Mixed cation phases in sputter deposited HfO2–TiO2 nanolaminates

Abstract

Nanolaminate HfO2–TiO2 films are grown by reactive sputter deposition on unheated fused SiO2, sequentially annealed at 573to973K, and studied by x-ray diffraction. A nanocrystalline structure of orthorhombic (o) HfTiO4 adjacent to an interface followed by monoclinic (m) Hf1−xTixO2 is identified. m-Hf1−xTixO2, a metastable phase, is isomorphous with m-HfO2 and a high pressure phase, m-HfTiO4. A Vegard’s law analysis shows that the Ti atomic fraction in m-Hf1−xTixO2 is much greater than Ti equilibrium solubility in m-HfO2. A space group-subgroup argument proposes that m-Hf1−xTixO2 arises from an o∕m-HfTiO4 second order phase transition to accommodate the larger Hf atom.

Sputtered Hf–Ti nanostructures: A segregation and high-temperature stability study

“…Since we observed some oxidation of the samples, the hafnia-titania phase diagram was also examined, but itdoes not predict the degree of segregationshown in Fig. 6 [38].Strong segregation was reported in previous work with nanostructured hafnia-titania samples [38][39][40][41][42][43][44], indicating that the oxidation may influence the Hf and Ti segregation, butit does not explain the differences in grain evolutionbetween the multilayered and monolithic samples. In order to better understand the configurational changes in the multilayered samples, Monte Carlo simulations were conducted for the Hf-Ti system.…”

Optical properties of anatase and rutile TiO${}_{2}$ studied by GGA + U *

“…TiO 2 , as one of the wide band-gap semiconductors, with stable, nontoxic and efficient photocatalytic activity, has been widely used in photocatalytic, solar battery, sensor, self-cleaning materials and so on [1][2][3][4] . TiO 2 thin films usually exist in two polymorphs after high-temperature annealing, i.e., the anatase and the rutile, shorted as a-and r-TiO 2 , respectively [5][6][7][8][9] .…”

HfO2-TiO2Ultra-Thin Gate Dielectric by RF Sputtering

“…Further increasing the annealing temperature to 900 • C, there are several weak diffraction peaks observed at 30.64 • , 32.38 • and 53.2 • , corresponding to (111), (020) and (220) of orthorhombic HfTiO 4 respectively [5]. It suggests that these films based on sub-nanometer laminate stacks would exhibit improved thermal stability whereas the crystallization temperature of conventional HfTiO 4 gate dielectric is reported at 700 • C [2,5,7]. Accompanied with the structure evolution, the 900 • C-annealed films demonstrate the remarkable increase in surface roughness from 0.24 nm of as-deposited to 0.38 nm, as shown in Fig.…”