p-i-n heterojunctions with BiFeO3 perovskite nanoparticles and p- and n-type oxides: photovoltaic properties.

We formed p-i-n heterojunctions based on a thin film of BiFeO3 nanoparticles. The perovskite acting as an intrinsic semiconductor was sandwiched between a p-type and an n-type oxide semiconductor as hole- and electron-collecting layer, respectively, making the heterojunction act as an all-inorganic oxide p-i-n device. We have characterized the perovskite and carrier collecting materials, such as NiO and MoO3 nanoparticles as p-type materials and ZnO nanoparticles as the n-type material, with scanning tunneling spectroscopy; from the spectrum of the density of states, we could locate the band edges to infer the nature of the active semiconductor materials. The energy level diagram of p-i-n heterojunctions showed that type-II band alignment formed at the p-i and i-n interfaces, favoring carrier separation at both of them. We have compared the photovoltaic properties of the perovskite in p-i-n heterojunctions and also in p-i and i-n junctions. From current-voltage characteristics and impedance spectroscopy, we have observed that two depletion regions were formed at the p-i and i-n interfaces of a p-i-n heterojunction. The two depletion regions operative at p-i-n heterojunctions have yielded better photovoltaic properties as compared to devices having one depletion region in the p-i or the i-n junction. The results evidenced photovoltaic devices based on all-inorganic oxide, nontoxic, and perovskite materials

Secure Mobile Payments Without Network Connectivity

Mobile payments depend on the availability of internet connectivity, e.g., to enable a centralized service to authenticate a payment. This disclosure describes techniques to enable peer-to-peer mobile payments in the absence of a network. A user has an initial amount, referred to as the balance, that is transferred to their mobile device from a balance provider, e.g., a financial institution. The balance is digitally signed by both the user and the balance provider. To transact in the absence of a network, peer users perform a contactless payment as follows. The receiver of funds verifies the availability of funds by examining the prior, authenticated, transaction records of the sender. A transaction record including the transaction amount is created and made immutable and secure using cryptographic techniques. When either the sender or receiver regains network connectivity, the transaction is settled with the balance provider. Double-spend attempts by a malicious sender are forestalled by enabling secure maintenance of the true balance on a sender’s device (even in the absence of a network), and by enabling the receiver to settle with the sender’s balance provider on the basis of an authenticated transaction record

Scalable synthesis of highly exfoliated, water-dispersible boron nitride nanosheets for nano-fibrillated cellulose membrane toughening

A very simple solid-state Diels Alder reaction of bulk boron nitride (BN) with maleic anhydride followed by ultrasonication in an aqueous solution was used to mass production of maleic acid functionalized highly exfoliated water dispersible single and few layers of boron nitride nanosheets (BNNS-MA). We demonstrate that as-synthesized BNNS-MA can be used to reinforce and toughen nano-fibrillated cellulose membranes.publishedVersionPeer reviewe

Formation of a gold-carbon dot nanocomposite with superior catalytic ability for the reduction of aromatic nitro groups in water

We report the synthesis of a gold-carbon dot nanocomposite and its utility as a recyclable catalyst for the reduction of aromatic nitro groups. The presence of carbon dots on gold nanosurfaces enhanced the reduction rate by two-fold

Aligned magnetic domains in p- and n-type ferromagnetic nanocrystals and in pn-junction nanodiodes

We form pn- and np-junctions between monolayers of p- and n-type nanocrystals that exhibit current rectification in the nanodiodes when characterized with a scanning tunneling microscope (STM) tip. With the use of ferromagnetic nanocrystals, we study the effect of mutual alignment of magnetization vectors on current rectification in the junction between the two nanocrystals. We show that when the magnetization vectors of the p- and of the n-type nanocrystals are parallel to each other (and both facing toward the apex of the STM tip) tunneling current in both bias modes increases with correspondingly a higher rectification ratio. This is in contrast to the parameters of the nanodiodes in which magnetization vectors of the components are unaligned or randomized. To analyze the results, we record scanning tunneling spectroscopy of the monolayer of the components having magnetization vectors aligned or unaligned to locate their valence and conduction band edges and to determine the effect of the alignment on the band edges. Upon alignment of the magnetization vectors of the nanocrystals in a monolayer, the conduction band edge of the p-type and valence band edge of the n-type semiconductor shift towards the Fermi energy leading to a change in energy levels of the pn-junctions and accounting for the improved parameters of the nanodiodes

A novel characterization method of fiber reinforced polymers with clustered microstructures for time dependent mass transfer

© 2017 Walter de Gruyter GmbH, Berlin/Boston. Some variation in the topological distribution of fibers inside the matrix phase of fiber reinforced polymers (FRP) is inevitable. Such irregularities can accelerate moisture diffusion and adversely affect the life of FRP. This paper presents a hierarchical technique for characterization of clustered microstructures and their transient moisture diffusion response. The clustering descriptors are derived for different fiber volume fractions (dilute to dense) for the quantitative definition of a given fiber matrix architecture. The metrics are normalized to remove dependence on volume fraction. The microstructures are analyzed for Fickian moisture diffusion. Suggested descriptors show a good correlation with transient diffusion response in relation to saturation time. The results can be used to predict the time-dependent moisture diffusion response of FRPs for any given fiber volume fraction

Photphysical properties of tetrahydroisoquinoline: evidence for flipped intramolecular charge transfer (FICT) emission

Photphysical properties of tetrahydroisoquinoline (THIQ) have been studied in various solvents. It has been found that in aprotic solvents a secondary amine THIQ shows a charge transfer emission band in addition to the expected locally excited xylene type emission band, though there is no corresponding charge transfer band in the absorption spectrum. It is ascribed to a charge transfer process in the excited state after flipping the N-atom across the average molecular plane. The ratio of FICT emission to locally excited xylene type emission is sensitive to the pH of the solution. This is due to the blocking of the lone pair of the nitrogen atom of THIQ by H+

Spin-Polarized Electron Transfers in Organic/Inorganic Hybrid (Rectifying) Junctions

We formed a heterojunction based on a monolayer of nickel phthalocyanine (NiPc) and another layer of cobalt-doped ZnO (Co@ZnO) nanoparticles on an electrode. By tunneling current through a monolayer of the components that in turn yielded density of states (DOS) of the semiconductors, we located energy levels of NiPc, which were electron donating in nature, and also the band edges of the <i>n</i>-type nanoparticles. Energies of the components in a heterojunction showed that there would be a preferential transfer of electrons from Co@ZnO to NiPc in junctions formed in either sequence (NiPc|Co@ZnO and Co@ZnO|NiPc). We then proceeded to form heterojunctions with the magnetization vector of Co@ZnO and the easy magnetization axis of the metalorganic parallel to each other. When such aligned junctions were characterized with spin-polarized scanning tunneling spectroscopy (SP-STS), we observed that the configuration acted as a unique diode applicable to spin-polarized electrons

Aligned Magnetic Domains in <i>p</i>- and <i>n</i>‑Type Ferromagnetic Nanocrystals and in <i>pn</i>-Junction Nanodiodes

We form <i>pn</i>- and <i>np</i>-junctions between monolayers of <i>p</i>- and <i>n</i>-type nanocrystals that exhibit current rectification in the nanodiodes when characterized with a scanning tunneling microscope (STM) tip. With the use of ferromagnetic nanocrystals, we study the effect of mutual alignment of magnetization vectors on current rectification in the junction between the two nanocrystals. We show that when the magnetization vectors of the <i>p</i>- and of the <i>n</i>-type nanocrystals are parallel to each other (and both facing toward the apex of the STM tip) tunneling current in both bias modes increases with correspondingly a higher rectification ratio. This is in contrast to the parameters of the nanodiodes in which magnetization vectors of the components are unaligned or randomized. To analyze the results, we record scanning tunneling spectroscopy of the monolayer of the components having magnetization vectors aligned or unaligned to locate their valence and conduction band edges and to determine the effect of the alignment on the band edges. Upon alignment of the magnetization vectors of the nanocrystals in a monolayer, the conduction band edge of the <i>p</i>-type and valence band edge of the <i>n</i>-type semiconductor shift towards the Fermi energy leading to a change in energy levels of the <i>pn</i>-junctions and accounting for the improved parameters of the nanodiodes