Surface Potential Characteristics Research Articles

Natural nanoscale surface potential of clinochlore and its ability to align nucleotides and drive DNA conformational change

The knowledge of the surface properties of minerals is of great importance in understanding both basic and applied technological issues, such as for example liquid/surface interactions, microfluidity, friction or tribology and biomolecule self-assembly and adhesion. Recent developments of scanning probe microscopy (SPM) have widened the spectrum of possible investigations that can be performed at a nanometric level on the surface of minerals. They range from physical properties such as electric field topological determination to chemical and spectroscopic analysis in a variety of environments (air, liquid, gas and vacuum). Here we show that the surface potential characteristics of chlorite can be assessed by working in electric force microscopy (static and dynamic EFM) and in Kelvin probe modes of operation. In particular, this work reports electrostatic force simulations through finite element analysis and electric force microscopy observations of cleaved surfaces of chlorite before and after nucleotide and DNA deposition. As expected, chlorite presents a surface potential anisotropy at the nanoscale related to its peculiar crystal chemistry. A freshly cleaved surface is usually made up of positively and negatively charged layers with a lateral extent of a few nm. After nucleotide deposition at room temperature (25 °C) and atmospheric pressure, spontaneous formation of ordered structures and micrometre long aligned segments of nucleotides occur because of topologically driven electrostatic interaction. The surface potential anisotropy is also able to order and stretch larger molecules such as DNA filaments thus inducing a natural change in its conformation. The relevance of these results has to be considered in the context of the possible role played by the surface of mixed-oxide minerals, such as chlorite which is rich in Bronsted and Lewis sites, in the prebiotic synthesis and polymerization of biomolecules with important implications for earth and life sciences. The ability to control the binding of biomolecules onto non-conductive solid substrates with atomically flat boundaries has also important and promising applications in nano-biotechnology such as in microelectronics, microarrays and sensors.

Salient Features in the Capacitance Characteristics of Ultrathin High-K Devices

Salient features of MOS (Metal Oxide Silicon) devices with ultra-thin high-Κ gate dielectrics are outlined here, which include the following. In the case of the ultra-thin (EOT < 2 nm) gate dielectrics, the capacitance-voltage (C-V) and the surface potential versus bias characteristics are dominated by the accumulation and the strong inversion regimes, in contrast to the case of the thicker gate dielectrics, where these characteristics are dominated by depletion and weak inversion regimes. In the strong accumulation regime, the experimental lnCp versus the surface potential plot (Cp is the sum of the space charge capacitance Csc and the interface trap capacitance Cit) was found to be a straight line, and its slope varied strongly with the gate dielectric material and was found to be inversely proportional to [square root(Pbm*/m)]K/Cdi, where Pb is the conduction/valence band offset, m* is the effective electron/hole tunneling mass, K is the dielectric constant, and Cdi is the gate dielectric capacitance.

Body surface potential maps in patients with familial amyloid polyneuropathy

The purpose of this study was to evaluate the characteristics of body surface potential maps in patients with cardiac amyloidosis. The study population consisted of 30 patients with familial amyloid polyneuropathy and 50 agematched normal volunteers. The patients were classified into one of the following three stages: stage I, peripheral neuropathy limited to the lower limbs; stage II, neuropathy involving both the lower and upper limbs; and stage III, bedridden because of extensive progressive neuropathy. Electrodes for the body surface potential maps were placed at 87 points (59 anterior and 28 posterior) on the chest. To analyze these body surface electrocardiograms, isopotential maps, isochrone maps, and isointegral maps were used. The mean values of the positive potential were significantly lower in the advanced stage (1.9 ± 0.2 mV in stage I, 1.0 ± 0.2 mV in stage II, and 0.7 ± 0.2 mV in stage III). Prolongation of ventricular activation time was observed on the anterior and lateral chest. The mean QRST isointegral maps of the patients in the advanced stage of cardiac amyloidosis showed a large negative area over the anterior and left lateral chest, the positive areas were small and their potentials were very low. In addition, 18 (60%) of the 30 patients had a multipolar pattern in the QRST isointegral maps. The changes of the body surface potential maps correlated with clinical staging and echocardiographic findings.

Effect of thickness on surface potential characteristics of corona charged poly(acrylonitrile-butadiene-styrene) layers

Effect of thickness on surface potential characteristics of corona charged poly(acrylonitrile-butadiene-styrene) layers

The interaction among the polar head groups in ampholytic phospholipid monolayer as analyzed by surface potential and radiotracer measurements of counterion binding

Radiotracer measurement shows that the adsorption of calcium ions to ampholytic phospholipid monolayers freely occurs up to the particular film density of lipid, but is considerably suppressed by exceeding the critical film density when aqueous 45CaCl 2 is injected to the monolayer substrate. A similar behavior is also seen in the surface potential characteristics of the monolayer when sodium chloride or calcium chloride was introduced to the aqueous substrate. No potential change was observed above the critical film density. The phenomenon is reasonably explained by assuming two-dimensional phase separation accompanied by the formation of multiple ion-pairs among the polar head groups of phospholipids. The surface potential analysis showed that the polar head groups of dipalmitoylphosphatidyl-ethanolamine are oriented almost parallel to the plane of the film.

Study of surface potential characteristics of corona charged ethyl cellulose layers for its relevance in electrothermography

AbstractA solution cast layer of ethyl cellulose on aluminium substrate shows high charge acceptance on corona charging. Its surface potential decay characteristics are studied at room temperature and at higher temperatures. Addition of a thermosensitive dye in the polymer matrix shows enhanced contrast potential at constant IR exposure. Optimum conditions for suitability of the polymer in electrothermography is determined by studies on different weight proportions of dye. The effect of layer thickness on surface potential characteristics is also investigated.

Self-Consistent Many-Electron Theory of Electron Work Functions and Surface Potential Characteristics for Selected Metals

Electron work functions, surface potentials, and electron number density distributions and electric fields in the surface region of 26 metals were calculated from first principles within the free electron model. Calculation proceeded from an expression of the total energy as a functional of the electron number density, including exchange and correlation energies, as well as a first inhomogeneity term. The self-consistent solution was obtained via a variational procedure. Surface barriers were due principally to many-body effects; dipole barriers were small only for some alkali metals, becoming quite large for the transition metals. Surface energies were inadequately described by this model, which neglects atomistic effects. Reasonable results were obtained for electron work functions and surface potential characteristics, maximum electron densities varying by a factor of over 60.

Self-Consistent Many-Electron Theory of Electron Work Functions and Surface Potential Characteristics for Selected Metals

Electron work functions, surface potentials, and electron number density distributions and electric fields in the surface region of 26 metals are calculated from first principles within the free-electron model. The number of free electrons per atom is taken as the group number as listed in the Periodic Table. Grain orientation effects are not considered. The calculation proceeds from an expression of the total energy as a functional of the electron number density including exchange and correlation energies as well as a first inhomogeneity term. The self-consistent solution is then obtained via a variational procedure akin to the Ritz method. Surface barriers are found, in most cases, to be due principally to many-body effects, but dipole barriers are small only for a number of alkali metals, becoming quite large for the transition metals. As one might expect, surface energies are found to be inadequately described by this model which neglects atomistic effects. Considering the simplicity of the model, reasonable results are obtained for electron work functions and surface potential characteristics for all metals studied, maximum electron densities varying by a factor of over 60.

The surface properties of lung extract

The surface tension, surface potential, and surface flow characteristics of crude lung surfactant (LS) monolayers were studied as functions of surface compression and also as functions of age of extract solution. The surface tension characteristics show almost no change with age whereas the surface potential data have maxima at one to two weeks of age. The surface flow measurements, which show qualitative as well as quantitative changes with age, indicate that LS forms a two-dimensional network. The ability to form this network decreases with the age of the extract, and the variation correlates with the surface potential pattern. The rate of network formation is accelerated by compression and/or flow of the LS film. These results suggest that the nonlipid components of LS are probably involved in the formation of the network and that the LS network may be involved in the mechanism which stabilizes the alveoli.

The surface properties of pure phospholipids in relation to those of lung extracts

An investigation has been undertaken into the surface pressure and surface potential of thin films of certain pure and mixed phospholipids in relation to the surface properties exhibited by crude lung extracts. The high stable surface pressures obtained by compression of monolayers of saturated, choline-containing phospholipids, in contrast to the corresponding ethanolamine phospholipids, has been attributed to the uniquely close surface packing of the former molecules, which is possible almost throughout their entire length. Certain foreign molecules render such structures unstable, but others are eliminated by “squeeze-out” during compression. The “characteristic” surface properties of lung surfactant can be ascribed to various causes as follows. High surface pressure: to high dipalmitoyllecithin content with perhaps some contribution by other disaturated choline phospholipids and sphingomyelin; instability and gel-liquid state at high pressure : to heterogeneity of the compressed film; “hysteresis”: to replacement from a “surface store”, during expansion, of surfactant eliminated by “squeeze-out” during previous compression; plateau in the compression phase at about 45–50 dyne/cm : to rapid “squeeze-out” of some of the more readily eliminated substances, this “squeeze-out” then continuing at a slower rate throughout the remainder of the compression phase but remaining incomplete. In addition, it has been suggested that a conformational change of the choline moiety from a co-planar to a co-axial arrangement occurs during compression of saturated choline phospholipids and may contribute to the surface pressure and surface potential characteristics of monolayers of such substances and of lung extracts.

Reaction between stearic acid and calcium ions at the air/water interface using surface viscometry. Part 3.—Mechanism

Monolayers of stearic acid have been spread on calcium containing substrates and new data obtained on the surface viscosity, force area and surface potential characteristics of the films, under a variety of experimental conditions. The mechanism of the reaction and the nature of the reaction product are discussed.

Surface Soil Textural and Potential Erodibility Characteristics of Some Southern Sierra Nevada Forest Sites

AbstractAnalyses of texture and potential erodibility were made on 208 samples of residual, upland forest soils collected at elevations from 6,500 to 8,000 feet in the southern Sierra Nevada in California. Multiple regression tests showed that soil texture and erodibility indexes were significantly related to variation in parent rock type, vegetative cover type, aspect, slope, and elevation. Prediction equations implied that granitic forest soils at high elevations may be twice as erodible as soils developed under similar soil forming conditions at low elevations.