In this blog post, we will examine the principles behind X-ray diffraction analysis and how it contributes to scientific advancement by revealing the internal structure of objects.
Glass doors are transparent, but wooden doors are not. Plastic cups break when stepped on, but aluminum cans dent. Even if you make them the same size, thickness, and shape, the differences remain because glass, wood, plastic, and aluminum are different. This difference not only means that the constituent elements are different but more accurately indicates that the internal structures of the objects are different. Internal structure affects various aspects of an object, such as its properties, strength, elasticity, and electrical properties. For example, even though iron and copper are both metals, their internal structures differ, resulting in different electrical conductivity. Similarly, diamond and graphite, which are composed of the same carbon atoms, appear as entirely different materials due to their differing internal structures. The internal structure, which describes how the particles that make up an object are connected or arranged in a regular pattern, serves as a useful tool for explaining numerous properties of objects and is widely utilized in various scientific fields.
So, how can we determine internal structure? Even with the most advanced microscopes, we cannot see how atoms are arranged inside an aluminum can. Therefore, materials engineering uses a method called X-ray diffraction analysis. X-ray diffraction analysis involves shooting X-rays at an object and analyzing the light that bounces back to determine the object’s internal structure. When there is a regular structure inside an object, X-rays interact with that structure to create a unique pattern. In this process, X-rays do not reflect off the object like a mirror but scatter in various directions depending on how the atoms are arranged. By analyzing the patterns created by the interference of these scattered X-rays, we can determine the internal structure.
To help you understand, think of a pinball game where you score points by hitting a ball with a stick. However, this game is different from a typical pinball game in several ways. First, when you put the ball in at the top, you can decide which direction and angle to hit it. Also, instead of a stick at the bottom of the machine to hit the ball back up, there are several holes through which the ball can escape. Finally, the machine is covered with a black cloth, so the player can only see where the ball is inserted and where it comes out, and cannot see how it bounces and moves inside. Nevertheless, as the game progresses, the player can discover a series of rules regarding which hole the ball will exit when inserted at a certain angle. Furthermore, they can predict how the ball must bounce under the black cloth for the rules to work. This process of inference is the core concept of X-ray diffraction analysis. X-rays are fired at an object from various angles, and the amount of light that returns is measured. The task of inferring how the light moved inside the object and the internal structure of the object is called X-ray diffraction analysis.
When examining X-ray diffraction analysis step by step, first, X-rays must be directed at an angle toward the object. This process of firing X-rays is referred to as “irradiation” in technical terms. The irradiated X-rays interact with the electrons within the atoms that make up the object, causing the atoms to re-emit the X-rays in all directions. A detector is placed opposite the X-ray laser to measure and record the intensity of the X-rays returning from the object. During this process, some of the numerous X-rays emitted from the laser collide with the atoms on the outermost surface of the object and return to the detector, while other X-rays penetrate deeper into the object, interact with atoms inside the object, and return to the detector. The X-rays that penetrated deeper travel a longer distance than those that only reached the surface. If the difference in the distances traveled by these two X-rays is an integer multiple of the X-ray wavelength, the two X-rays arrive at the detector in exactly the same shape, causing the intensity of the light to increase. This phenomenon is known as constructive interference in scientific terms. For constructive interference to occur, the difference in travel distance must be an integer multiple of the X-ray wavelength, which requires the object’s internal structure and the angle at which the X-rays are incident to satisfy a mathematical relationship. Therefore, the intensity of light is measured most strongly at specific angles. By determining the angles at which X-rays return brightly and solving complex equations, the internal structure of the object can be calculated in reverse.
In this process, researchers must analyze a large amount of data and use the results to model the internal structure of the object. The structural model obtained in this way plays an important role in predicting and understanding the physical and chemical properties of the material. For this reason, X-ray diffraction analysis has become an essential tool in various fields, including materials engineering, biology, and chemistry. X-ray diffraction analysis, which works on the same principle, can be considered a powerful tool in crystallography, a field of materials science. Before the discovery of X-ray diffraction analysis, there was no way to determine the internal structure other than logically inferring that ‘to exhibit such properties, it must have the following structure’.” However, with the advent of X-ray diffraction analysis, scientists gained the confidence to say, “Upon closer inspection, this is what it looks like.” Armed with this new tool, scientists began using X-rays to obtain fundamental data required in physics and chemistry, such as atomic structure and bond lengths, and eventually expanded its application to the analysis of proteins, vitamins, and even DNA. Additionally, X-ray diffraction analysis has driven significant academic advancements not only in physics and materials science but also in fields such as biology.
Although X-rays were discovered in 1895, it might seem that everything worth investigating has already been done, but X-ray diffraction analysis is still widely used today. It is used not only in academic fields such as new material structure analysis but also in practical applications. More practical applications, such as new drug development, fire safety testing of coatings, and analysis of concrete walls in nuclear power plants, have been consistently proposed in recent research. Furthermore, with the advancement of the latest technology, the accuracy and speed of X-ray diffraction analysis have greatly improved, enabling the identification of new material properties that were previously unknown and the verification of existing theories. Thanks to its simple yet powerful ability to observe atomic-level particles within objects, X-ray diffraction analysis remains highly valued despite being over 100 years old, and its potential applications are virtually limitless.
