1,720,980 research outputs found
Dall’evoluzione in vitro alle nanotecnologie: gli aptameri come biosensori
No full textUna nuova frontiera per la ricerca nel campo dei biosensori è stata aperta in anni recenti dall’uso degli aptameri come elementi di riconoscimento molecolare. Gli aptameri sono piccole molecole di DNA o RNA selezionate per legare con elevata affinità un determinato bersaglio, sia esso una molecola semplice oppure una struttura complessa come una proteina o una superficie cellulare. La Selex, acronimo di Systematic Evolution of Ligands by EXponential enrichment, è la metodologia di evoluzione in vitro che permette di ottenere l’aptamero con l’attività specifica desiderata a partire da una libreria di acidi nucleici, sfruttando i principi di variazione, selezione e replicazione.
La Selex è stata resa possibile dagli sviluppi della tecnologia del DNA ricombinante e dal progresso tecnologico che per mezzo della sintesi chimica automatizzata ha permesso di ottenere a costi contenuti librerie combinatoriali di acidi nucleici. Il processo di selezione di individui presenti nella libreria e della loro successiva amplificazione permette di isolare tra molteplici e differenti conformazioni quella con il fenotipo adatto (aptus), coniugando in questo modo chimica e biologia. Gli aptameri selezionati possono poi essere facilmente modificati e funzionalizzati in modo da impiegarli nelle più svariate tecniche di rilevazione e offrire così nuove possibilità di ingegnerizzazione e nanofabbricazione rispetto a quelle fin qui usate nei biosensori convenzionali
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Electrical characterization of inhomogeneous Ni2Si/SiC Schottky contacts
No full textThe electrical characterization of nickel silicide (Ni2Si) Schottky contacts on 4H-SiC is reported in this work. In spite of the nearly ideal behaviour observed at room temperature (n=1.05), a deviation from the ideality was observed at lower temperatures, thus suggesting that an inhomogeneous Schottky barrier has actually formed. The experimental results were described by the Tung's model on inhomogeneous Schottky barriers, which considers low barrier regions embedded in a uniform high barrier Ni2Si contact. The inhomogeneity of the barrier is responsible of the commonly observed discrepancy between the experimental values of the Richardson's constant A** (i.e. 2.6 A/cm(2)K(2) in our contacts) from its theoretical value of 146 A/cm(2)K(2) in 4H-SiC
Hot carrier aging degradation phenomena in GaN based MESFETs
No full textIn this paper hot carrier degradation study in unpassivated and passivated GaN MESFETs will be presented: the observed drain current decrease will be proven to be consequent of a drain access resistance increase. In order to discriminate the effects due to traps on the device surface from those related with epitaxial material substrate and its interfaces, the influence of illumination on the drain current has been investigated by means of DC and gate-lag pulsed characterization. The measurements under light and under dark conditions lead us to suppose that the drain access resistance increase can be attributed to the generation of deep levels and/or to increased trapped charge after hot-carrier test on the device surface in the access regions between the gate and the drain contacts. The amount of degradation has been found to be remarkably higher in unpassivated devices with respect to passivated ones. Hot carrier degradation has been observed to be recovered by thermal or room temperature storage without applied bias
Schottky SiC Diodes in Power Applications
No full textThe first Silicon Carbide power diodes have only recently become commercially available [1]: the high electrical breakdown field and the very high thermal conductivity of this material make it particularly suited to the manufacturing of power devices. The characteristics of a 4A, 600V SiC Schottky diode –the Infineon SDP04S60- is experimentally evaluated and its performance in a typical power application is compared with two ultra-fast, soft-recovery, silicon power diodes with same ratings -the RURD460 and the recently presented STTH5R06D- in terms of efficiency improvement and EMI reduction
Schottky SiC Diodes in Power Switching Applications
No full textThe first Silicon Carbide power diodes have only recently become commercially available: the high electrical breakdown field and the very high thermal conductivity of this material make it particularly suited to the manufacturing of power devices. The characteristics of a 4A, 600V SiC Schottky diode –the Infineon SDP04S60- is experimentally evaluated and its performance in a typical power application is compared with two ultra-fast, soft-recovery, silicon power diodes with same ratings -the RURD460 and the recently presented STTH5R06D- in terms of efficiency improvement and EMI reduction
Temperature stability of Breakdown Voltage on SiC power Schottky diodes with different barrier heights
No full textThe static and dynamic electrical characterization of power Schottky rectifiers both with Ti and Ni2Si as Schottky metals having low negative coefficient of the breakdown voltage versus temperature will be presented in this paper. The values of the barrier height are respectively 1.28eV and 1.68eV, as extracted using the Tung’s model for inhomogeneous contacts from forward currentvoltage characteristics. These values were found to be in good agreement with those obtained by means of capacitance-voltage measurements. The breakdown voltage shows an almost linear dependence from the temperature for both types of devices. The extracted coefficients are respectively -0.08V/oC and -0.11V/oC, thus guarantying stable and reliable behaviour. Very short reverse recovery time at RT and at 125°C confirms the good thermal stability of these devices
Influence of gate-leakage current on drain current collapse of unpassivated GaN/AlGaN/GaN high electron mobility transistors
No full textWe report on a correlation between the gate leakage currents and the drain current collapse of
GaN/AlGaN/GaN high electron mobility transistors. Unpassivated devices on intentionally
undoped and doped sSi, 531018 cm−3d heterostructures were investigated. We observed in the
devices that the larger the gate leakage current, the smaller the drain current collapse measured at
50 ns gate-voltage pulse turn on, and this correlation is independent of the doping of the structure.
The correlation holds for two orders of magnitude in the gate-leakage current and up to 15% in drain
current collapse.We believe that the leakage current can modulate trapped surface charge so that the
time constant of the current collapse becomes much faster and dependent on the amount of leakage
current itself
Analysis of hot carrier aging degradation in GaN MESFETs
No full textIn this paper the study of the effects of illumination on the drain current of GaN
MESFETs are presented with the aim of discriminating effects due to traps on the
device surface from those related with epitaxial material substrate and its
interfaces. Illumination together with on-state stress are also used to investigate
hot carrier degradation phenomena which consist in drain access resistance
increase and consequently in drain current decrease: this can be attributed to the
generation of deep levels and/or to increased trapped charge after hot-carrier test
on the device surface access regions between the gate and the drain contacts. The
degradation level is remarkably higher in unpassivated devices with respect to
passivated ones. Hot carrier degradation can be recovered by thermal or R.T.
storage without bias
- …
