Synthesis of Silicon and Germanium Oxide Nanostructures via Photonic Curing; a Facile Approach to Scale Up Fabrication

Abstract

Silicon and Germanium oxide (SiO_x and GeO_x) nanostructures are promising materials for energy storage applications due to their potentially high energy density, large lithiation capacity (~10X carbon), low toxicity, low cost, and high thermal stability. This work reports a unique approach to achieving controlled synthesis of SiO_x and GeO_x nanostructures via photonic curing. Unlike conventional methods like rapid thermal annealing, quenching during pulsed photonic curing occurs rapidly (sub-millisecond), allowing the trapping of metastable states to form unique phases and nanostructures. We explored the possible underlying mechanism of photonic curing by incorporating laws of photophysics, photochemistry, and simulated temperature profile of thin film. The results show that photonic curing of spray coated 0.1 M molarity Si and Ge Acetyl Acetate precursor solution, at total fluence 80 J cm^-2 can yield GeO_x and SiO_x nanostructures. The as-synthesized nanostructures are ester functionalized due to photoinitiated chemical reactions in thin film during photonic curing. Results also showed that nanoparticle size changes from ~48 nm to ~11 nm if overall fluence is increased by increasing the number of pulses. These results are an important contribution towards large-scale synthesis of the Ge and Si oxide nanostructured materials which is necessary for next-generation energy storage devices.

Keywords: germanium oxide; nucleation and growth; photonic curing; roll-to-roll manufacturing; silicon oxide.

Figure 1

Schematic illustration of photonic curing process using PulseForge 1300. Nitrogen (N₂) with 2 bar pressure is used to spray precursor solution on a glass substrate. The thin films are then processed via photonic curing and then characterized.

Figure 2

(a & b) SEM images at high and low‐resolution for Si precursor 0.1 M, treated at 600 V for 10 pulses, (c&d) at high and low‐resolution SEM images for Ge precursor 0.1 M photonically processed at 600 V for 10 pulses resulting in a total fluence of 80 Jcm⁻². (e–f) molecular structure for Si, Ge precursor, and (g) is the molecular structure for mono and tri substitutes for the precursors.

Figure 3

(a) Intensity of incident radiation vs. thickness of the material, the red line shows for the conventional thermal equilibrium processes the intensities varies by following the Beer‐Lambert law, I₀ is initial intensity whereas I is the intensity at any instant of time (and thickness). (b) Temperature vs. time profile for substrate and thin film temperature during photonic curing showing peak temperature is higher than 1000 ^oC but substrate remains relatively cool.

Figure 4

(a) Simulated temperature Vs. time profile for photonic curing of Ge and Si precursor thin films at 600 V bank voltage for 10 pulses, (b) Temperature Vs. time comparison for photonic curing (orange line), rapid thermal annealing (black dotted line) and conventional processing (black solid line).

Figure 5

Histogram for (a) Si (b) Ge oxide nanoparticles, the histogram is obtained by using the SEM images shown in Figure 1. The average diameter of SiO_x and GeO_x nanoparticles is 48.4 nm and 347.6 nm respectively.

Figure 6

FTIR spectrum for (a) Si and (b) Ge precursors before and after curing. Various modes are labelled with corresponding wavenumbers. The peaks evolve with the change in oxygen content.

Figure 7

UV‐Vis results for (a) Si and (b) Ge oxide nanoparticles synthesized at xenon flashlamp bank voltage 600 V using 10 pulses. The transmission spectra shows maximum transmission ~510 nm and ~500 nm for silicon and germanium based nanoparticles.

Figure 8

Raman results for (a) Si and (b) Ge oxide nanoparticles. The active Raman modes in both spectra indicate the presence of SiO_x and GeO_x nanoparticles while the D and G peaks show that the nanoparticles are not reduced and there is rGO.

Figure 9

(a) SEM images for Si precursor photonically cured at 600 V for 20 pulses with high‐resolution SEM in the inset on the top left corner, (b) Histogram for the silicon oxide nanoparticles synthesized by photonic (10 pulses). The number density of nanoparticles decreased with increasing the number of pulses as well the size of nanoparticles also decreased.