In situ Raman characterization of nanoparticle aerosols during flame synthesis

Abstract

Raman spectroscopy is applied to diagnose nanoparticle presence and characteristics in a gaseous flow field. Specifically, in situ monitoring of the Raman-active modes of TiO 2 and Al 2 O 3 nanoparticles in aerosol form is demonstrated in high-temperature flame environments. This technique serves as a sensitive and reliable way to characterize particle composition and crystallinity (e.g. anatase versus rutile) and delineate the phase conversion of nanoparticles as they evolve in the flow field. The effect of temperature on the solid-particle Raman spectra is investigated by seeding nanoparticles into a co-flow jet diffusion flame, where local gas-phase temperatures are correlated by shape-fitting the N 2 vibrational Stokes Q-branch Raman spectra. Applying the technique to a flame synthesis environment, the results demonstrate that in situ Raman of as-formed nanoparticles can be readily applied to other gas-phase synthesis systems, especially as an on-line diagnostic.

Flame aerosol synthesis of nanostructured materials and functional devices: Processing, modeling, and diagnostics

“…Raman diagnosis of nanoparticle aerosol formation during flame synthesis was first performed by Liu et al [492] for charactering TiO 2 , revealing phase transitions from amorphous to anatase to rutile. In general, it is believed that the use of in situ Raman scattering for the composition of crystalline nanomaterials needs more investigation.…”

“…Allendorf et al[491] studied the influence of silica nanoparticles on flame structure by using Raman spectroscopy and suggested N 2 as the best choice for Raman measurement. Our co-workers Liu et al[492] and Zhang et al[493] utilized N 2 Raman to determine gas-phase temperatures. SRS is self-calibrating and relatively easy to operate but weak in intensity and not suitable for highly luminous particle-laden flames due to interference[494].Coherent anti-Stokes Raman spectroscopy (CARS) was developed as an approach to enhance Raman signal levels, in which the vibrational fingerprints of certain molecules are measured by phase mixing during the intersection of three laser beams.…”

Nanoparticles in analytical laser and plasma spectroscopy – a review of recent developments in methodology and applications

“…The application of lasers in monitoring the NP generation opens up further possibilities via selectively exciting particle populations even at different stages of their formation. Various approaches exist, depending on the laser-particle interaction initiated, such as laser-induced incandescence (LII), 52 laserinduced breakdown spectroscopy (LIBS), 53 elastic, 54 or inelastic 55 scattering, or absorption, 56 to mention but a few. In the following sub-chapters, we will summarize some of the most recent laser-and plasma spectroscopy methods applied for the monitoring of NP generation, aer a brief description of the plasma diagnostic methodology related to this analytical problem.…”

Four-Wave-Mixing Approach to In Situ Detection of Nanoparticles

“…The intermediate regime between initial nucleation and nanoparticle growth particles with sizes of 10-20 nm is particularly challenging for nanoparticle detection. The only optical technique previously applied in this regime is Raman spectroscopy [17]. However, Raman spectroscopy only probes nanoparticle structure and does not provide nanoparticle dimensional information.…”