SPECIFIC-HEAT STUDY OF NANOCRYSTALLINE PALLADIUM

We have performed measurements of the low-temperature specific heat for T = 0.7-20 K and magnetic susceptibility for T = 1.8-300 K of Pd nanocrystals with average particle size 84 Angstrom. An enhancement of the specific heat is observed at temperatures T > 3.5 K for 84-Angstrom Pd nanocrystals. This enhancement is primarily related to the softening of and the size effect on the phonons. The temperature coefficient of specific heat gamma decreases to a lower value as compared to that of bulk Pd. An estimated surface coefficient of specific heat gamma(s) is about 30% that of the bulk. This is also reflected in a reduction of the magnetic susceptibility of the Pd nanocrystals. The peak of the magnetic susceptibility observed at similar to 80 K in bulk Pd is not observed in the nanocrystals; this could be due to a change of the energy band structure in the Pd nanocrystals.