RESUMEN
GeSbTe-based materials exhibit multiple crystalline phases, from disordered rocksalt, to rocksalt with ordered vacancy layers, and to the stable trigonal phase. In this paper we investigate the role of the interfaces on the structural and electrical properties of Ge2Sb2Te5. We find that the site of nucleation of the metastable rocksalt phase is crucial in determining the evolution towards vacancy ordering and the stable phase. By properly choosing the substrate and the capping layers, nucleation sites engineering can be obtained, thus promoting or preventing the vacancy ordering in the rocksalt structure or the conversion into the trigonal phase. The vacancy ordering occurs at lower annealing temperatures (170 °C) for films deposited in the amorphous phase on silicon (111), compared to the case of SiO2 substrate (200 °C), or in presence of a capping layer (330 °C). The mechanisms governing the nucleation have been explained in terms of interfacial energies. Resistance variations of about one order of magnitude have been measured upon transition from the disordered to the ordered rocksalt structure and then to the trigonal phase. The possibility to control the formation of the crystalline phases characterized by marked resistivity contrast is of fundamental relevance for the development of multilevel phase change data storage.
RESUMEN
A combination of far-infrared and Raman spectroscopy is employed to investigate vibrational modes and the carrier behavior in amorphous and crystalline ordered GeTe-Sb2Te3 alloys (GST) epitaxially grown on Si(111). The infrared active GST mode is not observed in the Raman spectra and vice versa, indication of the fact that inversion symmetry is preserved in the metastable cubic phase in accordance with the Fm3 space group. For the trigonal phase, instead, a partial symmetry break due to Ge/Sb mixed anion layers is observed. By studying the crystallization process upon annealing with both the techniques, we identify temperature regions corresponding to the occurrence of different phases as well as the transition from one phase to the next. Activation energies of 0.43 eV and 0.08 eV for the electron conduction are obtained for both cubic and trigonal phases, respectively. In addition a metal-insulator transition is clearly identified to occur at the onset of the transition between the disordered and the ordered cubic phase.
RESUMEN
We report a 73 years old man with a diagnosis of Paget Disease (PD) and symptomatic Multiple Myeloma (MM). Coexistence of MM and PD has rarely been described. PD mimics many of the features of bone destructive process in MM, making differential diagnosis more complicated. In addition, the presence of serious muscolo-skeletal and metabolic complications in both diseases makes management of patients difficult, worsening the prognosis.The comparison of these two diseases has led to the characterization of a common molecular mechanism represented by the receptor activator of nuclear factor-kB ligand (RANKL)/Osteoprotegerin signaling pathway. The improved comprehension of these mechanisms led to the development of new pharmacologic agents (bisphosphonates, cytokines inhibitors) effective for the treatment of these bone diseases.
RESUMEN
The distributions of the size of islands and of the capture zones are discussed comparatively, both experimentally and numerically, for the case of a sudden nucleation process with and without coarsening. The experiments were performed by growing InAs islands on GaAs(001) and the coarsening was altered by varying the temperature. In the two-dimensional kinetic Monte Carlo simulations a single-species diffusing adatom was taken into account, and the coarsening was altered in this case by modifying the binding energy between adatoms and islands. The results show that size and capture zone distributions overlap only when coarsening can be disregarded.
RESUMEN
The evolution of InAs and In(0.85)Mn(0.15)As quantum dots grown at 270 °C is studied as a function of coverage. We show that, in contrast to what occurs at high temperature, the two-dimensional to three-dimensional transition is not abrupt but rather slow. This is due to the finding that part of the deposited material also contributes to the wetting layer growth after quantum dot formation. This aspect is particularly accentuated in In(0.85)Mn(0.15)As deposition. The Voronoi area analysis reveals a significant spatial correlation between islands.
Asunto(s)
Arsénico/química , Arsenicales/química , Indio/química , Manganeso/química , Nanotecnología/métodos , Puntos Cuánticos , Frío , Difusión , Cinética , Microscopía de Fuerza Atómica/métodosRESUMEN
A population of 31 patients with sporadic amyotrophic lateral sclerosis (ALS) was selected for a prospective open study based on treatment with riluzole. A neurophysiological evaluation was performed by means of single and paired transcranial magnetic stimulation (TMS). The examined parameters, excitability threshold, motor evoked potential (MEP) duration, silent period (SP) duration and time course of intracortical inhibition to paired TMS after 6 months treatment, were matched against those recorded from the patients themselves before the beginning of treatment and from 20 (single TMS) or 10 (paired TMS) age-matched control subjects. Normal behaviour of the SP in response to increasing TMS was found in the treated patients; they showed a significant linear correlation between these two parameters (r=0.96) comparable to that calculated for controls (r=0.98), and significantly different with respect to drug-free patients (r=0.8, P=0.014). A significant reduced size of the 'conditioned' MEPs to paired stimulation was documented in the treated patients compared with the untreated patients (P=0.002). Our neurophysiological contribution to the assessment of the effect of riluzole on the motor cortical inhibitory property in ALS may be considered a setting for controlled trials in extended patient series, even in a pre-clinical phase.
