Probing Compositional Variation within Hybrid Nanostructures

Abstract

Ќ These authors contributed equally to this work. P latinum-based bimetallic alloys are highly desirable for their potential in magnetic storage, sensing, and catalysis, 1Ϫ5 often displaying properties that are independent of their constituent materials. 6 In addition to changes in the geometric distribution of the individual atoms, the unique structure and bonding in bimetallics can also lead to alterations in the electronic structure of the material. For example, PtNi alloys show enhanced activity for oxygen reduction relative to pure Pt, 7 as do similar alloys, including Pt 3 Co.8 However, bimetallic nanomaterials are not as well-understood outside of singlecrystalline studies or theoretical modeling, and the practical application of more complex nanostructures is further complicated by factors such as varied growth conditions, the presence of surface stabilizing agents, and the increased surface-to-volume ratio of nanoscale materials. Bimetallic nanoparticles have even been shown to undergo dynamic metal segregation in response to oxidizing or reducing environments. 9As nanostructured systems increase in complexity, the potential for structural and compositional variations with respect to the individual components rises dramatically. Hybrid nanostructures, the combination of two or more nanoscale materials to form a new heterostructure, are being actively pursued for a number of applications, 10 including device integration and assembly, 11Ϫ13 chemical and biological sensing, 14,15 and photocatalysis. 16Ϫ23 In particular, the integration of a metallic component with an optically active semiconductor, directly in solution, can lead to novel materials that exhibit new functionalities that result from the coupling between the individual components. For example, photocatalytic heterostructures can promote efficient charge separation across a metalϪsemiconductor junction, followed by catalytic reaction at the surface of the metal component.The development of semiconductorϪ metal hybrid nanostructures for magnetic and catalytic applications requires a thorough understanding of the metallic structure, which is difficult to predict for a complex system where nucleation and growth proceeds on the tip of a semiconductor. In a previous communication, we reported the selective growth of Pt, PtCo, and PtNi nanoparticles on the tips of CdS rods in solution. 24 Here, we present a detailed analysis of the structural and magnetic properties of PtCoϪCdS hybrid structures in comparison to similar free-standing PtCo nanoparticles. X-ray absorption spectroscopy (XAS) is utilized as a sensitive probe for identifying subtle differences in the local structure and composition of the hybrid materials, which can be difficult to discern using traditional analytical methods such as electron microscopy and X-ray diffraction (XRD). While the electronic and atomic structures of noble metal-based bimetallic alloys and free-standing PtCo

Cu2ZnSnS4–PtM (M = Co, Ni) Nanoheterostructures for Photocatalytic Hydrogen Evolution

“…Such hybrid nanoheterostructures, with the ferromagnetic component grown directly onto the semiconductor, could be also useful for studying nanoscale spin injection into semiconductor nanostructures. 27,28 ■ CONCLUSION In summary, monodisperse CZTS nanocrystals were synthesized via a hot-injection method and further used as support to produce CZTS−PtCo and CZTS−PtNi nanoheterostructures. CZTS-PtCo materials showed much higher photocatalytic hydrogen generation activity than CZTS and even CZTS-Pt nanoparticles.…”

Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

“…For example, at the high temperatures at which colloidal synthesis is typically carried out, the overgrown material may adapt to the lattice parameters of the seed at the interface (coherency strain) (Dunstan, 1997;Chen et al, 2003;Xu et al, 2015). In other circumstances, the constituent atomic species of the connected materials may interdiffuse, accommodating variation in the chemical composition and/or crystal-lattice parameters across the heterojunction regions (Koo and Korgel, 2008;Yuhas et al, 2009). In the extreme cases of exceedingly large misfit, plastic relaxation may induce formation of interfacial defects, such as dislocations and stacking faults (Dunstan, 1997;Markov, 2003;Carbone and Cozzoli, 2010;Li et al, 2014).…”

“…In the extreme cases of exceedingly large misfit, plastic relaxation may induce formation of interfacial defects, such as dislocations and stacking faults (Dunstan, 1997;Markov, 2003;Carbone and Cozzoli, 2010;Li et al, 2014). Experimental results (Casavola et al, , 2009Koo and Korgel, 2008;Deka et al, 2009;Yuhas et al, 2009;Liakakos et al, 2014) and thermodynamic modeling (Sadowski and Ramprasad, 2010;Xu et al, 2015) have indicated that the temperature and the particular chemical pathways underlying MHNC formation are decisive in determining whether either uniformly alloyed, graded, or abrupt interfaces may be attained.…”

“…Standard pyrolytic organometallic routes were suitably combined and utilized to synthesize CdX-Me and Me-CdX-Me heterostructructures (Figures 7C,D) based on CdX (X = Se, S) nanorods functionalized with magnetic and nonmagnetic domains (Me = Au, Pt, PtNi, PtCo, Co, Ni) (Mokari et al, 2004Habas et al, 2008;Jen-La Plante et al, 2009;Maynadiè et al, 2009;Yuhas et al, 2009;Nakibli and Amirav, 2016). For these systems, a high degree of selectivity for metal nucleation at both seed apexes was readily achievable (Figure 7A, path 1) (Habas et al, 2008;Jen-La Plante et al, 2009;Wang et al, 2009d;Nakibli and Amirav, 2016), whereas indiscriminate deposition at random sites was observed when large aspect-ratio nanorods/nanowires were used as starting seeds, or when the synthesis was carried out at exceedingly high reactant-to-seed concentration ratios ( Figure 7A, path 3).…”

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques

“…XAS is used to detect small differences in the structure of colloidal nanocrystals 209 which can be difficult to discern using EM and XRD. 206 Nevertheless, structural evaluation of bimetallic NPs (Ru-Pt NPs) 207 is clarified by using EXAFS, XANES and XRD. 7 Moreover, it is possible to monitor different reaction steps 137 by checking both the NPs surface passivation and the different oxidation states of CdSe quantum dots.…”