ICMCTF2016 Session F4-2: Functional Oxide and Oxynitride Coatings

Wednesday, April 27, 2016 2:10 PM in Room Royal Palm 1-3

Wednesday Afternoon

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2:10 PM F4-2-3 Plasma Electrolytic Fabrication of Dielectric Surface Layers for Insulated Metal Substrates
Noratiqah Yaakop, Aleksey Yerokhin, Allan Matthews (University of Sheffield, UK)
Insulated metal substrates produced by direct conversion of metal surface into thin dense dielectric layer are of great interest in modern power electronic devices. The main trend for miniaturisation of such devices imposes a challenging combination of requirements to the insulating layer, including low thickness along with high thermal conductivity, dielectric, adhesion strengths and operating temperatures. This is often unattainable using conventional surface engineering techniques, such as anodising, sol-gel, sprayed and PVD coatings. In this work, we explore the potential of plasma-assisted electrolytic treatments of Al substrates to form thin yet compact dielectric surface layers with nanocrystalline structure to ensure the required set of properties. Effects of treatment time and electrolyte composition on thickness, porosity, phase composition, thermal, dielectric and physical properties of oxide ceramic surface layers produced by Plasma Electrolytic Oxidation of Al 6082 alloy are studied. Coating thickness was evaluated by both eddy current gauge and cross-sectional SEM analysis, whereas the surface plane SEM images were used to study porosity. The distribution of alpha and gamma alumina phases in the surface layer was evaluated from the analysis of XRD patterns obtained at various glancing angles. The coating thermal conductivity on the composites was measured by Laser Flash method. Processing conditions corresponding to optimum combination of surface properties are identified.
2:30 PM F4-2-4 On the Intrinsic Wettability of Rare Earth Oxide Ceramics
Haitao Liu (University of Pittsburgh, USA)
Many applications require materials that are both intrinsically hydrophobic and robust to harsh chemical environments. The current technology in hydrophobic coating is limited to organic materials that are easily degraded. Recently, it was suggested

that rare-earth oxides are intrinsically hydrophobic because their electronic structure prohibits their bonding with water on the surface. Here we show that rare-earth oxide ceramics are intrinsically hydrophilic. The previously reportedhydrophobic behavior are likely due to airborne hydrocarbon contamination. Our results highlights the significant impact of environment on the wettability of oxide coating materials.

2:50 PM F4-2-5 Structural and Optical Properties of BixNbyOz Films Deposited by Co-sputtering
Osmary Depablos-Rivera (Instituto de Investigaciones en Materiales - UNAM, Mexico City, Mexico; Posgrado en CIencia e Ingeniería de Materiales - UNAM, Mexico City, Mexico); Sandra Rodil (Instituto de Investigaciones en Materiales - UNAM, Mexico City, Mexico)

Different phases of the Bi2O3 – Nb2O5 pseudo-binary system have been reported with niobium oxide molar percentages up to 50%. These materials show optical and electrical properties interesting for applications such as solid electrolytes, photocatalysts and high-k dielectrics. They are commonly produced by solid state reaction varying the proportion of the binary oxides in the mixtures. Less works have reported their synthesis as thin films, particularly magnetron sputtering have been used with a single target having fixed composition. We proposed the synthesis of Bi-Nb-O phases by co-sputtering, starting from Bi2O3 and Nb targets. In this way, it could be possible to vary the composition into a wider range than the solid state reactions.

The aim is to correlate the structural and optical properties with the deposition conditions. The radio-frequency power applied to the Bi2O3 target was fixed at 30 W, while the DC power of the Nb target was varied; 20, 30, 50, 70, 100 and 150W. The films preparation was done under a reactive atmosphere of Ar:O2 (16sccm:4sccm) and the substrates were silicon (100) and glass, heated at 150°C for 30 min before the deposition. The films structure was characterized by X-ray diffraction and Raman spectroscopy, and the morphology and composition were studied by scanning electronic microscopy and energy dispersion spectroscopy, respectively. The films resulted crystalline when the Nb target power was up to 50 W, above this value the films were amorphous. Also, the amorphous films were annealed at 600°C in air during 2 h, leading to structural changes showing Nb rich phases. Five crystalline structure have already being identified; BiNbO solid solution, Bi3NbO7, Bi5Nb3O15, BiNbO4 and Bi8Nb18O57. The optical properties were obtained by UV-visible transmittance and reflectance spectroscopy observing that the band gap ranges between 2.7 to 3.3 eV depending on the composition and structure.

Acknowledgments: The research leading to these results has received funding from the BisNano project (125141) and the PHOCSCLEEN project (318977). ODR thanks to CONACYT for the PhD scholarship.
3:10 PM F4-2-6 HiPIMS Plasma Diagnostic and Low Temperature Deposition of Photo-active Titania Thin Films in an Industrial-scale Rig
Brice Delfour-Peyrethon, Glen West, Peter Kelly, Marina Ratova (Manchester Metropolitan University, UK)

In the field of PVD techniques, the High Power Impulse Magnetron Sputtering (HiPIMS) process [1] is one of the newest and most promising development for low temperature depositions. Its understanding is still intensely investigated and reported in numerous articles and reviews every year [3]. Indeed, a better knowledge of the processes occurring within the plasma with precision is fundamental for its use to be effective during thin films depositions.

The study of the process is more complex than Direct Current Magnetron Sputtering (DCMS) and mid-frequency pulsed magnetron sputtering - due to a longer list of parameters and phenomena occurring - and need to be conducted with caution [2]. In particular, for the case of reactive sputtering: it has been demonstrated several times that the reactive gas has a huge impact on the plasma behaviour. It is also a very sensitive process. The hysteresis behaviour widely described in the literature [4] [5] implies that the reactive gas content should be regulated with precision along time during the deposition duration to keep the plasma stoichiometry constant. To do so, the Speedflo™ gas controller for HiPIMS systems [4] has been used for the work presented here. This gas flow controller measures the optical signal emitted by the energetic species of the plasma and regulates the reactive gas flux in order to keep the stoichiometry to a chosen value. The effectiveness of the device has been confirmed and used to conduct a more precise study on the influence of the oxygen content while sputtering a titanium target.

Ti and Ti-O discharges have been analysed in terms of deposition rates, thermal load at the substrate position and pulse shapes modifications while varying the whole range of conditions: pressure, voltage, pulse width, frequency and oxygen content. A stable process envelope has been determined for the rig used in this study. Within this envelope, each parameter’s influence has been studied and understood for both metallic and stoichiometric discharges. The consequences of these variations have then been observed for film growth processes. Several analysis techniques have been used (SEM, EDX, Raman, XRD, etc…) to determine which conditions resulted in a crystalline growth of the deposited film. Photocatalytic tests and contact angle measurements have also been conducted, to confirm the deposition conditions corresponding to the production of the most effective film in terms of photo-reactivity for dye degradation and hydrophilicity.
3:30 PM F4-2-7 Phase Stability of Oxide Overgrowths on Metals, Alloys and Metallic Coatings
Lars Jeurgens (Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland)

Engineering of functional oxide films and oxide-based coating systems requires comprehensive knowledge of the microstructure-property relationships of the developing oxide phases that form during synthesis and subsequent long-term operation. Namely, depending on the growth method (e.g. PVD, CVD, anodization, thermal oxidation) and the growth conditions, different single- or hetero-phase oxide phases with variable compositions and (defect) structures may form by competing nucleation and growth. Evidently, the applicability of synthesized oxide microstructures ultimately depend on their durability (i.e. the thermal, chemical and mechanical stability) during long-term operation in harsh environments (e.g. at high temperatures, in reactive liquids or gasses, during thermal cycling).

This talk will address advanced thermodynamic and kinetic model descriptions of oxide nucleation and growth on pure metals, alloys and their coating systems, while accounting for the crucial roles of free surfaces, internal interfaces and the relative mobilities of the reactant species on oxide phase stability [1-3]. As an example, model predictions on the thermodynamic stability of amorphous and metastable crystalline Al2O3 thin films (< 10 nm) on Al metal are compared with experiments [1]. Furthermore, a coupled thermodynamic–kinetic modelling approach for the high temperature oxidation of a (Ni,Co)CrAlY bondcoat at 1373 K is presented, which computes composition–depth profiles in the alloy, as well as the amount of each oxide phase developed as a function of oxidation time, including the formation of multiple oxide phases during the initial stage of fast oxidation [2]. Finally, the superior corrosion behaviour of pre-oxidized amorphous Al1-xZrx coating systems is highlighted, which from detailed experimental observations and thermodynamic assessments can be attributed to the thermodynamically-preferred formation of a structurally and chemically uniform amorphous (Al0.33Zr0.67)O1.83 overlayer [3].


[1] L.P.H. Jeurgens, W.G. Sloof, F.D. Tichelaar, E.J. Mittemeijer, Phys Rev B 62 (2000) 4707.

[2] T.J. Nijdam, L.P.H. Jeurgens, W.G. Sloof, Acta Materialia 53 (2005) 1643-1653

[3] K. Weller, Z.M. Wang, L.P.H. Jeurgens, E.J. Mittemeijer, Acta Materialia 94 (2015) 134.
4:10 PM F4-2-9 Characterization of Zinc Oxide Films Deposited in Helium-oxygen and Argon-helium-oxygen Atmospheres by Sputtering
Kartik Patel, Sushant Rawal (Chandubhai S. Patel Institute of Technology (CSPIT), Charotar University of Science and Technology (CHARUSAT), India)

Zinc oxide (ZnO) thin films were deposited onto glass substrates by radio frequency (RF) magnetron sputtering using a metallic zinc target. Zinc oxide films were prepared in two different gas atmospheres; in the first set helium and oxygen gas flow ratio (He:O2) was varied from 87.5% to 37.5%. In the second set of experiment, oxygen flow rate was kept constant at 2.5sccm while argon and helium gas flow ratio (Ar:He) was varied from 9.0% to 87.5%. The structural, wettability and optical properties of ZnO films were investigated by X-ray diffractometry (XRD), contact angle measuring system and UV-Vis-NIR spectrophotometer. The XRD results shows increased preferred orientation along (002) plane for deposited ZnO films in both cases. The average crystallite size of ZnO films increases with increase in the gas ratio for both set of experiments. The deposited films are hydrophobic by nature for water and ethylene glycol. Optical transmittances greater than 80% were observed in the wavelength interval from 450 nm to 650 nm for both cases.

4:30 PM F4-2-10 Growth of Fe-doped ZnO Film by E-beam Evaporation from Self-made Target Source
Ya-Chih Cheng (National Cheng Kung University, Taiwan, Republic of China); Sean Wu (Tung-Fang Design University, Taiwan, Republic of China); Jow-Lay Huang (National Cheng Kung University, Taiwan, Republic of China); Ding-Fwu Lii (Cheng Shiu University, Taiwan, Republic of China); Wen-Kuan Yeh (National Nano Device Laboratories, Taiwan, Republic of China)

Zinc oxide (ZnO) is a very wide-spread used material for surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices because of its excellent performance in piezoelectricity. Many researches have done by others in order to increase the piezoelectric coefficient (d33) of ZnO by doping tiny amount of different elements, such as Vanadium (V), Chromium (Cr), Iron (Fe) by magnetron sputtering method. In our research, we chose Fe as a doping element out of consideration that V is too expensive for massive production and Cr holds human health and environmental concern. The smaller ions substitute Zn sites make the piezo effect respond greater while the dopant ions bigger than Zn do the opposite. This guide us that Fe3+ is smaller than Zn2+ and will exhibit a better properties compared with undoped ZnO films.

Among three formula types of iron oxide, Fe2O3 is the most stable one and is cheap enough to make it a candidate in this research. For a process costs reduction method, we use self-made target source from ceramics powder (ZnO and 0.6mole% Fe2O3, target tablet is made under calcined 600℃-900℃ for 3hr, sintered 1100℃ for 4hr). Iron oxideis selected to add into ZnO powder as Fe contributor better than Iron metal because Iron for most use is magnetic and it brings difficulty when the magnetron sputtering is carrying out. Therefore, we use e-beam evaporation method to deposit Fe-doped ZnO films on silicon substrate.

The X-ray diffraction results of powder mixture show a shift to higher angle and then shift to lower angle as the calcination temperature increase. The XRD results of the Fe-doped ZnO thin films are high c-axis orientated. The valence of Fe in ZnO was confirmed by XPS and the results reveal a correlation to the XRD results. The cross-section SEM image shows that the Fe-doped ZnO films are highly aligned columns with the c-axis perpendicular to the substrate.

4:50 PM F4-2-11 Ultraviolet Photodetectors Based on MgZnO Thin Film Grown by RF Magnetron Sputtering
Jr-Shiang Shiau, Chuan-Pu Liu, Jow-Lay Huang (National Cheng Kung University, Taiwan, Republic of China)

Ultraviolet (UV) photodetection has been widely applied in various commercial and military purposes. To this end, ZnO has been regarded as one of the most promising candidates for UV photodetectors because of its wide band-gap energy (~3.3eV). Moreover, low cost in raw materials and fabrication makes ZnO even more appealing for commercialization compared with others semiconductor counterparts. To further extend the detection region from near UV to deep UV, MgxZn1-xO ternary compound by incorporating Mg into ZnO is considered, where the fundamental band gap energy can be increased proportionally from 3.3 up to 7.7 eV.

In this research, high quality MgxZn1-xO thin films with strong c-axis preferred orientations are grown on p-type Si(111) by magnetron sputtering using ZnO and Mg0.3Zn0.7O as targets. In this setup, we show that Mg content of MgxZn1-xO alloys can still be varied in a large range by changing substrate temperature from 25°C to 250°C . The crystallinity and crystal orientation of the thin films are analyzed by x-ray diffraction, revealing that phase transformation takes place from hexagonal to cubic phase when substrate temperature is above 150°C. The surface morphology and microstructure are examined by using scanning electron microscopy. Accordingly, the absorption edge exhibits a blue shift from 380nm to 280nm measured by UV–vis–IR spectrophotometry. The piezo-phototronic effect is applied to boost the optoelectronic performance of devices by modulating charge-carriers generation, separation and transport. Finally, preliminary results on UV detectors based on selective MgZnO thin films are reported and discussed.

5:10 PM F4-2-12 Wastewater Remediation Using Titanium Dioxide-Graphene Composite Material
Chanbasha Basheer (King Fahd University of Petroleum and Minerals, Saudi Arabia)

Since conventional wastewater treatment plants (WWTPs) effects only partial removal of alkylphenols, advanced oxidation process (AOP) involving titanium dioxide is a promising remediation technique. However, the low photodegradation efficiency of titanium dioxide limits its practical application. In this paper, it is proposed that the presence of graphene can enhance the photocatalytic efficiency of titanium dioxide. The titanium dioxide-graphene (TiO2-G) composites were prepared via sonochemical and calcinations methods. The synthesized composite was characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), tunneling electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and fluorescence spectroscopy. The photocatalytic efficiency was evaluated by studying the degradation profiles of 3 alkylphenols using gas chromatography-flame ionization detector (GC-FID). It was found that the synthesized TiO2-G composites exhibit enhanced photocatalytic efficiencies as compared to pristine TiO2. The presence of graphene not only provides a large surface area support for the TiO2 photocatalyst, but also stabilizes charge separation by trapping electrons transferred from TiO2, thereby hindering charge transfer and enhancing its photocatalytic efficiency.

Time Period WeA Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2016 Schedule