Analysis of nascent silicon phase-change gratings induced by femtosecond laser irradiation in vacuum

Abstract

The formation of periodic surface structures is a general effect of femtosecond laser irradiation of solid targets showing promising interest in material science and technology. However, the experiments are typically carried out in air, a condition in which the target surface becomes densely decorated with nanoparticles that can influence the formation of the surface structures in the early stage of the irradiation process. Here we report an investigation of structures generation on a silicon surface irradiated in vacuum (10−5 mbar) with a low number of laser pulses (N ≤ 10) that exploits several microscopy techniques (optical, atomic force, electron and Raman). Our analyses allow identifying the creation of silicon phase-change gratings consisting of alternating amorphous and crystalline periodic lines, with almost no material removal, located at the periphery of a shallow ablation crater. These gratings originate from two different kinds of defects: (i) the first is characterized by a peculiar lobed shape that is produced by the first few laser pulses; (ii) the second is provided by the one-dimensional, linear singularity defined by the ablation edge of the nascent crater. Both kind of defects lead to grating structures extending outwards the amorphous central area of the crater along the direction of the laser polarization. Comparative analysis with the surface formed in air, in the same experimental conditions, evidences the important role played by nanoparticles densely decorating the target in air and the striking variation occurring in vacuum.

Tuning the period of femtosecond laser induced surface structures in steel: From angled incidence to quill writing

“…When a material surface is exposed to laser light under certain conditions in terms of pulse number, pulse duration, fluence, and light polarization, it is possible to fabricate self-organized surface structures, known as Laser Induced Periodic Surface Structures (LIPSS) [7]. LIPSS can be fabricated in metals [8][9][10][11][12], semiconductors [13][14][15], dielectrics [16][17][18][19], which has generated an enormous interest in the scientific community due in order to unravel the underlying mechanisms, as well as in industry because of the countless applications that are foreseen for these structures. Amongst the variety of different structure types that can be fabricated, the most common ones are the so-called ripples (parallel lines with a period near the laser wavelength usually perpendicular to its polarization), grooves (parallel lines with supra-wavelength period orientated parallel to the polarization), and spikes (disordered supra-wavelength cone-like structures).…”

Femtosecond-laser-irradiation-induced structural organization and crystallinity of Bi2WO6

“…This control is due to the fact that lasers can deposit a large amount of energy per unit area over a temporal scale shorter than the phonon-electron relaxation time 64 . Recently, fs-laser-induced crystallization in glasses 65 , aspirin 66 and many different kinds of films such as Si [67][68][69][70] , Ti 71 , Ge 72 , and diamond 73 , among others [74][75][76][77][78][79] , has been demonstrated 80 .…”

Tailoring metal-dielectric nanocomposite materials with ultrashort laser pulses for dichroic color control

“…This structure is similar to one of the structures reported in our former work 14 obtained at this speed and belongs to the class of laser-induced periodic surface structures (LIPSS). [15][16][17][18][19][20][21] LIPSS can be formed when a material is exposed to multiple short or ultrashort laser pulses at energies above the modification threshold. 15,[22][23][24] The underlying mechanism of this self-organization process is attributed to the interference of the incident laser light with a surface wave, which leads to a periodic intensity modulation that is imprinted into the material.…”