Somyod Denchitcharoen

Growth and characterization of nanostructured TiCrN films prepared by DC magnetron cosputtering

Nanostructured TiCrN films were grown on Si (100) wafers by reactive DC unbalanced magnetron cosputtering technique without external heating and voltage biasing to the substrates. The effects of Ti sputtering current on the chemical composition, chemical state, electronic structure, crystal structure, and morphology of the TiCrN films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission scanning electron microscopy (FE-SEM), respectively. The results showed that all prepared films were formed as an understoichiometric (Ti, Cr)N solid solution with the fcc B1 type phase. The films exhibited a nanostructure with a crystallite size of less than 14 nm. The deconvolution of XPS spectra revealed the chemical bonding between Ti, Cr, N, and O elements. The addition of Ti contents led to the decrease of valence electrons filled in the d conduction bands which result in the change of binding energy of electrons in core levels. The roughness of the films was found to increase with increasing ITi. The cross-sectional morphology of the films showed columnar structure with dome tops.

Effect of N Incorporation on Growth Behavior of InGaAsN/GaAs/Ge Multi-Layered Structure by MOVPE

We have investigated an effect of N incorporation on InGaAsN on Ge (001), which is proposed to be a part of the InGaP(N)/InGaAs/InGaAsN/Ge four-junction solar cell, and on its growth behavior. Results obtained from high resolution X-ray diffraction and Raman scattering demonstrated that high quality In0.11Ga0.89As1-yNy films with N (y) contents up to 5% were successfully grown on n-type doped Ge (001) substrate by metalorganic vapor phase epitaxy using low-temperature (500°C) GaAs buffer layer. As expectation, the In0.11Ga0.89As0.96N0.04 film is examined to be under lattice-matching condition. Anti-phase domains were observed for the film without N incorporation, which exhibits submicron-size domains oriented along the [110] direction on the grown surface. With increasing N content, the domains become less orientation, and present in a larger domain size. Based on results of transmission electron microscopy, a high density of anti-phase domains was clearly observed at the interface of low-temperature GaAs buffer layer and Ge substrate. On the other hand, it is found to drastically reduce within the N-contained InGaAsN region. Furthermore, the lattice-matched In0.11Ga0.89As0.96N0.04 film is well developed to reduce the density of anti-phase domains.

Development of Nanohole Array Patterned by Laser Interference Lithography Technique

Periodic nanohole pattern was created in spin-coated photoresist S1805 on Si substrates by Laser Interference Lithography (LIL). Wavelength of a laser source used in the optical system is 442 nm with the photon energy 2.80 eV. The system was set up to employ two laser beams from a beam splitter to generate interference pattern and expose to the photoresist. There are two parameters (incident angle and exposure time) which are determined due to affecting the ordering and feature of nanohole array. Therefore, the relation of these two parameters and actual dose were investigated and theoretically analyzed to optimize the resolution of LIL technique for nanoholes. The prepared samples after developing in the M26A for 5 sec were analyzed by field-emission scanning electron microscopy (FE-SEM). The results show that the pitch of the pattern is 440 nm and the smallest hole size is 190 nm The best feature is found for a laser fluence of 140 mJ/cm2. This nanohole array patterned by LIL consists of periodic nanostructures for high density storage to fabricate various nanodevices.

TEM Analysis of Planar Defects in InGaAsN and GaAs Grown on Ge (001) by MOVPE

InGaAsN on Ge (001) is proposed to be a part of the InGaP(N)/InGaAs/InGaAsN/Ge four-junction solar cell to increase a conversion efficiency over 40%. In this work, InGaAsN lattice-matched film and GaAs buffer layer grown on Ge (001) substrate by metal organic vapor phase epitaxy (MOVPE) were examined by transmission electron microscopy (TEM). Electron diffraction pattern of InGaAsN taken along the [110]-zone axis illustrates single diffracted spots, which represent a layer with a uniformity of alloy composition. Cross-sectional bright field TEM image showed line contrasts generated at the GaAs/Ge interface and propagated to the InGaAsN layer. Dark field TEM images of the same area showed the presence of boundary-like planar defects lying parallel to the growth direction in the InGaAsN film and GaAs buffer layer but not in the Ge substrate. TEM images with the (002) and (00-2) reflections and the four visible {111} planes reflections illustrated planar defects which are expected to attribute to antiphase boundaries (APBs). Moreover, the results observed from atomic force microscopy (AFM) and field emission electron microscopy (FE-SEM) demonstrated the surface morphology of InGaAsN film with submicron-sized domains, which is a characteristic of the APBs.

Effect of N2 Flow Rate on Structure and Morphology of (Ti,Cr)N Thin Films Deposited by Unbalanced Magnetron Co-Sputtering

The (Ti,Cr)N thin films were deposited with various N2 flow rates on silicon wafers by reactive unbalanced magnetron co-sputtering without heating and biasing substrates. The effects of N2 flow rate on the structure and morphologies of the films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDS). The results revealed that the (Ti,Cr)N thin films formed solid solutions with the fcc structure. The crystallite sizes calculated from Scherrer formula are about 13 nm. The root-mean-square roughness (Rrms) and the thickness (Tth) of the films were slightly decreased with the increase in N2 flow rate. The cross-sectional morphology showed columnar structure corresponding to zone 2. In addition, the N atomic concentration was also increased with the increase in N2 flow rate.

Heating Effect on the Qualities of Cr-Zr-N Thin Films by Increasing in Zr Sputtering Current

Chromium zirconium nitride (Cr-Zr-N) thin films have been prepared by reactive dc closed field unbalanced magnetron co-sputtering on Si (100) wafers without external heating and voltage biasing. Heating effect on chemical composition, microstructure, and adhesion of the films by increasing in Zr sputtering current was investigated by using field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX). The results suggested that heating in the film and substrate during the deposition with high Zr target current was caused by bombarding the growing film with high energetic particles. From EDX analysis, the decrease of N content could be an effect of nitrogen desorption caused by heating and bombarding of high energetic particles. FE-SEM cross-sectional morphology revealed that grain refinement by Zr addition and high atomic diffusivity on both surface and bulk by heating and bombarding of high energetic particles resulted in denser fibrous grain microstructure. However, the increase of Zr target current leaded to the film with high compressive stress and could affect the film adhesion.

Preparation of Carbon Nanoparticles by Long Pulsed Laser Ablation in Water with Different Laser Energies

Carbon nanoparticles were synthesized via laser ablation of graphite target in distilled water. The particle sizes of carbon nanoparticles were investigated as a function of laser energy: 1, 1.5, and 2 J/pulse. Using water as a matrix during synthesis is another potential way to control the particle size. The mean size increases when increasing the laser energy. The particle morphology is a globular shape. The sizes of the nanoparticle were evaluated from both SEM image analysis and Scherrer’s equation. The sizes from the equation are smaller than those obtained from SEM, which indicates that the particles are polycrystallines.