NIRT: "Surface State Engineering" Charge Storage and Conduction in Organo-Silicon Heterostructures as a Basis for Nanoscale Devices John C. Bean (PI) 1, Avik Ghosh 1, Lloyd R. Harriott 1, Lin Pu 2, Keith Williams 3 1 Department of Electrical and Computer Engineering, 2 Department of Chemistry, 3 Department of Physics University of Virginia, Charlottesville Virginia Basic Idea: Create highly-pure, highly-ordered bound organo-silicon hybrids Bound so intimately that electron waves pass easily between components Allowing for:1) Precise charge transfer into and out of Si surfaces 2) Conduction based on quantum mechanical resonance In future nanoscale MOSFETs this could: 1) Replace conventional trace donor/acceptor charge creation 2) Enhance performance by minimizing ionized impurity scattering 3) Open door to devices based on quantum interference phenomenon Our background: UVA investigated Moletronics through earlier NIRT & DARPA "MOLEapps" But unlike others, OUR goal was to transform hero results into technology Led us into use develop: Extremely pure vapor phase molecular Si-based planar devices:deposition techniques: Resulting in: TRUE self-assembled monolayers: single step, self-limiting 5X increase in device yields over liquid phase standard Deposition Chamber 2: Converted to Organics Center Loading & Processing Chamber Deposition Chamber 1: Original semiconductor process Silicon 100 nm SiO 2 Focused Ion Beam milled hole (approx. 50nm) Self Assembling Monolayer of molecules 200 nm Au 5 nm Ti NIRT Building Block #2) Vapor Phase Synthesis of Organo-Si Heterostructures Goals: Electrically activate desired silicon sites, passivate (neutralize) all others (2x1) reconstruction of Silicon (100) surface On hydrogen covered surfaces, we will use our proven tool of hydrosilylation: Alkene/Alkyne terminated organic approaching Si-H Surface hydrogen eliminated by UV or heat leaving Si surface radical C=C / C≡C bond breaks, C1 attaches to Si, C2 becomes radical C2 radical grabs neighboring H, creating new Si surface radical Or other chemical options on bare reconstructed Silicon surfaces: Cyclo-addition Diels-Alder Reactions Or more complex reactions: Acetylene → Si Butadiene → Si Cyclooctatetracene → Si Base molecules = Surface passivating units Altered to produce electrical activity / transport by adding: Electron withdrawing or electron contributing groups Fallback option (if unsatisfactory passivation of bare Si) = Attachment of molecules to electron transparent thin SiO 2 on Si Preliminary Results: - Model of Random Telegraph Signal in nanoFET: - Successful measurement of RTS in nanotube FETs - Design of UVA SOI nanoFET device test structure: Data 4 Our Model 4 Xiao, Yablonovitch et al., Nature 430, p. 435 (2004) Education and Outreach building on two earlier NSF Grants: 1) 1999 Course Curriculum & Laboratory Improvement (CCLI) Grant Led to creation of UVA Virtual Lab Science Education Website 50 + intuitive 3D-animated presentations focusing on micro and nano technology Over 3.5 million hits to website since early 2005 Including visitors from over 1000 Universities and 300 K-12 schools & districts Semiconductor Crystals How transistors work How IC's are made Nanocarbon DNA self- assembly 2) 2005 Nanoscience Undergraduate Education (NUE) Grant To develop freshman/sophomore "Hands on Intro to Nanoscience" Using miniature AFMs and STMs (fully explained on website in virtual reality) To now partner with multi-site Science Museum of Virginia - Help develop new exhibits, as well as new museum in DC suburbs - Incorporate "Intro to Nanoscience" into their K-12 teacher training programs And to spin off "Hands on Nanoscience" class to other schools: - E.G. Danville VA's new C.C. class in support of their Nanotech Incubator Our VR recreation of class's AFMsOur VR recreation of class's STMs NIRT Building Block #3) Device Evaluation of Quantum Surface States Use "Random Telegraph Signals" in nanoFETs for molecule-Si spectroscopy Analogous to role served by DLTS in bulk semiconductors Using basic nanoFET geometries:Or more exotic FIN-FETs: Analyzing with NIRT partners:SOITEC (leading manufacturer of SOI for ICs) National Institute of Standards and Technology To evaluate utility in nanoFETs & explore new modes of quantum conduction NIRT Building Block #1) Models of Organo-Si Charge Conduction & Storage Formal Challenge: Coupling weak and strong quantum correlation (wires vs. dots): Semiconductors normally treated via macroscopic quasi-continuum models Molecules dominated by QM and Many Body Effects Organo-Si hybrids straddle this boundary. Team will model by combining: Density Functional Theory (for Si) and Extended Hückel Theory (for molecules) Within framework of Non-Equilibrium Green's Functions for Si FETs, coupled with multi-electron rate equation for molecular SETs Very different modeling approaches! Very different computational techniques! (U=Coulomb energy,  = level broadening)