Applications

What is the Recrystallization Process?   Recrystallization is an important phenomenon in materials science that involves the microstructural recovery of material after plastic deformation. This process is crucial for understanding material properties and optimizing processing techniques.   Mechanisms and Classification of Recrystallization   Recrystallization processes are typically triggered by heat treatment or thermal deformation and involve the natural recovery of materials after the generation of defects during deformation. Defects such as dislocations and grain boundaries promote the reduction of system-free energy at high temperatures through dislocation rearrangement and annihilation, leading to the formation of new grain structures. Recrystallization can be classified into static recrystallization (SRX) and dynamic recrystallization (DRX). SRX occurs during annealing processes, while DRX takes place during thermal deformation. Furthermore, recrystallization can be further subdivided based on specific mechanisms, such as continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX), geometric dynamic recrystallization (GDRX), and metadynamic recrystallization (MDRX). These classifications are not strictly defined, and researchers may have different interpretations.   Factors influencing recrystallization   The recrystallization process is influenced by various factors, including the stacking fault energy (γSFE), initial grain size, thermal processing conditions, and second-phase particles. The magnitude of the stacking fault energy determines the dislocation breakdown and mobility, thereby affecting the recrystallization rate. Smaller initial grain sizes and suitable thermal processing conditions, such as high temperature and low strain rates, facilitate recrystallization. Second-phase particles can significantly influence the recrystallization process by hindering grain boundary motion.   Application of imaging techniques   EBSD and TEM are two classic imaging techniques used in recrystallization studies. EBSD analyzes the distribution and percentage of recrystallized grains using the DefRex map, although resolution limitations may pose accuracy issues. TEM, on the other hand, provides a direct observation of material substructures, such as dislocations, offering a more intuitive perspective for recrystallization studies.   Application of EBSD in recrystallization studies   EBSD is used to determine whether grains have undergone recrystallization by observing grain boundaries. For example, in the DefRex maps of forged TNM alloys, grains surrounded by high-angle boundaries are typically considered recrystallized grains. This technique provides detailed information about grain orientations and grain boundary types, aiding in the understanding of microstructural changes during recrystallization.   BC+GB (grain boundary) map of forged TiAl alloy  ...

Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM) are indispensable tools in modern scientific research. Compared to optical microscopes, electron microscopes offer higher resolution, allowing for the observation and study of specimens' microstructure at a smaller scale.   Electron microscopes can provide high-resolution and high-magnification images by utilizing the interactions between an electron beam and a specimen. This enables researchers to obtain critical information that may be difficult to obtain through other methods.   Which microscope is more suitable for you?   When choosing the appropriate electron microscopy technique for your needs, various factors need to be considered to determine the best fit. Here are some considerations that can help you make a decision:     Field Emission TEM | TH-F120 Analysis Purpose: First, it is important to determine your analysis purpose. Different electron microscopy techniques are suitable for different types of analysis. a. If you are interested in surface features of a specimen, such as roughness or contamination detection, a Scanning Electron Microscope (SEM) may be more suitable. b. However, a transmission electron microscope (TEM) may be more appropriate if you want to understand the crystal structure of a specimen or detect structural defects or impurities.   Resolution Requirements: Depending on your analysis requirements, you may have specific resolution needs. In this regard, TEM generally has a higher resolution capability compared to SEM. If you need to perform high-resolution imaging, especially for observing fine structures, TEM may be more suitable.   Specimen Preparation: An important consideration is the complexity of specimen preparation. a. SEM specimens typically require minimal or no preparation, and SEM allows for more flexibility in specimen size, as they can be directly mounted on the specimen stage for imaging. b. In contrast, the specimen preparation process for TEM is much more complex and requires experienced engineers to operate. TEM specimens must be extremely thin, typically below 150 nm, or even lower than 30 nm, and as flat as possible. This means that TEM specimen preparation may require more time and expertise.   Type of Images: SEM provides detailed three-dimensional images of the specimen surface, while TEM provides two-dimensional projection images of the internal structure of the specimen. a. Scanning Electron Microscope (SEM) provides three-dimensional images of the surface morphology of the specimen. It is mainly used for morphology analysis. If you need to examine the surface morphology of a material, SEM can be used, but you need to consider the resolution to see if it meets your experimental requirements. b. If you need to understand the internal crys...

Since the discovery of the classic double helix structure of DNA by Watson and Crick in the 1950s, DNA has become the core of life science research. The number and arrangement of the four bases in DNA lead to genetic diversity, and its spatial structure affects gene expression.   In addition to the traditional DNA double helix structure, a special four-stranded DNA structure called G-quadruplex has been discovered in human cells. G-quadruplex is a higher-order structure formed by the folding of DNA or RNA rich in tandem repeats of guanine (G). G-quadruplexes are highly abundant in rapidly dividing cells, such as cancer cells. Therefore, G-quadruplexes can serve as drug targets in cancer research. Investigating the structure of G-quadruplexes and their binding modes with ligands is of great significance for the diagnosis and treatment of cancer cells.   Electron-electron Double resonance (DEER)   Electron-electron double resonance (DEER) using pulsed dipolar electron paramagnetic resonance (PDEPR) has been developed as a reliable and versatile tool for structure determination in structural and chemical biology. DEER combined with site-directed spin labeling (SDSL) techniques can provide distance information at the nanoscale. In the study of G-quadruplex structures, DEER technology combined with SDSL can differentiate different lengths of G-quadruplex dimers and reveal the binding modes of G-quadruplex ligands with dimers.   PDEPR techniques can distinguish different lengths of G-quadruplex dimers.   The spin-label used for distance measurements in DEER experiments is Cu(pyridine)4. The Cu(pyridine)4 complex is covalently bound to G-quadruplexes, and the dipole-dipole interactions between two paramagnetic Cu2+ ions in the π-stacked G-quartet monomers can be measured. This allows for the study of dimer formation.   [Cu2+@A4] (TTLGGG) and [Cu2+@B4] (TLGGGG) are two oligonucleotides with different sequences. Figure 1 and Figure 2 show the DEER experimental results of [Cu2+@A4]2 and [Cu2+@B4]2, respectively. From the DEER results, the average distance between individual Cu2+-Cu2+ ions in [Cu2+@A4]2 dimer is dA = 2.55 nm. The G-quadruplexes at the 3' ends of the G-quartets form G-quadruplex dimers through tail-to-tail stacking, and the gz axes of the two Cu2+ spin labels in the G-quadruplex dimer are arranged in parallel.   Compared to the [Cu2+@A4]2 dimers, the π-stacking distance in [Cu2+@B4]2 is longer (dB-dA = 0.66 nm), confirming the presence of an additional G-quartet in each [Cu2+@B4] monomer, which is consistent with the expected distance. Therefore, DEER measurements can differentiate different lengths of G-quadruplex dimers.   Figure 1 (A) Pulsed EPR spectrum (black line) of the [Cu2+@A4]2 dimer and its corresponding simulation (red line) (34 GHz, 19 K); (B) Background-corrected DEER time-domain traces (black line) at four field positions (a-d) and the b...

The Scanning Electron Microscope (SEM) is an important tool for observing micro-scale morphology and is widely used in fields such as materials science, biology, and environmental science. With the continuous development of technology, the Field Emission Scanning Electron Microscope (FESEM) has emerged. Compared to traditional SEM, FESEM offers advantages such as higher resolution, greater depth of field, and stronger signal stability. This article will provide a detailed introduction to the principles, characteristics, and advantages of FESEM compared to SEM.   Principles of Field Emission Scanning Electron Microscope (FESEM):   1. Electron Source: FESEM uses a field emission electron source instead of the concurrent electron source used in SEM. The field emission electron source has higher electron beam density and better-focusing performance, resulting in higher resolution.   2. Electron Optics System: FESEM employs advanced electron optics systems, including electromagnetic lenses and electrostatic lenses, to achieve higher imaging quality and stronger signal stability.   3. Sample Preparation: Sample preparation for FESEM is relatively simple, requiring only mild surface treatment to ensure conductivity.   4. Signal Detection: FESEM utilizes multiple signal detection methods, such as secondary and back-scattered electrons, to obtain rich sample information.   Characteristics of Field Emission Scanning Electron Microscope (FESEM):   1. High Resolution: FESEM, with its field emission electron source and advanced electron optics system, offers higher resolution, enabling the observation of finer sample structures.   2. Large Depth of Field: FESEM has a larger depth of field, maintaining good imaging quality during observations and facilitating the observation of three-dimensional sample structures.   3. Strong Signal Stability: FESEM exhibits strong signal stability, ensuring stable imaging over long observation periods.   4. Simple Sample Preparation: Sample preparation for FESEM is relatively simple, reducing the difficulty and cost of sample preparation.   5. Multiple Signal Detection: FESEM can utilize various signal detection methods, providing abundant sample information and offering more evidence for analysis and research.   Advantages of Field Emission Scanning Electron Microscope (FESEM) over SEM:   1. Improved Resolution: FESEM offers higher resolution, allowing for the observation of finer sample structures and expanding the applications of micro-scale observations.   2. Increased Depth of Field: FESEM has a larger depth of field, facilitating the observation of three-dimensional sample structures and providing more realistic observation results.   3. Stronger Signal Stability: FESEM exhibits stronger signal stability, reducing errors during observations and improving imaging quality.   4. Simplified Sample Preparat...

Humans rely on their senses to perceive the world, and these microscopic analysis instruments extend human perception. We are all familiar with optical microscopes, but these microscopes, which work based on lens imaging, are limited by the Abbe limit, where the resolution is limited to half the wavelength of the light used.   Therefore, the resolution of optical microscopes is only at the micrometer level due to the limitation of the wavelength of light. However, fast-moving electrons have wave-particle duality, and as a wave, an important characteristic of electrons is their wavelength.   With increasing acceleration voltage, the electron wavelength decreases. By using higher acceleration voltages, such as 30 kV, it is possible to obtain electrons with a wavelength of approximately 7 pm. Electron microscopes are created by using electrons as the "light" and substituting magnetic lenses for conventional optical lenses.   When electrons interact with a solid specimen, they produce a series of specimen-related information, including induced electromotive force, cathodoluminescence, characteristic X-rays, back-scattered electrons, Auger electrons, secondary electrons, absorbed electrons, transmitted electrons, etc. By utilizing this information, it is possible to obtain structural information at the microscopic scale.   The differences between SEM and TEM   Source Image from Nanoscience Instrument  SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscope) are two common forms of electron microscopes. SEM uses Secondary Electrons (SE) and Back-scattered Electrons (BSE) to capture images of the specimen surface, while TEM detects transmitted electrons to generate projection images through the specimen's interior.   SEM scans the specimen surface with a focused electron beam and collects the signals generated at each point to construct an amplified image pixel by pixel. The scanning coil located below the objective lens guides the beam precisely through the specimen's surface in the X-Y plane. Depending on the magnification (up to 2 million times), the beam scans a field of view ranging from a few micrometers to millimeters.   Typical acceleration voltages for SEM range from 1 kV to 30 kV. Lower acceleration voltages provide a gentler beam, which is useful for imaging beam-sensitive and insulating specimens. Secondary electrons are less sensitive to atomic numbers and more suitable for observing surface topography. In contrast, backscattered electrons yield higher signals for specimens with larger atomic numbers, making them suitable for compositional imaging.   TEM typically operates at acceleration voltages between 30 kV and 300 kV, which is much higher than the voltages used in SEM instruments, allowing for higher-resolution images. Corrected aberration TEMs can achieve spatial resolutions below 1Å, enabling the observation of very fine details...

The principle of a Scanning Electron Microscope (SEM) involves the emission of an electron beam from an electron gun, which is accelerated by an electric field.    The electron beam scans the specimen surface line by line, exciting the specimen to produce various physical signals. These signals are collected by detectors and converted into video signals in sequential and proportional order.   By detecting a specific signal, amplifying the video signal, and signal processing, a scanning image reflecting the surface features of the specimen is obtained on the display screen.   Common Issues:   1. Does the magnetic nature of a specimen affect SEM testing?   a. Magnetic Field Interference: The electron beam in SEM is focused by electromagnetic lenses. Magnetic elements in the specimen may generate a magnetic field that interferes with the path of the electron beam, resulting in image distortion or reduced resolution.   b. Signal Detection: SEM forms images by detecting Secondary Electrons, Back-Scattered Electrons, and other signals resulting from the interaction between electrons and the specimen. If the specimen contains magnetic elements, these elements may affect electron scattering and detection, which can impact the image quality and accuracy of the compositional analysis.   c. Specimen Preparation: specimens containing magnetic elements may present challenges during preparation, as these elements may adhere to other magnetic surfaces. Therefore, special specimen preparation techniques may be required to ensure specimen stability and representativeness.   d. Compositional Analysis: During Energy Dispersive Spectrometer (EDS) analysis, if the specimen contains magnetic elements, their magnetic fields may alter the path of X-rays, potentially affecting the detection of X-rays.   e. Heating Effects: In certain cases, the interaction between the electron beam and the specimen may generate heat. If the specimen contains magnetic elements, this heating may cause local magnetic changes in the specimen, which can affect the results of SEM analysis.   2. What are the effects of radioactive specimens on SEM testing?   a. Specimen Stability: Radioactive decay processes can cause changes in the structure of the specimen, affecting the stability and reproducibility of the analysis results.   b. Specimen Heating: Radioactive decay may generate heat, leading to localized or overall heating of the specimen, which can influence the microstructure of the specimen and the interaction with the electron beam.   c. Signal Interference: Radioactive specimens may emit alpha particles, beta particles, or gamma rays, which can interfere with the detectors in SEM, resulting in increased image noise and degraded imaging quality. &n...

With the widespread use of gamma rays in industries, agriculture, medicine, and food, accurate measurement of radiation dose has become increasingly important. EPR Spectrometer is currently the only direct method to detect unpaired electrons in a sample, allowing for the precise measurement of radiation dose by detecting the free radicals generated in the irradiated material.   The radiation dose can be categorized into low dose (less than 1 kGy), medium dose (1-10 kGy), and high dose (greater than 10 kGy), and its effects can range from no clinical symptoms to severe symptoms, early fatal clinical symptoms, and early death.   After decades of research, various chemical, physical, and biological methods have been developed for radiation dose measurement, including multi-modal products with photoacoustic indicators. With the development of molecular biology, it has been recognized that certain biological molecules, such as chromosomes, are sensitive to radiation and can be used to measure the radiation dose. However, at high radiation doses, the inactivation of biological molecules can hinder the detection process, and biological dosimeters based on this principle require longer sample processing and analysis times.   When a material is irradiated by various radiation or neutrons, it generates free radicals. Therefore, using Electron Paramagnetic Resonance (EPR) spectroscopy to detect the free radicals generated in the irradiated material is a direct and convenient method. Dose meters designed based on EPR for this purpose are called EPR dosimeters, which have unique advantages compared to other dosimeters:        High sensitivity to detect clinically significant dose levels      Provides highly specific and reliable data with sufficient accuracy      Wide range of coverage suitable for fast detection      Can work in various environments      Non-invasive and non-destructive to the sample      Specialized instruments that are easy to operate   Case 1: Food Irradiation Testing Food irradiation is the process of using radiation to delay certain physiological processes (such as sprouting and ripening) in fresh food or to treat food for purposes such as insect control, disinfection, sterilization, and mold prevention, thereby extending its shelf life and stabilizing and improving its quality.   Various foods, including meats, bones, fruits, dried fruits, and food, produce detectable EPR signals of free radicals when irradiated. The intensity of the free radical signal is related to the nature of the various materials and processing methods, particularly the radiation dose. EPR technology is the most direct method for detecting free radicals.   Figure 1 shows the EPR spectra of a certain brand of powdered milk before and after irradiation, with radiation doses of 0 kGy, 2.0 kGy, 4.0 kGy, 6.0 kGy, and 8.0 kGy. It can be...

Temperature The temperature requirements for Electron Microscopes are not particularly high. Typically, temperatures around 26 degrees Celsius in summer and 20 degrees Celsius in winter are acceptable for comfort and energy efficiency. However, the temperature change rate is important, with common requirements being ≤0.5°C/3 minutes or ≤0.5°C/5 minutes.   Good-quality central air conditioning systems can usually meet these requirements. For example, a well-known brand of split air conditioner has a four-minute cycle with temperature fluctuations of around 1 degree Celsius. Using precision air conditioning systems usually doesn't offer significant benefits in terms of price, maintenance costs, and applicability.   In practice, High-precision Electron Microscopes tend to be bulky and have larger heat capacities. As long as the temperature variation inside the room is not significant, minor fluctuations within a short period are unlikely to have a noticeable impact.   It's important to avoid excessively low temperatures in the electron microscope room to prevent condensation and dripping water on cooling water pipes, liquid nitrogen pipes, and Dewar flasks. For example, there was a case where an improperly placed old-fashioned spectroscopic circuit board under a liquid nitrogen Dewar flask got damaged due to condensation dripping.   Regarding auxiliary equipment rooms, such as those housing circulation cooling water tanks, air compressors, uninterrupted power supply (UPS) units, and vacuum pumps, it's necessary to calculate the required capacity of the air conditioning system based on the heat dissipation provided in the equipment specifications.   If the temperature in the auxiliary equipment room is too high, it can reduce the cooling efficiency of the circulation cooling water tank and increase the thermal drift of lenses.   Therefore, it is recommended to keep the temperature in the auxiliary equipment room below 35 degrees Celsius throughout the year.   Humidity Frozen samples have high humidity requirements, and some users prefer a relative humidity below 25%. However, extremely low humidity can lead to electrostatic discharge. To address this, the freeze-fracture preparation machine can be moved closer to the Electron Microscope to minimize the exposure time of frozen samples, thereby reducing the humidity requirements.   Usually, relative humidity of below 65% is sufficient for the electron microscope room, which is a relatively low requirement that most air conditioning systems can easily meet (assuming the room door is kept closed and the time for personnel entry and exit is minimized).   If it is a newly constructed building within a year, it may take some time to eliminate the building's moisture. In such cases, a dehumidifier can be added to regulate the humidity.   Airflow Another consideration is the airflow from the air conditioning system. In most cases, as lo...