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排序方式: 共有76条查询结果,搜索用时 46 毫秒
1.
M. Adams P. Mascher A. H. Kitai 《Applied Physics A: Materials Science & Processing》1995,61(2):217-220
Positron lifetime and optical absorption techniques were employed to track the microstructural evolution of polycrystalline ZnS grown by Chemical Vapor Deposition (CVD). As grown material and material treated with Hot Isostatic Pressure (HIP) was sintered at temperatures ranging from 400 to 1000°C for 2–18 h. A 290 ps defect lifetime could be resolved in all samples, while an additional longer lifetime (=430 ps) was found only in samples annealed at low temperatures. This component gradually disappeared during annealing at 800°C. Associated with the disappearance of the long-lived component, the apparent bulk lifetime of the material changed from 235 to 215 ps. A 215±2 ps bulk parameter was also found for HIP-treated material annealed at temperatures greater than 400°C and hence is taken to represent the delocalized state of the positrons in ZnS. Optical absorption measurements showed that annealing at 800°C also caused the absorption profiles of the CVD and HIP samples to converge. The rate of the bulk lifetime transition correlates with the absorption changes. The observed sharpening of the absorption profile is attributed to a decrease in scattering from grain boundaries and voids, and a decrease in absorption from point defects. The 430 ps lifetime is believed to be due to trapping at voids and grain boundaries, while the 290 ps lifetime likely is due to a monovacancy stabilized as a small complex.Paper presented at the 132nd WE-Heraeus-Seminr on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994 相似文献
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3.
Dr. Yohei Hattori Tatsuya Maejima Yumi Sawae Jun-ichiro Kitai Prof. Masakazu Morimoto Dr. Ryojun Toyoda Prof. Hiroshi Nishihara Prof. Satoshi Yokojima Dr. Shinichiro Nakamura Prof. Kingo Uchida 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11441-11450
The cyclization reaction of diarylethenes having an azulene ring occurs only via higher excited states. Novel diarylethenes having an azulene ring with a strong donor or acceptor were synthesized and examined in these reactions. A derivative having an electron-donating 1,3-benzodithiol-2-ylidenemethyl group at the 1-position of the azulene ring showed photochromism, whereas neither a derivative having a π-conjugated electron-donating group at the 3-position of the azulene ring nor derivatives having a π-conjugated electron-withdrawing group at the 1- or 3-position of the azulene ring showed any photochromism. The photoreactivities of these compounds were explained by calculating forces and bond orders on the excited states using density functional theory (DFT) and time-dependent (TD)-DFT. 相似文献
4.
Nobuyuki Ichinose Masahide Hagiri Jun-ichiro Kinugasa Nobuyuki Shichi Toshihiro Nakayama 《Research on Chemical Intermediates》2013,39(1):425-435
A charge-transfer (CT) complex of NOBF4 and hexamethoxybenzene (HMB), which gives out HMB?+ as a “fluorescent radical cation probe,” upon one-electron oxidation, has been designed to explore the excited state dynamics of contact radical ion pairs by laser-induced fluorescence and femtosecond transient absorption spectroscopic techniques. The acetonitrile solution of the CT complex showed weak fluorescence with a similar spectrum to that observed for free excited HMB radical cation (HMB?+*), suggesting the formation of HMB?+* upon the one-photonic excitation of the CT complex. The laser-power dependence of the fluorescence intensity supported the one-photonic excitation event. We have also observed a short-lived transient species but no long-lived species by femtosecond laser flash photolysis of the CT complex. The lifetime (6.5 ps) was in good accordance with its fluorescence quantum yield (2.5 × 10?5) and was able to assign the transient species to the fluorescent state, an excited radical ion pair [HMB ?+*/NO?]. All the events were completed within the inner sphere and the short lifetime of the transient species could be attributed to rapid back-electron transfer. It is concluded that the excited radical cation character in the excited state of the CT complex originates from the radical ion character in the CT complex in the ground state and that a relatively long lifetime of HMB?+* facilitates its observation even in the contact ion pair. 相似文献
5.
Y. I. Belov S. D. Kitai A. P. Naumov V. A. Rassadovsky M. Y. Yablokov 《Radiophysics and Quantum Electronics》2000,43(3):187-195
We study the physical conditions for balloon-borne radiometric sounding of the humidity height profile in the 3-mm atmospheric
transparency window, an unusual spectral band for such problems, using a balloon drifting in the tropopause. We solve the
inverse problem and discuss the accuracy of reconstruction of the humidity profiles.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 43, No. 3, pp. 207–216, March 2000 相似文献
6.
Sh. D. Kitai 《Radiophysics and Quantum Electronics》1999,42(3):211-215
We analyze the characteristics of radio emission from the middle atmosphere during limb sounding of minor gas constituents
with rotational transitions of the molecules located in the atmospheric transparency windows 105–118 GHz and 180–210 GHz.
Optimal frequencies and height ranges for the sounding of minor gases are found by numerical modeling for typical values of
the receiver bandwidth.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 42, No. 3, pp. 235–239, March 1999. 相似文献
7.
We consider magnetotransport properties in a conducting chiral helimagnet, where the magnetic kink crystal (MKC) is formed under weak magnetic field applied perpendicular to the helical axis. The MKC behaves as a magnetic superlattice potential and results in Bragg scattering of conduction electrons. Tuning of the weak magnetic field enables us to control the size of the superlattice Brillouin zone and gives rise to a series of divergent resistivity anomalies originating from resonant Bragg scatterings. We discuss as well a nontrivial magnetic structure in the resonant states realized in the subsystem of the itinerant electrons. 相似文献
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9.
Kawae T Kinoshita K Nakaie Y Tateiwa N Takeda K Suzuki HS Kitai T 《Physical review letters》2006,96(2):027210
We have studied non-Fermi-liquid (NFL) behavior in Pr(x)La(1-x)Pb3 with Gamma3 quadrupolar moments in the crystalline-electric-field ground state. The specific heat C/T shows NFL behavior in the very dilute region for x 相似文献
10.
Bis(azafulvene) was isolated in 55% yield by the reaction of 4 equivalents of phenyllithium with 5,5'-diformyl-3,3',4,4'-tetraethyl-2,2'-bipyrrole followed by quenching with acetic anhydride. Unstable bis(azafulvene)s were obtained in much higher yields by dehydrating 5,5'-bis(hydroxymethyl) derivatives of 2,2'-bipyrrole and gem-dimethyl-2,2'-dipyrrylmethane with (Boc)2O-DMAP at room temperature. X-Ray crystallography of two bis(azafulvene)s is reported. 相似文献