However, reports on the fabrication of core shell NPs through ALD are very limited and often involves relatively complex processes. NPs grown by ALD show well controlled size by tuning the ALD process 30, 31, 32, 33. The ALD method also allows well dispersed NPs directly grown in porous structures as well as on high aspect ratio substrate 28, 29. Recently, gas phase methods such as atomic layer deposition (ALD) have been applied to the synthesis of supported monometallic NPs such as Pd, Pt and so on 23, 24, 25, 26, 27. In addition, it still remains a challenge to fabricate core shell NPs with precisely controlled composition and shell thickness due to the difficulty of purification and separation for the solvent based synthesis method. However, the size of as synthesized core shell NPs is generally larger than 10 nm 22, which is not ideal for some chemical reactions that require a larger surface area. Wet chemical synthesis methods have been tried to fabricate the bimetallic core shell NPs by commonly reducing a second metal onto the preformed cores 2, 9. Synthesizing core shell nanoparticles (NPs) with well controlled shell thickness and composition is of great importance in optimizing their reactivity 17, 18, 19, 20, 21. From cost perspective, replacing the noble metal cores with a less expensive metal could also lower the overall materials cost and make commercial applications of core shell NPs more favorable. For instance, the Pd/Pt core shell NPs show enhanced activity for the oxygen reduction reaction and methanol oxidation 8, 12, whose enhancement of catalytic performance can be attributed to the lowering of the surface electronic d-band center 14, 15, 16. Compared with the physical mixture of monometallic NPs or the alloyed bimetallic NPs, the enhanced properties of core shell structure may originate from the lattice strain, bonding interaction and electron transfer due to the unique core shell interface 12, 13. It is found that the formation of core shell NPs could further enhance the activity, selectivity and stability 9, 10, 11. This SAMs assisted area-selective ALD method of core shell structure fabrication greatly expands the applicability of ALD in fabricating novel structures and can be readily applied to the growth of NPs with other compositions.īimetallic nanoparticles (NPs) have attracted great attention due to their unique properties for catalytic applications 1, 2, 3, 4, 5, 6, 7, 8. Such core shell structures can be realized by using regular ALD recipes without special adjustment. The size, shell thickness and composition of the NPs can be controlled precisely by varying the ALD cycles. Since new nucleation sites can be effectively blocked by surface ODTS SAMs in the second deposition stage, we demonstrate the successful growth of Pd/Pt and Pt/Pd NPs with uniform core shell structures and narrow size distribution. Take the usage of pinholes on SAMs as active sites for the initial core nucleation and subsequent selective deposition of the second metal as the shell layer. The method involves utilizing octadecyltrichlorosilane (ODTS) self-assembled monolayers (SAMs) to modify the surface.

We report an atomic scale controllable synthesis of Pd/Pt core shell nanoparticles (NPs) via area-selective atomic layer deposition (ALD) on a modified surface.

Core shell atomic layer deposition cds