Enhancement of the Carbothermal Reduction of Hafnium Oxide by Silicon

Abstract

Mixtures of hafnia and carbon powders, containing 0.0-10 mol% of silicon, are heated and analyzed by XRD, SEM, TEM, and DTA. Furthermore, hafnia and carbon pellets, with varying degrees of silicon content, are investigated to determine the nature of the silicon influence on the reaction. The addition of up to 5.0 mol% silicon increases the yield of carbide by 400%. TEM reveal that silicon causes the formation of an amorphous layer on the hafnia particles, on which nucleation of the carbide phase take place. Taking into account that the carbide formation in Si-free samples is only observed on the carbon surfaces, the authors conclude that the silicon-induced layer on the hafnia surfaces increases the accessible area for carbide formation and consequently the reaction rate.

In-Gap States of HfO2 Nanoislands Driven by Crystal Nucleation: Implications for Resistive Random-Access Memory Devices

“…This reaction consumes three C atoms for the incorporation of one carbon into a mixed HfO x C y compound. Strictly speaking, the temperature of T = 650 °C in our PLD system should be too low for a completed chemical reaction . On the other hand, additional energy is provided by the PLD process and a partial HfC formation is reported also for oxygen-deficient grown HfO 2 thin films during a vacuum annealing process at a temperature of T = 600 °C .…”

“…Strictly speaking, the temperature of T = 650 °C in our PLD system should be too low for a completed chemical reaction. 21 On the other hand, additional energy is provided by the PLD process and a partial HfC formation is reported also for oxygen-deficient grown HfO 2 thin films during a vacuum annealing process at a temperature of T = 600 °C. 20 To further investigate the crystal nucleation and the interaction of HfO 2 with carbon from the topmost layer of HOPG, we employed an ab initio calculation to simulate the ground-state structures for a series of small HfO 2 clusters.…”

“…19 This may induce the formation of hafnium carbide (HfC), like observed recently, 20 despite the need for temperatures of 1600−2000 °C for a carbothermic reduction otherwise. 21 Here, we perform a careful adaption of the growth conditions to ensure the growth of low-defect thin HfO 2 films, while the damage to the HOPG surface is kept low.…”

“…In order to obtain crystalline oxides with a stoichiometric composition, the growth of oxide thin films or islands usually is carried out at high temperatures and in oxidizing conditions, where the chemical stability of HOPG is low . This may induce the formation of hafnium carbide (HfC), like observed recently, despite the need for temperatures of 1600–2000 °C for a carbothermic reduction otherwise . Here, we perform a careful adaption of the growth conditions to ensure the growth of low-defect thin HfO 2 films, while the damage to the HOPG surface is kept low.…”