Towards a scanning thermal microscope for measurements below 20K

Scanning thermal microscopy (SThM) allows the local temperature imaging at the nanometer scale with an excellent sensitivity. So far its applications were limited over 20K as no suited probe had been developed. The local thermometry of nanometer scale systems at very low temperatures thus remain a widely unknown research field. Indeed, thermal aspects of known quantum effects such as the quantum Hall effect remain to be investigated. The cross-coupling of the thermal conductivity with other quantities, such as the magnetic field, could reveal new quantum phenomena and new ways to control nanosystems. The manipulation of these systems can also be directly performed using a hot tip. For instance, the manipulation of encapsulated van der Waals heterostructures is a major issue that could be overcome with cryogenic scanning thermal microscopy. This work aims at the realisation of a SThM set-up for temperature measurement below 20K. To achieve this, an Akiyama probe with on its tip a resistive element suited for thermal measurements below 20K was designed. This probe was simulated using finite elements. Its resonance frequency, spring constant and different calibration parameters could be obtained. Major advances towards the microfabrication of such probes were realised. Among them, the fabrication of two stages sharp AFM tips with TMAH was demonstrated. The deposition of metals on their apex using a single partial spin-coating opens new paths to their batch production without EBL or photolithography. A vacuum compatible AFM set-up with a self-sensing amplitude-based feedback was successful implemented. These realisations pave the way to the implementation of a fully operational cryogenic SThM set-up.