Epitaxial growth and characterization of (001) [NiFe/M]20 (M = Cu, CuPt and Pt) superlattices

We present optimization of [(15 \uc5) Ni80Fe20/(5 \uc5) M]20 single crystal multilayers on (001) MgO substrates, with M being Cu, Cu50Pt50 and Pt. These superlattices were characterized by high resolution X-ray reflectivity (XRR) and diffraction (XRD) as well as polar mapping of important crystal planes. It is shown that cube on cube epitaxial relationship can be obtained when depositing at substrate temperature of 100 \ub0C regardless of the lattice mismatch (5% and 14% for Cu and Pt, respectively). At lower substrate temperatures poly-crystalline multilayers were obtained while at higher substrate temperatures {111} planes appear at ∼10\ub0 off normal to the film plane. It is also shown that as the epitaxial strain increases, the easy magnetization axis rotates towards the direction that previously was assumed to be harder, i.e. from [110] to [100], and eventually further increase in the strain makes the magnetic hysteresis loops isotropic in the film plane. Higher epitaxial strain is also accompanied with increased coercivity values. Thus, the effect of epitaxial strain on the magnetocrystalline anisotropy is much larger than what was observed previously in similar, but polycrystalline samples with uniaxial anisotropy (Kateb et al. 2021)

Coherence properties of infrared thermal emission from heated metallic nanowires

Coherence properties of the infrared thermal radiation from individual heated nanowires are investigated as function of nanowire dimensions. Interfering the thermally induced radiation from a heated nanowire with its image in a nearby moveable mirror, well-defined fringes are observed. From the fringe visibility, the coherence length of the thermal emission radiation from the narrowest nanowires was estimated to be at least 20 um which is much larger than expected from a classical blackbody radiator. A significant increase in coherence and emission efficiency is observed for smaller nanowires.Comment: 4 pages,figures include

Tailoring microstructure and stress through energetic ion bombardment: A molecular dynamic simulation

Pre-print (óritrýnt handrit)We studied high power impulse magnetron sputtering (HiPIMS) and different substrate bias for the epitaxial growth of Cu film on Cu (111) substrate by molecular dynamics simulation. We assumed a fully ionized deposition flux to represent the high ionization fraction in the HiPIMS process. Three different substrate biases, roughly low, moderate and high, were applied to the kinetic energy of the deposition flux with a flat energy distribution in each range. In low energy regime, the results were compared to the case of completely neutral flux, in analogy with thermal evaporation. In the low energy range, HiPIMS presents a slightly smoother surface and more interface mixing compared to that of thermal evaporation. However, in the moderate energy HiPIMS an atomically smooth surface was obtained with a slight increase in the interface mixing compared to low energy HiPIMS. In the high energy regime, HiPIMS presents severe interface mixing with a smooth surface with a limited growth due to resputtering from the surface. The results also indicate that in the film obtained by moderate energy HiPIMS fewer crystal defects appear. This behavior can be attributed to the repetition frequency of collision events demonstrated recently by Kateb et al. (2019). In particular high energy HiPIMS suffers from high repetition of collision events which does not allow recrystalization of the film. In the low energy HiPIMS, collision events are not enough to overcome island growth. At moderate energy, collision events repeat in a manner that provides enough time for recrystalization that results in a smooth surface, fewer defects and limited intermixing.This work was partially supported by the University of Iceland Research Funds for Doctoral students, the Icelandic Research Fund Grant Nos. 196141, 130029 and 120002023