LIPPS-dots on Si(100) surface after ex situ pulsed laser irradiation in air: (a) Ripple pattern with protruding dots formed after irradiation by 2000 laser pulses at repetition rate of 2 Hz and with energy density of . (b) Atomic force microscopy (AFM) image of LIPSS-dot ripple pattern. (c) Autocorrelation function image obtained from squared portion in (a). (d) Line profiles along horizontal (above) and vertical (below) lines in (c). The periodic distance between adjacent dots is 120 nm between 1/5 and 1/4 of ripple line periodicity (530 nm) and light wavelength (532 nm).
(a) SEM images of LIPPS-dots on Si(100) surface after multiple numbers of laser shots in a low-pressure chamber (1.33 Pa), respectively, 1000, 1500, 3000, and 4000 (from left to right) at repetition rate of 2 Hz and with energy density of . Laser incidence was normal to surfaces and polarization was horizontal to images. (b) Schematically illustrated LIPSS-dot formation process. First stage (i): atomic cluster formation by laser irradiation with periodic surface modulation. Second (II) and third (III) stages: cluster aggregation to ripple lines and growth to larger dots due to self-organization, respectively.
In situ laser irradiation and observation using laser-HVEM for formation and self-organization process of ordering dots on thinned TEM Si(100) specimen during multiple numbers of laser irradiation at repetition rate of 2 Hz and with energy density of . (a) Snapshots of dots and ripple line development on surface at certain pulse numbers recording from 30 pulses of laser irradiation using laser-HVEM. (b) Schematic illustration of plane view configuration for in situ observation using laser-HVEM (c) Height map image by AFM analysis on protruding dots and ripple pattern formation on sample surface after irradiation to 140 pulses inside laser-HVEM. (d) Height profile along the indicated line in (c). The height of the lined dots was a few tens of nanometers, and dots were separated by approximately 100–150 nm.
High-resolution TEM (HREM) image of a small protruded dot on Si(100) surface after ex situ pulsed laser irradiation in air with 1500 laser pulses at repetition rate of 2 Hz and with energy density of . (a) The cross section HREM of the sample dot prepared along the dotted ripple line. (b) Low magnification of (a). (c) Diffraction including the dot. The HREM image in (a) (with EDS analysis: not shown) indicate that the dot was grown Si, epitaxial to the bulk surface, surrounded by the locally removed surface portion.
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