• Journal of Electrochemical Science and Technology
• /
• v.13 no.2
• /
• pp.321-321
• /
• 2022

• Korean Chemical Engineering Research
• /
• v.48 no.3
• /
• pp.292-299
• /
• 2010

Graphene is a two-dimensional nanosheet consisting of honeycomb lattices of $sp^2$ carbon atoms. It is one of promising active materials for the anode of lithium-ion battery and the electrode of supercapacitor, due to its large specific surface area(theoretically $2600m^2\;g^{-1}$), high electric conductivity(typically $8{\times}10^5S\;cm^{-1}$), and mechanical strength. In this review, the synthetic methods of graphene nanosheet and graphene-based nanocomposite are introduced. Also, the electrochemical properties obtainable when the graphene-based materials are adopted to the electrodes of lithium-ion battery and supercapacitor are discussed along with their nanostructures.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.27 no.6
• /
• pp.289-294
• /
• 2017

Films fabricated using atomic layer 2-dimensional nanosheets exhibit various physical properties depending on the size of the nanosheet. This is because the physical properties of the film depend on the interfacial properties between the sheets. Therefore, the synthesis of large-sized nanosheets is very important because it can reduce the dependency of the film on the interfacial properties. In this study, we succeeded in fabricating $TiO_x$ nanosheets with atomic layer thickness over micrometer size by using single-crystallized starting material and its chemical exfoliation. In addition, it was revealed that the mechanical agitation speed (the stirring speed of a magnetic bar) during the exfoliation step using the organic material is closely related to the nanosheet size and the colloidal concentration of the nanosheets.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.105-106
• /
• 2013

Surface plasmon resonance (SPR) is classified into the propagating surface plasmon (PSP) excited on flat metal surfaces and the local surface plasmon (LSP) excited by metalnanoparticles. It is known that fluorescence signals are enhanced by these two SPR-fields.On the other hand, fluorescence is quenched by the energy transfer to metal (FRET). Bothphenomena are controlled by the distance between dyes and metals, and the degree offluorescence enhancement is determined by the correlation. In this study, we determined thecondition to achieve the maximum fluorescence enhancement by adjusting the distance of ametal nanoparticle 2D sheet and a quantum dots 2D sheet by the use of $SiO_2$ spacer layers. The 2D sheets consisting of myristate-capped Ag nanoparticles (AgMy nanosheets) wereprepared at the air-water interface and transferred onto hydrophobized gold thin films basedon the Langmuir-Schaefer (LS) method [1]. The $SiO_2$ sputtered films with different thickness (0~100 nm) were deposited on the AgMy nanosheet as an insulator. TOPO-cappedCdSe/CdZnS/ZnS quantum dots (QDs, ${\lambda}Ex=638nm$) [2] were also transferred onto the $SiO_2$ films by the LS method. The layered structure is schematically shown in Fig. 1. The result of fluorescence measurement is shown in Fig. 2. Without the $SiO_2$ layer, the fluorescence intensity of the layered QD film was lower than that of the original QDs layer, i.e., the quenching by FRET was predominant. When the $SiO_2$ thickness was increased, the fluorescence intensity of the layered QD film was higher than that of the original QDs layer, i.e., the SPR enhancement was predominant. The fluorescence intensity was maximal at the $SiO_2$ thickness of 20 nm, particularly when the LSPR absorption wavelength (${\lambda}=480nm$) was utilized for the excitation. This plasmonic nanosheet can be integrated intogreen or bio-devices as the creation point ofenhanced LSPR field.

• Applied Chemistry for Engineering
• /
• v.31 no.6
• /
• pp.668-673
• /
• 2020

In this work, ultrathin and two-dimensional (2D) cobalt hydroxide [Co(OH)2] nanosheets were synthesized by a sonication assisted liquid-phase exfoliation of bulk Co(OH)2. The resulting exfoliated Co(OH)2 is a hexagonal mono-layered nanosheet with a high specific surface area of 27.5 ㎡ g-1. The depolymerization of polyethylene terephthalate (PET) based on glycolysis reaction was also performed using an exfoliated Co(OH)2 catalyst. Excellent catalytic reaction performances were demonstrated; a high PET conversion and bis(2-hydroxyethyl) terephthalate (BHET) yield of both 100% using the nanosheet catalyst were achieved within a reaction time and temperature of 30 min and 200 ℃, respectively. The long-term stability of exfoliated Co(OH)2 catalysts was also demonstrated by recyclability tests of the catalyzed glycolysis reaction of PET over four cycles, showing both 100% of high PET conversion and BHET yield.

• Journal of Sensor Science and Technology
• /
• v.23 no.6
• /
• pp.388-391
• /
• 2014

The most promising application of the biofuel cells is implantable devices, so the biofuel cells should have an appropriate shape for the vascular vessel. We demonstrated the biofuel cell roll for using in tubes. MWNTs were aggregated by vacuum filtration on a nitrocellulose membrane filter, which was biocompatible and flexible. The MWNT aggregated nitrocellulose membrane used the electrodes of the biofuel cells because it was conductive as well as nanostuructured. Then, the membrane was rolled into the roll shape. The maximum power density of the biofuel cell roll was $7.9{\mu}W/cm^2$ at 153mV and 50 mM glucose. Also, the power density is expected to increase in its practical application if there is flow in the tube, which makes the transportation of fuel easy. The biofuel cell roll contacts with the wall of the tube, so flow in the tube does not disturb. Also, the biofuel cell roll has multi-layers offering more electroactive area.

• Korean Journal of Materials Research
• /
• v.30 no.12
• /
• pp.641-649
• /
• 2020

A facile microwave assisted solvothermal process is designed for fabricating SnS nanoparticles decorated on graphene nanosheet, which used as visible light driven photocatalyst. Some typical characterization techniques such as XRD, FT-IR, SEM with EDX analysis, and TEM and BET analysis are used to analyse the physical characteristics of as-prepared samples. Spherical SnS nanoparticles are uniformly dispersed on the surface of graphene nanosheet due to ammonia, which can prevent the aggregation of graphene oxide. Meanwhile, microwave radiation provides fast energy that promotes the formation of spherical SnS nanoparticles within a short time. The visible light photocatalytic activity of as-prepared SnS-GR nanocomposites is analysed through photodegradation efficiency of methylene blue with high concentration. According to the higher photocatalytic property, the as-prepared SnS-GR nanocomposites can be expected to be an efficient visible light driven photocatalyst. After five cycles for decolorization, the rate decreases from 87 % to 78 % (about 9 %). It is obvious that the photocatalytic activity of SnS-GR nanocomposite has good repeatability.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.32 no.2
• /
• pp.51-54
• /
• 2022

The physical properties of the noble metal current-collector used for fuel cells are greatly influenced by the material porosity. Therefore, increasing the porosity of the material studies has attracted much attention. One of the most representative strategies is to use porosity additives in sintering materials. The conventional porosity additive had a threedimensional structure of a spherical powder. In this study, porosity additive with 2-dimensional (2D) nanosheet was used to decrease the sintering density of Ag current-collector and its effect was confirmed. As a 2D layered structure material, 1 nm-thick RuO₂ nanosheets were used as porosity additives.

• Vacuum Magazine
• /
• v.5 no.2
• /
• pp.18-22
• /
• 2018

wo dimensional (2D) van der Waals (vdW) nanosheet semiconductors have recently attracted much attention from researchers because of their potentials as active device materials toward future nano-electronics and -optoelectronics. This review mainly focuses on the features and applications of state-of-the-art vdW 2D material devices which use transition metal dichalcogenides, graphene, hexagonal boron nitride (h-BN), and black phosphorous: field effect transistors (FETs), complementary metal oxide semiconductor (CMOS) inverters, Schottky diode, and PN diode. In a closing remark, important remaining issues of 2D vdW devices are also introduced as requests for future electronics and photonics applications.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.60-60
• /
• 2015

Nanosheets of graphene and related 2D materials have attracted much attention due to excellent physical, chemical and mechanical properties. Single-layer graphene (SLG) was first synthesized by Blakely et al in 1974 [1]. Following his achievements, we initiated the growth and characterization of graphene and h-BN on metal substrates using surface segregation and precipitation in 1980s [2,3]. There are three important steps for nanosheet growth; surface segregation of dopants, surface reaction for monolayer phase, and subsequent 3-D growth (surface precipitation). Surface phase transition was clearly demonstrated on C-doped Ni(111) by in situ XPS at elevated temperatures [4]. The growth mode was clarified by inelastic background analysis [5]. The surface segregation approach has been applied to C-doped Pt(111) and Pd(111), and controllable growth of SLG has been demonstrated successfully [6]. Recently we proposed a promising method for producing SLG fully covering an entire substrate using Ni films deposited on graphite substrates [7]. A universal method for layer counting has been proposed [8]. In this paper, we will focus on the effect of competitive surface-site occupation between carbon and other surface-active impurities on the graphene growth. It is known that S is a typical impurity of metals and the most surface-active element. The surface sites shall be occupied by S through surface segregation. In the case of Ni(110), it is confirmed by AES and STM that the available surface sites is nearly occupied by S with a centered $2{\times}2$ arrangement. When Ni(110) is doped with C, surface segregation of C may be interfered by surface active elements like S. In this case, nanoscopic characterization has discovered a preferred directional growth of SLG, exhibiting a square-like shape (Fig. 1). Also the detailed characterization methodologies for graphene and h-BN nanosheets, including AFM, STM, KPFM, AES, HIM and XPS shall be discussed.