Seok-Kyun Song

Improving wettability of polycarbonate and adhesion with aluminum by Ar + ion irradiation

Improving wettability of the polycarbonate (PC) surface to triple distilled water has been carried out by Ar + ion irradiation with blowing oxygen gas. The amount of Ar + was changed from 10 14 to 5 × 10 16 ions/cm 2 at 1 keV energy by a Kaufman-type ion source. Contact angle of the water to PC has been reduced from 78°to 50°with Ar + irradiation, and to 12°with Ar + irradiation in various vacuum pressures adjusted by oxygen gas flow rate (0-4 sccm). Strong O-H stretching vibration peaks at about 3370 cm −1 on FT-IR spectra of the polymer appeared after the surface treatments, and the wetting angle of the treated PC was returned to its value (78°) when the PC was exposed in air environment. The minimum contact angles were maintained with the same value when the irradiated polymers were kept in dilute HCl solution. The improved wettability and surface chemical reaction by Ar + ion irradiation with oxygen was explained by the formation of a hydrophilic functional group. Enhanced adhesion between aluminum and PC was confirmed by the scotch tape test, and was discussed with relation between the hydrophilic group on the polymer surface and the deposited metal.

H2 gas-sensing characteristics of SnOx sensors fabricated by a reactive ion-assisted deposition with/without an activator layer

Abstract SnOx-based gas-sensor devices have been fabricated by a reactive ion-assisted deposition technique. SnOx films of 400 A thickness are deposited on sputtered amorphous SiO2 substrates and then Pt films (600 A) are sputtered on top of them as upper electrodes. From XRD and TEM studies, as-deposited SnOx films are seen to be amorphous and become polycrystalline after annealing at 500°C in air. In quantitative XPS analyses, the O/Sn atomic ratio in the annealed films shows the nearly stoichiometric value of two and the binding energy of Sn 3d5/2 is 486.43 eV, very close to 486.75 eV of the standard tin oxide powder. When sensitivity is defined as a relative decrement in resistance, these sensor devices show nearly 100% sensitivities to 1000–5000 ppm H2 in air at 200°C and above. By attaching an ultra-thin metal activator, the response time can be reduced to less than one tenth of its previous value.

Structure and gas-sensing characteristics of undoped tin oxide thin films fabricated by ion-assisted deposition

Abstract Undoped SnOx thin films were deposited by a reactive ion assisted deposition technique at various ion beam potential (VI) onto amorphous SiO2/Si substrates at room temperature. Crystalline structures of the films were investigated in terms of grain size, composition ratio, porosity and peak area percent of adsorbed oxygen. Sensitivities for propane (C3H8), methane (CH4) and hydrogen (H2) gas in SnOx gas sensor devices were characterized at the substrate temperatures of 100–500°C. The gas sensitivities depend on the grain size rather than the porosity. It is also proportioned to the amounts of adsorbed oxygen at room temperature by XPS analysis.

The characterization of undoped SnOx thin film grown by reactive ion-assisted deposition

Abstract Undoped oxygen-deficient SnO x films were deposited on Si (100) and BK7 glass substrates by the reactive ion-assisted deposition technique. The average impinging energy ( E a ) of the oxygen ion on depositing a Sn atom, a relative arrival ratio of ion to atom ( Γ ), was varied from Γ = 0.025 ( E a = 25 eV atom −1 ) to Γ = 0.1 ( E a = 100 eV atom −1 ) by controlling the discharge voltage at a fixed ion-beam potential of 500 V. Crystalline structures of as-deposited SnO x films appeared to be amorphous for all E a values. In order to precisely examine the dependence of oxidation from SnO to SnO 2 on initial oxygen content and annealing temperature, as-deposited SnO x films containing initially different oxygen contents were annealed at 400 ∼ 500 °C in a low vacuum (∼5 × 10 −3 Torr) for 1 h to remove the external oxygen diffusion effect during the annealing process. The heat-treated SnO x films at 400 °C showed polycrystalline SnO structure until E a = 50 eV atom −1 and were still amorphous over E a = 75 eV atom −1 . But after annealing over 500 °C those films over E a = 75 eV atom −1 exhibited diffraction peaks at (110), (101), and (211), characteristic of polycrystalline SnO 2 . Scanning electron microscopy (SEM) micrographs for the as-deposited SnO x films show grains as small as a few tens of angstroms in size, but those after 500 °C annealing reveals that the number of granular grain became larger in cross-sectional SEM and the grain grew to 300 A at E a = 100 eV atom −1 . For as-deposited films, the root-mean-square of surface roughness ( σ ) slightly increased from 9 to 25 A as E a was increased, but conversely it reduced from 36 A to 13 A after annealing. From quantitative Auger electron spectroscopy, it was observed that characteristic transitional Auger peaks of Sn MNN shift to lower kinetic energy by as much as 3.8 ∼ 4.2 ± 0.02 eV in the case of the SnO films and 4.8 ∼ 5.2 ± 0.02 eV for SnO 2 films, respectively, with respect to that of Sn metal (Sn 0 ). Based on the valence band spectra taken by using He I angle-resolved ultraviolet photoelectron spectroscopy (angle-resolved UPS), two different phases of polycrystalline SnO and SnO 2 films were clearly distinguished. The binding energy difference between the first peaks derived from SnO and SnO 2 films in angle-resolved UPS spectra below the Fermi level was 1.6 eV. This value is very close to the value obtained from clean SnO and SnO 2 samples by previous valence-band XPS spectra. As-deposited and annealed films showed optical transmittance as high as more than 80% grown at higher than E a = 50 eV atom −1 in the visible wavelength and refractive index close to the bulk SnO 2 value for the film deposited at E a = 100 eV atom −1 after annealing.

Auger Electron and X-Ray Photoelectron Spectroscopy Studies of Oxidation of Tin Using SnOx Thin Films Grown by Reactive Ion-Assisted Deposition

In order to accurately determine the oxidation state of tin and to investigate the chemical shifts between tin and its oxides, quantitative Auger electron spectroscopy and X-ray photoelectron spectroscopy studies were performed using Sn metal, stoichiometric SnO2 powder, and polycrystalline SnOx thin films. Films with different oxygen contents were grown using a reactive ion-assisted deposition technique. As the atomic ratio of tin to oxygen in the deposited films increased to the stoichiometric value of 2, the tin M4N4,5N4,5 Auger transition and the corresponding Sn 3d5/2 core-level photoelectron line gradually shifted to lower kinetic energy and higher binding energy by as much as 6±1 eV and 2.39±0.02 eV, respectively, relative to those of the tin metal. An explanation for the observed systematic difference between the chemical shifts of Auger and photoelectron lines is given. It is based on the difference in electronic polarization energy between the final two-hole state produced by the Auger electron emission and the final single-hole state produced by the photoelectron emission.

Improving Wettability of PoIyMethylMetiiAcrylate by Ar+ ion Irradiation in Oxygen Environment

Ion irradiation has been carried out to improve wettability of PMMA to water. The polymer was irradiated by argon and oxygen ions, and amount of ions was changed from 10 14 ArVcm 2 to 5xl0 16 Ar + /cm 2 . Ions energies were varied from 0.5 keV to 1.5 keV, and oxygen gas was flowed from 0 seem to 6 scan near the polymer surface during ion irradiation. Wetting angle was reduced from 68 degree to 49 degree with increasing Ar + ion irradiation, to 43 degree with Ch + ion irradiation, and dropped to 8 degree with Ar + ion irradiation with flowing 4 seem oxygen gas near the polymer surface. Recovery of wettability in dry air condition, and maintenance of it in dilute HC1 solution were explained in a view of formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and flowing oxygen near the surface. Reactions among polymer matrix, energetic ions and oxygen gas to form hydrophilic group by energetic ions were discussed in terms of a two-step reaction, in which the first step is the creation of an unstable polymer chain by the ion irradiation and the second step is a reaction between the radicals and the oxygen gas.

Comparison of properties of tin oxide films deposited by reactive-partially ionized beam, ion assisted, and hybrid ion beam methods

Abstract A hybrid ion beam (HIB) technique that consists of a reactive-partially ionized beam deposition (R-PIBD) and a gas ion gun was adopted to deposit tin oxide thin films on Si (100) substrate under various deposition conditions. Tin oxide films grown by R-PIBD showed nonstoichiometric composition and the main phases of the films consisted of Sn metal and SnO. Surface roughness of the films deposited by R-PIBD were changed from 4.7 to 27.4 nm with increasing acceleration voltage from 0 to 4 kV. The films assisted by oxygen ion show the chemical state of Sn4+ which is similar to that of a standard SnO2 powder. Also, the films represent flat surface roughness much less than the case of R-PIBD. A film with a highly preferred orientation along the SnO2 (200) plane and with grain size 80.5 nm was successfully grown by IAD. The SnOx films composed of grains with nanosize are discussed in terms of chemical state, composition ratio, crystallinity, and surface roughness.

MODELING OF ELECTRICAL CONDUCTANCE VARIATION IN SUBSTRATE DURING INITIAL GROWTH OF ULTRA THIN FILM

A model of the electrical conductance of a resistive or semiconductive substrate, as a function of the average thickness d of a deposited film in initial growth on the substrate is proposed. The total conductance has two terms: one proportional to d2/3 for three-dimension (3D) growth, and one proportional to d for 2D growth or for increasing number of islands. The model was applied to the conductance of a Sn film deposited on a SiOx substrate showing that the initial growth is dominated by 3D growth. The proposed model may be useful for in situ study of the growth of ultra thin films prior to the onset of tunneling conductance.

Initial growth characteristics of gold thin films by a nozzle beam and ion-assisted deposition

The electrical conductance characteristics due to tunneling of Au films on glass substrates as a function of deposition rate and Ar+ ion current density have been investigated by in situ measurement. The onset thickness for conductance was 8.5–29 A lower than that obtained by other researchers due to the use of a nozzle beam in this study. The degree of agglomeration, t, attained its maximum value at a deposition rate R=1.0 A/s. The degree of coalescence increased with increasing deposition rate. The onset thickness for conductance decreased to a nearly linear line with increasing ion beam irradiation.

Modeling and Initial Growth Mode of Ultrathin Film on the basis of Electrical Conductivity of Substrate

A model for the electrical conductance of a semiconductive substrate with an average thickness is proposed for a region of initial growth before the appearance of a tunneling effect. Based on this model, we propose 6 different growth modes according to the film thickness, measuring in situ electrical conductivity. As the film thickness increased, the island size was constant and then increased, while the number of islands first increased and then decreased. The proposed model may be useful for in situ study of the growth of ultrathin films prior to the onset of tunneling conductance.