Improved techniques for the diffusion of lithium in silicon are described. These techniques have been studied in view of their application to the fabrication of lithium‐doped silicon solar cells. The basic process selected consists of lithium diffusion, in a gas atmosphere, from a vacuum‐evaporated lithium layer. The improvements introduced afford protection of this layer from chemical reaction with the humidity of the laboratory atmosphere prior to diffusion. One way to obtain this protection is to combine the evaporation chamber with the diffusion furnace. Another way consists of converting the freshly evaporated lithium into Li3N by reaction with nitrogen. This delays the hydroxidation in the laboratory atmosphere without reducing the quantity of lithium available for diffusion. Experimental results obtained with both techniques are presented. They concern the doping density and profile, the electrical parameters of uniformly diffused slices, and the alloying effects observed at the surface. The diffusion constants of lithium in silicon have also been verified.

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Diffuse light has been shown to alter plant leaf photosynthesis, transpiration and water‐use efficiency. Despite this, the angular distribution of light for the artificial light sources used with common gas exchange systems is unknown. Here, we quantify the angular distribution of light from common gas exchange systems and demonstrate the use of an integrating sphere for manipulating those light distributions. Among three different systems, light from a 90° angle perpendicular to the leaf surface (±5.75°) was <25% of the total light reaching the leaf surface. The integrating sphere resulted in a greater range of possible distributions from predominantly direct light (i.e., >40% of light from a 90 ± 5.75° angle perpendicular to the leaf surface) to almost entirely diffuse (i.e., light from an even distribution drawn from a nearly 0° horizontal angle to a perpendicular 90° angle). The integrating sphere can thus create light environments that more closely mimic the variation in sunlight under both clear and cloudy conditions. In turn, different proportions of diffuse light increased, decreased or did not change photosynthetic rates depending on the plant species observed. This new tool should allow the scientific community to explore new and creative questions about plant function within the context of global climate change.

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