Fluorinated Layer Research Articles

Electrowetting movement of an aqueous droplet between two three-dimensional electrode surfaces

In an effort to develop a novel electronic paper image display technology based on the electrowetting principle, a 3-D electrowetting cell is designed and fabricated, which consists of two 3-D bent electrodes, each having a horizontal surface made of gold and a vertical surface made of indium tin oxide (ITO) glass as a color display window, a layer of dielectric material on the 3-D electrodes, and a highly fluorinated hydrophobic layer on the surface of the dielectric layer. Results of this work show that an electrowetting-induced motion of an aqueous droplet in immiscible oils can be achieved reversibly across the boundary of the horizontal and vertical surfaces of the 3-D electrode surface. It is also shown that the droplet can maintain its wetting state on a vertical sidewall electrode free of a power supplier when the voltage is removed. This phenomenon may form the basis for color contrast modulation applications, where a power-free image display is required, such as electronic paper display technology in the future.

X-ray photoelectron spectroscopic study of Ge2Sb2Te5 etched by fluorocarbon inductively coupled plasmas

X-ray photoelectron spectroscopy was used to determine the level of surface fluorination damage of Ge2Sb2Te5 (GST) etched by fluorocarbon gases at different F/C ratios. When blank GST was etched, the gas with a higher F/C ratio produced a thinner C–F polymer on the etched surface but fluorinated Ge, Sb, and Te compounds were observed in the remaining GST. When the sidewall of the etched GST features was investigated, a thicker fluorinated layer was observed on the GST sidewall etched by the higher F/C ratio gas, indicating more fluorination due to the difficulty in preventing F diffusion into the GST through the thinner C–F layer.

Large area dye-sensitized solar cells: material aspects of fabrication

Dye-sensitized photoelectrochemical solar cells of large area are fabricated using highly conducting and optically transparent glass consisting of an inner layer of indium-tin oxide and an outer layer of fluorine doped tin oxide. A method is described for the deposition of nanocrystalline films of TiO2 consisting of large and small median size particles (30 and 5 nm, respectively) which promote porosity and light scattering. Incorporation of trace quantities of magnesium oxide into TiO2 increased the efficiency of the cells. The energy conversion efficiency of a cell (AM 1·5, 1000 W m−2 simulated sunlight) of area 21 cm2 was found to be 7·2% compared to 5·6% in the absence of magnesium oxide. The mechanisms by which the magnesium oxide improves the cell performance are discussed. Copyright © 2006 John Wiley & Sons, Ltd.

Enhancement of the chemical resistance of nitrile rubber by direct fluorination

AbstractNitrile rubber (NBR), poly(acrylonitrile‐co‐butadiene) or NBR packers, are used to seal oil‐well tubing, where they often come into contact with ZnBr2 brines at high temperatures and pressures. Under these conditions, NBR exhibits accelerated chemical degradation, which results in embrittlement and cracking. Although alternative fluoropolymers exhibit excellent chemical resistance, their strength is less than NBR, and replacement of the usual gasket materials with fluoroelastomers is expensive. We have demonstrated that a fluoropolymer surface on a nitrile elastomer provides the necessary chemical resistance while the elastomer retains strength. This can be achieved by direct fluorination, a rather easy and inexpensive process. Samples of NBR O‐rings were fluorinated by exposure to F2 and F2/HF mixtures at various temperatures. Although fluorination by F2 produced the desired fluoropolymer layer, fluorination by F2/HF (hydrofluoric acid) mixtures gave a smoother fluorinated layer at lower temperatures and shorter reaction times. Elemental analysis showed that the fluorinated layer eliminated ZnBr2 diffusion into the NBR polymeric matrix. Surface fluorination also significantly retarded the loss of the mechanical properties of NBR when it was exposed to zinc bromide fluid. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 971–979, 2003

Theoretical study of the adsorption of a CaF 2 molecule at the ( [formula omitted]) surface of CaF 2 II. Surface diffusion

This paper is concerned with a theoretical study of the diffusion pathways of a CaF 2 molecule on the terrace of the (1 1 1) surface of a CaF 2 crystal. Altogether, the surface diffusion can be described by a staggering movement, where the molecule swings in every jump around one of its fluorine ions being fixed to a calcium ion of the outermost surface triple layer of the crystal. The diffusion can include exchanges of fluorine ions between the admolecule and the outermost fluorine layer at the surface. The jump distance results as a 0/ 2 =3.86 Å and the activation energy for diffusion as 0.80±0.10 eV. Assuming a vibration frequency in the order of 10 13 s −1 the surface diffusion coefficient becomes D s=3.73×10 −3exp(−9.280×10 3/ T) cm 2 s −1. With the desorption time from the terrace τ des=10 −13exp(1.972×10 4/ T) s with a mean adsorption energy of −1.70±0.03 eV the mean diffusion displacement on the terrace becomes x s =2 D s τ des =3.86×10 −8 exp(5.220×10 3/T) cm with a saddle point energy of E s=0.90±0.13 eV.

SIMS depth profiling of working environment nanoparticles

Morphology of working environment nanoparticles was analyzed using sample rotation technique in secondary ion mass spectrometry (SIMS). The particles were collected with nine-stage vacuum impactor during gas tungsten arc welding (GTAW) process of stainless steel and shielded metal arc welding (SMAW) of mild steel. Ion erosion of 300–400 nm diameter nanoparticles attached to indium substrate was performed with 2 keV, 100 μm diameter, Ar + ion beam at 45° ion incidence and 1 rpm sample rotation. The results show that both types of particles have core-shell morphology. A layer of fluorine, chlorine and carbon containing compounds covers stainless steel welding fume particles. The cores of these particles are enriched in iron, manganese and chromium. Outer shell of mild steel welding fume particles is enriched in carbon, potassium, chlorine and fluorine, while the deeper layers of these nanoparticles are richer in main steel components.

Effects of F-treatment on degradation of Mg 2Ni electrode fabricated by mechanical alloying

The effects of surface fluorination on the electrochemical charge–discharge properties of a Mg 2Ni electrode, prepared by mechanical alloying in Ni-MH batteries are investigated. After 20 h milling, Mg and Ni powder form nanocrystalline Mg 2Ni. The discharge capacity of this alloy increases greatly on the initial cycle but, due to the formation of a Mg(OH) 2 passive layer, displays rapid degradation in alkaline solution within 10 cycles. In a 6 M KOH+ x M KF electrolyte ( x=0.5, 1, and 2), a continuous and stable fluorinated layer is formed and the durability of the Mg 2Ni electrode increases marketly and a high rate discharge capability is obtained (90–100 mAh/g). Addition of 2 M KF leads to the highest durability of all the electrodes tested. The improvement is due to a thin MgF 2—flourinated layer, which reduces the charge-transfer resistance and protects the Mg 2Ni electrode from forming a Mg(OH) 2 layer.

Atomic force microscopy study of the CaF 2(111) surface: from cleavage via island to evaporation topographies

The development of (111) cleavage faces of CaF 2 upon thermal treatment is studied by atomic force microscopy (AFM). Vacuum-cleaved surfaces show the atomic periodicity of the uppermost fluorine layer. Cleavage steps have heights of about 0.32 nm, corresponding to the spacing of neighboring F −–Ca 2+–F − triple layers, or integer multiples thereof. The steps exhibit ‘lightning’-shaped arrangements with tips pointing in the direction of cleavage. Steps run essentially parallel to the 〈110〉, 〈211〉, and 〈321〉 directions. At about 820 K the original cleavage topography transforms into a topography with trigonal and hexagonal islands. The islands develop from the cleavage tips by a melt-off process mediated by step and/or surface diffusion. During further heat treatment at even higher temperatures the surface flattens and the formation of triangular islands with one type of 〈110〉 step is observed. The atomic configuration for this type of step is discussed. Strongly vaporized surfaces studied by an electron microscopic shadowing technique exhibit hexagonal evaporation pits. The exposure to stray electrons from the heater filament at a temperature of 820 K results in a strong surface erosion with deep triangular etch pits with edges parallel to 〈110〉. The formation of these etch pits is probably caused by a combined action of electron-stimulated desorption of fluorine, vaporization of metallic calcium clusters and a partial healing of the surface via step and/or surface diffusion.

Silicon etching in NF3/O2 remote microwave plasmas

The etching of silicon in remote microwave discharges fed with NF3/O2 has been investigated. In situ ellipsometry and x-ray photoelectron spectroscopy (XPS) were used to monitor surface effects, while mass spectrometry was used to monitor the gas phase dynamics. Varying the microwave power from 600 to 1400 W has little effect, due to the near complete dissociation of the NF3, even at lower powers. For discharges containing pure NF3, the poly-Si etch rate increases linearly with NF3 flow. When a low proportion of O2 (O2/NF3=0.1) is added to the discharge, the etch rate increases quickly to its maximum of ∼700 nm/min. With further O2 addition, this etch rate decreases below that observed for pure NF3 processing. The fluorine concentration in the processing region decreases for all O2 additions by a dilution effect. For pure NF3 discharges, XPS measurements reveal 1–2 nm thick, highly fluorinated reaction layers with a gradual loss of fluorine content as the NF3 flow is increased. Specimens processed with both NF3 and O2 show much less surface fluorination that decreases with increasing O2 content in the feed gas. At the etch rate maximum, the observed N (1s) signal is also maximized. The reaction layer thickness increases with added O2 and continues to more than 10 nm at O2:NF3 ratios greater than unity. We discuss the enhanced reactivity of the modified Si surface and compare our results with the role of admixed N2 into the CF4/O2 system. We also injected NO directly into the effluent of NF3 and CF4/O2 discharges. For fluorine rich discharges, NO removes the modified surface layer on Si and provides for an enhanced etch rate. In the oxygen rich regime, NO injection can increase both the etch rate and the reaction layer thickness. We will present a mechanism for the enhanced etching of Si in the presence of fluorine, oxygen and the NO molecule.

Reversible Electrowetting and Trapping of Charge: Model and Experiments

We derive a model for voltage-induced wetting, so-called electrowetting, from the principle of virtual displacement. Our model includes the possibility that charge is trapped in or on the wetted surface. Experimentally, we show reversible electrowetting for an aqueous droplet on an insulating layer of 10 μm thickness. The insulator is coated with a highly fluorinated layer impregnated with oil, providing a contact-angle hysteresis lower than 2°. Analyzing the data with our model, we find that until a threshold voltage of 240 V, the induced charge remains in the liquid and is not trapped. For potentials beyond the threshold, the wetting force and the contact angle saturate, in line with the occurrence of trapping of charge in or on the insulating layer. The data are independent of the polarity of the applied electric field and of the ion type and molarity. We suggest possible microscopic origins for charge trapping.

Polymer replication of 3D microstructures employing a high content fluorine separation layer

The combination of prototyping with a subsequent replication process has long been the choice for time efficient and economic production schemes. We adopted this method and developed a new technology for the fabrication of three dimensional microstructures based on excimer laser ablation of acrylic polymers and direct inverse replication. Our replicas are made of an acrylic monomer blend cured with UV-photons and electrons. In order to protect the master copy and to secure a safe and non-destructive separation of master copy and replica, the master copy was homogeneously coated with a high content fluorine layer. This coating was applied employing an adjusted C 6F 14 plasma polymerization process, resulting in an even 5 nm to ≤2 μm thin anti-adhesion layer. In order to characterize the physical and chemical properties of the laser processed master copy and replicas, we employed SEM, XPS and optical profiling. The coating's surface smoothness was measured to be as low as 4 nm (rms-value) and the surface's fluorine atomic concentration could be raised up to 68.6%. We have been observing a constant chemical composition at the replica's and master copy's surface over a period of 20 replication cycles and, in addition, no increase in master copy's surface roughness. The results demonstrate that the utilized anti-adhesion layer serves as an enduring separation coating.

The structure of PF 3 adsorbed on Cu(111)

The structure of PF 3 adsorbed on Cu(111) at 110 K has been determined using both near edge X-ray absorption fine structure (NEXAFS) and normal incidence X-ray standing wave (NIXSW) methods. Two X-ray reflection conditions were used, the (111) and ( 1 ̄ 11) , to determine the atomic positions of the phosphorus and fluorine atoms by triangulation using NIXSW, whereas NEXAFS was used to determine the alignment of the molecule. PF 3 adsorbs at atop sites with the fluorine atoms away from the surface and its C 3 axis aligned along the surface normal. The Cu–P distance is 2.25±0.04 Å, and the distance between the copper and the fluorine layers along the C 3 axis is 3.05±0.04 Å. The adsorbed molecule maintains its gas-phase geometry and undergoes either free rotation about the C 3 axis, or is azimuthally orientated such that the projections of the P–F bonds on to the surface point towards the next nearest neighbour copper atoms. The NIXSW analysis for the fluorine photoemission data was carried out using a backward/forward asymmetry parameter to compensate for a breakdown in the dipole approximation for photoemission that occurs for fluorine 1s photoemission under the NIXSW conditions used here.

Correlation of EIS Data to Corrosion Damages through Organic Coatings: A Transparent Electrode Approach

A simple design based on a metal deposited on a transparent conducting substrate was described and tested as a way to investigate the correlation between the EIS data and the corrosion processes on an organic coating - metal system. The break-point frequency method (BFM) was applied. The samples consisted of a transparent thin layer of fluorine - doped SnO 2 and a thin metal layer (iron in this work) deposited successively on a glass sheet. An alkyd - silicone paint of various thicknesses was applied on top of the metal layer. The validity of the sample has been tested in a NaCl 30 g/dm 3 solution as a function of the immersion time. The contribution of each element of the transparent sample was studied systematically; a bulk sample coated with a transparent varnish film was used as reference. No artifact was evidenced. As a stable electrode material and an efficient cathode for oxygen reduction, fluorine - doped SnO 2 is a useful electrode for investigating an overlayer of metal deposit as well an organic coating. Corrosion can be simultaneously monitored by EIS measurements and video or photograph recording. From this study, it is concluded that BFM characterizes the undamaged film area, and not the corroded or active areas.

The effect of thermal stressing on perfluoropolyalkylethers at elevated temperatures

Fultz et al. have reported that the thermo‐oxidative properties of linear PFPAEs can be improved by stressing the fluid at elevated temperature (371°C) in the presence of air. A study of M‐50 steel coupons exposed to unstressed and stressed linear PFPAE fluids at 260 °C and 330 °C each reveal complex surface layers. For the coupon exposed to the unstressed fluid at 260 °C, a subsurface layer is observed between the iron oxide and iron substrate that has been characterized as being composed of FeF2. In contrast, the coupon exposed to the stressed fluid has a marked increase in the iron oxide thickness ∼2–3 times) when compared to the unstressed sample and shows no evidence of a buried fluorine‐containing layer. An increase in temperature (330 °C) in the stressed fluid O–C test was required to form a subsurface FeF2 layer. It is proposed that the elimination of the fluorine layer found on the M‐50 substrate increases the upper temperature limit found from the oxidation–corrosion studies. The increase in the oxide layer thickness implies that the FeF2 layer found in the unstressed sample acts like a diffusion barrier which inhibits the outward movement of Fe0 and the decreased rate of iron oxide growth.

The distribution of motional correlation times in superionic conductors: nuclear magnetic resonance of tysonite-like

Fluorine mobility at different structural positions in monocrystalline with the tysonite structure is analysed using NMR line-shape analysis. The method is sensitive to ionic exchange with correlation times in the range . For the temperature range between 240 K and 400 K the motion is restricted mainly to the ions in the fluorine layers perpendicular to the main symmetry axis (the sublattice), while ions in the La plane remain immobile. No significant anisotropy of the -ionic diffusion within the layers and along the c-axis is found ( at 400 K). From NMR spectra it is clear that mobility is strongly heterogeneous. The motional disorder can be described well by a broad distribution of correlation times, , which has a shape close to a log - Gaussian function and reflects the potential energy landscape in the superionic state. The variation of the centre position and width of with temperature differs from an Arrhenius law behaviour. Ionic mobility on the microscopical scale, therefore, cannot be considered a process which is activated only thermally. Applying MD techniques shows that the presence of vacancies may lead to pronounced changes of the potential energies, and supports the idea that there is a distribution of activation energies.

A new stage-2 graphite intercalation compound: C 2F with nestled fluorine atoms

A new stage-2 graphite intercalation compound, C 2F, with nestled fluorine atoms, has been synthesized by flowing fluorine gas in anhydrous liquid HF at −76°C. This compound can be prepared only from such a well-defined host as highly oriented pyrolytic graphite (HOPG), and has a large I c value of 11.14 Å with intercalated thickness, d i = 4.44 A ̊ . XPS and IR spectroscopy have revealed the ionic character of C-F bonding, and the electrical conductivity was found to be much higher than that of pristine graphite. Based on these experimental results, a structural model in which two nestled fluorine layers are superposed between two carbon sheets has been proposed. The nestling effect well explains the high air stability of this compound.

Ion-induced fluorination in electron cyclotron resonance etching of silicon studied by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been used to investigate the effect of varying substrate bias when silicon is etched in a CF4 electron cyclotron resonance plasma. After etching, the silicon surface is found to be covered by a two layer structure consisting of damaged, fluorinated silicon and a fluorocarbon overlayer. The thickness of the fluorinated silicon layer depends on the self-bias voltage. Reduction of the ion energy leads to a thinner fluorinated layer as well as a lower etch rate, suggesting that damage and fluorination of the crystal lattice are important in the ion enhanced etching of silicon in fluorine containing plasmas.

Effects of Contact-Hole-Etching Damage on Aluminum Chemical Vapor Deposition

The effects of contact-hole-etching damage on aluminum (Al) chemical vapor deposition (CVD) have been investigated. When Si wafers were etched by reactive ion etching (RIE) under the conditions of contact hole etching, two kinds of damage were observed on the etched surface; i.e., an amorphized layer at a depth of 30 Å and a contaminated (carbon, oxygen, and fluorine) layer at a depth of 100 Å. Aluminum deposited on the as-etched wafer had granular structure and the grains were not connected with each other, which indicates that the growth of Al is suppressed by the damages. The effect of these damages was be removed by annealing at 1050°C or etching at a depth of 30 Å (slight etching). In both cases, the amorphized layer was disappeared by recrystallization or was removed by etching, but the contaminated layer still remained. Therefore, it is concluded that the nucleation of Al is suppressed by the amorphized layer, but not by the contaminated layer. When this slight etching is made after contact hole etching, perfect contact hole filling with Al can be achieved by selective CVD.

Chemistry of titanium dry etching in fluorinated and chlorinated gases

Abstract

Role of lattice mismatch and surface chemistry in the formation of epitaxial semiconductor-insulator interfaces.

The formation of ${\mathrm{SrF}}_{2}$/Si(111) and Ge/${\mathrm{CaF}}_{2}$/Si(111) interfaces is studied with photoemission and compared to previous results for the ${\mathrm{CaF}}_{2}$/Si(111) interface. The interface between ${\mathrm{SrF}}_{2}$ and Si(111) is found to be nonstoichiometric, similar to the interface between ${\mathrm{CaF}}_{2}$ and Si(111): the bonding is between Si and the cation, with a layer of fluorine missing at the interface. In the case of Ge growth on ${\mathrm{CaF}}_{2}$/Si(111), a variety of effects are noted: The ${\mathrm{CaF}}_{2}$/Si(111) valence-band offset is reduced by about 1 eV upon deposition of Ge at room temperature. The sticking coefficient of the Ge is significantly increased by preparing the ${\mathrm{CaF}}_{2}$ surface with electron bombardment to remove the top layer of fluorine. For both the irradiated and nonirradiated cases, annealing of thin room-temperature-deposited films resulted in Ge island formation.