nano materials improving gas

8/6/2019 Nano Materials Improving Gas

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Nanomaterials: improving gas

sensor performance

John SaffellAlphasense Ltd.

Technical Director

[email protected]

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

nano materials improving gas

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