Quanli Hu

Thermoluminescence on polycrystalline AlN after γ and electron irradiation

Abstract The irradiation effect on Aluminum nitride (AlN) (AlN-a (99 wt% AlN +0.9 wt% O), AlN-b (94.9 wt% AlN +4.3 wt% Y 2 O 3 ), AlN-c (59.5 wt% AlN +40% BN)) was studied by thermoluminescence method from the viewpoint of defect production. Two main thermoluminescence peaks were observed around 400 and 600 nm for these samples. For γ irradiation, it was found that the peak position of the thermoluminescence peak around 400 nm varies between 390 and 450 nm at the temperature range from 500 to 873 K for AlN-b and c. It was considered that the varying of the peak position was influenced by the transformation of the two kinds of oxygen-related complex defects. For electron irradiation, the relative intensity of the peak around 400 nm was found to decrease with the increasing dose of electron irradiation.

In-situ luminescence measurement for AlN ceramics under reactor irradiation

Abstract The behavior of luminescence emission of AlN ceramics under reactor and gamma irradiation has been studied with in-situ luminescence and thermoluminescence methods. A broad emission peak (around 370 nm), which had a different position for AlN samples with different oxygen concentration, was found. The intensity of luminescence emission has close relations with reactor power (fast neutron flux) and temperature. Influence on emission behavior from radiation defects (vacancies and interstitials) and intrinsic defects (oxygen-related defect complexes) was discussed.

In Situ Growth of Isotopically Enriched 28Si Nanowires Using the Floating-Zone (FZ) Melting Method

Isotopically enriched 28Si nanowires have been synthesized using a simple and noncontaminating floating-zone (FZ) method. The growth of the nanowires was performed in the top area, 1.5–2 cm from the floating melting zone (2 mm width) of a raw material bar under a flow of Ar gas. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed that the nanowires of isotopically enriched 28Si crystalline had diameters ranging from 20–50 nm. The special shape of the tip of the isotopically enriched 28Si nanowires was observed to reveal the isotopic effect on the growth of nanowires.

Study of radiation defects for AlN ceramics under O+ irradiation

Abstract The behavior of radiation defects in AlN ceramics under O + ion irradiation has been studied with in situ luminescence method. The intensity of luminescence emission had close relationship with absorbed dose. The aggregation of F-type defects in AlN has also been confirmed because of the occurrence of 470 nm emission peak. After O + irradiation, the behavior of F-type defects was investigated by ESR measurement at 77 K. Influence of radiation defects on the characteristics of emission and ESR was discussed.

Low-temperature specific heat of isotopically modified boron single crystals

The measurement of specific heat at low temperature for isotopically modified boron single crystals was performed between 0.5 and 100 K using a calorimetric technique known as the time-constant or relaxation method. The results indicate that the specific heat has obvious divergencies at 1.3 K<T<5 K and the divergencies for four kinds of isotopically modified boron samples vary with different 10B contents. The influence of lattice vibration modes and the isotopic effect on specific heat and thermal conductivity for isotopically modified boron are discussed.

Luminescence in Li2O under ion beam irradiation

Abstract The luminescence emitted under light ion (H + , He + ) irradiation in Li 2 O single crystal has been measured at 313–773 K by an optical multi-channel detector. The temperature and absorbed dose dependences of the luminescence spectrum were investigated. The luminescence emission in Li 2 O induced by both H + and He + ion beam irradiations was observed at about 5.0–1.8 eV. The luminescence intensity decreased with absorbed dose. This effect is associated with the diminution of the concentration of oxygen vacancies and concentration quenching due to the high damage density and stresses in the ion track region. The luminescence intensity of the 2.35 eV band (F-center aggregates) gradually increases with irradiation dose at temperatures below 423 K. Alternatively, the intensities of the luminescence emissions originated from F + (3.3 eV) and F 2 (2.9 eV) centers increase with irradiation dose in the temperature range of 423–573 K. These phenomena are thought to be connected with the efficient temperature for the generation of different radiation defects.

Aggregation of radiation defects in AIN ceramics under He+ ion irradiation

Abstract The aggregation of F-type defects in AIN has been observed for the first time under He+ ion irradiation by using in-situ luminescence measurement. The concentration of aggregation of F-type defects shows a strong dependence on irradiation temperature (300–773 K) under He+ ion irradiation. The mechanism of growth and annihilation of the aggregation of F-type defects was discussed.

Influence of Silicon Dioxide Doping on Morphology of Silicon Nanowires Grown by Floating Zone Method

On the surface of silicon sticks with one end melted, which were doped with different mass percentages of silicon dioxide (x=0, 0.5%, 2%, 6% and 10%), silicon nanowires with different morphologies were synthesized by the floating-zone (FZ) melting method. The change of morphology was studied by scanning electron microscopy (SEM) and field emission SEM (FESEM). All the nanowires have a uniform diameter of about 20 nm when x ≤0.5%, but when x ≥2%, there coexist several nanowires that have different diameters ranging from 20 nm to 500 nm. As x increases to 10%, thick nanowires of about 400 nm diameter become dominant and the thin ones become deteriorated. A model for the growth mechanism was assumed based on the morphology change of the nanowire.