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>

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>

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>

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>

Anomalous magnetoimpedance in Co–Fe–Al–O thin films

Tuan, L. A.,Phan, M. H.,Ha, N. D.,Kim, C. G.,Kim, C. O.,Yu, S. C. Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica Status Solidi C Vol.4 No.12

<P>The high-frequency giant magnetoimpedance (GMI) effect in a Co<SUB>47.5</SUB>Fe<SUB>21.9</SUB>Al<SUB>17.2</SUB>O<SUB>15.2</SUB> thin film was systematically investigated. In the frequency range of 100–500 MHz, GMI profiles showed a double-peak characteristic, reflecting an evident existence of the transverse magnetic anisotropy in the film, which coincided with the magnetization data. Interestingly, there was an anomalous transformation in the GMI profile from “positive” to “negative” and this was associated with the complex phase transformation of permeability. The GMI ratio decreased with decreasing film-thickness, due to an increase of the electrical resistivity and a decrease of the magnetic softness. (© 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>

Structural and electrical properties of Zn(Al)O layers for transparent metal oxide applications

Kwon, Y. B.,Abouzaid, M.,Ruterana, P.,Je, J. H. Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica Status Solidi. B Vol.244 No.5

<P>The microstructure and electrical properties of low temperature (250 °C) RF sputtered Al doped ZnO layers are investigated. By varying the Al composition from 0 to 15 at%, it is shown that the morphology of the layers is improved whereas the crystalline structure changes from highly oriented monocrystalline domains to textured and misoriented nanocrystallites. It is also noticed that the best metallic properties are attained for a quite low Al concentration in the AZO (3 at%), when the Al content is further increased, the mobility, carrier density and resistivity saturate. The annealing in air at higher temperatures does not seem to improve the conduction properties, instead at 800 °C, the resistivity drops by more than one order of magnitude and the carrier density by almost five orders of magnitude. At this high temperature, the strong increase of the mobility is tentatively attributed to the better crystalline quality of the annealed layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Reduction of low‐frequency noise in multilayer MoS₂ FETs using a Fermi‐level depinning layer

Kim, Yonghun,Park, Woojin,Yang, Jin Ho,Cho, Chunhum,Lee, Sang Kyung,Lee, Byoung Hun Wiley - VCH Verlag GmbH & Co. KGaA 2016 Physica Status Solidi. Rapid Research Letters Vol.10 No.8

<P>Two‐dimensional transition metal dichalcogenides (TMDCs) are potential candidate materials for future thin‐film field effect transistors (FETs). However, many aspects of this device must be optimized for practical applications. In addition, low‐frequency noise that limits the design window of electronic devices, in general, must be minimized for TMD‐based FETs. In this study, the low‐frequency noise characteristics of multilayer molybdenum disulphide (MoS<SUB>2</SUB>) FETs were investigated in detail, with two different contact structures: titanium (Ti) metal–MoS<SUB>2</SUB> channel and Ti metal–TiO<SUB>2</SUB> interlayer–MoS<SUB>2</SUB> channel. The results showed that the noise level of the device with a TiO<SUB>2</SUB> interlayer reduced by one order of magnitude compared with the device without the TiO<SUB>2</SUB> interlayer. This substantial improvement in the noise characteristics could be explained using the carrier number of fluctuation model. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)</P>

Humidity controlled crystallization of thin CH₃NH₃PbI₃ films for high performance perovskite solar cell

Jeong, Beomjin,Cho, Suk Man,Cho, Sung Hwan,Lee, Ju Han,Hwang, Ihn,Hwang, Sun Kak,Cho, Jinhan,Lee, Tae‐,Woo,Park, Cheolmin Wiley - VCH Verlag GmbH & Co. KGaA 2016 Physica Status Solidi. Rapid Research Letters Vol.10 No.5

<P>Control of crystallization of a solution‐processed perovskite layer is of prime importance for high performance solar cells. In spite of the negative effect of water on perovskite solar energy conversion in several previous works, we observed that humidity plays a critical role to develop a thin uniform, dense perovskite film with preferred crystals, in particular, in a device with architecture of ITO/PEDOT:PSS/CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>/ PC<SUB>71</SUB>BM/LiF/Al fabricated by two‐step sequential spin‐coating process. Humidity controlled spin‐coating of CH<SUB>3</SUB>NH<SUB>3</SUB>I on the pre‐formed PbI<SUB>2</SUB> layer was the most influential process and systematic structural investigation as a function of humidity revealed that grains of CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> perovskite crystals increase in size with their preferred orientation while film surface becomes roughened as the humidity increases. The performance of a device was closely related to the humidity dependent film morphology and in 40% relative humidity, the device exhibited the maximum power conversion efficiency of approximately 12% more than 10 times greater than that of a device fabricated at 20% humidity. The results suggest that our process with controlled humidity can be another efficient route for high performance and reliable perovskite solar cells. (© 2016 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>