Addition Of Fluorine Research Articles

Hydrodesulfurization of DBT, 4-MDBT, and 4,6-DMDBT on fluorinated CoMoS/Al 2O 3 catalysts

CoMoS/Al 2O 3 catalysts containing different amounts of fluorine have been tested for the hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT), and the results have been analyzed based on three fundamental reactions involved in the HDS mechanism: hydrogenation of the aromatic ring, hydrogenolysis of the C–S bond, and migration of methyl groups in the ring structure. Fluorine addition to the catalyst promotes all of these three reactions due to the enhancement of two factors: the metal dispersion and the catalyst acidity. The extents that the HDS rates are improved by fluorine addition increase in the order of DBT<4-MDBT<4,6-DMDBT. Product distributions change in characteristic trends with fluorine addition depending on the individual reactants. That is, in DBT HDS, CHB obtained by the ring saturation is enhanced more than BP produced by the direct desulfurization, while the opposite trend is observed in 4-MDBT HDS. 4,6-DMDBT HDS shows an intermediate trend: products of both types are promoted to similar extents on fluorinated catalysts. The migration of methyl groups in the reactant ring structure due to the catalyst acidity, which reduces the steric hindrance to the C–S bond, is responsible for the characteristic trends in the product distribution observed with the individual reactants.

Effect of high-dose γ-irradiation on the critical current density of fluorinated Tl-1223

The effect of high-dose γ-irradiation up to 50 MRad on the hysteresis width and critical current density J c of two fluorinated Tl-1223 samples is reported. γ-irradiation was found to affect the critical current density of the sample Tl-1223/F x with x=1.0 both at low and high doses, but it has no effect on J c of the sample with x=2.2. This means that addition of fluorine in a controlled manner to the Tl-1223 enhances J c and makes this material very sensitive to γ-irradiation. These results are in agreement with our previous findings for the low-dose γ-irradiation.

Effects of fluorine addition on driving force for CVD diamond growth

The driving force for the diamond growth from the vapor phase with fluorine addition was studied according to a non-equilibrium thermodynamic coupling model. There exists a temperature range that the driving force for diamond growth is positive but that for activated graphite is negative. Inside the temperature range, the growth of diamond under low pressures is possible. The effects of fluorine content on driving force for the diamond growth were also discussed. The theoretical results can offer quantitative predictions for optimizing experimental conditions.

Hydrogen and fluorine binding to the sidewalls of a (10,0) carbon nanotube

The ONIOM method is used to study the addition of H and F atoms to the side of a (10,0) carbon nanotube. The entire model uses 200 carbon atoms, while the accurate section includes 24 carbon atoms. The B3LYP functional is used for the accurate calculation of the reaction site, while the Universal Force Field (UFF) is used to describe the neighboring atoms. The F atoms appear to favor bonding next to existing F atoms. Unlike the addition of fluorine, the addition of two or four H atoms to a (10,0) tube is computed to be endothermic.

Relationship between the energy characteristics of formation of fluorozirconates

A correlation is established between the mean energy of fluorine addition in a particular coordination polyhedron and the fluorine content in fluorozirconates by quantum chemical model cluster calculations and analysis of structural data for crystalline fluorozirconates. A new energy approach to studies of complex fluorides is suggested. It is shown that the mean energy of fluorine addition varies within a narrow range for any structural unit met in real fluorozirconate crystals. Based on the energy approach to analysis of vibrational spectra it is found that the coordination number of zirconium in a series of barium fluorozirconate glasses is 7 or 8.

Syntheses of fluorinated ligands to probe binding of antigenic determinants of Vibrio cholerae O:1, serotypes Inaba and Ogawa, to antibodies

Derivatives of methyl α-glycosides of antigenic determinants of Vibrio cholerae O:1, serotypes Inaba and Ogawa, specifically fluorinated at position 2′ or 4′ have been synthesized by coupling the appropriately fluorinated derivatives of 3-deoxy- l- glycero-tetronic acid with the methyl α-glycosides of perosamine. The compound having the fluorine atom at position 2 was obtained by electrophilic addition of fluorine to the glycal derived from the parent antigenic determinant, serotypes Inaba, using Selectfluor ™ as a fluorination reagent.

Decrease in Deposition Rate and Improvement of Step Coverage by CF4 Addition to Plasma-Enhanced Chemical Vapor Deposition of Silicon Oxide Films

The low dielectric constant of F-doped silicon dioxide film makes it suitable for use as an intermetal film to improve the performance of ultra-large scale integrated circuits (ULSIs). One of the properties required by an intermetal film is good gap filling. It is known that fluorine addition to silicon oxide decreases the film deposition rate and improves the step coverage. In order to investigate these phenomena, we study the reaction mechanism of plasma-enhanced chemical vapor deposition (PECVD) silicon oxide film and its change by fluorine addition. Using a two film-forming species model, we explain the dependence of the deposition rate and the step coverage on the residence time for a SiH4/N2O-based PECVD system. The precursor produced by the dissociation of SiH4 has a relatively high sticking probability (≈0.5), while an intermediate species has a low (<10-4) sticking probability. The concentration of each species for deposition is changed by the residence time of the gas, thus the deposition rate and the step coverage show dependence on the residence time. The deposition rate of silicon oxide films is decreased and the step coverage is improved by CF4 addition during SiH4/N2O-based PECVD. From the estimation of the sticking probability, we suggest that the reason for the improvement of the step coverage by fluorine addition is not the etching effect by CF4 addition, but the decrease in sticking probability of the precursor produced by the dissociation of SiH4.

Electron and ion mobilities in argon plasma with fluorine as additive

Results of the numerical evaluation of the electron and ion mobilities in plasmas from mixtures of argon and fluorine are given. The temperature dependence of the number densities of the components and their mobilities as a function of temperature for low-pressure (from 0.1 kPa to 1.0 kPa) and low-temperature (from 500 K to 5000 K) argon plasmas with 20% and 30% of added fluorine are evaluated. It is assumed that the system is kept under constant pressure and that a corresponding state of local themodynamical equilibrium is attained in it. The previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas as weakly non-ideal in the whole temperature range, is used and the cut-off at the Landau length rather than at the smallest ionic radius is introduced. This alteration in the evaluation procedure gives different changes in the final numerical results for all the relevant quantities. It was found that the equilibrium plasma composition depends considerably on the presence of fluorine in the whole temperature range for both the pressures; the addition of fluorine significantly enhances the number densities of all relevant charged constituents. This fact influences the electron and ion collision frequencies as well as their mobilities.

Junction Depth Reduction of ion Implanted Boron in Silicon Through Fluorine ion Implantation

AbstractThe interaction between boron and excess silicon interstitials caused by ion implantation hinders the formation of ultra-shallow, low resistivity junctions. Previous studies have shown that fluorine reduces boron transient enhanced diffusion, however it is unclear whether this observed phenomenon is due to the fluorine interacting with the boron atoms or silicon self-interstitials. Amorphization of a n-type Czochralski wafer was achieved with a 70 keV Si+ implantation at a dose of 1×1015/cm2. The Si+ implant produced a 1500Å deep amorphous layer, which was then implanted with 1.12 keV 1×1015/cm2 B+. The samples were then implanted with a dose of 2×1015/cm2F+ at various energies ranging from 2 keV to 36 keV. Ellipsometry measurements showed no increase in the amorphous layer thickness from either the boron or fluorine implants. The experimental conditions allowed the chemical species effect to be studied independent of the implant damage caused by the fluorine implant. Post-implantation anneals were performed in a tube furnace at 750° C. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Transmission electron microscopy (TEM) was used to study the end-of-range defect evolution. The addition of fluorine reduces the boron transient enhanced diffusion for all fluorine energies. It was observed that both the magnitude of the boron diffusivity and the concentration gradient of the boron profile vary as a function of fluorine energy.

Fluorine Incorporation Effects in Cl2 Plasma Etching of Silicon: Quadrupole Mass Spectrometer Analysis

We investigated the etch characteristics of Si in plasmas with addition of fluorine in an electron cyclotron resonance etching system. The addition of fluorine‐containing gas, , increased the etch rate and selectivity, whereas anistropy was decreased. The ion‐assisted etch mechanism was dominant in a pure plasma, whereas chemical etching was dominant at the ratio of 0.65 of gas flow rate . In the transition region, 0.65-0.9, the small addition of the fluorine containing gas brought about the generation of fluorine radicals, and this can chemically detach the chlorinated layer on feature sidewalls. Anistropy was abruptly reduced by this chemical etching. © 1999 The Electrochemical Society. All rights reserved.

Changes in Orientational Polarization and Structure of Silicon Dioxide Film by Fluorine Addition

Use of F‐doped silicon dioxide film as a low dielectric constant intermetal film for ultralarge scale integrated circuits (ULSI) is useful from the viewpoint of product cost and compatibility with present processing technologies. By adding to plasma‐enhanced chemical vapor deposition, we obtained F‐doped films with a dielectric constant as low as 2.6. The mechanism behind this decrease was investigated by estimating the dielectric constants due to the polarization components using capacitance‐voltage measurements, Kramers‐Kronig transformation, and spectroscopic ellipsometry. Fluorine addition lowers the orientational polarization by decreasing the number of ‒OH bonds, and this decrease in Si‒OH concentration is a key factor which is responsible for the lower dielectric constant in the F‐doped film. Orientational polarization due to the Si‒OH bond disappears in the far infrared with increasing frequency, thus the dielectric constant is composed only of ionic and electronic polarization components in the frequency range beyond the far infrared. The quantitative analysis of fluorine and OH shows that excess Si‒F bonds replace Si‒O and form . We suggest that the water absorption for F‐doped film can be minimized by suppressing fluorine addition at the time that the Si‒OH bonds vanish in order to avoid forming and destroying the threefold rings. © 1999 The Electrochemical Society. All rights reserved.

Effect of the fluorine-addition order on the hydrodesulfurization activity of fluorinated NiW/Al2O3 catalysts

Fluorinated NiW/Al2O3 catalysts with different orders of fluorine addition have been prepared, tested for hydrodesulfurization (HDS) of thiophene, and characterized using nitric oxide chemisorption and temperature-programmed sulfidation. The catalyst surface area has been affected by fluorine addition but not by the order of fluorination. The fluorine addition-order does not affect the amount of fluorine retained in the catalysts after the calcination and the reaction steps, either. On the other hand, the order of fluorine addition changes the dispersion of the nickel and the tungsten species, incorporation of nickel with the tungsten edge sites, and consequently the HDS activity of the catalysts. The catalyst fluorinated in the last step, i.e., after addition of both tungsten and nickel, shows the highest activity in thiophene HDS, which is supported by other experimental results indicating the most nitric oxide chemisorption and the largest incorporation of nickel with the tungsten species. Accordingly, enhancement of the catalyst activity by fluorination is due to the repartition of the metal species rather than to partial solubilization of alumina in the fluorine-addition step.

Reactivity of fluorocarbon radicals in the low-temperature fluorination of unsaturated perfluorocarbons

Calorimetry and ESR spectroscopy were used to study the low-temperature fluorination (77–300 K) of unsaturated perfluorocarbons with fluorine. In the solid phase at 77–100 K (glassy or crystalline state) fluorination does not occur. On transition from glassy systems to the supercooled liquid state formation of molecular complexes in which fluorine is attached to the >CC bond becomes possible. These complexes are stabilized on crystallization of the system; with a further increase in temperature, efficient addition of molecular fluorine takes place in the crystal phase. However, the addition of fluorine by a chain or carbene mechanism must not be ruled out for such systems. Thus, in the case of hexafluoropropene trimer, the addition proceeds as a chain reaction producing long-living free radicals at the initial stage.

The sintering of v–SiO 2 and quartz

We have investigated the crystalline phases, density and porosity of sintered silica samples produced from Brazilian quartz powder and fumed silica to complete vitrification. The affect of fumed silica on the transformation of quartz-cristobalite and the role of fluorine addition on the porosity of the silica compacts are analyzed. Both additions have an affect on the sintering of quartz. Fumed silica nucleates quartz crystals but it is not as effective as fluorine on decreasing the porosity of the compacts.

Effect of fluorine on the phase formation and superconducting properties of Tl-1223 superconductors

Fluorination of (Tl 0.5, Pb 0.5)Sr 1.6Ba 0.4Ca 2Cu 3O y high-temperature superconductors has been performed through partial replacement of CuO by CuF 2 in the starting materials. Seven samples with nominal fluorine content x atom per formula unit (0≤ x≤3.6) were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), resistivity and magnetization M( H) measurements. Fluorine addition has raised the onset transition temperature to 128 K, and increased the critical current density to 300%, the value of the fluorine free sample. XRD, SEM and energy dispersive X-ray (EDX) results showed that the formation of the Tl-1223 phase was enhanced as fluorine was introduced, and the formation of large grains was observed. EDX spot analysis revealed the presence of fluorine as a species of the structure of the Tl-1223 grains. The c-axis of Tl-1223 decreased with increasing x, indicating that fluorine had replaced oxygen in the structure. The behavior of the normal state resistivity with temperature indicated that fluorine addition changed this material from overdoped to optimally doped, and upon further fluorine addition, changes it to slightly underdoped state. That provided an additional evidence that fluorine addition changes the density of charge carrier concentration in the Cu–O planes and improves the superconducting properties of this material.

Effects of oxygen and fluorine on the dry etch characteristics of organic low-k dielectrics

The etch characteristics of the low-k dielectrics DVS BCB (BCB hereafter) and SILK in oxygen/fluorine based plasmas are studied. In an O2/NF3 plasma afterglow, the etch rate of both polymers first increases linearly with increasing NF3 concentration, then decreases monotonously. A pure fluorine plasma afterglow does not practically etch either BCB nor SILK but significantly changes their chemical and optical properties. The fluorinated polymers are more chemically stable and have lower refractive indices. Reactive ion etching (RIE) of the polymers shows a different behavior. The etch rate of SILK in a pure oxygen plasma is maximal, but BCB is etched slowly. Fluorine addition results in an increased etch rate of BCB. However, the etch rate of SILK decreases with increasing fluorine concentration. RIE in a pure SF6 plasma shows good etch characteristics and can be used for some practical applications. Mechanisms of the reactions are discussed.

Structire, Properties, and Process Characteristics of Low-K Materials Prepared by PECVD

AbstractLow dielectric constant F-doped silicon oxide films (SiO:F) can be prepared by adding fluorine source, like as CF4 to the conventional PECVD processes. We could obtain SiO:F films with dielectric constant as low as 2.6 from the reaction mixture of SiH4/N2 O/CF4. The structural changes of the oxides were sensitively detected by Raman spectroscopy. The three-fold ring and network structure of the silicon oxides were selectively decreased by adding fluorine into the film. These structural changes contribute to the decrease ionic polarization of the film, but it was not the major factor for the low dielectric constant. The addition of fluorine was very effective to eliminate the Si-OH in the film and the disappearance of the Si-OH was the key factor to obtain low dielectric constant. A kinetic analysis of the process was also performed to investigate the reaction mechanism. We focused on the effect of gas flow rate, i.e. the residence time of the precursors in the reactor, on growth rate and step coverage of SiO:F films. It revealed that there exists two species to form SiO:F films. One is the reactive species which contributes to increase the growth rate and the other one is the less reactive species which contributes to have uniform step coverage. The same approach was made on the PECVD process to produce low-k C:F films from C2F4, and we found ionic species is the main precursor to form C:F films.

Toward the synthesis of novel fluorinated building blocks: 3,4-difluorothiophene-1,1-dioxide

Addition of elemental fluorine to 2,5-dihydrothiophene-1,1-dioxide ( 4) provided a mixture of isomeric 3,4-difluoro-2,3,4,5-tetrahydrothiophene-1,1-dioxides ( 5) in moderate yield. Photochemical chlorination of each of these isomers gave the same product mixture consisting mainly of trans-3-chloro-3,4-difluoro-2,3,4,5-tetrahydrothiophene-1,1-dioxide ( 9a) and trans-3,4-dichloro-3,4-difluoro-2,3,4,5-tetrahydrothiophene-1,1-dioxide ( 11b). Dehydrohalogenation of the former gave 3,4-difluoro-4,5-dihydrothiophene-1,1-dioxide ( 12) as the main product, whereas dehydrohalogenation of the latter gave 3,4-difluorothiophene-1,1-dioxide ( 3) as the main product.

Evaluation of the growth condition of chemical vapour deposition diamond under fluorine addition

Effects of fluorine addition on the growth conditions of chemical vapour deposition (CVD) diamond are discussed in the light of thermodynamics. Phase diagrams in the C-H-F system for low-pressure diamond growth are calculated in the usual conditions: 0.1–6.67 kPa, 900–1100 K. The effects of substrate temperature and fluorine addition on the diamond growth region are explored. From these phase diagrams, we find that the diamond growth region is small and near the CH 4-HF line at low temperature; it gradually moves to the H-HF line with increasing temperature.

Crack-resistant ceramics based on bauxites

Low-iron Timan bauxites (the Komi Republic, Russia) can be used for the production of a ceramic material with high mechanical properties suitable for engineering structural purposes. Specific natural and some synthetic oxide and fluorine additives promote the sintering and increase the strength and the crack resistance of alumina ceramics, which is also attributed to the special features of the microstructure. 1 Komi Institute of Chemistry of the Scientific Center of the Ural Branch of the Russian Academy of Sciences, Russia.