Mesoscopic Films Research Articles

Facile Synthesis, Sintering, and Optical Properties of Single-Nanometer-Scale SnO2 Particles with a Pyrrolidone Derivative for Photovoltaic Applications

We investigate the preparation of mesoscopic SnO2 nanoparticulate films using a Sn(IV) hydrate salt combined with a liquid pyrrolidone derivative to form a homogeneous precursor mixture for functional SnO2 nanomaterials. We demonstrate that N-methyl-2-pyrrolidone (NMP) plays a crucial role in forming uniform SnO2 films by both stabilizing the hydrolysis products of Sn(IV) sources and acting as a base liquid during nanoparticle growth. The hydrolysis of Sn(IV) was controlled by adjusting the reaction temperature to as low as 110 °C for 48 h. High-resolution TEM analysis revealed that highly crystalline SnO2 nanoparticles, approximately 3–5 nm in size, were formed. The SnO2 nanoparticles were deposited onto F-doped SnO2 glass and converted into dense particle films through heat treatments at 400 °C and 500 °C. This pyrrolidone-based nanoparticle synthesis enabled the production of not only crystallized SnO2 but also transparent and uniform films, most importantly by controlling the slow hydrolysis of Sn(IV) and polycondensation only with those two chemicals. These findings offer valuable insights for developing stable and uniform electron transport layers of SnO2 in mesoscopic solar cells, such as perovskite solar cells.

Resistive Avalanches in La1-xSrxCoO3-δ (x = 0, 0.3) Thin Films and Their Reversible Evolution by Tuning Lattice Oxygen Vacancies (δ).

Strong correlations are often manifested by exotic electronic phases and phase transitions. LaCoO3-δ (LCO) is a system that exhibits such strong electronic correlations with lattice-spin-charge-orbital degrees of freedom. Here, we show that mesoscopic oxygen-deficient LCO films show resistive avalanches of about 2 orders of magnitude due to the metal-insulator transition (MIT) of the film at about 372 K for the 25 W RF power-deposited LCO film on the Si/SiO2 substrate. In bulk, this transition is otherwise gradual and occurs over a very large temperature range. In thin films of LCO, the oxygen deficiency (0 < δ < 0.5) is more easily reversibly tuned, resulting in avalanches. The avalanches disappear after vacuum annealing, and the films behave like normal insulators (δ ∼0.5) with Co2+ in charge ordering alternatively with Co3+. This oxidation state change induces spin state crossovers that result in a spin blockade in the insulating phase, while the conductivity arises from hole hopping among the allowed cobalt Co4+ ion spin states at high temperature. The chemical pressure (strain) of 30% Sr2+ doping at the La3+ site results in reduction in the avalanche magnitude as well as their retention in subsequent heating cycles. The charge nonstoichiometry arising due to Sr2+ doping is found to contribute toward hole doping (i.e., Co3+ oxidation to Co4+) and thereby the retention of the hole percolation pathway. This is also manifested in energies of crossover from the 3D variable range hopping (VRH) type transport observed in the temperature range of 300-425 K, while small polaron hopping (SPH) is observed in the temperature range of 600-725 K for LCO. On the other hand, Sr-doped LCO does not show any crossover and only the VRH type of transport. The strain due to Sr2+ doping refrains the lattice from complete conversion of δ going to 0.5, retaining the avalanches.

Thermophase Seebeck Coefficient in Hybridized Superconductor-Quantum-Dot-Superconductor Josephson Junction Side-Coupled to Majorana Nanowire.

The dc Josephson current is generated from phase difference between two superconductors separated by a mesoscopic thin film (Josephson junction) without external bias voltage. In the presence of a temperature gradient across the superconductors, a thermal phase is induced under the condition of open circuit. This is very similar to the Seebeck effect in the usual thermoelectric effect, and the thermal phase is thus named as thermophase Seebeck coefficient (TPSC). Here we find obvious enhancement and sign change of the TPSC unique to the Josephson junction composing of two superconductors connected to a semiconductor quantum dot (QD), which is additionally side-coupled to a nanowire hosting Majorana bound states (MBSs), the system denoted by S-MQD-S. These result arise from the newly developed states near the Fermi level of the superconductors due to the QD-MBS hybridization when the dot level is within the superconducting gap. The sign change of the TPSC provides a strong evidence of the existence of MBSs, and is absent if the QD is coupled to regular fermion, such as another QD (system denoted by S-DQD-S). We show that the magnitude and sign of the TPSC are sensitive to the physical quantities including interaction strength between the QD and MBSs, direct overlap between the MBSs, system equilibrium temperature, as well as hopping amplitude between the QD and the superconductors. The obtained results are explained with the help of the current-carrying density of the states (CCDOS), and may be useful in interdisciplinary research areas of Josephson and Majorana physics.

Closed vortex state in three-dimensional mesoscopic superconducting films under an applied transport current

By using the full 3D generalized time-dependent Ginzbug-Landau equation, we study a long superconducting film of finite width and thickness under an applied transport current. We show that, for sufficiently large thickness, the vortices and the antivortices become curved before they annihilate each other. As they approach the center of the sample, their ends combine, producing a single closed vortex. We also determine the critical values of the thickness for which the closed vortex sets in for different values of the Ginzburg-Ladau parameter. Finally, we propose a model of how to detect a closed vortex experimentally.

SuperScreen: An open-source package for simulating the magnetic response of two-dimensional superconducting devices

Quantitative understanding of the spatial distribution of magnetic fields and Meissner screening currents in two-dimensional (2D) superconductors and mesoscopic thin film superconducting devices is critical to interpreting the results of magnetic measurements of such systems. Here, we introduce SuperScreen, an open-source Python package for simulating the response of 2D superconductors to trapped flux and applied time-independent or quasi-DC magnetic fields for any value of the effective magnetic penetration depth, Λ. Given an applied magnetic field, SuperScreen solves the 2D London equation using an efficient matrix inversion method [1,2] to obtain the Meissner currents and magnetic fields in and around structures composed of one or more superconducting thin films of arbitrary geometry. SuperScreen can be used to model screening effects and calculate self- and mutual-inductance in thin film superconducting devices. Program summaryProgram title: SuperScreenCPC Library link to program files:https://doi.org/10.17632/bds57s4c83.1Developer's repository link:http://www.github.com/loganbvh/superscreenCode Ocean capsule:https://codeocean.com/capsule/5305996Licensing provisions: MIT licenseProgramming language: PythonNature of problem:SuperScreen solves for Meissner screening currents in structures composed of 2D or thin film superconductors in the presence of an applied magnetic field, pinned vortices, and trapped flux.Solution method: This package solves the 2D London equation for superconducting thin films using a matrix inversion method [1,2].

Clusters of vortices induced by thermal gradient in mesoscopic superconductors

The structural and magnetic properties of the vortex matter in mesoscopic superconductors have been of great interest in the last decades. Recently, it has been found that vortex-vortex interaction, which is generally repulsive, can be non-monotonic under some special circumstances. Here, we have studied this issue by applying the three dimensional time dependent Ginzburg-Landau equations to a thin type-I mesoscopic superconducting film under a thermal gradient. We find that this favors the formation of small clusters of vortices in some special domains of the superconductor. We also find that this is intimately related to the non-monotonic vortex-vortex interaction by investigating the behavior of two constrained vortices in the presence of a thermal gradient. We show that the vortex-vortex interaction alternates between short range attraction and long range repulsion. This study shows that the thermal gradient has the potential to be an important tool to manipulate the vortex matter.

Tuning spin excitations in magnetic films by confinement.

Spin excitations of magnetic thin films are the founding element for magnetic devices in general. While spin dynamics have been extensively studied in bulk materials, the behaviour in mesoscopic films is less known due to experimental limitations. Here, we employ resonant inelastic X-ray scattering to investigate the spectrum of spin excitations in mesoscopic Fe films, from bulk-like films down to three unit cells. In bulk samples, we find isotropic, dispersive ferromagnons consistent with previous neutron scattering results for bulk single crystals. As the thickness is reduced, these ferromagnetic spin excitations renormalize to lower energies along the out-of-plane direction while retaining their dispersion in the in-plane direction. This thickness dependence is captured by simple Heisenberg model calculations accounting for the confinement in the out-of-plane direction through the loss of Fe bonds. Our findings highlight the effects of mesoscopic scaling on spin dynamics and identify thickness as a knob for fine tuning and controlling magnetic properties.

Self-supported mesoscopic tin oxide nanofilms for electrocatalytic reduction of carbon dioxide to formate.

Here we report a self-supported SnO2 nanofilm prepared by a robust electrochemical process as an electrocatalyst for the CO2 reduction reaction. The SnO2 film had a large surface area originating from its nano-architecture and manifested high selectivity toward formate (over 60%), which resulted in CO2-to-formate current density up to 33.66 mA cm-2 that is among the state-of-the-art. We unveiled that the high performance of the SnO2 nanofilm is attributable to the presence of a metastable oxide under reductive conditions in addition to the abovementioned advantages.

A Combined Experimental and Theoretical Study of Screen-printing High Transparent\xa0Conductive Mesoscopic ITO Films

We have successfully fabricated transparent conductive mesoporous indium tin oxide (TCM-ITO) films by a screen-printing method. The TCM-ITO films possess approximately 22 nm mesopores and obtain electrical conductivity up to 14.96 S/cm by adjusting the mass ratio of cubic-shaped ITO nanoparticles to ethyl cellulose (EC) and precisely controlling the annealing process. The regulation mechanism of EC and the heat-induced recrystallization process of ITO nanoparticles are elaborated. The internal kinetic processes of the films based on different surface states are analysed, and an extensible impedance model is established.

Heat rectification via a superconducting artificial atom

In developing technologies based on superconducting quantum circuits, the need to control and route heating is a significant challenge in the experimental realisation and operation of these devices. One of the more ubiquitous devices in the current quantum computing toolbox is the transmon-type superconducting quantum bit, embedded in a resonator-based architecture. In the study of heat transport in superconducting circuits, a versatile and sensitive thermometer is based on studying the tunnelling characteristics of superconducting probes weakly coupled to a normal-metal island. Here we show that by integrating superconducting quantum bit coupled to two superconducting resonators at different frequencies, each resonator terminated (and thermally populated) by such a mesoscopic thin film metal island, one can experimentally observe magnetic flux-tunable photonic heat rectification between 0 and 10%.

Formation and Annihilation of Vortex-Antivortex Pairs by Magnetic Dipoles in a Mesoscopic Superconducting Film

Formation and Annihilation of Vortex-Antivortex Pairs by Magnetic Dipoles in a Mesoscopic Superconducting Film

PREPARATION OF MESOSCOPIC STRUCTURE POLY METHYL METHACRYLATE THIN FILMS FOR AFM DATA STORAGE DEVICES.

Poly methyl methacrylate (PMMA) thin films were prepared by dip coating method. Benzene was used as a solvent to prepare PMMA thin films for the time periods ranging from 1 min. to 1 h. The thickness of the films deposited was measured by using an electronic thickness measuring instrument (Tesatronic-TTD-20). Fourier Transform Infrared spectrum was used to identify the above said films. X-ray diffraction spectra indicated the predominantly amorphous nature of the films. Surface morphology of the coated films studied by using scanning electron microscope (SEM) indicated the absence of any pits, cracks and pin holes in the surface. Both as grown and annealed films showed smooth and amorphous structures. The closer SEM inspection revealed the presence of self assembled mesoscopic cells. The mesoscopic structure PMMA thin films could be used as an AFM-based data storage which is promising alternative to conventional magnetic data storage because it offers great potential for considerable storage density improvements.

Control of the pore size of honeycomb polymer film from micrometers to nanometers via substrate-temperature regulation and its application to photovoltaic and heat-resistant polymer films

Honeycomb porous polystyrene (PS) films with an aspect ratio of pore depth to pore diameter at approximately 1.0 were fabricated using the breath figure (BF) method. Two modes of water droplet coalescence in the pore growth were observed in real-time by optical microscopy. Pore size significantly increases with the increase in humidity and the decrease in substrate temperature. The porous pattern could emerge even at room temperature under high humidity of 80%. Boiling point and solvent density significantly influence the pore distribution and pore depth. Chloroform and tetrahydrofuran achieve more uniform hexagonal patterns than benzene and dichloromethane. Subsequently, to obtain nanometer porous PS film, the fast-evaporation BF process was designed by regulating the gradient substrate temperature and evaporation time, and porous mesoscopic PS film was obtained. The minimum pore diameter and corresponding pore depth are about 120 nm and 27 nm, respectively. Finally, the fast-evaporation BF process was applied to the honeycomb film formation of photovoltaic polymer poly(3-hexylthiophene) (P3HT), and the heat-resistant polymers polysulfone (PSF) and polyimide (PI).

Magnetic properties dependence of mesoscopic scale thick films on thickness and surface roughness characteristics: Case of nickel samples in Ni/Pt system

Thickness (d) and surface roughness (σ) of material thin films are inseparable characteristics engendered by the same deposition process. Both are crucial parameters for magnetic properties (p) of real mesoscopic scale thick ferromagnetic films. When condition (d/σ) < 102 is validated, sorting out samples of a series is possible only by means of τ = (d/σ) geometrical ratio which enables their coherent comparison. Their magnetic properties (p) are thereby expressed in a single function form p = f(τ). Application of that approach to a series of nanostructured Ni electrodeposits reveals that these samples are consistent with the ratio range 1.23 ≤ τ ≤ 82.00 concurring with the reported description. Their coercivity (Hc) and magnetic domain size (w) behave in agreement with their respective predicted general curve profile when d is substituted by τ, which depicts quite well the similar role of both parameters. The study of these properties evolution using the normalization model indicates a discontinuity in the magnetism of the investigated samples. Bloch magnetic domains (MD)B are associated with mixed domain walls (DWN + DWB) below a critical position (τ0−1) ≈ 0.35, while Néel domain walls (DWN) coexist with mixed magnetic domains (MDB + MDN) beyond that position.

Magnetic-Field-Induced Vortices and Antivortices in a Mesoscopic Ferromagnet/Insulator/Superconductor Strip

The time-dependent Ginzburg–Landau equations have been solved numerically by a finite element method for a hybrid system consisting of a finite-size superconducting film with a magnetic strip on top. It is demonstrated that the coexistence of vortices and antivortices could occur in the mesoscopic superconducting film due to the important influence of the magnetic strip, which could help us to understand the experimental results.

Collective Motion in the Interfacial and Interior Regions of Supported Polymer Films and Its Relation to Relaxation.

To understand the role of collective motion in the often large changes in interfacial molecular mobility observed in polymer films, we investigate the extent of collective motion in the interfacial regions of a thin supported polymer film and within the film interior by molecular dynamics simulation. Contrary to commonly stated expectations, we find that the extent of collective motion, as quantified by string-like molecular exchange motion, is similar in magnitude in the polymer-air interfacial layer as the film interior and distinct from the bulk material. This finding is consistent with Adam-Gibbs description of the segmental dynamics within mesoscopic film regions, where the extent of collective motion is related to the configurational entropy of the film as a whole rather than a locally defined extent of collective motion or configurational entropy.

Highly Efficient Organic Blue Electroluminescent Materials and Devices with Mesoscopic Structures.

Due to the difficulty in achieving high efficiency and high color purity simultaneously, blue emission is the limiting factor for the performance and stability of OLEDs. Since 2003, we have been working on organic light-emitting diodes (OLEDs), especially on blue light. After a series of molecular designs, novel strategies have been proposed from different aspects. At first, highly efficient deep blue emission could be achieved through molecular design with highly twisted structure to suppress fluorescence quenching and redshift. Deep blue emitters with high efficiency in solid state, a twisted structure with aggregation induced emission (AIE) characteristics was incorporated to inhibit molecular aggregation, and triplet-triplet fusion (TTF) and hybridized localized charge transfer (HLCT) were adopted to increase the ratio of triplet exciton used. Secondly, a highly efficient blue OLED could be achieved through improving charge transport. New electron transport materials (ETMs) with wide band gap were developed to control charge transport balance in devices. Thirdly, a highly efficient deep blue emission could be achieved through a mesoscopic structure of out-coupling layer. A mesoscopic photonic structured organic thin film was fabricated on the top of metal electrode by self-aggregation in order to improve the light out-coupling efficiency.

Extraordinary Field Enhancement of TiO2 Porous Layer up to 500‐Fold

AbstractTitanium dioxide (TiO2) is known as a very important material for photocatalysts, the photoelectrode for hydrogen evolution reaction, and the porous layer of perovskite solar cells. Their properties as well as device performances such as photoconversion efficiencies are significantly enhanced if integration of TiO2 providing a large field enhancement of light is made possible. However, the field enhancement has not been revealed for TiO2 materials, and then increased device performances have not been reported either so far. Here, extraordinary field enhancement of a porous TiO2 layer, mesoscopic film, prepared by a facile wet process in conjunction with ball milling and drop casting is shown. The field enhancement is investigated with respect to the fluorescence intensity of a dye molecule and an enhancement factor (EF) of up to 500 is achieved, which corresponds to the largest EF for a semiconductor. Furthermore, EF is up to 30 000 after numerical corrections. The large EF is realized for a porous TiO2 layer composed of a specific particle size of 550 nm, which is consistent with the results of fluorescence intensity, scattering intensity, and two different theoretical calculations based on Mie scattering theory, with respect to particle size. A special advantage of the current system is the mesoscopic porous layer giving many hot spots among TiO2 particles of the specific size.

Electrochemically Synthesized Mesoscopic Nickel Oxide Films as Photocathodes for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) have been considered as promising and reliable solar energy conversion devices that are suitable for various applications. In general, mesoscopic TiO2 films are of...

Nonlocal optical response of weakly confined excitons in Cu2O mesoscopic films

We have demonstrated size-dependent radiative coupling in a ${\mathrm{Cu}}_{2}\mathrm{O}$ mesoscopic film, where the spatial matching between the center-of-mass exciton motion and light waves plays an essential role. The observed quadratic increase and oscillation of the photoluminescence intensity with varying film thicknesses (16--1000 nm) indicate a nonlocal response that is unique to mesoscopic systems. Optimally, a ${10}^{4}$-fold enhanced radiative rate was found compared with bulk ${\mathrm{Cu}}_{2}\mathrm{O}$. A new degree of freedom in the light-matter interaction is presented, which differs from the mode volume control in cavity quantum electrodynamics.