Editing Scanning probe microscopy (section)

==Probe tips==
The nature of an SPM [[probe tip]] depends entirely on the type of SPM being used. The combination of tip shape and topography of the sample make up a SPM image.<ref>{{Cite journal|title = Scanning Probe Microscopy|journal = Analytical Chemistry|date = May 19, 1998|pages = 425–476|volume = 70|issue = 12|doi = 10.1021/a1980011o| vauthors = Bottomley LA |url = http://www.nnin.org/education-training/k-12-teachers/nanotechnology-curriculum-materials/scanning-probe-microscopy|url-access = subscription}}</ref>{{citation needed| date=November 2015}} However, certain characteristics are common to all, or at least most, SPMs.{{citation needed| date=November 2015}}

Most importantly the probe must have a very sharp apex.{{citation needed| date=November 2015}} The apex of the probe defines the resolution of the microscope, the sharper the probe the better the resolution. For atomic resolution imaging the probe must be terminated by a single atom.{{citation needed| date=November 2015}}

For many cantilever based SPMs (e.g. [[atomic force microscope|AFM]] and [[magnetic force microscope|MFM]]), the entire cantilever and integrated probe are fabricated by acid [etching],<ref>{{Cite journal | doi = 10.1063/1.103677 | volume = 57 | issue = 3 | pages = 316–318 | vauthors = Akamine S, Barrett RC, Quate CF | title = Improved atomic force microscope images using microcantilevers with sharp tips | journal = Applied Physics Letters | year = 1990 |bibcode = 1990ApPhL..57..316A }}</ref> usually from silicon nitride. Conducting probes, needed for [[scanning tunneling microscopy|STM]] and [[scanning capacitance microscopy|SCM]] among others, are usually constructed from platinum/iridium wire for ambient operations, or tungsten for [[Ultra high vacuum|UHV]] operation. Other materials such as gold are sometimes used either for sample specific reasons or if the SPM is to be combined with other experiments such as [[Raman spectroscopy#Variants|TERS]]. Platinum/iridium (and other ambient) probes are normally cut using sharp wire cutters, the optimal method is to cut most of the way through the wire and then pull to snap the last of the wire, increasing the likelihood of a single atom termination. Tungsten wires are usually electrochemically etched, following this the oxide layer normally needs to be removed once the tip is in UHV conditions.

It is not uncommon for SPM probes (both purchased and "home-made") to not image with the desired resolution. This could be a tip which is too blunt or the probe may have more than one peak, resulting in a doubled or ghost image. For some probes, ''in situ'' modification of the tip apex is possible, this is usually done by either crashing the tip into the surface or by applying a large electric field.  The latter is achieved by applying a bias voltage (of order 10V) between the tip and the sample, as this distance is usually 1-3 [[Angstrom]]s, a very large field is generated.

The additional attachment of a quantum dot to the tip apex of a conductive probe enables surface potential imaging with high lateral resolution, [[scanning quantum dot microscopy]].