Search results for " interface"
showing 10 items of 1741 documents
Hole localization in thermoelectric half-Heusler (Zr0.5Hf0.5)Co(Sb1−xSn ) thin films
2019
Abstract The (Ti, Zr, Hf)Co(Sb 1 − x Snx) material class has recently come into focus as an attractive p-type high-temperature thermoelectric material. This study experimentally demonstrates that homogeneous, highly textured (Zr0.5Hf0.5)Co(Sb 1 − x Snx) thin films can be grown on single crystalline MgO. By varying the sputter power, samples with both positive and negative Seebeck coefficient can be grown. The underlying reason for the sign change is the segregation of Sn nano-inclusions, which lower the effective doping of the half-Heusler matrix. Similarly the Hall constant also switches sign at low temperatures, which is modeled assuming semi-metal behavior and low temperature hole locali…
Half-Heusler materials as model systems for phase-separated thermoelectrics
2015
Semiconducting half-Heusler compounds based on NiSn and CoSb have attracted attention because of their good performance as thermoelectric materials. Nanostructuring of the materials was experimentally established through phase separation in (T1−x′Tx″)T(M1−yMy′) alloys when mixing different transition metals (T, T′, T″) or main group elements (M, M′). The electric transport properties of such alloys depend not only on their micro- or nanostructure but also on the atomic-scale electronic structure. In the present work, the influence of the band structure and density of states on the electronic transport and thermoelectric properties is investigated in detail for the constituents of phase-sepa…
Barrier inhomogeneity in vertical Schottky diodes on free standing gallium nitride
2019
Abstract In this paper, the electrical behavior of a Ni/Au Schottky barrier on free standing GaN has been studied employing a variety of techniques and correlated with the material and interface quality. The temperature dependence of the ideality factor (n) and of the Schottky barrier height (ΦB) revealed a spatial inhomogeneity of the barrier. This behavior has been described by means of the Tung's model on inhomogeneous Schottky barriers. The origin of the barrier inhomogeneity can be likely associated to the surface quality of the GaN epilayer or to microstructure of the Ni/GaN interface.
Structural characterization of TiO2/TiN O (δ-doping) heterostructures on (1 1 0)TiO2 substrates
2003
Abstract TiO2/TiNxOy δ-doping structures were grown on the top of (1 1 0)TiO2 rutile substrates by low pressure metal-organic vapor phase epitaxy (LP-MOVPE) technique at 750 °C. The samples were analyzed by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and X-ray diffraction techniques (rocking curves and φ-scans). The presence of satellites in the (1 1 0)TiO2 rocking curve revealed the epitaxial growth of 10 period δ-doping structures. The thickness of the TiO2 layers, 84 nm, was deduced from the satellites period. HRTEM observations showed around 1.5 nm thick δ-doping layers, where the presence of nitrogen was detected by EELS. The analy…
Influence of spray trajectories on characteristics of cold-sprayed copper deposits
2021
Abstract Industrial robots are widely used in cold spray (CS) as well as thermal spray to produce various coatings by precisely controlling kinematic parameters during the process. However, the robot trajectory and its effect on the characteristics of CS deposits are important, but not fully studied. This article introduces four typical spray trajectories, including zigzag path, cross path, parallel path, and spiral path, to elaborate thick CS Cu deposits, and characterizes the corresponding Cu deposits, respectively. The experimental results revealed that the spray trajectories have a major influence on the associated thermal history and the residual stress distribution. However, no signif…
Effect of surface finishing on the oxidation behaviour of a ferritic stainless steel
2017
Abstract The corrosion behaviour and the oxidation mechanism of a ferritic stainless steel, K41X (AISI 441), were evaluated at 800 °C in water vapour hydrogen enriched atmosphere. Mirror polished samples were compared to as-rolled K41X material. Two different oxidation behaviours were observed depending on the surface finishing: a protective double (Cr,Mn) 3 O 4 /Cr 2 O 3 scale formed on the polished samples whereas external Fe 3 O 4 and (Cr,Fe) 2 O 3 oxides grew on the raw steel. Moreover, isotopic marker experiments combined with SIMS analyses revealed different growth mechanisms. The influence of surface finishing on the corrosion products and growth mechanisms was apprehended by means o…
Wear and corrosion resistant performance of thermal-sprayed Fe-based amorphous coatings: A review
2019
Abstract Thermal sprayed Fe-based amorphous coatings exhibit excellent wear and corrosion resistance, and thus have been widely utilized for enhancing the performance of material surfaces. In this paper, important research progresses achieved in regards to deposition technologies and properties of thermal sprayed Fe-based amorphous coatings are reviewed. In particular, the dependence of wear and corrosion resistance of the coatings on processing parameters, e.g., kinetic energy, particle size, gas flow rate, and heat treatment temperature are summarized. Moreover, the utilization of reinforced phases and alloy elements for enhancing the wear and corrosion resistance of the coatings are pres…
Microstructure and electric properties of low-pressure plasma sprayed β-FeSi 2 based coatings
2017
Abstract Thermoelectric material β-FeSi 2 based coating was fabricated by the technique low-pressure plasma spray (LPPS) on the Al 2 O 3 substrate from different alloy powders. During the process LPPS, the phase transformation had occurred through the peritectoid, eutectoid reaction and their inverse reaction. The grain size of the as-sprayed β-FeSi 2 doped Co coatings was reduced comparing with the original feedstock powders, which implied the thermal conductivity could effectively decreased by the LPPS process. The room temperature electrical conductivity showed metal and semiconductor properties on the as-sprayed and annealed coatings. This method and the results could solve the problems…
Deposition of hollow sphere In2O3 coatings by liquid flame spray
2019
Hollow sphere In(OH)3 coatings were deposited by a simple liquid flame spray with hollow sphere In(OH)3 suspension, which was synthesized by improved soft template methods. The morphology of the In...
Evaluation of nano/submicro pores in suspension plasma sprayed YSZ coatings
2019
Abstract Nano-submicro pores could considerably influence the coating performances and thus should be properly designed for the intended applications. However, it is challenging to characterize accurately such small pores in coatings. In this study, YSZ coatings were firstly manufactured by suspension plasma spray (SPS) and the nano-submicro pores in as-prepared coatings were investigated using Ultra-small-angle X-ray scattering (USAXS). Afterwards, a multivariate analysis on the effect of five different process parameters was carried out. The two main results showed that: 1) the nano-submicro pores content in coatings has a negative correlation with suspension mass load and powder size, an…