| Summary: | Cooling physical experiments to low temperatures removes thermal excitations to reveal quantum mechanical phenomena. The progression of nanotechnologies provides new and exciting research opportunities to probe nature at ever smaller length scales. The coupling of nanotechnologies and low temperature techniques has potential for scientific discoveries as well as real world applications. This work demonstrates techniques to further extend physical experimental research into the millikelvin-nanoscale domain. The challenge of thermometry becomes an increasingly complex problem as the temperature of a physical system lowers. We describe the development and methods for a specially modified Coulomb blockade thermometer to achieve electron thermometry below 4mK overcoming the challenge of electron thermalisation for on-chip devices. Mechanically vibrating devices can directly probe bulk and surface fluid properties. We developed practical measurement techniques and analysis methods to demonstrate the use of nanomechanical resonators, which for the first time were used to probe both the normal and the superfluid phases of helium-4. The doubly clamped beams had a cross section of 100nm by 100nm and were tested in length variants between 15um to 50um, The flexural resonance between 1MHz and 10MHz in response to the helium temperature dependent properties showed an encouraging agreement with established theories, providing experimental verification on a new smaller length scale. The smallest beams achieved a mass sensitivity in liquid of 10ag. We also created and analysed a new method of sampling peak-like functions that is applicable to many physical systems to provide around 20% improvements over the existing methods under certain situations. This was verified in ultra low temperature applications as a drop-in addition to accompany existing techniques.
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