Helium nanodroplet assisted synthesis of bimetallic Ag@Au nanoparticles with tunable localized surface plasmon resonance

Abstract

Nanoparticles with tunable localized surface plasmon resonance have been prepared by synthesis in helium nanodroplets. Subsequent surface deposition allows for the formation of substrates which can be employed for surface-enhanced Raman spectroscopy (SERS). The assembly of Ag@Au core@shell clusters of about 5 nm diameter in helium droplets with different Ag:Au ratio allows to tune the surface plasmon resonance between the plain Ag resonance at 447 nm and the Au resonance at 555 nm. For the fabricated substrates only a single plasmon resonance is observed in the UV/vis absorption spectra. The prepared nanostructures have been functionalized with 4-methylbenzenethiol (4-MBT) molecules and SERS spectra have been recorded. The results demonstrate the potential of the helium droplet synthesis approach, opening up a new route to the formation of tailored plasmonic nanoparticles and functional nanostructures.

Special issue: Dynamics of systems on the nanoscale (2018). Editorial

“…These software packages have been designed to become powerful and universal instruments of computational research in the field of MBN Science, which should play a role of a "virtual microscope" and a "camera" capable to explore, simulate, record and visualize both structure and dynamics of the MBN-world with an atomistic level of accuracy, in order to both reproduce its known features and predict the new ones. In this Topical Issue, many contributions [12][13][14][15][16][17][18][19][20][21][22][24][25][26][27][28][29][30][31][32][33][34][35] provide case studies conducted with these packages and demonstrate their application to a broad variety of topical areas in MBN science as listed at the beginning of this Editorial. To be noted that these universal and powerful software packages are fully applicable to a broad variety of the topical areas of the MBN Science listed above in the introductory part of the Editorial.…”

“…Precious metal nanoparticles such as gold and silver nanoparticles are frequently used for surface-enhanced Raman scattering (SERS), where the electric field enhancement upon excitation of the surface plasmon resonance is exploited [13]. Lackner et al have presented an interesting way to synthesize Ag@Au core-shell nanoparticles in helium nanodroplets [14]. The advantage of this method is that the Ag:Au ratio can be precisely controlled, which in turn allows the spectral position of the surfaceplasmon resonance to be turned.…”

Metal clusters synthesized in helium droplets: structure and dynamics from experiment and theory

“…Since the pickup cells are separately controlled, the amount of doped core and shell material can be adjusted independently. This allows for a tailoring of the core diameter and the shell thickness of the synthesized nanoparticles within a certain range, as has been shown for Ag@Au 63 and Fe@Au. 64 After leaving the pickup region, the He N beam reaches a third chamber at UHV conditions (E5 Â 10 À10 mbar), where a time-of-flight mass spectrometer (TOFMS) with reflectron (Stefan Kaesdorf RFT50) is mounted, which is specifically designed for the detection of large compounds.…”

“…55 For optical absorption measurements of cluster samples, fused silica microscope slides for deposition and a Shimadzu UV-1800 spectrophotometer have been employed. 63 Plasmon resonances of metal clusters obtained this way, represent an average over a certain size distribution, but significant differences for single metal as opposed to core shell particles were found. Furthermore, such ensemble averaged measurements were conducted for surface enhanced Raman studies.…”

“…Furthermore, such ensemble averaged measurements were conducted for surface enhanced Raman studies. 63 Plasmon resonances for individual nanoparticles on a thin h-BN substrate, which provides very low background absorption, could be studied with EELS. 75 Atomic Force Microscopy (AFM) required exposure to air and was only applied to Ag@Au core@shell particles on fused silica (see Fig.…”