Surface monolayers Siliconization

Quayum, M. E., Kondo, T., Nihonyanagi, S., Miyamoto, D. and Uosaki, K. Formation of organic monolayer on a hydrogen terminated Si(l 11) surface via silicon-carbon bond monitored by ATR FT-IR and SFG spectroscopy Effect of orientational order on the reaction rate. Chemistry Letters, 208 (2002). 

The model surfaces chosen for this study are shown in Figs. 15 and 16. A bare silicon surface, a silicon surface with a single monolayer of Cl chemisorbed (Fig. 15), and a silicon surface with about 2.3 monolayers of Cl mixed into the top 20 A were chosen (Fig. 16). The potentials were Feil-Stillinger-Weber, and the simulations are described by Helmer and Graves (1998). For the results shown here, Ar+ and C1+ are used as the incident ions. 

In the case of semiconductors, it was first shown in this laboratory that the arrangements of the atoms in the surface monolayers of (100) and (111) germanium and silicon are not the same as those for these planes in the bulk (25). The altered arrangements were revealed by the presence of fractional order beams for the surface gratings in certain azimuths. This was later found to be the case for all crystals tested which have a diamond-type lattice, including semiconducting diamond and several of the intermetallic compounds. The surface structure of silicon was observed to be much more complex than that of germanium. In some azimuths, several fractional orders less than one-half were observed. 

For coverages beyond 15 monolayers, there is still no pure Au present, but only a Au film containing dissolved Si between two regions of silicide. There is, additionally, a surface enrichment of silicon. The effect of heating is to diffuse more Au further into the Si substrate, leaving a surface more silicon-rich. Figure 33 is a schematic representation of the composition of a room temperature deposit. 

A quantity of interest in many studies of surfaces and interfaces is the concentration of adsorbed atomic or molecular species. The SHG/SFG technique has been found to be a useful probe of adsorbate density for a wide range of interfaces. The surface sensitivity afforded by the method is illustrated by the results of figure Bl.5.9 [72]. These data show the dramatic change in SH response from a clean surface of silicon upon adsorption of a fraction of a monolayer of atomic hydrogen. 

LB lithography for spatially controlled attachment of initiator to form regular stripes of PS and poly(n-butyl-acrylate) (PBA) brushes was reported by Studer and coworkers [16]. Mixed monolayers of L-adipalmytoyl-phosphatidylcholine (DPPC) and TEMPO-derived alkoxyamines 4 or 5 (Scheme 5) were transferred by the LB technique onto oxidized silicon wafer in regular stripes with submicrometer lateral dimensions. Physisorbed DPPC was removed by washing, and NMP of styrene from the surface of silicon wafer covalently bonded to 4 was performed at 125°C for 24 h in the presence of 6 as sacrificial polymerization regulator. NMP of n-butyl acrylate was conducted with a surface modified with 5 in the presence of 7 at 105°C for 24 h. Polymer stripe width was controlled by the concentration of alkoxyamine in the mixed phase and adjusted from about 0.2 to 1.3 pm. The height of the stripes increased to 8 0.2 nm for PS and 4.7 0.2 nm for PBA (Scheme 6). 

Contrary to these results more than 90 % of the HE covalently attached to silicone were located at the surface as shown by comparising the ESCA and HPLC data. The amounts of HE bonded to the surface are in the same range as theoretically calculated for HE monolayers The ESCA investigations of surface modified silicone tubes were done with fluorine labelled HE derivatives to increase the ESCA sensitivity of the HE molecules. In the past fluorine containing labelling reagents have been used... 

Figure Bl.22.3. RAIRS data in the C-H stretching region from two different self-assembled monolayers, namely, from a monolayer of dioctadecyldisulfide (ODS) on gold (bottom), and from a monolayer of octadecyltrichlorosilane (OTS) on silicon (top). Although the RAIRS surface selection rules for non-metallic substrates are more complex than those which apply to metals, they can still be used to detemiine adsorption geometries. The spectra shown here were, in fact, analysed to yield the tilt (a) and twist (p) angles of the molecular chains in each case with respect to the surface plane (the resulting values are also given in the figure) [40].

This represents a large signal for a small number of atoms on the surface. With care, 10 monolayers of gold on silicon can be detected. 

Finally, in 1985, the results of an extensive investigation in which adsorjDtion took place onto an aluminium oxide layer fonned on a film of aluminium deposited in vacuo onto a silicon wafer was published by Allara and Nuzzo 1127, 1281. Various carboxylic acids were dissolved in high-purity hexadecane and allowed to adsorb from this solution onto the prepared aluminium oxide surface. It was found that for chains with more than 12 carbon atoms, chains are nearly in a vertical orientation and are tightly packed. For shorter chains, however, no stable monolayers were found. The kinetic processes involved in layer fonnation can take up to several days. 

In other materials synthesis applications, the utilization of the strong bonding of fullerenes to clean silicon surfaces, has led to the application of a monolayer... 

In Section V, a general discussion of how silicon surfaces can be used to obtain monolayers is presented. The functionalization of silicon surfaces using radical chemistry is an area of intense and active investigation because of the potential for a myriad of practical applications.In order to help those readers who are not familiar with silyl radical chemistry, we discuss some general aspects of silyl radicals in Section II, together with some recent findings. 

Chidsey and coworkers made pioneering works in preparing covalently bonded monolayer films on silicon surfaces by the radical-initiated reaction of 1-alkenes with the H-Si(lll) surfaces. Reactions were carried out in neat deoxygenated alkenes using thermal decomposition of diacyl peroxides as the... 

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