Band-Gap Tunability in Partially Amorphous Silicon Nanoparticles Using Single-Dot Correlative Microscopy

Abstract

Silicon nanoparticles (Si-NPs) represent one of many types of nanomaterials, where the origin of emission is difficult to assess due to a complex interplay between the core and surface chemistry. Band-gap tunability in Si-NPs is predicted to span from the infrared to the ultraviolet spectral range, which is rarely observed in practice. In this work, we directly assess the size dependence of the optical band gap using a single-dot correlative microscopy tool, where the size of the individual NPs is measured using atomic force microscopy (AFM) and the optical band gap is evaluated from single-dot photoluminescence measured on the very same NPs. We analyze 2–8 nm alkyl-capped Si-NPs prepared by a sol–gel method, followed by annealing at 1300 °C. Surprisingly, we find that the optical band gap is given by the amorphous shell, as evidenced by the convergence of the optical band gap size dependence toward the amorphous Si band gap of ∼1.56 eV. We propose that the structural disorder might be the reason behind the often reported limited emission tunability from various Si-NPs in the literature. We believe that our message points toward a pressing need for development and broader use of such direct correlative single-dot microscopy methods to avoid possible misinterpretations that could arise from attempts to recover size–band gap relation from ensemble methods, as practiced nowadays.

Microscopic Proof of Photoluminescence from Mechanochemically Synthesized 1-Octene-Capped Quantum-Confined Silicon Nanoparticles: Implications for Light-Emission Applications

“…The PL image shows agglomerated NPs, similar to what we observed in TEM and SEM images (Figure b,c). This agglomeration restricts us from correlating the single-dot PL with its AFM profile directly, as we have done in the past on a different material . The same area of the PL image is subsequently slowly scanned with AFM in tapping mode (part of the scanned region is shown in Figure b) to measure the size of SiNPs and to confirm whether the SiNPs are agglomerated, which is indeed observed.…”

“…This agglomeration restricts us from correlating the single-dot PL with its AFM profile directly, as we have done in the past on a different material. 34 The same area of the PL image is subsequently slowly scanned with AFM in tapping mode (part of the scanned region is shown in Figure 3 b) to measure the size of SiNPs and to confirm whether the SiNPs are agglomerated, which is indeed observed. We could find a pattern in the clustered NPs by observing real-time AFM tip movement on the image constructed by CCD, and that is highlighted by a red square.…”

Incorporation of N and O into the Shell of Silicon Nanoparticles Offers Tunable Photoluminescence for Imaging Uses

“…Therefore, extrapolation to obtain EG op deliberately neglects the low-energy part of the absorption to avoid discrete energy levels localized in the forbidden gap and originating in impurities and defects of the silicon structure, as those resulting from the incorporation of N and O atoms functionalities evidenced by XPS and IR-ATR spectra. Moreover, the obtained EG op values of the order of 3.6 eV for 2.5–2.8 nm-size SiNPs do not fall within reported size–band gap relations . In fact, EG op ∼ 3.6 eV has only been reported for crystalline SiNPs of ca.…”

“…Moreover, the obtained EG op values of the order of 3.6 eV for 2.5−2.8 nm-size SiNPs do not fall within reported size−band gap relations. 38 In fact, EG op ∼ 3.6 eV has only been reported for crystalline SiNPs of ca. 1 nm size.…”

Strong spin filtering by silicon nanoparticles with adsorbed bismuth atom clusters: Role of symmetry and electrostatic control of the direction of spin polarization

“…Here we propose a different class of curved bismuth-on-silicon nanostructures that consist of a bismuth monolayer adsorbed on a solid silicon nanoparticle core. Since silicon nanoparticles ranging in size from 2 to 64 nm have already been synthesized, 12,13 the experimental realization of such bismuth-on-silicon nanostructures by depositing bismuth atoms on silicon nanoparticles by molecular beam epitaxy should be feasible, and would open the way for pioneering experimental studies of spin transport in curved bismuth monolayer nanostructures. Our calculations based on DFT and tight binding models predict systems of this type to be nearly perfect two-terminal spin filters in the absence of magnetic fields.…”