Nonstoichiometric Tin Research Articles

Preparation and characterization of PcBN composites with high entropy ceramic bonding

The polycrystalline cubic boron nitride (PcBN) composites were prepared at 5.5 GPa, 1400 °C, and 10 min holding time. The influence of different formulations on the composition, microstructure, microhardness, fracture toughness and abrasive ratio of PcBN composites was investigated by X-ray diffraction (XRD), field scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results show that: aluminum can improve the toughness and reduce the hardness of the material; WC/VC and cBN can generate hard intermediate phase to improve the hardness and reduce the toughness of the material; ZrC can achieve phase change toughening by generating ZrO 2 ; WC system, WC/VC system and WC/ZrC system all have high improvement on the hardness, denseness and abrasive ratio of the sintered body. • The non-stoichiometric ratio TiN 0.3 was used as a binding agent component. • The reaction of WC and VC with cBN increased the binding strength. • ZrC generates ZrO 2 to achieve phase change toughening to hinder the crack extension.

Exploring the functional properties of PVP/PVA blend incorporated with non-stoichiometric SnS for optoelectronic devices

The functional properties of polyvinyl pyrrolidone/polyvinyl alcohol (PVP/PVA) blend incorporated with non-stoichiometric tin sulphide (SnS) have been explored for optoelectronic devices. PVP/PVA blend incorporated with non-stoichiometric Sn/S ratios (1:0.8–1:1.2) of 1.0 wt.% SnS were prepared by casting method. The effect of the non-stoichiometric Sn/S ratio of SnS on the structure, optical and photoluminescent (PL) properties of the composite was examined by Fourier transform infrared, UV-visible-NIR and photoluminescence spectrophotometers. The optical band gap energy decreases, while Urbach energy increases via SnS incorporation. The lattice dielectric constant is improved about three times, while the free carriers’ concentration to the effective mass is enhanced by one order of magnitude due to SnS1.2 incorporating. PL measurements reveal that PVP/PVA blends incorporated with SnS could emit spectra in the visible region. Designing the optical and photoluminescent properties of the PVP/PVA blend reveal their role in advanced optoelectronic devices.

Controlled Synthesis of Highly Active Nonstoichiometric Tin Phosphide/Carbon Composites for Electrocatalysis and Electrochemical Energy Storage Applications

Three types of new-structured phosphorized tin microspheres (Sn–P), phosphorized tin microsphere-carbon (Sn–P–C), and phosphorized tin nanoparticles embedded in interconnected porous carbon microspheres (Sn–P@PCMs) were prepared through a carbothermal reduction-assisted phosphorization strategy. The characterization of the formation mechanism and microstructure of Sn–P, Sn–P–C, and Sn–P@PCMs composites demonstrated that the controllable evaporation of coordinated phosphorus in the thermally unstable tin phosphide intermediate by accurate thermal treatment contributed to the formation of a ca. 3 wt % P-doped metallic tin structure featuring a nonstoichiometric SnxPy (y/x = 0.2) core, a Sn-rich phosphorized metallic (y/x = 0.05) shell, and an increased phosphorus concentration from the outer surface to the inner core. The as-prepared phosphorized tin-based composites were applied as counter electrode materials for dye-sensitized solar cells (DSSCs), in which the Sn–P–C counter electrode exhibited the lowest charge transfer resistance of 3.47 Ω and the assembled DSSCs delivered an optimum power conversion efficiency of 8.59%, superior to those of Pt-based cells (6.78 Ω and 7.46%, respectively). The unique bifunctional structure of the SnxPy conductive core coupled with the phosphorized metallic Snδ+ (0 < σ < 0.6) electrocatalytic shell accounts for its excellent electrocatalytic activity and electrical conductivity. In addition, the phosphorized tin-based composites were utilized as potential anodic material for lithium-ion batteries, in which the Sn–P@PCMs electrode showed a specific capacity of 743 mAh g–1 at 0.1C after 400 cycles and 435 mAh g–1 at 5C after 30 cycles. The superior Li-ion storage, cyclability, and rate performance of Sn–P@PCMs could be attributed to the incorporation of Sn–P nanoparticles into interconnected porous carbon microspheres that effectively buffered the large volumetric change and enhanced the electronic–ionic conductivity during the lithiation and delithiation process.

Multilayer sensor structure based on porous silicon

The work is devoted to the creation of a sensor structure based on a porous silicon membrane. The structure under study integrates a porous layer used as a gas transport layer and a gas sensitive layer of non-stoichiometric tin oxide. The paper investigates the morphology of the structure and shows the gas permeability of the membrane on porous silicon. The gas sensitivity of the test structure obtained by passing a gas-air mixture containing NO2 has been studied. Keywords: porous silicon, membrane, non-stoichiometric tin oxide, thin films, resistive gas sensor.

X-Ray Photoelectron Spectroscopy Depth Profiling of As-Grown and Annealed Titanium Nitride Thin Films

Titanium nitride thin films were grown on Si(001) and fused silica substrates by radio frequency reactive magnetron sputtering. Post-growth annealing of the films was performed at different temperatures from 300 °C to 700 °C in nitrogen ambient. Films annealed at temperatures above 300 °C exhibit higher surface roughness, smaller grain size and better crystallinity compared to the as-grown film. Bandgap of the films decreased with the increase in the annealing temperature. Hall effect measurements revealed that all the films exhibit n-type conductivity and had high carrier concentration, which also increased slightly with the increase in the annealing temperature. A detailed depth profile study of the chemical composition of the film was performed by x-ray photoelectron spectroscopy confirming the formation of Ti-N bond and revealing the presence of chemisorbed oxygen in the films. Annealing in nitrogen ambient results in increased nitrogen vacancies and non-stoichiometric TiN films.

Spectroscopic Ellipsometry Characterization of As-Deposited and Annealed Non-Stoichiometric Indium Zinc Tin Oxide Thin Film.

A spectroscopic ellipsometry study on as-deposited and annealed non-stoichiometric indium zinc tin oxide thin films of four different compositions prepared by RF magnetron sputtering was conducted. Multi-sample analysis with two sets of samples sputtered onto glass slides and silicon wafers, together with the analysis of the samples onto each substrate separately, was utilized for as-deposited samples. Annealed samples onto the glass slides were also analyzed. Spectroscopic ellipsometry in a wide spectral range (0.2–6 eV) was used to determine optical constants (refractive index n and extinction coefficient k) of these films. Parameterized semiconductor oscillator function, together with Drude oscillator, was used as a model dielectric function. Geometrical parameters (layer thickness and surface roughness) and physical parameters (direct optical bandgap, free carrier concentration, mobility, and specific electrical resistivity) were determined from spectroscopic ellipsometry data modeling. Specific electrical resistivity determined from the Drude oscillator corresponds well with the results from electrical measurements. Change in the optical bandgap, visible especially for annealed samples, corresponds with the change of free carrier concentration (Moss–Burstein effect). Scanning electron microscope did not reveal any noticeable annealing-induced change in surface morphology.

Features of water vapor adsorption and desorption on the surface of non-stoichiometric tin dioxide films

Herein, the influence of water vapor adsorption and desorption processes on the surface of SnO2−δ nanocrystalline films with different concentrations of oxygen vacancies on their electrical conductivity at room temperature was studied. SnO2−δ films were synthesized by means of reactive magnetron sputtering of tin in an argon-oxygen plasma followed by 2-stage oxidative annealing. The concentration of oxygen vacancies in the films was varied by changing the 2nd stage annealing temperature within the range 350–400 °C. It was found that in the films with the highest concentration of oxygen vacancies (~1020 cm−3) in the region of low relative humidity (less than ~30 %), an increase in electrical conductivity was observed due to the dissociative adsorption of water molecules with the formation of hydroxyl groups. The adsorption of water vapor on the surface of SnO2−δ films at room temperature at relative humidity values higher than ~30 % was found to induce a decrease in the electrical conductivity of the samples. The generation of positive and negative EMF pulses between the open surface of SnO2−δ nanocrystalline films and the one covered by waterproof materials under the adsorption and desorption of water vapor, respectively, was detected. The change of resistance and the generated EMF value under the adsorption-desorption processes was found to increase with the concentration of free charge carriers in the films.

Nonstoichiometric tin oxide films: study by X-ray diffraction, Raman scattering and electron paramagnetic resonance

Nonstoichiometric SnO/SnO2/SnO2−δ films were fabricated by DC magnetron sputtering and reactive DC magnetron sputtering of tin target with further 2-stage temperature annealing of synthesized materials. X-ray diffraction analysis, Raman spectroscopy and electron paramagnetic resonance (EPR) spectroscopy were employed to study the influence of oxygen content in the plasma during the sputtering process and the temperature of annealing on the stoichiometric and phase composition of synthesized films. It was found that the tin monoxide phase prevailed in the films fabricated by DC magnetron sputtering in the argon plasma followed by a 2-stage annealing process. Nanocrystalline films containing both tin monoxide and tin dioxide were synthesized when reactive magnetron sputtering with a small content of oxygen (of about 1 vol.%) was used. The increase of oxygen content in the plasma to the value of about 2 vol.% leads to the formation of amorphous films. The intensity of the Raman peaks inherent in SnO2 vibration modes was found to depend on the content of the tin monoxide phase in the films. This effect can be attributed to the dissipative transition of electronic excitation from tin monoxide to tin dioxide nanocrystallites.

Co-doping effect on the electronic properties of nonstoichiometric tin telluride

ABSTRACTThe search for nontoxic compositions in the thermoelectric field has motivated many researches to find alternatives to the toxic Pb-based systems, capable of reaching their high conversion efficiency. SnTe is gaining much attention during the past years due to its superior eco-friendly character, and its very similar crystal and band structure to that of PbTe. These makes SnTe a promising compound with great potential to answer the demand and use as a fair thermoelectric candidate. Most of the recently published studies mainly discuss the stoichiometric SnTe alloy. Only several focus on the effect of introducing excess tin/tellurium to the system. For that reason, this research aims to investigate in detail the nonstoichiometric SnxTe1-x co-doped by bismuth and indium/iodine, in an attempt to optimize the electronic properties.

ELECTRICAL CONDUCTING AND MECHANISM OF OXYGEN-DEFICIENT TIN OXIDE FILMS DEPOSITED BY RF MAGNETRON SPUTTERING AT VARIOUS O2/Ar RATIOS

Oxygen-deficient tin oxide thin films were prepared by radiofrequency magnetron sputtering with a sintered non-stoichiometric tin oxide ceramic target under an atmosphere of various ratios of O2/Ar from pure Ar to 1:1. X-ray diffraction analysis showed that the thin films were polycrystalline with relatively strong (1 1 0), (1 0 1) and (2 1 1) diffraction peaks. Scanning electron microscopy observation revealed that the thin films prepared at different O2/Ar ratios were all of relatively dense and homogeneous structure. With increasing O2/Ar ratio, the grain size of the films decreased slightly, and their chemical composition became close to the stoichiometric SnO2; but the deposition rate as well as film thickness increased first and then decreased sharply. It was revealed that the main defect in obtained films was oxygen vacancy (VO), and as the O2/Ar ratio increased, the concentration of VO fell down monotonously, which would lead to an increased electrical resistivity.

The formation of layers of porous crystalline tin dioxide from a composite on the basis of multiwalled carbon-nanotube arrays

A new method for the synthesis of porous crystalline tin-dioxide (SnO2) layers from composites on the basis of multiwalled carbon nanotubes (MWCNTs) and nonstoichiometric amorphous tin oxide (MWCNT/SnO x ) is proposed. An MWCN/SnO x composite layer produced by magnetron sputtering is annealed in air atmosphere at 500°C for 30 min. A homogeneous porous layer comprised of crystalline SnO2 spherical particles with a size of about 0.1 μm is obtained as a result. In the process of annealing, nearly all the amount of carbon is removed in the form of gaseous oxides (only a small amount remains in the upper part of the porous SnO2 layer). The structural defectiveness of nanotube walls, which increases because of the magnetron deposition of tin, plays a crucial role in the carbon oxidation and destruction of MWCNTs.

Synthesis and characterization of three-dimensional flower-like tin dioxide-based structures

Three-dimensional flower-like SnO2-based structures have been produced by the alkaline hydrothermal treatment of t-SnO2 powder with no additive and in the presence of aminoterephthalic acid (ATPA). The synthesis products have been characterized by a variety of physicochemical techniques (scanning electron microscopy, transmission electron microscopy, Raman and IR spectroscopies, X-ray diffraction, and others). The results demonstrate that raising the ATPA concentration in the reaction mixture changes the morphology of the materials and leads to the SnO2 → SnO2/Sn3O4 → Sn3O4 phase transformation in the structures through the formation of SnO x nonstoichiometric tin oxide phases with 1 < x < 2. Hydrothermal treatment of the starting reagents in the presence of ≤75 wt % ATPA leads to the formation of hierarchical structures dominated by a nonstoichiometric tin oxide, which is thermally unstable at t ≥ 500°C. The morphology and phase composition of the synthesized structures have been shown to have a significant effect on the electronic conductivity of the material.

Organic Photovoltaics with Non-Stoichiometric InZnSnO Thin Film Cathodes

Non-stoichiometric indium zinc tin oxide (IZTO) thin films were deposited onto glass substrates at 400 °C by DC magnetron sputtering using non-stoichiometric (In0.5Zn0.25−xSn0.25+xO1.5 and In0.4Zn0.3−xSn0.3+xO1.5, where x = ±0.05) IZTO ceramic targets. After deposition, all of the films were given annealing treatment at 450 °C in argon. The crystallization behavior was examined by X-ray diffraction, while the optical properties were measured by ultraviolet-visible spectroscopy, in which the average transmittance values higher than 80% were observed from all films. The minimum resistivity of approximately 6.3 × 10−4 Ω·cm was observed from the Sn-rich In0.5Zn0.2Sn0.3O1.5 film. The resistivity values of Sn-rich IZTO thin films were a little smaller than those of Zn-rich IZTO films. An OPV cell with the so-called inverted structure was fabricated using various IZTO films deposited under optimized conditions as the cathode electrode. It was found that the solar cell efficiency could reach up to 7.9% which is the same with the OPV cell with conventional ITO film.

Phonon-Mediated KIDs as Light Detectors for Rare Event Search: The CALDER Project

Background suppression plays a crucial role in particle physics experiments searching for rare events, such as neutrinoless double beta decay and dark matter interactions. Bolometers, that are among the most competitive devices in this field, would largely benefit from the development of ultrasensitive light detectors, as the combined readout of the bolometric and light signals enables the particle identification. The CALDER collaboration is developing superconducting light detectors that will match the requirements of next generation experiments: noise lower than 20 eV, large active area (>20 cm 2 ), wide temperature range of operation, high radiopurity, and ease in fabricating hundreds of channels. For this purpose, we are exploiting the excellent energy resolution and the natural multiplexed readout provided by kinetic inductance detectors (KIDs). KIDs have already demonstrated their potentiality as direct detectors of photons for different astrophysical applications. The aim of our project is to apply this technology in particle physics, using indirect detection. These devices can be operated in a phonon-mediated approach, in which KIDs are coupled to a large insulating substrates in order to increase the active surface from a few mm2 to 25 cm 2 . We have already demonstrated the feasibility of a phonon-mediated KIDs-based light detectors, using aluminium sensors. These device reached a baseline sensitivity of around 80 eV with an overall efficiency of about 20%. Currently, we are testing new materials (e.g., Ti-Al and nonstoichiometric TiN) to enhance the sensitivity and reach the goal of our project. We present our results and the physical interpretation of the device behavior. Finally, we also discuss the impact of this project on the most advanced bolometric experiments searching for neutrinoless double beta decay and dark matter.

Formation of tin-tin oxide core–shell nanoparticles in the composite SnO2−x/nitrogen-doped carbon nanotubes by pulsed ion beam irradiation

The complex methods of transmission electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy were used to investigate the changes in the morphology, phase composition, and electronic structure of the composite SnO2−x/nitrogen-doped multiwalled carbon nanotubes (SnO2−x/N-MWCNTs) irradiated with the pulsed ion beam of nanosecond duration. The irradiation of the composite SnO2−x/N-MWCNTs leads to the formation of nanoparticles with the core–shell structure on the surface of CNTs with a sharp interfacial boundary. It has been established that the “core” is a metal tin (Sn0) with a typical size of 5–35nm, and the “shell” is a thin amorphous layer (2–6nm) consisting of nonstoichiometric tin oxide with a low oxygen content. The “core–shell” structure SnSnOx is formed due to the process of heating and evaporation of SnO2−x under the effect of the ion beam, followed by vapor deposition on the surface of carbon nanotubes.

Morphology and phase transformations of tin oxide nanostructures synthesized by the hydrothermal method in the presence of dicarboxylic acids

A new approach to the synthesis of non-stoichiometric tin oxide structures with different morphologies and the phase compositions has been evaluated. The nanostructures were synthesized by hydrothermal treatment of the mixtures of dicarboxylic acids ― aminoterephthalic or oxalic ― with nanocrystalline SnO2 powder, which was obtained via the sol-gel technology. The products were characterized by Raman and IR spectroscopy, SEM, HRTEM, and XRD analysis. It was shown that the controlled addition of a dicarboxylic acid leads not only to a change in the morphology of the nanostructures, but also to SnO2–SnO2/Sn3O4–Sn3O4–SnO phase transformations. A single-phase Sn3O4 in the form of the well-separated hexagonal nanoplates and mixed SnO2/Sn3O4 phases in the form of hierarchical flower-like structures were obtained in the presence of organic additives. The effects of concentration, redox activity of the acids and heat treatment on the basic characteristics of the synthesized tin oxide nanostructures and phase transformations in the synthesized materials are discussed.

IMPEDANCE SPECTROSCOPY OF POLYCRYSTALLINE TIN DIOXIDE FILMS

The aim of this work is the analysis of the influence of annealing in an inert atmosphere on the electrical properties and structure of non-stoichiometric tin dioxide films by means of impedance spectroscopy method. Non-stoichiometric tin dioxide films were fabricated by two-step oxidation of metallic tin deposited on the polycrystalline Al 2 O 3 substrates by DC magnetron sputtering. In order to modify the structure and stoichiometric composition, the films were subjected to the high temperature annealing in argon atmosphere in temperature range 300–800 °С. AC-conductivity measurements of the films in the frequency range 20 Hz – 2 MHz were carried out. Variation in the frequency dependencies of the real and imaginary parts of the impedance of tin dioxide films was found to occur as a result of high-temperature annealing. Equivalent circuits for describing the properties of films with various structure and stoichiometric composition were proposed. Possibility of conductivity variation of the polycrystalline tin dioxide films as a result of аnnealing in an inert atmosphere was demonstrated by utilizing impedance spectroscopy. Annealing induces the recrystallization of the films, changing in their stoichiometry as well as increase of the sizes of SnO 2 crystallites. Variation of electrical conductivity and structure of tin dioxide films as a result of annealing in inert atmosphere was confirmed by X-ray diffraction analysis. Analysis of the impedance diagrams of tin dioxide films was found to be a powerful tool to study their electrical properties.

Multi-Layer Structures “Por-Si-on-insulator”/SnOx for Gas Sensing Application

In this paper multi-layer “Por-Si-on-Insulator”/SnOx sensor structures based on porous silicon and non-stoichiometric tin oxide are fabricated and studied. Two-layer structures “macro-porous silicon–meso-porous silicon”, with two types of porous silicon, bound by skeleton elements on a single substrate are grown. Oxide on macro-porous silicon walls and a buried layer of oxidized meso-porous silicon play the role of the insulator. Non-stoichiometric tin oxide deposited onto the extended surface of oxidized macro-porous silicon by magnetron sputtering process is the sensitive layer. The gas sensitivity is studied upon exposure to CO and H2S. The sensitivity of the multi-layer “Por-Si-on-Insulator”/SnOx sensor structures is higher than the sensitivity of tin-oxide film samples.

Formation of two-layer composite-on-insulator structures based on porous silicon and SnO x . Study of their electrical and gas-sensing properties

The objective of this work is to fabricate and study multilayer “composite-on-insulator” sensor structures based on porous silicon and nonstoichiometric tin oxide. Two-layer structures “macroporous silicon-mesoporous silicon” on single-crystal silicon with sharp geometrical boundaries are grown. Test “composite-on-insulator” structures are fabricated. Oxide on macroporous silicon walls and a buried layer of oxidized mesoporous silicon play the role of the insulator. Nonstoichiometric tin oxide deposited onto the extended surface of oxidized macroporous silicon by chemical vapor deposition (CVD) is the sensitive layer. The gas sensitivity is studied upon exposure to NO2 and degassing in air at room temperature. The sensitivity of the por-Si/SnO x composite structures is higher than the sensitivity of tin-oxide film samples.

Electrical and gas sensing properties of por-Si/SnO x nanocomposite layers

The electrical characteristics and chemical reactant sensitivity of layers of heterogeneous nanocomposites based on porous silicon and nonstoichiometric tin oxide por-Si/SnO x , fabricated by the magnetron sputtering of tin with subsequent oxidation, are studied. It is shown that, in the nanocomposite layers, a system of distributed heterojunctions (Si/SnO x nanocrystals) forms, which determine the electrical characteristics of such structures. The sensitivity of test sensor structures based on por-Si/SnO x nanocomposites to NO2 is determined. A mechanism for the effect of the adsorption of NO2 molecules on the current-voltage characteristics of the por-Si(p)/SnO x (n) heterojunctions is suggested.