Gordon M. Berger

A novel methane sensor based on porous SnO2 nanorods: room temperature to high temperature detection

We report for the first time a novel room temperature methane (CH(4)) sensor fabricated using porous tin oxide (SnO(2)) nanorods as the sensing material. The porous SnO(2) nanorods were synthesized by using multiwall carbon nanotubes (MWCNTs) as templates. Current versus time curves were obtained demonstrating the room temperature sensing capabilities of the sensor system when exposed to 0.25% CH(4) in air. The sensor also exhibited a wide temperature range for different concentrations of CH(4) (25-500 °C), making it useful in harsh environments as well.

The chemistry of premixed flame synthesis of carbon nanotubes using supported catalysts

A premixed flame is used to create the reactive environment for carbon nanotube (CNT) synthesis using stainless steel mesh supporting Co as catalyst. The CNT relative growth density, morphology, and internal structure are interpreted in terms of the chemical composition of the flame gases. Different flame gas compositions are produced by varying the fuel/air equivalence ratio, . For> 1.62, carbon deposition occurs too rapidly relative to reactive etching of surface carbon by species such as H2, CO2, and H2O. For

Synthesis Methods, Microscopy Characterization and Device Integration of Nanoscale Metal Oxide Semiconductors for Gas Sensing

A comparison is made between SnO2, ZnO, and TiO2 single-crystal nanowires and SnO2 polycrystalline nanofibers for gas sensing. Both nanostructures possess a one-dimensional morphology. Different synthesis methods are used to produce these materials: thermal evaporation-condensation (TEC), controlled oxidation, and electrospinning. Advantages and limitations of each technique are listed. Practical issues associated with harvesting, purification, and integration of these materials into sensing devices are detailed. For comparison to the nascent form, these sensing materials are surface coated with Pd and Pt nanoparticles. Gas sensing tests, with respect to H2, are conducted at ambient and elevated temperatures. Comparative normalized responses and time constants for the catalyst and noncatalyst systems provide a basis for identification of the superior metal-oxide nanostructure and catalyst combination. With temperature-dependent data, Arrhenius analyses are made to determine activation energies for the catalyst-assisted systems.

Chemical Sensors Based on Metal Oxide Nanostructures

This paper is an overview of sensor development based on metal oxide nanostructures. While nanostructures such as nanorods show significan t potential as enabling materials for chemical sensors, a number of s ignificant technical challenges remain. The major issues addressed in this work revolve around the ability to make workable sensors. This paper discusses efforts to address three technical barriers related t o the application of nanostructures into sensor systems: 1) Improving contact of the nanostructured materials with electrodes in a microse nsor structure; 2) Controling nanostructure crystallinity to allow co ntrol of the detection mechanism; and 3) Widening the range of gases that can be detected by using different nanostructured materials. It is concluded that while this work demonstrates useful tools for furt her development, these are just the beginning steps towards realizati on of repeatable, controlled sensor systems using oxide based nanostr uctures.

Application of laser-induced incandescence to the detection of carbon nanotubes and carbon nanofibers

Laser-induced incandescence applied to a heterogeneous, multielement reacting flow is characterized by temporally resolved emission spectra, time-resolved emission at selected detection wavelengths, and fluence dependence. Two-pulse laser measurements are used to further probe the effects of laser-induced changes on the optical signal. Laser fluences above 0.6 J/cm2 at 1064 nm initiate laser-induced vaporization, yielding a lower incandescence intensity, as found through fluence-dependence measurements. Spectrally derived temperatures show that values of excitation laser fluence greater than this value lead to superheated plasmas with temperatures well above the vaporization point of carbon. The temporal evolution of the emission signal at these fluences is consistent with plasma dissipation processes, not incandescence from solidlike structures. Two-pulse laser experiments reveal that other material changes are produced at fluences below the apparent vaporization threshold, leading to nanostructures with different optical and thermal properties.

The Development of Metal Oxide Chemical Sensing Nanostructures

This paper discusses sensor development based on metal oxide nanostructures and microsystems technology. While nanostructures such as nanowires show significant potential as enabling materials for chemical sensors, a number of significant technical challenges remain. This paper discusses development to address each of these technical barriers: 1) Improved contact and integration of the nanostructured materials with microsystems in a sensor structure; 2) Control of nanostructure crystallinity to allow control of the detection mechanism; and 3) Widening the range of gases that can be detected by fabricating multiple nanostructured materials. A sensor structure composed of three nanostructured oxides aligned on a single microsensor has been fabricated and tested. Results of this testing are discussed and future development approaches are suggested. It is concluded that while this work lays the foundation for further development, these are the beginning steps towards realization of repeatable, controlled sensor systems using oxide based nanostructures.

The development of micro/nano chemical sensor systems for aerospace applications

Aerospace applications require a range of chemical sensing technologies to monitor conditions related to both space exploration and aeronautic aircraft operations. These applications include leak detection, engine emissions monitoring, fire detection, human health monitoring, and environmental monitoring. This paper discusses efforts to produce microsensor platforms and Smart Sensor Systems that can be tailored to measure a range of chemical species. This technology development ranges from development of base sensor platforms to the evaluation of more mature systems in relevant environments. Although microsensor systems can have a significant impact on aerospace applications, extensive application testing is necessary for their long-term implementation. The introduction of nanomaterials into microsensor platforms has the potential to significantly enable improved sensor performance, but control of those nanostructures is necessary in order to achieve maximum benefits. Examples will be given of microsensor platform technology, Smart Sensor Systems, application testing, and efforts to integrate and control nanostructures into sensor structures.

Nanostructured material sensor processing using microfabrication techniques

Purpose – The development of chemical sensors based on nanostructures, such as nanotubes or nanowires, depends on the capability to reproducibly control the processing of the sensor. Alignment and consistent electrical contact of nanostructures on a microsensor platform is challenging. This can be accomplished using labor‐intensive approaches, specialized processing technology, or growth of nanostructures in situ. However, the use of standard microfabrication techniques for fabricating nanostructured microsensors is problematic. The purpose of this paper is to address this challenge using standard photoresist processing combined with dielectrophoresis.Design/methodology/approach – Nanostructures are suspended in photoresist and aligned between opposing sawtooth electrode patterns using an alternating current (AC) electric field (dielectrophoresis). The use of photoresist processing techniques allow the burying of the nanostructures between layers of metal, thus improving the electrical contact of the nano...