Itaru Yamashita

Quantum Chemistry Study of Surface Structure Effects on Secondary Electron Emission in MgO Protecting Layers for Plasma Displays

MgO protecting layers, which have high ion induced secondary electron emission coefficient (γ), are required in order to decrease the firing voltage of plasma displays. Theoretical estimation of ideal γ value is needed for a design of better protecting layers. In this study, we report our developed γ calculation method based on a tight-binding quantum calculation and application to an estimation of γ values of MgO protecting layers. From our calculation results, it was revealed that electron trap sites arising from surface roughness would work as an effective emission sites and increase γ value. Especially for Xe+ species as induced ion, the γ value changed drastically by the presence of the trapped electron. It is also suggested that a presence of chemisorbed water on the MgO surface decreases the γ values because of the contribution of the electrons at the low energy levels originated from surface OH groups.

Quantum chemistry and QSPR study on relationship between crystal structure and emission wavelength of Eu2+‐doped phosphors

— The relationship between crystal structures and emission properties has been computationally investigated for Eu2+-doped phosphors. The electronic structure of the Eu2+-doped BaMgAl10O17 phosphor was analyzed by using the quantum chemistry method. The different effects of O and Ba atoms on the Eu 5d states were determined. The presence of O and Ba atoms increases and decreases the energy level of the Eu 5d orbital by forming anti-bonding and bonding interactions, respectively. According to the electronic-structure analysis, the structure index that represents the local geometrical information of the Eu atom was defined. The relationship between the crystal structures and the emission wavelengths of the 1 6 Eu2+-doped oxide phosphors were studied by using the quantitative structure-property relationship (QSPR). The QSPR model suggested that the both O and alkaline-earth atoms around the Eu atom are of importance in the determination of the emission wavelength. The interaction between the Eu and the nearest O atoms make the Eu2+ emission wavelength short. On the other hand, the interaction from the alkaline-earth atoms around the Eu atom lengthens the Eu2+emission wavelength. This evaluation method is useful in selecting the host material that indicates a desirable emission wavelength of the Eu2+-doped phosphors.

A Theoretical Study of Initial Deposition Processes of Mg on MgO: A Novel Quantum Chemical Molecular Dynamics Approach

Initial deposition processes of Mg on MgO were studied using our novel quantum chemical molecular dynamics (QCMD) simulator. This novel simulator was developed on the basis of our tight-binding quantum chemical molecular dynamics (TB-QCMD) simulator and our molecular dynamics simulator. The justification of the novel QCMD simulator was shown by the excellent agreement of the QCMD result with the first-principles results and experimental results for the physicochemical properties of the MgO crystal. Dynamic behaviors of Mg atom deposited on the MgO(001) and (111) surfaces were simulated by the novel QCMD method. It was shown that the mobility of Mg deposited on the MgO(001) surface was larger than that on the (111) surface, which suggests the difference between the interaction of the deposited Mg atom with the MgO(111) surface and that with the MgO(001) surface.

Theoretical Study on Effect of SiC Crystal Structure on Carrier Transfer in Quantum Dot Solar Cells

Quantum dot (QD) solar cells are proposed as high-efficiency solar cells. However, their reported conversion efficiencies have been lower than half of the ideal value. To improve their efficiency, the optimization of their cell structure in terms of various parameters, e.g., dot size, interdot distance, type of materials, and QD/bulk interface structure, is necessary. In this paper, we focused on the most important factor for the improvement in the conversion efficiency of Si/SiC type QD solar cells and investigated the effect of the atomistic structure of the QD/bulk interface on carrier transfer by tight-binding simulation. We constructed models of Si/SiC systems and analyzed the effect of QD/bulk interface defects on their electronic structure and carrier transfer properties. It was suggested that electrons trapped at the QD/bulk interface and the type of SiC crystal structure affect electron transfer.

Computational Analysis of Electron Injection on Light-Emitting Polymer/Cathode Interface

Tohoku Univ., Dept. Chem. Eng., Grad. School Eng., 6-6-10-205 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Phone: +81-22-795-7237 E-mail: itaru@aki.che.tohoku.ac.jp Tohoku Univ., Dept. Appl. Chem., Grad. School Eng., 6-6-10-205 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tohoku Univ., NICHe, 6-6-10-205, Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tohoku Univ., FRI, Grad. School Eng., 6-6-11-701 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan

Development of Computational Analysis Method for Carrier Transport Pathway in Light-Emitting Polymers

Tohoku Univ., Dept. Chem. Eng., Grad. School Eng., 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Phone: +81-22-795-7237 E-mail: itaru@aki.che.tohoku.ac.jp Tohoku Univ., Dept. Appl. Chem., Grad. School Eng., 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tohoku Univ., NICHe, 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tohoku Univ., FRI, Grad. School Eng., 6-6-11-701 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Univ. of Utah, Salt Lake City, Utah, USA.

Development of Experiment Integrated Computational Chemistry and Its Application to Advanced Materials

Tohoku Univ., Dept. Appl. Chem., Grad. School of Eng., 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Phone: +81-22-795-7236 E-mail: endou@aki.che.tohoku.ac.jp Tohoku Univ., Dept. of Chem. Eng., Grad. School of Eng., 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tohoku Univ., NICHe, 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tohoku Univ., FRI, Grad. School of Eng., 6-6-11-701 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan

A Large Scale Quantum Chemistry Study for the High γMgO Protecting Layer of Plasma Display Panels

1 Tohoku Univ., Dept. Appl. Chem., Grad. Sch. Eng., 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Phone: +81-22-795-7237 e-mail: kazumi@aki.che.tohoku.ac.jp 2 Hiroshima Univ., Dept. of Semiconductor Elec. and Integration Sci., Grad. Sch. Adv. Sci. Matt., 1-3-1 Kagamiyama, Higashihiiroshima, Hiroshima 739-8530, Japan 3 Tohoku Univ., Dept. Chem. Eng., Grad. Sch. Eng., 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan 4 Tohoku Univ., NICHe, 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan 5 Tohoku Univ., FRI, Grad. Sch. Eng., 6-6-11-701 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan

19.3: Electronic Structure Calculation and QSPR Analysis of Eu2+‐doped Oxide Phosphors: Relationship between Emission Wavelength and Crystal Structure

In this study, we have computationally revealed the relationship between crystal structure and emission wavelength for Eu2+-doped oxide phosphors. The quantum chemistry calculations and quantitative analysis of structure-property relationship suggested that both O and alkaline-earth (A) atoms around the Eu atom in phosphors are of importance for emission wavelength. This extension of the consideration range for interaction of A atoms gave the simple guideline for the emission wavelength control of Eu2+-doped phosphors: 1) The host materials which have many A atoms and shorter/longer A-A/A-O distances are suitable to get longer Eu2+ emission wavelength, 2) The host materials which have less A atoms and longer/shorter A-A/A-O distances are suitable to get shorter Eu2+ emission wavelength.

Novel Method Based on Quantum Chemistry for Calculation of Ion Induced Secondary Electron Emission Coefficient of MgO Surfaces

High ion induced secondary electron emission (IISEE) coefficient (γ) MgO protecting layers are required in order to decrease the firing voltage of plasma display panels (PDPs). Theoretical calculation of γ for MgO surfaces provides an effective way to design better protecting layers. Here, we have developed a novel γ value estimation method based on an ultra accelerated quantum chemical molecular dynamics simulation considering the collision effect of Ne+ into a flat MgO(100) surface. Compared with experimentally obtained results, our estimated γ values are only marginally different. Our study shows that γ is primarily influenced by impact sites and Ne+ acceleration voltage. To interpret the behavior of γ in terms of these two variables, we analyzed the electronic structure of the MgO surface during the collision of Ne+. Our analyses show that the work function depends on impact sites and Ne+ acceleration voltage since Ne+ interacts with the surface. Our newly developed methodology enabled γ estimation from quantum chemical instances alone, considering the effect of Ne+ collision onto the MgO surface.