1,328 research outputs found
Textured Crystallization of Ultrathin Hafnium Oxide Films on Silicon Substrate
The effects of rapid thermal annealing are reported here on the structure of 2 nm thick hafnium oxide films grown on silicon (100) substrates. The films grown by atomic layer deposition have a 1 nm SiO2 transition layer between silicon and the HfO2 layer. The amorphous structure of the as-deposited films is retained after annealing at 600°C. The HfO2 films crystallized into an orthorhombic phase with an out-of-plane texture after annealing at 800°C or higher. In contrast, films grown on thick amorphous SiO2 substrates crystallize without any texture. The authors attribute the texture of HfO2 on Si (100) to the role of interfacial SiO2 transition layer
Strategy for reliable strain measurement in InAs/GaAs materials from high-resolution Z-contrast STEM images
Geometric phase analysis (GPA), a fast and simple Fourier space method for strain analysis, can give useful information on accumulated strain and defect propagation in multiple layers of semiconductors, including quantum dot materials. In this work, GPA has been applied to high resolution Z-contrast scanning transmission electron microscopy (STEM) images. Strain maps determined from different g vectors of these images are compared to each other, in order to analyze and assess the GPA technique in terms of accuracy. The SmartAlign tool has been used to improve the STEM image quality getting more reliable results. Strain maps from template matching as a real space approach are compared with strain maps from GPA, and it is discussed that a real space analysis is a better approach than GPA for aberration corrected STEM images
Point group symmetry of cadmium arsenide thin films determined by convergent beam electron diffraction
Cadmium arsenide (Cd3As2) is one of the first materials to be discovered to
belong to the class of three-dimensional topological semimetals. Reported room
temperature crystal structures of Cd3As2 reported differ subtly in the way the
Cd vacancies are arranged within its antifluorite-derived structure, which
determines if an inversion center is present and if Cd3As2 is a Dirac or Weyl
semimetal. Here, we apply convergent beam electron diffraction (CBED) to
determine the point group of Cd3As2 thin films grown by molecular beam epitaxy.
Using CBED patterns from multiple zone axes, high-angle annular dark-field
images acquired in scanning transmission electron microscopy, and Bloch wave
simulations, we show that Cd3As2 belongs to the tetragonal 4/mmm point group,
which is centrosymmetric. The results show that CBED can distinguish very
subtle differences in the crystal structure of a topological semimetal, a
capability that will be useful for designing materials and thin film
heterostructures with topological states that depend on the presence of certain
crystal symmetries.Comment: Accepted for publication in Physical Review Material
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