrated. Studies to extend the wavelength range of these pentacene dyes into the near infra-red are underway.

High performance of pentacene organic thin film transistors by doping of iodine on source/drain regions

Contact doping was conducted by iodine in a top contact configuration in a pentacene organic thin film transistor (OTFT), to investigate its effects on contact resistance and the resulting electrical performance. Iodine doping in the pentacene film caused the change of pentacene structure, thus leading to an increase in electrical anisotropy, i.e. ratio of lateral to vertical resistivity. The two resistive components of doped pentacene film underneath the Au contacts were major contributors to the contact resistance, and a model to explain the dependence of contact resistance on iodine doping was presented. Finally, OTFTs fabricated on iodine doped source/drain contacts exhibited high mobility of 1.078cm2/Vs, two times that of OTFTs with undoped contacts, due to the low contact resistance.

Mechanism behind Improved Apparent Field-Effect Mobility in Pentacene Thin-Film Transistors with Thin Molybdenum Trioxide Layer

Insertion of a thin layer of the Lewis acid molybdenum trioxide (MoO3) improves the apparent mobility of charge carriers in organic field-effect transistors (OFETs). In order to identify the dominant mechanism responsible for this, we characterized devices having a bottom pentacene (70-z nm)/MoO3 (1 nm)/top pentacene (z nm) structure and those having pentacene (69 nm)/MoO3 (1 nm) only under the gold source and drain electrodes. The former devices exhibited large drain currents (IDS) and mobilities, regardless of the z value. Moreover, the latter devices exhibited comparable IDS and mobilities to those of conventional pentacene OFETs, suggesting that the formation of CT complexes just above the conduction channel is the critical mechanism. Carriers generated by dissociation of CT complexes at the pentacene/MoO3 interface contribute to the formation of an effective channel and the apparent mobility.

Mechanism behind Improved Apparent Field-Effect Mobility in Pentacene Thin-Film Transistors with Thin Molybdenum Trioxide Layer

Insertion of a thin layer of the Lewis acid molybdenum trioxide (MoO3) improves the apparent mobility of charge carriers in organic field-effect transistors (OFETs). In order to identify the dominant mechanism responsible for this, we characterized devices having a bottom pentacene (70-z nm)/MoO3 (1 nm)/top pentacene (z nm) structure and those having pentacene (69 nm)/MoO3 (1 nm) only under the gold source and drain electrodes. The former devices exhibited large drain currents (IDS) and mobilities, regardless of the z value. Moreover, the latter devices exhibited comparable IDS and mobilities to those of conventional pentacene OFETs, suggesting that the formation of CT complexes just above the conduction channel is the critical mechanism. Carriers generated by dissociation of CT complexes at the pentacene/MoO3 interface contribute to the formation of an effective channel and the apparent mobility.

ORGANIC PHOTOSENSING COMPOSITE STRUCTURE ON THE BASE OF PENTACENE AND POLYANILINE

Organic photosensing composite polyaniline:pentacene structure with a wide spectrum of photosensitivity (1.7-2.7 eV) by means of vacuum co-deposition of polyaniline and pentacene on flexible substrate (PET) with ITO layer was fabricated. As rectifying contact the deposited aluminum film on composite structure was used. The bulk and barrier properties of composite structure were evaluated by means of current-voltage measurements.

Chemisorption of Pentacene on Si(111)-7 × 7 Studied via Scanning Tunneling Microscopy and Density Functional Theory

The chemisorption of pentacene on Si(111)-7 × 7 surface was studied using scanning tunneling microscopy and density functional theory calculations. On the basis of the STM results, three binding configurations, each involving four C−Si covalent bonds, can be identified from the orientations of pentacene with respect to the underlying substrate atoms. One of the configurations involves the unique engagement between three adatoms and one rest atom on the surface with four of the C atoms on pentacene such that the double bonds conjugation on pentacene is preserved despite of a loss in the aromaticity. Pentacene in another configuration binds to two center adatom−rest atom pairs within one-half of the surface unit cell. The third configuration entails a twisted pentacene structure as the molecule terminally bridges two oppositely oriented adatom−rest atom pairs that span across the faulted and unfaulted halves of a unit cell. The different binding configurations modified the electronic structures of the adsorbed pentacene as evidenced by their STM images, which were modeled by theoretical simulation. Structural modeling and adsorption energies calculations were carried out using DFT method. Factors affecting the relative thermodynamic stabilities based on the calculation results and the relative populations of pentacene in the different binding configurations as observed experimentally were discussed.

Photoemission, NEXAFS and STM studies of pentacene thin films on Au(1 0 0)

We have investigated the initial stages of the growth of pentacene thin films on the Au(1 0 0) substrate using synchrotron radiation photoelectron spectroscopy (PES), near edge X-ray absorption fine structure (NEXAFS) and scanning tunnelling microscopy (STM). Results indicate a well-ordered structure with the pentacene molecules adopting a predominantly flat orientation with respect to the substrate for coverages of less than three monolayers. NEXAFS and photoemission data indicates the presence of a second molecular orientation for thicker films, with the introduction of a slight tilting away from planar bonding geometry at higher pentacene coverages. STM images of coverages less than three monolayers indicate a well-ordered pentacene structure allowing for the calculation of pentacene unit cell parameters. The pentacene molecular rows adopt a side-by-side bonding arrangement on the surface. For pentacene deposited at room temperature, step edges were observed to act as nucleation centres for film growth. Annealing of the substrate to 373 K was found to remove excess molecules and improve film quality, but did not otherwise change the bonding geometry of the pentacene with respect to the surface.

Flexible Pentacene/PMMA Thin-Film Transistors Fabricated on Aluminium Foil Substrates

AbstractPentacene thin-film transistors (TFT) were fabricated on aluminum foils using polymethyl methacrylate (PMMA) as gate dielectric. In such structure, the aluminum substrate acts as the gate electrode itself. A bottom gate inverted structure was used to study the influence of the dielectric and the aluminum substrate on the device performance.Pentacene thin-films were deposited by thermal evaporation in high-vacuum at deposition rates around 3 Ås-1 and three different substrate temperatures (30, 60 and 90°C). The maximum process temperature achieved was 170°C, corresponding to the baking of polymethyl methacrylate. The TFTs exhibit field-effect mobility values of ∼ 10-3 cm2V-1s-1 and threshold voltage values around –15 V. The influence of the dielectric and the substrate temperature on the pentacene structure and device field-effect mobility is discussed.

Electronic and Structural Evidences for Charge Transfer and Localization in Iodine-Doped Pentacene

We have investigated the doping mechanism of pentacene with iodine and its impact on the structure and on the electronic properties of single crystals, powders, and thin films in a large range of iodine concentration up to six iodine per pentacene (PEN) molecule (I/PEN = 6). Three regimes of doping have been identified. In the low doping regime I/PEN < 0.05, the pristine pentacene structure of single crystals is maintained. Electron spin resonance (ESR) evidences a Pauli susceptibility, that is, the characteristic fingerprint of delocalized holes in the valence band of pentacene. In the intermediate doping regime (0.1 < I/PEN ≤ 2.0), iodine diffuses between the (a,b) planes of the pentacene structure and forms an intercalate. Charge transfer between iodine and pentacene is witnessed by both UV−vis and IR signatures of PEN+ cations and related species, for example, cation dimers (PEN+)2 and typical Raman signatures of the I3- and I5- species. Spin pairing of pentacene cation radicals is further supported b...