Negative Ions of Trifluoromethyl Fullerene Derivatives: First Thermodynamic Data

Abstract

The mixtures of trifluoromethyl derivatives of C₆₀ were studied by Knudsen cell mass‐spectrometry. Ion–ion and electron exchange equilibria between charged and neutral species in the gas phase were investigated and the electron affinity (EA) values for C₆₀(CF₃)₆, C₆₀(CF₃)₈, and C₆₀(CF₃)₁₀ were estimated.     

Effect of doping elements on ZnO etching characteristics with CH4/H2/Ar plasma

Effect of doping elements on the etching characteristics of doped-ZnO (Ag, Li, and Al) thin films, etched with a positive photoresist (PR) mask, and an etch process window for infinite etch selectivity were investigated by varying the CH₄ flow ratio and self-bias voltage, V_dc, in inductively coupled CH₄/H₂/Ar plasmas. Increased doping of ZnO films decreased the etch rates significantly presumably due to lower volatility of reaction by-products of doped Li, Ag, and Al in CH₄/H₂/Ar plasmas. The etch rate of AZO (Al-doped ZnO) was most significantly decreased as the doping concentration is increased from 4 to 10 wt%. It was found that process window for infinite etch selectivity of the doped ZnO to the PR is closely related to a balance between deposition and removal processes of a-C:H (amorphous hydrogenated carbon) layer on the doped-ZnO surface. Measurements of optical emission of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, implied that the chemical reaction of CH radicals with Zn atoms in doped-ZnO play an important role in determining the doped-ZnO etch rate together with an ion-enhanced removal mechanism of a-C:H layer as well as Zn(CH_x)_y etch by-products.     

Effect of intrinsic 239Pu α-radiation on its extraction with a 40% solution of Tri-n-butyl phosphate in formal n2

In extraction regeneration of spent nuclear fuel, namely, in refining of solutions containing 0.2 M Pu and more, the radiolytic effects caused by intrinsic Pu α-radiation become noticeable. To examine this effect, Pu extraction from an aqueous solution containing 0.21 M Pu(IV) nitrate and 3 M HNO₃ with a 40% solution of TBP in bis(octafluoroamyl) formal, CH₂[OCH₂(CF₂)₃CF₂H]₂, was performed without intercycle treatments. As a result, after 2-month contact with aqueous Pu solution, the organic phase got an irradiation dose of 470 kGy. This led to a decrease in the Pu distribution ratio by a factor of 4.1 and in the phase separation rate by a factor of 1.3 and to an increase in the viscosity by 12%; the density varied within 1–3%.     

ISOLATION AND CHARACTERISATION OF C60(CF3)2

ABSTRACT

From the products of reactions of [60]fullerene with either K₂PtF₆ at 470?°C or AgF at 520?°C, we have isolated C₆₀(CF₃)₂, the simplest trifluoromethylfullerene, which gives a single ¹⁹F NMR line at ?69.5?ppm. The HPLC retention time is less than that of C₆₀F₂ confirming the trend observed for other fluoro- vs. trifluoromethylfullerenes namely that the latter elute more rapidly. Other trifluoromethyl- containing species, C₆₀(CF₃)₄O, C₆₀F₅CF₃, C₆₀(CF₃)₄H₂, C₆₀(CF₃)₆H₂, and C₆₀(CF₃H)₃ were detected in the product mixture.     

Direct imaging by atomic force microscopy of surface-localized self-assembled monolayers on a cuprate superconductor and surface X-ray scattering analysis of analogous monolayers on the surface of water

A self-assembled monolayer of CF₃(CF₂)₃(CH₂)₁₁NH₂ atop the (001) surface of the high-temperature superconductor YBa₂Cu₃O_7-x was imaged by atomic force microscopy (AFM). The AFM images provide direct 2D-structural evidence for the epitaxial 5.5 Å square √2 × √2R45° unit cell previously predicted for alkyl amines by molecular modeling [J.E. Ritchie, C.A. Wells, J.-P. Zhou, J. Zhao, J.T. McDevitt, C.R. Ankrum, L. Jean, D.R. Kanis, J. Am. Chem. Soc. 120 (1998) 2733]. Additionally, the 3D structure of an analogous Langmuir monolayer of CF₃(CF₂)₉(CH₂)₁₁NH₂ on water was studied by grazing-incidence X-ray diffraction and specular X-ray reflectivity. Structural differences and similarities between the water-supported and superconductor-localized monolayers are discussed.     

Mechanism of thermal decomposition of HFO-1234yf by DFT study

Twenty-two chemical reaction pathways of thermal decomposition of 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf, CF₃CFCH₂) are proposed to investigate the formation mechanism of some possible products (CF₃H, CF₄, HF, H₂) by using density function theory (DFT) simulations with M06-2X/6–311++(d,p) level of theory. The results point out that the ground state CF₃CFCH₂ will excite into the lowest triplet state CF₃CF-CH₂ favorably in the first step with an energy barrier of 264.67 kJ mol⁻¹ and pathway 5 is the most preferred route of homolytic cleavage reactions with the lowest energy barrier of 205.70 kJ mol^-1. F radical is hard to generate during thermal decomposition processes because of its higher energy barrier. H radical and CF₃ radical play a dominant role in thermal decomposition of HFO-1234yf. H-abstraction and F-abstraction reactions are proposed in subsequent radical attacking chain reactions. CF₃H and H₂ are easier to be generated due to their lower energy barriers. Our work presents the mechanism of thermal decomposition of HFO-1234yf from the molecule level and provides a reference for studying the thermal stability of other working fluids.     

Trifluoromethylated [60]Fullerenes: Synthesis and Characterization

Abstract

The high temperature reaction of C₆₀ with silver(I) trifluoroacetate followed by 500°C sublimation and HPLC purification has led to the characterization of the trifluoromethyl‐[60]fullerenes 1,4‐C₆₀(CF₃)₂, C _s‐C₆₀(CF₃)₄, C ₁‐C₆₀(CF₃)₄, and C ₁‐C₆₀(CF₃)₆ by EI‐MS and ¹⁹F NMR. The compounds C ₁‐C₆₀(CF₃)₄ and C ₁‐C₆₀(CF₃)₆ were obtained with 90+% compositional purity. A sample of C₆₀(CF₃)₂ also contained ca. 15–20% of a C _s‐symmetry isomer of C₆₀(CF₃)₄. The structural assignments are based on calculations at the AM1 and DFT levels of theory.     

Preparation and properties of fluorinated aliphatic alcohols/silica nanocomposites – Application to the encapsulation of anatase titanium oxide nanoparticles into these composite cores

A variety of fluorinated aliphatic alcohols [R_F-CH₂CH₂OH; R_F = CF₃(CF₂)₃CH₂(CF₂)₅, CF₃(CF₂)_n; n = 3, 5, 7] were applied to the preparation of the corresponding fluorinated alcohols/silica nanocomposites [R_F-CH₂CH₂OH/SiO₂] through the sol–gel reactions with tetraethoxysilane (TEOS) and silica nanoparticles under alkaline conditions. R_F-CH₂CH₂OH/SiO₂ nanocomposites thus obtained have a good dispersibility and stability in not only water but also traditional organic solvents such as methanol, ethanol, 1,2-dichloroethane and tetrahydrofuran. FE–SEM (field emission scanning electron microscopy) and dynamic light scattering (DLS) measurements show that these composites are nanometer size-controlled fine particles in methanol. These fluorinated nanocomposites were also applied to the surface modification of glass to exhibit a superhydrophilic characteristic with a superoleophobicity on the modified surface. Interestingly, R_F-CH₂CH₂OH/SiO₂ nanocomposites were found to exhibit no weight loss behavior corresponding to the contents of the alcohols in the composites even after calcination at 800 °C. In addition, anatase TiO₂ nanoparticles (an-TiO₂) were effectively encapsulated into R_F-CH₂CH₂OH/SiO₂ nanocomposite cores under the similar sol–gel reactions to give the corresponding fluorinated alcohol/SiO₂/an-TiO₂ nanocomposites. These obtained nanocomposites can give a higher photocatalytic activity even after calcination at 1000 °C for the decolorization of methylene blue under UV light irradiation than that of the an-TiO₂ nanoparticles under the similar conditions, although the parent TiO₂ nanoparticles after calcination were unable to give a photocatalytic activity.     

Efficient red electrophosphorescent organic light-emitting diodes based on the new sensitized heteroleptic tris-cyclometalated Ir(III) complexes

Organic light-emitting device (OLED) was fabricated using the novel red phosphorescent heteroleptic tris-cyclometalated iridium complex, bis(2-phenylpyridine)iridium(III)[2(5′-methylphenyl)-4-diphenylquinoline] [Ir(ppy)₂(dpq-5CH₃)], based on 2-phenylpyridine (ppy) and 2(5′-methylphenyl)-4-diphenylquinoline (dpq-5CH₃) ligand. Generally, the ppy ligand in heteroleptic iridium complexes plays an important role as “sensitizer” in the efficient energy transfer from the host (CBP; 4,4,N,N′-dicarbazolebiphenyl) to the luminescent ligand (dpq-5CH₃). We demonstrated that high efficiency through the “sensitizer” can be obtained, when the T₁ of the emitting ligand is close to T₁ of the sensitizing ligand. The device containing Ir(ppy)₂(dpq-5CH₃) produced red light emission of 614 nm with maximum luminescence efficiency and power efficiency of 8.29 cd/A (at 0.09 mA/cm²) and 5.79 lm/W (at 0.09 mA/cm²), respectively.     

Effects of applied power on hydrogenated amorphous carbon (a-C:H) film deposition by low frequency (60 Hz) plasma-enhanced chemical vapor deposition (PECVD)

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass substrates using low frequency (60 Hz) plasma-enhanced chemical vapor deposition and the effects of the applied power on a-C:H films deposition were investigated. During deposition, the electron temperature and the density of CH₄-H₂ plasma were 2.4-3.1 eV and about 10⁸ cm⁻³, respectively. The main optical emission peak of the carbon species observed in the CH₄-H₂ plasma is shown to be excited carbon CH* at 431 nm. The sp³/sp² ratio, band gap, hydrogen content, and refractive index of a-C:H films gradually increased up to a power of 25 W and then saturated at higher power. This tendency is similar to the variation of plasma parameters with varying applied power, thereby indicating that a strong relationship exists between the properties of the films and the plasma discharge.     

Synthesis of tadpole-shaped Au nanoparticles using a Langmuir monolayer of fluorocarbon surfactant

Tadpole-shaped nanoplates, linearly arranged nanoparticles and triangular and hexagonal nanoplates were synthesized under a Langmuir monolayer of a cationic fluorocarbon surfactant, FC-4 (C₃F₇O(CF(CF₃)CF₂O)₂CF(CF₃)CONH(CH₂)₃N⁺(C₂H₅)₂CH₃I^?) through interfacial reduction of AuCl₄^? by formaldehyde gas. Reports about such tadpole-shaped nanoparticles are relatively scarce. The predominantly plate-like particles are mainly nearly perfect triangular and hexagonal nanocrystals, of micrometer scale in diameter. The Au nanoparticles are characterized using transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). The atomically flat planar surfaces of the Au nanoplates correspond to {111} planes and the lateral surfaces are {110} planes. The surface pressure strongly influences the formation of different Au nanostructures. A potential mechanism of such diverse morphologies is also discussed.     

Hydroboration of polymethylvinylsilane — a novel route to silicon boron carbide ceramics

Polymethylvinylsilanes (PMVS) of the general composition [R₂Si] _m [RRSi] _n with R=CH₃ and R=CH=CH₂ (vinyl) have been synthesized by the dechlorination of dichlordimethylsilane (CH₃)₂SiCl₂ and dichlormethylvinylsilane CH₃(CH₂=CH) SiCl₂ with sodium in toluene. Subsequently, the vinyl groups have been hydroborated by the reaction of the as-synthesized polysilane with various borane adduct compounds such as dimethylsulphide borane (CH₃)₂S·BH₃. The hydroborated polymer was characterized by infrared and ¹³C-, ¹H-, and ¹¹ B-NMR spectroscopy as well as by the measurement of the molecular weight distribution. The pyrolysis of the boron-containing polysilane at 1100 °C in argon results in the formation of X-ray amorphous silicon boron carbide, Si_xC_x+yB_z in 63% yield. The crystallization behaviour of the polymer-derived covalent ceramic product at temperatures up to 2200 °C is discussed. The microstructure was characterized by transmission electron microscopy. Analytical results were obtained with the novel electron spectroscopic imaging (ESI) technique.     

Importance of H2 gas for growth of hot-wire CVD nanocrystalline 3C-SiC from SiH4/CH4/H2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH₄/CH₄/H₂ and the influence of H₂ gas flow rate (F(H₂)) on the film properties was investigated. The SiH₄ gas flow rate was 1 sccm. At the CH₄ gas flow rate (F(CH₄)) of 1 sccm, nanocrystalline cubic SiC (nc-3C-SiC) grew even without H₂. On the other hand, at F(CH₄) = 2 sccm, amorphous SiC grew without H₂ and nc-3C-SiC grew above F(H₂) = 50 sccm. As F(H₂) was increased, the crystallinity improved both at F(CH₄) = 1 and 2 sccm. However, the mean crystallite size decreased at F(CH₄) = 1 sccm and increased at F(CH₄) = 2 sccm. We discuss growth mechanisms of nc-3C-SiC.     

Linear antenna microwave plasma CVD deposition of diamond films over large areas

Diamond thin films were grown by linear antenna microwave plasma CVD process over large areas (up to 20 × 10 cm²) from a hydrogen based gas mixture. The influence of the gas composition (H₂, CH₄, CO₂) and total gas pressure (0.1 and 2 mbar) on the film growth is presented. For CH₄/H₂ gas mixtures, the surface crystal size does not show dependence on the methane concentration and total pressure and remains below 50 nm as observed by SEM. Adding CO₂ (up to 10%) significantly improves the growth rate. However, still no significant change of morphology is observed on films grown at 2 mbar. The crucial improvement of the diamond film purity (as detected by Raman spectroscopy) and crystal size is found for deposition at 0.1 mbar. In this case, crystals are as large as 500 nm and the growth rate increases up to 38 nm/h.     

Synthesis of co-ordination networks from flexible bis-(4-pyridyl) ligands and cadmium salts.

Crystallisation of flexible dipyridyl ligands with Cd(NO₃)₂·4H₂O, Cd(ClO₄)₂·xH₂O or Cd(NO₃)₂·4H₂O and KSCN gives co-ordination networks of composition [Cd(ClO₄)₂(Py₂C₃H₆)₂(H₂O)₂]·Py₂C₃H₆ 1 (Py₂C₃H₆ =1,3-bis(4-pyridyl)propane); [Cd(ClO₄)₂(Py₂C₂H₄)₃] 2 (Py₂C₂H₄ =1,2-bis(4-pyridyl)ethane); [Cd(NCS)₂(Py₂C₃H₆)] 3; [Cd₂(NO₃)₄(o-C₆H₄(CH₂CH₂4-Py)₂)₄] 4 (o-C₆H₄(CH₂CH₂Py)₂ =1,2-bis[2-(4-pyridyl)ethyl] benzene and [Cd(NO₃)₂(PyCH₂CH₂CH=CHCH₂CH₂Py)₃] 5 (PyCH₂CH₂CH=CHCH₂CH₂Py =1,6-bis(4-pyridyl)hex-3-ene). The compounds were characterised by X-ray single crystal diffraction studies which revealed the presence of different polymeric motifs. Structures 1 and 5 consist of 1-D polymeric chains, structure 4 consists of a 2-D polymeric network and structure 3 is a 3-D polymeric network. None of these exhibit lattice interpenetration. However structure 2 consists of three identical but independent interpenetrating 3-D lattice networks.     

Derivatives of α-zirconium phosphate with two different functional groups

The syntheses of derivatives of α-zirconium phosphate having the general formula Zr(RPO₃)_x(R′PO₃)_2−x (where R and R′ are generally organic radicals, but may also indicate −H or −OH groups) have been achieved by precipitating a mixture of two phosphonic acids with a zirconium salt in the presence of hydrofluoric acid. Different mixed compounds, classified in the following three classes

• 1.(a) Zr (HPO₄)_x (R′PO₃)_2−x (R′ = −H; −C₆H₅; −CH₂CH ₂COOH)
• 2.(b) Zr (RPO₃)_x (R′PO₃)_2−x (R′ = −CH₂COOH;R′ = −CH₂OH)
• 3.(c) Zr (HPO₃)_x (R′PO₃)_2−x (R′ = −CH₆H₅; −CH₂OH; −CH₂COOH; −CH₂CH₂COOH)

were prepared and characterized with regard to their compositions, X-ray powder patterns and densities. It was found that the system is discontinuous, not all x values from 0 to 2 being possible. No single crystals for X-ray structure determination were obtained; however, some chemical evidence shows that the mixed compounds possess a layered structure similar to that of α-zirconium phosphate. Some considerations on the reciprocal disposition of the R and R′ pendent groups in the layered structure are reported. Many other derivatives are expected to be obtained easily by using other mixtures of phosphonic acids than those employed in this work. Owing to the large variety of possible combinations of R and R′ groups, the mixed compounds should exhibit a large spectrum of properties and show promise for application in the field of ion exchange, adsorption, intercalation and heterogeneous catalysis.     

Theoretical assessment of the nonlinear optical properties of substituted oligoacenes

The β and γ nonlinear optical coefficients of substituted oligoacenes (1–10 rings) with the donors (D) groups –CH₃, –CH₂CH₃, –CH₂CH₂CH₃, –CH₂CH₂CH₂CH₃, –C(CH₃)₃, –CH₃CHN(CH₃)₂, –N(CH₃)₂, –OCH₃, –OCH₂CH₃, –OCH₂CH₂CH₃, –OCH₂CH₂CH₂CH₃, –OC(CH₃)₃, and –OCHCH₃N(CH₃)₂ and the acceptor (R) group –CHC(CN)₂ is calculated by the AM1/TDHF method. A partial least squares regression analysis of electronic and structural parameters is performed to investigate their correlation with β and γ hyperpolarizabilities. It is found that the dipole moment, the HOMO–LUMO energy gap, the ionization potential, the number of π-electrons, and the number of rings in the bridge are parameters that significantly affect β and γ magnitudes. The dipole moment and the number of π-electrons are positively correlated with β values, while the HOMO–LUMO energy gap and the ionization potential are negatively correlated. Calculations indicate that the hyperpolarizabilities increase with the number of rings in the bridge and that the dimethylamine/dicyanoethenyl pair leads to the highest hyperpolarizabilities values. Optimization of β and γ is obtained through several substitution patterns of the oligoacenes. The present methodology shows that more extended systems containing two D/R pairs have high values of β and γ coefficients, which indicates that these systems can be employed in manufacturing nonlinear optics devices.     

Chemical vapor deposition of pyrolytic carbon on SiC fibers

We carried out thermodynamic analysis of reactions underlying the preparation of pyrolytic carbon from a number of carbon-containing compounds and experimentally determined the optimal temperature range for the deposition of thin (1–3 μm) pyrolytic carbon layers onto continuous silicon carbide fibers. The results indicate that, among the compounds studied, the highest deposition rate of pyrolytic carbon is ensured by the pyrolysis of toluene and n-heptane. The slowest deposition rate is observed in methane pyrolysis. Rate data are used to determine the apparent activation energies for the pyrolysis of C₇H₈, C₇H₁₆, (CH₃)₂CO, CCl₄, and CH₄. Original Russian Text ? P.M. Silenko, A.N. Shlapak, V.P. Afanas’ev, 2006, published in Neorganicheskie Materialy, 2006, Vol. 42, No. 3, pp. 288–291.     

Dry etching of TaN thin film using CH4/Ar inductively coupled plasma

In this research, we investigated the TaN etch rate and selectivity with under layer (HfO₂) and mask material (SiO₂) in inductively coupled CH₄/Ar plasma. As the CH₄ content increased from 0% to 80% in CH₄/Ar plasma, the TaN etch rate was increased from 11.9 to 22.8 nm/min. From optical emission spectroscopy (OES), the intensities for CH [431 nm] and H [434 nm] were increased with the increasing CH₄ content from 0% to 100% in CH₄/Ar plasma. The results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed no accumulation of etch by-products from the etched surface of TaN thin film. As a result of OES, AES and XPS analysis, we observed the etch by-products from the surfaces, such as Ta–N–CH and N–CH bonds. Based on the experimental results, the TaN etch was dominated by the chemical etching with the assistance of Ar sputtering in reactive ion etching mechanism.     

Fabrication of Nb-doped bismuth titanate thin films using nonionic block copolymer: Enhanced ferroelectric properties

Crack-free Nb-doped Bi₄Ti₃O₁₂ (Nb-BIT-p) ferroelectric thin films were fabricated utilizing nonionic block copolymer, HO(CH₂CH₂O)₂₀(CH(CH₃)CH₂O)₇₀(CH₂CH₂O)₂₀H (EO₂₀PO₇₀EO₂₀), on Pt/Ti/SiO₂/Si substrates by a processing route of metalorganic solution deposition. The Nb-BIT-p films after calcination showed only a Bi₄Ti₃O₁₂-type crystalline phase with a random orientation and small grains (< 0.4 μm). The remanent polarization (2P_r) and the coercive field (E_c) values of Nb-BIT-p capacitors were unusually high, such as 42 ± 3 μC/cm² and 72 ± 5 kV/cm, respectively, at a maximum applied field of 160 kV/cm. After 1.5 × 10¹⁰ read/write cycles with ± 8 V amplitude (160 kV/cm) at 1 MHz frequency, the 2P_r value was partially reduced, but recoverable close to the original one by repeated switching at a high field.