Thermal Expansion Coefficient of Silicon Nanoparticles with Nanometer Resolution

With the size of electronic devices becoming increasingly smaller, it has become important to understand thermal expansion coefficients (TECs) and thermal properties of materials, particularly at interfaces, on the sub-nanometer scale. However, traditional techniques, such as scanning thermal microscopy or Raman thermometry are limited in spatial resolution due to mechanical constraints or optical diffraction limit. According to the free electron model, the plasmon resonance energy of a material is related to the temperature through its electron density. Using this property, several studies have shown that nanoparticles, such as Al or Si, can be used as nanothermometers to measure the local temperature with high resolution and high accuracy.

Here, we utilize a novel approach of non-contact thermometry based on the combination of low-loss electron energy-loss spectroscopy (EELS) with first principles density functional theory (DFT) modeling to measure the TEC of materials with nm resolution. The approach has previously been tested on 2D materials, such as transition metal dichalcogenides (TMDs), graphene and MoS₂  by Hu et al.  In present work, we will extend the approach to Si nanoparticles to determine its TEC as a function of temperature. We will also explore pitfalls as well as the limits of measuring the local temperature using this approach.