We show that perfect absorption can be achieved in a system comprising a single lossy dielectric layer of thickness much smaller than the incident wavelength on an opaque substrate by utilizing the nontrivial phase shifts at interfaces between lossy media. This design is implemented with an ultra-thin (∼λ/65) vanadium dioxide (VO2) layer on sapphire, temperature tuned in the vicinity of the VO2 insulator-to-metal phase transition, leading to 99.75% absorption at λ = 11.6 μm. The structural simplicity and large tuning range (from ∼80% to 0.25% in reflectivity) are promising for thermal emitters, modulators, and bolometers.

/pdf/ultra-thin-perfect-absorber-employing-a-tunable-phase-change-2v33xdk55a.pdf

Ultra-thin perfect absorber employing a tunable phase change material

A new high-yield method of doping VO2 nanostructures with aluminum is proposed, which renders possible stabilization of the monoclinic M2 phase in free-standing nanoplatelets in ambient conditions and opens an opportunity for realization of a purely electronic Mott transition field-effect transistor without an accompanying structural transition. The synthesized free-standing M2-phase nanostructures are shown to have very high crystallinity and an extremely sharp temperature-driven metal–insulator transition. A combination of X-ray microdiffraction, micro-Raman spectroscopy, energy-dispersive X-ray spectroscopy, and four-probe electrical measurements allowed thorough characterization of the doped nanostructures. Light is shed onto some aspects of the nanostructure growth, and the temperature-doping level phase diagram is established.

Doping-Based Stabilization of the M2 Phase in Free-Standing VO2 Nanostructures at Room Temperature

Pure single-crystal rutile-type VO2 has been synthesized via the hydrothermal reaction of V2O5, oxalic acid, and tungstenic acid at low temperatures. The products have been characterized by means of X-ray diffraction, transmission electron microscopy, scanning electron microscopy, selected area electron diffraction, differential scanning calorimetry, and X-ray photoelectron spectroscopy. It is shown that a part of VO2 powders have a “snowflake” morphology assembled by VO2 rods which have a monoclinic structure with a preferential orientation along 110 direction. The adulterating agent tungstenic acid plays a key role in the synthesis of rutile phase. The DSC results indicated that the metal-semiconductor transition temperature of VO2 powders was reduced to room temperature or below. The reaction details and mechanisms are described and discussed. The substitution of a part of V atoms with larger W atoms induces the distortion of the VO6 octahedra, promoting the transition from VO2 (B) to VO2 (R).

Pure Single-Crystal Rutile Vanadium Dioxide Powders: Synthesis, Mechanism and Phase-Transformation Property

http://jcvalmal.univ-tln.fr/articles/TFVO2.pdf

Optimized infrared switching properties in thermochromic vanadium dioxide thin films: role of deposition process and microstructure

Ultrathin plasmonic metasurfaces have proven their ability to control and manipulate light at unprecedented levels, leading to exciting optical functionalities and applications. Although to date metasurfaces have mainly been investigated from an electromagnetic perspective, their ultrathin nature may also provide novel and useful mechanical properties. Here we propose a thin piezoelectric plasmonic metasurface forming the resonant body of a nanomechanical resonator with simultaneously tailored optical and electromechanical properties. We experimentally demonstrate that it is possible to achieve high thermomechanical coupling between electromagnetic and mechanical resonances in a single ultrathin piezoelectric nanoplate. The combination of nanoplasmonic and piezoelectric resonances allows the proposed device to selectively detect long-wavelength infrared radiation with unprecedented electromechanical performance and thermal capabilities. These attributes lead to the demonstration of a fast, high-resolution, uncooled infrared detector with ∼80% absorption for an optimized spectral bandwidth centered around 8.8 μm.

https://escholarship.org/content/qt1n4480pg/qt1n4480pg.pdf?t=qakdta

Plasmonic piezoelectric nanomechanical resonator for spectrally selective infrared sensing

Vanadium dioxide (VO 2 ) thin films are materials for uncooled microbolometer due to their high temperature coefficient of resistance (TCR) at room temperature. This paper describes the design and fabrication of eight-element uncooled microbolometer linear array using the films and micromachining technology. The characteristics of the array is investigated in the spectral region of 8–12 μm. The fabricated detectors exhibit responsivity of over 10 kV/W, detectivity of approximate 1.94×10 8  cm Hz 1/2 /W, and thermal time constant of 11 ms, at 300 K and at a frequency of 30 Hz. Furthermore, the uncorrected response uniformity of the linear array bolometers is less than 20%.

Characterizations of VO2-based uncooled microbolometer linear array

Linear uncooled microbolometer array based on VOx thin films

Vanadium dioxide thin films are used for uncooled microbolometers due to their high temperature coefficient of resistance (TCR). This paper describes the preparation and properties of the films. The films are deposited on a quartz substrate by low temperature reactive ion-beam sputtering and post annealing at a temperature of 500/spl deg/C. The X-ray photoelectron spectroscopy (XPS) indicates that the films are mixed vanadium oxides of mainly V/sup 4+/ and V/sup 5+/. The TCR value of -1.86%K/sup -1/ at a temperature of 25/spl deg/C is achieved through electrical conductivity measurements.

Preparation and properties of vanadium dioxide thin films for uncooled microbolometer

Vanadium dioxide thin films are materials for uncooled microbolometers due to their high temperature coefficient of resistance (TCR) at room temperature. This paper describes the design and fabrication of 8-element linear array IR uncooled detectors using the films and micromachining technology. The characteristics of the array are investigated in the spectral region of 8-12 /spl mu/m. Tne fabricated detectors exhibit responsivity of over 10 kV/W, detectivity typically exceeding 1.0/spl times/10/sup 8/ cmHz/sup 1/2//W, and thermal time constant of 11 ms, at 300 K and at a frequency of 30 Hz. Furthermore, the uncorrected response uniformity of the linear array bolometers is less than 20%.

Xingrong Zhao

Papers

Characterizations of VO2-based uncooled microbolometer linear array

Linear uncooled microbolometer array based on VOx thin films

Preparation and properties of vanadium dioxide thin films for uncooled microbolometer

Design and fabrication of linear array IR bolometers using VO/sub 2/ thin films