Scanning probe microscopy
Scanning Probe Microscopy (SPM) is a branch of microscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...

 that forms images of surfaces using a physical probe that scans the specimen. An image of the surface is obtained by mechanically moving the probe in a raster scan
Raster scan
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems...

 of the specimen, line by line, and recording the probe-surface interaction as a function of position. SPM was founded with the invention of the scanning tunneling microscope
Scanning tunneling microscope
A scanning tunneling microscope is an instrument for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer , the Nobel Prize in Physics in 1986. For an STM, good resolution is considered to be 0.1 nm lateral resolution and...

 in 1981.

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. They owe this largely to the ability of piezoelectric actuators
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...

 to execute motions with a precision and accuracy at the atomic level or better on electronic command. One could rightly call this family of techniques "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 of scanning probe microscopy

  • AFM, atomic force microscopy
    • Contact AFM
    • Non-contact AFM
    • Dynamic contact AFM
    • Tapping AFM
  • BEEM, ballistic electron emission microscopy
    Ballistic electron emission microscopy
    Ballistic electron emission microscopy or BEEM is a technique for studying ballistic electron transport through a variety of materials and material interfaces. BEEM is a three terminal scanning tunneling microscopy technique that was invented in 1988 at the Jet Propulsion Laboratory in Pasadena...

  • CFM, chemical force microscopy
    Chemical force microscopy
    Chemical force microscopy is a variation of atomic force microscopy which has become a versatile tool for characterization of materials surfaces...

  • C-AFM, conductive atomic force microscopy
    Conductive atomic force microscopy
    Conductive atomic force microscopy is a variation of atomic force microscopy and scanning tunneling microscopy , which uses electrical current to construct the surface profile of the studied sample. The current is flowing through the metal-coated tip of the microscope and the conducting sample...

  • ECSTM electrochemical scanning tunneling microscope
    Electrochemical scanning tunneling microscope
    The electrochemical scanning tunneling microscope, or ESTM, was invented in 1988 by Kingo Itaya in Japan. With ESTM, the structures of surfaces and electrochemical reactions in solid-liquid interfaces can be observed at atomic or molecular scales....

  • EFM, electrostatic force microscopy
  • FMM, force modulation microscopy
  • FOSPM, feature-oriented scanning probe microscopy
    Feature-oriented scanning
    Feature-oriented scanning is a method of precision measurement of surface topography with a scanning probe microscope in which surface features are used as reference points for microscope probe attachment...

  • KPFM, kelvin probe force microscopy
    Kelvin probe force microscope
    Kelvin probe force microscopy , also known as surface potential microscopy, is a noncontact variant of atomic force microscopy that was invented in 1991. With KPFM, the work function of surfaces can be observed at atomic or molecular scales...

  • MFM, magnetic force microscopy
  • MRFM, magnetic resonance force microscopy
    Magnetic Resonance Force Microscopy
    Magnetic resonance force microscopy is an imaging technique that acquires magnetic resonance images at nanometer scales, and possibly at atomic scales in the future. MRFM is potentially able to observe protein structures which cannot be seen using X-ray crystallography and protein nuclear...

  • NSOM, near-field scanning optical microscopy (or SNOM, scanning near-field optical microscopy)
  • PFM, Piezoresponse Force Microscopy
    Piezoresponse Force Microscopy
    Piezoresponse force microscopy is a variant of atomic force microscopy that allows imaging and manipulation of ferroelectric domains...

  • PSTM, photon scanning tunneling microscopy
  • PTMS, photothermal microspectroscopy
    Photothermal microspectroscopy
    Photothermal microspectroscopy , alternatively known as photothermal temperature fluctuation , is derived from two parent instrumental techniques: infrared spectroscopy and atomic force microscopy...

  • SCM, scanning capacitance microscopy
    Scanning capacitance microscopy
    Scanning capacitance microscopy is a variety of scanning probe microscopy in which a narrow probe electrode is held just above the surface of a sample and scanned across the sample...

  • SECM, scanning electrochemical microscopy
  • SGM, scanning gate microscopy
    Scanning gate microscopy
    Scanning gate microscopy is a scanning probe microscopy technique with an electrically conductive tip used as a movable gate that couples capacitively to the sample and probes electrical transport on the nanometer scale. Typical samples are mesoscopic devices, often based on semiconductor...

  • SHPM, scanning Hall probe microscopy
  • SICM, scanning ion-conductance microscopy
    Scanning ion-conductance microscopy
    The scanning ion-conductance microscope consists of an electrically charged glass micro- or nanopipette probe filled with electrolyte lowered toward the surface of the sample in an oppositely charged bath of electrolyte...

  • SPSM spin polarized scanning tunneling microscopy
    Spin polarized scanning tunneling microscopy
    Spin polarized scanning tunneling microscopy is a specialized application of scanning tunneling microscopy that can provide detailed information of magnetic phenomena on the single-atom scale additional to the atomic topology gained with STM...

  • SSRM, scanning spreading resistance microscopy
  • SThM, scanning thermal microscopy
    Scanning thermal microscopy
    Scanning thermal microscopy is a type of scanning probe microscopy that maps the local temperature and thermal conductivity of an interface. The probe in a scanning thermal microscope is sensitive to local temperatures - providing a nanoscale thermometer...

  • STM, scanning tunneling microscopy
  • STP, scanning tunneling potentiometry
  • SVM, scanning voltage microscopy
    Scanning voltage microscopy
    Scanning voltage microscopy -- sometimes also called nanopotentiometry -- is a scientific experimental technique based on atomic force microscopy. A conductive probe, usually only a few nanometers wide at the tip, is placed in full contact with an operational electronic or optoelectronic sample...

  • SXSTM, synchrotron x-ray scanning tunneling microscopy

Of these techniques AFM and STM are the most commonly used for roughness measurements.

Probe tips

Probe tips are normally made of platinum/iridium, silicon nitride or gold. There are two main methods for obtaining a sharp probe tip, acid etching and cutting. The first involves dipping a wire end first into an acid bath and waiting until it has etched through the wire and the lower part drops away. The remainder is then removed and the resulting tip is often one atom in diameter. An alternative and much quicker method is to take a thin wire and cut it with a pair of scissors or a scalpel. Testing the tip produced via this method on a sample with a known profile will indicate whether the tip is good or not and a single sharp point is achieved roughly 50% of the time. It is not uncommon for this method to result in a tip with more than one peak; one can easily discern this upon scan due to a high level of ghost images.

Advantages of scanning probe microscopy

  • The resolution of the microscopes is not limited by diffraction
    Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

    , but only by the size of the probe-sample interaction volume (i.e., point spread function
    Point spread function
    The point spread function describes the response of an imaging system to a point source or point object. A more general term for the PSF is a system's impulse response, the PSF being the impulse response of a focused optical system. The PSF in many contexts can be thought of as the extended blob...

    ), which can be as small as a few picometre
    A picometre is a unit of length in the metric system, equal to one trillionth, i.e. of a metre, which is the current SI base unit of length...

    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 (nanolithography
    Nanolithography is the branch of nanotechnology concerned with the study and application of fabricating nanometer-scale structures, meaning patterns with at least one lateral dimension between the size of an individual atom and approximately 100 nm...

  • 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 of scanning probe microscopy

  • 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 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.

External links

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