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    Questions for review

  • What makes the SEM such a useful instrument? What can it do that a normal optical microscope cannot?
  • Explain the usage of the electron beam in the SEM.
  • What is meant by “images of high resolution"?

Scanning tunneling microscopes

A Brief Historical Note

The scanning tunneling microscope (STM) had its birth in 1981, invented by Gerd Binnig and Heinrich Rohrer of IBM, in Zurich, Germany. They won the 1986 Nobel Prize in physics for this accomplishment, but use of the microscope itself was somewhat slow to spread into the academic world. STM is used to scan surfaces at the atomic level, producing a map of electron densities; the surface science community was somewhat skeptical and resistant of such a pertinent tool coming from an outside, industrial source. There were questions as to the interpretations of the early images (how are we really sure those are the individual silicon atoms?), as well as the difficulty of interpreting them in the first place – the original STMs did not include computers to integrate the data. The older electron microscopes were generally easier to use, and more reliable; hence they retained preference over STMs for several years after the STM development. STM gained publicity slowly, through accomplishments such as IBM’s famous xenon atom arrangement feat (see fig. 3) in 1990, and the determination of the structure of “crystalline” silicon.

false-color STM image of xenon atoms arranged on a nickel background. From: D.M. Eigler, E.K. Schweizer. Positioning single atoms with a scanning tunneling microscope. Nature 344, 524-526 (1990).

How STMs Work: The Basic Ideas

  • I. the probe

    Scanning Tunneling Microscopy relies on a tiny probe of tungsten, platinum-iridium, or another conductive material to collect the data. The probe slowly “scans” across a surface, yielding an electron-density map of the nanoscale features of the surface. To achieve this resolution, the probe must be a wire with a protruding peak of a single atom; the sharper the peak, the better the resolution. A voltage difference between the tip and the sample results in an electron “tunneling” current when the tip comes close enough (within around 10 Å). This “tunneling” is a phenomenon explained by the quantum mechanical properties of particles; the current is either held constant and probe height recorded, or the probe’s height is maintained and the change in current is measured to produce the scanning data. In constant current microscopy, the probe height must be constantly adjusted, which makes for relatively slow scanning, but allows fairly irregular surfaces to be examined. By contrast, constant height mode allows for faster scanning, but will only be effective for relatively smooth sample surfaces.
  • Ii. piezoelectric scanner

    In order to make the sub-nanometer vertical adjustments required for STM, piezoelectric ceramics are used in the scanning platform on which the sample is held. Piezoelectric materials undergo infinitesimally small mechanical changes under an applied voltage; therefore in the positioning device of a STM, they provide the motion to change the tip height at small enough increments that collision with the sample surface can be avoided. A data feedback loop is maintained between probe and piezoelectric positioner, so that the tip’s height can be adjusted as necessary in constant-current mode, and can be brought close enough to the sample to begin scanning in the first place.
  • Iii. the computer

    Though the earliest STMs did not include a computer with the scanning apparatus, current models have one attached to filter and integrate the data as it is received, as well as to monitor and control the actual scanning process. Grayscale primary images can be colored to give contrast to different types of atoms in the sample; most published STM images have been enhanced in this way.

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Nanotechnology: content and context. OpenStax CNX. May 09, 2007 Download for free at http://cnx.org/content/col10418/1.1
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