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A new era in microscopy: How is the scientific miracle of atomic-scale imaging achieved?
Since the advent of the scanning tunneling microscope (STM) in 1981, scanning probe microscopy (SPM) has become a cutting-edge technology for studying surface structures. This technique was first demonstrated by Gerd Binnig and Heinrich Rohrer, who used a feedback loop to precisely control the distance between the probe and the sample, thus enabling atomic-scale imaging. With the evolution of technology, today's SPM can not only obtain high-resolution images of surface structures, but also simultaneously image multiple physical interactions, providing scientists with a new perspective to explore the microscopic world.
The key to scanning probe microscopy is the use of piezoelectric actuators to control precise motion at the atomic level.
The diversity of scanning probe microscopy lies in the many technologies it has derived, including atomic force microscopy (AFM), chemical force microscopy (CFM), electrostatic force microscopy (EFM), scanning tunneling microscopy (STM), etc. Each technology has its unique advantages and application areas. For example, AFM uses tiny movements of a probe to measure forces on a sample's surface, creating a high-resolution image of the surface topography.
Different scanning modes such as constant interaction mode and constant height mode allow scientists to obtain detailed information about the sample in different ways.
In constant interaction mode, the probe maintains a constant interaction with the sample surface, and the measured data is converted into a thermal map showing the topography of the sample surface. In constant height mode, the sample surface is scanned without moving the probe. Although the constant height mode can eliminate artifacts caused by feedback, its operation is relatively difficult and requires extremely high control of the probe.
In order to achieve atomic-level resolution, the design and material of the probe are also crucial. Typically, the very tip of the probe must be very sharp for single-atom tip probes to provide the best imaging results. This involves not only the manufacturing technology of the probe, but also a deep understanding of material selection.
Current scanning probe microscopy resolution is limited by the probe-sample interaction volume rather than the diffraction limit.
The advantage of scanning probe microscopy is that it does not require a vacuum environment to operate, allowing observations to be made in conventional air or liquids. But at the same time, this technology also faces some challenges, such as slow image acquisition speed and the impact of the specific shape of the probe on the data when the sample has large height changes.
A related technique is scanning photocurrent microscopy (SPCM), which uses a focused laser beam rather than a probe to enable spatially resolved testing of materials. This technique is particularly important in the optoelectronics industry because it allows analysis of how the optical properties of a material vary with position.
SPCM excites semiconductor materials through lasers to generate photocurrent, and scans at different positions to obtain a map of optoelectronic properties.
Researchers using SPCM can analyze information such as the material's defect dynamics, minority carrier diffusion length, and electric field, which can help further improve the material's optical properties.
With the advancement of computer technology, modern SPM systems usually rely on advanced visualization and analysis software to generate images. In this process, image rendering software becomes indispensable, and different software packages such as Gwyddion and SPIP are widely used in the processing and analysis of SPM data.
With the continuous advancement of technology, the application scope of scanning probe microscopes has continued to expand. It is not only limited to basic material science research, but also widely used in biology, chemistry, nanotechnology and other fields. These technologies allow scientists to explore the microscopic world from a whole new perspective and achieve more precise observations.
In exploring the endless microscopic world, we have only peeled off a thin layer of science. What unnoticed miracles will be revealed in the future?
