Sebastián Caicedo Dávila

José Ferney Rivera Miranda

Jaime Velasco Medina

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

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

Taken from 1995 BBC Horizon documentary “A Code in the Nose” about Luca Turin's vibration theory of olfaction.

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.

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.

Cu Electrode Cu Electrode

InP Barriers

InAs Wells

InAs

Wire

InAs

Wire

Right Well

Left

Well

Source Drain

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.

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

Non-equilibrium density of States

Spectral function

In the Eigenstates Basis

A E( ) = i G E( ) -G E( )+é

ëùû

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+{ }

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.

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.

I-V characteristic curve showing peaks and valleys (resonant device). The

latter are the regions most suitable for gas sensing.

• 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.

• 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.

Questions?