Seminars and Events
Nanostructures, Surfaces, Coatings and Molecular Astrophysics
Coordinator: Rául Gago
21 September 2017, 15:00 h. Salón de Actos
Ion Irradiation Induced Highly Periodic and Crystalline Nanopatterns on Semiconductor Surfaces
Debasree Chowdhury and Debabrata Ghose
Variable Energy Cyclotron Centre, Kolkata, India
In recent era of device miniaturization, ordered arrays of crystalline nanostructures in large areas on semiconductor surfaces are essential. Here, I show the fabrication of highly crystalline and ordered nanostructures on Si(100), Ge(100) and GaAs surfaces by single step ion beam sputtering (IBS) technique by easy tuning of processing of different process parameters. Due to substrate rotation 5 rpm during 500 eV Ar+ ion irradiation at grazing incidence 75°, Si surface shows hexagonally ordered pure and crystalline nanodots. While, Ge surfaces show crystalline four-fold symmetric checkerboard patterns due to normal incidence 30 eV Ar+ ion irradiation. For similar condition of irradiation as Ge surface, GaAs surfaces show anisotropic nanoripples. These ripples show independent behavior with ion flux but coarsen with ion energy and become highly regular and nearly defect-free for 1 keV ion irradiation. Pattern formation at room temperature can be explained by the competition effect between curvature dependent ion erosion and surface diffusion processes, whereas, the temperature induced nanostructures is attributed to the biased diffusion of vacancies or adatoms arising from ES barrier.
05 September 2017, 12:00 h. Sala de Seminarios, 182
Thermal Scanning Probe Lithography: nano-patterning and nano-devices with high-resolution, within less processing steps, on novel materials
Yu Kyoung Ryu Cho
IBM Research Laboratory Zurich, Switzerland
An Atomic Force Microscope (AFM) can imaging molecules with atomic resolution. It also can fold and unfold a protein at high speed to study molecular dynamics. It can give information about the mechanical, compositional, electrical, magnetic properties of different materials with high resolution and minimal sample damage.
The AFM also can be used as a mask-less lithography technique, performed under ambient conditions applicable to any kind of materials. High resolution is achievable since only the area close to a sharp tip will be modified. Unlike optical lithography, it does not have diffraction limit. Unlike electron beam lithography, it does not have proximity effect or possible charging disturbance. Two factors that favors SPL in terms of resolution and overlay accuracy.
Some of the last results on thermal Scanning Probe Lithography (t-SPL) are being presented in the seminar: It is able to pattern arrays of 14 nm half-pitch lines that are transferable to a targeted substrate by reactive ion etching processing. The same process is used to a) make single electron transistors on an ultrathin silicon on insulator with sub-25 nm wide constrictions by etching the silicon and b) to make source-to-drain contacts with 50 nm distance on an InAs nanowire by lift-off processing. Finally, the same process is applicable to pattern sub-20 nm wide nanoribbons on MoS2 monolayers-based field-effect transistors.
16 March 2017, 11:00 h. Salón de Actos
Organic field effect transistors in biosensing and neurosciences
Life Sciences Dept., Università di Modena e Reggio Emilia, Modena , Italy
Organic bioelectronics is an emerging platform with impact in diagnostics,
loco-regional treatments and theranostics. It is largely based on organic field effect transistors (OFET) that can be operated as ultra-sensitive biosensors, transducers of electrical and electrochemical signals from cells, and stimulators for electroactive cells. Their applications range from detection of biomarkers in bodily fluids to implants for bidirectional communication with the central nervous system. Several OFET layouts have been demonstrated to be effective in aqueous operations, which are distinguished either by their architecture or by the respective mechanism of doping by the ions in the electrolyte solution. In this work we discuss first some fundamental aspects that concern the coupling mechanism of these devices with the biological systems, in particular we elucidate the role of
the different interfaces into greatly enhancing the sensitivity of these devices and their capability to amplify very small potential variations at the interfaces. We also show that this device, operated as a biosensor for a primary inflammatory citokine, i.e. TNF-alpha, responds
super-exponentially, and not linearly, in current vs analyte concentration in the sub-nM range. We unify the super-exponential and linear regimes by means of an alaysis of the density of states of the organic semiconductor channel upon the change of the electro-chemical potential caused by the adsorption of TNF-alpha. We finally show that the response is modulated by the gate voltage applied, and that is possible to measure the association binding constant of the antibody-antigen recognition, the molar free energy, and the electrostatic contribution to the
21 February 2017, 15:00 h. Sala de Seminarios, 182
Atomic Force Microscopy in controlled environment: a powerful tool for original experiments on hybrid systems, biomaterials, and biocomposites
Université Bretagne Sud, CNRS Centre de Recherche C. Huygens
There is a growing research interest on hybrid systems, biomaterials, and biocomposites because of their industrial application demands. Owing unique properties of these materials make more attractive in electronic, medical and transport applications.
Whatever the application field, a constant need of miniaturization, performance, structure lightening necessitates working and exploring the material properties at nanoscale. To do this, one of the most powerful tool is Atomic Force Microscopy (AFM). By using AFM nanoscale tips, which interact with matter due to attractive and repulsive forces, numerous properties can be studied systematically. Due to its strong impact on properties and behaviour, temperature is considered as a key parameter. Indeed, its variations induce a significant change in material behaviour which can be positive (adhesion for example) or negative (electrical change). Consists of tip, micro-lever, photodetector, laser and control loop, the AFM can be used in different modes i.e. tapping, contact, non-contact, and PeakForce QNM. Consequently, a wide selection of measurements can be made under controlled environment (humidity, liquids, temperature, etc.,), and with different purposes such as topography, electrical measurements, force measurements, PeakForce-QNM.
To illustrate the contribution of the technics, different applications are presented. In the first part, a combination of AFM and RX reflectivity is used to understand the structure and interfaces of hybrid nanofilms (Polystyren/Gold) at different temperatures (-20°C to 220°C). In this way, AFM has been used to highlight different properties which are not possible to study by other technics such as electrical behaviour, adhesion and surface characterization with a new method
23 January 2017, 12:00 h. Salón de Actos
Semiconductor nanowire photonics
Friedrich-Schiller-University of Jena, Germany
The miniaturization of light sources, the confinement and manipulation of light on a sub-wavelength scale as well as the detection of single photons are key challenges for the realization of future photonic circuits. Here, semiconductor nanowires are of major interest as a serving material platform, since they do not only offer superior photonic properties, but can also bridge the interface to electronic circuits enabled by their semiconducting properties. The efficient and sub-wavelength waveguiding of light is one of such superior photonic properties specifying nanowires as truly one-dimensional systems for photons. It is also an important prerequisite and defines the geometrical diameter limit for enabling lasing oscillations within nanowire cavities. High pumping powers and gain values are necessary in order to overcome the thresholds for amplified spontaneous emission (ASE) and laser oscillations. We determined those thresholds for both ZnO and CdS nanowires as well as the geometrical limitations. Furthermore, the laser output originating out of the end facet of a single nanowire was detected “head-on”, and a double pump technique was applied to measure the laser dynamics. Finally, I will present in this seminar a route for “optical doping” of such nanowires, which provides a useful benchmark for the future development of these nanoscale devices, as well as the possibility of coupling with plasmonic structures.