A5006571034- Organic Light-Emitting Diodes Research
- Crystallization and Solubility Studies
- X-ray Diffraction in Crystallography
- Organic Electronics and Photovoltaics
- Conducting polymers and applications
- X-ray Spectroscopy and Fluorescence Analysis
- Electron and X-Ray Spectroscopy Techniques
- Luminescence and Fluorescent Materials
- Molecular Junctions and Nanostructures
- Advanced X-ray Imaging Techniques
- Crystallography and molecular interactions
- Advanced Chemical Physics Studies
- Particle Accelerators and Free-Electron Lasers
- Advanced Electron Microscopy Techniques and Applications
- Boron Compounds in Chemistry
- Organoboron and organosilicon chemistry
- Graphene research and applications
- Crystallography and Radiation Phenomena
- Thin-Film Transistor Technologies
- Radioactive element chemistry and processing
- Synthesis and Biological Evaluation
- Diamond and Carbon-based Materials Research
- Transition Metal Oxide Nanomaterials
- Chalcogenide Semiconductor Thin Films
- Ion-surface interactions and analysis
Pohang University of Science and Technology
2015-2024
Pohang Accelerator Laboratory
2002-2024
Korea University
2008-2014
Korea Institute of Science and Technology
2013
Ewha Womans University
2008
Columbia University
2008
Institute for Advanced Engineering
2005
Yonsei University
1998-2001
Carborane-based host materials were prepared to fabricate deep blue phosphorescence organic light-emitting diodes (PHOLEDs), which constituted three distinctive geometrical structures stemming from the corresponding different isomeric forms of carboranes, namely, ortho-, meta-, and para-carboranes. These consist two carbazolyl phenyl (CzPh) groups as photoactive units on each side carborane carbons be bis[4-(N-carbazolyl)phenyl]carboranes, o-Cb, m-Cb, p-Cb. To elaborate role comparative...
A bright combination: a new type of donor-acceptor dyad, carbazolylaryl-substituted ortho-carboranes, which are conveniently prepared from the corresponding acetylenes and decaborane pathways, showed unique excited-state behavior associated with electron transfer unlike meta- para-counterparts.
The construction of Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), a 0.1-nm hard free-electron laser (FEL) facility based on 10-GeV S-band linear accelerator (LINAC), is achieved in Pohang, Korea by the end 2016. 1.11 km-long building was completed 2014, and installation LINAC undulators started January 2015. LINAC, together with beamlines, commissioning began April 2016, first lasing FEL line 14 June progress PAL-XFEL its commission are reported here.
Inverted quantum dot based light-emitting diodes (QDLED) were simply fabricated by an all solution processing. Polyethylenimine ethoxylated (PEIE) was used as a surface modifier in the device, to reduce indium tin oxide (ITO) electrode work function below 3.08 eV. Based on transmission electron microscopy (TEM) results, CdSe–ZnS QDs with 8 nm size uniformly distributed form monolayer PEIE/ITO glass substrate. In this inverted QDLED, hybrid polymers [poly(N-vinylcarbazole) +...
Abstract o ‐Carborane‐based donor–acceptor dyads comprising an ‐carboranyl phenyl unit combined with N‐ carbazole ( 1 ) or 4‐phenyl‐ N ‐carbazole 2 were prepared, and their dyad characters confirmed by steady‐state photochemistry photodynamic experiments as well electrochemical studies. The absorption properties of the essentially sum those units; this indicates negligible interaction between ‐carborane units in ground state. However, emission spectra indicated that fluorescence was...
Using light to control transient phases in quantum materials is an emerging route engineer new properties and functionality, with both thermal non-thermal observed out of equilibrium. Transient are expected be heterogeneous, either through photo-generated domain growth or by generating topological defects, this impacts the dynamics system. However, nanoscale heterogeneity has not been directly observed. Here we use time- spectrally resolved coherent X-ray imaging track prototypical induced...
Carrier dynamics affects photocatalytic systems, but direct and real-time observations in an element-specific energy-level-specific manner are challenging. In this study, we demonstrate that the of photo-generated holes metal oxides can be directly probed by using femtosecond X-ray absorption spectroscopy at free-electron laser. We identify energy level life time with a long (230 pico-seconds) nano-crystal materials. also observe trapped show distribution bandgap region formation 0.3...
Color-tunable Zn(II) complexes of the type Zn( N,O-OPh (OxZ)ArX) 2 ( 5), where ligand consists an oxazolylphenolate ion connected at 4-position by a 2,4-substituted aryl functional group with X = NMe a, OMe b, Ph c, Cl d, F e, and CN f, were prepared. X-ray structural studies 5a, 5b, 5e showed that zinc atom was positioned in distorted tetrahedral coordination environment created two ligands N,O-chelation. Hammet plots absorption emission maxima, respectively, UV photoluminescence (PL)...
Eine einleuchtende Verbindung: neue Klasse von Donor-Akzeptor- Systemen – Carbazolylaryl-substituierte ortho-Carborane wurde aus den entsprechenden Acetylenen und Decaboran hergestellt. Sie zeigen ein ungewöhnliches Verhalten der angeregten Zustände, indem sie, anders als die para- meta-Verbindungen, Elektronentransfers eingehen (siehe Bild). Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents peer-reviewed, but not copy-edited or...
A series of bulky aryl-substituted asymmetric anthracene blue host materials, 9-(2-naphthyl)-10-(3-(1-naphthyl)phenyl)anthracene, where phenyl was varied from H (5a), Me (5b), Ph (5e), and 1-Naph (5f) at the 6-position (5c) 2-position, synthesized by Suzuki coupling reaction between 10-(2-naphthyl)anthracene-9-boronic acid 1-(3-iodophenyl)naphthalene derivatives. less anthracene, 9-(2-naphthyl)-10-(2,5-diphenyl)phenyl)anthracene (5d), also for comparison. All anthracenes showed high glass...
Wide-band-gap phosphorescent organic light-emitting diode (OLED) host materials were developed employing the tetrahedral structural motif of silicon atom, which functioned further to connect 4-(N-carbazolyl)phenyl (CP) units in its periphery (2a−2d). The thermal, photophysical, and electrochemical properties, X-ray studies as well OLED device characteristics fully investigated. Silicon effectively disconnected charge delocalization between CP units. By low temperature PL study, triplet...
Hematite, α-Fe2O3, is an important semiconductor for photoelectrochemical water splitting. Its low charge carrier mobility and the presence of midgap states provide favourable conditions electron-hole recombination, hence affecting semiconductor's efficiency. The nature excited state transport in hematite strongly debated. In order to further understand fundamental properties photoexcited state, we conducted femtosecond 2p (L3) X-ray absorption (XAS) 2p3d resonant inelastic scattering (RIXS)...
We report an overview of soft X-ray scientific instruments and optics at the free electron laser (FEL) Pohang Accelerator Laboratory, with selected first-commissioning results. The FEL exhibited a pulse energy 200 μJ/pulse, width <50 fs full half maximum, bandwidth 0.44% photon 850 eV. Monochromator resolving power 10 500 was achieved. estimated total time resolution between optical pulses <270 fs. A resonant inelastic scattering spectrometer set up; its commissioning results...
A series of trimethylsilyl-substituted dithieno-spiro-siloles (3), with a four- to six-membered silacycloalkyl substituent at the 1,1-position, were prepared by reacting 3,3′-dilithio-5,5′-bis(trimethylsilyl)-2,2′-dithiophene (2) corresponding dichlorosilane precursors (1). Arylamino-substituted bis(diarylamino)dithieno-spiro-siloles (6) also using same synthetic protocol 3,3′-dilithio-5,5′-bis(diarylamino)-2,2′-dithiophene (5) 1. structural study five-membered dithieno-spiro-silole,...
The interfacial energy level alignment of hole injection layers with WO3 insertion in an inverted organic light-emitting diode structure and its influence on electroluminescence have been studied using situ X-ray, ultraviolet photoelectron spectroscopy, device measurements. barrier for N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) upon Al deposition was estimated to be 1.37 eV, which makes anode unfavorable injection. With a thin layer deposited onto the NPB, NPB...
Resonant elastic x-ray scattering has been widely employed for exploring complex electronic ordering phenomena, such as charge, spin, and orbital order, in particular, strongly correlated systems. In addition, recent developments pump–probe allow us to expand the investigation of temporal dynamics orders. Here, we introduce a new time-resolved Soft X-ray Scattering (tr-RSXS) endstation developed at Pohang Accelerator Laboratory Free Electron Laser (PAL-XFEL). This an optical laser...
Abstract A series of four‐coordinate boron compounds the type N , O ‐(OPh OxZ ArX)BPh 2 or NPh )BPh ( 5a – g ) has been prepared by treating triphenylboron (TPB) with2‐(4,4‐dimethyl‐4,5‐dihydrooxazol‐2‐yl)‐4‐X‐arylphenols(HOPh ArX; 4a f 2‐(4,4‐dimethyl‐4,5‐dihydrooxazol‐2‐yl)‐4‐(4‐diphenylamino)phenol (HOPh ; 4g ). systematic change in electronic structures is achieved these incorporating electron‐withdrawing (EW) and ‐donating (ED) groups [ArX (X = 4‐cyano‐, 2,4‐difluoro‐, 4‐chloro‐,...
A coherent green fluorescence was obtained by butylation at the 2-position of panchromatic 2,3-diaryl-5,8-diarylquinoxalines (2) to give corresponding 2-butyl-2,3-diaryl-5,8-diaryl-1H-quinoxalines (3). Full color quinoxaline derivatives were prepared from electronic modification either 2,3- or 5,8-positions peripheral ArX group X (X = -H, -OMe, -NPh(2), -NMe(2), -NMePh) quinoxalines. 2-Butylation converted one imine unit pyrazine ring an amine group, which effectively altered electron donor...
Femtosecond carrier dynamics in layered 2H-MoTe2 semiconductor crystals have been investigated using soft x-ray transient absorption spectroscopy at the free-electron laser (XFEL) of Pohang Accelerator Laboratory. Following above-bandgap optical excitation 2H-MoTe2, photoexcited hole distribution is directly probed via short-lived transitions from Te 3d 5/2 core level (M5-edge, 572-577 eV) to transiently unoccupied states valence band. The optically excited electrons are separately reduced...
Hematite (α-Fe2O3) is a photoelectrode for the water splitting process because of its relatively narrow bandgap and abundance in earth's crust. In this study, photoexcited state hematite thin film was investigated with femtosecond oxygen K-edge X-ray absorption spectroscopy (XAS) at PAL-XFEL order to follow dynamics states. The 200 fs decay time hole valence band observed via corresponding XAS feature.