Silicon Nanosheets and Their Self-Assembled Regular Stacking Structure

Abstract

Silicon nanomaterials are encouraging candidates for application to photonic, electronic, or biosensing devices, due to their size-quantization effects. Two-dimensional silicon nanosheets could help to realize a widespread quantum field, because of their nanoscale thickness and microscale area. However, there has been no example of a successful synthesis of two-dimensional silicon nanomaterials with large lateral size and oxygen-free surfaces. Here we report that oxygen-free silicon nanosheets covered with organic groups can be obtained by exfoliation of layered polysilane as a result of reaction with n-decylamine and dissolution in an organic solvent. The amine residues are covalently bound to the Si(111) planes. It is estimated that there is ca. 0.7 mol of residue per mole of Si atoms in the reaction product. The amine-modified layered polysilane can dissolve in chloroform and exfoliate into nanosheets that are 1-2 microm wide in the lateral direction and with thicknesses on the order of nanometers. The nanosheets have very flat and smooth surfaces due to dense coverage of n-decylamine, and they are easily self-assembled in a concentrated state to form a regularly stacked structure. The nanosheets could be useful as building blocks to create various composite materials.

Synthesis and modification of two-dimensional crystalline silicon nanosheets

“…We developed SiNSs modified with amino groups, and performed the amination reaction in an inert atmosphere, following a previously published method. 45) Internal structures were detected by XRD in the agglomerated n-decylamine (C10)SiNS state. A very strong narrow peak for C10SiNS was found at 2ª = 2.96°[ Fig.…”

Stability and Exfoliation of Germanane: A Germanium Graphane Analogue

“…[14][15][16][17] It has been previously shown that layered Zintl phases such as CaSi2 and CaGe2 can be topochemically deintercalated in aqueous HCl at low temperatures to produce layered silicon and germanium solids. [18][19][20] The resultant four-coordinate puckered lattice of Si and Ge atoms has an analogous geometry to sp 3 -hybridized graphane, or a Si/Ge(111) surface in which every Si/Ge atom is terminated with either -H or -OH above or below the layer. 18,21 There is a great propensity for the silicon lattice to oxidize, initially forming siloxene (SiH0.5(OH)0.5) sheets that are terminated with either Si-H or Si-OH bonds at the fourth coordination site, which eventually degrade to form SiO2 under ambient conditions.…”

Improving the stability and optical properties of germanane via one-step covalent methyl-termination

“…Researchers have recently developed layered van der Waals systems in which each surface atom requires a covalent ligand to become coordinatively saturated, such as the metal carbide/ nitride MXenes, the amine coordinated II-VI chalcogenides, and the group IV graphene analogues such as silicane or germanane 9,[16][17][18][19][20] . Because the valence/conduction bands of these materials are comprised of metal-metal or metal-anion bonding within the 2D plane 21 , rather than the p-bands such as that in graphene, these systems offer the possibility to tune the entire electronic properties on the basis of the identity and electron withdrawing capability of the substituent, without completely disrupting the relevant electronic states.…”

“…The creation of many of these surface-terminated layered materials often relies on topotactic methods to interconvert a precursor layered crystal structure directly into the van der Waals material, frequently through deintercalation in acidic aqueous conditions that can result in partial surface termination with unwanted oxide or hydroxide states. For example, the deintercalation of layered Zintl phases, such as CaSi 2 in aqueous HCl produces the air and water reactive, partially hydroxide-terminated silicane SiH x (OH) 1 À x as evidenced by the existence of broad Si-O stretches that occur between 1,000-1,200 cm À 1 in the Fourier Transform Infrared (FTIR) spectrum 19,20 . This ambiguity in surface functionalization convolutes efforts to correlate the effects of surface functionalization on the optoelectronic properties of these single-atom thick semiconductors 9,20,[22][23][24] .…”

“…For example, the deintercalation of layered Zintl phases, such as CaSi 2 in aqueous HCl produces the air and water reactive, partially hydroxide-terminated silicane SiH x (OH) 1 À x as evidenced by the existence of broad Si-O stretches that occur between 1,000-1,200 cm À 1 in the Fourier Transform Infrared (FTIR) spectrum 19,20 . This ambiguity in surface functionalization convolutes efforts to correlate the effects of surface functionalization on the optoelectronic properties of these single-atom thick semiconductors 9,20,[22][23][24] . Furthermore, it is well established that H-terminated Si(111) and Ge(111) surfaces are extremely air reactive, whereas the -CH 3 terminated surfaces can be resilient towards oxidation 25,26 .…”