Selectivity of the Chemisorption of Vinylacetic Acid on the Si(001)2×1 Surface

Chemoselective Adsorption of Allyl Ethers on Si(001): How the Interaction between Two Functional Groups Controls the Reactivity and Final Products of a Surface Reaction

Selective adsorption of multifunctional molecules is rarely observed when the different functional groups react via nonactivated reaction channels. Although the latter is also the case for ether cleavage and the adsorption of C=C double bonds on the highly reactive Si(001) surface, we find that allyl ethers, which combine both functional groups, react on Si(001) selectively via the cleavage of the molecules' ether group. In addition, our XPS measurements at 90, 150, and 300 K indicate an increased reactivity of the ether group when compared to monofunctional ethers. STM investigations furthermore reveal different final adsorption configurations after ether cleavage of allyl methyl ether when compared to diethyl ether as the monofunctional reference molecule. The interaction of the two functional groups in one molecule thus leads to new reaction channels with higher reactivity for ether cleavage on Si(001). As a further consequence, the reactivity of the C=C double bond is suppressed up to room temperature, leading to the observed selective adsorption.

Combined XPS and DFT investigation of the adsorption modes of methyl enol ether functionalized cyclooctyne on Si(001)

The reaction of methyl enol ether functionalized cyclooctyne on the silicon (001) surface was investigated by means of X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Three different groups of final states were identified; all of them bind on Si(001) via the strained triple bond of cyclooctyne but they differ in the configuration of the methyl enol ether group. The majority of molecules adsorbs without additional reaction of the enol ether group; the relative contribution of this configuration to the total coverage depends on substrate temperature and coverage. Further configurations include enol ether groups which reacted on the silicon surface either via ether cleavage or enol ether groups which transformed on the surface into a carbonyl group.

Carboxylic acid chemistry at the Ge(100)-2 x 1 interface: bidentate bridging structure formation on a semiconductor surface

The reactions of acetic acid, acetic-d3 acid-d, and formic acid with the Ge(100)-2 x 1 surface have been investigated using multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The infrared and photoelectron data provide experimental evidence for an O-H dissociation product at 310 K. DFT calculations indicate that the O-H dissociation pathway is significantly favored, both kinetically and thermodynamically, over other potential reaction pathways. All of the carboxylic acids studied exhibit unexpected vibrational modes between 1400 and 1525 cm(-1), which are attributed to the presence of a bidentate bridging structure where both oxygen atoms interact directly with the surface.

Selective Functionalization of the Si(100) Surface by a Bifunctional Alkynylamine Molecule: Density Functional Study of the Switching Adsorption Linkage. 2

The reaction of the bifunctional organic molecule 1-(dimethylamino)-2-propyne (DMAP) on the Si(100) surface has been investigated by density functional calculations employing a two-dimer cluster model. We found that, once in the physisorbed dative bonded well (-20.0 kcal mol(-1)), DMAP can proceed via a number of pathways, involving the formation of Si-C sigma bonds, which lead to thermodynamically more stable configurations. We first considered the cycloaddition of the CC triple bond, leading to a Si-C di-sigma bonded product (-58.7 kcal mol(-1)), for which we computed an energy barrier of only 12.5 kcal mol(-1), consistently with the observed switching of DMAP adsorption linkage at 300 K. We also explored the dissociative pathway involving the methylene C-H bond cleavage on the dative bonded DMAP, leading to three adsorption products with one (-57.3 kcal mol(-1)) and three Si-C sigma bonds (-58.7 and -60.6 kcal mol(-1)). The energy barrier for this pathway is computed 24.7 kcal mol(-1) and may therefore compete at temperature above 300 K with the reaction pathway involving the addition of the alkyne unit.