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 °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 °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.