Vacuum null-point scanning thermal microscopy: Simultaneous quantitative nanoscale mapping of undisturbed temperature and thermal resistance

Null-point scanning thermal microscopy (NP SThM) quantitatively measures undisturbed temperature without the influence of changes in physical properties and surface topography of the specimen. Simultaneously NP SThM measures the ratio of the sum of the tip-specimen contact thermal resistance and the spreading thermal resistance of the specimen to the effective thermal resistance of the SThM probe. Hence, arguably, NP SThM is an ideal SThM that meets all the requirements of SThM. However, in practice, the use of NP SThM has been limited to one-dimensional profiling only, and two-dimensional extension of NP SThM has been virtually impossible so far. This is because NP SThM is very difficult to implement and ensure a sufficient measurement sensitivity. In this study, we enable two-dimensional extension of NP SThM with almost a 20-fold improvement in measurement sensitivity even under mild vacuum conditions (<10⁻³ Torr). Through rigorous analysis of the two-dimensional imaging results of vacuum NP SThM (VNP SThM), we demonstrate the ideal characteristics and performance of VNP SThM. With the ideal measurement characteristics, and the greater sensitivity and convenience, VNP SThM is proven to be an essential tool in the analysis of nanoscale energy transport and conversion occurring inside nanodevices and nanomaterials.