J. C. Jiang

Abrasive wear/corrosion properties and TEM analysis of Al2O3 coatings fabricated using plasma electrolysis

Abstract Alumina coatings were deposited on Al alloy substrates using an electrolytic plasma technique, based on a dielectric barrier discharge created during anodic oxidation in an aqueous electrolyte. The substrate material (BS Al 6082) was biased anodically with an unbalanced AC high voltage. During processing, a plasma current density of 100 mA/cm2 was used, at which a coating deposition rate of 1.67 μm/min was achieved. Coating abrasive wear and corrosion properties were assessed by conducting dry and wet rubber wheel abrasive tests and potentiodynamic polarization experiments, respectively. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the coating microstructure, and the coating/substrate interface. The property test results show that the coatings possess excellent abrasive wear and corrosion resistance. XRD analyses indicate that the coatings consist of α- and γ-Al2O3. An amorphous+nanocrystalline inner layer (1.5-μm thick) and a nanocrystalline (50–60 nm) intermediate layer in the coating were observed by TEM. The higher resistance to wear and corrosion can in part be attributed to the presence of these interlayers.

Oxide nano-engineering using MBE

Abstract Molecular beam epitaxy (MBE) has achieved unparalleled control in the integration of semiconductors at the nanometer level; its use for the integration of oxides with similar nanoscale customization appears promising. This paper describes the use of reactive MBE to synthesize layered oxide heterostructures, including new compounds and metastable superlattices, involving monolayer-level integration of the dielectric and ferroelectric oxides SrO, SrTiO 3 , BaTiO 3 , PbTiO 3 , and Bi 4 Ti 3 O 12 . The controlled synthesis of such layered oxide heterostructures offers great potential for tailoring the dielectric and ferroelectric properties of materials. Oxide nano-engineering is accomplished by supplying the incident species in the desired layering sequence with submonolayer composition control. Comparisons between the growth of compound semiconductors and oxides by MBE are made.

Epitaxial growth of dielectric Ba0.6Sr0.4TiO3 thin film on MgO for room temperature microwave phase shifters

Dielectric Ba0.6Sr0.4TiO3 thin films were epitaxially grown on (001) MgO by using pulsed laser ablation. Microstructure studies from x-ray diffraction and electron microscopy suggest that the as-grown films are c-axis oriented with an interface relationship of 〈100〉BSTO//〈100〉MgO. A room temperature coupled microwave phase shifter has been developed with a phase shift near 250° at 23.675 GHz under an electrical field of 40 V/μm and a figure of merit of ∼53°/dB. The performance of the microwave phase shifter based on the epitaxial Ba0.6Sr0.4TiO3 thin films on (001) MgO is close to that needed for practical applications in wireless communications.

Electrolytic plasma processing for cleaning and metal-coating of steel surfaces

Abstract Electrolytic plasma processing (EPP) involves electrolysis and electrical discharge phenomena and it is an emerging, environmentally friendly surface engineering technology. Electrolytic-plasma/material surface interactions during processing can be used for cleaning of metal surfaces, formation of diffusion layers and/or deposition of metal, ceramic and composite coatings. The present work was concerned with cleaning and deposition of metal coatings on steel surfaces for corrosion protection. The effects of processing parameters on (i) cleaning steel surfaces (oxides and contamination); and (ii) Zn and Zn–Al coating deposition were investigated. Surface roughness and oxygen content prior to and after cleaning were evaluated by profilometry and energy dispersive X-ray analysis (EDAX), respectively. The structure of the EPP cleaned outer surface layer as it evolves after the electrolytic–plasma interaction was studied by high resolution TEM. Morphology, microstructure, composition, adhesion and density of EPP-deposited Zn and Zn–Al coatings on cleaned surfaces were studied as a function of processing parameters. Corrosion properties of the cleaned and coated steels were evaluated by corrosion potential and potentiodynamic polarization measurements. The results show that EPP can effectively produce clean surfaces and also metal and alloy coatings at high deposition rates, and it has a great potential as a new plasma surface engineering technique.

Large dielectric tunability and microwave properties of Mn-doped (Ba,Sr)TiO3 thin films

Ferroelectric Ba0.6Sr0.4TiO3 thin films with 2% Mn additional doping were grown on (001) MgO by pulsed laser deposition. The microstructural studies from x-ray diffraction and transmission electron microscopy indicate that the films are highly epitaxial with c-axis oriented and atomic sharp interface. Dielectric property measurements at 1 MHz and room temperature reveal that the as-grown films have outstanding dielectric properties with large tunability of 80% at 40KV∕cm, very large dielectric constant value of 3800, and extra low dielectric loss of only 0.001. The high frequency (10–30 GHz) dielectric measurements demonstrate that the films are excellent in both dielectric property and very low dielectric insertion loss. Compared with the pure BSTO films or traditional doping, the additional doping of Mn in BSTO thin films can significantly improve the dielectric property of the as-grown films.

Epitaxial growth of dielectric CaCu3Ti4O12 thin films on (001) LaAlO3 by pulsed laser deposition

High dielectric CaCu3Ti4O12 (CCTO) thin films were epitaxially grown on (001) LaAlO3 (LAO) substrates by pulsed laser deposition. Microstructural studies by x-ray diffraction, pole figure measurements, and transmission electron microscopy show that the as-grown films are good single crystalline quality with an interface relationship of (001)CCTO//(001)LAO and [100]CCTO//[100]LAO. Dielectric property measurements show that the films have an extremely high dielectric constant with value of 10 000 at 1 MHz at room temperature. It is interesting to note that the twinned substrate results in the formation of twinning or dislocations inside the CCTO film.

High-dielectric-tunability of ferroelectric (Pb,Sr)TiO3 thin films on (001) LaAlO3

Ferroelectric (Pb,Sr)TiO3 (PSTO) thin films were epitaxially grown on (001) LaAlO3 (LAO) by using pulsed laser deposition. Microstructural characterizations with x-ray diffraction and transmission electron microscopy indicate that the as-grown films have excellent single crystalline quality and a (001)PSTO∕∕(001)LAO and [100] PSTO∕∕ [100] LAO interface relationship. Dielectric property measurements reveal that the as-grow films have a very high dielectric constant value of 3100 and very large dielectric tunability of 48% at 40V∕cm at room temperature. These excellent results suggest that the highly epitaxial ferroelectric (Pb,Sr)TiO3 thin films can be developed for room-temperature tunable microwave elements in wireless communication applications.

Structural evidence for enhanced polarization in a commensurate short-period BaTiO3/SrTiO3 superlattice

A short-period (BaTiO3)6∕(SrTiO3)5 superlattice was characterized by x-ray diffraction and transmission electron microscopy. The superlattice is epitaxially oriented with the c axes of BaTiO3 and SrTiO3 normal to the (001) surface of the SrTiO3 substrate. Despite the large in-plane lattice mismatch between BaTiO3 and SrTiO3 (∼2.2%), the superlattice interfaces were found to be nearly commensurate. The crystallographic c∕a ratio of the superlattice was measured and the results agree quantitatively with first-principles calculations and phase-field modeling. The agreement supports the validity of the enhanced spontaneous polarization predicted for short-period BaTiO3∕SrTiO3 superlattices.

Domain structure of epitaxial SrRuO3 thin films on miscut (001) SrTiO3 substrates

The microstructure of epitaxial SrRuO3 thin films grown on vicinal (001) SrTiO3 substrates with miscut angle of 1.9° and miscut direction of 12° away from [100] direction was studied using transmission electron microscopy (TEM). Cross-section as well as plan-view TEM studies revealed that these films are single domain with the in-plane epitaxial orientation relationship of SrRuO3[001]//SrTiO3[010] and SrRuO3[110]//SrTiO3[100]. This result is in contrast to the previous studies of the SrRuO3 thin films grown on exactly (001) SrTiO3, which are composed of two types of [110] domains with nearly the same volume fraction. The occurrence of these different domain structures is attributed to the step-flow growth of the film on the substrate surface due to the miscut.

Structure and mechanics of W-DLC coated spur gears

Abstract A detailed structural characterization of W-containing diamond-like carbon (W-DLC) coatings deposited on spur gears was carried out with plan-view and cross-section transmission electron microscopy (TEM). W-DLC coated spur gears were tested in a ‘four-square’ gear-testing machine and examined with TEM in both the as-deposited and tested conditions. High-resolution microscopy clearly shows the presence of nanometer scale structural/compositional modulation within the W-DLC coatings and further reveals the existence of a micrometer scale columnar structure and intercolumnar defects within the coating. Defect morphologies were examined and related to failure mechanisms of coated gears.