Ordered mesoporous carbon (OMC) and metal-doped (M-doped) OMC composites are prepared, and their electromagnetic (EM) parameters are measured. Using the measured EM parameters we calculate the EM wave absorption properties of a double-layer absorber, which is composed of OMC as an absorbing layer and M-doped OMC as the matching layer. The calculated results show that the EM wave absorption performance of OMC/OMC-Co (2.2mm/2.1mm) is improved remarkably. The obtained effective absorption bandwidth is up to 10.3 GHz and the minimum reflection loss reaches 47.6 dB at 14.3 GHz. The enhanced absorption property of OMC/OMC-Co can be attributed to the impedance match between the air and the absorber. Moreover, it can be found that for the absorber with a given matching layer, a larger value of -tanδε (= tan δε absorbing tan δε matching ) can induce better absorption performance, indicating that the difference in impedance between the absorbing layer and the matching layer plays an important role in improving the absorption property of double-layer absorbers.
The effects of B and N dopings and H2O adsorption on the structural stability and the field emission properties of cone-capped carbon nanotubes（CCCNTs） were investigated by using the density-functional theoretical calculation.The adsorption of H2O can increase the structural stability and decrease the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital（HOMO-LUMO gap） of the CCCNTs.The strength of total electric field on the top of the H2O-adsorbed CCCNTs is larger than that of the B-doped and the N-doped CCCNTs, electrons will be emitted primarily from the H2O-adsorbed CCCNTs at the same applied voltage.Therefore,the H2O adsorption can lower the threshold voltage for the CCCNTs.While the B and the N dopings produce opposite effects. The HOMO-LUMO gap of the N-doped CCCNTs is the widest among all the gaps of the CCCNTs.
