The main characteristics of the ENEA Discharge Produced Plasma (DPP) Extreme Ultraviolet (EUV) source are presented together with results of irradiations of various materials. The DPP EUV source, based on a Xe–plasma heated up to a temperature of 30 ÷ 40 eV, emits more than 30 mJ/sr/shot at 10 Hz rep. rate in the 10 ÷ 18 nm wavelength spectral range. The DPP is equipped with a debris mitigation system to protect particularly delicate components needed for patterning applications. The ENEA source has been successfully utilized for sub–micrometer pattern generation on photonic materials and on specifically designed chemically amplified resists. Details down to 100 nm have been replicated on such photoresists by our laboratory–scale apparatus for contact EUV lithography. Preliminary EUV irradiations of graphene films aimed at modifying its properties have been also performed.
Due to its chemical specificity, the near edge X-ray absorption fine structure spectroscopy is an interesting technique to study the changes in hybrid organic-inorganic photoresists. In this work, we analyzed the chemical changes occurring in photoresists synthesized from organically modified precursors and transition metal alkoxides by sol-gel route. These systems are nonchemically amplified resists for ultraviolet, extreme ultraviolet, and electron beam lithography. They are based on Si, Zr, and Ti oxides or a combination of these. The experiments were conducted at the PolLux beamline of the Swiss Light Source, by a scanning transmission X-ray microscopy, which combines the spatially-resolved microscopy and fine structure spectroscopy at once. The absorption spectra were collected in the energy range of the carbon edge (≈ 290 eV) before and after in situ exposure of the photoresists to 500 eV photons. The variations in peak intensity after exposure reveal the changes in the chemical environment of carbon and the chemical configuration of the organic ligands, regardless of the inorganic part. It was found that the photon exposure induced sizable photodegradation or photopolymerization of organic groups (phenyl or methyl methacrylate, respectively). These mechanisms contribute to the foundation for the exposure reaction in negative-tone hybrid photoresists. Interestingly, it was also found that the detachment of the phenyl ligand occurs in a variety of possible pathways to condensation. We believe that our results and approach can provide a better understanding of photochemistry of resists, in particular for extreme ultraviolet lithography.
Nanoporous TiO2 anatase film has been investigated as sensitive layer in Surface Plasmon Resonance sensors for the
detection of hydrogen and Volatile Organic Compounds, specifically methanol and isopropanol. The sensors consist of a
TiO2 nanoporous matrix deposited above a metallic plasmonic grating, which can support propagating Surface Plasmon
Polaritons. The spectral position of the plasmonic resonance dip in the reflectance spectra was monitored and correlated
to the interaction with the target gases.
Reversible blue-shifts of the resonance frequency, up to more than 2 THz, were recorded in response to the exposure to
10000 ppm of H2 in N2 at 300°C. This shift cannot be explained by the mere refractive index variation due to the target
gas filling the pores, that is negligible.
Reversible red-shifts were instead recorded in response to the exposure to 3000 ppm of methanol or isopropanol at room
temperature, of magnitudes up to 14 THz and 9 THz, respectively. In contrast, if the only sensing mechanism was the
mere pores filling, the shifts should have been larger during the isopropanol detection.
We therefore suggest that other mechanisms intervene in the analyte/matrix interaction, capable to produce an injection
of electrons into the sensitive matrix, which in turn induces a decrease of the refractive index.
Engineered organic-inorganic hybrid materials, HyMat, offer new opportunities for the easy, fast and cheap development
of miniaturized functional devices. The integration of inorganic oxide networks, organic functional groups and optically
active molecules or nanoparticles allows to obtain combinations of properties and structures otherwise impossible with
traditional materials.
In particular, a simple and highly versatile synthesis platform enabling preparation of HyMat is presented, which is built
up by a bottom-up sol-gel approach at low processing temperatures. A few types of key building blocks pave the way for
accessing HyMat and make up their formulation, providing a means to synthesize innovative materials enabling to get:
- optically active micro and nanostructures;
- miniaturized sensors for analytes in gaseous or liquid media;
- direct patternability with a range of lithographic techniques;
- variable inorganic and organic compositions, and controlled porosity.
Examples of micro and nanostructures based on these spin-on materials with ceramic (i.e. SiO2, GeO2, Al2O3, ZrO2,
TiO2,) and hybrid compositions will be presented for different applications including plasmonic or fluorescent sensors,
dry-etching masks with outstanding resistance, optically active micro and nanostructured platforms and high resolution
patterns.
We present the design, realization and characterization of active deformable gratings for extreme-ultraviolet monochromators for ultrashort pulses. The core device consists of a bimorph deformable mirror on the top of which a diffraction grating with laminar profile is realized by UV lithography. The curvature radius of the grating substrate can be varied changing the voltage applied to an underlying piezo-actuator. The advantage of this technology is to provide gratings with high optical quality, robust, compatible with any coating deposition and realized with only vacuumcompatible materials. We present the characterization of a time-delay compensated monochromator realized with these devices, showing that the active grating can optimize the beam focusing through its rotation and deformation. Two equal active gratings have been mounted in a compensated configuration to realize a grazing-incidence double-grating monochromator for the spectral selection of ultrashort pulses and the simultaneous compensation of the pulse front-tilt given by the diffraction. The wavelength scanning is performed by the first grating through rotation. The radiation is focused on the intermediate plane, where a slit carries out the spectral selection. Finally, the second grating compensates for the pulse front-tilt given by the first one. The spectral focusing of both gratings is maintained at the different wavelengths through the variation of the radii of curvature. The instrument has been tested with a Ti:Sa laser operated at 800 nm. We have been able to demonstrate that the double-grating configuration with active gratings compensates for the pulse front-tilt, that is reduced from 1 ps at the intermediate plane to 100 fs at the output. The final value is limited by the group delay dispersion of the monochromator within the 10-nm bandwidth of the laser. A configuration for the selection on XUV ultrashort pulses has been theoretically studied and the expected performances presented. Active gratings may be considered as a cheaper and more flexible alternative to standard gratings for the realization of extremeultraviolet monochromators for ultrafast pulses, such as free-electron lasers and high-order laser harmonics.
In the last years inorganic semiconductor (particularly CdSe and CdS) quantum dots (QDs) have received great attention
for their important optical properties. The possibility to tune the emission wavelength, together with their high
fluorescence quantum efficiency and photostability, can be exploited in photonic and optoelectronic technological
applications. The design of DFB devices, based on QDs as active optical material, leads to the realization of compact
laser systems. In this work we explore the use of an inorganic/organic hybrid material composed of CdSe-ZnS
semiconductor quantum dots doped into a zirconia sol-gel matrix for optical gain applications. Through the use of soft
lithography on a sol-gel germania-silica hybrid, large scale distributed feedback gratings can be created. Used in
conjunction with the CdSe-ZnS/ZrO2 hybrids, these gratings can act as microcavities and allow for the realization of true
lasing action. The lasing properties within these devices are characterized in the femtosecond regime by both one- and
two-photon excitation. From experimental data the value of the optical gain of the core-shell quantum dot samples has
been estimated. Moreover, one- and two-photon lasing threshold and stability are reported.
Two and three dimensional structures with micron and submicron resolution have been achieved in commercial resists,
polymeric materials and sol-gel materials by several lithographic techniques. In this context, silicon-based sol-gel
materials are particularly interesting because of their versatility, chemical and thermal stability, amount of embeddable
active compounds. Compared with other micro- and nano-fabrication schemes, the Two Photon Induced Polymerization
is unique in its 3D processing capability. The photopolymerization is performed with laser beam in the near-IR region,
where samples show less absorption and less scattering, giving rise to a deeper penetration of the light. The use of
ultrashort laser pulses allows the starting of nonlinear processes like multiphoton absorption at relatively low average
power without thermally damaging the samples.
In this work we report results on the photopolymerization process in hybrid organic-inorganic films based
photopolymerizable methacrylate-containing Si-nanobuilding blocks. Films, obtained through sol-gel synthesis, are
doped with a photo-initiator allowing a radical polymerization of methacrylic groups. The photo-initiator is activated by
femtosecond laser source, at different input energies. The development of the unexposed regions is performed with a
suitable solvent and the photopolymerized structures are characterized by microscopy techniques.
In this work we report on the study of the photopolymerization process in hybrid organic-inorganic films containing photopolymerizable acrylic and methacrylic groups and. The films are doped with a proper photo-initiator for radical polymerization of (meth)acrylic units and are prepared using the sol-gel technique.
The photo-initiator is activated by using continuum (single-photon polymerization) or pulsed (two-photon polymerization) laser sources at different wavelengths. After the development of the unexposed regions with a suitable solvent, the photopolymerized structures are observed with microscopy techniques. The effects of the composition of the photopolymerizable mixture, the irradiation parameters (laser power and exposure time) and the external atmosphere in which the photopolymerization is performed are investigated.
The fabrication of 3D microstructures using multiphoton absorption processes is a promising technique that involves low amount of incident exposure dose with potentially high spatial resolution.
Organic-inorganic hybrid materials, composed of inorganic oxide structures and interpenetrated cross-linked organic
polymers, are promising candidates for electro/optical applications, combining the most important glasslike and
polymerlike properties. This is particularly true when large laser power density is used: these materials show high laser
damage resistance compared with that of polymeric systems.
A deep study of effects and causes of laser damage has never been done, especially for hybrid materials. The
mechanisms of optical damage depend on different factors like laser experimental parameters, such as pulse duration,
beam size and wavelength, or the microstructural characteristics and defects of the material.
Hybrid materials possessing desired shapes and optical and mechanical properties are well synthesized by the sol-gel
technique. The use of Glycidoxypropyltrimethoxysilane (GPTMS) allows preparing heterogeneous and resistant
materials, with good optical properties.
Different sol-gel matrices have been prepared in order to study their laser damage resistance. The possibility of varying
the catalysts and precursors or the synthesis protocol allows obtaining materials with similar chemical composition and
different microscopical properties. By this way, it is possible to study the laser damage threshold of these samples and to
find the way to enhance and optimize the laser damage resistance, useful in non-linear optical devices.
A hybrid organic-inorganic sol-gel material based on 3-(glycidoxypropyl)-trimethoxysilane (GPTMS), an organically modified alkoxide containing an epoxy ring in the organic functional group, and titanium isopropoxide Ti(OPri)4 has been synthesised. The presence of Ti alkoxide is important in order to increase the refractive index and to improve the mechanical and physical properties of the film. A basic catalysis has been used to perform the hydrolysis/condensation reactions of the inorganic network and to preserve the presence of unreacted epoxy rings. The epoxy groups are thus available in the final solid state films for the UV-photopolymerization process. The photopolymerization allows one to increase the refractive index and to pattern the film directly.
The modification of the hybrid sol-gel TiO2 matrix microstructure during the thermal treatment and the interaction with the UV light have been investigated by FT-IR and UV-Vis spectroscopies, DTA and TGA thermal analysis. The sol-gel film thickness and roughness have been analyzed by a profilometer: the films possess high optical quality and well controlled thickness, ranging from 500 nm to 2 μm. The refractive index of sol-gel thin films was measured by m-line spectroscopy and ellipsometry. An increase of the refractive index in the range 0,02÷0,1 was achieved, depending on the UV irradiation dose.
A novel scheme for implementing the joint exploitation of different, somehow complementary mechanisms of nonlinear transmission in an optical limiting device is proposed. As active materials we have chosen the fullerene derivative FULP, as a reverse saturable absorber, and a new heterocyclic quadrupolar dye, PEPEP, with highly efficient multiphoton absorption for nanosecond pulses. The nonlinear absorption properties of PEPEP in solution are extensively investigated for both femtosecond and nanosecond pulses. When Z-scan experiments are performed with nanosecond pulses, much larger effective cross sections are measured than with femtosecond pulses and with remarkably different wavelength dispersion. This is interpreted as due to two-photon absorption followed by one-photon absorption from the excited state. Chemically modified nonlinear molecules are incorporated in a hybrid organic-inorganic sol-gel matrix. Sufficiently high concentrations are achieved to allow the assembling of thin sol-gel disks into a "tandem" limiter with a total thickness smaller than the Rayleigh range of the focused laser beam. Preliminary testing of our limiter is reported and shows encouraging results. The resistance of the FULP-doped sol-gel glass to laser damage is substantially improved and the nonlinear attenuation at high pulse energies is enhanced.
A hybrid organic-inorganic material derived 3- (glycidoxypropyl)-trimethoxysilane (GPTMS) and fullerene derivatives has been developed for optical limiting applications. The control of the final material has been achieved by engineering the matrix-fullerene solid-state system. Different Lewis acids (Zr(OBut)4, Ti(OBut)4, BF3, SiCl4, and TiCl4) have been used as the catalysts of the epoxy ring opening of (GPTMS) and the polyethylene oxide formation, in three different syntheses, to control and optimize the matrix- fullerene interaction and the optical limiting properties. The microstructure of the hybrid matrix has been studied by Fourier Transform Infra-Red Spectroscopy. UV-vis spectra and optical limiting measurements of the doped materials showed that in the Zr(OBut)4, TiCl4, BF3 derived matrices clustering of fulleropyrrolidine molecules is avoided and optical limiting is obtained. In the Ti(OBut)4, SiCl4, and not epoxy catalyzed derived matrices, instead, the aggregation of fulleropyrrolidines degraded the optical limiting properties. The laser damage threshold in the Zr(OBut)4, TiCl4 and especially BF3 derived matrices was larger than in the other matrices. Moreover, a multilayer system has been fabricated to develop an optical limiting device.
We report the synthesis of sol-gel materials based on highly efficient heterocycle-based push-pull chromophores showing second- and third-order nonlinear optical activity. We show the proper functionalization of the best performing chromophores and their incorporation into a hybrid organic- inorganic sol-gel matrix. Different types of functionalization of the active molecule have been considered, including hydroxyl and alkoxysilyl end-groups. The functionalization strategy responded to different criteria such as stability and synthetic availability of the final molecular precursors, their solubility, and the used synthetic approach to the sol-gel material. The synthesis of the sol-gel materials has been tuned in order to preserve molecular properties and control important factors such as final concentration of the active dye in the matrix. Both acid- and base-catalyzed sol-gel synthesis has been taken into account. 3-Glycidoxypropyltrimethoxysilane and 3- aminopropyltriethoxysilane have been used as the organically modified alkoxides to prepare the hybrid organic-inorganic matrix. Characterization of the spectroscopic properties of the sol-gel materials is presented.
Some recent results of a research work aimed at exploiting the potentialities of fullerene derivatives to obtain sol- gel glassy materials for use as optical limiters are reported. The solubility of fullerene derivatives in organic solvents compatible with the sol-gel process has been increased by more than two orders of magnitude by suitable functionalization of C60. Covalent linking to the glassy matrix is favored by introducing silicon alkoxide groups in the fullerenes. The optical limiting properties of these derivatives in toluene solution are comparable to those of the parent compound and exhibit enhancement in the red spectral range. Optical-quality films of various thickness are obtained by incorporating the C60 derivatives at high concentration in organically modified sol-gel matrices. These materials exhibit high resistance to laser damage and can be used to build multilayer structures optimized for optical limiting.
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