Abstract
Tip-enhanced Raman spectroscopy is combined with polarization angle-resolved spectroscopy to investigate the nanometer-scale structural properties of core–shell silicon nanowires (crystalline Si core and amorphous Si shell), which were synthesized by platinum-catalyzed vapor–liquid–solid growth and silicon overcoating by thermal chemical vapor deposition. Local changes in the fraction of crystallinity in these silicon nanowires are characterized at an optical resolution of about 300 nm. Furthermore, we are able to resolve the variations in the intensity ratios of the Raman peaks of crystalline Si and amorphous Si by applying tip-enhanced Raman spectroscopy, at sample positions being 8 nm apart. The local crystallinity revealed using confocal Raman spectroscopy and tip-enhanced Raman spectroscopy agrees well with the high-resolution transmission electron microscopy images. Additionally, the polarizations of Raman scattering and the photoluminescence signal from the tip–sample nanogap are explored by combining polarization angle-resolved emission spectroscopy with tip-enhanced optical spectroscopy. Our work demonstrates the significant potential of resolving local structural properties of Si nanomaterials at the sub-10 nanometer scale using tip-enhanced Raman techniques.
Highlights
The properties of silicon are long standing topics of various investigations because silicon is still the most widely used semiconductor material for a broad range of micro- and nano-electromechanical systems, microelectronics, and photovoltaics [1,2]
We clearly show a decrease in the fraction of crystallinity from the center to the perimeter of the silicon nanowires (SiNWs), which can be resolved with the optical resolution of 8 nm
Applying tip-enhanced Raman spectroscopy, we show that variations of the intensity ratio between the crystalline Si and amorphous Si Raman peaks at sample positions as close as eight nanometers can be revealed
Summary
The properties of silicon are long standing topics of various investigations because silicon is still the most widely used semiconductor material for a broad range of micro- and nano-electromechanical systems, microelectronics, and photovoltaics [1,2]. A high-resolution technique that reveals both, the structural and the optical properties at the nanometer scale is needed to study the fraction of crystalline phases and defects within the SiNWs. Tip-enhanced Raman spectroscopy (TERS) has distinguished itself as a powerful characterization technique, which allows to obtain both the morphology and the so-called chemical “finger print” information simultaneously with a resolution of a few nanometers.
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