Electronic states of ultrathin Co layers on Cu

Lee, Hangil,Lee, Dohyun,Kim, W.,le Hung, N.,Kim, Hyojin,Hwang, Chanyong Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>We studied ultrathin Co overlayers on top of vicinal Cu(100) and Cu(111) surface using high resolution photoemission spectroscopy to clarify the phenomena of surface alloying at low coverage. The valence band spectrum of Co/Cu(100) clearly shows the change in its electronic structure. A peak at the binding energy of 0.3 eV represents the mixing of Co and Cu at the surface, as has been reported by STM. This state becomes more enhanced upon annealing. Mixing the Co overlayer with Cu atoms on top of Cu (111) surface is relatively small at room temperature. Instead, wetting along the step edge has been found for low coverage. Interesting state responsive to the electric field of the incident photon has been found and a possible origin has been discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Vortex dynamics in submicron exchange-biased disks

Moon, Jung Hwan,Kim, Woo Jin,Lee, Taek Dong,Lee, Kyung-Jin Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>Using micromagnetic simulation we have investigated the vortex dynamics in an exchange-biased permalloy nanodisk with 500 nm-radius and 10 nm-thickness. We found the exchange bias plays an important role in the vortex dynamics. The exchange bias results in the elliptical trajectory. The vortex dynamics in the exchange-biased nanodisk is strongly affected by the angle between the exchange bias field and the external field. We found that it is possible to selectively transform the vortex state into the single domain state with a pulsed magnetic field by controlling the magnitude and the angle of the external magnetic field. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Effects of growth temperature and oxygen pressure on the properties of heteroepitaxial ZnO thin films on sapphire (0001) substrates by pulsed laser deposition

Liu, Chunli,Chang, S. H.,Noh, T. W.,Song, J.-H.,Xie, J. Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>We report a systematic study on the effect of growth temperature and O<SUB>2</SUB> pressure on the structural, optical, and electrical properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates. The combination of high growth temperature and low O<SUB>2</SUB> pressure was found to improve the crystalline quality of initial heteroepitaxial ZnO films, which can be attributed to the enhanced surface migration of adatoms and thermal energy. The low-temperature photoluminescence spectra from ZnO films were dominated by donor-bound exciton emission with very weak deep level emission. The temperature dependent Hall measurement showed that the films are highly degenerated, mainly due to the high defect density near the interface region. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Study on defect states using deep level transient spectroscopy of ZnO grown by pulsed laser deposition

Kim, Jae-Hoon,Kim, Eun Kyu Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>The pulsed laser deposition (PLD) was used for fabrication of ZnO films on a sapphire substrate. We modulated the parameters, temperature and gas pressure, for the growth condition. After the growth, X-ray diffraction, photoluminescence (PL), and deep level transient spectroscopy (DLTS) measurements were performed. We had got PL spectra of high intensity from the ZnO film grown at low temperature. And the existence of the defect states was fewer, according to the result. But the crystalline quality was good for the film grown at high temperature. It seems to be that the relation between crystallization and defined electronic bandgap is weak. The DLTS measurements show some defects, but the signal is noisy. A Schottky contact by using Ti/Au and a high conductance seem to be the cause. We had simulated the DLTS spectra from assumed defects and matched to measurement results. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Low temperature growth of ZnO thin film by metalorganic chemical vapor deposition

Kim, Dong Chan,Kong, Bo Hyun,Cho, Hyung Koun,Lee, Jeong Yong,Park, Dong Jun Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>Polycrystalline ZnO thin films with a preferred orientation were successfully grown by metal organic chemical vapor deposition at temperatures ≤300 °C. By injecting additional Ar gas through a by-pass line, good quality ZnO films were grown at low temperature. The ZnO films grown at substrate temperatures <200 °C showed a porous microstructure whereas a dense undoped ZnO film showing a high conductivity and no Zn phases was grown at 210 °C. The ZnO film grown at low temperatures by MOCVD showed improved emission properties compared with the films grown by sputtering. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Inhomogeneous spin accumulation in Py/Au/Py spin valve

Ku, Jang Hae,Chang, Joonyeon,Eom, Jonghwa,Koo, Hyuncheol,Han, Suk-Hee,Kim, Gyutae Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>We present that inhomogeneous spin accumulation in a Py/Au/Py spin valve is due to the formation of an edge point contact at the interface. Nonlocal measurements with different voltage probe configurations were carried out to understand the effect of probe location on the spin signal. The spin signal is strongly affected by the probe configuration because of inhomogeneous spin current distribution in the channel as well as different channel length depending on the probe position. Inhomogeneous spin accumulation initiating from the point contact induces the different distribution of spin accumulation flowing into a detector. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Extended Drude model analysis of noble metals

Youn, S. J.,Rho, T. H.,Min, B. I.,Kim, Kwang S. Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>We have applied the extended Drude model (EDM) to noble metals of Cu, Ag, and Au. Drude parameters are obtained self-consistently without using the sum rule or any approximation. The core polarization contribution ϵ<SUB>∞</SUB> is shown to be large due to shallow d-orbitals. The frequency dependent mass enhancement factor λ (ω) and the scattering rate 1/τ (ω) are obtained. The Drude region can be identified when 1/τ (ω) deviates from the Fermi liquid behavior due to interband transitions. The onset frequency for the interband transition is found to be lower than the frequency value at the minimum of the imaginary part of the dielectric constant. The validity of the approximation of ωτ ≫ 1, which is commonly employed in analyzing optical data, has been checked based on the EDM for noble metals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Application of ellipsometry in immersion lithography

Jeong, H.,Cheon, H.,Kyoung, J.,Oh, H.,An*, I. Wiley - VCH Verlag GmbH & Co. KGaA 2008 Physica Status Solidi C Vol.5 No.5

<P>Optical lithography with an ArF excimer laser (193 nm) can produce sub 100nm patterns. Without the reduction of wavelength, further increase in resolution is expected by employing an immersion technique in which a liquid medium is filled between the objective lens and underlying photoresist. In this case, resolution can be enhanced through the increase of numerical aperture. However, in order for immersion lithography to be successful, many problems associated with the liquid environment need to be solved. One of the serious problems is the interaction between liquid and photoresist. Liquid may penetrate into the photoresist and cause leaching problem. This in turn modifies the physical and chemical properties of the photoresist. Thus, it is important to monitor the modification of the photoresist by immersion liquid. In this work, spectroscopic ellipsometry and imaging ellipsometry are used to investigate the absorption of liquid by photoresist as well as top coat which is used to prevent water penetration into underlying photoresist. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Effect of the thermal conductivity of substrate on the temperature of nanowire for current induced domain wall motion

Ha, Seung-Seok,You, Chun-Yeol Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica Status Solidi. A Vol.204 No.12

<P>We investigate the Joule-heated nanowire temperature for current induced domain wall motion with a finite thickness insulator layer. The dependence of the temperature on the thermal conductivities of substrates and insulator layers, and the insulator layer thickness are studied by employing finite element method. We find that the increment of the temperature is roughly proportion to the inverse of thermal conductivity of the substrate and insulator layer. Furthermore, the increment of the temperature rises with the insulator thickness, and then saturates for the thick enough insulator layers. The results of the numerical calculations can be explained reasonably with the analytic solution for the Joule-heated nanowire temperature, even though it is valid only for the case without an insulator layer. Our results suggest appropriate guideline for the design of the experiments. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Depinning field from notches on Co/Pd multilayer nanowires with perpendicular magnetic anisotropy

Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica Status Solidi C Vol.4 No.12

<P>Domain-wall pinning and depinning mechanisms of ferromagnetc nanowires with perpendicular magnetic anisotropy were investigated. Micromagnetic simulation results revealed that the depinning field from notches were determined solely by the gap distance between the notches, irrespective to the wire width and the notch size. The double-notch wires exhibited two-fold décalcomanie domain patterns and one half patterns were identical to those of single-notch wires. Therefore, the double-notch wires showed the same depinning field compared to single-notch wires with half width. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>