SnO2 Thin Films Research Articles

Elaboration and characterization of Ni and Al co-doped SnO2 thin films prepared by spray pyrolysis technique for photovoltaic applications

In the present study, aluminum and nickel co-doped SnO2 thin films on glass substrates were successfully synthesized using the spray pyrolysis method. This study aims to discover the effect of aluminum (Al) dopant on the structural, optical, and electrical properties of the prepared thin layers. All films deposited (pure, Ni-doped, and Al-Ni-codoped SnO2) were polycrystalline with a tetragonal structure and had a preferential orientation [110], according to XRD analyzes. The optical measurements revealed that all of the synthesized films have good transparency. Depending on the dopant concentration, Ni-Al-codoped SnO2 thin films had a transmittance that ranged between 75% and 85% in the visible and near-infrared spectrum. The electrical measurement confirmed that the electrical resistivity of the elaborated thin films decreases as the Al concentration increases. Therefore, these thin layers are promising for use as a transparent conductive layer in photovoltaic solar cells.

Resisting Dendrites in Lithium Batteries, One Pinhole at a Time

For humanity to successfully transition from fossil fuels, the mismatch in the demand and supply of renewable energy must be addressed by reliable, high energy storage systems. One promising energy storage system is the lithium metal battery (LMB), owing to the high gravimetric capacity of lithium (3860 mAh/g). The potential gain in volumetric and gravimetric energy density offered by LMBs could usurp today’s lithium-ion battery technology and revolutionize energy storage. However, the lifetime of LMBs is hindered by morphological instabilities experienced during the electrodeposition of lithium.Modifications of the solid electrolyte interphase (SEI) and electrolyte are the most common strategies for improving lithium metal morphology. However, electrolyte and SEI engineering are often tedious, based on trial and error, and insufficient for enhancing lithium electrodeposition. Here, we demonstrate a new, alternative strategy for controlling lithium metal morphology and improving electrochemical performance that is independent of the electrolyte and SEI. By modifying the current collector with atomic layer deposited (ALD) thin films of ZnO, SnO2, and Al2O3, we show that lithium deposits atop, rather than beneath, the thin films, resulting in changes in lithium morphology and battery performance that are strongly dependent on the electrical resistance of the ALD films. The results show that low resistance copper modification films like SnO2 and ZnO provide numerous sites for lithium nucleation and promote the formation of high surface area (fast electrolyte consuming) lithium deposits, while the highly resistive Al2O3-modified copper reduces the available sites for lithium nucleation and promotes the formation of low surface area (slow electrolyte consuming) clusters of lithium deposits.We propose and demonstrate the first recorded mechanism for the connection between electrical resistance and lithium growth - we propose that, in resistive substrates, lithium metal nucleates atop only pinhole sites, then grows laterally by the radial diffusion of lithium ions from the electrolyte. We prove this mechanism analytically, using diffusion controlled current equations, and experimentally by introducing patterned pinholes into a resistive, pinhole-free substrate. We generalize the concept of resistance-controlled morphology and demonstrate high battery performance in three distinct classes of electrolytes, culminating in anode-free pouch cells that retain 60% of their initial discharge capacity after 100 cycles. This work presents a new approach for understanding the electrodeposition of lithium and tuning the performance of lithium metal batteries.

Structural, electrical, and optical properties of rare-earth Sm3+ doped SnO2 transparent conducting oxide thin films for optoelectronic device applications: Synthesized by the spin coating method

Various concentrations of Sm (1, 2, 3, 4, and 5 at%) doped SnO2 thin films were synthesized by the sol-gel spin coating method and investigated the structural, optical, and electrical properties. According to X-ray diffraction studies, all deposited films exhibited the polycrystalline rutile tetragonal structure. The average crystallite size decreased with Sm doping concentration in SnO2, while the dislocation density and lattice strain values were increased. Both XPS and Raman spectra confirm that Sm3+ enters the host SnO2. The higher average optical transmittance is above 86% in pure SnO2, while Sm: SnO2 films exhibit a decreasing trend with the increase of Sm doping concentration and reached up to 77% in 5 at% Sm: SnO2 film. The optical bandgap energy increased with the increase of Sm doping concentration up to 3 at % Sm: SnO2 film (4.23 eV) which is attributed to the Moss-Burstein (MB) effect and then slightly decreased for 4 at% and 5 at% Sm: SnO2 films. Further, the room temperature sheet resistance and resistivity values were found to decrease with the increase of Sm doping concentration up to 3 at % Sm: SnO2 film then it slightly increased in 4 and 5 at% Sm: SnO2 films. Additionally, the efficiency parameter figure of merit (φ) for all the deposited films was calculated.

High mobility p-channel tin monoxide thin-film transistors with hysteresis-free like behavior

In this Letter, we report a demonstration of p-channel tin monoxide (SnO) thin-film transistors (TFTs) with high field-effect mobility (μFE) exceeding 10 cm2/Vs and hysteresis-free like behavior. We demonstrate that maintaining metallic states before encapsulation is a key process to enhance μFE in p-type SnO thin-films. Sustaining this meta-stability involves the following two processes during fabrication: (1) postdeposition annealing (PDA) in two steps and (2) encapsulation in the middle of each PDA. This simple process not only suppresses creation of oxidized states such as adverse Sn4+ but also facilitates the lateral growth of crystals with improved crystallinity by interfacial energy stabilization. The resultant SnO TFT reveals a record-high μFE up to 15.8 cm2/Vs with a negligible hysteresis of 0.1 V. This study suggests a practical route to grant high μFE to p-channel SnO TFTs without any dopant or complex postdeposition treatment.

Exploitation of SnO2/Polypyrrole Interface for Detection of Ammonia Vapors Using Conductometric and Optical Techniques: A Theoretical and Experimental Analysis.

This study describes the construction of a lab-built Surface Plasmon Resonance (SPR) system for gas sensing applications employing a highly sensitive and trustworthy optical approach. The nanocomposite thin film of tin oxide (SnO2) and Polypyrrole (PPy) were prepared for sensing highly toxic gas, i.e., ammonia (NH3) gas. The gas sensor was validated by both optical and conductometric techniques of gas sensing. The optical SPR gas sensor is based on the change in refractive index at the SnO2/Polypyrrole (PPy) interface with gas adsorption (NH3). The thickness of SnO2 and Polypyrrole thin films was optimised using theoretical calculations for a sharp SPR reflectance curve. The manuscript also offers theoretical SPR curves for different PPy and SnO2 layer thicknesses. To support the theoretical conclusions, the effects of NH3 gas on the prism/Au/SnO2/Polypyrrole system were also investigated experimentally. In comparison to other research described in the literature, it was observed that the constructed sensor’s sensitivity was higher. The obtained results demonstrate the utility of the SPR setup in the investigation of the interactions of adhered gas molecules with dielectrics and gas sensing. For conductometric gas sensing studies, the film having optimised thicknesses for sharp SPR reflectance curves was separately prepared on Interdigitated Electrodes. At a low working temperature of roughly 150 °C, the sensing response of the constructed film was observed and found to be maximal (60).

Annealing Effects on SnO2 Thin Film for H2 Gas Sensing.

Hydrogen (H2) is attracting attention as a renewable energy source in various fields. However, H2 has a potential danger that it can easily cause a backfire or explosion owing to minor external factors. Therefore, H2 gas monitoring is significant, particularly near the lower explosive limit. Herein, tin dioxide (SnO2) thin films were annealed at different times. The as-obtained thin films were used as sensing materials for H2 gas. Here, the performance of the SnO2 thin film sensor was studied to understand the effect of annealing and operating temperature conditions of gas sensors to further improve their performance. The gas sensing properties exhibited by the 3-h annealed SnO2 thin film showed the highest response compared to the unannealed SnO2 thin film by approximately 1.5 times. The as-deposited SnO2 thin film showed a high response and fast response time to 5% H2 gas at 300 °C of 257.34% and 3 s, respectively.

Influence of MgPc modification on NO2 sensing characteristics of RGTO grown SnO2 thin films

In the present study, we report a 100% enhancement in NO2 sensing response of tin oxide (SnO2) thin films through surface modification utilizing magnesium phthalocyanine (MgPc). For this purpose, SnO2 thin films were grown by Rheotaxial Growth and Thermal Oxidization (RGTO) method and were later modified by MgPc. Deposition of MgPc over SnO2 film was carried out by vacuum sublimation method. During deposition of MgPc, the substrates were heated to 200 °C. The MgPc modified SnO2 films (SnO2: MgPc) exhibit higher sensor response (18.5 for 5 ppm NO2), faster response/recovery time (6 s/169 s) and lower operating temperature (175 °C) as compared to pristine SnO2 films which exhibit maximum response at an operating temperature of 300 °C. Work function measurements and X-ray photoelectron spectroscopy (XPS) studies indicate formation of p-n hetero junctions in modified films due to electron transfer from SnO2 (n-type) to MgPc (p-type). In addition, MgPc modification results into intensification of oxygen adsorption sites (from 6.5% to 32.5%) on the sensor surface. Formation of p-n junctions at the interface and enhancement of adsorbed oxygen on the surface establish the basis for superior response i.e higher sensor response and faster response and recovery time of SnO2: MgPc films.

Investigation of Cobalt Substitution on the Structural, Optical Band Gap, and Photocatalytic Dye Degradation Properties of Spray Deposited SnO2Thin Films

Pure and cobalt substituted tin oxide thin films are successfully formed on a glass substrate using the simple spray pyrolysis technique. XRD patterns reveal the polycrystalline nature of the samples with tetragonal rutile structure. The shift in X-ray diffraction peak to a higher 2θ value and its subsequent contraction of the SnO2 rutile lattice along the c-axis manifests the infusion of the guest cobalt ions. Crystallite size and microstrain values are found to vary with cobalt substitution. SEM analysis shows the uniform dispersion of the nanoparticles in the prepared thin films. The optical band gap values are found to narrow down with cobalt substitution from 4.04 eV–3.93 eV. Photoluminescence study hints at the presence of intermediate states within the forbidden energy band gap of SnO2. Photocatalytic dye degradation of Methylene blue (MB) highlights the role of cobalt with a high photocatalytic activity of 86 % compared to other investigated thin films.

A Bilayer SnO2/MoS2-Coated Evanescent Wave Fiber Optic Sensor for Acetone Detection-An Experimental Study.

The need for sensors that measure the acetone content of exhaled breath for diabetes severity has recently increased. Clinical researchers have reported less than 0.8 ppm acetone concentration in the exhaled breath of an average individual, while that for a diabetic patient is higher than 1.8 ppm. This work reports the development of two sets of evanescent wave-based fiber optic sensor coated with SnO2 thin film and bilayer of SnO2/MoS2 to detect different acetone concentrations (0–250 ppm). In each set, we have studied the effect of clad thickness (chemical etch time 5min, 10 min, 15 min, 25 min, 40 min, and complete clad removal) to optimize the clad thickness for a better response. In Set 1, SnO2 thin film was used as the sensing layer, while in Set 2 a bilayer of SnO2 thin film/ MoS2 was used. Enhanced sensor response of ~23.5% is observed in the Set 2 probe with a response and recovery time of ~14 s/~17 s. A SnO2/MoS2-coated sensor prototype is developed using LEDs of different wavelength and intensity detector; its potential to detect different concentrations of acetone is tested. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Ultraviolet (UV) Spectroscopy, and Ellipsometry were used to study the structural, morphological and optical properties of the sensing layers. The present study indicates that the SnO2/MoS2-coated sensor has the potential to create a handheld sensor system for monitoring diabetes.

A Multimodal Sensing Device for Simultaneous Measurement of Dissolved Oxygen and Hydrogen Ions by Monolithic Integration of FET-Based Sensors.

We examined the possibility of measuring dissolved oxygen by using a potentiometric solid-state semiconductor sensor. Thin films of tin (IV) oxide (SnO2) are widely used in oxygen gas sensors. However, their ability to detect dissolved oxygen (DO) in solutions is still unknown. In this paper, we present a method for investigating the dissolved oxygen-sensing properties of SnO2 thin films in solutions by fabricating a SnO2-gate field-effect transistor (FET). A similarly structured hydrogen ion-sensitive silicon nitride (Si3N4)-gate FET was fabricated using the same method. The transfer characteristics and sensitivities were experimentally obtained and compared. The transfer characteristics of the FET show a shift in threshold voltage in response to a decrease in DO concentration. The SnO2-gate FET exhibited a sensitivity of 4 mV/ppm, whereas the Si3N4-gate FET showed no response to DO. Although the SnO2-gate FET responds to pH changes in the solution, this sensitivity issue can be eliminated by using a Si3N4-gate FET, which is capable of selectively sensing hydrogen ions without DO sensitivity. The experimental results indicate the promising properties of SnO2 thin films for multimodal sensing applications.

Preparation and Investigation of TiO2, SnSx, and SnO2 Thin Film Properties for Use as UV Detectors

TiO2 thin films were prepared using the hydrothermal technique at 150, 160, 170, and 180 oC with a 6-hour holding period, while SnSx films were prepared using the SILAR method. XRD analysis reveals that the shape of the TiO2 compound in all samples is quaternary rutile with a preferred growth direction of (101), and that the peak intensity decreases as the temperature rises. The samples produced using the SILAR approach were validated by XRD analyses to include the two phases of SnS and SnS2, with SnS having a rhombic structure and SnS2 having a hexagonal structure. We note that all the manufactured FTO/TiO2/Al, FTO/n-TiO2/p-SnSx/Al, FTO/n-TiO2/p-SnO2/Al optical reagents have a nonlinear Schottky behavior. Al-TiO2 reagents at different temperatures have a high sensitivity of about 9900%, and the sensitivity of the detector decreases with the increase in the applied voltage, and it has a slow response, so we dope it with materials SnSx, SnO2. As for the TiO2/SnSx, TiO2/SnO2 reagents, we note that the highest sensitivity is 40400% for the FTO/n-TiO2/p-SnSx/Al detector with at a voltage of 0 V. Also, the sensitivity decreases with an increase in the applied voltage and its response is fast.

Electron dephasing processes in the thin and thick Ta-doped SnO2 films

We have systematically investigated the electron dephasing processes of the thin and thick Ta-doped SnO2 films. All samples exhibit electron transport characteristics of degenerate semiconductors. At low temperature T (below ∼70 K), the weak-localization-induced negative magnetoresistance (MR) is observed. For the thick films with the thicknesses of ∼300 nm, the observed MR can be well described by three-dimensional weak-localization theory. The electron dephasing rate 1/τφ varies linearly with T3/2, indicating that the electron–electron scattering dominates the electron dephasing process. This is different from the common observation that the electron–phonon scattering is the main dephasing process for electrons in three-dimensional disordered conductors. For the thin films with the thicknesses of ∼30 nm, the MR can be well described by two-dimensional weak-localization theory. By analyzing the electron dephasing rate as a function of T, we find that both large- and small-energy-transfer electron–electron scattering processes play an important role in the electron dephasing.

Structure of Atomically Dispersed Pt in a SnO2 Thin Film under Reaction Conditions: Origin of Its High Performance in Micro Electromechanical System Gas Sensor Catalysis.

A battery-driven micro electromechanical system (MEMS) gas sensor has been developed for household safety when using natural gas. The heart of the MEMS gas sensor is a 7.5 at % Pt-SnO2 thin film catalyst deposited on the SnO2 sensor layer. The catalyst enhances the sensitivity to methane, though its structure under working conditions is unclear. In this study, in situ XAFS was applied to a 7.5 at % Pt-SnO2 catalyst layer deposited on a Si substrate, and we demonstrated that atomically dispersed Pt maintains its lattice position in SnO2 with a small loss of surrounding lattice oxygen in the presence of 1% CH4 and a more reducing gas of 1% H2 at the reaction temperature (703 K), i.e., no Pt aggregation is observed. The lost oxygen is easily recovered by re-oxidation by air. This work has revealed that the atomically dispersed Pt in the SnO2 lattice is the active structure and it is stable even under reaction conditions, which guarantees a long lifetime for the gas sensor.

Flexible sensor based on multi-walled carbon nanotube-SnO2 nanocomposite material for hydrogen detection

This study aimed to develop a high-performance hydrogen flexible sensor based on multi-walled carbon nanotube (MWCNT):SnO2 material. The MWCNT:SnO2 thin film was deposited onto a flexible polyimide substrate by the electron-beam deposition method to perform the low temperature detection of hydrogen. The thickness and surface morphology of the sensing layers have been determined by the thickness measuring profilometer and the scanning electron microscope (SEM), respectively. The flexible MWCNT:SnO2 sensor exhibited excellent sensitive characteristics to hydrogen in a range of 25–3000 ppm. H2 sensing parameters like sensor response, recovery, and response times were investigated at different operating temperatures. The minimum response and recovery times of the sensor corresponding to 1000 ppm H2 concentrations were found to be 37 and 554 s, respectively. The investigated sensing parameters demonstrate that this work can provide the possibility of a versatile route to fabricate flexible hydrogen sensor with high sensitivity and selectivity, which demonstrates its great potential in hydrogen leakage monitoring.

Influence of post-deposition annealing on the novel alloyed SnSxO1-x semiconductor in p-type thin-film transistors

SnO is an oxide semiconductor that has the potential to be used in the development of thin-film transistors (TFTs) with a p-type channel. SnO on the other hand is a metastable phase, and the oxidation of the SnO films makes high-performance TFTs with good mobility and high on/off current ratios challenging. In this study, based on the SnO–SnO2 phase transformation mechanism, a novel alloyed semiconductor SnSxO1-x was reported to prevent the conversion of SnO to SnO2. Pulsed laser deposition was used to grow SnO and SnSxO1-x thin films on Si/SiO2 substrates, which were then exposed to rapid annealing procedures. From Raman spectroscopic analysis, SnSxO1-x exhibited better antioxidant performance than pure SnO at the same post-deposition annealing process. The developed SnSxO1-x TFTs exhibited better stability and an improved on/off ratio than SnO TFTs after high-temperature annealing. Additionally, we fabricated bilayer SnSxO1-x/SnO thin-film transistors with typical p-channel conduction and a 10−11 A off-state current.

Role of Materials Chemistry on Transparent Conductivity of Amorphous Nb-Doped SnO2 Thin Films Prepared by Remote Plasma Deposition

In this study, remote plasma sputtering deposition of niobium-doped SnO2 transparent conductive oxides on glass substrates was carried out at ambient temperature with no post-deposition annealing. The microstructure, optical, electrical, and surface morphology of the thin films were characterized using a combination of advanced techniques, such as X-ray diffraction (XRD), UV-Vis spectrophotometer, Hall-effect measurements, as well as field emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy, and high-resolution X-ray photoelectron spectroscopy. It was determined that the oxygen defects of the films have a substantial impact on their transparent conductivity. The crystalline films, which were crystallized by annealing at 450 °C, had higher resistivities due to a decreased concentration of oxygen vacancies, which restricted conduction. In comparison, the amorphous films exhibited remarkable conductivity. The best amorphous films (Nb:SnO2) exhibited a resistivity of less than 4.6 × 10−3 Ω·cm, with a 3 × 1020 cm−3 carrier concentration and a 4.4 cm2/(V·S) of Hall mobility. X-ray amorphous Nb:SnO2 films can be used to make conductive and transparent protective layers that can be used to shield semiconducting photoelectrodes used in solar water splitting. These layers can also be used with more conductive TCO films (ITO or AZO) when needed.

Transparent conductive SnO2 thin films via resonant Ta doping

Transparent conductive oxide (TCO) thin films are highly desired as electrodes for modern flat-panel displays and solar cells. Alternative indium-free TCO materials are highly needed, because of the scarcity and the high price of indium. Based on the mechanism of resonant doping, Ta has been identified as an effective dopant for SnO2 to achieve highly conductive and transparent TCO. In this work, we fabricated a series of Ta-doped SnO2 thin films (Sn1−xTaxO2, x = 0.001, 0.01, 0.02, 0.03) with high conductivity and high optical transparency via a low-cost sol-gel spin coating method. The Sn0.98Ta0.02O2 film achieves the highest electrical conductivity of 855 S cm−1 with a carrier concentration of 2.3 × 1020 cm−3 and high mobility of 23 cm2 V−1 s−1. The films exhibit a very high optical transparency of 89.5% in the visible light region. High-resolution X-ray photoemission spectroscopy and optical spectroscopy were combined to gain insights into the electronic structure of the Sn1−xTaxO2 films. The optical bandgaps of the films are increased from 3.96 eV for the undoped SnO2 to 4.24 eV for the Sn0.98Ta0.02O2 film due to the occupation of the bottom of conduction band by free electrons, i.e., the Burstein-Moss effect. Interestingly, a bandgap shrinkage is also directly observed due to the bandgap renormalization arising from many-body interactions. The double guarantee of transparency and conductivity in Sn1−xTaxO2 films and the low-cost growth method provide a new platform for optoelectronic and solar cell applications.

Electrical, electronic and magnetic behaviours of F-doped SnO2 thin film

Electrical, electronic and magnetic behaviours of F-doped SnO2 thin film

Structural, optical and electrical properties of r-TiO2:Sn/SnO2:(F/Nb) tandem film by aerosol-assisted chemical vapor deposition

A novel F and Nb co-doped SnO2 thin film with a rutile TiO2:Sn buffer layer (r-TTO/NFTO) was obtained using an aerosol-assisted chemical vapor deposition, and its micro-nano interface structure, electrical and optical properties were studied in detail. Due to the little lattice mismatch between the interfaces of NFTO and r-TTO layers as well as the synergistic enhancement effect of F and Nb co-doping, the tandem film shows an improved crystallinity with minimum residual stress and fewer planar defects. The heterogeneous structure formed between r-TTO and NFTO is conducive to the transfer of electrons in TiO2 to NFTO, increasing the carrier concentration of NFTO film. Compared with FTO film, both of the carrier concentration and Hall mobility were obviously improved, the sheet resistance (5 Ω/□) and resistivity (2.82 × 10−4 Ω cm) were reduced by 40% and 37%, respectively. Particularly, an extremely low emissivity of 0.08 was obtained, which is the lowest value for hard coatings to our knowledge.

Optimizing Laser-Induced Voltage Signal in SnO2 Thin Films by Changing Oxygen Pressure

Laser-induced voltage (LIV) effect of the thin film can be applied for the laser energy measurement and millimeter-wave detection. The amplitude and corresponding velocity of LIV signals depended on the film material and preparation process. In the study, the effect of oxygen pressure on the LIV signals of SnO2 thin films was studied and got the surprised result that the maximum LIV peak reach about 4.02 V and response time with only 98 ns when oxygen pressure was 30 Pa. The crystal quality of the films was analyzed by X-ray diffraction (XRD) and LIV measurements, and a linear relationship between LIV peak voltage and laser energy was also disclosed. Those findings indicate that the laser energy/power meters designed with SnO2 thin film with optimized oxygen pressure would have the merits high precision, high sensitivity, and fast response.