Effect of Triple Treatment on the Surface Structure and Hardness of 304 Austenitic Stainless Steel

Nitriding, annealing, and carbonitriding processes are conducted to modify the surface of AISI 304 austenitic stainless steel via radio frequency plasma. A ~20 μm thick nitride layer is obtained in ten minutes at a plasma power of 450 W. Hence, all nitrided samples are annealed under vacuum for one hour at 400 ̊C. The nitrided-annealed samples are carbonitrided via the identical technique at various C2H2/N2 gas pressure ratios. Numerous analytical techniques, including X-ray diffractometry, glow discharge optical spectroscopy (GDOS), Talysurf Intra Profilemeter, optical microscopy (OM), scanning electron microscopy (SEM), and Vickers microhardness tester, were employed to investigate the triple-treated specimens. Microstructure analysis of the triple-treated samples reveals the formation of N2 expanded austenite phase (γN), γʹ-Fe4N, CrN, Fe3C, and Fe7C3. The results indicate that the elemental composition, microhardness, and thickness of the triple-treated layers are all depending on the gas composition. After carbonitriding, the total thickness of the compound layer grew from ~20 to ~34.5 μm. The surface microhardness of the triple-treated samples increased as the C2H2/N2 gas composition ratio increased up to 70%, reaching 1,497±33.5 HV0.1, which is ~6.8 and ~1.42 folds higher than the untreated and prenitrided samples, respectively

First-time synthesis of a magnetoelectric core-shell composite via conventional solid-state reaction

In recent years, multiferroics and magnetoelectrics have demonstrated their potential for a variety of applications. However, no magnetoelectric material has been translated to a real application yet. Here, we report for the first time that a magnetoelectric core–shell ceramic, is synthesized via a conventional solid-state reaction, where core–shell grains form during a single sintering step. The core consists of ferrimagnetic $CoFe_{2}O_{4}$, which is surrounded by a ferroelectric shell consisting of $(BiFeO_{3})_{x}–(Bi_{1/2}K_{1/2}TiO_{3})_{1−x}$. We establish the core–shell nature of these grains by transmission-electron microscopy (TEM) and find an epitaxial crystallographic relation between core and shell, with a lattice mismatch of 6 ± 0.7%. The core–shell grains exhibit exceptional magnetoelectric coupling effects that we attribute to the epitaxial connection between the magnetic and ferroelectric phase, which also leads to magnetic exchange coupling as demonstrated by neutron diffraction. Apparently, ferrimagnetic $CoFe_{2}O_{4}$ cores undergo a non-centrosymmetric distortion of the crystal structure upon epitaxial strain from the shell, which leads to simultaneous ferrimagnetism and piezoelectricity. We conclude that in situ core–shell ceramics offer a number of advantages over other magnetoelectric composites, such as lower leakage current, higher density and absence of substrate clamping effects. At the same time, the material is predestined for application, since its preparation is cost-effective and only requires a single sintering step. This discovery adds a promising new perspective for the application of magnetoelectric materials

Tailoring of surface plasmon resonances in TiN/(Al0.72Sc0.28)N multilayers by dielectric layer thickness variation

Alternative designs of plasmonic metamaterials for applications in solar energy-harvesting devices are necessary due to pure noble metal-based nanostructures incompatibility with CMOS technology, limited thermal and chemical stability, and high losses in the visible spectrum. In the present study, we demonstrate the design of a material based on a multilayer architecture with systematically varying dielectric interlayer thicknesses that result in a continuous shift of surface plasmon energy. Plasmon resonance characteristics of metal/semiconductor TiN/(Al,Sc)N multilayer thin films with constant TiN and increasing (Al,Sc)N interlayer thicknesses were analyzed using aberration-corrected and monochromated scanning transmission electron microscopy-based electron energy loss spectroscopy (EELS). EEL spectrum images and line scans were systematically taken across layer interfaces and compared to spectra from the centers of the respective adjacent TiN layer. While a constant value for the TiN bulk plasmon resonance of about 2.50 eV was found, the surface plasmon resonance energy was detected to continuously decrease with increasing (Al,Sc)N interlayer thickness until 2.16 eV is reached. This effect can be understood to be the result of resonant coupling between the TiN bulk and surface plasmons across the dielectric interlayers at very low (Al,Sc)N thicknesses. That energy interval between bulk and decreasing surface plasmon resonances corresponds to wavelengths in the visible spectrum. This shows the potential of tailoring the materials plasmonic response by controlling the (Al,Sc)N interlayer thickness, making TiN-based multilayers good prospects for plasmonic metamaterials in energy devices.Funding Agencies|Swedish Research Council [2011-6505, 2013-4018]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; National Science Foundation; U.S. Department of Energy [CBET-1048616]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT); Karlsruhe Nano Micro Facility [2015-015-010151]</p

Compensation of native donor doping in ScN: Carrier concentration control and p-type ScN

Scandium nitride (ScN) is an emerging indirect bandgap rocksalt semiconductor that has attracted significant attention in recent years for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices and as a substrate material for high quality GaN growth. Due to the presence of oxygen impurities and native defects such as nitrogen vacancies, sputter-deposited ScN thin-films are highly degenerate n-type semiconductors with carrier concentrations in the (1-6) x 10(20) cm(-3) range. In this letter, we show that magnesium nitride (MgxNy) acts as an efficient hole dopant in ScN and reduces the n-type carrier concentration, turning ScN into a p-type semiconductor at high doping levels. Employing a combination of high-resolution X-ray diffraction, transmission electron microscopy, and room temperature optical and temperature dependent electrical measurements, we demonstrate that p-type Sc1-xMgxN thin-film alloys (a) are substitutional solid solutions without MgxNy precipitation, phase segregation, or secondary phase formation within the studied compositional region, (b) exhibit a maximum hole-concentration of 2.2 x 10(20) cm(-3) and a hole mobility of 21 cm(2)/Vs, (c) do not show any defect states inside the direct gap of ScN, thus retaining their basic electronic structure, and (d) exhibit alloy scattering dominating hole conduction at high temperatures. These results demonstrate MgxNy doped p-type ScN and compare well with our previous reports on p-type ScN with manganese nitride (MnxNy) doping. Published by AIP Publishing.Funding Agencies|National Science Foundation; U.S. Department of Energy [CBET-1048616]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT); Swedish Research Council [2011-6505, 2013-4018]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; Karlsruhe Nano Micro Facility [2015-015-010151]; ERC [NanoTEC 240497]; INFANTE Project [201550E072]; FPI from the Project PHOMENTA [MAT2011-27911]</p

Conductivity Optimization of Tysonite-type La_1–<i>x</i>Ba_<i>x</i>F_3–<i>x</i> Solid Electrolytes for Advanced Fluoride Ion Battery

Use of lithium ion batteries is currently the method of choice when it comes to local stationary storage of electrical energy. In the search for an alternative system, fluoride ion batteries (FIBs) emerge as a candidate due to their high theoretical capacity, and no lithium is needed for its operation. To improve the cycling performance and lower the working temperature of a solid-state battery, one of the critical components is the electrolyte, which needs advanced performance. This paper aims at developing an electrolyte with enhanced ionic conductivity for fluoride ions, to be used in a FIB. Tysonite La_1–<i>x</i>Ba_<i>x</i>F_3–<i>x</i> (0 ≤ <i>x</i> ≤ 0.15) solid solutions were synthesized by a facile wet chemical method, and its ionic conductivity was analyzed using electrochemical impedance spectroscopy. A composition study shows that the conductivity reaches a maximum of 1.26 × 10^–4 S·cm^–1 at 60 °C for the La_0.95Ba_0.05F_2.95 pellet sintered at 800 °C for 20 h, which is 1 order of magnitude higher than that for the as-prepared pellet and 2 times higher than the conductivity of sintered ball-milled batches. The reason for this dramatic increment is the more efficient decrement of grain boundary resistance upon sintering. Morphological, chemical, and structural characterizations of solid electrolytes were studied by X-ray diffraction, scanning electron microscopy , energy dispersive X-ray spectroscopy, physisorption by the Brunauer–Emmett–Teller method, and transmission electron microscopy. Electrochemical testing was carried out for the FIB cell using La_0.95Ba_0.05F_2.95 as electrolyte due to its highest conductivity among the compositions, Ce as anode, and BiF₃ as a cathode. The cycling performance was found to be considerably improved when compared to our earlier work, which used the ball-milled electrolyte

High-Performance All-Printed Amorphous Oxide FETs and Logics with Electronically Compatible Electrode/Channel Interface

Oxide semiconductors typically show superior device performance compared to amorphous silicon or organic counterparts, especially when they are physical vapor deposited. However, it is not easy to reproduce identical device characteristics when the oxide field-effect transistors (FETs) are solution-processed/printed; the level of complexity further intensifies with the need to print the passive elements as well. Here, we developed a protocol for designing the most electronically compatible electrode/channel interface based on the judicious material selection. Exploiting this newly developed fabrication schemes, we are now able to demonstrate high-performance all-printed FETs and logic circuits using amorphous indium–gallium–zinc oxide (a-IGZO) semiconductor, indium tin oxide (ITO) as electrodes, and composite solid polymer electrolyte as the gate insulator. Interestingly, all-printed FETs demonstrate an optimal electrical performance in terms of threshold voltages and device mobility and may very well be compared with devices fabricated using sputtered ITO electrodes. This observation originates from the selection of electrode/channel materials from the same transparent semiconductor oxide family, resulting in the formation of In–Sn–Zn–O (ITZO)-based-diffused a-IGZO–ITO interface that controls doping density while ensuring high electrical performance. Compressive spectroscopic studies reveal that Sn doping-mediated excellent band alignment of IGZO with ITO electrodes is responsible for the excellent device performance observed. All-printed n-MOS-based logic circuits have also been demonstrated toward new-generation portable electronics