Embed Size (px)
DESCRIPTION
Force Microscopy. Principle of Operation. Force Microscopy. Basic Principle of Operation: detecting forces between a mass attached to a spring (cantilever), that feels some force when it is brought very close to the surface. Ideally the mass (tip) would not damage the surface. - PowerPoint PPT Presentation
Citation preview
Force Microscopy
Principle of Operation
Force Microscopy
• Basic Principle of Operation: detecting forces between a mass attached to a spring (cantilever), that feels some force when it is brought very close to the surface. Ideally the mass (tip) would not damage the surface.
• Sensor that responds to a force and a detector that measures it.
• The sensor-a cantilever beam with an effective spring constant k, moves in accordance with the forces acting on its tip
Force Microscopy
• Frequency of atoms vibration, , at room temperature ~ 1015 Hz
• The mass, m, of an atom ~ 10-30 kg The effective spring constant, k, between atoms is
k=2m1N/m
Materials Characterization
AFM -PrincipleAFM -Principle
AFM -PrincipleAFM -Principle
Materials Characterization
Courtesy Dr. Z. Barkai
Materials Characterization
AFM Images2. Carbon nanotube
3. Human chromosomes
TappingMode AFM image of single carbon-nanotube molecule on electrodes. These images represent an important breakthrough where we measured electronic transport through a single nanotube molecule for the first time. 530nm x 300nm scan courtesy C. Dekker and Sander Tans, Delft University of Technology, Department of Applied Physics and DIMES, The Netherlands.
Materials Characterization
Courtesy Dr. Z. Barkai
Materials Characterization
AFM Images1. Au (111)
High resolution scan of Au (111) surface, with reconstruction strips (inset)
hexagonal atomic structure. Scan size: 5nm; inset: 20 nm
Contact - Atomic Force Microscopy
All rights reserved @ Norbert
Hooke Law F = kx so x =1
k F = F + F T v c
F
Total Repulsive
Total Atractive
Fv
Fc
Laser
AFM -CantileversAFM -Cantilevers
kEwt
l
w
N
Tip radii A
3
3
4
4,
E - Young Module
width, l - lenght, t - thickness
Comercial cantilivers - SiO and Si
- 300
2 3
AFM -CantileversAFM -Cantilevers
Diamond-coated AFM tip FIB Sharp Tip
AFM -CantileversAFM -Cantilevers
Gold-coated Si3N4 Tip
Pyramidal, tetrahedral, or conical tips are the most
common tip shapes
AFM -CantileversAFM -Cantilevers
Depositing a Si3N4 layer on an etch pit in Si
Tips are broader then Si conical tips, harder, and thinner (stress in the film)
not suitable for non-contact (small thickness, small )
AFM -Resolution
AFM
• STM-single atom interaction
STM
AFM-several atoms on tip interact with
several atoms on surface
In contact, not necessarily a single atom
contact, radius of contact ~(Rd)1/2
(d-penetration depth, R-radius of tip)
AFM -Resolution
• Interaction of atom 1 : t=0 different from interaction of atom 3,2
• Each tip atom produces a signals with offset to each other
• Periodicity reproduced but no true atomic resolution
