Niina Halonen

Three-Dimensional Carbon Nanotube Scaffolds as Particulate Filters and Catalyst Support Membranes

Three-dimensional carbon nanotube scaffolds created using micromachined Si/SiO2 templates are used as nanoparticulate filters and support membranes for gas-phase heterogeneous catalysis. The filtering efficiency of better than 99% is shown for the scaffolds in filtering submicrometer particles from air. In the hydrogenation of propene to propane reaction low activation energy of E(a) approximately 27.8 +/- 0.6 kJ x mol(-1), a considerably high turnover rate of approximately 1.1 molecules x Pd site(-1) x s(-1) and durable activity for the reaction are observed with Pd decorated membranes. It is demonstrated that appropriate engineering of macroscopic-ordered nanotube architectures can lead to multifunctional applications.

Electrical Transport and Field-Effect Transistors Using Inkjet-Printed SWCNT Films Having Different Functional Side Groups

The electrical properties of random networks of single-wall carbon nanotubes (SWNTs) obtained by inkjet printing are studied. Water-based stable inks of functionalized SWNTs (carboxylic acid, amide, poly(ethylene glycol), and polyaminobenzene sulfonic acid) were prepared and applied to inkjet deposit microscopic patterns of nanotube films on lithographically defined silicon chips with a back-side gate arrangement. Source-drain transfer characteristics and gate-effect measurements confirm the important role of the chemical functional groups in the electrical behavior of carbon nanotube networks. Considerable nonlinear transport in conjunction with a high channel current on/off ratio of approximately 70 was observed with poly(ethylene glycol)-functionalized nanotubes. The positive temperature coefficient of channel resistance shows the nonmetallic behavior of the inkjet-printed films. Other inkjet-printed field-effect transistors using carboxyl-functionalized nanotubes as source, drain, and gate electrodes, poly(ethylene glycol)-functionalized nanotubes as the channel, and poly(ethylene glycol) as the gate dielectric were also tested and characterized.

INCREASING CHEMICAL SELECTIVITY OF CARBON NANOTUBE-BASED SENSORS BY FLUCTUATION-ENHANCED SENSING

Nowadays gas detection in the ppm and sub-ppm domain is essential in terms of environmental protection as well as reducing sanitary risks. However, detecting systems to perform these measurements (e.g., gas chromatographs) are expensive and take up too much space, thus their use is not likely to become wide-spread. Small, cheap and easily mountable sensors, such as resistive sensors are more applicable for this purpose. But the main disadvantage of these sensors is the lack of chemical selectivity. Yet, a novel method called fluctuation-enhanced sensing (FES), which considers the sensor noise as the source of chemical information, can be used to improve selectivity. Since carbon nanotube (CNT)-based sensors are regarded as promising devices for FES measurements, we investigated whether stationary fluctuations in output signal (dc-resistance) of a CNT sensor could be used to increase chemical selectivity. In this work we prove that FES is applicable to increase selectivity of CNT sensors: air polluting gases (N2O, NH3 and H2S) and their mixtures can be distinguished. Furthermore, we also show that different concentrations of the same analyte can be differentiated and chemical selectivity can be extended into the sub-ppm region.

Low temperature co-fired ceramic packaging of CMOS capacitive sensor chip towards cell viability monitoring

Cell viability monitoring is an important part of biosafety evaluation for the detection of toxic effects on cells caused by nanomaterials, preferably by label-free, noninvasive, fast, and cost effective methods. These requirements can be met by monitoring cell viability with a capacitance-sensing integrated circuit (IC) microchip. The capacitance provides a measurement of the surface attachment of adherent cells as an indication of their health status. However, the moist, warm, and corrosive biological environment requires reliable packaging of the sensor chip. In this work, a second generation of low temperature co-fired ceramic (LTCC) technology was combined with flip-chip bonding to provide a durable package compatible with cell culture. The LTCC-packaged sensor chip was integrated with a printed circuit board, data acquisition device, and measurement-controlling software. The packaged sensor chip functioned well in the presence of cell medium and cells, with output voltages depending on the medium above the capacitors. Moreover, the manufacturing of microfluidic channels in the LTCC package was demonstrated.

LTCC Packaged Ring Oscillator Based Sensor for Evaluation of Cell Proliferation

A complementary metal-oxide-semiconductor (CMOS) chip biosensor was developed for cell viability monitoring based on an array of capacitance sensors utilizing a ring oscillator. The chip was packaged in a low temperature co-fired ceramic (LTCC) module with a flip chip bonding technique. A microcontroller operates the chip, while the whole measurement system was controlled by PC. The developed biosensor was applied for measurement of the proliferation stage of adherent cells where the sensor response depends on the ratio between healthy, viable and multiplying cells, which adhere onto the chip surface, and necrotic or apoptotic cells, which detach from the chip surface. This change in cellular adhesion caused a change in the effective permittivity in the vicinity of the sensor element, which was sensed as a change in oscillation frequency of the ring oscillator. The sensor was tested with human lung epithelial cells (BEAS-2B) during cell addition, proliferation and migration, and finally detachment induced by trypsin protease treatment. The difference in sensor response with and without cells was measured as a frequency shift in the scale of 1.1 MHz from the base frequency of 57.2 MHz. Moreover, the number of cells in the sensor vicinity was directly proportional to the frequency shift.

Gas Sensing and Thermal Transport Through Carbon-Nanotube-Based Nanodevices

Designing nanoscale devices, such as gas sensors and thermal dissipators, is challenging at multiple levels. Exploring their properties through combined experimental and theoretical collaborations is a valuable approach that expands the understanding of their peculiarities and allows for the optimization of the design process. In order to select the most relevant functional molecules for carbon-based gas sensors, and provide the best sensitivity and selectivity possible, we study the electronic transport properties of functionalized carbon nanotubes (CNTs), both through experiments and theoretical calculations. The measurements are carried out both in argon and synthetic air, using CO, NO, and H2S as test cases, with carboxyl-functionalized CNTs. The calculations, performed in the framework of density functional theory, consider both metallic and semi-conducting prototype CNTs, with respective chiralities (6,6) and (7,0), exploring a broader range of functional molecules and gases. The behavior of individual carboxyl-functionalized CNTs deduced from the multiscale results consistently reflect what happens at a larger scale and provides useful insights regarding the experimental results. CNTs are excellent thermal conductors as well and show much promise as heat dissipators in microelectronics. However, in practice, thermal properties of CNTs are affected due to the unavoidable presence of defects and interface with the environment. We investigated these limitations using a multiscale approach. Using molecular dynamics simulations, here we investigate the heat flow across the interface of a (10,10) CNT with various substances, including air and water. We also analyzed computationally the impact of CNT defects on its thermal transport properties using first principles calculations.

Thermal management of micro hotspots in electric components with carbon nanotubes

The excellent thermal and electrical conductivity as well as the remarkable mechanical properties of Carbon Nanotubes (CNTs) all point towards an unbeatable and facile route towards replacing traditional thermal management materials, like copper, in the electronics industry. In spite of that, the technology is still suffering from considerable challenges. In order to realise an actual electronics, which uses CNTs for thermal management, inevitable trade-offs have to be made. Our work is focusing on proposing novel ideas and manufacturing techniques which show a reasonable potential and could justify the practicality of this technology. The paper is reporting on the recent results in hotspot removal by using tailored multi-layer chips and CNTs grown directly on the heat affected zone.