View source for Scanning probe microscopy

{{short description|Branch of microscopy}}
{{more citations needed|date=November 2015}}
{{Nanotech}}
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'''Scanning probe microscopy''' ('''SPM''') is a branch of [[microscopy]] that forms images of surfaces using a physical probe that scans the specimen. SPM was founded in 1981, with the invention of the [[scanning tunneling microscope]], an instrument for imaging surfaces at the atomic level. The first successful scanning tunneling microscope experiment was done by [[Gerd Binnig]] and [[Heinrich Rohrer]]. The key to their success was using a feedback loop to regulate gap distance between the sample and the probe.<ref name="SalapakaSalapaka2008">{{cite journal| vauthors = Salapaka SM, Salapaka MV |title=Scanning Probe Microscopy|journal=IEEE Control Systems Magazine|volume=28|issue=2|year=2008|pages=65–83|issn=0272-1708|doi=10.1109/MCS.2007.914688|s2cid=20484280|url=http://www.nnin.org/education-training/k-12-teachers/nanotechnology-curriculum-materials/scanning-probe-microscopy|url-access=subscription}}</ref>

Many scanning probe microscopes can image several interactions simultaneously. The manner of using these interactions to obtain an image is generally called a mode.

The resolution varies somewhat from technique to technique, but some probe techniques reach a rather impressive atomic resolution.{{citation needed| date=November 2015}} This is largely because [[piezoelectricity|piezoelectric actuators]] can execute motions with a precision and accuracy at the atomic level or better on electronic command. This family of techniques can be called "piezoelectric techniques". The other common denominator is that the data are typically obtained as a two-dimensional grid of data points, visualized in [[false color]] as a computer image.

==Established types==
{{prose|section|date=November 2015}}
* AFM, [[atomic force microscopy]]<ref>{{cite journal | vauthors = Binnig G, Quate CF, Gerber C | title = Atomic force microscope | journal = Physical Review Letters | volume = 56 | issue = 9 | pages = 930–933 | date = March 1986 | pmid = 10033323 | doi = 10.1103/PhysRevLett.56.930 | doi-access = free | bibcode = 1986PhRvL..56..930B }}</ref>
** Contact AFM
** [[Non-contact atomic force microscopy|Non-contact AFM]]
** Dynamic contact AFM
** Tapping AFM
** AFM-IR
** CFM, [[chemical force microscopy]]
** C-AFM, [[conductive atomic force microscopy]]<ref>{{Cite journal | vauthors = Zhang L, Sakai T, Sakuma N, Ono T, Nakayama K | doi = 10.1063/1.125377 | volume = 75 | issue = 22 | pages = 3527–3529 | title = Nanostructural conductivity and surface-potential study of low-field-emission carbon films with conductive scanning probe microscopy | journal = Applied Physics Letters | year = 1999|bibcode = 1999ApPhL..75.3527Z }}</ref>
** EFM, [[electrostatic force microscopy]]<ref>{{Cite journal | vauthors = Weaver JM, Abraham DW | doi = 10.1116/1.585423 | volume = 9 | issue = 3 | pages = 1559–1561 | title = High resolution atomic force microscopy potentiometry | journal = Journal of Vacuum Science and Technology B | year = 1991|bibcode = 1991JVSTB...9.1559W }}</ref>
** KPFM, [[kelvin probe force microscope|kelvin probe force microscopy]]<ref>{{Cite journal | vauthors = Nonnenmacher M, O'Boyle MP, Wickramasinghe HK | doi = 10.1063/1.105227 | volume = 58 | issue = 25 | pages = 2921–2923 | title = Kelvin probe force microscopy | journal = Applied Physics Letters | year = 1991 | bibcode=1991ApPhL..58.2921N}}</ref>
** MIM, [[microwave impedance microscopy]]
** MFM, [[magnetic force microscopy]]<ref>{{Cite journal | doi = 10.1063/1.341836 | volume = 64 | issue = 3 | pages = 1561–1564 | vauthors = Hartmann U | title = Magnetic force microscopy: Some remarks from the micromagnetic point of view | journal = Journal of Applied Physics | year = 1988|bibcode = 1988JAP....64.1561H }}</ref>
** PFM, [[piezoresponse force microscopy]]<ref>{{Cite journal | vauthors = Roelofs A, Böttger U, Waser R, Schlaphof F, Trogisch S, Eng LM | doi = 10.1063/1.1328049 | volume = 77 | issue = 21 | pages = 3444–3446 | title = Differentiating 180° and 90° switching of ferroelectric domains with three-dimensional piezoresponse force microscopy | journal = Applied Physics Letters | year = 2000|bibcode = 2000ApPhL..77.3444R }}</ref>
** PTMS, [[photothermal microspectroscopy]]/microscopy
** SCM, [[scanning capacitance microscopy]]<ref>{{Cite journal | doi = 10.1063/1.334506 | volume = 57 | issue = 5 | pages = 1437–1444 | vauthors = Matey JR, Blanc J | title = Scanning capacitance microscopy | journal = Journal of Applied Physics | year = 1985|bibcode = 1985JAP....57.1437M }}</ref>
** SGM, [[scanning gate microscopy]]<ref>{{Cite journal | doi = 10.1063/1.117801 | volume = 69 | issue = 5 | pages = 671–673 | vauthors = Eriksson MA, Beck RG, Topinka M, Katine JA, Westervelt RM, Campman KL, Gossard AC | title = Cryogenic scanning probe characterization of semiconductor nanostructures | journal = Applied Physics Letters | date = July 29, 1996 | bibcode = 1996ApPhL..69..671E | doi-access = free }}</ref>
** SQDM, [[scanning quantum dot microscopy]]<ref>{{cite journal | vauthors = Wagner C, Green MF, Leinen P, Deilmann T, Krüger P, Rohlfing M, Temirov R, Tautz FS | title = Scanning Quantum Dot Microscopy | journal = Physical Review Letters | volume = 115 | issue = 2 | pages = 026101 | date = July 2015 | pmid = 26207484 | doi = 10.1103/PhysRevLett.115.026101 | arxiv = 1503.07738 | s2cid = 1720328 | bibcode = 2015PhRvL.115b6101W }}</ref>
** SVM, [[scanning voltage microscopy]]<ref>{{Cite journal | doi = 10.1116/1.589812 | journal = Journal of Vacuum Science and Technology B | volume = 16 | issue = 1 | pages = 367–372 | vauthors = Trenkler T, De Wolf P, Vandervorst W, Hellemans L | title = Nanopotentiometry: Local potential measurements in complementary metal--oxide--semiconductor transistors using atomic force microscopy | year = 1998 |bibcode = 1998JVSTB..16..367T }}</ref>
** FMM, [[force modulation microscopy]]<ref>{{Cite conference | publisher = AVS | doi = 10.1116/1.587278 | conference = The 1993 international conference on scanning tunneling microscopy | volume = 12 | pages = 1526–1529 | vauthors = Fritz M, Radmacher M, Petersen N, Gaub HE | title = Visualization and identification of intracellular structures by force modulation microscopy and drug induced degradation | book-title = The 1993 international conference on scanning tunneling microscopy | location = Beijing, China | access-date = October 5, 2009 | date = May 1994 | url = http://link.aip.org/link/?JVB/12/1526/1 | bibcode = 1994JVSTB..12.1526F | doi-access = free | archive-date = March 5, 2016 | archive-url = https://web.archive.org/web/20160305094007/http://scitation.aip.org/content/avs/journal/jvstb/12/3/10.1116/1.587278 | url-status = dead }}</ref>
** TAFM, Tomographic AFM<ref>{{Cite journal | vauthors = Luria J, Kutes Y, Moore A, Zhang L, Stach EA, Huey BD |date=September 26, 2016 |title=Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy |url=https://www.nature.com/articles/nenergy2016150 |journal=Nature Energy |language=en |volume=1 |issue=11 |page=16150 |doi=10.1038/nenergy.2016.150 |bibcode=2016NatEn...116150L |osti=1361263 |s2cid=138664678 |issn=2058-7546}}</ref><ref>{{cite journal | vauthors = Steffes JJ, Ristau RA, Ramesh R, Huey BD | title = Thickness scaling of ferroelectricity in BiFeO<sub>3</sub> by tomographic atomic force microscopy | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 116 | issue = 7 | pages = 2413–2418 | date = February 2019 | pmid = 30683718 | pmc = 6377454 | doi = 10.1073/pnas.1806074116 | doi-access = free | bibcode = 2019PNAS..116.2413S }}</ref><ref>{{Cite journal | vauthors = Song J, Zhou Y, Huey BD | title = 3D structure–property correlations of electronic and energy materials by tomographic atomic force microscopy. | journal = Applied Physics Letters | date = February 2021 | volume = 118 | issue = 8 |url=https://pubs.aip.org/apl/article/118/8/080501/39967/3D-structure-property-correlations-of-electronic |access-date=March 11, 2024 |doi=10.1063/5.0040984| bibcode = 2021ApPhL.118h0501S | s2cid = 233931111 | url-access = subscription }}</ref>
* STM, [[scanning tunneling microscopy]]<ref>{{Cite journal | doi = 10.1063/1.92999 | volume = 40 | issue = 2 | pages = 178–180 | vauthors = Binnig G, Rohrer H, Gerber C, Weibel E | title = Tunneling through a controllable vacuum gap | journal = Applied Physics Letters | year = 1982|bibcode = 1982ApPhL..40..178B | doi-access = free }}</ref>
** BEEM, [[ballistic electron emission microscopy]]<ref>{{cite journal | vauthors = Kaiser WJ, Bell LD | title = Direct investigation of subsurface interface electronic structure by ballistic-electron-emission microscopy | journal = Physical Review Letters | volume = 60 | issue = 14 | pages = 1406–1409 | date = April 1988 | pmid = 10038030 | doi = 10.1103/PhysRevLett.60.1406 | bibcode = 1988PhRvL..60.1406K }}</ref>
** ECSTM [[electrochemical scanning tunneling microscope]]<ref>{{Cite journal | publisher = AVS | doi = 10.1116/1.589098 | volume = 14 | pages = 1360–1364 | vauthors = Higgins SR, Hamers RJ | title = Morphology and dissolution processes of metal sulfide minerals observed with the electrochemical scanning tunneling microscope | journal = Journal of Vacuum Science and Technology B | access-date = October 5, 2009 | date = March 1996 | issue = 2 | url = http://link.aip.org/link/?JVB/14/1360/1 | bibcode = 1996JVSTB..14.1360H | archive-date = March 5, 2016 | archive-url = https://web.archive.org/web/20160305105359/http://scitation.aip.org/content/avs/journal/jvstb/14/2/10.1116/1.589098 | url-status = dead | url-access = subscription }}</ref>
** SHPM, [[scanning Hall probe microscopy]]<ref>{{Cite journal | doi = 10.1063/1.108334 | volume = 61 | issue = 16 | pages = 1974–1976 | vauthors = Chang AM, Hallen HD, Harriott L, Hess HF, Kao HL, Kwo J, Miller RE, Wolfe R, van der Ziel J, Chang TY | title = Scanning Hall probe microscopy | journal = Applied Physics Letters | year = 1992|bibcode = 1992ApPhL..61.1974C | s2cid = 121741603 }}</ref>
** SPSM [[spin polarized scanning tunneling microscopy]]<ref>{{Cite journal | doi = 10.1016/S0038-1098(01)00103-X | issn = 0038-1098 | volume = 119 | issue = 4–5 | pages = 341–355 | vauthors = Wiesendanger R, Bode M | title = Nano- and atomic-scale magnetism studied by spin-polarized scanning tunneling microscopy and spectroscopy | journal = Solid State Communications | date = July 25, 2001 | bibcode=2001SSCom.119..341W }}</ref>
** PSTM, [[photon scanning tunneling microscopy]]<ref>{{cite journal | vauthors = Reddick RC, Warmack RJ, Ferrell TL | title = New form of scanning optical microscopy | journal = Physical Review B | volume = 39 | issue = 1 | pages = 767–770 | date = January 1989 | pmid = 9947227 | doi = 10.1103/PhysRevB.39.767 | bibcode = 1989PhRvB..39..767R }}</ref>
** STP, [[scanning tunneling potentiometry]]<ref>[http://wwwex.physik.uni-ulm.de/lehre/physikalischeelektronik/phys_elektr/node252.html Vorlesungsskript Physikalische Elektronik und Messtechnik] {{in lang|de}}</ref>
** SXSTM, [[synchrotron x-ray scanning tunneling microscopy]]<ref>{{Cite book | publisher = Springer | doi = 10.1007/978-1-4419-7167-8_14 | edition = 1st | location = New York | pages = [https://archive.org/details/scanningprobemic00kali/page/n424 405]–431 | chapter = New Capabilities at the Interface of X-Rays and Scanning Tunneling Microscopy | editor = Kalinin, Sergei V. |editor2=Gruverman, Alexei| title = Scanning Probe Microscopy of Functional Materials: Nanoscale Imaging and Spectroscopy | url = https://archive.org/details/scanningprobemic00kali | url-access = limited | isbn = 978-1-4419-6567-7 | year = 2011 | vauthors = Volker R, Freeland JF, Streiffer SK }}</ref>
* SPE, Scanning Probe Electrochemistry
** SECM, [[scanning electrochemical microscopy]]
** SICM, [[scanning ion-conductance microscopy]]<ref>{{cite journal | vauthors = Hansma PK, Drake B, Marti O, Gould SA, Prater CB | title = The scanning ion-conductance microscope | journal = Science | volume = 243 | issue = 4891 | pages = 641–643 | date = February 1989 | pmid = 2464851 | doi = 10.1126/science.2464851 | bibcode = 1989Sci...243..641H }}</ref>
** SVET, [[scanning vibrating electrode technique]]
** SKP, [[scanning Kelvin probe]]
* FluidFM, [[fluidic force microscopy]]<ref name="MeisterGabi2009">{{cite journal | vauthors = Meister A, Gabi M, Behr P, Studer P, Vörös J, Niedermann P, Bitterli J, Polesel-Maris J, Liley M, Heinzelmann H, Zambelli T | title = FluidFM: combining atomic force microscopy and nanofluidics in a universal liquid delivery system for single cell applications and beyond | journal = Nano Letters | volume = 9 | issue = 6 | pages = 2501–2507 | date = June 2009 | pmid = 19453133 | doi = 10.1021/nl901384x | bibcode = 2009NanoL...9.2501M }}</ref>
* FOSPM, [[Feature-oriented scanning|feature-oriented scanning probe microscopy]]
* MRFM, [[magnetic resonance force microscopy]]<ref>{{Cite journal | doi = 10.1103/RevModPhys.67.249 | volume = 67 | issue = 1 | pages = 249–265 | vauthors = Sidles JA, Garbini JL, Bruland KJ, Rugar D, Züger O, Hoen S, Yannoni CS | title = Magnetic resonance force microscopy | journal = Reviews of Modern Physics | year = 1995 | bibcode=1995RvMP...67..249S}}</ref>
* NSOM, [[near-field scanning optical microscopy]] (or SNOM, scanning near-field optical microscopy)<ref>{{cite journal | vauthors = Betzig E, Trautman JK, Harris TD, Weiner JS, Kostelak RL | title = Breaking the diffraction barrier: optical microscopy on a nanometric scale | journal = Science | volume = 251 | issue = 5000 | pages = 1468–1470 | date = March 1991 | pmid = 17779440 | doi = 10.1126/science.251.5000.1468 | s2cid = 6906302 | bibcode = 1991Sci...251.1468B }}</ref>
** nano-FTIR, [[Nano-FTIR|broadband nanoscale SNOM-based spectroscopy]]<ref>{{cite journal | vauthors = Huth F, Govyadinov A, Amarie S, Nuansing W, Keilmann F, Hillenbrand R | title = Nano-FTIR absorption spectroscopy of molecular fingerprints at 20 nm spatial resolution | journal = Nano Letters | volume = 12 | issue = 8 | pages = 3973–3978 | date = August 2012 | pmid = 22703339 | doi = 10.1021/nl301159v | bibcode = 2012NanoL..12.3973H }}</ref>
* SSM, [[scanning SQUID microscopy]]
* SSRM, [[scanning spreading resistance microscopy]]<ref>{{Cite journal | doi = 10.1063/1.113636 | volume = 66 | issue = 12 | pages = 1530–1532 | vauthors = De Wolf P, Snauwaert J, Clarysse T, Vandervorst W, Hellemans L | title = Characterization of a point-contact on silicon using force microscopy-supported resistance measurements | journal = Applied Physics Letters | year = 1995|bibcode = 1995ApPhL..66.1530D }}</ref>
* SThM, [[scanning thermal microscopy]]<ref>{{Cite journal | doi = 10.1063/1.1145225 | volume = 65 | issue = 7 | pages = 2262–2266 | vauthors = Xu JB, Lauger L, Dransfeld K, Wilson IH | title = Thermal sensors for investigation of heat transfer in scanning probe microscopy | journal = Review of Scientific Instruments | year = 1994|bibcode = 1994RScI...65.2262X }}</ref>
* SSET [[scanning single-electron transistor microscopy]]<ref>{{cite journal | vauthors = Yoo MJ, Fulton TA, Hess HF, Willett RL, Dunkleberger LN, Chichester RJ, Pfeiffer LN, West KW | title = Scanning Single-Electron Transistor Microscopy: Imaging Individual Charges | journal = Science | volume = 276 | issue = 5312 | pages = 579–582 | date = April 1997 | pmid = 9110974 | doi = 10.1126/science.276.5312.579 }}</ref>
* STIM, scanning thermo-ionic microscopy<ref>{{Cite journal| vauthors = Nasr Esfahani E, Eshghinejad A, Ou Y, Zhao J, Adler S, Li J |date=November 2017|title=Scanning Thermo-Ionic Microscopy: Probing Nanoscale Electrochemistry via Thermal Stress-Induced Oscillation|journal=Microscopy Today|volume=25|issue=6|pages=12–19|doi=10.1017/s1551929517001043|issn=1551-9295|arxiv=1703.06184|s2cid=119463679}}</ref><ref>{{Cite journal| vauthors = Eshghinejad A, Nasr Esfahani E, Wang P, Xie S, Geary TC, Adler SB, Li J |date=May 28, 2016|title=Scanning thermo-ionic microscopy for probing local electrochemistry at the nanoscale|journal=Journal of Applied Physics|volume=119|issue=20|pages=205110|doi=10.1063/1.4949473|issn=0021-8979|bibcode=2016JAP...119t5110E|s2cid=7415218}}</ref>
* CGM, charge gradient microscopy <ref>{{cite journal | vauthors = Hong S, Tong S, Park WI, Hiranaga Y, Cho Y, Roelofs A | title = Charge gradient microscopy | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 111 | issue = 18 | pages = 6566–6569 | date = May 2014 | pmid = 24760831 | pmc = 4020115 | doi = 10.1073/pnas.1324178111 | doi-access = free | bibcode = 2014PNAS..111.6566H }}</ref><ref>{{Cite journal | vauthors = Esfahani EN, Liu X, Li J |title=Imaging ferroelectric domains via charge gradient microscopy enhanced by principal component analysis|journal=Journal of Materiomics|volume=3|issue=4|pages=280–285|doi=10.1016/j.jmat.2017.07.001|year=2017|arxiv=1706.02345|s2cid=118953680}}</ref>
* SRPM, scanning resistive probe microscopy <ref>{{cite journal| vauthors = Park H, Jung J, Min DK, Kim S, Hong S, Shin H |date=March 2, 2004|title=Scanning resistive probe microscopy: Imaging ferroelectric domains|journal=Applied Physics Letters|volume=84|issue=10|pages=1734–1736|doi=10.1063/1.1667266|issn=0003-6951|bibcode=2004ApPhL..84.1734P}}</ref>

==Image formation==
To form images, scanning probe microscopes [[raster scan]] the tip over the surface. At discrete points in the raster scan a value is recorded (which value depends on the type of SPM and the mode of operation, see below). These recorded values are displayed as a [[heat map]] to produce the final STM images, usually using a black and white or an orange color scale.

===Constant interaction mode===
In constant interaction mode (often referred to as "in feedback"), a feedback loop is used to physically move the probe closer to or further from the surface (in the ''z'' axis) under study to maintain a constant interaction. This interaction depends on the type of SPM, for scanning tunneling microscopy the interaction is the tunnel current, for contact mode AFM or MFM it is the [[Cantilever#In microelectromechanical systems|cantilever]] deflection, etc. The type of feedback loop used is usually a PI-loop, which is a [[PID controller|PID-loop]] where the differential gain has been set to zero (as it amplifies noise). The ''z'' position of the tip (scanning plane is the ''xy''-plane) is recorded periodically and displayed as a heat map. This is normally referred to as a topography image.

In this mode a second image, known as the ″error signal" or "error image" is also taken, which is a heat map of the interaction which was fed back on. Under perfect operation this image would be a blank at a constant value which was set on the feedback loop. Under real operation the image shows noise and often some indication of the surface structure. The user can use this image to edit the feedback gains to minimise features in the error signal.

If the gains are set incorrectly, many imaging artifacts are possible. If gains are too low features can appear smeared. If the gains are too high the feedback can become unstable and oscillate, producing striped features in the images which are not physical.

===Constant height mode===
In constant height mode the probe is not moved in the ''z''-axis during the raster scan. Instead the value of the interaction under study is recorded (i.e. the tunnel current for STM, or the cantilever oscillation amplitude for amplitude modulated non-contact AFM). This recorded information is displayed as a heat map, and is usually referred to as a constant height image.

Constant height imaging is much more difficult than constant interaction imaging as the probe is much more likely to crash into the sample surface.{{citation needed| date=November 2015}} Usually before performing constant height imaging one must image in constant interaction mode to check the surface has no large contaminants in the imaging region, to measure and correct for the sample tilt, and (especially for slow scans) to measure and correct for thermal drift of the sample. Piezoelectric creep can also be a problem, so the microscope often needs time to settle after large movements before constant height imaging can be performed.

Constant height imaging can be advantageous for eliminating the possibility of feedback artifacts.{{citation needed| date=November 2015}}

==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]].

==Advantages==
The resolution of the microscopes is not limited by [[diffraction]], only by the size of the probe-sample interaction volume (i.e., [[point spread function]]), which can be as small as a few [[picometre]]s. Hence the ability to measure small local differences in object height (like that of 135 picometre steps on <100> silicon) is unparalleled. Laterally the probe-sample interaction extends only across the tip atom or atoms involved in the interaction.

The interaction can be used to modify the sample to create small structures ([[Scanning probe lithography]]).

Unlike electron microscope methods, specimens do not require a partial vacuum but can be observed in air at standard temperature and pressure or while submerged in a liquid reaction vessel.

==Disadvantages==
The detailed shape of the scanning tip is sometimes difficult to determine. Its effect on the resulting data is particularly noticeable if the specimen varies greatly in height over lateral distances of 10&nbsp;nm or less.

The scanning techniques are generally slower in acquiring images, due to the scanning process. As a result, efforts are being made to greatly improve the scanning rate. Like all scanning techniques, the embedding of spatial information into a time sequence opens the door to uncertainties in metrology, say of lateral spacings and angles, which arise due to time-domain effects like specimen drift, feedback loop oscillation, and mechanical vibration.

The maximum image size is generally smaller.

Scanning probe microscopy is often not useful for examining buried solid-solid or liquid-liquid interfaces.

== Scanning photo current microscopy (SPCM) ==
SPCM can be considered as a member of the Scanning Probe Microscopy (SPM) family. The difference between other SPM techniques and SPCM is, it exploits a focused laser beam as the local excitation source instead of a probe tip.<ref>{{Cite journal |last1=GRAHAM |first1=RION |last2=YU |first2=DONG |date=2013-09-23 |title=Scanning Photocurrent Microscopy in Semiconductor Nanostructures |url=http://dx.doi.org/10.1142/s0217984913300184 |journal=Modern Physics Letters B |volume=27 |issue=25 |pages=1330018 |doi=10.1142/s0217984913300184 |bibcode=2013MPLB...2730018G |issn=0217-9849|url-access=subscription }}</ref>

Characterization and analysis of spatially resolved optical behavior of materials is very important in opto-electronic industry. Simply this involves studying how the properties of a material vary across its surface or bulk structure. Techniques that enable spatially resolved optoelectronic measurements provide valuable insights for the enhancement of optical performance. Scanning electron microscopy (SPCM) has emerged as a powerful technique which can investigate spatially resolved optoelectronic properties in semiconductor nano structures.

=== Principle ===
[[File:Laser scan of the scanning photocurrent microscope.png|thumb|Laser scan of the scanning photocurrent microscope]]

In SPCM, a focused laser beam is used to excite the semiconducting material producing excitons (electro-hole pairs). These excitons undergo different mechanisms and if they can reach the nearby electrodes before the recombination takes place a photocurrent is generated. This photocurrent is position dependent as it, raster scans the device.

=== SPCM analysis ===
Using the position dependent photocurrent map, important photocurrent dynamics can be analyzed.

SPCM provides information such as characteristic length such as minority diffusion length, recombination dynamics, doping concentration, internal electric field  etc.

== Visualization and analysis software ==
In all instances and contrary to optical microscopes, rendering software is necessary to produce images.
Such software is produced and embedded by instrument manufacturers but also available as an accessory from specialized work groups or companies.
The main packages used are freeware: [[Gwyddion (software)|Gwyddion]], WSxM (developed by Nanotec) and commercial: SPIP (developed by [[Image Metrology]]), FemtoScan Online (developed by [[Advanced Technologies Center]]),  [[MountainsMap|MountainsMap SPM]] (developed by [[Digital Surf]]), [[TopoStitch]] (developed by [[Image Metrology]]).

== References ==
{{reflist}}

== Further reading ==
{{refbegin}}
* {{cite book | title = Scanning Probe Microscopy | vauthors = Voigtländer B | publisher=Springer |year=2015 | isbn=978-3-662-45239-4 | doi=10.1007/978-3-662-45240-0 | series=NanoScience and Technology | bibcode=2015spma.book.....V | s2cid=94208893 | url=http://www.nnin.org/education-training/k-12-teachers/nanotechnology-curriculum-materials/scanning-probe-microscopy }}
* {{cite book | title = Atomic Force Microscopy | vauthors = Voigtländer B | publisher=Springer |year=2019 | isbn=978-3-030-13653-6 | doi=10.1007/978-3-030-13654-3 | series=NanoScience and Technology | bibcode = 2019afm..book.....V | s2cid=199490753 }}
{{refend}}

== External links ==
* [https://wecanfigurethisout.org/VL/SPM_operation.htm Scanning Probe Microscope - An Animated Explanation of its Inner Workings] WeCanFigureThisOut.org
* [https://wecanfigurethisout.org/VL/SPM_piezoelectric.htm Scanning Probe Microscope - An Animated Explanation of its Piezoelectric Crystals] WeCanFigureThisOut.org

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[[Category:Scanning probe microscopy| ]]