Liquid photocathodes

The mechanism of the liquid photocathode can be described as follows. The photon is absorbed by the TMAE. If the photon energy is greater than the ionization energy of TMAE in the liquid itself (3.55 eV) or in the hydrocarbon solution (--3.9 eV), a separated electron/positive ion pair results. The electron is drawn toward the liquid/vapor interface and, eventually, it is emitted into the gas space. The apparent quantum yield, r, observed is the product of the quantum yield for ionization of TMAE, Otot, the escape yield of charge carrier pairs in the liquid (or solid) bulk, Y, and by the emission probability, such that... 

Anderson, D. F., Extraction of electrons from a liquid photocathode into a low-pressure wire chamber, Phys. Lett., 118B, 230,1982. 

The main parts of a scintillation counter are sketched schematically in Fig. 7.13. In the transparent crystal or liquid the radiation is absorbed and photons are emitted. At the photocathode of the photomultiplier tube the photons release electrons which are multiplied by the dynodes of the multiplier to give pulses of several mV. Some examples of solid and liquid scintillators are listed in Table 7.1. 

Heller A., Miller B. and Thiel F. A. (1981b), 11.5% solar conversion efficiency in the photocathodically protected p-lnPW -V -HCl/C semiconductor liquid junction cell , Appl. Phys. Lett. 38, 282-284. 

Particles in a liquid show a random velocity distribution with V(u = 1 mm/s. What is the spectral line profile of the beat signal, if the direct beam of a HeNe laser at A, = 630 nm and the laser light scattered by the moving particles is superimposed on the photocathode of the detector ... 

If the efficiencies for photoelectric emission from the photocathodes of the phototubes in the liquid scintillation counter are a and the geometry is close to 100% efficient, the probability of measuring a coincidence due to the emission of two or more photons during the resolving time A will be approximately... 

The use of the liquid scintillation counter for chemiluminescence in the out-of-coincidence mode, at phototube-amplifier gains such that single photoelectrons are detected also means that the thermionic emission of the phototube photocathode will be counted with equal efficiency. If N and N represent the thermionic electron noise of the phototubes, the signal-to-noise ratio for chemiluminescence measurements will be approximately... 

Semiconductor-Liquid Junction From Fundamentals to Solar Fuel Generating Structures, Fig. 17 Energy schematic of a Z-scheme analogon light absorber/catalyst structure using a tandem-type cell design n- and p-type semiconductors act as photoanode and photocathode, respectively (see text) VB, CB valence and conduction band edges, respectively n", p" ... 

An alternative to the photochemical reduction is the photoelectrochemical reduction. p-Type semiconductor/liquid junctions are extensively studied as PV devices. The p-type semiconducting electrodes can act as photocathodes for photoassisted... 

The development of photocathode materials for either single- or dual-absorber cells has also received considerable attention [80, 101, 102]. Thermodynamic equilibrium dictates that p-type semiconductors will exhibit upward band bending when in contact with a liquid electrolyte. This behaviour is the opposite to that of n-type semiconductors described previously, and will result in the movement of photogenerated electrons towards the semiconductor-electrolyte interface while the holes are driven into the bulk of the electrode, towards the electrical back contact. At the surface, provided that the energy carried by the electrons is sufficient, H2 is evolved. As discussed previously, one of the electronic properties of metal oxides that makes them suitable for water photo-oxidation purposes is the O 2p character of the valence electrons, which places the VB edge at potentials... 

Figure 12 Absolute quantum yield for photocathodes with TMAE 1 — TMAE and solid neopentane 2 — TMAE and liquid neopentane 3 — liquid TMAE. (Redrawn from the data of Peskov, V., Charpak, G., Min P/ Sauli, F., Scigocki, D., Seguinot, J., Schmidt, W.F., and Ypsilantis, T., Nucl Instrum, Methods, A269,149,1988.)...

Small amounts of organic compounds of low ionization potential (see Section 4.2) can be dissolved in liquefied rare gases. The solubility increases from argon to xenon. The scintillation light leads to single photon ionization from which electron/ion pairs originate. The electrons are detected in the usual manner with a charge-sensitive amplifier (see Section 2.10). This way the sensitivity and resolution of rare gas liquid detectors can be improved. Another method uses the scintillation photons to eject electrons from a photocathode (Aprile et al., 1994). 

Charpak, G., Peskov, V., Sdgocki, D., and Lemenovski, D., Liquid and solid photocathodes and their applications for fast gaseous particle detectors, IEEE Trans. Electr. Insul, 26, 623,1991. 

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