This article presents a new simple method of creating light-absorbing carbon material for optical devices such as bolometers. A simple method of laser microstructuring of graphene oxide is used in order to create such material. The absorption values of more than 98% in the visible and more than 90% in the infrared range are achieved. Moreover thermal properties of the films, such as temperature dependence and the thermal response of the samples, are studied. The change in resistance with temperature is 13 Ohm K, temperature coefficient of resistance (TCR) is 0.3% K, and the sensitivity is 0.17 V W at 300 K. Thermal conductivity is rather high at ∼104 W m K at 300 K. The designed bolometer operates at room temperature using incandescent lamp as a light source. This technique suggests a new inexpensive way to create a selective absorption coating and/or active layer for optical devices. Developed GO and rGO films have a large surface area and high conductivity. These properties make carbon coatings a perfect candidate for creating a new type of optoelectronic devices (gas sensors, detectors of biological objects, etc.).
The
mechanical properties of the layered crystals in the few layer
limit are largely unexplored. We employ a picosecond ultrasonic technique
to access the corresponding mechanical parameters. Temporal variation
of the reflection coefficient of the Al film that covers hBN/WSe2/hBN (where hBN is hexagonal boron nitride) heterostructures
on a sapphire substrate after the femtosecond laser pulse excitation
is carefully measured using an interferometric technique with spatial
resolution. The laser pulse generates a broadband sound wave packet
propagating perpendicularly to the Al plane and partially reflecting
from the heterostructural interfaces. The demonstrated technique allows
one to resolve a WSe2 monolayer embedded in
hBN. We apply a multilayered model of the optoacoustical response
to evaluate the mechanical parameters, in particular, the rigidity
of the interfaces. Mapping of the Fourier spectra of the response
visualizes different composition regions and may serve as an acoustic
tomography tool. Almost zero phonon dissipation below 150 GHz demonstrates
the van der Waals heterostructures’ potential for nanoacoustical
applications.
This work studies the scattering of coherent acoustical phonons within the frequency range of 30−200 GHz in strained SiGe/Si heterostructures with uniform SiGe layers and layers where the initial stage of self-organized islands formation was observed. Coherent phonon pulses reflected by single SiGe layers were detected, and phonon interference in the systems composed of two thin (approximately 10 nm) SiGe layers was observed. Acoustical properties were determined for single SiGe layers, and lateral acoustical inhomogeneity of the layers was estimated in the subterahertz frequency range. The results show that within the range of germanium content of 10%−32% acoustical properties of an approximately 10-nm SiGe layer are insensitive to internal strains governed by lattice mismatch and non-uniformities caused by initial stage of Stranski–Krastanov growth. The sound velocity and wave impedance of SiGe layers can be determined within 5% error, using the corresponding parameters of relaxed SiGe solid solutions with the same germanium content.
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