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STM as used for Material Studies The study of materials is known as materials science. In current technology, all kinds of different materials are used for different purposes. The unique properties of a material are what make it interesting and useful. Some materials, for example, have electrical properties which make them useful for computers, in particular silicon (Si) which comes from collumn IV of the periodic table. Si is a type of material called a "semiconductor" and is used in almost all of modern day computer chips. But other types of "chips" are made using other semiconductor materials besides Si, for example chips used in cellular phones, which are made from compounds like GaAs. GaAs is composed of elements gallium (Ga) from column III and arsenic (As) from column V of the periodic table; the Ga and As atoms are arranged into a specific crystalline arrangement and become a III-V compound semiconductor. GaAs has certain advantages over Si for use in cell phones. It can be used for operation at higher frequencies than Si can, which allows data to be transferred more efficiently. Many other materials are also used for diverse applications like optical detectors, semiconductor lasers, and flat panel displays. STM is used in the study of these materials. As is often the case, making Si into a computer chip or GaAs into a cellular phone chip requires the formation of tiny structures with these materials. The STM, because it can image tiny structures with very high resolution, is used to study test structures made from these unique materials. The information obtained by the STM can be used by the people who make the chips or the materials in order to know what to do differently in order to make a better chip or material for a chip. For many devices made from semiconductors, thin layers are deposited onto what we call a "substrate." One use for the STM is to examine the top surface of these layers to see how smooth and uniform they are. After depositing layer upon layer of semiconductor onto the same substrate, we created a a sandwich-type structure. The top layer is like the bread of a roast beef sandwich and is easy to study. However, it is also important to examine the layers lying below, similar to the layers of roast beef. By breaking the sample in half, we can expose those layers in cross-section. Then we can use the STM to examine them by careful positioning of the STM tip into the region of the layers. Finally, we take STM images which show us how the different layers are stacked on top of each other and how smooth the interfaces between the layers are.