Mechanical Wave Isolation in Ultrathin van der Waals Heterostructures
Abstract
The purpose of this project is to explore the propagation and isolation of mechanical waves in deeply subwavelength systems of heterogeneous atomic layers. Mechanical wave isolation is a need that is prevalent throughout many naval technologies. Isolating these waves in subwavelength systems is a grand challenge and extremely valuable for niche applications that require small physical profiles. Despite numerous approaches to acoustic metamaterials, many require complex fabrication, are not physically scalable, or are not conformal with arbitrary or flexible surfaces. The objectives of this project are to provide theoretical and experimental evidence of mechanical wave isolation in ultrathin anharmonic films, called van der Waals heterostructures, and applythem as a technology on bulk surfaces like fiber optics. This project shall also explore new sensor modalities that arise from the application of hydrostatic or acoustic pressure to heterostructures.Atomically layered materials are crystalline systems that are comprised of interfaces. The structure of these materials consists of sheets of covalently bound atoms, called two-dimensional materials, weakly coupled by a van der Waals force. In these materials, sound is carried between layers by flexural acoustic phonons. These flexural phonons represent out of plane bending of each 2D layer and are fundamentally distinct from the vibrational modes of bulk materials. For instance, they are marked by a quadratic dispersion and low group velocity in the low-wavevector limit where sound is carried. Moreover, these phonons can move ballistically between layers with mean free paths much larger than the nanometer-thick films being explored in this project, thus supporting an acoustic mismatch model. Recently, it has become possible to synthetically layer dissimilar 2D materials, or modify the rotation between layers, to form anharmonic heterostructures. This project shall construct models for elastic wave propagation in these heterostructures. Heterostructuresshall be fabricated from scalable chemical vapor deposition techniques and characterized structurally and acoustically. The acoustic characterization shall focus on the isolation or guiding of ultrasound. We shall then demonstrate the physical integration of heterostructures with fiber optics and their ability to isolate ultrasound traveling within the fiber.This project is aligned with several objectives of the Chief of Naval Research s Framework Priorities. The anticipated outcome of this project is the isolation of 0.1-1 MHz ultrasound in an ultrathin film technology. This project should also provide new atomistic understandings and innovation in the coupling of acoustic energy into a fiber optic. Furthermore, this project should lead to new fiber optic concepts that can potentially monitor environmental parameters, like temperature, strain, or acoustic emission. This includes areas of non destructive evaluation, polymer matrix composites, or detecting and suppressing undersea sound.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 17, 2020
- Source ID
- N000142012520
Entities
People
- Kevin Brenner
Organizations
- Office of Naval Research
- Southern Methodist University
- United States Navy