Ga1−xInxAs alloys in the composition range 0≤x≥0.52 and band-gap (Eg) range of 1.38 to 0.74 eV were activated with Cs and O2. Samples of different carrier concentrations were investigated. For band gaps down to about 0.8 eV, the photothreshold was equal to the band gap. The longest wavelength threshold determined was 1.58 μm. To the best of our knowledge, this represents the longest wavelength response yet achieved for photoemission into vacuum from a III-V compound. The surface escape probability, B, was derived from the quantum yield data for each sample. The B-vs-Eg data were analyzed according to a surface escape model which includes the effects of (i) a finite-width initial energy distribution of photoexcited carriers, (ii) the bent-band region and (iii) various types of surface potential barriers. Surface escape probability data pertaining to a single doping density could be explained by a model that includes only a work-function barrier or simple step potential. However, in order to explain the data for the several doping concentrations in a consistent manner, it was necessary to include an electron-semitransparent energy barrier above the vacuum level. A barrier width of 8 Å gives good agreement with the experimental data. This dimension is consistent with the thickness of the Cs–O activation layer which was experimentally determined to be on the order of a monolayer. These results are interpreted in terms of a surface double-dipole model.

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The Na2KSb photocathode has a longer threshold wavelength than the K2CsSb photocathode. This contradicts the general experience that cathode materials containing Cs tend to have longer threshold wavelengths. An attempt is made to explain this contradiction in terms of the energy-band models for the two materials.

A study of the electron diffraction diagram of Valonia ventricosa cellulose has confirmed the conclusions reached by Honjo and Watanabe concerning the size of its unit cell. The a and c axes of the cell are twice the length of those usually accepted for cellulose I. The symmetry of the cell is P1, but the evidence available at present does not allow a decision to be made concerning the symmetry of the molecular chains. Consideration of x‐ray diffraction and infrared spectroscopic data suggests that bacterial cellulose probably has the same unit cell as Valonia ventricosa, but that other native celluloses may have different cells.