Effect of film thickness controlled by ink‐jet printing method on the optical properties of an electroluminescent polymer

Ink‐jet printing (IJP) represents a highly promising liquid processed polymer deposition method for the film preparation of functional polymers in photo‐electronic devices. In this report, the results on the IJP of a fluorene‐based electroluminescent polymer, poly(9,9‐dihexylfluorene‐alt‐2,5‐dioctyloxybenzene) (PF6OC8), from a piezoelectric droplet generator are presented. The polymer film thickness has been found to show an approximate linear relation with the number of droplets per unit area; it is thus convenient to control the film thickness by the space of printed dots in IJP process. In comparison, spin coating approach is also used to prepare polymer films with different thicknesses by varying solution concentration and spinning speed. However, it is found that spin coating is difficult to control the film thickness quantitatively. The influence of film thickness on the photoluminescence (PL) properties of PF6OC8 films prepared by IJP and spin coating is comparatively investigated. For both ink‐jet printed and spin coated films, the intensity of PL spectra first increases and then decreases with increase in the film thickness, probably due to the exciton quenching in thicker films. When the polymer film thickness is at nanoscale, the major peak in the PL spectrum is the 0–0 vibronic emission at about 420 nm, and with increase in the film thickness, the 0–1 vibronic peak at about 440 nm becomes dominant. The red‐shifted PL spectra with increase in film thickness show the change from the 2D exciton state to the 3D one. Copyright © 2009 John Wiley & Sons, Ltd.     

Optical Viscometry of Spinning Sol Coatings

Optical interferometric monitoring of spin coating (optospinography) has allowed close observation of the temporal evolution of a thin silicate sol film (typically at 2000 rpm, 100 Hz data acquisition). The kinematic viscosity data obtained, using a simple analytical model, are validated with those from a mineral oil standard, with agreement well within the experimental uncertainties. For spin coating in open air, the influence of variations in refractive index, rheological properties and air flow are discussed. Inflections in the temporal evolution of the optical thickness of silicate sol films are analyzed, which indicate the usefulness of optospinography, particularly when applied in the proximity of the rotation axis and evaporation is minimized, to monitor time variations in the kinematic viscosity of these sols during spin coating.     

Time-resolved light scattering studies of Spin-coated titanium dioxide

Spin coating of titanium alkoxides is a fast and straightforward method of forming compact and durable titanium dioxide thin films. In this report, an optical interference technique is used to understand the dynamics of titanium dioxide thin film formation during the spin coating process of titanium (IV) ethoxide sols, and a 4-stage thinning model is proposed. Optical monitoring of interference fringes as a function of time enables determination of the time-dependent film thickness through measurement of the interference fringe separation while the sol to gel transition can be monitored by analyzing the fringe visibility. For films that are spun at 2,000 rpm or faster, a spin duration of 5 s is sufficient for the film to reach its final thickness. At a given spin speed, spin times longer than 5 s do not affect the final film thickness. However, thinner final film thicknesses can be achieved by increasing the spin speed. All films were found to densify on annealing with an annealed thickness approximately 0.4 times that of the pre-anneal thickness regardless of spin speed. Spin-coated titanium dioxide films are expected to play an important role in low-cost and scalable next generation solar cells employing dyes and quantum dots as the light harvesting agents.     

Effect of processing temperature during spin-on application on the properties of sol-gel silica films

The effect of the temperature (of the substrate and the solution) during film deposition on spin coating process of sol-gel films is discussed. The increase of substrate temperature as well as coating solution liquid temperature leads to formation of thicker films with higher porosity. The temperature dependence of films thickness is mainly determined by the change of solvent vapour pressure with consideration for the change of liquid viscosity.     

Pattern formation in PMMA film induced by electric field

Micro‐sized patterns were created on thin poly(methyl methacrylate) (PMMA) films by the effect of external field, perpendicular to the film surface. The PMMA film, prepared by spin‐coating onto Si wafer, was heated to the fluid temperature (275 °C) and a linear pattern was created by the effect of electric field produced by a strip electrode. In another experiment, a round pattern was created as a result of local laser heating of the PMMA film under homogenous electrical field. The created patterns were analyzed by optical microscopy and profile meter. The dependence of the form and size of the created patterns on the intensity of the electric field, exposure time, and initial film thickness was examined. Wave guiding property of a linear pattern, produced by the above technique, was examined in a simple experiment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1131–1135, 2009     

Thermochromic Meltable Materials with Reverse Spin Transition Controlled by Chemical Design

We report a series of meltable Fe^II complexes, which, depending on the length of aliphatic chains, display abrupt forward low-spin to high-spin transition or unprecedented melting-triggered reverse high-spin to low-spin transition on temperature rise. The reverse spin transition is perfectly reproducible on thermal cycling and the obtained materials are easily processable in the form of thin film owing to their soft-matter nature. We found that the discovered approach represents a potentially generalizable new avenue to control both the location in temperature and the direction of the spin transition in meltable compounds.     

The Electron Spin as a Chiral Reagent

We show that enantioselective reactions can be induced by the electron spin itself and that it is possible to replace a conventional enantiopure chemical reagent by spin‐polarized electrons that provide the chiral bias for enantioselective reactions. Three examples of enantioselective chemistry resulting from electron‐spin polarization are presented. One demonstrates the enantioselective association of a chiral molecule with an achiral self‐assembled monolayer film that is spin‐polarized, while the other two show that the chiral bias provided by the electron helicity can drive both reduction and oxidation in enantiospecific electrochemical reactions. In each case, the enantioselectivity does not result from enantiospecific interactions of the molecule with the ferromagnetic electrode but from the polarized spin that crosses the interface between the substrate and the molecule. Furthermore, the direction of the electron‐spin polarization defines the handedness of the enantioselectivity. This work demonstrates a new mechanism for realizing enantioselective chemistry.     

Thickness, Morphology and Structure of Sol-Gel Hybrid Films: I—The Role of the Precursor Solution's Ageing

The physical properties of inorganic-organic sol-gel hybrid films are determined by a large number of processing parameters, as the initial recipe, the catalysis conditions and the film deposition technique. This work focuses on the influence of the precursor solution's ageing on the quality and structure of hybrid silica-polytetrahydrofuran films, prepared by spin coating. The inorganic precursor, tetraethylorthosilicate, was hydrolysed under acid catalysis and using ethanol as co-solvent. The hydrolysis molar ratio (R) was fixed at 4. Different polymer concentrations of two average molecular weights (M _n = 650 and 2900) were added to the initial colloidal solutions. Ageing took place in open containers. The thickness and surface texture parameters of the films were determined by profilometry, and their structures studied by FTIR. It is shown that the films' thickness increases with the ageing of the precursor solution, more steeply for the hybrid films with higher polymer content and higher M _n. The best films obtained, which present the highest thickness and the lowest relative roughness, are those prepared from the most aged solutions. The FTIR results show that the films' porosity increases with the ageing of the precursor solution, and that the distribution of oligomeric species in solution is maintained upon film deposition. Therefore, the structure of the film is essentially determined by the extension of the condensation reactions until the spinning moment.     

Studies of a Large Odd‐Numbered Odd‐Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8Mn

The spin dynamics of Cr₈Mn, a nine‐membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr₈Mn is a rare example of a large odd‐membered AF ring, and has an odd‐number of 3d‐electrons present. Odd‐membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated‐spin ground states. The chemical synthesis and structures of two Cr₈Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground‐spin‐state crossing from S=1/2 to S=3/2 in Cr₈Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin‐pair correlations and scalar‐spin chirality, shows a non‐collinear spin structure that fluctuates between non‐planar states of opposite chiralities.     

Scanning force microscopy study of the morphology of spin‐cast molecular‐imprinted nylon thin films

The morphology of thin, selectively imprinted films of Nylon‐6 was investigated by scanning force microscopy. Four amino acids were used as template molecules in the spin‐cast films. Film thickness ranged from 2 µm to 500 nm, depending on the nylon and template concentration in the casting solution. The thin‐film properties, including the presence of nanometer‐ to micrometer‐sized pores, are clearly associated with the imprinting process. The larger features observed by scanning force microscopy are attributed to amino acid clustering during the casting process. Copyright © 2004 John Wiley & Sons, Ltd.     

Recent progress in EPR study of spin labeled polymers and spin probed polymer systems

The EPR technique is commonly used for the detection and characterization of paramagnetic centers in chemical science. This method can provides a lot of information, such as identity, structure, dynamics, interaction, orientation, glass transition temperature, adsorption behavior, functionality, phase behavior, nano-inhomogeneities, and conformation of the free-radical portion of the polymer chain. Most polymers intrinsically possess diamagnetic properties, so in order to study polymers with EPR, paramagnetic centers need to be incorporated into the polymer systems. Spin labeling and spin probing are main methods of covalently attaching paramagnetic centers to polymer chains or embedding them in polymer matrices through non-covalent interactions, respectively. Spin labeling and spin probing techniques for polymers and polymer systems (especially with nitroxide radicals) have also been studied, which have a profound impact on polymer science. This review focuses on the continuous wave EPR technique and introduces the recent advances in spin labeled polymers and spin probed polymer systems in EPR research.     

Short-time dynamics of proteins in solutions studied by neutron spin echo

Dynamics of proteins in solutions include translational, rotational, and internal motions that are linked to different protein properties. Because most proteins are small with the sizes of just a few nanometers, the timescale for their short-time dynamics usually ranges from a few nanoseconds to a few hundreds of nanoseconds, during which a protein usually does not rotate too much. Protein short-time dynamics has been shown to be useful to study liquid theories, protein cluster formation, gelation transitions of concentrated protein systems, and protein internal motions. Neutron spin echo, which is able to measure protein motions with the right correlation time at the appropriate length scale, is ideally suitable to study the short-time dynamics of proteins in solutions. Here, we review recent activities of using neutron spin echo to study the protein short-time motions. Despite all progresses, there are still both theoretical and experimental challenges to exploit the full capability of neutron spin echo to study protein dynamics.     

Nanostructured Crosslinkable Micropatterns by Amphiphilic Dendrimer Stamping

Summary: Microcontact printing was used to deposit stable, nanostructured, amphiphilic and crosslinkable patterns of poly(amidoamine organosilicon) (PAMAMOS)‐dimethoxymethylsilyl (DMOMS) dendrimer multilayers onto silicon wafers, glass, and polyelectrolyte multilayers. The effects of dendrimer ink concentration, contact time, and inking method, on the thickness, uniformity, and stability of the resulting patterns were studied using optical microscopy, fluorescence microscopy, atomic force microscopy (AFM), and contact‐angle analysis. Microarrayed dendrimer film thickness was found to be controllable by conditions used during spin self‐assembly.

Optical micrograph of the circular patterns, obtained from a 0.5% PAMAMOS dendrimer solution, on a glass substrate.     

Spin-inversion mechanisms in O2 binding to a model heme complex revisited by density function theory calculations

Spin-inversion mechanisms in O₂ binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet–triplet, singlet–quintet, triplet–quintet, and quintet–septet spin-inversion processes. We found that the singlet–triplet spin-inversion points are located around the potential energy surface region at short Fe–O distances, whereas the singlet–quintet and quintet–septet spin-inversion points are located at longer Fe–O distances. This suggests that both narrow and broad crossing models play roles in O₂ binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed.     

旋转涂布法制备MoO3变色薄膜的研究

近二十年来,过渡金属氧化物半导体薄膜因其具有光致变色/电致变色特性,可作为无机变色材料广泛应用于信息存储、显示以及灵敏器件等方面,而成为材料科学领域的研究热点之一^[1～4].     

Local physical quantities for spin based on the relativistic quantum field theory in molecular systems

Local physical quantities for spin are investigated on the basis of the four‐ and two‐component relativistic quantum theory. In the quantum field theory, local physical quantities for spin such as the spin angular momentum density, spin torque density, zeta force density, and zeta potential play important roles in spin dynamics. We discuss how to calculate these local physical quantities based on the two‐component relativistic quantum theory. Some different types of relativistic numerical calculations of local physical quantities in Li atom and C₆H₆ are demonstrated and compared. Local physical quantities for each orbital are also discussed, and it is seen that a total local zeta potential is given as a result of some cancellation of large contributions from each orbital. © 2016 Wiley Periodicals, Inc.     

Pump–probe second harmonic generation study of ultrafast spin dynamics in semiconductor multilayers

We report the first application of pump–probe second harmonic generation (SHG) measurements to characterize optically induced magnetization in non‐magnetic multilayer semiconductors. In the experiment, spin‐polarized electrons are excited selectively by a pump beam in the GaAs layer of GaAs/GaSb/InAs structures. However, the resulting net magnetization manifests itself through the induced SHG probe signal from the GaSb/InAs interface, thus indicating a spin‐polarized electron transport across the heterostructure. We find that the magnetization dynamics are governed by an interplay between the spin density evolution at the interfaces and the spin relaxation. Copyright © 2003 John Wiley & Sons, Ltd.     

Temperature and scattering contrast dependencies of thickness fluctuations in surfactant membranes

Temperature and scattering contrast dependencies of thickness fluctuations have been investigated using neutron spin echo spectroscopy in a swollen lamellar phase composed of nonionic surfactant, water, and oil. In the present study, two contrast conditions are examined; one is the bulk contrast, which probes two surfactant monolayers with an oil layer as a membrane, and the other is the film contrast, which emphasizes an individual surfactant monolayer. The thickness fluctuations enhance dynamics from the bending fluctuations, and are observed in a similar manner in both contrast conditions. Thickness fluctuations can be investigated regardless of the scattering contrast, though film contrasts are better to be employed in terms of the data quality. The thickness fluctuation amplitude is constant over the measured temperature range, including in the vicinity of the phase boundary between the lamellar and micellar phases at low temperature and the boundary between the lamellar and bicontinuous phases at high temperature. The damping frequency of the thickness fluctuations is well scaled using viscosity within the membranes at low temperature, which indicates the thickness fluctuations are predominantly controlled by the viscosity within the membrane. On the other hand, in the vicinity of the phase boundary at high temperature, thickness fluctuations become faster without changing the mode amplitude.     

Infrared dielectric mirrors based on thin film multilayers of polystyrene and polyvinylpyrrolidone

Thin film polymer multilayers were prepared by spin coating alternating layers of polystyrene and polyvinylpyrrolidone. Samples with 10, 20, 30, 40, and 50 layers were prepared with individual layer thickness values in the range 223–508 nm. These samples were measured using a Fourier transform infrared spectrometer and were found to display narrow photonic band gaps (～ 0.04 to 0.06 μm wide) in their spectral response over the wavelength range 1.6 ? 2.6 μm. The position of the photonic band gaps was controlled by varying the thickness of the individual layers within the multilayer structures. This was achieved by varying the spin speed used during the deposition of the polymer layers. The peak reflectance of the multilayers was controlled by varying the number of layers within the multilayer samples giving values in the range 20–80% (corresponding to transmittances of 80–20%). Calculated transmittance spectra were also obtained using an optical transfer matrix method. These calculated spectra were shown to be in good agreement with the experimental data obtained. These experiments demonstrate a facile approach to the production of low cost dielectric mirrors that have tailored photonic properties over a range of wavelengths that are currently important for applications in fibre optic based telecommunications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

DNA‐backbone radio resistivity induced by spin blockade effect

Coherent control of OH‐free radicals interacting with the spin‐triplet state of a DNA molecule is investigated. A model Hamiltonian for molecular spin singlet‐triplet resonance is developed. We illustrate that the spin‐triplet state in DNA molecules can be efficiently populated, as the spin‐injection rate can be tuned to be orders of magnitudes greater than the decay rate due to small spin‐orbit coupling in organic molecules. Owing to the nano‐second life‐time of OH free radicals, a non‐equilibrium free energy barrier induced by the injected spin triplet state that lasts approximately longer than one‐micro second in room temperature can efficiently block the initial Hydrogen abstraction and DNA damage. For a direct demonstration of the spin‐blockade effect, a molecular simulation based on an ab‐initio Car‐Parrinello molecular dynamics is deployed. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010