Slide #

Heated microcantilevers sensors

IR image of the cantileverMicrocantilever with CNT sensing layers

Heated microcantilever

The heated cantilever can be used as an excellent sensor for (i) chemical analysis of trapped molecules in the CNT layers, (ii) measuring thermal properties of surrounding gases, and (iii) various SPM probing methods, including lithography

Slide #2

Noise in piezoresistive microcantilever

• Electrical noise– Johnson noise (Random thermal motion of carriers)

– 1/f low frequency noise (Carrier mobility fluctuation due to bulk defects or carrier number fluctuation due to surface traps)

• Vibration noise– Thermo-mechanical noise (Random movement of molecular in

air surrounding mechanical structures leads to random fluctuations in the energy transfer between structure and damping gas)

Slide #3

Johnson noise

TRkS BV 4SV: Noise power spectrum density

kB: Boltzmann's constant

T : Temperature

R : Resistance

pAR

fTkrms B

noiseI 89.34

R = 1100 Ω

Measurement bandwidth Δf = 1 Hz

Electrical noise

Deflection sensitivity = 11e-5 per µm, Vbias = 1.0 V

RMS noise JOHNSON = 0.03 nm

Slide #4

dfNf

Vrms

f

f

biasf

noiseI

2

1

2/1

1/f low frequency noise (Flicker noise)

SV : noise power spectral density [V2/Hz]

N : the number of carriers (depends on the piezoresistor volume and implant

dose)

Vbias : bias voltage , f : the frequency, n: unity (n=1)

α: empirical coefficient depends on annealing length:

fNf

VS

nbias

V

162 1018.2

)/ln(1018.21018.2

1216

162 2

1

ffdff

ef

fnoise

pARerms noiseI 1.302/

fmax= 100 Hz

fmin= 1 Hz

R = 99.2 Ω

Lr = 54 µm

Wr = 14 µm

Hr = 2 µm

Vbias = 1 V

µ = 400 cm2/Vs

kBT = 0.026 eV

α=1.0e-6

nbias

V Nf

VS

2

Electrical noise

Slide #5

Vibration noise

Thermo-mechanical noise

0

4

kTBQk

noiserms BTM

L=250 µm

W=140 µm

H=2 µm

E = 179GPa

Q = 69

w0 = 2*pi* 31.5 kHz

KBT = 0.026 eV

k= 3.11N/m

B = 1 Hz

RMS noise TM = 0.0013 nm

P. G. Datskos, N. V. Lavrik, and S. Rajic, “Performance of uncooled microcantilever thermal detectors”, Rev. Sci. Intr., 75, 1134 (2004)

Force noise spectrum density

At resonance:

)2/(4 0QfTkkS BF

At resonance, Vac = 5.0 sin (ωt)

nmrmsrmsrms noiseVibnoiseElecttotal 031.0)( 5.022

V

kQ

ZC

V

rms

ac

total 12

Minimum Δφ = 12 μV

Slide #

Nanowire based chemical sensing

6

InN/In2O3 nano core/shell based FET sensor

J. Liu, Z. Cai, G. Koley, “Charge transport and trapping in InN nanowires investigated by scanning probe microscopy”, J. Appl. Phys. 106, 124907 (2009)

µ = 150 cm2

/Vs

SEM image

TEM image Diffraction pattern

Morphology Probe current

Slide #7

…Continued

45 ppb (parts-per-billion) NO2 could be detected

InN core

In2O3 shell layer

Vth shifted

TEM image of nano core/shell InN/In2O3 NWs

SEM image of NanoFET

NO2 sensing

Slide #8

TMV nanofiber based sensor

Z. Niu, J. Liu, L. A. Lee, M. A. Bruckman, D. Zhao, G. Koley, Q. Wang, “Biological Templated Synthesis of Water-Soluble Conductive Polymeric Nanowires”, Nano Lett. 7, 3729 (2007)

Conductivity σ = 2.93 x10-5

Ω-1

cm-1

TEM image of TMV nanofibers

Slide #9

…Continued

M. A. Bruckman, J. Liu, G. Koley, Y. Li, B. Benicewicz, Z. Niu, and Q. Wang, “Tobacco mosaic virus based thin film sensor for detection of volatile organic compounds”, J. Mater. Chem. 20, 5715 (2010)

Good selectivity toward Methanol and Ethanol vapor

Methanol

On

Off

Time (s)