Investigation of molecular diffusion across organic multilayers using neutron specular reflectivity

Englisch, Uwe; Katholy, S; Penacorada, Florencio; Reiche, J.; Pietsch, U.

doi:10.1016/s0928-4931(99)00062-4

Cited by 5 publications

(4 citation statements)

References 10 publications

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“…The estimated transition enthalpies of H = 32.3 ± 4.8 J·g -1 and H = 29 ± 4.8 J·g -1 correspond to values found in the bulk material. These values are typical for chain melting and interlayer diffusion in Langmuir−Blodgett multilayers …”

Section: Resultsmentioning

confidence: 78%

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Structure and Temperature Behavior of Metallo-supramolecular Assemblies

et al. 2005

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A detailed structural analysis of a Langmuir-Blodgett (LB) multilayer composed of a polyelectrolyte-amphiphile complex (PAC) is presented. The PAC is self-assembled from metal ions, ditopic bis-terpyridines, and amphiphiles. The vertical structure of the LB multilayer is investigated by X-ray reflectometry. The multilayer has a periodicity of 57 A, which corresponds to an architecture of flat lying metallo-supramolecular coordination polyelectrolyte (MEPE) rods and upright-standing amphiphiles (dihexadecyl phosphate, DHP). In-plane diffraction reveals hexagonal packing of the DHP molecules. Using extended X-ray absorption fine structure (EXAFS) experiments, we prove that the central metal ion is coordinated to the terpyridine moieties in a pseudo-octahedral coordination environment. The Fe-N bond distances are 1.82 and 2.0 A, respectively. Temperature resolved measurements indicate a reversible phase transition in a temperature range up to 55 degrees C. EXAFS measurements indicate a lengthening of the average Fe-N bond distance from 1.91 to 1.95 A. The widening of the coordination cage upon heating is expected to lower the ligand field stabilization, thus giving rise to spin transitions in these composite materials.

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Section: Resultsmentioning

confidence: 78%

“…These values are typical for chain melting and interlayer diffusion in Langmuir-Blodgett multilayers. 28 It is interesting to note that the Debye-Waller factors remain constant through the phase transition. Generally, spin transitions are accompanied by an increase in the Debye-Waller factors.…”

Section: Resultsmentioning

confidence: 99%

Structure and Temperature Behavior of Metallo-supramolecular Assemblies

et al. 2005

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“…The data represent the total of the layers deposited on the surface by adding the data from the individual layers. The surface roughness was determined by taking into account the deviations of the decaying reflectivity curves of a rough surface from those of a perfectly flat surface. − Errors in the fittings were calculated by taking a 10% error determined by altering χ 2 values, which represent fits within a 10% range of the film thickness.…”

Section: Methodsmentioning

confidence: 99%

DNA Release Dynamics from Bioreducible Layer-by-Layer Films

Blacklock

Mao²,

Oupický³

et al. 2010

Langmuir

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DNA release dynamics from layer-by-layer (LbL) films is an important aspect to consider with regards to localized gene delivery systems. The rate of DNA release and the condensation state of DNA during release are of particular interest in the field of gene delivery. A hyperbranched poly (amido amine) (RHB) containing bioreducible disulfide bonds is used to form interpolyelectrolyte complexes with DNA during LbL film assembly. During films disassembly, DNA is released in physiologic conditions due to the reducing nature of the RHB. Uncondensed DNA deposited on the surface was compared to DNA condensed by RHB in polyplex form by using two types of LbL films, RHB/DNA/RHB and polyplex terminated films, RHB/DNA/polyplex. LbL films with up to three layers are used in order to facilitate high-resolution AFM imaging. X-ray reflectivity, ellipsometry, and Fourier transform infrared spectroscopy are also used. The film disassembly, rearrangement and release of molecules from the surface due to thiol-disulfide exchange is conducted in reducing dithiothreitol (DTT) solutions. Salt is found to accelerate the overall rate of film disassembly. Additionally, it was found that the polyplex layer disassembles faster than the DNA layer. The predominant intermediate structure is the toroid structure for the polyplex layer and the fiber bundle structure for the DNA layer during film disassembly. This study offers a simple means to modulate DNA release from LbL films by utilizing both condensed and uncondensed DNA in different layers. The study highlights nanostructures, toroids and bundles, as dominant intermediate DNA structures during the DNA release from LbL films.

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“…13,22,23 Most techniques mentioned above are surface sensitive, and therefore the value and validity of such studies is contingent upon the very thin organic films remaining static from the time the deposition ends until it is characterized in situ or ex situ. Post-deposition reorganization of thin films, for example by dewetting, intermixing 24,25 or Ostwald ripening 26,27 can introduce significant errors and artifacts when characterization is performed post-mortem, and may get in the way of serious progress in the field of organic electronics. Dewetting has been reported in vacuum-deposited 28 and solutionprocessed polymers, 29,30 polymer blends, 31 and even in some inorganic systems.…”

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confidence: 99%

Post-deposition reorganization of pentacene films deposited on low-energy surfaces

et al. 2009

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We demonstrate that small-molecule organic thin films of pentacene deposited from thermal and supersonic molecular beam sources can undergo significant reorganization under vacuum or in N 2 atmosphere, beginning immediately after deposition of thin films onto SiO 2 gate dielectric treated with hexamethyldisilazane (HMDS) and fluorinated octyltrichlorosilane (FOTS). Films deposited on bare SiO 2 remain unchanged even after extended aging in vacuum. The changes observed on low-energy surfaces include the depletion of molecules in the interfacial monolayer resulting in the population of upper layers via upward interlayer transport of molecules, indicating a dewetting-like behavior. The morphology of pristine, as-deposited thin films was determined during growth by in situ real-time synchrotron X-ray reflectivity and was measured again, ex situ, by atomic force microscopy (AFM) following aging at room temperature in vacuum, in N 2 atmosphere, and in ambient air. Important morphological changes are observed in ultra-thin films (coverage < 5 ML) kept in vacuum or in N 2 atmosphere, but not in ambient air. AFM measurements conducted for a series of time intervals reveal that the rate of dewetting increases with decreasing surface energy of the gate dielectric. Films thicker than $5 ML remain stable under all conditions; this is attributed to the fact that the interfacial layer is buried completely for films thicker than $5 ML. This work highlights the propensity of small-molecule thin films to undergo significant molecular-scale reorganization at room temperature when kept in vacuum or in N 2 atmosphere after the end of deposition; it should serve as a cautionary note to anyone investigating the behavior of organic electronic devices and its relationship with the initial growth of ultra-thin molecular films on low-energy surfaces.Small-molecule thin films of pentacene exhibit among the highest field effect mobilities reported to date, in large partly because of the propensity of pentacene to form highly ordered thin films with efficient p-stacking along the channel of the organic thin film transistor (OTFT). 1-3 The charge carrier mobility in pentacene thin films is presumed to be severely affected by defects and trap sites at grain boundaries located near the semiconductordielectric interface. 4-7 The first 2 or 3 monolayers (ML) of pentacene are especially important to OTFT applications, as they account for the majority of charge transport during transistor operation. 8 Attempts have been made to improve charge transport by chemically modifying the surface of the dielectric (typically SiO 2 ) with self-assembled monolayers (SAMs) and interfacial organic layers, 9,10 or by employing hydrophobic polymers as gate dielectrics. 11,12 The use of these hydrophobic coatings, such as hexamethyldisilazane (HMDS), octadecyltrichlorosilane (ODTS) and others, has improved device performance significantly, resulting in systematically higher values of field effect mobility for pentacene films deposited from both thermal and superson...

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Investigation of molecular diffusion across organic multilayers using neutron specular reflectivity

Cited by 5 publications

References 10 publications

Structure and Temperature Behavior of Metallo-supramolecular Assemblies

Structure and Temperature Behavior of Metallo-supramolecular Assemblies

DNA Release Dynamics from Bioreducible Layer-by-Layer Films

Post-deposition reorganization of pentacene films deposited on low-energy surfaces

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