Thick-film hydrocarbon gas sensors

Lee, Duk–Dong; Choi, Dong-Han

doi:10.1016/0925-4005(90)80207-g

“…Different polymorphs of iron oxides are well known and studied, but from the technological and scientific points of view, three polymorphs are of major interest, namely, maghemite (γ‐Fe 2 O 3 ), magnetite (Fe 3 O 4 ), and hematite (α‐Fe 2 O 3 ). The iron oxides are widely applied in electrochromics, anodes in Li‐ion batteries, and gas sensors . Furthermore, iron oxides have been successfully used as catalysts for Fischer–Tropsch and CO 2 hydrogenation processes …”

Section: Introductionmentioning

confidence: 99%

Tailored β‐Ketoiminato Complexes of Iron: Synthesis, Characterization, and Evaluation towards Solution‐Based Deposition of Iron Oxide Thin Films

Sadlo

¹

,

Beer

²

,

Rahman

³

et al. 2018

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The synthesis and characterization of five new and closely related homoleptic iron(II) -ketoiminate complexes is reported. Molecular structures of compounds 1, 2, and 5 were determined by single-crystal XRD, which revealed monomeric four-and sixfold coordination, depending on the functionalized side chain. The stepwise elimination of the ligand from the complex observed by thermogravimetric analysis and the stability in solution are encouraging features for solution-based [a] 1824 processing of hematite thin films. As a representative example, compound 1 was successfully employed in a straightforward spin-coating process. The fabricated iron oxide films were characterized in terms of their structure and phase by XRD and Raman spectroscopy, morphology by SEM, and composition by Rutherford backscattering spectrometry accompanied by nuclear reaction analysis, which revealed the formation of crystalline and stoichiometric α-Fe 2 O 3 films. sition (CSD) techniques of iron oxides such as spin coating, [12] sol-gel processes, [13] and spray pyrolysis [14,15] are of particular interest due to their simple and cost-efficient setup, easy scaleup, and ambient processing conditions. [16] Ideally, precursors for CSD should combine specific characteristics such as high solubility and stability in organic solvents, nontoxicity, and a good compromise between stability to handling in ambient atmosphere and hydrolysis (reactivity) that can enable easy cleavage of ligands to obtain high-purity films on processing. Commonly used iron precursors for CSD of iron oxide are FeCl 2 , [7] FeCl 3 , [14,17] Fe(NO 3 ) 3 , [18,19] and [Fe 4 (mdea) 6 ·6CHCl 3 ]. [20] However, most of these compounds do not feature high solubility and stability in solution, and thus necessitate the use of additives such as amines or long-chain alcohols to enhance the solubility and stabilize the solution. [19,21] Metal alkoxides, for example, [Fe(OtBu) 3 ] 2 , are stable in solution but prone to hydrolysis on exposure to ambient conditions. [22] In the search for suitable precursors for CSD of iron oxide thin films under ambient conditions, the class of metal -ketoiminates is a potential candidate. This ligand class, which has already been successfully applied in metal oxide and nitride CVD and atomic layer deposition (ALD) processes involving metals such as Fe, Zr, Pd, Ga, Ir, Ti, Nb, Ta, and Zn,[23][24][25] features both oxygen and nitrogen coordination, which is a compromise between the highly reactive and thermally unstable nitrogen-bonded metal -diketiminates and the highly stable oxygen-coordinated metal -diketonates. As recently demonstrated by us, iron(II) -ketoiminates are highly promising for gas-phase deposition of iron oxide nanostructures via both ALD and CVD routes at low temperatures. [26] Our next goal was to evaluate this class of compounds for a simple and cost-effective CSD process for iron oxide thin films. As mentioned above, CSD requires precursors with suitable characteristics. The advantageous properties associated with Eur.

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“…As noted previously (Section 2.2.2) commercial sensors based on polycrystalline SnO 2 (''Taguchi sensors'') [107] are produced by companies such as Figaro Inc., for a wide range of industrial and domestic applications, including gas monitors, leak detectors, and alarm systems for toxic or inflammable gases. Apart from SnO 2 , an n-semiconductor, many other inorganic semiconducting oxides can serve as sensitive materials in gas sensors, including TiO 2 , ZnO, and Fe 2 O 3 with various additives and dopants [13], [108]. Certain organic semiconductors such as phthalocyanines with appropriate central metal atoms, or polymers like polypyrrole or polysiloxane, also show sensitivity to gaseous compounds.…”

Section: Conductance Devicesmentioning

confidence: 99%

“…These sensors are often referred to as homogeneous or heterogeneous semiconductors, or as dielectric sensors. Detailed lists of materials sensitive to detectable gaseous compounds together with the corresponding operating temperatures are provided in [89][90][91][92], [108]. The design principle upon which such sensors are based is quite simple: a sensitive semiconducting sample is placed between two metallic contacts, and the combination is equipped with a resistance heater capable of maintaining the appropriate working temperature, usually between 100 C and 700 C. Semiconductor sensors have dimensions in the range of millimeters, and are easily fabricated by either thick-or thin-film technology [109].…”

Section: Conductance Devicesmentioning

confidence: 99%

Chemical and Biochemical Sensors

Cammann¹,

Roß²,

Katerkamp³

et al. 2001

Ullmann's Encyclopedia of Industrial Chemistry

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The article contains sections titled: 1. Introduction to the Field of Sensors and Actuators 2. Chemical Sensors 2.1. Introduction 2.2. Molecular Recognition Processes and Corresponding Selectivities 2.2.1. Catalytic Processes in Calorimetric Devices 2.2.2. Reactions at Semiconductor Surfaces and Interfaces Influencing Surface or Bulk Conductivities 2.2.3. Selective Ion Conductivities in Solid‐State Materials 2.2.4. Selective Adsorption ‐ Distribution and Supramolecular Chemistry at Interfaces 2.2.5. Selective Charge‐Transfer Processes at Ion‐Selective Electrodes (Potentiometry) 2.2.6. Selective Electrochemical Reactions at Working Electrodes (Voltammetry and Amperometry) 2.2.7. Molecular Recognition Processes Based on Molecular Biological Principles 2.3. Transducers for Molecular Recognition: Processes and Sensitivities 2.3.1. Electrochemical Sensors 2.3.1.1. Self‐Indicating Potentiometric Electrodes 2.3.1.2. Voltammetric and Amperometric Cells 2.3.1.3. Conductance Devices 2.3.1.4. Ion‐Selective Field‐Effect Transistors (ISFETs) 2.3.2. Optical Sensors 2.3.2.1. Fiber‐Optical Sensors 2.3.2.2. Integrated Optical Chemical and Biochemical Sensors 2.3.2.3. Surface Plasmon Resonance 2.3.2.4. Reflectometric Interference Spectroscopy 2.3.3. Mass‐Sensitive Devices 2.3.3.1. Introduction 2.3.3.2. Fundamental Principles and Basic Types of Transducers 2.3.3.3. Theoretical Background 2.3.3.4. Technical Considerations 2.3.3.5. Specific Applications 2.3.3.6. Conclusions and Outlook 2.3.4. Calorimetric Devices 2.4. Problems Associated with Chemical Sensors 2.5. Multisensor Arrays, Electronic Noses, and Tongues 3. Biochemical Sensors (Biosensors) 3.1. Definitions, General Construction, and Classification 3.2. Biocatalytic (Metabolic) Sensors 3.2.1. Monoenzyme Sensors 3.2.2. Multienzyme Sensors 3.2.3. Enzyme Sensors for Inhibitors ‐ Toxic Effect Sensors 3.2.4. Biosensors Utilizing Intact Biological Receptors 3.3. Affinity Sensors ‐ Immuno‐Probes 3.3.1. Direct‐Sensing Immuno‐Probes without Marker Molecules 3.3.2. Indirect‐Sensing Immuno‐Probes using Marker Molecules 3.4. Whole‐Cell Biosensors 3.5. Problems and Future Prospects 4. Actuators and Instrumentation 5. Future Trends and Outlook

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“…There are a few scattered reports which discuss the potential of iron oxide as a gassensing material [8][9][10][11][12][13][14][15][16][17]. Iron oxide can exist in various forms such as ␣-Fe 2 O 3 , ␥-Fe 2 O 3 and Fe 3 O 4.…”

Section: Introductionmentioning

confidence: 99%