An atmospheric pressure surface-wave microwave discharge and a kHz plasma jet are used to activate purified water. It is shown, that by varying the treatment distance and the initial Ar/N 2 /O 2 mixture composition of the surface-wave microwave discharge the concentration ratio of NO 3 − and H 2 O 2 radicals created in the plasma activated water (PAW) can be varied over three orders of magnitude, which can be preserved during months of storage at room temperature. At the same time, with the 5min treatment of the 32ml water the absolute radical concentrations are varied in the range of 0.5-85mg l −1 for H 2 O 2 , 20-180mg l −1 for NO 3 − and 0.5-14mg l −1 for NO 2 −. In the case of the N 2 kHz plasma jet this concentration ratio can be tuned within one order of magnitude by varying the treatment distance. By treating different volumes very similar concentration ratios are obtained, which evolve differently during storage, as the ageing dynamics is determined by the absolute concentration of radicals. In general, the radical most affected by ageing is NO 2 − , whose recombination is found to be determined by the H 2 O 2 radical. In order to control the H 2 O 2 concentration and thus the NO 2 − radicals recombination, the application of a Fenton type reaction is suggested, which is implied by inserting a copper surface into PAW during or after plasma treatment.

The metastable He atoms play an important role in atmospheric pressure plasma jet (APPJ) chemistry processes and in the plasma generation. This work presents cavity ringdown spectroscopy (CRDS) investigation of metastable helium atom (2 S 3 1 ) densities in a single electrode APPJ during sample treatment. A spatially resolved density distribution of a free jet (without sample) was measured at a He flow rate of 2 slm. The maximum measured density of a free jet was around × 7 10 11 cm −3 . With the insertion of a sample the densities increased up to 10 times. Helium metastable atoms, in a single electrode helium APPJ (2 slm, ≈2.5 kV, pulsed DC, 10 kHz repetition rate), decayed exponentially with a mean lifetime of ± 0.27 0.03 μs. Eight different samples of the same sizes but different conductivities were used to investigate the influence of a sample material on the He metastable densities. The correlation between sample conductivities and metastable He densities above the sample surface was found. Metastable He density can also be further increased with decreasing sample distance, increasing conductive sample surface area and by increasing He flow.

The temperature-induced reversible phase transition of N′-2-propylidene-4-hydroxy­benzo­hydrazide from the polymorphic Form II to Form III, and vice versa, is accompanied by the dramatic change of the macroscopic dimensions of the crystal which resulted in the pronounced mechanical motion (jumping) during the phase transition. Prior to the phase transition, the extremely large uniaxial negative thermal expansion along one crystal axis (b axis) was observed, together with the positive thermal expansions along the other two crystal axes. Form III of N′-2-propylidene-4-hydroxy­benzo­hydrazide exhibits the thermal expansion α c = 360 × 10–6 K–1, which is the largest value ever noticed in any organic or metal–organic crystal. From the structural point of view, a thermosalient effect is escorted by the springlike behavior of the zig-zag molecular assemblies along the c axis. First-principles electronic structure calculations show that negative thermal expansion arises from the elastic properties of the crystal which show uniaxial negative compressibilities, NLC. Form III exhibits the negative compressibility along the 001 direction β3 = −28 TPa–1, which is 1 order of magnitude larger than that of any organic compound and, in fact, is comparable to compressibilities of molecular frameworks showing the most pronounced NLC behavior. Elastic properties are also the reason for the reversibility of Form II to Form III transition in contrast to the irreversible Form I to Form II transition. Low energy springlike phonons are easily thermally excited and can assist in the overcoming of the energy barrier between the two phases that precedes thermosalient transition.

Pulsed cavity ring-down spectroscopy (CRDS) is a direct absorption, highly sensitive, versatile technique suitable for the analysis of a wide range of plasmas. CRDS belongs to a wide class of cavity-enhanced spectroscopies. This work briefly describes the basic principles of CRDS and summarizes the main literature specifically related to applications for atmospheric pressure plasma jets (APPJ). Emphasis is given to the temporal resolution and pulsed character of the plasma sources. As an example we present in more detail the determination of metastable helium density in the 2s S 3 1 state produced in a single-electrode atmospheric pressure plasma jet driven by a pulsed high-voltage waveform. Measured He( S 3 1 ) number densities ranged from × −

Low‐pressure nonequilibrium plasmas can be a source of intense radiation in the vacuum ultraviolet (VUV) range which can play an important role in the surface modification of solid materials. Herein, we review the available literature on VUV radiation from low‐pressure gaseous plasmas sustained by inductively and capacitively coupled radiofrequency discharges, microwave, and magnetized discharges. The reported VUV fluxes range from about 1014–1017 photons cm−2·s−1 while electron density range from 109 to 1012 cm−3. The correlations between the measured VUV fluxes and parameters, such as gas pressure, electron density, and discharge power are shown. The results summarized in this study represent a rough guide for the scientists involved in plasma–surface interactions. As the flux of VUV photons depends on numerous parameters, it is currently only possible to estimate its order of magnitude.