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46 results on '"Yoon, Im Taek"'

9. Fabrication and characterization of Mn-implanted GaN layers followed by annealing

Author

Yoon, Im Taek and Fu, Dejun

Abstract

We report the effect of Mn incorporation on the structural and optical properties of GaN grown on a sapphire substrate in a plasma-enhanced molecular-beam epitaxy system followed by Mn ion implantation and annealing. The crystalline quality and phase purity were determined by high-resolution X-ray diffraction (XRD). The XRD results indicated that no macroscopic second phases were present in the Mn-implanted GaN layer after the annealing process. High-resolution transmission microscopy and energy dispersive X-ray spectroscopy revealed that the as-grown GaN epilayer and Mn-implanted GaN layer after annealing were single crystals with a hexagonal wurtzite structure, and they grew with a c-axis orientation perpendicular to the sapphire substrate. The Raman and photoluminescence spectra showed that the Mn-implanted GaN layer fabricated with a Mn ion dose of 5 × 1015cm−2followed by annealing at 800 °C for 30 min had higher crystalline quality than the Mn-implanted GaN layers fabricated with Mn ion doses of 5 × 1015and 2 × 1016cm−2followed by annealed at 900 °C for 30 and 80 min.

Published
2024
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10. Two-step preparation and characterization of ZnO Core–Si shell coaxial nanorods

Author

Yoon, Im Taek and Cho, Hak Dong

Abstract

This study compares and analyzes the key characteristics of the ZnO core–Si shell coaxial nanorod (Si@ZnO NR) heterostructures that were grown on semi-insulating, (100)-oriented Si substrates at Si layer temperatures of 450, 500, 550 and 600 °C for optoelectronic device applications. The Si@ZnO NRs were prepared in two separate stages. Vapor-phase transport produced the ZnO NRs, whereas rapid thermal chemical vapor deposition formed the Si layers. Results obtained from X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman tests indicate that the ZnO NRs were single crystals with a zincblende configuration. The findings also reveal that the Si layer was polycrystalline in nature, poly-Si, with a würtzite configuration. The present research is beneficial to the optoelectronic devices such as light-emitting diodes, solar cells and photodetectors in the UV–infrared range using the Si@ZnO coaxial nanostructures.

Published
2024
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31. Accounting for the thermo-stability of PdHx (x=1-3) by density functional theory

Author

Long, Debing, Li, Mingkai, Meng, Dongxue, He, Yunbin, Yoon, Im Taek, Ahuja, Rajeev, Luo, Wei, Long, Debing, Li, Mingkai, Meng, Dongxue, He, Yunbin, Yoon, Im Taek, Ahuja, Rajeev, and Luo, Wei

Abstract

We calculate the formation enthalpies of PdHx (x = 0-3) by cluster expansion (CE) and calculations based on density functional theory. CE predicts the stable palladium hydride structures PdH, PdH2.62, and PdH2.75. The band structures and density of states indicate that the amount of hydrogen in the palladium lattice does not alter the metallic character of the palladium significantly. However, all PdH X structures with x > 1 have greater formation enthalpies than that of the given reaction path 4PdH(2) = 2PdH + 2Pd + 3H(2) and thus they are thermodynamically unstable. The shorter bond length of Pd-H and the smaller bond angle of Pd-H-Pd imply a higher cohesive energy in zincblende (ZB) PdH than that in rocksalt (RS) PdH. Bader charge analysis shows a stronger electronegativity of H atoms in ZB-PdH than that in RS-PdH. This results in a stronger Pd-H bond in ZB-PdH than that in RS-PdH. Thus ZB-PdH has lower formation enthalpy than that of RS-PdH. However, regarding the dynamic stability, we conclude that hydrogen atoms prefer to occupy the octahedral sites of the palladium lattice because of the lower zero-point energy and vibration free energy than that of occupying the tetrahedral sites.

Published
2018
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45. Enhanced ferromagnetism by preventing antiferromagnetic MnO2 in InP:Be/Mn/InP:Be triple layers fabricated using molecular beam epitaxy.

Author

Lee, D.J., Park, C.S., Lee, Cheol Jin, Song, J.D., Koo, H.C., Yoon, Chong S., Yoon, Im Taek, Kim, H.S., Kang, T.W., and Shon, Yoon

Subjects
*INDIUM phosphide, *FERROMAGNETISM, *ANTIFERROMAGNETIC materials, *MANGANESE oxides, *MICROFABRICATION, *MOLECULAR beam epitaxy
Abstract

Abstract: The p-type InP:Be/Mn/InMnP:Be triple epilayers were prepared using MBE to increase T c (>300 K) by preventing MnO2. After milling 1–3 nm of epilayers thickness from the top surface, the transmission electron microscopy (TEM) and X-ray diffraction (XRD) revealed no MnO2 and precipitates, and TEM and XRD results coincide with results of ferromagnetism. The enhanced ferromagnetic transition at >300 K corresponds to InMnP:Be. The increased ferromagnetic coupling without MnO2 is considered to originate from the increased p–d hybridation. These results demonstrate that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be formed by above process. [Copyright &y& Elsevier]

Published
2014
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46. Polarity Control of ZnO Films Grown on Ferroelectric (0001) LiNbO 3 Substrates without Buffer Layers by Pulsed-Laser Deposition.

Author

Yoon IT, Lee J, Tran NC, and Yang W

Abstract

For this study, polarity-controlled ZnO films were grown on lithium niobate (LiNbO 3 ) substrates without buffer layers using the pulsed-laser deposition technique. The interfacial structure between the ZnO films and the LiNbO 3 was inspected using high-resolution transmission electron microscopy (HR-TEM) measurements, and X-ray diffraction (XRD) measurements were performed to support these HR-TEM results. The polarity determination of the ZnO films was investigated using piezoresponse force microscopy (PFM) and a chemical-etching analysis. It was verified from the PFM and chemical-etching analyses that the ZnO film grown on the (+z) LiNbO 3 was Zn-polar ZnO, while the O-polar ZnO occurred on the (-z) LiNbO 3 . Further, a possible mechanism of the interfacial atomic configuration between the ZnO on the (+z) LiNbO 3 and that on the (-z) LiNbO 3 was suggested. It appears that the electrostatic stability at the substrate surface determines the initial nucleation of the ZnO films, leading to the different polarities in the ZnO systems.

Published
2020
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