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Ballistic Phonons in Ultrathin Nanowires
Daniel Vakulov1, Subash Gireesan1,2, Milo Y Swinkels3
1Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
Nano Letters
|February 25, 2020
Summary
Heat flow in ultrathin gallium phosphide (GaP) nanowires defies Fourier's law, showing length-independent conductance. This ballistic heat flow, observed up to 15 μm at room temperature, transitions to diffusive behavior with increased diameter.
Area of Science:
- Condensed matter physics
- Nanotechnology
- Materials science
Background:
- Fourier's law describes diffusive heat flow, where thermal conductance is inversely proportional to system length.
- Diffusive heat transport is characterized by linear temperature profiles and length-dependent thermal conductance.
Purpose of the Study:
- To investigate heat flow mechanisms in ultrathin gallium phosphide (GaP) nanowires.
- To determine if heat transport in these nanowires deviates from classical Fourier's law.
- To explore the influence of wire dimensions on heat flow characteristics.
Main Methods:
- Fabrication of ultrathin GaP nanowires with a diameter of 25 nm.
- Experimental measurement of heat conductance as a function of nanowire length (up to 15 μm).
- Systematic variation of nanowire diameter to observe transitions in heat transport behavior.
Main Results:
- Observed length-independent heat conductance in ultrathin GaP nanowires, contradicting Fourier's law.
- Demonstrated ballistic heat flow persisting up to 15 μm at room temperature.
- Identified a sharp transition from ballistic to diffusive heat flow upon doubling the nanowire diameter.
Conclusions:
- Ultrathin GaP nanowires exhibit ballistic heat flow due to exceptionally long phonon mean free paths, as described by Landauer's formalism.
- Nanowire diameter is a critical factor controlling the transition between ballistic and diffusive heat transport regimes.
- These findings challenge conventional understanding of heat conduction at the nanoscale and offer insights for thermal management in nanodevices.
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