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Sebastián Caicedo Dávila
José Ferney Rivera Miranda
Jaime Velasco Medina
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Taken from: www.vernier.com
James, D., Scott S. M., Zulfiqur Ali, O’Hare, W. Chemical
Sensors for Electronic Nose Systems. Microchimica Acta,
2005
Yi Cui, Qingqiao Wei Hongkun Park, Charles M.
Lieber. Nanowire Nanosensors for Highly Sensitive
and Selective Detection of Biological and Chemical
Species. Science 2001
Larry Senesac and Thomas G. Thundat.
Nanosensors for trace explosives
Detection. Mat. Today 2008
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Taken from: Ilia A. Solov'yov,. “Vibrationally assisted
electron transfer mechanism of olfaction: myth or
reality?” Phys. Chem. Chem. Phys., 2012,14
Vibration of protein alpha helix, taken
from Wikipedia
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Taken from 1995 BBC Horizon documentary “A Code in the Nose” about Luca Turin's vibration theory of olfaction.
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Very sharp energy levels can be used as allowed states, lessing the effect of
thermionic excitation’s current. Such levels (QB-states) can be created by
confinement in 1D. Heterostructures are suitable candidates for the job.
Semiconductor sensors are very effective and easily integrated with
conventional electronics.
A. P. Horsfield, L. Tong, Y.-A. Soh, and P. A. Warburton, “How to use a nanowire to measure vibrational frequencies:
Device simulator results,” Journal of Applied Physics, vol. 108, no. 1, 2010.
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Bias applied accross the TBH shifts the energy profile (and the QB states).
Vibrational modes of an adsorbate at the middle PB can be excited by
electrons that will lose energy and tunnel through the device, just as Turin’s
theory proposes.
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Cu Electrode Cu Electrode
InP Barriers
InAs Wells
InAs
Wire
InAs
Wire
Right Well
Left
Well
Source Drain
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E1
E2
E3
E4
En
...
H
{Ψ}
Stationary QM system: closed
system represented WF
doesn’t change in time.
E1
E2
E3
E4
En
...
H
{Ψ}
µ
HR
{ΦR}
[τ]
Coupling to the contacts broadens the
discrete energy states.
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e + ig
2
æ
èç
ö
ø÷F = EF
E -e - ig
2
æ
èç
ö
ø÷F = 0
E -e - ig
2
æ
èç
ö
ø÷F = S
G = E -e - ig
2
æ
èç
ö
ø÷
-1
Homogeneous equation Non-homogeneous equation
Green’s Function
F{ } = EI -H - S[ ]-1S{ }
G = i S- S*éë
ùû
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Non-equilibrium density of States
Spectral function
In the Eigenstates Basis
A E( ) = i G E( ) -G E( )+é
ëùû
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Current as change in Electron DensityF{ } = EI -H - S[ ]
-1S{ }
i¶
¶tF{ } = E F{ }
Remember
Equivalent to the Landauer Formula
T E( ) = Trace G1G G2G+{ }
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Potential profile (dashed blue), LDOS in the wells regions (solid red and
magenta) and transmission (solid black), showing the whole energy picture of
the system at thermal equilibrium.
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Transmission coefficient vs. Energy for the system at thermal equilibrium. The
transmission peaks (double due to bonding-antibonding combinations) arise
due to the alignment of quasi-bound states of the wells. The red dashed line
shows the bottom of the conduction band.
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I-V characteristic curve showing peaks and valleys (resonant device). The
latter are the regions most suitable for gas sensing.
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• A gas nanosensor, based on an InAs/InP triple-barrier
heterostructure, devised to achieve high selectivity and detect
vibrational modes of molecules was simulated at room
temperature.
• We proposed a simplified 1D model and used NEGF, and a single-
band effective-mass Hamiltonian, to calculate the I-V characteristic
curve of the semiconductor triple-barrier heterostructure at low
computational expense.
• We were able to demonstrate the plausibility of the device, by
analyzing the LDOS in the wells regions, which showed that our
model device would be able to sense different vibrational modes of
SO2.
• NEGF lets us include all kind of interactions between the system
and external stimuli. We can include electron-phonon interactions
and the interaction with vibrating molecules adsorbed at the device
region, only by adding extra self-energy matrices.
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• Consider a self-consistent potential in order to include space-charge effects.
• Build and simulate a 3D model with finite cross-section,attached to metallic contacts.
• Analyze the phonons of the simplified model, and build aself-energy matrix describing the electron-phononinteraction.
• Calculate the Hamiltonian and self-energy matrices usingself-consistent DFT.
• Build additional self-energy matrices that describe theinteraction of vibrating molecules with the device.
• Determine the selectivity of the device by performingcalculations of the interaction with several molecules.
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Questions?