A. Gasparotto

Co3O4/ZnO nanocomposites: from plasma synthesis to gas sensing applications.

Herein, we describe the design, fabrication and gas sensing tests of p-Co(3)O(4)/n-ZnO nanocomposites. Specifically, arrays of (001) oriented ZnO nanoparticles were grown on alumina substrates by plasma enhanced-chemical vapor deposition (PECVD) and used as templates for the subsequent PECVD of Co(3)O(4) nanograins. Structural, morphological and compositional analyses evidenced the successful formation of pure and high-area nanocomposites with a tailored overdispersion of Co(3)O(4) particles on ZnO and an intimate contact between the two oxides. Preliminary functional tests for the detection of flammable/toxic analytes (CH(3)COCH(3), CH(3)CH(2)OH, NO(2)) indicated promising sensing responses and the possibility of discriminating between reducing and oxidizing species as a function of the operating temperature.

On the performances of CuxO-TiO2 (x = 1, 2) nanomaterials as innovative anodes for thin film lithium batteries.

CuxO-TiO2 (x = 1, 2) nanomaterials are synthesized on polycrystalline Ti substrates by a convenient chemical vapor deposition (CVD) approach, based on the initial growth of a CuxO matrix (at 400 and 550 °C for x = 1 and 2, respectively) and the subsequent overdispersion of TiO2 at 400 °C. All CVD processes are carried out in an oxygen atmosphere saturated with water vapor. The obtained systems are investigated by means of glancing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical experiments. Galvanostatic charge/discharge measurements indicate that Cu2O-TiO2 nanomaterials exhibit very attractive high-rate capabilities (∼400 mA h g(-1) at 1 C; ∼325 mA h g(-1) at 2 C) and good stability after 50 operating cycles, with a retention of 80% of the initial capacity. This phenomenon is mainly due to the presence of TiO2 acting as a buffer material, i.e., minimizing volume changes occurring in the electrochemical conversion. In a different way, CuO-TiO2 systems exhibit worse electrochemical performances as a consequence of their porous morphology and higher thickness. In both cases, the obtained values are among the best ever reported for CuxO-based systems, candidating the present nanomaterials as extremely promising anodes for eventual applications in thin film lithium batteries.

Interaction between Fe, dopants, and secondary defects in MeV Fe ion implanted InP

We investigate the role of damage production and annealing in determining the Fe redistribution properties when implanting Fe at MeV energies in n-type InP. Fe ion implantation is performed at 2 MeV on (100) InP substrates, both undoped and Sn doped (1.5×1018 cm−3). Implants are performed both at room temperature (RT) and at 200 °C (HT), with doses ranging from 1×1013 to 1.2×1015 cm−2. A double implantation experiment is also performed, coimplanting Fe and P to investigate the influence of the P induced damage on the Fe redistribution/accumulation. Annealing is performed in the temperature range between 650 and 800 °C using flowing phosphine to prevent surface decomposition. To characterize the damage of our samples before and after annealing we employ Rutherford backscattering spectrometry in channeling condition and transmission electron microscopy; Fe depth profiles are measured by secondary ions mass spectrometry. A strict correlation is found between the position of Fe accumulation peaks and that of ...

HIGH-RESISTANCE BURIED LAYERS BY MEV FE IMPLANTATION IN N-TYPE INP

We performed 2 MeV Fe implantation at a temperature of 200 °C on n-type InP substrates with different background doping concentrations. We studied the activation of Fe atoms as compensating deep acceptors and the electrical properties of the implanted layers. Simulation of the current–voltage characteristics coupled with secondary ion mass spectrometry depth profiling was used to extract important parameters such as the activated Fe fraction, the resistivity, and the thickness of the compensated layers. Our results show that resistivities of the order of 107 Ω cm can also be obtained for background doping concentrations higher than 1×1018 cm−3, with active Fe concentration well above the known solid solubility limit.

Axial channeling of boron ions into silicon

Abstract Channeling boron implants were performed into (100) and (110) silicon substrates in the energy range 80–700 keV. The dose ranged between 3.5 × 1011 and 1 × 1015 atoms/cm2. The axial channeling concentration profiles of implanted B+ were compared with that obtained for incidence along the random direction of the crystal and with that obtained by implantation in amorphous silicon. The electrical and chemical boron distributions were obtained by spreading resistance and secondary ion mass spectrometry measurements, respectively. The inelastic stopping power, Sc, was extracted from the experimental maximum ranges for the [100] and [110] axis. The energ dependence of the electronic stopping power is given by Sc = KEp with p[100] = 0.469±0.010 and p[110] = 0.554±0.004. Simulations obtained by the MARLOWE code, using the Oen-Robinson impact parameter dependent formula, for the electronic energy loss reproduce quite well the experimental depth profiles.

Al‐O interactions in ion‐implanted crystalline silicon

The formation and dissolution of Si‐O‐Al precipitates have been investigated in Czochralski silicon wafers implanted with 6 MeV Al ions and thermally processed. The data have been compared to the O precipitation in samples implanted with 6 MeV Si or P ions. The amount of precipitated O atoms is about one order of magnitude higher for Al than for Si or P implanted samples. Moreover, a strong gettering of the Al atoms by the silicon dioxide precipitates has been observed. The precipitate evolution has been studied for different annealing times and temperatures. The oxygen precipitation has been simulated by the classical theory of nucleation and growth, with the introduction of new factors that take into account the implant damage distribution, the agglomeration of point defects during the initial stages of the annealing and the oxygen outdiffusion from the sample surface.

Fluorine doped Fe2O3 nanostructures by a one-pot plasma-assisted strategy

The present work reports on the synthesis of fluorine doped Fe2O3 nanomaterials by a single-step plasma enhanced-chemical vapor deposition (PE-CVD) strategy. In particular, Fe(hfa)2TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine) was used as molecular source for both Fe and F in Ar/O2 plasmas. The structure, morphology and chemical composition of the synthesized nanosystems were thoroughly analyzed by two-dimensional X-ray diffraction (XRD2), field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM). A suitable choice of processing parameters enabled the selective formation of α-Fe2O3 nanomaterials, characterized by an homogeneous F doping, even at 100 °C. Interestingly, a simultaneous control of the system nanoscale organization and fluorine content could be achieved by varying the sole growth temperature. The tailored properties of the resulting materials can be favourably exploited for several technological applications, ranging from photocatalysis, to photoelectrochemical cells and gas sensing.

Al‐O complex formation in ion implanted Czochralski and floating‐zone Si substrates

Aluminum ions at 100 MeV were implanted into floating‐zone (FZ) and Czochralski (CZ) grown Si substrates. At this energy the influence of the surface on the subsequent thermal treatment is negligible. In FZ samples the electrical active dose, as measured by spreading resistance profilometry, is independent of the annealing time at 1200 °C. In the CZ samples instead it considerably decreases with time. Secondary ion mass spectrometry analysis in CZ samples have revealed the presence of a multipeak structure around the projected range region for both Al and O signals. In FZ the structure is just detectable. The results imply that the Al‐O complex formation is enhanced by the presence of oxygen but that it is catalyzed by the damage created during the implant. The carrier profiles coincide in both CZ and FZ diffused substrates by predeposition of Al from a solid source, i.e., in damage‐free samples.

Mechanisms for the activation of ion-implanted Fe in InP

In this paper we present structural and electrical investigations on high temperature Fe-implanted InP. The aim of the work is to relate the lattice position of the implanted atoms after annealing treatments (from 300to600°C) with their electrical activation as compensating deep traps and to draw a comprehensive picture of the activation mechanisms. The overall results demonstrate that the electrical behavior and the Fe2+ deep trap activation properties are strictly connected to the annealing evolution of the implant-induced damage and to the escape process of the Fe atoms from substitutional sites, which in turn is controlled by the background doping density in the substrates.

Production of semi‐insulating layers in n‐doped InP by Fe implantation

A detailed study of Fe implantation and damage annealing in indium phosphide is presented. The technological goal was to obtain thermally stable semi‐insulating layers in n‐type InP. Different characterization techniques were employed, including structural (x‐ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy), chemical (secondary ions mass spectrometry), and electrical (current‐voltage) measurements. Both undoped and n‐type (Sn) doped substrates were implanted with Fe doses ranging from 5×1011 to 2.2×1014 cm−2 and annealed at a temperature of 650 °C. The high doses used to compensate n+ doping caused amorphization of the material. The reordering process of the amorphous layers and its influence on the Fe redistribution properties were studied in detail. The activation of the implanted Fe atoms after annealing was derived. Although the recovery process of the amorphized layer appears to be rather complex, our results show that good crystal quality and full compen...