Gas mixture for deep-UV plasma emission in a hollow-core photonic crystal fiber

We report on the first deep-ultraviolet/ultraviolet (DUV/UV) emission using a highly compact microwave-driven plasma-core photonic crystal fiber. The latter consists of a few centimeter long micro-plasma column of a gas mixture in the core of Kagome hollow-core photonic crystal fiber. The plasma is generated by nonintrusively exciting a ternary gas mixture of argon, nitrogen, and oxygen (Ar/N₂/O₂) with a microwave resonator. Several spectral lines in the wavelength range of 200-450 nm were produced, guided by an Ar-N₂-O₂ plasma-filled fiber, and controlled by simply varying the gas ratio of this gas mixture. An optimum gas mixture ratio was experimentally and theoretically identified for the strongest emission in the DUV range of 200-275 nm. The developed DUV emitting plasma-core fiber represents an important milestone towards the development of tunable and miniaturized DUV/UV laser sources.

Towards large-scale in free-standing graphene and N-graphene sheets

One of the greatest challenges in the commercialization of graphene and derivatives is production of high quality material in bulk quantities at low price and in a reproducible manner. The very limited control, or even lack of, over the synthesis process is one of the main problems of conventional approaches. Herein, we present a microwave plasma-enabled scalable route for continuous, large-scale fabrication of free-standing graphene and nitrogen doped graphene sheets. The method's crucial advantage relies on harnessing unique plasma mechanisms to control the material and energy fluxes of the main building units at the atomic scale. By tailoring the high energy density plasma environment and complementarily applying in situ IR and soft UV radiation, a controllable selective synthesis of high quality graphene sheets at 2 mg/min yield with prescribed structural qualities was achieved. Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Near Edge X-ray-absorption fine-structure spectroscopy were used to probe the morphological, chemical and microstructural features of the produced material. The method described here is scalable and show a potential for controllable, large-scale fabrication of other graphene derivatives and promotes microwave plasmas as a competitive, green, and cost-effective alternative to presently used chemical methods.

Generation and confinement of microwave gas-plasma in photonic dielectric microstructure

We report on a self-guided microwave surface-wave induced generation of ~60 μm diameter and 6 cm-long column of argon-plasma confined in the core of a hollow-core photonic crystal fiber. At gas pressure of 1 mbar, the micro-confined plasma exhibits a stable transverse profile with a maximum gas-temperature as high as 1300 ± 200 K, and a wall-temperature as low as 500 K, and an electron density level of 10¹⁴ cm⁻³. The fiber guided fluorescence emission presents strong Ar⁺ spectral lines in the visible and near UV. Theory shows that the observed combination of relatively low wall-temperature and high ionisation rate in this strongly confined configuration is due to an unprecedentedly wide electrostatic space-charge field and the subsequent ion acceleration dominance in the plasma-to-gas power transfer.

Modeling of surface-wave discharges with cylindrical symmetry

This paper presents the modeling of microwave (2.45GHz) discharges with cylindrical symmetry, produced in the absence of an external magnetic field by TM00 surface waves (SW) within either cylindrical or coaxial structures. A stationary, one-dimensional (radial) moment model (including the continuity and the momentum-transfer equations for electrons and positive ions, and the electron mean energy transport equations) is solved self-consistently coupled to Poisson's equation for the space-charge electrostatic field and the appropriated Maxwell's equations for the SW electromagnetic field. The model is solved for argon discharges over a broad range of operating conditions: Average electron densities from 10;{11}to3x10;{12}cm;{-3} and gas pressures from 10;{-2}to5Torr . Results are compared to those of a simplified classical model that disregards charge separation near discharge boundaries, ignoring also the development of electron-plasma resonances caused by the severe electron density gradients within space-charge sheath regions. Simulations show that the presence of a sheath-resonance region has a strong influence on the values of the SW attenuation constant, particularly at low pressures and high electron densities, affecting also the local budget of the discharge power deposition (hence discharge maintenance).

Natural infection by Giardia sp. and Cryptosporidium sp. in dairy goats, associated with possible risk factors of the studied properties

Visits were made to six farms raising dairy goats located in the mountain region of the state of Rio de Janeiro, Brazil, seeking to identify parasitism by Giardia sp. and Cryptosporidium sp. During the visits, fecal samples were collected from approximately 10% of the stock of each property. A questionnaire was given to the keepers on each property to obtain data for epidemiological analysis. A total of 105 fecal samples was collected, 56 from adult animals (over 12 months of age) and 49 from juvenile animals (less than 12 months). The fecal material was processed and subjected to the centrifuge-flotation technique and to staining with safranine-methylene blue. Protozoans of the genus Cryptosporidium were found at two properties, where the hygiene conditions of the installations were considered average and the stalls were made of wood slats raised from the ground. A total of five (4.8%) of the samples was found to be positive for the presence of this protozoan, all from juvenile animals. Cysts of the genus Giardia were found at two properties. Of the 105 samples analyzed, the protozoan was detected in 15 (14.3%), all in juvenile animals, and animals in the age range of 1-3 months had significantly more infections. Age, sanitary condition of the stalls and stalls made of wood slats and raised from the ground, can be pointed out as possible risk factors for infection by Giardia sp. and Cryptosporidium sp. The study reports for the first time the occurrence of Cryptosporidium sp. and Giardia sp. in goats in the state of Rio de Janeiro.