Ordered arrays of copper nanostructures were fabricated and modified with porphyrin molecules in order to evaluate fluorescence enhancement due to the localized surface plasmon resonance. The nanostructures were prepared by thermally depositing copper on the upper hemispheres of two-dimensional silica colloidal crystals. The wavelength at which the surface plasmon resonance of the nanostructures was generated was tuned to a longer wavelength than the interband transition region of copper (>590 nm) by controlling the diameter of the underlying silica particles. Immobilization of porphyrin monolayers onto the nanostructures was achieved via self-assembly of 16-mercaptohexadecanoic acid, which also suppressed the oxidation of the copper surface. The maximum fluorescence enhancement of porphyrin by a factor of 89.2 was achieved as compared with that on a planar Cu plate (CuP) due to the generation of the surface plasmon resonance. Furthermore, it was found that while the fluorescence from the porphyrin was quenched within the interband transition region, it was efficiently enhanced at longer wavelengths. It was demonstrated that the enhancement induced by the proximity of the fluorophore to the nanostructures was enough to overcome the highly efficient quenching effects of the metal. From these results, it is speculated that the surface plasmon resonance of copper has tremendous potential for practical use as high functional plasmonic sensor and devices.

We achieved a reduction in the misregistration of overlying patterns printed on a flexible plastic film and a drastically shorter processing time with fully printed thin-film transistor (TFT) fabrication. This was achieved using a newly developed wet-on-wet (WoW) printing process wherein a subsequent layer can be printed on a previous semi-dried (not-sintered) layer. In the WoW process, as examined by rheological measurements, a semi-dried (highly solidified) state of ink was attained before transferring by utilizing the solvent uptake of a PDMS blanket in offset printing to ensure the structural integrity of the ink layer, and to reduce the inter-contamination of adjoining layers. Loss-on-drying tests and resistivity measurements indicated that molecular penetration at the boundary of adjoining layers with a length of c.a. 70 nm occurred in the WoW process; however, with thicker electrodes, we successfully fabricated a WoW-processed TFT whose performance was comparable with a TFT formed by a conventional printing process.

We describe efficient visible- and near-infrared (vis/NIR) light-driven photocatalytic properties of hybrids of CuO and plasmonic Cu arrays. The CuO/Cu arrays were prepared simply by allowing a Cu half-shell array to stand in an oxygen atmosphere for 3 h, which was prepared by depositing Cu on two-dimensional colloidal crystals with a diameter of 543 or 224 nm. The localized surface plasmon resonances (LSPRs) of the arrays were strongly excited at 866 and 626 nm, respectively, at which the imaginary part of the dielectric function of Cu is small. The rate of photodegradation of methyl orange was 27 and 84 times faster, respectively, than that with a CuO/nonplasmonic Cu plate. The photocatalytic activity was demonstrated to be dominated by Cu LSPR excitation. These results showed that the inexpensive CuO/Cu arrays can be excellent vis/NIR-light-driven photocatalysts based on the efficient excitation of Cu LSPR.

Mechanisms, materials, and processes of high-resolution printing techniques dedicated to printed electronics are reviewed. Advanced printing methods, including reverse offset printing and adhesion contrast planography, use absorption of ink solvents by polydimethylsiloxane (PDMS) to semi-solidify inks before ink-transfer. The patterning principle transforms from wetting to adhesion and fracture; resolution problems encountered during the patterning of liquid inks (e.g. spreading, splitting, coalescence, bulges, and coffee ring shapes) can be avoided, and single-μm features can be achieved. After summarizing the fundamentals of reverse offset printing, details on the patterning mechanism and contact mechanics encountered during the process are shown together with the design concept of the ink formulation. Complementary processes for multilayered electronic devices (e.g. wet-on-wet for high-throughput production, buried electrode formation, taper formation, and vertical interconnections) and the prediction of pattern size integrity are presented.

Reverse‐offset printing (ROP) is a novel printing technique capable of forming electronics‐industry‐relevant linewidths (≈1 µm) with good thickness control and sharp edge definition. It is demonstrated that through a controlled oxygen‐plasma treatment, the energy of the surfaces related to the process steps of ROP can be optimized to allow the patterning of metal‐oxide semiconductor layers using a simple printing ink based on metal nitrates dissolved in an organic solvent. The steps of the ROP process are analyzed using surface‐energy measurements and Fourier transform infrared spectra of the ink during drying. Thin‐film transistors (TFTs) fabricated using a roll‐to‐plate ROP of In2O3 semiconductor and evaporated Al source/drain (S/D) contacts show, on average, mobilities of 3.1 and 3.5 cm2 V−1 s−1, and ON/OFF‐ratios up to 108 and 107 on a Si/SiO2 substrate and on a flexible polyimide‐type substrate, respectively. TFTs on the flexible substrate with also the S/D‐contacts printed with ROP using Ag nanoparticle ink exhibit a 1.4 cm2 V−1 s−1 mobility. To demonstrate the scalability of the process, continuous lines of In2O3 are printed using a roll‐to‐roll‐compatible (R2R) ROP with linewidths down to ≈2 µm. This process is expected to lead to miniaturized metal‐oxide circuits as required by flexible high‐resolution sensor arrays and displays.

We developed a novel offset-printing process that permits the fabrication of silver-nanoparticle electrodes embedded in a dielectric layer. We succeeded in embedding approximately 1 µm thick silver electrodes to a dielectric layer with thickness ratio of 1:1.4. The surface-height difference between the embedded electrode and the surrounded dielectric layer was less than 80 nm. By virtue of the surface uniformity of this embedding process, the interconnect breakage of orthogonal wires printed on top of the underlying wire was drastically reduced to 4%, compared to 41% for non-embedded wires. The electric conductivity of embedded electrodes with thickness ≈110 nm was about 10 µΩ cm−1, which was comparable to that of a silver pattern formed on a glass substrate alone. We also examined the characteristics of fully printed thin-film transistors composed of the embedded electrodes, and measured an average mobility of 0.07 cm2 V−1s−1. These results demonstrate the applicability of the proposed technique to the fabrication of printed circuits and devices including active elements.

We demonstrated the usefulness of Cu light-harvesting plasmonic nanoantennae for the development of inexpensive and efficient artificial organic photoelectric conversion systems. The systems consisted of the stacked structures of layers of porphyrin as a dye molecule, oxidation-suppressing layers, and plasmonic Cu arrayed electrodes. To accurately evaluate the effect of Cu nanoantenna on the porphyrin photocurrent, the production of CuO by the spontaneous oxidation of the electrode surfaces, which can act as a photoexcited species under visible light irradiation, was effectively suppressed by inserting the ultrathin linking layers consisting of 16-mercaptohexadecanoic acid, titanium oxide, and poly(vinyl alcohol) between the electrode surface and porphyrin molecules. The reflection spectra in an aqueous environment of the arrayed electrodes, which were prepared by thermally depositing Cu on two-dimensional colloidal crystals of silica with diameters of 160, 260, and 330 nm, showed clear reflection dips at 596, 703, and 762 nm, respectively, which are attributed to the excitation of localized surface plasmon resonance (LSPR). While the first dip lies within the wavelengths where the imaginary part of the Cu dielectric function is moderately large, the latter two dips lie within a region of a quite small imaginary part. Consequently, the LSPR excited at the red region provided a particularly large enhancement of porphyrin photocurrent at the Q-band (ca. 59-fold), compared to that on a Cu planar electrode. These results strongly suggest that the plasmonic Cu nanoantennae contribute to the substantial improvement of photoelectric conversion efficiency at the wavelengths, where the imaginary part of the dielectric function is small.

The interaction forces between silanated silica surfaces on which there were neither nanobubbles nor a gas phase were measured using colloidal probe atomic force microscopy (AFM). To obtain hydrophobic surfaces without attached nanobubbles, an aqueous solution was introduced between the surfaces after an exchange process involving several solvents. In the approaching force curves obtained, an attractive force was observed from a distance of 10-25 nm, indicating the existence of an additional attractive force stronger than the van der Waals attraction. In the retracting force curves, a strong adhesion force was observed, and the value of this force was comparable to that of the capillary bridging force. The data clearly showed that although the bridging of nanobubbles is responsible for long-range hydrophobic attraction, there also exists an additional attractive force larger than the van der Waals attraction between hydrophobic surfaces without nanobubbles. Both the ionic strength and the temperature of the solution had little influence on the force. The possible origin of the force is discussed on the basis of the obtained results.