• Journal of the Korean Applied Science and Technology
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• v.16 no.4
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• pp.313-316
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• 1999

Organic semiconductors based on conjugated thiophene oligomer have great potential to be utilized as an active layer for electronic and optoelectronic devices. In this study, a conjugated oligomer such as ${\alpha}$-sexithiophene (${\alpha}$-6T) thin films was prepared by the Organic Molecular Beam Deposition (OMBD), and various electrode materials were also deposited by a simple vacuum evaporation, respectively. Those films were photolithographically patterned for the electrical measurements. Electrical charact-erization of the thin film transistor with various channel length were executed and the field effect mobility of these thin film transistors were also calculated by the formula using the experimental data.

• Advances in nano research
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• v.5 no.2
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• pp.141-169
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• 2017

In this paper, a nanobeam connected to a rotating molecular hub is considered. The vibration behavior of rotating functionally graded nanobeam based on Eringen's nonlocal theory and Euler-Bernoulli beam model is investigated. Furthermore, axial preload and porosity effect is studied. It is supposed that the material attributes of the functionally graded porous nanobeam, varies continuously in the thickness direction according to the power law model considering the even distribution of porosities. Porosity at the nanoscopic length scale can affect on the rotating functionally graded nanobeams dynamics. The equations of motion and the associated boundary conditions are derived through the Hamilton's principle and generalized differential quadrature method (GDQM) is utilized to solve the equations. In this paper, the influences of some parameters such as functionally graded power (FG-index), porosity parameter, axial preload, nonlocal parameter and angular velocity on natural frequencies of rotating nanobeams with pure ceramic, pure metal and functionally graded materials are examined and some comparisons about the influence of various parameters on the natural frequencies corresponding to the simply-simply, simplyclamped, clamped-clamped boundary conditions are carried out.

• Advances in Energy Research
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• v.3 no.2
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• pp.117-124
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• 2015

In this paper, we have reported an enhancement in thermoelectric properties of un-doped zinc oxide (ZnO) grown by molecular beam epitaxy (MBE) on silicon (001) substrate by annealing treatment. The grown ZnO thin films were annealed in oxygen environment at $500^{\circ}C-800^{\circ}C$, keeping a step of $100^{\circ}C$ for one hour. Room temperature Seekbeck measurements showed that Seebeck coefficient and power factor increased from 222 to $510{\mu}V/K$ and $8.8{\times}10^{-6}$ to $2.6{\times}10^{-4}Wm^{-1}K^{-2}$ as annealing temperature increased from 500 to $800^{\circ}C$ respectively. This observation was related with the improvement of crystal structure of grown films with annealing temperature. X-ray diffraction (XRD) results demonstrated that full width half maximum (FWHM) of ZnO (002) plane decreased and crystalline size increased as the annealing temperature increased. Photoluminescence study revealed that the intensity of band edge emission increased and defect emission decreased as annealing temperature increased because the density of oxygen vacancy related donor defects decreased with annealing temperature. This argument was further justified by the Hall measurements which showed a decreasing trend of carrier concentration with annealing temperature.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1604-1611
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• 2018

Utilizing Sb-based bulk epilayers on large-scale low-cost substrates such as GaAs for fabricating infrared (IR) photodetectors is presently attracting significant attention worldwide. For this study, three sample series of $GaAs_xSb_{1-x}$, $In_{1-x}Ga_xSb$, and $InAs_xSb_{1-x}$ with different compositions were grown on semi-insulating GaAs substrates by using molecular beam epitaxy (MBE) and appropriate InAs quantum dots (QDs) as a defect-reduction buffer layer. Photoluminescence (PL) signals from these samples were observed over a wide IR wavelength range from $2{\mu}m$ to $12{\mu}m$ in agreement with the expected bandgap, including bowing effects. In particular, interband PL signals from $InAs_xSb_{1-x}$ and $In_{1-x}Ga_xSb$ samples even at room temperature show promising potential for IR photodetector applications.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.701-708
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• 2022

The mass attenuation coefficients (μ_m) of polyethylene glycol (PEG) of different molecular weights (1000-200,000) were measured using single-beam photon transmission. The X-ray fluorescent (XRF) photons from Zinc (Zn), Zirconium (Zr), Molybdenum (Mo), Silver (Ag) and Cadmium (Cd) targets were used to determine the attenuation of gamma radiation of energy range between 8.67 and 23.19 keV in PEG samples. The results were compared to theoretical values using XCOM and Monte Carlo simulation using Geant4 toolkit which was developed to validate the experiment at those certain energies. The mass attenuation coefficients were then used to compute the effective atomic numbers, electron density and half value layers for the studied samples. The outcomes showed good agreement between experimental and simulated results with those calculated theoretically by XCOM within 5% deviation. The PEG 1000 sample showed slightly higher μ_m value compared with the other samples. The dependence of the photon energy and PEG composition on the values of μ_m and HVL were investigated and discussed. In addition, the values of Z_eff and N_eff for all PEG samples behaved similarly in the given photon energy range, and they decreased as the photon energy increased.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.612-619
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• 2002

The dynamic behavior of Al-Mg alloys plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser irradiation. The keyhole fluctuated both in size and shape and its fluctuation period was about 440 ${\mu}{\textrm}{m}$. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling point and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic diagnostics of plasma induced in the pulsed YAG laser welding of Al-Mg alloys in air and argon atmospheres. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectrum of AlO, MgO and AIH. It was confirmed that the resonant lines of Al and Mg were strongly self-absorbed, in particular in the vicinity of pool surface. The self-absorption of atomic Mg line was more eminent in alloys containing higher Mg. These facts showed that the laser-induced plasma was relatively a low temperature and high density metallic vapor. The intensities of molecular spectra of AlO and MgO were different each other depending on the power density of laser beam. Under the low power density irradiation condition, the MgO band spectra were predominant in intensity, while the AlO spectra became much stronger in higher power density. In argon atmosphere the band spectra of MgO and AlO completely vanished, but AlH molecular spectra was detected clearly. The hydrogen source was presumably the hydrogen solved in the base Metal, absorbed water on the surface oxide layer or H$_2$ and $H_2O$ in the shielding gas. The temporal change in spectral line intensities was quite similar to the fluctuation of keyhole. The time average plasma temperature at 1 mm high above the surface of A5083 alloy was determined by the Boltzmann plot method of atomic Cr lines of different excitation energy. The obtained electron temperature was 3, 280$\pm$150 K which was about 500 K higher than the boiling point of pure aluminum. The electron number density was determined by measuring the relative intensities of the spectra1lines of atomic and singly ionized Magnesium, and the obtained value was 1.85 x 1019 1/㎥.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.103-108
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• 2019

Non-equilibrium molecular dynamics simulation on the thermal boundary resistance(TBR) of an aluminum(Al)/silicon(Si) interface was performed in the present study. The constant heat flux across the Si/Al interface was simulated by adding the kinetic energy in hot Si region and removing the same amount of the energy from the cold Al region. The TBR estimated from the sharp temperature drop at the interface was independent of heat flux and equal to $5.13{\pm}0.17K{\cdot}m^2/GW$ at 300K. The simulation result was experimentally confirmed by the time-domain thermoreflectance technique. A 90nm thick Al film was deposited on a Si(100) wafer using an e-beam evaporator and the TBR on the film/substrate interface was measured using the time-domain thermoreflectance technique based on a femtosecond laser system. A numerical solution of the transient heat conduction equation was obtained using the finite difference method to estimate the TBR value. Experimental results were compared to the prediction and discussions on the nanoscale thermal transport phenomena were made.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.95.1-95.1
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• 2010

Transparent conducting ZnO films were deposited to apply DSSC Substrate on glass substrates at $500^{\circ}C$ by ionbeam-assisted deposition. Crystallinity, microstructure, surface roughness, chemical composition, electrical and optical properties of the films were investigated as a function of deposition parameters such as ion energy, and substrate temperature. The microstructure of the polycrystalline ZnO films on the glass substrate were closely related to the oxygen ion energy, arrival ratio of oxygen to Zinc Ion bombarded on the growing surface. The main effect of energetic ion bombardment on the growing surface of the film may be divided into two categories; 1) the enhancement of adatom mobility at low energetic ion bombardment and 2) the surface damage by radiation damage at high energetic ion bombardment. The domain structure was obtained in the films deposited at 300 eV. With increasing the ion energy to 600 eV, the domain structure was changed into the grain structure. In case of the low energy ion bombardment of 300 eV, the microstructure of the film was changed from the grain structure to the domain structure with increasing arrival ratio. At the high energy ion bombardment of 600 eV, however, the only grain structure was observed. The electrical properties of the deposited films were significantly related to the change of microstructure. The films with the domain structure had larger carrier concentration and mobility than those with the grain structure, because the grain boundary scattering was reduced in the large size domains compared with the small size grains. The optical transmittance of ZnO films was dependent on a surface roughness. The ZnO films with small surface roughness, represented high transmittance in the visible range because of a decreased light surface scattering. By varying the ion energy and arrival ratio, the resistivity and optical transmittance of the films were varied from $1.1{\times}10^{-4}$ to $2.3{\times}10^{-2}{\Omega}cm$ and from 80 to 87%, respectively. The ZnO film deposited at 300 eV, and substrate temperature of $500^{\circ}C$ had the resistivity of $1.1{\times}10^{-4}{\Omega}cm$ and optical transmittance of 85% in visible range. As a result of experiments, we provides a suggestition that ZnO thin Films can be effectively used as the DSSC substrate Materials.

• Journal of the Korean Vacuum Society
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• v.21 no.5
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• pp.264-272
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• 2012

In this paper, we report THz generation and detection characteristics investigated by InGaAs semiconductor epilayers, as results of a basic study obtained from the InGaAs-based THz transmitter/receiver (Tx/Rx). High-temperature and low-temperature (LT) grown InGaAs epilayers were prepared by the molecular beam epitaxy technique for the characterization of THz generation and detection, respectively, and the surface emission based on the photo-Dember effect was tried for THz generation. THz wave was generated by irradiation of a Ti:Sapphire fs pulse laser (60 ps/83 MHz), and a LT-GaAs Rx was used for the THz detection. The frequency band shown in the spectral amplitudes Fourier-transformed from the measured current signals was ranging in 0.5~2 THz, and the signal currents were exponentially increased with the Tx beam power. The THz detection characteristics of LT-InGaAs were investigated by using an Rx with dipole (5/20 ${\mu}m$) antenna, and the cutoff frequency was ~2 THz.

• Radiation Oncology Journal
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• v.35 no.2
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• pp.112-120
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• 2017

Purpose: To evaluate the effect of adjuvant external beam radiation therapy (EBRT) on local failure-free survival rate (LFFS) for papillary thyroid cancer (PTC) invading the trachea. Materials and Methods: Fifty-six patients with locally advanced PTC invading the trachea were treated with surgical resection. After surgery, 21 patients received adjuvant EBRT and radioactive iodine therapy (EBRT group) and 35 patients were treated with radioactive iodine therapy (control group). Results: The age range was 26-87 years (median, 56 years). The median follow-up period was 43 months (range, 4 to 145 months). EBRT doses ranged from 50.4 to 66 Gy (median, 60 Gy). Esophagus invasion and gross residual disease was more frequent in the EBRT group. In the control group, local recurrence developed in 9 (9/35, 26%) and new distant metastasis in 2 (2/35, 6%) patients, occurring 4 to 68 months (median, 37 months) and 53 to 68 months (median, 60 months) after surgery, respectively. Two patients had simultaneous local recurrence and new distant metastasis. There was one local failure in the EBRT group at 18 months after surgery (1/21, 5%). The 5-year LFFS was 95% in the EBRT group and 63% in the control group (p = 0.103). In the EBRT group, one late grade 2 xerostomia was developed. Conclusion: Although, EBRT group had a higher incidence of esophagus invasion and gross residual disease, EBRT group showed a better 5-year LFFS. Adjuvant EBRT may have contributed to the better LFFS in these patients.