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•A strong fluorine depletion from the PTFE surface after H2 plasma treatment.•Already only VUV radiation itself can cause depletion of fluorine.•The strongest F depletion observed ...after a synergistic exposure to VUV and H atoms.•Only H atoms without the help of VUV were not effective enough.
Modification of polytetrafluoroethylene (PTFE) surface upon treatment with reactive species from hydrogen plasma (ions, neutral atoms, and UV/VUV) as well as synergistic effects are presented and explained. PTFE samples were either directly exposed to hydrogen plasma or separately to UV/VUV radiation or atomic hydrogen, and the resulting evolution of the surface composition was determined by X-ray photoelectron spectroscopy. High-density plasma was created by an inductively-coupled radiofrequency discharge in the H-mode. Samples placed in specially designed holders were covered with various optical windows (magnesium fluoride, quartz glass, or borosilicate glass), to allow for separate treatments with either VUV, UV or visible radiation. Rapid fluorine depletion was observed either at a direct exposure to plasma or to VUV; however, the best results were observed at a combined treatment with VUV/UV and atomic hydrogen. For direct treatment, a minimum in the F/C ratio was observed at the shortest time of 1 s. The F/C dropped from 2.2 to 0.4, whereas at longer times it increased to 1. For treatment with UV/VUV and for the combined treatment with UV/VUV and atoms, the F/C decreased with treatment time and stabilized at 0.6 and 0.4, respectively. Exposure to the afterglow did not result in significant modification.
Phase-pure crystalline micropowder samples of BaGeF6 were prepared and studied under excitation by tuneable synchrotron radiation and 10 keV electron beam. Time-resolved photoluminescence emission ...and excitation spectra and a set of single emission decay curves were recorded at 7 K for the exciting photon energy region of 4.3–45 eV. Several intrinsic emissions were revealed in BaGeF6 and their origin investigated. A single broad emission band peaking at 455 nm is assigned to be of excitonic origin due to its long decay time in the μs range and due to the presence of an intense excitation peak at 10.1 eV right in the region of the host absorption onset. The energy gap width of BaGeF6 was determined experimentally from the photoluminescence excitation spectra of the 455 nm emission to be 10.9 eV. Several emission bands, including distinct peaks at 270 and 455 nm, with the main decay component of ∼180 ps were revealed across the wavelength range of 200–500 nm. The revealed ultrafast emissions were studied by means of time-resolved photoluminescence spectroscopy and their origin was assigned to cross-luminescence resulting from radiative transitions between the Ba 5p core level and sub-bands of the valence band (Ge 4s, Ge 4p and F 2p hybridized states) and to intraband luminescence between the valence band sub-bands. Photoluminescence excitation spectra of the ultrafast emissions revealed a gently sloping onset at 17 eV, related to transitions from the Ge 4s states. It is followed by a distinct peak at 19.4 eV, which corresponds to the ionization of the Ba 5p cation states and is related to the excitation threshold of cross-luminescence.
•Crystalline BaGeF6 microrods were synthesized and characterized using XRD and SEM.•Ultrafast emissions (∼180 ps) were revealed in the UV-to-visible spectral range.•Cross-luminescence is due to transitions from Ba 5p to Ge 4s, 4p and F 2p states.•Intraband luminescence is due to transitions between Ge 4s,4p, F 2p valence bands.•Electronic band structure parameters of BaGeF6 were experimentally determined.
•Proton transfer processes in gaseous clusters of Acrylonitrile (ALN) and acetonitrile (ATN) molecules.•Effect of conjugation and hyperconjugation.•The conjugation effect in ALN induces a high proton ...transfer barrier.•The hyperconjugation in the ATN molecule makes the proton transfer process a low-barrier or no-barrier process.
Acrylonitrile (ALN) and acetonitrile (ATN) are two important interstellar molecules that contain nitrogen atoms. Herein, we explore the proton transfer processes occurring in gaseous clusters of ALN and ATN molecules with the aid of synchrotron vacuum ultraviolet radiation. We investigated the proton transfer phenomenon by use of time-of-flight mass spectrometry as well as theoretical calculations. We observe that the mass spectra of ALN and ATN clusters are apparently different from each other. In the mass spectrum of ALN clusters, the peaks related to un-protonated cluster cations are dominant. Unlike the ALN clusters, the protonated cluster cations are dominant in the mass spectrum of ATN clusters. These results are attributed to the different conjugate and hyperconjugate molecular structures in ALN and ATN, respectively. Theoretical calculations show that the conjugation effect between the πC=C orbital and πC≡N orbital in ALN induces a high proton transfer barrier that determines the dominant peaks of its non-protonated clusters cations. Conversely, the hyperconjugation between the σCα-H and πC≡N orbital in the ATN molecule determines that the proton transfer process in ATN is a low-barrier or even a no-barrier process. This favors the formation of protonated clusters. The present results reveal that ALN clusters are more aprotic than those consisting of ATN, and a relative high energy barrier is needed to surmount the proton transfer process of ALN clusters. This property of ALN makes it an appropriate candidate molecule to form the membrane alternative in the liquid methane lakes of Titan. ATN is not an appropriate candidate.
The parameters of a discharge in xenon formed by voltage pulses with a duration at half-maximum of 0.7 ns were studied. It has been confirmed that at the stage of the formation of the diffuse ...discharge, the most intense radiation in the 120-800-nm region is concentrated in the band with a maximum at the wavelength of 172 nm (the second continuum of xenon dimers). It was found that recombination continua appear after the discharge contraction, which occurs faster with a decrease in the interelectrode distance or an increase in the input energy. It is shown that the Xe<inline-formula> <tex-math notation="LaTeX">_{2}^\ast </tex-math></inline-formula> radiation pulse duration at gas pressures of 0.3-3 atm significantly exceeds the duration of the incident voltage pulse. In their articles, Baryshnikov and Paperny claim that there is no radiation of the second continuum in a diffuse discharge plasma of xenon. Thus, the results obtained indicate that the data given in these articles require additional verification of the measuring techniques of VUV radiation, as well as, the voltage across the gap and discharge current.
•Crystalline K2GeF6 particles were synthesized by co-precipitation.•Fast cross- and intraband luminescence with decay times 300–500 ps was observed.•Transitions between valence sub-bands (Ge 4s,4p, F ...2p) cause intraband luminescence.•The decay of K 3p cation excitons results in the formation of Ge 4s,4p holes.•Electronic band structure parameters of K2GeF6 were experimentally determined.
Highly crystalline K2GeF6 micropowders were prepared by co-precipitation in the hydrofluoric acid-water-alcohol solution and studied by means of the cathodoluminescence and time-resolved luminescence spectroscopy under synchrotron radiation excitation at 7 K. The nature of various intrinsic emissions was revealed. The luminescence band at 510 nm detected under excitation by photons with the energy above 9 eV is related to the radiative decay of self-trapped excitons. Fast emission bands with ~400 ps decay time found in the spectral range from VUV to visible (8–2.4 eV) are assigned to the cross-luminescence transitions from K 3p hole states and intraband luminescence transitions due to the presence of the Ge 4s, 4p valence states. The creation of cation excitons was detected in the energy range 18–20 eV. Their non-radiative decay results in the formation of hole states in the Ge energy bands, which finally recombine with electrons from the above lying valence states and provide fast intraband luminescence. Important electronic band structure parameters including the energy gap width of 11 eV, cation exciton formation energy 18.1 eV and ionization energy of cation states 20.0 eV were determined from the luminescence excitation spectra.
This paper reports laboratory measurements of the spectrum of the most abundant transition Fe ions in the universe. Spectrum of iron of low-lying excited states has been observed in the wavelength ...range 250–400
Å at Chinese Institute of Atomic Energy on the HI-13 tandem accelerator with beams of 130
MeV. A number of spectral lines have been mainly classified as transitions of magnesium-, sodium-, neon-, fluorine-like ions. A total of 54 lines have been measured. Most of them have been mainly ascribed to 3s3p
k
–3p
k+1
, 3s
23p
k
–3s3p
k+1
, 2p
53s–2p
53p, 3s3d–3p3d and 2p
53p–2p
53d resonance transitions. These spectral lines have been identified, among which 21 are new and accurately measured. The analysis of the spectra was based on a comparison with other experimental results and calculated values.
Obtaining new data on the gas-dynamic responses from the polymer samples (polytetrafluoroethylene, PTFE) irradiated by powerful VUV radiation from compressed plasma flows is in the focus of the ...present study. An erosion type magnetoplasma compressor (MPC), a type of plasma focus discharge, was used as a radiation source. The operating voltages of the MPC were between 15 and 25 kV, the maximum measured discharge current was 200 kA, and the radiation energy in the VUV range was ≈1–2 kJ. The VUV fluxes on the sample surface were high and equal to ≈1022–1024 photons cm−2·s−1. Double-exposure laser holographic interferometry and schlieren photography were used to diagnose and visualize the gas-dynamic structures. The spatial distribution of the parameters (temperature, pressure and concentrations of electrons and ions) was defined based on the assumption of local thermodynamic equilibrium. It has been demonstrated that the maximum temperature ranged from ≈ 10 to 15 kK in the plasma layer. The electron concentration was ≈ (0.7–1.6) × 1018 cm−3 in this region. The used techniques of optical diagnostics and procedures of result processing make it possible to obtain data on the dynamics of polymer ablation, which occurs when their surface is exposed to powerful energy fluxes (thermal, shock-wave, radiation, and other extreme loads).
Defluorination of polytetrafluoroethylene (PTFE) surface film is a suitable technique for tailoring its surface properties. The influence of discharge parameters on the surface chemistry was ...investigated systematically using radio-frequency inductively coupled H
plasma sustained in the E- and H-modes at various powers, pressures and treatment times. The surface finish was probed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The measurements of water contact angles (WCA) showed increased wettability of the pristine PTFE; however, they did not reveal remarkable modification in the surface chemistry of the samples treated at various discharge parameters. By contrast, the combination of XPS and ToF-SIMS, however, revealed important differences in the surface chemistry between the E- and H-modes. A well-expressed minimum in the fluorine to carbon ratio F/C as low as 0.2 was observed at the treatment time as short as 1 s when plasma was in the H-mode. More gradual surface chemistry was observed when plasma was in the E-mode, and the minimal achievable F/C ratio was about 0.6. The results were explained by the synergistic effects of hydrogen atoms and vacuum ultraviolet radiation.
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