Fractional Surface Coverage Research Articles

Estimation of Fractional Surface Coverage of Particles for Oxide CMP

The surface coverage of particles between pad and wafer has been studied as a function of down load, particle size, and concentration in order to investigate oxide chemical mechanical polishing (CMP) mechanism. In situ friction force measurements have been conducted to investigate the interfacial contact behavior during polishing. In the absence of particles, friction force increased with increasing down load. In the presence of particles, friction force increased with an increase in down load and solids loading. An equation derived from Amonton’s second law was used to determine the fraction of abrasive particles that actually come into contact with the wafer. The fractional surface coverage of abrasive particles was independent of down load and increased with increasing solids loading and decreasing particle size. Determination of the amount of abrasive particles effectively involved in polishing will make clearer the oxide CMP polishing mechanisms improving slurry design leading to further optimization of the CMP process. © 2004 The Electrochemical Society. All rights reserved.

Retention of progesterone by four carbonaceous materials: Study of the adsorption equilibrium

The adsorption process of a natural steroid hormone (progesterone) by four carbonaceous adsorbents has been studied. The corresponding equilibrium isotherms have been analyzed according to a previously proposed model which establishes a kinetic law satisfactorily fitting the C versus t isotherms. The obtained equilibrium isotherms consist of three segments, which have been separately discussed. Different equations corresponding to each of the referred segments have been proposed, the experimental data being fitted to such equations. From the values of the kinetic equilibrium constant corresponding to the second—and more significant—of the above mentioned segments, values of standard average adsorption enthalpy (Δ H°) and entropy (Δ S°) have been calculated. Finally, information related to variations of differential adsorption enthalpy (Δ H) and entropy (Δ S) with the surface coverage fraction ( θ) was obtained by using the corresponding Clausius-Clapeyron equations.

Atomic Force Microscopy Study of the Adsorption and Electrostatic Self-Organization of Poly(amidoamine) Dendrimers on Mica

The adsorption behavior of poly(amidoamine) dendrimers to mica surfaces was investigated as a function of ionic strength and pH. The conformation and lateral distribution of the adsorbed dendrimers of generations G8 and G10 were obtained ex situ by tapping mode atomic force microscopy (AFM). The deposition kinetics of the dendrimers was found to follow a diffusion-limited process. Fractional surface coverage and pair correlation functions of the adsorbed dendrimers were obtained from the AFM images. The data are interpreted in terms of the random sequential adsorption (RSA) model, where electrostatic repulsion due to overlapping double layers is considered. Although the general trends typical for an RSA-determined process are well-reproduced, quantitative agreement is lacking at low ionic strengths.

A Multiscale-Linking Algorithm for the Simulation of Irreversible Deposition

A multiscale-linking algorithm has been developed for the efficient simulation of irreversible deposition of particles on a two-dimensional substrate. The algorithm combines Brownian dynamics simulation (BDS) for the evaluation of particle trajectories with the solution of the continuum-level conservation law for particle concentration. This allows for the use of a simulation box with relatively small dimensions in the flux direction, resulting in significant CPU-time savings. The instantaneous flux of particles into the box is computed from the solution of the transient diffusion equation with an adaptive Neumann boundary condition. The incoming particles are placed in the box in accordance with the probability distribution function associated with the motion of particles. The algorithm is applied for the simulation of irreversible monolayer deposition of noninteracting hard spheres. Results are presented for the kinetics (fractional surface coverage, $\theta$) and the surface structure (radial distribut...

Electrooxidation of borohydride on platinum and gold electrodes: implications for direct borohydride fuel cells

The electrochemical oxidation of BH 4 − in 2 M NaOH on Pt and Au (i.e. catalytic and non-catalytic electrodes, respectively, for BH 4 − hydrolysis accompanied by H 2 evolution) has been studied by cyclic voltammetry, chrono-techniques (i.e., potentiometry, amperometry, coulometry) and electrochemical impedance spectroscopy. In the case of Pt the cyclic voltammetry behaviour of BH 4 − is influenced by both, the catalytic hydrolysis of BH 4 − yielding H 2 (followed by electrooxidation of the latter at peak potentials between −0.7 and −0.9 V versus Ag/AgCl, KCl std) and direct oxidation of BH 4 − at more positive potentials, i.e., between −0.15 and −0.05 V. Thiourea (TU, 1.5×10 −3 M) was an effective inhibitor of the catalytic hydrolysis associated with BH 4 − electrooxidation on Pt. Therefore, in the presence of TU, only the direct oxidation of BH 4 − has been detected, with peak potentials between −0.2 and 0 V. It is proposed that TU could improve the BH 4 − utilization efficiency and the coulombic efficiency of direct borohydride fuel cells using catalytic anodes. The electrooxidation of BH 4 − on Pt/TU is an overall four-electron process, instead of the maximum eight electrons reported for Au, and it is affected by adsorbed species such as BH 4 − (fractional surface coverage ∼0.3), TU and possibly reaction intermediates.

A nonlinear kinetic model introduced for the corrosion inhibitive properties of some organic inhibitors

Corrosion kinetics of low-carbon steel in hydrochloric acid was studied at various concentrations of mimosa tannin inhibitor. This system was subjected to impedance spectroscopy and quasi steady-state polarization. The inhibition efficiency, η was derived from the corrosion current, icorr and charge transfer resistance, Rct data. The fractional surface coverage as a function of the inhibitor concentration was calculated from the rate of hydrogen evolution reaction (h.e.r.) at constant cathodic potential. Based on the theoretical model and the observed experimental relationship between the ratio of the corrosion current densities in the uninhibited and the inhibited systems and the surface coverage, the relative influences of the geometric blocking action and the energy effect of the inhibitor on the corrosion process were estimated. Fitting of the nonlinear model to the experimental data was carried out by the Levnberg–Marquardt nonlinear fit method implemented into the programming system Mathematica®. Restructuring of the adsorbed layer and change in the orientation of adsorbed inhibitor molecules upon the increase of surface coverage was assumed on the basis of the experimentally observed functional relationship of the double layer capacitance and the surface coverage. The results were explained with respect to the molecular properties of the inhibitor – geometry and size of the molecule, electronic orbital structure and dipole moment.

A Mechanistic Study of the Fischer–Tropsch Synthesis Using Transient Isotopic Tracing. Part 2: Model Quantification

A quantitative mechanistic model for the low-pressure Fischer–Tropsch synthesis reaction on a Co/Ru/TiO2 catalyst is presented. Although the Fischer–Tropsch synthesis is operated at dry conditions, the presence of a physisorbed state is essential in the mechanism. The monolayer coverage of the C3 to C20 hydrocarbons in the physisorbed state is low at 0.3%. The most abundant chemisorbed surface species are COads and two single-C species, Cα,ads and Cβ,ads. The fractional surface coverage of growing hydrocarbon chains is low at 1.4%. With increasing H2/CO feed ratio, the surface concentrations of Hads and free sites increase. The rate coefficient for chain initiation is one order of magnitude lower than that for chain growth. The rate coefficient of ethene readsorption is one order of magnitude higher than that for the readsorption of higher 1-olefins. Chain branching and bond shift are important secondary reactions at atmospheric pressure, transforming reactive 1-olefins into unreactive internal and isoolefins and thus decreasing the asymptotic chain growth probability. As is to be expected, the termination to paraffin is represented by a hydrogenation reaction. The termination to olefin, however, appears to be a desorption reaction rather than a hydrogenation or a dehydrogenation reaction. The growing hydrocarbon chain is therefore represented by a CiH2i species.

Dynamical Monte Carlo simulation of surface atomic recombination

We present a dynamical Monte Carlo model for heterogeneous atomic recombination in terms of the theory developed by Fichthorn and Weinberg (1991 J. Chem. Phys. 95 1090) to simulate a Poisson process. The transient and steady-state solutions for the fractional surface coverage of reversible and irreversible sites, which hold physisorbed and chemisorbed atoms, respectively, are compared with the results from a phenomenological mean field model. The effects of low and high activation energies for desorption are investigated. It is observed that the results from the Monte Carlo simulation are in excellent agreement with those obtained from the phenomenological model in the limit of low occupation of adsorption sites.

Elucidation of the miniemulsion stabilization mechanism and polymerization kinetics

Styrene/hexadecane miniemulsions were polymerized at 50°C using a redox initiator. The miniemulsions and their corresponding latexes were characterized in terms of size, polymerization rate, and surface properties. The resulting data were analyzed to elucidate the miniemulsion stabilization and polymerization mechanisms. It was found that the free surfactant concentration exceeded the critical micelle concentration when large amounts of surfactant (60 mM sodium lauryl sulfate) were used, resulting in simultaneous micellar and droplet nucleation. Most surfactant was on the surface of the droplets (85%) or particles (95%). The fractional surface coverage was proportional to the surfactant concentration to the 0.55 power. Using a particle diameter equation, the number of particles was calculated to be proportional to the surfactant concentration to the 1.35 power. Through direct particle size measurements, a power of 1.38 was confirmed. The rate of polymerization was determined by reaction calorimetry to be proportional to the number of particles to the 0.59 power, in contrast to classical Smith–Ewart kinetics for conventional emulsions (1.0 power). The average number of radicals per particle was estimated from the rate and number data, and varied with the particle diameter to the 0.97 power. The observed kinetic dependencies were validated through an extension of Smith–Ewart theory. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3987–3993, 2003

Vapor-Phase Adsorption Kinetics of 1-Decene on H-Terminated Si(100)

We have investigated in situ and in real time vapor-phase self-assembly of 1-decene on Si, using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIRS). The adsorption of 1-decene on hydrogenated Si(100) results in a decane-terminated hydrophobic surface, indicated by the sessile-drop water contact angle at 107 ± 2°. This maximum contact angle is achieved at 160 °C under 30 mTorr of vapor-phase 1-decene. The fractional surface coverage of decane, calculated from the IR absorbance of C−H stretching vibrational modes near 2900 cm-1, follows a Langmuir isotherm. The absolute surface coverage calculated from the IR absorbance saturates at 3.2 × 1014 cm-2. On the basis of this isotherm, the empirical rate constant ( ) that governs the rate-limiting step in 1-decene adsorption on HF-treated Si(100) is (3.3 ± 0.7) × 10-2 min-1. The thickness and cant angle of the decane monolayer at the saturation coverage are calculated from angle resolved X-ray photoelectron spectroscopy (AR-XPS). The calculated thickness ranges from 8.4 to 18 Å due to the uncertainty in the attenuation lengths of C(1s) and Si(2p) photoelectrons through the decane layer. For the same uncertainty, the calculated cant angle ranges from 0 to 55°. Spectroscopic ellipsometry is independently used to approximate the film thickness at 16 Å. Monitoring the decane monolayer over a period of 50 days using AR-XPS indicates that the Si surface underneath the decane monolayer gets oxidized with time, leading to the degradation of the decane layer.

Enzymes as Ultrasensitive Probes for Protein Adsorption in Flow Systems

We have developed an assay system that can quantitatively determine protein adsorption of different materials down to submonolayer surface coverage at low solution concentrations under flow conditions. Understanding and controlling protein adsorption under these conditions will be a key element in the performance of microdevices that interact with proteins and other biomolecules because the surface area to volume ratio of these devices is substantially larger than those of current systems. Alkaline phosphatase and glucose oxidase were evaluated as probes for quantitative protein adsorption, and loss of protein due to adsorption onto capillary surfaces under flow conditions has been determined at fractional surface coverages on a variety of microfluidic materials. It was found that polyether ether ketone (PEEK) and Teflon had high affinity for both enzymes, while unmodified fused silica, fused silica treated with poly(ethylene glycol), and polyacrylamide had much lower affinity for the two enzymes under the conditions tested. Experimental confirmation of laminar diffusion was also demonstrated with this assay system.

Fluorinated Silane Self-Assembled Monolayers as Resists for Patterning Indium Tin Oxide

We report the formation of self-assembled monolayers (SAMs) on indium tin oxide (ITO) substrates with perfluoroorganosilanes in liquid and supercritical carbon dioxide and a method of patterning the monolayer that does not use any organic solvents. The monolayers formed were used as an etch resistant during the formation of patterns as small as 300 nm. The monolayers were characterized using wettability experiments, surface FT-IR, cyclic voltammetry, and AFM. The effects of temperature and adsorption time on the formation of SAMs were explored. Advancing contact angles as high as 105° and fractional surface coverages up to 0.96 were achieved by exposing the ITO surfaces to silanes in scCO2 for 15 h. Surface FT-IR results show peaks at 1212 and 1152 cm-1, typical for disordered monolayers. Yet, these SAMs are resistant to wet etching for over 10 h, indicating that dense carbon dioxide is a superior solvent for SAM formation of perfluorosilanes on ITO.

귀금속(Au, Rh) 전극계면에서 Langmuir 흡착등온식에 관한 위상이동방법

The Langmuir adsorption isotherms of the over-potentially deposited hydrogen (OPD H) fur the cathodic <TEX>$H_2$</TEX> evolution reaction (HER) at the poly-Au and <TEX>$Rh|0.5M\;H_2SO_4$</TEX> aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift <TEX>$(0^{\circ}{\leq}{-\phi}{\leq}90^{\circ})$</TEX> for the optimum intermediate frequency corresponds well to that of the fractional surface coverage <TEX>$(1{\geq}{\theta}{\geq}0)$</TEX> at the interfaces. The phase-shift profile <TEX>$({-\phi}\;vs.\;E)$</TEX> for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm <TEX>$({\theta}\;vs.\;E)$</TEX> of the OPD H for the cathodic HER at the interfaces. At the poly-Au|0.5M <TEX>$H_2SO_4$</TEX> aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy <TEX>$({\Delta}G_{ads})$</TEX> of the OPD H are <TEX>$2.3\times10^{-6}$</TEX> and 32.2kJ/mol, respectively. At the poly-Rh|0.5M <TEX>$H_2SO_4$</TEX> aqueous electrolyte interface, K and <TEX>${\Delta}G_{ads}$</TEX> of the OPD H are <TEX>$4.1\times10^4\;or\;1.2\times10^{-2}$</TEX> and 19.3 or 11.0kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, the two different Langmuir adsorption isotherms of the OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of the OPD H correspond to the two different adsorption sites of the OPD H on the poly-Rh electrode surface.

Producing Super-Hydrophobic Surfaces with Nano-Silica Spheres

Abstract Polycrystalline alumina substrates were dip-coated in dilute suspensions formed with dispersed, nano-silica particles. The fractional surface coverage of the alumina substrate was varied between ≈ 0.05 to ≈ 0.4 by changing concentration of particles in the silica slurry. After a heat treatment to partially sinter the particles to the surface, the surface was made hydrophobic by a reaction with a solution containing fluorosilane molecules. Wetting measurements showed that the contact angle between the surface and water droplets increased with decreasing area coverage of nano-silica spheres, consistent with a previous theory, modified here to include the pressure of the water droplet. The modification of the theory predicts that the super-hydrophobic effect disappears when the particles become too widely spaced, causing the pressure of the water droplet to spontaneously wet the substrate.

Fabrication of Surfaces with Nanoislands of Chemical Functionality by the Phase Separation of Self-Assembling Monolayers on Silicon

In this paper we outline a method to prepare surfaces with nanoisland-sized domains of one terminal chemical functionality in a matrix of a second by using self-assembling monolayers (SAMs). We deposit a SAM solution consisting of two different alkylsilane amphiphiles (CH3(CH2)17SiCl3 (OTS) and NH2C6H4Si(OMe)3 (APhMS)) which phase separate on the oxide surface of silicon due to the stronger cohesive interaction of OTS and the exclusive hydrogen bonding of APhMS. We vary the deposition conditionssolvent polarity and composition ratio at constant total concentrationto control the surface morphology (i.e., which surfactant occupies the island and which the matrix phase), island size, and density. We change the solvent polarity by either changing solvents (using, in order of increasing polarity, carbon tetrachloride, toluene, chloroform, and tetrahydrofuran) or changing the water content when chloroform is used. Composition ratios are varied depositing from chloroform. We find that the island morphology is determined by which surfactant has the higher concentration on the surface; islands are formed only from the minor component although area fractions are not equivalent to composition fractions in the depositing solvent. For 1:1 composition ratios, the more polar the solvent or the higher the water content in the solvent, the more affinity the solvent has for the amine, and islands of the amine are formed. In chloroform, composition ratios strongly favoring either amphiphile result in continuous phases of that amphiphile, while 1:1 ratios can, depending on the water content, result in either amine (high water content) or OTS (low water content) islands. Under similar small fractional surface coverages of the minor phase (i.e., less than 10%), when OTS forms the island phase, the islands tend to be larger and less dense, while when the amine forms the island phase, the islands are smaller and more finely dispersed. In the latter case we achieve finely distributed islands 25−50 nm in diameter, and O(30) islands/μm2. Surfaces chemically patterned with nanosized islands are of broad technological interest because they can be used to localize adsorption by functionalizing the islands to bind individual molecules or nanosized particles and designing the matrix to be inert to their adsorption. Previous nanometer patterning techniques using SAMs utilize the tip of a scanning probe microscope to write directly or alter a preexisting SAM; these methods pattern only planar areas, on the order of tens or hundreds of microns squared in area. Our nanometer-scale patterning can pattern large as well as curved areas.

Determination of the equilibrium constant and standard free energy of the over-potentially deposited hydrogen for the cathodic H 2 evolution reaction at the Pt–Rh alloy electrode interface using the phase-shift method

The Langmuir adsorption isotherm of the over-potentially deposited hydrogen (OPD H) for the cathodic H 2 evolution reaction (HER) at the Pt–Rh (Pt:Rh; 80: 20 wt% ) alloy/0.5 M H 2 SO 4 aqueous electrolyte interface has been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift (0°⩽− φ⩽90°) for the optimum intermediate frequency can be linearly related to that of the fractional surface coverage (1⩾ θ⩾0) of the OPD H for the cathodic HER at the interface. The phase-shift profile (− φ vs. E) for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm ( θ vs. E) of the OPD H for the cathodic HER at the interface. At the Pt–Rh alloy electrode interface, the equilibrium constant ( K) and the standard free energy (Δ G ads) of the OPD H are 2.2×10 −4 and 20.9 kJ/ mol , respectively. At the steady state, the behaviors of the cyclic voltammogram and the Langmuir adsorption isotherm of the OPD H for the cathodic HER at the Pt–Rh alloy electrode interface are similar to those of the pure Pt electrode interfaces. At the steady state, the effect of Rh on the OPD H for the cathodic HER can be neglected at the Pt–Rh (Pt:Rh; 80: 20 wt% ) alloy/0.5 M H 2 SO 4 aqueous electrolyte interface.

Langmuir Adsorption Isotherms of Overpotentially Deposited Hydrogen at Poly-Au and Rh / H 2 SO 4 Aqueous Electrolyte Interfaces : Qualitative Analysis Using the Phase-Shift Method

The Langmuir adsorption isotherms of over-potentially deposited hydrogen (OPD H) for the cathodic hydrogen evolution reaction (HER) at poly-Au and Rh/0.5 M aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift for the optimum intermediate frequency can be linearly related to that of the fractional surface coverage of OPD H for the cathodic HER at the interfaces. The phase-shift profile (−ϕ vs. E) for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm (θ vs. E) of the OPD H for the cathodic HER at the interfaces. At the poly-Au/0.5 M aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy of the OPD H are and 32.2 kJ/mol, respectively. At the poly-Rh/0.5 M aqueous electrolyte interface, K and of the OPD H are or and 19.3 or 11.0 kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, two different Langmuir adsorption isotherms of OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of OPD H correspond to two different adsorption sites of OPD H on the poly-Rh electrode surface. © 2003 The Electrochemical Society. All rights reserved.

Structured Silicon Anodes for Lithium Battery Applications

Pillar arrays fabricated on silicon substrates have been tested as potential anodes for lithium batteries. Electrodes of array characteristics, diameter 580 ′ 150 nm: fractional surface coverage 0.34: height 810 nm are reported here. Cyclic voltammetry (CV) and cyclic galvanostatic tests of alloying/dealloying of electrochemically produced lithium with silicon were carried out, and results correlated with SEM studies. Aerial current densities in the low and fractional mA cm - 2 , and voltage 25 mV to 2 V (vs. L/Li + ) were used. CV features correspond to various Zintl phase compounds (ZPCs). Structured electrodes of Si pillars maintained their structural integrity throughout cycling; planar Si electrodes showed cracks (2 μm features) after 50 cycles. A model is advanced in which lithium diffuses through a layer of ZPC to react with Si: growing ZPCs plastically deforms where necessary. Upon lithium dealloying vacancies coalesce to form voids at the ZPC/Si interface, Si rejoins the substrate. or precipitates out as a nanocrystalline material, and the voids appear as a fine pattern of cracks, looking like dried mud. The extra surface area that a pillar structure can confer on Si electrodes is essential and makes it practical to consider the possible eventual use of such anodes in integrated battery structure;.

Characterization of the Surface Redox Process of Adsorbed Cercosporin (CER) at Glassy Carbon Electrodes by Anodic Stripping Square‐Wave Voltammetry

AbstractThe adsorptive accumulation of cercosporin (CER) at glassy carbon electrodes is studied by square‐wave voltammetry (SWV). The Freundlich adsorption isotherm resulted in being the best one to describe the specific interaction of CER with glassy carbon electrodes by using a fitting procedure of experimental fractional surface coverage vs. the CER bulk concentration (c*CER). SWV was also used to generate Q vs. c*CER and Ip, n. vs. c*CER calibration plots from pure commercial reagent solutions. Theoretical detection limits of 1.8×10−7 and 9.7×10−8 M were calculated from Q. vs. c*CER and Ip, n vs. c*CER plots, respectively. The lowest concentration value measured experimentally from calibration plots performed at a f =40 Hz for a signal to noise ratio of 2 : 1 was 3.7×10−8 M, being this value two orders of magnitude smaller than that obtained previously by us from the diffusion controlled CER reduction peak. Ip, n./f vs. f plots from SW voltammograms performed at different c*CER as well as different accumulation times showed the so‐called “quasi‐reversible maxima”. A splitting of the voltammetric peak was also observed by increasing the SW amplitude at a given frequency. A value of (−0.260±0.011) V was determined for the formal potential of the adsorbed redox couple from the split voltammetric peak. A full characterization of the surface redox process was obtained by applying the methods of the “quasi‐reversible maximum” and the “split SW peak”. In 1 M HClO4 aqueous solution, the formal rate constant and the anodic transfer coefficient were (3.5±0.5)×102 s−1 and (0.50±0.03), respectively. Besides, the number of electrons exchanged during the redox reaction was calculated as n≈1.

A small-angle neutron scattering investigation of the structure of highly swollen block copolymer micelles

The structure of highly swollen micelles of an amphiphilic poly(oxyethylene)–poly(oxybutylene) diblock copolymer with a lengthy hydrophilic poly(oxyethylene) block has been investigated by small-angle neutron scattering (SANS). The density profile of the tethered polymer brush is obtained by fitting the SANS data using analytical expressions for the form factor of a micelle with a spherical core and self-avoiding chains. The decrease in coronal chain radius of gyration with increasing temperature, and the decrease in water content in the poly(oxybutylene) core lead to an increase in association number, in good agreement with previous light scattering experiments. The increase in polymer volume fraction close to the core on increasing temperature is related to the increase in fractional surface coverage and reduction in interfacial curvature.