Ramp-shaped feature

After an exposure of 20 L the surface topography changes in certain areas. Figure 4.18e shows such a location of the sample the circle marks the same area as the circle in Fig. 4.18d. Two different features were observed first, a large number of disc-like islands second, occasionally ramp-shaped features. The disclike islands have a diameter of 35 A and a height of about 3 A (see Fig. 4.19a). The patterned area appears to be rough compared to the smooth Gd or H/Gd surface on each terrace and is induced by the surface modification which will be... 

The computer signals the selection mirror to position itself so that one of the beams enters the White cell. A ramp voltage is then produced with 128 steps over a range just wide enough to encompass the absorption feature used for the measurement of species A. The line is scanned under computer control at a rate of approximately 10 Hz for 3 seconds (the approximate residence time of the gas in the White cell) and an accumulated "2f" line shape is acquired. 

As mentioned in the previous section, the apparatus is able to work in non-isother-mal conditions. This is a useful feature since in the chemical industry very often the reactions are initiated on a temperature ramp. A first series of experiments was carried out by successive injections of Q with the temperature ranging from 75 to 130 °C and a scanning rate of 0.12 °C min (see Figure 12). The first portion of Cl was injected just after the stable dynamic base line was reached all other injections were initiated after the heat evolution of the previous step had ceased. As expected, the shape of the curves representing the heat evolution with polymerization changes from two peaks at low temperatures (up to 95 °C) to one peak with a small shoulder at the highest injection temperature (about 105 °C). The intensity of the first peak is not influenced by temperature, but the intensity of the second one strongly increases with temperature, and consequently the monomer conversion also increases. 

A successful laser weld in the application of a hermetic seal requires precision aiming stability, vibration isolation between the work surface and the environment, accurate location of the weld position, and real-time optical power feedback. Good coordination among the laser power supply, the motion control system, the vision system, the control computer, and operator is critical. Advanced laser-welding systems often have features, such as real-time power feedback, power ramping, and pulse shaping, to achieve the best weld quality possible. 

Consider the cyclic voltammetry trace of electrically activated iridium oxide (the so called AIROF) which features reversible reactions (Fig. 3.3). The scan rate is very slow, so the dynamic behavior of the Helmholtz capacitance has a negligible effect on the measured trace. The positive peaks A and B correspond to two distinct oxidation reactions at the surface of the electrode, pertaining to different electrode potentials. The negative peaks C and D correspond to reduction reactions. C matches A and D matches B, as they have similar shape. The reduction potential peak (for example at C, Epc) does not happen at a negative electrode-electrolyte voltage drop, but at a positive one even near to the potential where oxidation potential peak (at A, Epa) is located. If the surface redox reactions are fast and the reaction rate is limited by the diffusion of the reactants in the solution, the difference between the oxidation and reduction peaks is only 59 mV/n for a reaction where n electrons are transferred in the stoichiometry of the reaction. This state is called electrochemical reversibility, which means that the thermodynamic equilibrium in the redox reaction at the surface is established fast at every applied electrode potential. Note that this concept is not the same as the chemical reversibility explained before. A system can be electrochemically irreversible but chemically reversible. As seen in Fig. 3.3, iridium oxide is already electrochemically irreversible even at the very slow potential ramp of 50 mV/s, as the , 4 — is already larger than 59 mV. 

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