Dielectric Nanolayers Research Articles

Magnetoresistance and Magnetocapacitance Effect in Magnetic Tunnel Junction with Perpendicular Anisotropy of Magnetic Electrodes Tb22−δCo5Fe73/Pr6O11/Tb19−δCo5Fe76

This paper presents the results of studies of the effects of magnetoresistance and magnetocapacitance in magnetic tunnel junctions [Formula: see text]Co5[Formula: see text]/Pr6[Formula: see text]/[Formula: see text]Co5[Formula: see text] with perpendicular anisotropy of magnetic electrodes and a paramagnetic barrier layer. Experimentally measured values of tunnel magnetic resistance and tunnel magnetic capacitance in such contacts exceed 100% at room temperature. The paper analyzes the effect of magnetization reversal of one of the electrodes on the conductivity of magnetic tunnel junctions with electrodes that have perpendicular anisotropy. It is shown that significant changes in tunnel magnetic resistance and tunnel magnetic capacity in such contacts can be explained by the separation of electrons with major and minor spin polarization in the inverse nanolayer in the interface region. The separation of polarized electrons is caused by the magnetomotive force acting on the electron spin in a strongly gradient magnetic field. Such a magnetomotive force occurs with antiparallel magnetization of the magnetic electrodes and it has opposite directions for major and minor polarized electrons. As a result of the spatial separation of polarized electrons in the inversion layer, an inhomogeneous distribution of the electron density along the direction of magnetization of the magnetic contacts occurs. As a result, an additional Coulomb barrier between the magnetic electrodes and the dielectric nanolayer appears in the tunnel contacts and an additional spin capacitance appears.

Ion‐Charged Dielectric Nanolayers for Enhanced Surface Passivation in High Efficiency Photovoltaic Devices

AbstractThe power conversion efficiency of solar cells is strongly impacted by an unwanted loss of charge carriers occurring at semiconductor surfaces and interfaces. Here the use of ion‐charged oxide nanolayers to enhance the passivation of silicon surfaces via the field effect mechanism is reported. The first report of enhanced passivation from rubidium and cesium ion‐charged oxide nanolayers is provided. The charge state and formation energy of ion‐charged silicon dioxide are calculated from first principles. Ion embedding is demonstrated and exploited to control the interface population of carriers and minimize electron‐hole pair recombination. The passivation quality directly improves with charge concentration, yet excess ions can produce detrimental interface states. An optimal ionic charge concentration of ≈1.5 × 1012 q cm−2 is deduced, and a recombination velocity and current density as low as 2.8 cm s−1 and 7.8 fA cm−2 are achieved at the Si‐SiO2 interface. Maximized charge is shown to provide efficiency improvements as high as 0.7% absolute. This work provides a unique route to enhance passivation without compromising the film synthesis, thus retaining the antireflection and hydrogenation film properties. As such, ion‐charged dielectrics provide complementary paths for surface and interface optimization in future single‐junction and tandem solar cells.

Combined breakdown of a dielectric nanolayer to form a Josephson bridge

The electrical breakdown of a dielectric nanolayer between film electrodes under the combined action of direct current and capacitor discharge current makes it possible to form Josephson bridges with a reproducible resistance exceeding 1 Ω. A new feature of the formation of a bridge during the electrical breakdown, which is preceded by a series of preliminary breakdowns (auto breakdowns) of a dielectric nanolayer, has been discovered. The mechanism of the process and the role of the cathode film's thickness in forming the bridge are discussed.

Electrical breakdown of a dielectric for the formation of a superconducting nanocontact

Electrical breakdown of the dielectric nanolayer between film electrodes of niobium and an alloy of 50% indium and 50% tin forms a bridge of this alloy between the electrodes. The bridge resistance depends on the breakdown current. The length of the bridge is equal to the thickness of the dielectric (30 nm), and its diameter is 25 nm. The calculated coherence length of the alloy at 2 K is close to the length of the bridge. The calculated critical current of a bridge with a resistance of 1 Ω at a temperature of 0 K is 1 mA. It is concluded that such a bridge should have the properties of a Josephson contact at a temperature lower than the critical temperature of the alloy (6.5 K).

Quantum Theory of Longitudinal-Transverse Polaritons in Nonlocal Thin Films

When midinfrared light interacts with nanoscale polar dielectric structures, optical phonon propagation cannot be ignored, leading to a rich nonlocal phenomenology that we have only recently started to uncover. In properly crafted nanodevices this includes the creation of polaritonic excitations with hybrid longitudinal-transverse nature, which are predicted to allow energy funneling from longitudinal electrical currents to far-field transverse radiation. In this work we study the physics of these longitudinal-transverse polaritons in a dielectric nanolayer in which the nonlocality strongly couples epsilon-near-zero modes to longitudinal phonons. After having calculated the system's spectrum solving Maxwell's equations, we develop an analytical polaritonic theory able to transparently quantify the nonlocality-mediated coupling as a function of the system parameters. Such a theory provides a powerful tool for the study of longitudinal-transverse polariton interactions and we use it to determine the conditions required for the hybrid modes to appear.

Far-field directional emission of fluorescence enhanced by dielectric microsphere and metallic planar nanolayers

Controlling the emission characteristics of fluorescent substances and increasing the intensity of fluorescence emission are crucial for fluorescence detecting technology in single-molecule detection, biomedicine, and sensing applications. Since fluorescence emission is isotropic in nature, the collected fluorescence is only accounted for a small fraction of the total emitted fluorescence. In this paper, a composite structure composed of dielectric microsphere and metallic planar nanolayers is proposed to enhance the fluorescence far-field directional emission intensity and improve the fluorescence collection efficiency. The excitation process and the emission process of quantum dots (QDs) located between the dielectric microspheres and the gold layer are investigated by the finite difference time domain (FDTD) method. In the emission process, the emission of QDs in a homogeneous medium is isotropic. Therefore, we usually select several special polarizations in theoretical analysis state for research. In this paper, we first study the effect of the structure on the fluorescence emission enhancement of QDs when the QDs are in the <i>x-</i>, <i>y-</i>, and<i> z-</i>polarization state. Some results can be obtained as shown below. When the radiation direction of the QDs is perpendicular to the microsphere plane layered structure, the structure is coupled with the emitted fluorescence, thereby realizing the directional enhancement of the emitted fluorescence of the QDs, and the obvious fluorescence enhancement is obtained in the <i>x-</i> and <i>y-</i>polarization state. Therefore, in the research, we choose and investigate the dipole light source of <i>x</i>-polarization state. We mainly study the influence of microsphere radius, refractive index, and QDs position on the fluorescence directional enhancement. The QDs as a fluorescent material are coated in polymethyl methacrylate (PMMA) to control the distance from the gold layer to tune the fluorescence enhancement. The structure is based on the synergistic effect among plasmon coupling, whispering gallery mode and photonic nanojet, which enhances the far-field fluorescence of QDs by a factor of 230, and the fluorescence collection efficiency is as high as 70%. Comparing with the enhanced fluorescence of the dielectric microspheres and the gold sphere dimer composite structure, the distance between the gold sphere dimers is not easy to control, and the QDs should be placed at specific positions between the gold spheres. The structure we propose is more convenient to implement. In this paper, not only the emission enhancement process of QDs is studied in detail, but also the excitation process of QDs is investigated. Our proposed dielectric microsphere metal planar nanolayered structure can enhance the excitation of QDs in most areas, proving that our designed structure can effectively realize the excitation enhancement of QDs. The above results have very important applications in the fluorescence biological detection, imaging, and light-emitting devices.

Assessing the Potential of Inversion Layer Solar Cells Based on Highly Charged Dielectric Nanolayers

The production and performance of p‐type inversion layer (IL) Si solar cells, manufactured with an ion‐injection technique that produces a highly charged dielectric nanolayer, are investigated. It is demonstrated that the field‐induced electron layer underneath the dielectric can reach a dark sheet resistance of 0.95 kΩ sq−1 on a 1 Ω cm n‐type substrate, lower than any previously reported. In addition, it is shown that the implied open‐circuit voltage of a p‐type IL cell precursor with a highly charged dielectric is equivalent to that of a cell with a phosphorous emitter. In the cell precursor, light‐beam‐induced current measurements are performed, and the uniformity and performance of the IL is demonstrated. Finally, simulations are used to explain the physical characteristics of the interface leading to extremely low sheet resistances, and to assess the efficiency potential of IL cells. IL cells are predicted to reach an efficiency of 24.5%, and 24.8% on 5/10 Ω cm substrates, by replacing the phosphorous emitter with a simpler manufacturing process. This requires a charge density of beyond 2 × 1013 cm−2, as is demonstrated here. Moreover, IL cells perform even better at higher charge densities and when negative charge is optimized at the rear dielectric.

Hyperspectral Molecular Orientation Mapping in Metamaterials

The four polarisation method is adopted for measurement of molecular orientation in dielectric nanolayers of metal-insulator-metal (MIM) metamaterials composed of gold nanodisks on polyimide and gold films. Hyperspectral mapping at the chemical finger printing spectral range of 4–20 μμm was carried out for MIM patterns of 1–2.5 μμm period (sub-wavelength). Overlay images taken at 0,π4,π2,3π4 orientation angles and subsequent baseline compensation are shown to be critically important for the interpretation of chemical mapping results and reduction of spurious artefacts. Light field enhancement in the 60-nm-thick polyimide (I in MIM) was responsible for strong absorption at the characteristic polyimide bands. Strong absorbance A at narrow IR bands can be used as a thermal emitter (emittance E=1−R), where R is the reflectance and A=1−R−T, where for optically thick samples the transmittance is T=0.

Tunable photonic nanojets from a micro-cylinder with a dielectric nano-layer

Recently, tunable photonic nanojets (PNJs) utilizing a mask have been investigated to produce narrow PNJs and curved PNJs (photonic hooks, PHs). Herein, a dielectric nano-layer is employed to tune the PNJs from a micro-cylinder. Symmetric and asymmetric illumination caused by the nano-layer are studied separately with finite element method. The results show that, for the symmetric illumination, narrow PNJs and twin PNJs (t-PNJs) can be generated through controlling the width of the layer. For the asymmetric illumination, it has the ability to produce PHs and asymmetric t-PNJs by changing the thickness of the nano-layer. Based on these results, an optical switch for light-route selection depending on the incident light wavelength is presented. This work may have great potential in the fields of optomechanical manipulation, super-resolution imaging and optical nanolithography.

Mid-Infrared Nanofocusing Using Fragmented High-Order Transformation Optics

An approach to design a hyperbolic lenslet for mid-infrared nanofocusing based on fragmented high-order transformation optics (TO) (FHTO) method is proposed, which can be realized with binary realistic metal and dielectric nanolayers. The conceptual idea is achieved by discretizing the lenslet into $N(N>1)$ concentric fragments and perform high-order TO in each fragment with different values of azimuthal $s$ parameter — an unconstrained parameter that defines the operation point of the nanofocusing device. To highlight the superior performance of using the FHTO in the nanofocusing versus the unitary $(N=1)$ high-order TO (UHTO), both methods are adopted to design the hyperbolic lenslet. The numerical simulation results show that the FHTO (e.g., $N\to \infty $ and $N = 5$ ) exhibits superior focusing performance compared with the UHTO. For example, the performance of the FHTO is better than that of the UHTO by ~2.5 (5.3) times in spectral resolution (power throughput). Remarkably, even the manufacturable lenslet designed using FHTO-approach with realizable number of metal-dielectric binary layers (five pairs) demonstrates superior performance than the UHTO. It is noteworthy to mention that the design of FHTO-based devices enabled by circular effective-medium theory (CEMT) provides a means to bridge the gap between theoretical design and practical realization of nanophotonics systems.

Formation of Dielectric Nanolayers of Aluminum and Silicon Oxides on AIIIBV Semiconductors

The results of investigations of the synthesis of silicon and aluminum oxide nanolayers on the GaAs, InAs, and InSb binary semiconductor surface by molecular layering (atomic layer deposition) are generalized. The conditions for the layer-by-layer growth of the surface nanostructures are established and some of their dielectric characteristics are estimated.

Bifunction-Integrated Dielectric Nanolayers of Fluoropolymers with Electrowetting Effects.

Fluoropolymers play an essential role in electrowetting (EW) systems. However, no fluoropolymer possesses the desirable properties of both hydrophobicity and dielectric strength. In this study, for the first time, we report the integration of two representative fluoropolymers—namely, Teflon AF (AF 1600X) and Cytop (Cytop 809A)—into one bifunctionalized dielectric nanolayer. Within this nanolayer, both the superior hydrophobicity of Teflon AF and the excellent dielectric strength of Cytop were able to be retained. Each composed of a 0.5 μm Cytop bottom layer and a 0.06 μm Teflon AF top layer, the fabricated composite nanolayers showed a high withstand voltage of ~70 V (a dielectric strength of 125 V/μm) and a high water contact angle of ~120°. The electrowetting and dielectric properties of various film thicknesses were also systemically investigated. Through detailed study, it was observed that the thicker Teflon AF top layers produced no obvious enhancement of the Cytop/Teflon AF stack.

Interconnections between Electronic Structure and Optical Properties of Multilayer Nanolaminate TiAlN/Ag and Al2O3/Ag Coatings

Multilayer nanolaminate TiAlN/Ag and Al2O3/Ag metal-insulator-metal (MIM) coatings with thicknesses of individual layers from a few to several hundreds of nanometers were fabricated by direct current magnetron sputtering. Their optical transmittance and reflectance spectra were measured for photon energies 1–5 eV (1240–248 nm). The spectra were non-monotonous as their transmission and reflection bands were strongly dependent on the coating architecture. A set of advanced electron spectroscopy methods was used to analyse the electronic structure of the coatings controlling optical properties. Energies of plasmons peaks and the distribution of their intensities are functions of the Ag layers thickness as well as the composition and thickness of the dielectric nanolayers in the MIM nanocomposite. Statistical analysis established the cross-correlations between geometrical parameters of the coatings, transmissions and reflection bands on the optical spectra and parameters of the electronic structure. Particularly, the blue side of the transmittance band is controlled by plasmons while the dielectric band gap determines the transmittance of the red side. The obtained experimental results allowed us to fulfil the computed architectural design of a multilayer Al2O3/Ag coating with a narrow bandwidth in the visible light region and strong reflection in the infrared and ultraviolet regions.

Effective interface thermal resistance and thermal conductivity of dielectric nanolayers

Analytical expressions for the effective interface thermal resistance (ITR) and thermal conductivity k of dielectric nanolayers are derived and analyzed, based on the analytical solution of the phonon Boltzmann transport equation under the gray relaxation time approximation. This is achieved by using accurate expressions for the temperature and one-dimensional heat flux propagating across nanolayers supporting a diffusive phonon scattering at their interfaces. It is shown that the effective ITR between two layers can be symmetric on their thermal properties, such that its asymptotic value in the ballistic regime is higher than that in the diffusive one. In the ballistic-diffusive regime, the effective ITR depends strongly on the ratio λ=L/l, between the layer thickness L and mean free path l of phonons. Our predictions for the effective ITR in the ballistic regime are in good agreement with those of the diffuse mismatch model, while they differ by about 16% in the diffusive regime. On the other hand, k increases with λ until reaching saturation for bulk layers and agrees rather well with previous predictions reported in the literature. The obtained results could be useful for analytically describing the heat transport in dielectric nanothin films and superlattices, in which the gray approximation is valid.

Enhanced efficiency and stability of carbon based perovskite solar cells using terephthalic acid additive

We report an effective method to modulate the perovskite crystallization by incorporating terephthalic acid (TPA) additive into the perovskite precursor solutions. The addition of TPA additive simultaneously facilitate nucleation and modulate the kinetics of crystal growth from solutions, enabling preparation of smooth and compact perovskite morphology with improved crystallization, grain uniformity, loading of perovskite into the TiO2 mesopores and coverage area. Before deposition of perovskite films, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated onto porous TiO2 to retard the carrier recombination at the interface in the devices. The mechanism of the interaction between TPA and Pb2+ on the film-forming process of perovskite crystal was also analyzed. Consequently, by optimizing the TPA concentration, we obtained highly efficient and stable low-temperature processed electron transport material (HTM)-free carbon based perovskite solar cells (PSCs). The performance of the PSCs is significantly improved with the mean efficiency increasing from 11.5% ± 0.67% for the control structure to 14.29% ± 0.37% for the TPA modified structure. Furthermore, the TPA modified perovskite films and devices present much better thermal, UV and ambient air stability than the pristine perovskite films and devices, and the corresponding PSCs with TPA modification show excellent stability with efficiency approaching 94% after being exposed to ambient air for 21 days without encapsulation.

Role of highly doped Si substrate in bipolar resistive switching of silicon nitride MIS-capacitors

Bipolar resistive switching of the metal-insulator-semiconductor (MIS) capacitor-like structures with the inert Au top electrode and Si3N4 dielectric nanolayer (6nm thick) has been investigated. The effect of highly doped n+-Si substrate is revealed related to the changes in semiconductor space charge region on the small-signal parameters of parallel and serial equivalent circuit models measured in the high- and low-resistive capacitor states, as well as under laser illumination. The increase in conductivity of semiconductor capacitor plate significantly reduces the charging and discharging times of capacitor-like structures.

Design of a Structured Bulk Plasmon Illumination Source for Enhancing Plasmonic Cavity Superlens Imaging

A structured bulk plasmon illumination (BPI) source is designed for achieving a uniform high spatial frequency illumination field. By employing the hyperbolic metamaterial (HMM) composed of alternatively stacked metal and dielectric nanolayers, the deep subwavelength bulk plasmon polaritons (BPPs) can be launched. The obtained BPP modes are then utilized as a structured illumination source for improving the imaging resolution. More importantly, the BPI intensity can be improved remarkably by adding an extra Ag layer to the original BPI source. When two nano-slits are illuminated by the BPI source, the imaging resolution of plasmonic cavity superlens is improved obviously. Especially, after adding an extra Ag layer to the original BPI source, one can find the obvious improvement of the image contrast. The proposed BPI source promises some potential in near-field super resolution lithography.

MgO Nanoparticle Modified Anode for Highly Efficient SnO2-Based Planar Perovskite Solar Cells.

Reducing the energy loss and retarding the carrier recombination at the interface are crucial to improve the performance of the perovskite solar cell (PSCs). However, little is known about the recombination mechanism at the interface of anode and SnO2 electron transfer layer (ETL). In this work, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO2:F (FTO) electrode and SnO2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties. With the use of this electrode modifier, a power conversion efficiency of 18.23% is demonstrated, an 11% increment compared with that without MgO modifier. These improvements are attributed to the better properties of MgO‐modified FTO/SnO2 as compared to FTO/SnO2, such as smoother surface, less FTO surface defects due to MgO passivation, and suppressed electron–hole recombinations. Also, MgO nanolayer with lower valance band minimum level played a better role in hole blocking. When FTO is replaced with Sn‐doped In2O3 (ITO), a higher power conversion efficiency of 18.82% is demonstrated. As a result, the device with the MgO hole‐blocking layer exhibits a remarkable improvement of all J–V parameters. This work presents a new direction to improve the performance of the PSCs based on SnO2 ETL by transparent conductive electrode surface modification.

Parallel Nanoshaping of Brittle Semiconductor Nanowires for Strained Electronics.

Semiconductor nanowires (SCNWs) provide a unique tunability of electro-optical property than their bulk counterparts (e.g., polycrystalline thin films) due to size effects. Nanoscale straining of SCNWs is desirable to enable new ways to tune the properties of SCNWs, such as electronic transport, band structure, and quantum properties. However, there are two bottlenecks to prevent the real applications of straining engineering of SCNWs: strainability and scalability. Unlike metallic nanowires which are highly flexible and mechanically robust for parallel shaping, SCNWs are brittle in nature and could easily break at strains slightly higher than their elastic limits. In addition, the ability to generate nanoshaping in large scale is limited with the current technologies, such as the straining of nanowires with sophisticated manipulators, nanocombing NWs with U-shaped trenches, or buckling NWs with prestretched elastic substrates, which are incompatible with semiconductor technology. Here we present a top-down fabrication methodology to achieve large scale nanoshaping of SCNWs in parallel with tunable elastic strains. This method utilizes nanosecond pulsed laser to generate shock pressure and conformably deform the SCNWs onto 3D-nanostructured silicon substrates in a scalable and ultrafast manner. A polymer dielectric nanolayer is integrated in the process for cushioning the high strain-rate deformation, suppressing the generation of dislocations or cracks, and providing self-preserving mechanism for elastic strain storage in SCNWs. The elastic strain limits have been studied as functions of laser intensity, dimensions of nanowires, and the geometry of nanomolds. As a result of 3D straining, the inhomogeneous elastic strains in GeNWs result in notable Raman peak shifts and broadening, which bring more tunability of the electrical-optical property in SCNWs than traditional strain engineering. We have achieved the first 3D nanostraining enhanced germanium field-effect transistors from GeNWs. Due to laser shock induced straining effect, a more than 2-fold hole mobility enhancement and a 120% transconductance enhancement are obtained from the fabricated back-gated field effect transistors. The presented nanoshaping of SCNWs provide new ways to manipulate nanomaterials with tunable electrical-optical properties and open up many opportunities for nanoelectronics, the nanoelectrical-mechanical system, and quantum devices.

Metal-insulator-metal capacitors based on lanthanum oxide high-κ dielectric nanolayers fabricated using dense plasma focus device

Metal-insulator-metal (MIM) capacitors with lanthanum oxide (La2O3) high-κ dielectric, for potential applications in mixed-signal integrated circuit (IC), have been fabricated using a dense plasma focus device. The electrical characteristics and morphological properties of the fabricated nanodevices are studied. The MIM capacitors were further annealed to enhance the electrical properties in terms of the low leakage current density, the high capacitance density, and the improved capacitance voltage linearity. The minimum leakage current densities of ∼1.6 × 10−9 A/cm2 and ∼2.0 × 10−10 A/cm2 at −1 V are obtained along with the maximum capacitance densities of ∼17.96 fF/μm2 at 100 kHz and ∼19.10 fF/μm2 at 1 MHz, 0 V for as-fabricated and annealed MIM capacitors having 15 nm thick dielectric layers as measured using ellipsometry. The nanofilms with the minimum root mean square roughness of ∼10 nm are examined using atomic force microscopy. The results are superior compared to some other MIM capacitors and can be optimized to achieve the best electrical parameters for potential applications in radio frequency (RF)/mixed signal ICs. The high frequency C-V measurements indicate an increase in the capacitance density upon increasing the frequency which supports the possibility of potential high-frequency/RF applications of the MIM capacitors.