Applications

First, let's discuss the causes of low-frequency vibrations. Repeated tests have shown that low-frequency vibrations are primarily caused by the resonances of the building. The construction specifications for industrial and civil buildings are generally similar in terms of floor height, depth, span, beam and column sections, walls, floor beams, raft slabs, etc. Although there may be some differences, particularly regarding low-frequency resonances, common characteristics can be identified. Here are some patterns observed in building vibrations: 1. Buildings with linear or point-shaped floor plans tend to exhibit larger low-frequency resonances, while those with other shapes such as T, H, L, S, or U have smaller resonances. 2. In buildings with linear floor plans, vibrations along the long axis are often more pronounced than those along the short axis. 3. In the same building, the first floor without a basement typically experiences the smallest vibrations. As the floor height increases, the vibrations worsen. The vibrations in the first floor of a building with a basement are similar to those in the second floor, and the lowest vibrations are typically observed in the lowest level of the basement. 4. Vertical vibrations are generally larger than horizontal vibrations and are independent of the floor level. 5. Thicker floor slabs result in smaller differences between vertical and horizontal vibrations. In the majority of cases, vertical vibrations are larger than horizontal vibrations. 6. Unless there is a significant vibration source, vibrations within the same floor of a building are generally consistent. This applies to locations in the middle of a room as well as those near walls, columns, or overhead beams. However, even if measurements are taken at the same location without any movement and with a few minutes interval, the values are likely to differ. Now that we know the sources and characteristics of low-frequency vibrations, we can take targeted improvement measures and make advanced assessments of the vibration conditions in certain environments. Improving low-frequency vibrations can be costly, and sometimes it is not feasible due to environmental constraints. Thus, in practical applications, it is often advantageous to choose or relocate to a better site for operating an electron microscope laboratory. Next, let's discuss the impact of low-frequency vibrations and potential solutions. Vibrations below 20 Hz have a significant disruptive effect on electron microscopes, as depicted in the following figures.   Image 1   Image 2 Image 1 and Image 2 were taken by the same Scanning Electron Microscope (both at 300kx magnification). However, due to the presence of vibration interference, Image 1 has noticeable jaggedness in the horizontal direction (in segments), and the clarity and resolution of the image are significantly reduced. Image 2 is the result obtained from the same sample after eliminating the vibration interference...

The environment of an electron microscopy lab does not directly impact the electron microscope itself but rather affects the imaging quality and overall performance of the microscope. During the operation of an electron microscope, the fine electron beam needs to travel in a high vacuum environment, covering a distance of 0.7 meters (for Scanning Electron Microscope) to over 2 meters (for Transmission Electron Microscope). Along the path, external factors such as magnetic fields, ground vibrations, noise in the air, and airflows can cause the electron beam to deviate from its intended path, leading to a degradation in imaging quality. Therefore, specific requirements need to be met for the surrounding environment.   Passive low-frequency electromagnetic shielding primarily involves two methods, which differ in the shielding material used: one method uses high-permeability materials (such as steel, silicon steel, and mu-metal alloys), and the other method uses high-conductivity materials (such as copper and aluminum). Although the working principles of these two methods are different, they both achieve effective reduction of environmental magnetic fields.   A. The high-permeability material method, also known as the magnetic circuit diversion method, works by enclosing a finite space (Region A) with high-permeability materials. When the environmental magnetic field strength is Ho, the magnetic reluctance of the high-permeability material is much smaller than that of air (common Q195 steel has a permeability of 4000, silicon steel ranges from 8000 to 12000, mu-metal alloys have a permeability of 24000, while air has an approximate value of 1). Applying Ohm's law, when Rs is much smaller than Ro, the magnetic field strength within the enclosed space (Region A) decreases to Hi, achieving demagnetization (see Figure 1 and Figure 2, where Ri represents the air reluctance within space A, and Rs represents the shielding material reluctance). Inside the shielding material, the magnetic domains undergo vibration and dissipate magnetic energy as heat under the action of the magnetic field.   Since silicon steel and mu-metal alloys exhibit anisotropy in permeability and cannot be hammered, bent, or welded during construction (although theoretically, heat treatment can improve these properties, it is impractical for large fixed products), their effective performance is significantly reduced. However, they can still be used for supplementary or reinforcement purposes in certain special areas without hammering, bending, or welding.   High-permeability materials are expensive, so they are generally not extensively used in electron microscope shielding and are only seen in a few specific areas (such as door gaps, waveguide openings, etc.).   The effectiveness of the magnetic circuit diversion method is roughly linearly related to the thickness of the shielding material, which can theoretically be infinitely thin.   B. The high-conduc...

The environment of an electron microscopy lab does not directly impact the electron microscope itself but rather affects the imaging quality and overall performance. During the operation of an electron microscope, the fine electron beam needs to travel in a high vacuum environment, covering a distance of 0.7 meters (for Scanning Electron Microscope) to over 2 meters (for Transmission Electron Microscope). Along the path, external factors such as magnetic fields, ground vibrations, noise in the air, and airflows can cause the electron beam to deviate from its intended path, leading to a degradation in imaging quality. Therefore, specific requirements need to be met for the surrounding environment.   The Active Low-frequency Demagnetization System, mainly composed of a detector, controller, and demagnetization coil, is a specialized device used to mitigate low-frequency electromagnetic fields from 0.001Hz to 300Hz, referred to as a Demagnetizer.   Demagnetizers can be categorized into AC and DC types based on their working ranges, and some models combine both types to meet different working environments. The advantages of low-frequency demagnetizers include their small size, lightweight, space-saving design, and the ability to be installed post-construction. They are particularly suitable for environments where it is difficult to construct magnetic shielding, such as cleanrooms.   Regardless of the brand, the basic working principles of demagnetizers are the same. They use a three-axis detector to detect electromagnetic interference signals, dynamically control and output anti-phase currents through a PID controller, and generate anti-phase magnetic fields with three-dimensional demagnetization coils (typically three sets of six quasi-Helmholtz rectangular coils), effectively neutralizing and canceling the magnetic field in a specific area, reducing it to a lower intensity level.   The theoretical demagnetization accuracy of demagnetizers can reach 0.1m Gauss p-p, or 10 nT, and some models claim even better accuracy, but this is only achievable at the center of the detector and cannot be directly measured by other instruments due to mutual interference at close distances or the "Equipotential Surface" phenomenon at greater distances.   Demagnetizers automatically adjust the demagnetization current based on changes in the environment. At times, the current can be significant. It is important to pay attention to the wiring layout when other sensitive instruments are in close proximity to avoid interference with their normal operation. For example, electron beam exposure devices have been affected by nearby operating magnetic field detectors.   The power consumption of the demagnetizer controller is generally around 250W to 300W.   The detector of the demagnetizer can be a combination type or an AC/DC separate type, and there is no significant difference in performance. It is generally fixed in the mid...

The environment of an electron microscopy lab does not directly impact the electron microscope itself but rather affects the imaging quality and overall performance of the microscope. During the operation of an electron microscope, the fine electron beam needs to travel in a high vacuum environment, covering a distance of 0.7 meters (for Scanning Electron Microscope) to over 2 meters (for Transmission Electron Microscope). Along the path, external factors such as magnetic fields, ground vibrations, noise in the air, and airflows can cause the electron beam to deviate from its intended path, leading to a degradation in imaging quality. Therefore, specific requirements need to be met for the surrounding environment.   As is well known, electromagnetic waves consist of alternating magnetic and electric fields. However, it is important to consider the frequency when measuring electromagnetic waves using either magnetic or electric fields. In practice, it is necessary to take the frequency into account.   At very low frequencies (as the frequency tends to zero, equivalent to a DC magnetic field), the magnetic component of the electromagnetic wave becomes stronger while the electric component weakens. As the frequency increases, the electric component strengthens and the magnetic component decreases. This is a gradual transition without a distinct turning point. Generally, from zero to a few kilohertz, the magnetic field component can be well characterized, and units such as Gauss or Tesla are used to measure the field strength. Above 100 kHz, the electric field component is better measured, and the unit used for field strength is volts per meter (V/m). When dealing with a low-frequency electromagnetic environment with a strong magnetic field component, reducing the magnetic field directly is an effective approach.   Next, we will focus on the practical application of shielding a low-frequency (0-300 Hz), electromagnetic field with a magnetic field strength ranging from 0.5 to 50 milligauss (peak-to-peak) in a shielded volume of 40-120 cubic meters. Considering cost-effectiveness, the shielding material used is typically low-carbon steel plate Q195 (formerly known as A3).   Since the eddy current loss of a single thick material is greater than that of multiple thin layers (with the same total thickness), thicker single-layer materials are preferred unless there are specific requirements. Let's establish a mathematical model:   1. Derivation of the formula Since the energy of low-frequency electromagnetic waves is mainly composed of magnetic field energy, we can use high-permeability materials to provide magnetic bypass paths to reduce the magnetic flux density inside the shielding volume. By applying the analysis method of parallel shunt circuits, we can derive the calculation formula for the parallel shunting of magnetic flux paths. Here are some definitions: Ho: External magnetic field strength Hi: Magnetic field strength ins...

Diffraction Limit Diffraction spots Diffraction occurs when a point light source passes through a circular aperture, creating a diffraction pattern behind the aperture. This pattern consists of a series of concentric bright and dark rings known as Airy discs. When the Airy discs of two point sources overlap, interference occurs, making it impossible to distinguish between the two sources. The distance between the centers of the Airy discs, which is equal to the radius of the Airy disc, determines the diffraction limit.   The diffraction limit imposes a limitation on the resolution of optical microscopes, preventing the resolvable distinction of objects or details that are too close together. The shorter the wavelength of light, the smaller the diffraction limit and the higher the resolution. Moreover, optical systems with a larger numerical aperture (NA) have a smaller diffraction limit and thus higher resolution. Airy discs The formula for calculating resolution,  NA represents the numerical aperture: Resolution（r） = 0.16λ /  NA   Throughout history, scientists have embarked on a long and challenging journey to surpass the diffraction limit in optical microscopes. From early optical microscopes to modern super-resolution microscopy techniques, researchers have continuously explored and innovated. They have attempted various methods, such as using shorter wavelength light sources, improving the design of objectives, and employing specialized imaging techniques.   Some important breakthroughs include:   1. Near-field scanning optical microscopy (NSOM): NSOM uses a probe placed close to the sample surface to take advantage of the near-field effect and achieve high-resolution imaging.   2. Stimulated emission depletion microscopy (STED): STED utilizes the stimulated emission depletion effect of fluorescent molecules to achieve super-resolution imaging.   3. Structured illumination microscopy (SIM): SIM enhances imaging resolution through specific illumination patterns and image processing algorithms.   4. Single-molecule localization microscopy (SMLM): SMLM achieves super-resolution imaging by precisely localizing and tracking individual fluorescent molecules.   5. Oil immersion microscopy: Immersing the objective lens in a transparent oil increases the numerical aperture in the object space, resulting in improved resolution.   6. Electron microscope: By substituting electron beams for light beams, electron microscopy takes advantage of the wave nature of matter according to the de Broglie principle. Electrons, having mass compared to photons, possess a smaller wavelength and exhibit less diffraction, enabling higher imaging resolution.   Inverted fluorescence microscope     CIQTEK 120kV Field Emission Transmission Electron Microscope TH-F120 These developments have allowed us to observe the microscopic world at a highe...

Did you know that light can create sound? In the late 19th century, scientist Alexander Graham Bell (considered one of the inventors of the telephone) discovered the phenomenon of materials producing sound waves after absorbing light energy, known as the photoacoustic effect.   Alexander Graham Bell Image Source: Sina Technology   After the 1960s, with the development of weak signal detection technology, highly sensitive microphones and piezoelectric ceramic microphones appeared. Scientists developed a new spectroscopic analysis technique based on the photoacoustic effect - photoacoustic spectroscopy, which can be used to detect substances of samples and their spectroscopic thermal properties, becoming a powerful tool for physicochemical research in inorganic and organic compounds, semiconductors, metals, polymer materials, etc.     How can we make light create sound?As shown in the figure below, a light source modulated by a monochromator, or a pulsed light such as a pulsed laser, is incident on a photoacoustic cell. The material to be measured in the photoacoustic cell absorbs light energy, and the absorption rate varies with the wavelength of the incident light and the material. This is due to the different energy levels of the atomic molecules constituted in the different materials, and the absorption rate of light by the material increases when the frequency ν of the incident light is close to the energy level hν. The atomic molecules that jump to higher energy levels after absorbing light do not remain at the higher energy levels; instead, they tend to release energy and relax back to the lowest ground state, where the released energy often appears as thermal energy and causes the material to expand thermally and change in volume.When we restrict the volume of a material, for example, by packing it into a photoacoustic cell, its expansion leads to changes in pressure. After applying a periodic modulation to the intensity of the incident light, the temperature, volume, and pressure of the material also change periodically, resulting in a detectable mechanical wave. This oscillation can be detected by a sensitive microphone or piezoelectric ceramic microphone, which is what we call a photoacoustic signal.   Principle Schematic     How does a lock-in amplifier measure photoacoustic signals?   In summary, the photoacoustic signal is generated by a much smaller pressure signal converted from very small heat (released by atomic or molecular relaxation). The detection of such extremely weak signals necessarily cannot be done without lock-in amplifiers.   In photoacoustic spectroscopy, the signal collected from the microphone needs to be amplified by a preamplifier and then locked to the frequency signal we need by a lock-in amplifier. In this way, a high signal-to-noise ratio photoacoustic spectroscopy signal can be detected and the properties of the sample can be measured.   CIQTEK has launc...

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, enabling 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 must be considered to determine the best fit. Here are some considerations that can help you make a decision:   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, if you want to understand the crystal structure of a specimen, and detect structural defects or impurities, a Transmission Electron Microscope (TEM) may be more appropriate.   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 crystal or atomic struct...

What is antiferromagnetic material?   Figure 1: Magnetic Moment Arrangement in Antiferromagnets   The common iron properties are ferromagnetism, ferroelectricity, and ferroelasticity. Materials with two or more iron properties at the same time are called multiferroic materials. Multiferroics usually have strong iron coupling properties, i.e., one iron property of the material can modulate another iron property, such as using an applied electric field to modulate the ferroelectric properties of the material and thus affect the ferromagnetic properties of the material. Such multiferroic materials are expected to be the next generation of electronic spin devices. Among them, antiferromagnetic materials have been widely studied because they exhibit good robustness to the applied magnetic field.   Antiferromagnetism is a magnetic property of a material in which the magnetic moments are arranged in an antiparallel staggered order and do not exhibit a macroscopic net magnetic moment. This magnetically ordered state is called antiferromagnetism. Inside an antiferromagnetic material, the spins of adjacent valence electrons tend to be in opposite directions and no magnetic field is generated. Antiferromagnetic materials are relatively uncommon, and most of them exist only at low temperatures, such as ferrous oxide, ferromanganese alloys, nickel alloys, rare earth alloys, rare earth borides, etc. However, there are also antiferromagnetic materials at room temperature, such as BiFeO3, which is currently under hot research.   Application Prospects of Antiferromagnetic Materials The knowledge of antiferromagnetism is mainly due to the development of neutron scattering technology so that we can "see" the arrangement of spins in materials and thus confirm the existence of antiferromagnetism. Maybe the Nobel Prize in physics inspired researchers to focus on antiferromagnetic materials, and the value of antiferromagnetism was gradually explored.   Antiferromagnetic materials are less susceptible to ionization and magnetic field interference and have eigenfrequencies and state transition frequencies several orders of magnitude higher than typical ferromagnetic materials. Antiferromagnetic ordering in semiconductors is more readily observed than ferromagnetic ordering. These advantages make antiferromagnetic materials an attractive material for spintronics.   The new generation of magnetic random access memory uses electrical methods to write and read information to ferromagnets, which may reduce the immunity of ferromagnets and is not conducive to stable data storage, and the stray fields of ferromagnetic materials can be a significant obstacle for highly integrated memories. In contrast, antiferromagnets have zero net magnetization, do not generate stray fields, and are insensitive to external fields. Therefore, antiferromagnet-based memory perfectly solves the problem of ferromagnetic memory and becomes a very attractive potential me...