Surface structures of equimolar mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy

Surface structures of equimolar mixtures of imidazolium-based ionic liquids (ILs) having a common cation (1-butyl-3-methylimidazolium ([C₄MIM]) or 1-hexyl-3-methylimidazolium ([C₆MIM])) and different anions (bis(trifluoromethanesulfonyl)imide ([TFSI]), hexafluorophosphate ([PF₆]) or chlorine) are studied using high-resolution Rutherford backscattering spectroscopy (HRBS). Both cations and anions have the same preferential orientations at the surface as in the pure ILs. In the mixture, the larger anion is located shallower than the smaller anion. The [TFSI] anion is slightly enriched at the surface relative to [PF₆] with coverage of ~ 60% for the equimolar mixtures of [C₄₍₆₎MIM] [TFSI] and [C₄₍₆₎MIM] [PF₆]. No surface segregation is observed for [C₆MIM] [TFSI]_0.5[Cl]_0.5 and [C₆MIM] [PF₆]_0.5[Cl]_0.5. These results are different from the recent TOF-SIMS measurement where very strong surface segregation of [TFSI] was concluded for the mixture of [C₄MIM] [TFSI] and [C₄MIM] [PF₆].     

Acoustic cavitation in 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide based ionic liquid

In this work, a comparison between the temperatures/pressures within acoustic cavitation bubble in an imidazolium-based room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide ([BMIM][NTf₂]), and in water has been made for a wide range of cavitation parameters including frequency (140–1000 kHz), acoustic intensity (0.5–1 W cm⁻²), liquid temperature (20–50 °C) and external static pressure (0.7–1.5 atm). The used cavitation model takes into account the liquid compressibility as well as the surface tension and the viscosity of the medium. It was found that the bubble temperatures and pressures were always much higher in the ionic liquid compared to those predicted in water. The valuable effect of [BMIM][NTf₂] on the bubble temperature was more pronounced at higher acoustic intensity and liquid temperature and lower frequency and external static pressure. However, confrontation between the predicted and the experimental estimated temperatures in ionic liquids showed an opposite trend as the temperatures measured in some pure ionic liquids are of the same order as those observed in water. The injection of liquid droplets into cavitation bubbles, the pyrolysis of ionic liquids at the bubble-solution interface as well as the lower number of collapsing bubbles in the ionic liquid may be the responsible for the lower measured bubble temperatures in ionic liquids, as compared with water.     

Influence of water on the surface structure of 1-hexyl-3-methylimidazolium chloride

The molecular surface structure of an ionic liquid (IL) with and without the presence of water was studied with the surface sensitive technique neutral impact collision ion scattering spectroscopy (NICISS). The IL chosen is 1-hexyl-3-methylimidazolium chloride, which is known to be hydrophilic. Binary mixtures were investigated within the water mole fraction range 0.43 ≤ χ_water ≤ 0.71 at 283 K. During approximately 3 h exposition time in vacuum, we have observed a very low water loss rate from sample. The NICISS measurements suggest that admixture of water to [HMIm]Cl leads to a layered surface structure. Three layers were identified (layer 1 — cations, layer 2 — cations and water, layer 3 — cations, water, and anions). While the first layer is unaffected by water, the thickness of the second layer depends on the water concentration. The thickness of layer 2 is relatively constant for water concentrations χ_water ≤ 0.61, but increases for water contents χ_water ≥ 0.68. The concentration range 0.61 ≤ χ_water ≤ 0.68 seems to play a key role in water network formation.     

Surface segregation in binary mixtures of imidazolium-based ionic liquids

Surface composition of binary mixtures of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry at room temperature over a wide composition range. The imidazolium cations with longer aliphatic groups tend to segregate to the surface, and a bis(trifluoromethanesulfonyl)imide anion (Tf₂N^?) is enriched at the surface relative to hexafluorophosphate (PF₆^?). The surface of an equimolar mixture of Li[Tf₂N] and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) has a nominal composition of [bmim][Tf₂N] because of surface segregation and ligand exchange. The surface segregation of cations and anions is likely to result from alignment of specific ligand-exchanged molecules at the topmost surface layer to exclude more hydrophobic part of the molecules.     

Optical properties of LiNbO3:Cr crystals co-doped with germanium oxide

Lithium niobate (LiNbO₃) crystals doped with chromium ions show a clear green colouring reflecting the absorption profile of the dominating [Cr]_Li defect centres. A significant change in its colouration takes place when it is co-doped with other valency impurities such as Mg²⁺, Sc³⁺ and W⁶⁺, above a certain threshold concentration. This concentration singularity has been attributed to the formation of [Cr]_Nb centres coexisting with the [Cr]_Li centres.In this work, we extended the investigation on the effect of co-dopant ions in Cr:LiNbO₃ to tetravalent cation such as GeO₂. A singularity in the relative intensity of the ⁴A₂→⁴T₁ and ⁴A₂→⁴T₂ absorption band was observed for a concentration of ～1.5 mol%, compared with 4.5 mol% for Mg²⁺. The photoluminescence emission spectra also reveal a new emission band, at a lower energy than the [Cr]_Li centre, corresponding to this threshold concentration. A charge compensation model is proposed to explain the role of cation impurities and results are compared with those of other valence impurities.     

Investigating gate metal induced reduction of surface donor density in GaN/AlGaN/GaN heterostructure by electroreflectance spectroscopy

The internal field of GaN/AlGaN/GaN heterostructure on Si-substrate was investigated by varying the thickness of an undoped-GaN capping layer using electroreflectance spectroscopy. The four samples investigated are AlGaN/GaN heterostructure without a GaN cap layer (reference sample) and three other samples with GaN/AlGaN/GaN heterostructures in which the different thickness of GaN cap layer (2.7 nm, 7.5 nm, and 12.4 nm) has been considered. The sheet carrier density (n_s) of a two-dimensional electron gas has decreased significantly from 4.66 × 10¹² cm⁻² to 2.15 × 10¹² cm⁻² upon deposition of a GaN capping layer (12.4 nm) over the reference structure. Through the analysis of internal fields in each GaN capping and AlGaN barrier layers, it has been concluded that the undiminished surface donor states (n_s) of a reference structure and the reduced n_s caused by the Au gate metal are approximately 5.66 × 10¹² cm⁻² and 1.08 × 10¹² cm⁻², respectively.     

Near-infrared LIF spectroscopy of HfF

The molecular ion HfF⁺ is the chosen species for a JILA experiment to measure the electron electric dipole moment (eEDM). Detailed knowledge of the spectrum of HfF is crucial to prepare HfF⁺ in a state suitable for performing an eEDM measurement [1]. We investigated the near-infrared electronic spectrum of HfF using laser-induced fluorescence (LIF) of a supersonic molecular beam. We discovered eight unreported bands, and assign each of them unambiguously, four to vibrational bands belonging to the transition [13.8]0.5 ← X1.5, and four to vibrational bands belonging to the transition [14.2]1.5 ← X1.5. Additionally, we report an improved measurement of vibrational spacing of the ground state, as well as anharmonicity ω_ex_e.     

Bulk and surface properties of ionic salt CsH5(PO4)2

We report a comparative study of transport and thermodynamic properties of single-crystal and polycrystalline samples of the ionic salt CsH₅(PO₄)₂ possessing a peculiar three-dimensional hydrogen-bond network. The observed potential of electrolyte decomposition ≈ 1.3 V indicates that the main charge carriers in this salt are protons. However, in spite of the high proton concentration, the conductivity appears to be rather low with a high apparent activation energy E_a ≈ 2 eV, implying that protons are strongly bound. The transport anisotropy though is not large, correlates with the crystal structure: the highest conductivity is found in the [001] direction (σ_130 °C ∼ 5.6 × 10^− 6 S cm^− 1) while the minimal conductivity is in the [100] direction (σ_130 °C ∼ 10 ⁻⁶ S cm^− 1). The conductivity of polycrystalline samples appears to exceed the bulk one by 1–3 orders of magnitude with a concomitant decrease of the activation energy (E_a ≈ 1.05 eV), which indicates that a pseudo-liquid layer with a high proton mobility is formed at the surface of grains. Infrared and Raman spectroscopy used to study the dynamics of the hydrogen-bond system in single-crystal and polycrystalline samples have confirmed the formation of such a modified surface layer in the latter. However, no bulk phase transition into the superionic disordered phase is observed in CsH₅(PO₄)₂ up to the melting point T_melt ∼ 151.6 °C, in contrast to its closest relative compound CsH₂PO₄.     

A FT-IR spectroscopic study of ultrasound effect on aqueous imidazole based ionic liquids having different counter ions

Ultrasound (US) effect on 1-butyl-3-methyl-imidazolium (BMI) ionic liquids having different counter anions, BF₄⁻, PF₆⁻ and Cl⁻ in aqueous medium was studied by FT-IR spectroscopy. Their deconvolution spectra were used to analyze the change of hydrogen bond in the absence and presence of US exposure to the ionic liquid. The FT-IR spectra were measured in different water contents without and with US at 23 kHz. These results indicated that the counter anion species in the imidazole based the ionic liquids played an important role for water solvation, when the US was exposed. The US hardly changed hydrogen bonding in the aqueous BMI–PF₆, while the BMI–BF₄ and BMI–Cl showed obvious change in their FT-IR spectra. Especially for the BMI–Cl, significant change was observed by the US exposure in the range of 2.6 wt% to 20 wt% of water contents. The results showed that the US could break the hydrogen bond in the BMI–Cl ionic liquids. In the case of BMI–BF₄, the FT-IR band at 950–1152 cm⁻¹ was significantly intensified under US exposure, due to that the US influenced BF₄⁻-water interaction. But, it was observed that the ionic liquid having PF₆⁻ was very less changed in the US system.     

Vibrational spectroscopy of oxygen on the (100) and (111) surfaces of lanthanum hexaboride

Reflection absorption infrared spectroscopy (RAIRS) and high resolution electron energy loss spectroscopy (HREELS) have been used to study the adsorption of oxygen on the (100) and (111) surfaces of lanthanum hexaboride. Exposure of the surface at temperatures of 95 K and above to O₂ produces atomic oxygen on the surface and yields vibrational peaks in good agreement with those observed in previous HREELS studies. On the La-terminated (100) surface, RAIRS peaks correspond to vibrations of the boron lattice that gain intensity due to a decrease in screening of surface dipoles that accompanies oxygen adsorption. A sharp peak at ～ 734 cm^?1 in the HREEL spectrum shows isotopic splitting with RAIRS into two components at 717 and 740 cm^?1 with full widths at half maxima of only 12 cm^?1. The sharpness of this mode is consistent with its interpretation as a surface phonon that is well separated from both the bulk phonons and other surface phonons of LaB₆. On the boron-terminated LaB₆(111) surface, broad and weak features are assigned to both vibrations of the boron lattice and of boron oxide. On the (100) surface, oxygen blocks the adsorption sites for CO, and adsorbed CO prevents the dissociative adsorption of O₂.     

Effects of Room Temperature Ionic Liquids on Fluorescence Characteristics of 17β-estradiol and its Derivative

Previous reports have seldom concerned about the RTILs (Room temperature ionic liquids), and their effects on derivatization reaction or derivatives. In this study, we reported that the effects of four different RTILs, i.e., [EMIM]PF₆, [BMIM]PF₆, [HMIM]PF₆ and [OMIM]PF₆, on fluorescence spectra of 17 β-estradiol (E2), and its derivatization solvent dansyl chloride (DNSCl) and the derivative. [BMIM]PF₆ had a significant quenching effect on the fluorescence intensity of E2, suggesting the formation of [BMIM]PF₆/E2 complexes and possible buried E2 molecular in a more hydrophobic microenvironment. The estimated Stern-Volmer quenching constant (Ksv = 0.3519) proved that E2 quenching caused by [BMIM]PF₆ was a dynamic quenching process. Four RTILs, with different alkyl chain-length in imidazolium cation, resulted in different quenching intensities to E2 as follows: [EMIM]PF₆ > [BMIM]PF₆ > [HMIM]PF₆ > [OMIM]PF₆. At 5 mg L⁻¹ of DNSCl, [BMIM]PF₆, [HMIM]PF₆ and [OMIM]PF₆ increased the fluorescence intensities of E2 in water by 8.5, 7.6 and 6.1 times, respectively, and a 37-nm hypsochromic shift occurred. The fluorescence intensity for [BMIM]PF₆-extracted derivative of E2 increased more than two times compared with that for the control. In conclusion, this study demonstrated that above four hexafluorophosphate salt ionic liquids could be used in derivatization reaction to enhance fluorescent sensitivity in E2 trace residual analysis.     

Photolysis of SF6 adsorbed on Si(111)-7 × 7 by monochromatic soft X-ray

Continuous-time photoelectron spectroscopy (PES) and photon-exposure-dependent photon-stimulated desorption (PSD) were employed to investigate the monochromatic soft X-ray-induced dissociation of SF₆ molecules adsorbed on Si(111)-7 × 7 at 30 K (SF₆ dose = 3.4 × 10¹³ molecules/cm², ～ 0.5 monolayer). The photon-induced evolution of adsorbed SF₆ was monitored at photon energies of 98 and 120 eV [near the Si(2p) edge], and sequential valence-level PES spectra made it possible to deduce the photolysis cross section as a function of energy. It was found that the photolysis cross sections for 98 and 120 eV photons are ～ 2.7 × 10^? 17 and ～ 3.7 × 10^?17 cm², respectively. The changes in the F^? and F⁺ PSD ion yields were also measured during irradiation of 120 eV photons. The photon-exposure dependencies of the F^? and F⁺ ion yields show the characteristics: (a) the dissociation of adsorbed SF₆ molecules is ascribable to the substrate-mediated dissociations [dissociative attachment (DA) and dipolar dissociation (DD) induced by the photoelectrons emitting from the silicon substrate]; (b) at early stages of photolysis, the F^? yield is mainly due to DA and DD of the adsorbed SF₆ molecules, while at high photon exposure the F^? formation by electron capture of the F⁺ ion is likely to be the dominant mechanism; (c) the F⁺ ion desorption is associated with the bond breaking of the surface SiF species; (d) the surface SiF is formed by reaction of the surface Si atom with the fluorine atom or F^? ion produced by scission of S–F bond of SF_n (n = 1–6) species.     

Ultrasonic energy enhanced the efficiency of advance extraction methodology for enrichment of trace level of copper in serum samples of patients having neurological disorders

An innovative dual dispersive ionic liquid based on ultrasound assisted microextraction (UDIL-μE), for the enrichment of trace levels of copper ion (Cu²⁺), in serum (blood) of patients suffering from different neurological disorders. The enriched metal ions were subjected to flame atomic absorption spectrometry (FAAS). In the UDIL-μE method, the extraction solvent, ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆], was dispersed into the aqueous samples using an ultrasonic bath. The(PAN) 1-(2-pyridylazo)-2-naphthol was used as ligand for the complexation of Cu ion in IL (as extracting solvent). The various variables such as sonication time, pH, concentration of complexing agent, time and rate of centrifugation, IL volume that affect the extraction process were optimized. The enhancement factor (EF) and detection limit (LOD) was found under favorable condition was 31 and 0.36 μg L⁻¹, respectively. Reliability of the proposed method was checked by relative standard deviation (%RSD), which was found to be <5%. The accuracy of developed procedure was assured by using certified reference material (CRM) of blood serum. The developed procedure was applied successfully to the analysis of concentration of Cu ion in blood serum of different neurological disorders subjects and referents of same age group. It was observed that the levels of Cu ion was two folds higher in serum samples of neurological disorders patients as related to normal referents of same age group.     

An efficient enzymatic modification of cordycepin in ionic liquids under ultrasonic irradiation

A comparative study of the immobilized Candida antarctica lipase B (Novozym 435)-catalyzed acylation of cordycepin with vinyl acetate in ionic liquids (ILs) under ultrasonic irradiation and shaking was conducted. The application of ultrasonic irradiation instead of shaking during acylation resulted in an enhanced reaction rate and a higher level of substrate conversion. Among the various ILs examined, 1-butyl-3-methylimidazolium tetrafluorobrate ([C₄MIm][BF₄]) was the best medium for the reaction because it produced the highest substrate conversion. In [C₄MIm][BF₄], the optimal ultrasonic power, water activity, and reaction temperature were 120 W, 0.33, and 50 °C, respectively. The acylation of cordycepin in [C₄MIm][BF₄] proved to be regioselective under both conditions: the C5′-OH was acylated. Novozym 435 exhibited a much higher operational stability in [C₄MIm][BF₄], and 58.0% of its original activity was maintained after ten reuse cycles under ultrasonic irradiation. Compared with the cordycepin, the rate of adenosine deaminase-catalyzed deamination was greatly reduced when the 5′-OH was substituted by acetyl group. These results demonstrated that the combined application of ultrasonic irradiation and IL as a medium was an efficient approach for the enzymatic modification of cordycepin.     

Effect of film thickness on the transport properties of MgB2 synthesized by spray pyrolysis

Polycrystalline MgB₂ films of different thickness have been prepared by employing spray pyrolysis technique on MgO (1 0 0) substrate. The MgB₂ and other phases have been confirmed using X-ray diffraction technique and no trace of impurities phases have been found. The resistivity behavior shows that the superconducting transition temperature lies in the range of 37–39 K with narrow transition width. The transport critical current density vary with films thickness and achieved highest value ～1.2 × 10⁶ A/cm² at 20 K for 2.0 μm thick film and its values increase as thickness increases.     

Surface structure of γ-Fe2O3(111)

The surface structure of γ-Fe₂O₃(111) has been investigated with a range of surface techniques. Two different surface structures were discovered depending upon surface preparation techniques. Sputtering followed by annealing in vacuum produced a reduced surface characterised by a (2 × 2) LEED pattern, whereas sputtering followed by annealing in 1 × 10^? 6 mbar oxygen produced a surface characterised by a (√3 × √3)-R30° LEED pattern. The latter appears to be a very low conductivity surface, whereas the former has the band gap expected for maghemite (~ 2.0 eV). We propose that the reduced surface is a magnetite-like layer, whereas the oxidised surface is an Fe₂O₃-like layer.     

Thermodynamic properties of the mixtures of some ionic liquids with alcohols using a simple equation of state

In the present work, we have used a simple equation of state called the GMA EoS to calculate the density of three ionic liquid mixtures including 1-butyl-3-methylimidazolum hexafluorophosphate, [BMIM] [PF₆] + methanol, 1-butyl-3-methylimidazolum tetrafluoroborate, [BMIM] [BF₄] + methanol, and [BMIM] [BF₄] + ethanol at different temperatures, pressures, and compositions. The isothermal compressibility, excess molar volumes, and excess Gibbs molar energy of these mixtures have been computed using this equation of state. The values of statistical parameters show that the GMA EoS can predict these thermodynamic properties very well within the experimental errors. The results show that isothermal compressibility of ionic liquids is lower than alcohols and the effect of temperature and pressure on the isothermal compressibility of ionic liquids is lower than alcohols. The excess molar volumes and excess molar Gibbs energy for these ionic liquid mixtures with alcohols are all negative at various temperatures and pressures over the whole composition range. The results have been interpreted in terms of intermolecular interactions and structural factors of the ionic liquids and alcohols.     

Sonoluminescence quenching and cavitation bubble temperature measurements in an ionic liquid

A comparison between the temperatures within imploding acoustic cavitation bubbles and the extent of sonoluminescence (SL) quenching by C₁–C₅ aliphatic alcohols in 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO₄], a well known imidazolium based room temperature ionic liquid (RTIL)), has been made at an ultrasound frequency of 213 kHz. The temperatures obtained ranged from 3500 ± 200 K, in neat [EMIM][EtSO₄], to about 3200 ± 200 K in RTIL-alcohol containing solutions. It was also found that the SL intensity decreased with increasing concentration (up to 1 M) of the alcohols to a greater extent compared with the relative changes to the bubble temperatures. Both the extent of the reduction in the bubble temperatures and the SL quenching were much smaller than those obtained in comparable aqueous solutions containing aliphatic alcohols. Possible reasons for the differences in the observed trends between water/alcohol and [EMIM][EtSO₄]/alcohol systems under sonication at 213 kHz are discussed.     

Development of high resolution 3D hyperpolarized carbon-13 MR molecular imaging techniques

The goal of this project was to develop and apply techniques for T₂ mapping and 3D high resolution (1.5 mm isotropic; 0.003 cm³) ¹³C imaging of hyperpolarized (HP) probes [1-¹³C]lactate, [1-¹³C]pyruvate, [2-¹³C]pyruvate, and [¹³C,¹⁵N₂]urea in vivo. A specialized 2D bSSFP sequence was implemented on a clinical 3T scanner and used to obtain the first high resolution T₂ maps of these different hyperpolarized compounds in both rats and tumor-bearing mice. These maps were first used to optimize timings for highest SNR for single time-point 3D bSSFP acquisitions with a 1.5 mm isotropic spatial resolution of normal rats. This 3D acquisition approach was extended to serial dynamic imaging with 2-fold compressed sensing acceleration without changing spatial resolution. The T₂ mapping experiments yielded measurements of T₂ values of > 1 s for all compounds within rat kidneys/vasculature and TRAMP tumors, except for [2-¹³C]pyruvate which was ~ 730 ms and ~ 320 ms, respectively. The high resolution 3D imaging enabled visualization the biodistribution of [1-¹³C]lactate, [1-¹³C]pyruvate, and [2-¹³C]pyruvate within different kidney compartments as well as in the vasculature. While the mouse anatomy is smaller, the resolution was also sufficient to image the distribution of all compounds within kidney, vasculature, and tumor. The development of the specialized 3D sequence with compressed sensing provided improved structural and functional assessments at a high (0.003 cm³) spatial and 2 s temporal resolution in vivo utilizing HP ¹³C substrates by exploiting their long T₂ values. This 1.5 mm isotropic resolution is comparable to ¹H imaging and application of this approach could be extended to future studies of uptake, metabolism, and perfusion in cancer and other disease models and may ultimately be of value for clinical imaging.     

Type B epitaxy of Ge on CaF2(111) surface

It was known experimentally that type B orientation, which is rotated 180° about the [111] axis, dominated the heteroepitaxial growth of Ge(111) on a CaF₂(111) substrate at an elevated temperature. We performed first principles calculations using density functional theory to determine the energetics of the Ge(111)/CaF₂(111) interface and found that the type B orientation of the Ge film is most likely a result of a direct bonding between Ge atoms and Ca²⁺ at the CaF₂ surface with the top F^? layer depleted. Our theoretical prediction is supported by our X-ray diffraction experiments on {111} < 121> biaxially textured Ge/CaF₂ samples.