Abstract
The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching and thermal cloaking. While this could be achieved by making use of composites and metamaterials at bulk length-scales, engineering the thermal conductivity at micro- and nano-scale dimensions is considerably more challenging. In this work, we show that the local thermal conductivity along a single Si nanowire can be tuned to a desired value (between crystalline and amorphous limits) with high spatial resolution through selective helium ion irradiation with a well-controlled dose. The underlying mechanism is understood through molecular dynamics simulations and quantitative phonon-defect scattering rate analysis, where the behaviour of thermal conductivity with dose is attributed to the accumulation and agglomeration of scattering centres at lower doses. Beyond a threshold dose, a crystalline-amorphous transition was observed.
Highlights
The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching and thermal cloaking
The effect of defects created by helium ions below the transition dose threshold on the nanowire thermal conductivity is discussed with theoretical support from the kinetic theory of phonon gas model and non-equilibrium molecular dynamics (NEMD) simulations
The silicon nanowire is suspended between two temperature sensors comprising platinum (Pt) loops on silicon nitride membranes, each of which is suspended by six nitride beams
Summary
The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching and thermal cloaking. We show that the local thermal conductivity along a single Si nanowire can be tuned to a desired value (between crystalline and amorphous limits) with high spatial resolution through selective helium ion irradiation with a well-controlled dose. The thermal conductivity of each irradiated nanowire segment was measured by an electron beam heating technique that is capable of spatially resolving the thermal conductivity along the nanowire’s length[30] (Methods section present the detailed measurement and calculation procedure) Using this technique, the effect of different helium ion dose can be measured conveniently along a single nanowire, thereby eliminating potential discrepancies that could arise from sample-to-sample variations in the nanowire diameter and from uncertainty in the thermal contact resistance between the nanowire ends and the thermometers. The ability to tune the thermal conductivity along silicon nanowires with high spatial resolution by a well-controlled helium ion irradiation, and to measure the local thermal conductivity thereafter, provides a new platform to study nanoscale thermal transport
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
