Monolayer physisorbed

Fig. 24. Schematic nonnal mode spectrum of a rare gas monolayer physisorbed on a single crystal surface. (4/fer Rrf. 52.)...

H. Freimuth, H. Wiechert, and H.J. Lauter. The Commensurate-Incommensurate Transition of Hydrogen Monolayers Physisorbed on Graphite. Surf. Sci. 189/190 548 (1987). 

R.D. Diehl, M.F. Toney, and S.C. Fain, Jr. Orientational Ordering of Nitrogen Molecular Axes for a Commensurate Monolayer Physisorbed on Graphite. Phvs. Rev. 48 177 (1982). 

Fig. 9. Surface photovoltage spectra of undoped a-Si H at 25 °C and — 168 °C after various surface treatments 9, T = 25 °C, sputtered only X, T= 25°C, sputtered and annealed O, r= 25 C, sputtered and annealed with one monolayer physisorbed O2 , — 168°C,...

H. Mannebach, U. G. Volkmann, J. Faul, K. Knorr, Order-parameter kinetics in the liquid-gas coexistence region of Ar monolayers physisorbed on graphite, Phys. Rev. Lett. 67 (1991) 1566-1569. 

Giancarlo L C and Flynn G W 1988 Scanning tunneling and atomic force microscopy probes of self-assembled, physisorbed monolayers A/ / . Rev. Phys. Chem. 49 297... 

The BET monolayer capacity N, calculated from the first water isotherm included both physisorbed and chemisorbed water, whereas that from the second isotherm iV, included only the physisorbed water. Thus the difference (iV, - N,) gave the amount of chemisorbed water taken up as hydroxyl groups during the isotherm determination. N, + iV ) was therefore the total concentration of hydroxyl groups on the surface when the second water isotherm was being measured. 

Representative results are given in Table 5.4. From column 7, it is seen that the ratio iV,/ Afj - - N/,) is in the region of 1 2 (in contrast to the 1 1 found with silica) suggesting that each molecule of water in the physisorbed monolayer is bonded to two surface hydroxyl groups. 

The principle underlying surface area measurements is simple physisorb an inert gas such as argon or nitrogen and determine how many molecules are needed to form a complete monolayer. As, for example, the N2 molecule occupies 0.162 nm at 77 K, the total surface area follows directly. Although this sounds straightforward, in practice molecules may adsorb beyond the monolayer to form multilayers. In addition, the molecules may condense in small pores. In fact, the narrower the pores, the easier N2 will condense in them. This phenomenon of capillary pore condensation, as described by the Kelvin equation, can be used to determine the types of pores and their size distribution inside a system. But first we need to know more about adsorption isotherms of physisorbed species. Thus, we will derive the isotherm of Brunauer Emmett and Teller, usually called BET isotherm. 

The relative product yields depend on the CHa to Cl ratio on the surface. In the studies reported here, this ratio has been adjusted to 1 1 (consistent with the CHa Cl stoichiometry in CHaCl) on the basis of a Cl(181 eV) C(272 eV) Auger peak ratio of 6.5 which is the same as that measured for physisorbed monolayers of dimethyldichlorosilane. Monolayer coverages of CHa + Cl having 1 1 stoichiometry were obtained by a 20 L exposure from the methyl radical source (approximately sahiration coverage) followed by a 9.5 L dose of CI2. 

All Pt(0) nanoparticles were washed with water and ethanol to completely remove physisorbed polymers from the nanoparticle surface. The final particles were stable and stored in water at the same concentration (3 x 10 M based on the original Pt salt concentration). The long-term stability is attributed to PVP monolayer(s) coating the... 

Fig. 2 (a) Edwards E308 evaporator. One quartz-crystal thickness monitor is pointed towards the Au source to monitor Au vapor deposition on chamber walls the other monitors Au deposited through the shadow mask atop the organic layer. In the cold Au deposition, a small amount of Ar gas is added to the chamber to cool the Au atoms to room temperature before they physisorb atop the cryocooled organic monolayer, (b) Geometry of an Au I monolayer I Au pad sandwich, with electrical connections made using a Ga/In eutectic... 

Another example consider the adsorption of bromine on silica. We start by placing elemental bromine and silica at either end of a long sealed vessel. Having a relatively high vapour pressure, bromine volatilizes and molecules of bromine soon chemisorp onto the surface of the silica. When the chemisorbed monolayer is complete, successive layers of bromine form by physisorption. The first physisorbed layer is unique,... 

For many systems, in particular physisorbed monolayers such as noble gases (He, Ar, Kr, etc.) adsorbed on grafoil " , a lattice gas model description is not microscopically realistic, since the corrugation potential is rather weak, forming only rather shallow minima at the preferred lattice sites. However, rather than studying a more realistic model, it is still possible to infer... 

Figure 9.6 Simulated CVD cluster morphology for coverages of -0.07 and 0.25 monolayer, showing the effect of differential dissociation probability, (a) and (b), versus the effect of a uniform dissociation probability, (c) and (d) the physisorbed precursor molecules are mobile in each case. Note, (c) and (d) are equivalent to the simulated morphology for growth by PVD. (Reproduced with permission from Reference [73].)...

On Au(lll) with o =10, a single H2O desorption peak is observed at 168 K, as shown in the right panel of Figure 6. This peak is due to physisorbed water on the oxygen monolayer. This coverage of oxygen blocks the high temperature desorption state, which indicates that the direct adsorption of water to the Au(lll) surface is blocked. 

Ex situ measurements in the presence of dissolved oxygen have proved that the mixed monolayer was stable in the solution free of 6TG and guanine. Madueno etal. [Ill] have also studied adsorption and phase formation of 6TG on mercury electrode. At high potentials, the molecules were chemisorbed and were able to form a self-assembled monolayer. When the potential was scanned to more negative values, reductive desorption of the monolayer was observed. Cathodic voltam-metric peaks, which are typical of a 2D condensed phase transition, divided the potential window into two regions one, in which self-assembled monolayer was stable, and the second, in which a physisorbed state existed. 

Preferential adsorption of a surfactant from a mixture depends on the structures of the amphiphiles and the substrate. Self assembly by physisorption is reversible, while that by chemisorption is irreversible. Thus, surfactants physisorbed in monolayers can be replaced by surfactants which are able to chemisorb. Such behavior was demonstrated by allowing a donor cyanine surfactant, D (capable of physisorption), and OTS (known to chemisorb) to... 

Removal of reversibly adsorbed (physisorbed) cyanine-dye molecules, D, led to skeletonized, SA silane monolayers having pinholes in the shape of D (Fig. 18) [185]. Such pinholes can, in turn, serve as templates for similarly shaped guest molecules. This approach opens the door for molecular recognition and device construction based on molecular recognition [186-190]. The idea relies upon the construction of a well-packed, SA monolayer from a mixture of OTS molecules and a solvent removable guest species. Removal of the guest molecules leaves pinholes with precise dimensions which only accept molecules with... 

The surface chemical groups present on the adherend surfaces consist of species chemically bonded to the surface. A real surface exposed to the environment contains not only the surface chemical groups but also physisorbed water, carbon monoxide and carbon dioxide molecules. The amount adsorbed depends on the surface free energy of the adherend and can range in thickness from portions of a monolayer to multilayers of material. 

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