Solvents Of Low Dielectric Constant Research Articles

The Novel Highly-Selective Etching Process of SiO2 to TiSix for Nano-Scale Device Fabrication

It was demonstrated firstly that the relative higher etch rate of titanium silicide relative to silicon oxide in HF-based solution was ascribed to the interaction of the positively-charged hydrogen with titanium, which has very low electron affinity relative to other metal. Based on the electron transfer mechanism of TiSix dissolution, we have developed the highly-selective novel etching material (T-Block) which is mainly composed of fluoride salt and low dielectric-constant solvent. In order for this novel solution to be applicable in the real fabrication process, we devised the novel iterative treatment process, suitable for single wafer spin equipment. In contrast to normal solution-treated group, any kind of failure regarding TiSix dissolution for T-Block-treated group was not found even when TiSix underlying direct contact was disclosed to T-Block in eBC process. Therefore, if T-Block is applied in fabrication process with 6F2 cell design, the significant enhancement of productivity through process simplification as well as yield will be expected.

Improvement of Barrier Anodic Oxide Al2O3 Passivation of Aluminum Alloy for LSI/FPD Plasma Process Equipment

Barrier type anodic oxides film of the aluminum alloy in nonaqueous electrolyte solution has some excellent characteristics as a passivation film. In electrolyte that used the ethylene glycol as nonaqueous solution, the thickness of the anodic oxides film was able to be formed only up to about 0.3μm. However, the thickness of 0.5μm or more is demanded from the viewpoint of mechanical strength in actual manufacturing equipments. The barrier type anodic oxides film that exceeded 0.5μm was able to be formed by the use of a low dielectric constant glycol system solvent, the viscosity control of the electrolyte and other optimizations. The thick nonaqueous anodic oxides will be put to actual use as the passivation film for the plasma process equipment of the LSI/FPD manufacturing.

Simulations of phase transitions and free energies for ionic systems

A review of simulation studies of phase equilibria and free energies for systems dominated by coulombic interactions is presented. Phase transitions occur for ionic systems in the strong-coupling limit realized in low-dielectric constant solvents, at low temperatures, or for high charge valences. The majority of simulation results to date are for primitive models that treat the solvent as a uniform dielectric continuum. Transitions involving fluid and solid phases for such models have been studied extensively in the past decade. There is now strong evidence that the vapour–liquid transition is in the Ising universality class. For highly charged colloids the vapour–liquid transition becomes metastable with respect to the fluid–solid transition and the behaviour matches that of charged hard plates. Phase transitions of charged chains illustrate sensitivity of the phase behaviour to the charge pattern. Studies of salt solubilities using models with explicit solvent suggest that reasonable agreement with experiment can be achieved with existing force fields, but there is considerable room for improvement. Areas of future research needs are briefly discussed.

π-Dimer Formation as the Driving Force for Calix[4]arene-Based Molecular Actuators

Stable pi-dimers are formed upon oxidation of the model units of proposed calix[4]arene-based molecular actuators in a solvent of low dielectric constant (CH 2Cl 2) at room temperature. Evidence from UV-vis, EPR, and DPV are all in agreement with the pi-dimer formation. In addition, pi-dimer formation is dependent upon the conformational flexibility of the calix[4]arene hinge.

Properties of TRPO-HNO3 complex used for direct dissolution of lanthanide and actinide oxides in supercritical fluid CO2

The mixed trialkylphosphine oxide-nitric acid (TRPO-HNO3) complex prepared by contacting pure TRPO with concentrated HNO3 may be used as additives for direct dissolution of lanthanide and actinide oxides in the supercritical fluid carbon dioxide (SCF-CO2). Properties of the TRPO-HNO3 complex have been studied. Experimental results show when the initial HNO3/TRPO volume ratio is varied from 1:7 to 5:1, the concentration of HNO3 in the TRPO-HNO3 complex changes from 2.12 to 6.16 mol/L, the [HNO3]/[TRPO] ratio of the TRPO-HNO3 complex changes from 0.93 to 3.38, and the content of H2O in the TRPO-HNO3 complex changes from 0.97% to 2.70%. All of the density, viscosity and surface tension of the TRPO-HNO3 complex change with the concentration of HNO3 in the complex. The protons of HNO3 and H2O in the complex undergo rapid exchange to exhibit a singlet resonance peak in NMR spectra with D2O insert. When the TRPO-HNO3 complex dissolves in a low dielectric constant solvent, small droplets of HNO3 appear which can be detected by NMR.

Studies of electrical moment and thermodynamic properties of water in organic solvents at 298.15 K

We report in this paper on measurements of static dielectric constant ( ε) at 1 kHz for solutions of water dissolved in organic solvents (benzene and 1,4-dioxane) of low dielectric constant at 298.15 K. The solutions having different water activities and hence concentrations were prepared by isopiestic technique. The solubility data indicate validity of Henry's law only near solutions of unit water activity. The variation of ε with concentration of water is subjected to analysis using the Kirkwood–Fröhlich equation. The calculated dipole moment values ( μ) for water molecules indicate presence of monomers in 1, 4-dioxane solutions while μ values in case of the H 2O–benzene system reveal change of monomer to cyclic-trimer species. Also, an attempt is made to apply McMillan–Meyer theory to the data of the H 2O–benzene system. The results of these indicate presence of pair and triplet interactions (osmotic virial coefficients) for water molecules in the condensed phase.

Study on Properties of TBP‐HNO3 Complex Used for Direct Dissolution of Lanthanide and Actinide Oxides in Supercritical Fluid CO2

AbstractThe tri‐n‐butyl phosphate‐nitric acid (TBP‐HNO3) complex prepared by contacting the pure TBP with the concentrated HNO3 can be used for direct dissolution of lanthanide and actinide oxides in the supercritical fluid carbon dioxide (SCF‐CO2). Properties of the TBP‐HNO3 complex have been studied. Experimental results showed that when the initial HNO3/TBP volume ratio was varied from 1:7 to 5:1, the concentration of HNO3 in the TBP‐HNO3 complex changed from 1.95 to 5.89 mol/L, the [HNO3]/[TBP] ratio of the TBP‐HNO3 complex changed from 0.61 to 2.22, and the content of H2O in the TBP‐HNO3 complex changed from 2.02% to 4.19%. All of the density, viscosity and surface tension of the TBP‐HNO3 complex changed with the concentration of HNO3 in the complex, and were higher than those of the pure TBP. The protons of HNO3 and H2O in the complex underwent rapid exchange to exhibit a singlet resonance peak in nuclear magnetic resonance spectra. When the TBP‐HNO3 complex was dissolved in a low dielectric constant solvent, small droplets of HNO3 were formed that can be detected by NMR.

A Review of the Chemical Manipulation of Nanomaterials Using Solvents: Gelation Dependent Structures

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A review of the chemical manipulation of nanomaterials using solvents: Gelation dependent structures

The hydrolysis of Mg, Zr, and Ti alkoxides by water in solvent-alcohol mixtures has been examined in the absence of added acid or base catalysts, and herein, these data are reviewed. The presence of low dielectric constant solvents (benzene, toluene, or anisole), in varying ratios with methanol (or other alcohols), caused much more rapid gelation, subsequently yielding mesoporous materials with higher surface areas and larger pore volumes as fibrous, open web-like structures. The presence of high dielectric constant (polar aprotic) solvents such as acetone, acetonitrile, DMF, DMSO, or dimethyaniline was not effective in this way. A partial charge model was employed to explain why the low dielectric solvents forced more rapid hydrolysis, and it is concluded that the hydrolysis step is rate determining, approaching diffusion control, in this gelation process. The use of these “spectator solvents” helps simplify and enhance sol-gel and xerogel/aerogel synthesis schemes, and yields higher quality materials.

Solvation Properties of N-Substituted Cis and Trans Amides Are Not Identical: Significant Enthalpy and Entropy Changes Are Revealed by the Use of Variable Temperature 1H NMR in Aqueous and Chloroform Solutions and ab Initio Calculations

The cis/trans conformational equilibrium of N-methyl formamide (NMF) and the sterically hindered tert-butylformamide (TBF) was investigated by the use of variable temperature gradient 1H NMR in aqueous solution and in the low dielectric constant and solvation ability solvent CDCl3 and various levels of first principles calculations. The trans isomer of NMF in aqueous solution is enthalpically favored relative to the cis (deltaH(o) = -5.79 +/- 0.18 kJ mol(-1)) with entropy differences at 298 K (298 x deltaS(o) = -0.23 +/- 0.17 kJ mol(-1)) playing a minor role. The experimental value of the enthalpy difference strongly decreases (deltaH(o) = -1.72 +/- 0.06 kJ mol(-1)), and the contribution of entropy at 298 K (298 x deltaS(o) = -1.87 +/- 0.06 kJ mol(-1)) increases in the case of the sterically hindered tert-butylformamide. The trans isomer of NMF in CDCl3 solution is enthalpically favored relative to the cis (deltaH(o) = -3.71 +/- 0.17 kJ mol(-1)) with entropy differences at 298 K (298 x deltaS(o) = 1.02 +/- 0.19 kJ mol(-1)) playing a minor role. In the sterically hindered tert-butylformamide, the trans isomer is enthalpically disfavored (deltaH(o) = 1.60 +/- 0.09 kJ mol(-1)) but is entropically favored (298 x deltaS(o) = 1.71 +/- 0.10 kJ mol(-1)). The results are compared with literature data of model peptides. It is concluded that, in amide bonds at 298 K and in the absence of strongly stabilizing sequence-specific inter-residue interactions involving side chains, the free energy difference of the cis/trans isomers and both the enthalpy and entropy contributions are strongly dependent on the N-alkyl substitution and the solvent. The significant decreasing enthalpic benefit of the trans isomer in CDCl3 compared to that in H2O, in the case of NMF and TBF, is partially offset by an adverse entropy contribution. This is in agreement with the general phenomenon of enthalpy versus entropy compensation. B3LY/6-311++G** and MP2/6-311++G** quantum chemical calculations confirm the stability orders of isomers and the deltaG decrease in going from water to CHCl3 as solvent. However, the absolute calculated values, especially for TBF, deviate significantly from the experimental values. Consideration of the solvent effects via the PCM approach on NMF x H2O and TBF x H2O supermolecules improves the agreement with the experimental results for TBF isomers, but not for NMF.

FTIR study of ion dissociation in PMMA based gel electrolytes containing ammonium triflate: Role of dielectric constant of solvent

The effect of dielectric constant of solvent on the presence of ion aggregates/undissociated salt and their dissociation with the addition of polymer has been studied by FTIR for polymethylmethacrylate (PMMA) based gel electrolytes containing ammonium triflate (NH 4CF 3SO 3). Salt is fully dissociated in electrolytes containing dimethylacetamide (DMA)—a high dielectric constant solvent and some ion aggregates are also present whereas in electrolytes containing diethylcarbonate (DEC)—a low dielectric constant solvent, some undissociated salt is present. The conductivity behaviour of polymer gel electrolytes has been found to depend upon the dielectric constant of the solvent used. PMMA plays the role of a stiffener in electrolytes containing DMA and results in a small decrease in conductivity whereas in electrolytes containing DEC, the addition of PMMA results in an increase in conductivity which has been explained to be due to an increase in free ion concentration by the dissociation of undissociated salt and ion aggregates. The presence of free ions, ion aggregates, undissociated salt has also been examined by FTIR spectroscopy.

Nucleophile influence on the complex reaction network of 2-isopropylnaphthalene hydroperoxide decomposition

Acid-catalysed decomposition of 2-isopropylnaphthalene hydroperoxide (2-IPNHP), which is of industrial importance for the productions of 2-naphthol and acetone simultaneously, proceeds through a complex ionic reaction mechanism. Since two steps of the ionic reactions in series are nucleophilic reactions, the presence, character and concentration of nucleophile reagents in the decomposition reaction medium are important. In the present study, the effects of the neutral oxygen nucleophiles: H 2O 2, water, 2-IPNHP and dimethyl-2-naphthylcarbinol (DMNC) were investigated. 2-IPNHP is the reactant of the process, water is another reactant of the nucleophilic addition reaction, DMNC is the by-product of the preceding 2-IPNHP production process and H 2O 2 is initially added into the medium to oxidise the DMNC to 2-IPNHP. Among the neutral oxygen nucleophiles, H 2O 2, water and DMNC decreased, but 2-IPNHP increased the production rate of 2-naphthol in accordance with the mechanism and with the following descending order of the strength of nucleophiles: DMNC > 2-IPNHP > H 2O 2 > water. The influence of nucleophile characters of aprotic solvents of low dielectric constant (propyl acetate and acetone), aprotic solvents of high-dielectric constant (acetonitrile and nitrobenzene), protogenic solvent (acetic acid) and amphiprotic solvent (methyl alcohol) on the 2-IPNHP decomposition were also discussed in the paper.

Conductivity and viscosity behaviour of PMMA based gels and nano dispersed gels: Role of dielectric constant of the solvent

The conductivity and viscosity behaviour of nano dispersed lithium ion-conducting polymer gel electrolytes containing solvents with different (low and high) dielectric constants have been studied. The conductivity of liquid electrolytes depends upon the dielectric constant of the solvent used and the addition of polymethylmethacrylate (PMMA) results in an increase in conductivity for electrolytes containing low dielectric constant solvent. This is an interesting behaviour observed for the first time in lithium ion-conducting polymer gel electrolytes where gels have higher conductivity than the corresponding liquid electrolytes which is due to the role of polymer in the dissociation of undissociated salt present in these electrolytes containing low dielectric constant solvent. The addition of nano size fumed silica to polymer gel electrolytes show different conductivity behaviour for electrolytes containing low and high dielectric constant solvent along with an increase in viscosity in each case. The nano dispersed gels so obtained show high conductivity ∼10 − 2 S/cm at 25 °C along with better mechanical properties. The conductivity does not show any appreciable change with time which is desirable for their use in devices.

Identification of 1,3-Dialkylimidazolium Salt Supramolecular Aggregates in Solution

The nature of the interactions between 1,3-dialkylimidazolium cations and noncoordinating anions such as tetrafluoroborate, hexafluorophosphate, and tetraphenylborate has been studied in the solid state by X-ray diffraction analysis and in solution by (1)H NMR spectroscopy, conductivity, and microcalorimetry. In the solid state, these compounds show an extended network of hydrogen-bonded cations and anions in which one cation is surrounded by at least three anions and one anion is surrounded by at least three imidazolium cations. In the pure form, imidazolium salts are better described as polymeric supramolecules of the type {[(DAI)(3)(X)](2+)[(DAI)(X)(3)](2-)}(n) (where DAI is the dialkylimidazolium cation and X is the anion) formed through hydrogen bonds of the imidazolium cation with the anion. In solution, this supramolecular structural organization is maintained to a great extent, at least in solvents of low dielectric constant, indicating that mixtures of imidazolium ionic liquids with other molecules can be considered as nanostructured materials. This model is very useful for the rationalization of the majority of the unusual behavior of the ionic liquids.

P.2.025 The efficacy of combined therapy of clozapineand haloperidol in the treatment-resistant schizophrenic patients

Studies of the NMR spectra of β-bromopropionitrile over a range of concentrations in nine suitable solvents indicate that both the rotationally averaged values of the vicinal coupling parameters and the corresponding chemical shift vary with both solvent and concentration, while the two geminal coupling parameters resonably appear to be constant within experimental error. The CN dipole-dipole interaction appearing in the solvents of low dielectric constants has been indicated as the prominent factor causing the concentration dependence of the spectral parameters in the said solvents. General dielectric effects alone can provide a complete explanation for the combination of factors including solute-solute and solute-solvent interactions in the solutions.The calculation of the solvent dependence of the NMR spectrum of β-bromopropionitrile, gave results in good agreement with the experiment for the energy difference between the two rotational isomers in the liquid state and the results have been used to derive the HH couplings of the two individual isomers of the compound. The values of the HH trans and gauche couplings thus obtained have been shown to be critically dependent on the orientations and nature of the substituents attached to the C-atom.

Voltammetric behaviour, homogeneous charge transport dynamics and electrocatalytic properties of an Os 2+ functionalised pyrrole monomer

The Os 2+ functionalised pyrrole monomer, osmium-bis- N,N′-(2,2′-bipyridyl)- N-(pyridine-4-yl-methyl- (8-pyrrole-1-yl-octyl)-amine)chloride, 1, has been synthesised and characterised by spectroscopic (UV–Vis, 1H NMR, IR spectroscopy) techniques and cyclic voltammetry. Solution phase studies of 1 gave a redox couple associated with the Os 3+/2+ and an irreversible wave associated with the oxidation of the pyrrole moiety. Attempts to form stable polymeric films of 1 on vitreous carbon electrodes, by homopolymerisation, proved unsuccessful. However electroactive films of 1 were obtained by the electrooxidation of 1 through the Os 3+/2+ couple in low dielectric media such as toluene + acetonitrile mixtures. The efficiency of film deposition and properties depend upon the supporting electrolyte and the solvent employed. Films formed in mixtures of acetonitrile and low dielectric constant solvents (dichloromethane and toluene) are electrochemically active and exhibit a redox couple associated with the Os 3+/2+ system. The voltammetric behaviour of these solid-state films was investigated in both aqueous and non-aqueous solvents with a variety of supporting electrolytes. Upon redox switching between the Os 3+/2+ redox states the solid-state charge-transfer processes are coupled to the insertion/expulsion of anions from/to the solution phase. Scanning electron microscopy reveals that films formed in the presence of acetonitrile exhibit different morphology from films formed in acetonitrile-free solutions. Slow and fast linear sweep voltammograms have been employed to provide an absolute determination of the fixed site concentration as 1.5 M and an apparent diffusion coefficient of 5.2 × 10 −12 cm 2 s −1 in 0.3 M KCl. Electroactive films of 1 were then investigated for their electrocatalytic ability towards the oxidation of ascorbic acid in acidic medium. The anodic oxidation peak current was linearly dependent on the ascorbic acid concentration and a linear calibration curve was obtained in the range 0.1–2 × 10 −3 M of ascorbic acid with a correlation coefficient of 0.9993. The detection limit (3 σ) was found to be 5.5 × 10 −5 M.

Ion-Pair Formation of the Ionic Liquid 1-Ethyl-3-methylimidazolium bis(trifyl)imide in Low Dielectric Media

A proton nuclear magnetic resonance (1H NMR) study of the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifyl)imide, dilute in low dielectric constant solvent media is presented. Equilibrium species are directly observed in the 1H NMR spectrum as two sets of resonance features, thus displaying unusually long lifetimes. In mixed solvent systems the species mole fractions are directly proportional to the bulk dielectric constant of the solution. The two sets of resonance features are assigned to the freely dissolved ions and ion-pair aggregates. The assignment is supported by measured spin lattice relaxation rates, and the observed temperature and concentration dependencies of the equilibrium. The thermodynamic quantities Δ G m , Δ S m , and Δ H m are also evaluated from the temperature-dependent data.

Structure and criticality of ionic fluids

Abstract Two properties render electrolyte theories difficult, namely the long-range nature of the Coulomb interactions and the high figures of the Coulomb energy at small ion separations. In solvents of low dielectric constant, where the Coulomb interactions are particularly strong, electrical conductance and dielectric spectra suggest that the ion distribution involves dipolar ion pairs, which then interact with the free ions and with other dipolar pairs. The dipole-dipole interactions between ion pairs lead to an increase of the dielectric constant, which in turn stabilizes the free ions, thus leading to redissociation at high salt concentrations. An equation of state that accounts for ion pairing, ion-ion pair, and ion pair-ion pair interactions rationalizes the basic features of the ion distribution. It also predicts a fluid-phase transition at low reduced temperatures, which closely corresponds to simulation results and to experimentally observed liquid-liquid phase transitions. The long-range nature of the Coulomb potential driving these transitions raises questions concerning their universality class. Experiments suggest that the Ising universality class applies, but there is cross-over to mean-field behavior rather close to the critical, not yet well explained by theory.

Characterization of a Tri-n-butyl Phosphate−Nitric Acid Complex: a CO2-Soluble Extractant for Dissolution of Uranium Dioxide

Tri-n-butyl phosphate (TBP) reacts with nitric acid to form a hydrogen-bonded complex TBP(HNO3)x(H2O)y that is highly soluble in supercritical fluid carbon dioxide (SF-CO2). The value of x can be up to 2.5, whereas the value of y varies between 0.4 and 0.8 determined by acid−base and Karl Fischer titrations. The protons of HNO3 and H2O in the complex undergo rapid exchange and exhibit a singlet resonance peak in NMR spectra. When the complex is dissolved in a low dielectric constant solvent, small droplets of nitric acid are formed that can be detected by NMR. Phase behavior studies indicate that the complex forms a single phase with SF-CO2 above a certain pressure for a given temperature. This CO2-soluble Lewis acid−base complex provides a method of introducing nitric acid in SF-CO2 for effective dissolution of uranium dioxide, lanthanide oxides, and perhaps other metal oxides.

Ion pairing and host-guest complexation in low dielectric constant solvents.

We report an equilibrium treatment for complexation of ionic species in low dielectric constant media that explicitly includes ion pairing of one of the components. Experimental validation was achieved through study of pseudorotaxane formation between dibenzylammonium salts and dibenzo-24-crown-8. In particular, we show that concentration-dependent fluctuations in the apparent K(a,exp) values as usually reported are attributable to ion pairing, with dissociation constant K(ipd), and that the constant K(ap) for complexation of the free cationic guest species, G(+), by the host crown ether is independent of counterion. More generally, using a simple extension of our model, we show the ability to diagnose the relative extent of ion pairing of the complex, which may be readily applied to other host-guest systems involving ionic species.