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Cs2O is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Cs2O sheets oriented in the (0, 0, 1) direction. Cs1+ is bonded in a distorted T-shaped geometry to three equivalent O2- atoms. All Cs–O bond lengths are 2.89 Å. O2- is bonded to six equivalent Cs1+ atoms to form edge-sharing OCs6 octahedra.
Cs2O is zeta iron carbide structured and crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. Cs1+ is bonded in a distorted trigonal planar geometry to three equivalent O2- atoms. There are two shorter (2.84 Å) and one longer (3.27 Å) Cs–O bond lengths. O2- is bonded to six equivalent Cs1+ atoms to form a mixture of edge and corner-sharing OCs6 octahedra. The corner-sharing octahedral tilt angles are 52°.
The oxidation of cesium on silver substrates has been studied using photoyield measurements and X-ray photoelectron spectroscopy. The occurrence of two O1s peaks in the core-level spectrum at 527.5 and 531.5-eV binding energy for cesium and oxygen exposures giving the optimum photoyield proves that two oxides of cesium exist in high-photoyield surfaces, and not Cs2O alone as previously thought. From the shape and position of the cesium peaks and the Auger parameter, the assignment of the O1s peaks at 527.5- and 531.5-eV binding energies to oxygen in Cs2O and Cs11O3, respectively, can be made. Hence the total cesium-oxygen layer is a mixed phase consisting of Cs2O + Cs11O3, approximately 20-40 A thick.
Zinc-doped InGaAsP quaternary III-V material of the proper composition range shows superior photoemission properties to either InGaAs or InAsP ternary material. The minority-carrier diffusion length in the quaternary material is at least as long as that in InAsP and much longer than observed in InGaAs. The barrier height at the InGaAsP-Cs2O interface is lowered by cooling, giving increased electron escape probability and new highs in quantum efficiency over a wide wavelength range. For example, a 1.06-micron quantum efficiency of 7.5%/incident photon was observed at -90 C.
Cesium carbonate (Cs2CO3) was heated to the decomposition temperature of approximately 600 C. The nonvolatile decomposition products were condensed on a nickel substrate while the carbon dioxide was removed by pumping. The deposited material is characterized by an effective work function of between 1.05 and 1.15 eV at 450 K and by photoemission in the visible and near-infrared region of the spectrum. It is suggested that the deposited material consists of Cs2O, possibly Cs2O2, and adsorbed cesium. Silver, evaporated from a heated silver bead, produced the typical photoemissive and thermionic properties of a silver-oxygen-cesium (S-1) photocathode. The material may be of interest for thermionic energy converters and for the formation of silver-oxygen-cesium photocathodes.
Superficially oxidized cesium antimonide photoemitting surfaces prepared in ultrahigh vacuum were studied by X-ray photoelectron spectroscopy. Oxidation of Cs3Sb to produce a surface with enhanced photosensitivity converts part of the antimony to elemental antimony and part of the cesium to cesium suboxide. The latter is identified on the basis of an O1 s peak at 531.3 eV, characteristic of Cs11O3. The production of Cs2O is not ruled out in this process since its signature at 527.5 eV is masked by an antimony shake-up peak at 527 eV.
An explanation is given for the results of recent enhanced Raman scattering studies of photomultiplier tubes with S-1 photocathode surfaces which indicated the presence of Cs11O3 but not Cs2O. The reason for the discrepancy between the currently accepted model of the S-1 and this recent result is discussed.