Photodissociation dynamics of water at Lyman alpha (121.6nm)

Yi, Whikun,Park, Jaehong,Lee, Jungwoo Elsevier 2007 Chemical physics letters Vol.439 No.1

<P><B>Graphical abstract</B></P><P>Laser induced fluorescence studies of hydrogen atom using four wave mixing technique are reported for the photodissociation of H<SUB>2</SUB>O and D<SUB>2</SUB>O at Lyα (121.6nm). The average kinetic energy of hydrogen atom, H/D ratio, and absolute quantum yield for water molecule are obtained.</P><ce:figure></ce:figure> <P><B>Abstract</B></P><P>Laser induced fluorescence studies of hydrogen atom using four-wave mixing technique are reported for the photodissociation of H<SUB>2</SUB>O and D<SUB>2</SUB>O at Lyα (121.6nm). The source of dissociating and probe radiation was one and the same (delay time⩽20ns). The average translational energy of ejected hydrogen atoms (34.5Kcal/mol) revealed that H<SUB>2</SUB>O+<I>hν</I>→H+OH(<I>X</I><SUP>2</SUP>Π) and H<SUB>2</SUB>O+<I>hν</I>→H<SUB>2</SUB>+O(<SUP>1</SUP>D) were the main dissociation processes. The absolute quantum yield for H<SUB>2</SUB>O and D<SUB>2</SUB>O were <I>Φ</I><SUB>H</SUB>(H<SUB>2</SUB>O)=1.39±0.09 and <I>Φ</I><SUB>H</SUB>(D<SUB>2</SUB>O)=1.21±0.20, respectively. The branching ratio of HDO, <I>Φ</I><SUB>H</SUB>(HDO)/<I>Φ</I><SUB>D</SUB>(HDO), was found to be 1.66±0.50, following the procedure developed by Shafer et al. [Shafer et al., J. Chem. Phys. 90 (1999) 6807].</P>

Single-Walled Carbon Nanotubes as a Chemical Sensor for <tex> $\hbox{SO}_{2}$</tex> Detection

SeGi Yu,Whikun Yi IEEE 2007 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol.6 No.5

<P>Single-walled carbon nanotubes (SWNTs) are Introduced as a chemical sensor for the detection of sulfur dioxide (SO<SUB>2</SUB>) molecules. For a single bundle of SWNTs, current-voltage (I-V) curves were measured for a series of different temperatures under adsorption of SO<SUB>2</SUB> molecules. The I-V characteristics for a 'MAT'-type thin film SWNTs, with respect to the amount of SO<SUB>2</SUB> adsorbed, were measured at room temperature and compared directly with O<SUB>2</SUB> adsorption. The change in current upon the adsorption of SO<SUB>2</SUB> is distinctly higher than that of O<SUB>2</SUB>, and is also reversible for adsorption and successive evacuation. Thus, the results strongly suggested that a thin film of SWNTs can be used as a chemical sensor in the nanometer scale devices.</P>

Improved Field Emission Currents of Carbon Nanotubes after Laser Irradiation

이정우,Jaehong Park,Whikun Yi* 대한화학회 2006 Bulletin of the Korean Chemical Society Vol.27 No.10

Field emission (FE) currents were measured for silver-pasted and glass-pasted single-walled carbon nanotubes (SWNTs) after illuminating the tubes with a pulsed 532 nm laser. A very low turn-on field of approximately 0.4 V/m m and a high current density ~1700 m A/cm2 at 3.5 V/m m was obtained for the silver-pasted SWNTs after laser irradiation but on the whole, no improvements were found for the glass-pasted SWNTs. Two roles of laser irradiation for the silver-pasted SWNTs were proposed. First, the embedded SWNTs and SWNT bundles inside the silver paste were immerged on the outer surface due to an instantaneous melting or annealing of the silver metals by the laser resulting in an increase of the field emission sites. Second, the laser irradiation was thought to improve the electrical contact between SWNTs and the silver metal by reducing the contact resistance via laser-induced thermal annealing, which was responsible for increasing the FE currents.

Double - to one - humped secondary electron emission curve change for thermal silicon oxide layers

SeGi Yu,TaeWon Jeong,Whikun Yi,Jeonghee Lee,S.H. Jin,J.M. Kim,D. Jeon 한국진공학회 2000 한국진공학회 학술발표회초록집 Vol.- No.-

Field emission enhancement of PbS colloidal quantum dot-decorated single-walled carbon nanotubes

Yang, Jonghee,Lee, Junyoung,Yi, Whikun Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.809 No.-

<P><B>Abstract</B></P> <P>Herein, a simple and effective PbS colloidal quantum dot (CQD) decoration method for single-walled carbon nanotube (SWNT) is demonstrated. By dipping the SWNT film into a CQD dispersion followed by a solid-state ligand exchange, CQDs were successfully decorated onto the wall of SWNT without compromising a narrow size distribution. Spectroscopic studies suggested that (1) the CQD decoration and subsequent ligand exchange process did not alter the chemical nature of the SWNT framework and (2) there was a charge (electron) transfer process from the PbS CQD to the SWNT. Field emission (FE) characteristics of the CQD-decorated SWNT films revealed that FE enhancement was indeed established from SWNTs with a moderate degree of CQD decoration, while those with excessive decoration (coating) exhibited notable FE suppression. Horizontal current-voltage measurements with perpendicular-directional external electric field modulation suggested that electron supplement of SWNT from PbS CQD was pronounced as the amount of decorated CQDs increased. Based on the experimental results, we proposed a new mechanism demonstrating FE enhancement of a CQD/SWNT heterostructure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Colloidal quantum dots (CQDs) are decorated to single-walled carbon nanotubes (SWNTs) via iodide-based ligand exchange. </LI> <LI> Several evidences for electron transfer from CQD to SWNT and the resultant field emission enhancement are observed. </LI> <LI> <I>I</I>-<I>V</I>-<I>E</I> measurement support that the external electric field additionally supply electrons from CQD to SWNT. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electric-Field Enhancement of Photovoltaic Devices: A Third Reason for the Increase in the Efficiency of Photovoltaic Devices by Carbon Nanotubes

Lee, Wonjoo,Lee, Jungwoo,Yi, Whikun,Han, Sung-Hwan WILEY-VCH Verlag 2010 Advanced Materials Vol.22 No.20

<B>Graphic Abstract</B> <P>Electric-field enhancement of photovoltaic devices by carbon nanotubes (CNTs) is reported as a third alternative for increasing the efficiency of photovoltaic devices. Due to the formation of an efficient electronic energy-cascade structure, the decrease of the interfacial resistance, and the improvement of the electrical field, the power-conversion efficiency of solar cells was increased by 22% in the presence of the SWNTs. <img src='wiley_img_2010/09359648-2010-22-20-ADMA200903841-content.gif' alt='wiley_img_2010/09359648-2010-22-20-ADMA200903841-content'> </P>

Field emission properties of a three-dimensional network of single-walled carbon nanotubes inside pores of porous silicon.

Lee, Jungwoo,Park, Taehee,Lee, Jongtaek,Yi, Whikun American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.8

<P>We report characteristic field emission (FE) properties of single-walled carbon nanotubes (SWCNTs) synthesized inside the pores as well as on the top surface of a porous silicon (PS) substrate. Turn-on fields and emission current densities were measured and compared with those of other types of SWCNTs in similar environments. Investigation of the FE properties of SWCNTs synthesized inside the pores of a PS substrate revealed a low turn-on field of approximately 2.25 V/μm at 10 μA/cm2 and a high field-enhancement factor (6182) compared with other samples. A life-time stability test was performed by monitoring the current density before and after repeated exposure to O2, suggesting that the pore channel can effectively prevent O2(+) ion etching from destroying SWCNTs within the pores of the PS layer.</P>

Oxygen annealing of the ZnO nanoparticle layer for the high-performance PbS colloidal quantum-dot photovoltaics

Yang, Jonghee,Lee, Jongtaek,Lee, Junyoung,Yi, Whikun Elsevier 2019 Journal of Power Sources Vol.421 No.-

<P><B>Abstract</B></P> <P>Though numerous researches regarding the influence of annealing atmospheric condition of ZnO have been carried out, the impact of annealing atmosphere on the carrier transporting properties and the performance of the ZnO-based optoelectronics has not been well-established. Here, the effects of annealing atmosphere (<I>i.e.</I>, N<SUB>2</SUB>, ambient air, and O<SUB>2</SUB>) used to generate ZnO nanoparticle (NP) layers are elucidated. The chemical nature of ZnO layers, especially the amount of oxygen vacancies in ZnO NPs, is modulated by the annealing atmosphere. As the composition of O<SUB>2</SUB> gas increases in the annealing atmosphere, a notable reduction of oxygen vacancies of ZnO NPs and electron mobility enhancement are observed, indicating that O<SUB>2</SUB> gas contributes to a reduction of surface defects on ZnO NPs during the annealing process. In addition, trap-filling by reduced oxygen vacancies of air- and O<SUB>2</SUB>-annealed ZnO layers, induces the enhanced built-in potential in colloidal quantum-dot photovoltaic (CQDPV) devices. As expected, PbS CQDPVs with an air- and O<SUB>2</SUB>-annealed ZnO layer demonstrate significantly improved power conversion efficiencies than CQDPVs with an N<SUB>2</SUB>-annealed ZnO layer. Further analysis shows that the interfacial recombination is reduced for CQDPVs with an air- and O<SUB>2</SUB>-annealed ZnO layer due to the reduced trap states of ZnO NPs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of annealing atmosphere on the surface defects of ZnO were elucidated. </LI> <LI> PbS quantum dot solar cell with an O<SUB>2</SUB>-annealed ZnO showed enhanced open-circuit voltage. </LI> <LI> As increasing O<SUB>2</SUB> concentration during annealing, the defects of ZnO were passivated. </LI> <LI> Defect passivation suppressed interfacial charge recombination in the solar cell. </LI> <LI> The suppression of charge recombination induced the improved V<SUB>OC</SUB> of the solar cell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Photodetachment of aryl moieties from covalently functionalized single-walled carbon nanotubes by UV laser irradiation

Lim, Jong Kuk,Yoo, Bum Keun,Yi, Whikun,Hong, Seunghun,Paik, Hyun-jong,Chun, Keunho,Kim, Seong Keun,Joo, Sang-Woo Royal Society of Chemistry 2006 Journal of materials chemistry Vol.16 No.24

<P>Photodetachment of aryl moieties from covalently functionalized SWNTs was studied by temperature-dependent and UV Raman spectroscopic tools. The sidewall functionalized SWNTs were prepared <I>via</I> diazonium reactions from 4-bromoaniline and isoamyl nitrite. <I>I</I>–<I>V</I> conductivity measurements were performed for the functionalized SWNTs, after purification from pristine SWNTs using their different solubility. Temperature dependent Raman data appeared to be in line with thermal gravimetric (TGA) data exhibiting removal of aryl moieties above 590 °C. Raman spectra of the functionalized SWNTs were examined using ultraviolet excitation at 244 nm (5.08 eV) and 325 nm (4.82 eV) as well as visible irradiation at 633 nm (1.96 eV). Our experimental results indicated that the disorder-induced D mode should change significantly, whereas the tangential G modes do not become different under UV irradiation. The D mode for the functionalized SWNTs was found weakly at ∼1410 cm<SUP>−1</SUP> at a low power of UV irradiation, whereas it was observed strongly at ∼1310 cm<SUP>−1</SUP> upon 633 nm irradiation. The attached aryl moieties appeared to be removed by UV irradiation as indicated from almost identical spectra with those of pristine SWNTs.</P> <P>Graphic Abstract</P><P>Photodetachment of aryl moieties from covalently functionalized single-walled carbon nanotubes by UV laser irradiation. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b602165d'> </P>

Electron Transfer Properties of Iodine-Doped Single-Walled Carbon Nanotubes Using Field Effect Transistor

Park, Taehee,Sim, Kijo,Lee, Jongtaek,Yi, Whikun American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.7

<P>Single-walled carbon nanotubes (SWNTs) are known to have a p-type charge transfer character in the atmosphere. The energy state of SWNTs can be modulated by doping with either an electron donor or an acceptor. In this study, iodine molecules are chosen for intercalation to SWNTs to predict the charge transfer tendency between them. Field-effect transistors (FETs) using iodine intercalated SWNTs (I-SWNTs) are fabricated and their electronic properties are investigated to better understand the charge transfer between iodine and SWNTs by changing gate voltages. Under vacuum, I-SWNT FETs exhibit weak n-type character, indicating that electrons are transferred slightly from the iodine to the SWNTs. After exposure to O2 gas, n-type characters are reduced; however, they still retain their original type.</P>