纳米世界介绍——原子力显微技术（AFM）和电子探针.pptVIP

Introduction to the Nanoworld Atomic Force Microscope (AFM) Scanning Probe Microscope (SPM) Force and its direction Force and its direction From Potentials to Forces: Example I From Potentials to Forces: Example From Potentials to Forces: Example Interatomic force vs Distance Forces between atoms: Interatomic force Forces between atoms: Interatomic force Interatomic force vs Distance Force vs Potential Energy STM Spectroscopy STM enables electronic spectroscopy of a single surface atom to be performed. The simplest form of STM tunneling spectroscopy involves placing the tip above a specific site on the surface, continually changing the tip (or sample) bias between two limits and measuring the change in tunnel current as a function of bias voltage. STM Spectroscopy STM Spectroscopy: What’s happening? STM Spectroscopy: What’s happening? STM Spectroscopy: What’s happening? STM Spectroscopy: What’s happening? STM Spectroscopy: What’s happening? STM Spectroscopy: What’s happening? STM Spectroscopy: What’s happening? STM Spectroscopy STM Spectroscopy STM Image SEM * * Force is a vector quantity. In addition to its magnitude, we need to define a direction. Force = 5 N Friction = 3 N A box is pulled along the ground with a force of 5N, a friction of –3N is acting on the box. Draw a cartoon diagram of this system. In a coordinate system, x Force Positive force here Force directed towards Right hand side Positive force here Force directed towards Right hand side Negative force here ? Force directed towards Left hand side Negative force here ? Force directed towards Left hand side 0 Potential Energy U(r) = kr2 Force F(r) = -d(U(r))/dr F(r) = -2kr Potential Energy U(r) = 0.3r2+0.1r3+0.2 Force F(r) = -d(U(r))/dr F(r) = -2x0.3r-3x0.1r2 Potential Energy U(r) = exp(-r/5) – 5/r6 Force F(r) = -d(U(r))/dr F(r) =1/5 exp(-r/5) – 30/r7 Why repulsive force has a positive sign while attractive force has a negative sign? A B r From A’s view, define coordinate system, to