Supanee Limsuwan

Chemical Bonding in Composite SiNx/Diamond-Like Carbon Films Prepared by Filter Cathodic Arc Deposition of Graphite Incorporated with Radio Frequency Sputtering of Silicon Nitride

SiNx and diamond-like carbon (DLC) films were prepared simultaneously on Si substrates by the RF magnetron sputtering of a silicon nitride (Si3N4) target and the filtered cathodic arc (FCA) deposition of graphite, respectively. The RF power was fixed at 100 W, while the arc current of graphite for the FCA deposition was varied from 20 to 80 A. The structure of composite SiNx/DLC films was investigated by Raman spectroscopy. The chemical composition and chemical state of the films were analyzed by X-ray photoelectron spectroscopy (XPS). Results revealed that the atomic concentration of carbon (C) increased, while those of silicon (Si) and nitrogen (N) decreased with increasing arc current. In addition, the sp3 content in the composite films was found to increase with the arc current. This result indicates that the structure and property of the composite films can be controlled according to their required applications by varying the arc current.

Raman spectroscopy of DLC/a-Si bilayer film prepared by pulsed filtered cathodic arc

DLC/a-Si bilayer film was deposited on germanium substrate. The a-Si layer, a seed layer, was firstly deposited on the substrate using DC magnetron sputtering and DLC layer was then deposited on the a-Si layer using pulsed filtered cathodic arc method. The bilayer films were deposited with different DLC/a-Si thickness ratios, including 2/2, 2/6, 4/4, 6/2, and 9/6. The effect of DLC/a-Si thickness ratios on the sp3 content of DLC was analyzed by Raman spectroscopy. The results show that a-Si layer has no effect on the structure of DLC film. Furthermore, the upper shift in G wavenumber and the decrease in ID/IG inform that sp3 content of the film is directly proportional to DLC thickness. The plot modified from the three-stage model informed that the structural characteristics of DLC/a-Si bilayer films are located close to the tetrahedral amorphous carbon. This information may be important for analyzing and developing bilayer protective films for future hard disk drive.

A volumetric flask as a projector

A lens based on liquid in the confined volume of a volumetric flask was presented as a potential projector to observe microscopic floating organisms or materials. In this experiment, a mosquito larva from a natural pond was selected as a demonstration sample. By shining a light beam from a laser pointer of any visible wavelength through the volumetric flask filled with liquid, the movements of floating objects were clearly observed on a screen. The magnification was simply controlled by changing either the volume of the flask or the distance of the screen from the flask.

Green Approach for the Reduction of Graphene Oxide by Thai Shallot

In this paper, we used shallots in the reduction of graphene oxide for the first time. Flavone, sulfur-containing compounds, and polyphenolic derivatives in the bulb of shallot acted as good reducing agent for the reduction of GO. The GO and reduced graphene oxide (RGO) were characterized by scanning electron microscopy (SEM), ultraviolet (UV)-visible spectroscopy, thermogravimetric analysis (TGA) and Raman spectroscopy. GO and RGO were the transparent sheets with the sheet edges tend to scroll and fold slightly. RGO showed a maximum absorption peak at 267 nm and had better thermal stability than graphene oxide. Raman spectra indicated removal of oxygen at the surface of GO and formation of the defect in the graphene sheet.

EFFECT OF SURFACE ENERGY ON THE GROWTH OF DIAMOND-LIKE CARBON/AMORPHOUS SILICON FILMS ON VARIOUS SUBSTRATES

Diamond-like carbon/amorphous silicon bilayer films were deposited on SiO2, Ge, and Ta2O5 substrates using a pulsed filtered cathodic arc (PFCA) system. Amorphous silicon (a-Si) layer was firstly deposited on three substrates using DC magnetron sputtering, then diamond-like carbon (DLC) film was deposited on a-Si layer via pulsed filtered cathodic arc. The thicknesses of a-Si layer and DLC film as monitored by in-situ ellipsometry during the film deposition were 7 and 10 nm, respectively. The surface energy of SiO2, Ge, and Ta2O5 substrates was determined by measuring the contact angle of water on these substrates. It was found that the contact angles of water on SiO2, Ge, and Ta2O5 substrates were 53°, 63°, and 75°, respectively. This result indicates that SiO2 has the highest surface energy while Ta2O5 has the lowest surface energy. The thickness of the a-Si layer and DLC film was determined from the cross-section transmission electron microscopy (TEM) images. The thinnest a-Si layer of 5.64 nm was obtained from SiO2 substrate which has the highest surface energy. The thickest a-Si layer of 6.97 nm was obtained from Ta2O5 corresponding to the lowest surface energy. This study shows that the thickness of the growth film strongly depends on the surface energy of the substrate. However, the DLC films deposited on each a-Si layer of three substrates have the same thickness approximately of 9.9 nm, because all of them were deposited on a-Si layers having the same surface energy.

Investigation of Thermal Expansion Coefficient of Metals from Light Diffraction Pattern

In this work, an experimental set for determining the linear thermal expansion coefficient (α) of a metal was designed and constructed. It was divided into three parts: metal rod holder, light source, and heating system. A cylindrical plastic pipe with an inner diameter of 16 cm was used as a metal rod holder. The sample metal rod with unknown linear thermal expansion coefficient was inserted vertically into a holder and covered by the first razor blade at one end, while the other end was fixed. The second razor blade was attached with posts. Two razor blades were aligned and separated with a distance of 0.05 cm; therefore, two razor blades were acted as a thin single slit. The steam generated from heating system was transferred into metal rod holder; subsequently, the length of metal rod increased with increasing temperature. The design of the apparatus for this proposed method based on decreasing the width of single slit with the same amount of increasing the metal rod length due to linear thermal expansion. A He-Ne laser with a wavelength of 632.8 nm used as a light source was passed through a single slit and produced a diffraction pattern on a screen. The decrease in slit width was determined by measuring the fringe width. The value of linear thermal expansion coefficient of a metal can be calculated from alteration of fringe width. In our case, stainless steel (314), copper (UNS C11000), and aluminium (6063) rods with the original length of 45.3 cm were used as samples. The experimental values of α for stainless steel, copper, and aluminium are 15.25 × 10-6, 17.74 × 10-6, and 23.13 × 10-6 (°C)-1, respectively. These values are in good agreement with the standard values as reported by the National Metal and Materials Technology Center (MTEC), Thailand. The error of this proposed method is found to be less than 1.2%.

Construction of a Cost Effective Current Balance for Physics Teaching

In this work, a method to measuring the magnitude of a uniform magnetic field in space using current balance was described. A simple experimental set was designed and constructed using low-cost materials. This constructed current balance consists of copper sheet, weight pan, and acrylic sheet. A copper sheet was cut into a U-shape and attached at the end of acrylic balance arm. A weight pan was hanged in the opposite side of the balance arm with high sensitivity to a small torque. The horizontal segment of the U-shaped copper sheet, which the length l was 3 cm, was located inside the influence of an uniform magnetic field produced by two parallel bar magnets with opposite poles facing each other. The magnetic field direction was perpendicular to the horizontal segment. When a current was supplied to the copper sheet, the magnetic force acting on a horizontal segment of length l carrying a current I in a magnetic field B was given by. In the experiment, the current was varied from 0 1 A. For each value of applied current, the magnetic force on a thin straight sheet of length l was measured by adding masses to the pan until the balance arm moved to the equilibrium between opposing gravitational and magnetic forces. The results showed that the magnetic force increased linearly with increasing applied current. By plotting a linear graph of magnetic force versus applied current, the magnetic field B can be calculated from . The calculated and actual values of B were 100.32 and 100.13 mT, respectively. This constructed current balance is an excellent tool for high school and undergraduate fundamental physics courses. Students will be excited when they see the balance arm rising or going down due to magnitude and direction of current flowing in a conductor wire.

XPS and Spectroscopic Ellipsometry Study of Composite SiNx/DLC Prepared by Co-Deposition of RF Magnetron and Filtered Cathodic Arc

Composite SiNx/DLC films were deposited on silicon substrate by co-deposition system. The carbon plasma was generated by filtered cathodic arc source, simultaneously incorporated with silicon nitride from RF magnetron sputtering. The silicon nitride sputtering rate was maintained by fixed RF power at 100W while the arc current of FCA was varied from 20 to 80A.The SiNx/DLC film composition and optical properties were investigated by X-ray photoelectron spectroscopy and spectroscopic ellipsometry respectively. The results revealed that the atomic concentration of carbon increased while those of silicon and nitrogen decreased with increasing arc current. The oxidation was found on the film surface and related to the atomic concentration of silicon. The optical properties can be changed as a function of carbon concentration by setting different arc current. In this work, the volume percentage of carbon obtained from spectroscopic ellipsometry using Bruggeman EMA model showed good numerical correlation with the atomic percentage of carbon from XPS analysis with the range spanning across 75-95 at. %.

Effect of Sericin Protein on Growth of Hydroxyapatite over Surface of Silk Fibers Using Simulated Body Fluid

Crystal of hydroxyapatite (HAp) was grown on silk fibers using simulated body fluid (SBF) at a temperature of 37 °C. Effect of SBF concentrations and sericin protein on the growth of HAp crystals on the silk fiber was discussed. The results showed that sericin protein was an important parameter to induce HAp crystals. Furthermore, the crystal was grown perfectly for both 1.0 and 1.5  standard SBF concentrations but difference in HAp crystal size. Sericin protein may lower nucleation barrier and high surface area to absorb SBF for HAp nucleation. These results may be a new research topic on HAp crystallization using protein as a seed. It may lead to further improvement and applied for many HAp-based biomaterial applications.

ESR dating of laterite from Ban Tha Ta Suea, Kanchanaburi, Thailand.

Electron spin resonance (ESR) dating was carried out on laterite samples collected from Ban Tha Ta Suea, the original deposit of the laterite used in the construction of Muang Sing Historical Park. Ban Tha Ta Suea is about 6 km east of Muang Sing Historical Park in Kanchanaburi province (181 km far from Bangkok). The dose response of the g=2.0028 ESR signal was found to be suitable for age determination. An exponential saturation function was fitted to the ESR signal growth on additional γ-irradiation. Extrapolation of this function resulted in the accumulated dose 144±5 Gy. Gamma spectroscopy and neutron activation analysis (NAA) were used to determine concentrations of (238)U, (232)Th and (40)K in the samples from which the annual dose rate 16±2 mGy was calculated. In addition, the dose rate of cosmic rays was taken into account. The ESR age of laterite samples was found to be 9.0±0.9 ka. This age falls within the Holocene epoch of the Quaternary on the geological time scale. Samples from Muang Sing Historical Park were assigned to the same epoch. Both results agree with the geological map.