We present a review and discussion of the physical meaning of the vector potential in
electromagnetism by means of a classical experiment in which a long solenoid, connected to
a sinusoidal voltage supply, produces an electric field and a vector potential in a circuit
exterior to the solenoid itself. Some basic considerations are recalled concerning the
meaning of action-at-a-distance and local description, in terms of ‘real fields’ of the induced
electromotive force on the circuit outside the solenoid. From this viewpoint the
roles played by the magnetic field, the electric field and the vector potential to
account for the physical effects are reviewed. Finally, the connections between
these considerations and the magnetic Aharonov–Bohm effect are recalled in the
light of recent theoretical work aimed at explaining the Aharonov–Bohm phase
shift in terms of the magnetic field without resorting to the vector potential.
High rate deposition of diamond like carbon films by very high frequency plasma enhanced chemical vapor deposition at 100 MHz Wide band gap amorphous hydrogenated carbon films grown by plasma enhanced chemical vapor depositionThe use of very high frequency (VHF) plasma enhanced chemical vapor deposition in a capacitive discharge is investigated to fabricate hydrogenated amorphous silicon carbon alloys, using silane and methane as silicon and carbon precursors, respectively, and hydrogen dilution of the gas mixture. The properties of samples differ significantly from that is normally observed for rf deposition. A wide band-gap material is obtained, with a carbon ratio ranging from 0.2 to 0.63. An energy gap up to 3.4 eV is measured, indicating a large sp 3 content. The most interesting properties are observed using 90% hydrogen dilution and 350°C as substrate temperature. In this case, a Siu C bond concentration up to 6 ϫ 10 22 cm −3 was measured for stoichiometric samples, associated to a highly crosslinked structure and no detectable Siu CH 3 bending signal. The role of hydrogen in determining the optical properties of the film is established and is shown to affect mainly the valence electron concentration. Based on the free energy model, hydrogen bonding is observed to lie in between a random and chemically ordered configuration. The results are obtained at a deposition rate much larger than both rf and electron cyclotron resonance deposition, and are associated to a limited gas consumption, both aspects being advantageous for practical applications. The large Siu C bond concentration, associated to a limited silicon and carbon hydrogenation, makes the VHF deposited a-SiC : H a good starting material for subsequent crystallization.
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