The search of novel tools controlling the physical and chemical properties of matter at the nanoscale is crucial for developing next-generation integrated systems, with applications ranging from computing to medicine. Here, we show that thermal scanning probe lithography (t-SPL) can be a flexible tool for manipulating with nanoscale precision the surface properties of a wide range of specifically designed systems. In particular, we show that via t-SPL, we pattern nanoscale chemical patterns on polymeric substrates, which are then used to specifically bind extracellular matrix (ECM) proteins to the polymer surface. We demonstrate that the concentration of immobilized proteins can be controlled by varying the tip temperature, so that nanoscale protein gradients can be created. On a different system, we show that, by performing t-SPL on a thin film magnetic multilayer, in an external magnetic field, we are able to write reversibly magnetic patterns with arbitrarily oriented magnetization and tunable magnetic anisotropy. This demonstrates that t-SPL represents a novel, straightforward and extremely versatile method for the nanoscale engineering of the physicalchemical properties in a wide variety of materials.
Integrated Mach-Zehnder interferometers, ring resonators, Bragg reflectors or simple waveguides are commonly used as photonic biosensing elements. They can be used for label-free detection relating the changes in the optical signal in realtime, as optical power or spectral response, to the presence and even the quantity of a target analyte on the surface of the photonic waveguide. The label-free method has advantages in term of sample preparation but it is more sensitive to spurious effects such as temperature and refractive index sample variation, biological noise, etc. Label methods can be more robust, more sensitive and able to manipulate the biological targets.
In this work, we present an innovative labeled biosensing technique exploiting magnetic nano-beads for enhancement of sensitivity over integrated optic microrings. A sandwich binding is exploited to bring the magnetic labels close to the surface of the optical waveguide and interact with the optical evanescent field.
The proximity and the quantity of the magnetic nano-beads are seen as a shift in the resonance of the microring. Detection of antibodies permits to reach a high level of sensitivity, down to 8 pM with a high confidence level. The sizes of the nano-beads are 50 to 250 nm. Furthermore, time-varying magnetic fields permit to manipulate the beads and even induce specific signals on the detected light to easy the processing and provide a reliable identification of the presence of the desired analyte. Multiple analytes detection is also possible.
We report on the measurements of spin diffusion length and lifetime in Germanium with both magneto-electro-optical
and magneto-electrical techniques. Magneto-electro-optical measurements were made by optically inject in Fe/MgO/Ge
spin-photodiodes a spin polarized population around the Γ point of the Brillouin zone of Ge at different photon energies.
The spin diffusion length is obtained by fitting by a mathematical model the photon energy dependence of the spin
signal, due to switching of the light polarization from left to right, leading to a spin diffusion length of 0.9±0.2 μm at
room temperature. Non-local four-terminals and Hanle measurements performed on Fe/MgO/Ge lateral devices, at room
temperature, instead lead to 1.2±0.2 μm. The compatibility of these values among the different measurement methods
validates the use all of all of them to determine the spin diffusion length in semiconductors. While electrical methods are
well known in semiconductor spintronics, in this work we demonstrate that the optical pumping versus photon energy is
an alternative and reliable method for the determination of the spin diffusion length whereas the band structure of the
semiconductor allows for a non-negligible optical spin orientation.
Toward the design of large-scale electronic circuits that are entirely spintronics-driven, organic semiconductors
have been identified as a promising medium to transport information using the electron spin. This requires a
ferromagnetic metal-organic interface that is highly spin-polarized at and beyond room temperature, but this key building
block is still lacking. We show how the interface between Co and phthalocyanine molecules constitutes a promising
candidate. In fact, spin-polarized direct and inverse photoemission experiments reveal a high degree of spin polarization
at room temperature at this interface.
We report on spin-photodiodes based on fully epitaxial Fe/MgO/Ge(001) heterostructures for room temperature
integrated detection of light helicity at 1300 nm and 1550 nm wavelengths. The degree of circular polarization of
light determines the spin direction of photo-carriers in Ge that are filtered by the Fe/MgO analyzer. Spin-detection
experiments are performed by measuring the photocurrent while illuminating the spin-photodiodes with left or right
circularly polarized light, under the application of a magnetic field parallel to the light direction which drives the Fe
magnetization out of plane. We found that the spin-photodiodes spin filtering asymmetry is reduced by ∼40% in
forward bias and by less than 15% in reverse bias, when increasing the photon wavelength from 1300 nm to
1550 nm. This result, apparently counterintuitive because of the larger spin polarization of the photo-carriers
generated at 1550 nm with respect to that at 1300 nm, is explained in terms of the different spatial profile of carrier
generation inside Ge. The larger penetration depth of light at 1550 nm leads to a smaller polarization of photocarriers
when they reach the MgO tunneling barrier, due to the more efficient spin relaxation during transport.