Toshiharu Ohnuma

Intersystem crossing and intramultiplet mixing of excited Zn atoms by Xe

The intersystem crossing of Zn(4 1P1) and the intramultiplet mixing of Zn(4 3PJ) by Xe were examined by using pulsed laser techniques. The following thermally averaged cross sections were obtained: Zn(4 1P1)+Xe→Zn(4 3P2)+Xe: 3.4, Zn(4 1P1)+Xe→Zn(4 3P1)+Xe: 0.4, Zn(4 1P1)+Xe→Zn(4 3P0)+Xe: <0.01, Zn(4 3P1)+Xe→Zn(4 3P2)+Xe: 12.0×10−3, Zn(4 3P1)+Xe→Zn(4 3P0)+Xe: 6.3×10−3, in units of 10−16 cm2. These experimental results could well be reproduced by quantum close‐coupling calculations by assuming suitable potential energy curves. The intersystem crossing by He was found to be inefficient.

Cd(5 3P1)-photosensitized luminescence of N,N,N′,N′-tetramethyl-1,3-propanediamine

Cd(5 3P1)-Photosensitized luminescence of N,N,N′,N′-tetramethyl-1,3-propanediamine has been studied under the conditions of steady-state illumination and pulsed laser excitation. There are two emission bands for the sensitized luminescence, the quantum yields of which were determined as well as the overall quenching rate constant of Cd(5 3P1) by the steady-state experiment. The temporal profiles of the two emission bands and that of the resonance fluorescence were measured under pulsed excitation conditions. It is suggested that both the emitters of the two bands are formed directly from Cd(5 3P1) and there are collision-induced mixing processes between these two kinds of emitters. The energy and entropy differences between these emitters were estimated.

The intramultiplet relaxation of Cd(53P2) induced by collisions with 4He, 3He and Ar

The intramultiplet relaxation processes of Cd(53P2) by rare-gas atoms were studied by employing a pump-and-probe technique. Cd atoms in the 53P2 state can be produced by exciting Cd-rare-gas collision complexes with the output of a XeCl laser at 308 nm. The cross sections for the 53P2 to 53P1 and 53P2 to 53P0 processes induced by collisions with 4He, 3He and Ar were determined to be: sigma 21(4He)=8.6, sigma 20(4He)=0.8, sigma 21(3He)=14.7, sigma 20(3He)=1.2, sigma 21(Ar)=15.1 and sigma 20(Ar)=4.3 in units of 10-20 cm2. Close-coupling calculations were carried out to evaluate the cross sections by assuming various interaction potentials. Information on the potentials could be obtained by comparing the calculated cross sections with those obtained experimentally.

The intramultiplet mixing of Zn(43PJ) by collisions with 4He and 3He

The intramultiplet mixing processes of Zn(43PJ ) by collisions with 4He and 3He were studied by employing pulsed laser techniques. The following cross sections were obtained: Zn(43P1)+4He→Zn(43P2)+4He: 3.1; Zn(43P1)+4He→Zn(43P0)+4He: 1.5; Zn(43P1)+3He→Zn(43P2)+3He: 4.7; Zn(43P1)+3He→Zn(43P0)+3He: 1.8; in units of 10−17 cm2. A quantum close‐coupling calculation was carried out by assuming various interaction potentials. The cross sections for the production of Zn(43P2) from Zn(43P1) could be well reproduced by the calculation for both 4He and 3He. On the other hand, the calculated cross sections for the production of Zn(43P0) were found to be always smaller than the experimental ones.

The intramultiplet relaxation of Cd (53P2) by He

Abstract Cadmium atoms in the 5 3 P 0,1,2 states could be detected when a mixture of Cd vapor and He was irradiated with the output of a XeCl laser at 308 nm. It was revealed that CdHe collision complexes are excited to one of the repulsive levels correlating with Cd(5 3 P 2 ) + He. Cd (5 3 P 0,1 ) atoms are formed by collisions with He. The cross sections for the intramul- tiplet relaxation of Cd(5 3 P 2 ) to produce Cd(5 3 P 1 ) and Cd(5 3 P 0 ) by He were determined to be 8.6 × 10 −20 and 7.5 × 10 −21 cm 2 , respectively. These values are compared with the results of a close-coupling calculation.

The intramultiplet relaxation of Cd(5 3P2) by H2 and D2

The deactivation processes of Cd(5 3P2) by H2 and D2 were studied by employing pulsed laser techniques. The cross sections for the intramultiplet relaxation to produce Cd(5 3P1) and Cd(5 3P0) were determined as follows: Cd(5 3P2)+H2→Cd(5 3P1)+H2; 6.3,   Cd(5 3P2)+H2→Cd(5 3P0)+H2; 1.0, Cd(5 3P2)+D2→Cd(5 3P1)+D2; 4.4,   Cd(5 3P2)+D2→Cd(5 3P0)+D2; 0.9, in units of 10−16 cm2 at 630 K. The cross sections for the overall deactivation of Cd(5 3P2) by H2 and D2 were determined to be 9.8×10−16 cm2 and 6.9×10−16 cm2, respectively. These values are compared with the calculated results based on a semiclassical curve crossing mechanism. It is suggested that electronic‐to‐rotational energy transfer without sharp resonances plays an important role in the deactivation of Cd(5 3P2).

Enhancement of piezoelectric constants induced by cation-substitution and two-dimensional strain effects on ZnO predicted by density functional perturbation theory

Using density functional perturbation theory, we investigated the effect of various substitutional dopant elements and in-plane strain on the piezoelectric properties of ZnO. The piezoelectric stress constant e33 of doped ZnO was found to depend on the formal charge of the substitutional dopant. By decomposing the piezoelectric stress constant e33 into the individual atomic contributions, the change in the piezoelectric properties was found to originate from a change in the coupling between the atomic displacement and the strain. Furthermore, we found that in-plane tensile strain along the a axis, which is specific to the thin film, can enhance the piezoelectric constant of ZnO. A phase transition from wurtzite to h-BN-type structure was found to occur with increasing in-plane tensile. The piezoelectric strain constant d33 was predicted to reach ∼200 pC/N for 2.78 at. % V-substituted ZnO at 5.5% in-plane strain, just before the phase transition. These theoretical results suggest that the piezoelectric con...

Theoretical and experimental investigation of defect formation / migration in Gd2Ti2O7: General rule of oxide-ion migration in A2B2O7 pyrochlore

We investigated the intrinsic defect formation energy and oxide-ion migration mechanism in Gd2Ti2O7 pyrochlore. It was found that the vacancy formation energy of Gd is lower than that of Ti. For the oxygen vacancy, O(48f) was found to show lower vacancy formation energy than O(8b). The formation energy of the vacancy complex showed that the Gd vacancy is accompanied with the O(48f) vacancy, which is consistent with our experiment. The migration energy of O(48f) along the direction, which is dominant migration path for ionic conduction, was calculated to be 0.43 eV. On the other hand, we found that Gd vacancy increases O(48f) migration energy. For example, the migration energy of O(48f) along the direction was increased to be 1.36 eV by the local compressive strain around Gd vacancy. This finding could explain our previous experimental result of decreasing conductivity with increasing Gd deficiency. Along with the oxide-ion migration mechanism in Gd2Ti2O7, O(48f) migration energies along both <...

The intramultiplet mixing of Zn (43PJ) by collisions with Ar

The intramultiplet mixing processes of Zn(43 PJ ) by collisions with Ar were studied by employing pulsed laser techniques. The cross sections were obtained for: Zn(43 P1 )+Ar to Zn(43 P2 )+Ar and Zn(43 P1 )+Ar to Zn(43 P0 )+Ar as 2.2 and 5.5 in units of 10-19 cm2 . These experimentally obtained cross sections were compared with the results of a close-coupling calculation on the basis of various potential curves for the 3 Pi and 3 Sigma + states of ZnAr. It is suggested that not only 3 Pi states but also 3 Sigma + states of ZnAr are slightly attractive.

Effects of guest atomic species on the lattice thermal conductivity of type-I silicon clathrate studied via classical molecular dynamics

The effects of guest atomic species in Si clathrates on the lattice thermal conductivity were studied using classical molecular dynamics calculations. The interaction between a host atom and a guest atom was described by the Morse potential function while that between host atoms was described by the Tersoff potential. The parameters of the potentials were newly determined for this study such that the potential curves obtained from first-principles calculations for the insertion of a guest atom into a Si cage were successfully reproduced. The lattice thermal conductivities were calculated by using the Green-Kubo method. The experimental lattice thermal conductivity of Ba8Ga16Si30 can be successfully reproduced using the method. As a result, the lattice thermal conductivities of type-I Si clathrates, M8Si46 (M = Na, Mg, K, Ca Rb, Sr, Cs, or Ba), were obtained. It is found that the lattice thermal conductivities of M8Si46, where M is IIA elements (i.e., M = Mg, Ca, Sr, or Ba) tend to be lower than those of M...