Fu-Hsing Lu

XPS analyses of TiN films on Cu substrates after annealing in the controlled atmosphere

Abstract X-ray photoelectron spectroscopy (XPS) has been used to investigate the thermal annealing of TiN films in the controlled atmosphere. The films were prepared by a cathodic arc plasma deposition technique on Cu substrates. The flowing gases used in the annealing are air, N 2 , Ar, and CO 2 /N 2 /H 2 gas mixtures, which possess extremely different nitrogen and oxygen partial pressures. Annealing the samples in air at 300, 400, and 500°C causes the gradual transformation from amorphous TiO 2 to crystalline TiO 2 on the TiN surface. Annealing in N 2 and Ar at slightly different temperatures results in various adsorbed nitrogen states. After annealing in CO 2 /N 2 /H 2 =10:81:9 and N 2 /H 2 =9 gas mixtures from 400°C to 700°C, the relative intensity of crystalline TiO 2 increases with temperature and that of titanium oxynitride decreases. The adsorbed nitrogen associated with the oxidation of TiN is discussed. The TiN oxidation chemistry under these controlled oxygen and nitrogen partial pressures is also discussed.

Phase changes of CrN films annealed at high temperature under controlled atmosphere

Abstract CrN films were deposited onto (100) Si wafers by cathodic arc plasma deposition. After that, the films were annealed between 400 and 1200°C for 2 h in air, N 2 , and N 2 /H 2 =9, which possess dramatically different P n 2 and P o 2 . XRD results showed that oxidation of CrN films occurred above 700°C in all gases but the relative amount of the resultant oxide Cr 2 O 3 decreased with rising ( P n 2 / P o 2 ) ratio in the gases for a given temperature. The driving force for oxidation of the nitride is the Gibbs free energy changes in the oxidation reaction. Meanwhile, the β-Cr 2 N phase appeared at 500°C, diminished at 700°C, and showed up again at 1100°C under all atmospheres. The reason for the presence of β-Cr 2 N at temperatures above 1100°C is that Cr 2 N is thermodynamically more stable than CrN in the high temperature range, as analyzed from thermodynamics. The phase transforming from CrN to Cr 2 N in the low temperature range is possibly due to the large stress relaxation occurring in the film during annealing, as observed in the in situ stress measurements.

Oxidation behavior of titanium nitride films

The oxidation behavior of titanium nitride (TiN) films has been investigated by using x-ray diffraction, Raman scattering spectroscopy, and field emission scanning electron microscopy. TiN films were deposited onto Si substrates by using cathodic arc plasma deposition technique. After that, the films were annealed in the air at 500–800 °C for 2 h. The x-ray diffraction spectra showed that rutile–TiO2 appeared above 600 °C. The relative intensity of TiO2 rapidly increased with temperatures. Only rutile–TiO2 was detected above 700 °C. Raman scattering spectra indicated the presence of rutile–TiO2 signals above 500 °C. Meanwhile an additional Si peak appeared at 700 °C in Raman spectra, above which only Si peak appeared. Many nano pores were found on the surface of films annealed at temperatures between 600 and 700 °C in field emission scanning electron microscopy, while the granular structure existed at 800 °C. The as-deposited TiN films had an apparent columnar structure. The thin and dense oxide overlayer...

Eutectic reaction between copper oxide and titanium dioxide

Abstract Eutectic reaction between copper oxide (CuO) and titanium dioxide (TiO2) was investigated by using directly Cu and TiO2 samples and by employing optical microscopy, X-ray diffraction (XRD), scanning electron microscopy, and electron probe for microanalysis (EPMA). Different types of samples including Cu plate/TiO2 pellet samples and TiO2/Cu/TiO2 sandwiched samples were prepared. The samples would react with each other at as considerably low as about 900°C in air, which is due to a eutectic reaction. The reaction diagram was generated, in which different reaction categories were denoted at various temperatures (300–1070°C) and times. After annealing, the weight changes normalized to the original Cu samples were also analyzed to verify the eutectic reaction. The eutectic was identified to be the CuO–TiO2 system characterized from XRD and EPMA analyses. Annealing in N2/O2=9 at the same temperature as in air resulted in similar but not so drastic eutectic melting phenomena. The eutectic reaction would enhance significantly the grain growth of TiO2 and the oxidation of Cu. The changes in the microstructures and the morphologies of the samples were also investigated. The eutectic temperatures of CuO and other oxide systems were compared and discussed. The eutectic points as well as the phase diagram of the CuO–TiO2 system were calculated and analyzed. Several potential applications of the reactions were also proposed.

Characterization of titanium nitride films deposited by cathodic arc plasma technique on copper substrates

Abstract TiN films were deposited directly on Cu substrates by a cathodic arc plasma deposition technique. The films were then characterized by X-ray diffraction (XRD), grazing incidence X-ray diffraction (GID), (TEM), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The preferred orientation of the film changed from (200) to (111) with increasing film thickness. Analyses of both the XRD and GID results showed that in the highly (111) textured grains, the (111) plane was approximately parallel to the film surface, while in the (200) textured grains, the (200) plane was tilted away from the film surface. Small-elongated crystallites with a large aspect ratio and textured grains were found on the TiN surface. AES, which was employed to examine the concentration depth profile, showed no apparent interdiffusion between Cu and TiN during the growth of the film. XPS results showed that amorphous TiO 2 , as well as titanium oxynitride, was present on the TiN surface. The spectra of Ti-2p, N-1s, O-1s and Cu-2p before and after the film being sputter etched through the entire film region were also discussed.

Corrosion resistance of BaTiO3 films prepared by plasma electrolytic oxidation

Abstract Barium titanate films were directly synthesized on Ti plates by plasma electrolytic oxidation in highly alkaline solutions using Ba(CH 3 COO) 2 and NaOH as the electrolyte. SEM and X-ray diffraction results showed that crater-shaped and large-grained cubic BaTiO 3 films near 10 μm thick were formed at an anodic voltage of 90 V for 55 °C. The corrosion behavior of the films was studied by means of open-circuit potential measurements and potentiodynamic polarization in the 0.1 M NaOH corrosive environment. Anodized TiO 2 films and pure titanium specimens were also investigated for comparison. Open-circuit potential measurements showed that BaTiO 3 and TiO 2 films exhibited quite stable corrosion potential of approximately 0.02 V (vs. Ag/AgCl). This corrosion potential is very close to the open-circuit potential of the cathode and therefore the electrochemical reaction is anodically controlled. The shift of open-circuit potential of BaTiO 3 and TiO 2 films toward positive values represents the increased anodic polarization resistance and reduced corrosion current, which is consistent with the mixed potential theory. From potentiodynamic polarization results, the high polarization resistance of BaTiO 3 films suggested that the anodic current may be due to the O 2 evolution on the exposed Ti surface by transporting OH − ion through open pores of the oxide to react on the titanium surface. The obtained thick oxide layers of BaTiO 3 films could close up the pores in the films and hinder the transportation of OH − ions. Hence the BaTiO 3 films possess better corrosion resistance than TiO 2 and pure Ti specimens.

Corrosion and tribological studies of chromium nitride coated on steel with an interlayer of electroplated chromium

Abstract The electrochemical and tribological behavior of CrN coatings on steel are investigated. A single layer of chromium nitride coating is compared with a double layer of the coating (CrN/Cr/steel) in which the interlayer chromium was produced by electroplating with the aim of improving the corrosion and tribological performance of the steel. The CrN coatings are deposited by using a reactive cathodic arc plasma deposition technology in an industrial scale, while the interlayer of chromium produced by electroplating. The coating assemblies have been compared in terms of hardness, wear and corrosion resistance. The composition and structure of the chromium nitride have been studied by X-ray diffraction (XRD), using both θ/2θ diffraction mode and the glancing-incidence X-ray diffraction mode. The surface morphology was examined by using SEM. The improvement in wear and corrosion resistance after cathodic arc plasma deposition with and without a hard chrome as an interlayer are discussed in considering the microstructure changes.

Point defects and cation tracer diffusion in (Co, Fe, Mn)3−δO4 spinels: II. Mixed spinels (CoxFezMn2z)3−δO4

Abstract This is the second paper reporting results of systematic studies of the nonstoichiometry and the cation tracer diffusion in quaternary oxide spinels comprised of Co, Fe, and Mn cations. In the first paper, point defects and cation tracer diffusion were discussed for compositions of the type (CoxFe2yMny)3−δO4 (x + 3y = 1). In this study, compositions of the type (CoxFezMn2z)3−δO4 (x + 3z = 1) are considered. The deviation from stoichiometry, δ, has been measured at 1200°C as a function of oxygen activity, aO2, and cationic composition by thermogravimetric measurements. The obtained δ versus log10aO2 curves are basically S-shaped for all cationic compositions investigated. This suggests that two types of point defects, cation vacancies and cation interstitials, are present as majority point defects. Cation tracer diffusion in these spinels has been investigated at 1200°C as a function of oxygen activity and cationic composition by simultaneously using radioactive isotopes, 60Co, 59Fe and 54Mn. Cation tracer diffusion coefficients as a function of oxygen activity in general show a minimum indicating that two types of point defects, cation vacancies and cation interstitials, contribute to the cation tracer diffusion.

The effect of Cr interlayer on the microstructure of CrN coatings on steel

The effect of electroplated Cr interlayer on the microstructure of CrN coatings on AISI 4140 steel were investigated. Two types of CrN-coated specimens by cathodic arc plasmas were prepared with and without an intermediate layer deposited by electroplated hard chrome (CrN/steel and CrN/Cr/steel). The microstructure and crystallinity of chromium nitride have been investigated using X-ray diffraction (XRD), cross-sectional transmission electron microscopy (XTEM) and selected area diffraction (SAD). Both CrN/steel and CrN/Cr/steel coating assemblies exhibit microcolumnar morphologies. However, it is noted that the columnar structure of CrN coating directly on steel is less evident, strong, and upward in comparison with that deposited on electroplated chromium layer. For CrN/Cr/steel assembly, the preferred orientations of CrN(220) and Cr(200) are observed.

Degradation of ZrN films at high temperature under controlled atmosphere

The degradation of CrN films was investigated over temperatures of 400–1200 °C in air, nitrogen, and forming gas (N2/H2=9) by analyzing changes in color and appearance, as well as microstructures. The degradation mainly included color changes and cracks occurring on the film surface. The color change resulting from low-temperature/short-time annealing was due to the formation of an additional Cr2N phase, as well as a thin oxide overlayer. The color change appearing at higher temperatures/longer times stemmed from the formation of a thicker Cr2O3 layer, whose content depended on the pN2/pO2 ratio in the atmosphere. The driving force of the oxidation was the Gibbs free-energy change for CrN and Cr2O3. Cracks that showed up at relatively high temperatures were attributed to the large thermal mismatch between the CrN film and Cr2O3 overlayer. The thermal stresses were calculated and discussed. The degradation diagrams were generated based on the above analyzed results.