Optical properties of isolated silicon nanocrystals ͑nc-Si͒ with a mean size of ϳ4 nm embedded in a SiO 2 matrix that was synthesized with an ion beam technique have been determined with spectroscopic ellipsometry in the photon energy range of 1.1-5.0 eV. The optical properties of the nc-Si are found to be well described by both the Lorentz oscillator model and the Forouhi-Bloomer ͑FB͒ model. The nc-Si exhibits a significant reduction in the dielectric functions and optical constants and a large blueshift ͑ϳ0.6 eV͒ in the absorption spectrum as compared with bulk crystalline silicon. The band gap of the nc-Si obtained from the FB model is ϳ1.7 eV, showing a large band gap expansion of ϳ0.6 eV relative to the bulk value. The band gap expansion is in very good agreement with the first-principles calculation of the nc-Si optical gap based on quantum confinement.

The radio and gamma-ray pulsar PSR J2032+4127 was recently found to be in a decadeslong orbit with the Be star MT91 213, with the pulsar moving rapidly towards periastron. This binary shares many similar characteristics with the previously unique binary system PSR B1259−63/LS 2883. Here, we describe radio, X-ray, and optical monitoring of PSR J2032+4127/MT91 213. Our extended orbital phase coverage in radio, supplemented with Fermi LAT gamma-ray data, allows us to update and refine the orbital period to 45-50 yr and time of periastron passage to 2017 November. We analyse archival and recent Chandra and Swift observations and show that PSR J2032+4127/MT91 213 is now brighter in X-rays by a factor of ∼ 70 since 2002 and ∼ 20 since 2010. While the pulsar is still far from periastron, this increase in X-rays is possibly due to collisions between pulsar and Be star winds. Optical observations of the Hα emission line of the Be star suggest that the size of its circumstellar disc may be varying by ∼ 2 over timescales as short as 1-2 months. Multiwavelength monitoring of PSR J2032+4127/MT91 213 will continue through periastron passage, and the system should present an interesting test case and comparison to PSR B1259−63/LS 2883.

Densely stacked silicon nanocrystal layers embedded in the gate oxide of MOSFETs are synthesized with Si ion implantation into an SiO 2 layer at an implantation energy of 2 keV. In this letter, the memory characteristics of MOSFETs with 7-nm tunnel oxide and 20-nm control oxide at various temperatures have been investigated. A threshold voltage window of ∼ 0.5 V is achieved under write/erase (W/E) voltages of +12 V/−12 V for 1 ms. The devices exhibit good endurance up to 10 5 W/E cycles even at a high operation temperature of 150 • C. They also have good retention characteristics with an extrapolated ten-year memory window of ∼ 0.3 V at 100 • C. Index Terms-Low energy ion beam, memory effect, silicon nanocrystal (nc-Si).

Central compact objects (CCOs) are a handful of young neutron stars found at the center of supernova remnants (SNRs). They show high thermal X-ray luminosities but no radio emission. Spin-down rate measurements of the three CCOs with X-ray pulsations indicate surface dipole fields much weaker than those of typical young pulsars. To investigate if CCOs and known radio pulsars are objects at different evolutionary stages, we carried out a census of all weak-field (< 10 11 G) isolated radio pulsars in the Galactic plane to search for CCO-like X-ray emission. None of the 12 candidates are detected at X-ray energies, with luminosity limits of 10 32 − 10 34 erg s −1 . We consider a scenario in which the weak surface fields of CCOs are due to a rapid accretion of supernova materials and show that as the buried field diffuses back to the surface, a CCO descendant is expected to leave the P -Ṗ parameter space of our candidates at a young age of a few ×10 kyr. Hence, the candidates are likely to just be old ordinary pulsars in this case. We suggest that further searches for orphaned CCOs, which are aged CCOs with parent SNRs that have dissipated, should include pulsars with stronger magnetic fields.

We report a systematic analysis of the spin, orbital, and superorbital modulations of 4U 0114+650, a high-mass X-ray binary that consists of one of the slowest spinning neutron stars. Using the dynamic power spectrum, we found that the spin period varied dramatically and is anticorrelated with the long-term X-ray flux variation that can be observed using the Rossi X-ray Timing Explorer ASM, Swift BAT, and the Monitor of All-sky X-ray Image. The spin-up rate over the entire dataset is consistent with previously reported values; however, the local spin-up rate is considerably higher. The corresponding local spin-up timescale is comparable to the local spin-up rate of OAO 1657−415, indicating that 4U 0114+650 could also have a transient disk. Moreover, the spin period evolution shows two ∼1000-day spin-down/random-walk epochs that appeared together with depressions of the superorbital modulation amplitude. This implies that the superorbital modulation was closely related to the presence of the accretion disk, which is not favored in the spin-down/random-walk epochs because the accretion is dominated by the direct wind accretion. The orbital period is stable during the entire time span; however, the orbital profile significantly changes with time. We found that the depth of the dip near the inferior conjunction of the companion is highly variable, which disfavors the eclipsing scenario. Moreover, the dip was less obvious during the spin-down/random-walk epochs, indicating its correlation with the accretion disk. Further monitoring in both X-ray and optical bands could reveal the establishment of the accretion disk in this system.

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In this work, we report a mapping of charge transport in silicon nanocrystals (nc-Si) embedded in SiO2 dielectric films with electrostatic force microscopy. The charge diffusion from chargednc-Si to neighboring uncharged nc-Si in the SiO2 matrix is found to be the dominant mechanism for the decay of the trapped charge in the nc-Si. The trapped charge and the charge decay have been determined quantitatively from the electrical force measurement. An increase in the area of the charge cloud due to the charge diffusion has been observed clearly. In addition, the blockage and acceleration of charge diffusion by the neighboring charges with the same and opposite charge signs (i.e., positive or negative), respectively, have been observed.

NGC 7793 P13 is an ultraluminous X-ray source harboring an accreting pulsar. We report on the detection of a ∼65 d period X-ray modulation with Swift observations in this system. The modulation period found in the X-ray band is P = 65.05 ± 0.10 d and the profile is asymmetric with a fast rise and a slower decay. On the other hand, the u-band light curve collected by Swift UVOT confirmed an optical modulation with a period of P = 64.24 ± 0.13 d. We explored the phase evolution of the X-ray and optical periodicities and propose two solutions. A superorbital modulation with a period of ∼2,700-4,700 d probably caused by the precession of a warped accretion disk is necessary to interpret the phase drift of the optical data. We further discuss the implication if this ∼65 d periodicity is caused by the superorbital modulation. Estimated from the relationship between the spin-orbital and orbital-superorbital periods of known disk-fed high-mass X-ray binaries, the orbital period of P13 is roughly estimated as 3-7 d. In this case, an unknown mechanism with a much longer time scale is needed to interpret the phase drift. Further studies on the stability of these two periodicities with a long-term monitoring could help us to probe their physical origins.