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42 results on '"Lim, Juhwan"'

4. Production of Magnetic Arsenic–Phosphorus Alloy Nanoribbons with Small Band Gaps and High Hole Conductivities

Author

Zhang, Feng Fei, primary, Aw, Eva, additional, Eaton, Alexander G., additional, Shutt, Rebecca R. C., additional, Lim, Juhwan, additional, Kim, Jung Ho, additional, Macdonald, Thomas J., additional, Reyes, Cesar III D. L., additional, Ashoka, Arjun, additional, Pandya, Raj, additional, Payton, Oliver D., additional, Picco, Loren, additional, Knapp, Caroline E., additional, Corà, Furio, additional, Rao, Akshay, additional, Howard, Christopher A., additional, and Clancy, Adam J., additional

Published
2023
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5. Room-Temperature Photoluminescence Mediated by Sulfur Vacancies in 2D Molybdenum Disulfide

Author

Zhu, Yiru, primary, Lim, Juhwan, additional, Zhang, Zhepeng, additional, Wang, Yan, additional, Sarkar, Soumya, additional, Ramsden, Hugh, additional, Li, Yang, additional, Yan, Han, additional, Phuyal, Dibya, additional, Gauriot, Nicolas, additional, Rao, Akshay, additional, Hoye, Robert L. Z., additional, Eda, Goki, additional, and Chhowalla, Manish, additional

Published
2023
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7. Air-stable bismuth sulfobromide (BiSBr) visible-light absorbers: optoelectronic properties and potential for energy harvesting.

Author

Guo, Xiaoyu, Huang, Yi-Teng, Lohan, Hugh, Ye, Junzhi, Lin, Yuanbao, Lim, Juhwan, Gauriot, Nicolas, Zelewski, Szymon J., Darvill, Daniel, Zhu, Huimin, Rao, Akshay, McCulloch, Iain, and Hoye, Robert L. Z.

Abstract

ns2 compounds have recently attracted considerable interest due to their potential to replicate the defect tolerance of lead-halide perovskites and overcome their toxicity and stability limitations. However, only a handful of compounds beyond the perovskite family have been explored thus far. Herein, we investigate bismuth sulfobromide (BiSBr), which is a quasi-one-dimensional semiconductor, but very little is known about its optoelectronic properties or how it can be processed as thin films. We develop a solution processing route to achieve phase-pure, stoichiometric BiSBr films (ca. 240 nm thick), which we show to be stable in ambient air for over two weeks without encapsulation. The bandgap (1.91 ± 0.06 eV) is ideal for harvesting visible light from common indoor light sources, and we calculate the optical limit in efficiency (i.e., spectroscopic limited maximum efficiency, SLME) to be 43.6% under 1000 lux white light emitting diode illumination. The photoluminescence lifetime is also found to exceed the 1 ns threshold for photovoltaic absorber materials worth further development. Through X-ray photoemission spectroscopy and Kelvin probe measurements, we find the BiSBr films grown to be n-type, with an electron affinity of 4.1 ± 0.1 eV and ionization potential of 6.0 ± 0.1 eV, which are compatible with a wide range of established charge transport layer materials. This work shows BiSBr to hold promise for indoor photovoltaics, as well as other visible-light harvesting applications, such as photoelectrochemical cells, or top-cells for tandem photovoltaics. [ABSTRACT FROM AUTHOR]

Published
2023
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9. Production of Magnetic Arsenic-Phosphorus Alloy Nanoribbons with Small Band Gaps and High Hole Conductivities

Author

Zhang, Fengfei, primary, Aw, Eva, additional, Eaton, Alexander, additional, Shutt, Rebecca, additional, Lim, Juhwan, additional, Kim, Jung Ho, additional, Macdonald, Thomas, additional, De Leon Reyes, Cesar, additional, Ashoka, Arjun, additional, Pandya, Raj, additional, Payton, Oliver, additional, Picco, Loren, additional, Knapp, Caroline, additional, Rao, Akshay, additional, Howard, Christopher, additional, and Clancy, Adam, additional

Published
2023
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10. Room-Temperature Photoluminescence Mediated by Sulfur Vacancies in 2D Molybdenum Disulfide

Author

Zhu, Yiru, Lim, Juhwan, Zhang, Zhepeng, Wang, Yan, Sarkar, Soumya, Ramsden, Hugh, Li, Yang, Yan, Han, Phuyal, Dibya, Gauriot, Nicolas, Rao, Akshay, Hoye, Robert L.Z., Eda, Goki, Chhowalla, Manish, Zhu, Yiru, Lim, Juhwan, Zhang, Zhepeng, Wang, Yan, Sarkar, Soumya, Ramsden, Hugh, Li, Yang, Yan, Han, Phuyal, Dibya, Gauriot, Nicolas, Rao, Akshay, Hoye, Robert L.Z., Eda, Goki, and Chhowalla, Manish

Abstract

Atomic defects in monolayer transition metal dichalcogenides (TMDs) such as chalcogen vacancies significantly affect their properties. In this work, we provide a reproducible and facile strategy to rationally induce chalcogen vacancies in monolayer MoS2 by annealing at 600 °C in an argon/hydrogen (95%/5%) atmosphere. Synchrotron X-ray photoelectron spectroscopy shows that a Mo 3d5/2 core peak at 230.1 eV emerges in the annealed MoS2 associated with nonstoichiometric MoSx (0 < x < 2), and Raman spectroscopy shows an enhancement of the ∼380 cm-1 peak that is attributed to sulfur vacancies. At sulfur vacancy densities of ∼1.8 × 1014 cm-2, we observe a defect peak at ∼1.72 eV (referred to as LXD) at room temperature in the photoluminescence (PL) spectrum. The LXD peak is attributed to excitons trapped at defect-induced in-gap states and is typically observed only at low temperatures (≤77 K). Time-resolved PL measurements reveal that the lifetime of defect-mediated LXD emission is longer than that of band edge excitons, both at room and low temperatures (∼2.44 ns at 8 K). The LXD peak can be suppressed by annealing the defective MoS2 in sulfur vapor, which indicates that it is possible to passivate the vacancies. Our results provide insights into how excitonic and defect-mediated PL emissions in MoS2 are influenced by sulfur vacancies at room and low temperatures., QC 20230911

Published
2023
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17. Terahertz, optical, and Raman signatures of monolayer graphene behavior in thermally reduced graphene oxide films.

Author

Lim, Juhwan, Choi, Kyujin, Rani, J. R., Kim, Jin-Seon, Lee, Changgu, Hoon Kim, Jae, and Chan Jun, Seong

Subjects
*GRAPHENE, *SILICA, *ABSORPTION, *ATOMIC force microscopy, *SPIN coating
Abstract

We report on our joint spectroscopic study of the thermal reduction process of quasi-monolayer graphene oxide films grown on fused silica substrates by spin-coating. We estimate that about 65% of our film area consists of monolayer platelets of reduced graphene oxide, based on our quantitative analysis of the local atomic force microscopy topography. With thermal annealing under suitable conditions, clear signatures of monolayer graphene behavior were identified in the resonant excitonic absorption at 4.55 eV, the overall decrease in the visible-range transmission, the re-emergence of the Raman 2D band, the red-shift of the Raman G band toward the monolayer position, and the decrease in the optical sheet resistance in the terahertz range. [ABSTRACT FROM AUTHOR]

Published
2013
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18. Comparisons of service quality perceptions between full service carriers and low cost carriers in airline travel.

Author

Lim, Juhwan and Lee, Hyun Cheol

Subjects
QUALITY of service, LOW cost airlines, WORD frequency, SENSORY perception, AIRLINE industry
Abstract

We apply latent Dirichlet allocation topic modeling to a vast number of passenger-authored online reviews for airline services to compare service quality between full service carriers (FSCs) and low cost carriers (LCCs). Representing key features of airline service quality, topics are extracted from the reviews and matched to the five typical dimensions used by the SERVQUAL model. Based on the measure of word frequency statistically distributed to topics, we quantitatively determine the dimensions of service quality that are deemed as most essential by travelers. The results show that the most significant dimensions for FSCs and LCCs are tangibles and reliability, respectively. The least significant dimensions are assurance and empathy, respectively. By comparing extracted features in detail, we discover specific differences in traveler perceptions between FSCs and LCCs. Air carriers should be aware of these differences, as it would help them better differentiate themselves. Moreover, inflight meal services and seats, which have typically been regarded as tangible features, are subdivided into different topics, and the subdivisions are simultaneously matched to multiple dimensions (eg tangibles, empathy, and reliability). This suggests that research needs to reflect the diverse aspects of traveler perceptions for primary service items. [ABSTRACT FROM AUTHOR]

Published
2020
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32. Terahertz study of reduced graphene oxide

Author

Choi, Kyujin, primary, Lim, Juhwan, additional, Hong, Taeyoon, additional, Ha, Taewoo, additional, Park, Byung Cheol, additional, Sim, Kyung Ik, additional, Kim, Jin-Seon, additional, Lee, Changgu, additional, Jun, Seong Chan, additional, and Kim, Jae Hoon, additional

Published
2012
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34. Microwave transmission characteristics of ZnO nanowire

Author

Cho, Joon Hyong, primary, Ha, Ryong, additional, Choi, Heon-Jin, additional, Yoon, Hyong Seo, additional, Lim, Juhwan, additional, Jun, Seong Chan, additional, Kim, Whan Kyun, additional, Oh, Juyeong, additional, Kang, Ji Yoong, additional, and Choi, Jung Han, additional

Published
2012
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42. Direct Imaging of Carrier Funneling in a Dielectric Engineered 2D Semiconductor

Author

Gauriot, Nicolas, Ashoka, Arjun, Lim, Juhwan, See, Soo Teck, Sung, Jooyoung, and Rao, Akshay

Abstract

In atomically thin transition-metal dichalcogenides (TMDCs), the environmental sensitivity of the strong Coulomb interaction offers promising approaches to create spatially varying potential landscapes in the same continuous material by tuning its dielectric environment. Thus, allowing for control of transport. However, a scalable and CMOS-compatible method for achieving this is required to harness these effects in practical applications. In addition, because of their ultrashort lifetime, observing the spatiotemporal dynamics of carriers in monolayer TMDCs, on the relevant time scale, is challenging. Here, we pattern and deposit a thin film of hafnium oxide (HfO2) via atomic layer deposition (ALD) on top of a monolayer of WSe2. This allows for the engineering of the dielectric environment of the monolayer and design of heterostructures with nanoscale spatial resolution via a highly scalable postsynthesis methodology. We then directly image the transport of photoexcitations in the monolayer with 50 fs time resolution and few-nanometer spatial precision, using a pump probe microscopy technique. We observe the unidirectional funneling of charge carriers, from the unpatterned to the patterned areas, over more than 50 nm in the first 20 ps with velocities of over 2 × 103m/s at room temperature. These results demonstrate the possibilities offered by dielectric engineering via ALD patterning, allowing for arbitrary spatial patterns that define the potential landscape and allow for control of the transport of excitations in atomically thin materials. This work also shows the power of the transient absorption methodology to image the motion of photoexcited states in complex potential landscapes on ultrafast time scales.

Published
2023
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