• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1998.06a
• /
• pp.57-60
• /
• 1998

Lean zirconate titanate (PZT) is an attractive material for the memory device applications. We have investigated Pt and{{{{ { RuO}_{2 } }}}} as a botton electrode for a device application of PZT thin film. The bottom electrodes were prepared by using an RF magnetron sputtering method. The substrate temperature influenced the resistivity of Pt and {{{{ { RuO}_{2 } }}}} a s well as the film crystal structure. XRD examination shows that a preferred(111) orientations for the substrate temperature of 30$0^{\circ}C$. From the XRD and AFM results, we recommend the substrate temperature of 30$0^{\circ}C$ for the bottom electrode growth. We investigated and anneal temperature effect because Perovskite PZT structure is recommended for the memory device applications and the structural transformation is occurred only after and elevated heat treatment. As post anneal temperature was increased from RT to $700^{\circ}C$, the resistivity of Rt and {{{{ { RuO}_{2 } }}}} w as decreased. Surface morphology was observed by AFM as a function of post anneal temperature.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.45 no.7
• /
• pp.32-36
• /
• 2008

In this study, $In_2O_3-ZnO$ thin films are prepared on quartz substrates by the pulsed laser deposition and their optical and electrical properties are investigated as the function of substrate temperatures ($200{\sim}600^{\circ}C$) at the fixed oxygen pressure of 200 mTorr. The XRD measurement shows that polycrystalline $In_2O_3-ZnO$ thin films are formed. In the XRD measurement, the intensity of the (400) $In_2O_3$ peak at $35.5^{\circ}$ decreases and that of the (222) $In_2O_3$ peak at $30.6^{\circ}$ increases with the increase substrate temperature up to $500^{\circ}C$. From the result of AFM measurement, the morphology of $In_2O_3-ZnO$ thin films are observed as round-type grains. The lowest surface roughness (6.15 nm) is obtained for the $In_2O_3-ZnO$ thin film fabricated at $500^{\circ}C$. The optical transmittance of $In_2O_3-ZnO$ thin films are higher than 82% in the visible region. The maximum carrier concentration of $2.46{\times}10^{20}cm^{-3}$ and the minimum resistivity of $1.36{\times}10^{-3}{\Omega}cm$ are obtained also for the $In_2O_3-ZnO$ thin film fabricated at $500^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.233-233
• /
• 2012

위상절연체(Bi2Te3)와의 격자상수 불일치 비율이 서로 다른 Si (111)와 Ge (111) 기판을 선택하여 Bi3Te3 박막의 성장 조건을 찾고 이에 따른 특성 분석을 수행하였다. 시료 제작은 초고진공 분위기에서 MBE를 이용하였고, AFM, XRD와 XPS로 각각 구조적 변화, 결정 상태 및 화학적 상태를 분석하였다. 우선 Si 위에 형성된 Bi2Te3의 경우, 초기 박막이 형성된 후, 증착 시간이 증가함에 따라 섬(island)모양의 구조물들이 step edge 부분에 분포되는 모습을 AFM 이미지에서 확인하였다. 형성된 박막의 스텝 단차는 약 1 nm 또는 이 값의 정수 배였고, 이것은 Bi2Te3 unit cell의 quintuple layer (QL) 값과 일치하였다. 또한 측정된 XRD pattern으로 Bi2Te3가 hexagonal 구조의 c-축에 따라 결정성이 이루어졌음을 확인할 수 있었다. XPS 스펙트럼에서는 Bi 4f가 높은 에너지 방향으로 2.3 eV, Te 3d는 낮은 에너지 방향으로 약 0.7 eV 만큼 구속 에너지의 화학적 이동이 나타남을 알 수 있었다. 이러한 결과는 Si 위에 Bi2Te3 박막이 높은 결정성을 가지고 형성되었다는 것을 의미한다. 또한 Si (111) 기판보다 Bi2Te3 결정과 격자상수 불일치의 비율이 상대적으로 작은 Ge (111)을 기판으로 하여 Bi2Te3 박막을 성장시켜 두 표면에서의 박막 성장의 특성을 비교, 논의할 것이다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.598-598
• /
• 2013

The short lifetime of Proton Exchange Membrane Fuel Cell (PEMFC) is the one of the main problems to be solved for commercializing. Especially, the weak adhesion between metal nanoparticles and supports deteriorate the performances of nanocatalysts, therefore, it is considered to be a major failure mechanism. Using force-distance spectroscopy of atomic force microscopy (AFM), we characterized the adhesion between Pt nanoparticles and carbon supports that is crucially related to the durability for membrane fuel cell (MFC) electrode. In our study, force distance curves measured with Pt coated AFM cantilever, mimicking the behavior of corresponding nanoparticles on carbon supports, leads to the adhesion between metal nanoparticles and carbon supports. We found that theadhesion between Pt and HNO3-treated carbon is enhanced by a factor of 4, compared to Pt and bare carbon support, that is consistent with the macroscopic durability test of PEMFC. The higher adhesion between Pt and HNO3-treated carbon can be explained in light of the stronger chemical interaction by C/O functional groups.

• KSTLE International Journal
• /
• v.5 no.1
• /
• pp.1-6
• /
• 2004

Nano-scale studies on adhesion and friction were conducted in Si-wafer (100) using Atomic Force Microscopy (AFM). Glass (Borosilicate) balls of radii 0.32$\mu\textrm{m}$, 1.25$\mu\textrm{m}$, and 2.5$\mu\textrm{m}$, mounted on cantilever (Contact Mode type NPS) were used as tips. Adhesion and friction between Si-wafer and glass tips were measured at ambient temperature (24${\pm}$1$^{\circ}C$) and humidity (45${\pm}$5%). Friction was measured as a function of applied normal load in the range of 0-160 nN. Results showed that, both adhesion and friction increased with the tip radii. Also, friction increased linearly as a function of applied normal load. The effect of tip size on adhesion and friction was explained as the influence of the capillary force exerted by meniscus and that of the contact area on these parameters respectively. The coefficient of friction was estimated in two different ways, as the slope from the plot of friction force against the applied normal load and as the ratio between the friction force and the applied normal load. Both these estimates showed that the coefficient of friction increased with the tip size. Further, the influence of the adhesion force on the coefficient of friction was also discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.12 no.6
• /
• pp.117-124
• /
• 2013

Recently, the cell adhesion phenomenon that occurs in or between cells and other substances has become an important field of research in biology and biomedical engineering. Among the research, the foundational studies primarily experiment using biomedical materials (e.g. Glass Beads) attached to an AFM cantilever. For cell adhesion research, the mechanism where biomedical materials can be attached to the cantilever must be developed for this purpose; however, the mechanism remains an insufficient step. In this paper, a new stage where the Glass Bead can be attached to the cantilever is designed and fabricated;, the mm range movement in the stage is controlled using the stepping motor with a minimum displacement of $1{\mu}m$. The adhesive flow is also controlled using a PZT actuator. In addition, through the air suction, the cantilever holder can be fixed to the stage. The new stage including the bond inflows mechanism is evaluated and analyzed using theory and experiments.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.55-55
• /
• 2011

질소 등을 GST225 상변화재료에 첨가시켜 비저항을 증가시킴으로서 PCRAM의 동작 전류를 감소시킨 연구가 선행된 바 있다. 본 연구에서는 GST225와 달리 고속 동작 특성을 갖는 것으로 널리 알려진 Ge-doped SbTe (GeST) 상변화 재료에 Carbon을 첨가하여 박막 특성을 연구하여 동작 전류 감소의 가능성을 타진하였다. 실험을 위한 박막 제작을 위해 2 inch size의 GeST 및 C doped GeST (C-GeST) single target을 이용하여 RF magnetron co-sputtering 하였다. 박막은 carbon이 첨가되지 않은 GeST와 carbon 첨가량이 늘어나는 순서로 C-GeST 1, C-GeST 2, C-GeST 3로 구성된다. 이 때 제작한 박막의 composition analysis를 위해 XRF/RBS/AES가 사용되었고 제작된 박막의 기본적인 특성평가를 위해 resistivity(${\rho}$)와 crystallzation temp.(Cx), surface morphology(AFM), x-ray diffraction pattern(XRD)를 측정하였다. 실험결과 GeST, C-GeST 1, C-GeST 2, C-GeST 3 박막의 Cx는 각각 209, 225, 233, $245^{\circ}C$로 측정되어 carbon 첨가량이 증가됨에 따라 결정화 온도가 증가되는 것을 알 수 있었다. 또한 ${\rho}$도 마찬가지로 annealing 온도를 약 $320^{\circ}C$로 할 경우 ${\rho}$(as-dep)와 ${\rho}$(crystalline) 모두 0.03 / $2.61*10^{-6}$, 0.08 / $7.93*10^{-6}$, 0.09 / $11.99*10^{-6}$, 0.13 / $13.49*10^{-6}{\Omega}{\cdot}m$로 증가하였다. 증가된 ${\rho}$의 원인이 박막의 grain size의 감소라고 단언 할 수는 없으나 AFM 측정결과 grain이라고 추측되는 박막 feature들의 size가 점차 감소하는 것을 확인하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.132-132
• /
• 2008

Silicon carbide (SiC) is an attractive material for high-power, high-temperature, and high-frequency applications. So far, atomic force microscopy (AFM) has been extensively used to study the surface charges, dielectric constants and electrical potential distribution as well as topography in silicon-based device structures, whereas it has rarely been applied to SiC-based structures. In this work, the surface potential and topography distributions SiC with different doping levels were measured at a nanometer-scale resolution using a scanning kelvin probe force microscopy (SKPM) with a non-contact mode AFM. The measured results were calibrated using a Pt-coated tip and a metal defined electrical contacts of Au onto SiC. It is assumed that the atomically resolved surface potential difference does not originate from the intrinsic work function of the materials but reflects the local electron density on the surface. It was found that the work function of the Au deposited on SiC surface was higher than that of original SiC surface. The dependence of the surface potential on the doping levels in SiC, as well as the variation of surface potential with respect to the schottky barrier height has been investigated. The results confirm the concept of the work function and the barrier heights of metal/SiC structures.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.05a
• /
• pp.289-290
• /
• 2006

In general, atomic force microscope (AFM) used for metrological purpose has measuring range less than a few hundred micrometers. We design and fabricate an AFM with long measuring range of $200mm{\times}200mm$ in X and Y axes. The whole stage system is composed of surface plate, global stage, microstage. By combining global stage and microstage, the fine and long movement can be provided. We measure the position of the stage and angular motions of the stage by laser interferometer. A piezoresistive type cantilever is used for compact and long term stability and a flexure structure with PZT and capacitive sensor is used for Z axis feedback control. Since the system is composed of various actuators and sensors, a real time control program is required for the implementation of AFM. Therefore, in this work, we designed a multi-axis control program using a FPGA module, which has various functions such as interferometer signal converting, PID control and data acquisition with triggering. The control program achieves a loop rate more than 500 kHz and will be applied for the measurement of grating pitch and step height.

• Applied Chemistry for Engineering
• /
• v.29 no.3
• /
• pp.318-324
• /
• 2018

In this study, PAN (polyacrylonitrile) based activated carbon fibers were prepared by water vapor activation method which is a physical activation method. Activation was performed with temperature and time as parameters. When the activation temperature reached 700, 750 and $800^{\circ}C$, the activation was carried out under the condition of a water vapor flow rate of 200 ml/min. In order to analyze the pore structure of activated carbon fibers, the specific surface area ($S_{BET}$) was measured by the adsorption/desorption isotherm of nitrogen gas and AFM analysis was performed for the surface analysis. Tensile tests were also conducted to investigate the effect of the pore structure on mechanical properties of fibers. As a result, the $S_{BET}$ of fibers after the activation showed a value of $448{\sim}902m^2/g$, the tensile strength decreased 58.16~84.92% and the tensile modulus decreased to 69.81~83.89%.