Abstract
The study of Si nanostructures is a very active field of research because of their strong room temperature photoluminescence. In recent years, a strong red luminescence has been often observed after surface oxidization in air. In this study, Si nanomaterials were prepared by a thermal evaporation system, and four kinds of Si nanomaterials, nanoparticles, nanoclusters, nanoclusters with HF treatment, and nanoclusters with CH3COOH treatment, were studied.The average size and size distribution of Si nanoparticles were determined by XRD and TEM, respectively. From the SEM and AFM images, the spherical aggregation was observed. The surface bonding was be analyzed from the FTIR spectroscopy, and the absorption band gap was examined by UV-visible light spectroscopy.Four parts of PL experiment were conducted. In the first part, the Si nanoparticles showed a strong red light emission in air when the Ar working pressure was less than 1torr. The second experiment was focused on nanoclusters prepared at 0.5 torr Ar, and their surface effect was examined. After the cyclic PL analysis, the characteristic of PL in air was different from that in O2 or N2. The change in PL intensity was not reversible in this cycling. Besides the physisorption (air adsorption), the weak chemisorption (air oxidization) might be the factor to cause this difference. After water treatment, the PL intensity of Si clusters was twice as high as that of untreated clusters. This proves that the adsorption of water could help Si clusters to emit higher PL intensity, which is due to the creation of a new set of recombination traps confined in the clusters. From the aging experiment, it could be concluded that the samples were naturally oxidized after exposure to air and this oxidization might enhance the intensity. By changing the laser power, the relationship between the magnitude of laser power and the level of oxidization of Si nanoclusters was established.The third part of experiment was to remove the surface oxide SiOx by etching with HF and to study the influence of air oxidization on the PL properties. After the HF solution treatment, the PL showed a blue shift caused by the core of Si nanoparticles. However, after air exposure, the PL slowed a red shift and the intensity was increased, implying that the air oxidization played an important role in PL. Finally, after the CH3COOH solution treatment, the intensity of PL increased due to the stronger Si-O bond on the surface of Si nanoclusters.