SnO2 Monolayer Research Articles

InOx Doped SnO2 Nanostructure Deposited on MEMS Device by PE-ALD Process for Detection of NO2

The micro-electro-mechanical systems (MEMS) method makes the gas sensing element. The sensing layer uses RF Sputter and plasma-enhanced atomic layer deposition (PE-ALD) technology to deposit indium oxide (InOx) thin films on Tin oxide (SnO2) to form an n-n type double-layer structure. The results show that the response of SnO2-InOx and monolayer SnO2 is 153% and 55%, respectively, which is an improvement of 98% under exposure to 0.6 ppm NO2, and the sensor can obtain the best sensing at 200 °C (∼14 mW). In response, the lowest NO2 concentration was 0.2 ppm, and the selectivity test was carried out with four other gases, such as SO2, H2, CO, and NH3, and the test results showed the specificity for NO2.

Well-organized SnO2 inverse opal monolayer as structured electron transport layer for high-efficiency perovskite solar cells

In mesoporous perovskite solar cells (mp-PSCs), an electron transport layer (ETL) plays an important role in charge extraction and transportation, and also its structure largely affects the crystallization and optical property of perovskite films. At present, the performance of PSCs based mesoporous SnO2 (mp-SnO2) still lags behind that based planar SnO2 due to problems in the fabrication process of mp-SnO2. Herein, a well-organized monolayer SnO2 inverse opal (SIO) is prepared as the structured ETL for perovskite solar cells. The unique periodic SIO structure exhibits an obvious optical coupling phenomenon, which enhances the light absorption of the perovskite layer. Furthermore, the well-organized SIO structure with appropriate pore size triggers the confined crystallization of perovskite films and optimizes the interface of SnO2/perovskites, suppressing the interfacial electron–hole recombination. As a result, the power conversion efficiency of mp-PSCs fabricated by the monolayer SIO is boosted from 19.63% to 22.01%. This work provides a creative strategy for construction of high-efficiency mp-PSCs based on SnO2.

Mechanical manipulation of electronic properties of SnO2 monolayer

A unique and novel SnO2 monolayer structure was introduced and studied by first-principles calculations based on the density functional theory (DFT). Bonding nature and band gap relation to elastic properties were obtained by fitting elastic energy as a function of Green-Lagrangian strain and calculating the elastic constants. The application of uniaxial strain produced a small in-plane stiffness with high Poisson’s ratio. These values revealed no lateral stress was resulted on bonds by the applied longitudinal strain. Area stiffness constant was defined for in-plane area expansion or compression. A higher area stiffness was found for biaxially placed strains, attributed to bending of the Sn-O-Sn bonds, which imposed a direct strain on the Sn-O bonds. Also, the electrons band gap varied from semiconductor energy at equilibrium atomic geometry to narrower gap with the application of biaxial strain. The variance was insignificant for the uniaxial strain case. We Show that the stability in the atomic bonding at strained conditions with fixed unit cell area gave controllability over the electronic state. Interlayer hybridization between O and Sn atoms made the band gap distinctly tunable with biaxial strain.

Chemiresistive trimethylamine sensor using monolayer SnO2 inverse opals decorated with Cr2O3 nanoclusters

Two-dimensional SnO2 inverse opal (2D IO) structures with uniform surface decoration of Cr2O3 nanoclusters were prepared using a Sn-solution-dipped sacrificial polystyrene monolayer template method and were employed for chemiresistive gas-sensor applications. The responses (resistance ratio) of the pure SnO2 2D IO sensor to 5 ppm trimethylamine (TMA) and ethanol were as high as 209.5 and 242.3, representing improvements of two orders of magnitude compared with that of a dense SnO2 thin film sensor. The high gas response of the porous SnO2 IO sensor is attributed to the superior gas accessibility as well as the large chemiresistive variation at the thinnest neck region of the 2D IO structures. Further enhancements of the TMA selectivity and response were achieved by decorating the surface of the SnO2 IO structure with Cr2O3 nanoclusters. The control of the TMA-sensing characteristics of the SnO2 2D IO sensor through the decoration with Cr2O3 nanoclusters was explained by the change of the electron-depletion layer in the SnO2 particles due to the formation of the p(Cr2O3)-n(SnO2) junction, as well as the catalytic promotion of the gas-sensing reaction by Cr2O3. The oxide 2D IO films with high gas accessibility and chemiresistive neck structures are promising nanoarchitectures for gas-sensor applications, and the formation of hetero-nanostructures via decoration with different oxide semiconductor nanoclusters having dissimilar work functions and catalytic activity allows the enhancement of the selectivity toward a specific gas, as well as the gas response.

Band structure and optical properties of MoS2/SnO2 hetero-bilayer from hybrid functional calculations

The electronic structure and optical properties of MoS2/SnO2 hetero-bilayer have been systematically investigated with hybrid functional calculations. The band dispersion character of monolayer MoS2 at the VBM and that of monolayer SnO2 at CBM are well preserved in the MoS2/SnO2 hetero-bilayer, and thus the effective separation of electrons and holes is expected. Besides, the band gap narrowing in the MoS2/SnO2 hetero-bilayer can accordingly enhance the effective utilization of the solar spectrum, especially in the visible light region. Additionally, the MoS2/SnO2 hetero-bilayer that is active for both the photo-oxidation and photo-reduction of water possesses superior photocatalytic activity than that of monolayer MoS2 and SnO2.

Protecting the Nanoscale Properties of Ag Nanowires with a Solution-Grown SnO2 Monolayer as Corrosion Inhibitor

The chemical reactivity and/or the diffusion of Ag atoms or ions during thermal processing can cause irreversible structural damage, hindering the application of Ag nanowires (NWs) in transparent conducting films and other applications that make use of the material's nanoscale properties. Here, we describe a simple and effective method for growing monolayer SnO2 on the surface of Ag nanowires under ambient conditions, which protects the Ag nanowires from chemical and structural damage. Our results show that Sn2+ and Ag atoms undergo a redox reaction in the presence of water. First-principle simulations suggest a reasonable mechanism for SnO2 formation, showing that the interfacial polarization of the silver by the SnO2 can significantly reduce the affinity of Ag to O2, thereby greatly reducing the oxidation of the silver. The corresponding values (for example, before coating: 17.2 Ω/sq at 86.4%, after coating: 19.0 Ω/sq at 86.6%) show that the deposition of monolayer SnO2 enables the preservation of high transparency and conductivity of Ag. In sharp contrast to the large-scale degradation of pure Ag-NW films including the significant reduction of its electrical conductivity when subjected to a series of harsh corrosion environments, monolayer SnO2 coated Ag-NW films survive structurally and retain their electrical conductivity. Consequently, the thermal, electrical, and chemical stability properties we report here, and the simplicity of the technology used to achieve them, are among the very best reported for transparent conductor materials to date.

Room‐Temperature NO2 Gas Sensing with Ultra‐Sensitivity Activated by Ultraviolet Light Based on SnO2 Monolayer Array Film

AbstractChemiresistive‐type gas sensors, which are driven by the thermal activation, have exhibited extraordinary promise for the detection of air pollutions, such as highly toxic gas of nitrogen dioxide (NO2), but are often limited to its high operating temperature, because of the raising explosive risk in inflammable gases. This study reports the construction of a close‐packed SnO2 monolayer film, and uses it as the NO2 room‐temperature sensing layer induced by ultraviolet (UV)‐light irradiation. Such SnO2 monolayer array film shows excellent sensing performances toward NO2 gas with a striking selectivity under the UV‐light irradiation even in high humidity. Additionally, by precisely controlling the sensing film thickness, it is observed that the NO2 sensing characteristics can be optimized to provide ultra‐selectivity and high gas response. Through the systematic analysis, it reveals that the “clean effect” of UV‐light for surface‐adsorbed O2b− ions and the competitive adsorption between NO2 and O2 gas during sensing process are responsible for the possible sensing mechanism. More importantly, this work exhibits the intrinsic relation between sensing performances and the film thickness under the UV‐light illumination, which is of vital importance to actual sensing requirements.

Strong phonon anharmonicity and low thermal conductivity of monolayer tin oxides driven by lone-pair electrons

Motivated by the excellent electronic and optoelectronic properties of two-dimensional (2D) tin oxides, we systematically investigated the thermal conductivity (κ) of monolayers SnO and SnO2 by the first-principles calculations. The room-temperature κ of monolayers SnO and SnO2 reaches 9.6 W/(m K) and 98.8 W/(m K), respectively. The size effect is much weaker for monolayer SnO than for monolayer SnO2, due to the coexistence of size dependent and independent components in the κ value of monolayer SnO. The large difference between the κ values of 2D tin oxides can be attributed to the small phonon group velocity and strong anharmonicity strength of monolayer SnO. Further electronic structure analysis reveals that the existence of sterically active lone-pair electrons is the key factor for the small κ value of monolayer SnO. These results provide a guide for the manipulation of thermal transport in electronic or thermoelectric devices based on 2D tin oxides.

A first-principles study of the SnO2 monolayer with hexagonal structure.

We report the structural, electronic, magnetic, and elastic properties of a two-dimensional (2D) honeycomb stannic oxide (SnO2) monolayer based on comprehensive first-principles calculations. The free-standing and well-ordered 2D centered honeycomb SnO2 (T-SnO2) monolayer with D3d point-group symmetry has good dynamical stability, as well as thermal stability at 500 K. The T-SnO2 monolayer is a nonmagnetic wide-bandgap semiconductor with an indirect bandgap of 2.55/4.13 eV obtained by the generalized gradient approximation with the Perdew-Burke-Ernzerhof/Heyd-Scuseria-Ernzerhof hybrid functional, but it acquires a net magnetic moment upon creation of a Sn vacancy defect. The elastic constants obtained from the relaxed ion model show that the T-SnO2 monolayer is much softer than MoS2. The bandgap monotonically decreases with increasing strain from -8% to 15%. An indirect-to-direct bandgap transition occurs upon applying biaxial strain below -8%. Synthesis of the T-SnO2 monolayer is proposed. We identify the Zr(0001) surface as being suitable to grow and stabilize the T-SnO2 monolayer. The unique structure and electronic properties mean that the T-SnO2 monolayer has promising applications in nanoelectronics. We hope that the present study on the stable free-standing SnO2 monolayer will inspire researchers to further explore its importance both experimentally and theoretically.

The Electronic Structure and Optical Properties of Ag-Doped SnO2 Monolayer

The electronic structure and optical properties of Ag-doped SnO2 monolayer are investigated using first-principles FLAPW method. The results show that Ag:SnO2 monolayer is a direct-gap semiconductor, and band gap becomes narrow. Several obvious optical absorption peaks are observed in low energy region in Ag-doped SnO2 monolayer. The (Ag,Vo) co-doped SnO2 monolayer has a wider impurity band and narrower gap. The optical spectrum edges shift to lower energy region and enhance visible and infrared photocatalytic activity. The absorb capacity become stronger in visible region with increasing Ag concentrations. These findings can be utilized in producing new-style solar cell and light sensor.

Photochemistry-Based Method for the Fabrication of SnO2 Monolayer Ordered Porous Films with Size-Tunable Surface Pores for Direct Application in Resistive-Type Gas Sensor

A new photochemistry-based method was introduced for fabricating SnO2 monolayer ordered porous films with size-tunable surface pores on ceramic tubes used for gas sensors. The growth of the spherical pore walls was controlled by two times irradiation of the ultraviolet light using polystyrene microsphere two-dimensional colloidal crystal as a template. The surface pore size of the final obtained porous films was well tuned by changing the second irradiation time rather than replacing the template microspheres. The monolayer ordered porous films on the tubes were directly used, for the first time, as gas sensors. The sensitivity of the sensor depended on the surface pore size and was carefully analyzed by ethanol gas detection. The sensor also exhibited short response-recovery time and long-term stability at lower than 300 °C in practical applications. Therefore, this study opens up a kind of construction method for gas sensors, provides a new strategy for controlling the surface pore size of the monolayer ordered porous film, and introduces a new type of sensitivity-controllable gas sensor.

General Fabrication of Monolayer SnO2 Nanonets for High‐Performance Ultraviolet Photodetectors

AbstractA facile approach for the fabrication of monolayer SnO2 nanonet is presented using polymer colloid monolayer nanofilms from oil–water interface self‐assembly as sacrificial templates. The hole size of the nanonets can be adjusted easily by the mean diameter of polymer colloidal spheres. This method can be extended to the fabrication of a series of monolayer nanonets of semiconducting oxides such as TiO2, ZnO, and CeO2. Furthermore, the first photoresponse nanodevice based on monolayer SnO2 nanonet is fabricated. This device presents ultrahigh photocurrent and sensitivity, excellent stability, and reproducibility.

SnO2 monolayer porous hollow spheres as a gas sensor

The authors report on gas sensing properties ofSnO2 hollow spheres with diverse microstructures, which are synthesized through controlled precipitationof Sn(OH)4 layers on carbon sphere templates, followed by heat treatment at differenttemperatures. Hollow spheres derived at 973 K consist of monolayerSnO2 grains, which lead to a huge activated surface area. The sensitivity of sensors based onSnO2 monolayer hollow spheres is up to 51 at 100 ppm ethanol, which is much higher than that oftwo other samples. We attribute this enhancement mostly to the enhanced depletion effectarising from the increased exposed surface. Our results suggest a direction forimproving the performance of gas sensors by using monolayer porous hollow spheres.