Slide 1

Report
NSF- NIRT: "Surface State Engineering"
Charge Storage and Conduction in Organo-Silicon Heterostructures as a Basis for
Nanoscale Devices
John C. Bean
1Department
1
(PI) ,
Avik
1
Ghosh ,
Lloyd R.
1
Harriott ,
Lin
2
Pu ,
Keith
3
Williams
of Electrical and Computer Engineering, 2Department of Chemistry, 3Department of Physics
University of Virginia, Charlottesville Virginia
Basic Idea:
Create highly-pure, highly-ordered bound organo-silicon hybrids
Molecules bound so intimately that electron waves pass easily
between components
Multiscale Modeling of Trap Modified Transport:
Coupling weak and strong quantum correlation (wires vs. dots):
Effect of Traps on CNT and Graphene Transport:
Basic studies + “concurrent engineering” of experimental techniques
and modeling tools for later use with full SOI MOSFET device
Density Functional Theory (Si) / Extended Hückel (molecules)
Electron beam induced traps in CNT and graphene FETs:
Within framework of Non-Equilibrium Green's Functions
Yielding:
1) Precise charge transfer in to and out of Si surfaces
Applied to Random Telegraph Signals (RTS) of molecules on FETs:
2) Conduction based on quantum mechanical resonance
RTS successfully modeled, including multi-trap interactions
In nanoscale MOSFETs this could:
Inter vs. intra layer transport in Graphene:
Supplant conventional trace donor/acceptor charge creation
Minimize ionized impurity scattering => Enhanced transport
Could differentiate between molecules and alternate binding
states:
Despite common 2D idealizations, real data likely to include both!
Raman highly sensitive to layer edges => Decorate with metals
Enable devices based on quantum interference phenomenon
Three pronged investigation strategy:
First principles modeling
Studies of trap-influenced transport in CNT & graphene surrogates
Development of full organo-Si MOSFET device structure
Engineering Molecular Surface States on Silicon:
Task 1: Achieve dense high-quality organic attachment to Si
normal HOPG
decorated HOPG
Outreach:
Complete class website (with visitors from over 1000 schools):
www.virlab.virginia.edu/Nanoscience_class/Nanoscience_class.htm
Or via dilution of surface-state-inducing molecules with passivating molecules
Cited in 2009 Award of IEEE Undergraduate Teaching Medal to PI
(e.g. alkyne => alkene + attachment):
Dipole induced surface band bending actually more intense in diluted layers:
Task 2: Identify organics capable of passivating Si surfaces
Evidence that polar organics partially
depolarize if in immediate proximity
Hydrosilylated acetylene proved very effective as verified by pulsed
Plus ongoing summer Nano classes for K-12 science teachers
Recent Project Publications:
photoconductivity measurement of near surface Si minority carrier lifetimes
Task 4: Fabrication of back-gated SOI MOSFET device structure
Goal: Assess channel modification via phenomena such as RTS signals
Surface charge transfer:
of graphene edges
Begun under 2005 NSF NUE grant
Achieved via UV-enhanced
Surface dipoles:
Raman of Ag edge
Continuing Development of “Hands-on Intro to Nano” Class
Fine-tuned with fluorine induced dipoles vs. quadrupoles:
Task 3: Develop palette of organic surface state inducers
Raman of
Signature should facilitate deconvolution of transport modes
(Engineering of Molecular Surface States on Si continued):
UHV vacuum hydrosilylation
Colloidal Ag decoration
Pursuing both micron and deep sub-micron channel width device designs
Reversal of current blockade in nanotube-based field effect transistors through
multiple trap correlations, J. Chan et al., Phys. Rev. B 80, 033402 (2009)
Controlling transistor threshold voltages using molecular dipoles, S. Vasudevan et al.,
J. Appl. Phys. 105, 093703 (2009)
Modeling electrostatic and quantum detection of molecules, S. Vasudevan et al., IEEESensors Journal 8, 6 (2008)
Former: Easier to fabricate / Latter: More subtle surface state information
First achieved with variants of phenylacetylene:
Plus In-Press / In-Preparation:
Component processes for both designs essentially complete:
Quantum Transport through Metal-Molecule-Semiconductor heterostructures: the
role of interfacial charges and barriers, A Bahuguna et al.
Coupling nano and microscale transport for electronic read-out of quantum dot
dynamics, S. Vasudevan et al.
Single Molecule Characterization using Random Telegraph Signals, S. Vasudevan et al.
Design
Pads
Channel
Side-gates
Microscopic model for trap-generated noise in nano-devices, S. Vasudevan et al.

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