170,712 research outputs found
Raman Spectroscopy and In Situ XRD Probing of the Thermal Decomposition of Sb2Se3 Thin Films
No full textSb2Se3 thin films have received increasing interest for their applications in optoelectronics. However, technological intervention demands a material-specific understanding of the reactivity to different environments. Both thermal annealing and laser irradiation carried out in an ambient atmosphere are expected to induce changes in the pristine crystallographic phase of Sb2Se3, causing the creation of additional secondary phases. Here, we investigate by means of Raman spectroscopy the effect of thermal annealing and laser irradiation at different fluencies on the structural and vibrational properties of Sb2Se3 thin films. The vacuum-annealed Sb2Se3 thin films at 290 °C and subjected to laser excitation power above 2 mW exhibit a secondary phase, revealing the occurrence of selenization. Further,in situX-ray diffraction over a broad range of annealing temperatures in N2and ambient atmospheres was employed to study the structural properties of the Sb2Se3thin films.In situXRD performed in a N2atmosphere does not show the formation of the Sb2O3cubic phase upon annealing until 500 °C. Conversely, a thermally activated systematic crystallization was observed upon annealing in an ambient atmosphere with the formation of the Sb2O3phase in the temperature range between 280 and 420 °C, until the complete decomposition of the material at 500 °C. Further, the orientation of vertically stacked (hk1) planes remains unchanged under a N2atmosphere, while horizontally stacked (hk0) planes dominate the (hk1) planes under ambient atmospheres
Growth study and characterization of In-Sb-Te compounds deposited onto different substrates by metal-organic chemical vapour deposition
No full textA systematic study of the deposition parameters for the metal–organic chemical vapour deposition growth of In–
Sb–Te (IST), of interest for phase change memory applications, was performed. Samples were grown on Si/SiO2
and patterned substrates in the (220÷350)°C temperature range and working pressure from 35 to 100×102 Pa,
which resulted in the formation of thin films (down to 30 nm) or IST crystals. The chemical composition of the
IST films was mainly dependent on the deposition temperature. We have demonstrated the possibility to obtain
a conformal and smooth morphology with improved surface roughness for films grown at 260 °C when the
substrate surface is treated with the TrisDimethylaMinoAntimony ([N(CH3)2]3Sb) precursor. The IST-based
chalcogenide films exhibited different crystalline and partially amorphous phases, which may be favourable
for multilevel data storage. The IST growth mechanism was analysed in terms of the structural, compositional
and electrical properties
thin films up to 550 °C
No full textThe temperature dependent thermal conductivity of In–Sb–Te thin films has been measured by modulated photothermal radiometry in the 20–550 °C range for samples with different Te content. Significant changes with temperature are observed and ascribed to a sequence of structural transformations on the basis of in-situ Raman spectra. The data suggest that the as-deposited material consisting of a mixture of polycrystalline InSb0.8Te0.2and amorphous Te first undergoes a progressive crystallization of the amorphous part, mostly above 300 °C. Further increase in temperature above 460 °C leads, for higher Te content in the alloy, to the formation of crystalline In3SbTe2, intertwined with a less conductive compound, possibly InTe and/or InSb. Upon cooling to room temperature, the initial polycrystalline InSb0.8Te0.2phase is mostly recovered along with other compounds, with a slightly higher thermal conductivity than that of the as deposited material. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim
Structural and electrical analysis of In–Sb–Te‐based PCM cells
No full textTwo In–Sb–Te compounds with low Te content (12 at.% and 17 at.%), deposited by metalorganic chemical vapour deposition, were implemented into prototype phase-change memory devices of size 50 × 50 nm2 and 93 × 93 nm2. These chalcogenides yielded devices with higher threshold voltage than those based on Ge–Sb–Te alloys. The endurance and programming window were markedly improved (from 103 to 106 cycles and from 1 to 2 orders of magnitude, respectively) when employing the Te-richer alloy. Moreover, in situ structural and electrical analysis on TiN/In–Sb–Te/dielectric stacks provided additional insight on the thermal stability of the two ternary phases In3SbTe2 and InSb0.8Te0.2, which were found to coexist in these compounds
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
HighSTEPS. A high strain temperature pèressure and speed apparatus to study earthquake mechanics
No full textWe present a state of-the-art biaxial apparatus able to study both earthquake rupture nucleation and propagation at conditions typical of the seismogenic crust. The HighSTEPS, High Strain TEmperature Pressure Speed, apparatus simulates fault deformation in a wide range of slip velocities, i.e., from 10-5m/s to 0.25 m/s. Within this velocity range, it is possible to study, the rate-and-state friction, the fault dynamic weakening, and healing under unique boundary conditions, i.e., normal stress up to 100 MPa, confining pressure up to 100 MPa, pore fluid pressure up to 100 MPa and temperature up to 120 °C. The apparatus consists of a hydraulic system integrated with four linear motors. The hydraulic system allows
for the application of normal stress, confining pressure and pore fluid pressure. The main peculiarity of this apparatus is the system of four linear motors that are mounted in series in order to apply shearing velocities up to 0.25 m/s, accelerations up to 10 m/s2 and shear stresses up to 200 MPa. Moreover, both experiments in sliding velocity control or shear stress control on the experimental faults are possible. Preliminary experiments on carbonate and silicate bearing rocks are coherent with the previous literature. The investigation of fault friction under a wide range of velocities, normal stresses, confining pressures and pore fluid pressures will provide insights into the mechanics of earthquakes and reduce the gap between
natural and laboratory observations
Nanowires
No full textThe self-assembly of Ge(1)Sb(2)Te(4) nanowires (NWs) for phase change memories application was achieved by metal organic chemical vapor deposition, catalyzed by Au nanoislands in a narrow range of temperatures and deposition pressures. In the optimized conditions of 400 °C, 50 mbar, the NWs are Ge(1)Sb(2)Te(4) single hexagonal crystals. Phase change memory switching was reversibly induced by nanosecond current pulses through metal-contacted NWs with threshold voltage of about 1.35 V
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
MOCVD growth and structural characterization of In–Sb–Te nanowires
No full textIn this work, the self-assembly of In3Sb1Te2 and In-doped Sb4Te1 nanowires (NWs) for phase change memories application was achieved by metal organic chemical vapor deposition, coupled with vapor–liquid–solid (VLS) mechanism, catalyzed by Au nanoparticles. Single crystal In3Sb1Te2 and In-doped Sb4Te1 NWs were obtained for different reactor pressures at 325 °C. The parameters influencing the NW self-assembly were studied and the compositional, morphological, and structural analysis of the grown structures was performed, also comparing the effect of the used substrate (crystalline Si and SiO2). In both cases, NWs of several micrometer in length and with diameters as small as 15 nm were obtained
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