Dielectric function and interband critical points of compressively strained ferroelectric KNaNbO thin film with monoclinic and orthorhombic symmetry.

The dielectric function and interband critical points of compressively strained ferroelectric KNaNbO thin film grown by metal-organic vapor phase epitaxy (MOVPE) are studied in broad spectral and temperature ranges by spectroscopic ellipsometry (SE). The temperature dependence of the measured pseudodielectric functions is strongly affected by a structural phase transition from the monoclinic M-phase to the orthorhombic c-phase at about 428 K. Using a parametric optical constant model, the corresponding dielectric functions as well as the interband optical transitions of the film are determined in the spectral range of 0.

Selective Growth of GaP Crystals on CMOS-Compatible Si Nanotip Wafers by Gas Source Molecular Beam Epitaxy.

Gallium phosphide (GaP) is a III-V semiconductor with remarkable optoelectronic properties, and it has almost the same lattice constant as silicon (Si). However, to date, the monolithic and large-scale integration of GaP devices with silicon remains challenging. In this study, we present a nanoheteroepitaxy approach using gas-source molecular-beam epitaxy for selective growth of GaP islands on Si nanotips, which were fabricated using complementary metal-oxide semiconductor (CMOS) technology on a 200 mm n-type Si(001) wafer.

Large-Area Synthesis of Ferromagnetic Fe GeTe /Graphene van der Waals Heterostructures with Curie Temperature above Room Temperature.

Van der Waals (vdW) heterostructures combining layered ferromagnets and other 2D crystals are promising building blocks for the realization of ultracompact devices with integrated magnetic, electronic, and optical functionalities. Their implementation in various technologies depends strongly on the development of a bottom-up scalable synthesis approach allowing for realizing highly uniform heterostructures with well-defined interfaces between different 2D-layered materials. It is also required that each material component of the heterostructure remains functional, which ideally includes ferromagnetic order above room temperature for 2D ferromagnets.

Dynamical X-ray diffraction imaging of voids in dislocation-free high-purity germanium single crystals.

White-beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation-free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density.

Ferroelectric monoclinic phases in strained KNaNbO thin films promoting selective surface acoustic wave propagation.

We present a detailed analysis of the ferroelectric domain structure of KNaNbO thin films on (110) TbScO grown by metal-organic chemical vapor deposition. Upon piezoresponse force microscopy and nanofocus x-ray diffraction measurements we derive a domain model revealing monoclinic M domains. The complex domain pattern is formed out of four co-existing in-plane orientations of the shearing direction of the monoclinic unit cell resulting in four types of superdomains each being composed of well-ordered stripe domains.

Hierarchy and scaling behavior of multi-rank domain patterns in ferroelectric KNaNbO strained films.

The formation process of a ferroelectric multi-rank domain pattern in the thickness range of 7-52 nm is investigated for monoclinic KNaNbO strained epitaxial films on (110) NdScO substrates. Although the elastic strain energy density is degenerated for two pseudocubic orientations, a distinctive hierarchy of domain evolution is observed with exclusive in-plane aa domains for very thin films and the retarded onset of a ferroelectric M phase at larger film thickness. This is accompanied by a thickness dependent transformation from stripe domains to a herringbone pattern and, eventually, for the thickest film, to a checkerboard-like structure.

Strain engineering of monoclinic domains in K Na NbO epitaxial layers: a pathway to enhanced piezoelectric properties.

A novel concept to obtain a ferroelectric material with enhanced piezoelectric properties is proposed. This approach is based on the combination of two pathways: (i) the evolution of a ferroelectric monoclinic phase and, (ii) the coexistence of different types of ferroelectric domains leading to polarization discontinuities at the domain walls. Each of these pathways enables polarization rotation in the material which is responsible for giant piezoelectricity.

Scanning X-ray nanodiffraction from ferroelectric domains in strained KNaNbO epitaxial films grown on (110) TbScO.

Scanning X-ray nanodiffraction on a highly periodic ferroelectric domain pattern of a strained KNaNbO epitaxial layer has been performed by using a focused X-ray beam of about 100 nm probe size. A 90°-rotated domain variant which is aligned along [1[Formula: see text]2] has been found in addition to the predominant domain variant where the domains are aligned along the [[Formula: see text]12] direction of the underlying (110) TbScO (TSO) orthorhombic substrate. Owing to the larger elastic strain energy density, the 90°-rotated domains appear with significantly reduced probability.

High-precision absolute lattice parameter determination of SrTiO3, DyScO3 and NdGaO3 single crystals.

The lattice parameters of three perovskite-related oxides have been measured with high precision at room temperature. An accuracy of the order of 10(-5) has been achieved by applying a sophisticated high-resolution X-ray diffraction technique which is based on the modified Bond method. The results on cubic SrTiO(3) [a = 3.