Electron microscope images open a window to an invisible world, operating on a scale beyond the reach of conventional light microscopes. These instruments provide a level of detail that transforms our understanding of biology, materials science, and chemistry. The images they produce reveal the intricate architecture of the smallest components of our world, from the machinery inside a single cell to the atomic structure of a metal.
Creating Images with Electrons
The magnification of an electron microscope is possible because it uses a beam of electrons instead of visible light to create an image. Electrons have a much shorter wavelength than photons (the particles of light), which allows for significantly higher resolution and the ability to see much smaller objects. This fundamental difference is what allows electron microscopes to magnify objects up to several million times, revealing details at the nanometer scale. The entire process occurs inside a vacuum, as air molecules would otherwise interfere with the electron beam.
There are two primary types of electron microscopes. A Scanning Electron Microscope (SEM) scans a focused electron beam across the surface of a specimen. The electrons interact with the surface atoms, and detectors collect the resulting secondary or backscattered electrons to form an image. This process generates a detailed, three-dimensional-like view of the sample’s surface topography.
A Transmission Electron Microscope (TEM) provides a look inside the object. For a TEM to work, the specimen must be sliced into an extremely thin section, often less than 100 nanometers. A broad beam of high-energy electrons is passed through this thin slice. As the electrons travel through, they are scattered by the internal structures, and the resulting pattern is projected onto a detector, creating a flat, two-dimensional image akin to an X-ray of the specimen’s inner workings.
Interpreting Image Appearance
Electron microscope images are in black and white. This is because the microscopes use electrons, not light, to generate the image, and electrons do not possess color properties that our eyes can perceive. The resulting image is a map of electron intensity; areas where many electrons are detected appear bright, while areas where fewer electrons are detected appear dark.
To make these images easier to interpret and to highlight specific features, scientists often add “false color.” This colorization is done with image-editing software after the initial image is captured. Scientists assign colors to different shades of gray to distinguish various components, such as coloring the nucleus of a cell blue and its membrane green. Note that these colors are artificially added for clarity or aesthetic appeal and do not represent the actual color of the subject.
A Gallery of the Microscopic World
An image of a virus, for instance, moves beyond a simple sphere and shows the intricate geometric protein shell that houses its genetic material. It allows scientists to visualize the very machinery the virus uses to infect a cell. These details are foundational for developing targeted treatments and vaccines.
The fly’s compound eye, which appears as a simple red dot to the naked eye, is revealed to be an ordered, honeycomb-like array of thousands of individual lenses. Each lens captures a sliver of the world, contributing to the insect’s panoramic vision. The images also show fine hairs between the lenses, which help detect changes in air currents.
An image of red blood cells discards their simple dot-like appearance and displays their distinct biconcave, or flattened donut, shape. This structure maximizes the surface area for oxygen exchange and provides the flexibility needed to squeeze through narrow capillaries. SEM images can even capture the effects of diseases, showing how sickle cell anemia distorts this shape.
The tip of a steel needle, which feels perfectly sharp to the touch, appears under an electron microscope as a rounded and textured landscape. The microscopic view reveals the grain of the metal and the imperfections left behind by the manufacturing process, offering insights into material strength and durability at a fundamental level.