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The growth and the electronic properties of sexithiophene thin films on silicon surfaces have been studied by angle resolved ultraviolet photoelectron spectroscopy while morphology and crystalline order have been assessed by atomic force microscopy and x-ray diffraction. The influence of the surface modification of the substrate as well as of the growth temperature and the growth rate were investigated in ultrahigh vacuum through controlled multistep growth sequences ranging from (sub)monolayer coverage up to thick films. Depending on the preparation, two electronically distinct sexithiophene (6T) films could be produced, as revealed by their ionization potentials which differed by ∼0.7 eV. The evolution of the electronic energy levels with film thickness is considered in terms of the concepts of interface dipole and band bending, with the latter being argued to be inappropriate. Irrespective of substrate or growth conditions the thick 6T films were found to all have the same work function of ∼0.4 eV, which is related to near vertically oriented molecules on the films surface. Against general expectations 6T grown at a low rate on the reactive Si(111) substrate and those grown at high rates on the oxide surface produces films that are more uniform and crystalline than those grown at low rates on the passive oxidized Si surfaces. The latter promotes the formation of small three-dimensional crystallites and a much poorer morphology for planar devices. [ABSTRACT FROM AUTHOR]

Abstract: The structure of a 30 nm thick pentacene film grown by molecular beam deposition on an oxygen passivated Cu(110) single crystal has been investigated ex-situ by X-ray diffraction methods. It is shown that pentacene crystallizes in two known bulk polymorphs with four unique crystal orientations. In all four cases, a principal pentacene direction is aligned along the surface corrugation provided by the Cu(110)–(2×1)O reconstruction. Since overlayer and substrate form incommensurate lattices, the results cannot be understood by classical criteria of organic epitaxy and the importance of one dimensional alignment is discussed. [Copyright &y& Elsevier]

Abstract: This is a report on sexithiophene thin films (6–300Å) grown on (110) single crystal surfaces. The films are investigated by atomic force microscopy and both laboratory and synchrotron X-ray diffraction techniques. Different growth stages are identified: after the formation of a first lying monolayer, small clusters are formed. Thicker films show needle like morphologies with two distinct needle directions. The morphology can be assigned to the obtained crystal alignments and a growth model is derived: the oxygen rows of the surface direct the alignment of initially adsorbed molecules parallel to the surface corrugation. Further molecules form small clusters on top of this monolayer. At a sufficient cluster size they merge and crystallize in the so-called low temperature phase with the contact plane {010} having a mosaicity of 1–. Furthermore, the observed crystallites show a distinct in-plane alignment, with a distribution of few degrees which perfectly explains the two needle directions. However, the molecules of the crystallites are slightly rotated to the oxygen rows, which is ascribed to a lattice match effect. Therefore it is concluded that the molecules of the monolayer are integrated in the crystal structure and undergo a slight realignment during 3D crystal growth. Finally the importance of an atomically ordered substrate surface is illustrated by a comparison to a film grown on an intentionally disordered surface leading to standing molecules without in-plane order. [Copyright &y& Elsevier]

The layer growth of ultra-thin films of sexiphenyl on Au(111) has been studied as a function of substrate temperature under well-defined ultra-high-vacuum conditions. In situ X-ray photoelectron spectroscopy in combination with thermal desorption spectroscopy was applied to reveal the kinetics of layer growth and recrystallisation. Ex situ atomic force microscopy and X-ray diffraction were used to determine the film morphology and film structure. A continuous small-grain film is obtained at 93 K. The crystalline structure of the grains has been confirmed by X-ray diffraction. However, the grains are not preferentially oriented with respect to the substrate. Around room temperature, recrystallisation takes place and the molecules within the crystallites orient parallel to the substrate surface. Further small substrate temperature changes during growth lead to further changes of the film morphology and to reorientation of the crystallites. However, the molecules in the crystallites stay aligned parallel to the surface. At temperatures greater than 350 K, terraced islands of standing molecules are observed, in addition to needle-like islands with flat-lying molecules. [ABSTRACT FROM AUTHOR]

Abstract: This work focuses on structural and morphological studies of para-sexiphenyl thin films grown on freshly cleaved KCl(100) surfaces. Atomic force microscopy images show different morphologies, namely terrace like growth and different kinds of needle like growths. By X-ray diffraction methods different crystal alignments of the organic film on the substrate are found. The different crystal alignments are assigned to the observed morphologies by transmission electron microscopy and diffraction. Regarding the incommensurate interfaces (on the part of the surface unit cells) it is concluded that the epitaxy is dominated by an alignment of small crystallites on the KCl(100) surface. [Copyright &y& Elsevier]

An X-ray method is presented to characterize thin films with unknown crystal structure with specific crystal orientations. The method maps large volumes of the reciprocal space by a series of pole-figure measurements using a standard texture goniometer. The data can be used for lattice indexing and texture evaluation and in subsequent steps for a complete structural thin-film characterization. The application of the method is demonstrated on an organic monodomain thin film consisting of uniaxially aligned crystallites. [ABSTRACT FROM AUTHOR]

Presents a correction to the article "Sexithiophene films on clean and oxidized Si(111) surfaces: Growth and electronic structure," by J. Ivanco et al. in the 2004 issue.

Abstract: In this work we use atomic force microscopy and X-ray diffraction to study morphology and growth kinetics of para-sexiphenyl layers deposited by hot wall epitaxy on crystalline KCl(001) substrates. It is shown that the growth on KCl(001) is characterized by co-existence of long needles (“laying” molecules) and terraces structured islands (“standing” molecules). The former are the initial growth stage of the films, generating a rectangular network in accordance with surface symmetry of the substrate. It is in contrast to mica substrates, where para-sexiphenyl forms only needles with one preferential direction. [Copyright &y& Elsevier]

Abstract: Quaterphenyl thin films were grown on Au(111) surfaces which were intentionally covered by different amounts of carbon. The films were investigated by X-ray diffraction and atomic force microscopy. An epitaxial character of the quaterphenyl crystallites could be confirmed for films grown on a clean Au(111) surface, with the (211) plane of quaterphenyl parallel to the Au(111) surface. It was found that the in-plane orientation of the quaterphenyl crystallites is determined by aligning the long molecular axes along and , facing the aromatic units of the molecules parallel to Au(111). Carbon coverages of 15% or 50% of the Au(111) surface cause a change in the orientation of the crystallites and a loss of the epitaxial orientation of the crystallites. In case of 15% carbon coverage the (201) plane of quaterphenyl crystallites develops parallel to Au(111), and 50% carbon coverage causes a (001) orientation of the crystallites. Both planes are cleavage planes of quaterphenyl. The film morphology consists of aligned needles for quaterphenyl films grown on the clean Au(111) surface, bent and randomly oriented needles at 15% carbon coverage and of uniformly distributed hillocks at 50% carbon coverage. The corresponding morphologies can be explained by the crystal structure features of quaterphenyl in combination with the orientation of the molecules within the thin films. [Copyright &y& Elsevier]

Abstract: In this study we report on an innovative nanoimprint process for the fabrication of entirely patterned submicron OTFTs in a bottom-gate configuration. The method is based on UV-Nanoimprint Lithography (UV-NIL) combined with a novel imprint resist whose outstanding chemical and physical properties are responsible for the excellent results in structure transfer. In combination with a pretreated stamp the UV-curable resist enables residue-free imprinting thus making etching obsolete. A subsequent lift-off can be done with water. The UV-NIL process implies no extra temperature budget, is time saving due to short curing times, eco-friendly due to a water-based lift-off, simple because it is etch-free and completely r2r compatible. It works perfectly even if ultra-thin organic and hybrid films are used as gate dielectrics. On this basis entirely patterned functional submicron OTFTs with pentacene as the semiconductor are fabricated showing clear saturation, low switch-on voltage (∼3V) and a sufficiently high on–off ratio (103). [Copyright &y& Elsevier]