Due to their superior properties in single-molecule detection, plasmonic and nanopore-based sensors have attracted research interest. In recent times, they have been combined in a single device, resulting in plasmonic nanopores-based sensors. These solid-state devices featured unprecedented enhancements in single-molecule and nanoparticle detection, optical spectroscopies and trapping, control of local temperature. In this context, we have investigated two kinds of nanostructures: plasmonic nanopores and plasmonic nanoantennas, both of which were fabricated on free-standing Si3N4 membranes. As regards the nanopores, we were able to prove that their plasmonic coating enhanced their conductance when illuminated at 631 nm. On the other side, antenna-shaped nanopores (i.e., nanoantennas) were fabricated via plasmonic photochemical deposition. At this regard, we demonstrated that it was possible to fabricate nanoantennas with different internal diameters by different time of plasmon-induced photochemical deposition of metal precursors at the free tip of the nanoantenna. In conclusion, we proved that it was possible to use each nanoantenna (i.e., each decreasing internal diameter) to detect the translocation of nanoparticles with correspondingly decreasing diameters or of DNA.
The SERS-based detection of DNA and protein sequences with single nucleotide or amino acid sensitivity still represent a huge challenge. Recently, a new method based on the trapping of a gold nanoparticle in a plasmonic nanohole has been demonstrated. The plasmonic platform obtained by the combination of a nanoparticle trapped inside a nanopore enables to generate a single SERS hot spot for single-molecule detection with a spatial resolution high enough to resolve single element within a biomolecule. The superior spectral and spatial resolution of this approach can be applied to single DNA molecule and single-protein analysis, fingerprinting, and sequencing.
Here, we propose easy and robust strategies for the versatile integration 2D material flakes on plasmonic nanoholes by means of site selective deposition of MoS2. The methods can be applied both to simple metallic flat nanostructures and to complex 3D metallic structures comprising nanoholes. The deposition methods allow the decoration of large ordered arrays of plasmonic structures with single or few layers of MoS2. We show that the plasmonic field generated by the nanohole can interact significantly with the 2D layer, thus representing an ideal system for hybrid 2DMaterial/ Plasmonic investigation. The controlled/ordered integration of 2D materials on plasmonic nanostructures opens a pathway towards new investigation of the following: enhanced light emission; strong coupling from plasmonic hybrid structures; hot electron generation; and sensors in general based on 2D materials.
Modulating the fractal dimension of nanoporous gold is possible to tune the effective dielectric response over a wide spectral range of infrared wavelengths. The plasma edge and effective plasma frequency depend on the fractal dimension, which can be controlled by varying the preparation condition. The fractal porous metal has superior plasmonic properties compared to bulk gold. The long skin depth of porous metal on the order of 100-200 nm, enables the penetration of optical energy deep into the nanopores where molecules can be loaded, thus achieving more effective light-matter coupling. These findings may open new pathways to engineering the optical response of fractal-like or selfsimilar metamaterials.
Extreme UltraViolet instrumentation often requires the use of multilayer coated optics. Such coatings have a limited working bandwidth, and therefore are optimized to perform in correspondence of specific EUV spectral lines. Nevertheless, contemporary observations of the same target in other spectral region would strongly improve scientific knowledge. In this work we present a study on multilayers optimized to achieve high efficiency also in other spectral bands. These coatings would allow the realization of very compact instruments, such as UVCI on board of the Solar Orbiter.
Surface plasmon waves carry an intrinsic transverse spin angular momentum, which is locked to their propagation direction. On the other hand, helical plasmonic distributions may also carry an orbital angular momentum that is linked to the field topology. Apparently, when such a singular plasmonic mode propagates on a surface or is guided on a conic structure its helicity and the transverse spin can be coupled to the far-field spin and orbital angular momentum. We discuss the mechaism of such a coupling by using 2D and 3D guiding architetures. We analyze the coupling efficiency in each case as well as the intriguing spin-locking phenomenon occurring in our system. Finally we experimentally demonstrate the efficient beaming of a single-handed mode decorated by a desired orbital angular using accurately fabricated nanostructures.
Nanoporous gold is a very promising material platform for several plasmonic applications. Nanoporous gold can be
formed by dealloying Au–Ag alloys, previously grown by means of Ag-Au co-sputtering. The optical response is
completely determined by the nanostructured film features, that only depend on the initial alloy composition. It has been
extensively used as SERS substrate both as thin film and nanofabricated fancy designs. Here we explore the potential
application of nanoporous gold as SERS substrate as it is coupled and decorated with Ag nanoparticles. Significant
enhancement has been observed in comparison with bare nanoporous film.
When Palladium film is exposed to hydrogen, it becomes palladium hydride. A change in the complex permittivity of the metal film results in a change of the optical properties that depends on hydrogen concentration. Ellipsometry is the technique of choice to measure the optical constants prior and during hydrogenation. Sensors are then usually designed and optimized to measure changes in transmittance or reflectance of the palladium films. Films of different thicknesses have been realized and tested to verify potential applications in hydrogen sensing by studying the optical response prior, during and after hydrogenation, to assess in particular the reversibility of the process. Within this work a deep analysis carried out by x–ray reflectance (XRR) shows that during hydrogenation the films change also their thickness, and the amount has been assessed for a specific hydrogen concentration. Ellipsometric measurements have been therefore corrected taking into account such variation to determine the optical constants. Such structural property of the palladium hydride may be exploited in surface plasmon resonance transducers, which are sensitive also to the change of the sensing film thickness during detection.
Nanoporous gold is a very promising and novel material platform for mid-infrared and THz plasmonics. Nanoporous gold can be formed by dealloying of Au–Ag alloys, previously grown by means of Ag-Au co-sputtering. The optical response is completely determined by the nanostructural film features, that depends on the initial alloy composition and on the preparation procedure. The behavior of the material in mid-infrared and its peculiar morphology with a very high surface/volume ratio can be applied for nanostructure fabrication, such for example nanoantennas. Here we report the design and fabrication of nanoporous antennas engineered to support resonances in the 1500-1700 cm-1 range where them can be exploited, for example, in the detection of protein conformational states. This novel paradigm points toward the development of a new class of efficient and high-selective biosensors.
The preparation, optical characterization and plasmonic biosensing properties of self-standing nanoporous gold leaves are presented. Respect to the bulk gold, the material shows metallic behaviour at higher wavelengths and a lower imaginary part of the dielectric constants. The plasmonic properties in the near infrared range have been investigated probing the resonance shift after a self-assembling monolayer functionalization. Due to a great increase of the active surface the presence of an organic molecule adsorbed on its surface leads to important optical responses. This demonstrates how nanoporous gold reveals benefits for better reaction efficiency and detection sensitivity and how plasmonic properties in the near-IR range can assure employment in plasmonic devices.
We propose a conceptually novel scheme for generation and beaming of optical angular momentum using plasmonic
multilayer nanostructure We calculate the optical modes generated by the structure in near and far-field. Our proposed
structure architecture, consisting of a plasmonic vortex lens is shown to convert impinging light to an almost pure and
well defined orbital angular momentum state capable of propagating to the far-field.
In this work, we study how the Orbital Angular Momentum of a Plasmonic Vortex (an SPP carrying OAM) can be probed by the LSPR of nanoantennae conveniently integrated inside a Plasmonic Vortex Lens. We show that the turning “on” or “off” of the antennae acts as a fingerprint of the OAM of the PV and we discuss a particularly meaningful case. The integrated structure is fabricated and experimentally characterized in the near field. The results are in good agreement with the simulations and seem to prove the capability to transfer OAM properties control at the nanoscale.
We report our results on arrays of transparent metal coated wedges for plasmonic nanofocusing. FIB milling and
chemical etching were used for the fabrication. FEM simulations were used to design the system. The design, fabrication
and characterization of wedge structures are presented. The structure shows plasmonic properties in the optical spectral
range, with excitation and propagation of surface plasmon polaritons at the wedge tip. The particular designs proposed
allow the condensation of plasmonic waves at the wedge tips leading to the nanofocusing effects.
Depth-graded multilayer structures are widely considered as the preferred technology for the next generation of hard Xray
telescopes operating in the spectral range up to several tens of keV. This contrasts to earlier generation telescopes
which operated in the 1-10 keV range, and utilized single material reflection layers (e.g. Au). Several future space
missions are scheduled to include optics comprising up to hundreds of nested shells with Wolter-I profile. Therefore, the
need for an industrial strength (in terms of robustness, reliability and precision) manufacturing process for such
multilayers has emerged. In this paper, we will discuss the enabling technologies towards "industrial" Physical Vapor
Deposition (PVD) technology we have developed for this precision coating process. More specifically, we will review
the results obtained on periodic and a-periodic W/Si multilayers, which have been produced on shells of 600 mm height
and 300 mm diameter. Points that will be discussed include:
· Advanced process control based on in-situ sensors and its effect on repeatability and stability of the process.
· Ex-situ metrology methods
· Thickness homogeneity over large areas
A summary of the research performed on the optical characterization of Sc and of several lanthanides from the visible to
the soft x-rays is presented. The low absorption of these materials mainly below the O2,3 edge (L2,3 edge for Sc) turns
them promising materials for the realization of multilayer mirrors in a spectral range in which most materials in nature
absorb strongly. Thin-film samples with several thicknesses of the target material were deposited by evaporation over
thin-film substrates in UHV, and their transmittance was measured in situ. A wide spectral range of direct
characterization, along with extrapolations to longer and shorter wavelengths either using literature data (when available)
or model predictions, enabled the development of consistent optical constants over the whole spectrum. An assortment of
consistency sum rules has been used, and it was found that each of them highlights a given spectral range, which may
help evaluate the consistency of each part of the combined spectrum.
The extinction coefficient of Pr, Eu and Tm thin films prepared by evaporation in ultra high vacuum has been obtained in the spectral ranges 4-1600, 8.3-1400 and 10-1400 eV, respectively. These data were calculated from experimental values of the transmittance of the films performed in situ, which means that the samples were not exposed to the atmosphere before and during their characterization. Several films of increasing thickness were deposited onto grids coated with a thin C support film. The results show that Pr, Eu and Tm, similar to other lanthanides, have a lowabsorption band right below the O2,3 edge onset, with lowest absorption measured at about 16.9, 16.7 and 23 eV, respectively. Therefore, these materials are promising for filters and multilayer coatings in the energy range below O2,3 edge in which materials typically present a strong absorption. In the cases of Pr and Eu the sum rule was applied to the extinction coefficient data in the whole spectrum, that included the current data along with those of the literature and extrapolations. The obtained values of the number of electrons contributing to the optical properties of the materials were close to predictions, which shows the consistency of current data. In the case of Pr, the real part of the index of refraction was also calculated through the Kramers-Kronig analysis, and the consistency of the results was assessed by means of the inertial sum rule.
Within a National Project on nanotechnologies, a Micro-Exposure Tool (MET) for projection lithography at 14.4 nm,
based on a laser-produced plasma source, is being developed at the Frascati ENEA Center. The choice of this "exotic"
wavelength is due to the higher efficiency of a Debris Mitigation System (DMS) working in the interval of
approximately 14 nm < λ < 15 nm. It has to be noted that Mo/Si multilayer mirrors (MLM) can still have a high
reflectivity also at these wavelengths.
The solid-tape-target laser-generated plasma is driven by a XeCl excimer laser, with an optimized intensity of about
3•1010 W/cm2, generating an extreme ultraviolet (EUV) source with a diameter of about 0.2 mm. Clearly, this kind of
source emits a lot of debris (both atomic and particulate types) and the 7-cm-far collector mirror must be protected
against them.
The paper is mostly devoted to the accurate and systematic study of these debris and to their reduction. The results of
mitigation efficiency obtained with a DMS prototype are very encouraging and lead to the design and patenting of its
improved version.
The transmittance of thin films of Yb deposited by evaporation in ultra high vacuum (UHV) conditions have been investigated in the 23-1,700 eV spectral range. Transmittance measurements were performed in situ on Yb films deposited over grids coated with a thin, C support film. Transmittance measurements were used to obtain the extinction coefficient of Yb films at each individual photon energy investigated. The energy range investigated encompasses M, N, and O edges of Yb. The current results, along with data in the literature, show that Yb has an interesting low-absorption band in the ~12-24 eV range. The promising characteristics of Yb as a filter material in this region requires the development of a protection material due to the reactivity of Yb under normal atmosphere. The low absorption of Yb in the above range makes it also a candidate for a component of multilayer coatings in a spectral region in which few developments have been performed due to the lack of low absorption materials. The fl sum-rule was applied to extinction coefficient data in the whole spectrum that included the current data along with those of the literature, resulting in a value of 70.26, which is close to the expected value of 69.32.
The research on rare earths conducted by the current team addresses in this proceeding the transmittance measurement of
Ce films. Several thin films of Ce were deposited by evaporation in ultra high vacuum (UHV) conditions and their
transmittance was measured in situ in the 6-1,200 eV spectral range. Ce films were deposited onto grids coated with a
thin, C support film. Transmittance measurements were used to obtain the extinction coefficient of Ce films at each
individual photon energy investigated. Literature data for Ce films had been restricted to some parts of the current range,
with various experimental data at the strong N edge, a single set of data at the M edge, and no data at the O edge. The
energy range here investigated provides data encompassing M, N, and O edges of Ce, and this data set is extended
towards smaller energies with experimental data and towards larger energies with semi-empirical data and calculations.
Ce, as has been measured with other lanthanides, has a low-absorption band right below the O edge, with lowest
absorption at 16.1 eV. This makes Ce a promising material for filters and multilayer coatings in this spectral range, in
which few developments have been performed due to the lack of low absorption materials. The f1 sum-rule was applied
to the extinction coefficient data in the whole spectrum that included the current data along with those of the literature,
resulting in a value close to predictions, which shows the consistency of the current data.
B4C optical coating represents, together with Ir, Pt, SiC, one of best choice for high reflectance in the extreme ultraviolet
region (EUV 160-30 nm). This material is also used in multilayer for soft X-ray applications, such as Si/B4C or W/B4C,
or as interlayer in Mo/Si multilayer to avoid interdiffusion also because of its high thermal stability. Our work concerns
on B4C thin films deposited on Si [100] substrates by means of three different deposition techniques: RF plasma
magnetron sputtering, e-beam evaporation, pulsed laser ablation (PLD). We performed reflectance vs incidence angle
measurements from 5 nm to 152 nm on different samples deriving the optical constants with a least-square fitting
method. Complete films characterization have been carried out with compositional (XPS), structural (XRD) and
morphological (AFM, SEM) analyses.
In the extreme ultra-violet region, multilayer coatings are the only technique to obtain high reflectivity in normal incidence optical configurations. The interference process which regulates periodic multilayers behavior offers narrow-band spectral filtering without the use of additional filters, fact that makes these coatings particularly suitable for lines emission observations. Despite the large amount of possible materials combinations, Mo/Si multilayers are the standard choice for space research on plasma physics in the 13 - 30 nm spectral region. In this work Si/B4C is presented as an alternative material couple for the 30.4 nm selection. Attractive features are the better spectral purity and the second order reflectivity reduction. A possible application to the Sounding CORonagraph Experiment is described as an example. B4C thin films have been used to characterize this material in terms of optical constants in the 40 nm - 150 nm spectral region where, currently, only few data are available.
Long UV radiation exposure can result in damages of biological tissues, as burns, skin aging, erythema and even melanoma cancer. In the past years an increase of melanoma cancer has been observed and associated to the atmospheric ozone deployment. Attendance of sun tanning unit centers has become a huge social phenomena, and the maximum UV radiation dose that a human being can receive is regulated by law. On the other side, UV radiation is largely used for therapeutic and germicidal purposes. In all these areas, spectroradiometer and radiomenter are needed for monitoring UVA (315-400 nm), UVB (280-315 nm) and UVC (100-280 nm) irradiance. We have selected some commercial photodiodes which can be used as solid state detectors in these instruments. We have characterized them by measuring their absolute spectral response in the 200 - 400 nm spectral range.
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