The sheath potential &fgr;Mis calculated from the difference between the plasma potential and the floating potential. The plasma potential has been measured by using a retarding field analyzer with an entrance slit located in front of it. The electron temperatureTeand ion temperatureTiare also measured with the same analyzer in an electron cyclotron resonance plasma. Comparing the normalized sheath potential,−e&fgr;M/kTe, with the different theoretical values, it is found that the secondary electron emission could not be neglected in our experiment and is noncritical. The critical emission corresponds to zero electric field at the emitter. The various calculations have shown that the thermionic electron emission need not be required to be taken into consideration. The total energy transmission factors&dgr;T(=W/FTe, whereWis the energy flux from the plasma,Fis the ion flux, andTeis the electron temperature at the sheath edge) for hydrogen, nitrogen, and argon plasmas are calculated from the estimated secondary electron emission coefficient and the sheath potential, respectively. ©1997 American Institute of Physics.