Screening length and quantum capacitance in graphene by scanning probe microscopy.

A nanoscale investigation on the capacitive behavior of graphene deposited on a SiO2/n(+) Si substrate (with SiO2 thickness of 300 or 100 nm) was carried out by scanning capacitance spectroscopy (SCS). A bias V(g) composed by an AC signal and a slow DC voltage ramp was applied to the macroscopic n(+) Si backgate of the graphene/SiO(2)/Si capacitor, while a nanoscale contact was obtained on graphene by the atomic force microscope tip. This study revealed that the capacitor effective area (A(eff)) responding to the AC bias is much smaller than the geometrical area of the graphene sheet. This area is related to the length scale on which the externally applied potential decays in graphene, that is, the screening length of the graphene 2DEG. The nonstationary charges (electrons/holes) induced by the AC potential spread within this area around the contact. A(eff) increases linearly with the bias and in a symmetric way for bias inversion. For each bias V(g), the value of A(eff) is related to the minimum area necessary to accommodate the not stationary charges, according to the graphene density of states (DOS) at V(g). Interestingly, by decreasing the SiO(2) thickness from 300 to 100 nm, the slope of the A(eff) versus bias curve strongly increases (by a factor of approximately 50). The local quantum capacitance C(q) in the contacted graphene region was calculated starting from the screening length, and the distribution of the values of C(q) for different tip positions was obtained. Finally the lateral variations of the DOS in graphene was determined.

Atomic Force Microscopy Study of the Kinetic Roughening in Nanostructured Gold Films on SiO2.

Dynamic scaling behavior has been observed during the room-temperature growth of sputtered Au films on SiO2using the atomic force microscopy technique. By the analyses of the dependence of the roughness, σ, of the surface roughness power,P(f), and of the correlation length,ξ, on the film thickness,h, the roughness exponent,α = 0.9 ± 0.1, the growth exponent,ß = 0.3 ± 0.1, and the dynamic scaling exponent,z = 3.0 ± 0.1 were independently obtained. These values suggest that the sputtering deposition of Au on SiO2at room temperature belongs to a conservative growth process in which the Au grain boundary diffusion plays a dominant role.

Thermodynamic Properties of Supported and Embedded Metallic Nanocrystals: Gold on/in SiO2.

We report on the calculations of the cohesive energy, melting temperature and vacancy formation energy for Au nanocrystals with different size supported on and embedded in SiO2. The calculations are performed crossing our previous data on the surface free energy of the supported and embedded nanocrystals with the theoretical surface-area-difference model developed by W. H. Qi for the description of the size-dependent thermodynamics properties of low-dimensional solid-state systems. Such calculations are employed as a function of the nanocrystals size and surface energy. For nanocrystals supported on SiO2, as results of the calculations, we obtain, for a fixed nanocrystal size, an almost constant cohesive energy, melting temperature and vacancy formation energy as a function of their surface energy; instead, for those embedded in SiO2, they decreases when the nanocrystal surface free energy increases. Furthermore, the cohesive energy, melting temperature and vacancy formation energy increase when the nanocrystal size increases: for the nanocrystals on SiO2, they tend to the values of the bulk Au; for the nanocrystals in SiO2 in correspondence to sufficiently small values of their surface energy, they are greater than the bulk values. In the case of the melting temperature, this phenomenon corresponds to the experimentally well-known superheating process.

Effect of surrounding environment on atomic structure and equilibrium shape of growing nanocrystals: gold in/on SiO2.

We report on the equilibrium shape and atomic structure of thermally-processed Au nanocrystals (NCs) as determined by high resolution transmission electron microscopy (TEM). The NCs were either deposited on SiO2surface or embedded in SiO2layer. Quantitative data on the NCs surface free energy were obtained via the inverse Wulff construction. Nanocrystals inside the SiO2layer are defect-free and maintain a symmetrical equilibrium shape during the growth. Nanocrystals on SiO2surface exhibit asymmetrical equilibrium shape that is characterized by the introduction of twins and more complex atomic defects above a critical size. The observed differences in the equilibrium shape and atomic structure evolution of growing NCs in and on SiO2is explained in terms of evolution in isotropic/anisotropic environment making the surface free energy function angular and/or radial symmetric/asymmetric affecting the rotational/translational invariance of the surface stress tensor.

Persistence of BCR/ABL mRNA-expressing bone-marrow cells in patients with chronic myelogenous leukemia in complete cytogenetic remission induced by interferon-alpha therapy.

Complete hematologic and cytogenetic responses can be obtained with interferon-alpha (IFN-alpha) in 15-25% of the patients with chronic myelogenous leukemia (CML). In these patients, reverse-transcription polymerase chain reaction (RT-PCR) can be used to evaluate minimal residual disease. We studied 12 patients who remained Philadelphia-negative for a median period of 21 months on IFN-alpha therapy. Using RT-PCR, the specific transcript was found in all bone marrow (BM) samples. Ten patients still exhibiting a persistent residual clone remained in cytogenetic remission for a median period of 14 months. As we observed a dissociation between bcr-abl expression in BM and peripheral blood (PB) cells, and given the known fluctuations of the bcr-abl PCR results, we suggest that PB negative results should be confirmed on BM specimens. Alternatively, it remains to be demonstrated whether longitudinal monitoring of residual disease would benefit from quantitative PCR or double fluorescence in situ hybridization.

[Presence of Aedes albopictus in Liguria]. / Osservazioni sulla presenza di Aedes albopictus in Liguria.

Further data about the presence of Aedes albopictus in the area of Genoa are given with some comments concerning the ecology of this oriental mosquito in the town and the dermatological problems it implies.

[Effect of metallic copper on the larva of Aedes albopictus: 1st laboratory data]. / Effetto del rame metallico sullo sviluppo larvale di Aedes albopictus: primi dati di laboratorio.

Laboratory experiments were carried out to test the larvicidal properties of metallic copper against Ae albopictus, a species which has spread in Italy during the last 3 years. The results show the strongest lethal effect on 1st stage larvae and support the use of copper as a simple, cheap and environmentally safe agent to control larval breeding of Ae albopictus in peridomestic containers.

Aedes albopictus in Europe: a new challenge for dermatologists.

A patient is reported who was bitten by Aedes albopictus, commonly known as tiger mosquito. The biology of the insect, originally living in the forests of southeastern Asia, and its role in transmitting exotic infectious agents is discussed. Up to this day, only Albania and northern Italy have been colonized, but the biologic characteristics of the insect make its spreading all over Europe highly probable, unless serious attempts to eradicate it are quickly undertaken. Dermatologists should think of the tiger mosquito in the presence of painful, purpuric, large wheals and when patients report a history of multiple attack during daylight.

[Further data on the spread to Genoa of Aedes albopictus]. / Ulteriori dati sulla diffusione a Genova di Aedes albopictus.

Further data are presented on the presence of Aedes albopictus in the town of Genoa (Italy) where this oriental mosquito was first reported in September 1990. Scattered foci of Ae albopictus were documented during the 1991 summer months in spite of a rather long and rigid '90-'91 winter season with temperatures frequently below 0 degree C. The newly imported mosquito shows the capacity to become a permanent pest in Italy where it could also increase the probability of transmission of pathogens such as arboviruses and filariae.

[Aedes albopictus in Italy and possible diffusion of the species into the Mediterranean area]. / Aedes albopictus in Italia e possibile diffusione della specie nell'area mediterranea.

Aedes albopictus (Skuse), the important Asian vector mosquito recently introduced in United States and Brazil, is reported from Genoa, North Italy. The infestation was discovered in a kindergarten pre-school center in September 1990 just after the summer holidays. Many discarded tires, well known to provide excellent breeding places for Ae albopictus, had been left in the school playground to be used as toys by the children. After sampling a few biting mosquito specimens for identification, the local health service carried out on September 18 an extensive indoor/outdoor treatment with pyrethroid insecticide. The extent of the infestation in the city of Genoa and in other areas of the Ligurian region has not been evaluated since the identification of the species was available in October, at the end of Ae albopictus reproductive period. A general survey in various Italian regions is being planned for the 1991 spring-summer period. The present record, together with the previous report of Ae albopictus in Albania, clearly supports the hypothesis of a spreading of the species in the Mediterranean area.