ESF provides the COST Office

through a European Commission contractCOST is supported

by the EU Framework Programme

European Network on New Sensing Technologies for Air Pollution Control

and Environmental Sustainability - EuNetAir

COST Action TD1105

WGs and MC Meeting at ISTANBUL, 3-5 December 2014 Action Start date: 01/07/2012 - Action End date: 30/06/2016

Year 3: 1 July 2014 - 30 June 2015 (Ongoing Action)

MASTERING VOC DETECTION FOR BETTER

INDOOR AIR QUALITY

Donatella Puglisi / donpu@ifm.liu.se

Participant

Linköping University / Sweden

2

Scientific context and objectives in the Action

Bad air quality causes serious

problems on environment,

health, society

Good air quality is a key-issue!

Stringent legislation for

NOx and VOCs

Adequate control of emissions for more efficient reduction of

hazardous air pollutants

• Background / Problem statement: +85 % time spent indoor / costly HVAC systems

• Brief reminder of MoU objectives:

• WG1: sensor materials and nanotechnology

• Research on gas-sensitive materials for detection of specific air pollutants

• Integration in gas sensor devices for indoor AQC

• Functionalization and surface modification to enhance gas adsorption and sensitivity;

stability, reproducibility, and selectivity

• Material characterization (e.g. AFM, SEM)

• WG2: Sensors, devices and sensor systems for AQC

• Design, fabrication, testing, characterization of cost-effective high-performance gas sensors

• Innovative sensor technologies: SiC-FET and graphene-based sensors

M. Gemelli

3

Current research activities (SiC-FET)

Sensor processing /

characterization

Addressed challenges

0 1 2 3 4 5 6 7 8 9 10 11 12

0.85

0.90

0.95

1.00

Recovery

time

Response

time

10 %

90 %

100 pts smooth

Dry air1 ppm

100 ppb

10 ppb0.5 ppb1 ppb 0.2 ppb

330 °C

Sensor

Sig

nal (n

orm

. valu

es)

Time (h)

Formaldehyde (CH2O)

0.0 0.5 1.0 1.5 2.0750

800

850

900

950

Se

nso

r S

ign

al (m

V)

Time (h)

10 ppb

5 ppb

1 ppb

Naphthalene (C10

H8)

20 % r.h.

330 °C V

GS = 2.8 V

0.5 ppb

-5

-4

-3

-2

-1

0

1

2

3

4

5

2

nd

dis

cri

min

an

t fu

nctio

n (

1.1

2 %

)

40

ppb

20

ppb

10

ppb

5

ppb2.5

ppb0 ppb

(air)

naphthalene

20 % and 40 % r.h.

-12 -8 -4 0 4 8 12 16 20 240

1530456075

co

un

ts

1st discriminant function (98.72 %)

Pt-gate

Sensing mechanisms /

device operation

Sensitivity

Selectivity

4

Current research activities (Graphene)

As-grown Thin porous metallization5 nm

1LG

Morphology Surface potential

100 mV

As-grown Au ≈ 5 nm

Morphology Surface potential

Morphology Morphology

Surface potential Surface potential

10 µm 10 µm

1 µm2 1 µm2 1 µm2

1LG2LG

Au ≈ 2 nm Pt ≈ 2 nm Pt ≈ 0-1 nm

1 nm

Sensor processing / characterization

Sensing mechanisms / device operation Addressed challenges

50 ppb

CH2O

120 150 180 210 240 270 300

1796

1798

1800

1802

1804

1806

1808

1810

1812

Re

sis

tan

ce

Time (min)

Annealed at 250°C

20% r.h.

125°C

60 70 80 90 100 110 120 130 1401,00

1,05

1,10

1,15

1,20

1,25

NO2

Air

100 ppb50 ppb

No

rmaliz

ed R

esis

tan

ce

Time (hours)

sensor 1

sensor 3

sensor 2

Sensitivity

Reproducibility

Selectivity

Ongoing research topics

+15 years experience on high-performance, low-cost FE gas sensors

for room and high temperature applications, such as

• car/truck engines and power plants

• emission monitoring

• combustion control and exhaust systems

• indoor air quality applications

5

Why SiC-FET sensors?

• Chemical inertness

• Wide band gap (3.26 eV 4H-SiC)

HARSH ENVIRONMENTS

HIGH-TEMPERATURE

OPERATION

n-type 4H-SiC substrate

p-type buffer layer

n-type active layer

S D

VDS VGS

- High, stable, reproducible performance - Flexibility when using temperature cycling mode

- Possibility to use high temperature for regeneration of the sensor surface

…No! Yole Développement: transition to 4-inch SiC wafers - a milestone towards reduced cost of SiC technology

6

But SiC is so expensive…

The ongoing transition to 6-inch wafers will usher in further cost reduction and SiC market growth

4-inch SiC wafer ~ 1800 chips (cost < 1 euro/each)

The ongoing wafer cost reduction and market expansion in SiC will spill over also to EG/SiC

Further steps towards cost-efficient preparation of EG/SiC through up-scaling of sample size in combination with a novel epitaxy technique allowing growth on inexpensive SiC substrates

FE sensor platform

7

Gate composed by a porous catalytic metal (Ir, Pt) as sensing layer

Gas adsorption/reaction

at the gate contact

I-V shift

Absence of gas

Presence of gas

Sensitivity by

Number of three phase

boundaries gas-metal-oxide

Adsorption sites on the insulator

Selectivity by

Choice of temperature

Different catalytic materials

Structure of the metal

• FET current controlled by VGS

• Gas molecules decompose

and react on the catalytic metal

• Simple electronics

Cross section of a SiC-FET

M. Andersson, R. Pearce, A. Lloyd Spetz,

Sens. & Act. B 179 (2013) 95-106.

Sensor operation

8

High sensitivity:

excellent detection limits

0 10 20 30 40 50 60

0

1

2

3

4

5

6

7

8

9

10

Dete

ctio

n L

imit (

ppb

)

Relative Humidity (%)

Formaldehyde

Benzene

Naphthalene

Ir-gate SiC-FET

330 °C

< 0.5

In cooperation with Saarland University

High selectivity:

discrimination of VOCs

Multi-dimensional data evaluated by pattern recognition techniques Linear discriminant analysis (LDA) + cross-validation to avoid over-fitting data For on demand ventilation, «below threshold» means ventilation not needed Robust discrimination against changing humidity level and varying concentration of VOCs

-8 -6 -4 -2 0 2 4 6 8

-5

-4

-3

-2

-1

0

1

2

3

4

5

cv-rate: 89.7 %

below threshold

synth. air

formaldehyde 50 ppb

napthalene 2.5 ppb

benzene 1.5 ppb

formaldehyde

75, 100, 200 ppb

20 % + 40 % r.h.

2n

d d

iscri

min

an

t fu

nctio

n (

15

.77

%)

1st discriminant function (80.68 %)

naphthalene

5, 10, 20 ppbbenzene

2.5, 3.5,

4.5 ppb

Innovation – SiC-FET • Detection limits under threshold of legal requirements

• Discrimination and quantification of specific VOCs

• Stability during long-term operation

9

Morphology Surface potential

Height (nm) 60 nm ΔVpot (mV) 200 mV

10 µm

Insulator Gate Insulator Gate

ΔVpot (mV) 30 mV Height (nm) 30 nm

3 μm × 3 µm

Ir-gate before and after two weeks operation

Iridium - Sensing layer not degraded

is extremely important for our target

application (indoor AQC)

Suggested R&I Needs for future research

Research directions as R&I

NEEDS:

Development of new materials as

sensing layers using PLD (work in

progress in cooperation with Univ. Oulu)

Ongoing research topics

10

Why gas sensors in graphene?

• Increased sensitivity and reproducibility

• Functionalization with metal and metal oxide nanostructures for

selectivity tuning

• Controlling layer uniformity and doping

• Effect of surface restructuring during graphene growth on SiC

• Effect of humidity on sensor performance

Unique band structure of graphene leads to a low density of states near the Dirac point (ED) – small changes in the number of charge carriers result in large changes in the electronic state

Every atom at the surface – ultimate surface to volume ratio

Low noise, chemically stable (in non-oxidizing environment) – enables very low detection limits

p

p*

|e|<1eV

Graphene is highly sensitive to chemical gating due to its linear energy

dispersion and vanishing density of states near the Dirac point and therefore has

potential as a low noise, ultra-sensitive transducer.

11

manufactures and supplies

Very high quality, wafer scale, epitaxially grown

Graphene on SiC

Spin off from Linköping University,

Sweden

22.11.2011

Produced by sublimation of Si from SiC in Ar at 2000 ºC

Scalable, wafer-size graphene films compatible with standard semiconductor processing

High thickness uniformity (> 90 % 1LG, rest 2LG)

Thickness controlled by temperature

Graphene sensors issues: sensitivity, reproducibility

12

1LG is more sensitive to NOx than

2LG or MLG

Uniform 1LG required for

maximum sensitivity and reproducibility

Different sensors fabricated on 100 % 1LG show identical

response

Epitaxial graphene on SiC enables

highly reproducible sensor fabrication

NO2 withdraws electrons

Ambient 1 ppm NO2

R. Pearce, J. Eriksson, T. Iakimov, L. Hultman, A. Lloyd Spetz, and R. Yakimova,

ACS Nano 7 (5), pp 4647–4656 (2013)

Same change in charge carriers causes larger shift of the Fermi energy for 1LG

ΔS depends on thickness due to differing band structures for 1LG, 2LG,... MLG

NO2 sensing interesting for:

• Emission control (few ppm)

• Air quality control (few ppb)

60 70 80 90 100 110 120 130 1401,00

1,05

1,10

1,15

1,20

1,25

NO2

Air

100 ppb50 ppb

No

rmalize

d R

esis

tan

ce

Time (hours)

sensor 1

sensor 3

sensor 2

Uniform 1LG leads to very reproducible sensor characteristics

100 °C

Graphene sensors issues: selectivity,

response/recovery time

13

Functionalization with metal and metal oxides nanostructures for selectivity tuning

Aim: To develop a reproducible method for functionalization with metal nano structures

• Thin layers of Au and Pt DC sputtered onto EG/SiC at elevated pressure

• Ideally we want islands or nanoparticles to maximize metal-graphene-gas boundaries

SI 4H-SiC

on-axis

Epitaxial graphene

Au, Pt

0 5 10 15 20 25 30 35

1,0

1,1

1,2

1,3

1,4

1,5

1,6

1,7

Re

sis

tan

ce

ch

an

ge

R/R

0

Time (hours)

0

20

40

60

80

100

120

140

100°C

NO

2 c

on

ce

ntr

atio

n (

pp

b)

in N

2As grown graphene

0 2 4 6 8 10 12 14 16 18 20 22

1,0

1,2

1,4

1,6

1,8

2,0

Re

sis

tan

ce

ch

an

ge

R/R

0

Time (hours)

0

200

400

600

800

1000

NO

2 c

on

ce

ntr

atio

n (

pp

b)

in N

2

Au on graphene 100°C

RT

0 2 4 6 8 10 12 14 16 18

0,50,60,70,80,91,01,11,21,31,41,51,6

Resis

tance c

han

ge R

/R0

Time (hours)

500 ppb

NO2

40 ppm

NH3

50 ppm

NH3

100 ppb

NO2

250 ppm

H2

500 ppm

CO

50 ppb

NO2

30 ppb

NO2

400 ppb

NO2

100°C

RT

Effect of Au decoration on sensor response

Detection limit < 1 ppb NO2 Selectivity: blind to H2 and CO J. Eriksson, D. Puglisi, Y. H. Kang, R. Yakimova, A. Lloyd Spetz , Physica B 439 (2014) 105–108

Innovation - Graphene Reproducible growth

Wafer-scale films compatible with standard semiconductor processing

High thickness uniformity (> 90 % 1LG, rest 2LG)

Decoration changes the surface chemistry but does not alter the graphene band structure

14

Suggested R&I Needs for future research

Research directions as R&I

NEEDS:

Designed nanoparticles by pulsed plasma:

it is expected that decoration with different

metals or metal-oxide nanostructures will allow

careful targeting of selectivity to specific

molecules

Designed Nanoparticles by Pulsed Plasma

Preliminary results show that TiO2 NPs allow enhanced sensitivity towards formaldehyde and benzene

The effect depends on the size of the deposited NPs (< 5 nm, sensitive to benzene; > 50 nm, sensitive to formaldehyde)

Plasma-based nanoparticle (NP) synthesis process

Highly versatile (metals, metal-oxides, core-shells) and reproducible thin film deposition technique

15

20 nm 100 nm

TiO2 NPs (Ø < 5 nm and Ø ≈ 50 nm) Ø < 5 nm

50 ppb

CH2O

120 150 180 210 240 270 300

1796

1798

1800

1802

1804

1806

1808

1810

1812

Resis

tance

Time (min)

Annealed at 250°C

20% r.h.

125°C

16

Research Facilities available for current research

• Clean room, ISO 6 (magnetron sputtering, lithography, CVD, etc.)

• Sensor processing and characterization (gas mixing systems,

readout electronics, bonding machine, spot welding, scribers,

thermal evaporation, shadow masks, optical microscopes, AFM,

SEM, etc.)

• Hardware and software for data acquisition and data analysis

• Gas bottles: CH2O, C6H6, CO, NO, NO2, NH3, N2, O2, synthetic air

• Other facilities available at: Saarland University, SenSiC,

GraphenSiC

17

Acknowledgements Special thanks to (in alphabetic order):

Dr. Mike Andersson, associate professor Linköping University and SenSiC

Manuel Bastuck, PhD student Saarland University

Dr. Robert Bjorklund, senior researcher Linköping University

Christian Bur, joint PhD student Saarland University and Linköping University

Dr. Jens Eriksson, assistant professor Linköping University

Joni Huotari, PhD student University Oulu

Prof. Jyrki Lappalainen, University Oulu

Prof. Anita Lloyd Spetz, Action Vice-Chair, Director of FunMat, Linköping University

Peter Möller, tech. engineer and PhD student Linköping University

Dr. Michele Penza, Action Chair, ENEA

Prof. Andreas Schuetze, SENSIndoor coordinator, Saarland University

Prof. Rositsa Yakimova, Linköping University and GraphenSiC

Thank you for your attention!

18

(Looking forward to see you in Linköping!)