This article explains how and why X-ray diffraction analysis reveals the internal structure of objects and explores how this technique plays an important role in a variety of scientific fields, including materials science, biology, and chemistry. It highlights the impact that X-ray diffraction has had on scientific advances and its practical applications, and why it remains so important.
Glass doors are transparent, wooden doors are not. A plastic cup shatters when stepped on, but an aluminum can dents. Even if you make them the same size, thickness, or shape, the differences are still there, because glass and wood, plastic and aluminum are different. This difference refers to the different elements that make up the material, but more accurately, it refers to the internal structure of the object. The internal structure of an object affects its properties, strength, elasticity, electrical properties, and more. For example, the same metal can have different electrical properties due to differences in the internal structure of iron and copper, and materials composed of the same carbon, such as diamond and graphite, can have different internal structures. The internal structure, which describes how the particles that make up an object are connected to each other or arranged in a certain regularity, is a useful tool for explaining many properties of an object and is used in many fields of science.
But how do we know the internal structure? No matter how powerful a microscope is, it can’t see how the atoms in an aluminum can are arranged, so materials science uses a method called X-ray diffraction analysis. In a nutshell, X-ray diffraction is a method of determining the internal structure of an object from the light that bounces back when X-rays are shone at it. When there is a regular structure inside an object, the X-rays interact with that structure to create a special pattern. X-rays are not reflected from the inside of an object like a mirror, but rather scattered in different directions depending on how the atoms of the object are arranged, and the internal structure is revealed by analyzing the patterns created by these scattered X-rays interfering with each other.
To illustrate, think of a pinball game where you bounce a ball off a stick to score points. However, this game differs from a typical pinball game in a few ways. First of all, when you hit the ball from the top, you can decide which direction and at what angle to hit the ball. Also, instead of a stick at the bottom of the machine to bounce the ball back up, there are several holes for the ball to exit through. Finally, the machine is covered with a black cloth, so you can only see where you put the ball and the hole it comes out of, and you have no idea how the ball bounces and moves inside. Nevertheless, as you continue to play, you’ll discover a set of rules about what angle you put the ball in and what hole it comes out of. They can even predict how the ball would have to bounce under the black cloth for those rules to hold true. This process of inference is the core idea behind X-ray diffraction analysis. You shoot X-rays at an object from different angles and measure how much light bounces back. This is what X-ray diffraction analysis is all about: understanding how light travels inside an object and inferring its internal structure.
To go through the steps of X-ray diffraction analysis in order, you first need to shoot X-rays at an angle to the object. The technical term for this is irradiation. The X-rays meet and interact with the electrons in the atoms that make up the object, and as a result, the atoms radiate the X-rays that came to them back out in all directions. A detector is placed across from the X-ray laser to measure and record the intensity of the X-rays coming back from the object. In this process, some of the many X-rays from the laser will hit atoms on the outermost surface of the object, react with them, and return to the detector, while other lucky X-rays will go deeper, react with atoms inside the object, and return to the detector, traveling a greater distance than the X-rays that went only to the surface. If the difference in the distance traveled by the two X-rays is a multiple of the wavelength of the X-rays, the two X-rays will arrive at the detector in exactly the same shape, resulting in a stronger intensity of light. In scientific terms, this phenomenon is called enhanced interference, and when the difference in travel distance is a multiple of the X-ray wavelength, the intensity of the light is only measured strongly at a specific angle of irradiation because the internal structure of the object and the angle at which the X-rays are irradiated must satisfy a mathematical relationship. Therefore, by finding the angle at which the X-rays returned brightly and solving a complex formula, the internal structure of the object can be calculated backwards.
This process requires researchers to analyze a lot of data, and the results are used to model the internal structure of the object. The resulting structural model plays an important role in predicting and understanding the physical and chemical properties of a substance. For this reason, X-ray diffraction analysis has become an essential tool not only in materials science, but also in biology, chemistry, and many other fields. This principle makes X-ray diffraction a truly powerful weapon in crystallography, a branch of materials science. Before the discovery of X-ray diffraction, there was no way to determine the internal structure of a material other than by logical inference, such as “it must have the following structure to exhibit these properties.” But with X-ray diffraction, scientists were able to say with certainty, “Here’s what it looks like when you look at it.” With a new weapon in their arsenal, scientists used X-rays to obtain fundamental data in physics and chemistry, such as atomic structure and bond lengths, to analyze proteins, vitamins, and even DNA. X-ray diffraction also led to important scientific advances in fields as diverse as physics and materials science, as well as biology.
You might think that the discovery of X-rays in 1895 would have exhausted the possibilities for investigation, but X-ray diffraction is still used in many fields. It’s used in academic fields like analyzing the structure of new materials. More practical applications, such as drug discovery, measuring the fire safety of paints, or analyzing the concrete in the walls of nuclear power plants, are constantly being proposed in recent research. In addition, recent advances in technology have greatly improved the accuracy and speed of X-ray diffraction analysis, which is helping to identify new, previously unrecognized properties of materials and validate existing theories. Thanks to its simple and powerful role in observing the atomic-scale particles inside objects, X-ray diffraction is still recognized for its value more than 100 years after its inception, and its applications are endless.
