The effective heat of formation (pH') concept allows heats of formation to be calculated as a function of concentration. In this work the effective heat of formation rule is used to predict first phase formation in metal-aluminum thin-film systems and to predict subsequent phase sequence for thin metal films on thick aluminum or thin aluminum on thick metal substrates. The effective concentration at the growth interface is taken to be that of the lowest temperature eutectic (liquidus) for the binary system. Although the effective heat of formation rule may predict that formation of a certain phase would lead to the largest free energy change, this phase does not necessarily form at the moving reaction interface if it has difficulty to nucleate. By excluding phases with a large number of atoms per unit cell and which thus have difficulty to nucleate, the effective heat of formation rule successfully predicts first phase aluminide formation for all 15 metal-aluminum binary systems for which experimental data could be found. It is also shown how the effective heat of formation rule can be used to predict formation and decomposition of aluminide phases in contact with each other or in contact with their component metals.

No abstract

No abstract

Articles you may be interested inComparative analysis of electronic structure and optical properties of crystalline and amorphous silicon nitrides

Temperature-dependent measurements of the photoluminescence ͑PL͒ intensity, PL lifetime, and infrared photocurrent, were performed on an erbium-implanted silicon p -n junction in order to investigate the energy transfer processes between the silicon electronic system and the Er 4 f energy levels. The device features excellent light trapping properties due to a textured front surface and a highly reflective rear surface. The PL intensity and PL lifetime measurements show weak temperature quenching of the erbium intra-4 f transition at 1.535 m for temperatures up to 150 K, attributed to Auger energy transfer to free carriers. For higher temperatures, much stronger quenching is observed, which is attributed to an energy backtransfer process, in which Er deexcites by generation of a bound exciton at an Er-related trap. Dissociation of this exciton leads to the generation of electron-hole pairs that can be collected as a photocurrent. In addition, nonradiative recombination takes place at the trap. It is shown for the first time that all temperature-dependent data for PL intensity, PL lifetime, and photocurrent can be described using a single model. By fitting all temperature-dependent data simultaneously, we are able to extract the numerical values of the parameters that determine the ͑temperature-dependent͒ energy transfer rates in erbium-doped silicon. While the external quantum efficiency of the photocurrent generation process is small (1.8ϫ10 Ϫ6 ) due to the small erbium absorption cross section and the low erbium concentration, the conversion of Er excitations into free e -h pairs occurs with an efficiency of 70% at room temperature.