How do scientists construct the single atom tip for scanning tunneling
microscopes as shown in
http://nobelprize.org/physics/educational/microscopes/scanning/

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Request for Question Clarification by cynthia-ga on 12 Jun 2005 02:44 PDT

Hi wangstar,

I think this is the Answer, however, it's very complex, certainly not
in laymans terms...

Manipulating, Reacting and Engineering of Single Molecules with an STM Tip
NOTE: See page _63_ of 138 pages in this PDF file - the "document page" is 54.
http://www.physics.uiuc.edu/Conferences/Mwssc/abstract_book.pdf
..."An extremely sharp and reliable single atom tip is then fabricated by
transferring of an iodine atom to the tip-apex using the 'vertical
manipulation'. With this iodinated tip, phenyl fragments are relocated
on Cu(111) surface applying the 'lateral manipulation' procedure. Bond
formation between the phenyls is performed by electronic excitation
with the iodinated tip. Finally, the iodine from the tip-apex is
transferred back to the surface. This experiment demonstrates that the
STM tip can be used as an engineering tool to construct single
molecules from the basic molecular building blocks..."

This is also interesting:

The Scanning Tunneling Microscope (scroll a bit to this)
http://users.ox.ac.uk/~oums0308/Research/Research_01.html
..."The ideal tip would funnel down to a single atom tip which would
be the source of tunneling. Tips, however, are seldom so perfect.
Instead, researchers must tease and adapt the tip in a variety of ways
to ensure that only one atom will tunnel. This can be done by smashing
the tip into the sample to rearrange the atoms on the tip, by heating
the tip, by applying high voltage differences between the tip and
sample to draw the atoms down the tip, etc..."


This is an excellent example of how Researchers are expert searchers,
not necessarily expert in what they search for.  --If this qualifies
as an Answer, please 'clarify' and I will post it in the Answer Box...


~~Cynthia


Search terms:
construct "single atom tip" STM

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Clarification of Question by wangstar-ga on 12 Jun 2005 09:07 PDT

Thank you for your answer Cynthia

wangstar,

Thanks for accepting my research as your answer, here it is in the Answer Box:

Manipulating, Reacting and Engineering of Single Molecules with an STM Tip
NOTE: See page _63_ of 138 pages in this PDF file - the "document page" is 54.
http://www.physics.uiuc.edu/Conferences/Mwssc/abstract_book.pdf
..."An extremely sharp and reliable single atom tip is then fabricated by
transferring of an iodine atom to the tip-apex using the 'vertical
manipulation'. With this iodinated tip, phenyl fragments are relocated
on Cu(111) surface applying the 'lateral manipulation' procedure. Bond
formation between the phenyls is performed by electronic excitation
with the iodinated tip. Finally, the iodine from the tip-apex is
transferred back to the surface. This experiment demonstrates that the
STM tip can be used as an engineering tool to construct single
molecules from the basic molecular building blocks..."

This is also interesting:

The Scanning Tunneling Microscope (scroll a bit to this)
http://users.ox.ac.uk/~oums0308/Research/Research_01.html
..."The ideal tip would funnel down to a single atom tip which would
be the source of tunneling. Tips, however, are seldom so perfect.
Instead, researchers must tease and adapt the tip in a variety of ways
to ensure that only one atom will tunnel. This can be done by smashing
the tip into the sample to rearrange the atoms on the tip, by heating
the tip, by applying high voltage differences between the tip and
sample to draw the atoms down the tip, etc..."


~~Cynthia

Good question. Making the tips is always problematic. There are many
fabrication techniques, but some of them amount to a pretty crude
procedure of sharpening the tip in much the same way you might sharpen
an awl on a grinding stone. The picture in the web link, shows a
highly idealized view of what the tip might look like. Fortunately,
tunneling depends exponentially on the distance between the tip and
the sample, so if one atom is a tiny bit closer, the tunneling
proceeds through that atom. This is an important part of the
explanation for the incredible horizontal resolution of a tunneling
microscope tip.

Here's some interesting info too:  Check EDN magazine, "design ideas"
for 11-27-03.  Article on fabricating microneedles by etching.