Formation of (Functionalized) Monolayers and Simultaneous Surface Patterning by Scribing Silicon in the Presence of Alkyl Halides

Abstract

Silicon is arguably the most important material in modern technology and there has been much recent interest in chemically modifying its surface. 1,2 Linford and co-workers 3 recently published a new method of simultaneously preparing alkyl monolayers on silicon and patterning silicon by scribing it with a diamond-tipped rod while it is wet with 1-alkenes or 1-alkynes. They proposed that scribing creates highly active Si species that condense with unsaturated molecules. Here, we report that monolayers on Si can also be produced and Si surfaces concomitantly patterned by scribing Si that is wet with 1-chloro-, 1-bromo-, and 1-iodoalkanes. 4 As before, 3 this process takes place under ambient conditions, without the need to degas reagents. A dry Si surface with its thin (10-20 Å) native oxide layer is simply wet with an alkyl halide and the surface is scribed. We propose that surface species on scribed silicon, which may include SidSi (double) bonds and Si dangling bonds (Si • ), as are present on Si(100)-(2 × 1) and Si(111)-(7 × 7), respectively, 2 react with alkyl halides to produce Si-X (X is Cl, Br, or I) and Si-alkyl species. This process is shown below for Si • : homolytic scission of a C-X bond is followed by condensation of Si • with an alkyl radical.While • CH 2 (CH 2 ) n-1 H could diffuse away from the surface, it is likely that it will return to it by a random walk (a cage effect would also increase the likelihood of reaction with the surface). Bond strength tabulations support this mechanismsthe CH 3 -X 5 and C-X 6 bonds are weaker than the Si-X bond.Step (2) is clearly energetically favorable. 5 Bronikowski and Hamers 7 similarly suggested the following mechanism to explain the 2-fold excess of -Cl over -CH 3 on Si(001) dosed with gaseous CH 3 Cl:A number of reports on unpassivated silicon 2 and on monolayer formation on silicon 1 and gold serve as important precedents to this work. Abbott, Folkers, and Whitesides 8 removed regions of thiol monolayers on gold by micromaching techniques, for example, with a scalpel or a carbon fiber, and subsequently formed a second thiol monolayer in the exposed regions. Xu and Liu 9 used an AFM tip to scrape away areas of a thiol monolayer on gold while it was immersed in a solution of a different thiol. They showed that the thiol in solution adsorbs in the exposed regions. Linford 10 has shown that functionalized particles can be produced in a single step by grinding silicon in the presence of reactive compounds. CH 3 I, 11 CH 3 Cl, 7,12 and CH 3 CH 2 -Br 13,14 undergo dissociative adsorption onto Si(100)-(2 × 1) under ultrahigh vacuum to form Si-X and Si-CH 3 (or Si-CH 2 CH 3 ) species. Sailor and co-workers 15 derivatized both planar and porous silicon by electrochemical reduction of haloalkanes. Monolayers on planar and/or porous Si have been prepared by reacting H-terminated Si with diacylperoxides, 16 alkenes, Dorff, M. J.; Berges, D. A.; Linford, M. R. Langmuir 2001, 19, 5889-5900.(4) Preliminary results from our laboratory also indicate that monolayers are ...

Chemical manipulation of multifunctional hydrocarbons on silicon surfaces

“…3.75 puts the upper limit on the concentrational dependence of surface reactions. The 1-alkenes [443][444][445], 1-alkynes [443,445], aldehydes [446], alcohols [444], alkyl halides [445,447,448], epoxides [449], and acid chlorides [450] all react with the scribed silicon surface in a manner similar to that expected for Si (100) and Si(111) substrates. According to the review [442], the examples of epoxides [449] and acid chlorides [450] were the first demonstration of the reactivity of this type of compounds with bare silicon.…”

Photoluminescence‐Based Sensing With Porous Silicon Films, Microparticles, and Nanoparticles

“…The grafting of organic species via SiÀC bonds is generally achieved by chemical or electrochemical reaction of hydrogenterminated Si with an organic molecule containing either a halogen leaving group, [152][153][154] an alkene, or an alkyne functionality. [34] An example of thermal hydrosilylation of porous Si with a carboxy-terminated alkane is shown in Equation 9.…”

Reaction of Porous Silicon with Both End-Functionalized Organic Compounds Bearing α-Bromo and ω-Carboxy Groups for Immobilization of Biomolecules

“…26 Recently, Linford and co-workers reported a simple strategy to react alkyl halides with the scribed silicon surface, which may include the SidSi double bonds and Si • (silicon dangling bonds) radicals. [27][28] A bromo radical is typically used in organic chemistry. Since the grafting of organic monolayers goes through a radical mechanism, can bromo-substituted organic compounds react directly with Si-H species?…”