Ultraviolet photoelectron spectroscopy (UPS) measurements of EMIM-DCA vapors have been conducted. Density functional theory (DFT), Møller–Plesset perturbation theory (MP2) and many-body perturbation ...theory calculations (GW) have been used to interpret the experimentally measured spectra. The vapor of ionic liquids normally consists of isolated ion-pairs and the corresponding photoemission spectra should reflect the electronic binding energies of the molecular orbitals. The UPS spectra have revealed that many photolines are shifted when compared to ab initio calculation results. The hybrid DFT functionals, which performed very good in the description of the UPS spectra of many other ionic liquid vapors have shortcomings in the EMIM-DCA case. The MP2 calculation and the quasiparticle GW approach are shown to offer a better description of the experimental UPS spectra. The charge distribution analysis showed that there seems to be a favorable charge transfer from the cation to the anion upon ionization. The new data provides strong support to the argument that in some cases DFT still has difficulties in the modeling of IL ion-pairs.
Ultraviolet photoelectron spectroscopy (UPS) investigations of several gas-phase ionic liquid (IL) ion pairs have been conducted. EMIMOTF, PYR14OTF, EMIMDCA, PYR14DCA, PYR14TCM, PYR14FSI, ...PYR14PF6, S222TFSI, P4441TFSI, and EMMIMTFSI vapor UPS spectra are presented for the first time. The experimental low-binding-energy cutoff value (highest occupied molecular orbital, HOMO energy) of the ionic liquid ion pairs, which is of great interest, has been measured. Many studies use calculated gas-phase electronic properties to estimate the liquid-phase electrochemical stability. Hybrid density functional theory (DFT) calculations have been used to interpret the experimental data. The gas-phase photoelectron spectra in conjunction with the theoretical calculations are able to verify most HOMO energies and assign them to the cation or anion. The hybrid M06 functional is shown to offer a very good description of the ionic liquid electronic structure. In some cases, the excellent agreement between the UPS spectra and the M06 calculation validates the conformer found and constitutes as a first indirect experimental determination of ionic liquid ion-pair structure. Comparisons with recent theoretical studies are made, and implications for electrochemical applications are discussed. The new data provide a much-needed reference for future ab initio calculations and support the argument that modeling of IL cations and anions separately is incorrect.
Photoelectron spectroscopy (PES) investigation of two widely used herbicide compounds MCPA and 2,4-D is reported. The GW calculations are shown to offer a good description of their electronic ...structure. There is excellent agreement between the experimental and theoretical energies of the HOMO states of 2,4-D and MCPA, which are at 8.7 eV and 8.5 eV binding energy, respectively. The low energy tail of the HOMO state extends to about 8 eV. The good agreement between the UPS (ultraviolet photoelectron spectroscopy) spectra and the simulation validates the proposed conformer. The presented gas phase data will help researchers to analyze data from liquid and diluted samples of these herbicide molecules and perform additional theoretical modelling.
•The UPS spectra of two widespread herbicides MCPA and 2,4-dichlorophenoxyacetic acid have been obtained and analyzed.•A side-by-side comparison of the geometric and electronic structures is presented.•There is excellent agreement between the experimental and theoretical energies of the HOMO states of 2,4-D and MCPA, which are at 8.7 eV and 8.5 eV binding energy, respectively.
•N2210(OTf) | molybdenum carbide derived carbon interface was investigated.•in situ X-ray photoelectron spectroscopy, mass-spectroscopy, impedance were applied.•Electroreduction of N2210+ started at ...E ≤ −1.30 V vs. Ag-QRE.•At E > 1.50 V ( vs. Ag), remarkable passivation of the carbon electrode took place.•Range of the nearly ideal polarizability for the RTIL | carbon system was 2.60 V.
The electrochemical behaviour of a protic quaternary amine cation based room-temperature ionic liquid (RTIL), diethylmethylammonium trifluoromethanesulfonate N2210(OTf), has been investigated at negatively and positively polarized molybdenum carbide derived micro-mesoporous carbon mmp-C(Mo2C) electrodes by in situ X-ray photoelectron spectroscopy (XPS), in situ mass-spectroscopy (MS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Collected data indicate that N2210(OTf) adsorbs strongly at E ≤ −1.10 V (vs. Ag-QRE) at the mmp-C(Mo2C) electrode. Intensive electroreduction of N2210+ cation took place at E ≤ −1.20 V (vs. Ag-QRE) producing various organic gases, instead of hydrogen, detected in situ by a restgas analyser. At E > 1.50 V (vs. Ag-QRE), remarkable passivation of the mmp-C(Mo2C) electrode took place. C1 s, O1 s, F1 s and S2p photoelectron signals became slightly distorted at E = 1.50 V (vs. Ag-QRE) indicating the formation of a surface film at mmp-C(Mo2C) involving triflate anion decomposition products.
•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.
FinEstBeAMS is a new materials science beamline at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It has been built based on grazing incidence monochromatization of synchrotron ...light, which allows to cover a remarkably wide excitation energy range from ultraviolet to soft x-rays (4.5–1450 eV). A new mobile luminescence spectroscopy end station has been commissioned with design benefitting from the advantages of a high flux elliptically polarizing undulator light source. We report on the design of the luminescence end station, its technical realization and performance achieved so far. Special attention is paid to the experimental challenges for luminescence spectroscopy under grazing incidence excitation conditions. The first luminescence results obtained demonstrate a reliable performance of the advanced setup at FinEstBeAMS.
FinEstBeAMS (Finnish–Estonian Beamline for Atmospheric and Materials Sciences) is a multidisciplinary beamline constructed at the 1.5 GeV storage ring of the MAX IV synchrotron facility in Lund, ...Sweden. The beamline covers an extremely wide photon energy range, 4.5–1300 eV, by utilizing a single elliptically polarizing undulator as a radiation source and a single grazing‐incidence plane grating monochromator to disperse the radiation. At photon energies below 70 eV the beamline operation relies on the use of optical and thin‐film filters to remove higher‐order components from the monochromated radiation. This paper discusses the performance of the beamline, examining such characteristics as the quality of the gratings, photon energy calibration, photon energy resolution, available photon flux, polarization quality and focal spot size.
The performance of the new Finnish–Estonian Beamline for Atmospheric and Materials Sciences is characterized and discussed.
The electrochemical properties of the C(Mo2C) | EMImB(CN)4 system have been analyzed using cyclic voltammetry, in situ X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy ...techniques. The cyclic voltammetry and electrochemical impedance measurements indicated that the tetracyanoborate anions started to electrooxidize and electropolymerize at E = 2.12 V (vs. Ag/AgCl in EMImBF4). However, despite of the formation of compact dielectric polymer layer at the micro-mesoporous C(Mo2C) electrode surface very slow electrochemical polymerization of tetracyanoborate anions continued further at E > 2.12 V leading to the blocking of the C(Mo2C) electrode porous structure and to the reduction of the electrochemically active surface area necessary for the construction of the high energy density supercapacitors. Thus, the tetracyanoborate anion based ionic liquids can be used as the electrolytes for the initial formation of the passivating solid-electrolyte interface for the very wide cell potential supercapacitor positive electrodes, as an electrolyte additives for the solid-electrolyte interface formation or for the correction of the solid-electrolyte interface damages.
We investigate yttrium-doped hematite thin-film photoelectrochemical properties and find yttrium incorporation to amply improve the performance as a photoanode for water splitting under visible ...light. We used the spray pyrolysis method to prepare a set of yttrium doped Fe2-xYxO3 (x = 0, 0.05, 0.10, 0.15, 0.2) thin films (thickness below 500 nm) on glass and transparent conductive oxide coated glass slides. Using a substitutional homovalent (Y3+) dopant, the effect on functionality is rationalised as a combined effect on the electronic structure and small polaron mobility from the lattice structure, impurity levels, lattice stability and variance in hybridisation. The photoelectrochemical response measurements indicate highest performance at Fe1.9Y0.1O3 composition.
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.
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