No abstract

The field emission properties of “porous diamond-like” carbon structures have been characterized. A hot filament chemical vapor deposition system fed with ethyl alcohol vapor diluted in helium was used to deposit the samples. Morphological analysis by field emission scanning electron microscopy revealed that they had a highly porous structure, which was attributed to the modification of the kinetics of the carbon deposition process due to the presence of helium as a buffer gas. Micro-Raman spectroscopy showed two peaks in the graphene and microcrystalline graphite frequencies and a new peak at 1620 cm−1. Low threshold fields (Et) and hysteresis in the current versus voltage characteristic have been observed, and a model to explain the hysteresis is proposed.

Fabrication and testing of micro-reactors for the characterization of nanosensors is presented in this work. The reactors have a small volume (100 μl) and are equipped with gas input/output channels. They were machined from a single piece of kovar in order to avoid leaks in the system due to additional welding. The contact pins were electrically insulated from the body of the reactor using a borosilicate sealing glass and the reactor was hermetically sealed using a lid and an elastomeric o-ring. One of the advantages of the reactor lies in its simple assembly and ease of use with any vacuum/gas system, allowing the connection of more than one device. Moreover, the lid can be modified in order to fit a window for in situ optical characterization. In order to prove its versatility, carbon nanotube-based sensors were tested using this micro-reactor. The devices were fabricated by depositing carbon nanotubes over 1 μm thick gold electrodes patterned onto Si/SiO(2) substrates. The sensors were tested using oxygen and nitrogen atmospheres, in the pressure range between 10(-5) and 10(-1) mbar. The small chamber volume allowed the measurement of fast sensor characteristic times, with the sensors showing good sensitivity towards gas and pressure as well as high reproducibility.

Parallel, portable dye-sensitized solar cell modules with 5 × 5 cm2 of area containing either a polymer gel electrolyte or a standard liquid electrolyte were assembled and characterized as a function of time. For modules sealed with the thermoplastic Surlyn, a rapid loss of performance was observed, due to an insufficient protection of the metallic current collectors (silver grids) of the module and, sometimes, also associated with electrolyte leakage. Similar results were obtained using a glass frit layer as the only material for protective overcoat of the silver grids. Thus, the combination of the Surlyn with a glass frit was investigated. The process based on the combination of two materials allowed achieving a more effective sealing, with enhanced process yield and sample reproducibility. The modules assembled by this method, filled with either a polymer gel electrolyte or liquid electrolyte, showed an enhanced stability. Concomitantly, the formulation of the polymer gel electrolyte was also addressed and had to be tuned to allow an easier filling of the modules.