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Organic/oxide interfaces exhibit an energy-level-alignment universal behaviour when a bias is applied. Coulomb-blockade regime is ruled by the organic electronegativity.
The crystalline-Si/amorphous-SiO 2 (c-Si/a-SiO 2 ) interface is an important system used in many applications, ranging from transistors to solar cells. The transition region of the c-Si/a-SiO 2 interface plays a critical role in determining the band alignment between the two regions. However, the question of how this interface band offset is affected by the transition region thickness and its local atomic arrangement is yet to be fully investigated. Here in this study, by controlling the parameters of the classical Monte Carlo bond switching algorithm, we have generated the atomic structures of the interfaces with various thicknesses, as well as containing Si at different oxidation states. A hybrid functional method, as shown by our calculations to reproduce the GW and experimental results for bulk Si and SiO 2 , was used to calculate the electronic structure of the heterojunction. This allowed us to study the correlation between the interface band characterization and its atomic structures. We found that although the systems with different thicknesses showed quite different atomic structures near the transition region, the calculated band offset tended to be the same, unaffected by the details of the interfacial structure. Our band offset calculation agrees well with the experimental measurements. This robustness of the interfacial electronic structure to its interfacial atomic details could be another reason for the success of the c-Si/a-SiO 2 interface in Si-based electronic applications. Nevertheless, when a reactive force field is used to generate the a-SiO 2 and c-Si/a-SiO 2 interfaces, the band offset significantly deviates from the experimental values by about 1 eV
A simple one-step pulsed laser deposition (PLD) method has been applied to grow self-assembled metal-oxide nanocomposite thin films. The as-deposited Co-BaZrO 3 films show high epitaxial quality with ultra-fine vertically aligned Co nanopillars (diameter <5 nm) embeded in BZO matrix. The diameter of the nanopillars can be further tuned by varying the deposition frequency. The metal and oxide phases grow separately without inter-diffusion or mixing. Taking advantage of this unique structure, a high saturation magnetization of ~1375 emu/cm 3 in the Co- BaZrO 3 nanocomposites has been achieved and further confirmed by Lorentz microscopy imaging in TEM. Furthermore, the coercivity values of this nanocomposite thin films range from 600 Oe (20 Hz) to 1020 Oe (2 Hz), which makes the nanocomposite an ideal candidate for high-density perpendicular recording media.
Tunable plasmonic structure at the nanometer scale presents enormous opportunities for various photonic devices. In this work, we present a hybrid plasmonic thin film platform: i.e., a vertically aligned Au nanopillar array grown inside a TiN matrix with controllable Au pillar density. Compared to single phase plasmonic materials, the presented tunable hybrid nanostructures attain optical flexibility including gradual tuning and anisotropic behavior of the complex dielectric function, resonant peak shifting and change of surface plasmon resonances (SPRs) in the UV-visible range, all confirmed by numerical simulations. Lastly, the tailorable hybrid platform also demonstrates enhanced surface plasmon Raman response for Fourier-transform infrared spectroscopy (FTIR) and photoluminescence (PL) measurements, and presents great potentials as designable hybrid platforms for tunable optical-based chemical sensing applications.
Fabrication of high-conductivity ion exchange membranes (IEMs) is crucial to improve the performance of non-aqueous vanadium redox flow batteries (NAVRFBs). In the present work, anion exchange membranes with high-conductivity were fabricated by aligning ion channels of the polymer electrolyte impregnated in porous polytetrafluoroethylene (PTFE) under electric fields. It was observed that the ion channels of the polymer electrolyte were uniformly orientated in the atomic-force microscopy image. Its morphological change could minimize detouring of the transport of BF 4 - ions. The results showed through-plane conductivity was improved from 12.7 to 33.1 mS cm -1 . The dimensional properties of the fabricated membranes were also enhanced compared with its cast membrane owing to the reinforcing effect of the substrate. Especially, the NAVRFB assembled with the optimized membrane showed increased capacities, with a 97% coulombic efficiency and 70% energy efficiency at 80 mA cm -2 . Furthermore, the optimized membrane made it possible to operate the NAVRFB at 120 mA cm -2 . Its operating current density was 120 times higher than that of a frequently used AHA membrane for RFBs.
Selective shear deposition of polymer-wrapped semiconducting carbon nanotubes (s-CNTs) into densely packed, highly aligned arrays of s-CNTs using removable chemical and topographical patterns.
Surfaces with tunable microscale textures are vital in a large variety of technological applications, including heat transfer, antifouling and adhesion. To facilitate such broad-scale use, there is a need to create surfaces that undergo reconfigurable changes in topology and thus, enable switchable functionality. To date, there is a relative dearth of methods for engineering surfaces that can be actuated to change topography over a range of length scales, and hence, form tunable hierarchically structured layers. Combining modeling and experiments, we design a geometrically patterned, thermo-responsive poly (N-isopropylacrylamide) gel film that undergoes controllable hierarchical changes in topology with changes in temperature. At the bottom, the film is covalently bound to a solid, curved substrate; at the top, the film encompasses longitudinal rectangular ridges that are oriented perpendicular to the underlying cylindrical curves. At temperatures below lower critical solution temperature (LCST), the swollen gel exhibits 3D variations in polymer density and thickness defined by the gel's top and bottom topography. As the temperature rises above LCST, the interplay between the upper ridges and lower curves in the gel drives non-uniform, directional solvent transport, the nucleation and propagation of a phase-separated higher-density skin layer, and the resulting pressure buildup within the film. These different, interacting kinetic processes lead to an instability, which produces transient microscopic blisters in the film. Through simulations, we show how tuning the width of the ridges modifies the propagation of a skin layer and creates localized pressure build-up points, which enables control over the emergence, distribution, and alignment of the microscopic blisters. Futhermore, we provide a simple argument to predict the size of such microscopic features. Experiments confirm our predictions and further highlight how our computational model enables the rational design of topographical transitions in these tunable films. The development of actuatable, hierarchically structured films provides new routes for achieving switchable functionality in actuators, drug release systems and adhesives.
This work demonstrates the application of pilot-scale surface functionalization of cellulose nanofibrils (CNFs) by aqueous grafting-through polymerization and subsequent spray drying in 3D printed poly(lactic acid) (PLA) composites. Grafted-CNF composites attain an ultimate tensile strength of 88 ± 3 MPa and a tensile modulus of elasticity of 7.8 ± 1.3 GPa in the printing direction at 20 wt% reinforcement loading. These increases, 42% and 139% over neat PLA, respectively, represent the strongest reported 3D printed CNF/PLA composite to date in the literature. The mechanisms behind these improvements are investigated by comparisons to neat PLA and unmodified spray-dried CNF/PLA controls using melt rheology, dynamic mechanical analysis, and assessment of the reinforcement dispersion. These experiments reveal that improved network formation and shear-induced alignment of the grafted CNFs facilitate the remarkable tensile properties of the printed composites.
ZnO thin films have attracted significant interest in the past decades owing to their unique wide band gap properties, piezoelectric properties, non-linearity and plasmonic properties. Recent efforts have been made in coupling ZnO with secondary phases to enhance its functionalities, such as Au–ZnO nanocomposite thin films with tunable optical and plasmonic properties. In this work, magnetic nanostructures of Ni are incorporated in ZnO thin films in a vertically aligned nanocomposite (VAN) form to couple magnetic and plasmonic response in a complex hybrid metamaterial system. Nickel (Ni) is of interest due to its ferromagnetic and plasmonic properties along with gold (Au) which is also plasmonic. Therefore, two approaches, namely, tuning of the deposition pressure and use of a ZnO–Au seeding layer have been attempted to achieve unique Ni nanostructures in addition to tuning of the microstructure. Together, both approaches demonstrate a range of microstructures such as core–shell, nanodisk, nanocup, and nanocube-like morphologies not previously attempted. Additionally, there is effective tuning of properties. Specifically, the seeding layer thickness causes hyperbolic behavior as well as redshift in the surface plasmon resonance (SPR) wavelength. The addition of the ZnO–Au seeding layer directly influences the optical properties. Plus, regardless of the different approaches, the films demonstrate magnetic anisotropy based on the composition and microstructure of the film which impacted the saturation magnetization and coercivity. This study demonstrates the potential of ZnO-based complex hybrid metamaterials with coupled electro-magneto-optical properties for integrated photonic devices.
The chiral magnetic effect (CME) in high-energy heavy-ion collisions arises from the interplay between the chirality imbalance and the intense magnetic field and will cause a charge separation along the magnetic field direction. While the CME search is still ongoing in experiments, the non-CME contributions need to be excluded from the CME observables. In this work, we examine the influence of globally spin-aligned ρ mesons on the γ 112 correlator, the R Ψ 2 (ΔS) correlator, and the signed balance functions, via a toy model and a multiphase transport model (AMPT). We find that the CME observables are sensitive to the 00-component of the spin density matrix, ρ 00 : they receive positive (negative) contributions when ρ 00 is larger (smaller) than 1/3.
The band alignment of Al{sub 2}O{sub 3}/n-Ga{sub 2}O{sub 3} was investigated by x-ray photoelectron spectroscopy (XPS). With a band gap of 6.8 ± 0.2 eV measured for Al{sub 2}O{sub 3}, the conduction and valence band offsets at the interface were estimated to be 1.5 ± 0.2 eV and 0.7 ± 0.2 eV, respectively. The conduction band offset was also obtained from tunneling current in Al{sub 2}O{sub 3}/n-Ga{sub 2}O{sub 3} (2{sup ¯}01) metal-oxide-semiconductor (MOS) diodes using the Fowler-Nordheim model. The electrically extracted value was in good agreement with the XPS data. Furthermore, the MOS diodes exhibited small capacitance-voltage hysteresis loops, indicating the successful engineering of a high-quality Al{sub 2}O{sub 3}/Ga{sub 2}O{sub 3} interface.
The double exchange is a well-known and technically important phenomenon in solid state physics. Ionizing a system composed of two antiferromagnetically coupled high-spin units, the ground state of which is a singlet state, may actually produce a high-spin ground state. This work illustrates the possible occurrence of such a phenomenon in organic chemistry. The here-considered high-spin units are triangulenes, the ground state of which is a triplet. Bridging two of them through a benzene ring produces a molecular architecture of singlet ground state. A careful exploitation of a series of unrestricted density functional calculations enables one to avoid spin contamination in the treatment of the doublet states and shows that under ionization the system becomes of quartet multiplicity in its ground state. The possibility to align more than three spins from conjugated hydrocarbon polyradicals is explored, considering partially hydrogenated triangulenes. A dramatic example shows that ionization of a singlet ground state molecule may generate a decuplet.
Electronic open-shell ground-state properties of selected alkali-metal–alkaline-earth-metal polar molecules are investigated. We determine potential energy curves of the {sup 2}Σ{sup +} ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes ({sup 23}Na, {sup 39}K, {sup 85}Rb)–({sup 40}Ca, {sup 88}Sr) are compared with available theoretical and experimental results. The variation of the permanent dipole moment (PDM), average dipole polarizability, and polarizability anisotropy with internuclear distance is determined using finite-field perturbation theory at the CCSD(T) level. Owing to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u., RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for alignment and orientation in combined intense laser and external static electric fields.
Energy-band alignments for molybdenum disulphide (MoS{sub 2}) films on high-k dielectric oxides have been studied using photoemission spectroscopy. The valence band offset (VBO) at monolayer MoS{sub 2}/Al{sub 2}O{sub 3} (ZrO{sub 2}) interface was measured to be 3.31 eV (2.76 eV), while the conduction-band offset (CBO) was 3.56 eV (1.22 eV). For bulk MoS{sub 2}/Al{sub 2}O{sub 3} interface, both VBO and CBO increase by ∼0.3 eV, due to the upwards shift of Mo 4d{sub z{sup 2}} band. The symmetric change of VBO and CBO implies Fermi level pinning by interfacial states. Our finding ensures the practical application of both p-type and n-type MoS{sub 2} based complementary metal-oxide semiconductor and other transistor devices using Al{sub 2}O{sub 3} and ZrO{sub 2} as gate materials.
Self-aligned ZnO nanorods (NRs) were grown on n-Si(100) substrate by RF sputtering techniques. The NRs are uniformly grown on 2-inch wafer along [0001] direction. Single-crystalline wurtzite structure of ZnO NRs was confirmed by X-ray diffraction. The average diameter, height, and density of NRs are found 48 nm, 750 nm, and 1.26 × 10{sup 10} cm{sup −2}, respectively. The current-voltages (I-V) characteristics of ZnO NRs/Si heterojunction (HJ) were studied in the temperature range of 120–300 K and it shows a rectifying behavior. Barrier height (ϕ{sub B}) and ideality factor (η) were estimated from thermionic emission model and found to be highly temperature dependent in nature. Richardson constant (A{sup *}) was evaluated using Richardson plot of ln(I{sub o}/T{sup 2}) versus q/kT plot by linear fitting in two temperature range 120–180 K and 210–300 K. Large deviation in Richardson constant from its theoretical value of n-Si indicates the presence of barrier inhomogeneities at HJ. Double Gaussian distribution of barrier height with thermionic equation gives mean barrier heights of 0.55 ± 0.01 eV and 0.86 ± 0.02 eV for two different temperature regions 120–180 K and 210–300 K, respectively. Modified Richardson plot provided two values of Richardson constant for two temperature regions. However, for higher temperature range (210–300 K), the calculated value of Richardson constant ∼123 A cm{sup −2} K{sup −2} was close to the ideal Richardson constant for n-Si.
The cross-magnetic-field (i.e., perpendicular) profile of ion temperature and the perpendicular profile of the magnetic-field-aligned (parallel) plasma flow are sometimes inhomogeneous for space and laboratory plasma. Instability caused either by a gradient in the ion-temperature profile or by shear in the parallel flow has been discussed extensively in the literature. In this paper, (1) hydrodynamic plasma stability is investigated, (2) real and imaginary frequency are quantified over a range of the shear parameter, the normalized wavenumber, and the ratio of density-gradient and ion-temperature-gradient scale lengths, and (3) the role of inverse Landau damping is illustrated for the case of combined ion-temperature gradient and parallel-flow shear. We find that increasing the ion-temperature gradient reduces the instability threshold for the hydrodynamic parallel-flow shear instability, also known as the parallel Kelvin-Helmholtz instability or the D'Angelo instability. We also find that a kinetic instability arises from the coupled, reinforcing action of both free-energy sources. For the case of comparable electron and ion temperature, we illustrate analytically the transition of the D'Angelo instability to the kinetic instability as (a) the shear parameter, (b) the normalized wavenumber, and (c) the ratio of density-gradient and ion-temperature-gradient scale lengths are varied and we attribute the changes in stability to changes in the amount of inverse ion Landau damping. We show that near a normalized wavenumber k{sub ⊥}ρ{sub i} of order unity (i) the real and imaginary values of frequency become comparable and (ii) the imaginary frequency, i.e., the growth rate, peaks.
The band alignment between Ga-face GaN and atomic-layer-deposited ZrO{sub 2} was investigated using X-ray photoelectron spectroscopy (XPS). The dependence of Ga 3d and Zr 3d core-level positions on the take-off angles indicated upward band bending at GaN surface and potential gradient in ZrO{sub 2} layer. Based on angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ΔE{sub V} of 1 ± 0.2 eV and conduction band discontinuity ΔE{sub C} of 1.2 ± 0.2 eV at ZrO{sub 2}/GaN interface were determined by taking GaN surface band bending and potential gradient in ZrO{sub 2} layer into account.
The valence band offset (VBO) of InN/6H-SiC heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be −0.10 ± 0.23 eV and the conduction band offset is deduced to be −2.47 ± 0.23 eV, indicating that the heterojunction has a type-II band alignment. The accurate determination of the valence and conduction band offsets is important for applications and analysis of InN/6H-SiC optoelectronic devices.