This study presents an outline of the 12 principles of green relevance in nanomaterial synthesis. The goal of using green renewable resources is to protect the environment from negative effects, which can be achieved via several main directions, including the choice of innocuous solvents, such as supercritical (SC) fluids or water, and/or additives (i.e. stabilizers, capping, and reducing agents) such as polysaccharides, using alternative reaction circumstances, and the development of energy-efficient synthetic methods. This review shows how different green renewable resources routes are reducing the impact of chemical processes on the environment and how their benefit can be achieved in nanotechnology applications such as green energy.

The development of porosity in single-crystal germanium and silicon-germanium alloys (c-Si1−x Gex) of (100) orientation was studied under bombardment with 140 keV Ge− ions over a wide range of temperatures (−180 to 400 °C) and ion fluences up to 1 × 1018 ions/cm2. The surface swelling and morphology were investigated using multi-characterization techniques including optical profilometry, transmission electron microscopy, and scanning electron microscopy. The initiation of porosity and the evolution of the near-surface microstructure strongly depend on the ion fluence, the irradiation temperature, and the stoichiometry of the substrate. Significant results and new findings include: (i) the fact that, over the entire temperature and stoichiometry range, porosity is only developed once the substrate is rendered amorphous; (ii) with increasing Si content in the alloy, the onset of porosity is pushed to higher fluences; (iii) porosity is observed for Si contents in the alloy up to 23% but not higher under the irradiation conditions used; and (iv) in all cases the initiation of porosity was observed to occur at the surface of the amorphous alloy above a threshold fluence. This last result strongly suggests that the mechanism for initiation of porosity is via preferential vacancy segregation and clustering at the surface of the amorphous alloy. Particularly at elevated temperatures, preferential sputtering of the Si-Ge atomic species in the alloy also plays an important role in developing the surface topography and porosity in alloys. Such effects are discussed along with the implications of our results for mechanisms of porosity in Ge and its alloys.

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Ion induced porosity in Ge has been investigated with and without a cap layer for two ion species, Ge and Sn, with respect to ion fluence and temperature. Results without a cap are consistent with a previous work in terms of an observed ion fluence and temperature dependence of porosity, but with a clear ion species effect where heavier Sn ions induce porosity at lower temperature (and fluence) than Ge. The effect of a cap layer is to suppress porosity for both Sn and Ge at lower temperatures but in different temperatures and fluence regimes. At room temperature, a cap does not suppress porosity and results in a more organised pore structure under conditions where sputtering of the underlying Ge does not occur. Finally, we observed an interesting effect in which a barrier layer of aGe that is denuded of pores formed directly below the cap layer. The thickness of this layer ($ 8 nm) is largely independent of ion species, fluence, temperature, and cap material, and we suggest that this is due to viscous flow of aGe under ion irradiation and wetting of the cap layer to minimize the interfacial free energy. Published by AIP Publishing.

Crystalline Ge and Si 1Àx Ge x alloys (x ¼ 0.83, 0.77) of (100) orientation were implanted with 140 keV Ge À ions at fluences between 5 Â 10 15 to 3 Â 10 17 ions/cm 2 , and at temperatures between 23 C and 200 C. The energy deposition of the ions leads to the formation of porous structures consisting of columnar pores separated by narrow sidewalls. Their sizes were characterized with transmission electron microscopy, scanning electron microscopy, and small angle x-ray scattering. We show that the pore radius does not depend significantly on the ion fluence above 5 Â 10 15 ions/cm 2 , i.e., when the pores have already developed, yet the pore depth increases from 31 to 516 nm with increasing fluence. The sidewall thickness increases slightly with increasing Si content, while both the pore radius and the sidewall thickness increase at elevated implantation temperatures.