Nanoscale structural and electrical properties of graphene grown on AlGaN by catalyst-free chemical vapor deposition.

The integration of graphene (Gr) with nitride semiconductors is highly interesting for applications in high-power/high-frequency electronics and optoelectronics. In this work, we demonstrated the direct growth of Gr on Al0.5Ga0.5N/sapphire templates by propane (C3H8) chemical vapor deposition at a temperature of 1350 °C. After optimization of the C3H8 flow rate, a uniform and conformal Gr coverage was achieved, which proved beneficial to prevent degradation of AlGaN morphology. X-ray photoemission spectroscopy revealed Ga loss and partial oxidation of Al in the near-surface AlGaN region. Such chemical modification of a ∼2 nm thick AlGaN surface region was confirmed by cross-sectional scanning transmission electron microscopy combined with electron energy loss spectroscopy, which also showed the presence of a bilayer of Gr with partial sp2/sp3 hybridization. Raman spectra indicated that the deposited Gr is nanocrystalline (with domain size ∼7 nm) and compressively strained. A Gr sheet resistance of ∼15.8 kΩ sq-1 was evaluated by four-point-probe measurements, consistently with the nanocrystalline nature of these films. Furthermore, nanoscale resolution current mapping by conductive atomic force microscopy indicated local variations of the Gr carrier density at a mesoscopic scale, which can be ascribed to changes in the charge transfer from the substrate due to local oxidation of AlGaN or to the presence of Gr wrinkles.

Selective synthesis of turbostratic polyhedral carbon nano-onions by arc discharge in water.

Carbon nano-onions (CNOs), in their spherical or polyhedral forms, represent an important class of nanomaterials, due to their peculiar physical and electrochemical properties. Among the different methods of production, arc discharge between graphite electrodes sustained by deionized water is one of the most promising to obtain good quality CNOs in gram quantities. We applied the method with the aim to optimize the production of CNOs, using an innovative experimental arrangement. The discharges generate dispersed nanomaterials and a black hard cathodic deposit, which were studied by transmission electron microscopy-high-resolution TEM, scanning electron microscopy, Raman, thermogravimetric analysis and energy-dispersive x-ray spectroscopy. A simple mechanical grinding of the deposits permitted us to obtain turbostratic polyhedral CNOs that exhibited higher stability towards burning in air, compared to CNOs found in water. We propose a mechanism for the formation of the CNOs present in the deposit, in which the crystallization is driven by a strong temperature gradient existing close to the cathode surface at the beginning of the process, and subsequently close to the deposit surface whenever it is growing.

Anisotropic extended misfit dislocations in overcritical SiGe films by local substrate patterning.

In this work we will show how local substrate patterning leads to a long range controlled propagation of dislocations in SiGe films grown on Si(001) substrates. Dislocations preferentially nucleate in the inhomogeneous strain field associated with the patterned pits, and then partialize on the local (111) surfaces which form the pit sidewalls. The resulting V-shaped defects extend for several microns and effectively block the propagation of randomly nucleated dislocations which propagate in the perpendicular direction. The surface morphology and strain fields associated with the extended defects have been characterized by atomic force microscopy and µRaman spectroscopy, and the defects have been directly observed with high resolution transmission electron microscopy.

Monitoring the kinetic evolution of self-assembled SiGe islands grown by Ge surface thermal diffusion from a local source.

In this paper we experimentally study the growth of self-assembled SiGe islands formed on Si(001) by exploiting the thermally activated surface diffusion of Ge atoms from a local Ge source stripe in the temperature range 600-700 °C. This new growth strategy allows us to vary continuously the Ge coverage from 8 to 0 monolayers as the distance from the source increases, and thus enables the investigation of the island growth over a wide range of dynamical regimes at the same time, providing a unique birds eye view of the factors governing the growth process and the dominant mechanism for the mass collection by a critical nucleus. Our results give experimental evidence that the nucleation process evolves within a diffusion limited regime. At a given annealing temperature, we find that the nucleation density depends only on the kinetics of the Ge surface diffusion resulting in a universal scaling distribution depending only on the Ge coverage. An analytical model is able to reproduce quantitatively the trend of the island density. Following the nucleation, the growth process appears to be driven mainly by short-range interactions between an island and the atoms diffusing within its vicinities. The islands volume distribution is, in fact, well described in the whole range of parameters by the Mulheran's capture zone model. The complex growth mechanism leads to a strong intermixing of Si and Ge within the island volume. Our growth strategy allows us to directly investigate the correlation between the Si incorporation and the Ge coverage in the same experimental conditions: higher intermixing is found for lower Ge coverage. This confirms that, besides the Ge gathering from the surface, also the Si incorporation from the substrate is driven by the diffusion kinetics, thus imposing a strict constraint on the initial Ge coverage, its diffusion properties and the final island volume.

Narrow intersubband transitions in n-type Ge/SiGe multi-quantum wells: control of the terahertz absorption energy trough the temperature dependent depolarization shift.

In this paper we present a detailed study of the intersubband absorption occurring between electron states confined in strained Ge multi-quantum wells as a function of the temperature. The high structural quality of the samples is reflected by the very narrow absorption line-shape constant with temperature. We observe a temperature driven charge transfer occurring between the ground and the first excited subband which, in turn, induces a change in the depolarization shift and consequently in the energy of the absorbance peak. The experimental observations are well accounted for by a multi-valley k·p model.

L10-FeNi films on Au-Cu-Ni buffer-layer: a high-throughput combinatorial study.

The fct L10-FeNi alloy is a promising candidate for the development of high performance critical-elements-free magnetic materials. Among the different materials, the Au-Cu-Ni alloy has resulted very promising; however, a detailed investigation of the effect of the buffer-layer composition on the formation of the hard FeNi phase is still missing. To accelerate the search of the best Au-Cu-Ni composition, a combinatorial approach based on High-Throughput (HT) experimental methods has been exploited in this paper. HT magnetic characterization methods revealed the presence of a hard magnetic phase with an out-of-plane easy-axis, whose coercivity increases from 0.49 kOe up to 1.30 kOe as the Au content of the Cu-Au-Ni buffer-layer decreases. Similarly, the out-of-plane magneto-crystalline anisotropy energy density increases from 0.12 to 0.35 MJ/m3. This anisotropy is attributed to the partial formation of the L10 FeNi phase induced by the buffer-layer. In the range of compositions we investigated, the buffer-layer structure does not change significantly and the modulation of the magnetic properties with the Au content in the combinatorial layer is mainly related to the different nature and extent of interlayer diffusion processes, which have a great impact on the formation and order degree of the L10 FeNi phase.

Cerebellar tumour presenting with pathological laughter and gelastic syncope.

There is no report of patients in whom pathological laughter, a rare condition characterized by uncontrollable episodes of laughter usually triggered by unrelated stimuli, was ever closely associated with a loss of consciousness overtly linked with the onset of such uncontrollable laughter, also referred to as a gelastic syncope. A 53-year-old man presented with a 4-month history of syncope following intense and uncoordinated laughter. Physical and neurological examination was normal and the patient had no other typical cerebellar signs. We found a mass in the cerebellar vermis abutting the floor of the fourth ventricle, which upon histological examination after surgery proved to be an ependymoma. We emphasize that pathological laughter and gelastic syncope could represent unique and sole features of a cerebellar disorder.

New model of liver regeneration induced through use of vascular endothelial growth factor.

INTRODUCTION: Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen. The objective of this study was to verify the proregenerative effects of VEGF in an experimental model of acute liver failure. MATERIALS AND METHODS: Sixty four rats that underwent intraperitoneal injection of carbon tetrachloride (CCl(4)) were randomly divided into two groups: group B animals received intravenous injection of VEGF(164) 1 hour following CCl(4) poisoning. Group A hosts were untreated. To obtain daily liver function tests (LFTs) and histological samples, on each day up to 8 days we sacrificed four rats in each group. RESULTS: The laboratory examinations showed notable alteration of LFTs in group A, while group B revealed only slight changes. The histological examination showed greater liver damage in group A compared with group B. CONCLUSION: Our results suggest that administration of exogenous VEGF protects the liver from CCl(4)-induced acute hepatic failure. Further studies are underway to assess whether exogenous VEGF is effective in other liver injuries.

Novel near-infrared emission from crystal defects in MoS2 multilayer flakes.

The structural defects in two-dimensional transition metal dichalcogenides, including point defects, dislocations and grain boundaries, are scarcely considered regarding their potential to manipulate the electrical and optical properties of this class of materials, notwithstanding the significant advances already made. Indeed, impurities and vacancies may influence the exciton population, create disorder-induced localization, as well as modify the electrical behaviour of the material. Here we report on the experimental evidence, confirmed by ab initio calculations, that sulfur vacancies give rise to a novel near-infrared emission peak around 0.75 eV in exfoliated MoS2 flakes. In addition, we demonstrate an excess of sulfur vacancies at the flake's edges by means of cathodoluminescence mapping, aberration-corrected transmission electron microscopy imaging and electron energy loss analyses. Moreover, we show that ripplocations, extended line defects peculiar to this material, broaden and redshift the MoS2 indirect bandgap emission.

The role of the interface in germanium quantum dots: when not only size matters for quantum confinement effects.

Quantum confinement (QC) typically assumes a sharp interface between a nanostructure and its environment, leading to an abrupt change in the potential for confined electrons and holes. When the interface is not ideally sharp and clean, significant deviations from the QC rule appear and other parameters beyond the nanostructure size play a considerable role. In this work we elucidate the role of the interface on QC in Ge quantum dots (QDs) synthesized by rf-magnetron sputtering or plasma enhanced chemical vapor deposition (PECVD). Through a detailed electron energy loss spectroscopy (EELS) analysis we investigated the structural and chemical properties of QD interfaces. PECVD QDs exhibit a sharper interface compared to sputter ones, which also evidences a larger contribution of mixed Ge-oxide states. Such a difference strongly modifies the QC strength, as experimentally verified by light absorption spectroscopy. A large size-tuning of the optical bandgap and an increase in the oscillator strength occur when the interface is sharp. A spatially dependent effective mass (SPDEM) model is employed to account for the interface difference between Ge QDs, pointing out a larger reduction in the exciton effective mass in the sharper interface case. These results add new insights into the role of interfaces on confined systems, and open the route for reliable exploitation of QC effects.

Monkey somatosensory cerebrocerebellar pathways: uneven densities of corticopontine neurons in different body representations of areas 3b, 1, and 2.

We have studied the anatomic organization of corticopontine neurons in the monkey cytoarchitectonic areas 3a, 3b, 1, and 2. The purpose was to provide information about the composition of somatosensory cortical influence on cerebellar operations. Large tracer injections were made in the pontine nuclei. Retrogradely labeled neurons were confined to cortical layer 5, with the largest cell bodies located in area 3a and the smallest in area 3b. The distribution of labeled cells was quantitatively recorded and displayed in three-dimensional reconstructions and in flat maps. We have: (1) compared the average densities of labeled cells among the cytoarchitectonic areas, and (2) outlined the distribution of labeled cells within the cortical map of the body surface representation. The average density of labeled cells was considerably higher in areas 3a, 1, and 2, compared to area 3b. This finding suggests that areas 3a, 1, and 2 are more engaged in cerebellar operations than area 3b. We found marked density gradients of labeled cells within areas 3b, 1, and 2, but not within area 3a. When the density maps from areas 3b, 1, and 2 were superimposed on previously published somatotopic maps, we found higher average densities of corticopontine neurons in regions representing the trunk and proximal limbs, than in regions representing the distal forelimb. Thus, the distal forelimb representation, which is known to be strongly emphasized in terms of cortical volume, appears not to be correspondingly emphasized in the corticopontine projection.

Behavioral changes induced by the thyrotropin-releasing hormone analogue, RGH 2202.

The behavioral activity of the thyrotropin-releasing hormone (TRH) analogue, L-6-ketopiperidine-2- carbonyl-leucyl-L-prolinamide (RGH 2202), has been studied in the rat. The number of errors in a radial maze test was reduced after acute intraperitoneal (IP) injection of RGH 2202 at the dose of 5 or 10 mg/kg. Grooming activity was increased with a lower dose, 1 mg/kg. Hypoxia-induced amnesia, as assessed with active and passive avoidance behavior tests, was reversed in rats treated with 5 or 10 mg/kg of the drug. The loss of learning and memory capacity shown by aged rats in the same behavioral tests was also reduced after injection of RGH 2202. In a test for sexual activity of male rats, the higher dose of the drug induced a facilitation of mounting and ejaculations, while smaller doses were ineffective. The rotorod test revealed a decreased number of falls in animals treated with 5 or 10 mg/kg of RGH 2202. In all behavioral tests, the same doses of natural thyrotropin-releasing hormone (TRH) were less effective, indicating that this analogue may be qualified as a potentially active drug in human pathologies.

Idiopathic left ventricular aneurysm: an unusual substrate of ventricular fibrillation and ventricular tachycardia.

Idiopathic left ventricular aneurysm (LVA) is a very rare clinical condition. This article describes a patient with idiopathic LVA associated with episodes of ventricular tachycardia and ventricular fibrillation. Clinical and instrumental examinations did not reveal the pathogenesis of the aneurysm. The malignant clinical course suggests that an aggressive antiarrhythmic treatment, including ICD implantation, may be warranted.

Homotopic transplant of fetal cortex to lesioned motor cortex of adult rats. A comportamental and anatomical study.

Previous investigations have shown that the transplant of fetal nervous tissue in adult, formerly injured, brain induces an improvement of the neurological deficits. The process underlying this finding is not yet known. It has been proposed that this process is favourably supported by the reconstruction of the damaged circuitry, replacing the injured neurons with the transplanted fetal cells. In the present study we have investigated the relation between the improvement of the neurological deficits and the anatomical integration of the transplanted neurons within the host brain. The plan of the investigation included two steps: the first step consisted of inducing neurological deficits by kainic acid lesion of the motor cortex and then studying the changes in the motor learning following a homotopic transplant of fetal cortex in the side of the lesion. The second step consisted of studying the anatomical integration of the transplanted cortex with the thalamus of the host. The results showed that the rats with injury of the motor cortex followed by solid transplant of fetal cortex (E 17) had a significantly greater recovery of the motor learning with respect to non-transplanted rats with a lesioned motor cortex. In the same rats, the connections between the transplanted cerebral cortex and the thalamus of the host has been investigated. WGA-HRP solution was injected in the thalamus and both labeled fiber terminals and labeled cells were searched for in the transplants. The results showed that: 1) the host thalamus projects to the transplanted cortex with a lower density than to the host cortex surrounding the transplant; 2) the thalamic projection to the host cortex is topographically organized, whereas the projection to the transplant is arranged in patches without any topographical organization; 3) the transplant does not send a significant projection to the thalamus of the host. In conclusion, the experimental findings demonstrate that the reconstruction of an injured thalamo-cortical circuitry of adult rats transplanting fetal neurons is not possible. The improvement of the functional deficits by the transplant of fetal tissue may be referred to aspecific factors enhancing the functional activity of the host cortex undamaged by the initial injury. The identification of the nature of the hypothesized factors requires further investigation.

[Innovative use of the vascular endothelial growth factor in an experimental model of acute liver failure]. / Utilizzo innovativo del fattore di permeabilità vascolare in un modello sperimentale di insufficienza epatica acuta.

Vascular Endothelial Growth Factor (VEGF) is an endothelial cell mitogen and an important stimulator of sinusoidal endothelial cell proliferation. The aim of this research was to study the effects of exogenous VEGF in a rat model of acute liver failure. The study was conducted on 64 rats (240-300 g). All rats underwent intraperitoneal injection (5 ml/kg) of 25% carbon tetrachloride (CCl4) and 75% paraffin oil. This dosage of CCl4 was devised to induce nonfatal acute liver failure with spontaneous recovery in 7 days. The animals were randomly divided into 2 groups. Group B animals underwent i.v. injection of 200 ng of VEGF165 one hour following intra-peritoneal injection of CCl4. To obtain daily liver functional tests (LFTS) and histological liver samples, 4 rats in each group were sacrificed daily up to 8 days. In group A, the liver histology showed massive periportal hepatocyte necrosis associated with portal lymphocytic infiltrates. The peak of the damage was documented at 72 hours following CCl4. Group B showed minimal necrosis, moderate periportal edema and a minimum periportal steatosis. At 48 hours steatotic changes had disappeared and the periportal edema was resolving. LFTs demonstrated severe liver damage in rats in group A. In group A the peak AST (mean 322.5 IU/L) and ALT (mean 250.25 IU/L) were recorded at 72 hours. In group B, at 72 hours the mean AST was 137 IU/L (normal < 95 IU/L) and ALT 68 IU/L(normal < 45 IU/L). The maximum levels of AST and ALT, in group B, were 152.3 IU/L and 72.3 IU/L, at 24 hours. According to our results exogenous VEGF successfully protects the liver from CCl4 induced acute liver failure. Further studies will demonstrate if exogenous VEGF can be effective in other liver injuries.

[Anatomic connections between homotopic transplant of fetal cortical tissue and optic thalamus in adult rats]. / Connessioni anatomiche tra trapianto omotopico di tessuto corticale fetale e talamo ottico di ratti adulti.

The present research was planned to study the possibility to reconstruct a damaged neural circuitry by replacing the injured neurons with homotopic fetal cells. In adult rats the motor cortex was injured with intracortical injection of kainic acid solution. After a delay of 10-14 days, a block of cerebral cortex of fetal rats (E17) was transplanted in the cavity produced by the kainic acid in the motor cortex. After 2-3 months, WGA-HRP solution was injected in the thalamus of the host and both anterogradely labeled fiber terminals and retrogradely labeled somata cells were researched in the transplanted cortex. The results showed that: 1) the host thalamus projects to the transplanted cortex with less density compared to the host cortex surrounding the transplant; 2) the thalamic projection to the transplant is not topographically organized whereas the projection to the host cortex is; 3) the transplant was virtually void of a significant projection to the thalamus of the host. In conclusion, the results offer direct evidence that the reconstruction of an injured thalamocortical circuitry of adult rat is not possible by transplanting homotopic fetal neurons.

Multiple representation in the nucleus lateralis of the cerebellum: an electrophysiologic study in the rat.

The motor organization of the nucleus lateralis (NL) of the rat's cerebellum was investigated by observing the motor effects of electrical microstimulations of the NL. The movements evoked by the NL mainly concerned forelimb and head segments. Only in a few cases were movements of hindlimb segments evoked. Motor effects were obtained according to a precise topographical pattern. This pattern delimited functional zones, or representations, within the NL, each zone being specifically related to a particular segment of the body. A few body segments were activated from single zones only (single representation) whereas some other body segments could be activated from different zones of the NL. Among them, the axio-proximal body segments were activated in a similar way from all sites (multiple representation) whereas the distal body segments were differently activated from the various representation zones (specific representation). The multiple and specific representations were distributed between the 3 cytoarchitectonic subregions of the NL (NLm, DLH and slp) in such a way that the body segments were usually represented only once in each individual NL subregion. Each NL subregion included sets of representations concerning body segments characterized by a topographical continuity (e.g. the different segments of the forelimb in both DLH and slp). Thus, the individual NL subregions may bring into play coordinate plurisegmental muscular activities of the limbs and/or of the head. The NLm controls movements of all the segments of the head and those of axio-proximal segments of both limbs. The DLH particularly controls movements of the head, including both the proximal (neck) and the oral regions. To a lesser degree, DLH controls movements of the various segments of the forelimb, including synchronous flexion of all the digits. The slp is specifically involved in the control of motor activities of: i) the proximal segment of the head (rotation of the neck) as well as its distal segments (displacement of individual vibrissae, rotation of the ear pinna) and ii) the various segments of the forelimb including individual digits. Functionally, the proximal segments would be concerned in the spatial displacement of the limbs or of the head whereas the distal segments would be involved in the realization of precise and discrete movements related to specific functions of the distal segments concerned. The 3 subregions of the NL may be concerned in different motor functions.(ABSTRACT TRUNCATED AT 400 WORDS)

[Motor organization of the lateral cerebellar nucleus of the rat]. / Organizzazione motoria del nucleo cerebellare laterale di ratto.

The motor organization of the nucleus lateralis (NL) of the cerebellum of the rat was investigated by studying the motor effects following the electrical microstimulation. The movements evoked by the NL stimulation concerned prevalently the forelimb and the head segments. The movements of the hindlimb segments were evoked in only few cases. The NL is organized as a mosaic of zones without, or at least very little overlap. The various body segments are differently represented in the NL. Some of them are once represented (single representations). In other cases, the same movements were evoked by different NL regions (multiple representations). Finally, in a last lot of cases, various representations concerned the same body regions but from each representation a different type of movement was evoked (specific representations, i.e. displacement of an individual digit and flexion of all digits together). The topographical distribution of the representations in the NL cytological regions (magnicellularis, NLm; dorsolateral hump, DLH; subnucleus lateralis parvocellularis, slp) suggests the idea that each of them may be concerned in a specific motor activity: the NLm would control the position of the body, or of part of it, in the space; the DLH would be concerned in the oral (prevalently) and in the forelimb motor activity; the slp would be concerned in the exploration of the environment as well as in skilled movements of the distalmost forelimb segments.