The role of wetting layer states on the emission efficiency of InAs/InGaAs metamorphic quantum dot nanostructures.

We report on a photoluminescence and photoreflectance study of metamorphic InAs/InGaAs quantum dot strain-engineered structures with and without additional InAlAs barriers intended to limit the carrier escape from the embedded quantum dots. From: (1) the substantial correspondence of the activation energies for thermal quenching of photoluminescence and the differences between wetting layer and quantum dot transition energies and (2) the unique capability of photoreflectance of assessing the confined nature of the escape states, we confidently identify the wetting layer states as the final ones of the process of carrier thermal escape from quantum dots, which is responsible for the photoluminescence quenching. Consistently, by studying structures with additional InAlAs barriers, we show that a significant reduction of the photoluminescence quenching can be obtained by the increase of the energy separation between wetting layers and quantum dot states that results from the insertion of enhanced barriers. These results provide useful indications on the light emission quenching in metamorphic quantum dot strain-engineered structures; such indications allow us to obtain light emission at room temperature in the 1.55 microm range and beyond by quantum dot nanostructures grown on GaAs substrates.

Disintegrating force as a new formulation parameter.

Some coated aspirin tablet formulations were evaluated by relating their properties to disintegrating force development patterns. The treatment of disintegrating force-time curves was effected using the Weibull distribution as proposed for dissolution. Such parameters as the maximum disintegrating force developed, the time needed to reach 63.2% maximum disintegrating force (tau d) the shape parameter, the lag time, and the input value were used for evaluating the formulas examined. It was concluded that the input values, the integrating force development rate at tau d, can be employed as a new formulation parameter since, when correlated with the crushing strength, it allows an overall evaluation of the formula examined.