2.2. Surface modification of AlNPSZ was applied on AlN by using dip-coating method as shownin Scheme 1. First, AlN was dipped and stirred in PSZ solution(AlN:PSZ = 2:1, w/w) at room temperature for 1 h. After that AlNdispersion was filtered to remove the exceed PSZ solution and thefiltered-PSZ coated AlN was placed in an oven at 180◦C for 24 h toallow crosslinking of PSZ on AlN surface (the first 3 h PSZ-coatedAlN was gently grinded every 30 min to prevent the aggregationof the modified AlN). Then, the pyrolysis of PSZ-coated AlN in air,Ar, N2and NH3atmospheres was carried out by using tube furnace(STF54434C, Thermo Scientific, USA). These procedures were per-formed with the heating rate of 3◦C per minute to the temperatureof 700◦C, then dwell of about 2 h, finally cooling with the rate of10◦C per minute to room temperature.