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29 results on '"Jeon, Seokmin"'

1. Impact of Surface Roughness in Measuring Optoelectronic Characteristics of Thin-Film Solar Cells

Author

Magginetti, David, Jeon, Seokmin, Yoon, Yohan, Choudhury, Ashif, Mamun, Ashraful, Qian, Yang, Gerton, Jordan, and Yoon, Heayoung

Subjects
Physics - Applied Physics, Physics - Optics
Abstract

Microstructural properties of thin-film absorber layers play a vital role in developing high-performance solar cells. Scanning probe microscopy is frequently used for measuring spatially inhomogeneous properties of thin-film solar cells. While powerful, the nanoscale probe can be sensitive to the roughness of samples, introducing convoluted signals and unintended artifacts into the measurement. Here, we apply a glancing-angle focused ion beam (FIB) technique to reduce the surface roughness of CdTe while preserving the subsurface optoelectronic properties of the solar cells. We compare the nanoscale optoelectronic properties before and after the FIB polishing. Simultaneously collected Kelvin-probe force microscopy (KPFM) and atomic force microscopy (AFM) images show that the contact potential difference (CPD) of CdTe pristine (peak-to-valley roughness of approximately 600 nm) follows the topography. In contrast, the CPD map of polished CdTe (roughness of approximately 20 nm) is independent of the surface roughness. We demonstrate the smooth CdTe surface also enables high-resolution photoluminescence (PL) imaging at a resolution much smaller than individual grains (< 1 micrometer). Our finite-difference time-domain (FDTD) simulations illustrate how the local light excitation interacts with CdTe surfaces. Our work supports low-angle FIB polishing can be beneficial in studying buried sub-microstructural properties of thin-film solar cells with care for possible ion-beam damage near the surface., Comment: 4 pages, 4 figures more...

Published
2023
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2. Heterogeneous Optoelectronic Characteristics of Si Micropillar Arrays Fabricated by Metal-Assisted Chemical Etching

Author

Qian, Yang, Magginetti, David J., Jeon, Seokmin, Yoon, Yohan, Olsen, Tony L., Wang, Maoji, Gerton, Jordan M., and Yoon, Heayoung P.

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science, Physics - Optics
Abstract

Recent progress achieved in metal-assisted chemical etching (MACE) has enabled the production of high-quality micropillar arrays for various optoelectronic applications. Si micropillars produced by MACE often show a porous Si/SiOx shell on crystalline pillar cores introduced by local electrochemical reactions. In this paper, we report the distinct optoelectronic characteristics of the porous Si/SiOx shell correlated to their chemical compositions. Local photoluminescent (PL) images obtained with an immersion oil objective lens in confocal microscopy show a red emission peak (about 650 nm) along the perimeter of the pillars that is threefold stronger compared to their center. On the basis of our analysis, we find an unexpected PL increase (about 540 nm) at the oil/shell interface. We suggest that both PL enhancements are mainly attributed to the porous structures, a similar behavior observed in previous MACE studies. Surface potential maps simultaneously recorded with topography reveal a significantly high surface potential on the sidewalls of MACE-synthesized pillars (+0.5 V), which is restored to the level of planar Si control (-0.5 V) after removing SiOx in hydrofluoric acid. These distinct optoelectronic characteristics of the Si/SiOx shell can be beneficial for various sensor architectures., Comment: 4 figures, 1 table more...

Published
2020
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3. Ultra-high-Q wedge-resonator on a silicon chip

Author

Lee, Hansuek, Chen, Tong, Li, Jiang, Yang, Ki Youl, Jeon, Seokmin, Painter, Oskar, and Vahala, Kerry J.

Subjects
Physics - Optics
Abstract

Ultra-high-Q optical resonators are being studied across a wide range of research subjects including quantum information, nonlinear optics, cavity optomechanics, and telecommunications. Here, we demonstrate a new, resonator on-a-chip with a record Q factor of 875 million, surpassing even microtoroids. Significantly, these devices avoid a highly specialized processing step that has made it difficult to integrate microtoroids with other photonic devices and to also precisely control their size. Thus, these devices not only set a new benchmark for Q factor on a chip, but also provide, for the first time, full compatibility of this important device class with conventional semiconductor processing. This feature will greatly expand the possible kinds of system on a chip functions enabled by ultra-high-Q devices., Comment: 5 pages, 4 figures more...

Published
2011

11. Pyrolytic Carbon Films with Tunable Electronic Structure and Surface Functionality: A Planar Stand‐In for Electroanalysis of Energy‐Relevant Reactions

Author

Parker, Joseph F., primary, So, Christopher R., additional, Sassin, Megan B., additional, Ko, Jesse S., additional, Jeon, Seokmin, additional, Chervin, Christopher N., additional, Lytle, Justin C., additional, Helms, Maya E., additional, Rolison, Debra R., additional, and Long, Jeffrey W., additional more...

Published
2020
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19. Structure, Chemistry, and Energetics of Organic and Inorganic Adsorbates on Ga-rich GaAs and GaP(00l) Surfaces

Author

Jeon, Seokmin, Jeon, Seokmin, Jeon, Seokmin, and Jeon, Seokmin

Abstract

The work described in this dissertation includes fundamental investigations into three surface processes, namely inorganic film growth, water-induced oxidation, and organic functionalization/passivation, on the GaP and GaAs(001) surfaces. The techniques used to carry out this work include scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Atomic structure, electronic structure, reaction mechanisms, and energetics related to these surface processes are discussed at atomic or molecular levels. First, we investigate epitaxial Zn3P2 films grown on the Ga-rich GaAs(001)(6×6) surface. The film growth mechanism, electronic properties, and atomic structure of the Zn3P2/GaAs(001) system are discussed based on experimental and theoretical observations. We discover that a P-rich amorphous layer covers the crystalline Zn3P2 film during and after growth. We also propose more accurate picture of the GaP interfacial layer between Zn3P2 and GaAs, based on the atomic structure, chemical bonding, band diagram, and P-replacement energetics, than was previously anticipated. Second, DFT calculations are carried out in order to understand water-induced oxidation mechanisms on the Ga-rich GaP(001)(2×4) surface. Structural and energetic information of every step in the gaseous water-induced GaP oxidation reactions are elucidated at the atomic level in great detail. We explore all reasonable ground states involved in most of the possible adsorption and decomposition pathways. We also investigate structures and energies of the transition states in the first hydrogen dissociation of a water molecule on the (2×4) surface. Finally, adsorption structures and thermal decomposition reactions of 1-propanethiol on the Ga-rich GaP(001)(2×4) surface are investigated using high resolution STM, XPS, and DFT simulations. We elucidate adsorpt more...

Published
2014

23. Perovskite–fullerene hybrid materials suppress hysteresis in planar diodes

Author

Xu, Jixian, primary, Buin, Andrei, additional, Ip, Alexander H., additional, Li, Wei, additional, Voznyy, Oleksandr, additional, Comin, Riccardo, additional, Yuan, Mingjian, additional, Jeon, Seokmin, additional, Ning, Zhijun, additional, McDowell, Jeffrey J., additional, Kanjanaboos, Pongsakorn, additional, Sun, Jon-Paul, additional, Lan, Xinzheng, additional, Quan, Li Na, additional, Kim, Dong Ha, additional, Hill, Ian G., additional, Maksymovych, Peter, additional, and Sargent, Edward H., additional more...

Published
2015
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28. Growth Mechanism and Electronic Structure of Zn3P2on the Ga-Rich GaAs(001) Surface

Author

Jeon, Seokmin, Bosco, Jeffrey P., Wilson, Samantha S., Rozeveld, Steve J., Kim, Hyungjun, and Atwater, Harry A.

Abstract

The growth of epitaxial Zn3P2films on III–V substrates unlocks a promising pathway toward high-efficiency, earth-abundant photovoltaic devices fabricated on reusable, single-crystal templates. The detailed chemical, structural, and electronic properties of the surface and interface of pseudomorphic Zn3P2epilayers grown on GaAs(001) were investigated using scanning tunneling microscopy/spectroscopy and high-resolution X-ray photoelectron spectroscopy. Two interesting features of the growth process were observed: (1) vapor-phase P4first reacts with the Ga-rich GaAs surface to form an interfacial GaP layer with a thickness of several monolayers, and (2) a P-rich amorphous overlayer is present during the entire film growth process, beneath which a highly ordered Zn3P2crystalline phase is precipitated. These features were corroborated by transmission electron micrographs of the Zn3P2/GaAs interface as well as density functional theory calculations of P reactions with the GaAs surface. Finally, the valence-band offset between the crystalline Zn3P2epilayer and the GaAs substrate was determined to be ΔEV= 1.0 ± 0.1 eV, indicating the formation of a hole-depletion layer at the substrate surface which may inhibit formation of an ohmic contact. more...

Published
2014
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29. Weak competing interactions control assembly of strongly bonded TCNQ ionic acceptor molecules on silver surfaces.

Author

Changwon Park, Rojas, Geoffrey A., Jeon, Seokmin, Kelly, Simon J., Smith, Sean C., Sumpter, Bobby G., Yoon, Mina, and Maksymovych, Petro

Subjects
*MOLECULES, *SILVER, *METALLIC surfaces, *ELECTRON research, *ORGANIC conductors
Abstract

The energy scales of interactions that control molecular adsorption and assembly on surfaces can vary by several orders of magnitude, yet the importance of each contributing interaction is not apparent a priori. Tetracyanoquinodimethane (TCNQ) is an archetypal electron acceptor molecule and it is a key component of organic metals. On metal surfaces, this molecule also acts as an electron acceptor, producing negatively charged adsorbates. It is therefore rather intriguing to observe attractive molecular interactions in this system that were reported previously for copper and silver surfaces. Our experiments compared TCNQ adsorption on noble metal surfaces of Ag(100) and Ag(111). In both cases we found net attractive interactions down to the lowest coverage. However, the morphology of the assemblies was strikingly different, with two-dimensional islands on Ag(100) and one-dimensional chains on Ag(111) surfaces. This observation suggests that the registry effect governed by the molecular interaction with the underlying lattice potential is critical in determining the dimensionality of the molecular assembly. Using first-principles density functional calculations with a van der Waals correction scheme, we revealed that the strengths of major interactions (i.e., lattice potential corrugation, intermolecular attraction, and charge-transfer-induced repulsion) are all similar in energy. The van der Waals interactions, in particular, almost double the strength of attractive interactions, making the intermolecular potential comparable in strength to the diffusion potential and promoting self-assembly. However, it is the anisotropy of local intermolecular interactions that is primarily responsible for the difference in the topology of the molecular islands on Ag(100) and Ag(111) surfaces. We anticipate that the intermolecular potential will become more attractive and dominant over the diffusion potential with increasing molecular size, providing new design strategies for the structure and charge transfer within molecular layers. [ABSTRACT FROM AUTHOR] more...

Published
2014
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