Correlation between XPS, Raman and TEM measurements and the gas sensitivity of Pt and Pd doped SnO2 based gas sensors

Nanocrystalline thick-film SnO₂ sensors with different dopants were fabricated by an optimized screen printing process and subsequent annealing. Powders were used as starting materials which were prepared by a wet chemical process from SnCl₄. Microanalysis was performed of both, the precursors and the final sensor materials with their different annealing conditions. Gas sensing tests with CO, CH₄ and NO₂ in air with controlled humidity were correlated with results from X-ray photoemission spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). As an interesting result, the distribution of the transition metal dopants Pd and Pt (as deduced from TEM and XPS data) rules out the existence of metallic clusters or even atoms in the metallic state at the surface. This finding does not allow to explain the sensor effects on SnO₂ based materials as usually done by means of spill-over effects or Fermi energy control.     

Stability of semiconductor sensors based on nanosized SnO2 and Pd/SnO2

Adsorption semiconductor hydrogen sensors were created from nanosized SnO₂ and Pd/SnO₂ materials by the sol-gel method. The sensors were shown to be stable over a long time of operation.     

Palladium embedded in SnO2 enhances the sensitivity of flame-made chemoresistive gas sensors

Microchimica Acta - This review (with 187 refs.) summarizes the progress that has been made in the design of lateral flow biosensors (LFBs) based on the use of micro- and nano-materials. Following...     

SnO2负载Au和M-Au(M=Pt,Pd)催化剂及其低温催化氧化CO性能

以SnO₂为载体, 采用沉积沉淀法(DP)、共沉淀法(CP)和浸渍法(IM)制备了金负载Au/SnO₂催化剂, 同时采用沉积沉淀法制备了M-Au/SnO₂(M=Pd, Pt)双金属负载催化剂. 通过X射线衍射(XRD)、BET比表面积测定、透射电镜(TEM)和X射线光电子能谱(XPS)等技术对样品进行表征, 并测定其对CO的催化活性. 结果表明: 与CP法和IM 法相比, DP法制备的Au/SnO₂-DP 催化剂, Au 颗粒(<5 nm)较小, 分布均匀; Au/SnO₂-DP 中的Au 是以金属态Au0存在, 而Au/SnO₂-CP 和Au/SnO₂-IM 中, 金以Au⁰和Au³⁺的混合价态存在, 在Au/SnO₂-DP和M-Au/SnO₂中的Au、Pt、Pd和SnO₂之间存在相互作用; Au/SnO₂-DP 催化性能明显优于Au/SnO₂-CP 和Au/SnO₂-IM. Au与Pt 和Pd的双金属复合催化剂催化活性明显提高. 不同方法制备Au/SnO₂催化活性的差别主要是由于Au颗粒大小和Au氧化态的不同而产生. 而M-Au/SnO₂活性提高, 可能是由于Au与Pt 和Pd之间的相互作用.     

Microwave-assisted hydrothermal synthesis of Pt/SnO2 gas sensor for CO detection

In this paper, the Pt/SnO₂ nanostructures were prepared via a facile one-step microwave assisted hydrothermal route. The structure of the introduced Pt/SnO₂ and its gas-sensing properties toward CO were investigated. The results from the TEM test reveal that Pt grows on the SnO₂ nanostructure, which was not found for bulk in this situ method, constructing Pt/SnO₂. The results indicated that the sensor using 3.0 wt% Pt/SnO₂ to 100 ppm carbon monoxide performed a superior sensing properties compared to 1.5 wt% and 4.5 wt% Pt/SnO₂ at 225 °C. The response time of 3.0 wt% sensor is 16 s to 100 ppm CO at 225 °C. Such enhanced gas sensing performances could be attributed to the chemical and electrical factors. In view of chemical factors, the presence of Pt facilitates the surface reaction, which will improve the gas sensing properties. With respect to the electrical factors, the Pt/SnO₂ plays roles in increasing the sensor’s response due to its characteristic configuration. In addition, the one-step in situ microwave assisted process provides a promising and versatile choice for the preparation of gas sensing materials.     

掺杂La2O3的SnO2纳米颗粒的制备及对三甲胺气敏性能的研究

采用均相沉淀法制备了SnO2以及掺杂不同La2O3质量比的SnO2纳米颗粒,对材料进行TG-DTA热分析、Zeta电位测定及XRD表征,将材料制作成烧结式La2O3-SnO2复合材料气敏元件,并测试了元件对三甲胺的气敏性能。研究表明:所得粉体粒径在4~10nm之间,且SnO2粉体粒径随La2O3掺杂量的增加而减小。少量La2O3的掺杂显著改善了SnO2对低浓度TMA的灵敏度,工作电压5V时,La2O3掺杂量为5wt%的SnO2纳米颗粒对12μg/L和173μg/L TMA的灵敏度分别达到6.4和120。     

Effect of heterogeneous catalytic methane oxidation on kinetics of conductivity response of adsorption semiconductor sensors based on Pd/SnO2 nanomaterial

Research on Chemical Intermediates - Nanosized semiconductive Pd-containing sensor materials based on SnO2 were obtained by sol–gel technique. The highly sensitive gas sensor based on...     

XPS study of the SnO2 films modified with Rh

In this paper, we have analyzed the effect of the rhodium surface modification on the surface state of SnO₂ films. SnO₂ films, subjected for the surface modification, were deposited by spray pyrolysis, while Rh was deposited by using a microelectron beam evaporation. The thickness of the Rh coating varied in the range 0 to 0.1 monolayer. An explanation of the observed effects was proposed. Basing on the results of X‐ray photoelectron spectroscopy, it was assumed that at a small thickness of the rhodium covering, Rh was in a the well‐dispersed state, close to atomically dispersed state. The growth in the size of the nanoparticles began mainly when the thickness of the Rh covering exceeeded 0.01 monolayer. The size of clusters did not exceed 0.5 to 1.0 nm.     

In-situ preparation and the characterization of Pt/SnO2

To enhance the cycling stability of Pt-based catalysts,the anti-corrosion property of support and the attachment of Pt with support should both get improved.For this purpose,a novel method is presented for in situ preparing Pt/SnO₂.The structure of Pt/ SnO₂ is characterized by X-ray diffraction（XRD） and transmission electron microscopy（TEM）,confirming the homogeneous deposition of Pt on SnO₂.The high resolution TEM（HRTEM） shows the large interfaces between Pt and SnO₂.The TEM photos recorded after accelerated durability tests with Pt/SnO₂ show that the agglomeration and size increment of Pt particles is not severe, indicating the good stability of Pt/SnO₂.The electrochemical active surface area（EAS） of Pt/SnO₂ keeps increasing during the 1000 cycles of cyclic voltammetric（CV） sweeping in H₂SO₄,while the EAS decayed by 35%when mixing Pt/SnO₂ with carbon nanotubes（CNTs）,indicating the superior anti-corrosion property of SnO₂ in contrast to CNTs.     

Fundamental and practical aspects in the design of nanoscaled SnO2 gas sensors: a status report

Gas sensors based on semiconducting materials have become of great interest to both sensor users and researchers. In this context, a huge number of publications have appeared in the literature which deal with metal oxide gas sensors, in general, and with the prototype material SnO₂, in particular. The amount of data published grows continuously and has led to a situation in which even experts in this field tend to lose an overview. The present review describes the reasons for this complexity and outlines unifying concepts to understand the huge amount of published, mostly empirical data. This leads to a comprehension of gas-sensing phenomena in both the application and research domains. Received: 7 December 1998 / Revised: 6 May 1999 / Accepted: 19 May 1999     

A computational chemist approach to gas sensors: modeling the response of SnO2 to CO, O2, and H2O gases

A general bottom-up modeling strategy for gas sensor response to CO, O(2), H(2)O, and related mixtures exposure is demonstrated. In a first stage, we present first principles calculations that aimed at giving an unprecedented review of basic chemical mechanisms taking place at the sensor surface. Then, simulations of an operating gas sensor are performed via a mesoscopic model derived from calculated density functional theory data into a set of differential equations. Significant presence of catalytic oxidation reaction is highlighted.     

Fundamental and practical aspects in the design of nanoscaled SnO2 gas sensors: a status report

Gas sensors based on semiconducting materials have become of great interest to both sensor users and researchers. In this context, a huge number of publications have appeared in the literature which deal with metal oxide gas sensors, in general, and with the prototype material SnO₂, in particular. The amount of data published grows continuously and has led to a situation in which even experts in this field tend to lose an overview. The present review describes the reasons for this complexity and outlines unifying concepts to understand the huge amount of published, mostly empirical data. This leads to a comprehension of gas-sensing phenomena in both the application and research domains.     

Hydrogen sensitivity of sensors based on Co x O y /SnO2/Sb2O5 nanomaterials obtained by the sol-gel method

The sensitivity to H₂ at 40 ppm concentration of adsorption-semiconductor sensors with a gassensitive layer based on SnO₂/Sb₂O₅ nanomaterial obtained by the sol-gel method was studied. The hydrogen sensitivity was shown to increase for materials with Co additions and smaller particles.     

XPS analysis of the effect of Pt addition to Pd catalysts for complete benzene oxidation

Pt-Pd bimetallic catalysts were prepared in order to develop and investigate catalysts having excellent activity and stability for benzene destruction. The effect of Pt addition to Pd catalysts is studied by XPS analysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

空气气氛中Pt和TiO2间强相互作用的STS和XPS研究

 在氧化铟锡(ITO)导电玻璃上制备了TiO2和Pt-TiO2膜,并利用扫描隧道谱(STS)和X射线光电子能谱(XPS)技术对空气气氛中Pt与TiO2间的强相互作用进行了研究. STS研究发现, 673 K空气气氛中处理后,Pt-TiO2/ITO表面出现两类新的隧道电流-偏压曲线,TiO2的费米能级从导带边移向价带边, 表明Pt和TiO2间发生了强相互作用. XPS结果证明,焙烧后Pt原子热扩散到TiO2晶格中并取代Ti原子形成可提供h+的缺陷,从而引起了STS谱的变化.     

Mononuclear (Pd, Pt), heterodinuclear (PdAg, PtAg), and tetranuclear (Pd2Ag2, Pt2Ag2) 1,1-ethylenedithiolato complexes

lp;&-5q;1 The reactions of [Tl2[S2C=C[C(O)Me]2]]n with [MCl2L2] (1:1) or with [MCl2(NCPh)2] and PPh3 (1:1:2) give complexes [M[eta2-S2C=C[C(O)Me]2]L2] [M = Pt, L2 = 1,5-cyclooctadiene (cod) (1); L2 = bpy, M = Pd (2a), Pt (2b), L = PPh3, M = Pd (3a), Pt (3b)] whereas with MCl2 and QCl (2:1:2) anionic derivatives Q2[M[eta2-S2C=C[C(O)Me]2]2] [M = Pd, Q = NMe4 (4a), Ph3P=N=PPh3 (PPN) (4a'), M = Pt, Q = NMe4 (4b)] are produced. Complexes 1 and 3 react with AgClO4 (1:1) to give tetranuclear complexes [[ML2]2Ag2[mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2]](ClO4)2 [L = PPh3, M = Pd (5a), Pt (5b), L2 = cod, M = Pt (5b')], while the reactions of 3 with AgClO4 and PPh3 (1:1:2) give dinuclear [[M(PPh3)2][Ag(PPh3)2][mu2,eta2-(S,S')-S2C=C[C(O)Me]2]]]ClO4 [M = Pd (6a), Pt (6b)]. The crystal structures of 3a, 3b, 4a, and two crystal forms of 5b have been determined. The two crystal forms of 5b display two [Pt(PPh3)2][mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2] moieties bridging two Ag(I) centers.     

Depth profile analysis of surface modified SnO2 gas sensors in a hollow cathode discharge

Depth profile analysis of a SnO₂/SiO₂/Si structure, modified with hexamethildisilazane and processed with rapid thermal annealing (RTA) in the temperature range of 800–1200 °C, is investigated in a hollow cathode discharge for the purpose of characterizing gas sensing solid state devices. The depth behavior of the elements tin, nitrogen, carbon and silicon in this structure is deduced from their emission spectra in the hollow cathode plasma. The hollow cathode used is a liquid nitrogen - cooled Al cylinder having 4 mm inner diameter and 12 mm length. Spectrally pure Ne at a pressure of 130 Pa is used as working gas. The hollow cathode discharge is supplied by a pulse generator with 10 μs pulse width, 4 kHz pulse frequency and 0.5 A pulse amplitude. The results are interpreted by possible reconstruction of hexamethyldisilazane molecule.