Formation Of Si-F Bonds Research Articles

Borane-Catalyzed C-F Bond Functionalization of gem-Difluorocyclopropenes Enables the Synthesis of Orphaned Cyclopropanes.

Herein, we disclose an approach to synthesize tert-alkyl cyclopropanes by leveraging C-F bond functionalization of gem-difluorocyclopropenes using tris(pentafluorophenyl)borane catalysis. The reaction proceeds through the intermediacy of a fluorocyclopropenium ion, which was confirmed by the isolation of [Ph2(C6D5)C3]+[(C6F5)3BF]-. We found that silylketene acetal nucleophiles were optimal reaction partners with fluorocyclopropenium ion intermediates yielding fully substituted cyclopropenes functionalized with two α-tert-alkyl centers (63-93% yield). The regioselectivity of the addition to cyclopropenium ions is controlled by their steric and electronic properties and enables access to 3,3-bis(difluoromethyl)cyclopropenes in short order. The resulting cyclopropene products are readily reduced to the corresponding orphaned cyclopropanes under hydrogenation conditions. Quantum chemical calculations reveal the nature of the C-F bond cleavage steps and provide evidence for catalysis by boron and not silylated oxonium ions, though Si-F bond formation is the enthalpic driving force for the reaction.

Strategic optimization of phase-selective thermochemically amended terra-firma originating from excavation-squander for geogenic fluoride adsorption: a combined experimental and in silico approach.

An inimitable adsorbent "FI-TM-BWCC," emanated from meta-phase-selective thermochemical modulation of excavation-squander (mine waste)-derived terra-firma (blackish white china clay, i.e., BWCC), is explored in the present work for fluoride (F-) adsorption purpose. FI-TM-BWCC portrayed an excellent adsorption efficiency (95% removal capacity and Qe: 99 mg/g, at initial adsorbate dose: 10 mg/L, pH: 7±0.5, adsorbent dosage: ~600 mg, exposure time: 60 min). At identical experimental conditions, the F- scavenging phenomenon was superior than two analogous adsorbents: (i) biopolymer chitosan and glutaraldehyde cross-linked BWCC (CG@BWCC, wherein F- removal efficiency: 74%) and (ii) meta-phase-selective thermally moduled BWCC (TM-BWCC, removal efficiency: 75%). BWCC predominantly comprises kaolinite and a trace amount of anatase along with prime elemental compositions: 41.71% Al2O3, 49.80 % SiO2, 4.25% Fe2O3, and 3.93% TiO2, as revealed by PXRD and XRF analyses. The thermochemical modulation pathway significantly escalated the BET surface area of BWCC (~11.92 m2/g, avg. pore radius: 23.64 Å, i.e., mesoporous in nature) to FI-TM-BWCC (216.95 m2/g, avg. pore radius: 31.41 Å). The fluoride-adsorbed F-•••FI-TM-BWCC species revealed a reduced surface area of 21.5 m2/g, which was explained in the light of ion exchange pathway on FI-TM-BWCC's non-uniform surface (surface roughness/SA of 1597 nm, reduced to 1179 nm after F- uptake). The spontaneous F-•••FI-TM-BWCC interaction (ΔG0 = -6.25 kJ) occurred following chemisorption-controlled ion exchange (CCIE) pathway as appearance of a F1s band at 685.5 eV was rationalized for Si-F bond formation; corroborating pseudo second-order (PSO) kinetics and resembling Freundlich isotherm. The usefulness of FI-TM-BWCC was diversified through field validation with natural groundwater specimens and proposition of a gravity-fed defluoridation unit. The flow rate was documented to be ~11 liters per hour (LPH) by implementing viscous turbulence fluent model. The experimental findings certainly followed the premise conventions of sustainability metrics upholding socio-economic equipoise.

Reduction of Fluorine Diffusion and Improvement of Dark Current Using Carbon Implantation in CMOS Image Sensor

Recently, the demand of a high resolution complementary metal-oxide semiconductor (CMOS) image sensor is dramatically increasing. As the pixel size reduces to submicron, however, the quality of the sensor image decreases. In particular, the dark current can act as a large noise source resulting in reduction of the quality of the sensor image. Fluorine ion implantation was commonly used to improve the dark current by reducing the trap state density. However, the implanted fluorine diffused to the outside of the silicon surface and disappeared after annealing process. In this paper, we analyzed the effects of carbon implantation on the fluorine diffusion and the dark current characteristics of the CMOS image sensor. As the carbon was implanted with dose of 5.0 × 1014 and 1 × 1015 ions/cm2 in N+ area of FD region, the retained dose of fluorine was improved by more than 131% and 242%, respectively than no carbon implantation indicating that the higher concentration of the carbon implantation, the higher the retained dose of fluorine after annealing. As the retained fluorine concentration increased, the minority carriers of electrons or holes decreased by more Si-F bond formation, resulting in increasing the sheet resistance. When carbon was implanted with 1.0 × 1015 ions/cm2, the defective pixel, dark current, transient noise, and flicker were much improved by 25%, 9.4%, 1%, and 28%, respectively compared to no carbon implantation. Therefore, the diffusion of fluorine after annealing could be improved by the carbon implantation leading to improvement of the dark current characteristics.

Structures of fluoride containing aluminosilicate low activity nuclear waste glasses: A molecular dynamics simulations study

Fluorine and other halides commonly exist in nuclear waste forms, and due to their volatile nature, halide retention poses an issue affecting waste loading during vitrification. The compositional effect on fluorine incorporation in aluminosilicate glasses is investigated through molecular dynamics simulations. Oxygen and fluorine coordination numbers around glass former and modifier cations, bond angle distributions, and medium range structure features such as Qn distributions, ring size distributions and neutron diffraction structure factors were calculated. It was found that fluorine has higher preference to bond to Ca2+ than to Na+, both in the melt and the glass, and there is no Si-F bond formation in the glass but they do exist in the melt. Consequently, CaO for Na2O substitution can be an effective way to help fluorine retention without significantly changing the glass chemistry. These results thus provide insights on fluorine incorporation in the aluminosilicate nuclear waste glasses and the strategy on how to improve fluorine retention both in the glass and the melt.

A general 11C-labeling approach enabled by fluoride-mediated desilylation of organosilanes

Carbon-11 (11C) is one of the most ideal positron emitters for labeling bioactive molecules for molecular imaging studies. The lack of convenient and fast incorporation methods to introduce 11C into organic molecules often hampers the use of this radioisotope. Here, a fluoride-mediated desilylation (FMDS) 11C-labeling approach is reported. This method relies on thermodynamically favored Si-F bond formation to generate a carbanion, therefore enabling the highly efficient and speedy incorporation of [11C]CO2 and [11C]CH3I into molecules with diversified structures. It provides facile and rapid access to 11C-labeled compounds with carbon-11 attached at various hybridized carbons as well as oxygen, sulfur and nitrogen atoms with broad functional group tolerance. The exemplified syntheses of several biologically and clinically important radiotracers illustrates the potentials of this methodology.

Open-Shell Fluorination of Alkyl Bromides: Unexpected Selectivity in a Silyl Radical-Mediated Chain Process.

We disclose a novel radical strategy for the fluorination of alkyl bromides via the merger of silyl radical-mediated halogen-atom abstraction and benzophenone photosensitization. Selectivity for halogen-atom abstraction from alkyl bromides is observed in the presence of an electrophilic fluorinating reagent containing a weak N-F bond despite the predicted favorability for Si-F bond formation. To probe this surprising selectivity, preliminary mechanistic and computational studies were conducted, revealing that a radical chain mechanism is operative in which kinetic selectivity for Si-Br abstraction dominates due to a combination of polar effects and halogen-atom polarizability in the transition state. This transition-metal-free fluorination protocol tolerates a broad range of functional groups, including alcohols, ketones, and aldehydes, which demonstrates the complementary nature of this strategy to existing fluorination technologies. This system has been extended to the generation of gem-difluorinated motifs which are commonly found in medicinal agents and agrochemicals.

Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydrofunctionalization and Formal Retro-hydrofunctionalization.

We report a contra-thermodynamic isomerization of internal olefins to terminal olefins driven by redox reactions and formation of Si-F bonds. This process involves chain-walking hydrosilylation of internal olefins and subsequent formal retro-hydrosilylation. The process rests upon the high activities of platinum hydrosilylation catalysts for isomerization of metal alkyl intermediates and a new, metal-free process for the conversion of alkylsilanes to alkenes. By this approach, 1,2-disubstituted and trisubstituted olefins are converted to terminal olefins.

Viscosity and related structure transformation of fluorine bearing silicate melt under ultrasonic field

The fluorine bearing and free silicate melts of Na2O-K2O-SiO2-CaF2 system were treated under ultrasonic field, and the melt structure and viscosity were measured. The results showed that the fluorine bearing silicate melt can be depolymerized and the polymerization decreased with the ultrasonic intensity. The viscosity of the fluorine bearing silicate melt decreased more quickly to the dynamic balance point between the dissociation and reconnection of the species, and reverted more slowly to the natural state than the fluorine free silicate melt, because fluorine ions join the silicate network via the formation of new Si-F bonds. The formation of SiF bonds can intensify the reduction of the viscosity, but the consumption of fluorine ions may lead to an increasing of the viscosity, which resulted in the weak decreasing trend in the viscosity as the ultrasonic intensity increased. The method may be helpful in assisting the synthesis of fluorine bearing bioactive glass.

Interaction between SiO2 and a KF–KCl–K2SiF6 Melt

The solubility mechanism of silica in a fluoride-chloride melt has been determined in situ using Raman spectroscopy. The spectroscopy data revealed that the silica solubility process involved Si-O bond breakage and Si-F bond formation. The process results in the formation of silicate complexes, fluorine-bearing silicate complexes, and silicon tetrafluoride in the melt. Mass spectrometry of the vapor phase over the KF-KCl-K2SiF6 and KF-KCl-K2SiF6-SiO2 melts and differential scanning calorimetry coupled with thermal gravimetric analysis of these melts were performed to verify the silica solubility mechanism.

Charge Trapping and Detrapping Behavior of Fluorinated $\hbox{HfO}_{2}/\hbox{SiON}$ Gate Stacked nMOSFET

The charge trapping and detrapping characteristics of the fluorinated hafnium oxide/oxynitride (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiON) gate stack are investigated. Although incorporation of fluorine in the bulk stack had been proven to eliminate both bulk and interface trap densities due to Hf-F and Si-F bond formation, respectively, the effective trapping barrier of the device with fluorine incorporation (1.29 eV) is deeper than without fluorine incorporation (1.13 eV), indicating that the detrapping ability of the fluorinated devices may limit future fluorine process applications.

Performance and reliability of poly-Si TFTs on FSG buffer layer

A novel and process-compatible scheme for fabricating poly-Si thin-film transistors (TFTs) on an FSG buffer layer was proposed and demonstrated. Experimental results reveal that remarkably improved device performance and uniformity can be achieved with appropriate fluorine concentration. The poly-Si TFTs fabricated on FSG layers have a higher on-current, a lower leakage current, and a higher field-effect mobility compared with the conventional poly-Si TFTs. Furthermore, the incorporation of fluorine also increased the reliability of poly-Si TFTs against hot carrier stressing, which is attributed to the formation of Si-F bonds.

Fluorinated Silicon Nitride Film Deposited at Low Temperatures from SiH4-SiF4-NH3

ABSTRACTThe effect of SiF4 addition on the deposition characteristics and film property has been studied for the improvement of long term stability of the SiNx:F film in TFT applications. During the deposition with SiF4 addition, atomic hydrogen species in the gas phase significantly decreased. A detailed bonding configuration of fluorine and hydrogen was investigated by XPS and FT-IR. Optical band gap increases with the increment of fluorine concentration in the film. High compressible stress turned to low tensile stress with increasing SiF4 flow rate. The breakdown strength and barrier height for the conduction of trapped electron were improved by SiF4 addition even in Si-rich SiNx:H films due to the stable Si-F bond formation.

Refractoriness of High-Current and Low Acceleration Voltage Arsenic-Ion Implanted Polycrystalline Silicon Against Fluorine Chemistry

ABSTRACTThe author observed that both high-current-ion-beam and low-accelerationvoltage arsenic-implanted polycrystalline silicon-film surfaces are resistant to radical-fluorine-gas-etching. If we accept the simple assumption that a depth profile of concentration distribution of the implanted high-dose As atoms in polycrystalline Si film can be expressed with a standardized distribution function in the previous report of S. Furukawa, H. matsumura, and H. Ishiwara [Jpn. J. Appl. Phys. 11, 134 (1972)], we can take the premise that the chemical bonding reaction itself between radical-fluorine atoms and silicon atoms is prevented rather than that the covering of an arsenic- metal thin layer like amorphous state prevents the chemical bonding- reaction. We present a model of the prevention Si-F bond formation by high-dose arsenic implantation at low acceleration voltage. The model seems to be related to potential barrier increase and lattice vibration suppression for electromagnetic force-phonon interaction.

Hot-electron hardened Si-gate MOSFET utilizing F implantation

A technique is presented for incorporating fluorine (F) into the gate-oxide film, and the subsequent improvement of channel-hot-electron hardness of the resulting MOSFET is reported. This technique uses low-energy F implantation onto the surface of the polysilicon gate-electrode, followed by annealing at 950 degrees C to diffuse F into the gate SiO/sub 2/ toward the SiO/sub 2//Si interface. The improved hot-electron hardness is explained by a model involving a strain relaxation near the SiO/sub 2//Si interface by fluorine incorporation that results from Si-F bond formation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>