Exoelectron emission

FIGURE 4.1. Agglomeration of Cu or Ag atoms in a noble gas matrix leads to electronically excited clusters that eject fluorescing atoms or dimers. 

As an example. Fig. 4.3 shows the intensity of electrons (a) and the variation of the work function (b) as a function of O2 exposure for a Li surface reacting with oxygen [9]. The electron yield increases continuously up to a maximum and then drops sharply, and the work function (f) decreases simultaneously continuously with progressing oxidation. The energy distribution of the emitted 

FIGURE 4.3. Emission of exoelectrons upon interaction of O2 with a Li surface [9]. (a) Electron intensity as a function of O2 exposure, (b) Variation of the work function with O2 exposure, (c) Kinetic energy distributions of the emitted electrons at three stages marked in (b). 

FIGURE 4.4. Potential diagram illustrating the mechanism of exoelectron 

Such a nonadiabatic reaction pathway appears to be rather improbable since the quenching of electronic excitations at metal surfaces is usually much faster than the timescale for nuclear motion, and with the02/Li system,theprobability for exoelectron emission is indeed 10 e/incident O2 molecule. The competition between nuclear and electronic motion is nicely reflected by the exponential increase of the electron )deld with the velocity of the impinging molecules as shown in Fig. 4.5 for the system O2 -I- Cs [11]. Note that a velocity of 2 x 10 m/s is equivalent to a distance of 0.2 nm in 100 fs, just in agreement with the timescales for electronic relaxation. 

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OSEE Optically stimulated exoelectron emission [143] Light falling on a surface in a potential held produces electron emission Presence and nature of adsorbates... 

NIRMS = noble-gas-ion reflection mass spectrometry OSEE = optically stimulated exoelectron emission PES = photoelectron spectroscopy PhD = photoelectron diffraction SIMS = secondary ion mass spectroscopy UPS = ultraviolet photoelectron spectroscopy ... 

In summary, the degradation of the PFPE lubricants is a complex process involving several mechanisms, including thermal decomposition, catalytic decomposition, tribo-chemical reactions activated by exoelectron emission, and mechanical scission, which comes into the play simultaneously. 

Electron emission occurs when plastic deformation, abrasion, or fatigue cracking disturbs a material surface. Triboelectrons are emitted from freshly formed surface. The emission reaches a maximum immediately after mechanical initiation. When mechanical initiation is stopped, the emission decays with time. Strong emission has been observed for both metals and metal oxides. There is a strong evidence that the existence of oxides is necessary. The exoelectron emission occurs from a clean, stain-free metallic surface upon adsorption of oxygen (Ferrante 1977). 

Kobzev, N.I. (1962) Exoelectronic Emission, Foreign Publishing House, Moscow, Russia. 

Nakahara, S. Fujita, T. Sugihara, K. Proc. 8th Exoelectron Emission Svmp.. 1985. 

CD ZnSe has also been demonstrated to passivate surface states, 0.92 eV below the conduction band edge (measured by thermally stimulated exoelectron emission) on single crystal GaAs. This passivation resulted in bandgap luminescence from the originally non-luminescent GaAs [49a]. 

In the meantime, the reactivity of milled aluminum correlated well with the intensity of exoelectron emission. Such an emission decayed with time after termination of milling, along with the suppression of the chemical reaction. The aluminum, which had entirely lost electron emission activity, did not react with butyl bromide at all. Alkyl halides capture free electrons. The emission intensity of the free (unused) electrons under butyl bromide atmosphere was less than 20% of that under benzene atmosphere. In other words, exoelectrons are captured with butyl bromide more easily than with benzene. Butyl bromide has much stronger electron affinity than benzene. 

Triboemission time is extremely short while after-emission time is much longer. The enhanced surface activity caused by rubbing processes produces exoelectrons emission, catalytic and structural factors, increased surface temperature, and pressure (Rowe and Murphy, 1974). 

The good correlation between the exoelectrons emission intensity and the standard heat of formation (AHf) of the compounds strongly suggests that the electrons are excited by the exothermic reactions (Nakayama et al., 1995 Wei and Lytle, 1976). Exoemission intensity is related to the maximum possible kinetic energy of the electrons, which can be expressed as tribochemical energy (TribEn)... 

Catalytic activity of rubbing surfaces (a) By reference to Table 5.5, find the metal hydroxides, oxides and nitrides that illustrate their highest exoelectrons emission intensity (I, cps), (b) Calculate the tribochemical energy (TribEn) TribEn = (AHf - WF) for the listed compounds and correlate them with measured exoelectrons emission intensity (I, cps). Explain differences. 

Connelly, M. and Rabinowicz, E., Detecting Wear and Migration of Solid-Film Lubricants Using Simultaneous Exoelectron Emission, ASLE Trans., 26, 139, (1983). 

The most important factor governing the tribochemical reactions under boundary friction is associated with the action of exoelectrons with lubricating oil components [21]. This is the basis of negative ion-radical action mechanisms, NIRAM. The general model of NIRAM assumes creation of two types of activated sites on friction surfaces, i.e. thermally activated sites and sites activated by exoelectron emission, FEE processes, Fig. 8.4. Comparison with thermally stressed solids and mechanically treated solids shows reactivity is often increased by several orders of magnitude, particularly in the low-temperature range. 

The author became interested in the models of confinement of the hydrogen atom inside finite volumes [2,14,17,18] in connection with the measurements of the hyperfine structure of atomic hydrogen trapped in a-quartz [19,20]. Ten years later, he extended his interests to confinement in semi-infinite spaces limited by a paraboloid [21], a hyperboloid [9] and a cone [22] in connection with the exoelectron emission by compressed rocks [23,24], Jaskolski s report [1] cited several of the above-mentioned works [9,14,17, 18,21], each one of which had formulated and constructed exact solutions for new types of confinement for the hydrogen atom. This subsection is focussed on his citation of our article [9] ... 

A. Scharmann and W. Kriegsels, in A. Bohan and A. Scharmann (Eds.), Symp. Exoelectron Emission Dosimetry, Zvikovske Podrahi, Prague, 1976, p. 5. 

Fluorescence was indeed observed for CI2 interacting with K surfaces, but with much lower yield than exoelectron emission, while in the reaction with O2 the light intensity was below the detection limit [16]. This is in agreement with general experience whereafter at metal surfaces, fluorescence is strongly suppressed by Auger deexcitation for energies up to 500 eV [17]. 

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