Fabrication and characterization of DNA-templated conductive gold nanoparticle chains

Kim, Hyung Jin,Roh, Yonghan,Kim, Seong Kyu,Hong, Byungyou American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7

<P>We present a fabrication of conductive nanowires made of gold nanoparticle (AuNP) chains based on lambda-DNA molecules immobilized on a surface of (3-aminopropyl)triethoxysilane-coated Si wafer as the template. A tilting technique was used to align and stretch the lambda-DNAs on the surface. Aniline-capped AuNPs (AN-AuNPs) were electrostatically assembled along the immobilized DNAs by careful control of the AN-AuNPs treatment time and the DNA concentration. AuNPs are attached on DNA with a reduction in Au surface potential as the treatment time increases. Also, the interparticle spacing is dependent on the treatment time and the DNA concentration. AuNP chains with a complete contact between particles were obtained when the treatment time and the DNA concentration were optimized. For electrical conductivity measurements, an isolated AuNP chain was fixed between two gold electrodes. The AuNP chain based on DNA showed an Ohmic behavior at room temperature with the conductivity of two orders of magnitude lower than the bulk value. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3091281]</P>

Numerical analysis on power loss mechanism of Fe55Al18O27 thin films for conduction noise through microstrip line

Ryu, Gi-Bong,Kim, Sung-Soo American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7

<P>With a simulation model of microstrip line attached by Fe55Al18O27 thin film of high magnetic loss, S parameters and power absorption has been analyzed by finite element method in the frequency range of available material parameters (0.1-1.5 GHz). It is demonstrated that the S parameters and power absorption are dominantly controlled by the electrical properties of the thin film. Although the film has a large value of magnetic loss resulting from ferromagnetic resonance, it is predicted that the power dissipation by magnetic loss is negligibly small. Simulation under assumption of high electrical resistivity shows that both S-11 and S-21 values approach to the value of original microstrip line. Another simulation of sheet resistance effect by film thickness control shows that higher value of power absorption is predicted in the films of small thickness mainly due to lower reflection loss. For the conductive and magnetic Fe55Al18O27 thin film, it is concluded that the dominant power loss mechanism is eddy current loss for magnetic field or Ohmic loss for electric field around the strip conductor in the frequency range investigated. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068014]</P>

Efficient multiphase green phosphor based on strontium thiogallate

Nazarov, Mihail,Noh, Do Young,Byeon, Clare Chisu,Kim, Hyojung American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7

<P>Efficient multiphase green phosphors based on strontium thiogallate were synthesized by solid state reaction at 900-1000 degrees C with carbon as a reduction atmosphere. The detailed x-ray diffraction analysis, energy dispersive spectroscopy, Raman spectroscopy, and photoluminescence were carried out in order to enlarge the understanding of the radiative processes in multiphase green phosphors based on strontium thiogallate. The crystal field splitting, Stokes shift, redshift, and centroidal shift were estimated, and the results are in good agreement with mathematical calculations. Our study confirms that the proposed multiphase green phosphor based on strontium thiogallate is a good candidate for solid state lighting and display devices with higher intensity and better chromaticity coordinates in comparison with the known commercial phosphors. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3093932]</P>

Enhanced photoluminescence of silicon oxide nanowires brought by prolonged thermal treatment during growth

Kim, Jung H.,An, Hyeun H.,Yoon, Chong S. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7

<P>Silicon oxide nanowires synthesized during carbonization of polyimide thin film on a silicon substrate exhibited marked enhancement in photoluminescence (PL) at 420 nm by prolonging the growth period. Maximum intensity was recorded when the nanowire diameter coarsened from 70 to 165 nm by extending the growth period from 1 to 3 h. The enhancement was attributed to the increase in concentration of neutral oxygen vacancies on the surface of the nanowires. It was also demonstrated that the PL peak can be shifted to 600 nm while maintaining the enhanced intensity by postannealing the nanowires in a reducing atmosphere. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3091261]</P>

Influence of interface state in Fe/MgO/Fe magnetic tunnel junction system: C modified interfaces-a first principle study

Wang, T. X.,Li, Y.,Lee, K. J.,Cho, J. U.,Kim, D. K.,Noh, S. J.,Kim, Y. K. American Institute of Physics 2011 JOURNAL OF APPLIED PHYSICS - Vol.109 No.8

<P>The Fe/MgO/Fe magnetic tunnel junction with C modified interfaces has been studied based on the first principle density function theory method under a finite bias voltage for thin (five layers) and thick (ten layers) MgO barriers. Positive and negative tunneling magnetic resistance (TMR) ratios are obtained as a function of the interface structure. We found that the tunneling conductance is highly nonlinear for asymmetric systems with C at one side of the barrier, and even a sign reversal of the TMR as a function of the bias was found to be in agreement with experiments. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3575337]</P>

Microstructural properties and dislocation evolution on a GaN grown on patterned sapphire substrate: A transmission electron microscopy study

Kim, Y. H.,Ruh, H.,Noh, Y. K.,Kim, M. D.,Oh, J. E. American Institute of Physics 2010 JOURNAL OF APPLIED PHYSICS - Vol.107 No.6

<P>The microstructural properties of a GaN layer grown on a patterned sapphire substrate (PSS) were studied in detail using transmission electron microscope techniques to determine dislocation and growth behaviors. Regular and uniform recrystallized GaN islands were observed on the protruding pattern. On a flat sapphire surface, the crystallographic orientation relationship of <(1) over bar2 (1) over bar0 >(GaN) (on) (FS)//< 1 (1) over bar 00 >(sapphire) and {1<(1over bar>01}(GaN) (on) (FS)//{1 (2) over bar 13}(sapphire) existed between the GaN and the substrate. On the other hand, the orientation relationship of <(1) over bar2 (1) over bar0 >(GaN) (layer)//<(1) over bar2 (1) over bar0 >(GaN) (island) (on IS)//< 1 (1) over bar 00 >(sapphire) and {1 (1) over bar 01}(GaN) (layer)//{0002}(GaN) (island) (on) (IS)//{1 (2) over bar 13}(sapphire) was confirmed among the GaN layer, the recrystallized GaN islands on an inclined sapphire surface and the PSS. The flat surface among the protruding patterns began to fill rapidly with GaN. Then, the GaN gradually overgrew the protruding pattern and coalesced near the summit as the growth time increased. The generation of threading dislocations was observed in the vicinity of the coalescence points near the top of the protruding patterns. (C) 2010 American Institute of Physics.[doi:10.1063/1.3327004]</P>

Novel Ni-Mn-Co ferrite for gigahertz chip devices

Lee, J. J.,Bae, S.,Hong, Y. K.,Jalli, J.,Abo, G. S.,Seong, W. M.,Park, S. H.,Choi, C. J.,Lee, J. G. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7

<P>The effect of Mn and/or Co doping in Ni-Mn-Co ferrite on the static, dynamic magnetic properties, and thermal magnetic stability were investigated for high frequency microwave applications up to the gigahertz range. Saturation magnetization and coercivity increased with increased substitution of Mn and Co, respectively. Both Mn and Co substituted Ni-Mn-Co ferrite exhibited higher thermal stability factor rather than Ni-Mn and Ni-Co ferrites. The highest thermal stability factor was achieved to be -12.0 X 10(-4) degrees C/ppm for Ni0.93Mn0.05Co0.02Fe2O4. The second highest, -11.88 X 10(-4) degrees C/ppm, was measured for Ni0.7Mn0.05Co0.02Fe2.23O4. Permeability (mu), permittivity (epsilon), and cutoff frequency of Ni0.93Mn0.05Co0.02Fe2O4 and Ni0.7Mn0.05Co0.02Fe2.23O4 showed 7.41, 4.56, 1084 MHz, and 3.87, 4.55, 1436 MHz, respectively. Furthermore, the mu/epsilon ratio of Ni0.93Mn0.05Co0.02Fe2O4 was found to be 1.63 (mu/epsilon = 7.41/4.56). (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068023]</P>

The change in permeability spectra due to ion irradiation in the Co-based amorphous ribbon

Park, D. G.,Park, C. Y.,Song, H.,Kim, C. G.,Cheong, Y. M. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7

<P>The Ar ion has been irradiated by an ion implanter with energy of 50, 70, and 100 keV and an ion dosage was set to 1.0 x 10(17) ion/cm(2) at a beam flux of 3.7 mu A/cm(2). The ion irradiation decreased the initial permeability and increased the relaxation frequency, and the behavior of permeability spectra due to ion irradiation was explained with damped harmonic model of domain wall on the general basis of magnetization mechanism. The ion irradiation gives rise to a significant change on the restoring force of domain wall but minor effect on the spin rotation. The enhancement in the permeability of the amorphous ribbon upon ion irradiation leads to a parallel improvement of giant magneto impedance response of the material, which is of practical use for sensing applications. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3086714]</P>

Dependence of the switching current density on the junction sizes in spin transfer torque

You, Chun-Yeol,Jung, Myung-Hwa American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.7

<P>We investigate the dependence of switching current density on the junction sizes in the in-plane spin transfer torque nanopillar structures by using micromagnetic simulations. While the macrospin model predicts weak dependence of switching current density on the junction sizes, we find that the switching current density is a sensitive function of the junction sizes. It can be explained with the complicated spin configurations and dynamics during the switching process. The detail spin configurations and dynamics are determined by spin wave excitation with the finite wave vector, which is related with the exchange coupling energy and junction shape. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792728]</P>

Quantitative investigation of magnetic domains with in-plane and out-of-plane easy axes in GaMnAs films by Hall effect

Lee, Sangyeop,Lee, Hakjoon,Yoo, Taehee,Lee, Sanghoon,Liu, X.,Furdyna, J. K. American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.17

<P>Magnetic anisotropy of ferromagnetic semiconductor GaMnAs film with a low Mn concentration grown on a (001) GaAs substrate was investigated by Hall effect measurements. The presence of domains with in-plane and out-of-plane easy axes was identified in the film by analyzing hysteresis loops observed via the Hall resistance measured in various geometries. Quantitative analysis of the planar Hall resistance showed that the fraction of the sample with magnetic domains having a dominant out-of-plane easy axis was about 6 times larger than the fraction corresponding to domains with easy axis in the sample plane. (C) 2013 American Institute of Physics.</P>