Summary The (110)-oriented misfit dislocation density reduction in the growth of Inx Gal−xAs (x-... more Summary The (110)-oriented misfit dislocation density reduction in the growth of Inx Gal−xAs (x-0.06) heterostructure on GaAs (001) substrate patterned with circular mesas has been observed with X-ray double-crystal topography. It has been found that, depending on the InGaAs thickness on the mesa sidewall, there is athreshold which inhibits the glide of threading dislocations through the mesas. No misfit dislocations are
Czechoslovak Journal of Physics - CZECH J PHYS, 2000
Precise knowledge of the incident and diffracted X-ray beams related to flat crystal diffractors ... more Precise knowledge of the incident and diffracted X-ray beams related to flat crystal diffractors is important for X-ray diffraction optics and for high resolution experiments. In the paper, three-dimensional reciprocal space concept has been applied to study general case of the flat diffractor. The incident and diffracted beams have been determined for the middle of the range of total reflection for both the standard asymmetrical and the inclined asymmetrical diffractor. For an asymmetric diffractor rotating about its reciprocal lattice vector unexpectedly large out-of-plane-of-diffraction components of the beams have been obtained. The largest ones have been found not for the angle of rotationω=90° corresponding to a symmetrical inclined diffractor but for the angle close to the grazing incidence case.
Hard X-rays (with energies in the 70 KeV - 1 MeV range) focusing is a crucial issue for astronomy... more Hard X-rays (with energies in the 70 KeV - 1 MeV range) focusing is a crucial issue for astronomy in the X-rays and gamma-ray energy range. Due to the narrow angular range of diffraction at high gamma-rays energies, perfect crystals cannot be used for such application. Mosaic crystals have been proposed, but their efficiency cannot exceed 50%. In order to increase the diffraction efficiency, bent crystals have been proposed showing good performances. For bent crystals the diffraction range is given by the total curvature of the crystal lattice planes and the diffraction eficiency can reach values close to 100%. In this work we propose a crystal bending procedure obtained by a controlled surface damaging. The damaging procedure introduces a defected superficial layer, undergoing a high compressive strain of a few tens nanometer in thickness. Several oriented silicon and gallium arsenide wafers have been treated. By using high resolution X-ray diffraction measurements in Bragg conditi...
Abstract GaAs, Cu, CdTe, and CdZnTe crystals have been studied as optical elements for lenses for... more Abstract GaAs, Cu, CdTe, and CdZnTe crystals have been studied as optical elements for lenses for hard x-ray astronomy. High-resolution x-ray diffraction at 8 keV in Bragg geometry and at synchrotron at energies up to 500 keV in Laue geometry has been used. A good ...
Nitroaromatic explosives are the most common explosives, and their detection is important to publ... more Nitroaromatic explosives are the most common explosives, and their detection is important to public security, human health, and environmental protection. In particular, the detection of solid explosives through directly revealing the presence of their vapors in air would be desirable for compact and portable devices. In this study, amino-functionalized carbon nanotubes were used to produce resistive sensors to detect nitroaromatic explosives by interaction with their vapors. Devices formed by carbon nanotube networks working at room temperature revealed trinitrotoluene, one of the most common nitroaromatic explosives, and di-nitrotoluene-saturated vapors, with reaction and recovery times of a few and tens of seconds, respectively. This type of resistive device is particularly simple and may be easily combined with low-power electronics for preparing portable devices.
In this paper, we model the electrical properties of germanium nanowires with a particular focus ... more In this paper, we model the electrical properties of germanium nanowires with a particular focus on physical mechanisms of electrical molecular sensing. We use the Tibercad software to solve the drift-diffusion equations in 3D and we validate the model against experimental data, considering a p-doped nanowire with surface traps. We simulate three different types of interactions: (1) Passivation of surface traps; (2) Additional surface charges; (3) Charge transfer from molecules to nanowires. By analyzing simulated I–V characteristics, we observe that: (i) the largest change in current occurs with negative charges on the surfaces; (ii) charge transfer provides relevant current changes only for very high values of additional doping; (iii) for certain values of additional n-doping ambipolar currents could be obtained. The results of these simulations highlight the complexity of the molecular sensing mechanism in nanowires, that depends not only on the NW parameters but also on the prop...
We describe a procedure for the optimization of a 3C-SiC buffer layer for the deposition of 3C-Si... more We describe a procedure for the optimization of a 3C-SiC buffer layer for the deposition of 3C-SiC on (001) Si substrates. A 100 – 150 nm thick SiC buffer was deposited after a standard carbonization at 1125 °C, while increasing the temperature from 1125 °C to 1380 °C. Ramp time influenced the quality and the crystallinity of the buffer layer and the presence of voids at the SiC/Si interface. After the optimization of the buffer, to demonstrate its effectiveness, a high-quality 3C-SiC was grown, with excellent surface morphology, crystallinity and low stress.
The results of a systematic investigation by transmission electron microscopy (TEM), cathodolumin... more The results of a systematic investigation by transmission electron microscopy (TEM), cathodoluminescence (CL), Rutherford backscattering (RBS), X-ray diffraction and topography and scanning force microscopy (SFM) techniques on several InGaAs/InP compressive and tensile strained layers covering the misfit range from −2.3 to 1.5×10−2 and grown by the metal organic vapor phase epitaxy (MOVPE) technique are reported. In compressively strained films the same dependence for the residual strain vs the film thickness as for the InGaAs/GaAs is found whereas a different strain release rate and different extended defects are found in tensile stressed InGaAs alloy. In particular in tensile stressed samples, grooves, planar defects and cracks are present in addition to the interfacial network of misfit dislocations. The correlation between the observed planar defects and the mechanisms of strain relaxation in the case of tensile strained layers is discussed.
Summary The (110)-oriented misfit dislocation density reduction in the growth of Inx Gal−xAs (x-... more Summary The (110)-oriented misfit dislocation density reduction in the growth of Inx Gal−xAs (x-0.06) heterostructure on GaAs (001) substrate patterned with circular mesas has been observed with X-ray double-crystal topography. It has been found that, depending on the InGaAs thickness on the mesa sidewall, there is athreshold which inhibits the glide of threading dislocations through the mesas. No misfit dislocations are
Czechoslovak Journal of Physics - CZECH J PHYS, 2000
Precise knowledge of the incident and diffracted X-ray beams related to flat crystal diffractors ... more Precise knowledge of the incident and diffracted X-ray beams related to flat crystal diffractors is important for X-ray diffraction optics and for high resolution experiments. In the paper, three-dimensional reciprocal space concept has been applied to study general case of the flat diffractor. The incident and diffracted beams have been determined for the middle of the range of total reflection for both the standard asymmetrical and the inclined asymmetrical diffractor. For an asymmetric diffractor rotating about its reciprocal lattice vector unexpectedly large out-of-plane-of-diffraction components of the beams have been obtained. The largest ones have been found not for the angle of rotationω=90° corresponding to a symmetrical inclined diffractor but for the angle close to the grazing incidence case.
Hard X-rays (with energies in the 70 KeV - 1 MeV range) focusing is a crucial issue for astronomy... more Hard X-rays (with energies in the 70 KeV - 1 MeV range) focusing is a crucial issue for astronomy in the X-rays and gamma-ray energy range. Due to the narrow angular range of diffraction at high gamma-rays energies, perfect crystals cannot be used for such application. Mosaic crystals have been proposed, but their efficiency cannot exceed 50%. In order to increase the diffraction efficiency, bent crystals have been proposed showing good performances. For bent crystals the diffraction range is given by the total curvature of the crystal lattice planes and the diffraction eficiency can reach values close to 100%. In this work we propose a crystal bending procedure obtained by a controlled surface damaging. The damaging procedure introduces a defected superficial layer, undergoing a high compressive strain of a few tens nanometer in thickness. Several oriented silicon and gallium arsenide wafers have been treated. By using high resolution X-ray diffraction measurements in Bragg conditi...
Abstract GaAs, Cu, CdTe, and CdZnTe crystals have been studied as optical elements for lenses for... more Abstract GaAs, Cu, CdTe, and CdZnTe crystals have been studied as optical elements for lenses for hard x-ray astronomy. High-resolution x-ray diffraction at 8 keV in Bragg geometry and at synchrotron at energies up to 500 keV in Laue geometry has been used. A good ...
Nitroaromatic explosives are the most common explosives, and their detection is important to publ... more Nitroaromatic explosives are the most common explosives, and their detection is important to public security, human health, and environmental protection. In particular, the detection of solid explosives through directly revealing the presence of their vapors in air would be desirable for compact and portable devices. In this study, amino-functionalized carbon nanotubes were used to produce resistive sensors to detect nitroaromatic explosives by interaction with their vapors. Devices formed by carbon nanotube networks working at room temperature revealed trinitrotoluene, one of the most common nitroaromatic explosives, and di-nitrotoluene-saturated vapors, with reaction and recovery times of a few and tens of seconds, respectively. This type of resistive device is particularly simple and may be easily combined with low-power electronics for preparing portable devices.
In this paper, we model the electrical properties of germanium nanowires with a particular focus ... more In this paper, we model the electrical properties of germanium nanowires with a particular focus on physical mechanisms of electrical molecular sensing. We use the Tibercad software to solve the drift-diffusion equations in 3D and we validate the model against experimental data, considering a p-doped nanowire with surface traps. We simulate three different types of interactions: (1) Passivation of surface traps; (2) Additional surface charges; (3) Charge transfer from molecules to nanowires. By analyzing simulated I–V characteristics, we observe that: (i) the largest change in current occurs with negative charges on the surfaces; (ii) charge transfer provides relevant current changes only for very high values of additional doping; (iii) for certain values of additional n-doping ambipolar currents could be obtained. The results of these simulations highlight the complexity of the molecular sensing mechanism in nanowires, that depends not only on the NW parameters but also on the prop...
We describe a procedure for the optimization of a 3C-SiC buffer layer for the deposition of 3C-Si... more We describe a procedure for the optimization of a 3C-SiC buffer layer for the deposition of 3C-SiC on (001) Si substrates. A 100 – 150 nm thick SiC buffer was deposited after a standard carbonization at 1125 °C, while increasing the temperature from 1125 °C to 1380 °C. Ramp time influenced the quality and the crystallinity of the buffer layer and the presence of voids at the SiC/Si interface. After the optimization of the buffer, to demonstrate its effectiveness, a high-quality 3C-SiC was grown, with excellent surface morphology, crystallinity and low stress.
The results of a systematic investigation by transmission electron microscopy (TEM), cathodolumin... more The results of a systematic investigation by transmission electron microscopy (TEM), cathodoluminescence (CL), Rutherford backscattering (RBS), X-ray diffraction and topography and scanning force microscopy (SFM) techniques on several InGaAs/InP compressive and tensile strained layers covering the misfit range from −2.3 to 1.5×10−2 and grown by the metal organic vapor phase epitaxy (MOVPE) technique are reported. In compressively strained films the same dependence for the residual strain vs the film thickness as for the InGaAs/GaAs is found whereas a different strain release rate and different extended defects are found in tensile stressed InGaAs alloy. In particular in tensile stressed samples, grooves, planar defects and cracks are present in addition to the interfacial network of misfit dislocations. The correlation between the observed planar defects and the mechanisms of strain relaxation in the case of tensile strained layers is discussed.
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Papers by C. Ferrari