7,540 research outputs found
Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells
Transition metal oxides (TMOs) have recently demonstrated to be a good alternative to boron/phosphorous doped layers in crystalline silicon heterojunction solar cells. In this work, the interface between n-type c-Si (n-Si) and three thermally evaporated TMOs (MoO3, WO3, and V2O5) was investigated by transmission electron microscopy, secondary ion-mass, and x-ray photoelectron spectroscopy. For the oxides studied, surface passivation of n-Si was attributed to an ultra-thin (1.9–2.8 nm) SiOx~1.5 interlayer formed by chemical reaction, leaving oxygen-deficient species (MoO, WO2, and VO2) as by-products. Carrier selectivity was also inferred from the inversion layer induced on the n-Si surface, a result of Fermi level alignment between two materials with dissimilar electrochemical potentials (work function difference ¿¿ = 1 eV). Therefore, the hole-selective and passivating functionality of these TMOs, in addition to their ambient temperature processing, could prove an effective means to lower the cost and simplify solar cell processing.Postprint (author's final draft
Laparoscopic image analysis for automatic tracking of surgical tools
Laparoscopy is a surgical technique nowadays embedded in the clinical routine. Recent researches have been focused on analysing video information captured by the endoscope for extracting cues useful for surgeons, such as depth information. In particular, the 3D pose estimation of the surgical tools presents three important added values: (1) to extract objective parameters for the surgical training stage, (2) to develop an image-guided surgery based on the knowledge of the surgery tools localization, (3) to design new roboticsystems for an automatic laparoscope positioning, according to the visual feedback. Tool’s shape and orientation in the image is the key to get its 3D position. This work presents an image analysis for automatic laparoscopic tool’s detection along the recorded video without extra tool markers, using an edges detection strategy. Also, this analysis includes a previous stage of barrel distortion correction for videoendoscopic image
Origin of the negative differential resistance in the output characteristics of a picene-based thin-film transistor
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this work, we have fabricated and studied p-type picene thin-film transistors. Although the devices exhibited good electrical performance with high field-effect mobility (up to 1.3 cm2/V¿s) and on/off ratios above 105, the output electric characteristics of the devices exhibited a Negative Differential Resistance for higher drain-source voltage. Finally, a possible explanation for this phenomenon is developed.Peer ReviewedPostprint (author's final draft
Superior performance of V2O5 as hole selective contact over other transition metal oxides in silicon heterojunction solar cells
Transition metal oxides (TMOs) have recently been proved to efficiently serve as hole-selective contacts in crystalline silicon (c-Si) heterojunction solar cells. In the present work, two TMO/c-Si heterojunctions are explored using MoO3 (reference) and V2O5 as an alternative candidate. It has been found that V2O5 devices present larger (16% improvement) power conversion efficiency mainly due to their higher open-circuit voltage. While V2O5/c-Si devices with textured front surfaces exhibit larger short-circuit currents, it is also observed that flat solar cell architectures allow for passivation of the V2O5/n-Si interface, giving significant carrier lifetimes of 200 µs (equivalent to a surface recombination velocity of Seff ~140 cm s-1) as derived from impedance analysis. As a consequence, a significant open-circuit voltage of 662 mV is achieved. It is found that, at the TMO/c-Si contact, a TMO work function enhancement ¿FTMO occurs during the heterojunction formation with the consequent dipole layer enlargement ¿’=¿+¿FTMO. Our results provide new insights into the TMO/c-Si contact energetics, carrier transport across the interface and surface recombination allowing for further understanding of the nature of TMO/c-Si heterojunctions.Peer ReviewedPostprint (published version
Chemical abundances of stars with brown-dwarf companions
It is well-known that stars with giant planets are on average more metal-rich
than stars without giant planets, whereas stars with detected low-mass planets
do not need to be metal-rich. With the aim of studying the weak boundary that
separates giant planets and brown dwarfs (BDs) and their formation mechanism,
we analyze the spectra of a sample of stars with already confirmed BD
companions both by radial velocity and astrometry. We employ standard and
automatic tools to perform an EW-based analysis and to derive chemical
abundances from CORALIE spectra of stars with BD companions. We compare these
abundances with those of stars without detected planets and with low-mass and
giant-mass planets. We find that stars with BDs do not have metallicities and
chemical abundances similar to those of giant-planet hosts but they resemble
the composition of stars with low-mass planets. The distribution of mean
abundances of -elements and iron peak elements of stars with BDs
exhibit a peak at about solar abundance whereas for stars with low-mass and
high-mass planets the [X/H] and [X/H] peak abundances
remain at ~dex and ~dex, respectively. We display these
element abundances for stars with low-mass and high-mass planets, and BDs
versus the minimum mass, , of the most-massive substellar companion
in each system, and we find a maximum in -element as well as Fe-peak
abundances at jupiter masses. We discuss the
implication of these results in the context of the formation scenario of BDs in
comparison with that of giant planets.Comment: Accepted for publication in Astronomy & Astrophysic
Inter-rater and intra-rater reliability of the extended TUG test in elderly participants
Background: To analyse the reliability, variance and execution time of the Extended Timed Up and Go (Extended
TUG) test in three age groups of elderly participants (G1: 55–64 years; G2: 65–74 years; G3: 75–85 years).
Methods: An analytical cross-sectional study of 114 recruited participants (63 women) of average age 70.17 (± 7.3) years
was undertaken. Each participant performed the Extended TUG three consecutive times, with a rest break between tests of
120 s. Both the intragroup and intergroup reliability of the measurements in the Extended TUG were analysed.
Results: The reliability of the Extended TUG test is excellent for the first and second decades but drops down to good for
the third decade. Specifically, intragroup reliability ranged from 0.784 for G3 to 0.977 for G1 (G2 = 0.858). Intergroup reliability,
compared with intragroup reliability, was slightly lower, ranging between 0.779 for G3 and 0.972 for G1 (G2 = 0.853).
Conclusion: The reliability of the Extended TUG test progressively decreases with increasing age, being excellent for the
younger age groups and good for the oldest age group
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