Concept/Principle/Structure/Features of Scanning Probe Microscope
Scanning probe microscope is a collective term for various new types of probe microscopes (atomic force microscope, electrostatic force microscope, magnetic force microscope, scanning ion conductivity microscope, scanning electrochemical microscope, etc.) developed on the basis of scanning tunneling microscope. It is a surface analysis instrument developed internationally in recent years.
The principle and structure of scanning probe microscopy
The basic working principle of a scanning probe microscope is to utilize the interaction between the probe and the surface atoms and molecules of the sample, that is, to form various physical fields of interaction when the probe and the sample surface are close to the nanoscale, and to obtain the surface morphology of the sample by detecting corresponding physical quantities. The scanning probe microscope consists of five parts: a probe, a scanner, a displacement sensor, a controller, a detection system, and an image system.
The controller moves the sample vertically and horizontally through a scanner to stabilize the distance (or physical quantity of interaction) between the probe and the sample at a fixed value; Simultaneously move the sample in the x-y horizontal plane, so that the probe scans the surface of the sample along the scanning path. The scanning probe microscope detects the relevant physical quantity signals of the interaction between the probe and the sample by the detection system while maintaining a stable distance between the probe and the sample; In the case of stable interacting physical quantities, the distance between the probe and the sample is detected by a vertical displacement sensor. The image system performs image processing on the surface of the sample based on the detection signal (or the distance between the probe and the sample).
According to the different physical fields of interaction between the probe and the sample used, scanning probe microscopes are divided into different series of microscopes. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are two commonly used types of scanning probe microscopes. Scanning tunneling microscope detects the surface structure of a sample by measuring the tunneling current between the probe and the sample being tested. Atomic force microscopy detects the surface of a sample by detecting the micro cantilever deformation caused by the interaction force between the needle tip and the sample using a photoelectric displacement sensor, which can be either attractive or repulsive.
The characteristics of scanning probe microscopy
Scanning probe microscope is the third type of microscope that observes the structure of matter at the atomic scale, in addition to field ion microscopy and high-resolution transmission electron microscopy. Taking scanning tunneling microscopy (STM) as an example, its lateral resolution is 0.1-0.2nm, and its longitudinal depth resolution is 0.01nm. This resolution allows for clear observation of individual atoms or molecules distributed on the surface of the sample. Meanwhile, scanning probe microscopy can also be used for observation and research in air, other gas or liquid environments.
Scanning probe microscopes have characteristics such as atomic resolution, atomic transport, and nanofabrication. However, due to the different working principles of various scanning microscopes, the results they obtain reflect very different surface information of the sample. The scanning tunneling microscope measures the distribution information of the electron stage on the surface of the sample, which has atomic level resolution but still cannot obtain the true structure of the sample. And atomic microscopy detects the interaction information between atoms, so it can obtain the arrangement information of the surface atomic distribution of the sample, which is the true structure of the sample. On the other hand, atomic force microscopy cannot measure electronic state information that can be compared with theory, so both have their own strengths and weaknesses.
