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Register a new userEffect of pre-oxidation treatments on the structural, microstructural, and chemical properties of (Ni,Pt)Al systems
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Added by
Juan Manuel Alvarado-Orozco
Publication date
2018
fields
Physics
and research's language is
English
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The effect of isothermal pre-oxidation treatments on the b{eta}-(Ni,Pt)Al + Rene N5 system degradation is here reported. The oxidation treatments were carried out from 900 (mostly {theta}-Al2O3 growing conditions) to 1200{deg}C (mainly {alpha}-Al2O3 growing conditions) for 5 h, under a purified Ar-stream with a fixed pO2= 1 x 10-5 atm. Results are discussed based on the correlation between the structural, microstructural and chemical properties of the b{eta}-(Ni,Pt)Al BC showing that pre-oxidation parameters have an important effect on the multi-elemental counter diffusion phenomena along BC. For instance, a significant BC+IDZ thickness increase of 55% at 1200 {deg}C was observed with respect to as-received sample just after 5 h of oxidation resulting in a severe BC degradation.
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We experimentally investigate the current-induced magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers combining the anomalous Hall effect and magneto-optical Kerr effect techniques in crossbar geometry. The magnetization reversal occurs through nucleation and propagation of a domain of opposite polarity for a current density of the order of 0.3 TA/m$^2$. In these experiments we demonstrate a full control of each stage: i)the {O}rsted field controls the domain nucleation and ii) domain-wall propagation occurs by spin torque from the Pt spin Hall effect. This scenario requires an in-plane magnetic field to tune the domain wall center orientation along the current for efficient domain wall propagation. Indeed, as nucleated, domain walls are chiral and Neel like due to the interfacial Dzyaloshinskii-Moriya interaction.
The structural and nanochemical properties of thin $AlO_x$ layers are decisive for the performance of advanced electronic devices. For example, they are frequently used as tunnel barriers in Josephson junction-based superconducting devices. However, systematic studies of the influence of oxidation parameters on structural and nanochemical properties are rare up to now, as most studies focus on the electrical properties of $AlO_x$ layers. This study aims to close this gap by applying transmission electron microscopy in combination with electron energy loss spectroscopy to analyze the structural and nanochemical properties of differently fabricated $AlO_x$ layers and correlate them with fabrication parameters. With respect to the application of $AlO_x$ as tunnel barrier in superconducting Josephson junctions, $Al/AlO_x/Al$-layer systems were deposited on Si substrates. We will show that the oxygen content and structure of amorphous $AlO_x$ layers is strongly dependent on the fabrication process and oxidation parameters. Dynamic and static oxidation of Al yields oxygen-deficient amorphous $AlO_x$ layers, where the oxygen content ranges from x = 0.5 to x = 1.3 depending on oxygen pressure and substrate temperature. Thicker layers of stoichiometric crystalline $gamma-Al_2O_3$ layers were grown by electron-beam evaporation of $Al_2O_3$ and reactive sputter deposition.
Laser ablation of Al-Ni alloys and Al films on Ni substrates has been studied by molecular dynamics simulations (MD). The MD method was combined with a two-temperature model to describe the interaction between the laser beam, the electrons and the atoms. The challenge for alloys and mixtures is to find the electronic parameters: electron heat conductivity, electron heat capacity and electron-phonon coupling parameter. The challenge for layered systems is to run simulations of an inhomogeneous system which requires modification of the simulation code. Ablation and laser-induced melting was studied for several Al-Ni compounds. At low fluences above the threshold ordinary ablation behavior occurred while at high fluences the ablation mechanism changed in Al$_3$Ni and AlNi$_3$ from phase explosion to vaporization. Al films of various thicknesses on a Ni substrate have also been simulated. Above threshold, 8 nm Al films are ablated as a whole while 24 nm Al films are only partially removed. Below threshold, alloying with a mixture gradient has been observed in the thin layer system.
We report an enhancement of the anomalous Nernst effect (ANE) in Ni/Pt (001) epitaxial superlattices. The transport and magneto-thermoelectric properties were investigated for the Ni/Pt superlattices with various Ni layer thicknesses (${it t}$). The anomalous Nernst coefficient was increased up to more than 1 ${mu}$V K$^{-1}$ for 2.0 nm ${leq}$ ${it t}$ ${leq}$ 4.0 nm, which was the remarkable enhancement compared to the bulk Ni. It has been found that the large transverse Peltier coefficient (${alpha}$$_{xy}$), reaching ${alpha}$$_{xy}$ = 4.8 A K$^{-1}$ m$^{-1}$ for ${it t}$ = 4.0 nm, plays a prime role for the enhanced ANE of the Ni/Pt (001) superlattices.
Sn$_{0.97-y}$Co$_{0.03}$Ni$_{y}$O$_{2}$ (0 $leq y leq$ 0.04) nanocrystals, with average crystallite size in the range of 7.3 nm ($y$=0.00) to 5.6 nm ($y$=0.04), have been synthesized using pH-controlled chemical co-precipitation technique. The non-stoichiometric Sn related defects and the O related stoichiometric Frenkel defects arising in the nanocrystals because of co-doping have been identified and their effect on the structural and optical properties of the nanocrystals have been extensively studied. It has been observed, using XPS that on increasing the Ni co-doping concentration ($y$), the non-stoichiometric Sn defect Sn$_{text{Sn}}^{}$ increases in compensation of existing defect Sn$_{i}^{....}$ for $y$ = 0.00 nanocrystals. High resolution transmission electron microscopy (HR-TEM) also confirms the existence of Sn$_{text{Sn}}^{}$. Regarding the Frenkel defect, XPS results indicate that the concentration of $V_{text{O}}$ and O$_{i}$, manifested in the form of dangling bond related surface defect states,increases with increase in $y$. Temperature dependent magnetisation measurement of the nanocrystals confirm the charge state of $V_{text{O}}$. The point defects have been found to affect the structural properties in a way that distortion in octahedral geometry of complete Sn-O octahderon effectively reduces whereas distortion in the trigonal planar coordination geometry of O increases. The investigation of Urbach edge indicates an enhancement in the disorder in the nanocrystals on co-doping. The optical band gap of the nanocrystals has been found to be red shifted upto $y$=0.02 and then a gradual blue shift has been observed. A direct effect of the O related defect has been observed on the blue luminescence of the nanocrystals such that the spectral contribution of blue luminescence in the total emission intensity increases by 72% for $y$=0.04 as compared to $y$=0.00.
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