Episode Synopsis "A feedback loop holds the electron current constant by keeping the distance from probe to sample constant."

Listen "A feedback loop holds the electron current constant by keeping the distance from probe to sample constant."

More episodes of the podcast Scanning Tunneling Microscope - How Nanoscientists see Atoms

• Scanning tunneling microscopes (STMs) allow nanoscientists to see individual atoms.
• To see how a Nanosurf easyScan STM works, let's take it apart in virtual reality.
• The heart of the STM is an atomically sharp probe.
• A voltage induces electrons to jump from the probe's tip to the sample atoms.
• A feedback loop holds the electron current constant by keeping the distance from probe to sample constant.
• But how can it move the probe over these tiny nanometer distances?
• Voltages to a piezoelectric crystal move the probe in and out.
• Another crystal moves it side to side.
• A third crystal moves it up and down.
• Let's see how these work together to create an atomic scale map of the sample surface.
• The voltage to the back crystal determines pixel color. Voltages on the other crystals move the probe and pixels side-to-side and up-and-down.
• But how do we first position the probe only a nanometer or so from the sample surface?
• It's done by ratcheting this cylinder in until an electron current is sensed.
• This STM is so simple that we use it in UVA classes. But it also earned two physicists the Nobel Prize in 1986.
• This podcast is drawn from the Virtual Lab presentations of WeCanFigureThisOut.org. The copyrighted material of this site was developed under funding from National Science Foundation CCLI, NIRT, MRSEC and NUE programs. This project is led by John C. Bean
• All of the scenes together