Questions and Answers
What is the characteristic of carbon nanotubes that makes them distinct from other semiconductors?
They can be made with metallic or semiconducting properties without doping
What is the size range at which the switch from discrete orbitals to bands occurs in semiconductors?
1–10 nm
What is the primary reason for the unique properties of metals at the nanoscale?
The increase in surface area
What is the term for the specific size range at which particles exhibit unique properties due to their size?
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What is the primary difference between the molecular orbitals of small molecules and the bands of macroscale materials?
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What is the term for the specific type of semiconductor that is typically found in the 1–10 nm size range?
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What is the primary advantage of using nanomaterials in electronics?
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What is the primary reason why graphene is considered a unique material?
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What is the primary difference between the intermolecular forces holding together graphite sheets and the forces holding together bulk metals?
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What is the primary application of nanomaterials in pharmaceuticals?
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Study Notes
Semiconductors
- Little energy is required to promote a donor level electron to the conduction band in n-type semiconductors.
- Vacancies in the valence band are referred to as holes in p-type semiconductors.
- Doping with phosphorus introduces an extra valence electron, which fills the donor level, close to the conduction band.
- Aluminum is a common p-type dopant, creating an acceptor level slightly higher than the valence band.
p-n Junctions
- A p-n junction can be constructed from p-type and n-type material, regulating the flow of electrons across the junction by applying voltage.
- Current flows across the junction when the negative pole of a battery is connected to the n-type material.
- Current does not flow across the junction when the negative pole is connected to the p-type material.
Band Theory and Conductivity
- Electrons fill the lowest energy band first, and the energy difference between the filled and empty bands determines the electrical properties of the bulk material.
- The band populated by valence electrons is the valence band, and the empty band above is the conduction band.
- The energy difference between the valence and conduction band is the band gap.
- Conductors have small band gaps, while insulators have large band gaps, and semiconductors have intermediate band gaps.
Doping
- Doping modifies the electrical conductivity of semiconductors by adding an element with more or fewer electrons.
- n-type semiconductors are prepared by doping with valence electron-rich elements, while p-type semiconductors are prepared by doping with valence electron-deficient elements.
Nanomaterials
- Particles with three dimensions on the 1-100 nm size are called nanomaterials, with unique properties studied in many labs.
- Semiconductors on the nanoscale, such as quantum dots, have sizes around 1-10 nm with unique properties.
- Carbon nanotubes can have metallic or semiconducting properties without doping and are very strong materials.
- Graphene, a single layer of graphite, has unique properties.
Applications of Nanotechnology
- Nanotechnology can be used to design pharmaceuticals that target specific organs or cells in the body.
- Nanomaterials can be added to cement, cloth, and other materials to make them stronger and lighter.
- Their size makes them extremely useful in electronics and environmental remediation.
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