Nanostructuring of GeTiO amorphous films by pulsed laser irradiation

Abstract

SummaryLaser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10–30 mJ/cm2. The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 °C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm2 and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms in the GeTiO matrix. The nanostructuring effects induced by the laser irradiation can be used in functionalizing the surface of the films.

SiGe nanocrystals in SiO2 with high photosensitivity from visible to short-wave infrared

“…Prior to deposition, the main chamber was pumped down to 1 × 10 −7 mTorr, and during deposition the work pressure were fixed at 4mTorr using Ar flux of 25 sccm. Films with two SiGe volume compositions in the SiO 2 were deposited, one type with the same Ge concentration as Si one and the other with highier Ge concentration with the aim to control the Ge loss by fast diffusion and oxidation 42 . The films were denoted with S1 for SiGe:SiO 2 ones with composition of 25%Si25%Ge:50%SiO 2 and with S2 for SiGe:SiO 2 films with 5%Si45%Ge:50%SiO 2 .…”

Dense Ge nanocrystals embedded in TiO2 with exponentially increased photoconduction by field effect

“…However, an in-depth analysis was not carried out in order to distinct between the contribution to the spectral photovoltage current of the light absorption in Ge NCs and in Si substrate. The influence of annealing temperature on the morphology and structure of Ge-TiO 2 films deposited by magnetron sputtering with 50:50 Ge:TiO 2 composition was previously studied by our group 37 , 38 . It was shown by annealing in a furnace that the amorphous state is preserved up to 500 °C, while for 600 °C and higher temperatures NCs of Ge and TiO 2 are formed.…”

GeSi Nanocrystals Photo-Sensors for Optical Detection of Slippery Road Conditions Combining Two Classification Algorithms

“…The GeSi nanocrystallization was made by rapid thermal annealing (RTA) at optimal temperature of 900 • C for 10 min in N 2 atmosphere. RTA temperature and time are critical in obtaining photosensitive GeSi NCs due to the competition between Ge fast diffusion and GeSi NCs formation in SiO 2 matrix [25][26][27][28].…”

“…Group IV, Si-Ge-Sn based photodetectors are very promising non-toxic alternatives to market available III-V devices. A cost-effective technique based on SiGeSn nanocrystals (NCs) embedded in an oxide matrix obtained by magnetron sputtering can be used for large-scale production of highly sensitive VIS-SWIR optical sensors [25][26][27][28][29][30]. In such composite materials, the oxide matrix has the role of the surface passivation of nanocrystals [28,29,[31][32][33].…”