Micro and Nanosystems - Volume 6, Issue 1, 2014

We highlight recent reviews and reports on the use of micro and nanosystems to solve biological problems. The matching length scale allows micro- and nanotechnology to create tools for engineering biological systems at molecular and cellular levels. Simple microdevices such as reactors, microchannels and concentration generators with features on the order of micrometers make the implementation of artificial life on a chip possible. These new tools allow for the investigation of complex gene expression dynamics and tissue or organ-level physiology. The next step will be the use of these tools as models for both health and disease for drug discovery.

The nanocomposites are innovative materials, which have gained great interest because of the opportunity for considerable improvement of the material properties like strength, modulus and dimensional stability, electrical conductivity, thermal stability, chemical resistance, surface appearance, optical clarity. Due to the specific structure, they could have new properties, which are unknown in the composed materials. Thus, the nanocomposites promise new applications in many fields as mechanically reinforced lightweight components, nanoelectromechanical systems, non-linear optics, energy conversion and storage, sensors and other systems in the defense, aerospace and automotive sectors. Usually, the nanocomposite structure is a matrix-filler combination, where a non-nanocrystalline matrix of one material is filled with nanoparticles, nanofibers or fragments surrounded and bound together as discrete units of an another material. Nanonanocomposite materials, where the size of all constituent material grains is in the nanometre range, exist as well. Amongst the large variety of nanocomposites, this issue is focused on novel solid nanocomposites for advanced applications having an inorganic component in the system such as ultra-nanocrystalline diamond/amorphous carbon composite films, nanostructured hard coatings, multi-ferric composite containing, metal matrix composites with high hardness, and enhanced wear resistance and corrosion resistance.

Microwave plasma chemical vapor deposition from CH4/N2 mixtures has been used for the preparation of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films on different substrates. We characterized these films with respect to their mechanical properties by nano-indentation, nano-scratch tests and micro- and nanotribometer measurements. The hardness and the Young's modulus of UNCD/a-C on Si, polycrystalline diamond (PCD) and c-BN determined by nanoindentations were on the order of 34-40 GPa and 325-390 GPa, respectively, higher than those of films on TiN. The best adhesion determined by Nano-Scratch tests was observed for the UNCD/a-C films on TiN, most probably as a result of the better adhesion between the silicon substrate and the intermediate layer. The tribotest measurements revealed that the UNCD/a-C films possess friction coefficient below 0.01 in humid air while it increases in dry oxygen, nitrogen and argon atmospheres. Although the presence of an amorphous matrix reduces the hardness by a factor of 2.5-3 in comparison with the monocrystalline diamond, it may be of advantage for the tribological performance of wear protecting coatings by improving their toughness.

Thin films of AlN on Si were fabricated by pulsed laser deposition in vacuum and in nitrogen ambient, and at laser repetition rate of 3 Hz or 10 Hz. The films were nanostructured according to the X-ray diffraction analysis and TEM imaging. Films deposited in vacuum were polycrystalline with hexagonal AlN phase and with columnar structure, while films deposited in nitrogen were predominantly amorphous with nanocrystallites inclusions. The Al-N phonon modes in the surface-enhanced Raman spectra were largely shifted due to stress in the films. Phonon mode of Al-O related to film surface oxidation is observed only for deposition at low pressures.

We present the structural and magnetic properties of a multiferroic Ba2Mg2Fe12O22 hexaferrite composite containing a small amount of MgFe2O4. The composite material was obtained by auto-combustion synthesis and, alternatively, by co-precipitation. The Ba2Mg2Fe12O22 particles obtained by co-precipitation have an almost perfect hexagonal shape in contrast with those prepared by auto-combustion. Two magnetic phase transitions, responsible for the composite’s multiferroic properties, were observed, namely, at 183 K and 40 K for the material produced by auto-combustion, and at 196 K and 30 K for the sample prepared by co-precipitation. No magnetic phase transitions in these temperature ranges were observed for a MgFe2O4 sample, which shows that the magnesium ferrite does not affect the multiferroic properties of this type of multiferroic metarials.

In this work is described a novel technique for surface modification of metals and its application for obtaining higher hardness and wear resistance of tools. The electrical discharge treatment in electrolyte gives a modified surface with specific combination of properties in result of nonequilibrium microstructural characteristics. The surface layers have a different structure in comparison with the metal matrix and higher hardness, wear resistance and corrosion resistance. The modification goes by a high energy thermal process in a very small volume on the metallic surface involving melting, vaporisation, activation and alloying in electrical discharges, and after that cooling of this surface with high rate in the electrolyte. The high energy process put together with the nonequilibrium phase transformations in the metallic system causes considerable modifications of the metallic surface and obtaining layers with fine-crystalline and nano-crystalline structure. The investigations show that layers obtained on tool steels have hardness which leads to a considerable increase in working life of tools and wide opportunities for industrial application.

Spark assisted chemical engraving (SACE) technology has the potential for micro machining glass with advantages of simplicity, high aspect ratio and less micro cracks. Typical micro SACE process utilizes cylindrical tool and suffers from poor electrolyte circulation along with machining depth. This work employed φ200µm tungsten carbide drill to experimentally fabricate micro holes on Pyrex Glass by applying SACE process. On the rotation of the drill, the micro grooves of the drill are capable of enhancing electrolyte circulation within machining zone and thus improve the processing performance. Several effects of process factors on drilling results were evaluated correspondently. The results revealed that machining time, drill rotation direction and rate, and the contact force affected the processing performance markedly. A deep hole of 245 ¿m in entrance diameter and 8.8 in aspect ratio was obtained by optimal process parameters. Tool wear has also been discussed herein.

The optical performance of plastics lenses depends on several quality criteria. One of the influencing factors is the alignment of the optical surfaces in relation to each other. Centering errors in the alignment of these two surfaces lead to aberrations and a lower optical performance. In spite of very precise moulds and processes, it is still not possible to avoid the occurrence of a lateral offset between the two mould halves. Thus, the offset occurs also in the optical inserts and leads to centering errors in the replicated optical components. A mould design with two integrated piezo-actuators allows the adjustment of the die-sided optical insert and with it the minimisation of the centering error in the micron-range. Therefore, it is possible to influence and reduce the geometrical error, to raise the geometrical accuracy of the lenses and with it the optical performance of plastics lenses without a further machining of the mould.

A simple and low-cost approach was proposed for prototyping PDMS based microfluidic devices by transferring adhesive film microstructures onto a flexible substrate as a mould for PDMS replicas. The microstructures were engraved on an adhesive coated film using a commercial cutting plotter and then transferred (or laminated) onto a flexible substrate, allowing for engraved isolated patterns. The proposed technique was demonstrated by a hydrodynamic focusing microfluidic device, having splitting and re-combining sheath channels. The whole processing could be finished within 1 h in a normal laboratory environment. This approach offers an easy, flexible and rapid prototyping of microfluidic and lab-on-a-chip devices to users without expertise in microfabrication. In addition, by minimizing the use of chemicals, the process becomes more environmentally friendly than conventional photolithography based micro-fabrication techniques.

To cope with the temperature drift of capacitive sandwich type micro-accelerometer, based on mechanics and thermal principle, mechanics equilibrium of sensing structure after thermal expansion is obtained. Then, in light of the accelerometer’s closed loop operation mode, the electrical equilibrium is obtained. On the basis of two equilibriums, the output drift induced by thermal expansion of sensing structure is attained, which implies that the drift is less than 0.002 gn per 10oC. Meanwhile, an experiment is conducted which indicates that the drift due to the temperature is from 0.1 gn to 0.2 gn per 10oC. The comparison implies that the thermal expansion of sensing structure is not a dominant reason for temperature drift of the accelerometer.

Effect of dielectric charging on the performance of SOI based Capacitive Micromachined Ultrasonic Transducers (CMUT) has been investigated. Measurements on an SOI based CMUT show that that the capacitance change as a function of DC bias is considerably higher than analytically calculated values. Investigation shows that this deviation in capacitance from analytically calculated values is due to the combined effects of different dielectric charging phenomena due to a strong electric field, trap charges in the SOI oxide layer, the charge motion associated with the leakage current through the buried oxide layer, and the air in the CMUT cavity. Additionally, this charging effect degrades the transduction efficiency as the induced polarization reduced the effective bias across the CMUT. It is concluded that the buried oxide (BOX) layers in SOI wafers are not suitable for use as dielectric spacers in electrostatic MEMS devices.

A microfluidic chip has been designed and fabricated for culture and stimulation of cells, and for subsequent cell biomarker monitoring using an on-chip performed magnetic bead-based immunoassay. As a proof of concept, we demonstrate monocytic cell (U937) culture, subsequent stimulation of the cells with lipopolysaccharide (LPS), and fluorescent detection of the cytokine interleukin-6 (IL6) released by the cells using magnetic beads functionalized with fluorescent antibodies (Abs) against IL6. The chip comprises two compartments which are separated by a vertical pillar-based filter. The immune cells are cultured in the first compartment and then differentiated to macrophages, while the second compartment is used for the immunoassay that is performed on magnetic beads, the surface of which is conjugated to an IL6-specific antibody. The magnetic beads are kept in place in the detection zone by soft magnetic tips that are part of an electromagnet circuit. The filter with a pore size of 2 μm allows the released cytokines to diffuse from the cell culture / cell stimulation chamber downstream to the chamber containing the magnetic beads, but prevents an exchange of cells and magnetic beads. We found a significant increase of the fluorescence obtained from streptavidin-phycoerythrin (PE)-IL6 conjugates formed on the surface of the magnetic beads, after treating the macrophages with LPS.