Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

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Plasma-liquid interactions: A review and roadmap

In recent years, structural colors have attracted great attention in a wide variety of research fields. This is because they are originated from complex interaction between light and sophisticated nanostructures generated in the natural world. In addition, their inherent regular structures are one of the most conspicuous examples of non-equilibrium order formation. Structural colors are deeply connected with recent rapidly growing fields of photonics and have been extensively studied to clarify their peculiar optical phenomena. Their mechanisms are, in principle, of a purely physical origin, which differs considerably from the ordinary coloration mechanisms such as in pigments, dyes and metals, where the colors are produced by virtue of the energy consumption of light. It is generally recognized that structural colors are mainly based on several elementary optical processes including thin-layer interference, diffraction grating, light scattering, photonic crystals and so on. However, in nature, these processes are somehow mixed together to produce complex optical phenomena. In many cases, they are combined with the irregularity of the structure to produce the diffusive nature of the reflected light, while in some cases they are accompanied by large-scale structures to generate the macroscopic effect on the coloration. Further, it is well known that structural colors cooperate with pigmentary colors to enhance or to reduce the brilliancy and to produce special effects. Thus, structure-based optical phenomena in nature appear to be quite multi-functional, the variety of which is far beyond our understanding. In this article, we overview these phenomena appearing particularly in the diversity of the animal world, to shed light on this rapidly developing research field.

https://iopscience.iop.org/article/10.1088/0034-4885/71/7/076401/pdf

Physics of structural colors

Biomimetics is the extraction of good design from nature. One approach to optical biomimetics focuses on the use of conventional engineering methods to make direct analogues of the reflectors and anti-reflectors found in nature. However, recent collaborations between biologists, physicists, engineers, chemists and materials scientists have ventured beyond experiments that merely mimic what happens in nature, leading to a thriving new area of research involving biomimetics through cell culture. In this new approach, the nanoengineering efficiency of living cells is harnessed and natural organisms such as diatoms and viruses are used to make nanostructures that could have commercial applications.

Biomimetics of photonic nanostructures

Members of the order Coleoptera are sometimes referred to as ‘living jewels’, in allusion to the strikingly diverse array of iridescence mechanisms and optical effects that have arisen in beetles. A number of novel and sophisticated reflectance mechanisms have been discovered in recent years, including three-dimensional photonic crystals and quasi-ordered coherent scattering arrays. However, the literature on beetle structural coloration is often redundant and lacks synthesis, with little interchange between the entomological and optical research communities. Here, an overview is provided for all iridescence mechanisms observed in Coleoptera. Types of iridescence are illustrated and classified into three mechanistic groups: multilayer reflectors, three-dimensional photonic crystals and diffraction gratings. Taxonomic and phylogenetic distributions are provided, along with discussion of the putative functions and evolutionary pathways by which iridescence has repeatedly arisen in beetles.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2008.0354.focus

Gold bugs and beyond: a review of iridescence and structural colour mechanisms in beetles (Coleoptera)

Electron–molecule collision calculations using the R-matrix method

A new experimental method is reported for the crossed beam measurement of absolute cross sections. It essentially consists in sweeping one of the beams across the other in a linear 'see-saw' motion. The method is applied to one case of electron-ion collisions. A description is given of an electron gun designed to realise a linear and distortionless motion of a ribbon electron beam. Measurements are reported regarding the electron impact ionisation of He+ in the energy range 55-74 eV.

https://iopscience.iop.org/article/10.1088/0022-3700/14/1/012/pdf

Crossed beam measurement of absolute cross sections: an alternative method and its application to the electron impact ionisation of He+

Samples of the cuticle taken from the body of Buprestidae Chrysochroa vittata have been studied by scanning electron microscopy and optical reflectance measurements, related to numerical simulations. The cause of the metallic coloration of the body of these insects is determined to be the structure of the hard carapace constructed as a stack of thin chitin layers separated by very thin irregular air gaps. In particular the change of color as a function of the observation angle is elucidated in terms of an infinite photonic-crystal model, confirmed by finite multilayer calculations. These mechanisms are used to develop an artificial bioinspired multilayer system which reproduces the visual effects provided by the insect surface.

Spectral filtering of visible light by the cuticle of metallic woodboring beetles and microfabrication of a matching bioinspired material

For pt.IV see ibid., vol.14, no.8, p.1353-671 (1981). Absolute cross sections for dissociative recombination of OH+, H2O+, H3O+ and D3O+ have been measured using a merged electron-ion beam apparatus through an energy interval from 0.01 to 1 eV. The recombination cross section for the diatomic OH+ is small, one of the smallest measured by the authors for a diatomic ion. The cross sections for the polyatomics H2O+, H3O+ and D3O+ are large and nearly identical. Like most other polyatomic ions they exhibit nearly an Ecm-1 energy dependence below approximately 0.1 eV. At higher energies the slope of the cross section versus electron energy is much steeper with an energy dependence near Ecm-2. Cross sections for D3O+ are less than those for H3O+ indicating the presence of a small isotope effect.

https://iopscience.iop.org/article/10.1088/0022-3700/16/16/028/pdf

Merged electron-ion beam experiments. V. Dissociative recombination of OH+, H2O+, H3O+ and D3O+

The dissociative recombination of the methane-derived group, CH+,...,CH5+, has been measured over the centre-of-mass energy interval 0.03 to 2 eV. Assuming a Maxwellian distribution of the electron velocities, the derived rate coefficients for CH+,...,CH5+ at 100K are, respectively, 5, 8.7, 12, 12.8 and 12.8*10-7 cm3 s-1. The recombination cross section for the diatomic ion CH+ is large. This has far reaching consequences for the theories of molecular formation in interstellar clouds. The cross sections for the polyatomics CH2+,...,CH5+ are also large and roughly equal in magnitude. Like CH+ they exhibit a close to E-1 energy dependence below 0.1 eV. For CH3+, CH4+ and CH5+ the slope of the cross sections increases above 0.1 eV.

https://iopscience.iop.org/article/10.1088/0022-3700/14/8/020/pdf

Merged electron-ion beam experiments. IV. Dissociative recombination for the methane group CH+,...,CH5+

Absolute cross sections have been measured for electron-impact ionization of Fe ions of initial charges 5+, 6+, and 9+ from below threshold to 1500-eV collision energies. Distorted-wave calculations including only direct ionization from ground-state ions underestimate the measured peak cross sections by 60--70Xdue to the effects of metastable states and contributions of excitation autoionization to the total cross sections. Ionization rate coefficients and fitting parameters are presented for this data and for Fe/sup +/ and Fe/sup 2+/.

Pierre Defrance

Papers

Crossed beam measurement of absolute cross sections: an alternative method and its application to the electron impact ionisation of He+

Spectral filtering of visible light by the cuticle of metallic woodboring beetles and microfabrication of a matching bioinspired material

Merged electron-ion beam experiments. V. Dissociative recombination of OH+, H2O+, H3O+ and D3O+

Merged electron-ion beam experiments. IV. Dissociative recombination for the methane group CH+,...,CH5+

Experimental Cross-sections for Electron-impact Ionization of Iron Ions - Fe5+, Fe6+, and Fe9+