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Kim, Min Su,Roy, Shrawan,Lee, Jubok,Kim, Byung Gu,Kim, Hyun,Park, Ji-Hoon,Yun, Seok Joon,Han, Gang Hee,Leem, Jae-Young,Kim, Jeongyong American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.42
<P>Monolayer transition-metal dichalcogenides (1L-TMDs) are atomically thin direct band gap semiconductors, from which the emission of light is determined by optical transitions of exciton complexes such as neutral excitons and trions. While the quantum yields of 1L-TMDs are quite low, the ability to control the populations of exciton complexes in 1L-TMDs through various doping processes is an interesting advantage, and provides ample possibilities for engineering the optical properties of these semiconductor monolayers. Here we demonstrate a simple method of controlling the populations of excitons and trions to enhance the light emission of 1L-TMDs by having them form heterostructures with ZnO thin films (TFs). 1Ls of MoS2 or MoSe2 showed up to 17-fold increases in photoluminescence (PL) when they were placed on similar to 50 nm thick ZnO TFs. This enhancement of the PL was due to charge exchanges occurring through the 1L-TMD/ZnO interface. The PL enhancements and changes in the PL spectra of the 1L-TMDs were greater when the 1L-TMD/ZnO heterostructures were subjected to 355 nm wavelength laser excitation than when they were excited with a 514 nm wavelength laser, which we attributed to the onset of energy transfer by photoexcited excitons and/or the additional p-doping by photoexcited holes in ZnO. The p-doping phenomenon and the enhanced light emission of 1L-TMD/ZnO heterostructures were unambiguously visualized in spatially resolved PL and Raman spectral maps. Our approach using the 1L-TMD/ZnO TF heterostructure suggests that a rich variety of options for engineering the optical properties of 1L-TMDs may be made available by carrying out simple and intuitive manipulations of exciton complexes, and these endeavors may yield practical applications for 1L-TMDs in nanophotonic devices.</P>
Kim, Min Su,Seo, Changwon,Kim, Hyun,Lee, Jubok,Luong, Dinh Hoa,Park, Ji-Hoon,Han, Gang Hee,Kim, Jeongyong American Chemical Society 2016 ACS NANO Vol.10 No.6
<P>Heterostacking of layered transition-metal dichalcogenide (LTMD) monolayers (1Ls) offers a convenient way of designing two-dimensional exciton systems. Here we demonstrate the simultaneous hosting of positive trions and negative trions in heterobilayers made by vertically stacking 1L MoSe2 and 1L MoS2. The charge transfer occurring between the 1Ls of MoSe2 and MoS2 converted the polarity of trions in 1L MoSe2 from negative to positive, resulting in the presence of positive trions in the 1L MoSe2 and negative trions in the 1L MoS2 of the same heterostacked bilayer. Significantly enhanced MoSe2 photoluminescence (PL) in the heterostacked bilayers compared to the PL of 1L MoSe2 alone suggests that, unlike other previously reported heterostacked bilayers, direct band transition of 1L MoSe2 in heterobilayer was enhanced after the vertical heterostacking. Moreover, by inserting hexagonal BN monolayers between 1L MoSe2 and 1L MoS2 we were able to adjust the charge transfer to maximize the MoSe2 PL of the heteromultilayers and have achieved a 9-fold increase of the PL emission. The enhanced optical properties of our heterostacked LTMDs suggest the exciting possibility of designing LTMD structures that exploit the superior optical properties of 1L LTMDs.</P>
Enhancement of light-matter interaction and photocatalytic efficiency of Au/TiO_2 hybrid nanowires
Lee, Jubok,Lee, Seonhee,Kim, Min Su,Shin, Hyunjung,Kim, Jeongyong The Optical Society 2016 Optics express Vol.24 No.14
<P>Metal/TiO2 hybrid nanostructures offer more efficient charge separation and a broader range of working wavelengths for photocatalytic reactions. The sizes and shapes of such hybrid nanostructures can affect the charge separation performance when the structures interact with light, but assessments of the interaction of light with these metal-TiO2 nanostructures have only been carried out on ensemble averages, hindering both systematic descriptions of such hybrid structures and the design of new ones. Here, we fabricated TiO2 nanotubes (NTs) with and without core Au nanowires (NWs), and used spectroscopy and calculations to assess their scattering and absorption of light at the single NW level. According to the results of spectral imaging and numerical calculations, the Au/TiO2 NWs scattered and absorbed light substantially more strongly than did the plain TiO2 NTs. Measurements of the degradation of the AO7 dye to assess the photocatalytic performance of the Au/TiO2 NWs were consistent with optical measurements demonstrating a two-fold improvement over plain TiO2 NTs under 360-nm-wavelength UV illumination. Our results suggests that nanoscale optical imaging can be used to visualize the performance of the photocatalytic reaction at the single nano-object level. (C) 2016 Optical Society of America</P>
Seo Changwon,Kim Jung Ho,Lee Jubok,Yun Seok Joon,Kim Teun-Teun,Kim Jeongyong 한국물리학회 2022 Current Applied Physics Vol.43 No.-
Although the spectral investigation of monolayer two-dimensional transition metal dichalcogenide (1L-TMD) has been extensively performed for identifying modulation of excitonic transition, study of excitonic transition in ferroelectric/TMD hybrid structure is essential to understand and design high speed and low loss devices based on in-plane junctions. Here, we demonstrate electrical modulation of excitonic transition by transferring 1L-tungsten disulfide (WS2) onto a ferroelectric domain surface, a periodically poled lithium niobate (PPLN). We observe that exciton (A0) and trion (A-) emissions of 1L-WS2 are spatially modulated depending on the sign of the phase domain, such that A0 and A- emission is stronger at the positive (D+) and negative (D-) domain, respectively. In addition, different trends of excitonic transition of 1L-WS2 between D+ and D- domain are demonstrated by applying a back-gate bias voltage. The spatial modulation of electrical and optical characteristics of 1L-TMDs will help to design the homo- or hetero p-n junctions based on TMDs.
Neupane, Guru P.,Dhakal, Krishna P.,Kim, Hyun,Lee, Jubok,Kim, Min Su,Han, Ganghee,Lee, Young Hee,Kim, Jeongyong American Institute of Physics 2016 JOURNAL OF APPLIED PHYSICS - Vol.120 No.5
<P>We report the controllable nanosized local thinning of multi-layer (2L and 3 L)-thickness MoS2 films down to the monolayer (1 L) thickness using the simple method of annealing in a dry oxygen atmosphere. The annealing temperature was optimized in the range of 240 degrees C to 270 degrees C for 1.5h, and 1L thick nanosized pits were developed on the uniform film of the 2 L and 3 L MoS2 grown using the chemical vapor deposition method. We characterized the formation of the 1 L nanosized pits using nanoscale confocal photoluminescence (PL) and Raman spectroscopy. We observed that the PL intensity increased and the Raman frequency shifted, representative of the characteristics of 1 L MoS2 films. A subsequent hydrogen treatment process was useful for removing the oxygen-induced doping effect resulting from the annealing. Published by AIP Publishing.</P>
Augmented Quantum Yield of a 2D Monolayer Photodetector by Surface Plasmon Coupling
Bang, Seungho,Duong, Ngoc Thanh,Lee, Jubok,Cho, Yoo Hyun,Oh, Hye Min,Kim, Hyun,Yun, Seok Joon,Park, Chulho,Kwon, Min-Ki,Kim, Ja-Yeon,Kim, Jeongyong,Jeong, Mun Seok American Chemical Society 2018 NANO LETTERS Vol.18 No.4
<P>Monolayer (1L) transition metal dichalcogenides (TMDCs) are promising materials for nanoscale optoelectronic devices because of their direct band gap and wide absorption range (ultraviolet to infrared). However, 1L-TMDCs cannot be easily utilized for practical optoelectronic device applications (e.g., photodetectors, solar cells, and light-emitting diodes) because of their extremely low optical quantum yields (QYs). In this investigation, a high-gain 1L-MoS<SUB>2</SUB> photodetector was successfully realized, based on the surface plasmon (SP) of the Ag nanowire (NW) network. Through systematic optical characterization of the hybrid structure consisting of a 1L-MoS<SUB>2</SUB> and the Ag NW network, it was determined that a strong SP and strain relaxation effect influenced a greatly enhanced optical QY. The photoluminescence (PL) emission was drastically increased by a factor of 560, and the main peak was shifted to the neutral exciton of 1L-MoS<SUB>2</SUB>. Consequently, the overall photocurrent of the hybrid 1L-MoS<SUB>2</SUB> photodetector was observed to be 250 times better than that of the pristine 1L-MoS<SUB>2</SUB> photodetector. In addition, the photoresponsivity and photodetectivity of the hybrid photodetector were effectively improved by a factor of ∼1000. This study provides a new approach for realizing highly efficient optoelectronic devices based on TMDCs.</P> [FIG OMISSION]</BR>
Haidilao Hotpot: Care and Innovation as Main Ingredients
Yebin An,Jubok kim,An Ni Yeoh,Yuhao Zhu,Ke Michael Mai Academy of Asian Business (AAB) 2021 Academy of Asian Business Review Vol.7 No.2
The paper examines how Haidilao, the Sichuan Hotpot chain, became a globally renowned catering business through its faithful adherence to the objective of creating a perfect dining experience through building rapport with customers and employees. Supplemented by unique organisational processes, Haidilao achieved transformational growth from humble beginnings and differentiated itself from its competitors by upholding the commonly neglected integrity for food safety, customer service, and care for employees in the catering industry. The paper highlights Haidilao’s customer and employee-centric philosophy during operation and management. Haidilao’s attentive customer service makes the customers feel respected and cared for, while its unique human resource management system cultivates trust and support within the workplace by empowering employees and prioritizing their opinions. Due to the competitiveness in the hotpot market, customers are typically viewed as profit generators and employees as expendable. However, Haidilao firmly espouses the Asian value of “community”, which touches the customers and motivates the employees. Along with an advantageous vertically integrated ecosystem, this value allowed Haidilao to establish itself as a global brand despite the challenges posed by hygiene issues, difficulties of penetrating the Western market, and the COVID19 pandemic. The team concludes the report by offering effective recommendations for Haidilao to overcome its limitations and adapt to the future.