(c) In an air atmosphere, an oxygen photodesorption occurs when the excitation is above bandgap due to free hole concentration in valence band.
While the effect of charging adsorbed molecules is dependent of the quantity of oxygen molecules in the atmosphere, now the efficiency of photodesorption is decreased as in the band bending no free holes are available in valence band to promote the discharge of negatively charged oxygen molecules on surface.
As the main reason for the photodesorption is the presence of free holes near surface, the illumination below bandgap relieves the desorption of oxygen in gaseous form as indicated by the behavior of photoconductivity in Figure 7(b) as compared to Figure 7(a) for vacuum and air atmosphere.
"We also saw them popping up around Army barracks, theme parks and hospitals - anywhere where large numbers of people might be milling around where there wasn't a free hole
in the wall."
Synthetic ruby is almost completely wear resistant and heat resistan t, and the Bird manufacturing procedure ensures a burr free hole
for extremely regulated and consistent flow.The 0.0004 in.
Designed for use in the automotive and other metalworking industries where a burr free hole
is required, this tool drills and deburrs both front and rear of a hole in a single pass combining two operations in one step.
where [u.sup.-], [u.sup.+] are thermal velocities of free electrons and holes, respectively; [[sigma].sup.-.sub.i] is the capture cross section of free electrons at the traps of i-type; [[sigma].sup.+.sub.i] is the capture cross section of the free holes at recombination centers; and [[sigma].sup.-.sub.i] is the capture cross section of free electrons at the recharged luminescence center (the recombination cross section).
Assuming that the probability of recombination of the free holes with localized electrons can be neglected, in comparison with the probability of their localization at the luminescence centers, the lifetime of free holes can be written as follows:
The energy-band offsets at the donor/ acceptor interface in organic photovoltaics are key for generating free holes
and electrons by photoabsorption.
"Zinc oxide is a wide band gap semi-conductor and generating p-type doping impurities that provide free holes
is very difficult--particularly in nanowires," says Wang.
Here, D is diffusion coefficient, [psi] is electrostatic potential, q is electron charge, G is generation rate, [zeta] is permittivity, and n, p, [n.sub.t], and [p.sub.t] are free holes
, free electrons, trapped holes, and trapped electrons, respectively.
And the government would not have launched its initiative to get hundreds of free holes
in the wall sited in low-income communities.