• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제30권11호
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• pp.683-687
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• 2017

We investigated the structure of an ultra-thin insulating board with low thermal conductivity along z-axis, which was based on the idea of void layers created during the glass infiltration process for the zero-shrinkage low-temperature co-fired ceramic (LTCC) technology. An alumina and four glass powders were chosen and prepared as green sheets by the tape casting method. After comparison of the four glass powders, bismuth glass was selected for the experiment. Since there is no notable reactivity between alumina and bismuth glass, alumina was selected as the supporting additive in glass layers. With 2.5 vol% of alumina powder, glass green sheets were prepared and stacked alternately with alumina green sheet to form the 'alumina/glass (including alumina additive)/alumina' structure. The stacked green sheets were sintered into an insulating substrate. Scanning electron microscopy revealed that the additive alumina formed supporting bridges in void layers. The depth and number of the stacking layers were varied to examine the insulating property. The lowest thermal conductivity obtained was 0.23 W/mK with a $500-{\mu}m-thick$ substrate.

• Journal of the Korean Ceramic Society
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• 제35권9호
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• pp.1002-1005
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• 1998

Bismuth titanate thin films were prepared on {{{{ { SrTiO}_{3 } }}(100) and Si(100) substrates by dipping-pyrolysis pro-cess using metal naphthenates as starting materials. crystallinity and in-phase alignment of the films were analyzed by X-ray diffraction $\theta$-2$\theta$ scans and $\beta$ scans (pole-figures) respectively. Highly c-axis-oriented {{{{ { { {Bi }_{4 }Ti }_{3 }O }_{12 } }} thin films with smooth surfaces were obtained after heat treatment at 75$0^{\circ}C$ on {{{{ { SrTiO}_{3 } }}(100) sub-strate while the films grown of Si(100) exhibited polycrstalline characteristics. C-axis oriented film show-ed an epitaxial relationship with the {{{{ { SrTiO}_{3 } }} substrate.

• Proceedings of the Korean Magnestics Society Conference
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• 한국자기학회 2010년도 임시총회 및 하계학술연구발표회
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• pp.80-81
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• 2010

We observed period of SdH oscillation in an individual Bi nanowire with the transverse and longitudinal magnetic fields along the axis of the nanowire grown by OFF-ON. Our results provide good qualitative description of the cyclotron behavior of the single-crystalline Bi nanowire in the ballistic regime.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.306-306
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• 2011

Three dimensional(3D) topological insulators(TIs) of Bi binary alloys are characterized by a bulk energy gap with strong spin-orbit coupling and metallic surface states protected by time-reversal symmetry. It was reported that film forms of such materials were advantageous over bulk forms due to less defect density and better crystallinity. So far, the films have been prepared on several substrates including semiconductors and graphene. But, there were no studies on metal substrates. For electronic transport experiments and device applications, it is necessary to know epitaxial relation between TIs and metal electrodes. In this study, Atomically flat films of Bi2Se3 were grown on a Au(111) metal substrate by in-situ molecular beam epitaxy. Using home-built scanning tunneling microscope, we observed hexagonal atomic structures which corresponded to the outmost selenium atomic layer of Bi2Se3. Triangular-shaped defects known as Selenium vacancy were also found.

• Journal of Magnetics
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• 제11권3호
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• pp.147-150
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• 2006

We have fabricated three-dimensional magnetophotonic crystals based on $\alpha$-$SiO_2$ opal films. Opal thin films grown on glass substrates were filled with bismuth substituted iron garnet (Bi:YIG). Scanning electron microscopy data, optical and magnetic properties of the synthesized samples confirm the presence of the Bi:YIG contentin the opal lattice. It is shown that the samples exhibit the (111) stop band, and transmissivity of the threedimensional magnetophotonic crystals is defined by both the film lattice and the Bi:YIG content.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.585-586
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• 2005

BSCCO thin films were fabricated by an ion beam sputtering method with an ultra-low growth rate, and sticking coefficients of the respective elements are evaluated. The sticking coefficient of Bi element in BSCCO film formation was observed to show a unique temperature dependence; it was almost a constant value of 0.49 below about $730^{\circ}C$ and decreased linearly over about $730^{\circ}C$. In contrast, Sr and Ca, displayed no such remarkable temperature dependence. This behavior of the sticking coefficient was explained consistently on the basis of the evaporation and sublimation processes of Bi2O3. It is considered that the liquid phase of the bismuth oxide plays an important role in the Bi 2212 phase formation in the co-deposition process.

• Journal of the Korean Society of Radiology
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• 제3권2호
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• pp.27-31
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• 2009

Now a days, the Medical X-ray equipments has become digitalized from analog type such as film, cassette to CR, DR. And many scientists are still researching and developing the Medical X-ray equipment. In this study, we used the Bismuth tri-iodide to conversion material for digital X-ray equipments and we couldn't get the satisfying result than previous study, but it opened new possibility to cover the disadvantage of a-Se is high voltage aplly and difficultness of make. In this paper, we use $BiI_3$ powder(99.99%) as x-ray conversion material and make films that have thickness of 200um and the film size is $3cm{\times}3cm$. Also, we deposited an ITO(Indium Tin Oxide) electrode as top electrode and bottom electrode using a Magnetron Sputtering System. To evaluate a characteristics of the produced films, an electrical and structural properties are performed. Through a SEM analysis, we confirmed a surface and component part. And to analyze the electrical properties, darkcurrent, sensitivity and SNR(Signal to Noise Ratio) are measured. Darkcurrent is $1.6nA/cm^2$ and sensitivity is $0.629nC/cm^2$ and this study shows that the electrical properties of x-ray conversion material that made by screen printing method are similar to PVD method or better than that. This results suggest that $BiI_3$ is suitable for a replacement of a-Se because of the reduced manufacture processing and improved yield.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.231-231
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• 2010

Thermoelectric properties of a multi-layered thin film, which was composed with indium selenide and bismuth telluride, were investigated. The structure of the layered thin film is Bi-Te /In-Se/Bi-Te and it was prepared on sapphire substrate by RF magnetron sputter using stoichiometric $Bi_2Te_3$ (99.9%) and $In_2Se_3$(99.99%) target at room temperature. Then, it was annealed at temperature range of 150 - $500^{\circ}C$ in Ar ambient. Structural characterizations were done using X-ray diffraction(XRD, BRUKER, D8, 60kW) and transmission electron microscopy (TEM, FEI, Tecnai, F30 S-Twin), respectively. Cross-section of multi-layer structure was observed by Scanning electron microscopy (SEM). The resistivity and Seebeck coefficient of these samples were also measured by conventional equipment at room temperature. The maximum value of power factor was $1.16\;{\mu}W/k^2m$ at annealing temperature of $400^{\circ}C$.

• Proceedings of the Korean Magnestics Society Conference
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• 한국자기학회 2010년도 임시총회 및 하계학술연구발표회
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• pp.79-79
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• 2010

Semimetallic bismuth (Bi) has been extensively investigated over the last decade since it exhibits very intriguing transport properties due to their highly anisotropic Fermi surface, low carrier concentration, long carrier mean free path l, and small effective carrier mass $m^*$. In particular, the great interest in Bi nanowires lies in the development of nanowire fabrication methods and the opportunity for exploring novel low-dimensional phenomena as well as practical application such as thermoelectricity[1]. In this work, we introduce a self-assembled interconnection of nanostructures produced by an on-film formation of nanowires (OFF-ON) method in order to form a highly ohmic Bi nanobridge. A Bi thin film was first deposited on a thermally oxidized Si (100) substrate at a rate of $40\;{\AA}/s$ by radio frequency (RF) sputtering at 300 K. The sputter system was kept in an ultra high vacuum (UHV) of $10^{-6}$ Torr before deposition, and sputtering was performed under an Ar gas pressure of 2m Torr for 180s. For the lateral growth of Bi nanowires, we sputtered a thin Cr (or $SiO_2$) layer on top of the Bi film. The Bi thin films were subsequently put into a custom-made vacuum furnace for thermal annealing to grow Bi nanowires by the OFF-ON method. After thermal annealing, the Bi nanowires cannot be pushed out from the topside of the Bi films due to the Cr (or $SiO_2$) layer. Instead, Bi nanowires grow laterally as a mean s of releasing the compressive stress. We fabricated a self-assembled Bi nanobridge (d=192 nm) device in-situ using OFF-ON through annealing at $250^{\circ}C$ for 10hours. From I-V measurements taken on the Bi nanobridge device, contacts to the nanobridge were found highly ohmic. The quality of the Bi nanobridge was also proved by the high MR of 123% obtained from transverse MR measurements. These results manifest the possibility of self-assembled nanowire interconnection between various nanostructures for a variety of applications and provide a simple device fabrication method to investigate transport properties on nanowires without complex patterning and etching processes.

• Journal of the Korean Ceramic Society
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• 제55권3호
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• pp.185-202
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• 2018

Photoelectrochemical (PEC) cells can convert solar energy, the largest potential source of renewable energy, into hydrogen fuel which can be stored, transported, and used on demand. In terms of cost competitiveness compared with fossil fuels, however, both photocatalytic efficiency and cost-effectiveness must be achieved simultaneously. Improvement of cost-effective, scalable, versatile, and eco-friendly fabrication methods has emerged as an urgent mission for PEC cells, and solution-based fabrication methods could be capable of meeting these demands. Herein, we review recent challenges for various nanostructured oxide photoelectrodes fabricated by solution-based processes. Hematite, tungsten oxide, bismuth vanadate, titanium oxide, and copper oxides are the main oxides focused on, and various strategies have been attempted with respect to these photocatalyst materials. The effects of nanostructuring, heterojunctions, and co-catalyst loading on the surface are discussed. Our review introduces notable solution-based processes for water splitting photoelectrodes and gives an outlook on eco-friendly and cost-effective approaches to solar fuel generation and innovative artificial photosynthesis technologies.