The scanning tunneling microscope (Scanning Tunneling Microscope) was invented in 1981 by Gerg Binnig and Heinrich Rohrer. Received the Nobel Prize for it in 1986. The STM uses the ability of electrons to traverse a potential barrier to record the electrical current that occurs between a tip (or probe), and the sample. An electron in a metal has a particular energy. The solid surface represents a potential barrier to be " jump" to get out of it. By bringing the metal (the probe), and applying an electric field to direct the electron to the metal, it creates a barrier with a distance small enough for the electron tunneling can be no need to jump the barrier.
The current can be recorded with an ammeter is proportional to the probability that the tunnel occurs. Which in turn depends on the distance between the tip and sample. In this way, recording the electrical current, information is obtained the distance that the tip is.
A simple schematic of an assembly of a STM tip is near a sample records the intensity tunnel occurs. The intensity controls a piezoelectric (material that varies in length by applying an electric field) acting on the tip to zoom in or removed from the sample, which is mounted on a table x, and the moves. Thus, to take a trip on y, the tip scans the sample, recording the intensity that occurs at each point.
There are several ways of operating in a VTS, but the most common is to maintain a constant tunneling current. This is achieved by maintaining distance between tip and sample constant. As the tip scans the sample in the x-axis and and , will control the tunneling current. When the tip reaches a point where the sample has valleys and outgoing, this current will vary. This variation indicates that you zoom the tip of the sample in the z axis to return to get the same stream, which is done through the piezoelectric. One computer had to be recorded as pan and zoom the point on the axis z , at that point ( x, y ) of the sample, so that after completing the sweep has a map that shows the variations in z axis. Ie a graph is related to the topography, the shape of the sample.
Another way to act is to maintain constant tip position, and record the power at each sample point, which varies as it passes through valleys and outgoing. However, there is a risk of crashing the tip into a projection of the sample, spoiling both the one and other. The end result also gives information on the topography of the sample.
Usually, the results are presented in map form x, y colors where the color code represents the z-axis values \u200b\u200b .
microscope Act, allowing " see "the surface of the sample. The accuracy of this instrument is that it can see the atoms of a solid. It is useful to study the surfaces of solids and their electronic properties. However, samples must be conductive. Another requirement for the STM is to be run dry, leading to integrate the system into vacuum chambers, with the hassle to change samples involved.
To see some images obtained by STM , you can do in the website nanotechnology.
View tunneling The
0 comments:
Post a Comment