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.