An amorphous Si (a-Si) solar cell with a back reflector composed of zinc oxide (ZnO) and silver (Ag) is potentially the most plausible and flexible solar cell if a graphite sheet is used as the substrate. Graphite supplies lightness, conductivity and flexibility to devices. When a graphite sheet is used as the substrate, carbon can diffuse into the Ag layer in the subsequent p-i-n process at 200–400 °C. To prevent this, we added an oxide layer as a carbon diffusion barrier between the carbon substrate and the back reflector. For the carbon diffusion barrier, silicon oxide (SiO2) or tin oxide (SnOx) was used. We evaluated the thermal stability of the back reflector of a carbon substrate using secondary-ion mass spectrometry (SIMS) to analyze the carbon diffusion barrier material. We confirmed the deposition characteristics, reflectance and prevention of carbon diffusion with and without the barrier. Finally, the structures were incorporated into the solar cell and their performances compared. The results showed that the back reflectors that were connected to a carbon diffusion barrier presented better performance, and the reflector with an SnOx layer presented the best performance.

Looking at the current status of beverages sold from vending machines in subway stations in Seoul, it was found that carbonated beverages accounted for the highest percentage of beverages on sale in vending machines, representing 36 % of all beverages sold. Survey respondents purchased carbonated drinks or sports drinks containing high levels of sugar to quench their thirst. Investigation of the sugar content of beverages frequently sold in vending machines showed that a serving of carbonated beverage contained an average of 30.4 g of sugar, or as much as 50.1 g of sugar (equivalent 10 to 17 cubes; 1 cube = 3 g of sugar). This amount corresponded, on average, with 60 % of the WHO recommended daily sugar intake (50 g). Surprisingly, with certain carbonated beverages, drinking a single can is equivalent to consuming the total recommended daily sugar intake of 50 g. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons. org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.