Scanning probe microscope

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Scanning probe microscope

  1. 1. Present Erfan Zaker EsfahaniEmail aref_z_e@yahoo.comCourse NanotechnologyNumber 09131299216Lecturer Dr. Monajati
  2. 2. Local density of states (LDOS) is a physicalspace-resolved quantity that describes thenumber of states at each energy level that areavailable to be occupied. According tocrystals structure, this quantity can bepredicted by computational methods, as forexample with density functional theoryArtifact is any perceived distortion orother data error caused by the instrument ofobservation
  3. 3. ..Terms DefinitionTerms Definition.Motivation.Motivation.Historical Overview.Historical Overview.SPM Overview.SPM Overview.AFM Overview.SPM Software.SPM Software.Summary.Summary
  4. 4. .Surface is the shell of a macroscopic object(the inside) in contact with its environment(the outside world). An interface is theboundary between two phases. Object insideis called bulk.In large objects with small surface area A tovolume V ratio (A/V) the physical andchemical properties are primarily defined bythe bulk.In small objects with a large A/V-ratio theproperties are strongly influenced by thesurface
  5. 5. Hydrophobic effectHydrophobic effectWaterWaterHydrophobic materialHydrophobic materialSurface structureSurface structure(20-100μm)(20-100μm)
  6. 6. Current flow near the surfaceCurrent flow near the surfaceIn modern semiconductor devices surface isIn modern semiconductor devices surface isdominantdominant
  7. 7. LayerLayerbybylayer …layer …SurfaceSurfacebybysurfacesurface ……
  8. 8.  surface topographyvalley, planes, hills• physical materials behavior (conducting /insulating)• polarity (hydrophilic / hydrophobic)• tribological behavior (friction on "rough" or"smooth" surface)• physical surface behavior (reflectivity)
  9. 9. • understanding and inhibition of corrosion• chip manufacturing / microelectronics• hard disks (anti-friction, ultra-smooth,...)• biological surfaces (patterned cell growth)• sensors (chemical, biological, electrical)• modification of anti-reflection (displays)• modification of wetting (inkjet printing)
  10. 10. • According to all the mentioned before ourmotivation as electrical engineers for surfaceresearch is clear. The modern physicalmaterials properties, in general, affected bysurface.• Moreover, we want not only passivelyreceive information about the surface, butactively affect on it topology, moving theatoms
  11. 11. Microscopy small, – seeScanning Probe Microscopy (SPM) is a branch ofmicroscopy that forms images of surfaces using aphysical probe that scans the specimen. SPM able toreceive 3D surface topography
  12. 12. Local density of states (LDOS) is a physical space-resolved quantity thatdescribes the number of states at each energy level that are available tobe occupied. According to crystals structure, this quantity can bepredicted by computational methods, as for example with densityfunctional theoryArtifact is any perceived distortion or other data error caused by theinstrument of observationInput transducer or sensorConvert nonelectrical signal to electrical oneOutput transducer or actuatorConvert electrical signal to nonelectrical onePiezoceramicCeramic that convert electrical field to mechanical deformation and viceversaPiezoelectric propertiesare time-depended
  13. 13. SPM Scanning Probe MicroscopeSTM Scanning Tunneling MicroscopeAFM Atomic Force MicroscopeSFM Scanning Force MicroscopeFFM Force-Modulated AFMLFM Lateral Force MicroscopeMFM Magnetic Force MicroscopeSThM Scanning Thermal MicroscopeEFM Electrical Force Microscope
  14. 14. ActuatorActuatorSensorSensorComputerComputerProbeProbeSampleSample
  15. 15. The blind mouse can’t see the object (sample), butusing the stick (probe), he can scan it.Arm skin (sensor) send the received from the probeinformation to the brain (computer), the computer“see” the picture, if it need receive additionalinformation about the sample (decision done usingfeedback), it send requirement to arm muscle(actuator), arm carefully moves the probe torequired coordinate and vice versa
  16. 16. All of the SPM techniques are based upon scanninga probe (typically called the tip, since it literally is asharp metallic tip) just above a surface whilstbetween scanned surface and probe exist interactionThe nature of this chosen interaction defines adevice accessory to this or that type within thefamily of Scanning Probe MicroscopeThe information on a surface is taken by fixing (bymeans of feedback system) or monitoring ofinteraction of a probe and the sample
  17. 17. Surface divided to matrix of N rows by M columnsScanning performed row by row, as result wereceive per each couple of coordinates {xi,yj},vector with measurement results that describedsurface at this point
  18. 18. We will present scanning probe microscopesbased on two kind of iteration1.Iteration is electrical current STM2.Iteration is atomic force AFM/SFMIn general, as mentioned, SPM have two modes,defined by tip movement over the surface1.Fixed probe Z coordinate, iteration or parameterdepended on iteration monitoring2.Fixed iteration, height change monitoring
  19. 19. CantileverLaserPhotodetector
  20. 20. Cantilever is a beam supported on only one end
  21. 21. 1. Contact Mode2. Friction mode3. Tapping Mode4. Phase mode
  22. 22. Contact (repulsive) mode: tip makes soft"physical contact" with the sample, thecontact force causes the cantilever to bendto accommodate changes in topography
  23. 23. Stoneys formula( ) 22LEv1σ3δ ⋅−⋅⋅=mkωL4ωEtδFk o33=⇔==σ is applied stressE, v are known physical parameterstwL
  24. 24. Lateral force / friction mode: AFM cantilever incontact mode is laterally deflected in thesampleplane due to scanning motion perpendicularto cantilever axes, lateral deflection ismeasuredand gives information on surface materialapart from topography
  25. 25. Intermittent contact: AFM cantilever isvibrated near the surface of a sample withspacing on the order of tens to hundreds ofangstromsIn this case the oscillator is non linear,mathematical calculation is prettycomplicated, it is out of scope of thispresentation
  26. 26. Phase mode: AFM cantilever is vibrated near thesurface of a sample with known amplitudefrequency equal to resonance cantilever one .Compare phase of driving signal and cantileverresponse( )( )( ) =+⋅=+⋅=⋅+⋅+QFkarctgωtcosZzFωtcosAzωzβ2zω200ϕϕ
  27. 27. Image of a Si surfaceimaged with a forcesensor. In the left half ofthe image, the cantileverdoes not oscillate, in theright half it oscillates withan amplitude of 0.09 nm,yielding a double imageof every atomImage size 3.3 nm x 3.3 nm.
  28. 28. AFM contact scanningafter scanningbefore scanning
  29. 29. • Repeat the scan to ensure that it looks thesame.• Change the scan direction and take a newimage.• Change the scan size and take an image toensure that the features scale properly.• Rotate the sample and take an image to identifytip imaging• Change the scan speed and take another image
  30. 30. • User-friendly interface, basic Windows tools• Offline simulation tool• Calibration tool, ability to see results• Variety of supported formats• Control unit monitoring• Filtering control• Mathematical tools• Programming tools• 3D studio – capture and editing images andvideos in real time
  31. 31. SPM standardization has onlyrecently begunas part of an effort by theInternational Organization forStandardization (ISO) !!!25 years of scanning probe microscopywww.nanowerk.com , 2007
  32. 32. Today, Jan 2008, 25 years of STM, UNDER DEVELOPMENT

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