Investigation of the Formation and Structure of Self-assembled Alkylsiloxane Monolayers on Silicon Using In Situ Attenuated Total Reflection Infrared Spectroscopy

Abstract

The formation of alkylsiloxane monolayers O x Si−(CH2) n −Y with different hydrocarbon chain lengths (n = 10, 16, 17) and different terminal substituents (Y = CH3, COOCH3, CN, Br) on native silicon (Si/SiO2) was studied by means of in situ internal reflection IR spectroscopy (ATR) at the interface between a Si ATR crystal and the precursor solution. The growth of the ν(CH2) stretching absorptions of the monolayer films, monitored with s-polarized and p-polarized radiation, provided information on the monolayer formation rates and on structural changes in the course of the growth process. The film molecules adsorb initially in a random, disordered configuration. With increasing coverage, the hydrocarbon chains gradually align and stand up on the surface. Their final orientation in the complete monolayer films depends both on the chain length and on the type of terminal substitution, whereby chain tilt angles between 7° for O x Si−(CH2)17−CH3 and 21° for O x Si−(CH2)16−CN and O x Si−(CH2)16−Br were found. The film growth follows essentially a Langmuir model of irreversible adsorption, from which the adsorption rate constants were derived. Whereas the chain length and the terminal substituent have relatively small influences on the adsorption rates, a higher water content of the precursor solutions strongly accelerates the film formation and, in addition, causes significant deviations from a Langmuir growth model. These findings were interpreted as a consequence of polycondensation of the precursor molecules in solution.

The effect of chain density on the frictional behavior of surfaces modified with alkylsiloxanes and immersed in n-alcohols

“…With OTS, all of the chlorine groups can hydrolyze, permitting the formation of both surface-chain and interchain siloxane linkages. 19,20,[31][32][33][34] When the oxide layer has an adsorbed layer of water as it does after piranha treatment, Si-Cl bonds may undergo hydrolysis to form a hydrogen bond with the adsorbed water layer on the surface or to react with the silanol groups on the oxide surface to form a siloxane bond. For very dilute silanizing solutions prepared from anhydrous solvents, deposition of oligomeric species from solution is negligible.…”

“…For very dilute silanizing solutions prepared from anhydrous solvents, deposition of oligomeric species from solution is negligible. The silanes adsorb by a continuous growth process initially 33 to form a maximum uniform coverage with a disordered film, and then continue to adsorb to form islands of ordered regions. Interchain siloxane linkages and van der Waals forces between the long alkyl chains cause these islands to coalesce into a homogeneous ordered monolayer.…”

Organic semiconductors for device applications: current trends and future prospects

“…In order to adjust the electrical conditions at different interfaces encountered in practice, various types of SAMs were developed in the past and used in different contexts such as patterning of nanoscale devices, corrosion prevention, and controlling surface properties [518,[552][553][554][562][563][564][565][566][567][568][569][570][571][572][573][574]. SAM modification of a metal surface offers a better possibility to improve the performance of OE devices as well [518,[562][563][564][565][566][567][568][569][570][571][572][573][574].…”

“…SAM modification of a metal surface offers a better possibility to improve the performance of OE devices as well [518,[562][563][564][565][566][567][568][569][570][571][572][573][574]. The formation of SAMs on a metal surface, in the present context of OFETs, is basically meant for improving the contact properties across a semiconductor-metal interface.…”

Structural characterization of self‐assembled monolayers by unenhanced Raman spectroscopy

“…7 Tremendous efforts have been made to evaluate, investigate and characterize self-assembled films from the macroscopic to the nanoscopic scale. 8 -10 Infrared spectroscopy 11 is one of the most useful techniques for the characterization of a selfassembled monolayer (SAM), 12 because it provides direct information on the nature, the conformation and the organization of the grafted film. Raman spectroscopy provides a better spatial resolution than and important complementary information to infrared spectroscopy, in particular about molecular chain order.…”