Here we describe a new and simple method for preparing alkyl monolayers on silicon, which consists of mechanically scribing oxide-coated silicon while it is wet with 1-alkenes or 1-alkynes (neat or in inert solvents) under ambient conditions. X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, wetting data, and stability tests suggest covalent bonding of unsaturated species to exposed silicon surfaces. Enclosures (hydrophobic corrals) made by scribing silicon that is wet with unsaturated hydrophobic species hold droplets of water and liquids with substantially lower surface tensions. Wetting tests suggest that 1-alkynes make better hydrophobic corrals than 1-alkenes, and theoretical results suggest it should be more difficult for alkyl chains of chemisorbed 1-alkenes to pack than those of 1-alkynes. Underivatized interior regions of hydrophobic corrals are functionalized with polyelectrolyte multilayers. Theoretical energies for water and methanol droplets (gravitational and surface) in hydrophobic corrals are calculated, and a model of failure of liquid droplets in hydrophobic corrals is presented.

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 ...

The chemomechanical method has emerged as a straightforward and convenient tool for simultaneously functionalizing and patterning silicon. This technique simply consists of wetting (or exposing) a silicon surface to a reactive chemical and then scribing. Scribing activates the surface and leads to monolayer formation. The properties of the monolayers are dependent on the reactive chemicals used, and mixed monolayers and funtionalized monolayers are easily produced with mixed chemicals or alpha,omega-bifunctional compounds, respectively. Both micrometer and nanometer sized functionalized features have been created. It has been shown that this technique has potential in a variety of applications.

Methyl-terminated and acyl chloride terminated monolayers are produced when silicon is scribed under mono- and diacid chlorides, respectively. To the best of our knowledge, this is the first report of the reaction between a bare silicon surface and acid chlorides. This reaction takes place by wetting the silicon surface in the air with the acid chloride and scribing. Scribing activates the silicon surface by removing its passivation layer. We propose that scribed silicon abstracts chlorine from an acid chloride to form an Si-Cl bond and that the resulting acyl radical diffuses back to the surface to condense with the surface and form an alkyl monolayer. X-ray photoelectron spectroscopy (XPS) confirms the presence of chlorine and shows a steady increase in the amount of carbon with increasing alkyl chain lengths of the acid chlorides. Time-of-flight secondary ion mass spectrometry shows SiCl(+) species and a steady increase in representative hydrocarbon fragments with increasing alkyl chain lengths of the acid chlorides. XPS indicates that diacid chlorides react primarily at one of their ends to create acyl chloride terminated surfaces in a single step. The resulting surfaces are shown to react with various amines (piperazine, morpholine, and octylamine) and a protein. Calculations at Hartree-Fock and density functional theory levels are consistent with the proposed mechanism.

Static time-of-flight secondary ion mass spectrometry (TOF-SIMS) was performed on monolayers on scribed silicon (Si(scr)) derived from 1-alkenes, 1-alkynes, 1-holoalkanes, aldehydes, and acid chlorides. To rapidly determine the variation in the data without introducing user bias, a multivariate analysis was performed. First, principal components analysis (PCA) was done on data obtained from silicon scribed with homologous series of aldehydes and acid chlorides. For this study, the positive ion spectra, the negative ion spectra, and the concatentated (linked) positive and negative ion spectra were preprocessed by normalization, mean centering, and autoscaling. The mean centered data consistently showed the best correlations between the scores on PC1 and the number of carbon atoms in the adsorbate. These correlations were not as strong for the normalized and autoscaled data. After reviewing these methods, it was concluded that mean centering is the best preprocessing method for TOF-SIMS spectra of monolayers on Si(scr). A PCA analysis of all of the positive ion spectra revealed a good correlation between the number of carbon atoms in all of the adsorbates and the scores on PC1. PCA of all of the negative ion spectra and the concatenated positive and negative ion spectra showed a correlation based on the number of carbon atoms in the adsorbate and the class of the adsorbate. These results imply that the positive ion spectra are most sensitive to monolayer thickness, while the negative ion spectra are sensitive to the nature of the substrate-monolayer interface and the monolayer thickness. Loadings show an inverse relationship between (inorganic) fragments that are expected from the substrate and (organic) fragments expected from the monolayer. Multivariate peak intensity ratios were derived. It is also suggested that PCA can be used to detect outlier surfaces. Partial least squares showed a strong correlation between the number of carbon atoms in the adsorbate and the number it predicted.

We have previously demonstrated a facile, chemomechanical method of simultaneously functionalizing and patterning silicon with single organic monolayers by scribing it while it is wet with 1-alkenes, [1] 1-alkynes, [1] and 1-haloalkanes. [2] Here we show that this method can be extended to create individual surfaces that have different monolayer coatings in distinct and precisely controlled regions (Figure 1). Like microcontact [*] Dr.

The reaction of epoxides with a bare silicon surface is reported (see scheme). Diepoxides yield amine‐reactive monolayers on scribed silicon. Controlled levels of epoxide functionality are obtained in mixed monolayers of 1,2‐epoxyoctane and 1,2,7,8‐diepoxyoctane.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed on monolayers prepared by scribing silicon under a homologous series of 1-alkenes, 1-alkynes, and 1-haloalkanes:  CH2CH(CH2) n CH3 (n = 2, 5, 9), HC⋮C(CH2) n CH3 (n = 2, 5, 9), Cl(CH2) n CH3 (n = 4, 7, 9), Br(CH2) n CH3 (n = 4, 7, 11), I(CH2) n CH3 (n = 0, 1, 2, 4, 7, 11), and I13CH3. Numerous SiC x H y + and C x H y + fragments and adduct ions were observed. The results support a proposed binding model that 1-haloalkanes bind to the silicon surface through one C−Si bond and that 1-alkenes and 1-alkynes generally bind through two C−Si bonds. For instance, silicon surfaces scribed under 1-haloalkanes show less carbon by X-ray photoelectron spectroscopy (XPS) than silicon scribed under 1-alkenes and 1-alkynes with the same number of carbon atoms, but they show more intense SiC x H y + fragments by ToF-SIMS. Above a certain chain length, the relative intensities of the fragment and adduct ions for a homologous series generally increase with increasing alkyl chain length, which is in agreement with carbon surface coverages measured by XPS and the proposed binding models. Anomalously strong SiCH3 + and SiC2H5 + fragments observed in silicon scribed under CH3I and CH3CH2I suggest formation of methyl- and ethyl-terminated silicon, respectively. An isotopic study of silicon scribed under 13CH3I and CH3I provides additional evidence for formation of methyl-terminated silicon and suggests sputter-induced decomposition of the near-surface region by ToF-SIMS. Ab initio calculations of a few SiC x H y + type fragments are shown to verify assignments of structure. We also note an alternative explanation for some of the results based on the density of alkyl chains on the surfaces.