Step Doubling Terms and Definitions

Stepped single crystal
A single crystal is a solid with its constituent atoms arranged in a regular array. The long range order of single crystals can be excellent; metals crystals inches long are grown while silicon single crystals are measured in feet! A stepped single crystal is a single crystal that has been cut in a special way to create single atom high steps at the surface.
Crystallographic directions
Single crystals are composed of regular arrays of atoms. Crystallographic directions tell us our orientation with respect to the atomic array.
Ni(977)
Ni(977) is a single crystal of nickel with a stepped surface structure. Ni(977) has terraces 8 atoms wide and steps one atom high.
Adsorption
Adsorption is the term for a particle (in this case an molecule) sticking to the a surface. This is not to be confused with absorption, where the particle penetrates below the surface.
K means "Degrees Kelvin"
Degrees Kelvin refers to a scale of temperature in which zero is defined as "absolute zero", a temperature at which there is no molecular or atomic movement, and all other values scale as does the Celsius scale.
To find Celsius degrees from degrees Kelvin, add 273.15.
Water boils at 373 degrees Kelvin, or 373 K
Angular dependence
This is just a fancy way of saying we are measuring the diffraction spectrum. Angular dependence means we look at the atom flux at a range of final scattering angles. Elastically scattered means no energy is exchanged between the helium atoms and the surface. Atom flux is the number of atoms moving past a reference point (in this case, our detector) within a certain amount of time.
diffraction peak
Diffraction peaks arise when waves constructively interfere with each other. In quantum mechanics, atoms can behave as waves. Consequently, in scattering, the helium atoms can interfere with each other as waves and are essentially focused into a single final direction.
STM
Scanning tunneling microscope. A neat instrument that allows us to "see" things as small as atoms! It works by holding a conducting wire and the conducting surface extremely close together, applying a voltage and measuring the resulting current. The current is a very sensitive function of the surface electronic structure and the distance between the wire and surface. An image of the surface can be obtained by moving the tip of the wire across the surface and monitoring the changes in the current.

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