In recent years, the ability to pattern large areas at the micro- and nano-scale with stimuli-responsive materials has opened the opportunity to engineer surface structures and trigger peculiar properties such as complex optical functionalities or surface properties by laser-matter interactions. The use of light-sensitive materials, such as azobenzene compounds, can open the opportunity to active manipulate in terms of morphology, physical and mechanical properties a pre-patterned architectures, which are intrinsically static once fabricated.
We employ azopolymers, in which the rapid and reversible photoisomerization reaction of azobenzene molecules can actuate mass transport phenomena typically parallel to the light polarization. The azopolymeric film is patterned by soft-imprinting as an array of micro-holes showing a well-defined isotropic round pores. Upon a linearly polarized illumination (365 nm, 150 W/cm2), we observe a deformation of the initial holes along the polarization direction, in such a way that the circular pores are transformed into long closed slits. A rotation of the polarization by 90° triggers a reconfiguration of the pristine round shape, with a good degree of control of the photo-induced pore reshaping. Due to the polarized-directionality of the photo-manipulation we demonstrate the possibility to tune the pristine morphology and properties along specific directions, providing a smart engineered platform with different reshaped micro-patterns. The light-induced contraction and expansion reshaping strategy of a porous polymeric structures shows exciting potential for a number of applications including microfluidics, lithography and tissue engineering. Tuning cells behavior in response to material manipulation cues is a promising goal in biology
In this work we investigate new degrees of freedom in controlling the physical properties of structured photo-sensitive materials that can be usefully exploited in many application fields. We employ azopolymers, a class of light responsive materials, which are structured in micro-pillar array. A reversible and controlled change in morphology of a pre-patterned polymeric film under properly polarized illumination is demonstrated to provide the opportunity to engineer surface structures and dynamically tune their properties. We exploit the laser process taking advantage of the light-induced deformation of a micro-textured azopolymeric film in order to modify the surface hydrophobicity along specific direction.
Optoelectronic properties of Er3+-doped slot waveguides electrically driven are presented. The active waveguides have been coupled to a Si photonic circuit for the on-chip distribution of the electroluminescence (EL) signal at 1.54 μm. The Si photonic circuit was composed by an adiabatic taper, a bus waveguide and a grating coupler for vertical light extraction. The EL intensity at 1.54 μm was detected and successfully guided throughout the Si photonic circuit. Different waveguide lengths were studied, finding no dependence between the waveguide length and the EL signal due to the high propagation losses measured. In addition, carrier injection losses have been observed and quantified by means of time-resolved measurements, obtaining variable optical attenuation of the probe signal as a function of the applied voltage in the waveguide electrodes. An electro-optical modulator could be envisaged if taking advantage of the carrier recombination time, as it is much faster than the Er emission lifetime.
In this work, the optoelectronic properties of silicon light emitting field-effect transistors (LEFETs) have been
investigated. The devices have been fabricated with silicon nanocrystals in the gate oxide and a
semitransparent polycrystalline silicon gate. We compare the properties of LEFET with a more conventional
MOS-LED (two-terminal light-emitting capacitor) with the same active material. The ~45 nm thick gate siliconrich
oxide is deposited in a size-controlled multilayer geometry by low pressure chemical vapor deposition
using standard microelectronic processes in a CMOS line. The multilayer stack is formed by layers of silicon
oxide and silicon rich silicon oxide. The nanocrystal size and the tunneling barrier width are controlled by the
thickness of silicon-rich silicon oxide and stochiometric silicon oxide layers, respectively. The silicon
nanocrystals have been characterized by means of spectrally and time resolved photoluminescence, high
resolution TEM, and x-ray photoelectron spectroscopy. Resistivity of the devices, capacitance, and
electroluminescence under direct and pulsed injection current scheme have been studied and here reported.
The optical power density and the external quantum efficiency of the LEFETs will be compared with the MOSLED
results. This study will help to develop practical optoelectronic and photonic devices via accurate
modeling and engineering of charge transport and exciton recombination in silicon nanocrystal arrays.
The convergence of photonics and microelectronics within a single chip is still lacking of a monolithical on-chip optical
amplifier. Rare-earth doped slot waveguides show a large potential as on-chip source. Slot waveguides with silicon
nanocrystals embedded in a dielectric host matrix can increase the light confinement in the active layer and allow
electrical injection. In this work, horizontal slot waveguides formed by two thick silicon layers separated by a thin
erbium doped silicon rich silicon oxide layer are studied as on-chip optical amplifiers. The waveguides are grown in a
CMOS line with the active material grown by low-pressure chemical vapor deposition. Optical tests are performed and
light propagation in the slot waveguides is observed. Using the cut-back technique, spectra propagation losses are
evaluated. Room temperature electroluminescence is observed at 1.54 μm. Transmitted optical signal resonant with Er
absorption is studied as a function of the injected current for different probing laser wavelengths.
The design, optical characterization and sensoristic capability provided by a complementary metal-oxide-semiconductor
(CMOS) compatible integrated sensor based on a μ-disk resonator cavity are reported. The working principle of the
presented device consists in monitoring the changes in the effective refractive index of the supported optical modes
induced by variations of the refractive index of the surrounding material. The detection system has been designed on the
base of a high quality factor (Q=1.4×104) Si-rich Si3N4 (SRSN) μ-disk - emitting in the VIS under optical pumping -
bottom coupled to a low loss passive stoichiometric Si3N4 waveguide (WG), with losses values under 1 dB/cm measured
in the same spectral region. The PL emission in the VIS range provided by the SRSN enable the use of Si-based
detectors, easily integrable using the current CMOS standard technology. Proof of concept measurements performed on
the coupled device revealed a good sensitivity of 51.79 nm/RIU (Refractive Index Unit), in accordance with the
simulated data, and a minimum detection limit of 1.1 × 10-3 RIU.