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Semiconducting and insulating polymers and copolymers/Au nanograins based hybrid multilayers (HyMLs) were fabricated on p-Si single-crystal substrate by an iterative method that involves, respectively, Langmuir-Blodgett and spin-coating techniques (for the deposition of organic film) and sputtering technique (for the deposition of metal nanograins) to prepare Au/HyMLs/p-Si Schottky device. The electrical properties of the Au/HyMLs/p-Si Schottky device were investigated by current-voltage (I–V) measurements in the thickness range of 1-5 bilayers (BL).
At different number of layers, current-voltage (I–V) measurements were performed. Results showed a rectifying behavior. Junction parameters, such as barrier height (BH), from the I–V measurements for example for the PMMA-b-PS based Au/HyMLs/p-Si structure were obtained as 0.72±0.02 eV at 1BL and 0.64±0.02eV at 5BL. It was observed that the BH value of 0.61 eV obtained for the 5 BL PS based Au/HyMLs/p-Si structure was lower than the value of 0.68 eV of conventional Au/p-Si Schottky diodes. Thus, modification of the interfacial potential barrier for Au/p-Si diodes has been achieved using a thin MLs of different polymers based HyMls semiconductor.
When a Ta layer is deposited at the Si/Ti interface a new phase has been detected, i.e. theTiSi2C40. The C40-C54 transformation kinetics and the film morphology are consistent with an increase of the nucleation density with respect to the C49-C54 transition. The activation energies for the nucleation rate (4.2±0.3 eV) and the growth velocity (4.0±0.4 eV) have been obtained from the in situ sheet resistance and the Transmission Electron Microscopy results. These results show that the process with a Ta layer at the Ti/Si interface has a greater scalability with respect to the standard TiSi2 process.
The effect of a thin Ta layer at the Ti/Si interface on the kinetic of the C49-C54 transition will be shown in detail. The transformation kinetic has been monitored by in situ sheet resistance measurements that, coupled to structural characterisation, allowed to evidence the presence of an intermediate phase before the C54 formation. The temperature of the C54 phase formation decreases with a Ta concentration of 4.5·1015 cm−2 and μ-Raman images of partially transformed samples indicates that the density of C54 grains in presence of Ta is about one order of magnitude higher with respect to pure Ti/Si samples.
We discuss the rather scattered measurements of the lattice parameters for C49 TiSi2, which are reported in literature, along with new and accurate X-ray diffraction measurements and ab-initio calculations. Both agree in indicating that the density of the metastable C49 structure cannot be much smaller than the one for the polymorphic C54 phase, as it is commonly reported. We conclude by demonstrating that only in the case of such a smaller difference in density between the two phases, the elastic strain contribution to the nucleation energy of the C54 structure in the C49 matrix can be neglected. The estimation of the critical radius strongly depends on this issue.
Semiconducting iron silicide dots with dimensions ranging between 5 and 100 nm can be obtained by ion implantation on Si wafers and exhibit interesting photo- and electro- luminescent properties.
In our study we use structural and optical characterization as well as theoretical modelling in order to: i) discriminate among intrinsic effects of FeSi2 dots and effects due to lattice damage and Si matrix; ii) identify the range of physical parameters (size, phase, electronic structure) corresponding to the luminescent dots.
Direct picosecond laser measurements of the critical fluence for melting have been performed for the first time, giving unambiguously consistent differences in the energy required for surface melting of relaxed and unrelaxed amorphous silicon. The different optical coupling cannot account for this variation which can only be explained in term of different melting temperatures. Heating of unrelaxed amorphous silicon samples at temperatures close to the melting point may result in relaxation of the material even when the treatment occurs in the nanosecond time scale. However nanosecond UV irradiation of relaxed and unrelaxed amorphous silicon samples have provided informations on the specific heat of the two amorphous states. The melting temperature of unrelaxed amorphous silicon has been derived independently via both picosecond data and via free energy calculations.
The difference in the melting temperature of ion implanted and relaxed amorphous silicon has been measured. Pulsed laser irradiation (λ=347 nm, τ=30 ns) has been used to induce surface melting in the amorphous layer and time resolved reflectivity to detect the melting onset. The threshold energy density for surface melting in the relaxed amorphous was found 15.9±.3% higher than that in the unrelaxed one. The estimate of the variation of the thermal parameters in amorphous silicon upon relaxation allowed a determination of ΔTM=45±10 K between relaxed and unrelaxed amorphous silicon.
The crystallization onset and the annealing thresholds have been nmeasured as a function of the absorbed energy density in ion implanted amorphous silicon irradiated with nanosecond Nd pulse. Thin amorphous layers (∼500 Å) require higher thresholds ccapared with thick (∼4000 Å) amorphous layers. This result can be explained in terms of balance between absorbed energy and heat flow. For a given thickness of the amorphous layer the thresholds depend on the absorption coefficient of the amorphous material. This last parameter has been varied frcm 104 to 102 CM−1 by low temperature (T<400°C) pre-treatment of the ion implanted sample. The observed drastic variations of both crystallizazion and annealing thresholds agree well with nunerical evaluation of heat flow.
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