ORCID Profile
0000-0003-0079-3525
Current Organisation
University of Technology
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Wiley
Date: 31-03-2015
Abstract: The thermal stability and molecular order in monolayers of two organic semiconductors, PBI-PA and PBI-alkyl, based on perylene derivatives with an identical molecular structure except for an anchor group for attachment to the substrate in PBI-PA, are reported. In situ X-ray reflectivity measurements are used to follow the stability of these monolayers in terms of order and thickness as temperature is increased. Films have thicknesses corresponding approximately to the length of one molecule molecules stand upright on the substrate with a defined structure. PBI-PA monolayers have a high degree of order at room temperature and a stable film exists up to 250 °C, but decomposes rapidly above 300 °C. In contrast, stable physisorbed PBI-alkyl monolayers only exist up to 100 °C. Above the bulk melting point at 200 °C no more order exists. The results encourage using anchor groups in monolayers for various applications as it allows enhanced stability at the interface with the substrate.
Publisher: American Chemical Society (ACS)
Date: 22-06-2015
Publisher: American Physical Society (APS)
Date: 21-12-2007
Publisher: Elsevier BV
Date: 11-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CE00479H
Abstract: Surface crystallisation yields an unknown polymorph of the phenoxazine molecule. Tuning the crystallisation conditions causes a defined crystal growth of either the thermodynamically stable phase or the kinetic phase observed exclusively within thin films.
Publisher: Wiley
Date: 09-07-2009
DOI: 10.1002/POLB.21759
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9CC05161A
Abstract: Vapour-phase deposition of copper dicarboxylate metal–organic framework thin films with an out-of-plane orientation and accessible porosity.
Publisher: American Chemical Society (ACS)
Date: 04-02-2013
DOI: 10.1021/CG301812M
Publisher: American Chemical Society (ACS)
Date: 08-12-2014
DOI: 10.1021/CG501391J
Publisher: American Chemical Society (ACS)
Date: 08-2007
DOI: 10.1021/JP072784+
Publisher: Elsevier BV
Date: 12-2009
Publisher: American Chemical Society (ACS)
Date: 08-07-2019
DOI: 10.26434/CHEMRXIV.8792171.V1
Abstract: Copper dicarboxylate metal-organic framework films are deposited via chemical vapour deposition. Uniform films of CuBDC and CuCDC with an out-of-plane orientation and accessible porosity are obtained from the reaction of Cu and CuO with vaporised dicarboxylic acid linkers.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6SM02541B
Abstract: Film forming properties of semiconducting organic molecules comprising alkyl-chains combined with an aromatic unit have a decisive impact on possible applications in organic electronics. In particular, knowledge on the film formation process in terms of wetting or dewetting, and the precise control of these processes, is of high importance. In the present work, the subtle effect of temperature on the morphology and structure of dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) films deposited on silica surfaces by spin coating is investigated in situ via X-ray diffraction techniques and atomic force microscopy. Depending on temperature, bulk C8-BTBT exhibits a crystalline, a smectic A and an isotropic phase. Heating of thin C8-BTBT layers at temperatures below the smectic phase transition temperature leads to a strong dewetting of the films. Upon approaching the smectic phase transition, the molecules start to rewet the surface in the form of discrete monolayers with a defined number of monolayers being present at a given temperature. The wetting process and layer formation is well defined and thermally stable at a given temperature. On cooling the reverse effect is observed and dewetting occurs. This demonstrates the full reversibility of the film formation behavior and reveals that the layering process is defined by an equilibrium thermodynamic state, rather than by kinetic effects.
Publisher: American Chemical Society (ACS)
Date: 16-04-2013
DOI: 10.1021/MA400147G
Publisher: American Chemical Society (ACS)
Date: 23-05-2012
DOI: 10.1021/LA301213D
Abstract: Temperature dependent structural and morphological investigations on semiconducting dioctyl-terthiophene (DOTT) thin films prepared on silica surfaces reveals the coexistence of surface induce order and distinct crystalline/liquid crystalline bulk polymorphs. X-ray diffraction and scanning force microscopy measurements indicate that at room temperature two polymorphs are present: the surface induced phase grows directly on the silica interface and the bulk phase on top. At elevated temperatures the long-range order gradually decreases, and the crystal G (340 K), smectic F (348 K), and smectic C (360 K) phases are observed. Indexation of diffraction peaks reveals that an up-right standing conformation of DOTT molecules is present within all phases. A temperature stable interfacial layer close to the silica-DOTT interface acts as template for the formation of the different phases. Rapid cooling of the DOTT s le from the smectic C phase to room temperature results in freezing into a metastable crystalline state with an intermediated unit cell between the room temperature crystalline phase and the smectic C phase. The understanding of such interfacial induced phases in thin semiconducting liquid crystal films allows tuning of crystallographic and therefore physical properties within organic thin films.
Publisher: Elsevier BV
Date: 2013
Publisher: American Chemical Society (ACS)
Date: 13-04-2016
Publisher: International Union of Crystallography (IUCr)
Date: 15-05-2007
DOI: 10.1107/S0021889807018407
Abstract: 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.
Publisher: International Union of Crystallography (IUCr)
Date: 31-05-2019
DOI: 10.1107/S1600576719004485
Abstract: GIDVis is a software package based on MATLAB specialized for, but not limited to, the visualization and analysis of grazing-incidence thin-film X-ray diffraction data obtained during s le rotation around the surface normal. GIDVis allows the user to perform detector calibration, data stitching, intensity corrections, standard data evaluation ( e.g. cuts and integrations along specific reciprocal-space directions), crystal phase analysis etc . To take full advantage of the measured data in the case of s le rotation, pole figures can easily be calculated from the experimental data for any value of the scattering angle covered. As an ex le, GIDVis is applied to phase analysis and the evaluation of the epitaxial alignment of pentacenequinone crystallites on a single-crystalline Au(111) surface.
Publisher: Springer Science and Business Media LLC
Date: 12-2008
Publisher: Springer Science and Business Media LLC
Date: 02-2009
Publisher: AIP Publishing
Date: 06-2022
DOI: 10.1063/5.0088176
Abstract: Grazing incidence x-ray diffraction (GIXD) is a frequently used tool for the crystallographic characterization of thin films in terms of polymorph identification and determination of the crystallographic lattice parameters. Even full structure solutions are possible. To obtain highly accurate diffraction patterns, the thin film s le has to be aligned carefully with the center of the goniometer, which allows a defined incidence of the primary x-ray beam relative to the s le surface. This work studies the effect of misalignment of a thin film s le on the acquired diffraction pattern. Three potential types of misalignments are considered: the deviation of the s le surface from the center of the goniometer, an error in the incidence angle of the primary beam, and an inclination of the goniometer rotation axis from the normal of the substrate surface. The consequence of these types of s le misalignments is the shift of diffraction peaks toward specific directions in reciprocal space. Mathematical equations are given that relate the error in positions of Bragg peaks for each type of s le misalignment. Experiments with intentionally misaligned s les confirm the given formulas. In a subsequent step, the errors in the peak positions are translated to systematic errors in the estimation of the unit cell parameters. Depending on the type of misalignment, some alignment errors can be reduced or even corrected in particular, azimuthal s le rotations prove to be advantageous in these cases. The results in this work improve the quality of GIXD measurements, in general, enabling deeper analysis like the full structure solution from the GIXD pattern on everyday basis.
Publisher: Springer Berlin Heidelberg
Date: 2009
Publisher: American Chemical Society (ACS)
Date: 09-02-2022
Publisher: American Chemical Society (ACS)
Date: 17-01-2015
DOI: 10.1021/AM5075908
Abstract: Substrate-induced phases (SIPs) are polymorphic phases that are found in thin films of a material and are different from the single crystal or "bulk" structure of a material. In this work, we investigate the presence of a SIP in the family of [1]benzothieno[3,2-b]benzothiophene (BTBT) organic semiconductors and the effect of aging and solvent vapor annealing on the film structure. Through extensive X-ray structural investigations of spin coated films, we find a SIP with a significantly different structure to that found in single crystals of the same material forms the SIP has a herringbone motif while single crystals display layered π-π stacking. Over time, the structure of the film is found to slowly convert to the single crystal structure. Solvent vapor annealing initiates the same structural evolution process but at a greatly increased rate, and near complete conversion can be achieved in a short period of time. As properties such as charge transport capability are determined by the molecular structure, this work highlights the importance of understanding and controlling the structure of organic semiconductor films and presents a simple method to control the film structure by solvent vapor annealing.
Publisher: Wiley
Date: 27-07-2009
Publisher: Wiley
Date: 27-05-2013
Abstract: The order in molecular monolayers is a crucial aspect for their technological application. However, the preparation of defined monolayers by spin-coating is a challenge, since the involved processes are far from thermodynamic equilibrium. In the work reported herein, the dynamic formation of dioctyl-benzothienobenzothiophene monolayers is explored as a function of temperature by using X-ray scattering techniques and atomic force microscopy. Starting with a disordered monolayer after the spin-coating process, post-deposition self-reassembly at room temperature transforms the initially amorphous layer into a well-ordered bilayer structure with a molecular herringbone packing, whereas at elevated temperature the formation of crystalline islands occurs. At the temperature of the liquid-crystalline crystal-smectic transition, rewetting of the surface follows resulting in a complete homogeneous monolayer. By subsequent controlled cooling to room temperature, cooling-rate-dependent kinetics is observed at rapid cooling, a stable monolayer is preserved at room temperature, whereas slow cooling causes bilayer structures. Increasing the understanding and control of monolayer formation is of high relevance for achieving ordered functional monolayers with defined two-dimensional packing, for future applications in the field of organic electronics.
Publisher: Elsevier BV
Date: 09-2005
Publisher: Springer Science and Business Media LLC
Date: 10-4199
DOI: 10.1038/NATURE07320
Publisher: MDPI AG
Date: 10-04-2020
Abstract: Direct plasma enhanced-atomic layer deposition (PE-ALD) is adopted for the growth of ZnO on c-Si with native oxide at room temperature. The initial stages of growth both in terms of thickness evolution and crystallization onset are followed ex-situ by a combination of spectroscopic ellipsometry and X-ray based techniques (diffraction, reflectivity, and fluorescence). Differently from the growth mode usually reported for thermal ALD ZnO (i.e., substrate-inhibited island growth), the effect of plasma surface activation resulted in a substrate-enhanced island growth. A transient region of accelerated island formation was found within the first 2 nm of deposition, resulting in the growth of amorphous ZnO as witnessed with grazing incidence X-ray diffraction. After the islands coalesced and a continuous layer formed, the first crystallites were found to grow, starting the layer-by-layer growth mode. High-temperature ALD ZnO layers were also investigated in terms of crystallization onset, showing that layers are amorphous up to a thickness of 3 nm, irrespective of the deposition temperature and growth orientation.
Publisher: Elsevier BV
Date: 07-2011
Publisher: Wiley
Date: 05-04-2022
Abstract: Metal–organic frameworks often display large positive or negative thermal expansion coefficients. MOF‐74, a material envisioned for many applications, shows a different behavior. Temperature‐dependent X‐ray diffraction reveals particularly small negative (positive) thermal expansion coefficients perpendicular (parallel) to the hexagonally arranged pores. These trends are explained by combining density‐functional theory calculations with the Grüneisen theory of thermal expansion, which allows tracing back thermal expansion to contributions of in idual phonons. On the macroscopic level, the small thermal expansion coefficients arise from compensation effects caused by the large coupling between perpendicular stress and strain and by the small magnitudes of the mean Grüneisen tensor elements, 〈 γ 〉. These provide information on how strains impact phonon frequencies. To understand the small value of 〈〉, the in idual mode contributions are analyzed using the corresponding atomic motions. This reveals that only the lowest frequency modes up to ≈3 THz provide non‐negligible contributions, such that 〈〉 drops sharply at higher temperatures. These considerations reveal, how the details of the anharmonic properties of specific phonon bands determine the magnitude and sign of thermal expansion in a prototypical material like MOF‐74. Beyond that, the authors also discuss, how the choice of the theoretical methodology impacts the obtained results.
Publisher: Elsevier BV
Date: 03-2009
Publisher: Elsevier BV
Date: 05-2007
Publisher: Wiley
Date: 25-10-2007
DOI: 10.1002/APP.27231
Publisher: EDP Sciences
Date: 27-03-2009
Publisher: Elsevier BV
Date: 05-2011
Publisher: AIP Publishing
Date: 28-11-2011
DOI: 10.1063/1.3665188
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CE00515F
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2RA20272G
No related grants have been discovered for Roland Resel.