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- Author or Editor: L. Niinistö x
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Abstract
Processing thin films for advanced applications, for instance in electronics and optoelectronics, involves several steps starting from precursor synthesis and ending up with the devices. Especially when optimizing the first steps of this chain of processes, thermoanalytical techniques play an important role. The review will focus on the main chemical deposition methods (CVD, ALE, spray pyrolysis, sol-gel) giving selected examples of problem-solving by thermal analysis. The techniques discussed are TG, DTA/DSC, EGA and their combinations. High-temperature X-ray diffraction (HTXRD) is also a powerful tool for in situ studies of thin films. The examples are taken from solar cell, superconductor and flat panel electroluminescent display technologies.
The thermal decomposition of rare earth oxysulfides (excluding Sc, Ce and Pm) has been studied in air. The oxysulfides are oxidized to oxysulfates between 600 and 900ℴ and the oxysulfate phase, which is unstable at higher temperatures, decomposes to oxide. The stability of the oxysulfate and its decomposition temperature decreases with decreasing radius of the rare earth ion. For the heavier rare earths the oxidation to oxysulfate takes place only partially before the decomposition to oxide begins.
The thermal behaviour ofγ-sulfur, monoclinicα-Se, S6Se2, S5Se3, S4Se4 and S3Se5, has been studied by hot-stage microscopy and differential scanning calorimetry. X-ray diffraction results show that S6Se2 and S5Se3 are isostructural with Sγ, but S4Se4 and S3Se5 are isostructural with monoclinicα-Se. The melting of Sγ, is accompanied by rapid crystallization of Sβ, which often occurs almost simultaneously with melting. The melting of S6Se2, S5Se3, S4S4 and S3Se5 is irreversible as the compounds decompose on melting. For monoclinicα-Se no phase transformation to monoclinicβ Se was observed at 110–120°, but it changes to hexagonalα-Se when the temperature is over 120°.
Abstract
Thermoanalytical (TA) methods are relatively seldom applied for assessing the physical and chemical proeprties of thin films, but they can be used in studies of composition, phase transitions and film—substrate interactions. In the present paper the possibilities of TA methods in thin film studies are reviewed. The thermoanalytical methods considered are the classical TG and DTA/DSC methods but some complementary methods will also be briefly mentioned. The main emphasis is given to true thin films. Details of sample preparation are also given. An important application of TA methods is characterization of precursors for the CVD growth of thin films, and this is also discussed.
Abstract
Four sulphato and nitrato complexes of cerium(IV),viz. (NH4)4Ce(SO4)4·2H2O (1), (NH4)2Ce(SO4)3 (2), (NH4)2Ce(NO3)6 (3) and Cs2Ce(NO3)6 (4) were studied by simultaneous TG/DTA under various experimental conditions in order to establish their decomposition mechanism and to compare the results with the literature data which have been reviewed. In the case of the ammonium compounds (1, 2 and3) the decompositions are accompanied by changes in the oxidation state of cerium; the presence of Ce(III) and Ce(IV) were studied byex situ magnetic susceptibility and XPS measurements. The crystal structure of (1) was determined as well. It forms monoclinic crystals with space groupP21/c; the parameters of the unit cell are:a=12.638(18) Å,b=11.362(10) Å,c=13.607(11) Å, β=110.17(9)°,V=1834.05 Å3.
