Si Nanosheets Research Articles

TWO-DIMENSIONAL MICROMETER-SIZED SINGLE-CRYSTALLINE Si THIN NANOSHEETS DERIVED FROM CaSi2

CaSi 2 with a Zintl phase was investigated for the synthesis of nanosheets due to its facile formation of Ca 2+( Si -)2. The anionic Si - is isoelectronic with V elements and forms anion partial lattices of corrugated layers like As. The Ca 2+ planar layers are sandwiched between the anion layers. This CaSi 2 precursor was dispersed in a tetrabutylammonium hydroxide (TBA+OH-), and the resulting solid was lamellar Si · TBA composite. Finally, simple heat treatment of the lamellar precursor at 950°C under vacuum leads to Si nanosheets. The Si nanosheets grown along [111] direction has lateral dimensions up to several hundreds of microns, and thickness of 20–70 nm. Photoluminescence measurements reveal that the present Si nanosheets have visible emission bands ranging from green to red.

Soft Synthesis of Single‐Crystal Silicon Monolayer Sheets

Transparent Si nanosheets with a thickness of 0.37 nm are produced by chemically exfoliating calcium disilicide with propylamine hydrochloride (PA⋅HCl; see picture, Ca white, Si red). The nanosheets have a two-dimensional silicon backbone and are an order of magnitude thinner than previously reported silicon nanostructures.

Optical properties of Ge and Si nanosheets––confinement and symmetry effects

Comparison between silicon and germanium quantum sheets has been made regarding their electronic and optical properties. Ab initio calculations have been applied for this purpose by mean of the linearized augmented plane wave method. Quantum confinement is found to shift the band gap of both Si and Ge bulk to the blue, however this upshift depends strongly on the surface orientation. Moreover also the nature of the band gap is related to the surface symmetry: for (1 0 0)-oriented films the band gap becomes direct for both semiconductors, whereas the (1 1 0)- and (1 1 1)-oriented films show a different behavior. In the first case the band gap is direct for Si and indirect for Ge, in the second it is direct for Ge and indirect for Si. Concerning the optical properties, since in the Si films the folded bulk band energies are found to retain their original indirect character, all the Si films have an intense absorption peak only at high energies corresponding to the blueshifted direct band gap of Si bulk. In Ge films the conduction band minimum retains a strong Γ component. Therefore, dielectric function calculations clearly show that Ge films have a strong optical absorption in the visual energy region. Analysis of the squared optical matrix elements is also presented and the data are compared to the results for GaAs.