The erosion behaviors of Y2O3 and YF3 coatings under fluorocarbon plasma

We deposited Y₂O₃ and YF₃ coatings using the electron beam evaporation method and investigated their erosion behavior under fluorocarbon plasma at various bias voltages. TEM analysis revealed that the Y₂O₃ coating was strongly fluorinated under the plasma, and the thickness of the fluorinated layer was increased up to a few hundred nm with bias voltage. XPS analysis also confirmed a significant Y-F bonding on the surface and showed fluorine content at a maximum on the surface, decreasing with the depth from the surface. The etch rate increased with bias voltage and it was slightly higher in YF₃ coating, implying that the etch rate depends on the surface fluorination and its removal by incident ions. Without applying bias voltage, the chemical reaction with the fluorocarbon plasma dominated, resulting in the formation of fine fluoride particles on the Y₂O₃ surface, but the YF₃ coating was intact and clean for the same condition. These results indicate that the YF₃ coating may be a new plasma-facing material that produces fewer contamination particles.     

Fluorinated epoxy resin as a low adhesive mould for composite material

The aim of this work is to decrease the adhesion between a cured modified epoxy-based substrate and an in situ cured virgin epoxy-based piece. The effect of perfluorinated additives on the non-adhesion output is investigated through an adapted pull-off test. It appears that additive migration initiates the surface fluorination. Longer the fluorinated chain is, higher the surface fluorination is and weaker the adhesion strength is. The weak chemical affinity between these two epoxy resins is shown to be mainly responsible for these results leading to an adhesive rupture.     

Fluorination of CN x Nanotubes

Abstract

Multiwall CN _x nanotubes have been prepared by thermal decomposition of acetonitrile over Co/Ni catalytic particles. The fluorination of nanotubes was performed at room temperature by using a gaseous mixture of BrF₃ and Br₂. Transmission electron microscopy (TEM) and x‐ray diffraction (XRD) indicated that only the outer shells of CN _x nanotubes were fluorinated, whereas the inner shells remained intact. X‐ray photoelectron spectroscopy (XPS) showed an oxidation of pyridinic‐type nitrogen with tube fluorination.     

One‐Step Formation of a Single Atomic‐Layer Transistor by the Selective Fluorination of a Graphene Film

In this study, the scalable and one‐step fabrication of single atomic‐layer transistors is demonstrated by the selective fluorination of graphene using a low‐damage CF₄ plasma treatment, where the generated F‐radicals preferentially fluorinated the graphene at low temperature (<200 °C) while defect formation was suppressed by screening out the effect of ion damage. The chemical structure of the C–F bonds is well correlated with their optical and electrical properties in fluorinated graphene, as determined by X‐ray photoelectron spectroscopy, Raman spectroscopy, and optical and electrical characterizations. The electrical conductivity of the resultant fluorinated graphene (F‐graphene) was demonstrated to be in the range between 1.6 kΩ/sq and 1 MΩ/sq by adjusting the stoichiometric ratio of C/F in the range between 27.4 and 5.6, respectively. Moreover, a unique heterojunction structure of semi‐metal/semiconductor/insulator can be directly formed in a single layer of graphene using a one‐step fluorination process by introducing a Au thin‐film as a buffer layer. With this heterojunction structure, it would be possible to fabricate transistors in a single graphene film via a one‐step fluorination process, in which pristine graphene, partial F‐graphene, and highly F‐graphene serve as the source/drain contacts, the channel, and the channel isolation in a transistor, respectively. The demonstrated graphene transistor exhibits an on‐off ratio above 10, which is 3‐fold higher than that of devices made from pristine graphene. This efficient transistor fabrication method produces electrical heterojunctions of graphene over a large area and with selective patterning, providing the potential for the integration of electronics down to the single atomic‐layer scale.     

Enhanced thermal conductivity of epoxy nanocomposites filled with hybrid filler system of triethylenetetramine-functionalized multi-walled carbon nanotube/silane-modified nano-sized silicon carbide

Multi-walled carbon nanotubes (MWCNTs) were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then triethylenetetramine (TETA) grafting was carried out. Nano-sized silicon carbide particles (SiC_np) were modified by the silane coupling agent. Epoxy nanocomposites filled with hybrid filler system containing TETA-functionalized MWCNTs and silane-modified SiC_np were prepared. The investigation on the thermal conductivity of epoxy nanocomposites filled with single filler system and hybrid filler system was performed. Chemical surface treatment is conducive to the enhancement of thermal conductivity of epoxy composites. The thermal conductivity of epoxy composites with hybrid filler system is higher than that of epoxy composites with any single filler system (functionalized MWCNTs or modified SiC_np), which is due to the effective combination of MWCNT-to-MWCNT and SiC_np-to-SiC_np conductive networks. Hybrid filler system could provide synergistic effect and cost reduction simultaneously.     

Sandwiched epoxy–alumina composites with synergistically enhanced thermal conductivity and breakdown strength

Development of polymer-based composites with simultaneously high thermal conductivity and breakdown strength has attracted considerable attentions owing to their important applications in both electronic and electric industries. In this study, we successfully design novel epoxy-based composites with nano-Al₂O₃/epoxy composite layer sandwiched between micro-Al₂O₃/epoxy composite layers, which show synergistically and significantly enhanced thermal conductivity and breakdown strength. Compared with the traditional composites, the bottleneck that both thermal conductivity and breakdown strength cannot be simultaneously enhanced can be overcome successfully. An optimized sandwiched alumina–epoxy composite with 70 wt% micro-Al₂O₃ fillers in the outer layers and 3 wt% nano-Al₂O₃ in the middle layer simultaneously displays a high thermal conductivity of 0.447 W m^?1 K^?1 (2.4 times of that of epoxy) and a high breakdown strength of 68.50 kV mm^?1, which is 6.3 % higher than that of neat epoxy (64.45 kV mm^?1). The experimental results on the thermal conductivity of multi-layered alumina–epoxy composites were in well accordance with the theoretical values predicted from the series conduction model. This novel technique simultaneously improves thermal conductivity and breakdown strength, which is of critical importance for design of perspective composites for electronic and electric equipments.     

Surface passivation of CeO2 catalyst and its ultraviolet screening effect

A new strategy was attempted to fabricate CeO2 nanoparticles using the surface fluorination technique to control the particle size and suppress the catalytic activity. The fluorinated CeO2 nanoparticles are fully characterized with XRD, XANES, UV-vis spectroscopy, HR-TEM, XPS along with the evaluation of photo and thermal catalytic activities. XRD patterns were not affected by surface fluorination. That is to say, the crystalline structure of CeO2 was not deteriorated upon fluorination. The TEM analysis showed that the fluorinated CeO2 nanoparticles with the primary particle size of 7 nm could be prepared. According to the X-ray absorption near edge structure (XANES) analysis, overall XANES spectrum was not changed upon fluorination, suggesting that the local structure of fluorinated CeO2 resembled that of the starting CeO2 nanoparticles. It was also revealed that both photo and thermal catalytic activities could be almost totally suppressed at the fluorination level of ca. 6.0 wt%. It is suggested that the selective surface fluorination with fluoride could lead to fluorinated CeO2 nanoparticles, which could be applied to new fields such as the cosmetics industries.     

A Study on Microsized Titanium Oxide-Filled Epoxy with Enhanced Heat Conductivity for Microelectronic Applications

This article presents a study on the thermal conductivity characterization of microsized TiO₂-filled epoxy composites. Titanium oxide (TiO₂) particles of about 100 µm mean size are embedded in epoxy resin to develop composites by hand layup technique. Effective thermal conductivity values of these samples are measured using Unitherm Model 2022 in accordance with ASTM-E 1530 standards. The measured values are then compared with those obtained from a mathematical correlation deduced basing upon a one-dimensional heat conduction model developed by the authors previously. This study reveals that there is a significant improvement in thermal conductivity of the composites with increase in TiO₂ content. With addition of 25 vol% of TiO_2, the thermal conductivity of epoxy composite improves by about 223%. On comparing the measured conductivity values with those obtained from the theoretical model, it has been observed that the measured values are in very good agreement with the theoretical values for low filler concentrations (0–17.5 vol%). It is further seen that TiO₂ particles show percolation behavior in epoxy matrix at about 17.5 vol% of filler content at which a sudden jump in the conductivity value is noticed.     

Effects of the surface treatment on the properties of polyaniline coated carbon nanotubes/epoxy composites

The effects of a surface treatment of carbon nanotubes (CNTs) on the electrical conductivity and the hydrophilicity of a polyaniline (PAni) coated CNTs (PAni-CNTs)/epoxy (EP) composites were examined. The surface of the CNTs was treated with various chemicals, such as acid mixtures (HNO₃:H₂SO₄), potassium persulfate (KPS) and sodium dodecyl sulfate (SDS), to improve their dispersion and reactivity with PAni. The electrical conductivity and hydrophilicity of PAni-CNTs and their EP composites were strongly affected by the surface treatment of the CNTs. The surface-treating materials remained on the surface of the CNTs affected the reactivity of the CNTs surface to PAni, and thus resulted in different PAni amounts in the PAni-CNTs. The electrical conductivity of the PAni-CNTs/EP composites decreased, but the hydrophilicity increased, with increasing the amount of PAni coating on the CNTs surface.     

Influence of the pitch fluoride on the electrical conductivity of the activated carbon cloth as electrodes of the supercapacitor

Fluorinated activated carbon cloth was prepared by impregnating a commercial activated carbon cloth in a pitch fluoride solution followed by carbonization. The surface properties of samples before and after treatment were characterized by X-ray Photoelectron Spectroscopy. Electrochemical Impedance Spectroscopy, Constant Current Charge-Discharge were employed to investigate the electrochemical properties of the samples. After the fluorination, the element fluorine was introduced to the surface of the activated carbon cloth. The electrical conductivity was improved from 2.51 to 33.21 Scm^− 1. As the electrodes of a supercapacitor, the equivalent series resistance of as-prepared sample was substantially decreased compared with the pristine material. The improvement of conductivity is ascribed to the creation of ionic fluorine-carbon bonds after fluorination, indicating the high power characteristics of this material.     

Superconductivity and microstructures of fluorinated and chlorinated YBa2Cu3Oz

Superconductivity and microstructures of fluorinated and chlorinated YBa₂Cu₃O _z were investigated with BaF₂ and BaCl₂ as the fluorination and chlorination agents. The incomplete decomposition of BaF₂ and BaCl₂ led to inhomogeneous phase and elemental distributions as shown by energy dispersive analysis of X-rays (EDAX) and X-ray diffraction (XRD) analysis. A high (y 2) chlorine concentration stabilized a tetragonal perovskite structure in the YBa₂Cu₃Cl _y O _z compositions while an orthorhombic structure was observed in samples with a lower chlorine concentration. The maximum superconductivity transition temperature,T _c, was 95 K in these fluorinated and chlorinated samples. Thus, our data are contradictory to the claims of high transition temperatures (155 K) recently reported for some of these compositions. The microstructural and phase composition data reported here could provide useful information in the search for possibly highT _c phases in these fluorinated and chlorinated compositions.     

Synergistic effects of hollow structure and surface fluorination on the photocatalytic activity of titania

To study the synergistic effects of hollow structure and surface fluorination on the photoactivity of TiO₂, TiO₂ hollow microspheres were synthesized by a hydrolysis–precipitate method using sulfonated polystyrene (PS) as templates and tetrabutylorthotitanate (TBOT) as precursor, and then calcined at 500 °C for 2 h. The calcined samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N₂ sorption. Photocatalytic activity was evaluated using reactive brilliant red X3B, an anionic organic dye, as a model pollutant in water. The results show that the photocatalytic activity of TiO₂ hollow microspheres is significantly higher than that of TiO₂ nanoparticles prepared in the same experimental conditions. At pH 7 and 3, the apparent rate constants of the former exceed that of the latter by a factor of 3.38 and 3.15, respectively. After surface fluorination at pH 3, the photoactivity of hollow microspheres and nanoparticles further increases for another 1.61 and 2.19 times, respectively. The synergistic effect of surface fluorination and hollow structure can also be used to prepare other highly efficient photocatalyst.     

Mass Spectrometry Study of C60 and C60-NiF2 Fluorination with Molecular Fluorine

Abstract

Fluorination of [60]fullerene and [60]fullerene-NiF₂(s) has been studied in situ by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination processes were controlled in the temperature range 500 ? 800 K at molecular fluorine pressure 10^?4 ? 10^?5 atm. Temperature, time of fluorination and fluorine pressure were varied during the investigation. It was found that variation of these parameters did not lead to the selective fluorination. It was shown that NiF₂(s) significantly influences the composition of the product mixture: a large amount of nickel difluoride in the system suppresses the fluorination reaction while the presence of a small amount promotes the selective fluorination. C₆₀Fi₁₈ (50% in the gas phase) was produced in our experiments under the following conditions: 20 h, 720 K, P(F₂) = 2 10^?4 atm in the prefluorinated (inner surface covered with NiF₂(s) layer) Ni-reactor. An important point of the study was verification of the thermodynamic equilibrium in the system. It was concluded that the equilibrium is not established in the system under study, and the fluorination is governed by kinetic factors.     

N2 plasma-assisted grafting of fluorinated chains onto partially cured epoxy resins

Two routes for the grafting of fluorinated molecules to an epoxy resin were studied. The first one deals with the grafting of the liquid-state resin whereas the second one is focused on the grafting onto the solid-state resin. These grafting reactions were shown to be similar as studied through FTIR and XPS spectroscopies. However, it appears that the grafting onto the solid-state resin is limited by the curing advancement. N₂ plasma-activation was used to solve this drawback and enhanced the grafting yield. This grafting improvement was mainly explained in terms of the surface wetting improvement and the attachment of nitrogen containing groups at the surface of the treated resin.     

The desirable dielectric properties and high thermal conductivity of epoxy composites with the cobweb-structured SiCnw–SiO2–NH2 hybrids

We report the preparation of epoxy-based composites by intercalating low loading of core–shell silicon carbide nanowire-silica-amino (named as SiCnw–SiO₂–NH₂) hybrids, exhibiting simultaneously high permittivity and thermal conductivity (TC) and maintaining rather low dielectric loss. More interestingly, the epoxy composites with the cobweb-structured SiCnw–SiO₂–NH₂ hybrids exhibited high thermal conductivity at low filler loading due to space micro-structures and hydrogen bond interaction. Specifically, permittivity of the sample with 3.0 vol% SiCnw–SiO₂–NH₂ hybrids reaches 61.9 under 0.1 Hz, while its dielectric loss is only 0.012, and possessing a high TC of 1.59 W/m K, respectively.

     

Development of nanocomposite with epoxidized natural rubber and functionalized multiwalled carbon nanotubes for enhanced thermal conductivity and gas barrier property

Multiwalled pristine carbon nanotubes (mwCNTs) were treated with conventional mixed acid to functionalize outer surface of nanotubes with two unique chemical approaches using aminosilane solution and TiO₂ dispersion. Pristine and functionalized mwCNTs were dispersed subsequently in matrices of natural rubber (NR)–chlorobutyl rubber (CIIR) and epoxidized natural rubber (ENR)–CIIR to prepare nanocomposites by simple and eco-friendly melt blending method. The effect of surface treatment of mwCNTs, and epoxidation of NR on the composite properties was evaluated for thermal conductivity and gas barrier property. Nanocomposites prepared with surface functionalized mwCNTs and epoxidized NR were found to exhibit greater thermal conductivity and excellent gas barrier properties compared to pristine mwCNT reinforced CIIR–NR nanocomposites. A maximum thermal conductivity was observed for nanocomposite obtained from 20% ENR and 3% (by weight) mwCNTs functionalized with aminosilane. While a maximum gas barrier property was exhibited by nanocomposite with 20% ENR and 3% (by weight) mwCNTs treated with TiO₂. Results indicate that the presence of epoxy moieties of ENR provided a stronger network formation between aminosilane treated mwCNT surface and rubber matrices to exhibit higher thermal conductivity and metal oxide particles adhered to TiO₂ treated mwCNTs found to impart maximum resistance in transfer of oxygen gaseous molecules nanocomposite.     

Fluorinated Low‐Dimensional Ruddlesden–Popper Perovskite Solar Cells with over 17% Power Conversion Efficiency and Improved Stability

Low‐dimensional Ruddlesden–Popper perovskites (RPPs) exhibit excellent stability in comparison with 3D perovskites; however, the relatively low power conversion efficiency (PCE) limits their future application. In this work, a new fluorine‐substituted phenylethlammonium (PEA) cation is developed as a spacer to fabricate quasi‐2D (4FPEA)₂(MA)₄Pb₅I₁₆ (n = 5) perovskite solar cells. The champion device exhibits a remarkable PCE of 17.3% with a J_sc of 19.00 mA cm^?2, a V_oc of 1.16 V, and a fill factor (FF) of 79%, which are among the best results for low‐dimensional RPP solar cells (n ≤ 5). The enhanced device performance can be attributed as follows: first, the strong dipole field induced by the 4‐fluoro‐phenethylammonium (4FPEA) organic spacer facilitates charge dissociation. Second, fluorinated RPP crystals preferentially grow along the vertical direction, and form a phase distribution with the increasing n number from bottom to the top surface, resulting in efficient charge transport. Third, 4FPEA‐based RPP films exhibit higher film crystallinity, enlarged grain size, and reduced trap‐state density. Lastly, the unsealed fluorinated RPP devices demonstrate superior humidity and thermal stability. Therefore, the fluorination of the long‐chain organic cations provides a feasible approach for simultaneously improving the efficiency and stability of low‐dimensional RPP solar cells.     

An XPS study of the fluorination of carbon anodes in molten NaF–AlF<Subscript>3</Subscript>–CaF<Subscript>2</Subscript>

In the Hall–Héroult process for aluminum production electrolysis takes place in molten cryolite (NaF–AlF₃–CaF₂) with carbon electrodes. Dewetting of the anode leads to operational instability. A surface energy change due to surface fluorocarbon formation during electrolysis is suggested as a contributing factor to diminishing the wettability of the anode. In this work the surface composition of graphite anodes after electrolysis in molten NaF–AlF₃–CaF₂ is investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) for evidence of fluorination. Fluorocarbon is identified on an electropolished region of an anode surface resulting from anode effect. The discovery of surface fluorination provides an insight into high temperature electrochemical reactions of carbon with molten fluoride salts and informs aluminum smelter cell operation.     

Reduction products of graphite intercalation compounds with nickel and iron halides

The H₂ reduction of graphite intercalation compounds (GICs) with nickel and iron chlorides before and after fluorination with BrF₃ solutions in HF has been studied by X-ray diffraction, thermal analysis, and Raman scattering spectroscopy. The results indicate that, up to 700°C, the thermolysis of the GICs with nickel and iron chlorides does not reach completion. Thermolysis of the fluorinated GICs in a hydrogen atmosphere at 600°C can be used to fabricate metal-graphite composites. This behavior is interpreted in terms of the thermal properties of the GICs.     

The effect of nanoparticles on the adhesion of epoxy adhesive

In this investigation, the influence of different nanoparticles and surface roughness on the adhesion between epoxy adhesive and steel substrate was primarily investigated. The results of pull-off adhesion tests indicated that nano-Al₂O₃ of the three kinds of nanoparticles had the most influence on adhesion strength, which was the optimal additive for the epoxy adhesive to improve the adhesion strength. Also, it was found that modified by 2% nano-Al₂O₃, the strength multiplication on the surface abraded with silicon carbide paper of 150 grits (150#) was the highest, of three different surface roughness. So, as the results showed that modified by 2% nano-Al₂O₃, the adhesion strength of epoxy adhesive on the surface abraded with 150# was visibly improved by about 5 times. Transmission electron microscope (TEM) displayed nano-Al₂O₃ homogeneously dispersed in epoxy adhesive. Field emission scanning electronic microscope (FE-SEM) revealed that the surface morphology of steel well coincided with that of epoxy adhesive.