Effects of calcination treatment on samples of mono-metallic Pd and Pd77-Ag23 alloy with primary particles around 8 nm were studied with the temperature-programmed reduction technique. Temperature profiles of hydrogen consumption for calcined samples from a stream of 10% H2 in N2 were monitored by a thermal conductivity detector. Two distinct peaks, i.e., a consumption of hydrogen for PdO reduction and a subsequent desorption of hydrogen from bulk palladium hydride, were observed. The extent of palladium oxidation upon calcinations increased with the temperature of calcination (T o):  i.e., chemisorption of oxygen on particle surface upon calcination at T o < 373 K, reconstruction into a surface PdO structure at 473 K and incorporation into sublayers to form bulk PdO structure at high T o. Minimum temperature (T r) required for reduction of oxidized palladium by the hydrogen stream was generally low (150 K < T r < 320 K) and increased with the extent of oxidation. A quantitative measurement of hydrogen desorbed from reduced samples suggested a formation of alloy phase in freshly prepared Ag77−Pd23 primary particles. The freshly prepared alloy was inhomogeneous in composition but became homogeneous upon calcination at T o > 673 K.

In this paper, combining low deposition rate with proper growth temperature, we have developed a way to prepare very low-density quantum dots (QDs) suited for the study of single QD properties without resorting to submicron lithography. Experiment results demonstrate that InAs desorption is significant during growing the low density QDs. Ripening of InAs QDs is clearly observed during the post-growth annealing. Photoluminescence spectroscopy reveals that the emission wavelength of low density InAs QDs arrives at 1332.4 nm with a GaAs capping layer.