Local Dielectric Constant Research Articles

Water's surface dielectric

Water Properties Theoretical studies predict that the inhibition of rotational motion of water near a solid surface will decrease its local dielectric constant. Fumagalli et al. fabricated thin channels in insulating hexagonal boron nitride on top of conducting graphene layers (see the Perspective by Kalinin). The channels, which varied in height from 1 to 300 nanometers, were filled with water and capped with a boron nitride layer. Modeling of the capacitance measurements made with an atomic force microscope tip revealed a surface-layer dielectric constant of 2, compared with the bulk value of 80 for water. Science , this issue p. [1339][1]; see also p. [1302][2] [1]: /lookup/doi/10.1126/science.aat4191 [2]: /lookup/doi/10.1126/science.aat9875

Electrically switchable metadevices via graphene.

Metamaterials bring subwavelength resonating structures together to overcome the limitations of conventional materials. The realization of active metadevices has been an outstanding challenge that requires electrically reconfigurable components operating over a broad spectrum with a wide dynamic range. However, the existing capability of metamaterials is not sufficient to realize this goal. By integrating passive metamaterials with active graphene devices, we demonstrate a new class of electrically controlled active metadevices working in microwave frequencies. The fabricated active metadevices enable efficient control of both amplitude (>50 dB) and phase (>90°) of electromagnetic waves. In this hybrid system, graphene operates as a tunable Drude metal that controls the radiation of the passive metamaterials. Furthermore, by integrating individually addressable arrays of metadevices, we demonstrate a new class of spatially varying digital metasurfaces where the local dielectric constant can be reconfigured with applied bias voltages. In addition, we reconfigure resonance frequency of split-ring resonators without changing its amplitude by damping one of the two coupled metasurfaces via graphene. Our approach is general enough to implement various metamaterial systems that could yield new applications ranging from electrically switchable cloaking devices to adaptive camouflage systems.

Transport phenomena of electrons at the carbon nanotube interface with molecular adsorption

The electric conductance of carbon-nanotube (CNT) films is affected by gas adsorption. Previous studies have shown that the adsorption of gas molecules on the CNT/CNT interface is the key to the changing CNT-film conductance. However, it is still unclear how the gas molecules affect the electric conduction of the CNT/CNT interface or its electron transport properties. We present here a study on the effects of gas-molecule adsorption on the CNT/CNT interface using a fluctuation-induced tunneling (FIT) model of the CNT-film electrical conduction. We demonstrated that the CNT-film conduction follows the FIT model, and the subsequently estimated electrostatic potential between the CNT/CNT interfaces was in good agreement with estimates from density functional theory simulations. Since the FIT model treats the CNT/CNT interface as a parallel-plate capacitor, we propose a modified FIT model that accounts for the change in the dielectric constant at the CNT/CNT interface due to the adsorption of gas molecules. This model well explained the electric-conductance change of the CNT film with respect to the gas pressure. Finally, we found that the adsorbed gas molecules affected the local dielectric constant at the CNT/CNT interface.

Evaluation of solvation free energies for small molecules with the AMOEBA polarizable force field.

The effects of electronic polarization in biomolecular interactions will differ depending on the local dielectric constant of the environment, such as in solvent, DNA, proteins, and membranes. Here the performance of the AMOEBA polarizable force field is evaluated under nonaqueous conditions by calculating the solvation free energies of small molecules in four common organic solvents. Results are compared with experimental data and equivalent simulations performed with the GAFF pairwise‐additive force field. Although AMOEBA results give mean errors close to “chemical accuracy,” GAFF performs surprisingly well, with statistically significantly more accurate results than AMOEBA in some solvents. However, for both models, free energies calculated in chloroform show worst agreement to experiment and individual solutes are consistently poor performers, suggesting non‐potential‐specific errors also contribute to inaccuracy. Scope for the improvement of both potentials remains limited by the lack of high quality experimental data across multiple solvents, particularly those of high dielectric constant. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

Surface‐enhanced Raman scattering properties of Lewis acid–base complexes ofp‐hydroxybenzoic andp‐mercaptobenzoic acids with CO2in the presence of silver

Effects of local environment on the sensitivity of surface‐enhanced Raman scattering have been recently considered as an important issue in experiments involving charge‐transfer mechanism between the adsorbed molecules and the metal surface. To theoretically investigate this issue, we consider the complexation ofp‐hydroxybenzoic acid (PHBA) andp‐mercaptobenzoic acid (PMBA) with carbon dioxide (CO2), and in contact with silver (Ag), by means of ab initio calculations. Within the Møller–Plesset perturbation theory, it is demonstrated that the carboxylic group of PHBA or PMBA can act as an electron‐donating site, binding the electron‐deficient carbon atom of CO2, via a Lewis acid–base (LA–LB) interaction. Changes in the vibrational spectra of these molecules are carefully determined and attributed to both LA–LB complexation with CO2and interaction with Ag. Calculated Raman scattering shifts for the complexes also indicate that the chemical nature of the substituent group atparaposition of the aromatic ring can dramatically alter the signal of typical shifts expected for LA–LB complexes, as well as affect surface‐enhanced Raman scattering intensities. The LA–LB complexation is also reinforced by the ultraviolet–visible absorption spectra for the complexes, calculated within time‐dependent density functional theory and combined with the polarizable continuum model, employed to simulate the local environment dielectric constant. It is demonstrated that the lowest singletπ–π* excitation of both LA–LB complexes, PHBA and PMBA weakly bound to CO2, is significantly red shifted, which gives evidence for such a complexation. Copyright © 2016 John Wiley & Sons, Ltd.

Contraction and Expansion of Stimuli-Responsive DNA Bonds in Flexible Colloidal Crystals.

DNA surface ligands can be used as programmable "bonds" to control the arrangement of nanoparticles into crystalline superlattices. Here, we study the intrinsic responsiveness of these DNA bonds to changes in local dielectric constant (εr) as a new approach to dynamically modulate superlattice structure. Remarkably, ethanol (EtOH) addition can be used to controllably tune DNA bond length from 16 to 3 nm and to increase bond stability by >40 °C, while retaining long-range order and crystal habit. Interestingly, we find that these structural changes, which involve the expansion and contraction of crystals by up to 75% in volume, occur in a cooperative fashion once a critical percentage of EtOH is reached. These results provide a facile and robust approach to create stimuli-responsive lattices, to access high volume fractions, and to improve thermal stability.

Shift of localized surface plasmon resonance in monolayer of small gold nanoparticles: Simulation predictions of interparticle coupling

Localized surface plasmon resonance of gold nanoparticle layer is investigated by the experiment as well as theoretical calculations. The limits of analytical models are illustrated for compact nanoparticle film revealing signify cant discrepancy between experimental and simulated results while the numerical calculations based on finite-difference time-domain using thin film optical parameters are shown as suitable. There it is shown that 3D finite-difference time-domain simulation can be replaced by 2D simulation without losing accuracy of the calculation of localized surface plasmon resonance. The dependence of the localized surface plasmon resonance wavelength on the nanoparticle size, separation as well as local dielectric constant of surrounding environment is presented and applied for the real nanoparticle size and separation distributions observed in the experiment. Tuning of plasmon resonance in a wide range is demonstrated as a promising way for further applications.

Impact of defects on local optical dielectric properties of Si/SiO2 interfaces by layered capacitor modeling

We present a new method to investigate the local optical dielectric permittivity using layered capacitors. The method has been applied to study the optical dielectric constants of Si/SiO2 structures without defects, with dangling bonds, and with dangling bonds passivated by H. For each of the three structures, models composed of 5, 7, and 12 Si layers were studied, and the effect of the Si layer thickness was assessed. The different local optical dielectric constants in the adjacent Si interface region were obtained for the nine models, and the effect of the Si layer thickness, the bond lengths, and the oxidation states of Si at the interface were analyzed. The results showed that the local optical dielectric constant of the structure with dangling bonds in the region adjacent to the Si interface was larger than that of the structure with no defects; and the effect of the interface defect Si+1 on the dielectric constant is stronger than that of the Si layer thickness, and effect scope of Si+1 reached approximate 7 A in silicon region.

Membrane Lateral Pressure Controls Hydration and Water Mobility at the Copper-Binding Site of the P1B-type Copper ATPase CopA from Legionella Pneumophila

P-type ATPases couple ATP hydrolysis to ion transport. We have reconstituted the copper-transporting P1B-type ATPase LpCopA from Legionella pneumophila into lipid nanodiscs in order to study the influence of membrane lateral pressure on the functionally relevant intra-membrane protein hydration at the ion-binding site. Using site-directed mutagenesis, the solvatochromic fluorophore BADAN was covalently linked to the cysteine residues at the conserved copper-binding CPC motif on transmembrane helix 4. The decomposition of the fluorescence spectra of labeled LpCopA in the micellar and the lipid-inserted state shows that membrane lateral pressure reduces hydration and water mobility in the environment of the more buried Cys-382 with a concomitant change of the local dielectric constant by −9. In contrast, the environment of Cys-384 which is located closer to the putative membrane surface, resembles a “hydrophobic gate” with low water mobility that is little affected by insertion into a bilayer (change of local dielectric constant by −3). The asymmetric hydration and water mobility around the CPC motif provides Cys-382 with a highly dynamic hydration. The data show that membrane lateral pressure may provide a restoring force in hydration / dehydration cycles around Cys-382 in the transmembrane domain during catalytic activity. The lower hydration and mobility in the Cys-384 environment, on the other hand, would favor the dehydration of copper and hinder its re-solvation from the intracellular side.

Electronic Structure Study And Dielectric Properties Of Amorphous ZrO2 And HfO2

ZrO2 and HfO2 powder samples were prepared by using the chemical precipitation method and subsequent annealing. Crystal structure, local electronic structure and dielectric constant of amorphous and crystalline powders of ZrO2 and HfO2 have been examined using the synchrotron X-ray diffraction, O K-edge X-ray absorption spectroscopy, Zr 3d and Hf 4f core-level X-ray photoelectron spectroscopy and temperature dependent dielectric measurements, respectively. Amorphous ZrO2 and HfO2 powders exhibit a local tetragonal structure, with mixed +3 and +4 valence states of Zr and Hf ions, and demonstrated the high dielectric performance. After the heat treatment, the tetragonal phase transforms into the monoclinic phase with dominant +4 valence state of Zr and Hf ions and the larger sized ZrO2 and HfO2 nanoparticles exhibited low dielectric constant. The manifestation of high dielectric constants in the amorphous ZrO2 and HfO2 samples is because of the hopping of electrons between the Zr +3 -Zr +4 and Hf +3 -Hf +4 networks.

Empirical estimation of local dielectric constants: Toward atomistic design of collagen mimetic peptides.

One of the key challenges in modeling protein energetics is the treatment of solvent interactions. This is particularly important in the case of peptides, where much of the molecule is highly exposed to solvent due to its small size. In this study, we develop an empirical method for estimating the local dielectric constant based on an additive model of atomic polarizabilities. Calculated values match reported apparent dielectric constants for a series of Staphylococcus aureus nuclease mutants. Calculated constants are used to determine screening effects on Coulombic interactions and to determine solvation contributions based on a modified Generalized Born model. These terms are incorporated into the protein modeling platform protCAD, and benchmarked on a data set of collagen mimetic peptides for which experimentally determined stabilities are available. Computing local dielectric constants using atomistic protein models and the assumption of additive atomic polarizabilities is a rapid and potentially useful method for improving electrostatics and solvation calculations that can be applied in the computational design of peptides.

Millimeter-wave near-field imaging with bow-tie antennas.

A near-field reflectometry experiment operating at 60 GHz is built in view of material and circuit inspection. Experiments are always obtained in constant height mode of operation. The bow-tie near-field probe acts mostly as a linearly-polarized electric dipole and allows strongly subwavelength resolution of ≈ λ/130. Its interaction with sample is shown polarization dependent and sensitive to both the local topography and the local dielectric constant or metal conductivity. Resonant and non-resonant probes are both evaluated.

Imaging the effects of annealing on the polymorphic phases of poly(vinylidene fluoride).

The effect of annealing on the phase transformation and the dielectric properties of poly(vinylidene fluoride) (PVDF) is explored using quasi-single molecule (quasi-SM) microscopy. The solvatochromic properties of nile red (NR) are employed to measure the spatial distribution of the local dielectric constant (ε) in ∼30 μm thick PVDF films before and after annealing at 90 °C. The results presented here demonstrate that nonannealed films exhibit much larger ε distributions, both in terms of magnitude and distribution, when compared to annealed films. The polymorphic phase of PVDF before and after annealing is also confirmed using X-ray diffraction. Nonannealed films are found to be in the γ-phase with annealing promoting the transition to primarily β-phase. Combining these results, we conclude that the decrease in ε with annealing time is due to the phase transformation from γ- to β-phase. Using quasi-SM imaging techniques one can readily visualize the ε environments present within different polymorphic phases of PVDF.

Mixed finite elements for electromagnetic analysis

The occurrence of spurious solutions is a well-known limitation of the standard nodal finite element method when applied to electromagnetic problems. The two commonly used remedies that are used to address this problem are (i) The addition of a penalty term with the penalty factor based on the local dielectric constant, and which reduces to a Helmholtz form on homogeneous domains (regularized formulation); (ii) A formulation based on a vector and a scalar potential. Both these strategies have some shortcomings. The penalty method does not completely get rid of the spurious modes, and both methods are incapable of predicting singular eigenvalues in non-convex domains. Some non-zero spurious eigenvalues are also predicted by these methods on non-convex domains. In this work, we develop mixed finite element formulations which predict the eigenfrequencies (including their multiplicities) accurately, even for nonconvex domains. The main feature of the proposed mixed finite element formulation is that no ad-hoc terms are added to the formulation as in the penalty formulation, and the improvement is achieved purely by an appropriate choice of finite element spaces for the different variables. We show that the formulation works even for inhomogeneous domains where ‘double noding’ is used to enforce the appropriate continuity requirements at an interface. For two-dimensional problems, the shape of the domain can be arbitrary, while for the three-dimensional ones, with our current formulation, only regular domains (which can be nonconvex) can be modeled. Since eigenfrequencies are modeled accurately, these elements also yield accurate results for driven problems.

Dielectric dependence of single-molecule photoluminescence intermittency: nile red in poly(vinylidene fluoride).

The dependence of single-molecule photoluminescence intermittency (PI) or “blinking” on the local dielectric constant (ε) is examined for nile red (NR) in thin films of poly(vinylidene fluoride) (PVDF). In previous studies, variation of the local dielectric constant was accomplished by studying luminophores in chemically and structurally different hosts. In contrast, the NR/PVDF guest–host pair allows for the investigation of PI as a function of ε while keeping the chemical composition of both the luminophore and host unchanged. The solvatochromic properties of NR are used to measure the local ε, while fluctuations in NR emission intensity over time provide a measure of the PI. PVDF is an ideal host for this study because it provides submicron-sized dielectric domains that vary from nonpolar (ε ≈ 2) to very polar (ε ≈ 70). The results presented here demonstrate that the local dielectric environment can have a pronounced effect on PI. We find that the NR emissive events increase 5-fold with an increase in ε from 2.2 to 74. A complex dependence on ε is also observed for NR nonemissive event durations, initially increasing as ε increases from 2.2 to 3.4 but decreasing in duration with further increase in ε. The variation in emissive event durations with ε is reproduced using a photoinduced electron-transfer model involving electron transfer from NR to PVDF. In addition, an increase in NR photostability with an increase in ε is observed, suggesting that the dielectric environment plays an important role in defining the photostability of NR in PVDF.

Ester carbonyl vibration as a sensitive probe of protein local electric field.

The ability to quantify the local electrostatic environment of proteins and protein/peptide assemblies is key to gaining a microscopic understanding of many biological interactions and processes. Herein, we show that the ester carbonyl stretching vibration of two non-natural amino acids, L-aspartic acid 4-methyl ester and L-glutamic acid 5-methyl ester, is a convenient and sensitive probe in this regard, since its frequency correlates linearly with the local electrostatic field for both hydrogen-bonding and non-hydrogen-bonding environments. We expect that the resultant frequency-electric-field map will find use in various applications. Furthermore, we show that, when situated in a non-hydrogen-bonding environment, this probe can also be used to measure the local dielectric constant (ε). For example, its application to amyloid fibrils formed by Aβ(16-22) revealed that the interior of such β-sheet assemblies has an ε value of approximately 5.6.

Ester Carbonyl Vibration as a Sensitive Probe of Protein Local Electric Field

AbstractThe ability to quantify the local electrostatic environment of proteins and protein/peptide assemblies is key to gaining a microscopic understanding of many biological interactions and processes. Herein, we show that the ester carbonyl stretching vibration of two non‐natural amino acids, L‐aspartic acid 4‐methyl ester and L‐glutamic acid 5‐methyl ester, is a convenient and sensitive probe in this regard, since its frequency correlates linearly with the local electrostatic field for both hydrogen‐bonding and non‐hydrogen‐bonding environments. We expect that the resultant frequency–electric‐field map will find use in various applications. Furthermore, we show that, when situated in a non‐hydrogen‐bonding environment, this probe can also be used to measure the local dielectric constant (ε). For example, its application to amyloid fibrils formed by Aβ16–22 revealed that the interior of such β‐sheet assemblies has an ε value of approximately 5.6.

Fabrication of Coaxial and Triaxial Atomic Force Microscope Imaging Probes

ABSTRACTHerein, we detail the fabrication of atomic force microscope (AFM) probes that have two and three coaxial electrodes at their tips. This fabrication strategy leverages the availability of conductive AFM probes and encompasses a general method for processing their complex and delicate structure through the deposition of insulating and conductive layers by shadow masked chemical and physical vapor deposition, respectively. Focused ion beam milling is used to expose the two electrode (coaxial) or three electrode (triaxial) structures at the tip of the AFM probe. Finally, we discuss new imaging modalities enabled by these probes including electrically-driven contact resonance imaging for nanoscale mechanical characterization, imaging the local dielectric constant by quantifying the dielectrophoretic force, and trapping functional particles at the tip of a probe using dielectrophoresis. These imaging techniques illustrate the generality and utility of this fabrication approach and suggest that such probes could be widely applied to image many nanoscale materials.

Band offsets and dielectric properties of the amorphous Si3N4/Si(100) interface: A first-principles study

By combining classical and ab-initio simulations, we generated a structural model of an amorphous silicon nitride/silicon(100) interface and we investigated its electronic and dielectric properties from first principles. We computed the valence band offset using many-body perturbation theory, within the GW approximation, and we found results in good agreement with experiments. Based on the computed local band edges and dielectric constants, we estimate that bulk properties are recovered for nitride films with thickness larger than 6–7 Å.

Measuring the spatial distribution of dielectric constants in polymers through quasi-single molecule microscopy.

The variation in dielectric constant is measured for thin films of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) using confocal fluorescence microscopy. Spatial variation in the local dielectric constant of the polymer films on the ~250 nm length scale is measured using the solvochromatic emission from incorporated nile red (NR) at "quasi-single molecule" (10(-7) M) and true single molecule (SM) concentrations (10(-9) M). Correlation of the NR fluorescence wavelength maximum with dielectric constant is used to transform images of NR's emission maxima to spatial variation in local dielectric constant. We demonstrate that the distributions of dielectric environments measured in the quasi- and true SM approaches are equivalent; however, the enhanced signal rates present in the quasi-SM approach result in this technique being more efficient. In addition, the quasi-SM technique reports directly on the continuous spatial variation in dielectric constant, information that is difficult to obtain in true SM studies. With regards to the polymers of interest, the results presented here demonstrate that a limited distribution of dielectric environments is present in PMMA; however, a broad distribution of environments exists in PVDF consistent with this polymer existing as a distribution of structural phases.