The reason light can't see inside atoms is related to the wavelength of light compared to the size of an atom. This is described by the diffraction limit, which is often expressed using the Rayleigh criterion: θ = 1.22 * (λ / D) Where: * θ (theta) is the [[Minimum resolvable angle]] * λ (lambda) is the wavelength of light * D is the diameter of the aperture of the optical system For visible light: * Wavelength (λ) ranges from about 380 to 700 nanometers (nm) * A typical atom has a diameter of about 0.1 to 0.5 nm The size of an atom is much smaller than the wavelength of visible light. This means that even with a perfect optical system (microscope), the wavelength of light itself prevents us from resolving structures smaller than about half its wavelength. We can also consider the Abbe diffraction limit, which gives the minimum resolvable distance: d = λ / (2n * sin(α)) Where: * d is the minimum resolvable distance * n is the refractive index of the medium * α (alpha) is the half-angle of the maximum cone of light that can enter the lens Even with optimal conditions, this equation shows that we can't resolve features much smaller than about half the wavelength of the light used. Since atoms are much smaller than the wavelength of visible light, the internal structures of atoms cannot be resolved using visible light microscopy. This fundamental limit is why we need to use other techniques, such as electron microscopy or X-ray crystallography, which use much shorter wavelengths, to study atomic and subatomic structures. ## How it is overcome In Scanning Electron Microscopy (SEM), the fundamental limitations of visible light are overcome by using electrons instead of photons. Here's how SEM achieves much higher resolution: 1. Electron wavelength: The de Broglie wavelength of electrons is much shorter than that of visible light. In SEM, electrons are typically accelerated to energies between 1-30 keV, resulting in wavelengths on the order of 0.01-0.12 nm. This is much smaller than the wavelength of visible light (380-700 nm) and even smaller than the size of atoms (0.1-0.5 nm). 2. Focused electron beam: SEM uses electromagnetic lenses to focus the electron beam into a very small spot (typically 1-10 nm in diameter) on the sample surface. 3. Scanning mechanism: The electron beam is scanned across the sample surface in a raster pattern, building up an image point by point. 4. Signal detection: As the electron beam interacts with the sample, it produces various signals (secondary electrons, backscattered electrons, X-rays) that are collected by specialized detectors. 5. Image formation: The detected signals are used to form a high-resolution image of the sample surface, with magnifications typically ranging from 10x to 300,000x or more. 6. Resolution: Modern SEMs can achieve resolutions better than 1 nm, allowing for detailed imaging of nanoscale structures and even large individual atoms under certain conditions. By using electrons instead of light, SEM bypasses the diffraction limit that constrains visible light microscopy, enabling the visualization of structures at the nanoscale and providing valuable information about the morphology, composition, and other properties of materials at extremely high magnifications. <hr/> <!-- Your main content goes here --> <div class="footer"> Carbonatik © 2024 </div>