Youngsin Park

Youngsin Park
Ulsan National Institute of Science and Technology | UNIST · School of Natural Science

About

139
Publications
18,677
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2,013
Citations
Additional affiliations
March 2001 - February 2010
Dongguk University
Position
  • Accociate professor

Publications

Publications (139)
Article
The self-assembly phenomenon plays a significant role in atomic, molecular, and biological self-assemblies. This phenomenon has also been found in colloidal nanocrystals (NCs). Self-assembly of colloidal NCs into superstructures is a flexible and promising approach for manipulating nanometre-sized particles and exploiting physical and chemical prop...
Article
Halide perovskites (HPs) are used in various applications, including solar cells, light-emitting diodes, lasers, and photodetectors. These materials have recently received a great deal of attention as high-energy radiation detectors and scintillators due to their excellent light yield, mobility-lifetime product (µτ), and X-ray sensitivity. In addit...
Article
The organic-inorganic hybrid perovskite methylammonium lead bromide nanocrystals are an important class of light-emitting materials. However, their poor stability under humid conditions hampers their practical applications. Herein, for the first time, MAPbBr3 NCs have been successfully assembled with various clays, such as kaolinite, montmorillonit...
Article
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The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nanolasers. While nonreso...
Preprint
Full-text available
The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nano-lasers. Whilst non-r...
Article
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We have characterized the carrier dynamics of the excitonic emission emerging from a monolayer of graphene grown on a Cu(111) surface. Excitonic emission from the graphene, with strong and sharp peaks both with a full-width at half-maximum of 2.7 meV, was observed near ~3.16 and ~3.18 eV at 4.2 K. The carrier recombination parameters were studied b...
Article
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Fe undergoes a corrosion process under aerobic conditions. Oxidized forms of Fe lose malleability, durability, and other critical physical properties. For spintronic applications, alloy forms or capping layers are used to modulate the properties of Fe. Observing the Fe(111) spin structure is critical for practical applications. We suggest a method...
Article
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The effect of surface passivation on the photoluminescence (PL) emitted by CsPbBr3 micro/nano-rods coated with Pb(OH)2 is investigated, where a high quantum yield and excellent stability for the emission are found. The CsPbBr3/Pb(OH)2 rods generally present a peak that is blue shifted compared to that seen in rods without a hydroxide cladding at lo...
Article
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Inorganic perovskite lasers are of particular interest, with much recent work focusing on Fabry-Pérot cavity-forming nanowires. We demonstrate the direct observation of lasing from transverse electromagnetic (TEM) modes with a long coherence time ~9.5 ps in coupled CsPbBr3 quantum dots, which dispense with an external cavity resonator and show how...
Article
Poor solubility of π-conjugated two-dimensional polymers (C2Ps) has been a significant roadblock in incorporating these emergent materials into electronic devices by simple solution processing. Here, we report a rational design of triphenylene-based building blocks that condense via a series of reversible reactions for self-error-correction and a f...
Article
Diminishing surface defect states in perovskite nanocrystals is a highly challenging subject for enhancing optoelectronic device performance. We synthesized organic/inorganic lead-halide perovskite MAPbBr3 (MA = methylammonium) clusters comprising nanocrystals with diameters ranging between 20–30 nm and characterized an enhanced photoluminescence (...
Article
Two-dimensional (2D) heterostructured or alloyed monolayers composed of transition metal dichalcogenides (TMDCs) have recently emerged as promising materials with great potential for atomically thin electronic applications. However, fabrication of such artificial TMDC heterostructures with a sharp interface and a large crystal size still remains a...
Article
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A numerical study on spin-polarized transport properties in a quasi-one-dimensional wire with Rashba quantum dots is presented. The ballistic spin transmission probability and spin density profiles are obtained using the quantum transmitting boundary method. The Fano-Rashba effect on the spin transmission is analyzed as a function of the Rashba spi...
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We report the electronic structure of the Au-intercalated graphene/Ni(111) surface using angle-resolved photoemission spectroscopy and low energy electron diffraction. The graphene/Ni(111) shows no Dirac cone near the Fermi level and a relatively broad C 1s core level spectrum probably due to the broken sublattice symmetry in the graphene on the Ni...
Article
Supercapacitors based on nanomaterial electrodes exhibit great potential as power sources for advanced electronic devices. From a practical viewpoint, it is desirable to fabricate highly active and sustainable nanomaterial electrodes consisting of non-precious elements using a simple technique in a controllable way. In this work, we report the synt...
Article
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We have investigated the emission from InGaN/GaN quantum disks grown on the tip of GaN nanorods. The emission at 3.21 eV from the InGaN quantum disk doesn’t show a Stark shift, and it is linearly polarized when excited perpendicular to the growth direction. The degree of linear polarization is about 39.3% due to the anisotropy of the nanostructures...
Article
Structural and optical properties of InxGa1-xN/GaN multi quantum disks (QDisks) grown on GaN nanorods by molecular beam epitaxy have been investigated by transmission electron microscopy and micro-photoluminescence (PL) spectroscopy. Two types of InGaN QDisks were grown: a pseudo-3D confined InGaN pillar-type QDisks embedded in GaN nanorods; and QD...
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Photoluminescence measurements in mono- and bilayer-MoS2 on SiO2 were undertaken to determine the thermal effect of the MoS2/SiO2 interface on the optical bandgap. The energy and intensity of the photoluminescence from monolayer MoS2 were lower and weaker than those from bilayer MoS2 at low temperatures, whilst the opposite was true at high tempera...
Article
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Through Bi deposition on the single-crystalline MoS2 surface, we find that the density of the sulfur vacancy is a critical parameter for the growth of the crystalline Bi overlayer or cluster at room temperature. Also, the MoS2 band structure is significantly modified near Γ due to the orbital hybridization with an adsorbed Bi monolayer. Our experim...
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We provide a new insight that the sulphur-depleted MoS2 surface can store hydrogen gas at room temperature. Our findings reveal that the sulphur-vacancy defects preferentially serve as active sites for both hydrogen chemisorption and physisorption. Unexpectedly the sulphur vacancy instantly dissociates the H2 molecules and strongly binds the split...
Article
Nanogranular tungsten oxide (WO3) with excess oxygen is synthesized and its battery performance is evaluated as an anode material for the Li-ion battery (LIB). The formation of a monoclinic WO3 phase is confirmed using X-ray diffraction (XRD) and micro (µ)-Raman spectroscopy analyses. The Rutherford back scattering results confirm the existence of...
Article
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We demonstrate a facile synthetic method to prepare lateral size controlled molybdenum diselenide (MoSe2) nanosheets using liquid phase exfoliated few-layer MoSe2 nanosheets as a starting material. By precisely controlling the centrifugation condition, preparation of MoSe2 nanosheets with a narrow size distribution ranging from several hundred nano...
Article
The current work reports on the effect of annealing temperatures on the morphology and photoluminescence properties of SrAl2O4: Eu, Dy thin films on sapphire (0001) substrates fabricated by pulsed laser deposition technique. Scanning electronic microscopy and atomic force microscopy were used to investigate the thickness, surface topography, and th...
Article
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The dataset presented here is related to the research article entitled “Highly Efficient Electro-optically Tunable Smart-supercapacitors Using an Oxygen-excess Nanograin Tungsten Oxide Thin Film” (Akbar I. Inamdar, Jongmin Kim, Yongcheol Jo, Hyeonseok Woo, Sangeun Cho, Sambhaji M. Pawar, Seongwoo Lee, Jayavant L. Gunjakar, Yuljae Cho, Bo Hou, Seung...
Article
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This spotlight discusses intriguing properties and diverse applications of graphene (Gr) and Gr analogs. Gr has brought us 2-dimensional (2D) chemistry with its exotic 2D features of density of states (DOS). Yet, some of the 2D or 2D-like features can be seen on surfaces and at interfaces of bulk materials. The substrate on Gr and functionalization...
Article
A smart supercapacitor shares the same electrochemical processes as a conventional energy storage device while also having electrochromic functionality. The smart supercapacitor device can sense the energy storage level, which it displays in a visually discernible manner, providing increased convenience in everyday applications. Here, we report an...
Article
Ruthenium oxide (RuO2) is fabricated on graphene (Gr)-coated Copper (Cu) foil by using a cathodic electroplating technique for flexible supercapacitor electrode applications. The electrochemical properties of the RuO2/Gr/Cu electrode are investigated with a conventional three electrode configuration in 0.5 M H2SO4 electrolyte. The graphene insertio...
Article
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Due to its unique layer-number dependent electronic band structure and strong excitonic features, atomically thin MoS2 is an ideal 2D system where intriguing photoexcited-carrier-induced phenomena can be detected in excitonic luminescence. We perform micro-photoluminescence (PL) measurements and observe that the PL peak redshifts nonlinearly in mon...
Article
Optical anisotropy in monolayer- and bilayer-MoS2 was investigated by polarization resolved photoluminescence measurements. The photoluminescence of monolayer-MoS2 is found to be partially polarized at 4.2 K and maintains this polarization characteristic up to room temperature, while the photoluminescence of bilayer-MoS2 shows no obvious polarizati...
Article
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A novel water-soluble inorganic Ca(NO3)2 salt electrode is investigated for its pseudocapacitance in an aqueous KOH electrolyte. Commercially available Ca(NO3)2 salt is directly used as the key electrode material. The supercapacitor electrode contains Ca(NO3)2 salt, carbon black, and polyvinylidene fluoride (PVDF) in a ratio of 80:10:10. The Ca(NO3...
Article
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Despite having outstanding electrical properties, graphene is unsuitable for optical devices because of its zero band gap. Here, we report two-dimensional excitonic photoluminescence (PL) from graphene grown on a Cu(111) surface, which shows an unexpected and remarkably sharp strong emission near 3.16 eV (full width at half-maximum ≤3 meV) and mult...
Article
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By using higher acceleration energies than the displacement energy of Mo atoms, the electron irradiation on the layered MoS2 single crystals is found to be an effective and simple method to induce the diamagnetic to ferromagnetic phase transition persisting up to room temperature. The easy axis can be controllable by regulating the electron dose an...
Article
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1 T phase incorporation into 2H-MoS2 via an optimal electron irradiation leads to induce a weak ferromagnetic state at room temperature, together with the improved transport property. In addition to the 1T-like defects, the electron irradiation on the cleaved MoS2 surface forms the concentric circle-type defects that are caused by the 2 H/1 T phase...
Article
Despite having outstanding electrical properties, graphene is unsuitable for optical devices because of its zero band gap. Here, we report two-dimensional excitonic photoluminescence (PL) from graphene grown on Cu(111) surface, which shows an unexpected remarkably sharp and strong emission near 3.16 eV (full-width at half-maximum $\leq$ 3meV) and m...
Article
Full-text available
We investigated the optical properties of Ge nanocrystals surrounded by Ge3N4. The broad emission ranging from infrared to blue is due to the dependence on the crystal size and preparation methods. Here, we report high resolution Photoluminescence (PL) attributed to emission from individual Ge nanocrystals (nc-Ge) spatially resolved using micro-pho...
Article
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We report that the hydrogenation of a single crystal 2H−MoS2 induces a novel-intermediate phase between 2H and 1T phases on its surface, i.e., the large-area, uniform, robust, and surface array of atomic stripes through the intralayer atomic-plane gliding. The total energy calculations confirm that the hydrogenation-induced atomic stripes are energ...
Article
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We have investigated an effective method to control the diameter and the density of carbon nanotubes (CNTs) by introducing a catalyst-embedded supporting layer (CSL) prepared by using rf-magnetron sputtering with a mixed target consisting of Fe and Al2O3. The type of CNTs was changed from single-walled CNTs with a diameter of 0.85 ~ 1.55 nm to mult...
Article
We investigate nontrivial surface effects on the optical properties of self-assembled crystalline GaN nanotubes grown on Si substrates. The excitonic emission is observed to redshift by ~ 100 meV with respect to that of bulk GaN. We find that the conduction band edge is mainly dominated by surface atoms, and that a larger number of surface atoms fo...
Article
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The optical transitions of the three-dimensionally confined GaN/AlGaN asymmetric multi quantum disks were characterized by micro photoluminescence and time-resolved photoluminescence. Several fine emission lines, originating from the wide and narrow quantum disks, were observed around 3.7 eV from a single nanocolumn dispersed on a patterned SiO2 su...
Article
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Graphene on metal substrates often shows different electronic properties from isolated graphene because of graphene-substrate interactions. One needs to remove the metals with acids and then to transfer graphene to weakly interacting substrates to recover electrical properties inherent in graphene. This process is not easy and besides causes undesi...
Article
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Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T C=50 K. It is likely that the ferromagne...
Article
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We report the effective methods to induce weak ferromagnetism in pristine ${\mathrm{MoS}}_{2}$ persisting up to room temperature with the improved transport property, which would lead to new spintronics devices. The hydrogenation of ${\mathrm{MoS}}_{2}$ by heating at $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ for 1 h leads to the ea...
Article
Semiconductor nanopyramids (NPs) provide advantages in the development of novel functional optoelectronic devices due to their unique size-dependent properties. Here we demonstrate a new method for the fabrication of selectively self-assembled single-crystalline GaN NPs on the m-plane of periodically strained GaN/InGaN multiquantum disks embedded i...
Article
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The electronic band structure of MoS2 single crystals has been investigated using angle-resolved photoelectron spectroscopy and first-principles calculations. The orbital symmetry and k dispersion of these electronic states responsible for the direct and the indirect electronic band gaps have been unambiguously determined. By experimentally probing...
Article
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We have investigated the magnetic and optical properties of dislocation-free vertical GaN nanorods with diameters of 150 nm grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by ext...
Article
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We have investigated the optical properties of vertical GaN nanorods with diameters of 150 nm grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photo...
Article
The optical properties of GaN nanocolumns containing pairs of InxGa1–xN (x ∼ 0.1) quantum disks (QDisks) have been experimentally measured. Strain simulations reveal an inhomogeneous distribution of strain, and furthermore, a relaxation between successive QDisks along the growth direction of the column. Although this inhomogeneous distribution of s...
Article
Time-integrated and time-resolved microphotoluminescence studies were carried out on In{sub x}Ga{sub 1-x}N quantum disks embedded in GaN nanocolumns grown by molecular beam epitaxy. Emission at {approx}3.33 eV from confined states was detected and observed to blueshift with excitation power; a result of charge screening and the quantum confined Sta...
Article
We investigated the carrier transition properties of the GaN/InGaN/GaN single quantum well bounded by AlGaN barriers. In order to confirm the carrier transition coming from the single quantum well, the single quantum well layer was etched by reactive ion etching method. The structural property of the samples was characterized by high resolution X-r...
Article
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Microphotoluminescence studies were carried out on a single GaN nanocolumn containing a single InGaN quantum disk (QDisk) that had been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in...