Местоположение издательства:Piscataway, NJ, United States
Первая страница:166
Последняя страница:166
Аннотация:Nowadays, arrays of silicon nanowires (SiNW) of about 100 nm attract great interest due to their
unique optical properties such as extremely high light absorption, enhanced spontaneous Raman
scattering, third-harmonic generation, and infrared interband photoluminescence, which are often
connected with the light trapping in SiNW arrays.
The SiNW sample was fabricated by means of metal-assisted chemical etching process [1] at
(110) crystalline silicon (c-Si) wafer. The formed SiNWs are strongly prolate parallelepipeds of
about 100 nm in diameter tilted to the surface at the angle of 45◦ with projection oriented along
(110) direction (Fig. 1a). The SiNW arrays demonstrate effective light scattering, therefore linear
reflectance measurements evidence no effect of the SiNW orientation. However, nonlinear-optical
processes, e. g. third-harmonic generation and coherent anti-Stokes Raman (CARS) scattering, which
strongly depend on the local fields could demonstrate their anisotropy. The broadband CARS signal
was generated at the frequency 2ω1 − ω2, where ω1 and ω2 were the frequencies of Nd:YVO4 laser
(1064 nm, 10 ps) radiation and continuum radiation generated in optical fiber, correspondingly. The
third-harmonic generation was carried out with the help of Cr: forsterite laser (1250 nm, 80 fs). In
all cases polarization dependences of the signals were obtained.
In contrast to spontaneous Raman, the SiNWarrays exhibit pronounced polarization dependences
of the CARS signal. The resonant CARS signal in SiNW ensemble is an order of magnitude less
than in c-Si in the case when pumping radiation propagates perpendicular to the SiNWs and the
CARS signal is collected in the direction along SiNWs and two orders of magnitude less than in c-Si
in another case. Although third-harmonic signal for SiNW array exhibits less expressed orientation
dependence then for c-Si, it exceeds the latter one the case of the fundamental radiation incident
perpendicular, whereas in the case of incident wave propagation along the SiNWs it falls several time
in comparison with c-Si (Fig. 1b). Thus, found in experiments anisotropy of the nonlinear-optical
signals evidences the sensitivity of the these techniques to the orientation of SiNWs in their highly
scattering arrays.
This work is supported by the Russian Foundation for Basic Research grant no. 15-29-01185.
