H. Niu

Enhancement of exchange field and reduction of GMR in PtMn-based spin valves by ion irradiation

C-ion irradiation was performed on PtMn-based spin valves and the effects of ion irradiation on magnetoresistance(MR) and on the exchange field were investigated. When ion irradiation was performed prior to post-annealing, the exchange field was substantially enhanced after annealing, especially for an annealing temperature below 240 ° C . The enhancement could be related to the formation of PtMn(C) phase, which might accelerate the formation of ordered PtMn phase and might increase the anisotropy of PtMn. Although the majority of C ions located in capping layers Ta and PtMn, small amounts of C ions may go into the interface of CoFe/Cu/CoFe, leading to a small MR.

Depth profiles of cluster-ion-implanted BSi in silicon

Abstract In this study, BSi cluster ions of 77 keV and B monomer ions of 22 keV were respectively implanted into silicon wafers at room temperature and geometrically tilted. Rapid thermal annealing of the as-implanted specimens at 1050 °C for 25 s was also employed. The results revealed that all the as-implanted and as-annealed range parameters ( R p , ΔR p , γ , β and ΔR t ) of the BSi cluster ion implantation are smaller than those of the B monomer ion implantation. The as-annealed range parameters are larger than the as-implanted ones for both the BSi cluster ion and the B monomer ion implantations mainly due to radiation enhanced diffusion (RED) effects. RED effects also tend to drive boron atoms out-diffusion towards the specimen surface. However, the SiO 2 layer at the surface acts as a diffusion barrier by which it traps boron atoms nearby. The existence of larger amounts of defects explains the presence of a more pronounced accumulation of out-diffused boron atoms in the as-annealed boron depth profile of the BSi cluster ion implantation compared to that of the B monomer ion implantation.

A novel method for alpha-source preparation using recoil implantation

Abstract A recoil implantation technique was investigated for fabricating thin film alpha-sources. The sources were prepared by dropping a solution containing 241 Am uniformly. The samples were processed by recoil implantation, using a 72 keV Cu ion beam to knock the 241 Am into the Si substrate. Examination using Rutherford backscattering spectrometry showed that the radioactive nuclide 241 Am was tightly fixed in the Si substrate and the samples could be regarded as sealed alpha sources. In comparison with a commercial 241 Am source, the recoil-implanted sources gave better energy resolution in the alpha spectra; the FWHM is estimated to be 11–13 keV for the 5.4 MeV peak.

Strain study of self-assembled InAs quantum dots by ion channeling technique

Ion channeling technique using MeV C++ ions was used to study strain in self-assembled InAs quantum dots (QDs) buried in GaAs matrix. Because of the use of heavy ions, we were able to observe an angular shift in the angular scan of the In signal relative to that of the Ga∕As signal. This provided a direct evidence that the InAs lattice is larger than that of GaAs in the growth direction. Combining the channeling results in [100] and [110] directions and the photoluminescence emission spectrum, we conclude that the InAs QDs are under tensile strain in the growth direction and have the same lattice constant as that of GaAs in the lateral direction. Thermal annealing causes the strain to relax, first in the growth direction and then in the lateral direction as the annealing temperature increases. The photoluminescence spectra of the QDs before and after annealing indicate, however, that composition intermixing also takes place during annealing and is the dominant factor in determining the band gap energy of ...

Monitoring of 7Be in surface air of varying PM10 concentrations

In this study, beryllium-7 ((7)Be) concentrations of surface air were monitored throughout a span of 23 years (1992-2012) in the Taiwanese cities Yilan, Taipei, Taichung, and Kaohsiung. During this period, particulate matter (PM) concentrations, in terms of PM10, were collected monthly from the nearest air-quality pollutant monitoring stations and compared against (7)Be concentrations. Seasonal monsoons influenced (7)Be concentrations in all cities, resulting in high winter and low summer concentrations. In addition, the meteorological conditions caused seasonal PM10 variations, yielding distinct patterns among the cities. There was no correlation between (7)Be and PM10 in the case cities. The average annual (7)Be concentrations varied little among the cities, ranging from 2.9 to 3.5 mBq/m(3), while the PM10 concentrations varied significantly from 38 μg/m(3) in Yilan to 92 μg/m(3) in Kaohsiung depending on the degree of air pollution and meteorological conditions. The correlation between the (7)Be concentration and gross-beta activities (Aβ) in air implied that the (7)Be was mainly attached to crustal PM and its concentration varied little among the cities, regardless of the increase in anthropogenic PM in air-polluted areas.

A new configuration of the Moxon–Rae detector based on Si detector

Abstract A new Moxon–Rae detector configuration based on Si semiconductor detector was proposed in this paper. Three γ -ray sources, 137 Cs , 60 Co , and 24 Na , were employed to make actual measurements using the new Moxon–Rae detector. The measured pulse height spectra and detection efficiencies were compared with the EGS4 simulated values. The results revealed that the proposed new configuration is indeed a successful method and specially a useful technique for higher energy γ -ray measurement.

A fast automatic RBS/w channeling system for damage depth profiling.

A computer-aided data acquisition coupling with goniometer-control system dedicated for damage depth profile measurements is established. The channeling direction searching is performed along tilt and azimuth directions. The system includes a computer code to convert the measured spectra into damage depth profile. The analyzing time for each sample requires approximately 20-30 min. The damage depth profiles of the self-implanted (100) silicon samples are in reasonable agreement with the calculated results yielded by the SRIM Monte-Carlo simulation code.