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ScN in the rock salt structure is a well-investigated material due to its desirable properties like the high hardness or large thermal conductivity. Recent computations by Adamski et al. [Appl. Phys. Lett. 115, 232103 (2019)] showed that ScN/GaN heterostructures exhibit an outstanding polarization gradient which would be beneficial for polarization induced electron gases. The pseudobinary semiconductor Sc x Al 1 − x N, when maintaining the cubic rock salt structure, could be beneficial for tailoring the polarization gradient using the Sc dependency of material properties. The structural properties of rs-Sc x Al 1 − x N are not fully discovered yet, thus in this work, DC-magnetron sputtered cubic rock salt Sc x Al 1 − x N thin films with 0.55 < x < 1.00 were grown and analyzed on ScN(111)/Si(111). The epitaxial relation of ScN(111) thin films on the Si(111) substrate is determined to be ScN[110] ∥ Si[100]. Furthermore, concentration dependent properties like the lattice parameter of Sc x Al 1 − x N were measured [a(ScN) = 4.50 Å, a(Sc0.55Al0.45N) = 4.30 Å] and the stress σ within the layers was determined. The crystal quality was evaluated using ω -scans, revealing FWHM = 1.14 ° for Sc0.95Al0.05N. The diameters of the columns were determined by atomic force microscopy and scanning electron microscopy and they are range from 34 to 59 nm for 0.55 < x < 1.00. At x = 0.55 , Sc x Al 1 − x N columns in the hexagonal wurtzite as well as cubic rock salt structure were detected. This information about the structural specifications of Sc x Al 1 − x N in the rock salt structure forms the basis for further investigations and experimental confirmation of the electric properties of ScN/GaN heterostructures or even a Sc x Al 1 − x N/GaN based approach for improved structures for high-electron-mobility transistors. [ABSTRACT FROM AUTHOR]

The direct impact of structural quality on the ferroelectric properties of hexagonal Al1–xScxN with an Sc-content of x = 0.3 was investigated using dynamic hysteresis measurements, high-resolution x-ray diffraction (HRXRD), and atomic force microscopy. The films investigated were deposited on p-doped (001)-Si substrates by reactive pulsed DC magnetron sputtering under different gas mixtures to vary the structural quality and surface morphology between samples. Misoriented grains were identified as ferroelectrically inactive, as these grains resulted in an underestimation and distortion of the ferroelectric quantities. In fact, a high amount of misoriented volume was found to have a significant effect on the coercive electric field, as this is mainly determined by the crystal strain in the ferroelectric [0001]-oriented regions, independent of its origin. Furthermore, it was concluded that the crystal quality does not have a pronounced effect on the coercive field strength. Conversely, the polarization in the film is mainly determined by the crystal quality, as a difference of 1° in the HRXRD FWHM of the ω-scan resulted in a 60% loss of polarization. The amount of polarization was influenced to a lesser extent by the misoriented grains since the ferroelectric volume of the layers was only slightly overestimated. This reveals that optimizing reproducible and transferable properties, such as crystal quality and surface morphology, is more reasonable, as the film with the lowest misoriented volume and the highest degree of c-axis orientation showed the highest polarization. [ABSTRACT FROM AUTHOR]

Coherently strained BiFeO3 epitaxial films deposited on (001)-oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 have a tetragonal crystal form, a stress-distorted version of the rhombohedral phase. A conversion from coherent BiFeO3 to a new, tilted pseudotetragonal phase with the c/a ratio exceeding 1.2 is observed beyond the critical thickness of 60 nm. X-ray reciprocal space maps display that this highly elongated metastable structure is monoclinically distorted by ~0.2° and exhibits an out-of-plane tilt of ~3°. These observations are at odds with traditional understandings that a coherent epilayer should turn into its parent structure upon increasing the thickness, providing a new insight into the strain relaxation mechanism of epitaxial films. We show that in the heating and cooling cycles, the transition between these two phases is completely reversible and is associated with the alleviation of thermal stress. Our results reveal that the coherent BiFeO3 epilayer with tetragonal symmetry stabilized by moderate compressive strain behaves as a structural bridge that links the thermally stable rhombohedral phase and the metastable tetragonal-like phase with a giant axial ratio. Moreover, the finding of a BiFeO3 phase mixture in our study extends the threshold in-plane strain of the stress-driven morphotropic phase boundary to a value as low as -2.3%. [ABSTRACT FROM AUTHOR]

Studies the sequence of phase transformations induced in the zirconium-aluminum binary system. Details on the experimental method; Experimental results; Conclusions.

Reports on high-energy ball milling of ruthenium (Ru) and aluminum-Ru. Cause of the deformation; Decrease of the crystal size to a nanometer scale; Increase of atomic-level strain.