Atomic layer deposition for rutile structure TiO2 thin films using a SnO2 seed layer and low temperature heat treatment

We study the rutile-TiO2 film deposition with a high-k value using a SnO2 seed layer and a low temperature heat treatment. Generally, heat treatment over 600 ℃ is required to obtain the rutile-TiO2 film. However, By using a SnO2 seed layer, we obtained rutile-TiO2 films with heat treatments as low as 400 ℃. The XPS analysis confirms that the SnO2 and TiO2 film were deposited. The XRD analysis showed that a heat treatment at 400 ℃ after depositing the SnO2 and TiO2 films was effective in obtaining the rutile-TiO2 film when the SnO2 film was thicker than 10nm. The TEM / EDX analysis show that no diffusion in the thin film between TiO2 and SnO2. The dielectric constant of the TiO2 film deposited on the SnO2 film (20 nm) was 68, which was more than twice as high as anatase TiO2 dielectric constant. The current density was 10-4A/cm2 at 0.7 V and this value confirmed that the leakage current was not affected by the SnO2 seed layer.

Competition and Cooperation between Fluorine and Oxygen in SnO2:F Films

The interaction of oxygen and fluorine (F&O) in an F-doped SnO2 film, prepared by regulating oxygen partial pressure and the content of doped fluorine from 2.5 at% to 10 at%, was investigated in the large perspective through characterization methods including XRD, Raman spectroscopy, photoluminescence spectroscopy, wettability measurement and a Hall effect test system. The results show that F&O’s competitive and cooperative relationship would be reflected in the structure and electrical characteristics of SnO2 films. The oxygen action is overwhelming and restricts fluorine, so a growing number of F atoms occupy the position by the order of co-edge oxygen of tin–oxygen octahedron chains > oxygen vacancies > segregation, which leads to that carrier concentration modestly increasing from ~1015 to ~1017/cm−3. As oxygen action is inadequate to restrain fluorine, more F atoms are likely to enter the SnO2 lattice in a solid-solution way to replace the O atoms at the co-edge position of the octahedron chains, causing a dramatic increase in carrier concentration from ~1016 to ~1019/cm−3. Furthermore, by continuing to weaken oxygen action, only 2.5 at% of fluorine content could bring about a carrier concentration augment from ~1016/cm−3 to ~1018/cm−3, then going up to ~1021/cm−3 by post-annealing. However, the impairment of oxygen action contributes to a more effective doping of fluorine on SnO2 film. Such mutual action between fluorine and oxygen provides a direction for highly efficient production and tunable regulation of SnO2 film on demand.

Self-Assembled Monolayers Coated Porous SnO2 Film Gas Sensor with Reduced Humidity Influence

Metal-oxide sensors, detect gas through the reaction of surface oxygen molecules with target gases, are promising for the detection of toxic pollutant gases, combustible gases, and organic vapors; however, their sensitivity, selectivity, and long-term stability limit practical applications. Porous structure for increasing surface area, adding catalyst, and altering the operation temperature are proposed for enhancing the sensitivity and selectivity. Although humidity can significantly affect the property and stability of the sensors, studies focusing on the long-term stability of gas sensors are scarce. To reduce the effects of humidity, 1H, 1H, 2H, 2H–perfluorooctyltriethoxysilane (PFOTS) was coated on a porous SnO2 film. The interconnected SnO2 nanowires improved the high surface area, and the PFOTS coating provided superhydrophobicity at water contact angle of 159°and perfect water vapor repellency inside E-SEM. The superhydrophobic porous morphology was maintained under relative humidity of 99% and operating temperature of 300 °C. The CO gas sensing of 5, 20, and 50 ppm were obtained with linearity at various humidity. Flame detection was also achieved with practical high humidity conditions. These results suggest the simple way for reliable sensing of nanostructured metal-oxide gas sensors with high sensitivity and long-term stability even in highly humid environments.

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

Here we report self-supported SnO2 nanofilm prepared by a robust electrochemical process as an electrocatalyst for CO2 reduction reaction. SnO2 film had large surface area originating from its nano-architecture and...