Charge Density Data Research Articles

300 mm SOI for High Volume Manufacturing

300 mm SOI for leading edge CMOS applications has been moving into high volume manufacturing recently but little information on the quality of these wafers is available. This paper reviews key characteristics of 300 mm SOI and how they compare to the status from several years ago. For physical characteristics, Si layer thickness and uniformity, surface quality and defects, flatness, surface roughness, metal contamination and slip are surveyed. Electron mobility, buried oxide charge and interface state density data obtained from pseudo MOSFET measurements are employed to monitor the electrical characteristics of the SOI structure.

Continua of Interactions between Pairs of Atoms in Molecular Crystals

The electron density distributions in crystals of five previously studied DMAN complexes and five Schiff bases (two new ones) have been analysed in terms of various properties of bond critical points (BCPs) found in the pair-wise interactions in their lattices. We analysed the continua of interactions including covalent/ionic bonds as well as hydrogen bonds and all other types of weak interactions for all pairs of interacting atoms. The charge density at BCPs and local kinetic and potential energy densities vary exponentially with internuclear distance (or other measures of separation). The parameters of the dependences appear to be characteristics of particular pairs of atom types. The Laplacian and the total (sum of kinetic and potential) energy density at BCPs show similar behaviour with the dependence being of the Morse type. The components lambda1, lambda2, lambda3 of the Laplacian at BCPs vary systematically with internuclear distance according to the type of atom pair. For lambda1 and lambda2 the distribution is of the exponential type, whereas lambda3 does not seem to follow any simple functional form, consistent with previous theoretical findings. Analytical nonlinear dependences of Laplacian on charge density have been found. They agree reasonably well with those obtained by least square fit of the Laplacian to charge density data. There are four distinct regions of the [symbol: see text]2rho(BCP)/rho(BCP) space, generated by E(BCP) = 0 and G(BCP)/rho(BCP) = 1 conditions. Two regions clearly correspond to the shared-shell and closed-shell interactions and the other two to some intermediate situation.

Accurate charge density data collection in under a day with a home X-ray source

Accurate charge density data for pentaerythritol were measured at 15 K in the laboratory in under a day using a Rigaku R-Axis Rapid high-power rotating-anode diffractometer with a curved image-plate detector, and open-flow liquid-helium cryostat. The experimental procedure and data treatment are briefly described, and data quality evaluated based on a number of criteria.

Electrochemical and PM-IRRAS Studies of the Effect of the Static Electric Field on the Structure of the DMPC Bilayer Supported at a Au(111) Electrode Surface

Differential capacity, charge density measurements, and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) were employed to study the fusion of small unilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) on a Au(111) electrode surface. The differential capacity and charge density data showed that the vesicles fuse onto the gold surface at charge densities between -10 microC/cm(2) < sigma(M) < 10 microC/cm(2) to form a bilayer. When sigma(M) < -10 microC/cm(2), the film is detached from the surface but it remains in close proximity to the surface. PM-IRRAS experiments provided IR spectra for the bilayer in the adsorbed and the desorbed state. Ab initio normal coordinate calculations were performed to assist interpretation of the IR spectra. The IR bands were analyzed quantitatively, and this analysis provided information concerning the conformation and orientation of the acyl chains and the polar head region of the DMPC molecule. The orientation of the chains, hydration, and conformation of the headgroup of the DMPC molecule strongly depend on the electrode potential.

Electrochemical, neutron reflectivity and in situ PM-FT-IRRAS studies of a monolayer of n-octadecanol at a Au(1 1 1) electrode surface

The horizontal touch and Langmuir–Blodgett techniques have been used to transfer a monolayer of n-octadecanol from the gas–solution interface of a Langmuir trough onto the metal–solution interface of a Au(1 1 1) electrode. Chronocoulometry has been used to determine the charge density at the electrode surface covered by the film of n-octadecanol. The surface pressure of this film was calculated from the charge density data and was found to be controlled by the electrode potential. We have demonstrated that by dialing the potential applied to the electrode via a potentiostat the monolayer adsorbed on the surface can be compressed or decompressed. Two states of the monolayer were observed. The transition between these states took place at a film pressure ∼12 mN m −1. Neutron reflectometry and polarization modulation Fourier transform infrared reflection absorption spectroscopy have been employed to determine the nature of the two states. The results show that octadecanol molecules form a two-dimensional solid film at all film pressures. At film pressures larger than 12 mN m −1, the film has low compressibility and n-octadecanol molecules assume a small tilt angle with respect to the surface normal. At film pressures lower than 12 mN m −1 a compressive film is formed in which the tilt angle progressively increases with decreasing surface pressure. We have demonstrated that the properties of a monolayer of n-octadecanol at the metal–solution interface display many similarities to the properties of that film at the air–solution interface.

Electrogravimetric investigation of formaldehyde oxidation at Pt electrodes in acidic media

The electrochemical and adsorptive behavior of formaldehyde at Pt electrodes in acidic media was investigated using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) techniques. All chemical and electrochemical steps related to formaldehyde oxidation (e.g. bulk adsorption and oxidation, CO (sub)monolayer adsorption and oxidation and electrons per Pt site) were analyzed. All the mass and charge density data in this paper are referred to the real surface area. The charge density associated with formaldehyde oxidation was close to 420 μC cm −2, which is related to the oxidation of approximately one CO monolayer with two electrons transferred. For CO adsorption the experimental mass value was 50 ng cm −2. In the region of CO oxidation the analysis of mass and charge variations indicates simultaneous CO oxidation, anion and water adsorption and CO readsorption. The mechanism was confirmed by CO and CO 2 flux calculations. From the analysis of the mass–charge ratio and species flux it was concluded that CO, an intermediate produced during formaldehyde oxidation, is adsorbed at the Pt surface and the main contribution to the mass increase during formaldehyde oxidation is CO readsorption, and water adsorption.

Evaluation of equilibrium parameters characterizing metal oxide/electrolyte solution interface

According to the surface complexation model (SCM), charging of a metal oxide surface in aqueous environment is due to interactions of active surface groups with ions from the bulk of the solution. Several models for mechanism of surface reactions were proposed. Interfacial equilibrium is determined by corresponding equilibrium constants, but also with the structure of the electrical interfacial layer (EIL). Therefore, evaluation of equilibrium parameters is not a simple task. Traditionally, the measurements of pH dependency of surface charge density was used for that purpose. This article shows that introduction of electrokinetic data produces more reliable results, especially in the case of specific adsorption. If surface charge density and/or adsorption data are not available, one may still deduce interfacial equilibrium constants from electrokinetic results combined with measurements of the surface potential.

Measurement of high-quality diffraction data with a Nonius KappaCCD diffractometer: finding the optimal experimental parameters

The influence of the different experimental parameters on the quality of the diffraction data collected on tetrafluoroterephthalonitrile (TFT) with a Nonius KappaCCD instrument has been examined. Data sets measured with different scan widths (0.25°, 0.50°, 1.0°) and scan times (70 s/° and 140 s/°) were compared with a highly redundant data set collected with an Enraf–Nonius CAD4 point detector diffractometer. As part of this analysis it was investigated how the parameters employed during the data reduction performed with theEvalCCDandSORTAVprograms affect the quality of the data. The KappaCCD data sets did not show any significant contamination from λ/2 radiation and possess good internal consistency with lowRintvalues. Decreasing the scan width seems to increase the standard uncertainties, which conversely are improved by an increase in the scan time. The suitability of the KappaCCD instrument to measure data to be used in charge density studies was also examined by performing a charge density data collection with the KappaCCD instrument. The same multipole model was used in the refinement of these data and of the CAD4 data. The two refinements gave almost identical parameters and residual electron densities. The topological analysis of the resulting static electron densities shows that the bond critical points have the same characteristics.

Electrochemical and Neutron Reflectivity Characterization of Dodecyl Sulfate Adsorption and Aggregation at the Gold−Water Interface

Chronocoulometry and the thermodynamic analysis of charge density data were employed to describe the energetics of sodium dodecyl sulfate (SDS) adsorption at the Au(111) electrode surface. Thermodynamic data such as the Gibbs excess, Gibbs energy of adsorption, and the film pressure of adsorbed SDS were determined for a broad range of electrode potentials, charge densities, and bulk SDS concentrations. The present results, combined with our previous scanning probe microscopy (SPM) studies, show that adsorption of SDS at the Au(111) electrode surface has a two-state character. At small or moderate absolute charge densities, the adsorbed SDS molecules aggregate into hemicylindrical stripelike micelles. This state is well-ordered. The unit cell of its two-dimensional lattice consists of two vectors that are 44 and 5.0 A long and are oriented at an angle of 70°. The Gibbs excess data indicate that five SDS molecules are accommodated into the unit cell. At large positive charge densities, the hemimicellar aggr...

Adsorption of bromide at the Ag(100) electrode surface

The adsorption and phase formation of bromide on Ag(100) has been studied by chronocoulometry and surface X-ray scattering (SXS). With increasing electrode potential, bromide undergoes a phase transition from a lattice gas to an ordered c(2×2) structure (θ=0.5). The degree of lateral disorder was estimated by comparing the SXS- and the electrochemical measurements. Based on chronocoulometric experiments, a thermodynamic analysis of charge density data was performed to describe the bromide adsorption at the Ag(100) electrode. The Gibbs surfaces excess, electrosorption valencies, Esin–Markov coefficients, and the Gibbs energy of adsorption, lateral interaction energies as well as surface dipole moments have been estimated. The experimental θ versus E- isotherms are modeled employing (i) a quasi-chemical approximation as well as (ii) the results of a recent Monte Carlo simulation. An attempt is made to discuss the structure data and thermodynamic quantities of bromide adsorption on Ag(100) on the basis of the Grahame–Parsons model of the Helmholtz layer.

Chronocoulometric studies of chloride adsorption at the Pt(111) electrode surface

Abstract Chronocoulometry and a thermodynamic analysis of charge density data were used to describe chloride adsorption at the Pt(111) electrode surface. The Gibbs excess, the Gibbs energy of adsorption, the number of electrons flowing to the interface per adsorbed chloride ion at a constant potential (electrosorption valency) and at constant chloride concentration (reciprocal of the Esin–Markov coefficient) were determined. Chloride forms a chemisorption bond with platinum. The charge numbers at constant potential and at constant chloride concentration are close to unity. This result suggests that the polarity of the chemisorption bond is very small. The highest packing density of chloride determined by the thermodynamic method corresponds to 0.43 ML. This number agrees well with coverage determined in recent surface X-ray scattering experiments [1] . Adsorption of chloride at Pt(111) is potential and pH dependent. We have demonstrated that at negative potentials, co-adsorption of Cl and hydrogen atoms has a synergistic character. In contrast the adsorption of chloride and OH at positive potentials has a competitive nature.

Electrochemical Studies of the Benzoate Adsorption on Au (111) Electrode

Cyclic voltammetry (CV), differential capacity (DC), and charge densitymeasurements have been employed to study the benzoate (BZ) adsorption at the Au(111)electrode surface. Thermodynamic analysis of charge density (σM) data has beenperformed to describe the properties of the adsorbed benzoate ion. The Gibbsexcess Γ, Gibbs energy of adsorption ΔG, and the number of electrons flowingto the interface per adsorbed benzoate ion at a constant potential (electrosorptionvalency) and at a constant bulk concentration of the benzoate (reciprocal of theEsin—Markov coefficient) have been determined. The results demonstrate thatalthough benzoate adsorption starts at negative charge densities, it takes placepredominantly at a positively charged surface. At the most positive potentials,the surface concentration of benzoate attains a limiting value of about 7.3×10−10mol-cm−2, which is independent of the bulk benzoate concentration. This valueis consistent with packing density corresponding to a closed-packed monolayerof vertically adsorbed benzoate molecules. At negative charge densities, benzoateassumes a flat (π-bonded) surface coordination. The surface coordination ofbenzoate changes, by moving from a negatively to positively charged surface.At the negatively charged surface, the electrosorption bond is quite polar. Thepolarity of the chemisorption bond is significantly reduced due either to a chargetransfer or a screening of the charge on the anion by the charge on the metal.

ELECTROCHEMICAL PROPERTIES OF ASPHALTENE PARTICLES IN AQUEOUS SOLUTIONS

The electrical properties of colloidal asphaltene/water solution interface were determined by carrying out the potentiometric titration and electrokinetic measurements. Asphaltenes in aqueous solutions exhibit typical organic colloid properties i.e. surface charge and electrophoretic mobility. It was considered that the surface charge at the asphaltene particles is a result of protonation and dissociation reactions of surface functional groups. On the base of the surface charge density data vs. pH the surface reaction constants were calculated by numerical method. The agreement of these values with calculated ones, on the base of ζ potential data, is noticeable. The characteristic feature of the investigated systems is the maximum, appearing on the curve ζ potential vs. electrolyte concentration. This behaviour is explained by ”hair layer ” structure of the asphaltene surface

The structure and 13C-NMR of an indolenium squaraine dye

Six conformational isomers of bis(1-isopropyl-2,3,3-trimethylindolen-2-ylidene)squaraine were studied using MM+ molecular mechanical and AM1 quantum chemical methods. The calculated energies and structures indicate that the planarity of the π system is of great importance. These results were confirmed by NMR spectroscopy. The structure of the aforementioned dye was shown to be the trans-planar isomer. The 13C-NMR spectrum of this isomer was assigned with the aid of C-atom charge density data derived from AM1 calculations.

Electrochemical and Spectroscopic Studies of Hydroxide Adsorption at the Au(111) Electrode

The adsorption of hydroxide ions at a Au(111) single-crystal electrode has been investigated quantitatively using chronocoulometry and subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS). By thermodynamic analysis of the charge density data, the Gibbs excess, Gibbs energy of adsorption, and number of electrons flowing to the interface per one adsorbed hydroxide ion at a constant electrode potential (electrosorption valency) were determined. The electrosorption data indicate that the adsorption of OH- has a three-state character. The adsorbed OH- forms quite a polar surface bond at a negatively charged surface, while the polarity of the surface bond is significantly decreased at positive charge densities. Oxide formation begins at higher charge densities. Infrared spectroscopy shows that oxide formation takes place when the surface concentration of hydroxide ions exceeds one-third of a monolayer. The integrated infrared intensity of the O−H stretching band correlates ver...

Quantitative studies of benzonitrile adsorption at the low-index gold single crystal electrodes

The adsorption of benzonitrile (BN) on the Au(111), Au(100), and Au(110) electrodes in aqueous solutions was investigated. The chronocoulometric technique was used to measure the charge density at the metal surface as a function of the electrode potential for BN concentrations ranging from 0 to 0.030 M. The adsorption parameters such as the film pressure, the surface concentration of the organic adsorbate, the standard Gibbs energy of adsorption (Δ G ads 0), and the charge flowing to the interface per one adsorbed molecule, were determined from the thermodynamic analysis of the charge density data. The analysis was carried out at constant electrode potential and at constant charge density. In addition, subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) was employed to determine the orientation of BN molecules at the Au(111) surfaces. The thermodynamic and spectroscopic data indicate that BN molecules assume a flat (π-bonded) state at the negatively charged surface and progressively reorient from the flat to the tilted (N-bonded) state as the charge at the metal surface becomes more positive. At very positive potentials the character of BN adsorption becomes reactive and the adsorbed molecules partially hydrolyze to form benzamide (BA).

Iodide adsorption at the Au(111) electrode surface

The adsorption of iodide at a Au(111) single crystal electrode has been investigated quantitatively using chronocoulometry. By analyzing the charge density data thermodynamically, the following parameters were determined: the Gibbs excess, Gibbs energy of adsorption, the number of electrons flowing to the interface per one adsorbed iodide ion at a constant electrode potential (electrosorption valency), and at a constant chemical potential. The thermodynamic data for iodide adsorption were compared to the results for bromide and chloride adsorption. All the three halides form a chemisorption bond with the gold surface. The bond is quite polar at the negatively charged surface, however, its polarity drops significantly at the positively charged surface. At low charge densities and coverages, the bond polarity is determined by the ability of free electrons to screen the dipole formed by the adsorbed anion and its image charge in the metal. At high charge densities and coverages, the chemisorption bond has a predominantly covalent character. The strength of the halide adsorption and the covalent character of the chemisorption bond increase progressively by moving from chloride to iodide.

Fluorescence Spectral Study of 9-Acridinecarboxylic Acid and Its Methyl Ester. Understanding the Unusual Fluorescence Behavior of 9-Anthroic Acid

The absorption and fluorescence spectral characteristics of 9-acridinecarboxylic acid (9-ACA) and 9-(methoxycarbonyl)acridine (9-MCA) were studied in a series of organic solvents and in aqueous solutions. Fluorescence quantum yields (Φf) and lifetimes (τf) of the compounds were measured in these solvents. Unlike 9-anthroic acid (9-AA), as reported in the literature, no large Stokes-shifted fluorescence emission band was observed for 9-ACA and 9-MCA in neutral organic solvents or water. The absence of large Stokes-shifted emission in the case of 9-ACA and 9-MCA suggests the existence of a charge-transfer emitting state in 9-AA in which the carboxyl group is nearly coplanar with the aromatic ring. The Φf values for both compounds increase as a function of hydrogen-bonding capacity of the solvents. In near neutral to slightly acidic solutions, 9-ACA exists mainly in the zwitterionic form. Both 9-ACA and 9-MCA form monoprotonated species in moderately concentrated acid solutions. The acidium cation of 9-AA formed in the excited state in moderately concentrated acid solution reorganizes to produce a carbocation centered at the carbon atom of the carboxyl group. However, there was no indication of the formation of such acidium cations in the case of 9-ACA and 9-MCA even in concentrated perchloric acid medium. The pKas of various prototropic equilibria involved in the ground electronic state of the compounds were estimated. Semiempirical AM1 calculations were performed to obtain the energies of the various configurations of 9-AA and 9-ACA in the ground (S0) as well as in the lowest excited singlet (S1) electronic state. The results suggest that the COOH group is oriented at an angle of ∼55° with respect to the aromatic ring in the S0 state in both the molecules. However, in the S1 state, it approaches coplanarity with the aromatic ring. The calculated bond lengths, charge densities, and dipole moments suggest that the resonance charge transfer from the aromatic ring to the COOH group increases in the S1 state of 9-AA. However, despite the decrease of twist angle of the COOH group, no significant charge transfer was observed in 9-ACA. The charge density data indicate that the ring nitrogen and the carbonyl oxygen of the COOH group become more basic upon electronic excitation.

Chloride adsorption at the Au(111) electrode surface

A thermodynamic analysis of charge density data was performed to describe chloride adsorption at the Au(111) electrode surface. The Gibbs excess, the Gibbs energy of adsorption, the number of electrons flowing to the interface per adsorbed chloride ion at a constant potential (electrosorption valency) and a constant chloride concentration (reciprocal of the Esin-Markov coefficient), and the dipole formed by adsorbed ion and its image charge in the metal were determined. Chloride forms a chemisorption bond with gold whose polarity is a strong function of the charge on the metal. The bond is fairly polar at the negatively charged surface; however its polarity drops significantly at positive charges. The adsorption behavior of this anion is asymmetric with respect to the charge on the metal.

Electrochemical and second harmonic generation study of bromide adsorption at the Au(111) electrode surface

A thermodynamic analysis of charge density data has been performed to describe bromide adsorption at the Au(111) electrode surface. The Gibbs excess, the Gibbs energy of adsorption, the number of electrons flowing to the interface per one adsorbed bromide ion at a constant potential (electrosorption valency) and at a constant bromide concentration (reciprocal of the Esin–Markov coefficient) and the surface dipole formed by the adsorbed ion and its image charge in the metal were determined. Bromide ion forms a chemisorption bond with the gold surface whose polarity is a strong function of the charge on the metal. The bond is quite polar at the negatively charged surface; however, its polarity drops significantly at positive charges. The adsorption behaviour of this anion is quite asymmetric with respect to the charge on the metal. At low charge densities and coverages, the change of the bond polarity is determined by the ability of the free electrons in the metal and surface solvent molecules to screen the dipole formed by adsorbed Br– and its image charge in the metal. At high charge densities and coverages, the chemisorption bond has a predominately covalent character as a result of charge transfer between the adsorbed bromide ion and the metal surface. The covalent character of Br– adsorption at the Au(111) is consistent with the results of independent SHG experiments. The SHG data indicate that adsorption of bromide strongly affects the electronic structure of the metal surface.