Soon Cheol Hong

Bio: Soon Cheol Hong is an academic researcher from University of Ulsan. The author has contributed to research in topics: Magnetism & Magnetic moment. The author has an hindex of 23, co-authored 178 publications receiving 4356 citations. Previous affiliations of Soon Cheol Hong include Seoul National University & Northwestern University.

Thickness and strain effects on electronic structures of transition metal dichalcogenides: 2H- M X 2 semiconductors ( M = Mo, W; X = S, Se, Te)

Abstract: Using the first-principles calculations, we explore the electronic structures of 2H-$M{X}_{2}$ ($M$ $=$ Mo, W; $X$ $=$ S, Se, Te). When the number of layers reduces to a single layer, the indirect gap of bulk becomes a direct gap with larger gap and the band curvatures are found to lead to the drastic changes of effective masses. On the other hand, when the strain is applied on the single layer, the direct gap becomes an indirect gap and the effective masses vary. Especially, the tensile strain reduces the gap energy and effective masses while the compressive strain enhances them. Furthermore, the much larger tensile stress leads to become metallic.

High-detectivity multilayer MoS(2) phototransistors with spectral response from ultraviolet to infrared.

Abstract: Phototransistors based on multilayer MoS(2) crystals are demonstrated with a wider spectral response and higher photoresponsivity than single-layer MoS(2) phototransistors. Multilayer MoS(2) phototransistors further exhibit high room temperature mobilities (>70 cm(2) V(-1) s(-1) ), near-ideal subthreshold swings (~70 mV decade(-1) ), low operating gate biases (<5 V), and negligible shifts in the threshold voltages during illumination.

Band-gap transition induced by interlayer van der Waals interaction in MoS 2

Abstract: We have investigated the electronic structures of single- and double-layered MoS${}_{2}$, composing of heterojunction structures such as graphene, MoS${}_{2}$, and SiO${}_{2}$ and MoS${}_{2}$ and SiO${}_{2}$, using scanning photoelectron microscopy. Negative shifts of both core levels and valence bands toward the Fermi energy have been observed. In connection with first-principles calculations, we have confirmed that the direct gap of single-layer MoS${}_{2}$ is changed to an indirect gap by stacking additional layers via van der Waals interlayer interactions.

Ferromagnetism in Mn-doped Ge

Abstract: We have successfully fabricated highly (up to 6%) Mn-doped bulk Ge single crystals. The lattice constant increases linearly with Mn concentration due to the larger Mn atomic radius compared with Ge, strongly indicating that Mn ions are being incorporated into the host Ge lattice. Alloys with lower Mn concentrations showed paramagnetism due to localized magnetic ions. ${\mathrm{Ge}}_{0.94}{\mathrm{Mn}}_{0.06}$ showed ferromagnetic ordering at \ensuremath{\sim}285 K, as determined from temperature-dependent magnetization and resistance measurements. The coersive field was 1260 Oe at 250 K.

Vacancy-induced magnetism in SnO 2 : A density functional study

Abstract: We study the magnetic and electronic properties of defects in ${\text{SnO}}_{2}$ using pseudopotential and all electron methods. Our calculations show that bulk ${\text{SnO}}_{2}$ is nonmagnetic, but it shows magnetism with a magnetic moment around $4.00{\ensuremath{\mu}}_{B}$ due to Sn vacancy $({V}_{\text{Sn}})$. The magnetic moment comes mainly from O atoms surrounding ${V}_{\text{Sn}}$ and Sn atoms, which couple antiferromagnetically with the O atoms in the presence of ${V}_{\text{Sn}}$. The coupling between different Sn vacancies is also studied and we found that these defects not only couple ferromagnetically but also antiferromagnetically and ferrimagnetically. Our calculations demonstrate that the experimentally observed giant magnetic moment of transition--metal-doped ${\text{SnO}}_{2}$ can be attributed to ${V}_{\text{Sn}}$.

Ultrasensitive photodetectors based on monolayer MoS2.

Abstract: A very sensitive photodector based on molybdenum disulphide with potential for integrated optoelectronic circuits, light sensing, biomedical imaging, video recording or spectroscopy is now demonstrated.

Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

Abstract: Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

Photodetectors based on graphene, other two-dimensional materials and hybrid systems

Abstract: Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.