Surface energy deposition

Surfa.ce Energy. The surface energies of Parylenes N, C, and D were measured by observing the contact angles for several standard probe hquids. AH three have surface energies of approximately 45 mj/m (= dyn/cm), ie, all test Hquids having less than 45 mj/m surface tension completely wet the as-deposited parylene surfaces (43). 

The sputtering yield is proportional to the number of displaced atoms. In the linear cascade regime that is appUcable for medium mass ions (such as argon), the number of displaced atoms, E (E, is proportional to the energy deposited per unit depth as a result of nuclear energy loss. The sputtering yield Y for particles incident normal to the surface can be expressed as foUows (31). 

An even more ambitious goal is to characterize an unsupported catalyst, because the surface is extremely rough and the target rapidly deteriorates under bombardment. Energy deposition leads to enormous erosion, because the substrate cannot get rid of the energy deposited, owing to the low heat conductivity. As a consequence static LEIS conditions have to be used to obtain information on the surface alone. In Fig. 3.60a we show a series of LEIS spectra obtained with 5 keV Ne" ions on a... 

Israelachvili and his colleagues have used the SEA to study the interactions between surface layers of surfactant and of other molecules representing functionalised polymer chains, adhesion promoters or additives. Typically a monolayer of the molecule concerned is deposited onto cleaved mica sheets. The values of surface energies obtained from the JKR equation (Eq. 18) throw some interesting light on the nature and roughness of surface layers in contact. 

In a typical experiment, Israelachvili deposited monolayers of surfactants onto cleaved mica sheets, and evaluated the surface energies using the JKR equation. Fig. 11 contrasts results for mica coated with monolayers of (a) L-a-dipalmitoyl-phosphatidylethanolamine (DMPE) where j/a = = 27 mJ/m and (b) hexa-decyltrimethylammonium bromide (CTAB) where = 20 mJ/m and = 50 mJ/m. ... 

The MD simulations provided the necessary thermodynamic information to obtain the equilibrium configurations of the films. Often the deposition process will produce films which are not in the equilibrium configuration, and then the problem is to determine the stablity of these films against changes in morphology. Here simulations can also be helpful, since data on the surface energies and chemical potentials of strained films can be used to calculate the probability of cluster nucleation, using classical nucleation theory. 

As the metal particle size decreases the filament diameter should also decrease. It has been shown that the surface energy of thirmer filaments is larger and hence the filaments are less stable (11,17-18). Also the proportion of the Ni(l 11) planes, which readily cause carbon formation, is lower in smaller Ni particles (19). Therefore, even though the reasons are diverse, in practice the carbon filament formation ceases with catalysts containing smaller Ni particles. Consequently, well dispersed Ni catalysts prepared by deposition precipitation of Ni (average metal particle size below 2-3 nm) were stable for 50 hours on stream and exhibited no filamentous coke [16]. 

In metal deposition, the primary products form adsorbates on the electrode surface rather than a supersaturated solution. Their excess chemical potential is directly related to polarization and given by nFAE. The total excess surface energy = 2 S,o,. Otherwise, all the results described above remain valid. 

The size of the deposit depends on the size of the hole and not on polarization time, denoting a certain balance between electrochemical energy and the surface energy of the cluster. This technique has been also employed to study the filling of Au cavities by Bi and Ag. In the latter work, the behavior of Bi is contrasted with that of Ag. While the holes are filled at underpotentials in the first... 

Carbon deposition from CO on a cobalt catalyst at low pressures is known to be a structure-sensitive process. CO is adsorbed molecularly on the low index surfaces (Co (0001)), but its dissociation occurs on the Co (1012), Co (1120), and polycrystalline surfaces.5762 Deposition of carbon on Co (1012) and the probable formation of Co3C have been established by Auger emission spectroscopy (AES) and low-energy electron diffraction (LEED) techniques.66... 

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