2015 Fall Semester MS482 Materials Characterization ( 재료분석 ) Lecture Note 11: Scanning Probe Microscopy Byungha Shin Dept. of MSE, KAIST 1
Course Information Syllabus 1. Overview of various characterization techniques (1 lecture) 2. Chemical analysis techniques (8 lectures) 2.1. X-ray Photoelectron Spectroscopy (XPS) 2.2. Ultraviolet Photoelectron Spectroscopy (UPS) 2.3. Auger Electron Spectroscopy (AES) 2.4. X-ray Fluorescence (XRF) 3. Ion beam based techniques (4 lecture) 3.1. Rutherford Backscattering Spectrometry (RBS) 3.2. Secondary Ion Mass Spectrometry (SIMS) 4. Diffraction and imaging techniques (7 lectures) 4.1. Basic diffraction theory 4.2. X-ray Diffraction (XRD) & X-ray Reflectometry (XRR) 4.3. Scanning Electron Microscopy (SEM) & EDS 4.4. Transmission Electron Microscopy (TEM) 5. Scanning probe techniques (1 lectures) 5.1. Scanning Tunneling Microscopy (STM) 5.2. Atomic Force Microscopy (AFM) 6. Summary: Examples of real materials characterization (1 lecture)
Scanning Tunneling Microscopy (STM) Gerd Binnig Heinrich Rohrer STM was invented by Binnig and Rohrer at IBM Research at Zurich They were awarded the Nobel Prize in physics in 1986 for their design of STM
Background Tunneling current, II zz = II 0 ee 2κκzz, where κ = 2mmΦ/ħ I 0 = f (applied voltage, the density of states in both tip and sample) Example: metals with Φ ~ 4 e, κ ~ 1A 1 z increases by 1A, the current drops by an order of magnitude Most of tunneling current carried by the most front atom of the tip
Instrumentation Constant current mode: vertical position of the tip altered for a constant sample-tip separation Constant height mode: variation in current topographic information
Instrumentation: tube scanner A tube of piezoelectric material Inner and outer surfaces coated with a thin metal electrode; outside separated to four sections
Filled-states and Empty-states Images (grounded) tunnel into empty states (positive) GaAs (110) surface Sample voltage: +1.9 Empty-states image Sample voltage: -1.9 Filled-states image Ga As (grounded) tunnel out of filled states (negative) Feenstra et al. Phys. Rev. Lett. 58, 1192 (1987)
Scanning Tunneling Spectroscopy Tip Sample I e E F,sample E F,tip LDOS: Local Density of States
Scanning Tunneling Spectroscopy Tip Sample I e E F,sample E F,tip LDOS: Local Density of States
Scanning Tunneling Spectroscopy Tip Sample I e E F,sample E F,tip LDOS: Local Density of States
Scanning Tunneling Spectroscopy Tip Sample I E g e E F,tip E g E F,sample LDOS: Local Density of States
Scanning Tunneling Spectroscopy Tip Sample I E g e E F,tip E g E F,sample LDOS: Local Density of States
Scanning Tunneling Spectroscopy Tip Sample I E g e E F,tip Numerical differentiation E g E F,sample di/d LDOS: Local Density of States E g
Atomic Force Microscopy (AFM)
Typical AFM setup reference signal laser Beam deflection method lens photodiode cantilever Piezo electrical scanner display
Contact Mode Tip engaging Constant height mode: Image from deflection Constant force mode: Image from the scanner s z-motion Possible sample damage Lateral friction force
Non-contact Mode & Tapping Mode Resonance frequency of cantilever, ff 0 tt ll 2 EE ρρ t: thickness l: length E: Young s modulus ρ: mass density f 0
Non-contact Mode & Tapping Mode Frequency modulation mode Amplitude modulation mode Amplitude modulation mode
Phase-Shift Image Phase shift contrast from differences in friction, viscoelasticity, adhesion, material, and etc. Hydrogel Coated Catheter Height Phase
Strengths and Limitations Strengths ersatile sample handling capability High resolution Platform accommodates many sensors Limitations Scan range limits 100 µm laterally 5 µm in z direction Tip convolution must be considered. Special equipment or methods required for complex geometries. Typically no chemical information provided. SPM images surface topography and other properties using a variety of sensors