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Problem Statement

Detecting Nanoparticles using Microplasmas Jeff Hopwood Professor, ECE Department Tufts University hopwood@ece.tufts.edu 617-627-4358 Supported by NSF CCF-0403460 (in progress). Problem Statement. nanoparticles are too small to detect by scattered laser light ( r <100nm).

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Problem Statement

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  1. Detecting Nanoparticles using MicroplasmasJeff HopwoodProfessor, ECE DepartmentTufts Universityhopwood@ece.tufts.edu617-627-4358Supported by NSF CCF-0403460 (in progress)

  2. Problem Statement • nanoparticles are too small to detect by scattered laser light (r<100nm). • nanoparticles may be too widely dispersed to sense and count accurately. • radio isotopes used for charging particles in DMA’s or IMS’s must be tracked. • current systems are not portable. Goals: To use low power, portable microplasma generators to charge particles. To use ‘potential wells’ to trap and concentrate charged particles. To investigate novel modes of detecting particles by charge, mobility, or chemical reactivity in microplasmas.

  3. ne = ni ne~ 0 (sheath) r(x) + + x V(x) -qZ -qZ x Charging Particles with PlasmasPlasma electrons will rapidly charge nanoparticles (negatively).These particles may then be trapped within the potential well of the plasma. charging trapping microplasma Table 1. Approximate charge on a nanoparticle with radius a (nm) trapped in a plasma with electron temperature Te (eV) -excludes photo-ionization

  4. Portable Microplasma System -- the Split Ring Resonator (SRR) -- Split Ring Resonator: SRR Power Amp (GSM Band Cell Phone, 4 watts, ~$1) VCO (900MHz) not shown: 6 v battery, power level control

  5. Prototype SRR operating in air(3 watts)

  6. Split Ring Resonator(SRR)Electric Field Intensity (@ 900 MHz) This device concentrates power from a cell phone into a volume of ~ 1 nanoliter 25 mm discharge gap Egap > 10 MV/m

  7. Microplasma Particle Trap Experiment Digital SLR Microscope 37 mm 632 nm filter Window “shaker” - - Argon microplasma (SRR) - 1 mm melamine particles - - - coaxial line - - - - HeNe 200 mm particle counter 20 mm pump

  8. Microplasma Particle Trap Experiment Digital SLR Microscope 632 nm filter Window “shaker” - - Argon microplasma - 1 mm melamine particles - - - coaxial line - - - - HeNe 200 mm particle counter 20 mm pump

  9. 2 cm Dtres = 2 s microplasma Time (sec) Particle Trapping and Localization 1 um - melamine formaldehyde

  10. Particles Trapped by a Microplasma(observed through a 632nm filter to block plasma emissions)

  11. 1. Trap and concentrate gas-borne nanoparticles 2. Pulse reactive gases SiF 4. Detect emission of light from the etch reaction products 3. Etch the nanoparticles Conceptualdetection and measurement of nanoparticles optical spectrometer O2 CF4 microplasma trap

  12. Other concepts • Use a voltage pulse to ‘push’ the charged nanoparticles from the trap, and detect particle size distribution using time-of-flight • Use a miniature Ion Mobility Spectrometer to sort and detect charged nanoparticles • See sionex.com, for example • Use a microplasma to charge the particles prior to entering a commercial DMA

  13. Contact InformationJeff HopwoodProfessor, ECE DepartmentTufts Universityhopwood@ece.tufts.edu617-627-4358

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