• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.1062-1070
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• 2022

In the present communication, pure and stable α-Bismuth Oxide (Bi₂O₃) nanoparticles (NPs) were synthesized by low temperature solution combustion method using urea as a fuel and calcined at 500℃. The synthesized sample was characterized by using powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy dispersive X-ray analysis (EDAX), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and UV-Visible absorption spectroscopy. The PXRD pattern confirms the formation of mono-clinic, stable and low temperature phase α-Bi₂O₃. The direct optical energy band gap was estimated by using Wood and Tauc's relation which was found to be 2.81 eV. The characterized sample was studied for X-ray/gamma ray shielding properties in the energy range 0.081-1.332 MeV using NaI (Tl) detector and multi channel analyzer (MCA). The measured shielding parameters agrees well with the theory, whereas, slight deviation up to 20% is observed below 356 keV. This deviation is mainly due to the influence of atomic size of the target medium. Furthermore an accurate theory is necessary to explain the interaction of X-ray/gamma ray with the NPs.The present work opens new window to use this facile, economical, efficient, low temperature method to synthesize nanomaterials for X-ray/gamma ray shielding purpose.

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4708-4714
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• 2022

The novelty in the present search, the Soda-Lime-Silica (SLS) glass waste to prepare free lead glass shielding was used in order to limit the accumulation of glass waste, which requires extensive time to decompose. This also saves on the consumption of pure SiO₂, which is a finite resource. Furthermore, the combining of BaO with Bi₂O₃ into a glass network leads to increased optical properties and improved attenuation. The UV-Visible Spectrophotometer was used to investigate the optical properties and the radiation shielding properties were reported for current glass samples utilizing the PhysX/PDS online software. The optical property results indicate that when BaO content increases in glass structure, the Urbach energy ΔE, and refractive index n increases while the energy optical band gap E_opt decreases. The result of the metallisation criteria (M) revealed that the present glass samples are nonmetallic (insulators). Furthermore, the radiation shielding parameter findings suggest that when BaO was increased in the glass structure, the linear attenuation coefficient and effective atomic number (Z_eff) rose. But the half-value layer HVL declined as the BaO concentration grew. According to the research, the glass samples are non-toxic, transparent to visible light, and efficient radiation shielding materials. The Ba5 sample is considered the best among all the samples due to its higher attenuation value and lower HVL and MFP values, which make it a suitable candidate as transparent glass shield shielding.

• Current Photovoltaic Research
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• v.11 no.2
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• pp.39-43
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• 2023

Carrier-selective contacts (CSCs) solar cells are considerably attractive on highly efficient crystalline silicon heterojunction (SHJ) solar cells due to their advantages of high thermal tolerance and the simple fabrication process. CSCs solar cells require a hole selective contact (HSC) layer that selectively collects only holes. In order to selectively collect holes, it must have a work function characteristic of 5.0 eV or more when contacted with n-type Si. The VO_x, NiO_x, and CuI_x thin films were fabricated and analyzed respectively to confirm their potential usage as a hole-selective contact (HSC) layer. All thin films showed characteristics of band-gap engergy > 3.0 eV, work function > 5.0 eV and minority carrier lifetime > 1.5 ms.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.582-587
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• 2023

The effects of the annealing temperature on the structural, morphological, and luminescent properties of SrWO₄:Sm³⁺ thin films grown on quartz substrates by radio-frequency magnetron sputtering were investigated. The thin films were annealed at various annealing temperatures for 20 min in a rapid thermal annealer after growing the thin films. The experimental results showed that the annealing temperature has a significant effect on the properties of the SrWO₄:Sm³⁺ thin films. The crystal structure of the as-grown SrWO₄:Sm³⁺ thin films was transformed from amorphous to crystalline after annealing at 800℃. The preferred orientation along (112) plane and a significant increase in average grain size by 820 nm were observed with increasing the annealing temperature. The average optical transmittance in the wavelength range of 500~1,100 nm was decreased from 72.0% at 800℃ to 44.2% at an annealing temperature of 1,000℃, where the highest value in the photoluminescence intensity was obtained. In addition to the red-shift of absorption edge, a higher annealing temperature caused the optical band gap energy of the SrWO₄:Sm³⁺ thin films to fall rapidly. These results suggest that the structural, morphological, and luminescent properties of SrWO₄:Sm³⁺ thin films can be controlled by varying annealing temperature.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1067-1072
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• 2023

We prepared AZO (Al₂O₃ : 3 wt %) thin films according to the substrate temperature using the pulsed laser deposition method and the structural, electrical, and optical properties of the thin films were investigated. The AZO thin film deposited at 400℃ showed the best (002) orientation and the FWHM was 0.38°. As a result of the investigation of electrical properties, it was confirmed that the carrier concentration and mobility increased and the resistivity decreased as the substrate temperature increased. The average transmittance in the visible light region showed a high value of 85% or more regardless of the substrate temperature. The Burstein-Moss effect, in which the carrier concentration would increase with increasing substrate temperature thereby widening the energy band gap, was also observed. The resistivity and the figure of merit of the AZO thin film deposited at a substrate temperature of 400℃ were 6.77 × 10^-4 Ω·cm and 1.02 × 10⁴ Ω^-1·cm^-1 respectively, showing the best value.

• The Journal of the Korea institute of electronic communication sciences
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• v.19 no.1
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• pp.39-46
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• 2024

In this study, GTZO(Ga-Ti-Zn-O) thin films were deposited at various working pressures (1~7mTorr) by RF magnetron sputtering to examine the structural, electrical, and optical properties. All GTZO thin films exhibited c-axis preferential growth regardless of working pressure, the GTZO thin film deposited at 1mTorr showed the most excellent crystallinity having 0.38˚ of FWHM. The average transmittance in the visible light region (400~800nm) showed 80% or more regardless of the working pressure. We could observed the Burstein-Moss effect that carrier concentration decrease with the increase of working pressure and thus the energy band gap is narrowed. Figure of merits of GTZO thin film deposited at 1mTorr showed the highest value of 9.08 × 103 Ω-1·cm-1, in this case resistivity and average transmittance in the visible light region were 5.12 × 10-4 Ω·cm and 80.64%, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.162-162
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• 2010

InSb has received great attentions as a promising candidate for the active layer of infrared photodetectors due to the well matched band gap for the detection of $3{\sim}5\;{\mu}m$ infrared (IR) wavelength and high electron mobility (106 cm2/Vs at 77 K). In the fabrication of InSb photodetectors, passivation step to suppress dark currents is the key process and intensive studies were conducted to deposit the high quality passivation layers on InSb. Silicon dioxide (SiO2), silicon nitride (Si3N4) and anodic oxide have been investigated as passivation layers and SiO2 is generally used in recent InSb detector fabrication technology due to its better interface properties than other candidates. However, even in SiO2, indium oxide and antimony oxide formation at SiO2/InSb interface has been a critical problem and these oxides prevent the further improvement of interface properties. Also, the mechanisms for the formation of interface phases are still not fully understood. In this study, we report the quantitative analysis of indium and antimony oxide formation at SiO2/InSb interface during plasma enhanced chemical vapor deposition at various growth temperatures and subsequent heat treatments. 30 nm-thick SiO2 layers were deposited on InSb at 120, 160, 200, 240 and $300^{\circ}C$, and analyzed by X-ray photoelectron spectroscopy (XPS). With increasing deposition temperature, contents of indium and antimony oxides were also increased due to the enhanced diffusion. In addition, the sample deposited at $120^{\circ}C$ was annealed at $300^{\circ}C$ for 10 and 30 min and the contents of interfacial oxides were analyzed. Compared to as-grown samples, annealed sample showed lower contents of antimony oxide. This result implies that reduction process of antimony oxide to elemental antimony occurred at the interface more actively than as-grown samples.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.293-293
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• 2014

Over last decade InGaN alloy structures have become the one of the most promising materials among the numerous compound semiconductors for high efficiency light sources because of their direct band-gap and a wide spectral region (ultraviolet to infrared). The primary cause for the high quantum efficiency of the InGaN alloy in spite of high threading dislocation density caused by lattice misfit between GaN and sapphire substrate and severe built-in electric field of a few MV/cm due to the spontaneous and piezoelectric polarizations is generally known as the strong exciton localization trapped by lattice-parameter-scale In-N clusters in the random InGaN alloy. Nonetheless, violet-emitting (390 nm) conventional low-In-content InGaN/GaN multi-quantum wells (MQWs) show the degradation in internal quantum efficiency compared to blue-emitting (450 nm) MQWs owing higher In-content due to the less localization of carrier and the smaller band offset. We expected that an improvement of internal quantum efficiency in the violet region can be achieved by replacing the conventional low-In-content InGaN/GaN MQWs with ultra-thin, high-In-content (UTHI) InGaN/GaN MQWs because of better localization of carriers and smaller quantum-confined Stark effect (QCSE). We successfully obtain the UTHI InGaN/GaN MQWs grown via employing the GI technique by using the metal-organic chemical vapor deposition. In this work, 1 the optical and structural properties of the violet-light-emitting UTHI InGaN/GaN MQWs grown by employing the GI technique in comparison with conventional low-In-content InGaN/GaN MQWs were investigated. Stronger localization of carriers and smaller QCSE were observed in UTHI MQWs as a result of enlarged potential fluctuation and thinner QW thickness compared to those in conventional low-In-content MQWs. We hope that these strong carrier localization and reduced QCSE can turn the UTHI InGaN/GaN MQWs into an attractive candidate for high efficient violet emitter. Detailed structural and optical characteristics of UTHI InGaN/GaN MQWs compared to the conventional InGaN/GaN MQWs will be given.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.284-284
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• 2016

Topological insulator (TI) is a bulk-insulating material with topologically protected Dirac surface states in the band gap. In particular, $Bi_2Se_3$ attracted great attention as a model three-dimensional TI due to its simple electronic structure of the surface states in a relatively large band gap (~0.3 eV). However, experimental efforts using $Bi_2Se_3$ have been difficult due to the abundance of structural defects, which frequently results in the bulk conduction being dominant over the surface conduction in transport due to the bulk doping effects of the defect sites. One promising approach in avoiding this problem is to reduce the structural defects by heteroepitaxially grow $Bi_2Se_3$ on a substrate with a compatible lattice structure, while also preventing surface degradation by encapsulating the pristine interface between $Bi_2Se_3$ and the substrate in a clean growth environment. A particularly promising choice of substrate for the heteroepitaxial growth is hexagonal boron nitride (h-BN), which has the same two-dimensional (2D) van der Waals (vdW) layered structure and hexagonal lattice symmetry as $Bi_2Se_3$. Moreover, since h-BN is a dielectric insulator with a large bandgap energy of 5.97 eV and chemically inert surfaces, it is well suited as a substrate for high mobility electronic transport studies of vdW material systems. Here we report the heteroepitaxial growth and characterization of high quality topological insulator $Bi_2Se_3$ thin films prepared on h-BN layers. Especially, we used molecular beam epitaxy to achieve high quality TI thin films with extremely low defect concentrations and an ideal interface between the films and substrates. To optimize the morphology and microstructural quality of the films, a two-step growth was performed on h-BN layers transferred on transmission electron microscopy (TEM) compatible substrates. The resulting $Bi_2Se_3$ thin films were highly crystalline with atomically smooth terraces over a large area, and the $Bi_2Se_3$ and h-BN exhibited a clear heteroepitaxial relationship with an atomically abrupt and clean interface, as examined by high-resolution TEM. Magnetotransport characterizations revealed that this interface supports a high quality topological surface state devoid of bulk contribution, as evidenced by Hall, Shubnikov-de Haas, and weak anti-localization measurements. We believe that the experimental scheme demonstrated in this talk can serve as a promising method for the preparation of high quality TI thin films as well as many other heterostructures based on 2D vdW layered materials.

• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.162-168
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• 2010

To increase the energy conversion efficiency of dye sensitized solar cells (DSSCs), it has been widely studied how to effectively transferred the electron generated from the adsorbed dye to the $TiO_{2}$ electrode for avoiding the recombination of injected electrons and iodide ions ($I^-/I_3^-$). For the blocking of the recombination, in this study, $Al_2O_3$-coated $TiO_{2}$ electrode was prepared and applied for DSSCs. In especial, the optimal preparation conditions of $Al_2O_3$ coated onto $TiO_{2}$ porous film was proposed for higher energy conversion efficiency. As a result, the solar cells fabricated from $Al_2O_3$-coated (i.e., particle size of bohemite sol : 100 nm) $TiO_{2}$ electrodes showed superior conversion efficiency (9.0%) compared to the bare $TiO_{2}$ electrodes (7.5%).