Ge2Sb2Te5 based devices attract the attention of researchers due to wide opportunities in designing phase change memory. Herein, we studied a possibility to fabricate periodic micro- and nanorelief at surfaces of Ge2Sb2Te5 thin films on silicon oxide/silicon substrates under multi-pulse femtosecond laser irradiation with the wavelength of 1250 nm. One-dimensional lattices with periods of 1250 ± 90 and 130 ± 30 nm were obtained depending on the number of acted laser pulses. Emergence of these structures can be explained by plasmon-polariton generation and laser-induced hydrodynamic instabilities, respectively. Additionally, formation of the lattices whose spatial period is close to the impacted laser wavelength can be modelled by considering the free carrier contribution under intensive photoexcitation. Raman spectroscopy revealed both crystallization and re-amorphization of the irradiated films. The obtained results show a possibility to fabricate rewritable all-dielectric data-storage devices based on Ge2Sb2Te5 with the periodic relief.
The photocatalytic activity of TiO2 depends on numerous factors, such as the chemical potential of electrons, charge transport properties, band-gap energy, and concentration of surface-active sites. A lot of research has been dedicated to determining the properties that have the most significant influence on the photocatalytic activity of semiconductors. Here, we demonstrated that the activity of TiO2 in the gas-phase reduction of CO2 is governed mainly by the desorption rate of the reaction intermediates and final products. This indicates that the specific surface area of TiO2 and binding strength of reaction intermediates and products are the main factors affecting the photocatalytic activity of TiO2 in the investigated process. Additionally, it was shown that rutile exhibits higher photocatalytic activity than anatase/rutile mixtures mainly due to its high efficiency in the visible portion of the electromagnetic spectrum.
The influence of illumination intensity and p-type silicon doping level on the dissolution rate of Si and total current by photo-assisted etching was studied. The impact of etching duration, illumination intensity, and wafer doping level on the etching process was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and Ultraviolet-Visible Spectroscopy (UV-Vis-NIR). The silicon dissolution rate was found to be directly proportional to the illumination intensity and inversely proportional to the wafer resistivity. High light intensity during etching treatment led to increased total current on the Si surface. It was shown that porous silicon of different thicknesses, pore diameters, and porosities can be effectively fabricated by photo-assisted etching on a Si surface without external bias or metals.
Laser-induced
periodic surface structures (LIPSS) can be fabricated
in virtually all types of solid materials and show great promise for
efficient and scalable production of surface patterns with applications
in various fields from photonics to engineering. While the majority
of LIPSS manifest as modifications of the surface relief, in special
cases, laser impact can also lead to periodic modulation of the material
phase state. Here, we report on the fabrication of high-quality periodic
structures in the films of phase-change material Ge2Sb2Te5 (GST). Due to considerable contrast of the
refractive index of GST in its crystalline and amorphous states, the
fabricated structures provide strong spatial modulation of the optical
properties, which facilitates their applications. By changing the
excitation laser wavelength, we observe the scaling of the grating
period as well as transition between formation of different types
of LIPSS. We optimize the laser exposure routine to achieve large-scale
high-quality phase-change gratings with controllable period and demonstrate
their reversible tunability through intermediate amorphization steps.
Our results reveal the prospects of fast and rewritable fabrication
of high-quality periodic structures for photonics and can serve as
a guideline for further development of phase-change material-based
optical elements.
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