16 research outputs found
Ultrafast broadband optical modulation in indium tin oxide/titanium dioxide 1D photonic crystal
Photonic crystals can integrate plasmonic materials such as Indium Tin Oxide (ITO) in their structure. Exploiting ITO plasmonic properties, it is possible to tune the photonic band gap of the photonic crystal upon the application of an external stimuli. In this work, we have fabricated a one-dimensional multilayer photonic crystal alternating ITO and Titanium Dioxide (TiO2) via radio frequency sputtering and we have triggered its optical response with ultrafast pump-probe spectroscopy. Upon photoexcitation, we observe a change in the refractive index of ITO. Such an effect has been used to create a photonic crystal that changes its photonic bandgap in an ultrafast time scale. All optical modulation in the visible region, that can be tuned by designing the photonic crystal, has been demonstrated
Hybrid 1D Plasmonic/Photonic Crystals are Responsive to Escherichia Coli
Photonic crystal-based biosensors hold great promise as valid and low-cost
devices for real-time monitoring of a variety of biotargets. Given the high
processability and easiness of read-out even for unskilled operators, these
systems can be highly appealing for the detection of bacterial contaminants in
food and water. Here, we propose a novel hybrid plasmonic/photonic device that
is responsive to Escherichia coli, which is one of the most hazardous
pathogenic bacterium. Our system consists of a thin layer of silver, a metal
that exhibits both a plasmonic behavior and a well-known biocidal activity, on
top of a solution processed 1D photonic crystal. We attribute the
bio-responsivity to the modification of the dielectric properties of the silver
film upon bacterial contamination, an effect that likely stems from the
formation of polarization charges at the Ag/bacterium interface within a sort
of bio-doping mechanism. Interestingly, this triggers a blue-shift in the
photonic response. This work demonstrates that our hybrid plasmonic/photonic
device can be a low-cost and portable platform for the detection of common
contaminants in food and water
Electrochromism in Electrolyte-Free and Solution Processed Bragg Stacks
Achieving an active manipulation of colours has huge implications in
optoelectronics, as colours engineering can be exploited in a number of
applications, ranging from display to lightning. In the last decade, the
synergy of the highly pure colours of 1D photonic crystals, also known as Bragg
stacks, with electro-tunable materials have been proposed as an interesting
route to attain such a technologically relevant effect. However, recent works
rely on the use of liquid electrolytes, which can pose issues in terms of
chemical and environmental stability. Here, we report on the proof-of-concept
of an electrolyte free and solution-processed electrochromic Bragg stack. We
integrate an electro-responsive plasmonic metal oxide, namely indium tin oxide,
in a 1D photonic crystal structure made of alternating layers of ITO and TiO2
nanoparticles. In such a device we observed 15 nm blue-shift upon application
of an external bias (5 V), an effect that we attribute to the increase of ITO
charge density arising from the capacitive charging at the metal
oxide/dielectric interface and from the current flowing throughout the porous
structure. Our data suggest that electrochromism can be attained in all-solid
state systems by combining a judicious selection of the constituent materials
with device architecture optimisation
Novel beamline for attosecond transient reflection spectroscopy in a sequential two-foci geometry
We present an innovative beamline for extreme ultraviolet (XUV)-infrared (IR)
pump-probe reflection spectroscopy in solids with attosecond temporal
resolution. The setup uses an actively stabilized interferometer, where
attosecond pulse trains or isolated attosecond pulses are produced by
high-order harmonic generation in gases. After collinear recombination, the
attosecond XUV pulses and the femtosecond IR pulses are focused twice in
sequence by toroidal mirrors, giving two spatially separated interaction
regions. In the first region, the combination of a gas target with a
time-of-flight spectrometer allows for attosecond photoelectron spectroscopy
experiments. In the second focal region, an XUV reflectometer is used for
attosecond transient reflection spectroscopy (ATRS) experiments. Since the two
measurements can be performed simultaneously, precise pump-probe delay
calibration can be achieved, thus opening the possibility for a new class of
attosecond experiments on solids. Successful operation of the beamline is
demonstrated by the generation and characterization of isolated attosecond
pulses, the measurement of the absolute reflectivity of SiO2, and by performing
simultaneous photoemission/ATRS in Ge.Comment: 18 pages, 9 figure
Ultrafast photochromism and bacteriochromism in one dimensional hybrid plasmonic photonic structures
Hybrid plasmonic photonic structures combine the plasmonic response with the
photonic band gap, holding promise for utilization as optical switches and
sensors. Here, we demonstrate the active modulation of the optical response in
such structures with two different external stimuli, e.g. laser pulses and
bacteria. First, we report the fabrication of a miniaturized (5 x 5 mm) indium
tin oxide (ITO) grating employing femtosecond laser micromachining, and we show
the possibility to modulate the photonic band gap in the visible via ultrafast
photoexcitation in the infrared part of the spectrum. Note that the
demonstrated time response in the picosecond range of the spectral modulation
have an industrial relevance. Moreover, we manufacture one-dimensional photonic
crystals consisting of a solution-processed dielectric Bragg stack exposing a
top-layer of bio-active silver. We assign the bacterial responsivity of the
system to polarization charges at the Ag/bacterium interface, giving rise to an
overall blue shift of the photonic band gap.Comment: 7 pages, 4 figure
The Impact of Bacteria Exposure on the Plasmonic Response of Silver Nanostructured Surfaces
Silver, especially in the form of nanostructures, is widely employed as an
antimicrobial agent in a large range of commercial products. The origin of the
biocidal mechanism has been elucidated in the last decades, and most likely
originates from silver cation release due to oxidative dissolution followed by
cellular uptake of silver ions, a process that causes a severe disruption of
bacterial metabolism and eventually leads to eradication. Despite the large
number of works dealing with the effects of nanosilver shape/size on the
antibacterial mechanism and on the (bio)physical chemistry pathways that drive
bacterial eradication, little effort has been devoted to the investigation of
the silver NPs plasmon response upon interaction with bacteria. Here we present
a detailed investigation of the bacteria-induced changes of the plasmon
spectral and dynamical features after exposure to one of the most studied
bacterial models, Escherichia Coli. Ultrafast pump-probe measurements indicate
that the dramatic changes on particle size/shape and crystallinity, which stem
from a bacteria-induced oxidative dissolution process, translate into a clear
modification of the plasmon spectral and dynamical features. This study may
open innovative new avenues in the field of biophysics of bio-responsive
materials, with the aim of providing new and reliable biophysical signatures of
the interaction of these materials with complex biological environments
Stimuli-Responsive Photonic Crystals
Recently, tunable photonic crystals (PhCs) have received great research interest, thanks to the wide range of applications in which they can be employed, such as light emission and sensing, among others. In addition, the versatility and ease of fabrication of PhCs allow for the integration of a large range of responsive elements that, in turn, can permit active tuning of PhC optical properties upon application of external stimuli, e.g., physical, chemical or even biological triggers. In this work, we summarize the most employed theoretical tools used for the design of optical properties of responsive PhCs and the most used fabrication techniques. Furthermore, we collect the most relevant results related to this field, with particular emphasis on electrochromic devices
Stimuli-Responsive Photonic Crystals
Recently, tunable photonic crystals (PhCs) have received great research interest, thanks to the wide range of applications in which they can be employed, such as light emission and sensing, among others. In addition, the versatility and ease of fabrication of PhCs allow for the integration of a large range of responsive elements that, in turn, can permit active tuning of PhC optical properties upon application of external stimuli, e.g., physical, chemical or even biological triggers. In this work, we summarize the most employed theoretical tools used for the design of optical properties of responsive PhCs and the most used fabrication techniques. Furthermore, we collect the most relevant results related to this field, with particular emphasis on electrochromic devices
Large Scale Indium Tin Oxide (ITO) One Dimensional Gratings for Ultrafast Signal Modulation in the Visible
We present a photophysical study on an indium tin oxide (ITO) one
dimensional grating, realized using femtosecond micromachining technology, a
technology very industrially accessible. The geometries, dimensions and pitch
of the various gratings analyzed are obtained by means of direct ablation in a
controlled atmosphere of a homogeneous thin layer of ITO deposited on a glass
substrate. The pitch has been selected in order to obtain a higher order of the
photonic band gap in the visible. By
means of ultrafast pump-probe spectroscopy we characterize both the plasmon and
inter-band temporal dynamics. We observe a large optical non-linearity of ITO
grating in the visible range, where the photonic band gap occurs, when pumped
at the surface plasmon resonance in the near infrared (1500 nm). All together
we show the possibility of all-optical signal modulation with heavily doped
semiconductors in their transparency window with a picosecond response time
through the formation of ITO grating structures
Large scale indium tin oxide (ITO) one dimensional gratings for ultrafast signal modulation in the visible spectral region
Indium tin oxide (ITO) is a heavily doped semiconductor with a plasmonic response in the near infrared region. When exposed to light, the distribution of conduction band electron induces a change in the real and imaginary parts of the dielectric permittivity. The coupling of the electromagnetic waves with the electrons in the conduction band of metallic nanostructures with ultrashort light pulses results in a nonlinear plasmonic response. Such optical modulation occurring on ultrafast time scales, e.g. picosecond response times, can be exploited and used to create integrated optical components with terahertz modulation speed. Here, we present a photophysical study on a one dimensional ITO grating, realized using a femtosecond micromachining process, a very industrially accessible technology. The geometries, dimensions and pitch of the various gratings analyzed are obtained by means of direct ablation in a controlled atmosphere of a homogeneous thin layer of ITO deposited on a glass substrate. The pitch has been selected in order to obtain a higher order of the photonic band gap in the visible spectral region. Femtosecond micromachining technology guarantees precision, repeatability and extreme manufacturing flexibility. By means of ultrafast pump–probe spectroscopy, we characterize both the plasmon and inter-band temporal dynamics. We observe a large optical nonlinearity of the ITO grating in the visible range, where the photonic band gap occurs, when pumped at the surface plasmon resonance in the near infrared (1500 nm) region. All together, we show the possibility of all-optical signal modulation with heavily doped semiconductors in their transparency window with a picosecond response time through the formation of ITO grating structures