Electrons In Layer Research Articles

Electron\u2013hole superfluidity in strained Si/Ge type II heterojunctions

Excitons are promising candidates for generating superfluidity and Bose–Einstein condensation (BEC) in solid-state devices, but an enabling material platform with in-built band structure advantages and scaling compatibility with industrial semiconductor technology is lacking. Here we predict that spatially indirect excitons in a lattice-matched strained Si/Ge bilayer embedded into a germanium-rich SiGe crystal would lead to observable mass-imbalanced electron–hole superfluidity and BEC. Holes would be confined in a compressively strained Ge quantum well and electrons in a lattice-matched tensile strained Si quantum well. We envision a device architecture that does not require an insulating barrier at the Si/Ge interface, since this interface offers a type II band alignment. Thus the electrons and holes can be kept very close but strictly separate, strengthening the electron–hole pairing attraction while preventing fast electron–hole recombination. The band alignment also allows a one-step procedure for making independent contacts to the electron and hole layers, overcoming a significant obstacle to device fabrication. We predict superfluidity at experimentally accessible temperatures of a few Kelvin and carrier densities up to ~6 × 1010 cm−2, while the large imbalance of the electron and hole effective masses can lead to exotic superfluid phases.

A two-dimensional electron gas suspended above a neutralizing background

We consider a two-dimensional electron gas system consisting of a layer of electrons suspended above its jellium neutralizing background counterpart. We investigate the energy of the system in the Hartree–Fock approximation as a function of separation distance between the layer of electrons and the background. We find that the energy of the system is influenced by the separation distance in such a way that the new energy contribution originating from such a separation behaves as an effective kinetic energy term. The increase of the overall energy with increase of the separation distance adversely affects the stability of electron liquid states at high density. The results are derived for a fully spin-polarized (spinless) system of electrons in the thermodynamic limit, but can easily be generalized to a spin unpolarized state.

СКОЛЬКО ДОЛЖНО БЫТЬ ПЕРИОДОВ В ТАБЛИЦЕ Д.И. МЕНДЕЛЕЕВА

The article discusses a new approach to the formation of periods of the Periodic Table of Mendeleev. With the help of the new formula and the first proposed quantum states of the outer electron shells of atoms of chemical elements, the periods of the periodic table are reformatted. It is supposed to reduce the number of periods in the table by introducing the corresponding sub-periods. This is confirmed by the material given in the article. The following description of the order of formation of electron layers is proposed: the principal quantum number (n), then the newly proposed quantum states of electrons («first» and «second»), which in turn constitute the electronic configurations of sub-periods in periods, and only then the remaining quantum orbitals (s, p, d and f).

Oxygen Sensing of Pt/PEO-TiO2 in Humid Atmospheres at Moderate Temperatures

Here, we show that the presence of adsorbed water improves the oxygen-sensing properties of Pt/TiO at moderate temperatures. The studied interface is based on porous plasma electrolytic oxidized titanium (PEO-TiO) covered with platinum clusters. The electrical resistance across Pt/PEO-TiO is explained by an electronic depletion layer. Oxygen adsorbates further increase the depletion by inducing extrinsic interface states, which are occupied by TiO conduction band electrons. The high oxygen partial pressure in ambient air substantially limits the electron transport across the interface. Our DC measurements at defined levels of humidity at 30 C show that adsorbed water counteracts this shortcoming, allowing oxygen sensing at room conditions. In addition, response and recovery times from temporal oxygen exposure decrease with humidity. We attribute the effects to competing adsorption processes and reactions of water with adsorbed oxygen species and/or lattice oxygen, which involve electron re-injection to the TiO conduction band. Elevated temperatures up to 170 attenuate the effects, presumably due to the lower binding strength to the surface of molecular water compared with oxygen adsorbates.

Strategic Customization of Polymeric Nanocomposites Modified by 2D Titanium Oxide Nanosheet for High‐k and Flexible Gate Dielectrics

Organic polymer-based dielectrics with intrinsic mechanical flexibility and good processability are excellent candidates for the dielectric layer of flexible electronics. These polymer films can become even more rigid and electrically robust when modified through cross-linking processes. Moreover, the composites formed by dispersing nanoscale inorganic fillers in a polymer matrix can exhibit further improved polarization property. However, these strategies can be challenging as homogeneous dispersion of nanomaterials in the matrix is difficult to achieve; thus, degradation of electrically insulating properties of nanocomposite layers is often observed. Here, a high-k, pinhole-free, and flexible poly(vinyl alcohol) (PVA)-based nanocomposite dielectric is presented, incorporating 2D TiO2 nanosheets (NSs) for the first time. Despite the attractive dielectric constant, exceptional flexibility, and electrically insulating property of PVA-TiO2 nanocomposites, only few studies on these materials have been reported. The organic/inorganic nanosheet hybrid layer, which reaches an unprecedentedly high dielectric constant of 43.8 (more than four times higher than that of cross-linked PVA), also exhibits an outstanding leakage current density as low as 10-9 A cm-2 . Furthermore, the repeated bending tests for nanocomposite capacitors reveal their capability of operating without any deterioration of their performances even after 1000 iterations of bending cycles at a bending radius of 3mm.

Intertwined Topological and Magnetic Orders in Atomically Thin Chern Insulator MnBi2Te4.

MnBi2Te4, a van der Waals magnet, is an emergent platform for exploring Chern insulator physics. Its layered antiferromagnetic order was predicted to enable even-odd layer number dependent topological states. Furthermore, it becomes a Chern insulator when all spins are aligned by an applied magnetic field. However, the evolution of the bulk electronic structure as the magnetic state is continuously tuned and its dependence on layer number remains unexplored. Here, employing multimodal probes, we establish one-to-one correspondence between bulk electronic structure, magnetic state, topological order, and layer thickness in atomically thin MnBi2Te4 devices. As the magnetic state is tuned through the canted magnetic phase, we observe a band crossing, i.e., the closing and reopening of the bulk band gap, corresponding to the concurrent topological phase transition in both even- and odd-layer-number devices. Our findings shed new light on the interplay between band topology and magnetic order in this newly discovered topological magnet.

Competition between fractional quantum Hall liquid and Wigner solid at small fillings: Role of layer thickness and Landau level mixing

What is the fate of the ground state of a two-dimensional electron system (2DES) at very low Landau level filling factors ($\nu$) where interaction reigns supreme? An ordered array of electrons, the so-called Wigner crystal, has long been believed to be the answer. It was in fact the search for the elusive Wigner crystal that led to the discovery of an unexpected, incompressible liquid state, namely the fractional quantum Hall state at $\nu=1/3$. Understanding the competition between the liquid and solid ground states has since remained an active field of fundamental research. Here we report experimental data for a new two-dimensional system where the electrons are confined to an AlAs quantum well. The exceptionally high quality of the samples and the large electron effective mass allow us to determine the liquid-solid phase diagram for the two-dimensional electrons in a large range of filling factors near $\simeq 1/3$ and $\simeq 1/5$. The data and their comparison with an available theoretical phase diagram reveal the crucial role of Landau level mixing and finite electron layer thickness in determining the prevailing ground states.

Competition of spinon Fermi surface and heavy Fermi liquid states from the periodic Anderson to the Hubbard model

We study a model of correlated electrons coupled by tunnelling to a layer of itinerant metallic electrons, which allows to interpolate from a frustrated limit favorable to spin liquid states to a Kondo-lattice limit favorable to interlayer coherent heavy metallic states. We study the competition of the spinon fermi surface state and the interlayer coherent heavy Kondo metal that appears with increasing tunnelling. Employing a slave rotor mean-field approach, we obtain a phase diagram and describe two regimes where the spin liquid state is destroyed by weak interlayer tunnelling, (i) the Kondo limit in which the correlated electrons can be viewed as localized spin moments and (ii) near the Mott metal-insulator-transition where the spinon Fermi surface transitions continuously into a Fermi liquid. We study the shape of LDOS spectra of the putative spin liquid layer in the heavy Fermi liquid phase and describe the temperature dependence of its width arising from quasiparticle interactions and disorder effects throughout this phase diagram, in an effort to understand recent STM experiments of the candidate spin liquid 1T-TaSe$_2$ residing on metallic 1H-TaSe$_2$. Comparison of the shape and temperature dependence of the theoretical and experimental LDOS suggest that this system is either close to the localized Kondo limit, or in an intermediate coupling regime where the Kondo coupling and the Heisenberg exchange interaction are comparable.

The Role of Metal-Organic Frameworks in Electronic Sensors.

MOFs have a highly ordered self-assembled nanostructure, high surface area, nanoporosity with tunable size and shape, reliable host-guest interactions, and responsiveness to physical and chemical stimuli which can be exploited to address critical issues in sensor applications. On the one hand, the nanoscale pore size of MOFs ranging from less than 1 nm to ≈ 10 nm not only allows the diffusion of small molecules into the pores or through the MOF layer, but also excludes other larger molecules depending on the size, shape, and conformation of MOFs. On the other hand, MOFs with flexible structure exhibit a dynamic response to external stimuli, including guest molecules, temperature, pressure, pH, and light. Due to the unsaturated coordination metal sites and active functional groups, the interaction between certain analytes and active sites results in high selectivity. In this review, we summarize the latest studies on MOF-based electronic sensors in terms of the function of MOFs, discuss challenges, and suggest perspectives.

Comparison of carrier-recombination in Ga(As,Bi)/Ga(N,As)-type-II quantum wells and W-type heterostructures

The realization of efficient semiconductor lasers on GaAs substrates operating at 1.55 μm and beyond remains a technological challenge. As a potential solution, epitaxial heterostructures with type-II band alignment are currently discussed as an active region. Each individual layer in such heterostructures features a comparably large bandgap energy; therefore, spurious effects in laser operation such as reabsorption, multi-photon absorption, or Auger scattering are expected to be suppressed. The actual laser operation occurs across the internal interfaces as the electron and hole wave functions have their extrema in adjacent layers. Hence, a large wave-function overlap is key for efficient recombination. A direct comparison of symmetric and asymmetric Ga(N,As)/Ga(As,Bi) type-II quantum well heterostructures reveals that the symmetry of the layer arrangement drastically influences the charge-carrier recombination: disorder in the Ga(As,Bi) layer has more prominent effects for the asymmetric configuration compared to the symmetric one. The temperature dependence of the emission energy is mainly influenced by the Ga(N,As)-electron layers, while the temperature dependence of the full width at half maximum and the excitation dependence of the emission energy are dominated by the Ga(As,Bi)-hole layers. Photoluminescence excitation spectroscopy reveals the corresponding carrier-relaxation paths to the type-II transition.

Subtractive photonics.

Realization of a multilayer photonic process, as well as co-integration of a large number of photonic and electronic components on a single substrate, presents many advantages over conventional solutions and opens a pathway for various novel architectures and applications. Despite the many potential advantages, realization of a complex multilayer photonic process compatible with low-cost CMOS platforms remains challenging. In this paper, a photonic platform is investigated that uses subtractively manufactured structures to fabricate such systems. These structures are created solely using simple post-processing methods, with no modification to the foundry process. This method uses the well-controlled metal layers of advanced integrated electronics as sacrificial layers to define dielectric shapes as optical components. Metal patterns are removed using an etching process, leaving behind a complex multilayer photonic system, while keeping the electronics'metal wiring intact. This approach can be applied to any integrated chip with well-defined metallization, including those produced in pure electronics processes, pure photonics processes, heterogeneously integrated processes, monolithic electronic-photonic processes, etc. This paper provides a proof-of-concept example of monolithic electronic-photonic integration in a 65 nm bulk CMOS process and demonstrates proof-of-concept photonic structures. The fabrication results, characterization, and measurement data are presented.

Dynamic LightPath Allocation in WDM Networks Using an SDN Controller

Core wavelength division multiplexed (WDM) networks are widely used to provide fixed physical connectivity and bandwidth to the logically connected upper electronic layer devices using optical signals. However, growing demands for bandwidth-intensive applications and cloud-based services push optical networks carriers’ to provide scalable and flexible services dynamically. Software defined networking (SDN) has the potential to program electronic layers by dynamically controlling and managing network resources using SDN controller applications. SDN’s on-demand characteristics combined with the optical circuit-switching can enable optical network service providers to customize their service provisioning dynamically to the user’s requirements. They enable fast provision of new services, and minimize under-utilization of resources. In this paper, a model is proposed to bring the dynamic allocation of resources which is a layer 2+ functionality, to the WDM layer using SDN. A middle-ware application based on SDN and OpenFlow for dynamic switching and provisioning of optical service is presented. The application abstracts the optical layer’s connectivity, also accounting for the switching constraints. Details of the model’s implementation are discussed considering classically used equipment and its performance in terms of CPU and memory utilization, topology emulation time, and latency is evaluated. Finally, the application is tested with a Cisco layer one switch. Performance results show that the latency doubles when increasing the number of fibers of an optical cross connect from 5 to 7 and keeping wavelengths equal to 8, with Clos fabric topology.

Stabilized covalent interfacial coupling design of Li3V2(PO4)3 with carbon framework for boosting lithium storage kinetics

LVP@C with stabilized electronic conductive layer is prepared by a facile organic–inorganic hybrid hydrogel-enabled methodology, in which LVP is chemically interacting with carbon framework via P–C and P–O–C bonds.

Study of Structures of Electronic Double Layer Formed in Ionic Liquids Using X-ray Reflectivity 2

Study of Structures of Electronic Double Layer Formed in Ionic Liquids Using X-ray Reflectivity 2

Картографирование экологической сбалансированности байкальского региона по отдельным категориям земель

The article discusses the main methods of assessing the ecological balance of the territories of the Baikal region through a system of quantitative estimates and expert characteristics of the studied processes on the basis of statistical data. The ecological balance of the Baikal Natural Territory as a balanced ratio of natural and modified geo-systems depends on the integrity of the natural frame of the region. The natural framework consists directly of the oz ecosystem. Baikal, the hydrographic network of the lake basin, the natural mountain-taiga and other ecologically significant geosystems that form the natural infrastructure of the region, inextricably linked to the socio-economic infrastructure (socio-economic framework) consisting of a network of human settlements and infrastructure. Natural geosystems, which form the natural framework, are also a special resource for ecological stability (balanced). The electronic map layers of the «Environmental Atlas of the Baikal Region» were used as basic cartographic materials. An inventory was carried out and a database of spatial and non-spatial data on the main indicators of the ecological stability of the territory (natural security, territorial tension and anthropogenic load) was compiled. Attribute data is represented in the form of a set of MapInfo tables with which it is easy to carry out re-structuring operations (changing the structure and composition of tables) data and SQL-queries. Spatial data are presented as a vector topological data model. For the study of the ecological condition of the land of the region, the analysis of land cadastre data reflecting the current state of industrial, forestry, agriculture and other impacts on natural and natural anthropogenic geosystems was carried out. The land of the Baikal region, which is subject to varying degrees of anthropogenic pressure, has been classified. The relative and absolute intensity ratios of the territory have been calculated. The natural land protection factor and the anthropogenic load factor have been determined. The administrative regions are ranked according to the intensity of the ecological state of the lands of the Baikal region.

Tuning electrical and thermal conductivities of the two-dimensional electron gas in AlN/GaN heterostructures by piezoelectricity

We investigate the electrical and thermal conductivities of the two-dimensional electron gas (2DEG) confined in the quantum well formed at the heterojunction between a thin GaN layer and an AlN layer strained by an Al x Ga1−x N capping layer in the temperature range from 10 to 360 K. The experimental protocol developed to deduce from calorimetric and Hall-effect measurements at a variable temperature the critical characteristics and transport properties of the confined 2DEG is presented. It is found that, in the measured temperature range (10–360 K), the electrical conductivity of the 2DEG is temperature-independent, due to the predominance of scattering processes by interface defects. However, the thermal conductivity shows a linear temperature dependence, mirroring the specific heat of free electrons. The temperature-independent relaxation time associated with the overall electron scattering means that the values obtained for electrical and thermal conductivities are in excellent agreement with those stipulated by the Weidemann–Franz law. It is also found that for weak strain fields in the AlN layer, both the electrical and thermal conductivities of the two-dimensional interfacial electrons increase exponentially with strain. The importance of 2DEG in AlN/GaN quantum wells lies in the fact that the strong piezoelectricity of AlN allows the transport properties of the 2DEG to be tuned or modulated by a weak electric field even with the high density of lattice mismatch induced defects at the AlN-GaN interface .

Experimental studies on the mechanism of seismoelectric logging while drilling with multipole source

SUMMARYWhen a seismic wave propagates in a fluid-saturated porous medium, a relative movement forms between the solid and the fluid and induces an electric current due to the electronic double layer. As a result, two kinds of seismoelectric coupling responses are generated in this procedure: the localized electric/magnetic field and interfacial electromagnetic wavefield. One important potential application of these two seismoelectric conversions is used for measuring formation P and S waves in well logging. Considering that the strong collar wave seriously affects the velocity measurements of formation P and S waves in current acoustic logging while drilling (LWD), the seismoelectric LWD method, which combines seismoelectric conversion and acoustic LWD technique, was suggested to be a novel method in oil and gas exploration. The collar wave cannot induce any seismoelectric signal on the metal collar since there is no double layer formed on a metal surface. In this paper, acoustic and seismoelectric LWD measurements are conducted in the laboratory. We build a scaled multipole acoustic LWD tool to conduct acoustic measurements in a water tank and a sandstone borehole model. We also build a multipole seismoelectric LWD tool and record the seismoelectric signals induced with the same acoustic source. Then, we compare the recorded acoustic and seismoelectric signals by using the experimental data. The result indicates that the apparent velocities of seismoelectric signals are equal to the formation P- and S-wave velocities and the collar waves do not induce any visible electric signal in the full waveforms. We further analyse the mechanism of seismoelectric LWD by a quantitative comparison of the amplitudes between the inner collar wave and outer collar wave. The results show that the amplitude of outer collar wave decreases significantly when it radiates out of the tool, so that the seismoelectric signals induced by collar waves are too weak to be distinguished in the full waveforms of seismoelectric LWD measurements. Thus, the formation P- and S-wave velocities are detected accurately from the recorded seismoelectric LWD data. These results verify the feasibility of the seismoelectric LWD method for measuring acoustic velocities of the borehole formation.

Electronic composition of Luciano Berio «Visage»: between tradition and experiment

The purpose of the article is to trace the interaction of innovative sound material and the embodiment of traditional principles of a musical organization in L. Berio's electronic play «Visage». The methodology of the study is based on the structural-functional methods, that allow identifying the components of the musical fabric, which serve as material for development. The scientific novelty lies in the fact that for the first time in Ukrainian musicology the patterns of creation and deployment of electronic sound complexes in L. Berio's play «Visage» were revealed, the method of analyzing electronic compositions without the author's score was improved. Conclusions. Analysis of L. Berio's electronic piece «Visage» demonstrates an organic combination of experimental searches and traditions renewed in accordance with specific sound material. Innovative trends prevail in the selection of sound elements. The sound space «Visage» is realized by means of electronic synthesis and taped voice. The vocal and electronic layers are not opposed to each other, but, on the contrary, coexist in unity. Using acoustic objects of different types, selected at the pre-compositional stage, L. Berio builds a thematic profile of the piece – from noises to the deployment of wide bands of electronic continua. The connections between the elements are provided not by the sound pitch identity, but due to sound, in particular phonetic, similarity. The connection with the art of previous eras is manifested in the desire to reveal deep philosophical ideas, which are carried out through the deployment of thematic fields, localized in certain compositional sections. The dramatic profile of the work, realized by electronic means, directs the vector of the perception to reveal the author's intention.

Effect of the Polyamide Type on the Physical Properties of Layered Polyaniline Composite Films

Abstract: The present work deals with the investigation of the dielectric properties of layered polyamide/polyaniline films and their correlation to the microstructure. A thin polyaniline (PANI) layer was polymerized in the subsurface of polyamide films. The dielectric relaxation spectroscopy was used to compare the electrical behaviour of flexible polyamide 6 (PA6) and polyamide 12 (PA12) surfaces loaded with PANI nanoparticles, while the roughness was investigated by the contact angle technique. Relatively high dielectric constants were recorded for PA12/PANI films compared to PA6/PANI ones due to the hydrophobic nature of the PA12 matrix. This also explained the wettability enhancement observed for PA12/PANI films up to 12 wt.% of aniline absorbed concentration, while PA6/PANI films needed no more than 9 wt.% to reach maximum wettability. This behavior was in good correlation with the microstructure of the films. SEM micrographs showed uniform surfaces for both films formed above these respective concentrations, where wettability started to decrease. The films of PA/PANI seemed to be good candidates as dielectric layers in flexible electronics. Keywords: Polymer, Polyamide, Polyaniline, Dielectric constant, Optical gap. PACS: 78.20.-ei, 78.20.-c, 68.60.-p, 82.35.Lr.

Ferromagnetic Weyl Fermions in Two-Dimensional Layered Electride Gd_{2}C.

Recently, two-dimensional layered electrides have emerged as a new class of materials which possess anionic electrons in the interstitial spaces between cationic layers. Here, based on first-principles calculations, we discover a time-reversal-symmetry-breaking Weyl semimetal phase in a unique two-dimensional layered ferromagnetic (FM) electride Gd_{2}C. It is revealed that the crystal field mixes the interstitial electron states and Gd-5d orbitals near the Fermi energy to form band inversions. Meanwhile, the FM order induces two spinful Weyl nodal lines (WNLs), which are converted into multiple pairs of Weyl nodes through spin-orbit coupling. Further, we not only identify Fermi-arc surface states connecting the Weyl nodes but also predict a large intrinsic anomalous Hall conductivity due to the Berry curvature produced by the gapped WNLs. Our findings demonstrate the existence of Weyl fermions in the room-temperature FM electride Gd_{2}C, therefore offering a new platform to investigate the intriguing interplay between electride materials and magnetic Weyl physics.