We study the electronic properties of GaAs-AlGaAs superlattices with intentional correlated disorder by means of photoluminescence and vertical dc resistance. The results are compared to those obtained in ordered and uncorrelated disordered superlattices. We report the first experimental evidence that spatial correlations inhibit localization of states in disordered low-dimensional systems, as our previous theoretical calculations suggested, in contrast to the earlier belief that all eigenstates are localized.

We describe a fast and versatile method to functionalize high-quality graphene with organic molecules by exploiting the synergistic effect of supramolecular and covalent chemistry. With this goal, we designed and synthesized molecules comprising a long aliphatic chain and an aryl diazonium salt. Thanks to the long chain, these molecules physisorb from solution onto CVD graphene or bulk graphite, self-assembling in an ordered monolayer. The sample is successively transferred into an aqueous electrolyte, to block any reorganization or desorption of the monolayer. An electrochemical impulse is used to transform the diazonium group into a radical capable of grafting covalently to the substrate and transforming the physisorption into a covalent chemisorption. During covalent grafting in water, the molecules retain the ordered packing formed upon self-assembly. Our two-step approach is characterized by the independent control over the processes of immobilization of molecules on the substrate and their covalent tethering, enabling fast (t < 10 s) covalent functionalization of graphene. This strategy is highly versatile and works with many carbon-based materials including graphene deposited on silicon, plastic, and quartz as well as highly oriented pyrolytic graphite.

The several processes required to achieve Er luminescence in Si are investigated. In particular, the role of Er-O interactions to obtain the incorporation of high Er concentrations, electrically and optically active, in crystalline Si is addressed. Multiple Er and O implants were performed on n-type (100) Si crystals to obtain flat concentrations of ∼1×${10}^{19}$ Er/${\mathrm{cm}}^3$ and ∼1×${10}^{20}$ O/${\mathrm{cm}}^3$ over an ∼2-μm-thick layer. These implants produced also a 2.3-μm-thick amorphous Si (a-Si) layer. A subsequent thermal treatment at 620 °C for 3 h induced the epitaxial regrowth of the whole layer and the incorporation of both Er and O in a good-quality single crystal. A further annealing at 900 °C for 30 sec produced the electrical activation of the implanted Er in the presence of O, with an Er donor concentration of ∼8×${10}^{18}$/${\mathrm{cm}}^3$ over an ∼1.8-μm-thick layer. This value is more than two orders of magnitude above the maximum Er donor concentration reported in the literature, demonstrating the crucial role of O in increasing the electrically active Er concentration in crystalline Si. The optical efficiency of this sample has been studied by photoluminescence. It is seen that an enhancement by a factor of ∼6 with respect to the literature data is obtained. Moreover, studies on the photoluminescence intensity as a function of the pump power give important information on the mechanisms underlying Er luminescence in Si and its competing phenomena. These data are presented and discussed. A plausible model based on the previous results is also presented.

Blends of reduced graphene oxide (RGO) and poly(3-hexylthiophene) (P3HT) are used as the active layer of field-effect transistors (FETs). By using sequential deposition of the two components, the density of RGO sheets can be tuned linearly, thereby modulating their contribution to the charge transport in the transistors, and the onset of charge percolation. The surface potential of RGO, P3HT and source–drain contacts is measured on the nanometric scale with Kelvin Probe Force Microscopy (KPFM), and correlated with the macroscopic performance of the FETs. KPFM is also used to monitor the potential decay along the channel in the working FETs.

The electrical and optical properties of Er-implanted Si are shown to be critically dependent on the presence of impurities and defects. A large enhancement in the electrical activation of Er (up to three orders of magnitude) is obtained by coimplanting Er with O or C at 300-degrees-C. The use of C also allows one to obtain a good quality crystal after implantation and annealing. This is shown to be crucial in the photoluminescence process. In fact, in spite of the large amount of active Er atoms, photoluminescence is inhibited in the presence of the high concentration of precipitates and crystallographic defects which are left after annealing of the Er and O coimplants. The photoluminescence intensity is, on the other hand, enhanced by the high concentration of active Er atoms in the defect-free crystal which is left after annealing of the Er and C coimplants. Moreover, a clear shift in the main photoluminescence peaks is observed in Er- and C-coimplanted samples as a result of the different surroundings experienced by the Er atoms