Vacuum-vaporized organic low-molecular-weight materials are well known to polycrystallize easily. Suppression of organic layer polycrystallization is effective for the improvement of practical devices. For this reason, we observed the polycrystallization of two hole-transporting diamine derivatives for organic light-emitting diodes (OLEDs). In addition, we discovered that the organic alloy method is very effective for the suppression of polycrystallization despite its simplicity. We describe the polycrystallization of an organic vacuum-deposited layer.
Formation of Ge3N4 on Ge(001) substrates by nitrogen radicals and their thermal stability were investigated in this study. A Ge3N4/Ge structure with a root-mean-square surface roughness of 0.18 nm is successfully formed by layer-by-layer manner at a substrate temperature of 300oC. In contrast, island growth and thermal decomposition of Ge3N4 occur during the nitridation at 600oC, and consequently island structures and locally-flat areas are formed. Ge3N4 thickness is saturated at a certain nitridation time and, not only saturation times but also saturation thicknesses are different depending on plasma condition. By a 2-step nitridation in which the nitridation at 300oC and 600oC for 900 sec were sequentially subjected to Ge surfaces, a Ge3N4 thickness much larger than that at the single-step nitridation can be obtained without surface roughening.
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