• Applied Science and Convergence Technology
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• v.25 no.2
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• pp.36-41
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• 2016

Similarity and diversity of various quantum ring structures are investigated by classifying energy dispersions of three different structures: an electrostatic quantum ring, a magnetic quantum ring, and a magnetic-electric quantum ring. The wave functions and the eigenenergies of a single electron in the quantum ring structures are calculated by solving the Schrdinger equation without any electron-electron interaction. Magnetoconductance is studied by calculating a two-terminal conductance while taking into account the backscattering via the resonance through the states of the quantum rings at the center of a quasi-one dimensional conductor. It is found that the energy spectra for the various quantum ring structures are sensitive to additional electrostatic potentials as well as to the effects of a nonuniform magnetic field. There are also characteristics of similarity and diversity in the energy dispersions and in the single-channel magnetoconductance.

• Journal of the Korean Vacuum Society
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• v.21 no.3
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• pp.151-157
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• 2012

The two dimensional electron gas system based on GaAs/$Al_xGa_{1-x}As$ heterostructure is widely used for fabricating quantum structures such as quantum dot, quantum point contact, electron interferometer and so on. However the conductance of the device is usually unstable due to the presence of random telegraph noise in the device. To overcome such problem, we have studied the effect of surface state on the stability of the device by altering the surface state of the device with oxygen plasma. The dramatic improvement of the device stability has been observed after cleaning the device surface with oxygen plasma (by 50 W~120 W plasma power) for 30 sec followed by etching in HCl : $H_2O$ (1 : 3) solution.

• Carbon letters
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• v.28
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• pp.60-65
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• 2018

Linear carbon chains (LCCs) encapsulated inside the hollow cores of carbon nanotubes (CNTs) have been experimentally synthesized and structurally characterized by Raman spectroscopy and transmission electron microscopy. However, in terms of electronic conductivity, their transportation mechanism has not been investigated theoretically or experimentally. In this study, the density of states and quantum conductance spectra were simulated through density functional theory combined with the non-equilibrium Green function method. The encapsulated LCCs inside (5,5), (6,4), and (9,0) single-walled carbon nanotubes (SWCNTs) exhibited a drastic change from metallic to semiconducting or from semiconducting to metallic due to the strong charge transfer between them. On the other hand, the electronic change in the conductance value of LCCs encapsulated inside the (7,4) SWCNT were in good agreement with the superposition of the individual SWCNTs and the isolated LCCs owing to the weak charge transfer.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.367-367
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• 2012

We investigate Landau level spectra of twisted bilayer graphene under a perpendicular magnetic field, showing that the layers provide rich electronic structure depending on misoriented angle. New types of excitations with Landau level sequences due to the reflection of interlayer coupling level are matter of interest in the present work. We calculate the electronic structure of bilayer systems with a relative small angle rotation of the two graphene layers. Calculated Landau level spectra for twisted bilayer graphene using a continuum formulation are in good agreement with existing experimental and theoretical studies. Twist angle dependent numerical simulations provide significant insights for the nature of the Landau level spectra in bilayer graphene, combining signals from both massive and massless Dirac fermions. We finally discuss the influence of the graphene layers in the experimental sample that related to the magneto-transport measurements including quantum Hall conductance.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.335.1-335.1
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• 2016

The electronic structures of a hybrid magnetic-electric quantum ring and two terminal conductance taking into account the resonant backscattering via both magnetic and electric edge channels are studied. The hybrid magnetic-electric quantum ring is formed by a magnetic quantum dot combined with an additional antidot electrostatic potential at the center of the dot. Electrons are both magnetically and electrically confined to the plane. The antidot potential repelling electrons from the center of the dot plays an important role in the energy spectra and magnetoconductance. The angular momentum transition in the ground state and the behavior of magnetoconductance due to a change of the antidot potential are shown in comparison with the conventional magnetic quantum dot.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.474-474
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• 2011

Graphene is considered as a potential candidate for the key material in the ideal 2D nanoelectronics. Recently, it is reported that graphene has an interesting sensitivity to molecular adsorption on it. Such properties are believed to be enhanced by the existence of disorders and ripples inside graphene as well as by the interaction with the substrate underneath. Here, we report the effect of introducing structural disorders to the graphene on its electrical properties such as conductance, transconductance, low frequency noise, which can be successfully described by a simple model of the continuum percolation. In addition, the response of the graphene device to gaseous molecular adsorption was systematically investigated and the results were discussed along with the change in Raman spectra.

• Current Applied Physics
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• v.18 no.11
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• pp.1275-1279
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• 2018

We investigate the change of the Fano effect by considering one Majorana zero mode to couple laterally to the single-dot Fano interferometer. It is found that the Majorana zero mode quenches the Fano effect thoroughly and causes the conductance to be independent of the dot level, the dot-lead coupling, and the increase of the Majorana-dot coupling. As a result, the linear conductance becomes only related to the interlead coupling and the magnetic-flux phase factor. These results can be helpful for the detection of Majorana zero mode.

• Journal of Korean Vacuum Science & Technology
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• v.1 no.1
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• pp.19-23
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• 1997

The conductance of a microscopic constriction in a two-dimensional electron gas is obtained as a function of both the constriction width and curvature. When the quantized conductance G at plateaus is given by the channel number Nc times the quantum unit 2e2/h, Nc is found to be a function of not only the width and but also the curvature. At a given W, Nc increases by one whenever the constriction curvature decreases by about a certain value. Until the shape smoothness becomes comparable to the two parallel boundaries, there exist more channels avaliable for conduction in a smaller-curvature constriction than in a larger-curvature one. This result is very interesting because Nc has been considered to depend on the width W only. this reflects that the number of the quantized transverse levels depend o both the constriction width and curvature in a two-dimensional electron gas.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.441-445
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• 2021

The components affecting the extrinsic transconductance (g_{m_ext}) in In_0.7Ga_0.3As quantum-well (QW) high-electron-mobility transistors (HEMTs) on an InP substrate were investigated. First, comprehensive modeling, which only requires physical parameters, was used to explain both the intrinsic transconductance (g_{m_int}) and the g_{m_ext} of the devices. Two types of In_0.7Ga_0.3As QW HEMT were fabricated with gate lengths ranging from 10 ㎛ to sub-100 nm. These measured results were correlated with the modeling to describe the device behavior using analytical expressions. To study the effects of the components affecting g_{m_int}, the proposed approach was extended to projection by changing the values of physical parameters, such as series resistances (R_S and R_D), apparent mobility (𝜇_{n_app}), and saturation velocity (𝜈_sat).

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.57-62
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• 2011

We have studied the electrical and magnetic transport properties of tunneling device with FePt magnetic quantum dots. The FePt nanoparticles with a diameter of 8~15 nm were embedded in a $SiO_2$ layer through thermal annealing process at temperature of $800^{\circ}C$ in $N_2$ gas ambient. The electrical properties of the tunneling device were characterized by current-voltage (I-V) measurements under the perpendicular magnetic fields at various temperatures. The nonlinear I-V curves appeared at 20 K, and then it was explained as a conductance blockade by the electron hopping model and tunneling effect through the quantum dots. It was measured also that the negative magneto-resistance ratio increased about 26.2% as increasing external magnetic field up to 9,000 G without regard for an applied electric voltage.