• Journal of the Korean Electrochemical Society
• /
• v.18 no.1
• /
• pp.38-44
• /
• 2015

This review article summarizes the recent progress of quantum dot (QD)-sensitized solar cells based on mesoporous $TiO_2$ thin films. From the intrinsic characteristics of nanoscale inorganic QDs with various compositions, it was possible to construct a variety of 3rd-generation thin film solar cells by solution process. Depending on preparation methods, colloidal QD sensitizers are pre-prepared for later deposition onto the surface of $TiO_2$ or in-situ deposition of QDs from chemical bath is done for direct growth of QD sensitizers over substrates. Recently, colloidal QD sensitizers have shown an overall power conversion efficiency of ~7% by a very precise control of composition while a representative CdS/CdSe from chemical bath deposition have done ~5% with polysulfide electrolytes. In the near future, it is necessary to carry out systematic investigations for developing new hole-conducting materials and controlling interfaces within the cell, thus leading to an enhancement of both open-circuit voltage and fill factor while keeping the current high value of photocurrents from QDs towards more efficient and stable QD-sensitized solar cells.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.2
• /
• pp.409-413
• /
• 2010

We fabricated 10 nm-thick cobalt silicide($CoSi_2$) as a buffer layer on a p-type Si(100) substrate to investigate the possibility of GaN epitaxial growth on $CoSi_2/Si(100)$ substrates. We deposited 500 nm-GaN on the cobalt silicide buffer layer at low temperature with a PA-MBE (plasma assisted-molecular beam epitaxy) after the $CoSi_2/Si$ substrates were cleaned by HF solution. An optical microscopy, AFM, TEM, and HR-XRD (high resolution X-ray diffractometer) were employed to determine the GaN epitaxy. For the GaN samples without HF cleaning, they showed no GaN epitaxial growth. For the GaN samples with HF cleaning, they showed $4\;{\mu}m$-thick GaN epitaxial growth due to surface etching of the silicide layers. Through XRD $\omega$-scan of GaN <0002> direction, we confirmed the cyrstallinity of GaN epitaxy is $2.7^{\circ}$ which is comparable with that of sapphire substrate. Our result implied that $CoSi_2/Si(100)$ substrate would be a good buffer and substrate for GaN epitaxial growth.

• Korean Chemical Engineering Research
• /
• v.53 no.6
• /
• pp.709-716
• /
• 2015

In this study, structural developments of polypropylene / ionomer / clay ternary composites were investigated depending on the dispersion and localization of clay. The changes in physical properties were observed adding organoclays 1~10wt% to 90% polypropylene and 10% ionomer blends. The organoclays were localized inside of the dispersed phase under the composition of 3wt%, however, over that composition, clay particles formed stiff network structure in the dispersed phase and additional clays were localized at the interface between two phases. According to the developments of microstructure, the interaction of ternary composites changed from polypropylene-ionomer to polypropylene-ionomer and ionomer-clay which affected rheological properties. The storage modulus (G') of the composites was similar to the blends when clays were localized inside of dispersed phase but increased when clays were localized at interface. Also, the fractured morphology of the composites showed phase boundary and growing radius of dispersed phase depending on addition of fillers when clays were found inside. However, when fillers found at the interface between blends, the radius of the dispersed phase decreased and compatibilized morphology were observed. The interfacial interaction of the ternary composite was quantified depending on the structural development of dispersed phase and localization of clay particles by the rheological properties. The interaction of composites at solid state which was measured through peel adhesion strength increased by growth of interfacial interaction of each component. Furthermore, the crystallinity of the composites was decreased when the clay particles were localized at the interface.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.43 no.1 s.343
• /
• pp.7-12
• /
• 2006

In this study, we developed irreversible and stable micro-size ferromagnetic structures utilizing hydrogenation and electron-beam lithography processes. The compositionally modulated (CM) Fe-Zr thin films that had average compositions $Fe_XZr_{100-x}$ with $x=65-85\%$ modulation periods of similar to 1 nm, and total thicknesses of similar to 100 m were prepared. The magnetic properties of CM Fe-Zr thin films were measured using a SQUID magnetometer, VSM and B-H loop tracer. After hydrogenation, the CM films exhibited larger magnetic moment increases than similar homogeneous alloy films for all compositions and かey showed largest increase in $Fe_{80}Zr_{20}$ composition. After aging in air at $300^{\circ}K$ the hydrogenated $Fe_{80}Zr_{20}$ CM films showed much larger magnetic moment increases, indicating that they relax to a stable, irreversible, soft magnetic state. The selective hydrogenation through electron-beam lithographed windows were performed after the circle shaped windows were prepared on $Fe_{80}Zr_{20}$ CM films by electron beam lithography. The hydrogenation through electron-beam resist and W lithographic techniques give a $49\%$ magnetic moment increase. This method can be applied to nano scale structures.

• Journal of the Korean Academy of Esthetic Dentistry
• /
• v.25 no.2
• /
• pp.98-108
• /
• 2016

In recent days, perhaps the biggest driver in new material development is the desire to improve restorations esthetics compared to the traditional metal substructure based ceramics or all-ceramic restorations. Each material type performs differently regarding strength, toughness, effectiveness of machining and the final preparation of the material prior to placement. For example, glass ceramics are typically weaker materials which limits its use to single-unit restorations. On the other hand, zirconia has a high fracture toughness which enables multi-unit restorations. This material requires a long time sintering procedure which excludes its use for fast chair side production. Hybrid ceramic material developed for CAD/CAM system is contained improved nano ceramic elements. This new material, called a Resin Nano Hybrid Ceramic is unique in durability of function and aesthetic base compositions. The new nano-hybrid ceramic material is not a composite resin. It is also not a pure ceramic. The material is a mixture of both and consists of nano-ceramic fillers. Like a composite, the material is not brittle and is fracture resistant. Like a glass ceramic, the material has excellent polish retention for lasting esthetics. The material is easily machined by chair side or in a dental lab side, could be an useful restorative option.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
• /
• v.20 no.3
• /
• pp.77-84
• /
• 2014

Biodegradable nanocomposites were fabricated with poly (lactic acid) (PLA) and Nanomer$^{(R)}$ I.44P using ultrasonication (US). Processing conditions were optimized to obtain the maximum tensile properties of the nanocomposites. Poly (ethylene glycol) (PEG) was used as a plasticizer to avoid the brittleness of nanocompsoties. In order to disperse nanoclay into the PLA matrix, PEG and Nanomer$^{(R)}$ I.44P were firstly mixed and dispersed in the chloroform and followed by ultrasonication for 1 min With 10% PEG 400, tensile stress and Young's modulus of the nanocomposites decreased from 53.5 MPa and 2225 MPa to 37.0 MPa and 1757 MPa, respectively, while the elongation was increased from 4% to 21%. Tensile stress, Young's modulus, and elongation of nanocomposites were also increased with nanoclay concentration up to 2% (w/w) and were decreased with further increase in the nanoclay concentration. Transmittance of nanocomposites were significantly decreased from 62.5% for pure PLA film to 7.8% for 5% nanoclay containing nanocomposites. Water vapor permeability of the nanocomposites was also significantly decreased with nanoclay concentration and the minimum WVP of $3.5{\times}10^{-11}g{\cdot}m/m^2{\cdot}s{\cdot}Pa$ was obtained with 5% (w/w) nanoclay concentration. The PLA/Nanomer$^{(R)}$ I.44P nanocomposites showed a great potential as a environmental friendly food packaging material.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
• /
• v.25 no.3
• /
• pp.69-77
• /
• 2019

Agar-based nanocomposite films were prepared by incorporation of zinc oxide nanoparticles (ZnONP) and grapefruit seed extract (GSE). The composite films were characterized using FT-IR, UV-visible spectroscopy and thermalgravimetric analysis (TGA). The composite films showed light absorption peaks at 220 and 380 nm, characteristic for GSE and ZnONP, respectively. The UV-light transmittance of the agar film was markedly reduced from 54.4 ± 1.3% to 5.8 ± 2.5% with little sacrifice of transparency when 3 wt% ZnONP and 5 wt% GSE were added. The mechanical and water vapor barrier properties increased slightly though they were not significant statistically by the addition of ZnONP and GSE. The nanocomposite films showed stronger antibacterial activity against L. monocytogenes than E. coli O157: H7 and the antibacterial activity was affected by bacterial types as well as concentrations of ZnONP and GSE. The nano-composite film incorporated with 3 wt% of ZnONP and 5 wt% of GSE exhibited strong antibacterial activity against Listeria monocytogenes and E. coli O157: H7. The results indicate that 3 wt% of ZnONP and 5 wt% of GSE are the optimal concentrations for producing functional agar/ZnONP/GSE composite films.

• Research in Plant Disease
• /
• v.15 no.2
• /
• pp.130-133
• /
• 2009

We have conducted in vitro experiments with nano-silver liquid for their effect against various plant pathogenic bacteria. Different types of nano-silver liquid WA-CV-WA13B, WA-AT-WB13R and WA-PR-WB13R were used. These are classified based on different manufacturing processes. The tested bacteria were provided by KACC. We experimented ten bacterial isolates in Clavibacter, Erwinia, Pseudomonas, Ralstonia, and Xanthomonas genera. In order to determine the level of concentrations of control effects, different concentrations (10, 25, 50, and 100 ppm) of each different nano-silver liquid were added in the culture media. As a result, WA-CV-WA13B showed high inhibition effect against C-1 at 10 ppm, and showed minor inhibition effects against P-6, X-1, and X-2. WA-AT-WB13R showed bactericidal effect against P-6 at 10 ppm. At 10 ppm, WA-AT-WB13R showed relatively high inhibition effects against C-1, X-1, and X-2. WA-PR-WB13R showed bactericidal effects against P-5, P-6 and X-2 at 10 ppm or higher concentrations. All the tested three nano-silver liquid showed bactericidal effects against all the tested plant pathogenic bacteria at concentrations of 25 ppm or higher. These results indicated the possible use of nano-silver liquid for the control of plant pathogenic bacteria.

• Journal of the Korean Society of Radiology
• /
• v.10 no.7
• /
• pp.483-487
• /
• 2016

The purpose of this study is to investigate whether gold nanoparticles had radiosensitization when combined with gamma and x ray beam. Cytotoxicity was mearsured with comparing survival fraction after incubated time 6,12,18 and 24 hours. Clonogenic assay was employed to assess survival fraction of cells with and without gold nanoparticles treatment following gamma ray irradiation. The most of gold nanoparticles were distributed in the cytoplasm. And the toxicity of gold nanoparticles used this study were found to be non-cytotoxic. And we also observed enhancement by about 40% in RBE value for gamma ray irradiation of cells treated with gold nanoparticles. Dose reduction of about half for gamma ray irradiation is demonstrated for gold nanoparticles treated cells as compared to untreated cells. In cells with exposed to gamma ray, DNA damage was increased when compared to only radiation exposed cells. The study revealed a significant reduction in radiation dose for killing the cells with internalized gold nanoparticles as compared to the cells without gold nanoparticles. The gold nanoparticles treatment resulted in enhancement of radiation effect as evident from increase in relative biological effectiveness values for photon irradiated cells.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2002.11a
• /
• pp.63-63
• /
• 2002

현재 기계적 합금화법에서는 주로 합금을 구성하는 성분원소 분말을 불활성분위기에서 볼밀처리 함으로써 함금화를 시키거나 모합금에 산화물을 분산시켜 복합화시키는 공정을 통하여 각종 화합물, 비정질상 및 과포화고용체등의 준안정상의 합성 뿐만이 아니라 초미세조직의 생성에 관한 폭 넓은 분야의 연구가 행하여지고 있다. 한편 MA에서는 볼멀처리중 기계적 에너지의 투여에 의하여 실제 반응온도보다 낮은 온도에서 발생하는 특이한 화학반응 즉 Mechanochemical 반응을 일으키 기도 한다. 본 연구에서는 헤마타이트($Fe_20_3$)와 금속윈소인 Ti의 MA처리에 의하여 고상환원반응 을 유기시켜 $Fe-TiO_2$계 nanocomposite 분말재료를 제조하고자 한다. 특히 MA 공정에 있어서 자기 물성의 변화와 X선 회절을 통하여 고상환원반응에 의한 복합분말의 생성과정을 조사하였다. 출발원료는 $Fe_20_3$(고순도화학제,99.9%, 평균입경 0.1$\mu\textrm{m}$)와 금속원소인 Ti(99.9%, 명균업경 150$\mu\textrm{m}$)을 몰비 2:3의 조성이 되도록 하여 MA를 실시하였다. 볼멀은 고에너지 유성형 볼밀장치(독일 제, Fritsch P-5)를 이용하였으며 진공치환형 용기에 원료분말을 장입하여 2회정도 진공배기한 후 아르곤 가스를 충전하여 볼밀을 행하였다. 얻어진 분말시료에 대하여 x-선 회절장치, 전자현미경 (SEM) 및 진동시료형자력계(VSM)를 통하여 결정구조, 미셰조직 빛 자기특성을 조사하였다. $Fe_2O_3-Ti$ 혼합분말의 MA처리 에 의하여 초기단계부터 환원반응과 함께 $Fe_3TIO_{lO}$ 중간상이 관찰 되었으나 30hrs의 MA처리 후 Fe와 산화물 $TiO_2$로 모두 환원되어 $Fe-TiO_2$계 나노복합분말이 얻어짐을 알 수 있었다. 이 때 X션 회절피크의 line broadening으로부터 복합분말의 Fe 명균 결정립 크기는 24nm로 초미세 결정럽의 분말합금이었다. 포화자화값은 볼밀처리에 따라 점점 증가하여 MA 30시간에는 20.3emu/g로 포화됨을 알 수 있었다. 또한 보자력 Hc는 MA초기단계에 350e로 매우 낮으나 30시간 후에는 Hc값이 2600e로 매우 큰 값을 나타내었다. 이것은 환원반응결과 초기에 생성된 Fe의 결정립이 비교적 크고 결정결함이 적으나 볼밀처리를 30시간까지 행하면 Fe 결정렵의 미세화 빛 strain 증가로 magnetic hardening이 일어나기 때문인 것으로 사료된다.