B4 Research Projects 2022
(Krüger)
Project 1: Theory and simulation of circular polarized emission (photoluminescence) from Eu3+ complexes.
Eu3+ complexes are widely used as light emitting materials (in Laser, LEDs etc). The photoluminescence spectra (color) depend on tiny details of the molecular structure through the ligand field. In 2021 we have developed a theory and computer code for computing photoluminescence of rare-earth ions in a ligand field. It was applied to Eu oxides and Eu3+ impurities in TiO2 and gave good results [1]. The aim of this project is to find out what kind of ligand field produces circular polarized light (in the Eu3+ 5D0 -> 7F1,2 emission lines) and compare with available experimental data (incl. by N.Kobayashi/K.Nakamura, Mat.Sci, Chiba U.) The project involves DFT calculations with VASP code and spectral calculations with a home-written (multiplet) code.[1] 氏家智,修論,千葉大3/2022.,
Project 2: P-doping of MoTe2 by ozone exposure: energetics and mechanism of chemical reaction, analysis of electronic structure
MoTe2 is a novel two-dimensional semi-conductor, which is promising for novel TFET (tunnel field effect transisitor) technology. In order to obtain a bi-polar I-V characteristic, MoTe2 must be p-doped. Prof. Aoki's group has shown that ozone exposure leads to p-doping. The aim of this project is to understand this phenonomenon by atom-level modeling using DFT calcualtions.[1] 池田駿太郎修論,
Project 3: Calculation of polarization energy in organic semiconductors upon addition of one hole or electron
Organic semiconductors are widely used in OLEDs. To control the position of the valence band maximum and conduction band minimum at interfaces is crucial for device performance. Direct and inverse photoemission are often used to measure these quantities which are somewhat different from the HOMO and LUMO position of the free molecule, because of various solid state effects. One of them is the interaction (polarization) energy between the charged molecule (after an electron was removed or added during an inverse of direct photoemission process) and the other molecules which becomes polarized. The aim of this project is to compute this energy using classical electrostatics and as input the (i) charge distribution of the charge molecule (ii) the polaribility of the surrounding molecules. (i),(ii) will be calculated using DFT software (VASP, Gaussian, etc) and for the polarization energy, an original code needs to be written.[1] 吉田先生の論文,
Project 4: Mn/Fe(110) thin film structure and magnetism
Antiferromagnetic materials are considered for information storage and antiferromagnetic films on ferromagnets can be used as spin-valve systems. The Mn/Fe(100) interface has been studied well in the past. Surprisingly, little is know about Mn/Fe(110), although the (110) face is the most stable surface in a bcc crystal. Recently Prof 山田豊和's group has grown thin layers of Mn on Fe(110) (which is the most stable of the bcc surfaces) and observed it by STM. The periodicity is complex (at least a 2x3 supercell) and the the contrast changes in STM may be due to corrugation (structure) or a complex magnetic state. The aim of this project is to compute the stable structure of 1 ML Mn on Fe(110) and analyze the electronic and magnetic state and the STM images.[1] 林宏樹修論,
[2] 応物春季_アブスト,
[3] related Nature article,
Project 5: Contribution to ARPES theory development
Several possibilities:- improve Kruger's multiple scattering code by using full potential T-matrices (to be calculated by code developed by 藤方悠さん.
- generalize t-matrix calculation (muffin-tin) to complex energies ...