Stefano Frabboni

Single-metalloprotein wet biotransistor

Metalloproteins are redox molecules naturally shuttling electrons with high efficiency between molecular partners. As such, they are candidates of choice for bioelectronics. In this work, we have used bacterial metalloprotein azurin, hosted in a nanometer gap between two electrically biased gold electrodes, to demonstrate an electrochemically gated single-molecule transistor operating in an aqueous environment. Gold-chemisorbed azurin shows peaks in tunneling current upon changing electrode potential and a related variation in tunneling barrier transparency which can be exploited to switch an electron current through it. These results suggest the wet approach to molecular electronics as a viable method for exploiting electron transfer of highly specialized biomolecules.

Strain determination in silicon microstructures by combined convergent beam electron diffraction, process simulation, and micro-Raman spectroscopy

Test structures consisting of shallow trench isolation (STI) structures are fabricated using advanced silicon (Si) technology. Different process parameters and geometrical features are implemented to investigate the residual mechanical stress in the structures. A technology computer aided design homemade tool, IMPACT, is upgraded and optimized to yield strain fields in deep submicron complementary metal–oxide–semiconductor devices. Residual strain in the silicon substrate is measured with micro-Raman spectroscopy (μ-RS) and/or convergent beam electron diffraction (CBED) for large (25 μm) and medium size (2 μm), while only CBED is used for deep submicron STI (0.22 μm). We propose a methodology combining CBED and technology computer aided design (TCAD) with μ-RS to assess the accuracy of the CBED measurements and TCAD calculations on the widest structures. The method is extended to measure (by CBED) and calculate (by TCAD) the strain tensor in the smallest structures, out of the reach of the μ-RS technique....

Highly efficient electron vortex beams generated by nanofabricated phase holograms

We propose an improved type of holographic-plate suitable for the shaping of electron beams. The plate is fabricated by a focused ion beam on a silicon nitride membrane and introduces a controllable phase shift to the electron wavefunction. We adopted the optimal blazed-profile design for the phase hologram, which results in the generation of highly efficient (25%) electron vortex beams. This approach paves the route towards applications in nano-scale imaging and materials science.

Application of convergent beam electron diffraction to two-dimensional strain mapping in silicon devices

A method of obtaining quantitative two-dimensional (2D) maps of strain by the convergent beam electron diffraction technique in a transmission electron microscope is described. It is based on the automatic acquisition of a series of diffraction patterns generated from digital rastering the electron spot in a matrix of points within a selected area of the sample. These patterns are stored in a database and the corresponding strain tensor at each point is calculated, thus yielding a 2D strain map. An example of application of this method to cross-sectioned cells fabricated for the 0.15 μm technology of flash memories is reported.

Fabrication by electron beam induced deposition and transmission electron microscopic characterization of sub-10-nm freestanding Pt nanowires

We present a method to reduce the size and improve the crystal quality of freestanding nanowires grown by electron beam induced deposition from a platinum metal organic precursor in a dual beam system. By freestanding horizontal growth and subsequent electron irradiation in a transmission electron microscope, sub-10-nm polycrystalline platinum nanowires have been obtained. A combined transmission electron microscopy–electron energy loss analysis has shown that the amorphous carbon, mixed to nanocrystalline platinum in the as-deposited material, is removed from the wires during irradiation. The same treatment progressively transforms nanocrystals dispersed in the amorphous matrix in a continuous polycrystalline platinum wire.

HELIUM-IMPLANTED SILICON : A STUDY OF BUBBLE PRECURSORS

The interaction of helium atoms with the radiation damage imparted to (100) silicon single crystal by He+ implantation at 5×1015 cm−2, 20 keV, and liquid–nitrogen temperature is investigated by means of various complementary techniques during and after thermal treatments. Thermal programmed desorption was used to study the dissociation kinetics of helium from the defects and to plan suitable heat treatments for the other techniques. The helium profiles were determined by 8 MeV 15N2+ elastic recoil detection, quantitative data on damage were obtained by channeling Rutherford backscattering spectrometry, double crystal x-ray diffraction, and positron annihilation spectroscopy. Isothermal treatments at 250 °C produce first helium redistribution and trapping in vacancy-like defects, rather than helium desorption from traps. The process is thermally activated with an effective activation energy, dispersed in a band from 1.1 to about 1.7 eV. For higher temperature treatments (2 h at 500 °C) the traps are almost...

Solid‐phase epitaxial growth of Ge‐Si alloys made by ion implantation

Solid‐phase epitaxial growth was studied in germanium‐implanted 〈100〉 silicon wafers as a function of germanium fluence, annealing temperature, and time. MeV He Rutherford backscattering in channeling conditions, cross‐sectional transmission electron microscopy, double‐crystal x‐ray diffraction, and secondary‐ion mass spectroscopy techniques were used to characterize the samples. At low fluences, up to 1×1015 cm−2 at 130 keV, the crystallization kinetics is similar to that measured on self‐amorphized silicon. In the high‐dose samples, prepared by multiple implants with a total dose of 3.12×1016 cm−2, the growth rate at fixed temperatures decreases. A comparison with literature data, obtained by similar experiments performed on amorphized uniform GexSi100−x films prepared by molecular‐beam epitaxy or chemical‐vapor deposition, reveals that the concentration gradient, unavoidable in implanted samples mainly at the end of the ion range region, is strictly connected with the observed decrease.

Techniques for mechanical strain analysis in sub-micrometer structures: TEM/CBED, micro-Raman spectroscopy, X-ray micro-diffraction and modeling

In this paper, three techniques are discussed that provide information on process-induced local mechanical stress in silicon: the convergent beam electron diffraction technique of transmission electron microscopy, X-ray micro-diffraction and micro-Raman spectroscopy. We discuss the principles of these techniques, their spatial resolution, the ease-of-use, the information that can be obtained, the required sample preparation, the measurement time, and the complementarities of these techniques. We demonstrate this for stress induced by shallow trench isolation and correlate the results to finite element analysis results.

Structure and stability of nickel/nickel oxide core–shell nanoparticles

The results of a combined x-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM) study of Ni nanoparticles (NP), before and after oxidation, are presented. An experimental set-up was realized for the preparation and study of pre-formed NP films, concentrating the attention on Ni NP in the diameter range between 4 and 8 nm. The XPS data were taken in situ from NPs after different stages of oxidation, including controlled dosing of O(2) gas in the experimental system and exposure to the atmosphere. The Ni 2p structure is a combination of spectra from metallic Ni in the NP core and from the oxide shell. The signal from the NP core was observed even for samples after exposure to air. From the comparison of HR-TEM experimental images with theoretical simulations, it was found that the Ni NP core has a regular multitwinned icosahedral structure, composed of single-crystal tetrahedra with (111) faces. The NiO phase is clearly observed forming islands on the NP surface.

nlinImproving spatial resolution of convergent beam electron diffraction strain mapping in silicon microstructures

Despite the use of nanometer-sized probes in field emission transmission electron microscopes, the spatial resolution in strain analysis performed by convergent beam electron diffraction is limited in one direction by the need for tilting the cross-sectional sample in the electron microscope off the vertical ⟨110⟩ direction. We demonstrate that it is possible to improve this resolution by using the ⟨340⟩ zone axis, instead of the ⟨230⟩ one, which has recently become of common use in the analysis of silicon microdevices. Quantitative strain information with good sensitivity and accuracy can be obtained in the new axis. An example of application to the two-dimensional strain mapping in shallow trench isolation structures, obtained with a scanning attachment and a high-angle annular dark-field detector, is reported.