Bài giảng Vật liệu học: Chương 6 - TS. Nguyễn Văn Dũng

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Bài giảng "Vật liệu học - Chương 6: Electrical properties" cung cấp cho người học các kiến thức về Ohm’s law, energy levels of an isolated atom, conduction & electron transport, charge carriers in insulators and semiconductors, energy bands, the mass action law,... Mời các bạn cùng tham khảo.

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Nội dung Text: Bài giảng Vật liệu học: Chương 6 - TS. Nguyễn Văn Dũng

Chapter 6 Electrical properties  Ohm’s law 1 CuuDuongThanCong.com https://fb.com/tailieudientucntt
• Ohm's Law: V=IR voltage drop (volts = J/C) resistance (Ohms) C = Coulomb current (amps = C/s) • Resistivity, : -- a material property that is independent of sample size and geometry surface area RA  of current flow l current flow path length • Conductivity,  1    2 CuuDuongThanCong.com  https://fb.com/tailieudientucntt
 Which will have the greater resistance? 2 2 8 D R1   D 2 D 2    2    R1 2D R2    2D  D 2 2 8       2   Analogous to flow of water in a pipe  Resistance depends on sample  geometry and size. 3 CuuDuongThanCong.com https://fb.com/tailieudientucntt
Further definitions J=E
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CONDUCTIVITY: COMPARISON • Room temperature values (Ohm-m)-1 = ( m)-1= S m-1 METALS conductors CERAMICS -10 Silver 6.8 x 10 7 Soda-lime glass 10 -10-11 Copper 6.0 x 10 7 Concrete 10 -9 Iron 1.0 x 10 7 Aluminum oxide
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EXAMPLE: What is the minimum diameter (D) of the wire so that V < 1.5 V? (=6.07 x 107 (Ohm-m)-1)  100 m Cu wire - I = 2.5 A + V  100 m < 1.5 V  V R  2.5 A D 2 A I 4 6.07 x 107 (Ohm-m)-1 Solve to get D > 1.87 mm 10 CuuDuongThanCong.com https://fb.com/tailieudientucntt
Energy levels of an isolated atom 11 CuuDuongThanCong.com https://fb.com/tailieudientucntt
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ELECTRON ENERGY BAND STRUCTURES 14 CuuDuongThanCong.com https://fb.com/tailieudientucntt
BAND STRUCTURE REPRESENTATION 15 CuuDuongThanCong.com https://fb.com/tailieudientucntt
16 CuuDuongThanCong.com https://fb.com/tailieudientucntt ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.
Metals Insulators Semiconductors 17 CuuDuongThanCong.com https://fb.com/tailieudientucntt
CONDUCTION & ELECTRON TRANSPORT • Metals (Conductors): -- for metals empty energy states are adjacent to filled states. -- thermal energy Partially filled band Overlapping bands excites electrons Energy Energy into empty higher empty energy states. band -- two types of band GAP empty structures for metals band - partially filled band partly - empty band that filled filled filled states band filled states overlaps filled band band filled filled band band 18 CuuDuongThanCong.com https://fb.com/tailieudientucntt
• Insulators: • Semiconductors: -- wide band gap (> 4 eV) -- narrow band gap (< 4 eV) -- few electrons excited -- more electrons excited across band gap across band gap Energy empty Energy empty conduction conduction band band GAP ? GAP filled filled filled states filled states valence valence band band filled filled band band 19 CuuDuongThanCong.com https://fb.com/tailieudientucntt
The Fermi energy is the maximum energy occupied by an electron at 0K. Fermi function where, E is the electron energy, EF is the Fermi energy, and T is the absolute temperature. Its physical meaning is that: f(E) is the probability of occupancy for an electron energy state at energy E by an electron. That is, the probability that this state is occupied by an electron is f(E), and the probability that it is vacant is 1 - f(E). 20 CuuDuongThanCong.com https://fb.com/tailieudientucntt