Concentration of atomic hydrogen in a dielectric barrier discharge measured by two-photon absorption fluorescence

Rapid Synthesis of Noble Metal Colloids by Plasma-Liquid Interactions

The interactions between plasma and liquids cause complex physical and chemical reactions at the gas-liquid contact surface, producing numerous chemically active particles that can rapidly reduce noble metal ions. This study uses atmospheric-pressure surface dielectric barrier discharge (DBD) plasma to treat ethanol aqueous solutions containing noble metal precursors, and stable gold, platinum, and palladium colloids are obtained within a few minutes. To evaluate the mechanism of the reduction of noble metal precursors by atmospheric-pressure surface DBD plasma, the corresponding metal colloids are prepared first by activating an ethanol aqueous solution with plasma and then adding noble metal precursors. It is found that the long-lived active species hydrogen peroxide (H2O2) plays a dominant role in the synthesis process, which has distinct effects on different metal ions. When HAuCl4 and H2PdCl4 are used as precursors, H2O2 acts as a reducing agent, and AuCl4- and PdCl42- ions can be reduced to metallic Au and Pd. However, when AgNO3 is the precursor, H2O2 acts as an oxidising agent, and Ag+ ions cannot be reduced to obtain metal colloids because metallic Ag can be dissolved in H2O2 under acidic conditions. A similar phenomenon was also observed for the preparation of Pd colloid-PA with a plasma-activated ethanol aqueous solution using Pd(NO3)2 as a Pd precursor.

An atomic hydrogen etching sensor for H2 plasma diagnostics

A simple and selective new technique for atomic hydrogen flux measurements in a hydrogen plasma environment is introduced and demonstrated in this work. This technique works by measuring the etching rate of an amorphous carbon film and translating this to an incoming hydrogen radical flux through a well-defined carbon etch yield per radical. Ions present in the plasma environment have a much higher etch yield than radicals do. For that reason, suppression of the ion flux toward the carbon film is crucial to ensure that the observed carbon etch rate is dominated by atomic hydrogen etching. It is demonstrated that this can be achieved using a simple cylindrical pipe (hereinafter "chimney") in which a bend is introduced to enforce ion-wall collisions, neutralizing the ions. The chimney is made out of Macor, a material with low catalytic surface activity, to preserve the incoming atomic hydrogen flux while effectively suppressing ions. Ultimately, the etching sensor is deployed in a radio frequency inductively coupled hydrogen plasma operated at low pressure (1-10 Pa). Atomic hydrogen fluxes are measured and compared with heat flux sensor and vacuum ultraviolet absorption spectroscopy measurements in the same setup. All sensors agreed within a factor 4 in the atomic hydrogen flux range 10¹⁹ to 10²¹ m^-2 s^-1.

Radical theory of hydride atomization confirmed after four decades - determination of H radicals in a quartz hydride atomizer by two-photon absorption laser-induced fluorescence

The knowledge of hydrogen radical distribution opens a way to an elegant and straightforward optimization of hydride atomizers.

In an externally heated quartz atomizer, the most often used hydride atomizer for atomic absorption spectrometry, two-photon absorption laser-induced fluorescence (TALIF) was employed (i) to bring after four decades for the first time conclusive proof of the existence of H radical population sufficient to atomize hydrides thus confirming unambiguously the radical theory of hydride atomization and (ii) to determine the distribution of H radicals in the atomizer. Under typical operating conditions, H radicals are concentrated in an approximately 3 mm long cloud in the center of the optical arm and their peak concentration exceeds 10²² m^–3, i.e. four orders of magnitude above the typical analytical concentration of hydride. The lowest detectable H radical concentration is in the order of 10¹⁹ m^–3. The superb power of TALIF to determine the spatial distribution of H radicals in hydride atomizers for atomic absorption/fluorescence provides a route for elegant optimization of hydride atomization – just by establishing how the atomizer design and parameters influence the distribution of H radicals.

Precursors for Atmospheric Plasma-Enhanced Sintering: Low-Temperature Inkjet Printing of Conductive Copper

Bidentate diamine and amino-alcohol ligands have been used to form solid, water-soluble, and air-stable monomeric copper complexes of the type [Cu(NH2CH2CH(R)Y)2(NO3)2] (1, R=H, Y=NH2; 2, R=H, Y=OH; 3, R=Me, Y=OH). The complexes were characterized by elemental analysis, mass spectrometry, infrared spectroscopy, thermal gravimetric analysis, and single-crystal X-ray diffraction. Irrespective of their decomposition temperature, precursors 1-3 yield highly conductive copper features [1.5×10-6 Ω m (±5×10-7 Ω m)] upon atmospheric-pressure plasma-enhanced sintering.