Near-Ideal Complete Coverage of CD₃ onto Si(111) Surfaces Using One-Step Electrochemical Grafting: An IR Ellipsometry, Synchrotron XPS, and Photoluminescence Study

Abstract

A one-step electrochemical grafting process using Grignard reagents has been performed to achieve a complete monolayer methyl-terminated Si(111) surfaces. Anodic treatment (0.5 mA/cm 2 for 300 s) has been applied to atomically flat Hterminated Si(111) surfaces in methylmagnesium bromide (CH 3 MgBr), methylmagnesium iodide (CH 3 MgI), and methyl-d 3magnesium iodide (CD 3 MgI) to obtain methylated Si(111) surfaces. Infrared spectroscopic ellipsometry (IRSE) clearly reveals a vibrational shift of the symmetric "umbrella" mode characteristic for methyl groups (CH 3 and CD 3 ) with a preferential zorientation. Additionally, X-ray photoelectron spectroscopy using synchrotron radiation (SXPS) shows a well-defined splitting of the Si 2p core level spectra from the methylated Si(111) surfaces. This splitting is more pronounced for the CD 3 -terminated Si(111) surfaces. Moreover, the C 1s spectra also confirm the well-defined structure of the CD 3 -terminated Si(111) surfaces by the presence of C−D vibrational stretching features. Photoluminescence (PL) measurements reveal better surface passivation in the case of CD 3 -terminated Si(111) surfaces. Finally, the quality of the surfaces depends strongly on the counterions. Grignard reagents containing iodine show the best performance in the formation of complete monolayer methylated Si(111) surfaces.

Stability of graphene–silicon heterostructure solar cells

“…For a light intensity of 100 mW cm −2 , a decrease of η to 1.5% was observed. This is consistent with the fact that a methylated silicon surface is stable in air . Moreover, the methylated silicon surface also withstands the graphene transfer process that requires the use of solvents and deionized water.…”

“…. The symmetric bending mode of the methyl groups (“umbrella” deformation) are well resolved and show an absorption maximum at about 1254 cm −1 (for more details on the experiment see Ref. ).…”

“…Methyl groups can provide a complete passivation of all Si dangling bonds on the Si(111) surface. Moreover, they prevent oxidation of the Si surface .…”

“…The electrochemical modification of the c‐Si substrates was performed under galvanostatic conditions using an anodic current of 0.5 A cm −2 for 300 s. Afterwards, the CH 3 terminated Si(111) substrates were rinsed in diethyl ether and bromobutane before removing them from the glove box. Details on the characterization of the methyl passivated c‐Si surface can be found elsewhere . The c‐Si substrates were rinsed with ethanol and deionized water and dried under a stream of dry nitrogen.…”

Nanostructured Si/Organic Heterojunction Solar Cells with High Open‐Circuit Voltage via Improving Junction Quality

“…While for PEDOT:PSS with GOPS, there is feature peak of Si, which indicates the GOPS uniform distribution in PEDOT:PSS fi lms. This chemical shift indicates the presence of Si 3+ state [ 38 ] as it is expected within the GOPS layer. This peak can be ascribed to Si 0 chemical state in bulk substrate.…”