Ilsu Rhee

Carbon-coated iron oxide nanoparticles as contrast agents in magnetic resonance imaging

Coprecipitated ferrite nanoparticles were coated with carbon using a hydrothermal method. From transmission electron microscope pictures, we could see that the coated iron oxide nanoparticles were spherical in shape with an average diameter of 90 nm. The strong bonding of carbon on the nanoparticle surfaces was checked by noting the C = O and C = C vibrations in Fourier transform infrared spectra. The spin-lattice relaxation process [T1] and spin-spin relaxation process [T2] relaxivities of hydrogen protons in the aqueous solution of coated nanoparticles were determined to be 1.139 (mM·s)-1 and 1.115 (mM·s)-1, respectively. These results showed that the carbon-coated iron oxide nanoparticles are applicable as both T1 and T2 contrast agents in magnetic resonance imaging.PACS: 81.05.y; 76.60.Es; 61.46; 75.50.k; 87.61.

Angle dependence of magnetoresistance peaks in thin nickel films

The angle dependence of magnetoresistance (MR) peaks in thin nickel films was investigated by rotating the sample in two different ways. The phase mixing of the positive M and negative MR signals was observed 1) with the sample located in the same plane as the field and rotated through an axis perpendicular to the field and 2) with the sample located in a plane perpendicular to the field and then rotated. In the latter case, the field difference between the two MR peaks increased. This behavior is well explained by the concept of effective magnetic field.

In situ characterization of the field-emission behaviour of individual carbon nanotubes

The current–voltage (I–V) characteristics of carbon nanotubes (CNTs) during field emission were investigated by in situ imaging and field-emission (FE) measurement inside a field-emission scanning electron microscope (FE-SEM). A primary electron of the FE-SEM could induce and enhance a large stimulated electron emission from a CNT which might be due to the strong local field on the tip of the CNT in the presence of an applied voltage. FE of bent nanotubes (BNTs) can initially occur after they are fully straightened or it can start in the bent state (during geometrical straightening) as the applied field increases. The FE from a single CNT follows FN (Fowler–Nordheim) behaviour with a single linear slope in the FN plot. The FE from two nanotubes with a geometrical change during FE showed transition of the FN slope from the low voltage to the high voltage region, which could be due to interactions between two dynamic neighbouring BNTs.

Characteristics of Cu2ZnSnSe4 Film Formed by Using Co-sputtered Precursors and Selenization

A Cu2ZnSnSe4 (CZTSe) film was formed by the selenization of Cu(Zn, Sn) (CZT) alloy precursors. The CZT precursor was prepared by depositing zinc onto a layer of Cu-Sn co-sputtered on molybdenum-coated soda-lime glass. Selenium was evaporated on the CZT precursor. The CZTSe film was then annealed for a minute at various substrate temperatures ranging from 350°C to 650°C in steps of 50°C in a rapid thermal process using tungsten halogen lamps. The lattice parameters of the CZTSe annealed at temperatures over 500°C were found to be a = 5.709 Å and c = 11.351 Å. We also found that the energy gap of the CZTSe was 1.137 eV, which was independent of the annealing temperature.

The finite-size scaling in thin ferromagnetic nickel films

The Curie point of nickel films has been determined by measuring the resistivity as a function of temperature. From these data, we observe the thickness dependence of Curie point shift in these films; that is, the thinner the film is, the larger the shift is. By analyzing the data in the light of finite-size scaling theory, we determine the shift exponent /spl lambda/ to be 0.92/spl plusmn/0.04, not the theoretical value of 1.48. Such a deviation from the theoretical value has also been noted in other papers.

Effect of ZnO Layer Thickness on Efficiency of Cu(In,Ga)Se2 Thin-film Solar Cells

The effect of intrinsic ZnO(i-ZnO) layer thickness on the efficiency of Cu(In,Ga)Se2 (CIGS) thin film solar cells was investigated using ITO/ZnO/CdS/CIGS/Mo structures. CIGS thin films were deposited on Mo-coated soda-lime glass using co-evaporation. CdS buffer layers of about 50nm thickness were then grown by chemical bath deposition on the top of CIGS layer. Finally, the ZnO and ITO layers were deposited using rf-magnetron sputtering, resulting in solar cells with ITO/ZnO/CdS/CIGS/Mo structure. From the optical and electrical characteristics of the solar cells, we found a close relationship between the transmittance of the ZnO layer and the efficiency of the solar cells. Several characteristics improved for solar cells with a 50 nm thick ZnO layer relative to those with both 90 nm thick and no ZnO layer. Therefore, we conclude that the optimum ZnO thickness for CIGS-based solar cells is around 50 nm.

The Change of Magnetoresistance Peaks According to the Direction of Sample Relative to the Magnetic Field

The change of magnetoresistance (MR) peaks according to the direction of the film sample relative to the magnetic field has been investigated for various angle configurations of the sample relative to the field. When the sample is in the same plane as that of the magnetic flux, the MR peaks are found to change their shapes, as the sample is rotated through an axis perpendicular to the sample surface, and finally to show their minima at the rotation angle of 45°. However, if the sample is inclined relative to the field, the MR peaks show their minima at a rotation angle higher than 45°. This behavior can be explained by the mixing of the negative MR (NMR) and positive MR (PMR) signals in MR. Furthermore, we also observe the increase of the magnetic field difference between two MR peaks (FDMP) as a function of the rotation angle, , for the angle configuration of the sample perpendicular to the field. This increase in FDMP is fitted well as a function of 1/cos , which is well explained by the concept of the effective magnetic field.

Silica-coated gadolinium-doped lanthanum strontium manganite nanoparticles for self-controlled hyperthermia applications

Gadolinium-doped lanthanum strontium manganite (LSM) nanoparticles were synthesized by using a citrate-gel technique. The particles were then annealed at 850 oC to remove defects for a good crystallinity, followed by coating with silica for possible biomedical application to magnetic hyperthermia. The chemical composition was determined to be La0.54Sr0.27Gd0.19MnO3 using an inductively coupled plasma mass spectrometer. The nanoparticles were characterized by X-ray diffraction, transmission electron microscope, and Fourier transform infrared spectrometer to check the perovskite crystalline structure and to observe the particles size and coating status of silica on the surface of the particles. The Curie temperature of the particles was found to be about 280 K. The saturation temperature of the aqueous solution of the particles remained at the hyperthermia target temperature of 42 oC with increasing concentration of particles from 6 to 60 mg/mL in the dispersion. This saturation temperature for a highly con...

Highly stable silica-coated manganese ferrite nanoparticles as high-efficacy T2 contrast agents for magnetic resonance imaging

Highly stable silica-coated manganese ferrite nanoparticles were fabricated for application as magnetic resonance imagining (MRI) contrast agents. The manganese ferrite nanoparticles were synthesized using a hydrothermal technique and coated with silica. The particle size was investigated using transmission electron microscopy and was found to be 40–60 nm. The presence of the silica coating on the particle surface was confirmed by Fourier transform infrared spectroscopy. The crystalline structure was investigated by X-ray diffraction, and the particles were revealed to have an inverse spinel structure. Superparamagnetism was confirmed by the magnetic hysteresis curves obtained using a vibrating sample magnetometer. The efficiency of the MRI contrast agents was investigated by using aqueous solutions of the particles in a 4.7 T MRI scanner. The T1 and T2 relaxivities of the particles were 1.42 and 60.65 s-1 mM-1, respectively, in water. The ratio r2/r1 was 48.91, confirming that the silica-coated manganese...

Damage-free surface treatment of polyethersulfone films using magnetized plasma generated by low-frequency (60 Hz) power

ABSTRACT Surface treatments of polyethersulfone (PES) films were performed using the magnetized plasma generated by low-frequency (60Hz) power for applying them to the flexible substrates of solar cells and electronic displays. The contact angle between the water droplet and PES films was observed to change from 80° to 30° after the plasma treatment. This indicates that the surface of the PES films changed from hydrophobic to hydrophilic. The surface roughness of the films did not change after the plasma treatment, and this indicates that the magnetized plasma did not damage the surface of the films. The trapping of energetic particles by the magnetic field is thought to be responsible for this result. It is concluded that the plasma treatment by using the magnetized plasma is useful for the surface modification of the polymeric materials suitable for flexible substrates of solar cells and electronic displays.