Use of luminescent gold compounds in the design of thin-film oxygen sensors

The use of two gold compounds incorporated into thin plastic films as luminescence quenching oxygen sensors is described. The films are sensitive both to gaseous oxygen and to oxygen dissolved in nonaqueous media such as ethanol. The luminescence quenching of these sensors by oxygen obeys the Stern-Volmer equation and Stern-Volmer constants of 5.35 x 10(-3) and 0.9 x 10(-3) Torr(-1) are found, respectively, for the two dyes in a polystyrene polymer matrix. The sensitivity of the films is strongly influenced by the nature of the polymer matrix, and greatest sensitivity was found in systems based an the polymers polystyrene or cellulose acetate butyrate. Sensitivity was not found to be temperature dependent though raising the temperature hom 15 to 50 degrees C did result in a slight decrease in emission intensity and a hypsochromic shift in the emission wavelength. The rate of response and recovery of the sensors can be increased either by decreasing film thickness or by increasing the operating temperature. The operational and storage stability of these films is generally good though exposure to light should be avoided as one of the dyes tends to undergo photobleaching probably due to a photoinduced ligand substitution reaction.

FLUORESCENCE PLASTIC THIN-FILM SENSOR FOR CARBON-DIOXIDE

The method of preparation of a novel plastic thin-film sensor that incorporates the fluorescent dye 8-hydroxypryrene-1,3,6-trisulfonic acid is described; the shelf-life of the film is over 6 months. The results of a study on the equilibrium response of the sensor towards different levels of gaseous CO2 fit a model there is a 1 + 1 equilibrium reaction between the deprotonated form of the dye (present in the film as an ion pair) and the concentration of gaseous CO2 present. In contrast to the situation in aqueous solution, in the plastic film the pK(a) of the excited form of the dye appears close to that of the ground-state form, although this does not interfere with its use as 8 CO2 sensor. The 0 to 90% response and recovery times of the film when exposed to an alternating atmosphere of air and 5% CO2 are typically 4.3 and 7.1 s, respectively.

Use of a random phase plate as a KrF laser beam homogenizer for thin film deposition applications

Fabrication of devices based on thin film structures deposited using the pulsed laser deposition technique relies on reproducibility and control of deposition rates over substrate areas as large as possible. Here we present an application of the random phase plate technique to smooth and homogenize the intensity distribution of a KrF laser footprint on the surface of a target which is to be ablated. It is demonstrated that intensity distributions over millimeter-sized spots on the target can be made insensitive to the typical changes that occur in the near-field intensity distribution of the ultraviolet output from a KrF laser. (C) 1999 American Institute of Physics. [S0034-6748(99)02504-6].

Simulations of magnetic microstructure in thin film elements used for programmable motion of magnetic particles

The results of two-dimensional micromagnetic modeling of magnetization patterns in Permalloy ellipses under the influence of rotating constant-amplitude magnetic fields are discussed. Ellipses of two different lateral sizes have been studied, 0.5m x 1.5m and 1m x 3m. The amplitude of the rotating magnetic field was varied between simulations with the condition that it must be large enough to saturate or nearly saturate the ellipse with the field applied along the long axis of the ellipse. For the smaller ellipse size it is found that the magnetization pattern forms an S state and the direction of the net magnetization lags behind the direction of the applied field. At a critical angle of the rotating magnetic field the direction of the magnetization switches by a large angle to a new S state. Both the critical angle and the angle interval of the switch depend on field amplitude. For this new state, it is instead the applied field direction that lags behind the magnetization direction. The transient magnetization patterns correspond to multi-domain patterns including two vortices, but this state never exists for the equilibrated magnetization patterns. The behavior of the larger ellipse in rotating field is different. With the field applied along the long-axis of the ellipse, the magnetization of the ellipse is nearly saturated with a vortex close to each apex of the ellipse. As the field is rotated, this magnetization pattern remains and the net-magnetization direction lags behind the direction of the field until for a certain angle of the applied field an equilibrium multi-domain state is created. Comparisons are made with corresponding experimental results obtained by performing in-field magnetic force microscopy on Permalloy ellipses.

Unusual photoresponse of indium doped ZnO/organic thin film heterojunction

Photoresponse of n-type indium-doped ZnO and a p-type polymer (PEDOT:PSS) heterojunction devices are studied, juxtaposed with the photoluminescence of the In-ZnO samples. In addition to the expected photoresponse in the ultraviolet, the heterojunctions exhibit significant photoresponse to the visible (532 nm). However, neither the doped ZnO nor PEDOT: PSS individually show any photoresponse to visible light. The sub-bandgap photoresponse of the heterojunction originates from visible photon mediated e-h generation between the In-ZnO valence band and localized states lying within the band gap. Though increased doping of In-ZnO has limited effect on the photoluminescence, it significantly diminishes the photoresponse. The study indicates that optimally doped devices are promising for the detection of wavelengths in selected windows in the visible. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704655]

Influence of test methodology and probe geometry on nanoscale fatigue mechanisms of diamond-like carbon thin film

The aim of this paper is to investigate the mechanism of nanoscale fatigue using nano-impact and multiple-loading cycle nanoindentation tests, and compare it to previously reported findings of nanoscale fatigue using integrated stiffness and depth sensing approach. Two different film loading mechanism, loading history and indenter shapes are compared to comprehend the influence of test methodology on the nanoscale fatigue failure mechanisms of DLC film. An amorphous 100 nm thick DLC film was deposited on a 500 μm silicon substrate using sputtering of graphite target in pure argon atmosphere. Nano-impact and multiple-load cycle indentations were performed in the load range of 100 μN to 1000 μN and 0.1 mN to 100 mN, respectively. Both test types were conducted using conical and Berkovich indenters. Results indicate that for the case of conical indenter, the combination of nano-impact and multiple-loading cycle nanoindentation tests provide information on the life and failure mechanism of DLC film, which is comparable to the previously reported findings using the integrated stiffness and depth sensing approach. However, the comparison of results is sensitive to the applied load, loading mechanism, test-type and probe geometry. The loading mechanism and load history is therefore critical which also leads to two different definitions of film failure. The choice of exact test methodology, load and probe geometry should therefore be dictated by the in-service tribological conditions, and where necessary both test methodologies can be used to provide better insights of failure mechanism. Molecular dynamics (MD) simulations of the elastic response of nanoindentation is reported, which indicates that the elastic modulus of the film measured using MD simulation was higher than that experimentally measured. This difference is attributed to the factors related to the presence of material defects, crystal structure, residual stress, indenter geometry and loading/unloading rate differences between the MD and experimental results.

Development of a doped titania immobilised thin film multi tubular photoreactor

This paper describes a novel doped titania immobilised thin film multi tubular photoreactor which has been developed for use with liquid, vapour or gas phase media. In designing photocatalytic reactors measuring active surface area of photocatalyst within the unit is one of the critical design parameters. This dictate greatly limits the applicability of any semi-conductor photocatalyst in industrial applications, as a large surface area equates to a powder catalyst. This demonstration of a thin film coating, doped with a rare earth element, novel photoreactor design produces a photocatalytic degradation of a model pollutant (methyl orange) which displayed a comparable degradation achieved with P25 TiO2. The use of lanthanide doping is reported here in the titania sol gel as it is thought to increase the electron hole separation therefore widening the potential useful wavelengths within the electromagnetic spectrum. Increasing doping from 0.5% to 1.0% increased photocatalytic degradation by ∼17% under visible irradiation. A linear relationship has been seen between increasing reactor volume and degradation which would not normally be observed in a typical suspended reactor system. © 2012 Elsevier B.V.

Solutions of fourth-order parabolic equation modeling thin film growth

In this paper we study the well-posedness for a fourth-order parabolic equation modeling epitaxial thin film growth. Using Kato's Method [1], [2] and [3] we establish existence, uniqueness and regularity of the solution to the model, in suitable spaces, namelyC⁰([0,T];L^p(Ω)) where  with 1<α<2, n∈N and n≥2. We also show the global existence solution to the nonlinear parabolic equations for small initial data. Our main tools are L_p–L_q-estimates, regularization property of the linear part of e^−tΔ2 and successive approximations. Furthermore, we illustrate the qualitative behavior of the approximate solution through some numerical simulations. The approximate solutions exhibit some favorable absorption properties of the model, which highlight the stabilizing effect of our specific formulation of the source term associated with the upward hopping of atoms. Consequently, the solutions describe well some experimentally observed phenomena, which characterize the growth of thin film such as grain coarsening, island formation and thickness growth.

Epitaxially Grown Strained Pentacene Thin Film on Graphene Membrane

Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investigate thin-film epitaxial behaviors. Using transmission electron microscopy, two distinct molecular packing structures of pentacene on graphene are found. One observed packing structure is similar to the well-known bulk-phase, which adapts a face-on molecular orientation on graphene substrate. On the other hand, a rare polymorph of pentacene crystal, which shows significant strain along the c-axis, is identified. In particular, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene. Through ab initio electronic structure calculations, including van der Waals interactions, the unusual polymorph is attributed to the strong graphene-pentacene interaction. The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions.

Electrode field penetration: A new interpretation of tunneling currents in barium strontium titanate (BST) thin films

This paper shows that penetration of the applied electric field into the electrodes of a ferroelectric thin film capacitor produces both an interfacial capacitance and an effective mechanism for electron tunneling. The model predictions are compared with experimental results on Au-BST-SrRuO3 capacitors of varying thicknesses, and the agreement is excellent.

Optical transmission properties and electric field distribution of interacting 2D silver nanorod Arrays

Silver nanorods have been grown by electrodeposition into thin film porous alumina templates (AAO). Optical transmission measurements using p-polarized incident white light shows clear plasmon resonance extinction peaks. We successfully model the dependence on angle in incidence of extinction peak height and position using a multiple-multipoles (MMP) approach with the different spectral features being clearly associated with the effective electric field distribution and coupling between individual nanorods.

Fluorescence-based thin plastic film ion-pair sensors for oxygen

A general method of preparation of thin-film sensors for O-2, incorporating the dye ion-pair tris(4,7-diphenyl-1,10-phenanthroline) rutheninm(II) ditetraphenylborate, in a variety of different thin film polymer/plasticizer matrices is described, The sensitivity of the sensor depends upon the nature of the polymer matrix and plasticizer, A detailed study of one of these systems utilising the polymer poly(methyl methacrylate), PMMA, is reported. The sensitivity of this O-2 sensor depends markedly upon the plasticizer concentration and is largely independent of temperature (24,5-52.5 degrees C) and age (up to 30 d), When exposed to an alternating atmosphere of O-2 and N-2, a typical oxygen film sensor in PMMA exhibits a 0-90% response and recovery time of 0.4 and 4.5 s, respectively.