Nobuhiro Kosugi - Academia.edu (original) (raw)

Papers by Nobuhiro Kosugi

Optica, Dec 20, 2019

Photoinduced quantum dynamics in molecules have hierarchical temporal structures with different e... more Photoinduced quantum dynamics in molecules have hierarchical temporal structures with different energy scales that are associated with electron and nuclear motions. Femtosecond-to-attosecond transient absorption spectroscopy (TAS) using high-harmonic generation (HHG) with a photon energy below 300 eV has been a powerful tool to observe such electron and nuclear dynamics in a table-top manner. However, comprehensive measurements of the electronic, vibrational, and rotational molecular dynamics have not yet been achieved. Here, we demonstrate HHG-based TAS at the nitrogen K-edge (400 eV) for the first time, and observe all the electronic, vibrational, and rotational degrees of freedom in a nitric oxide molecule at attosecond to sub-picosecond time scales. This method of employing core-to-valence transitions offers an all-optical approach to reveal complete molecular dynamics in photochemical reactions with element and electronic state specificity.

Meeting Abstracts of the Physical Society of Japan (Nihon Butsuri Gakkai koen gaiyoshu), 2011

Chemical Physics, Apr 1, 2003

The core hole localization, multiplets in the singly core-excited state, and their Auger-like two... more The core hole localization, multiplets in the singly core-excited state, and their Auger-like two-electron de-excitation are discussed in some diatomic systems from the viewpoint of the exchange interaction. The exchange repulsion arising from the core–core overlap is proved very small, indicating that the core electron is essentially localized on a specified atom, even in homonuclear systems. Relatively large core–valence exchange

Advanced Materials, Jun 8, 2018

high carrier mobility. [2,3] A typical perovskite has a 3D lattice structure with a formula of AB... more high carrier mobility. [2,3] A typical perovskite has a 3D lattice structure with a formula of ABX 3 where A + is composed of organic (CH 3 NH 3 + (MA +) or CH 3 (NH 2) 2 + (FA +)) or inorganic (cesium + (Cs +) or rubidium + (Rb +)) cation, B 2+ is the divalent metal (Pb 2+ or Sn 2+), and X − is the halide (Cl − , Br − , or I −). [2,4] To realize commercial applications, the long-term stability issues such as durability under humid, thermal, and light-soaking conditions should be further investigated and improved. [5] Most annoyingly, the perovskite thin film is quite sensitive to moisture and oxygen, resulting in degradation under atmosphere. The low formation energy of the perovskite structures tends to hydrolyze in the presence of moisture. [6] One of the methods to stabilize halide perovskite is to use the layered structure with 2D perovskites, the so-called Ruddlesden-Popper layered perovskites, where larger hydrophobic cation acts as a spacer to isolate the 3D MAPbI 3. [7-12] The general formula of Ruddlesden-Popper perovskites is defined as A′ 2 A n−1 B n X 3n+1 , where n is an integer between 1 and ∞ and A′ + is large-sized cation (typically ammonium-based cation such as phenyl ethylammonium (PEA), [10] polyethylenimine (PEI), [13] n-butylammine (BA), [14] cyclopropylamine (CA), [15] octadecylamine (OA), [16] or ammoniumvaleric The fabrication of multidimensional organometallic halide perovskite via a lowpressure vapor-assisted solution process is demonstrated for the first time. Phenyl ethyl-ammonium iodide (PEAI)-doped lead iodide (PbI 2) is first spincoated onto the substrate and subsequently reacts with methyl-ammonium iodide (MAI) vapor in a low-pressure heating oven. The doping ratio of PEAI in MAI-vapor-treated perovskite has significant impact on the crystalline structure, surface morphology, grain size, UV-vis absorption and photoluminescence spectra, and the resultant device performance. Multiple photoluminescence spectra are observed in the perovskite film starting with high PEAI/ PbI 2 ratio, which suggests the coexistence of low-dimensional perovskite (PEA 2 MA n−1 Pb n I 3n+1) with various values of n after vapor reaction. The dimensionality of the as-fabricated perovskite film reveals an evolution from 2D, hybrid 2D/3D to 3D structure when the doping level of PEAI/PbI 2 ratio varies from 2 to 0. Scanning electron microscopy images and Kelvin probe force microscopy mapping show that the PEAI-containing perovskite grain is presumably formed around the MAPbI 3 perovskite grain to benefit MAPbI 3 grain growth. The device employing perovskite with PEAI/PbI 2 = 0.05 achieves a champion power conversion efficiency of 19.10% with an open-circuit voltage of 1.08 V, a current density of 21.91 mA cm −2 , and a remarkable fill factor of 80.36%. Perovskite Solar Cells Organic-inorganic hybrid perovskite materials have attracted numerous attentions in solar energy conversion and various optoelectronic applications [1] due to their long carrier diffusion length, high absorption coefficients in the visible range, and The ORCID identification number(s) for the author(s) of this article can be found under

Journal of Electron Spectroscopy and Related Phenomena, Jul 1, 2004

In recent high-resolution and sophisticated soft X-ray molecular spectroscopies, small exchange i... more In recent high-resolution and sophisticated soft X-ray molecular spectroscopies, small exchange interaction (EX) involving the core electron has been revealed. Interatomic core-core EX is generally small; therefore, it is considered that even the core electron described as 1s g and 1s u in homonuclear systems is localized on an atom. However, small but appreciable interatomic core-valence EX in N 2 and C 2 H 2 results in observable g-u splittings in the core ionization, which are experimentally evaluated from extrapolation of the 1s local g → np u , np u and 1s local u → nsd g , nd g Rydberg series. Due to intermolecular Rydberg-valence EX, blue shifts in low-lying core-to-Rydberg excitations in N 2 and Ar are experimentally identified from gas phase to surface, from surface to bulk, and from large to small cage size of rare gas matrixes. EX involving the 2p core electron is anisotropic, depending on the relation between the 2p orbital direction and molecular structure. In some sulfur containing molecules, it is experimentally revealed that the S 2p and excited electrons have EX compatible to the 2p spin-orbit interaction (SO) for parallel 2p → * transitions and EX smaller than SO for perpendicular 2p → * transitions. In other words, the jj coupling scheme is not applicable to the parallel transitions. Furthermore, it is revealed that, in resonant photoelectron and soft X-ray emissions on the S 2p excitation of CS 2 and SF 6 , spin-forbidden shake-up valence ionizations with quartet spin couplings and spin-forbidden valence excitations with triplet spin couplings are observable via triplet components mixed in intermediate core-excited states.

Analytical Sciences, Nov 8, 2019

Soft X-ray absorption spectroscopy (XAS) involving excitation processes of a core electron to uno... more Soft X-ray absorption spectroscopy (XAS) involving excitation processes of a core electron to unoccupied states is an effective method to study local structures around excited C, N, and O atoms in liquid samples. Since soft X-rays are strongly absorbed by air and liquid itself, we have developed transmission-type liquid flow cells, where the absorbance of liquid samples can be easily reduced and optimized by controlling the liquid thickness. By using the transmission-mode XAS techniques, we have investigated local structures of several liquid samples such as concentration dependence of aqueous pyridine solutions and unexpected temperature-dependent structural changes in liquid benzene from the precise energy shift measurements in XAS spectra with the help of molecular dynamics simulation and inner-shell calculations. These XAS techniques are also applied to in situ/operando observation of chemical processes in solutions such as catalytic and electrochemical reactions.

XAS carbon and oxygen K-edge measurements of aqueous solutions of glyoxal and methylglyoxal and t... more XAS carbon and oxygen K-edge measurements of aqueous solutions of glyoxal and methylglyoxal and their mixtures with sodium chloride and ammonium sulfate. XAS oxygen K-edge measurements of aqueous glycerol and mixtures with the above-mentioned inorganic salts.

This document provides supplementary information to "Real-time observation of electronic, vibrati... more This document provides supplementary information to "Real-time observation of electronic, vibrational, and rotational dynamics in nitric oxide with attosecond soft X-ray pulses at 400 eV."

Photoinduced quantum dynamics in molecules have hierarchical temporal structures with entangled e... more Photoinduced quantum dynamics in molecules have hierarchical temporal structures with entangled electronic and nuclear motions. Femtosecond-to-attosecond transient absorption spectroscopy (TAS) using high-harmonic generation (HHG) in the extreme ultraviolet region with a photon energy below 100 eV has been a powerful method for observing such dynamics [1-9]. However, complete measurements of the electronic, vibrational, and rotational molecular dynamics have not yet been achieved. Recent progress of attosecond HHG in the soft X-ray (SX) region around the water window (284-543 eV) [10-13] has opened a new possibility of TAS [14-17] with element specificity by using well-defined core electronic states. Here, we show that TAS in the SX region, around 400 eV, can probe multi-timescale dynamics of the electronic, vibrational, and rotational degrees of freedom in a nitric oxide molecule at attosecond to subpicosecond time scales, which provides a complete view of the phototriggered dynamics. This method of employing a photon-in/photon-out measurement using broadband attosecond SX pulses offers a unified approach to understand complete molecular dynamics with element specificity. Main The observation of electronic and nuclear dynamics in molecules initiated by light is critical for understanding fundamental mechanisms in photoinduced chemical and physical processes [1]. Pump-probe spectroscopy using high harmonics (HHs) has enabled direct measurements of ultrafast dynamics with femtosecond-to-attosecond temporal resolution through photoelectron/ion spectroscopy [18-20], high-harmonic spectroscopy [21, 22], and transient absorption spectroscopy (TAS) [2-9]. In particular, TAS has unique advantages over other techniques: it is unaffected by the existence of strong laser fields, state-specific even if the probe pulse has a broadband spectrum, and free of the space charge problem. Because of these characteristics, TAS is one of the most ideal techniques for laser-based pump-probe experiments for a wide range of atoms and molecules. To date, by using TAS in the extreme ultraviolet (XUV) region below ~100 eV, real-time observations of electronic processes such as autoionization [2], tunnel ionization [3] or the emergence of laser-dressed states [4] and nuclear dynamics [5-7] have been demonstrated. Couplings between the electronic and nuclear degrees of freedom have also been observed [8, 9].

Meeting abstracts of the Physical Society of Japan, Sep 16, 1997

Japanese Journal of Applied Physics, 1993

The surface structure of (√3×√3)R30° S/Ni(7 9 11) was investigated at room temperature by the SEX... more The surface structure of (√3×√3)R30° S/Ni(7 9 11) was investigated at room temperature by the SEXAFS method. We found that the mixture of the step 4-fold site and terrace 3-fold hollow site could explain the observed polarization dependence of the EXAFS amplitude successfully. It should be noted that a (√3×√3)R30° LEED pattern can be observed only at low temperature for S adsorption on Ni(111). Present results suggest that the S atoms adsorbed on the step 4-fold site play an important role on stabilizing the S atoms on the terrace site, which yield the (√3×√3)R30° LEED pattern.

Journal of Chemical Physics, Apr 15, 2005

Core excitation from terminal oxygen OT in O3 is shown to be an excitation from a localized core ... more Core excitation from terminal oxygen OT in O3 is shown to be an excitation from a localized core orbital to a localized valence orbital. The valence orbital is localized to one of the two equivalent chemical bonds. We experimentally demonstrate this with the Auger Doppler effect which is observable when O3 is core-excited to the highly dissociative OT 1s −1 7a 1 1 state. Auger electrons emitted from the atomic oxygen fragment carry information about the molecular orientation relative to the electromagnetic field vector at the moment of excitation. The data together with analytical functions for the electron-peak profiles give clear evidence that the preferred molecular orientation for excitation only depends on the orientation of one bond, not on the total molecular orientation. The localization of the valence orbital "7a1" is caused by mixing of the valence orbital "5b2" through vibronic coupling of anti-symmetric stretching mode with b2-symmetry. To the best of our knowledge, it is the first discussion of the localization of a core excitation of O3. This result explains the success of the widely used assumption of localized core excitation in adsorbates and large molecules.

Atmospheric Chemistry and Physics, Feb 25, 2021

Glyoxal (CHOCHO) and methylglyoxal (CH 3 C(O)CHO) are well-known components of atmospheric partic... more Glyoxal (CHOCHO) and methylglyoxal (CH 3 C(O)CHO) are well-known components of atmospheric particles and their properties can impact atmospheric chemistry and cloud formation. To get information on their hydration states in aqueous solutions and how they are affected by the addition of inorganic salts (sodium chloride (NaCl) and sodium sulfate (Na 2 SO 4)), we applied carbon and oxygen K-edge X-ray absorption spectroscopy (XAS) in transmission mode. The recorded C K-edge spectra show that glyoxal is completely hydrated in the dilute aqueous solutions, in line with previous studies. For methylglyoxal, supported by quantum chemical calculations we identified not only C-H, C=O and C-OH bonds, but also fingerprints of C-OH(CH 2) and C=C bonds. The relatively low intensity of C=O transitions implies that the monohydrated form of methylglyoxal is not favored in the solutions. Instead, the spectral intensity is stronger in regions where products of aldol condensation and enol tautomers of the monohydrates contribute. The addition of salts was found to introduce only very minor changes to absorption energies and relative intensities of the observed absorption features, indicating that XAS in the near-edge region is not very sensitive to these intermolecular organic-inorganic interactions at the studied concentrations. The identified structures of glyoxal and methylglyoxal in an aqueous environment support the uptake of these compounds to the aerosol phase in the presence of water and their contribution to secondary organic aerosol formation.

Chemical Physics Letters, Feb 1, 1979

Abstract The He I and Mg Kα photoelectron spectra of TNAP in the vapor and solid state were measu... more Abstract The He I and Mg Kα photoelectron spectra of TNAP in the vapor and solid state were measured. The first ionization potentials in the vapor and solid states are determined to be 8.67 and 7.80 eV respectively. The interpretation of the observed photoelectron spectra is carried out with the aid of photoelectron spectroscopic data of related compounds and the results of a CNDO/2 calculation. The N is peak of TNAP shows a shake-up satellite.

Physica B-condensed Matter, Jun 1, 1989

Springer eBooks, 1984

The catalytic activity of a supported metal catalyst is known to depend on the nature of the supp... more The catalytic activity of a supported metal catalyst is known to depend on the nature of the support. But the metal-support interaction has not yet been well understood, because the metal-support interaction is hidden under much pronounced metal-metal interaction. In the cases of ordinary supported metal catalysts, it is hard to derive information on the metal-support interaction from the analysis of EXAFS data. In a carbonyl-derived catalyst, metal clusters are highly and uniformly dispersed over the support (less than 10 A in diameter); therefore, this kind of catalyst may be suitable for the study of the metal-support interaction [1].

Journal of Electron Spectroscopy and Related Phenomena, Jul 1, 2023