Probing atomic ordering and multiple twinning in metal nanocrystals through their vibrations

Area of Science:

• Materials Science
• Nanotechnology
• Physics

Background:

• Controlling nanocrystal (NC) crystallinity is crucial for physics modeling and technological applications.
• Recent advances in synthesizing single-crystalline NCs necessitate further investigation into crystallinity's effects on NC properties.
• The impact of NC crystallinity on vibrational properties remains understudied.

Purpose of the Study:

• To investigate how the crystallinity of gold nanocrystals influences their vibrational characteristics.
• To demonstrate the distinct vibrational signatures of single-domain versus multiply twinned gold NCs.
• To explore the potential of Raman spectroscopy for characterizing nanocrystallinity.

Main Methods:

• Low-frequency Raman scattering to analyze NC vibrations.
• Resonant ultrasound approach to calculate vibrational frequencies of a gold sphere.
• Comparison of experimental measurements with theoretical calculations.

Main Results:

• Gold NC crystallinity dramatically modifies their vibrational modes.
• Single-domain NCs show a splitting of quadrupolar vibrations, absent in multiply twinned NCs.
• Elastic anisotropy in gold spheres explains the observed lift of degeneracy in quadrupolar modes, aligning with experimental data.

Conclusions:

• Nanocrystal crystallinity is a key factor influencing vibrational properties.
• Raman spectroscopy can differentiate between single-domain and multiply twinned NCs based on vibrational splitting.
• These findings offer new avenues for using Raman spectroscopy to characterize nanocrystallinity.