Force-induced acoustic phonon transport across single-digit nanometre vacuum gaps

Heat transfer between bodies separated by nanoscale vacuum gap distances has been extensively studied for potential applications in thermal management, energy conversion and data storage. For vacuum gap distances down to 20 nm, state-of-the-art experiments demonstrated that heat transport is mediated by near-field thermal radiation, which can exceed Planck's blackbody limit due to the tunneling of evanescent electromagnetic waves. However, at sub-10-nm vacuum gap distances, current measurements are in disagreement on the mechanisms driving thermal transport. While it has been hypothesized that acoustic phonon transport across single-digit nanometre vacuum gaps (or acoustic phonon tunneling) can dominate heat transfer, the underlying physics of this phenomenon and its experimental demonstration are still unexplored. Here, we use a custom-built high-vacuum shear force microscope (HV-SFM) to measure heat transfer between a silicon (Si) tip and a feedback-controlled platinum (Pt) nanoheater in the near-contact, asperity-contact, and bulk-contact regimes. We demonstrate that in the near-contact regime (i.e., single-digit nanometre or smaller vacuum gaps before making asperity contact), heat transfer between Si and Pt surfaces is dominated by force-induced acoustic phonon transport that exceeds near-field thermal radiation predictions by up to three orders of magnitude. The measured thermal conductance shows a gap dependence of $d^{-5.7\pm1.1}$ in the near-contact regime, which is consistent with acoustic phonon transport modelling based on the atomistic Green's function (AGF) framework. Our work suggests the possibility of engineering heat transfer across single-digit nanometre vacuum gaps with external force stimuli, which can make transformative impacts to the development of emerging thermal management technologies.Comment: 9 pages with 4 figures (Main text), 13 pages with 7 figures (Methods), and 13 pages with 6 figures and 1 table (Supplementary Information

Separable states to distribute entanglement

It was shown that two distant particles can be entangled by sending a third particle never entangled with the other two [T. S. Cubitt et al., Phys. Rev. Lett. 91, 037902 (2003)]. In this paper, we investigate a class of three-qubit separable states to distribute entanglement by the same way, and calculate the maximal amount of entanglement which two particles of separable states in the class can have after applying the way.Comment: 4 pages, no figures, Revised argumen

A Novel Approach to Synthesize Helix Wave Hollow Fiber Membranes for Separation Applications

Helix wave hollow fiber membranes are promising candidate to mitigate fouling and polarization effects in membrane operations. Current study describes a novel but simple approach to synthesize hollow fiber membranes with helix wave configuration. Poly(ether sulfone) (PES) based helix-waved hollow fiber membranes have been fabricated by dry-wet phase inversion process by using asymmetric coagulation conditions. Frequencies of the wave cycle have been observed approximately 20 and the wave length 7.1-7.6mm under the specifically required operating conditions defined by dope solution extrudate rate of 1g/min through 4cm of air-gap heights with 8.6m/min of winding speeds. On the other hand, simple hollow fibers are formed when the elongation force exerted by the winder is much higher than the surface tension of the external coagulant. The process can be useful for making polymer fibers for other applications as well