Editing Scanning tunneling microscope (section)

== Instrumentation ==
[[File:Scanning tunneling microscope-MHS 2237-IMG 3819.JPG|thumb|A 1986 STM from the collection of [[Musée d'histoire des sciences de la Ville de Genève]]]]
[[File:STM at the London Centre for Nanotechnology.jpg|thumb|A large STM setup at the [[London Centre for Nanotechnology]]]]
The main components of a scanning tunneling microscope are the scanning tip, piezoelectrically controlled height (''z'' axis) and lateral (''x'' and ''y'' axes) scanner, and coarse sample-to-tip approach mechanism. The microscope is controlled by dedicated electronics and a computer. The system is supported on a vibration isolation system.<ref name="Chen" />

The tip is often made of [[tungsten]] or [[Platinum–iridium alloy|platinum–iridium]] wire, though [[gold]] is also used.<ref name="Bai" /> Tungsten tips are usually made by electrochemical etching, and platinum–iridium tips by mechanical shearing. The [[Image resolution|resolution]] of an image is limited by the [[radius of curvature]] of the scanning tip. Sometimes, image artefacts occur if the tip has more than one apex at the end; most frequently ''double-tip imaging'' is observed, a situation in which two apices contribute equally to the tunneling.<ref name="Bai"/> While several processes for obtaining sharp, usable tips are known, the ultimate test of quality of the tip is only possible when it is tunneling in the vacuum. Every so often the tips can be conditioned by applying high voltages when they are already in the tunneling range, or by making them pick up an atom or a molecule from the surface.

In most modern designs the scanner is a hollow tube of a radially polarized piezoelectric with metallized surfaces. The outer surface is divided into four long quadrants to serve as ''x'' and ''y'' motion electrodes with deflection voltages of two polarities applied on the opposing sides. The tube material is a [[lead zirconate titanate]] ceramic with a piezoelectric constant of about 5&nbsp;nanometres per volt. The tip is mounted at the center of the tube. Because of some crosstalk between the electrodes and inherent nonlinearities, the motion is [[Calibration|calibrated]], and voltages needed for independent ''x'', ''y'' and ''z'' motion applied according to calibration tables.<ref name="Chen" />

Due to the extreme sensitivity of the tunneling current to the separation of the electrodes, proper vibration isolation or a rigid STM body is imperative for obtaining usable results. In the first STM by Binnig and Rohrer, [[magnetic levitation]] was used to keep the STM free from vibrations; now mechanical spring or [[gas spring]] systems are often employed.<ref name="Chen" /> Additionally, mechanisms for vibration damping using [[eddy currents]] are sometimes implemented. Microscopes designed for long scans in scanning tunneling spectroscopy need extreme stability and are built in [[anechoic chamber]]s—dedicated concrete rooms with acoustic and electromagnetic isolation that are themselves floated on vibration isolation devices inside the laboratory.

Maintaining the tip position with respect to the sample, scanning the sample and acquiring the data is computer-controlled. Dedicated [[Scanning probe microscopy#Visualization and analysis software|software for scanning probe microscopies]] is used for [[image processing]] as well as performing quantitative measurements.<ref name="fospm2011">{{cite book |vauthors = Lapshin RV |year=2011 |contribution=Feature-oriented scanning probe microscopy |title=Encyclopedia of Nanoscience and Nanotechnology |veditors = Nalwa HS |volume=14 |pages=105–115 |publisher=American Scientific Publishers |location=USA |isbn=978-1-58883-163-7 |url=http://www.lapshin.fast-page.org/publications.htm#fospm2011 |format=PDF}}</ref>

Some scanning tunneling microscopes are capable of recording images at high frame rates.<ref>{{cite journal |vauthors = Schitter G, Rost MJ |year=2008 |title=Scanning probe microscopy at video-rate |journal=Materials Today |volume=11 |issue=special issue |pages=40–48 |doi=10.1016/S1369-7021(09)70006-9 |issn=1369-7021 |doi-access=free}}</ref><ref>{{cite journal |vauthors = Lapshin RV, Obyedkov OV |year=1993 |title=Fast-acting piezoactuator and digital feedback loop for scanning tunneling microscopes |url=http://www.lapshin.fast-page.org/publications.htm#fast1993 |format=PDF |journal=Review of Scientific Instruments |volume=64 |issue=10 |pages=2883–2887 |bibcode=1993RScI...64.2883L |doi=10.1063/1.1144377}}</ref> Videos made of such images can show surface [[diffusion]]<ref>{{cite journal | vauthors = Swartzentruber BS | title = Direct measurement of surface diffusion using atom-tracking scanning tunneling microscopy | journal = Physical Review Letters | volume = 76 | issue = 3 | pages = 459–462 | date = January 1996 | pmid = 10061462 | doi = 10.1103/PhysRevLett.76.459 | url = https://zenodo.org/record/1233907 | bibcode = 1996PhRvL..76..459S }}</ref> or track adsorption and reactions on the surface. In video-rate microscopes, frame rates of 80&nbsp;Hz have been achieved with fully working feedback that adjusts the height of the tip.<ref>{{cite journal |vauthors = Rost MJ |display-authors=etal |year=2005 |title=Scanning probe microscopes go video rate and beyond |url=https://openaccess.leidenuniv.nl/bitstream/handle/1887/61253/Review_of_Scientific_Instruments_78oe2005oe053710.pdf?sequence=1 |journal=Review of Scientific Instruments |volume=76 |issue=5 |pages=053710–053710–9 |bibcode=2005RScI...76e3710R |doi=10.1063/1.1915288 |issn=1369-7021 |hdl=1887/61253 |hdl-access=free}}</ref>