Optomechanical metamaterial nanobolometer

Abstract

Bolometers are detectors of electromagnetic radiation that usually convert the radiation-induced change in temperature of the detector into electric signals. Temperature-dependent electrical resistance in semiconductors and superconductors, the thermoelectric effect in thermocouples, and the pyroelectric effect of transient electric polarization of certain materials when they are heated or cooled are among the underlying physical phenomena used in bolometers. Here, we report that the dependence of the fundamental frequency of a nanowire string detected via scattering of light on the string can be used in a bolometer. Arrays of such nanowires can serve as detectors with high spatial and temporal resolution. We demonstrate a bolometer with 400 nm spatial resolution, 2–3 µs thermal response time, and optical power detection noise floor at 3–5 nW/Hz1/2 at room temperature.

Photothermal Responsivity of van der Waals Material-Based Nanomechanical Resonators

“…The values of reported in this work, with the exception of clean 1L-NbSe 2 , are fractions of reported for metamaterial string [ 31 ] and graphene trampoline NMR bolometers [ 27 ] at infrared and visible wavelengths, respectively. Apart from replacing NbSe 2 with thermally insulating vdW materials, a strategy to improve of NbSe involves decreasing the thermal conductivity of the drumheads with high-aspect-ratio tethers that resemble a trampoline geometry.…”

“…There are several approaches to quantifying the power absorbed by vdW NMRs. One can measure the mechanical mode temperature by resolving thermomechanical motion [ 6 , 31 ] while varying the incident laser power. Such detection requires low mass and high quality factors of NMRs, which can be difficult to ensure for vdW materials [ 24 , 25 , 26 ].…”

Microwatt Volatile Optical Bistability via Nanomechanical Nonlinearity

“…The laser heating reduces the tensile stress of the nanowire proportionally to the temperature increase 𝜎 = 𝜎 0 − 𝛼𝜂 × ΔT, where 𝛼 = 4 × 10 −6 K −1 is the thermal expansion coefficient of the nanowire. [15] As a result, the nanowire's natural frequency 𝜔 ′ 0 reduces with increase of the laser power The frequency shift 𝜒 thermal = − 41 kHz 𝜇W calculated from this formula is comparable to the experimentally observed laser-induced rate of frequency shift, thus confirming that the thermal mechanism of the light-induced frequency shift dominates. For the above estimates we derived the effective thermal conductivity 𝜅 = 31 W m −1 K −1 of the silicon nitride nanowire decorated with gold nanorods from a thermal circuit model and used volume weighted average values for the Young's modulus, density, and thickness of the nanowire (𝜂 = 202 GPa, 𝜌 = 8209 kg m −3 , h = 74 nm), see Table S1 (Supporting Information).…”

“…The laser heating reduces the tensile stress of the nanowire proportionally to the temperature increase σ = σ 0 − αη × Δ T , where α = 4 × 10 −6 K −1 is the thermal expansion coefficient of the nanowire. [ 15 ] As a result, the nanowire's natural frequency $$\omega _0^{\prime}$$ reduces with increase of the laser power $${\Delta}{\omega}_{0}^{\prime}\approx \ \ \frac{\partial {\omega}_{0}^{\prime}}{\partial T}\ {\Delta}T\ =\ -{\omega}_{0}^{\prime}\ \ensuremath{\times{}}\frac{\alpha}{6.8(\frac{h}{L})^{2}+\frac{2{\sigma}_{0}}{\eta}}\ \ensuremath{\times{}}\ \frac{\xi {P}^{\prime}L}{8\kappa \textit{wh}}$$. The frequency shift $${\chi}_{\mathrm{thermal}}=\ -\frac{41\ \mathrm{kHz}}{\mathrm{\mu}\mathrm{W}}$$ calculated from this formula is comparable to the experimentally observed laser‐induced rate of frequency shift, thus confirming that the thermal mechanism of the light‐induced frequency shift dominates.…”

Optical Control of Nanomechanical Brownian Motion Eigenfrequencies in Metamaterials

“…The metamaterial structure supports a near-infrared closed mode optical resonance at a wavelength of 1542 nm (see Supplementary Figure S1), underpinned by the excitation of antiparallel displacement currents in adjacent dissimilar silicon nanobricks by incident light polarized parallel to the long axis of the bricks. In the vicinity of this optical resonance, thermal (Brownian) motion of the nanowires, mutual positional fluctuations of pico- to nanometric amplitude, translate to fluctuations of metamaterial transmission (of order 0.1%) at their few MHz natural mechanical resonance frequencies. , These thermomechanical oscillations are detected as peaks in frequency spectra of transmission amplitude spectral density (Figure b,c): the metamaterial is mounted in a vacuum chamber at a pressure of 4 × 10 –3 mbar to exclude air damping of mechanical motion. (It should be noted here that while a classical Brownian particle in a fluid is thermally perturbed by “external” collisions with ambient atoms, the thermal motion of objects under vacuum is driven “internally” by momentum transfer from the annihilation, creation, and interference of phonons.)…”