W.M. Kim

Density-of-state effective mass and non-parabolicity parameter of impurity doped ZnO thin films

The density-of-state effective masses of impurity doped polycrystalline ZnO thin films were measured by the method of four coefficients technique. By applying the first-order non-parabolicity approximation, the polaron effective mass and the bare band mass at the conduction band minimum, together with the corresponding non-parabolicity parameters, were analysed successfully. The determined perpendicular polaron mass of 0.29 me and the bare band mass of 0.247 me at the conduction band minimum corresponded very well to the previous results obtained for ZnO single crystals. The non-parabolicity parameter of 0.457 eV−1 derived for the polaron effective mass was larger than 0.33 eV−1 which was obtained for the bare band mass due to the increasing function of the Frohlich coupling constant with respect to the bare band mass in polycrystalline ZnO films.

Optical analysis of doped ZnO thin films using nonparabolic conduction-band parameters

The optical properties of impurity doped ZnO thin films were analyzed by taking into account the nonparabolicity in the conduction-band and the optically determined carrier concentration and mobility were correlated with those measured by Hall measurement. The Drude parameters obtained by applying a simple Drude model combined with the Lorentz oscillator model for the optical transmittance and reflectance spectrum were analyzed by using the carrier density dependent bare band effective mass determined by the first-order nonparabolicity approximation. The squared plasma energy multiplied by the carrier density dependent effective mass yielded fairly linear relationship with respect to the carrier concentration in wide carrier density range of 1019 − 1021 cm−3, verifying the applicability of the nonparabolicity parameter for various types of impurity doped ZnO thin films. The correlation between the optical and Hall analyses was examined by taking the ratios of optical to Hall measurements for carrier densi...

Hydrogen in polycrystalline ZnO thin films

The influence and the states of hydrogen in polycrystalline ZnO thin films were investigated by preparing films with different amounts of oxygen vacancies at various hydrogen potentials. The most notable effect of hydrogen addition was passivation of grain boundaries. The majority of hydrogen incorporation in polycrystalline ZnO films was attributed to hydrogen interstitials, and a substantially smaller number of multicentre bonds at oxygen vacancies were formed even at high hydrogen potentials. The major source of free carriers in polycrystalline ZnO films deposited without intentional hydrogen addition was oxygen vacancies with 2+ charge state with large atomic relaxation.

Pump-probe optical switching in prism-coupled Au:SiO2 nanocomposite waveguide film

The resonance properties due to the surface plasmon excitation of metal nanoparticles make the nanocomposite films promising for various applications such as optical switching devices. In spite of the well-known ultrasensitive operation of optical switches based on a guided wave, the application of nanocomposite film has inherent limitation originating from the excessive optical loss related to the surface plasmon resonance. In this study, we address this problem and present the experimental and theoretical analyses on the pump-probe optical switching in prism-coupled Au(1vol%):SiO2 nanocomposite waveguide film.

Edge detection in phase-change optical data storage

A direct mark edge detection scheme for readout in phase-change optical disk systems is described. The medium for edge detetection must be optimized to have a 90° phase difference between the amorphous mark and the crystalline space. Theoretical analysis and numerical simulation have shown that the readout signal using mark edge detection is as good as that using conventional detection of reflectivity for long marks and superior for short marks. Noise level at the output of differential edge detection is lower than that at the output of conventional detection. We also show experimental results that confirm these predictions.

Optical Properties of Au Nanoparticle Dispersed (Ba,Sr)TiO3 Thin Films

Abstract Au nanoparticles dispersed (Ba,Sr)TiO3 thin films were fabricated using alternating sputtering method. With the nominal thickness of Au layer of 1 nm, the spherical Au particles of 3.83 nm size were obtained showing the spatial distribution referred to a Maxell-Garnett type effective medium geometry. The film shows the characteristic surface plasmon resonance absorption band at 571 nm. Based on the effective medium theory, the linear optical functions of the films were characterized. The third-order optical nonlinearity was analyzed by a single beam Z-scan technique with a picosecond pulse laser. The real and imaginary parts of third-order susceptibility can be resolved at several wavelengths around the SPR by virtue of wavelength tunable optical parametric generator. The maximum absolute value of third-order susceptibility as large as 3.847 × 10− 8 esu were obtained at the SPR frequency.

Optical and magneto‐optical properties of NdTbFeCo thin films

Three series of NdxTbyFe1−x−y−zCoz films have been fabricated for their potential application in magneto‐optical recording: (i) x=0–0.20, Tb was adjusted so that the coercivity at room temperature was 5–10 kOe; (ii) x+y=0.28–0.32 with x in the range of 0 to 0.25; and (iii) x+y=0.21–0.23 with x in the range of 0 to 0.17. These films have been characterized both optically and magneto‐optically by Kerr hysteresis trace, variable angle of incidence ellipsometry, and normal angle of incidence Kerr spectroscopy. From these measurements, the optical constants (n and k), magneto‐optical constants (Q1 and Q2), and maximum possible figure of merit (FOM) have been determined at wavelengths of 405, 546, and 633 nm. Results demonstrate that the magneto‐optical behavior of NdTbFeCo films is sensitive to the concentration of both Nd and Tb in the film. For samples in the series (i), the addition of Nd into TbFeCo alloys was shown not to enhance their magneto‐optic behavior at the short wavelengths. For samples in the se...

Effect of ion irradiation on internal stress of amorphic carbon films produced by pulsed laser

Abstract Amorphic carbon films either 50 or 160 nm thick were deposited on Si(100) and glass substrates at room temperature in a high-vacuum environment using a Q-switched Nd-YAG pulse laser focused on a graphite target. These films were irradiated with Ti+ or C+ ions having kinetic energies of 35 and 75 keV, and the changes in internal stresses of the films with varying ion influence were investigated by measuring substrate bending using stylus profilometry. The ion energy and the film thickness were chosen such that the ion penetration depth, Rp, corresponded to either the film thickness or one half of the film thickness. The results indicate that there is an optimum ion fluence leading to a stress-free film for a given ion species and energy. Interpretation of the resulting stress behavior from ion irradiation was made based on the relaxation resulting from damage inside the film together with interfacial mixing. The scanning electron microscopy pictures and surface roughness measurements showed a very smooth surface for both as-deposited and ion-irradiated films. The ion-irradiated films had a Vickers hardness greater than 22 GPa, and were adherent to both Si and glass substrates. An investigation of the film characteristics using Raman scattering and electron-energy loss spectra has revealed that high-energy ion irradiation of an intermediate ion fluence can be utilized successfully to deposit an adherent and hard carbon film with controlled internal stress without changing the film structure significantly.

OPTICAL NONLINEARITY OF Au METAL NANOPARTICLE DISPERSED (Ba,Sr)TiO3 THIN FILMS

Nearly spherical Au nanoparticles of about 3.83 nm diameter were embedded into the (Ba,Sr)TiO3 matrix using alternating sputtering method, showing the characteristic surface plasmon resonance absorption band at 571 nm. Dispersion in the third-order optical nonlinearity was investigated at several wavelengths from 450 to 680 nm around the resonance peak by a single beam Z-scan technique with a wavelength tunable picosecond laser system. The real and imaginary parts of third-order nonlinear susceptibility were resolved and the relative contributions are quantitatively compared at each wavelength. The maximum absolute value of third-order susceptibility as large as 4.312 × 10-8esu was obtained at the surface plasmon frequency. The temporal response was also characterized by the femtosecond time-resolved optical Kerr gate measurement and the nonlinear response time was evaluated to be 192 fs at the laser wavelength of 800 nm.

Properties of Ag Thin Films Deposited in Oxygen Atmosphere Using in- line Magnetron Sputter System

A study was made to examine the electrical, compositional, structural and morphological properties of Ag thin films deposited by DC magnetron sputtering in atmosphere with deposition temperature from room temperature to 15 using in-line sputter system. The Ag films deposited at temperature above in oxygen atmosphere gave a similar specific resistivity to and even lower oxygen content than those deposited using pure Ar sputter gas The Ag films deposited with pure Ar gas was mainly composed of crystallites with [111] preferred orientation, while, for those deposited in oxygen atmosphere, more than 50% of the volume was composed of crystallites with [100] orientation. The difference in the micro structure did not cause any difference in the specific resistivity of Ag films. The results showed that the transparent conducting oxide films and the Ag films could be processed sequentially in the same deposition chamber with careful control of deposition temperature, which might result in a cost reduction for constructing the large scale in-line deposition system.