Electrostatic Potential Barrier Research Articles

Polyelectrolyte Brush Interacting with Ampholytic Nanoparticles as Coarse-Grained Models of Globular Proteins: Poisson-Boltzmann Theory.

The self-consistent field Poisson-Boltzmann framework is applied to analyze equilibrium partitioning of ampholytic nanoparticles (NPs) between buffer solution and polyelectrolyte (PE) polyanionic brush. We demonstrate that depending on pH and salt concentration in the buffer solution, interactions between ionizable (acidic and basic) groups on the NP surface and electrostatic field created by PE brush may either lead to the spontaneous uptake of NPs or create an electrostatic potential barrier, preventing the penetration of NPs inside PE brush. The capability of PE brush to absorb or repel NPs is determined by the shape of the insertion free energy that is calculated as a function of NP distance from the grafting surface. It is demonstrated that, at a pH value below or slightly above the isoelectric point (IEP), the electrostatic free energy of the particle is negative inside the brush and absorption is thermodynamically favorable. In the latter case, the insertion free energy exhibits a local maximum (potential barrier) at the entrance to the brush. An increase in pH leads to the shallowing of the free energy minimum inside the brush and a concomitant increase in the free energy maximum, which may result in kinetic hindering of NP uptake. Upon further increase in pH the insertion free energy becomes positive, making NP absorption thermodynamically unfavorable. An increase in salt concentration diminishes the depth of the free energy minimum inside the brush and eventually leads to its disappearance. Hence, in accordance with existing experimental data our theory predicts that an increase in salt concentration suppresses absorption of NPs (protein globules) by PE brush in the vicinity of IEP. The interplay between electrostatic driving force for NP absorption and osmotic repelling force (proportional to NP volume) indicates that for large NPs with relatively small number of ionizable groups osmotic repulsion overcomes electrostatic attraction preventing thereby absorption of NPs by PE brush.

Disorder effects on the ballistic transport of gated phosphorene superlattices

In this paper, we carry out a theoretical study of the electronic ballistic transport in gated phosphorene superlattices. Our work is focused on the effects by the random introduction of structural disorder in the electrostatic potential barriers. Specifically, we consider various degrees of disorder in the width and height of the barriers. To explain the transport of the charge carriers (electrons and holes) in the armchair direction of phosphorene, we employ a low-energy two-band Hamiltonian derived from the tight-binding model. The transmission and conductance are calculated by the transfer matrix technique and the Landauer-B\"uttiker formalism, respectively. We have found that both types of disorder affect the transmission and conductance in different ways, and we also found distinct effects on the charge carriers. In general, the disorder significantly reduces the transmission as well as the peak zones associated with the tunneling effect. Particularly, for disorder in the width, the transmission miniband structure is greatly degraded, while for disorder in the height, the miniband structure is preserved. The variation in the width of the barriers interferes directly with the Fabry-P\'erot resonances of the propagating waves, while the variation in the height mainly reduces the magnitude of the transmission due to the dominance of evanescent waves. Consequently, the conductance loses its oscillatory characteristic and experiences flattening under the influence of disorder of the width, in contrast with the disorder of the height in which the oscillation prevails. Finally, we found that both types of disorder induce a redistribution of electron states. Specifically, the allowed energy bands are increased, and the occupation number as well as the accumulation of states are greatly reduced, which is in accordance with the effects of disorder observed in the transport properties.

Theory of sub-Sharvin charge transport in graphene disks

Ballistic graphene samples in a multimode regime show the sub-Sharvin charge transport, characterized by the conductance reduced by a factor of $\pi/4$ comparing to standard Sharvin contacts in two-dimensional electron gas, and the shot-noise power enhanced up to $F\approx{}1/8$ (with $F$ the Fano factor) [Phys. Rev. B 104, 165413 (2021)]. Here we consider the disk-shaped (Corbino) setup in graphene, with inner radius $r_1$ and outer radius $r_2$, finding that the multimode conductance is slightly enhanced for any $r_1<r_2$, reaching $(4\!-\!\pi)\approx{}0.8684$ of the Sharvin value for $r_1\ll{}r_2$. At the same limit, the Fano factor is reduced, approaching $(9\pi-28)/(12-3\pi)\approx{}0.1065<1/8$. Closed-form approximating expressions for any $r_1/r_2$ ratio are derived supposing incoherent scattering of Dirac fermions on asymmetric double barrier and compared with exact numerical results following from the mode-matching method. Sub-Sharvin values are restored in the narrow-disk limit $r_1/r_2\rightarrow{}1$. For experimentally-accessible radii ratios $0.5\leqslant{}r_1/r_2\leqslant{}0.8$ both the conductance and the Fano factor are noticeably closer to the values predicted for the $r_1\ll{}r_2$ limit, yet still differ from standard Sharvin transport characteristics. The system behavior upon tuning the electrostatic potential barrier from a rectangular to parabolic shape is studied numerically, and the crossover from the sub-Sharvin to standard Sharvin transport regime is demonstrated. Implications for a finite section of the disk are also discussed.

Work function of the oxygen functionalized graphenic surfaces – Integral experimental and theoretical approach

The effect of oxygen plasma functionalization of graphenic surface was thoroughly investigated experimentally (SEM, XPS, Raman spectroscopy, work function measurements, TG) and corroborated by DFT molecular modeling using periodic slabs (work function, surface dipoles, EF/DOS). It was found that the introduction of oxygen substantially modified the electrodonor properties of the graphenic surface and the work function changed in a non-monotonous way upon the plasma treatment time. At the short contact time (5–30 s) the work function significantly increased from 4.2 eV (parent graphenic surface) to 5.6 eV and after passing the maximum value it reached plateau at the level of 5.2 eV after 100–150 s. The XPS revealed that the plasma treatment leads to an increase in the oxygen surface concentration (up to ∼10 at.%). A comparison of SEM images and Raman spectra of unmodified and plasma-modified graphenic surfaces indicated that the induced changes are limited to the outermost surface. Indeed, the TGA stability profiles did not indicate any bulk structural changes. Based on the experimental and DFT results, the molecular models of the surface modification process was proposed taking into account the various location of surface oxygen functionalities. At the early stage of the plasma treatment, a generation of strongly polar surface functional groups (surf-OH with the local dipole moment of2.7 D) leads to the formation of an electrostatic potential barrier for electron transfer from the surface (observed increase in work function). Prolonging modification results in the insertion of oxygen heteroatoms into the carbon surface, more uniform electron density distribution, and hence work function decrease. Since the electronic properties of graphenic materials play a key role in their various applications, the obtained results provide rational guidelines for their design and optimization.

Electrical responses and dielectric properties of (Zn2+ + F−) co–doped CaCu3Ti4O12 ceramics

The effects of Zn2+ and F− ions on the ceramic microstructure, electrical properties, and colossal dielectric response of CaCu3Ti4O12 were investigated. The dopants influenced the microstructure of the CaCu3Ti4O12. The replacement of Zn2+ and F− ions reduced the low–frequency loss tangent while retaining the high dielectric constant of CaCu3Ti4O12. In co–doped ceramics, the high dielectric permittivity of around 5.76 – 7.59 × 104 and low loss tangent of 0.082 – 0.085 can be attained. The decrease in the loss tangent of the co–doped ceramic samples is commensurate with the significant increase in the grain boundary (GB) resistance and breakdown electric field. The Cu+ and Ti3+ ions in CaCu3Ti4O12 were identified using X–ray photoelectron spectroscopy and were found to be decreased by co–doping with Zn2+ and F−. The presence of these ions may play a crucial role in the semiconducting grains. The substitution of Zn2+ and F− ions can increase the electrostatic potential barriers at the GBs, resulting in improved GB resistance.

Perovskite semiconductor-engineered cascaded molecular energy levels in naturally-sensitized photoanodes

Naturally-sensitized photoanodes in dye-sensitized solar cells (DSSCs) are promising alternatives to enhance photoabsorption, electron excitation/injection, but voltage loss remains a challenge. Here, we focus on understanding the cascading of energy levels in perovskite semiconductor cosensitized naturally-sensitized photoanodes to leverage forward charge transport addressing the voltage loss arising from ITO/TiO2 heterojunction's built-in potential. The β-carotene-sensitized TiO2 photoanode modified with methylammonium lead iodide (MAPbI3) co-sensitizer causes an upward shifting in TiO2 Fermi level (EF). This phenomenon is predominantly attributed to increased initially injected electrons due to low MAPbI3 bandgap and high visible-light absorption. Enhanced charge separation and injection mechanisms at the TiO2/MAPbI3 interface increase the effective density-of-states (DOS >2.46 × 1021 cm−3) in the TiO2 conduction band (CB) and hence decrease its work function to 4.82 eV. The decrease in TiO2 work function suppressed CB bending at ITO/TiO2 heterojunction, which minimized the photoinduced electrostatic potential barrier up to 13.1%. The reduced Schottky barrier (φSBH<0.52 eV) only allows electrons tunneling, while inhibited back-electron transport reduced both current leakage and voltage loss yielding in high open-circuit voltage (Voc increase by 120%) and power conversion efficiency (PCE increase by 240%). The MAPbI3 incorporation also broadened photoanode absorbance by 2-fold, paving the way towards perovskite semiconductor cosensitization to avoid voltage loss from bio-integrated photoanodes for photovoltaic and other optoelectronic and photonic applications. Future works will focus on studying the series resistance, cathode electrode coating uniformity, recombination kinetics, solid electrolytes, as well as other aspects typically related to increasing the photocurrent levels of this β-carotene-sensitized solar cell.

Modeling of the Buried Multiple Junction (BMJ) Detector in Reach-Through (RT) Conditions

A physically-based model of the Buried Multiple Junction (BMJ) detector has been established with consideration of the device operation in reach-through (RT) conditions. In such a condition, the breakdown voltage of one junction can shift depending on its adjacent junction’s bias voltage. The modeling approach consists in detecting RT conditions, determining depletion limits, electrostatic potential barrier height and thermionic emission current. It allows computations of the detector’s dark currents and spectral responses to monochromatic light illumination. Computations of the detector’s static characteristics have been compared with TCAD simulations and they are in good agreement, which is a model validation. The proposed model explains and determines the detector’s breakdown voltage shift behavior, as well as its changes of spectral responses depending on bias voltages.

An effective molecular blocker of ion channel of M2 protein as anti-influenza a drug

Design of a drug compound that can effectively bind to the M2 ion channel and block the diffusion of hydrogen ions (H+) through and inhibit influenza A virus replication is an important task. Known anti-influenza drugs amantadine and rimantadine have a weak effect on influenza A virus. A new class of positively charged, +2 e.u., molecules is proposed here to block diffusion of H+ ion through the M2 channel. Several drug candidates, derivatives of a lead compound (diazabicyclooctane), were proposed and investigated. Molecular dynamics of thermal fluctuations of M2 protein structure and ionization-conformation coupling of all the ionizable residues were simulated at physiological pH. The influence of the most probable mutations of key drug-binding amino acid residues in the M2 ion channel were investigated too. It is shown that the suggested new blocker has high binding affinity for the M2 channel. There are two in-channel binding sites of high affinity, the first one has H-bonds with two of four serine residues Ser-31A (B) or Ser-31C(D), and the second one has H-bonds with two of four histidine residues His-37A (B), or His-37C(D). The main advantage of the new drug molecule is the positive charge, +2 e.u., which creates a positive electrostatic potential barrier (in addition to a steric one) for a transfer of H+ ion through M2 channel and may serve as an effective anti-influenza A virus drug. Communicated by Ramaswamy H. Sarma

Elucidating the Structural Basis of the Intracellular pH Sensing Mechanism of TASK-2 K2P Channels.

Two-pore domain potassium (K2P) channels maintain the cell’s background conductance by stabilizing the resting membrane potential. They assemble as dimers possessing four transmembrane helices in each subunit. K2P channels were crystallized in “up” and “down” states. The movements of the pore-lining transmembrane TM4 helix produce the aperture or closure of side fenestrations that connect the lipid membrane with the central cavity. When the TM4 helix is in the up-state, the fenestrations are closed, while they are open in the down-state. It is thought that the fenestration states are related to the activity of K2P channels and the opening of the channels preferentially occurs from the up-state. TASK-2, a member of the TALK subfamily of K2P channels, is opened by intracellular alkalization leading the deprotonation of the K245 residue at the end of the TM4 helix. This charge neutralization of K245 could be sensitive or coupled to the fenestration state. Here, we describe the relationship between the states of the intramembrane fenestrations and K245 residue in TASK-2 channel. By using molecular modeling and simulations, we show that the protonated state of K245 (K245+) favors the open fenestration state and, symmetrically, that the open fenestration state favors the protonated state of the lysine residue. We show that the channel can be completely blocked by Prozac, which is known to induce fenestration opening in TREK-2. K245 protonation and fenestration aperture have an additive effect on the conductance of the channel. The opening of the fenestrations with K245+ increases the entrance of lipids into the selectivity filter, blocking the channel. At the same time, the protonation of K245 introduces electrostatic potential energy barriers to ion entrance. We computed the free energy profiles of ion penetration into the channel in different fenestration and K245 protonation states, to show that the effects of the two transformations are summed up, leading to maximum channel blocking. Estimated rates of ion transport are in qualitative agreement with experimental results and support the hypothesis that the most important barrier for ion transport under K245+ and open fenestration conditions is the entrance of the ions into the channel.

Aluminosilicate Mineralogy and the Sorption of Organic Cations: Interplay between Electrostatic Barriers and Compound Structural Features.

Current predictive models of organic cation sorption assume that sorbates interact with all sites on aluminosilicate minerals in the same manner. To examine whether differences in aluminosilicate structure and the resultant changes in electrostatic potential influence the sorption of organic cations, seven smectites were chosen with different proportions of isomorphic substitutions (origin of clay charge) located in octahedral versus tetrahedral layers and with the presence or absence of aluminosilicate interlayers. Sorption coefficients for 14 benzylamine derivatives with systematic differences in compound structures were collected to understand the possible influence of aluminosilicate mineralogy. Benzylamine compounds with methyl group substitution on the charged amine or with electron-donating or -withdrawing ring substituents displayed decreases in cation exchange-normalized sorption coefficients (KCEC), by up to one order of magnitude, between hectorite (100% isomorphic substitution in the octahedral layer) and nontronite (100% isomorphic substitution in the tetrahedral layer). To understand this difference across aluminosilicates, stochastic molecular models of the various aluminosilicate minerals with interlayers were performed. These models showed that negative charge density associated with tetrahedral sites results in high positive electrostatic energy barriers within the interlayer, creating a penalty for compounds with positive charge spread over a larger compound surface area as occurs from primary to quaternary amines. Conversely, clays with charge originating from octahedral sites produce low electrostatic potential barriers within the interlayer, decreasing the penalty for quaternary amine sorption. Trends for nine cationic pharmaceutical compounds, which varied in size, group alkylation, and/or polar substituents, demonstrated similar decreases in KCEC values to aluminosilicate minerals with high electrostatic energy barriers. Overall, aluminosilicate mineralogy was found to exert a large influence (0.5-1 order of magnitude in sorption coefficients) on organic cation sorption. The application of atomistic electrostatic potential mapping of both sorbent and sorbate structures provided insights to explain trends in sorption coefficients that could not be described by the basic electrostatic potential theory or by assuming that sorbate structure moieties yielded additive sorption contributions.

Design of an Efficient Inhibitor for the Influenza A Virus M2 Ion Channel

Influenza A virus is capable of rapidly infecting large human populations, warranting the development of novel drugs to efficiently inhibit virus replication. A transmembrane ion channel formed by the M2 protein plays an important role in influenza virus replication. A reasonable approach to designing an effective antivirus drug is constructing a molecule that binds in the M2 transmembrane proton channel, blocks H^(+) proton diffusion through the channel, and thus the influenza A virus cycle. The known anti-influenza drugs amantadine and rimantadine have a weak effect on influenza A virus replication. A new class of positively charged molecules, diazabicyclooctane derivatives with a constant charge of +2, was proposed to block proton diffusion through the M2 ion channel. Molecular dynamics simulations were performed to study the temperature fluctuations in the M2 structure, and ionization states of histidine residues were established at physiological pH values. Two types of diazabicyclooctane derivatives were analyzed for binding with the M2 ion channel. An optimal structure was determined for a blocker to most efficiently bind with the M2 ion channel and block proton diffusion. The new molecule is advantageous over amantadine and rimantadine in having a positive charge of +2, which creates a positive electrostatic potential barrier to proton transport through the M2 ion channel in addition to a steric barrier.

Charge Neutralization in the Core of Plasma Treatment

At the COVID-19 time, viruses could easily contaminate humans, animals, and plants. In charge of several hospitalizations, many deaths, and widespread crop destruction, viruses lead to a considerable medical, economical, and biological burden. Several applied disinfection techniques are efficient and unfortunately possess inherent disadvantages. As a fresh, performant and green technology, cold plasma has attracted attention for its efficacy in viruses’ killing. This work presents a brief summary of the late developments in the domain of applying cold plasma in dealing with viruses. The “plasma” term refers to any gas-discharged setup with ions and energetic electrons, where charged particles and plasma-generated highly reactive species dictate the physiochemical features of the whole system. When the electron gaining sufficient energy to defeating the electrostatic potential barrier, the electron will be stripped away to produce a free electron and a positively charged ion. Such a phenomenon is named ionization. This phenomenon is similar to the coagulation/flocculation (C/F) processes that are due to charge neutralization (CN) and sweep flocculation (SF) mechanisms. Colloids may be inorganic (such as clay particles), organic (like humic particles and macromolecules), or biological (bacteria, viruses, etc.). The consequence of this smallness in size and mass and largeness in surface area is that in colloidal suspensions: gravitational effects are negligible and surface phenomena predominate. Hence, during C/F process, colloids are removed by CN and SF mechanisms which act on the anionic charge of the colloid by its neutralization prior to its removal by sedimentation/filtration. There is a CN mechanism dictated by the presence of positive ions formed through plasma utilization. Further research is requested to understand the CN mechanism related to plasma treatment and optimize such a promising technology.

Apparent Potential Difference Boosting Directional Electron Transfer for Full Solar Spectrum‐Irradiated Catalytic H2 Evolution

AbstractDirectional charge transfer among nanolayers of graphitic carbon nitride (g‐C3N4) is still inefficient because of the interlayer electrostatic potential barrier, which tremendously restricts the utilization of charges in conversion of solar energy into fuel. Herein, an apparent potential among nanolayers is introduced to boost interlayer electron transfer by curving planar g‐C3N4 nanosheets into carbon nitride square tubes (C3N4Ts), and Ni2P nanoparticles as electron acceptors are loaded on C3N4Ts (Ni2P/C3N4Ts) for highly efficient H2 evolution. Study results present H2‐evolution efficiency over the constructed Ni2P/C3N4Ts up to 19.25 mmol g−1 h−1 with a large number of visible H2 bubbles, which is more than 1.9 and 2.6 times of that over g‐C3N4 supported 1 wt%Pt and 3 wt%Pd, respectively. Density functional theory (DFT) and characterizations reveal efficient directional transfer through C3N4T interlayer (001) to Ni2P (111) is achieved under the apparent potential difference of C3N4Ts, which therefore ensures the high H2‐evolution performance of Ni2P/C3N4Ts. These results in the field of material engineering supply a novel strategy to boost directional charge transfer for solar energy conversion efficiency by introducing apparent potential difference.

Ultrahigh Permeable C2N-Inspired Graphene Nanomesh Membranes versus Highly Strained C2N for Reverse Osmosis Desalination.

The reverse osmosis (RO) desalination capability of hydrogenated and hydroxylated graphene nanomesh membranes (GNMs) inspired by the morphology of carbon nitride (C2N) has been studied by using molecular dynamics simulation. As an advantage, water permeance of the GNMs is found to be several orders of magnitude higher than that of the available RO filters and comparable with highly strained C2N (S-C2N) as follows: 6,6-H,OH > 12-H > S-C2N > 5,5-H,OH > 10-H. The reverse order is found for salt rejection, regardless of S-C2N. The hydrophilic character of the incorporated -OH functional group is believed to be responsible for linking the water molecules in feed and permeate sides via the formation of strong hydrogen bonds. This leads to a remarkable reduction in resistance of water molecules during penetration across GNMs. In fact, water permeance and salt rejection of the GNMs are controllable by adjusting the effective size and chemistry of their nanopores, while these kinds of adjustments are principally impossible for C2N, resulting in limiting the water permeance. More importantly, the C2N nanofilter works efficiently only under high tensile strain, which is not so straightforward in practice. These observations are also verified by computing electrostatic potential map interaction and barrier energies for transportation of water molecules/ions through GNMs based on quantum chemistry aspects.

Interfacial charge transfers and interactions drive rectifying and negative differential resistance behaviors in InAs/graphene van der Waals heterostructure

Vertical heterostructures of two-dimensional (2D) materials are excellent candidates for designing next-generation electronic devices with superior performance. By using both ab initio electronic calculations and quantum transport simulations, we investigated the electronic and transport properties of InAs/graphene heterostructure. The results reveal that electrons and holes accumulate at different layers after the adsorption of InAs layer, forming the built-in electronic field at the interface. The electrostatic potential energy of InAs layer is higher than that of graphene, and it favors more electrons transferring from InAs to graphene layer. Comparing the comment methods by introducing impurity and carriers' injection, rectifying and negative differential resistance behaviors can also be realized by the combined effects of electron-hole distribution, interfacial hybridization, and contact barrier in InAs/graphene heterostructure device. It shows that the rectifying ration gradually increases with bias voltage, and the negative differential resistance effect happens at either positive or at negative bias voltage regions. Electrostatic potential distribution and contact barrier play important roles in determining transport properties. Increasing interfacial hybridization is helpful for transmission enhancement in the weak interlayer interaction van der Waals heterostructure.

Tunable circular dipolelike system in graphene: Mixed electron-hole states

Coupled electron-hole states are realized in a system consisting of a combination of an electrostatic potential barrier and ring-shaped potential well, which resembles a circular dipole. A perpendicular magnetic field induces confined states inside the Landau gaps which are mainly located at the barrier or ring. Hybridizations between the barrier and ring states are seen as anticrossings in the energy spectrum. As a consequence, the energy levels show an oscillating dependence on the electrostatic potential strength in combination with an oscillating migration of the wave functions between the barrier and ring. At the anticrossing points the quantum state consists of a mixture of electron and hole. The present system mimics closely the behavior of a relativistic dipole on gapped graphene.

Distribution of Ionizable Groups in Polyampholyte Microgels Controls Interactions with Captured Proteins: From Blockade and "Levitation" to Accelerated Release.

A striking discovery in our work is that the distribution of ionizable groups in polyampholyte microgels (random and core-shell) controls the interactions with the captured proteins. Polyampholyte microgels are capable to switch reversibly their charges from positive to negative depending on pH. In this work, we synthesized differently structured polyampholyte microgels with controlled amounts and different distribution of acidic and basic moieties as colloidal carriers to study the loading and release of the model protein cytochrome c (cyt-c). Polyampholyte microgels were first loaded with cyt-c using the electrostatic attraction under pH 8 when the microgels were oppositely charged with respect to the protein. Then the protein release was investigated under different pH (3, 6, and 8) both with experimental methods and molecular dynamics simulations. For microgels with a random distribution of ionizable groups complete and accelerated (compared to polyelectrolyte counterpart) release of cyt-c was observed due to electrostatic repulsive interactions. For core-shell structured microgels with defined ionizable groups, it was possible to entrap the protein inside the neutral core through the formation of a positively charged shell, which acts as an electrostatic potential barrier. We postulate that this discovery allows the design of functional colloidal carriers with programmed release kinetics for applications in drug delivery, catalysis, and biomaterials.

Transport characteristics and dwell time in a bilayer phosphorene barrier

In this paper, transport properties, dwell time and electron conductance were theoretically investigated through a rectangular electrostatic potential barrier in bilayer phosphorene and compared the results with monolayer phosphorene and graphene. It has been shown that in bilayer phosphorene, in the presence of an interlayer induced bias, a four-band approximation describes transport process in the system. The results show that interlayer bias parameter drastically affect transport properties. These effects include: (1) appearance of eight transmission and reflection coefficients from a band within the same band and between the two bands; (2) appearance of the anti-Klein tunnelling phenomenon and tuning the bias of system in such a way which is observed in specified biases and removed in other biases; (3) tuning conductance of the system. Results of dwell time in bilayer phosphorene show that this parameter in terms of barrier thickness does not have a strictly ascending behaviour and in limited range of incident energies (incident angles), the dwell time in the barrier reduces significantly which can be exploited in designing switching devices in nano-electronics. We found that increasing the interlayer bias decreases the intrinsic gap of the bilayer phosphorene which enables us to control the electron transmission rate in the system. In addition, our findings also demonstrate that by tuning the interlayer bias, a large electrical conductance can be achieved which can be used in semiconductor technology. Our study could serve as a basis for investigations of the basic physics of tunnelling mechanisms and using bilayer phosphorene as a proper candidate in low dimensional semiconductor industry.

Influence of metal/semiconductor interface on attainable piezoelectric and energy harvesting properties of ZnO

The piezoelectric coefficient is a measure to quantify the potential use of a material in energy harvesting and sensor applications. High concentration of free charge carriers in piezoelectric materials can significantly impede the use of generated piezoelectric charge. In this study, undoped semiconducting ZnO single crystals with both Ohmic and Schottky contacts were prepared to quantify the effective piezoelectric response at temperatures from 20 °C to −140 °C and frequencies of mechanical loading from 0.5 Hz to 160 Hz. It was demonstrated that the formation of an electrostatic potential barrier at the metal-semiconductor interface increases the overall resistance, which provides access to unbiased piezoelectric coefficients of ZnO single crystals even at room temperature. These findings were verified using semiconducting ZnO for energy harvesting at room temperature and relatively low loading frequency.

Effect of thermal history on structural, microstructural properties and J – E characteristics of CaCu3Ti4O12 polycrystalline ceramic

We report, the effect of heat treatments slow cooling, rapid thermal cooling (quenching) and microwave-assisted heating, on structural, microstructural and J – E characteristics of CaCu3Ti4O12 polycrystalline ceramic. Rietveld refinement of X-ray data confirms the emergence of the mono-phasic cubic perovskite structure, diffraction line broadening and change in the relative intensity of diffraction peaks while scanning electron microscopy revealed completely different grain morphology. The observed modifications have been discussed in detail. The strong nonlinear J – E characteristics over the wide temperature range (300–823 K) indicated the existence of a Schottky-type electrostatic potential barrier at the grain boundaries. The parameters, nonlinear coefficient, threshold electric field, potential barrier height suggest suitability of the materials for low voltage varistor applications.