Nanomechanics: Resonators

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Nanomechanics Resonators
Roukes, Mohanty et al.
Ruoff et al.
Craighead, Cleland, Parpia et al.
de Heer et al.
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MHz-GHz mechanical resonators
Diamond like carbon pillars
Roukes, Mohanty et al.

• 1 GHz
• (Nature Jan 30, 2003)Q500 SiC

Fujita et al. JVST B, 19, 2834, 2001
What for? ultra-sensitive sensors (toward
single molecule detection) high frequency
electronics / optoelectronics . . .
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NanoElectroMechanical Systems

• Materials Si down to lt50 nm!
• But - Materials issues limit energy loss
• CNT may be better material
• Route to 1 nm

CNT SiO2 Au/Cr
Si Paddle Craighead group (Cornell)
CNT Torsional Beam NSRG (UNC)
North Carolina Center for Nanoscale Materials
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Fabrication of CNT Paddles
SiO2

• CNT deposition
• Ebeam lith in-situ
• Etch SiO2 (500nm)
• Critical Point Dry

Au
Au
CNT
Suspended CNT Torsional Beam (UNC)
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Carbon nanotubes are apparently p-type. Why?
EC

• Metal electrode-tube work function?
• Electrostatic effects due to charged species on
  SiO2 surface?
• Oxygen doping?

Hole
Vbias
p-type
oxide
Vgate 0
doped Si
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P-type semiconductor Majority carriers depleted
when Vgate gtgt0 Conductivity vanishes
Oxide SiO2
Ni/Au
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Simple Picture
Electron donor
Electron acceptor
N
O
O
Charge transfer is 0.1 e- per NO2
creates holes
CNT
CNT
annihilates holes
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Vbias
Vgate
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NO2 Sensing PERFORMANCE 200ppm Sensitivity
(Rbefore/Rafter) 100-1000 Response Time upon
exposure 2-10s (time for resistance to change
factor of 10) Recovery time in pure Ar 12
hrs in heated air 1 hr

• Compared t o conventional detector materials.
• Cd doped SiO2
• works at 250 C to detect 100 ppm
• response time 50s
• recovery time 8 min
• sensitivity 300
• Polymer (room temp)
• 0.1
• sensitivity 1.1
• response time 10 min

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NH3 Sensing PERFORMANCE NO2 1 Sensitivity
(Rbefore/Rafter) 10-100 Response Time upon
exposure 1-2 min (time for resistance to change
factor of 10)
Compared to conventional detector
materials. Metal oxide detectors 300-500
C response time 1 min sensitivity 100 (at
1) Conducting Polymer 1 response time 5-10
min sensitivity 1.3
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