Electrochemical Pd Nanodeposits on a Au Nanoisland Template Supported on Si(100): Formation of Pd-Au Alloy and Interfacial Electronic Structures

Palladium nanoparticles have uniformly been electrodeposited on a Au nanoisland template (NIT) supported on a Si(100) substrate, which exhibits Au-rich, Pd-rich, and/or polycrystalline mixed structures upon annealing to 700 degrees C. Glancing-incidence X-ray diffraction (GIXRD) and energy-dispersive X-ray (EDX) elemental analysis of the as-deposited sample both show metallic Pd, while depth-profiling X-ray photoelectron spectroscopy (XPS) further reveals the presence of Pd Au (and PdxSi) at the interfaces of the Pd nanodeposits on the Au NIT. Upon the sample being annealed to 700 degrees C, both Pd 3d(3/2) and Au 4f(7/2)XPS peaks are found to shift to lower binding energies, which further confirms Pd Au alloy formation. The convergence of respective GIXRD features of metallic Au and Pd toward intermediate peak positions supports the formation of alloy and their crystalline nature. Depth-profiling XPS analysis of the annealed sample further shows that the Pd nanoparticles are found to consist of an ultrathin shell of PdO2, and a PdO-rich (i.e., Pd-poor) inner-core, which is consistent with the observed GIXRD patterns of PdO and Pd Au alloy but indiscernible PdO2. We compare the above results with the experimental results for electrodeposited Pd on a bare Si(100) substrate. Our study provides new insight into the formation of Pd-Au alloy composite on Si by electrochemistry. The easy control of the Pd, Au, and Pd Au composition in the nanodeposits as illustrated in the present method offers new flexibility for developing hybrid nanocatalysts and other applications.