nano materials improving gas
TRANSCRIPT
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Nanomaterials: improving gas
sensor performance
John SaffellAlphasense Ltd.
Technical Director
Paul Midgley
Professor of Materials Science
NANOMATERIALS 2010 University of Cambridge
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We will consider:
Technologies and markets for gas sensing
Nanometrology
Nanomaterials as catalysts
Nanomaterials in optical gas sensing
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Technologies and markets in
gas detection
A roadmap, which includes the matrix oftechnologies and markets is availableon:
www.gas-sensor-roadmap.com
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Gas detection has many
marketsMarket segments
Domestic safety
Automotive
Industrial safety
Process control
Military
Emerging markets
Niche
Air quality
Homeland security- Explosives/ terrorism
Asthma, allergies
MedicalHydrogen: fuel cells
Extreme environments (space, volcanoes, oil)
Breath analysis & capnography
Existing markets
Fire and home safety
Leak detection
Car emissions
PM10, PM2.5
Industrial safety & LELConfined space entry
Stack emissions
Process control and analysis
Food processing, transport and storage
Breathalyser / alcohol & drugs
Ammonia
Benzene, BTEXOutdoor air, Indoor air
Odours (WWT, landfill)
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Many technologies are
employedComponents
Lasers and optics
UV, IR, microplasma sources
Wavelength separation MEMS
Low cost optics, detector arrays
Fibre opticsMicro GC
Micro MS
PID, IMS
QMB, SAW, BAW
Sensor arrays
Microprocessors/ FPGAs/ PICs/ ASIC
Wireless
Technologies
MEMS
Nanomaterials (QDs, CNT, catalysts, nano MO)
Polymers, liquid crystals
Electrochemistry
Separation sciencePhysical chemistry (enthalpy, speed of sound)
Products
NIR spectrometers
IR single line absorption
IMS
Micro GC/MSNanoparticle fluorescence
IR, Visible, THz gas cameras
Ultrasound, thermal conductivity imaging
Electrochem/ optical/polymer/ nano arrays
LIDAR, DOAS
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Nanometrology
Electron microscopy and AFM are regular tools
for both R&D and quality control
Scanning Electrochemical Microscopy,
improved Raman and near field microscopy
are offering new opportunities
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TEM: Daresbury analysis of our Pt/Ru catalyst,identifying oxides and allowing us to determine
the growth pattern
3nm
(010)
[001]
(001)
(011)
55o
(100)
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+12.72%
+4.6
5%
RuO2 Ru
- 4.28%
(010)
(100)
(001) (110)
+12.72%
-4.2
8%
(001)
(100)
(i)
(ii)
(iii)
+4.6
5%
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Zngrain
Pt islanddeposited
fromsolution
RuO2
deposited columnar
growth
Runanocrystal
s at oxidesurface
Growth
mechanism
time
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Oxygen Map
We also use Energy Filtered TEM toidentify the surface activity of our catalysts
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SEM is routinely used to quantify catalystprimary particle size distribution
2 4 6 8 10 120
5
10
15
20
25
30
35
ParticleCou
nts
Particle Diameter (nm)
Dart 181A
2 4 6 8 10 12 14 16 18 200
2
4
6
8
10
12
14
ParticleCou
nts
Particle diameter (nm)
PtBO2
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Nanoparticles agglomerate, so primary particlesize does not tell the entire story
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Ru black
5nm
100nm
Small 2-6 nm particles can agglomerate tolarge particles
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Nanomaterials as catalysts
We have been using nanomaterials ascatalysts for decades- they have just
been rebranded as nanoparticles.
With better analytical tools, we nowhave better control of our catalysts.
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Nanomaterials for gas detection:
many choices CNTsCNTs (MW)(MW)
CNTsCNTs + polymer+ polymer
CNTS + metal oxidesCNTS + metal oxides CNT + metal catalystsCNT + metal catalysts
ZnO nanowiresZnO nanowires
SnOSnO22 nanonano powderpowder
Tungsten oxidesTungsten oxides IIIIII--V quantum dotsV quantum dots
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Many growth/ deposition methods
CVD
PVD
Nanopipette: QDs, MMOs, polymers electropolymerisation (polymers)
in-situ CNT growth
Flame ablation
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Molecular structure of [Et2In(OS2CNMen
Bu)]2
NOAH: DTI funded project to make gas sensors from
quantum dots and nanorods using single component
CVD
(Universities of Manchester & Keele, Alphasense, Teer, Epichem)
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SEM image of InS nanorods
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-In2S3 films grown at 375 C
TEM shows straight In2S3 nanorods
with average diameter of
ca. 20 nm and ca. 400500 nm
in length.
High-resolution TEM confirms
crystallinity by indicating well-resolved
(103) lattice planes. The experimental
lattice spacing, 0.66 nm is consistent
with the 0.62 nm separation in bulkcrystals.
Good deposition, but poor gas response
TEM image of InS nanorods
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Flame Spray Pyrolysis
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SnO2 particles generated by
flame spray pyrolysis
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SnO2 by flame pyrolysis shows goodresponse and strong temperature
dependence
10 ppm C2H5OH (C). The sensors with Pd/Al2O3 filter (filled symbols) and without filter (open symbols)for both undoped SnO2 (black squares) and Pd-doped SnO2 (grey circles) are measured at 50% r.h. at 25C.
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Carbons
Graphite
CNT (single and multiwalled)
boron doped diamond glassy carbon
graphene?
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5nm
TEM can also be used to follow a processsuch as ball milling of graphite
2nm
2nm
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Increased ball milling increases theamorphous layer thickness
5nm
5nm
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PECVD Chamber for direct growth of
CNT Graphite heater usedto heat substrates
(Plasma) DC Voltage-630V
Temperature of
Growth: 550 900o
C Rotary PumpConnected to thebell jar
Gas Inlet for Ammonia,Acetylene and Nitrogen
GraphiteStage heater
connected
Gas Exposureoutlet for thesamples
Top View Showingsamples on agraphite stage
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Direct Growth of Carbon Nanotubes
Novel Technique to growCNTs direct on chip
Microheater heated to growCNTs locally on the desiredarea in 5mins in vacuum at0.2mbar.
MWCNTs grown locally on thesmall heaters , radius 12um.
SWCNTs can be grown athigher temperature and thinnercatalyst deposition.
Small heater withCNTs
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CNTs Grown on SOI Membranes
ResistiveElectrodeswith CNT
on SOIMembrane
Depositionfor 15minsusing 2nmFe catalyst
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How the CNTs will work as
sensors Gases like NO2 are
electrophillic so it canremove electrons fromCNTs (For SWCNTs)
For MWCNTs chargetransfer mechanism.
CNT conductanceincreases and therefore
the resistance of the filmdecreases.
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Reported CNT response to NO2
Room temperature Response Time (2ppm) = 30sec, Sensitivity = ~15%F.Udrea et al , IEDM 2007, December
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ZnO nanowires
Nanowire grew properly in case of resistive sensor withAl metallization
(Au plated)
Resistance 10 k 300 k
Growth on microhotplate: combining MEMS and nanomateria
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Nanomaterials in optical gas
sensingQuantum dots re-emit light at much longer wavelengths than
excitaion wavelength- this allows us to shift LED emissions tomuch longer wavelengths (Trackdale)
Controlled nanoparticles on surfaces give repeatable Surface
Enhanced Resonant Raman Spectroscopy (SERRS)
Nanoparticles can replace metal surfaces as the conductinglayer for surface plasmons (SPR)
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Conclusion
Improved, lower cost analytical tools (electron
microscopy and AFM) bring quality control to
nanomaterials
Catalyst are being improved with III-V and carbon
based materials now added to our catalyst choices
Optics are using the unusual emission and
conduction properties of nanomaterials
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Acknowledgements
Paul OBrien Manchester Chemistry
Rod Jones Cambridge Chemistry
Nicolae Barsan University of Tuebingen Physics
Bill Milne, Sumita Santra and Florin UdreaCambridge Engineering
James Covington and Julian GardnerWarwick Engineering
Paul Midgeley and Cate DucattiCambridge Materials Science and Metallurgy
Cambridge CMOS Sensors Daresbury Laboratory
Technology Strategy Board (ULoGS project funding)
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Thank you for your attention