Tero Mustonen

This work reports on the performance of a segmented polymer electrochromic display that was fabricated with solution-based processes in ambient atmosphere. An encapsulation process and the combination of structured wells for the polymer electrochrome and electrolyte layers as well as the use of a preoxidized counter polymer yields high contrasts and fast switching speeds. Asymmetric driving–with respect to time–of the display is investigated for the first time and the degradation effects in the electrochrome layer are analyzed and addressed to yield a stable device exceeding 100 000 switching cycles. A printed circuit board was integrated with the display, allowing the device to be run as a clock, where the segments only required short pulses to switch without the need for a constant current to maintain its state. Such an application pairs well with the advantages of electrochromic polymers, drawing on its high contrast, stability, and ability to maintain its colored or colorless state without the need for a constant power supply, to demonstrate the promise as well as the challenges of developing more sophisticated electrochromic devices.

Aqueous solutions of carboxyl functionalized single‐wall carbon nanotube (SWCNT) films are deposited on silicon chips by the inkjet printing technique. By varying the film thickness it is possible to obtain low‐ or high density networks of SWCNTs, having either nonlinear or linear current‐voltage characteristics, respectively. The electrical transport in the low‐density films is gate‐controllable and utilized as chemical field‐effect transistor sensors; whereas the high‐density SWCNT networks of nearly Ohmic behaviour are used as conventional resistive gas sensors. The response of both types of sensors is studied for hydrogen sulfide (H₂S) analyte.

A low‐noise electronic system is built and tested for fluctuation enhanced sensing. This latter is a new technique and based on the determination of the power spectral density of the stationary resistance fluctuations of semiconductor gas sensors. Its use is advantageous for improving the chemical selectivity of sensors. However, subsequent to an initial fast change of the sensor mean resistance, as a sensor is exposed to an analyte gas, a typical drift of the resistance can be observed. This effect hinders evolving stacionary conditions and thus acquiring fast measurements when applying fluctuation enhanced sensing. Therefore, this drift effect is studied both experimentally and theoretically. Functionalized carbon nanotube layers on silicon chips serve as active material for the experimental investigations. Power spectral density functions are measured and simulated numerically with and without drift conditions. The results are compared and the effect of resistive drift on fluctuation enhanced sensing is discussed.

We present the fabrication and characterization of logic elements (transistors and interconnects) built using our recently developed inkjet-printer-controlled deposition of single-wall carbon nanotube network films. The method requires no preselection of “metallic” or “semiconducting” nanotubes. By selecting the number of prints on a specified region, it is possible to have low-density, nonlinear, gate-voltage controllable transistors or high-density, linear, high-current-throughput metallic interconnects without any gate-voltage response. Intermediate steps drive the films between the nonlinear and linear regimes with precise controllability. The transport mechanism in these films as a function of bias, gate voltage, and temperature dependence have been investigated and analyzed using junction properties of metal-semiconductors in the context of networks of carbon nanotubes.

Nitric oxide (NO) gas sensing with carboxyl functionalized single‐ and multi‐walled carbon nanotubes (SWCNTs and MWCNTs) is demonstrated in this work. Stable solutions of the carboxylated nanotubes were made and then drop‐cast on alumina substrates equipped with gold electrodes and also with platinum heater elements. The obtained resistive nanotube sensors were tested in a 2‐point setup at different temperatures and NO gas concentrations up to 100 ppm in synthetic air and also in argon buffer. When exposed to NO, the conductivity of the sensors changed up to ∼40% for SWCNTs and ∼12% for MWCNTs; however, in the investigated regime, the response was found to be fairly independent on NO concentration. Though all sensors showed practically instantaneous gas response, the time needed for saturation (few tens of minutes) was found to be concentration dependent.

Transparent and conductive patterns of carboxyl functionalized single‐walled carbon nanotubes (SWCNT‐COOHs) and the composites of those with poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT‐PSS) were deposited on various substrates by inkjet printing. For low print repetitions, the PEDOT‐PSS/SWCNT‐COOH composite patterns show enhanced conductance as compared to the corresponding PEDOT‐PSS conductors. The results suggest a decreased percolation threshold for the printed composite since the nanotubes establish electrical interconnections between the separate PEDOT‐PSS (conductive phase) islands being dispersed in the insulating PSS‐phase. However, the interaction between PEDOT‐PSS and SWCNTs becomes insignificant and the conductivity is not enhanced by the nanotubes, when the amount of PEDOT‐PSS is sufficient to form a continuous conducting phase. Up to now, patterns having sheet resistivities as low as ∼1 kΩ/□ could be achieved. Though there is a trade‐off between transparency and conductivity – we achieved highly transparent patterns (∼90%) with a reasonably low resistivity of ∼10 kΩ/□. The ink and printing method proposed here offer new alternatives of conventional transparent conductive materials based on either polymers or indium oxides; and pose scaleable production of cost‐effective transparent electronics.