Structure of lipid bilayers

Functionalized acenes and heteroacenes for organic electronics.

Physical Review B

Acenes have long been the subject of intense study because of the unique electronic properties associated with their pi-bond topology. Recent reports of impressive semiconductor properties of larger homologues have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purification, as well as for fabricating organic electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in solution. These new functionalization strategies have recently allowed the synthesis of acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as investigation of their associated structure/property relationships.

The larger acenes: versatile organic semiconductors.

Journal of Physics Condensed Matter: Preface

Pentacene stands out as a model molecule among organic semiconductors due to its ability to form well-ordered films that show a high field effect mobility. We discuss the processes involved in pentacene film growth, emphasizing differences with respect to inorganic films. The influence of growth parameters such as the substrate nature and temperature, the deposition rate, and the kinetic energy of the molecular beam on the structure and morphology of pentacene films are discussed. Finally, we overview recent attempts to model pentacene film nucleation and growth, and draw attention to the role of dislocations.

Pentacene Thin Film Growth

Grazing incidence x-ray scattering was used to determine the temperature and ion-energy dependence of nanoscale corrugations that form on an amorphous SiO2 surface eroded by Ar+ ions. The corrugation wavelength lambda* shows a nearly linear dependence on ion energy. Between room temperature and approximately 200 degrees C, lambda* depends weakly on temperature and above approximately 200 degrees C it shows an Arrhenius-like increase. Ion-assisted viscous relaxation in a thin surface layer is shown to be the dominant smoothing process during erosion; the rate of viscous smoothing scales as (lambda*)(-4).

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Spontaneous nanoscale corrugation of ion-eroded SiO2: the role of ion-irradiation-enhanced viscous flow.

Spontaneous Nanoscale Corrugation of Ion-Eroded SiO2

Grazing incidence x-ray diffraction, x-ray reflectivity and atomic force microscopy have been performed to study the structure of pentacene thin films on oxidized Si substrates from submonolayer to multilayer coverages. The volume of the unit cell in the thin film phase is almost identical to that of the bulk phase, thus the molecular packing efficiency is effectively the same in both phases. The structure forming from the first monolayer remains the same for films at least 190A thick. The in-plane structure of the submonolayer islands also remains unchanged within a substrate temperature range of 0<Tsub<45°C while the island size changes by more than a factor of 4.

Structure of pentacene thin films

Synchrotron x-ray diffraction has been used to analyze the ({radical}3{times}{radical}3){ital R}30{degree} reconstruction of B/Si(111). Excellent agreement is obtained with in-plane data for a model in which boron sits in every third site of threefold symmetry. Out-of-plane diffraction, however, is only consistent with boron {ital below} the surface in the fivefold-coordinated substitutional site under a silicon {ital T}{sub 4} adatom. The structure is confirmed by the growth behavior under room-temperature Si deposition in which the silicon adatom is displaced from its ordered site leaving boron in a two-dimensional ordered substitutional array.

Randall L. Headrick

Papers

Pentacene Thin Film Growth

Spontaneous nanoscale corrugation of ion-eroded SiO2: the role of ion-irradiation-enhanced viscous flow.

Spontaneous Nanoscale Corrugation of Ion-Eroded SiO2

Structure of pentacene thin films

Structure determination of the Si(111): B(3×3)R30°surface: Subsurface substitutional doping