• Journal of Magnetics
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• 제15권1호
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• pp.7-11
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• 2010

Spin-orbit coupling (SOC) is a source of strong spin dephasing in two- and three-dimensional semiconducting systems. We report that spin dephasing in a two-dimensional electron gas can be suppressed by introducing a quantum point contact. Surprisingly, this suppression was not limited to the vicinity of the contact but extended to the entire two-dimensional electron gas. This facilitates the electrical control of the spin degree of freedom in a two-dimensional electron gas through spin-orbit coupling.

• 한국진공학회지
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• 제21권3호
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• pp.151-157
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• 2012

GaAs/$Al_xGa_{1-x}As$ 이차원 전자계는 양자점, QPC (quantum point contact), 전자 간섭계 등 다양한 형태의 양자구조 제작에 널리 사용된다. 하지만 일반적으로 GaAs 기반 양자소자는 극저온에서 소자의 전도도가 시간에 따라 변하거나 두 가지의 전 상태 사이를 왔다 갔다 하는 random telegraph noise 때문에 소자의 동작 특성이 상당히 불안하다. 이러한 문제점을 해결하기 위하여 산소 플라즈마를 이용한 소자의 표면처리가 소자의 안정성에 미치는 영향을 연구하였다. 이를 통해 소자의 표면을 산소 플라즈마를 이용하여 50 W~120 W 사이의 출력으로 30 초간 처리한 후 HCl : $H_2O$ (1 : 3) 용액을 이용하여 10초간 습식식각한 경우 전도도의 안정성이 매우 향상됨을 알 수 있었다.

• 대한화학회지
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• 제3권1호
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• pp.3-8
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• 1954

Fowler obtained thermodynamic quantities assuming the theory which could be derived by representing the system with microcanonical ensemble, in order to introduce the temperature T of the system proper, he considered the combined systems which are composed of the system proper and another arbitrary system that is in thermal contact with the former, and represented the combined system by a microcanonical ensemble, here, he used the steepest descent method in his calculation. This Fowler's treatment is not only unsatisfactory at the point of theoretical view but also he could not make the formulation of free energy of Helmholtz's so that this formular was forced to be assumed. From the point of Quantum Statistical Mechanical view, the materially closed system which is in an equilibrium state with the temperature T is best represented by canonical ensemble. At the actual derivation of the distribution law and thermodynamic quantities, however, in order to avoid the difficulty of calculation Tolman proceeded his calculation either representing the system proper by the grand-canonical ensemble or adding a certain limitation.

• 전자공학회논문지D
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• 제34D권12호
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• pp.89-100
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• 1997

This paper investigated a new type of low voltage threshold switch (LVTS). As distinguished from the many other types of electronic threshold switches, the LvTS is ; voltage controlled, occurs at low voltages ($V_{2}$ $O_{5}$lV devices. The average low threshold voltage < $V_{LVT}$>=218 mV (standard deviation =24mV~kT/q, where T=300K), and was independent of the device area (x100) and amorphous oxide occurred in an ~22.angs. thick interphase of the V/amorphous- $V_{2}$ $O_{5}$ contacts. At $V_{LVT}$ there was a transition from an initially low conductance (OFF) state into a succession of quantized states of higher conductance (ON). The OFF state was spatically homogeneous and dominated by tunneling into the interphase. The ON state conductances were consistent with the quantized conductances of ballistic transport through a one dimensional, quantum point contact. The temeprature dependence of $V_{LVT}$, and fit of the material parameters (dielectric function, barrier energy, conductivity) to the data, showed that transport in the OFF and ON states occurred in an interphase with the characteristics of, respectively, semiconducting and metallic V $O_{2}$. The experimental results suggest that the LVTS is likely to be observed in interphases produced by a critical event associated with an inelastic transfer of energy.rgy.y.rgy.

• Progress in Superconductivity
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• 제13권3호
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• pp.139-145
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• 2012

Electric activity of cardiac muscles generates magnetic fields. Magnetocardiography (or MCG) technology, measuring these magnetic signals, can provide useful information for the diagnosis of heart diseases. It is already about 40 years ago that the first measurement of MCG signals was done by D. Cohen using SQUID (superconducting quantum interference device) sensor inside a magnetically shielded room. In the early period of MCG history, bulky point-contact RF-SQUID was used as the magnetic sensor. Thanks to the development of Nb-based Josephson junction technology in mid 1980s and new design of tightly-coupled DC-SQUID, low-noise SQUID sensors could be developed in late 1980s. In around 1990, several groups developed multi-channel MCG systems and started clinical study. However, it is quite recent years that the true usefulness of MCG was verified in clinical practice, for example, in the diagnosis of coronary artery disease. For the practical MCG system, technical elements of MCG system should be optimized in terms of performance, fabrication cost and operation cost. In this review, development history, technical issue, and future development direction of MCG technology are described.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.188.1-188.1
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• 2014

Aluminum is widely used as a material for electrode on silicon based devices. Especially, aluminum films are used as backside and front-side electrodes in silicon quantum dot (QD) solar cells. In this point, the diffusion of aluminum is very important for the enhancement of power conversion efficiency by improvement of contact property. Aluminum was deposited on a Si (100) wafer and a Si QD layer by ion beam sputter system with a DC ion gun. The Si QD layer was fabricated by $1100^{\circ}C$ annealing of the $SiO_2/SiO_1$ multilayer film grown by ion beam sputtering deposition. Cs ion beam with a low energy and a grazing incidence angle was used in SIMS depth profiling analysis to obtain high depth resolution. Diffusion behavior of aluminum in the Al/Si and Al/Si QD interfaces was investigated by secondary ion mass spectrometry (SIMS) as a function of heat treatment temperature. It was found that aluminum is diffused into Si substrate at $450^{\circ}C$. In this presentation, the effect of heat treatment temperature and Si nitride diffusion barrier on the diffusion of Al will be discussed.