We have studied structures and properties of nanostructured films prepared with nanometer-sized lithium fluoride (Lif) clusters by inert gas condensation method, and then characterized by transmission electron microsc...We have studied structures and properties of nanostructured films prepared with nanometer-sized lithium fluoride (Lif) clusters by inert gas condensation method, and then characterized by transmission electron microscope, Fourier transform infrared spectra and Raman scattering spectra, etc. Following important results are obtained: Multi-order-like Raman scatterings from LiF clusters are obtained, including the fine structure of the spectra. The observed Raman peaks are discussed in terms of surface optical modes, LO, TO, LA modes and their combination form. As the cluster size decreases, the phonons are confined in nanoscale so that the q vector selection rule is relaxed or even totally free of q conservation, and prohibition at the first- and third-order scatterings in the bulk LiF crystal is relaxed. The surface modes appear and play an important role in Raman scattering processes. The infrared absorption spectra are obtained with different deposition conditions. When the clusters are in the medium size range from similar to 7 to 15 nm, most infrared absorption peaks are second-order feature, and no single surface mode emerges. For the smaller clusters, molecular-like vibration is observed whereas the broad band of long wavelength transverse-optical modes appear from 580 to 400 nm(-1) for the clusters larger than 19 nm.展开更多
文摘We have studied structures and properties of nanostructured films prepared with nanometer-sized lithium fluoride (Lif) clusters by inert gas condensation method, and then characterized by transmission electron microscope, Fourier transform infrared spectra and Raman scattering spectra, etc. Following important results are obtained: Multi-order-like Raman scatterings from LiF clusters are obtained, including the fine structure of the spectra. The observed Raman peaks are discussed in terms of surface optical modes, LO, TO, LA modes and their combination form. As the cluster size decreases, the phonons are confined in nanoscale so that the q vector selection rule is relaxed or even totally free of q conservation, and prohibition at the first- and third-order scatterings in the bulk LiF crystal is relaxed. The surface modes appear and play an important role in Raman scattering processes. The infrared absorption spectra are obtained with different deposition conditions. When the clusters are in the medium size range from similar to 7 to 15 nm, most infrared absorption peaks are second-order feature, and no single surface mode emerges. For the smaller clusters, molecular-like vibration is observed whereas the broad band of long wavelength transverse-optical modes appear from 580 to 400 nm(-1) for the clusters larger than 19 nm.
