Functional measurement

Mobility of this second kind is illustrated in Fig. XVIII-14, which shows NO molecules diffusing around on terraces with intervals of being trapped at steps. Surface diffusion can be seen in field emission microscopy (FEM) and can be measured by observing the growth rate of patches or fluctuations in emission from a small area [136,138] (see Section V111-2C), field ion microscopy [138], Auger and work function measurements, and laser-induced desorption... 

Swanson L W and Davis P R 1985 Work function measurements Solid State Physics Surfaces(Methods of Experimental Physics 22) cd R L Park and M G Lagally (New York Academic) chi... 

This function measures the correlation of the property A (it) to itself at two different times separated by the time interval t, averaged over the whole trajectory. The auto-correlation function is reversible in time [i.e., CaU) = it)], and it is stationary (i.e., (A(it + t)A(t))... 

Note that k(t = 0) = 1. What does this function measure The function Q[q(t) — q follows each trajectory and counts 1 if the trajectory is in the product well and 0 otherwise. 

Functional measurement Relating the check on the performance of an item of equipment to the design specification. 

Distribution functions measure the (average) value of a property as a function of an independent variable. A typical example is the radial distribution function g r) which measmes the probability of finding a particle as a function of distance from a typical ... 

Correlation functions measure the relationship between two variables, x and y. A common definition is... 

It seems hard to support the above hypothesis on the basis of work function measurements for Hg in the presence of residual gases. Adsorption of water indeed reduces the work function and this is also the case with inert gases. There remains the possibility of surface oxidation by residual oxygen, but the values of Ayr measured with the Hg stream have been shown42,43 to be stable even in the presence of 02 impurities provided the gas flows rapidly, as was the case during the experiments. The same conclusion has been reached recently by measuring the work function of Hg in ambient gas.46... 

Work function measurements of Sb alloys with Sn, In, and Zn have... 

S. Ladas, S. Bebelis, and C.G. Vayenas, Work Function Measurements on Catalyst Films subject to in-situ Electrochemical Promotion, Surf. Sci. 251/252, 1062-1068 (1991). 

The technique of photoemission electron spectroscopy (PEEM) is a particularly attractive and important one for spatially resolved work function measurements, as both the Kelvin probe technique and UPS are integral methods with very poor ( mm) spatial resolution. The PEEM technique, pioneered in the area of catalysis by Ertl,72-74 Block75 76 and Imbihl,28 has been used successfully to study catalytic oscillatory phenomena on noble metal surfaces.74,75... 

D. Tsiplakides, S. Neophytides, and C.G. Vayenas, Investigation of electrochemical promotion using temperature programmed desorption and work function measurements, Solid State Ionics 136-137, 839-847 (2000). 

R. Imbihl, J. Janek The groups of Professors Imbihl and Janek have made important contributions in the use of PEEM, work function measurement and XPS (Chapter 5) to establish the O2 backspillover mechanism of electrochemical promotion under UHV conditions. 

Metcalfe The group of Professor Metcalfe has combined kinetic and work function measurements to investigate the electrochemical promotion of CO oxidation on Pt/YSZ and, more recently, had made important modeling advances for the fundamental description of electrochemical promotion at the molecular level. 

Kelvin probe technique and work function measurement, 138, 205, 340 experimental details, 340 two-probe arrangement, 340 Kinetics... 

Bertel, E. and Netzer, F.P. (1980) Adsorption of bromine on the reconstructed Au(lOO) surface LEED, thermal desorption and work function measurements. Surface Science, 97, 409-424. 

Figure 2.1 Real-time photoemission study (hv = 6.2 eV) of the interaction of oxygen (Po2 = 10- Torr) with a nickel surface at 300 K. The photocurrent decreases initially (A B), then recovers (B-C), before finally decreasing (CD). Surface reconstruction occurs (B-C) with further support from studies of the work function. The work function measured by the capacitor method15 increases by 1.5 eV with oxygen exposure at 80 K followed by a rapid decrease on warming to 295 K and an increase on further oxygen exposure at 295 K. These observations suggest that three different oxygen states are involved in the formation of the chemisorbed overlayer. (Reproduced from Refs. 15, 42).

Fig. 4.1.6 Spin-velocity density function measured for water flowing through a 6-mm diameter tube at 0.1 mL min-1 (left) and 2.5 mL min-1 (right). The velocity density function is spatially resolved along the Z] direction.

An objective function measuring the deviation from the parameterized model and the target response, determined, for example, from density functional theory based methods can be defined as... 

In surface science, work function measurements are considered to be rather sensitive towards changes of the sample surface. Work function measurements are used to follow adsorption processes and to determine the dipole established at the surface. During oxygen adsorption and oxide formation the sign of the work function change allows one to distinguish between oxygen atom adsorbed on the surface or sub-surface [30]. 

These measurements have verified that the work function of an electrode, emersed with the double layer intact, depends only on the electrode potential and not on the electrode material or the state of the electrode (oxidized or covered with submonolayer amounts of a metal) [20]. Work function measurements on emersed electrodes do not serve the same purpose as in surface science investigations of the solid vacuum interface. At the electrochemical interface, any change of the work function by adsorption is compensated by a rearrangement of the electrochemical double layer in order to keep the applied potential i.e. overall work function, constant. Work function measurements, however, could well be used as a probe for the quality of the emersion process. Provided the accuracy of the measurement is good enough, a combination of electrochemical and UPS measurements may lead to a determination of the components of equation (4). 

Signal function (measurement function, analytical function in the signal domain)... 

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