XeF2 Research Articles

Atomic-emission analysis of high-purity oxides with concentration of impurities by distilling off the matrix during fluorination in autoclave

A unified technique was developed for chemical atomic-emission analysis of high-purity germanium(IV), molybdenum(VI), tellurium(IV) and tungsten(VI) oxides based on preliminary concentration of nonvolatile impurities by distilling off the matrices after chemical transformations into volatile fluorides by xenon difluoride vapor in an autoclave. The impurity concentrate was analyzed by atomic-emission method with arc and induction discharges. The detection limits of impurities in a gram analytical sample were found to be 10−6–10−8 wt.%.

ChemInform Abstract: X‐Ray Crystal Structures of [XeF][MF6] (M: As, Sb, Bi), [XeF][M2F11] (M: Sb, Bi) and Estimated Thermochemical Data and Predicted Stabilities for Noble‐Gas Fluorocation Salts Using Volume‐Based Thermodynamics.

AbstractThe crystal structures of [XeF][SbF6] (space group P21/c, Z = 4), [XeF][BiF6] (space group P21/c, Z = 4), and [XeF][Bi2F11] (space group P212121, Z = 4) are determined for the first time (single crystal XRD), and those of XeF2 (space group I4/mmm, Z = 2), [XeF][AsF6] (space group P21/n, Z = 4), [XeF][Sb2F11] (space group P21, Z = 2), and [XeF3][Sb2F11] (space group P$\bar 1$, Z = 2) are redetermined with greater precision at ‐173 °C.

(Invited) Ge/III-V Heterostructures and Their Applications in Fabricating Engineered Substrates

Chip level integration of III-V devices with Si-CMOS platform requires the use of engineered substrates. Fabrication of engineered substrates utilizes technologies such as epitaxy, wafer bonding and layer transfer. We report on two aspects of III-V/IV materials integration developments that are on the path to enabling Ge-on-insulator (GeOI) and GaAs-on-insulator (GaAsOI) on Si substrates without the use of SmartcutTM technology. We report on the establishment of Ge/AlAs/GaAs and GaAs/Ge/GaAs epitaxial structures/sequences with low defect density and surface properties suitable for wafer bonding. The epitaxial structures have embedded layers that offer highly selective etch properties that facilitate lift-off onto Si substrates. We demonstrate the use of these novel Ge/III-V heterostructures to liftoff layers of Ge through an aqueous hydrogen fluoride (HF) based epitaxial lift-off (ELO) process, or layers of GaAs through a gas phased ELO process enabled by xenon difluoride (XeF2) selective etching of Ge.

Transannular additions of selectfluor and xenon difluoride: regioselectivity and mechanism

AbstractThe addition of 1‐chloromethyl‐4‐fluoro‐1,4‐diazoniabicyclo[2.2.2]octane bis‐tetrafluoroborate (F‐TEDA) to unsaturated systems was modelled computationally at the ab initio levels and studied experimentally. The reaction of olefins with F‐TEDA is driven exclusively by charge transfer and displays the antibonding orbital picture in the transition structure for F‐transfer, similarly to that for the reactions of olefins with F‐radical. In contrast, the electrophilic and concerted fluorinations, respectively with H2O•••F+ complex and with F2, show strong bonding interactions between the fluorine and olefin moieties in the transition structures. The reaction with F‐TEDA involves an initial formation of highly delocalized charge‐transfer complexes in the first step with further low‐barrier (ca 4 kcal) migration of fluorine and is best described as an inner‐sphere electron transfer. This nonelectrophilic mechanism is operative for the transannular addition of F‐TEDA to 3‐methylene‐7‐ethylidenebicyclo[3.3.1]nonane studied experimentally. The addition mode is determined by the formation of a more stable complex via the ethylidene fragment and demonstrates selectivities that differ from conventional electrophilic additions. This mechanistic scenario may be extended to the fluorination with xenon difluoride where similar products are formed in high yields. Copyright © 2010 John Wiley & Sons, Ltd.

ChemInform Abstract: A New Method of Introducing a Trifluoromethyl Group into an Aromatic Ring.

Abstract Trifluoromethyl derivatives of aromatic molecules were prepared from aromatic halides, converted to dithiocarboxylic acids through formation of Grignard reagents, followed by fluorination with xenon difluoride at room temperature.

ChemInform Abstract: Reaction of Xenon Difluoride with Indene in Aqueous 1,2- Dimethoxyethane and Tetrahydrofuran

Xenon difluoride (XeF2) reacts with indene in 1,2-dimethoxyethane–water (90:10) to give cis- and trans-2-fluoro-1-hydroxyindans. Our data indicate that neither xenon oxide (XeO) nor hydroxyxenon fluoride (HOXeF) is an intermediate in this reaction even though XeO is a suspected intermediate from aqueous hydrolysis of XeF2.

ChemInform Abstract: Vinyl Fluorides from Vinyl Stannanes.

Abstract Fluorination of vinyl stannanes takes place in moderate yields with xenon difluoride in the presence of silver hexafluorophosphate. An electrophilic fluorination mechanism is assumed.

ChemInform Abstract: Synthesis of Bridgehead Fluorides by Fluorodeiodination.

Fluorodeiodination is found to be an attractive procedure for the synthesis of bridgehead fluorides. Thus, treatment of the corresponding iodide with xenon difluoride in dichloromethane at ambient temperature generally leads to high yields of the fluoride. Evidence suggests the intermediacy of the bridgehead cation in the reaction, and accordingly the substrates which are unfavorably disposed to fluorodeiodination are the bicyclo[n.1.1]alkyl iodides

Synthesis of [18F]xenon difluoride as a radiolabeling reagent from [18F]fluoride ion in a micro-reactor and at production scale

[18F]Xenon difluoride ([18F]XeF2), was produced by treating xenon difluoride with cyclotron-produced [18F]fluoride ion to provide a potentially useful agent for labeling novel radiotracers with fluorine-18 (t1/2=109.7min) for imaging applications with positron emission tomography. Firstly, the effects of various reaction parameters, for example, vessel material, solvent, cation and base on this process were studied at room temperature. Glass vials facilitated the reaction more readily than polypropylene vials. The reaction was less efficient in acetonitrile than in dichloromethane. Cs+ or K+ with or without the cryptand, K 2.2.2, was acceptable as counter cation. The production of [18F]XeF2 was retarded by K2CO3, suggesting that generation of hydrogen fluoride in the reaction milieu promoted the incorporation of fluorine-18 into xenon difluoride. Secondly, the effect of temperature was studied using a microfluidic platform in which [18F]XeF2 was produced in acetonitrile at elevated temperature (≥85°C) over 94s. These results enabled us to develop a method for obtaining [18F]XeF2 on a production scale (up to 25mCi) through reaction of [18F]fluoride ion with xenon difluoride in acetonitrile at 90°C for 10min. [18F]XeF2 was separated from the reaction mixture by distillation at 110°C. Furthermore, [18F]XeF2 was shown to be reactive towards substrates, such as 1-((trimethylsilyl)oxy)cyclohexene and fluorene.

Properties of Fluorinated Graphene Films

Graphene films grown on Cu foils have been fluorinated with xenon difluoride (XeF(2)) gas on one or both sides. When exposed on one side the F coverage saturates at 25% (C(4)F), which is optically transparent, over 6 orders of magnitude more resistive than graphene, and readily patterned. Density functional calculations for varying coverages indicate that a C(4)F configuration is lowest in energy and that the calculated band gap increases with increasing coverage, becoming 2.93 eV for one C(4)F configuration. During defluorination, we find hydrazine treatment effectively removes fluorine while retaining graphene's carbon skeleton. The same films may be fluorinated on both sides by transferring graphene to a silicon-on-insulator substrate enabling XeF(2) gas to etch the Si underlayer and fluorinate the backside of the graphene film to form perfluorographane (CF) for which calculated the band gap is 3.07 eV. Our results indicate single-side fluorination provides the necessary electronic and optical changes to be practical for graphene device applications.

Porous silicon and porous polymer substrates for optical chemical sensors

Mesoporous materials, such as porous silicon and porous polymer gratings (Bragg structures), offer an attractive platform for the encapsulation of chemical and biological recognition elements. These materials include the advantages of high surface to volume ratio, biocompatibility, functionality with various recognition elements, and the ability to modify the material surface/volume properties and porosity. Two porous structures were used for chemical and biological sensing: porous silicon and porous polymer photonic bandgap structures. Specifically, a new dry etching manufacturing technique employing xenon difluoride (XeF2) based etching was used to produce porous silicon Porous silicon continues to be extensively researched for various optical and electronic devices and applications in chemical and biological sensing are abundant. The dry etching technique to manufacture porous silicon offers a simple and efficient alternative to the traditional wet electrochemical etching using hydrofluoric acid. This new porous silicon material was characterized for its pore size and morphology using top and cross-sectional views from scanning electron microscopy. Its optical properties were determined by angular dependence of reflectance measurements. A new class of holographically ordered porous polymer gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. As an alternative structure and fabrication process, porous polymer gratings that include a volatile solvent as the phase separation fluid was fabricated. Porous silicon and porous polymer materials were used as substrates to encapsulate gaseous oxygen (O2) responsive luminophores in their nanostructured pores. These substrate materials behave as optical interference filters that allow efficient and selective detection of the wavelengths of interest in optical sensors.

Focused electron beam induced etching of silicon using chlorine

A new beam-assisted process for removing silicon from a surface in the nanometer scalein a conventional scanning electron microscope is presented. This approach isbased on focused electron beam induced etching with pure chlorine gas being usedas the precursor. In contrast to the established etching process using a focusedion beam (with or without the addition of a precursor), no amorphizationand gallium implanting of the substrate takes place. The observed low etchrates facilitate removal with sub-nanometer precision. No spontaneous etchingof silicon as in the case of xenon difluoride was observed. Etch rates of up to4 nm min − 1 could be achieved as well as a minimum feature size of below 80 nm. The effect of etchingparameters like electron beam energy, electron beam accelerating voltage or pixelspacing were systematically examined. Finally, the underlying etching mechanism interms of secondary electron interactions and precursor replenishment is discussed.

Free-standing AlxGa1−xAs heterostructures by gas-phase etching of germanium

We outline a facile fabrication technique for the realization of free-standing AlxGa1−xAs heterostructures of arbitrary aluminum content. Utilizing xenon difluoride (XeF2) we rapidly and selectively remove a sacrificial germanium (Ge) underlayer in a room temperature gas-phase etching procedure. We demonstrate two possibilities for exploiting this unique process: (1) bulk micromachining of a suspended high-frequency low-dissipation micro-optomechanical resonator consisting of an epitaxial GaAs/AlAs multilayer grown on a Ge substrate and (2) epitaxial lift-off of a GaAs film via removal of an embedded Ge sacrificial layer, resulting in lateral etch rates up to 3 mm/h and a conservative selectivity of ∼106.

ChemInform Abstract: Fluorine-18 Labeling of Methionine Derivatives in the Presence of Xenon Difluoride.

ChemInform Abstract: Fluorine-18 Labeling of Methionine Derivatives in the Presence of Xenon Difluoride.

ChemInform Abstract: vic-Difluorination of Fluoroalkenes with Xenon Difluoride: The Effect of Fluorine Substituents on the Reaction of Alkenes with Xenon Difluoride.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Rearrangement and Double Fluorination in the Deiodinative Fluorination of Neopentyl Iodide with Xenon Difluoride.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Reactions of Benzeneselenenyl Fluoride Generated by XeF2-(PhSe)2 System with Electron-Deficient Alkenes.

Abstract Fluoro-benzeneselenenylation of electron-deficient alkenes with benzeneselenenyl fluoride [PhSeF] generated in situ by the reaction of diphenyl diselenide and xenon difluoride proceeded smoothly in dichloromethane. The product yields increased remarkably in higher concentration of the seleno-reagent. The reactive seleno-reagent PhSeF may be stabilized in the higher concentration presumably by the favorable association of the reagent.

Determination of impurities in TeO2-WO3 fiber-optic glasses by chemical atomic emission spectrometry

We describe a procedure for arc source chemical atomic emission analysis of high-purity TeO2-WO3 tellurite glasses using preconcentration of nonvolatile impurities via reactive vaporization of the major glass constituents by fluorination with xenon difluoride in an autoclave. The detection limits of impurities are 10−8 to 10−6 wt %.

Dry etch fabrication of porous silicon using xenon difluoride

The authors report the fabrication of porous silicon material using a xenon difluoride (XeF2) dry etching technique. Using a XeF2 fabrication process, porous silicon can be formed selectively on silicon by employing a standard hard-baked photoresist layer as a masking layer. The authors demonstrate porous silicon with different pore sizes and configurations rendering this material as an attractive candidate for a wide spectrum of potential applications. The pore size, porosity and thickness of the various developed porous silicon samples were characterised with electron microscopy and optical reflectance measurements. This XeF2 etching technique offers flexible and straightforward fabrication of porous silicon and could allow simple monolithic integration of porous silicon devices with microelectronic circuitry, following the current trend of integrated microsystems.

Synthesis and characterisation of some iridium-carbonyl-fluoride complexes. Crystal structures of [IrF(CO){P(C6H4-2-CH3)3}2] and [IrF2(COD)py2][BF4

Two routes to iridium(III) fluorocomplexes are described. The direct reaction of tetrairidium dodecacarbonyl with elemental fluorine in aHF offers a clean, convenient, large scale route to [IrF(3)(CO)(3)]; addition of phosphines to [IrF(3)(CO)(3)] in THF affords mer-[IrF(3)(CO)L(2)] or [IrF(CO)L(2)]. Alternatively, cationic [IrF(2)(COD)L(2)](+) and [IrF(2)(CO)(2)L(2)](+) (L = phosphine, pyridine; L(2) = alpha-diimine) are accessible via the oxidation of the iridium(I) precursors with xenon difluoride.