This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

Transparent conductors—A status review

Spray pyrolysis has been applied to deposit a wide variety of thin films. These films were used in various devices such as solar cells, sensors, and solid oxide fuel cells. It is observed that often the properties of deposited thin films depend on the preparation conditions. An extensive review of the effects of spray parameters on film quality is given to demonstrate the importance of the process of optimization. The substrate surface temperature is the most critical parameter as it influences film roughness, cracking, crystallinity, etc. Processes involved in the spray pyrolysis technique are discussed in this review as well.

/pdf/thin-film-deposition-using-spray-pyrolysis-1mpmpe8sum.pdf

Thin film deposition using spray pyrolysis

Semiconductor gas sensors

A critical review of thin-film semiconducting materials that are used as gas sensors is presented in this paper. These materials can be approximately divided into two main groups: the first includes sensors that detect oxygen with variations of bulk or surface conductance; the second comprises all the materials that detect oxidizing and reducing gases in air at constant oxygen partial are described. The long-term stability and the selectivity to a particular species are the main properties of a reliable gas sensor; these properties are also discussed in detail in relation to the second group of sensors. The properties of tin oxide, the most investigated material for gas sensing, are reviewed; some new ternary semiconducting compounds are also presented, together with their growth techniques. An almost novel method for growing thin films, the RGTO (rheotaxial growth and thermal oxidation) technique will be presented, since it is capable of preparing mixed oxide thin fimms with high surface area and nanosized crystallites. It is well known that the main possibility for sensor development lies in device arrays; therefore, the utilization of different materials for gas detection and the measurement techniques of signals supplied by sensor arrays will be outlined.

Recent developments in semiconducting thin-film gas sensors

The oxidation of reactive gases at the surface of a semiconducting metal oxide is accompanied by a change in the electrical conductance. The effect was first used to detect gaseous components in air by Seiyama in 1964. In the meantime, numerous materials have been studied in attempts to optimize this effect, and at this time tin oxide seems to be a material with favorable properties. The very simple mounting of a detector on this base is a great advantage. But unfortunately some disadvantages still prevent the common application of this effect for the exact measurement of gases. One of them is the long time the detector needs to tend to the 90 % value and to regenerate. Using the method of spray pyrolysis, we prepared thin film SnO2 sensors which in contact with gas tend to the 90 % value within 30 ms and regenerate in less than 10 s.

https://iopscience.iop.org/article/10.1143/JJAP.19.513/pdf

Preparation of Fast Detecting SnO2 Gas Sensors

Solid state gas sensors based on thin films of SnO2 can be very sensitive to small amounts of hazardous gases like hydrocarbons and carbonmonoxide. There are two models to explain the observed change in conductance, when the sensors are exposed to the gases: (1) Adsorption of the gas molecule at the surface and electron transfer from the gas molecule to the SnO2 or (2) adsorption of the gas followed by a reaction of the gas with previously adsorbed oxygen. The conductivity change is caused by the released electron which was captured by the oxygen during its adsorption. Experiments were carried out which support the second model. In order to get a stable gas sensor it is necessary to keep the surface of the SnO2 thin film in such a condition that the oxygen adsorption/desorption process can operate for a long time.

https://iopscience.iop.org/article/10.7567/JJAPS.19S1.513/pdf

Operation and Stability of SnO2Gas Sensors

Herstellung von lichtleitfasern nach einem fluessigphasen-abscheidungsverfahren

The range of transferred hyperfine interactions in EuS

A method of producing a light conducting fiber by providing a rotating, heatable crucible having a cylindrical interior wall, successively depositing optical material forming layers from a liquid phase with the first layer being deposited on the interior wall of the rotating crucible and subsequent layers being deposited on a previous deposited layers, transforming each layer into a film of optical material to form a workpiece having a plurality of concentric cylindrical films of optical materials, and subsequently pulling the fiber from the workpiece while it is still in the crucible.

Hans Pink

Papers

Preparation of Fast Detecting SnO2 Gas Sensors

Operation and Stability of SnO2Gas Sensors

Herstellung von lichtleitfasern nach einem fluessigphasen-abscheidungsverfahren

The range of transferred hyperfine interactions in EuS

Method for producing a light conducting fiber