Gas Mixture Atmosphere Research Articles

Studies on Mechanical and Optical Characteristics of TiN Films Deposited on Al, Ti Buffer Layers

The TiN ceramic films were deposited on Si (100) substrates with Al and Ti buffer layers by direct current reactive magnetron sputtering in the mixture gas atmosphere of argon and nitrogen. X-ray diffraction (XRD), Raman spectroscopy, scanning electronic microscope (SEM), nanohardness test and ultra violet-visible-near infrared (UV-VIS-NIR) spectrophotometer were employed to analyze the structure, mechanics and optical characteristics of the TiN films respectively. Analyses of XRD and Raman showed that all the TiN films deposited on Al and Ti buffer layers with TiN (111)-preferred orientations had polycrystalline structures, and the TiN film deposited on Ti buffer layer had a better crystallinity, smaller surface roughness, higher hardness and larger elastic modulus than those of the TiN film deposited on Al buffer layer. Moreover, the reflectivity of the Ti/TiN film became higher than Al/TiN film above λ=645 nm. At λ=1200 nm, the Ti/TiN film showed the maximum reflectivity of 81.8%. These conclusions also showed that the metal multilayer TiN films have important application and research prospect in terms of solar control coatings or resistance to high temperature in building coating material.

Synthesis and characterization of low-friction Al-DLC films with high hardness and low stress

Al-diamond-like carbon films were successfully deposited by the reactive magnetron sputtering of Al target (>99.9%) in the argon and methane gas mixture atmosphere under selected substrate negative bias with high pulse cycle duty (50%). The microstructure, mechanical and tribological properties of the as-prepared Al-diamond-like carbon films were investigated. Results showed that these films were dominated by the typical amorphous structure, and the internal stress of films dramatically decreased while the hardness remained a high level (∼20 GPa) with increasing substrate pulse negative bias. Especially, the Al-diamond-like carbon film fabricated at substrate bias of −500 V displayed a longer wear life and lower friction coefficient due to both itself superior mechanical properties and the formation of continuous and compact graphitized transfer layer, making it a good candidate for solid lubricating film in engineering applications.

Effect of the bias voltage on the structure of nc-CrC/a-C:H coatings with high carbon content

Nanocomposite coatings consisting of a hard nanocrystalline carbide phase and a-C:H amorphous matrix are the focus of many investigations because of their mechanical and tribological properties such as high hardness, low friction coefficient and high resistance to wear. In this work, nanocomposite coatings of nanocrystalline chromium carbide embedded in an amorphous matrix (nc-CrC/a-C:H) were deposited onto silicon substrates by cathodic vacuum arc deposition using a Cr target in an Ar/C2H2 gas mixture atmosphere. A linear magnetic shield was employed to reduce the macroparticle content in the films. A range of negative bias voltages from 50 to 450V was applied to substrates during deposition. X-ray diffraction (XRD) analysis showed that amorphous or nanocrystalline thin films were formed in all cases. The hydrogen bonding in the material was studied by Fourier transform infrared spectroscopy (FTIR). X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and electron energy loss spectroscopy (EELS) were used to determine the carbon bonding and to study the presence of different forms of amorphous carbon. High resolution transmission electron microscopy (HRTEM) revealed a nanocomposite structure with chromium carbide nanocrystallites embedded in an amorphous hydrocarbon matrix. It was observed that the negative bias voltage significantly affected the carbon bonding and the hydrogen content.

Effects of bias voltage on structure and properties of TiAl‐doped a‐C:H films prepared by magnetron sputtering

AbstractHydrogenated TiAl‐doped a‐C:H films were deposited on Si substrates by middle frequency magnetron sputtering TiAl target in argon and methane gas mixture atmosphere. Effects of substrate bias voltage on structure and properties of the films, such as the surface morphology, hardness, chemical nature and bond types, were investigated by means of atomic force microscopy (AFM), XPS, Raman spectroscopy and nanoindentation. The friction and wear behaviors of the deposited films were characterized on an UMT‐2MT tribometer. SEM was utilized to analyze the wear scar on steel balls and debris after sliding on the deposited films under dry friction conditions. The results demonstrated that the film deposited at − 100 V exhibited low friction coefficient which is attributed to the easier formation of graphitized transfer layer. Copyright © 2010 John Wiley & Sons, Ltd.

Effects of Al incorporation on the mechanical and tribological properties of Ti-doped a-C:H films deposited by magnetron sputtering

Ti-and TiAl-doped a-C:H films were deposited on silicon substrates by magnetron sputtering Ti and TiAl target in argon and methane gas mixture atmosphere. To better elucidate the structural evolution after Al adding, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to comparatively analyze the structural transformation in the as-deposited films. Compared with Ti-doped a-C:H films, the introduction of Al enhanced carbon films graphitization effectively lowered the residual stress from 1.35 GPa to 0.65 GPa. Furthermore, though the hardness of TiAl-doped a-C:H films was moderately lowered, TiAl-doped a-C:H films exhibited higher toughness, lower friction coefficient and lower wear rate. The better tribological performances of TiAl-doped a-C:H films may originate from the formation of graphitized transfer layer during the friction test.

Effects of ambient pressure and gas mixture on a numerical model of subglottal acoustics and vowel spectra.

Divers’ speech in hyperbaric heliox environments becomes significantly distorted, making communication between divers and with surface-based personnel difficult. Previous research identified two basic mechanisms underlying this distortion. First, the speed of sound increases significantly in heliox, causing a linear increase in the second and higher formant frequencies. Second, in hyperbaric conditions the specific impedance of air in the vocal tract approaches that of the vocal tract walls, leading to a nonlinear increase in the first formant frequency. Effects of ambient pressure and gas mixture on subglottal acoustics and subglottal-vocal tract coupling in vowel spectra have not been sufficiently investigated. In this paper, such an investigation is carried out using a numerical model of subglottal and vowel acoustics. It is shown that subglottal resonance frequencies increase linearly as the speed of sound increases, and the corresponding subglottal pole-zero pairs in vowel spectra become disproportionately prominent as ambient pressure increases. Increased acoustic coupling between the subglottal system and the vocal tract in hyperbaric heliox therefore constitutes a third significant source of speech distortion. The results have implications for understanding subglottal coupling in vowels and for heliox speech unscrambling techniques. [This work was supported in part by NSF Grant No. 0905250.]

Microstructure and high-temperature corrosion behaviors of aluminide coatings by low-temperature pack aluminizing process

Aluminide coatings were produced on carbon steel and Fe–5Cr–Mo alloy at a relatively lower temperature below 600 °C in shorter treatment time by a combination of surface refinement process and pack aluminizing process. Repetitive ball impact, generated by mechanical vibration, caused the top-layer refinement of substrates in a conventional pack aluminizing process. The effects of temperature and treatment time on the formation of aluminide coatings were analyzed. The microstructure of the coatings was investigated by SEM, AFM and XRD. The aluminide coatings were one-layer, compacted structure with ultrafine grains and uniform elemental distribution. High-temperature oxidation and sulphidation tests were carried out at 600 °C in air for 200 h and 10% SO 2 + Ar gas mixture atmosphere for 50 h, respectively. The mass gains and spallation indicated that the aluminide coatings significantly improved the high-temperature oxidation and sulphidation resistance.

Influence of methane flow on the microstructure and properties of TiAl‐doped a‐C:H films deposited by middle frequency reactive magnetron sputtering

AbstractHydrogenated TiAl‐doped a‐C:H films were deposited on Si substrates by middle frequency magnetron sputtering TiAl target in argon and methane gas mixture atmosphere. The surface morphology, hardness, chemical nature and bond types of the films were characterized by means of atomic force microscopy (AFM), XPS, Raman spectroscopy and nanoindentation. The friction and wear behaviors of the deposited films were characterized on an UMT‐2MT test system. SEM was utilized to analyze the wear scar and debris on steel balls after sliding on the deposited films under dry friction conditions. The wear rate of the deposited films was calculated from traces of surface profiles taken across the wear track using an optical profile. The results demonstrated that the film deposited at 60 sccm methane flow exhibited higher hardness, as well as low friction coefficient and wear rate, which is attributed to the formation of a graphitized transfer layer. Copyright © 2009 John Wiley & Sons, Ltd.

Investigation of the ignition behaviour of the noble metal catalyzed catalytic partial oxidation of methane

Catalytic partial oxidation (CPO) of methane to hydrogen and carbon monoxide over Pt-Rh/Al2O3 and Pt/Al2O3 was studied in-situ with a new QEXAFS setup. The structural changes of the catalysts were investigated on the subsecond timescale during two reaction steps by recording both XANES and full EXAFS spectra: (1) heating and ignition in 6%CH4/3%O2/He, (2) periodic changes between the reaction gas mixture and H2 atmosphere. The results showed that the ignition occurred at lower temperatures for Pt-Rh/Al2O3 while it was completed in a significant shorter time interval for Pt/Al2O3. Some structural changes during the heating phase were detectable before the reaction ignited, especially for Pt/Al2O3, as reflected by the performed principle component analysis. However, a closer analysis of the FT-QEXAFS data did not evidence a defined intermediate. In addition, the composition of the gas atmosphere was altered between hydrogen and the reaction mixture, enabling modulation excitation spectroscopy. This technique was for the first time applied to QEXAFS data and resulted in significantly enhanced data quality.

Mechanical property of lotus-type porous carbon steel fabricated by continuous casting method

Lotus-type porous carbon steel (AISI1018) with aligned cylindrical pores was fabricated by continuous casting method in a mixture gas atmosphere (PN2=0.8MPa, PAr=1.7MPa). Compressive yield strength of the nonporous and the lotus carbon steels was measured in the direction parallel to the transference direction. The compressive stress of the lotus carbon steel is lower than that of the nonporous carbon steel because of the existence of pores. The specific compressive yield strength (σ0.2/ρ) of as-cast lotus carbon steel is higher than that of as-cast nonporous carbon steel, which is due to the solid solution hardening of nitrogen. Although the microstructure of carbon steel changes from Widmannstätten to homogeneous ferrite and pearlite by normalizing, the yield strength does not change significantly by normalizing. The microstructure of lotus carbon steel changes from Widmannstätten to martensite by quenching so that the yield strength increases significantly.

Nitrogen incorporation into titanium diboride films deposited by dc magnetron sputtering: Structural modifications

This work reports a study of titanium boron nitride (Ti–B–N) films deposited at room temperature by dc magnetron sputtering using a TiB 2 target in different Ar–N 2 gas mixture atmospheres. The influence of the nitrogen partial pressure on the structural, mechanical and tribological properties of these films has been studied. The films were analyzed by Rutherford backscattering spectrometry in order to determine their chemical composition and atomic density. X-ray diffraction (XRD) was used to probe the film microstructure and X-ray photoelectron spectroscopy (XPS) for the chemical characterization of the film surface. An atomic force microscope (AFM) was used to analyze the surface topography and, when operating in the lateral force mode, for the friction characterization of the films. The XPS results showed that the surface of the films deposited in pure argon atmosphere was composed essentially by Ti and B oxides, while TiB 2, TiB, TiN and BN phases were present in the sputtered Ti–B–N films. Characterization by XRD determined the nanocrystalline nature of the films structure. While internal stress and friction increase upon the nitrogen incorporation, AFM measurements reveal a strong reduction of the surface roughness.

Optical, electrical and structural properties of indium-doped cadmium oxide films obtained by the sol–gel technique

Indium-doped cadmium oxide films were obtained by mixing cadmium oxide and indium oxide precursor solutions by the sol–gel technique. The indium atomic concentrations in solution ( x) studied were 0, 2, 5 and 10 at%. The films were sintered at two different sintering temperatures ( T s) 350 and 450 °C, and after that annealed in a 96:4 N 2/H 2 gas mixture atmosphere at 350 °C. X-ray diffraction patterns showed that all films sintered at T s=350 °C only consisted of cadmium oxide crystals. The films sintered at T s=450 °C consisted of cadmium oxide crystals also; however, for the highest indium atomic concentration (10 at%) the formation of cadmium indate oxide crystals was evident. All films show high optical transmission (>85%) and an increase of the direct band gap value from 2.4 to 3.1 eV, as the indium atomic concentration in solution increases. The minimum resistivity value obtained was 6.3×10 −4 Ω cm for the films with x=5 at%, T s=450 °C and annealed at 350 °C.

Phosphorus-doped ZnO films grown nitrogen ambience by magnetron sputtering on sapphire substrates

We grew phosphorus-doped ZnO films at various temperatures on a sapphire substrate by magnetron sputtering to obtain a p-type ZnO film. The ZnO film grown under the ambient gas mixture of nitrogen and argon showed p-type behavior at a higher growth temperature. The electron concentration and mobility of the as-deposited p-type ZnO were 1.2×10 17 cm −3 and 25 cm 2/V s, respectively. The peak shift of X-ray diffraction and the strong acceptor-bound exciton peak of photoluminescence indicated that the incorporation of phosphorus was enhanced with increasing growth temperature.

Heating Temperature Effect on the Magnetic Property of α-Fe Nanoparticle

The effect of heating temperature on the magnetic property of α-Fe nanoparticle produced by thermal decomposition method has been investigated. The Fe2+-oleate2 ligand complex was annealed at 400°C in pyrex tube under 10−2 torr for 2 hrs, and then reduced at a different temperatures under Ar + 4% H2 mixture gas atmosphere. The magnetic property of α-Fe nanocrystallite was affected with the different heating temperatures. The structure and properties of prepared α-Fe nanoparticle was characterized by TGA, XRD, TEM, and VSM.

Annealing effect on structural, morphological, and optical properties of reactive sputtered WO3 films for mediated heterogeneous photocatalyst

The reactive facing-target sputtering method was used to deposit WO3 thin films from a metal tungsten disk in an Ar+O2 mixture gas atmosphere at different sputtering pressures. X-ray diffraction, scanning electron microscopy (SEM), UV-visible spectrophotometer, and Raman studies were performed to study structural, surface morphology, and optical properties of the as-deposited and annealed samples. Annealing treatments were done in oxygen atmospheres. All the as-deposited films were amorphous in structure. The films annealed at 400°C and deposited at 200W show preferential orientation. SEM images show nanorodlike growth for the films deposited at a sputtering pressure of 0.15Pa and annealed at 400°C. The optical absorption edge of the as-deposited films prepared at the sputtering pressures of 0.8–0.15Pa varied between 340 and 380nm and shifted up to 480nm when the samples were annealed at 400°C. From Raman spectra, we observed the O–W6+–O bonds, and the W6+O stretching mode of terminal atoms on the surface of WO3 microcrystalline grains. The crystal structures of the annealed films were of monoclinic phase. The suitability of the films for the WO3∕TiO2 heterogeneous photocatalyst are analyzed and discussed.

Reaction between laser ablation plume and ambient gas studied by laser-induced fluorescence imaging spectroscopy

We visualized the density distributions of C2 (plume), NO (ambient gas), and CN (reaction product) when a graphite target was ablated by irradiating YAG laser pulses at wavelengths of 1064 and 355 nm in ambient gas mixture of NO and He. It has been shown by the density distributions of C2 and NO that the expansion of the plume removes the ambient gas and the plume and the ambient gas locate exclusively in both the cases at 1064 and 355 nm. A high CN density was observed at the interface between the plume and the ambient gas at 1064 nm, which is reasonable since chemical reactions between the plume and the ambient gas may occur only at their interface. On the other hand, in the case at 355 nm, we observed considerable CN inside the plume, indicating that the chemical reaction processes in the laser ablation at 355 nm is different from that expected from the density distributions of the plume and the ambient gas.

Synthesis of Nanosized α-Fe and Enhancement of Magnetic Property

α-Fe magnetic nanoparticle was synthesized by using solventless thermal decomposition method. [1] It resulted in higher saturation magnetization (M s ) almost comparable to that of bulk Fe power (M bulk =210 emu/g). To prepare α-Fe nanoparticles, the Fe 2+ -oleate 2 ligand complex was annealed at 400 °C in pyrex tube under 0,3 torr for 2 hrs and reduced to α-Fe crystal structure at 700 °C with sodium chloride under Ar + 5% H 2 mixture gas atmosphere. [2] The crystallinity and structure of α-Fe nanoparticle was investigated by X-ray diffraction (XRD). The shape and size were confirmed by transmission electron microscope (TEM) images. The magnetic properties were characterized with saturation magnetization (M s ) from hysteresis loop by vibration sample magnetometer (VSM).

The influence of hydrogen gas in the ambient gas mixture on the properties of indium tin oxide films deposited on glass and acrylic substrates by dc magnetron sputtering

In this paper we report the results of our studies on the influence of adding hydrogen to the ambient gas mixture of argon and oxygen on the properties of indium tin oxide films deposited by the dc magnetron sputtering method. The substrates used are glass and acrylic. The hydrogen flow rate has been varied keeping other deposition parameters fixed. The electrical, optical, structural and morphological properties are studied. The sheet resistance is seen to attain a minimum at a certain flow rate of hydrogen while it increases at both lower and higher flow rates. The transmission characteristics attain a maximum at the highest hydrogen gas flow rate. X-ray analysis reveals a crystalline nature with peaks at the (222), (440) and (431) directions. Glass substrates show an additional peak at (541). SEM studies show a cluster of grains and in the case of glass a more regular pattern is observed.

Laser-induced ablation of a steel sample in different ambient gases by use of collinear multiple laser pulses

The sensitivity of laser-induced breakdown spectroscopy of solid samples depends on the number of ablated and excited analytes. Laser ablation of solid samples can be enhanced by using collinear multiple laser pulses, for example double or triple pulses, rather than single laser pulses with the same total laser pulse energy. The ablation rates and the plasma conditions are affected by the ambient gas. In this study laser ablation was examined by varying the interpulse separation of the multiple pulses, within double and triple-pulse bursts, and the gas mass density at constant gas pressure. Different ambient gases and gas mixtures consisting of argon, oxygen, and nitrogen were used to study their effect on ablation rates. In a pure argon atmosphere (99.999% v/v Ar) the ablation burst number required to penetrate a steel plate of thickness 100 microm is reduced by a factor of approximately six by use of triple-pulse bursts with a symmetric interpulse separation of 15 micros rather than single pulses with the same total burst energy of 105 mJ. For double and single pulses the factors are 1.6 for Ar and 2.8 for synthetic air. Analyte lines are 4 to 8 times more intense if an argon atmosphere, rather than air, is used.

Effects of oxygen partial pressure during sputtering growth on physical properties of Zn 0.93Mn 0.07O thin films

We have studied structural, optical, electrical, and magnetic properties of Zn 0.93Mn 0.07O thin films grown by RF magnetron sputtering under ambient gas mixtures of O 2 and Ar. As the oxygen partial pressure increases, the electron concentration systematically decreases and photoluminescence peaks related to oxygen vacancies gradually diminish. These results suggest that oxygen vacancies are majority donors. Smooth surface morphology and electron concentration as low as ∼10 15 cm −3 are obtained simultaneously for the film grown in an optimal oxygen partial pressure. This film exhibits ferromagnetism with the Curie temperature of 78 K, while other films grown in higher or lower oxygen partial pressure show paramagnetic behavior down to low temperature. The disappearance of the ferromagnetism can be explained in terms of crystalline quality and surface smoothness rather than electron concentration.