Write‐once–read‐many‐times memory (WORM) devices were fabricated using Ti/Au and Au as top contacts on ZnO thin films on Si. Electrical characterization shows that both types of WORM devices have large resistance OFF/ON ratio (R ratio), small resistance distribution range, long retention and good endurance. WORM devices with Au top contact have better performance of higher R ratio because of a larger work function of Au compared to Ti.
We demonstrate the self‐catalyst growth of vertically aligned InAs nanowires on bare Si(111) by droplet epitaxy. The growth conditions of indium droplets suitable for nucleation and growth of nanowires have been identified. We have then realized vertically aligned and non‐tapered InAs nanowires on bare Si(111) substrates through optimal indium droplets. It was found that the lateral dimensions and density of nano‐wires are defined by the indium droplets. This technique unravels a controllable, cost‐effective and time‐efficient route to fabricating functional monolithic hybrid structures of InAs nanowires on silicon.
Steady‐state and time‐resolved photoluminescence of silicon nanoparticles dispersed in low‐polar liquids at above room temperature is studied. The roles of low‐polar liquids as well as mechanisms responsible for their temperature‐dependent photoluminescence are discussed. The thermal sensitivity of the photoluminescence is estimated and application of the nanoparticles as nanothermometers is proposed.
By means of first‐principles calculations we predict the stability of silicene as buckled honeycomb lattice on passivated substrates of group‐IV(111)1 × 1 surfaces. The weak van‐der‐Waals interaction between silicene and substrates does not destroy its linear bands forming Dirac cones at the Brillouin zone corners. Only very small fundamental gaps are opened around the Fermi level.
We report on solution‐processible polymer solar cells (PSCs) fabricated on a papery substrate using carton. Highly conductive PEDOT:PSS was used as a bottom anode and planarization layer, and a semi‐transparent top cathode was applied. This research could be an important approach to the development of all‐solution‐processible papery PSCs as well as paper electronics.
Epitaxial TiC/SiC multilayers were grown by magnetron sputtering at a substrate temperature of 550 °C, where SiC is normally amorphous. The epitaxial TiC template induced growth of cubic SiC up to a thickness of ～2 nm. Thicker SiC layers result in a direct transition to growth of the metastable amorphous SiC followed by renucleation of nanocrystalline TiC layers.
We demonstrate the fabrication of a solid state heterojunction photovoltaic device with solution‐processed graphene oxide (GO) and n‐Si. Partially reduced GO with a high optical gap (2.8 eV) was spin‐coated on the n‐Si substrate and a heterojunction device was fabricated with the structure of Au/pr‐GO/n‐Si. In the fabricated device, incident light was transmitted through the thin GO film to reach the junction interface, generating photoexciton, and thereby a photovoltaic action was observed. By means of a built‐in electric potential at the GO/n‐Si junction, photoexcited electrons and holes can be separated, transported and collected at the electrodes.
Interaction between negatively charged Nafion® and a positively charged polybenzimidazole‐decorated carbon nanotube leads to the formation of an ionic complex with high charge density for proton conduction, which can lead to an improvement in transport properties. Here we investigate the high‐temperature and low‐humidity proton conductivity of this nanocomposite membrane as a potential membrane for fuel cell applications.
Quasi‐aligned molybdenum oxide nanowires are synthesized on silicon substrate by a thermal evaporation method, at a low temperature of 550 °C without using any catalyst. The diameter of these nanowires is about 100 nm, with steps in the top to form a sharp tip. The field emission measurement shows that these nanowires have strong electron field emission abilities, with high field enhancement factor and a relatively low turn‐on field of 2.16 V µm–1, suggesting that these molybdenum oxide nanowire arrays might be promising candidates as field emitters.
We study the spin ordering of a quantum dot defined via magnetic barriers in an interacting quantum spin Hall edge. The spin‐resolved density–density correlation functions are computed. We show that strong electron interactions induce a ground state with a highly correlated spin pattern. The crossover from the liquid‐type correlations at weak interactions to the ground state spin texture found at strong interactions parallels the formation of a one‐dimensional Wigner molecule in an ordinary strongly interacting quantum dot.
Optically transparent and high‐quality hybrid ZnO nanoparticle and anthracene embedded polyphenylsiloxane (PPS) glass films were spin‐coated on quartz substrates. A strong Förster resonant energy transfer (FRET) process was indicated by the observation of quenching of the ZnO emission and an enhancement of the anthracene emission at room temperature. The efficiency of this energy transfer between ZnO and the S1 vibronic states of the anthracene molecules can be optimized to exceed 90%.
Heteroepitaxial growth of III‐Sb nanowires allows for the formation of various interesting complex structures and enables the combination of their remarkable properties. In this Letter, we investigate the heteroepitaxial growth of Au‐seeded InSb and GaSb nanowires using metalorganic vapor phase epitaxy. We demonstrate successful single and double axial InSb–GaSb heterostructures in both directions. The formation properties of the grown nanowires including the compositional change of the particle and the interface sharpness are further discussed. In addition, the decomposition of InSb and GaSb segments and their side facet evolution are explained.
We have fabricated multi‐peak and chromaticity‐stable top‐emitting white organic light‐emitting diodes (TEWOLEDs) using single blue emitter. Besides the intrinsic emission of blue emitter, the additional emission can be well realized by simply adjusting the thickness of hole transporting layer (HTL), thus modifying the optical cavity length to obtain different resonant wavelengths. The detailed variation process for multi‐peak spectra with the increase of HTL thickness is studied, which provides a guidance for the design of microcavity TEWOLEDs.
This Letter reports on the assembly on the tip of an optical fibre of a metamaterial film fabricated by a self‐assembly bottom‐up method, composed of silver nanowires embedded in an alumina matrix. By illuminating the film through the fibre in a reflection configuration, we observe experimentally the optical response of the metamaterial in agreement with theoretical predictions and interpreted as the excitation of surface plasmon‐polaritons in the cylindrical surface of the nanowires. These results pave the way for low‐cost optical fibre devices that incorporate metamaterial films.
Thin amorphous tantalum films are prepared on Si(111) substrates in a metallic glassy state. The amorphous monoatomic state of the film is characterized by X‐ray diffraction studies. The glassy state leads to a negative t emperature c oefficient of the r esistivity (TCR) for low sample temperatures <200 K which is attributed to incipient localization. Above 200 K a positive TCR is observed as expected for a normal Boltzmann transport regime. Upon heating the Si substrate to 1200 K TaSi2 is formed out of the amorphous tantalum film and the silicon substrate. The TaSi2 layer is crystalline as evident from X‐ray diffraction data.
ZnO thin films with a rippled surface structure were used as electron‐collecting layers of inverted organic photovoltaics (OPVs). Using additional ultrathin layers of ZnO and TiO2 fabricated using atomic layer deposition (ALD), not only the power‐conversion efficiency of the OPVs could be increased (up to 3.5%), but also the photovoltaic performance became nearly constant within 100 days without any additional encapsulations of the solar cells under ambient conditions.
We demonstrate a novel sensor type, which is based on the monolithic integration of luminescent optical sensor spots together with ring‐shaped thin‐film organic photodiodes on one substrate. The organic photodiodes serve as integrated fluorescence detectors, simplifying the detection system by minimizing the number of required optical components. The proposed concept enables filter‐less discrimination between excitation light and generated fluorescence light. The functionality of the concept is demonstrated by an integrated oxygen sensor, exhibiting excellent performance. The sensor spots are excited by an assembled organic light emitting diode. The integrated optical sensor platform is suitable for the parallel detection of multiple parameters. Sensor schemes for the analytical parameters carbon dioxide, temperature and ammonia, are proposed.
Persistent layer‐by‐layer growth is demonstrated for pulsed‐laser homoepitaxy of ZnO thin films on $(000\bar 1)$ ZnO single crystals. Employing interval pulsed‐laser deposition (PLD), RHEED oscillations are stabilized over a film thickness of about 90 nm. For interval pulsed laser deposited films a considerably decreased root‐mean‐square surface roughness of 0.26 nm was found, in comparison to 0.74 nm for conventional PLD. A small asymmetry in the X‐ray diffraction (XRD) 2θ –ω scan reveals compressive strain in the thin film being slightly larger for interval PLD as compared to conventional PLD. The FWHM of the photoluminescence (PL) I6 line is higher with about 500 µeV as compared to 350 µeV for the conventional PLD. Consequently, both XRD as well as PL indicate a slightly higher amount of charged defects for the interval PLD.
Multicrystalline silicon wafer solar cells reveal performance‐ reducing defects by luminescence. X‐ray fluorescence spectra are used to investigate the elemental constituents from regions of solar cells yielding reverse‐bias or sub‐bandgap luminescence from defects. It is found that a higher concentration of metals is present in regions yielding reverse‐bias electroluminescence than in regions yielding sub‐bandgap electroluminescence. This suggests, dislocations do not create strong breakdown currents in the absence of impurity precipitates.
