• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.161-161
• /
• 2010

n-type 반도체 특성을 띄는 $SnO_2$ 나노선은 가스 센서, 투명 소자, 태양광 전지 등으로 널리 사용되고 있다. 본 연구에서는 화학기상증착법으로 성장한 $SnO_2$ 나노선으로 폴리이미드 (PMDA-ODA: PI) 박막을 게이트 절연막으로 이용한 전계효과트랜지스터를 플렉서블 기판에 제작하고 전기적 특성을 분석하였다. 전자 전달 특성 곡선으로부터 n-형의 반도체 특성을 확인하였으며, 대부분의 산화금속 나노선에서와 같이 매우 큰 전기적 히스테리시스가 관찰되었다. 산화금속계통 나노선 소자의 히스테리시스는 나노선 표면에 산소 및 물 분자가 흡착되어 생기는 전자 갇힘 현상이 가장 큰 원인으로 알려져 있는데, 이러한 히스테리시스를 조절하거나 없애는 것은 소자의 특성 향상에 있어 매우 중요하다. 한편 PI 절연막에는 느린 분극 현상을 만드는 OH 반응기가 존재하기 때문에 나노선과는 반대 방향의 히스테리시스를 보일 것으로 예상된다. 본 연구에서는 제작된 $SnO_2$ 나노선 FET에서 PI 게이트 절연막의 경화 정도에 따른 히스테리시스를 조사하였다. FT-IR 측정에 따르면, PI 필름에 존재하는 OH 반응기는 PI를 경화시킴에 따라 감소하였으며 전기적인 히스테리시스도 감소하였다. 따라서, 절연막을 경화시키지 않았을 때는 PI 내부에 다량의 OH 반응기가 존재하여, PI의 히스테리시스가 나노선 히스테리시스보다 더 크게 작용하여, 전체적으로는 PI의 특성인 반시계 (counterclockwise) 방향의 히스테리시스를 나타내었다. 한편, 절연막을 완전히 경화시키면, OH 반응기는 대부분 사라지고 나노선의 히스테리시스만 발현되어 소자는 시계방향의 히스테리시스를 보였다. 이러한 실험결과를 통해, PI 박막을 $250^{\circ}C$ 에서 약 7분간 경화시켰을 때 나노선과 절연막의 히스테리시스가 가장 이상적으로 상쇄되어 전체적으로 히스테리시스가 매우 작아진 것을 관찰할 수 있었다. 이는 향후 나노선 FET의 안정적인 응용에 매우 유용한 결과로 활용될 것으로 예측된다.

• Proceedings of the KIEE Conference
• /
• 2002.11a
• /
• pp.260-262
• /
• 2002

The determination of DNA hybridization can apply the molecular biology research. clinic diagnostics. bioengineering, environment monitoring, food science and other application area. So, The determination of hybridization is very important for the improvement of DNA detection system. In this study, we report the characterization of the DNA hybridization by the electricalchemical methods. The probe oligonucleotide was used to determine the amount of target oligonucleotide in solution using Methylen Blue(MB) as the electrochemical indicators. The cathodic peak currents($I_{peak}$) of MB were linearly related to the concentration of the target oligonucleotide sequence in the range $1[{\mu}M]{\sim}0.1[{\mu}M]$. The detection limit of this approach was 0.01[nM]. As a result, the match oligonucleotide(CR-1) was most stable state and the peak of redox current measured by DNA hybridization detection sensors by using electrochemical method seem to be similar to 1-mer terminal mismatch oligonucleotide(MR-3). The MR-2, MR-3, MR-22 and MR-33 have each mismatching sequence of central and terminal. With this set the role of point mutations was to be investigated. Terminal mismatch oligonucleotide (MR-3, 33) is shown more stable state than central mismatch oligonucleotide(MR-2, 22). And 1-mer mismatch oligonucleotide(MR-2 or 3) is shown more stable state than 2-mer mismatch oligonucleotide(MR-22 or 33).

• Journal of Sensor Science and Technology
• /
• v.4 no.4
• /
• pp.70-74
• /
• 1995

We have observed anisotropic anodisation process for porous silicon formation. The starting material was (100) silicon $n/n^{+}/n$ wafer structured by $n^{+}$-diffusion on n-type substrate and by subsequent n-epitaxial growth. After the top n-silicon epitaxial layer was etched to open the porous silicon layer(PSL) anodisation window, anodisation takes place only to $n^{+}$-buried layer. The process of porous silicon formation on (100) sample was anisotropic, which was evident from that the shapes of the reacted porous silicon layer was all squarelike regardless of the shapes of reaction windows. The experimental results show that the PSL anodisation process does not depend on chemical reaction but does on electrical conduction property, which is hole mobility depending on the crystal direction.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.239-239
• /
• 2011

최근에 감지막의 pH 감지특성을 평가하기 위해 electrolyte insulator semiconductor (EIS) 구조가 유용하게 이용되고 있다. EIS는 CMOS공정과 호환이 가능하고 구조가 간단하며 pH 변화에 반응속도가 빠르다는 장점을 가지고 있다. EIS 구조를 갖는 pH 센서의 동작 메커니즘은 pH 용액의 수소이온이 감지막의 표면에서 표면전위를 변화시키는 것에 기인한다. pH 감지막으로는 높은 유전율과 안정성이 뛰어난 high-k 물질이 많이 연구되고 있다. 그 중 high-k 물질인 ZrO2은 낮은 열전도도, 산성에서 알칼리성 영역까지의 넓은 화학안정성을 가지며 낮은 열 팽창성, 높은 유전상수 등 우수한 특성을 가지고 있다. 본 실험은 SiO2/ZrO2를 적층한 EIS 소자를 제작하여 열처리에 따른 전기적 특성과 pH 감지 특성을 평가해 보았다. EIS 적층막으로 사용된 SiO2는 실리콘과 high-k 감지막 사이의 계면상태를 양호하게 유지시키기 위한 완충막으로 성장되었다. 후속열처리는 rapid thermal annealing (RTA) 시스템을 이용하여 750$^{\circ}C$, 850$^{\circ}C$, 950$^{\circ}C$로 H2/N2 분위기에서 30초 동안 실시하였다. RTA 열처리 온도가 증가할수록 높은 pH 감지특성이 보였으며 hysteresis 현상과 drift 효과와 같은 non ideal 효과에 강한 immunity가 있는 것을 확인하였다. 결론적으로 SiO2/ZrO2 적층구조를 갖는 EIS는 RTA 950$^{\circ}C$ 열처리를 실시하였을 때 우수한 EIS pH 센서를 제작할 수 있을 것으로 기대된다.

• Journal of Sensor Science and Technology
• /
• v.31 no.4
• /
• pp.249-254
• /
• 2022

To achieve high-performance colloidal quantum dot light-emitting diodes (QD-LEDs), the use of a densely packed QD film is crucial to prevent the formation of leakage current pathways and increase in interface resistance. Spin coating is the most common method to deposit QDs; however, this method often produces pinholes that can act as short-circuit paths within devices. Since state-of-the-art QD-LEDs typically employ mono- or bi-layer QDs as an emissive layer because of their low conductivities, the use of a densely packed and pinhole-free QD film is essential. Herein, we introduce the Langmuir-Blodgett (LB) technique as a deposition method for the fabricate densely packed QD films in QD-LEDs. The LB technique successfully transfers a highly dense monolayer of QDs onto the substrate, and multilayer deposition is performed by repeating the transfer process. To validate the comparability of the LB technique with the standard QD-LED fabrication process, we fabricate and compare the performance of LB-based QD-LEDs to that of the spin-coating-based device. Owing to the non-destructiveness of the LB technique, the electroluminescence efficiency of the LB-based QD-LEDs is similar to that of the standard spin coating-based device. Thus, the LB technique is promising for use in optoelectronic applications.

• Applied Chemistry for Engineering
• /
• v.24 no.5
• /
• pp.551-557
• /
• 2013

In the present study, pristine carbon nanotube (p-CNT) and thiolated carbon naotube (t-CNT) electrodes were investigated to improve their detectabilities for cadmium (Cd) and lead (Pb). In addition, we evaluate which reaction mechanism is used when the electrolyte contains both Cd and Pb metals. Square wave stripping was employed for analyzing the sensitivity for the metals. A frequency of 30 Hz, a deposition potential of -1.2 V vs. Ag/AgCl and a deposition time of 300 s were used as optimal SWSV parameters. t-CNT electrodes show the better sensitivity for both Cd and Pb metals than that of p-CNT electrodes. In case of Cd, sensitivities of p-CNT and t-CNT electrodes were $3.1{\mu}A/{\mu}M$ and $4.6{\mu}A/{\mu}M$, respectively, while the sensitivities for Pb were $6.5{\mu}A/{\mu}M$ (p-CNT) and $9.9{\mu}A/{\mu}M$ (t-CNT), respectively. The better sensitivity of p-CNT electrodes is due to the enhancement in the reaction rate of metal ions that are facilitated by thiol groups attached on the surface of CNT. When sensitivity was measured for the detection of Cd and Pb metals present simultaneously in the electrolyte, Pb indicates better sensitivity than Cd irrespective of electrode types. It is ascribed to the low standard electrode potential of Pb, which then promotes the possibility of oxidation reaction of the Pb metal ions. In turn, the Pb metal ions are deposited on the electrode surface faster than that of Cd metal ions and cover the electrode surface during deposition step, and thus Pb metals that cover the large portion of the surface are more easily stripped than that of Cd metals during stripping step.

• Korean Chemical Engineering Research
• /
• v.48 no.2
• /
• pp.218-223
• /
• 2010

The zinc oxide thin film, which can be applied as the gas sensor of a semiconductor type, was grown on the silicon substrate by CFR(continuous flow reaction) method in this study. The growth property and the electrical property of the zinc oxide thin films synthesized by CFR method were also investigated. Zinc acetate solutions of 0.005~0.02 M were used as the precursor for the preparation of zinc oxide thin films. The size of ZnO particles consisted on the zinc oxide thin film increased not only with increasing concentration of precursor, but also the thickness of thin film increased. The growth rate of zinc oxide thin film by CFR method was proportionably depend on the concentration of precursor and the uniform ZnO thin film was prepared when zinc acetate of 0.01 M is used as the precursor. The charged currents on the zinc oxide thin films were obtained as its electrical property by I-V meter, and increased agree with increasing the thickness of zinc oxide thin film. Thus, it was concluded that the charged current on the zinc oxide thin film can be controlled with changing concentration of precursor solution in CFR method. The charged currents on the zinc oxide thin films also decreased when ZnO thin film is exposed under hydrogen sulfide of 500 ppmv at $300^{\circ}C$ for 5 min. From these results, it could be confirmed that the zinc oxide thin film prepared by CFR method can be used for the detection of sulfur compounds.

• Korean journal of food and cookery science
• /
• v.25 no.2
• /
• pp.252-259
• /
• 2009

Ergosterol is the significant component of the cell wall of fungi. Its presence is regarded as evidence of fungi contamination in grain and other foods. Many studies on ergosterol detection have been carried out using chemical methods, but those methods required complicated pre-treatments and long analysis times. In this study, an amperometric biosensor was developed for fast and precise ergosterol detection. The biosensor system used the electron transfer of hydrogen peroxide produced from the reaction of ergosterol with cholesterol oxidase. The biosensor system consisted of a peristaltic pump, a syringe loading sample injector, an enzyme reactor, a fabricated flow-through cell containing a working electrode, a reference electrode and a counter electrode, and a potentiostat/recorder. The working electrode was prepared by coating modified multi-wall carbon nanotube (MWNT) on glassy carbon electrode. The $MWNT-NH_2$ coated glassy carbon electrode linearly responded to hydrogen peroxide in the range of $1{\times}10^{-5}{\sim}8{\times}10^{-5}$ M with a detection limit of $10^{-7}$ M in the basic performance test. The currents produced from the ergosterol biosensor showed the linearity in a range from $1.0{\times}10^{-6}$ M to $1.0{\times}10^{-5}$ M ergosterol.

• Journal of the East Asian Society of Dietary Life
• /
• v.22 no.1
• /
• pp.88-94
• /
• 2012

Histamine is a kind of primary biogenic amine arising from the decarboxylation of the amino acid L-histidine. The toxicology of histamine and its occurrence and formation in foods are especially emphasized in fermented foods. In this study, the biosensor for detection of histamine with functionalized multi-walled carbon nanotubes (MWCNT) was developed. We also searched for an appropriate insoluble substrate to immobilize the enzyme. The developed biosensor showed a detection limit of $0.1{\mu}M$ hydrogen peroxide. The enzyme reactor was prepared with diamine oxidase immobilized on insoluble carriers including CNBr-activated sepharose 4B, calcium alginate, and controlled pore size glass beads. The coupling efficiency of CNBr-activated sepharose 4B, calcium alginate, and controlled pore size glass beads were 48.5%, 40.3%, and 51.0%, respectively. In addition, the response currents on histamine with each immobilized enzyme reactor prepared with CNBr-activated sepharose 4B, calcium alginate, and controlled pore size glass beads were 120 nA, 110 nA, and 140 nA at $100{\mu}M$ of histamine concentration, respectively. Therefore, it is suggested that controlled pore size glass beads are the best carriers for immobilizing diamine oxidase to detect histamine in this biosensor.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.615-615
• /
• 2013

탄소나노튜브(carbon nanotubes; CNT)는 강철보다 10~100배 견고할 뿐만 아니라 영률과 탄성률 은 각각 1.8 TPa, 1.3 TPa에 달하는 매우 우수한 기계적 강도를 지니고 있으며, 구리보다 좋은 전기 전도도와 다이아몬드의 2배에 이르는 열전도도를 지닌 물질이다. 이러한 탄소나노튜브의 우수한 특성을 이용하여 나노섬유, 고분자-탄소나노튜브의 고기능 복합체, 나노소자, 전계방출원(field emitter), 가스센서 등 다양한 분야로의 활용을 위한 연구가 진행되고 있다. 특히, 수백 ${\mu}m$ 이상의 길이로 수직 성장된 탄소나노튜브(VA-CNTs)의 합성은 길이 대 직경의 비(aspect ratio)가 비약적으로 증가하여 앞서 언급한 분야로의 활용이 더욱 유리하며, 그 중에서도 대량 생산, 나노섬유 및 나노복합체로서의 활용에 극히 유용하다. 최근에는 열 화학기상증착(thermal chemical vapor deposition; TCVD)법을 이용하여 탄소나노튜브의 구조를 제어하는 연구들이 많이 보고되고 있다. 열 화학기상증착을 이용한 수직 정렬된 탄소나노튜브의 합성에서 합성조건의 변화는 탄소나노튜브의 길이, 벽의 수, 직경, 결정성 등 구조에 큰 영향을 미친다. 탄소나노튜브는 이러한 구조에 따 라 물리적 특성이 달라지기 때문에 다양한 분야로의 응용을 위해서는 합성에 대한 근본적인 이해 가 절실히 요구된다. 본 연구에서는 열 화학기상증착법을 이용한 합성에서 성장압력의 변화에 따른 탄소나노튜브의 구조적 특성을 조사하였다. 성장압력의 변화는 탄소나노튜브의 밀도, 길이, 결정성에 큰 영향을 미치는 것을 주사전자현미경과 라만분광법을 이용하여 확인하였다. 이러한 결과 는 탄소나노튜브 박막(CNT forest)의 가장자리(edge)에 비정질 탄소(amorphous carbon)의 흡착으로 인한 나노튜브사이의 간격(intertube distance)이 좁아짐에 따른 가스공급 차단 효과로 설명이 가능 하다. 또한, 마이크로웨이브 플라즈마 화학기상증착법을 이용하여 탄소나노튜브를 합성하였다. 합성과정 중 산소(O2)를 주입 하였을 경우, 그렇지 않은 경우에 비하여 성장 속도가 증가하여 3시간 합성 시 2 mm가 넘는 수직 정렬된 탄소나노튜브를 합성 할 수 있었다. 이러한 결과는 과잉 공급 되어 탄소나노튜브로 합성되지 못하고 촉매금속의 표면과 탄소나노튜브의 벽에 비정질의 형태로 붙어있는 탄소 원자들을 추가 주입해 준 산소에 의하여 CO 또는 CO2 형태로 제거해 줌으로써 활성화된 촉매금속의 반응 시간을 향상 시켜주어 탄소공급이 원활하게 이루어졌기 때문이라 생각된다.