Scanning Probe Microscopy: 5 Important Concepts

Contents: Scanning Probe Microscopy

What is scanning probe microscopy?

Scanning probe microscopy or SPM is a microscopy technique that produces images by scanning the specimen with the help of a probe, capable of measuring small local differences in the height of the specific sample material with out being impacted by diffraction. These microscopes are able to carry out the imaging of several interactions with the sample simultaneously.

What are the types of scanning probe microscopes?

Scanning probe microscopes can be of several different types such as:

AFM (atomic force microscopy):

AFM (atomic force microscopy) is a very high-resolution microscopy technique in which the resolution has the order of a fraction of a nanometer. AFM can be further divided into-

Dynamic contact atomic force microscopy.

Tapping atomic force microscopy.

Contact atomic force microscopy.

Non-contact atomic force microscopy.

CFM or Chemical force microscopy.

KPFM or Kelvin probe force microscope.

MFM or Magnetic force microscopy.

AFM-IR or Atomic force microscopy-based infrared spectroscopy.

C-AFM or Conductive atomic force microscopy.

EFM or Electrostatic force microscopy.

PFM or The Piezo response force microscopy.

PTMS or Photo thermal micro-spectroscopy/microscopy.

SVM or The Scanning voltage microscopy.

FMM or Force modulation microscopy.

SGM or The scanning gate microscopy.

scanning probe microscopy
AFM representation. Image source: anonymous, Atomic force microscope block diagram, marked as public domain, more details on Wikimedia Commons

STM (scanning tunneling microscope):

STM images a sample with a very sharp conducting tip and capable to produce image-resolution ranging in between 0.1- 0.01nm scale and further divided into.

The scanning Hall probe microscopy or SHPM.

The spin-polarized scanning tunneling microscopy or SPSM .

The Ballistic electron emission microscopy or BEEM.

The Synchrotron x-ray scanning tunneling microscopy or SXSTM.

The electro chemical scanning tunneling microscope or ECSTM.

The Photon scanning tunneling microscopy or PSTM,.

The scanning tunneling potentiometry or STP.

1024px Scanning Tunneling Microscope schematic.svg
STM (scanning tunneling microscope) diagrammatic representation. Image source: Michael Schmid and Grzegorz PietrzakScanning Tunneling Microscope schematicCC BY-SA 2.0 AT

SPE, Scanning Probe Electrochemistry:

SPE, Scanning Probe Electrochemistry is a microscopic technique specially designed for examining electrochemical behavior of various solid or liquid samples. SPE can be further divided into:

The scanning vibrating electrode technique or (SVET).

The Scanning Kelvin probe or (SVP).

The Scanning ion conductance microscopy or (SICM).

The scanning electrochemical microscopy or(SECM).

SPE, Scanning Probe Electrochemistry diagrammatic representation. Image source: Paul venterSicm, marked as public domain, more details on Wikimedia Commons

NSOM | Near-field scanning optical microscopy:

The Near-field scanning optical microscopy (NSOM) or scanning near-field optical microscopy is a microscopic technique (SNOM) specifically designed for examining nanostructures and nanoscale analysis.

NanoFTIR is a type of NSOM technique capable to break the far resolutionlimit by utilizing the properties of evanescent wave.

1280px NSOM setup
NSOM setup Image source: Sgptch at English WikipediaNSOM-setup, marked as public domain, more details on Wikimedia Commons

Other variations of SPM are

The scanning thermo-ionic microscopy (STIM).

The charge gradient microscopy (CGM).

The scanning spreading resistance microscopy(SSRM).

The scanning resistive probe microscopy (SRPM).

The scanning single-electron transistor microscopy (SSET).

The scanning SQUID microscopy (SSM).

What is the type of probe tip used for scanning probe microscopy?

The type of SPM probe tip used is totally based on the kind of SPM being used and combination of the topographies of the specimen and the shaping of the tip generates an SPM image. However, some common characteristics are noticed in almost every SPMs and probe is required to have an extremely sharp apex and resolution of the microscope is defined mainly by the apex of the probe. Sharper probes provide better resolution than blunt probes, terminates by an atom for atomicresolution imaging.

For several cantilever dependent, Scanning Probe Microscopes such as AFM (atomic force microscopy) and MFM (magnetic force microscopy), the whole cantilever and integrated probe’s fabrication done by the etching process with silicon nitride and STM (scanning tunneling microscope) and SCM (scanning capacitance microscope) require conducting probes that are typically built from platinum/iridium wire and different materials like gold are occasionally used for sample related reasons or when the SPM needs to be merged with other experiments such as TERS.

Iridium/Platinum and other such ambient probes are usually cut by using sharp wire cutters. The most effective method is cutting a major of the way through the wire and then pulling to snap the remaining part of the wire, enhancing the chances of a single atom termination. The tungsten wires used for such purposes are generally  electrochemically etched and after that oxide layer is removed when the tip is in UHV conditions.

What are the advantages of scanning probe microscopy?

Advantages of Scanning probe microscopy

  • The image resolution will not be affected by diffraction in this method.
  • This is capable of measure very small (as small as picometer range ) local difference in the height sacale.
  • The interactions involved in image formation via scanning probe microscopy can be used for generating small structural changes (through the scanning probe lithography process).
  • There is no requirement for the specimen to be placed in a vacuum in scanning probe microscopy. This microscopic technique works well even in normal atmospheric conditions.

What are the disadvantages of scanning probe microscopy?

Like every other microscopy technique, scanning probe microscopy also has certain limitations:

  • In scanning probe microscopy, determining the detailed shape of the scanning tip becomes difficult at times. This error is especially noticeable when the sample varies significantly in height over lateral distances of less than 10 nm.
  • Images produced by a scanning probe microscope generally takes a lot of time to form. Nowadays, several modifications are being made in order to increase the rate of scanning samples.
  • The maximum size of image formed by using a scanning probe microscope is generally small.
  • This is not suitable for solid-solid or liquid-liquid sample interface.

What is scanning electron microscopy?

Scanning electron microscope has formed images by scanning the surface of a sample by utilizing the electron beam and they are two types.

  • Scanning transmission electron microscopy.
  • Scanning tunneling microscopy.

Scanning Electron Microscope is based on the secondary electron emission from the sample’s upper surface and Scanning electron microscopes are also used for counting cells or other particles, For determining the sizes of macromolecular complexes, and for process control for more details about scanning electron microscopes visit here .

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