Ahram Kim

Seoul National University, Sŏul, Seoul, South Korea

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Publications (5)6.18 Total impact

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    ABSTRACT: Using a scanning microwave microscope (SMM), we have investigated the phase separation in a 30% La <sub>5/8</sub> Sr <sub>3/8</sub> Mn O <sub>3</sub> ( LSMO )+70% Lu Mn O <sub>3</sub> ( LMO ) polycrystalline pressed powder sample, in which the LSMO phase is a perovskite ferromagnetic metal while the LMO phase is a hexagonal ferroelectric insulator. When the electrical properties of the sample were imaged using our SMM, the sample showed a significant contrast between the metallic LSMO and the insulating LMO grains, indicating a clear phase separation between the two phases. The metallic phase identified by the SMM clearly showed a ferromagnetic signal when investigated by a magnetic force microscope (MFM), providing solid evidence that the metallic phase is indeed the ferromagnetic LSMO. In addition, we have noticed a slight difference between the images generated by SMM and MFM, and we believe that this is due to the different depth scales probed by the two microscopy techniques.
    Applied Physics Letters 02/2005; · 3.52 Impact Factor
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    ABSTRACT: In this Note we provide the basic principle of obtaining topological data with a scanning microwave microscope. When samples are sufficiently “metallic,” the resonant frequencies as a function of the gap between the sample surface and the tip all fall on a universal curve despite differences in sheet resistance. Based on this result, we have built a surface-following feedback circuit and succeeded in measuring the topological images of many metallic surfaces. To date, the best topological resolution was 50 nm. However, we believe it can be further improved by reducing the background vibration and using electronics with lower noise. © 2003 American Institute of Physics.
    Review of Scientific Instruments 05/2003; 74(6):3164-3166. · 1.60 Impact Factor
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    ABSTRACT: A scanning microwave microscope (SMM) is a microscope which uses microwave as a media. And it can measure the dielectric constant and the conductivity of dielectric samples simultaneously. By modifying the electronics, an SMM can be made to acquire the topological data of a sample surface while measuring the local conductivity. The scanned image of the surface of a coin verifies its operation. With measuring a reference sample, it will be shown that the vertical resolution of the microscope is certified as less than 0.05 μm by showing our image taken on our reference sample.
    03/2002;
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    ABSTRACT: We obtained the electrical images of biological specimens using SMM. SMM investigates local electrical properties of materials in high frequency region ( 1.5 GHz) by detecting the shift of the resonant frequency and the quality factor Q of the resonator. At first, we investigated the NaCl solutions of various concentrations from the de-ionized water to the saturated solution, and observed the drastic change of the resonant frequency and Q depending on the concentration. Since the water was the dominant source of the dielectric signals in biological samples, the change of the resonant frequency and Q of the resonator could be a good reference interpreting various biological samples. We will present various high-frequency electrical images of the biological samples of a plant epidermal cell, and a bone section tissue.
    03/2002;
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    ABSTRACT: We investigated the twin domains of LaAlO3 (001) substrate using a scanning microwave microscope (SMM). Since the SMM can image the local dielectric constant of a sample quantitatively, we can observe the difference of the dielectric constant in the twin domains. Especially the (110) domains were observed more clearly than (100) domains, we attribute this to the difference of the strain in the ferroelastic LaAlO3.
    Japanese Journal of Applied Physics 01/2001; 40:6510-6513. · 1.07 Impact Factor