Ising film

Fig. 50. Magnetization profiles across thin Ising films [eq. (1) with H — H — 0], upper part, and near the surface of semi-infinite Heisenberg ferromagnels, lower part (where bulk behavior in the Monte Carlo simulation is enforced by an effective field boundary condition at z — 16). Note that in the Ising case (where three film thicknesses L = 5, 10, and 20 are shown) the surface layer magnetization m- — m(z — 0) is independent of L, and for L > 10 already the bulk value of the order parameter is reached in the center of the film. For the Heisenberg model, on the other hand, at a comparable temperature distance from % the free surface produces a Long-range perturbation of the local magnetization m(z). From Binder and Hohenbcrg (1974).

D. P. Binder, K. Landau and A. M. Ferrenberg, Character of the phase transition in thin Ising films with competing walls, Phys. Rev. Lett., 74, 298-301 (1995]. 

K. Binder, Monte-Carlo study of thin magnetic Ising films. Thin Sol. Films 20 (1974) 367-381. 

F. Schilbe, S. Siebentritt, K.-H. Rieder, Monte Carlo calculations on the dimensional crossover of thin Ising films, Rhys. Lett. A 216 (1996) 20-25. 

Despite the fact that a great lot of ion-selective electrodes (ISEs) with liquid and film polymeric membranes for the determination of physiologically active amines (PhAA) has been described, the factors responsible for their selectivity have not yet been studied sufficiently. In this work, the influence of plasticizer and ion-exchanger nature on the selectivity of ISEs reversible to PhAA cations of various stmctures has been discussed. 

The history of ion-selective electrodes (ISEs) [1] starts from the discovery of the pH response of thin film glass membranes by Cremer in 1906, thus making ISEs the oldest class of chemical sensors. They still are superior over other sensor types in a variety... 

A Selectrode with a plastic film [41, 145] has also been constructed. The membrane does not directly touch the graphite rod, but is separated by a layer consisting of saturated KCl, mercury and calomel (with valinomycin K ISE). 

The function of an immuno-electrode [28] containing a model antibody (Concanavalin A) fixed in a polymeric film on a platinum electrode is probably based on other effects than those utilized in ISEs. Immuno-electrodes suitable for direct determination of antibodies were prepared by fixing a conjugate of an ionophore and an immunogen (for example the compound of dibenzo-18-crown-6 with dinitrophenol) in a PVC membrane. This system responded to the antibody against dinitrophenol [52, 53]. 

We refer here only to the synthesis of 2D titania nanostruetured films, because several aspects regarding the synthesis of Ti02 ID nanostruetures (nano-tubes, -rods, -wires, etc.) were discussed in part l. ° In addition, this section will not provide a systematic analysis of the methodologies of synthesis of these materials, or of their charaeteristies, beeause only selected aspects relevant for the objective of diseussion on their use as catalysts will be analyzed. A number of reviews were published recently on Ti02 nanotubes ss.es.ise under-... 

Nitrilotriacetate was used as complexant in the deposition in Ref. 55. Cu-Se could be both electrodeposited and chemically deposited from this solution. The electrodeposited film was Cui.sSe with the berzelianite structure, while the CD one was Cui.iSe with the umangite structure. The XRD pattern of the CD films showed sharp peaks (instrument broadening) with no preferential texture. Electron microscopy of these films (Fig. 6.2) shows large (micron scale) particles that, from their faceted shape and together with the sharp XRD peaks, appear to be single crystals. This is a particularly large crystal size for a CD film from this and... 

A nitrate-selective potentiometric MIP chemosensor has been devised [197, 198]. For preparation of this chemosensor, a polypyrrole film was deposited by pyrrole electropolymerization on a glassy carbon electrode (GCE) in aqueous solution of the nitrate template. Potentiostatic conditions of electropolymerization used were optimized for enhanced affinity of the resulting MIP film towards this template. In effect, selectivity of the chemosensor towards nitrate was much higher than that to the interfering perchlorate ( o3 cio4 = 5.7 x 10-2) or iodide ( N03, r = x 10 2) anion. Moreover, with the use of this MIP chemosensor the selectivity of the nitrate detection has been improved, as compared to those of commercial ISEs, by four orders of magnitude at the linear concentration range of 50 pM to 0.5 M and LOD for nitrate of (20 10) pM [197]. 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

Pb2+, Cd2+, Zn2+, Fe3+ 12 Chalcogenide ISEs Solid-state thin-film sensors — [96]... 

The scope of ion-selective electrodes (ISEs) has been greatly enhanced by employing a poly(vinyl chloride) matrix to entangle sensor cocktail materials. Fbr ISFET devices an in situ photopolymerisation of monobutyl methacrylate provides a viable poly(butyl methacrylate) calcium sensor film with good gate adhesion properties. One or more enzymes can be chemically immobilized on modified nylon mesh. The resultant matrices are suitable for the amperometric assay of carbohydrates in blood and food products. 

The fluid nature of PTC cocktails allows them to conform to the shape of a surface. Consequently, on evaporation of the tetrahydro-furan the PTC sensor film is left as a particular contour. This has allowed improved designs of ISEs, e.g., coated wires/epoxy, tubular flow-through, micro and all solid-state epoxy models. Thus, a lithiun sensor cast on top of a small epoxy base in a flow injection system is suitable for the assay of lithium in the saliva of manic depressive patients (Beswick,C.W., MDody,G.J., Thomas,J.D.R., diversity of Wales College of Cardiff, unpublished data). 

The incorporation of vitamin B12 derivatives into plasticized poly(vinyl chloride) membranes has resulted in the development of several ion-selective electrodes (ISEs). The response of the electrodes has been related to principles of molecular recognition chemistry. In addition, ISEs have been prepared by electropolymerization of a cobalt porphyrin. These electrodes have selectivity properties that are controlled by both the intrinsic selectivity of the metalloporphyrin and the characteristics of the polymer film (e.g., pore size). 

In this paper, we report the development of ISEs that have been designed by using molecular recognition principles. Specific examples include the development of polymer membrane anion-selective electrodes based on hydrophobic vitamin B12 derivatives and a cobalt porphyrin. The selectivity patterns observed with these electrodes can be related to differences in the structure of the various ionophores, and to properties of the polymer film. 

The potentiometric behavior of electrodes based on these films was studied (Figure 8). These ISEs presented sub-Nemstian slopes for thiocyanate (from -40 to -53 mV/decade, depending on the buffer used), and had detection limits of 5xl0 7 M. The response time of the electrodes was typically less than 25 s. The selectivity pattern observed was thiocyanate > perchlorate > iodide > nitrite - salicylate bromide > chloride > bicarbonate > phosphate. This anion-selectivity behavior does not follow the Hofmeister series, with thiocyanate and nitrite being the ions that deviate the most from it. This indicates that there is a selective interaction of the immobilized porphyrin with the two anions. 

Figure 8. Selectivity pattern of an ISE based on an electropolymerized cobalt porphyrin film. The electrode was exposed to the following anions thiocyanate (1), perchlorate (2), iodide (3), nitrite (4), salicylate (5), bromide (6), chloride (7), bicarbonate (8), phosphate (9). The baseline potential was 364 mV. (Adapted from ref. 26.)...

In summary, it has been demonstrated that ISEs can be designed by employing molecular recognition principles. In particular, the feasibility of using hydrophobic vitamin B12 derivatives and electropolymerized porphyrin films in the development of polymer membrane anion-selective electrodes has been demonstrated. The studies indicated that the changes in the selectivity of these ISEs can be explained by the difference in structure of the ionophores. In addition, it was shown that by electropolymerization of a cobalt porphyrin, anion-selective electrodes can be prepared that have extended lifetimes compared with PVC-based ISEs, which use a similar compound as the ionophore. 

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