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The secrets of scanning probe microscopy: How to explore the microscopic world with atomic resolution?
Since the first invention of the scanning tunneling microscope in 1981, scanning probe microscopy (SPM) has become an important tool for studying surface microscopic properties. With this microscope, scientists can observe matter at the atomic level. The development of this technology not only improves our understanding of materials science, but also lays the foundation for innovation in semiconductor and nanotechnology.
The core principle of scanning probe microscopy is based on an extremely sensitive probe that scans the surface of a sample and records its interaction with the sample. The results of these interactions are often displayed as heat maps, which become microscopic images of what we see.
Scientists have demonstrated amazing flexibility and diversity in using this technology to explore microscopic structures.
The operation and imaging methods of scanning probe microscope
The imaging process of a scanning probe microscope usually depends on the operating mode of the probe, which can be roughly divided into two types: constant interaction mode and constant height mode.
Constant interaction mode
In constant interaction mode, the probe will continuously adjust its distance based on the parameters of the sample surface. Through a feedback loop, the probe can automatically move toward or away from the surface to maintain a certain level of interactivity. In this mode, the user can record the Z-axis position of the probe and form a topological image.
Constant height mode
Relatively speaking, the constant height mode is more complicated. In this mode, the probe does not move up and down, but rather records the values seen during the scan. This mode is more prone to "collapse" during operation than the constant interaction mode, where the probe directly hits the sample.
Types of probes and their effects
Different types of scanning probe microscopes are equipped with probes of different shapes and materials. The sharpness of these probes directly affects the resolution of the microscope. Sharper probes enable higher resolution, and ideally the tip of the probe should consist of only a single atom. Probe fabrication typically involves chemical etching and the selection of various materials, such as platinum-palladium alloys and tungsten.
Making probes sharper and more precise is a challenge, and for researchers it is key to achieving precise atomic resolution.
Advantages and challenges of scanning probe microscopy
The significant advantage of scanning probe microscopy is that it is not constrained by the diffraction limit and can make measurements with extremely small local interaction volumes. There is evidence that SPM can successfully measure small height changes such as those on the surface of silicon crystals, even height differences of 135 picometers. However, its scanning process is usually slow, which limits its imaging speed and affects the efficiency of experiments.
However, scanning probe microscopes also have their limitations. For example, the impact of probe shape on data is often difficult to grasp. The impact is particularly obvious when there are large undulations on the sample surface, which makes it difficult for SPM to obtain accurate data in some situations.
Future exploration: scanning photocurrent microscopy
With the continuous advancement of science and technology, scanning photocurrent microscopy (SPCM) is the new favorite of the scientific community. It uses a focused laser beam to detect the optoelectronic properties of materials. Compared with traditional SPM, SPCM can provide a new perspective for the analysis of optoelectronic materials.
SPCM generates photocurrent by exciting semiconductor materials. This process allows researchers to gain in-depth understanding of the electrical behavior of materials at different locations, allowing for a comprehensive evaluation of the material's optical properties.
Summary and reflection
The scanning probe microscope is undoubtedly a window that allows us to glimpse the mysteries of the microscopic world. Its development and application not only provide new tools for many scientific fields, but also enable our research scope and vision to continue to expand. While thinking about all this, can we imagine how these microscopic technologies will be explored and exploited in the future?
