Physical Measurements at Nanoscale by Local probes

Goal:  Introduction to local probes techniques in the field of nanosciences and nanotechnologies.  

Content:

1. Introduction to Scanning probes Microscopy (1h30)
- Comparison between surface analysis techniques: SEM/TEM, SFA
- Presentation of the SPM sub-families: STM / SFM / SNOM via examples of applications

2. The Scanning Tunneling Microscope (7h)
  The tunneling effect
               STM relevant parameters
               Expression of the tunneling current

  The STM instrument
  • Tip fabrication methods
  • Electronic and instrumental chain to measure and control  tunnelling current in the pico/nano-ampere
    range ADC/DAC, I/V converter, Lock-in amplifier
  • Source of Noises and detection limit
  • Vibration isolation (Tutorial on transfer function and damping)
  • Measurement at low temperature : How to operate an STM in a cryostat ?
Operating STM modes and associated measurements (1h30)
         Local density of states (LDOS) and I/V spectroscopy
         Constant current mode versus constant height mode

3. The Atomic Force Microscope (12h)
 Why mechanical oscillators?
  • Introduction and history
  • Mechanical susceptibility
  • Limits of sensitivity (readout noise and Brownian motion)
  • Working at resonance, decrease the size/mass

How to build an AFM

  • Micro fabrication of cantilever and tips
  • Nano positioning (piezo material and issues with them as hysteresis…)
  • Precision position measurements (optical and capacitive)
  • Signal analysis (Homodyne detection, PLL and PID)

Operating AFMs

  • Calibration process (cantilever stiffness, position detection)
  • What physical values are accessible (Van der Waals, electrical, magnetic, friction forces…)
  • Different modes of operation

Maps Analysis & Image processing

  • Surface analysis parameters: rms, ra, skewness, kurtosis, etc
  • Artefacts, tip dilation effect
  • Tilt correction via polynomial subtraction and Color scale
  • Tutorial on processing of the images  and spectroscopy curves obtained in PW via Gwyddion software