By using the gas-evaporation technique with an induction heating method, Zn nanoparticles coated with ZnO were prepared in Ar. The Raman spectra of the Zn/ZnO nanoparticles were studied over a wide range from room temperature through liquid nitrogen temperature and up to 873 K. With heating in air, the transformations from the surface phonon mode to bulk vibrational mode in Zn/ZnO were successfully observed for the Γrst time. 1998 ( John Wiley & Sons, Ltd.
Nanoparticles have many unique physical and chemical properties that bulk materials may not possess because of the quantum-conΓnement e β ects and surface e β ects.1h5 Nanoparticles have large surface-to-volume ratios. The states of the surface atoms play a key role in determining the properties of the nanometer-sized materials. The crystalline lattice spacing in nanoparticles, for example, can be altered by surface relaxation, stress or strain. It is now well established that for the case of real crystals, when their dimensions are relatively small, surface modes and e β ects of the dimensions will also manifest themselves in addition to the normal modes of the inΓnite lattice. When the dimensions become extremely small, only the surface modes persist. Raman scattering is one of the most important methods for obtaining information on phonons in nanometersized materials.6h10 Using the Raman scattering technique, Hayashi and Kanamori8 Γrst demonstrated that, for GaP microcrystals, a surface phonon mode appears between the TO and LO phonons. Metallic nanoparticles, prepared by the gas-evaporation technique in an inert gas, are always covered with an oxide layer during the preparation process or after being exposed to air owing to their reactivity. In a previous paper,10 we measured the Raman spectra in Zn/ZnO nanoparticles (Zn particles coated with ZnO) and found the surface phonon mode within the ZnO coating. No bulk ZnO modes were observed. In this work, we investigated the temperature dependence of the Raman spectra in Zn/ZnO nanoparticles.
By using the evaporation technique with an induction heating method, Γne Zn particles, with an average size of 80 nm, were prepared in argon at reduced pressure. X-ray di β raction and x-ray photoelectron spectroscopy proved that the particle is composed of a Zn core and a