Lide Zhang

Luminescence of nanometer‐sized amorphous silicon nitride solids

The energy levels of defect states in nanometer‐sized amorphous silicon nitride solids were systematically studied in terms of ultraviolet emission spectra. Six emission bands were observed, corresponding to 3.2, 2.8, 2.7, 2.4, 2.3, and 2.0 eV, respectively. With increasing the heat‐treated temperature from room temperature to 1000 °C in low vacuum, these emission bands became high. For the specimen heated at 1000 °C, a new emission band of 3.0 eV appeared. The appearance of these emission bands is closely related to the formation of the energy levels of the defect states in the energy gap. The origin of these emission bands are discussed in detail.

Size Effects on Structure and Raman Spectra of BaTiO3 Thin Films

To study the size effects in ferroelectric thin films, we investigated the crystal structure and Raman spectra of BaTiO 3 thin films deposited by rf magnetron sputtering technique. The results indicated that the characteristic of tetragonal phase disappears for thin films with an average size below 55 nm. The lattice parameters and the frequencies of Raman bands strongly depend on grain sizes of the thin films and monotonously increase with decreasing grain size. The possible origin for the size effects is discussed.

Fluorescence associated with Fe3+ ions in nanostructured Al2O3

The fluorescence phenomena of nanostructured Al2O3 without doping and after doping of nano‐Fe2O3 (4.61 and 48.01 wt %) were systematically investigated. The results show that a new fluorescence band with a peak position of about 17 500 cm−1 occurs for boehmite, η‐Al2O3 and γ‐Al2O3 and it disappears for α‐Al2O3. This band can be attributed to fluorescence of Fe3+ in the systems with low‐order degree (boehmite, η‐ and γ‐Al2O3 and interfaces), which arises from 6A1→4T1 d5 electron transitions of Fe3+.

Study of dangling bonds in nanometer‐sized granulet silicon nitride by electron‐spin resonance

The dangling bonds in pellets made by compacting nanometer‐sized silicon nitride (NASN) grains are studied by electron‐spin resonance (ESR). The ESR results of NASN show that the number of dangling bonds in NASN is about three orders of magnitude higher than that of coarse‐grained silicon nitride. It is also observed that compaction pressure and thermal treatment temperature affect the type and the number of dangling bonds. An explanation is presented for the changes in the dangling bonds caused by the processes of compaction and thermal treatment.

Internal friction and modulus of nano‐ZrO2 solids

The internal friction (IF) and elastic modulus were measured for bulk samples of nano‐ZrO2 from −200 °C to room temperature. An IF peak located on a high background was found for as‐compacted bulk nano‐ZrO2. At the same time, a large modulus defect appeared. After annealing, the IF background decreased substantially and both the IF peak and the modulus defect disappeared. When the sample was heat treated according to the schedule 700 °C/15 h+900 °C/21 h+1100 °C/18 h, the modulus jumped a factor of 2 comparison with the modulus of an as‐compacted sample. The modulus of as‐compacted nano‐ZrO2 was higher than that of coarse‐grained ZrO2 at low temperature. The origin of the IF peak is associated with the atomic relaxation in boundaries. The dramatic increase of the modulus for the annealed nano‐ZrO2 is mainly induced by the enhancement of the binding force and the decrease of the mobility of atoms and bonds in boundaries.