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Sohn, Ahrum,Gwon, Minji,Choi, Dukhyun,Kim, Dong-Wook Hindawi Limited 2013 Journal of nanomaterials Vol.2013 No.-
<P>We investigated optical properties of three-dimensional (3D) assemblies of Au nanoparticles (NPs), which were fabricated by dewetting of thin Au layers on anodic aluminum oxides (AAO). The NP assembly had hexagonal array of repeated multiparticle structures, which consisted of six trimers on the AAO surface and one large NP in the AAO pore (pore-NP). We performed finite-difference time-domain simulation to explain the optical response of the NP assemblies and compared the calculation results with experimental data. Such complementary studies clearly revealed how the plasmonic coupling between the constituent NPs influenced the spectral response of our NP assemblies. In particular, comparison of the assemblies with and without pore-NPs suggested that strong plasmonic coupling between trimers and pore-NP significantly affected the spectra and the field distribution of the NP assemblies. Plasmonic multi-NP assemblies could provide us new platforms to realize novel optoelectronic devices.</P>
Band Alignment at Au/MoS<sub>2</sub> Contacts: Thickness Dependence of Exfoliated Flakes
Sohn, Ahrum,Moon, Hankyoul,Kim, Jayeong,Seo, Miri,Min, Kyung-Ah,Lee, Sang Wook,Yoon, Seokhyun,Hong, Suklyun,Kim, Dong-Wook American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.40
<P>We investigated the surface potential (V-surf) of exfoliated MoS2 flakes on bare and Au-coated SiO2/Si substrates using Kelvin probe force microscopy. The V-surf of MoS2 single layers was larger on the Au-coated substrates than on the bare substrates; our theoretical calculations indicate that this may be caused by the formation of a larger electric dipole at the MoS2/Au interface leading to a modified band alignment. V-surf decreased as the thickness of the flakes increased until reaching the bulk value at a thickness of similar to 20 nm (similar to 30 layers) on the bare and similar to 80 nm (similar to 120 layers) on the Au-coated substrates, respectively. This thickness dependence of V-surf was attributed to electrostatic screening in the MoS2 layers. Thus, a difference in the thickness at which the bulk V-surf appeared suggests that the underlying substrate has an effect on the electric-field screening length of the MoS2 flakes. This work provides important insights to help understand and control the electrical properties of metal/MoS2 contacts.</P>
Ahrum Choi,Jong-Hag Choi,Byungcherl Charlie Sohn 한국산업경영학회 2013 한국산업경영학회 발표논문집 Vol.2013 No.4
This study investigates whether and how a firm’s real earnings management (REM) activities are influenced by the strength of a country’s legal regime, and then examines whether the role of Big 4 auditors to constrain REM is different between countries with strong and weak legal regimes. Using 36,927 firm-year observations from 25 countries across the world, we find that the intensity of REM increases as a country’s legal regime strengthens because more firms switch from accrual-based earnings management (AEM) to REM, suggesting a substitutive relation between AEM and REM. We find, however, that this increased use of REM in countries with stronger legal regimes is less pronounced for the clients of Big 4 auditors than for those of non-Big 4 auditors. These findings suggest that the high-quality audit service provided by Big 4 auditors reduces the client firms’ tendency to use REM, especially in countries with a strong legal regime.
Jo, Hanggochnuri,Sohn, Ahrum,Shin, Kyung-Sik,Kumar, Brijesh,Kim, Jae Hyun,Kim, Dong-Wook,Kim, Sang-Woo American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.2
<P>An efficient approach to producing hexagonally self-assembled and well-dispersed gold (Au) nanoparticles (NPs) in the pores of porous anodic aluminum oxide (AAO) is reported. This approach is particularly useful for tuning the surface plasmon resonance frequency of Au NPs by varying the effective dielectric constant of AAO. A strongly enhanced Raman spectrum of dye molecule rhodamine 6G using these well-dispersed Au NPs revealed that such a self-assembled Au NP array can induce a strong plasmonic field. Furthermore, we demonstrated a new architecture of plasmon excitation in a bulk heterojunction (BHJ) inverted organic solar cell (IOSC) using the Au NP array with AAO. The optical response of an active layer poly(3-hexylthiophene):(6,6)-phenyl-C<SUB>61</SUB>-butyric acid methyl ester was enhanced by this strong plasmonic field associated a well-dispersed Au NP array. A comparative study of AAO with and without Au NPs confirmed plasmonic improvement of the BHJ IOSC. Simulation results showed that Au NPs concentrate the incoming light into a strongly localized field and enhance light absorption in a wide wavelength range.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-2/am4045585/production/images/medium/am-2013-045585_0006.gif'></P>
Cho, Yunae,Sohn, Ahrum,Kim, Sujung,Hahm, Myung Gwan,Kim, Dong-Ho,Cho, Byungjin,Kim, Dong-Wook American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.33
<P>Molybdenum disulfide (MoS2) has increasingly attracted attention from researchers and is now one of the most intensively explored atomic-layered two-dimensional semiconductors. Control of the carrier concentration and doping type of MoS2 is crucial for its application in electronic and optoelectronic devices. Because the MoS2 layers are atomically thin, their transport characteristics may be very sensitive to ambient gas adsorption and the resulting charge transfer. We investigated the influence of the ambient gas (N-2, H-2/N-2, and O-2) choice on the resistance (R) and surface work function (WF) of trilayer MoS2 thin films grown via chemical vapor deposition. We also studied the electrical properties of gold (Au)-nanoparticle (NP)-coated MoS, thin films; their R value was found to be 2 orders of magnitude smaller than that for bare samples. While the WF largely varied for each gas, R was almost invariant for both the bare and Au-NP-coated samples regardless of which gas was used. Temperature-dependent transport suggests that variable range hopping is the dominant mechanism for electrical conduction for bare and Au-NP-coated MoS2 thin films. The charges transferred from the gas adsorbates might be insufficient to induce measurable R change and/or be trapped in the defect states. The smaller WF and larger localization length of the Au-NP-coated sample, compared with the bare sample, suggest that more carriers and less defects enhanced conduction in MoS2.</P>
권민지,이은송이,Ahrum Sohn,El Mostafa Bourim,김동욱 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.6
We investigated the resistive switching behaviors of metal/oxide junctions consisting of Pt electrodes and Nb-doped SrTiO3(001) single crystals. The doping level affected the resistive switching ratio and the transport mechanism (thermionic emission for low doping and thermionic field emission for high doping). Pulse-mode switching experiments showed that an increase in the interface electric field by several times could enhance the switching speed by hundreds of times. The dependence of the retention time on the doping ratio was also examined. All the results suggested that ionic migration and carrier trapping could explain the resistive switching characteristics.
Asymmetrically Coupled Plasmonic Core and Nanotriplet Satellites
Jo, Hanggochnuri,Yoon, Daesung,Sohn, Ahrum,Kim, Dong-Wook,Choi, Yeonho,Kang, Taewook,Choi, Dukhyun,Kim, Sang-Woo,Lee, Luke P. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.32
<P>Here, we report asymmetrical multiple electromagnetic coupling of plasmonic core and nanotriplet satellites. Within the plasmonic core and nanotriplet satellites, an enhanced local field is generated which expands across the core due to multiple electromagnetic coupling between a core and nanotriplets. Based on 3D simulations of our plasmonic nanosystem, the overall local field enhancement reaches to over 10<SUP>4</SUP> times, compared with that of a single nanoparticle array. A strong local field distribution across the core to nanotriplets as well as the critical role of the plasmonic core is demonstrated through the 3D simulations. It is proposed that a self-assembled nanotriplet array is completed through two stages of dewetting of a gold thin film on an anodic aluminum oxide (AAO) template. Formation of the core–nanotriplet satellites is significantly influenced by geometrical parameters (i.e., the pore diameter and depth) of the AAO template. Our experimental results show that the local field of our plasmonic nanostructures is amplified up to ∼110 times by adopting a core into the nanotriplet satellites, compared with that of the nanotriplets array without a core. This approach offers a promising strategy for creating an advanced nanoplasmonic platform with strong local field distribution and high-throughput production.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-32/jp505024k/production/images/medium/jp-2014-05024k_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp505024k'>ACS Electronic Supporting Info</A></P>