Chemical Vapor Deposition of Zirconium Oxide on Aerosolized Silicon Nanoparticles

Abstract

Nanoscale shells of ZrO2 were deposited onto size-selected, aerosolized Si nanoparticles by chemical vapor deposition (CVD). The CVD precursor was nitronium pentanitratozirconate (ZN, [NO2][Zr(NO3)5]), which has been used previously to deposit ZrO2 films on silicon wafers. Silicon nanocrystals were synthesized from silane in a low-pressure nonthermal plasma and were directly extracted from the plasma growth chamber into an atmospheric-pressure aerosol flow tube reactor. The particle streams flowed first through a preheating furnace, which could be set between room temperature and 1000 °C, and then through a differential mobility diameter (DMA) that was set to transmit particles having a mobility diameter of 12 nm. After size selection, ZN was mixed into the carrier gas stream, and the resulting nanocrystal/ZN/carrier gas mixtures passed through a heated reaction zone (T ≈ 100 °C), where deposition took place. The residence time in the reaction zone was approximately 8 s. The extent of deposition was determined by measuring the size distribution function of the postreaction aerosol with a second DMA. Particles were also analyzed by transmission electron microscopy (TEM). The measured changes in peak particle mobility diameter imply that at low-to-moderate ZN partial pressures (<100 Pa), the deposition rate is first-order in ZN partial pressure. At higher partial pressures, the rate increases more slowly with increasing ZN pressure. Possible reasons for these behaviors are discussed. The deposition rate increases with particle preheating temperature; the rate of particles that were preheated to 500 °C is roughly twice that of particles that are not preheated. This behavior is attributed to desorption of hydrogen from the particle surface leading to a more reactive substrate for CVD. We believe that these results are among the first in which CVD is used to coat size-selected, aerosolized nanoparticles and also among the first in which tandem differential mobility analysis (TDMA) is used to measure the rate of a CVD reaction.

When Size Really Matters: Size-Dependent Properties and Surface Chemistry of Metal and Metal Oxide Nanoparticles in Gas and Liquid Phase Environments

“…Particle sizing instruments have recently been used in novel ways to investigate Si nanoparticle surfaces. Roberts and co-workers have shown that the surface chemistry of Si nanoparticles can be investigated. − Surface chemistry ranging from measuring the desorption of a monolayer of hydrogen atoms from Si nanoparticles to oxidation kinetics of Si nanoparticles, chemical vapor deposition, and self-assembly of organic monolayers was investigated …”

Design of Nanomaterial Synthesis by Aerosol Processes

“…As a result, there is interest in developing gas-phase coating and functionalization processes that can occur before particle collection (Figure 2). Freshly aerosol-made TiO 2 , Fe 2 O 3 , Si, and Ag particles have been coated in situ with nanothin SiO 2 (56) or ZrO 2 shells (57) in sequential aerosol processes. The hermetic and smooth or granular texture of such shells is important for their applications (55).…”

Plasma‐Assisted Synthesis of Silicon Nanocrystal Inks

“…The subject of this paper is a novel non-thermal plasma method, which offers an all-gasphase approach to the synthesis and surface functionalization of silicon nanocrystals, which readily disperse in organic solvents to form stable silicon ink. Roberts and co-workers [18,19] first demonstrated that gas phase surface functionalization of silicon nanocrystals can avoid a lot of the inconveniences of liquid phase treatment. In ref.…”