Large-scale synthesis of copper nanoparticles by chemically controlled reduction for applications of inkjet-printed electronics

With increasing demands for more economic routes to the manufacture of electronic devices incorporating polymer- based printed circuit boards (PCBs), various techniques for the fabrication of microelectronic devices, including screen printing, nano-imprinting, inkjet printing, and direct printing, are generating increasing interest. Among these methods, inkjet printing is considered to be an economical and highly functional technology for the microscale patterning of metallic traces in microelectronic devices. Conventional lithographic processes are well developed but include multiple steps that are time consuming, uneconomical, and not versatile towards corrective repatterning  However, the employment of inkjet printing can solve many of the problems in a facile and effective manner. The inkjet printing method allows for the patterning of conductive traces onto a substrate in one step, therefore reducing the time, cost, and space consumed and the toxic waste created during the manufacturing process. Nanomaterials are considered to be highly useful for application of materials through inkjet printing technology based on size-dependent mesoscopic properties such as enhanced dispersibility, melting point depression below that of the same bulk material based on more significant surface energy instability, and greater compatibility with various chemical and physical environments due more significant effects from interchangeable surface coatings. Inkjet printing technology employing conductive silver inks has been developed recently in order to manufacture low-cost disposable electronics, such as smart packaging, RF-ID tags, and digital calendars. However, silver as a conductive material has problems due to ion migration at relatively high-temperature and humidity conditions as well as cost-benefit issues compared to copper, which is significantly less expensive for virtually identical bulk conductivities. In this research, a large-scale (5 l), high-throughput (0.2 M) process for the synthesis of copper nanoparticles was developed using a modified polyol process that includes chemical reduction and hot addition. Furthermore, these copper nanoparticles were dispersed into an ether-based solvent, patterned onto various substrates through inkjet printing, and then converted into conductive metallic traces through a relatively low-temperature, reductive sintering process. The results are optimistic, however, there are some disadvantages of copper which must be overcome are that the copper ion is not easily reduced under mild reaction conditions and copper nanoparticles tend to be easily oxidized in air under ambient atmospheric conditions in comparison to noble metals like gold and silver.

To read more: Lee, Youngil; Choi, Jun-rak. “Large-scale synthesis of copper nanoparticles by chemically  controlled reduction for applications of inket-printed electronics” Nanotechnology. 19(2008).

Cost reduction in manufacturing of aerospace composites.

Advanced fibre reinforced composites are already extensively used in modern aircraft, due to advantages offered for weight reduction, durability, mechanical performance, etc. However, composite structures in aerospace are usually not associated with low costs. Traditional design methods are very time consuming, materials and production processes very expensive as well as labour intensive. To make full use of the potential of composites, a complete redesign of aircraft structures is necessary. Owing to qualification and certification procedures the introduction of low cost materials or low cost production processes is hindered. This paper describes the results of a collaborative research project aimed at achieving significant cost reductions in the manufacturing of advanced composites for aerospace applications. As part of the cost reduction objectives of the project, an innovative knowledge based engineering approach was followed during the preliminary design and analysis of the wingbox structure. In order to develop a realistic demonstrator, an analysis of an aerodynamically loaded full generic wingbox structure of a business jet type of aircraft was performed. The sizing of the ribs, front spar and rear spar as well as upper and lower skin panels were determined by means of different load cases further on, an optimisation of the wingbox with respect to its weight was performed by using a standard structural concept which is sizing based on the feasilisation methodology. The results are gratifying, since is possible to build them reducing costs, however there is more to research, since some of the process should be carried out in vacuum.

To read more,  look for the work of Van Hattum et al. “Cost reduction in manufacturing of aerospace composites” published  in Plastics, Rubber and Composites 2011 Vol 40, No. 2.

Effect of Interface Structure on Mechanical Properties of Advanced Composite Materials.

Advanced composite materials have the unique combination of outstanding mechanical properties of matrices and reinforcements. The reinforcement/matrix interface in composite materials forms in manufacturing processes and determines the performances of the composite materials. Some reinforcements may not be compatible with matrices in view of their physical and/or chemical properties, which causes premature failure of the composites. Recently, development of nanofiber modified matrices containing reactive graphitic nanofibers has been proposed to promote the wetting of the matrices to certain types of fiber reinforcements. In this paper, the effect of interface structures on the mechanical properties of fiber reinforced composite materials is discussed. Hybrid composite materials/structures are frequently subjected to thermal and mechanical fatigue loading. Aside from external mechanical loadings, thermal effect is identified as an important factor that determines the stress distribution in composite materials. During the curing process, adhesively bonded composite/metal laminate structures are held at elevated temperatures over 120 ◦C, very high residual stresses could build up because of the difference in coefficients of thermal expansion (CTE) for different materials. This thermal mismatch results in delamination or debonding of hybrid composite materials, which facilitates fatigue crack growth in the polymer/metal interface. Thermal cyclic stresses can also be generated from the fluctuation of ambient temperatures. Therefore, the stress state in a hybrid composite material is not only dependent on service conditions, but also affected by the materials processing parameters. The research has suggested that a porous oxide structure is likely to be very suitable for adhesive bonding because of the increase in interface area of nanoporous structure, which results in the high shear loading capability. However, the interface nanostructure remains to be revealed by further systematic study.

To read more go to ACS and search: Gan, Yong. Effect of Interface Strcuture on Mechanical properties of Advanced Composite Materials.  International Journal of Molecular Sciences. 2009, 10, 5115-5134.

Surface Topology of Advanced Alumina/Zirconia Composite Femoral Head as Compared with Commercial Femoral Heads Made of Monolithic Zirconia

Wear of bearing couples is one of the most important factors determining the longevity of a total hip implant. Ceramics have been used as bearing materials in hip joints with the expectation of wear reduction due to their smooth surfaces, low friction, and good wetting properties. All these properties should contribute to extend the in vivo lifetime of the hip joint. However, in vivo surface degradation of some zirconia ceramics has been reported, with the presence of asperities at the articular surfaces of the hip joint becoming a factor in precipitating degenerative changes. Recent topographic analyses of residual stress fields, conducted by confocal Raman and fluorescence spectroscopy on retrieved ceramic femoral heads, revealed clear changes in stress distribution with exposure time in vivo, as well as a possible migration of the polar position of maximum stress. Metastability of zirconia, and the potential effect of surface roughening arising from transformation of tetragonal-to-mono- clinic zirconia, represents a typical environmental effect strongly affecting the structural performance of a hip joint. From a materials science viewpoint, the environmental stability of zirconia has been found to strongly depend on grain size and on the amount and type of stabilizing element Some aspects of zirconia metastability are useful to improve the bulk fracture toughness of the joint material and, thus, have been welcomed by joint designers; however, the drawback is a potential embrittlement and a roughening of the bearing surface with aging in vivo. On the one hand, it is somewhat surprising that manu- facturers are still distributing monolithic zirconia ceramic femoral heads (e.g., in Japan), but fundamental information is lacking on the characteristics of degradation with no direct comparison made among zirconia ceramic heads manufactured by different makers. On the other hand, a new generation of alumina/zirconia composite material has recently become avail- able to the orthopedic community.

In this paper, they tested such an advanced composite femoral head with respect to the topologic and phase-stability response of its bearing surface to hydrothermal environment, in comparison with commercially available monolithic zirconia femoral heads. They found and important improvement in terms of stability in the aluminia/zirconia, specially in their response in OH ^– on the surface. This adds stability, because it inhibits the addition of oxygen to the vacancies of the crystal cell and hydrogen being interstiatilly located in the lattice.

To read more about it, search: Pezzotti, Giuseppe; Saito, Takuma; Takahashi, Yasuhito. “Surface topology of advanced aluminia/zirconia composite femoral head compared with commercial femroral heads of monolithic zirconia”.  ACS 94:(3) 2011. 945-950.

Sodium Sensing in Neurons with a Dendrimer-Based Nanoprobe

Fluorescence imaging is widely used in biomedical sciences for a large spec- trum of applications ranging from the morphological analysis of anatomical struc- tures to time-resolved measurements of intracellular molecular events.

It enables noninvasive probing of biological processes with high spatial resolution in ex vivo tissue preparations as well as in whole organisms.

A powerful application of this technique is the ability to monitor in real- time the complex intracellular fluxes of ions and metabolites that underlie many essen- tial physiological functions. But some ions such as Cl^-, Na⁺, K⁺ are difficult to measure. Sodium imaging, in particular, is an attrac- tive way of assessing many fundamental cellular processes, from the transport of small molecules through epithelial barriers to the integration of complex signals in the brain, that depend on the transmembrane Na⁺ gradient. However, the poor characteristics of available Na⁺ probes have rendered Na⁺ imaging an uneasy task. Many strategyes have been developed, but they are limited in the size of the cell that can be sensed.

Dendrimers are branched poly- mers with well-defined sizes and geometry. After several layers of branching, they make spheres that contain solvent-filled cavities. These structural features endow them with the ability to encapsulate small guest molecules and act as nanocontainers. Dendrimer nanocontainers have been extensively used for drug and gene delivery applications. However, this property has not been used in molecular imaging yet. In this study, they ested whether a Naþ dye such as CG could be encapsulated in a dendrimer in order to prolong its intracellular half- life while maintaining its Naþ response characteristics.They also assessed whether a Naþ nanoprobe built on this principle could be used to probe cell functions in thick tissue preparations without disturbing baseline physiological parameters.

They obtained a sensitive molecule, that can sense even small concentrations of Na+.

To read more about this work, search in ACS:

Lamy, Christophe; Sallin, Oliver. Sodium  sensing in Neurons with a dendrimer-based nanoprobe. ACS NANO Vol 6. No 2. 1176-1187. 2012.

DNA Immobilization and Detection on Cellulose Paper using a Surface Grown Cationic Polymer via ATRPS

Synthesis of well-defined polymeric structures using ATRPS has been reported in a number of early publications. This method is robust and versatile in its capability to yield controlled chain growth and to achieve many different forms of polymers, including hyperbranched polymers, star-shaped polymers, and block copolymers. Moreover, several groups have recently reported the use of ATRP method for the “grafting from” of polymer brushes which have great potential in fabrication of medical devices and surface-modified nanoparticles. Compared to the “grafting through” method, “grafting from” polymerizations result in brush copolymers with high molecular weight side chains. In addition, this approach does not require the synthesis of a macromonomer, which is the most difficult step in the “grafting through” process.

The detection of nucleic acids in various solutions, including complex biological environments, has been the focus of many research groups who are trying to develop fast and reliable detection mechanisms of nucleic acid based disease biomarkers. Among the most significant nucleic acid biomarkers that have recently been discovered are microRNAs. The develop- ment of simple and effective diagnostic devices based on disease biomarkers such as microRNAs, DNA fragments and proteins have excelled in recent years. The detection of nucleic acids in solution provides simplicity but lacks the specificity and sensitivity offered by traditional surface based assays especially with regards to detection in complex biological environments, such as serum or blood. Aied etl al. presents a way to make the detection of DNA hybridization with out modifying the sample in any way. This system is capable of identifying DNA hybridization in serum on the basis of a combination of mechanisms omposed of polymer- ssDNA probe interaction, ssDNA-cDNA (cDNA) hybridization and finally, PicoGreen intercalation. By fluorescence they were able to identify DNA hybridization.

The full text can be found in

Ahmed Aied, Yu Zheng. DNA Immobilization and Detection on Cellulosa Paper using a Surface Grown Cationic Polymer via ATRP. ACS: Applied Material & Interfaces. 4. 2012. 826-831.

Large-Scale Fabrication of 4-nm-Channel Vertical Protein-Based Ambipolar Transistors

The increasing demand for smaller and faster complementary transistors (in which both n- and p-type devices exist on one wafer) arranged in dense arrays requires the development of new methods for the parallel fabrication of nanometer- sized transistors. However, because of limitations in current technology, the achievement of these goals is very challeng- ing. Although, some isolated examples of such devices and architectures have been demonstrated, they exhibit only moderate or limited performance, or are constructed via sophisticated multistep methodologies. In this publication Mentovich and his team suggest and demonstrate a universal method in which a new type of nanometer-sized, ambipolar, vertical molecular transistor is fabricated in parallel fashion. This centralgate molecular vertical transistor (C-Gate MolVeT) is fabricated by a combination of conventional microlithography techniques and self-assembly methods. The general fabrication methodology of the C-Gate MolVeT allows the process to be adapted for various materials and systems.

Protein used to fabricate the transistor

In this design, the nanometer channel length is determined by a protein-based self-assembled monolayer composed of bovine serum albumin protein, that is sandwiched between source and drain electrodes inside a microcavity, while a centered oxidized-metal-electrode column inside the cavity serves as the gate electrode. The results showed a transistor fully operational, that can be made with lithography thechniques, they messured the gate effect, and demonstrated the characteristic transistor curves when variating the voltage in the drain terminal.

Transference Curve

The full article can be found in nanoletters:

Large-Scale Fabrication of 4-nm-Channel Vertical Protein-Based Ambipolar Transistors

Elad D. Mentovich, Bogdan Belgorodsky, Itsik Kalifa, Hagai Cohen, and Shachar Richter

Nano Letters