Key Engineering Materials Vol. 659

Abstract: In this work, we study the resistive switching behavior of a new model metal/insulator/metal (MIM) junction. The MIM junction consists of titanium front electrode, zinc oxide insulation layer and molybdenum back electrode. The Ti/ZnO/Mo structure was prepared on 3x3 cm² soda lime glass substrates using dc magnetron sputtering for metal electrodes and rf magnetron sputtering for ZnO layer. The thicknesses of Ti, ZnO and Mo films were controlled at 200nm, 50nm and 500nm, respectively. The crystalline structure and microstructure of the films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The current-voltage (I-V) characteristics of the device cells were obtained by using dc voltage sweep mode. The XRD spectra of the devices show Mo(100) and ZnO(002) preferred orientations. The Mo and ZnO film surfaces exhibit dense crystallized grains with the root mean square roughness (RMS) of 1.0 and 1.4 nm, respectively. The device cells behave unipolar resistive switching characteristics with reversible, controllable and reliability within 150 cycles. The difference between high resistive state (HRS) and low resistive state (LRS) is about 10³ times. A low operating voltage range of 0.50-0.60V is obtained for switching from HRS to LRS at a current compliance of 10mA. The new MIM structure was demonstrated and suggested a potential to use as nonvolatile memory application.

Abstract: Transparent conductive Al-doped zinc oxide (ZnO:Al) films with different sputtering power were prepared on glass substrate using an RF sputtering technique. Two main peaks of the hexagonal wurtzite structure in the (002) and (004) direction were observed in every deposited ZnO:Al film. Intensities of these peaks were increased with the increasing sputtering power. Moreover, the surface roughness tended to increase with increasing sputtering power whereas the electrical resistance decreased with increasing sputtering power. The ZnO:Al film deposited at 150 and 200 W showed maximum optical transmittance of over 80% in the visible wavelength range. All results confirmed that the sputtering power directly affected film thickness because the higher sputtering power gave rise to a higher deposition rate; the surface morphology of the deposited films was dependent on the sputtering power and the optical properties were indirectly affected by the power of the deposition process.

Abstract: Granular Co_100-xCu_x films with different compositions of x = 19, 40, 54, 65 and 76 were deposited on glass substrates using sputter deposition. Co (HCP) and Cu (FCC) phases were observed in all deposited Co-Cu films. Film thickness was increased with increasing Cu-composition. The minimum and maximum values of electrical resistance measured using a four-point probe were observed on the Co₂₄Cu₇₆ and Co₄₆Cu₅₄ films, respectively, which confirmed that the electrical property of the films is a function of the film thickness and composition. The morphological and magnetic properties of all deposited films were clearly dependent on film composition. The AFM result confirmed the dependence of surface morphology and magnetic properties on the film composition because of the difference in the deposition rate between Co and Cu atoms during the sputtering process. The VSM results showed that all films had a ferromagnetic phase when the magnetic field was applied perpendicular to the film plane. All results confirmed that the desired morphological, electrical and magnetic properties of Co-Cu granular film can be achieved by manipulating its chemical composition.

Abstract: Indium oxide:tin nanoparticles were synthesized by co-precipitation method using InCl₃ and SnCl₄·5H₂O as starting precursor with different molar ratios of Sn:In. The crystalline structure, optical properties, chemical bonding and morphologies of all samples were characterized by X-ray diffraction (XRD), UV–vis spectrometer, Raman spectroscopy and field emission scanning electron microscope, respectively. The XRD results show that the crystallinity of as-synthesized powders was initially amorphous phase. After calcination at 400 °C for 2 h, a single phase ITO powder with 10% (mol%) SnO₂ was obtained. The particle size of each sample is approximately 20-25 nm. The color of indium oxide:tin nanopowders after heat treatment changed from white to yellow due to the substitution of oxygen vacancies in the sample. After calcination, the intensity of Raman peak significantly decreased with increasing amount of Sn loading. This phenomenon indicates that ion substitution may occur during the synthesis process. Moreover, it is noticed that the optical absorbance of obviously changed with increasing Sn loading.

Abstract: This study investigated the effect of polyethylene glycol (PEG), with high molecular weight of 1500 and 4000, on the formation of zinc oxide nanostructures synthesized by microwave radiation. Microwave heating was carried out at 2.45 GHz at 480 and 640 watts with 5s/15s on/off step time. The precursors used were Zn(NO₃)₂.6H₂O, NaOH and PEG. Microwave radiation generates heat to activate the formation of ZnO nanoparticles where the morphology can be controlled by the addition of PEG, time and heating power. The formation of wurtzite structure of ZnO was confirmed by X-ray diffraction. Morphology was investigated by a scanning electron microscope. PEG acted as a structure-directing agent or chelating agent resulting in the formation of rod-like and plate-like crystals. The average size of ZnO nanocrystals increased with increasing microwave power.

Abstract: A comparison of the properties for two ITO thin films was performed. The two films were as follows – as-deposited and annealed ITO films. The influence of annealing on the structural, morphological, electrical, and optical properties was studied. The post-annealing treatment was done at a temperature of 400 for 1 h in air. The ITO thin films were deposited onto glass substrates by RF magnetron sputtering of a ceramic In₂O₃: SnO₂ target in pure argon atmosphere at a low base pressure of <10^-6 mbar and a RF power of 50 W. The films were characterized by XRD, FTIR, contact angle measurements, FE-SEM combined with EDX, Hall-effect measurements and UV-Vis transmission spectroscopy. The ITO films showed a crystalline structure with a predominant orientation (400) and its intensity was increased after the film was annealed. The structure of the annealed film became reformed in more perfect columnar structure. The annealed film showed a decrease in contact angle and increase in FTIR spectra intensity. The annealing induced more tin incorporated into the film from 0.51 to 2.62 at%. The resistivity decreased from 2.7x10^-3 to 1.1x10^-3 Ω cm with increasing mobility from 7.5 to 27.5 cm² V^-1 s^-1 but decreasing carrier concentration from 3.0x10²⁰ to 2.0 x 10²⁰ cm^-3. The optical band gap increased from 3.43 to 3.50 eV. All films showed highly transparency (∼85%) in the visible light region. Compared with the non-annealed ITO film, the air-annealed ITO film revealed the better properties except for carrier concentration.

Abstract: The objective of this paper is an analysis of statistical discreteness and measurement capability of an eddy-current measurement system for residual stress assessment in stainless steel Grade 304 (SS304). Cylindrical specimens with 50 mm in diameter and 12 mm thickness were prepared to generate residual stress by Resistance Spot Welding at which the welding currents were set at 12, 14, and 16 kA. The eddy-current measurement system was including a probe with frequency range of 0.1 to 3 MHz and an eddy current flaw detector. They were performed by contacting the probe on the specimen. The measurements were performed particularly in the vicinity of heat affected zone (HAZ). In order to determine the results of the residual stress measurement, the calibration curves between static tensile stress and eddy current impedance at various frequencies were accomplished. The Measurement System Analysis (MSA) was utilized to evaluate the changed eddy-current probe impedance from residual stress. The results showed that using eddy current technique at 1 MHz for residual stress measurement was the most efficient. It can be achieved the Gauge Repeatability & Reproducibility %GR&R at 16.61479 and Number of Distinct Categories (NDC) at 8. As applied on actual butt welded joint, it could yield the uncertainty of ± 58 MPa at 95 % (U_ISO).

Abstract: Acoustic emission (AE) is a non-destructive technique which is well known for crack monitoring. Moreover, it has been widely used for corrosion and erosion damage on metallic structures. In this study, AE technique was applied for quick monitoring of corrosion resistance of lacquer coatings on tin free steel and laminated steel for food can-packaging. There were three types of coatings: (A) BPA-NI lacquer, (B) BPA-complied lacquer, and (C) PET lamination. These coatings were investigated in flat-sheet and in deformed sheet. Cathodic disbonding (CD) technique was carried out to cause separation between the coating and the metal substrate and initialize corrosion damage. AE signals was detected immediately with potential excitation, and showed good correlation with coating corrosion resistance during corrosion development. AE count signal matched with resulting current during CD, and proportional to corroded areas. In addition, coatings properties were measured before and after the CD process by electrochemical impedance spectroscopy (EIS). A combination of AE and CD techniques offers an in-situ non-destructive corrosion monitoring of coating quality before and during delamination development, and useful for can-packaging testing.

Abstract: This paper presents the determination of Remote Field Testing (RFT) frequencies to accomplish the inspection of duplex stainless steel tubes grade ASME/ASTM SA 789. The tube specimen was 25.4 mm of outside diameter, and thickness of 1.65 mm with the different artificial flaws. A dual-pickup coils type of RFT probe was employed to inspect the specimen by inserting a probe within the tube. Optimum of testing frequency Range was determined based on an eddy current through transmission generation to produce different magnetic field density. RFT inspection frequency range for duplex stainless steel was consequently determined from 5 to 25 kHz which was different than those inspection frequencies of general ferromagnetic steel tube. In the experiment, calculated frequencies were then generated to the Eddy current (ET) and RFT probes for detecting the flaws of the tube specimen. The inspection signals were specifically shown in function of impedance plane to identify the flaw characters. The results showed that the RFT can be utilized to quantify the wall loss levels of duplex stainless-steel tube better than the ET. Especially, phase angle of inspection signals can be used to evaluate the different depths of the wall losses. Sensitivity of RFT showed the detection performance at minimum 20% of tube wall loss.

Abstract: The objective of this paper is to study the different acoustic emission (AE) activities from material integrity and leakage which were obtained from CNG steel cylinder during pressurization. CNG type I cylinders were employed to test by hydrostatic stressing. The pressure was continuously increased to over 1.1 time of operating pressure or leakage occurrences. AE sensors, resonance frequency of 150 kHz, were mounted on the outside cylinder wall to detect the AE activities throughout the testing. AE activities were compared between AE of material expansion and leakage by amount of AE signals detected then analyzed by AE parameters. AE parameters including Amplitude, Count, Energy (MARSE), Duration and Rise time were analyzed to distinguish the AE data. The AE wave form in time and frequency domain were also considered in analysis process. The location of AE sources were located by the calculation the arriving differenced time of 2 or more sensors to indicate the position of cylinder faults. The results showed the AE signals of material expansion were randomly detected throughout the pressurization until the Enegy and Amplitude of detected signals were increased by high incresing rate where was leakage occurrences. AE parameters of Amplitude and Energy can be significantly represented the difference between material expansion and leakage. Addition, the Hit rate monitoring cloud be a notice activity before cylinder leaks. The benefits of this work are the AE characterization of the material expansion, leakage and noise for improvement of Type-1 CNG cylinder tests.