Electronic states of P donors in Si nanocrystals (nc-Si) embedded in insulating glass matrices have been studied by electron spin resonance. Doping of P donors into nc-Si was demonstrated by the observation of optical absorption in the infrared region due to intraconduction band transitions. P hyperfine structure (hfs) was successfully observed at low temperatures. The observed splitting of the hfs was found to be much larger than that of the bulk Si:P and depended strongly on the size of nc-Si. The observed strong size dependence indicates that the enhancement of the hyperfine splitting is caused by the quantum confinement of P donors in nc-Si.

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Photoluminescence (PL) from Si nanocrystals (nc-Si) dispersed in phosphosilicate glass thin films was studied. It was found that, at room temperature, the 1.4 eV PL due to the recombination of electron-hole pairs in nc-Si becomes intense as the P concentration increases. At low temperatures, an additional peak related to defects at interfaces between nc-Si and the matrix was observed at about 0.9 eV. In contrast to the 1.4 eV peak, the 0.9 eV peak became weaker with increasing P concentration and almost disappeared at a P concentration of 1.5 mol %. These results suggest that the number of interface defects decreases with increasing P concentration and that this decrease leads to an improvement of the band-edge PL of nc-Si.

Purpose: To investigate the usefulness of magnetic particle imaging (MPI) for predicting the therapeutic effect of magnetic hyperthermia (MH). Materials and Methods: First, we performed phantom experiments to investigate the relationship between the MPI value and the temperature rise of magnetic nanoparticles (MNPs) under an alternating magnetic field (AMF). The MPI value was defined as the pixel value of the transverse image reconstructed from the third-harmonic signals. Samples filled with various iron concentrations of MNPs (Resovist ®) were prepared and were imaged using our MPI scanner. These samples were also heated using the AMF, and the specific loss power (SLP) and volume-specific loss power (vSLP) were calculated from the initial slope of the time-dependent temperature rise. Second, we performed animal experiments using tumor-bearing mice, which were divided into untreated (n = 10) and treated groups (n = 20). The tumors in the treated group were injected with Resovist ® at an iron concentration of 250 mM (n = 10) or 500 mM (n = 10), and received MH for 20 min, during which the temperatures in the tumor and rectum were measured. The relative tumor volume growth (RTVG) was calculated from (V 15 − V 0)/V 0 , where V 0 and V 15 represented the tumor volume on day 0 and day 15 after MH, respectively. Results: In phantom experiments, the MPI value had significant correlations with the iron concentration of MNPs (r = 0.997), temperature rise (r = 0.981), and vSLP (r = 0.961). In animal experiments, the MPI value had significant correlations with the temperature rise in the tumor (r = 0.731) and RTVG (r = −0.687). Conclusion: Our preliminary results suggest that MPI is useful for predicting the therapeutic effect of MH.

SiO 2 and phosphosilicate glass ͑PSG͒ films containing Si nanocrystals ͑nc-Si͒ as small as a few nanometers were studied by electron spin resonance ͑ESR͒ and photoluminescence ͑PL͒, and the correlation between the two measurements was examined. It is shown that the incorporation of nc-Si in SiO 2 results in the drastic increase in the ESR signal; the signal is assigned to the Si dangling bonds at the interfaces between nc-Si and matrices (P b centers͒. The ESR signal becomes weaker by doping P into SiO 2 matrices, i.e., by using PSG as matrices. By increasing the P concentration, the ESR signal decreases further. By decreasing the ESR signal, the low-energy PL peak at 0.9 eV decreases, while the band-edge PL at 1.4 eV increases. These results suggest that the 0.9 eV peak is related to P b centers, and that the decrease in the density of the P b centers by P doping brings about an improvement in the band-edge PL efficiency of nc-Si.