Organometallic chemistry on silicon and germanium surfaces.

Porous silicon in drug delivery devices and materials

State-of-the-art membrane based CO2 separation using mixed matrix membranes (MMMs): An overview on current status and future directions

This review is about understanding and controlling organic molecular adsorption on silicon. The goal is to provide a microscopic picture of structure and bonding in covalently attached molecule-silicon surface systems. The bias here is that an unprecedented, detailed understanding of adsorbate-surface structures is required in order to gain the control necessary to incorporate organic function into existing technologies or, eventually, to make new molecule-scale devices. A discussion of recent studies of adsorbate structure is presented. This includes simple alkenes, polyenes, benzene, and carene adsorbed on Si(100). Also included is a discussion of wet chemical procedures for forming alkyl and alkoxy covalently functionalized silicon. These discussions are presented together with comments on the related issues of adsorption dynamics and nano-scale manipulation in an effort to point the way toward principles and procedures that will allow the hybrid properties of organic molecules and surfaces to be harnessed.

Controlled molecular adsorption on silicon: laying a foundation for molecular devices.

Self assembled monolayers on silicon for molecular electronics.

Despite the fact that H-terminated, HF-etched Si crystals are the starting point for construction of most contemporary electronic devices,1 little is known about the chemical reactions of H-terminated Si surfaces under ambient temperature and pressure.2,3 Functionalization of Si without partial oxidation and/or formation of electrical defects is potentially important in fabricating improved electronic devices4,5 as well as in measurement of charge transfer rate constants at semiconductor/ liquid contacts.6 One recently described approach involves the reaction of HF-etched Si(111) with olefins and organic diacyl peroxides, in which formation of a self-assembled (near)monolayer of Si-alkyls was hypothesized.2 We report here an alternative strategy to functionalize HF-etched Si surfaces involving halogenation and subsequent reaction with alkyl Grignard or alkyl lithium reagents. We report vibrational spectroscopic and temperature programmed desorption data which confirm that the alkyl groups are bonded covalently to the Si surface, and we demonstrate that such overlayer formation can impede the undesirable oxidation of Si in a variety of environments while providing surfaces of high electrical quality. The H-terminated Si surface7 was first exposed to PCl5 for 20-60 min at 80-100 °C, in chlorobenzene with benzoyl peroxide as the radical initiator.8,9 Upon chlorination, the XP survey spectra (Figure 1) showed peaks at 270.2 ( 0.4 binding electron volts, BeV, (Cl 2s) and 199.3 ( 0.4 BeV (Cl 2p), indicating that this procedure yielded Cl on the surface. The high-resolution XP spectrum of the Si 2p peak of this surface displayed, in addition to the substrate Si signal, an additional peak located at 0.98 ( 0.12 BeV higher in binding energy (Figure 2) whose position and intensity was consistent with the formation of a surface Si-Cl bond.10 Auger electron spectra

Alkylation of Si Surfaces Using a Two-Step Halogenation/Grignard Route

The adsorption and decomposition of acetylene on Si(100)-(2×1) have been studied in ultrahigh vacuum by Auger electron spectroscopy, temperature-programmed desorption, and changes in the partial pressure of acetylene as measured by a quadrupole mass spectrometer during the formation of a monolayer. Acetylene was found to chemisorb onto Si(100)-(2×1) via a mobile precursor. The difference between the activation energy for desorption from the precursor and that for reaction from the precursor into the chemisorbed state was found to be (E d -E r )=1.9±0.6 kcal mol -1

Adsorption and decomposition of acetylene on Si(100)-(2×1)

We have measured the initial probabilities of dissociative chemisorption of perhydrido and perdeutero cycloalkane isotopomers on the hexagonally close-packed Ru(001) and Ir(111) single-crystalline ...

Trapping-mediated dissociative chemisorption of cycloalkanes on Ru(001) and Ir(111): influence of ring strain and molecular geometry on the activation of C-C and C-H bonds.

The interaction of gas-phase atomic oxygen with chemisorbed deuterium on Ru(001) has been investigated by means of temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). Exposure of gas-phase atomic oxygen to the p(1×1) deuterium overlayer at a surface temperature of 80 K results primarily in the adsorption of oxygen atoms. Thermal desorption spectra measured after large atomic oxygen exposures show the desorption of D2O between 150 and 190 K as well as a large decrease in the activation energy for the recombinative desorption of deuterium. HREEL spectra demonstrate the presence of D2O following atomic oxygen exposure at 80 K and, together with TPD spectra, suggest the presence of chemisorbed OD. Since OD and D2O are formed at low surface temperatures, an Eley-Rideal-like mechanism is suggested in which oxygen atoms from the gas phase react with deuterium adatoms prior to being thermally accommodated to the surface.

Observation of the reaction of gas-phase atomic oxygen with Ru(001)-p(1×1)-D at 80 K

The dissociative chemisorption of cyclobutane on the Ru(001) surface has been studied using thermal desorption spectroscopy (TDS) and high-resolution electron energy loss spectroscopy (HREELS). Two distinct methodologies have been used to study this reaction. First, we investigated the trapping-mediated reaction by exposing the surface to cyclobutane at 180 K. Second, although an adsorbed monolayer of cyclobutane undergoes nearly complete desorption during subsequent heating, we find that the presence of the condensed multilayer induces significant reaction. Using HREELS we find that both reaction channels yield a common intermediate which we identify to be a C4H8 metallacycle. At moderate and high surface coverages, a small amount of butene from the isomerization of the metallacycle desorbs between 185 and 225 K. Following the desorption of butene, we observe a hydrocarbon fragment on the surface which is tentatively identified to be a C4H4 metallacycle.

W. H. Weinberg

Papers

Alkylation of Si Surfaces Using a Two-Step Halogenation/Grignard Route

Adsorption and decomposition of acetylene on Si(100)-(2×1)

Trapping-mediated dissociative chemisorption of cycloalkanes on Ru(001) and Ir(111): influence of ring strain and molecular geometry on the activation of C-C and C-H bonds.

Observation of the reaction of gas-phase atomic oxygen with Ru(001)-p(1×1)-D at 80 K

Trapping-Mediated and Multilayer-Induced Dissociative Chemisorption of Cyclobutane on Ru(001)