Research Express@NCKU - Articles Digest

More documents

Recommendations

Info

Research Express@NCKU - Articles DigestFIG 3. Schematic diagrams of the effect of defects on DOS. The dashed lines show the possiblecircumstances in forming metal-like DOS.The effect of defects on DOS is summarized schematically in FIG.3 which demonstrates the two possibletypes of formation for the defect bands. For N B , C B , O B , O N and Si B , the bonding abilities of theimpurities are stronger than the substituted host atoms (type I) while for Be B , Be N , B N , C N , Al N , and Si N ,the weaker bonding ability drives the defect bands (DBs) to the higher-energy region of the originalbands. The order in the bonding ability is found to be consistent with the electronegativity order basedon the Mulliken scale. The partially occupied defect bands for O N and Si B (Be B and O N ) are located atthe edge of the original extended CB (VB2) bands which are more likely to be extended in nature andthus lead to larger exchange energies as presented later. Of these studied defect systems, some consist ofeven numbers of electrons in the supercell, i.e. N B , B N , Al B , and Al N . The even numbers of electrons inthe supercell completely fill up the DBs, i.e. no formation of finite moments, and they are thereforeexcluded from the following discussions. The calculated magnetic moments in Be B and V B were found tovary as d D increases. However, their magnitudes converge to 1μ B as d D increases to 17.37 Å. For the restdefect systems, the calculated magnetic moments are always found to be 1μ B and independent of d D .3 of 5
Research Express@NCKU - Articles DigestFIG 4. Magnetization energy E M vs d D .To understand how stable these finite moments in the BN sheet are, the magnetization energies, i.e. E M ,obtained from the total-energy difference between the systems with and without spin-polarizedconfiguration were calculated (FIG.4). The E M ’s of these systems tend to increase as d D increase whichsuggests a definite preference for finite magnetic moments for those defect systems with distantnonmagnetic defects. Note that the defect concentrations of 3.125% and 0.78% correspond to a d D of10.03 Å and 20.05 Å respectively.4 of 5
Page 4 and 5: Research Express@NCKU - Articles Di

Research Express@NCKU - Articles Digest

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?