Low-energy

Kaibel, G., Distillation Column Arrangements with Low Energy Consumption, IChemE Symp. Ser., 109 43, 1988. 

LEED See low energy electron dilTraction. lei See chelate effect, iepargylic acid See azeleic acid. 

In the low-energy region (< 250 keV) the unsharpness of the system IP/Scanner (here up to 70 pm for the best systems used) leads to a contrast reduction of small structures, e g., such as fissures/cracks. But, the available resolution is comparable or better than this one of the best... 

Fig. 1 High re.solution X-ray refraction topography of low energy impact (5J) at CFRP epoxy laminate. Image area 2 mm X 4 mm. Horizontal resolution 0.2 mm. The image represents selectively an area of debonded fibers of vertical fiber orientation.

Adapted input window and screen substrate allowing transmission of low energy X-rays. For very low energy (typically below 30 keV) a thin Be window is used. Such a window in combination with a Be screen substrate will make possible imaging down to 3 keV. 

The diffraction pattern consists of a small number of spots whose symmetry of arrangement is that of the surface grid of atoms (see Fig. IV-10). The pattern is due primarily to the first layer of atoms because of the small penetrating power of the low-energy electrons (or, in HEED, because of the grazing angle of incidence used) there may, however, be weak indications of scattering from a second or third layer. 

LEED Low-energy electron diffraction [62, 75, 105] Elastic backscattering of electrons (10-200 eV) Surface structure... 

LEIS Low-energy ion scattering [155-157] A monoenergetic beam of rare-gas ions is scattered elastically by surface atoms Surface composition... 

In practice, 7s 7sv is negligible as is dys/dT for systems having large contact angles. Also, low energy surfaces have a relatively constant value of dyst/dT = 0.07 0.02 erg cm K , leaving... 

Fig. X-10. The wettability spectrum for selected low-energy surfaces. (From Ref. 155.)...

Equation X-S3 has been found to fit data on the adsorption of various vapors on low-energy solids, the parameters a and a being such as to predict the observed d [135, 148]. 

The interesting implication of Eq. XII-24 is that for a given solid, the work of adhesion goes through a maximum as 7b(a) is varied [69]. For the low-energy surfaces Zisman and co-workers studied, )3 is about 0.04, and Wmax is approximately equal to the critical surface tension yc itself the liquid for this optimum adhesion has a fairly high contact angle. 

The technique of low-energy electron diffraction, LEED (Section VIII-2D), has provided a considerable amount of information about the manner in which a chemisorbed layer rearranges itself. Somotjai [13] has summarized LEED results for a number of systems. Some examples are collected in Fig. XVlII-1. Figure XVIII-la shows how N atoms are arranged on a Fe(KX)) surface [14] (relevant to ammonia synthesis) even H atoms may be located, as in Fig. XVIII-Ih [15]. Figure XVIII-Ic illustrates how the structure of the adsorbed layer, or adlayer, can vary wiA exposure [16].f There may be a series of structures, as with NO on Ru(lOTO) [17] and HCl on Cu(llO) [18]. Surface structures of... 

G. Ertl and J. Kuppers, Low Energy Electrons and Surface Chemistry, Verlag Chemie, Berlin, 1985. 

There will probably be some similarities, but also some fiindamental differences. We have mainly considered small molecules with relatively rigid structures, in which the vibrational motions, although much different from the low-energy, near-hannonic nonnal modes, are nonedieless of relatively small amplitude and close to an equilibrium stmcture. (An important exception is the isomerization spectroscopy considered earlier, to which we shall return shortly.)... 

It has also been shown that sufiBcient surface self-diflfiision can occur so that entire step edges move in a concerted maimer. Although it does not achieve atomic resolution, the low-energy electron microscopy (LEEM) technique allows for the observation of the movement of step edges in real time [H]. LEEM has also been usefiil for studies of epitaxial growth and surface modifications due to chemical reactions. 

Electrons are extremely usefiil as surface probes because the distances that they travel within a solid before scattering are rather short. This implies that any electrons that are created deep within a sample do not escape into vacuum. Any technique that relies on measurements of low-energy electrons emitted from a solid therefore provides infonuation from just the outenuost few atomic layers. Because of this inlierent surface sensitivity, the various electron spectroscopies are probably the most usefid and popular teclmiques in surface science. 

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