8 research outputs found
VO2 Tungsten Doped Film IR Perfect Absorber
We investigated infrared reflectivity of undoped and Tungsten (W) doped Vanadium dioxide (VO2) films at varying temperatures. Undoped VO2 exhibited a clear phase transition at 100°C, achieving near 0% reflectivity, or perfect light absorption. As W doping concentration increased, the phase-transition temperature decreased, maintaining the zero-reflectivity condition. Only a 0.75% W doping enabled room temperature perfect absorption without heating the film
Large-area polycrystalline -MoO3 thin films for IR photonics
In recent years, excitation of surface phonon polaritons (SPhPs) in van der
Waals materials received wide attention from the nanophotonics community.
Alpha-phase Molybdenum trioxide (-MoO3), a naturally occurring biaxial
hyperbolic crystal, emerged as a promising polaritonic material due to its
ability to support SPhPs for three orthogonal directions at different
wavelength bands (range 10-20 m). Here, we report on the fabrication and
IR characterization of large-area (over 1 cm size) -MoO3
polycrystalline films deposited on fused silica substrates by pulsed laser
deposition. Single alpha-phase MoO3 films exhibiting a polarization-dependent
reflection peak at 1006 cm with a resonance Q-factor as high as 53 were
achieved. Reflection can be tuned via changing incident polarization with a
dynamic range of R=0.3 at 45 deg. incidence angle. We also report a
polarization-independent almost perfect absorption condition (R<0.01) at 972
cm which is preserved for a broad angle of incidence. The development of
a low-cost polaritonic platform with high-Q resonances in the mid-infrared
(mid-IR) range is crucial for a wide number of functionalities including
sensors, filters, thermal emitters, and label-free biochemical sensing devices.
In this framework our findings appear extremely promising for the further
development of lithography-free, scalable films, for efficient and large-scale
devices operating in the free space, using far-field detection setups.Comment: 17 pages, 12 figure
Large-area polycrystalline α-MoO3 thin films for IR photonics
In recent years, the excitation of surface phonon polaritons (SPhPs) in van der Waals materials
received wide attention from the nanophotonics community. Alpha-phase Molybdenum trioxide
(α-MoO3), a naturally occurring biaxial hyperbolic crystal, emerged as a promising polaritonic
material due to its ability to support SPhPs for three orthogonal directions at different
wavelength bands (range 10–20 µm). Here, we report on the fabrication, structural,
morphological, and optical IR characterization of large-area (over 1 cm2
size) α-MoO3
polycrystalline film deposited on fused silica substrates by pulsed laser deposition. Due to the
random grain distribution, the thin film does not display any optical anisotropy at normal
incidence. However, the proposed fabrication method allows us to achieve a single α-phase,
preserving the typical strong dispersion related to the phononic response of α-MoO3 flakes.
Remarkable spectral properties of interest for IR photonics applications are reported. For
instance, a polarization-tunable reflection peak at 1006 cm−1 with a dynamic range of ∆R = 0.3
and a resonance Q-factor as high as 53 is observed at 45â—¦
angle of incidence. Additionally, we
report the fulfillment of an impedance matching condition with the SiO2 substrate leading to a
polarization-independent almost perfect absorption condition (R < 0.01) at 972 cm−1 which is
maintained for a broad angle of incidence. In this framework our findings appear extremely
promising for the further development of mid-IR lithography-free, scalable films, for efficient
and large-scale sensors, filters, thermal emitters, and label-free biochemical sensing devices operating in the free space, using far-field detection setups
Tuning mid-infrared polarization sensitive reflectivity in GaN/AlGaN heterostructures
We present narrow-band polarization-sensitive reflectance of GaN/AlGaN heterostructures in the mid-infrared range. Experimental measurements performed at 15° angle of incidence show the excitation of a Berreman mode at the interface between GaN and sapphire substrate. A transfer matrix method for anisotropic layers has been used to analyze the obtained results. The contribution of the two-dimensional electron gas at the interfaces of the heterostructures has been included by proper modelization of an effective thin layer
Polycrystalline MoO3 films fabricated by pulsed laser deposition for infrared polarization manipulation
We performed infrared optical characterization of polycrystalline MoO3 films deposited by pulsed laser deposition on fused silica substrates. Several samples have been fabricated using different parameters such as temperature and oxygen pressure. Our analysis shows that under appropriate fabrication conditions it is possible to obtain a dominant -phase film, with a well-defined, normal to surface (z-axis) orientation.
These results are confirmed by reflection spectra performed at 45° incidence angle revealing a strong modulation of the sharp z-phonon Reststrahlen band as a function of the incident field linear polarization
Tunable IR perfect absorbers enabled by tungsten doped VO2 thin films
The temperature tunability of complex dielectric constants of vanadium dioxide (VO2) makes it a promising phase-change material for use in active, dynamic, tunable photonics applications. Specifically, the semiconductor-to-metal phase transition in VO2 enables reversible, broadband, and large complex refractive index variation and paves the way for a plethora of applications. Although the critical temperature for phase-transition is 68 °C for VO2 films, its transition temperature can be reduced to room temperature by tungsten-doping of vanadium dioxide. Such a degree of freedom in controlling the critical temperature through tungsten doping provides further tunability of the thermochromic behavior. In this work, we investigate a variety of W-doped VO2 thin films deposited by laser ablation of targets with increasing W doping content and report detailed infrared characterization together with numerical simulations. Our experimental results indicate that the perfect absorption can be achieved at different temperatures, within the VO2 insulator-to-metal phase transition process, as a function of W doping content. Tunable subwavelength layers allow perfect absorption under different temperature conditions around λ = 12 µm. We show that a high dynamic range of reflectivity can be achieved when the temperature is increased above the phase transition temperature. Furthermore, we observe perfect absorption at 11.8 µm at room temperature for a W content of 0.75%. We believe that W-doped VO2 thin films with tunable and controllable perfect absorption will open the way for a class of promising thermo-optical devices including thermos-photovoltaics, infrared filters, radiative cooling devices, and thermal emitters