Conductors play a crucial role in the operation of scanning tunneling microscopes (STMs) as they form one of the main components of the STM setup. STMs are powerful instruments used to observe surfaces at the atomic scale by scanning a sharp conducting tip very close to the sample surface. Here's how conductors contribute to the operation of scanning tunneling microscopes:
Tunneling Current Generation: The principle behind STM operation is based on the phenomenon of quantum mechanical tunneling. When a sharp conducting tip is brought extremely close to a conducting or semiconducting sample surface, a small bias voltage is applied between the tip and the sample. This voltage creates a potential difference that allows electrons to tunnel through the vacuum barrier between the tip and the surface. The current that flows due to this tunneling process is known as the tunneling current. Conductors are essential for both the tip and the sample because they facilitate the flow of these tunneling electrons.
Measurement of Tunneling Current: The tunneling current is extremely sensitive to the distance between the tip and the sample surface. As the tip scans across the surface, the tunneling current changes, providing information about the local electronic structure and topography of the sample. Conductive materials are necessary for accurate measurements of the tunneling current because they ensure a consistent and predictable current response based on the tip-sample distance.
Feedback Mechanism: Conductive materials are used to construct the STM tip, which is typically made of a metal wire that tapers down to an atomically sharp point. This sharp tip is brought close to the sample surface, and the tunneling current is monitored. A feedback loop is used to maintain a constant tunneling current by adjusting the vertical position of the tip. Conductors in both the tip and the sample enable the generation of this tunneling current and ensure that the feedback mechanism can work effectively.
Atomic Resolution Imaging: The tunneling current's sensitivity to distance allows STMs to achieve atomic resolution imaging. Conductive surfaces enable the precise measurement of the tunneling current, which can be used to map out the surface features of the sample at the atomic scale. This capability has revolutionized the field of nanotechnology and materials science, enabling researchers to study and manipulate individual atoms and molecules on surfaces.
In summary, conductors are essential components in the operation of scanning tunneling microscopes. They enable the generation of tunneling currents, accurate measurement of tunneling current variations, and the feedback mechanism that maintains a constant tunneling current during scanning. These contributions allow scientists and researchers to explore and manipulate materials at the atomic scale, leading to groundbreaking discoveries in various fields.