26,138 research outputs found
Fabrication of phase masks from amorphous carbon thin films for electron-beam shaping
Background: Electron-beam shaping opens up the possibility for novel imaging techniques in scanning (transmission) electron microscopy (S(T)EM). Phase-modulating thin-film devices (phase masks) made of amorphous silicon nitride are commonly used to generate a wide range of different beam shapes. An additional conductive layer on such a device is required to avoid charging under electron-beam irradiation, which induces unwanted scattering events.
Results: Phase masks of conductive amorphous carbon (aC) were successfully fabricated with optical lithography and focused ion beam milling. Analysis by TEM shows the successful generation of Bessel and vortex beams. No charging or degradation of the aC phase masks was observed.
Conclusion: Amorphous carbon can be used as an alternative to silicon nitride for phase masks at the expense of a more complex fabrication process. The quality of arbitrary beam shapes could benefit from the application of phase masks made of amorphous C
Recombination in polymer-fullerene bulk heterojunction solar cells
Recombination of photogenerated charge carriers in polymer bulk
heterojunction (BHJ) solar cells reduces the short circuit current (Jsc) and
the fill factor (FF). Identifying the mechanism of recombination is, therefore,
fundamentally important for increasing the power conversion efficiency. Light
intensity and temperature dependent current-voltage measurements on polymer BHJ
cells made from a variety of different semiconducting polymers and fullerenes
show that the recombination kinetics are voltage dependent and evolve from
first order recombination at short circuit to bimolecular recombination at open
circuit as a result of increasing the voltage-dependent charge carrier density
in the cell. The "missing 0.3V" inferred from comparison of the band gaps of
the bulk heterojunction materials and the measured open circuit voltage at room
temperature results from the temperature dependence of the quasi-Fermi-levels
in the polymer and fullerene domains - a conclusion based upon the fundamental
statistics of Fermions.Comment: Accepted for publication in Physical Review B.
http://prb.aps.org/accepted/B/6b07cO3aHe71bd1b149e1425e58bf2868cda2384d?ajax=1&height=500&width=50
Electrical properties of Bi-implanted amorphous chalcogenide films
The impact of Bi implantation on the conductivity and the thermopower of
amorphous chalcogenide films is investigated. Incorporation of Bi in Ge-Sb-Te
and GeTe results in enhanced conductivity. The negative Seebeck coefficient
confirms onset of the electron conductivity in GeTe implanted with Bi at a dose
of 2x1016 cm-2. The enhanced conductivity is accompanied by defect accumulation
in the films upon implantation as is inferred by using analysis of the
space-charge limited current. The results indicate that native coordination
defects in lone-pair semiconductors can be deactivated by means of ion
implantation, and higher conductivity of the films stems from additional
electrically active defects created by implantation of bismuth.Comment: This is an extended version of the results presented in Proc. SPIE
8982, 898213 (2014
Surface micromachined electrostatically actuated micro peristaltic pump
An electrostatically actuated micro peristaltic pump is reported. The micro pump is entirely surface micromachined using a multilayer parylene technology. Taking advantage of the multilayer technology, the micro pump design enables the pumped fluid to be isolated from the electric field. Electrostatic actuation of the parylene membrane using both DC and AC voltages was demonstrated and applied to fluid pumping based on a 3-phase peristaltic sequence. A maximum flow rate of 1.7 nL min^–1 and an estimated pumping pressure of 1.6 kPa were achieved at 20 Hz phase frequency. A dynamic analysis was also performed with a lumped-parameter model for the peristaltic pump. The analysis results allow a quantitative understanding of the peristaltic pumping operation, and correctly predict the trends exhibited by the experimental data. The small footprint of the micro pump is well suited for large-scale integration of microfluidics. Moreover, because the same platform technology has also been used to fabricate other devices (e.g. valves, electrospray ionization nozzles, filters and flow sensors), the integration of these different devices can potentially lead to versatile and functional micro total analysis systems (µTAS)
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Ion Write Microthermotics: Programing Thermal Metamaterials at the Microscale.
Considerable advances in manipulating heat flow in solids have been made through the innovation of artificial thermal structures such as thermal diodes, camouflages, and cloaks. Such thermal devices can be readily constructed only at the macroscale by mechanically assembling different materials with distinct values of thermal conductivity. Here, we extend these concepts to the microscale by demonstrating a monolithic material structure on which nearly arbitrary microscale thermal metamaterial patterns can be written and programmed. It is based on a single, suspended silicon membrane whose thermal conductivity is locally, continuously, and reversibly engineered over a wide range (between 2 and 65 W/m·K) and with fine spatial resolution (10-100 nm) by focused ion irradiation. Our thermal cloak demonstration shows how ion-write microthermotics can be used as a lithography-free platform to create thermal metamaterials that control heat flow at the microscale
Low-temperature process steps for realization of non-volatile memory devices
In this work, the low-temperature process steps required for the realization of nano-crystal non-volatile memory cells are discussed. An amorphous silicon film, crystallized using a diode pumped solid state green laser irradiating at 532 nm, is proposed as an active layer. The deposition of the subsequent functional layers (e.g., gate oxide) can be done using CVD and ALD reactors in a cluster tool. We show that a high nanocrystal density (Si-NC), required for a good functionality of the memory device, can be obtained by using disilane (Si2H6) or trisilane (Si3H8, known as Silcore®) as precursors for LPCVD instead of silane, at a deposition temperature of 325 °C. The nanocrystals are encapsulated with an ALD-Al2O3 layer (deposited at 300 °C), which serves as oxidation barrier. The passivation of the realized structure is done with an ALD-TiN layer deposited at 425 °C.
In this work, we realized Al/TiN/Al2O3/Si-NC/SiO2/Si(100) multilayer floating-gate structures, where the crystallized amorphous silicon film was for the time being replaced by a mono-crystalline silicon wafer, and the gate oxide was thermally grown instead of a low-temperature PECVD oxide. The structures were characterized in terms of their performance as memory cells. In addition, the feasibility to use laser crystallization for improving the amorphous silicon films (prior to the gate oxide deposition) was explored
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