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Understanding Atomic Force Microscopy: Principles, Modes, and Applications

This article dives into the fundamentals of Atomic Force Microscopy (AFM), detailing the working principles of this critical analytical tool. By exploring the mechanics of the microscope, including tip movement, contact and tapping modes, and the role of laser diodes and position sensors, we elucidate the methods used for surface characterization on single crystal substrates, particularly involving AlGaN/GaN quantum wells. Key insights into short-range interatomic forces, sample interaction, and AFM's capabilities in materials science are discussed, highlighting its applications in polymer growth and surface crystallography.

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Understanding Atomic Force Microscopy: Principles, Modes, and Applications

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  1. Get to the point!

  2. CD stamper AlGaN/GaN quantum well waveguide surface atoms on Si single crystal polymer growth AFM - atomic force microscopy A 'new' view of structure (1986) See Vocabulary of Surface Crystallography, Journal of Applied Physics 35, 1306 (1964), by Elizabeth A. Wood

  3. laser diode photodiode mirror Si3N4tip sample AFM - atomic force microscopy How does the microscope work? Tip scans sample Up and down movement of tip recorded by position sensing photodiode

  4. laser diode photodiode mirror Si3N4tip sample AFM - atomic force microscopy How does the microscope work? Tip scans sample Up and down movement of tip recorded by position sensing photodiode

  5. laser diode photodiode mirror Si3N4tip sample AFM - atomic force microscopy How does the microscope work? Two modes of operation

  6. Tip: 5-20 nm radius, 10-25 m high, on 50-400 m cantilever beam AFM - atomic force microscopy How does the microscope work? Contact mode - short-range interactions (Å) - interatomic forces

  7. AFM - atomic force microscopy How does the microscope work? Contact mode - short-range interactions (Å) - interatomic forces Tip: 5-20 nm radius, 10-25 m high, on 50-400 m cantilever beam Cantilever: low stiffness - can't deform surface Tip contacts surface Tip scans surface: either tip or specimen moved by piezoelectric positioning system over x and y Detector system can measure deflections in nm range

  8. AFM - atomic force microscopy How does the microscope work? Contact mode - short-range interactions (Å) - interatomic forces Two ways - 'constant force' ……. feedback system moves tip in z direction to keep force constant 'constant height'……. no feedback system - usually used when surface roughness small higher scan speeds possible

  9. AFM - atomic force microscopy How does the microscope work? Tapping mode - long-range forces - van der Waals, electrostatic, magnetic Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100 nm May at times lightly contact surface Suitable for soft materials

  10. Amplitude Tip height AFM - atomic force microscopy How does the microscope work? Tapping mode Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100 nm May at times lightly contact surface When near or on surface, oscillation is damped - tip z position corrected so that vibration amplitude stays constant

  11. AFM - atomic force microscopy From force-distance plot, can get: range & magnitude of attractive & repulsive forces elastic modulus & adhesion energy

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