On the structured imperfections of bulk GaSb using high resolution transmission electron microscopy

GaSb is a promising III-V direct band gap semiconductor with sphalerite type FCC structure. Its band gap value has made it an excellent candidate for the conversion of infrared radiation to electricity. The wafers of GaSb, that were studied, originated from ingots grown with the Liquid Encapsulated Chochralski method. In all cases, Energy Dispersive X-ray Spectroscopy and Particle Induced X-ray Emission measurements demonstrated an excess of Sb. In the present work conventional transmission electron microscopy (CTEM) and high resolution electron microscopy (HRTEM) were used in order to determine the effect of the Sb excess in the structural characteristics of the material, mainly after thermal treatment. A structure model based on the ordering of the Sb antisites (Sb(Ga)) rather than the Ga vacancies (V(Ga)) is proposed for the observed modulation in small areas of the material.     

The effect of the in-situ sublimation in the growth of HgI2 platelets from vapour

The Quality of HgI₂ platelets grown from the vapour phase has been studied, varying different growth parameters, i.e. starting material, addition of polyethylene, source/crystallisation temperature, in-situ sublimation. It has been found that the in-situ sublimation at high temperature is the essential factor for the production of HgI₂ platelets. This in-situ sublimation was made in the same growth ampoule at temperatures over 200 °C and prior to the growth process. All the other growth parameters studied in this work influenced the quality of the platelets although they did not affect their production. Finally, the grown platelets have been characterised by optical observation and by differential scanning calorimetry.     

Kinetic analysis of the α-β HgI2 phase transition

The kinetics of the α-β phase transition of HgI₂ were investigated by isothermal and non-isothermal differential scanning calorimetry. The effective activation energy of the transition, 415±40 kJ mol^-1, was determined applying the methods of Kissinger and Ozawa. The transition kinetics were described by the Johnson-Mehl-Avrami model and the value of the Avrami exponent n was found to range from high values (n>3) at the early stages to lower values at later stages of the transformation, with an average value of 2. This revised version was published online in August 2006 with corrections to the Cover Date.     

DSC study of the deposition reactions of zinc pack coatings up to 550°C

Zn pack coating formation takes place in three steps as differential scanning calorimetry shows. The initial step (at 193.9°C) is endothermic and involves the transformation of α-NH₄Cl to β-NH₄Cl and the NH₄Cl decomposition to NH₃ and HCl. During the second step (at 248.6°C), which is exothermic, Zn²⁺ salts are formed and most probably ZnCl₂. Finally at 264.1°C (endothermic reaction) it seems that ZnCl2 is decomposed to form Zn that is deposited on the ferrous substrate. The as-cast Zn diffuses in the iron substrate forming the gamma and delta phase of the Fe–Zn phase diagram. Al₂O₃ is not involved in the above-mentioned mechanism and acts only as filler.     

A differential scanning calorimetric study on phase transformations of HgI2

A quantitative study of the different factors that influence the- transformation of mercuric iodide was carried out with differential scanning calorimetry. The transformation temperature and the peak width during the heating of the material were followed. An attempt was made to explain the experimental results.

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Zusammenfassung Mittels Differential-Scanning-Kalorimetrie wurde der Einfluss verschiedener Faktoren auf die- Umwandlung von Quecksilberjodid quantitativ untersucht. Dabei wurde die Umwandlungstemperatur und die Signalbreite beim Erhitzen der Substanz beobachtet. Es wurde ein Versuch unternommen, die experimentellen Ergebnisse zu erklären.

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Characterization and phase transformation study of TlSbSe2 crystals

TlSbSe₂ monocrystals were grown using the modified Bridgman–Stockbarger method and were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Reflectivity spectra have been registered in the range 50 to 4000 cm^–1 for E parallel to a and E parallel to b polarizations, on the cleavage plane. A remarkable anisotropy at two directions was verified. With regard to previous observations, additional peaks were discriminated and the fundamental phonon parameters were determined using classical dispersion relations. The material presents a complex phase transformation – with two thermal effects – that was examined using differential scanning calorimetry (DSC). Non-isothermal measurements, at different heating and cooling rates (β), were used to study the thermal phenomena. The main effect is attributed to a structural displacement and the second one to a cation exchange procedure. The phase transformation temperature depends strongly on the cooling rate and the peaks are shifted by 30 K with the increase of this rate, on the contrary to the increase of the heating rate that has a smaller effect. Phenomena related with the influence of the previous, repeated heating and cooling cycles on the transformation are also examined and analytically discussed.