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.
Electrical characteristics of multi-walled carbon nanotubes (MWNTs) grown by chemical vapor deposition have been investigated as a function of the bias voltage, nanotubes length and temperature, in 2 and 4 terminal configurations. Nanotubes were deposited over metal electrodes using ac dielectrophoresis method. For better contacts between the nanotubes and electrodes, Ni and Pd films were deposited by an electroless deposition technique. Differential conductance was found to rise considerably with bias, and this effect was more pronounced for Ni. Using 2 and 4 terminal configurations, electrical resistance measurements for individual MWNTs were performed, and the results were interpreted using the model of nanotube as a resistive transmission line, where current at low bias flows mainly through the two outermost shells.
Ni electroless films were used as a material for hard mask during high-density ICP plasma etching. The results have shown that under the plasma exposure strong hardening of the mask occurs and the rate of Ni film removal falls at least an order of magnitude as compared with its initial value. Therefore, very high selectivities for Si etching over Ni are obtained, allowing for very deep etching required for some MEMS applications.
A method of ac dielectrophoresis was applied to align and deposit metallic multi-wall carbon nanotubes between pre-fabricated metal (Au, Pd) electrodes with a micron scale separation. For improvement of nanotube contacts with electrodes, Ni and Pd electroless processes were developed, and significant reduction of 2 terminals resistances was demonstrated. Further, using electron and ion beam deposited Pt contacts in two different configurations (“Pt-on-CNT” and “CNT-on-Pt”), 4 terminals measurements have been performed to evaluate intrinsic nanotube resistances. The values between 90 and 130 kΩ/μm were obtained, while systematically lower values (30-70 kΩ/μm) were estimated using 2 terminals method. The 4 terminals method was applied to study the effect of ion irradiation on the electrical parameters of supported nanotubes.
The influence of a magnetic field on electrodeposition of nickel films over polymeric substrates, which renders flexible membranes with a permanent magnet layer, has been studied. Samples of membranes with nickel deposited by electroplating in presence and absence of magnetic field are compared. The electroplated layer is deposited over an electroless contact layer, after a wet pre-treatment to improve adherence. Mechanical and magnetic properties of the samples were measured as function of process parameters. Experimental results confirm that the magnetic field has a positive impact over properties of deposited films. Pre-treatment using different process times influences uniformity and adherence of the deposited films. Results show also that films electroplated in presence of magnetic field outperformed those deposited in its absence, with enhanced maximum energy product and reduced surface roughness. On the other hand, films electroplated in presence of magnetic field tend to be less resistant to fracture during flexure tests.Nucleation.-The seed layer is obtained by sensitizing the polymer with an acid stannous chloride solution (1 g/l), then activating it with palladium chloride solution (0.25 g/l). The stannous ions (Sn 2þ ) absorbed on the surface reduce the palladium ions (Pd 2þ ), by the reaction (1). The palladium metal atoms form clusters and the seed layer which catalyzes the electroless nickel deposition. 35,36 z
An experimental investigation comparing the properties of plasma jets in dielectric barrier discharge (DBD) configurations using a powered electrode with and without a dielectric barrier, while keeping a second dielectric barrier over the grounded electrode, is reported in this work. For this purpose, two different power sources were used to produce the plasma jets, with one of them producing a pulsed high-voltage (HV) output and the other one producing a damped sine wave HV output, which acts as a pulse-like power source. Measurements of plasma parameters were performed for both configurations using argon and helium as working gases. As a result, if the pulsed power source is used, significant differences were found in discharge power (P dis ), rotational and vibrational temperatures (Tr and Tv, respectively) when switching from one configuration to the other. On the other hand, using the pulse-like HV only the P dis parameter presented significant differences when switching the electrode's configuration. For the pulsed source it has been observed that despite the remarkable increase in P dis when changing from the double barrier configuration to the single barrier one, the values obtained for Tr and Tv also increased, but not in the same proportion as the increase in P dis , which suggests a non-linear dependency between temperatures and discharge power in the plasma jet. As an example for application of plasmas in both configurations, tests in an attempt to remove copper films deposited on alumina substrates were performed and, as a result, there was significant material removal only when the powered electrode was in contact with the plasma. As a general conclusion, if higher power is really required for applications that do not involve in vivo targets it is better to use this configuration.
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