Converting Ceria Polyhedral Nanoparticles into Single-Crystal Nanospheres

Abstract

Ceria nanoparticles are one of the key abrasive materials for chemical-mechanical planarization of advanced integrated circuits. However, ceria nanoparticles synthesized by existing techniques are irregularly faceted, and they scratch the silicon wafers and increase defect concentrations. We developed an approach for large-scale synthesis of single-crystal ceria nanospheres that can reduce the polishing defects by 80% and increase the silica removal rate by 50%, facilitating precise and reliable mass-manufacturing of chips for nanoelectronics. We doped the ceria system with titanium, using flame temperatures that facilitate crystallization of the ceria yet retain the titania in a molten state. In conjunction with molecular dynamics simulation, we show that under these conditions, the inner ceria core evolves in a single-crystal spherical shape without faceting, because throughout the crystallization it is completely encapsulated by a molten 1- to 2-nanometer shell of titania that, in liquid state, minimizes the surface energy. The principle demonstrated here could be applied to other oxide systems.

Diameter-dependent dopant location in silicon and germanium nanowires

“…During the corresponding growth of larger diameter NWs, there is an enrichment of dopants in the surface region but the bulk of the NW also contains dopants. Several models for dopant surface segregation in nanostructures have been proposed (5,15,16,29). First, ''self-purification'' driven dopant surface segregation has been reported in nanoparticles during nucleation (5) or annealing (29).…”

“…Dopants can be introduced in well-defined concentrations during the growth of bulk crystal (1), yet in synthesized nanoscale structures, such as nanoparticles and NWs, the incorporation of dopants during growth may be affected by kinetic and thermodynamic factors associated with finite size (3)(4)(5)(6)(7)(8)(9). Difficulties in incorporating dopants into nanoparticles have been attributed to surface energetics within the context of the kinetics for colloidal growth (3,4) and thermodynamic factors during high-temperature growth (5). In the case of synthesized semiconductor nanowires, there is considerable evidence from electrical transport measurements that active dopants can be incorporated during growth (6)(7)(8)(9).…”

The Synthesis, Characterization and Optical Properties of Nanocrystallined Cerium Dioxide by the Hydrothermal Method

“…The Ce 3+ would be oxidized to Ce 4+ in a higher pH value solution 18) , i.e. Ce 3+ + H 2 O → ⋄Ce(OH) 3+ + H + + e − with subsequent hydrolysis to Ce(OH) 4 and precipitation. However, oxidation of Ce(OH) 3 also occurs readily in air at room temperature to form a slightly yellow Ce(OH) 4 , which is a hydrous oxide and can also be described as CeO 2 ·2H 2 O dehydrates progressively.…”

“…2) CeO 2 also has widespread applications in many elds, such as its uses as the solid-state electrolyte for fuel cells, 3) as an abrasive for chemical-mechanical planarization, 4) in automotive exhaust catalysts, 5) gas sensors 6) and UV-shielding materials. 7) In recent years, nano-sized CeO 2 has been the subject of much study because of improvements in its redox properties, transport properties and its surface-to-volume ratio with respect to bulk materials.…”

A lamellar ceria structure with encapsulated platinum nanoparticles

“…The non-toxic and inexpensive CeO 2 is widely used in the water gas shift (WGS) reaction [1], H 2 S removal [2], three-way catalytic (TWC) conversion [3], fuel cell electrodes [4], oxygen storage [5], and chemical-mechanical planarization [6].…”