Size-dependent polymorphism in HfO2 nanotubes and nanoscale thin films

Abstract

Many metal oxides exhibit size-dependent phase transitions among multiple polymorphs. In this work, the microstructure and crystallinity of ultrathin HfO2 films and utrathin-wall nanotubes were investigated by high-resolution electron microscopy and electron diffraction after high-temperature annealing. Nanotubes were formed by atomic layer deposition of HfO2 on epitaxial Ge ⟨111⟩ nanowire arrays on Si (111) substrates followed by selective etching of the Ge wires. A size-dependent phase transition sequence from amorphous (a-HfO2) to tetragonal (t-HfO2) and from tetragonal to monoclinic (m-HfO2) phase was observed with increasing film and nanotube wall thickness. These results are analyzed in light of recent predictions of surface energy-driven phase transitions in nanoscale fluorite-structure oxides.

First‐principles modeling of hafnia‐based nanotubes

“…[11,18,19] Thus, transmission electron microscopy study [11] of dimple layer underneath the as-grown nanotube arrays reveals the presence of a layer of ordered HfO 2 nanocrystals. [11,18,19] Thus, transmission electron microscopy study [11] of dimple layer underneath the as-grown nanotube arrays reveals the presence of a layer of ordered HfO 2 nanocrystals.…”

Study on the degradation mechanism of the ferroelectric properties of thin Hf0.5Zr0.5O2 films on TiN and Ir electrodes

“…Grazing angle incidence X-ray diffraction pattern of the Hf 0.5 Zr 0.5 O 2 films with various thicknesses on the (a) TiN electrode and (b) Ir electrode, respectively.film on the Ir BE. The different D avg is known as one of the critical factors that determine which polymorphism of HfO 2 and ZrO 2 will be obtained 25,26. This could be identified from the detailed GIXRD analysis.…”

Tetragonal Phase in Ge Doped HfO2 Films on Si Investigated by X-ray Absorption Spectroscopy

“…5 nm thick HfO 2 films were deposited with Ge atomic concentration ranging from 0 to 15at.%, as determined by in-situ Auger electron spectroscopy. This shows that the reduced size of the nanograins in a 5 nm thick HfO 2 film reduces the transition temperature to as low as 1000 o C [4]. Rutherford backscattering spectrometry (RBS) using 2 MeV He + ions was performed in a Tandem Accelerator in Porto Alegre.…”

“…Its polymorphism includes a monoclinic phase stable at room temperature, a tetragonal phase stable above 1700 o C, and a cubic phase stable above 2200 o C [1]. The stabilization of the tetragonal phase can be achieved by reducing the size of the nanograins, strain, and by doping (alloying) the dielectric [3][4][5]. The stabilization of the tetragonal phase can be achieved by reducing the size of the nanograins, strain, and by doping (alloying) the dielectric [3][4][5].…”