Soo-ghee Oh

Optical properties of Au nanocluster embedded dielectric films

Abstract Composite films of Au and dielectric material (TiO2 and/or mixed ZnS–SiO2) with a wide range of Au fractions were fabricated through a co-sputtering method utilizing a multi-target sputtering system. The optical absorption spectra of these composite films demonstrated an absorption peak due to surface plasmon resonance of embedded Au nanoclusters. It was found that, depending on the dielectric matrix, Au concentration, and post-deposition annealing, the wavelength of the surface plasmon resonance of nanoclusters shifted by 130 nm: from 550 to 680 nm. The third-order non-linear susceptibility χ(3) of these composite films, which also originates from field enhancement due to the surface plasmon resonance, demonstrated a corresponding variation.

Effects of metal buffer layers on the hot filament chemical vapor deposition of nanostructured carbon films

We examined how the addition of different metal buffer layers between the Ni/Fe-alloy-catalyst layer and the silicon substrate affected the growth of nanostructured carbon films; Cr, Ti, Ta, and W were tested as buffer layers. Even when the sputter-deposition of catalytic-metal layers and the hot filament chemical vapor deposition of carbon films were carried out under the identical conditions, different buffer layers resulted in substantially different carbon-film growth. More specifically, carbon-nanoparticle films were produced with the Cr and the W buffer layers, and carbon-nanotube films were produced with the Ti and the Ta buffer layers. X-ray diffraction (XRD) showed a significant and systematic difference between the carbon-nanoparticle and carbon-nanotube films. In the case of the carbon-nanoparticle films deposited with either the Cr or the W buffer layer, the peaks corresponding to the catalytic metal, the carbide phases of the catalytic metal, and the carbide phases of the respective buffer me...

Line-ratio determination of atomic oxygen and

Optical emission spectroscopy line-ratio methods are developed in order to estimate the absolute densities of nitrogen and oxygen atoms and metastable N2(A) molecules in the nitrogen late afterglow of an RF discharge, operating at p?=?8?Torr, Q?=?1?slm and P?=?100?W, in what constitutes an extension of the typical domain of application of these methods. [N] is obtained from the first positive (1+) emission with calibration by NO titration, [O] from the ratio of the NO? to 1+ bands, and [N2(A)] from the ratios of (i) the NO? and NO? bands, (ii) the second positive (2+) and NO? bands and (iii) the 1+ and 2+ bands. In addition to the determination of the N, O and N2(A) absolute densities, the present investigation gives an indication on the order of magnitude of the rate coefficient of the very important reaction N2(X, v???13)?+?O???NO?+?N at room temperature.

{\rm N}_2(A\,{}^3\Sigma_{\rm u}^+)

Silicon incorporated diamond-like carbon (Si-DLC) films were deposited by 13.56 MHz r.f. plasma assisted chemical vapor deposition (RF-PACVD), and the optical properties of the films were examined by spectroscopic ellipsometry analysis. In particular, the dispersion model developed by Jellison and Modine was used to determine the optical constants by fitting the measured ellipsometric spectra in the 300‐ 1200 nm range. Various mixtures of benzene and diluted silane (SiH4:H2a 10:90) were used as reaction gases, and the Si concentration in the film was found to increase monotonically up to 17 at.% as the diluted silane fraction in the reaction gas was increased from 0 to 95%. However, the variation of the optical gap exhibited distinctive silicon-concentration dependence; the minimum optical gap was found from the film with 5 at.% silicon concentration. The observed changes of the optical properties were attributed to the modification of the atomic bonding structures induced by silicon incorporation. In particular, the change in SP 2 -bonded carbon cluster sizes and the interlinking between SP 2 clusters are discussed. q 1999 Elsevier Science S.A. All rights reserved.

metastable absolute densities in an RF nitrogen late afterglow

The velocity distribution of a metallic neutral species sputtered in a dc magnetron discharge was measured using a planar Fabry–Perot interferometer and a hollow cathode lamp as a reference source. The measurement was performed under different angles of view relative to the target surface. The velocity distribution function in the direction perpendicular to the target becomes asymmetrical as the Ar pressure decreases, whereas it remains nearly symmetrical when the line of sight is parallel to the target surface. The average velocity of the sputtered Ti atoms was measured to be about 2km∕s.

Structure and optical properties of Si incorporated diamond-like carbon films deposited by r.f. plasma-assisted chemical vapor deposition

The dissociation of nitrogen molecules in an Ar–N2 inductively coupled plasma (ICP) discharge is studied both experimentally and theoretically. To measure the absolute N atom density and emission intensity of Ar and N2 excited levels, two-photon absorption laser-induced fluorescence (TALIF) spectroscopy and optical emission spectroscopy are used. We observe an increase in N atom density with increasing pressure whereas the N atom density decreases for pressures higher than 100 mTorr in a pure nitrogen discharge. On adding argon to the mixture, we observe that the dissociation rate is enhanced when going from a pure nitrogen discharge to an argon mixed discharge. To calculate the plasma parameters, a global (volume-averaged) model is developed. The variation of the electron temperature and the particle densities are calculated by solving the particle and energy balance equations. The model calculations are compared with the measurement results and the production and loss rates of each species are described under each discharge condition. From the model calculation, the dissociation of N2 molecules in the Ar–N2 mixed discharge occurs mainly by electron impact dissociation at low pressures, while at high pressures the dissociative recombination is enhanced by charge transfer between Ar+ and N2(X) as well as metastable–metastable pooling dissociation due to the high density. In addition, the surface sticking coefficient of nitrogen atoms in a planar ICP discharge (including glass and stainless steel walls) is deduced from TALIF measurements and is estimated to be 0.02 under our set-up conditions.

Velocity distribution of neutral species during magnetron sputtering by Fabry–Perot interferometry

Abstract Carbon nitride (CN) films were synthesized on silicon substrates by a combined ion-beam and laser-ablation method, and the variations of the structure, and the optical and the mechanical properties of the CN films were investigated as a function of ion-beam current. All the CN films were amorphous independent of the ion-beam current, and their refractive indices, extinction coefficients and optical band gaps exhibited a significant dependence on synthesis condition. In particular, the decrease of the refractive indices and the shrinkage of the optical band gap are noticeable as the ion-beam current increases. Also, the hardness of the CN films was found to decrease with ion-beam current. The observed variations of optical and mechanical properties are attributed to the changes of the atomic bonding structures which were induced by nitrogen incorporation; reduced interlinking of sp 2 clusters, increase in the number and size of sp 2 clusters, and increase of structural order in sp 2 clusters.

Modeling and experimental study of molecular nitrogen dissociation in an Ar–N2 ICP discharge

A planar Fabry?Perot interferometer was utilized to measure the velocity distribution function (vdf) of the atoms sputtered in a dc magnetron discharge. The measurements were performed during the sputtering of several metal targets under different discharge conditions such as applied power, working pressure and the distance from the magnetron target. The results demonstrate that there is a considerable shift of the vdf depending on the working pressure and the atomic weight of the sputtered atoms when the line of sight is perpendicular to the target. At the same time the velocity corresponding to the maximum of the vdf does not vary appreciably with the applied power. The typical net velocity of the sputtering atoms was found to be about 2?km?s?1, which is in good agreement with the data obtained recently by other diagnostic methods.

Optical and mechanical properties of amorphous CN films

Hydrogenated amorphous carbon (a-C:H) films were deposited on double-side polished germanium substrates by RF plasma-assisted chemical vapour deposition method using benzene as a precursor, and their optical properties were investigated in the wavelength range from 700 nm to 10 mm. In particular, we used a dispersion-function-based non-linear regression to fit the reflectance in the range from 700 to 1800 nm and the baselines of the infrared transmittance in the range from 1000 to 5000 cm ˇ1 , respectively. Optical constants determined in both ranges, together with their respective thickness values, showed overall consistency. As a function of self-bias, we found that the refractive index increased while the band gap decreased, which was indicative of film densification and increase of sp 2 -bonded carbons. Detailed information on the selfbias-dependent evolution of microscopic bonding structure in a-C:H films was revealed via the quantitative vibrationabsorption spectra in the mid-infrared region, which was obtained after taking Urbach-tail-like electronic absorption into consideration. More specifically, it was found that as self-bias was increased hydrogen content decreased, olefinic sp 2 -bonding decreased while aromatic sp 2 -bonding increased, and more carbon bonding was distorted due to increased cross-linking. Maximum sp 2 -bonding was observed between ˇ300 and ˇ400 V of self-bias. # 2001 Elsevier Science B.V. All rights reserved.

Fabry–Perot interferometry for measurements of the velocity of sputtered atoms in a magnetron discharge

The electron temperature of planar inductive argon plasma was studied as a function of the gas pressure between 3 and 100 mTorr with a spectral line ratio in optical emission spectroscopy (OES) and a single Langmuir probe. The electron energy probability function (EEPF) showed a bi-Maxwellian distribution at lower pressures and a Maxwellian distribution at higher pressures. Using optical and probe techniques, it was found that the electron temperature decreases as the pressure increases. The electron temperature determined by the spectral line ratio in OES using optical cross-sections was substantially smaller compared with the scope measured by a Langmuir probe. A novel technique that suppresses the large difference in the electron temperature by correcting the electron excitation kinetics was initiated. The correction factor α(P), which depends on the gas pressure, was derived from the balance between the measured light intensity and the degree of excitation by collisions via the EEPF and the electron density value obtained from the probe measurement. Taking into account α(P), the electron temperature according to the spectral line ratio approaches the effective electron temperature using a single Langmuir probe.