E N XPLORING THE ANOLANDSCAPE
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EXPLORING THE NANOLANDSCAPE Scanning Probe Microscopy 1 IMAGE GALLERY QuickTime™ and a GIF decompressor are needed to see this picture. 2 The Nanoscale • Atomic diameter ~ 0.3 nm = 3 Å • Microelectronics interconnect ~ 0.25 µm – http://www.intel.com/technology//itj/q31998/articles/art_1.htm • Red blood cell (5µm) 3 Proximal Probes 4 History • Topografiner • Tunneling through a controllable vacuum gap • Scanning Tunneling Microscope • Atomic Force Microscope (Scanning Force Microscope) 5 Operation of a Scanning Probe Microscope • • • • • • • Scanning with sub-Angstrom precision Probe detection (e.g., current, force, position, …) Electronics processing Computer control Image processing Vibration isolation Environmental control (e.g., vacuum, atmosphere, fluid; temperature) 6 Scanning Tunneling Microscope Omicron 7 Scanning Force Microscope 8 Tunneling • One-dimensional tunneling I o2 S o 2 2 d T e 2m 1/ 2 2 So = sample wavefunction To = tip wavefunction = workfunction • Density of electronic states of sample and tip 9 Forces F k x repulsive force Force Trace Retrace contact tip to sample separation non-contact Distance attractive force k 0.3N / m Typical: x = 10nm F = 3nN Contact vs. non-contact modes ... Forces to atto-newton (10-18 N) range ... 10 Themes • IMAGING • INTERROGATING • MANIPULATING atoms and nanoscale objects 11 IMAGING ATOMS AND NANOSCALE OBJECTS 12 Large-scale Atomic-scale DiNardo Gold Grating 30 µm 30 µm STM Graphite 4.2 nm 4.2 nm STM 13 Semiconductor Surfaces - Si(100) Tilted dimer SymmetricDimer Unreconstructed L) Occupied R) Unoccupied Hamers, 1986 14 Temperature-dependent Reconstructions • Low-temperature Si(100)-c(42) vs. (2 1) – Domain boundaries, p(2 2) regions Wolkow, 1992 15 Homoepitaxial Growth - Si(100) Mo, 1988 16 Fractional Images • Probing atomic orbitals – Frequency-modulated Atomic Force Microscopy – Si tip / Si(111)-77 Si atom Giessibl, 2000 17 Metal Surfaces Wahlström, 1998 18 0.4 ML Ag/Cu(110) c(102) model a, b) 230230 nm2 c) 5.45.4 nm2 d) 3.83.8 nm2 Sprunger, 1996 19 Interfaces - Cross-sectional Imaging Ohmori, 1999 20 Molecular Adsorption - CO/Pt(111) Pederson, 1996 21 Coatings - Colloidal Latex Particles Faulted Layer Orientation Interstitial Line Recovery Vacancy Defect Defect Change Brennan, 2000 22 Coatings - Latexes 23 Carbon Nanotubes Odom, 1998 24 Overlapping Nanotubes Avouris, 1999 25 Nanotube Shapes and Forces Avouris, 1999 26 Biological Macromolecules - Collagen Brennan, 2000 27 Biological Macromolecules - Fibronectin Brennan, 1999 28 INTERROGATING ATOMS AND NANOSCALE OBJECTS 29 Visualizing the Tunnel Junction STM-TEM Naitoh, 1996 30 Scanning Ohnishi, 1998 31 Bias-dependent imaging ~ Graphite DiNardo 32 Bias-dependent imaging ~ GaAs(110) • GaAs(110) (cleaved) surface Feenstra, 1987 33 Spectroscopy ~ on the Nanoscale • Beam techniques average over surface species • SPM techniques measure density of states related to the atom (or molecule) under the tip – electronic spectrum - measure dI/dV [or (dI/dV)/(I/V)] Hamers, 1986 34 Electronic Spectroscopy Atom by Atom • Reconstructed Si(100)-21 surface – Dimers – Occupied electronic states of dimers (between atoms) – Unoccupied electronic states of dimers (away from atoms) Hamers, 1986 35 Defects • Atomic-sized defects – Al/Si(111)-√3√3 structure – different electronic states Hamers, 1988 36 Chemical Reactivity NH3 reacted with the Si(111)-77 surface Wolkow, 1988 37 Vibrational Spectroscopy Molecule by Molecule Lauhon, 2000 38 Chemical Reactions Electron-induced dissociation product pyridine on Cu(100) at 8K Lauhon, 2000 39 Surface Diffusion Chasing Atoms with the Atom Tracker Swartzentruber, 1996 40 H-enhanced diffusion of Pt atoms QuickTime™ and a GIF decompressor are needed to see this picture. QuickTime™ and a GIF decompressor are needed to see this picture. an STM movie ... QuickTime™ and a GIF decompressor are needed to see this picture. Horch, 1999 41 Electrostatic Force Microscopy (EFM) • Application – Topography of integrated circuit – Monitoring an active integrated circuit Digital Instruments, www.di.com 42 Scanning Capacitance Microscopy Nakakura, 1999 43 Magnetic Force Microscopy (MFM) • Magnetic tip interaction with surface • Application: Disk drive – Morphology – Magnetic structure Digital Instruments, www.di.com 44 Scanning Chemical Microscopy • Measure chemical interaction between the tip and sample • Functionalize the tip with hydrophobic or hydrophilic species • Scan over surface and measure adhesion force or friction force 45 Carbon Nanotube Tips - Functionalization - Wong, 1998 46 Scanning Chemical Microscopy Frisbee, 1994 / Wong, 1998 47 Adhesion Forces Wong, 1998 48 Friction Force Microscopy • Macroscopic friction forces Ffr N • Microscopic friction forces 49 Polymer Thin Films Polypropylene film (a) AFM + (b) FFM, (c) non-contact AFM Nie, 1999 50 nN Bond Forces Strength of a Covalent Bond Grandbois, 1999 51 Ballistic Electron Emission Microscopy - BEEM • Three-terminal setup • Probe potential barrier at interface between metal and semiconductor • Electrons are forward-focused without scattering (ballistic) 52 BEEM Bell, 2000 53 MANIPULATING ATOMS AND NANOSCALE OBJECTS 54 Moving Atoms • Xe – Physisorbed noble gas - (low temperature) • Fe – Quantum “Corrals” Eigler, 1991 / Crommie, 1993 55 Confined Electrons • Reflections of free electron (waves) at boundaries • Standing waves solutions • One-dimensional free electron solution (infinite barrier) 56 Quantum Corral Crommie, 1993 57 Forming Nanowires Ohnishi, 1998 58 Nanowire modeling Okamoto, 1999 59 Measuring Currents through One- and Two-atomic-row Nanowires Ohnishi, 1998 60 Nanoelectronics • Nanoscale channels • Nanoscale objects • Currents - description based on quantummechanical transport 61 Nanoscale patterning • Desorption – H-terminated Si(100) • Deposition – Fe(CO)5 Adams, 1996 62 Nanotube Circuits Avouris, 1999 63 Nanotube FET Martel, 1998 / Avouris, 1999 64 Diamond-like Carbon Films STM AFM Mercer, 1996 65 Protein-folding Forces Rief, 1999 66 Comparison of Force Curves Rief, 1999 67 Related Techniques • Scanning Near-field Optical Microscopy • Scanning Thermal Microscopy 68 Some Acronyms ... • • • • • • STM STS AFM TM-AFM FFM, LFM CFM 69
