Editing Atomic force microscopy (section)

===Other deflection-measurement methods===
Many other methods for beam-deflection measurements exist. 
* ''Piezoelectric detection'' – Cantilevers made from [[quartz]]<ref>{{cite journal|last=Giessibl|first=Franz J.|title=High-speed force sensor for force microscopy and profilometry utilizing a quartz tuning fork|journal=Applied Physics Letters|date=1 January 1998|volume=73|issue=26|page=3956|doi=10.1063/1.122948|bibcode = 1998ApPhL..73.3956G |url=https://epub.uni-regensburg.de/25327/1/High-speed%20force%20sensor%20for%20force.pdf}}</ref>  (such as the [[Non-contact atomic force microscopy#qPlus sensor|qPlus]] configuration), or other [[piezoelectric]] materials can directly detect deflection as an electrical signal. Cantilever oscillations down to 10pm have been detected with this method.
* ''Laser Doppler vibrometry'' – A [[laser Doppler vibrometer]] can be used to produce very accurate deflection measurements for an oscillating cantilever<ref>{{cite journal|last=Nishida|first=Shuhei|author2=Kobayashi, Dai|author3= Sakurada, Takeo|author4= Nakazawa, Tomonori|author5= Hoshi, Yasuo|author6= Kawakatsu, Hideki|title=Photothermal excitation and laser Doppler velocimetry of higher cantilever vibration modes for dynamic atomic force microscopy in liquid|journal=Review of Scientific Instruments|date=1 January 2008|volume=79|issue=12|pages=123703–123703–4|doi=10.1063/1.3040500|bibcode = 2008RScI...79l3703N|pmid=19123565 }}</ref>  (thus is only used in non-contact mode). This method is expensive and is only used by relatively few groups.
* ''[[Scanning tunneling microscope]]'' (STM) — The first atomic microscope used an STM complete with its own feedback mechanism to measure deflection.<ref name="BinnigQuate1986"/> This method is very difficult to implement, and is slow to react to deflection changes compared to modern methods.
* ''Optical interferometry'' – [[Optical interferometry]] can be used to measure cantilever deflection.<ref>{{cite journal|last=Rugar|first=D.|author2-link=H. Jonathon Mamin|author2=Mamin, H. J.|author3= Guethner, P.|title=Improved fiber-optic interferometer for atomic force microscopy|journal=Applied Physics Letters|date=1 January 1989|volume=55|issue=25|page=2588|doi=10.1063/1.101987|bibcode = 1989ApPhL..55.2588R }}</ref> Due to the nanometre scale deflections measured in AFM, the interferometer is running in the sub-fringe regime, thus, any drift in laser power or wavelength has strong effects on the measurement. For these reasons optical interferometer measurements must be done with great care (for example using [[Refractive index|index matching]] fluids between optical fibre junctions), with very stable lasers. For these reasons optical interferometry is rarely used.
* ''Capacitive detection'' – Metal coated cantilevers can form a [[capacitor]] with another contact located behind the cantilever.<ref>{{cite journal|last=Göddenhenrich|first=T.|title=Force microscope with capacitive displacement detection|journal=[[Journal of Vacuum Science and Technology A]]|volume=8|issue=1|page=383|doi=10.1116/1.576401|year=1990|bibcode=1990JVSTA...8..383G}}</ref> Deflection changes the distance between the contacts and can be measured as a change in capacitance.
* ''Piezoresistive detection'' – Cantilevers can be fabricated with [[Piezoresistive effect|piezoresistive elements]] that act as a [[strain gauge]]. Using a [[Wheatstone bridge]], strain in the AFM cantilever due to deflection can be measured.<ref>{{cite journal|last=Giessibl|first=F. J.|author2=Trafas, B. M.|title=Piezoresistive cantilevers utilized for scanning tunneling and scanning force microscope in ultrahigh vacuum|journal=Review of Scientific Instruments|date=1 January 1994|volume=65|issue=6|page=1923|doi=10.1063/1.1145232|bibcode = 1994RScI...65.1923G |url=https://epub.uni-regensburg.de/33829/1/Piezoresistive%20cantilevers%20utilized%20for%20scanning.pdf}}</ref> This is not commonly used in vacuum applications, as the piezoresistive detection dissipates energy from the system affecting [[quality factor|Q]] of the resonance.