-+Defining+the+Atom

toc =- Democritus's Atomic Philosophy=

=- atom=

=- Dalton's Atomic Theory= An English schoolteacher and chemist named John Dalton was the first person to establish the real nature of atoms since Democritus, who lived 2000 years prior Dalton. He made connections that were observable on the atomic level. Dalton used Democritus’ ideas of atoms and created a scientific theory. Based on his experiments of combining elements through chemical reactions, he concluded that: § Elements are composed of tiny indivisible particles, which are known as atoms § The atoms of the same elements are identical; however, the atoms of one element differ from another element’s atoms § Different elements’ atoms can combine and physically mix together o They can also be chemically combined into whole-number ratios that form compounds § When atoms are separated, joined, or rearranged, a chemical reaction occurs o However, one element’s atoms cannot change into another element’s atoms resulting from a chemical reaction
 * atoms cannot be made or destroyed

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=- scanning tunneling microscopy (instrument to observe Atoms)= Scanning tunneling microscopy (STM) is the highest resolution-imaging and nanofabrication technique available. STM is a type of electron microscope; it shows 3D images of a sample. STM is used to demonstrate the principle of quantum mechanical tunneling between the microscope tip and the surface of a conducting sample. STM is an important contribution to Science. Thus the inventors of the STM have won t he

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** Components of STM: ** [[image:Figure_3._Schematic_view_of_an_STM_&_Figure_4._Sharp_and_blunt_tips.png align="right"]]
** Probe: ** It is very important that the tip is sharp for good accuracy (Look Figure 4); Tips typically are made out of tungsten, platinum or a Pt-Ir wire. A sharp tip can be produced by  • Cutting and grinding • Electrochemical etching ** Amplifier: ** It amplifies the tunneling current ** Feedback (distance control) unit: ** To prevent that the surface to crash into the tip, the distance between the tip and surface is kept constant during the measurement, The feedback system determines continuously the height of the needle by measuring the current between tip and sample. When this current is to large or to small the distance has to be adjusted. The feedback system readjust the distance in such a way that the current gets the right value by moving the tip up or down (Look Figure 5). ** Piezoelectric material: ** Piezo-material has the property to expand or shrink a little bit when a voltage is applied to it. For example the application of 5 V to a 5 mm cube of piezo-material gives an expansion of about 0.5 nm, it is controlled by feedback unit and the tip is attached to it.