Nanoscale characterization of silica soots and aluminium solution doping in optical fibre fabrication

Germania nanocrystals in Modified Chemical Vapour Deposition

“…Particles caught up in these vortices are carried to the end of the substrate tube without being deposited on the tube wall and are lost as waste material. These particles are generated in the cooler regions near the centre line of the tube and tend to be smaller than those generated in the hotter region near the tube wall, as observed for MCVD silica soot particles [7].…”

“…Proof of this scenario would be difficult to obtain. High resolution transmission electron microscopy (HRTEM) imaging of silica nanoparticles solutiondoped with AlCl 4 indicates $30 atomic layers of sometimes amorphous, sometimes crystalline alumino-silicate on the amorphous silica surface [7]. A similar technique might reveal germano-silicate compounds on the surface of SiO 2 particles generated in the presence of GeCl 4 vapour.…”

“…There has been some limited early work by other authors on characterisation of oxide soot particles formed in MCVD [6]. Recent studies of silica soot particles (SiO 2 ) in MCVD have found them to be invariably amorphous [7]. Several studies of the VAD process [8][9][10][11][12][13][14] have reported that under certain conditions some of the GeO 2 soot particles formed are crystalline.…”

Multiple solution-doping in optical fibre fabrication II – Rare-earth and aluminium co-doping

“…Comparison with published diffraction patterns indicates the presence of the hydrated aluminium chloride (peaks marked with dots) and the hydrated erbium chloride (peaks marked with asterisks). The broad peak centred around 22°is ascribed to amorphous silica [8]. As might be expected, low temperature solution-doping simply leaves a dried mixture of salts in the porous soot layer.…”

“…A series of SEM images showed that all soot layers were composed of partially fused silica particles with a significant porosity distribution [7,8]. The thickness of the soot layer was about 35 lm.…”