Multiscale Modeling and Simulation of Nanoengineering: Challenges and Opportunities DISTANCE TIME Angstrom meters femtosec hours QM MD MESO Continuum Atoms Engineering

Computational Nanoscience and Nanoengineering Nanotechnology: Computational Nanoscience and Nanoengineering Molecule Nano Micro Meso Macro Length (m): 10-12 10-9 10-6 10-3 100 The physical systems are too small for direct measurements, too large to be described by current first principles QM too few to be described by a statistical ensemble Fundamental understanding and highly accurate predictive methods are critical to successful manufacturing of nanostructured materials, devices, and systems

Assembly of Nanostructures (Bottom-Up) Quantum dots (AFM) Nanowire Nanowire network (STM) Quantum dots Unique physical and chemical properties are determined by their structural properties.

Nanoscale Electronic Devices (Top-Down) Existing materials and technologies are approaching to their physical limits as device sizes decrease significantly below 100 nm New Materials & Processes Nanoscale devices (New Device Concepts): single electron, quantum tunneling Year of Production: 2002 2005 2008 2011 2014 DRAM half-pitch (nm) 130 100 70 50 35 CD control (nm) 9 6 4 3 2 Oxide thickness (nm) 1.5-1.9 1.0-1.5 0.80-1.2 0.6-1.8 0.5-0.6 Junction depth (nm): 25-43 20-33 16-26 11-19 8-13 Inter-metal dielectric 2.7-3.5 1.6-2.2 1.5 <1.5 <1.5 no known solutions

Complexity in Nanoengineering Gas-solid and liquid-solid interactions Solid-solid interfacial interactions Defect-dopant dynamics + V Vacancy annihilation at the Si/SiO2 interface Kirichenco & Hwang, to be submitted gain B H2O adsorption on B-modified surface Wang & Hwang, Surf. Sci., in press (2003) O Si a-SiO2 on c-Si Yu and Hwang, AVS (2002)

Ultrashallow Junction Formation Computational Nanoengineering Ultrashallow Junction Formation Shallow vertical depth Lateral abruptness High doping level (> 1020 cm-3) Technology : 2002 2005 2008 2011 2014 node 130 nm 100 nm 70 nm 50 nm 35 nm Junction depth: 25-43 20-33 16-26 11-19 8-13 (nm)

Multiscale approach: strategy Experiment 100 B+ 200 300 400 500 600 700 Depth, Å B concentration, cm-3 1021 1022 1020 1019 1018 as implanted after annealing (> sec) Si explanation/ prediction Mesoscale simulation Kinetic Monte Carlo Continuum model [long time (>1 sec)] validation fundamental data density functional theory tight binding MD classical MD [short time (< nsec)] Atomic-scale calculation

Si Nanocrystal Synthesis in an Oxide Matrix: Computational Nanoengineering Si Nanocrystal Synthesis in an Oxide Matrix: Size and shape Spatial distribution Si-SiO2 interface SiO2 nc-Si Yun et al, Thin Solid Films 375, 137 (2000)

nc-Si/Ge in SiO2 SiO2 Ge Si Flash memory Electronic devices (floating gate) Optical devices 10 nm Si Ge SiO2 Flash memory Source Drain Nano- crystals Tunnel oxide Control oxide Gate

Multiscale Modeling of Nanoengineering Its success will offer tremendous opportunities for guiding the rational design and fabrication of a variety of nanosystems! Atomistic behaviors physical understanding quantitative prediction Structural Properties Fundamental processes, Atomic structures, Energetics, …. Shape, Size distribution, Spatial distribution, Interface structures, …. Time (sec): 10-12 10-9 10-6 10-3 100 Length (m): 10-9 10-8 10-7 10-6 Molecular Dynamics Statistical Mechanics Continuum Mechanics Quantum Mechanics

III. Metal growth on a binary metal-oxide Au on TiO2 (110) Pillay and Hwang

Ni, Fe, Co IV. Carbon Nanotube(fiber) Growth by PECVD Feed Gases: C2H2, NH3 (100) (110) (111) Ni, Fe, Co C2H2 / NH3 (a) 0.38 (b) 0.50 (c) 0.59 (d) 0.75

V. Electrochemical Micro/Nano-machining Kenney and Hwang + - tool workpiece A: transport of solvated molecules and ions B: double layer physical nature and its charging and discharging dynamics C: electrochemical reactions on an electrode surface.