A series of fully
suspended reduced graphene oxide (RGO) photodetectors
were fabricated based on free-standing thermally reduced graphene
oxide (GO) thin films with various annealing temperatures (from 200
to 1000 °C). A new phenomenon was found that under ultraviolet
(375 nm) to near-infrared (1064 nm) lasers irradiations, the photodetector
consisting of fully suspended thermally reduced graphene oxide thin
film and Au interdigital electrodes possess positive or zero or negative
response depending on the annealing temperature of GO. This may originate
from the competition between annealing temperature-dependent the positive
photoresponse from RGO and the negative photoconductivity of Au interdigital
electrodes. The annealing temperature-dependent wide spectral binary
photoresponse offers a good thinking for designing RGO-based light
triggered logic devices. Moreover, upon visible (405 nm) to near-infrared
(1064 nm) irradiations, all fully suspended RGO detectors prepared
at various annealing temperatures exhibit fast photoresponse, that
is, rise time is only tens of milliseconds, which are 1–4 orders
of magnitude faster than the reported photodetectors based on supported
RGO film and are on the same order of magnitude as the supported CVD-grown
and supported mechanically exfoliated graphene photodetectors. The
fast photoresponse originates from the fully suspended construction
of device and the thin thickness of film, which provides a new design
idea for fast response RGO-based device.
Antireflection (AR) thin films on optical substrates are of great significance in high-performance optoelectronic devices. Here, we present a rational design and construction of well-organized macro-mesoporous nanostructure toward robust high-performance self-cleaning antireflective thin films on the basis of effective medium theory and finite difference time domain (FDTD) simulations that combine the optical design principle. A hierarchical macro-mesoporous SiO thin film with very high porosity and gradient refractive indexes works as a λ/4-wavelength AR layer and significantly suppresses the reflection in the range from 350 to 1200 nm. Even after dip-coating a layer of high refractive index TiO nanocrystals, the nanostructured thin film still exhibits broadband AR properties which are much superior to conventional flat SiO/TiO thin films, especially in the range of 350-500 nm. In addition, the obtained thin film exhibits photocatalytic self-cleaning and durable superhydrophilicity. The advantages brought by the well-organized macro-mesoporous structure are also testified through comparing to the solely mesoporous SiO/TiO film counterpart. Moreover, the pencil hardness test and sandpaper abrasion test show favorable robustness and functional durability of the thin film, which make it extremely attractive for practical applications in optical devices, display devices, and photovoltaic cells.
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