In-situ high resolution transmission electron microscopy observation of silicon nanocrystal nucleation in a SiO2 bilayered matrix

Abstract

Solid-state nucleation of Si nanocrystals in a SiO 2 bilayered matrix was observed at temperatures as low as 450 C. This was achieved by aberration corrected high-resolution transmission electron microscopy (HRTEM) with real-time in-situ heating up to 600 C. This technique is a valuable characterization tool especially with the recent interest in Si nanostructures for light emitting devices, non-volatile memories, and third-generation photovoltaics which all typically require a heating step in their fabrication. The control of size, shape, and distribution of the Si nanocrystals are critical for these applications. This experimental study involves in-situ observation of the nucleation of Si nanocrystals in a SiO 2 bilayered matrix fabricated through radio frequency co-sputtering. The results show that the shapes of Si nanocrystals in amorphous SiO 2 bilayered matrices are irregular and not spherical, in contrast to many claims in the literature. Furthermore, the Si nanocrystals are well confined within their layers by the amorphous SiO 2 . This study demonstrates the potential of in-situ HRTEM as a tool to observe the real time nucleation of Si nanocrystals in a SiO 2 bilayered matrix. Furthermore, ideas for improvements on this in-situ heating HRTEM technique are discussed. V C 2014 AIP Publishing LLC. [http://dx.

Atom Probe Tomography Analysis of Boron and/or Phosphorus Distribution in Doped Silicon Nanocrystals

“…The isoconcentration surfaces were defined with a voxel size of 1 nm and a delocalization value of x = 3 nm, y = 3 nm, z = 3.5 nm. The mass spectra used in the reconstruction are shown in Supporting Information (Figure S1).The reconstructions indicate that the Si NCs were well-separated from each other in 3D, despite the Si-rich oxide film being deposited by cosputtering of Si and SiO 2 targets, which is different from creating a multilayer structure of Si-rich oxide and SiO 2 films that is known to create well-distributed Si NCs. , In the sliced images, the codoped sample has more B and P enrichment at the position where the local Si density is high compared to solely doped samples. This B and P enrichment is more prominent when the annealing temperature is increased from 1050 to 1250 °C (Supporting Information, Figure S2, for 3D reconstructions of codoped Si NCs in BPSG annealed at 1050 and 1250 °C).…”

High Si content SRO/SiO2 bilayer superlattices with boron and phosphorus doping for next generation Si quantum dot photovoltaics

“…This could either mean that the Si NCs are penetrating through the adjacent 1.8 nm SiO 2 layers as suggested by Di et al [24] or there could be an extensive nanocrystalline Si network within the SRO layers making the Si NCs non-spherical in shape. Furthermore, if the Si NCs are confined well within the layers, Si quantum well type structures could also be a possibility [25]. In HRTEM it is often difficult to find the true shape of the individual Si NCs, because limited information is provided to the viewer along the third dimension (depth) [25], [26].…”

“…Furthermore, if the Si NCs are confined well within the layers, Si quantum well type structures could also be a possibility [25]. In HRTEM it is often difficult to find the true shape of the individual Si NCs, because limited information is provided to the viewer along the third dimension (depth) [25], [26]. The shape has been suggested to be elliptical or even more eccentric as suggested by a few TEM studies [25]- [28].…”

“…In HRTEM it is often difficult to find the true shape of the individual Si NCs, because limited information is provided to the viewer along the third dimension (depth) [25], [26]. The shape has been suggested to be elliptical or even more eccentric as suggested by a few TEM studies [25]- [28]. In reality Si NCs which initially begin as small spherical NCs will over time most likely combine with neighboring Si NCs, which is more likely with high content Si SRO.…”

Dynamics of formation of Ru, Os, Ir and Au metal nanocrystals on doped graphitic surfaces

“…growth of metal nanocrystals and nanoparticles. 33,34 Recent advances allowing time-resolved investigations of self-assembly processes through atomic resolution and single-atom sensitivity include direct imaging of the dynamics of Si 6 clusters embedded in graphene pores, 35 observation of the trapping of metal atoms in graphene, 36 capture of atomic-level random walks of a defect in graphene, 37 and direct visualisation of small clusters of gold atoms. [38][39][40][41] Nonetheless, imaging the early stage of a nanocrystallisation process in real-time and in real-space is challenging and little is known about growth rates of nuclei, the minuscule clusters made of a few atoms formed in the earliest stage of nanocrystal synthesis.…”