Upper Critical Fields of Nb/Pd Multilayers

We measured critical temperature and critical magnetic fields of Nb/Pd multilayers where the Nb thickness is held constant (d _Nb =250 Å) while the Pd thickness, d _Pd , is systematically varied from 10 to 200 Å. The critical temperature shows a monotonic decrease as a function of the Pd thickness, which can be tentatively described using the classical de Gennes-Werthamer theory for proximity coupled systems. The critical magnetic field measurements reveal unusual behavior, like a positive curvature of H_c2(T) close to T _c and a dimensional 3D-2D crossover, already present in multilayers with very thin Pd layers. In particular the angular behavior of the upper critical field, in the case of small d _Pd values, confirm the 2D nature of all the samples at T=4.2 K, giving also indication of the columnar nature of the Nb layers. These unusual behaviors might be related to the strong paramagnetic nature of the Pd layers. On the other hand also the proximity theory for S/N systems describes the perpendicular critical field data, but some inconsistencies are found quantitatively.     

Scaling of Hc2⊥(T) in Nb/CuMn Multilayers

Measurements of the perpendicular upper critical magnetic field H _c2(T) are reported for several Nb/CuMn multilayers. It is found that, despite the magnetic nature of the samples, the data for samples with low Mn percentage in the CuMn layers are simply described by the Werthamer–Helfand–Honenberg theory for conventional type-II superconductors, neglecting both Pauli spin paramagnetism and spin orbit impurity scattering. For high Mn concentration a different theoretical approach is needed.     

Thin film silicon photovoltaics: Architectural perspectives and technological issues

Thin film photovoltaics is a particularly attractive technology for building integration. In this paper, we present our analysis on architectural issues and technological developments of thin film silicon photovoltaics. In particular, we focus on our activities related to transparent and conductive oxide (TCO) and thin film amorphous and microcrystalline silicon solar cells. The research on TCO films is mainly dedicated to large-area deposition of zinc oxide (ZnO) by low pressure-metallorganic chemical vapor deposition. ZnO material, with a low sheet resistance (<8 Ω/sq) and with an excellent transmittance (>82%) in the whole wavelength range of photovoltaic interest, has been obtained. “Micromorph” tandem devices, consisting of an amorphous silicon top cell and a microcrystalline silicon bottom cell, are fabricated by using the very high frequency plasma enhanced chemical vapor deposition technique. An initial efficiency of 11.1% (>10% stabilized) has been obtained.     

Metal versus dielectric back reflector for thin‐film Si solar cells with impact of front electrode surface texture

Thin‐film Si solar cells employ a back reflector (BR) for a more efficient use of the long wavelength light. Here, we have carried out a cross evaluation of metal (Ag‐based) and dielectric (white paint‐based) BR designs. Conclusive results have been reached regarding the most suitable BR type depending on the front electrode morphology, both with crater‐like and pyramidal texture. The ZnO/Ag BR is found to be optically more efficient because of improved light trapping, although the gain tends to vanish for rougher front electrodes. Thanks to non‐conventional Raman intensity measurements, this dependence on the front texture has been linked to the different weight of front and back interfaces in the light trapping process for the different morphologies. With rougher substrates, because the minor optical gain is accompanied by sputter‐induced electronic deterioration of the solar cell during the ZnO buffer layer deposition, the white paint‐based BR design is preferred. Copyright © 2016 John Wiley & Sons, Ltd.     

Talos: no more ransomware victims with formal methods

Ransomware is a very effective form of malware that is recently spreading out on an impressive number of workstations and smartphones. This malware blocks the access to the infected machine or to the files located in the infected machine. The attackers will restore the machine and files only after the payment of a certain amount of money, usually given in the form of bitcoins. Commercial solutions are still ineffective to recognize the last variants of ransomware, and the problem has been poorly investigated in literature. In this paper we discuss a methodology based on formal methods for detecting ransomware malware on Android devices. We have implemented our method in a tool named Talos. We evaluate the method, and the obtained results show that Talos is very effective in recognizing ransomware (accuracy of 0.99) even when it is obfuscated (accuracy still remains at 0.99).     

Deep learning for image-based mobile malware detection

Current anti-malware technologies in last years demonstrated their evident weaknesses due to the signature-based approach adoption. Many alternative solutions were provided by the current state of art literature, but in general they suffer of a high false positive ratio and are usually ineffective when obfuscation techniques are applied. In this paper we propose a method aimed to discriminate between malicious and legitimate samples in mobile environment and to identify the belonging malware family and the variant inside the family. We obtain gray-scale images directly from executable samples and we gather a set of features from each image to build several classifiers. We experiment the proposed solution on a data-set of 50,000 Android (24,553 malicious among 71 families and 25,447 legitimate) and 230 Apple (115 samples belonging to 10 families) real-world samples, obtaining promising results.

     

A framework for supporting ransomware detection and prevention based on hybrid analysis

Journal of Computer Virology and Hacking Techniques - Ransomware is a very effective form of malware, which recently raised a lot of attention since an impressive number of workstations was...     

Dynamic malware detection and phylogeny analysis using process mining

International Journal of Information Security - In the last years, mobile phones have become essential communication and productivity tools used daily to access business services and exchange...     

Improved micromorph solar cells by means of mixed‐phase n‐doped silicon oxide layers

A good light trapping scheme is necessary to improve the performance of amorphous/microcrystalline silicon tandem cells. This is generally achieved by using a highly reflective transparent conducting oxide/metal back contact plus an intermediate reflector between the component cells. In this work, the use of doped silicon oxide as alternative n‐layer in micromorph solar cells is proposed as a means to obtain high current values using a simple Ag back contact and no extra reflector between the component cells n‐doped silicon oxide layers with a wide range of optical and electrical properties have been prepared. The influence of different deposition regimes on the material properties has been studied. The main findings are the following: (i) when carbon dioxide is added to the gas mixture, sufficiently high hydrogen dilution is necessary to widen the transition region from highly conductive microcrystalline‐like films to amorphous material characterized by low electrical conductivity; (ii) lower refractive index values are found with lower deposition pressure. Optimal n‐doped silicon oxide layers have been used in both component cells of micromorph devices, adopting a simple Ag back contact. Higher current values for both cells are obtained in comparison with the values obtained using standard n‐doped microcrystalline silicon, whereas similar values of fill factor and open circuit voltage are measured. The current enhancement is particularly evident for the bottom cell, as revealed by the increased spectral response in the red/infrared region. The results prove the high potential of n‐doped silicon oxide as ideal reflector for thin‐film silicon solar cells. Copyright © 2011 John Wiley & Sons, Ltd.