Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate

Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions.     

Applying institutional theories to managing megaprojects

This paper contributes to Rodney Turner's initiative to develop a theory of project management from practice. Organizational scholars studying strategy suggest that more attention needs to be paid to practices involved in organizing, as well as the institutional contexts in which these practices are embedded. Taking a cue from strategy-in-practice approaches, it is proposed that institutional theories can be used to address some questions that have not been answered adequately regarding megaprojects. Institutional theories also seem to be gaining the attention of scholars investigating large, global, infrastructure projects as reported in engineering, management and construction journals. Increasingly, it is evident that the problem areas attached to these projects stretch beyond technical issues: they must be considered as socio-technical endeavours embedded in complex institutional frames. The authors suggest that studying how to deal with institutional differences in the environment of megaprojects has both theoretical and practical implications.     

Direct extraction of substrate network parameters for RF MOSFET modeling using a simple test structure

This letter presents a novel test structure to accurately extract the substrate network parameters for RF MOSFET modeling from two-port measurements. The test structure used in the common-gate configuration isolates the gate network to make the substrate network distinctly accessible to measurements. A methodology is developed to directly extract the substrate network from the measured data. The method is further verified and validated by the excellent match obtained between measured and simulated two-port parameters.     

Extraction of SiO2/SiC interface trap profile in 4H- and 6H-SiC metal-oxide semiconductor field-effect transistors from subthreshold characteristics at 25°C and 150°C

The profile of trap density at the SiO₂/SiC interface in SiC metal-oxide semiconductor field-effect transistors (MOSFETs) is critical to study the channel electron mobility and evaluate device performance under various processing and annealing conditions. In this work, we report on our results in determining the interface trap density in 4H- and 6H-SiC MOSFETs annealed in dry O₂, NO, and CO₂, respectively, based on the device transfer and currentvoltage characteristics in the subthreshold region at 25°C and 150°C. We also studied electron field-effect mobility, fixed oxide charge, and gate leakage in those devices.     

Low-temperature spin spray deposited ferrite/piezoelectric thin film magnetoelectric heterostructures with strong magnetoelectric coupling

We report low-temperature spin spray deposited Fe₃O₄/ZnO thin film microwave magnetic/piezoelectric magnetoelectric heterostructures. A voltage induced effective ferromagnetic resonance field of 14 Oe was realized in Fe₃O₄/ZnO magnetoelectric (ME) heterostructures. Compared with most thin film magnetoelectric heterostructures prepared by high temperature (>600 °C) deposition methods, for example, pulsed laser deposition, molecular beam epitaxy, or sputtering, Fe₃O₄/ZnO ME heterostructures have much lower deposition temperature (<100 °C) at a much lower cost and less energy dissipation, which can be readily integrated in different integrated circuits.     

Structural and optical properties of electrodeposited indium selenide thin films

Journal of Materials Science Letters -     

Microstructural properties of electrochemically synthesized ZnSe thin films

In this study, we report the electrosynthesis of zinc selenide (ZnSe) thin films on indium-doped tin oxide-coated glass substrates. The deposited ZnSe thin films have been characterized for structural (X-ray diffraction), surface morphological (scanning electron microscopy), compositional (energy dispersive analysis by X-rays), photo luminescence property, and optical absorption analysis. Formation of cubic structure with preferential orientation along the (111) plane was confirmed from structural analysis. In addition, the influence of the deposition potential on the microstructural properties of ZnSe is plausibly explained. The optical properties of ZnSe thin films are estimated using the transmission spectrum in the range of 400–1200 nm. The optical band gap energy of ZnSe thin films was found to be in the range between 2.52 and 2.61 eV. Photoluminescence spectra were observed at blue shifted band edge peak. The morphological studies depict that the spherical and cuboid shaped grains are distributed evenly over the entire surface of the film. The sizes of the grains are found to be in the range between 150 and 200 nm. The ZnSe thin film stoichiometric composition was observed at optimized deposition condition.     

Patterned Self‐Assembled Monolayers on Silicon Oxide Prepared by Nanoimprint Lithography and Their Applications in Nanofabrication

Nanoimprint lithography (NIL) is used as a tool to pattern self‐assembled monolayers (SAMs) on silicon substrates because of its ability to pattern in the micrometer and nanometer ranges. The polymer template behaves as a physical barrier preventing the formation of a SAM in the covered areas of the substrate. After polymer removal, SAM patterns are obtained. The versatility of the method is shown in various nanofabrication schemes. Substrates are functionalized with a second type of silane adsorbate. Pattern enhancement via selective electrostatic attachment of carboxylate‐functionalized particles is achieved. Further applications of the NIL‐patterned substrates include template‐directed adsorption of particles, as well as the fabrication of electrodes on top of a SAM.     

Dipolar versus octupolar triphenylamine-based fluorescent organic nanoparticles as brilliant one- and two-photon emitters for (bio)imaging

Two related triphenylamine-based dipolar and octupolar fluorophores are used to prepare aqueous suspensions of fluorescent organic nanoparticles (FONs) via the reprecipitation method. The obtained spherical nanoparticles (30-40 nm in diameter) are fluorescent in aqueous solution (up to 15% fluorescence quantum yield) and exhibit extremely high one- and two-photon brightness, superior to those obtained for quantum dots. Despite the two chromophores showing similar fluorescence in solution, the fluorescence of FONs made from the octupolar derivative is significantly red-shifted compared to that generated by the dipolar FONs. In addition, the maximum two-photon absorption cross section of the FONs made from the octupolar derivative is 55% larger than that of the dipolar derivative FONs. The experimental observations provide evidence that the different molecular shape (rodlike versus three-branched) and charge distribution (dipolar versus octupolar) of the two chromophores strongly affect the packing inside the nanoparticles as well as their spectroscopic properties and colloidal stability in pure water. The use of these FONs as probes for biphotonic in-vivo imaging is investigated on Xenopus laevis tadpoles to test their utilization for angiography. When using FONs made from the octupolar dye, the formation of microagglomerates (2-5 μm scale) is observed in vivo, with subsequent lethal occlusion of the blood vessels. Conversely, the nanoparticles of the dipolar dye allow acute imaging of blood vessels thanks to their suitable size and brightness, while no toxic effect is observed. Such a goal cannot be achieved with the dissolved dye, which permeates the vessel walls.