Surface State
Surface state, in physics, refers to the surface electrons of a material which have been atomically modified during preparation of the surface to create a region of electric conductivity. The states on the surface are generally different from those of the bulk due to the unique electric field, stress and temperature environment created at the surface. As such, surface states play an important role in the materials science of thin films and nanomaterials due to their direct impact on the properties and performance of thin film devices.
Surface states can be divided into two categories: surface chemical states and surface electrical states. Surface chemical states occur on the surface of a material due to a reaction with surface gases. The reaction between the surface and gases will introduce new surface species that can interfere with electronic processes. Surface electrical states are related to the alteration of the electric field in the surface layer through the deposition of metal or semiconductor materials. These states are characterized by a high density of electrons and holes in the conduction and valence band.
Surface states can be created through a variety of techniques, including epitaxy, chemical vapor deposition (CVD), sputter deposition, plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), and others. In epitaxy, cations residing in a lattice-matched material are implanted into the substrate. This process causes vacancies in the substrate material which can be filled by electrons from the cation resulting in a layer of conductive material. CVD is a widely used technique which involves the introduction of a gas precursor to a heated substrate resulting in the deposition of a thin film of material onto the substrate. Sputter deposition involves bombarding a target material with energetic particles to create a plume of material which is then deposited on the substrate. PECVD is similar to CVD but with the addition of plasma energy to enhance the process. ALD is an emerging technique that uses a series of self-limiting chemisorption reactions to deposit conformal layers of material atom by atom.
Surface states play an important role in determining the physical and chemical properties of materials because they govern the way in particles interact with the surface of the material. This makes them important to consider when designing nanomaterials and thin films. Also, by understanding the effects of surface states on the surface electronic structure, engineers can design materials with specific electronic properties to benefit specific applications. Surface states can also be used to modify nanomaterials, such as nanotubes, to create more efficient devices.
In summary, surface state are an important part of the materials science of thin films and nanomaterials. By understanding the effects that surface states have on the surface electrons of materials, engineers and scientists can design materials with desired physical and chemical properties. Further, surface states can be used to modify nanomaterials for specific applications, creating more efficient and useful devices.
