Multi-layered Ag film pattern printed by spatially modulated pulsed laser beam

Ag film solution-deposited on the glass source substrate was selectively transferred onto a receiver substrate by a spatially modulated pulsed ultraviolet laser beam. After printing a line pattern, an additional layer was orthogonally printed over the first layer. It was found that the thickness of the first layer is a crucial factor affecting the mechanical stability of the overall pattern. When the first layer was thicker than 0.7 μm, the second layer was cracked at the junction edges regardless of its thickness. This is attributed to the vertical elongation of the second layer at the edge areas. As long as the first layer remains below 0.7 μm thick, however, a very thick additional layer could be printed without any cracks. The printed patterns were mechanically robust and exhibited good electrical contact between the layers. The threshold pulse energy density for printing was measured to be 10 mJ/cm² and this threshold level made it possible to print over square centimeters by a single pulse.     

21.2%‐efficient fineline‐printed PERC solar cell with 5 busbar front grid

We evaluate industrial‐type PERC solar cells applying a 5 busbar front grid and fineline‐printed Ag fingers. We obtain finger widths down to 46 µm when using a stencil with 40 µm opening for the finger print, whereas the busbar is printed in a separate printing step with a different Ag paste (dual print). This compares to finger widths of 62 µm to 66 µm when applying print‐on‐print. The 5 busbar front grid with the best dual print process reduces the shadowing loss of the front grid to 4.0% compared to 5.8% for a conventional 3 busbar front grid printed with print‐on‐print. The 1.8% reduction in shadowing loss results in equal parts from the reduced finger width with dual print as well as from a reduced total busbar width of the 5 busbar design. The resulting PERC solar cells with 5 busbars demonstrate independently confirmed conversion efficiencies of 21.2% compared to 20.6% efficiency of the 3 busbar PERC solar cell. The increased conversion efficiency is primarily due to an increased short‐circuit current resulting from the reduced shadowing loss. To our knowledge, 21.2% conversion efficiency is the highest value reported so far for industry typical silicon solar cells with printed metal front and rear contacts. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Matrix Projection Exposure Using an Analogue Liquid Crystal Display Panel in Place of a Reticle

The most serious problems for the matrix projection exposure using a liquid crystal display (LCD) panel in place of a reticle are largely solved by a new breakthrough method. LCD matrix exposure is effective for small volume productions of print circuits, screen masks, micromachine parts, and other items. Since no reticles are needed, all reticle costs are saved, and turnaround times required for changing the patterns are greatly shortened. However, in the conventional method, pattern widths and positions were strictly restricted depending on the geometric size and pitch of the liquid crystal cells. In this paper, a new concept appointing the cell brightness grades continuously using an analogue interface LCD panel is proposed. Calculating the image intensity distributions for various appointments of cell brightness balances to print same wide patterns, it is clarified that the pattern widths and positions are not much different if the pattern widths are wider than 2 cell pitches of the LCD panel. Maximum width and position variations are less than ± 10% even when the patterns are printed at arbitrary positions, of course including halfway ones. The calculated results are proved by experiments using an analogue LCD panel with a cell pitch of 15 μm. Though the cell size are 13 × 10 μm², and different in x and y directions, almost same wide line-and-space patterns are successfully printed at all positions by only one exposure. It is not necessary to shift the reticle for overlapping exposures to print smooth patterns. Oblique patterns and complicated Chinese character patterns are also printed at arbitrary positions. The new breakthrough technology will make the LCD matrix exposure promising for wide uses of printing various rough patterns easily at small costs.     

Roughness influence on the sheet resistance of the PEDOT:PSS printed on paper

The use of paper as a platform to manufacture organic electronic devices, electronic paper, has expanding potential for many applications because of several properties offered. In this work, we show a study of PEDOT:PSS printed by inkjet on bond paper, vegetal paper and sheets of PET. The relation between the surface density of the deposited material, morphology and resistivity was investigated for samples printed with a commercial Hewlett-Packard(HP)^® printer and Microsoft Word^® software. The amount of material deposited, i.e. surface density, was controlled using the print number in the same position and changing the gray scale used in the image formation. Changing the surface density of printed PEDOT:PSS, it is possible to produce a continuous film permeating the papers fibers. Sheet resistances obtained, when 7.0 mg cm⁻² of PEDOT:PSS were deposited on the surfaces, were: (a) 413.2 kΩ/Sq for bond paper, (b) 5.6 kΩ/Sq for vegetable paper and (c) 2.3 kΩ/Sq for PET. The exponential dependence of sheet resistance with the surface density of printed material allows us to evaluate the strong influence of substrate roughness on PEDOT:PSS conductivity and to predict, for each one, conditions to minimize it.     

n‐type silicon solar cells with surface‐passivated screen‐printed aluminium‐alloyed rear emitter

Aluminium‐doped p‐type (Al‐p⁺) silicon emitters fabricated by means of a simple screen‐printing process are effectively passivated by plasma‐enhanced chemical‐vapour deposited amorphous silicon (a‐Si). We measure an emitter saturation current density of only 246 fA/cm², which is the lowest value achieved so far for a simple screen‐printed Al‐p⁺ emitter on silicon. In order to demonstrate the applicability of this easy‐to‐fabricate p⁺ emitter to high‐efficiency silicon solar cells, we implement our passivated p⁺ emitter into an n⁺np⁺ solar cell structure. An independently confirmed conversion efficiency of 19.7% is achieved using n‐type phosphorus‐doped Czochralski‐grown silicon as bulk material, clearly demonstrating the high‐efficiency potential of the newly developed a‐Si passivated Al‐p⁺ emitter. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Generation of transparent conductive electrodes by laser consolidation of LIFT printed ITO nanoparticle layers

Indium tin oxide (ITO) is one of the few materials available that display a high transparency in the visible wavelength region and at the same time can conduct electrical currents. Thus it is widespread in many optoelectronic applications such as displays or solar cells. Layers of this material are commonly deposited by vacuum deposition methods which are not compatible with inexpensive production methods such as roll-to-roll processing or printed electronics in general. In this work, we demonstrate the generation of arbitrarily shaped ITO layers by laser induced forward transfer of ITO nanoparticles. The transferred particle ink volumes range in the sub picoliter regime. Feature sizes as small as 20 μm are produced without any outward flow or “coffee-stain” effects. Furthermore, the feasibility of excimer laser consolidation of these nanoparticulate layers in ambient air for the generation of dense ITO films is shown. Conductivities of over 4000 Ω^?1?m^?1 were achieved. The presented methods are a promising alternative for the generation of transparent conducting layers for the inexpensive production of optoelectronics.     

Analysis of the magnetic losses in iron-based soft magnetic composites with MgO insulation produced by sol-gel method

This work investigated the magnetic losses of heat treated iron-based soft magnetic composites with a thin MgO insulating layer produced by sol-gel method. The samples were characterized by energy dispersive X-ray spectroscopy, X-ray analysis and Fourier transform infrared spectroscopy. The results show that the surface of the powders contains a thin layer of MgO insulation. The loss results indicate that the hysteresis part for both the core loss and total loss factor was approximately the same for the MgO-insulated compacts and conventional SOMALOY^TM samples with phosphate insulation after annealing at 600 °C. But the MgO-insulated compacts exhibited significantly lower eddy current contribution of both core loss and total loss factor with respect to SOMALOY^TM samples after annealing. Also the contribution of eddy current in the iron particles for MgO insulated compacts (k_p=0.91) was noticeably higher than this contribution for SOMALOY^TM samples (k_p=0.18) after annealing due to the higher electrical resistivity of the MgO-insulated compacts.     

Once again on the enhanced Raman scattering of light from a molecule near a small object

The effect of a significant (by a factor of more than 10⁷) increase in the rate of a one-photon spontaneous radiative transition is calculated for an excited atom (molecule) located near a metal (silver) nanocylinder. The atom radiates into a surface plasmon wave of the TM⁰ type. The TM⁰ wave is concentrated near the nanocylinder surface rather than spreads infinitely in space. Having a limited length, the nanocylinder efficiently radiates into free space, in contrast to the case of an infinite surface (plane or cylindrical). Under the conditions considered, the duration of the atomic dipole radiation is about a femtosecond. The situation discussed, which can be easily realized in experiments, may help in understanding the significant increase in the intensity of Raman scattering observed experimentally.     

Additive manufacturing of ammonium perchlorate composite propellant with high solids loadings

The effective solid propellant burning rate in a rocket depends on surface area and propellant composition. Currently, the surface area geometry in a rocket is limited to what can be practically cast using molds, etc. Additive manufacturing (AM) could allow the production of unique propellant grain geometries, however printing propellants with high solids loadings and viscosities is not readily possible using currently available printers. A new AM direct write system developed recently in our laboratory, is capable of printing visibly low-void propellants with high end mix viscosities into highly resolved geometries. The system was used to print ammonium perchlorate (AP) composite propellants at 85% solids loading using hydroxyl-terminated polybutadiene (HTPB) and a UV-curable polyurethane binder. The change in HTPB propellant viscosity with time after mixing was measured and the microstructure of the strands was evaluated with X-ray tomography scans. The burning rate of printed and cast strands was measured to compare the quality of the strands at high pressure, since propellants with significant voids should catastrophically fail due to flame spreading. The printed samples burned in a planar fashion up to pressures of 10.34 MPa with consistent rates that were comparable to the cast propellants. The HTPB propellant used was not optimized and showed some porosity due to gas generation, but strands printed with the UV binder exhibited extremely low porosity. A strand printed with no gaps in one half and gaps in the other failed catastrophically where intended at high pressure, demonstrating the ability to spatially grade propellants. This new system can produce adequate strands of composite propellant with high solids loadings without the addition of solvents, special binders (low viscosity, thermal softening, etc.), or restricting use to formulations with lower viscosities, and enables the fabrication of complex propellant grain geometries.     

Nanoparticles and Giant Raman Scattering

The field for linear aggregates of metallic nanospheres is calculated. This field is analogous to that of the surface TM₀ wave of a metallic cylinder with a negative dielectric permittivity. The spontaneous emission of an atom into a surface wave is shown to be greatly enhanced. This enhancement is as great as 10¹⁴ times for a two-photon process (Raman scattering). The TM₀ wave is concentrated in the vicinity of the nanocylinder surface instead of extending in space to infinity. Being restricted in its length, the nanocylinder radiates efficiently into free space in contrast to the case of an infinite (plane or cylindrical) surface. The duration of the atomic dipole radiation is about 1 fs under the conditions discussed. The situation considered can be realized readily in actual experiments. It can explain the pronounced increase in the Raman intensity in the experiments described by Nie and Emory in 1997.     

Molecular orientation and morphology of contact printed α-quaterthiophene films on gold

We present contact printing as a technique to deposit α-quaterthiophene (α-4T) films from the solid phase onto gold. The molecular orientation and morphology of both the printed film and the original polycrystalline α-4T film on silica were investigated with low energy ion scattering (LEIS), atomic force microscopy (AFM), X-ray diffraction (XRD) and optical microscopy. We show that the strong interaction between clean gold and α-4T induces a drastic change in the molecular orientation and morphology of a 380 nm thick α-4T film. On gold the α-4T molecules are orientated with the thiophene rings parallel to the substrate and form rod-like crystallites (typically 13×1.3 μm²), whereas on silica α-4T molecules stand almost upright and form large cobblestone-like crystallites (typical diameter 10 μm). Exposure of α-4T to a low energy ion beam (dose <1×10¹⁴ 3 keV ³He⁺ ions/cm²) prior to printing causes polymerisation, which decreases the ability to print and alters the morphology of the printed film.     

Tamarind seed polysaccharide biopolymer membrane for lithium-ion conducting battery

Solid biopolymers have gained much attention in the development of polymer electrolytes due to its biocompatibility, film-forming nature, and non-toxicity. In the present work, biopolymer membrane has been prepared using tamarind seed polysaccharide (TSP) as host polymer and various concentrations of lithium chloride (LiCl) salt as dopant by solution casting technique. The prepared biopolymer electrolyte has been characterized by XRD, FTIR, differential scanning calorimetry (DSC) analysis, AC impedance spectroscopy analysis, and transference number measurement. XRD analysis has been done to investigate the amorphous/crystalline nature of the polymer membrane. The highest amorphous nature has been found for 1 g of TSP with 0.4 g LiCl. FTIR spectrum analysis confirms the complex formation between TSP biopolymer with LiCl. From AC impedance conductivity analysis, the maximum ionic conductivity is of the order of 6.7?×?10^?3 S cm^?1 at room temperature for 1 g TSP with 0.4 g LiCl, whereas for pure TSP biopolymer membrane, the ionic conductivity is of the order of 5.48?×?10^?7 S cm^?1. The glass transition temperature for the highest conducting biopolymer membrane for the composition of 1 g TSP: 0.4 g LiCl has been found to be 44.25 °C using the DSC technique. Employing the maximum conducting biopolymer membrane, a lithium-ion conducting battery has been fabricated and its discharge characteristics have been studied.     

Effect of hydrogen defects on nanocrystallite layers of Si solar cells by hydrogen implantation

The Si solar cells were irradiated with high energy hydrogen ions of 10, 30, 60 and 120?keV at the dose rate of 10¹⁷ H⁺ ions (proton)/cm². The structural, optical and electrical properties of the implanted samples and fabricated cells were studied. The implantation induced defects bringing structural changes before and after annealing was evidenced by the transmission electron microscopy. The Raman spectrum showed a change of crystalline to amorphous state at 480?cm^?1 when the sample was implanted by hydrogen ion of 30?keV energy. Formation of nanocrystallite layers were observed after annealing. The electroluminescence images showed that hydrogen-related defect centers were involved in the emission mechanism. The photoluminescence emission from the implanted cells was attributed to nanocrystallite layers. From current–voltage measurements, the conversion efficiencies of implanted Si solar cells were found lower than the un-implanted reference cell. The ion implantation did not passivate the defects rather acted as recombination centers.     

Phase-matched second-harmonic generation at 440 nm in a LiNbO3 -Gd3Ga5O12 waveguide with a tunable stimulated Raman source

Using a tunable stimulated Raman source, we have observed second-harmonic generation in the blue in a sputtered LiNbO₃ film deposited on Gd₃Ga₅O₁₂. With the choice of Gd₃Ga₅O₁₂ as a substrate, it becomes possible to both phase-match a large range of fundamental wavelengths as well as have an excellent epitaxial quality surface. The SHG efficiency for the TM^ω₀ → TM^2ω₂ phase matched conversion process is estimated to be ～ 10^-4.     

Magnetic properties of iron-based soft magnetic composites with MgO coating obtained by sol-gel method

Soft magnetic composites with a thin MgO insulating layer were produced by a sol-gel method. Energy dispersive X-ray spectroscopy, X-ray analysis, Fourier transform infrared spectroscopy, density measurement and compositional maps confirmed that thin layers of MgO covered the iron powders. Coercivity measurement showed that the stress relaxation and reduction of hysteresis loss efficiently occurred at 600 °C. At this temperature, the phosphate insulation of commercial SOMALOY^TM samples degrade and their electrical resistivity, magnetic permeability and operating frequency decreases noticeably. The results show that the MgO insulation has a greater heat resistance than conventional phosphate insulation, which enables stress-relief at higher temperatures (600 °C) without a large increase in eddy current loss. The results of annealing at 600 °C show that the electrical resistivity and ferromagnetic resonance frequency increased from 11 μΩ m and 1 kHz for SOMALOY^TM samples to 145 μΩ m and 100 kHz for the MgO insulated composites produced in this work.     

Laser printing and characterization of semiconducting polymers for organic electronics

Hybrid organic/inorganic thin-film transistors (TFTs) with bottom-contact configuration were fabricated using the Laser Induced Forward Transfer (LIFT) process. The semiconducting polymer P3HT was laser printed from a donor to a receiver substrate in order to form the active layer of the TFTs. With a single laser pulse, P3HT pixels were successfully printed. The printed material was analyzed morphologically by means of Optical Microscopy and its thickness was measured by profilometry. In addition, structural characterization of P3HT thin films before and after laser printing took place by using UV-Visible absorption spectroscopy and X-Ray Diffraction. It was found that the crystallinity of the investigated films is improved upon annealing. An organic thin-film transistor (OTFT) with laser printed P3HT pixel as a channel layer was then fabricated. The OTFTs indicated a field-effect mobility up to 2.23?10^?4 cm²/Vs and an on/off ratio on the order of 10–100.     

Oxygen and hydrogen accumulation at buried implantation-damage layers in hydrogen- and helium-implanted Czochralski silicon

Oxygen and hydrogen accumulations at buried implantation-damage layers were studied after post-implant-ation annealing of hydrogen- and helium-implanted Czochralski (Cz) silicon. Hydrogen implantation was carried out at energies E=180 keV and doses D=2.7×10¹⁶ cm^-2, and helium implantation at E=300 keV and D=10¹⁶ cm^-2. For comparison hydrogen implantation was also done into float-zone (Fz) silicon wafers. Post-implantation annealing at 1000 °C was done either in H₂ or N₂ atmosphere. Hydrogen and oxygen concentration profiles were measured by secondary ion mass spectroscopy (SIMS). It is shown that the ambient during annealing plays a significant role for the gettering of oxygen at buried implantation-damage layers in Cz Si. For both hydrogen and helium implantations, the buried defect layers act as rather effective getter centers for oxygen and hydrogen at appropriate conditions. The more efficient gettering of oxygen during post-implantation annealing in a hydrogen ambient can be attributed to a hydrogen-enhanced diffusion of oxygen towards the buried implantation-damage layers, where a fast oxygen accumulation occurs. Oxygen concentrations well above 10¹⁹ cm^-3 can be obtained. From the comparison of measurements on hydrogen-implanted Cz Si and Fz Si one can conclude that at the buried defect layers hydrogen is most probably trapped by voids and/or may be stable as immobile molecular hydrogen species. Therefore hydrogen accumulated at the defect layers, and is preserved even after high-temperature annealing at 1000 °C. Received: 3 July 2000 / Accepted: 11 July 2000 / Published online: 22 November 2000     

Nonpolarizing and tunable perpendicular dual-grating guided-mode resonance filter

A perpendicular dual-grating (PDG) guided-mode resonance filter was constructed by placing two identical waveguide gratings close to and their grooves perpendicular to each other. Multilayer waveguide theory was used to estimate the resonant wavelength for the TE and TM polarization incidences, and the rigorous coupled wave analysis (RCWA) was used to investigate the resonant wavelength, the lineshape and linewidth of the resonant peaks for arbitrary polarization incidences. The filter presents identical spectral characteristics for normally incident wave with arbitrary polarization. The separation of the resonant reflection peaks corresponding to the TE₀ and TM₀ split modes were realized by properly selecting the geometrical and material parameters of the grating layers and the waveguide layers. Measurement of the nano air gap between 0 and 0.4 p by determining one of the two resonant reflection peaks of the TE₀/TM₀ split modes was achieved without being interfered by the TM₀/TE₀ split modes.     

Cell patterning without chemical surface modification: Cell-cell interactions between printed bovine aortic endothelial cells (BAEC) on a homogeneous cell-adherent hydrogel

Cell printing offers the unique ability to directly deposit one or multiple cell types directly onto a surface without the need to chemically pre-treat the surface with lithographic methods. We utilize biological laser printing (BioLP^™) to form patterns of bovine aortic endothelial cells (BAECs) onto a homogeneous cell adherent hydrogel surface. These normal cells are shown to retain near-100% viability post-printing. In order to determine whether BAECs encountered shear and/or heat stress during printing, immunocytochemical staining experiments were performed to detect potential expression of heat shock proteins (HSP) by the deposited cells. Printed BAECs expressed HSP at levels similar to negative control cells, indicating that the BioLP process does not expose cells to damaging levels of stress. However, HSP expression was slightly higher at the highest laser energy studied, suggesting more stress was present under these extreme conditions. Printed BAECs also showed preferential asymmetric growth and migration towards each other and away from the originally printed pattern, demonstrating a retained ability for the cells to communicate post-printing.     

Proton-conducting I-Carrageenan-based biopolymer electrolyte for fuel cell application

The essential part of electrochemical devices, such as fuel cells and batteries, is the polymer electrolyte with good mechanical, thermal, and chemical stability. The search for a new proton-conducting membrane with easy processability, non-toxic, and low-cost has been growing rapidly. The bio-based polymer electrolytes are now receiving much attention due to the green environment. Among the commercially available biopolymers, iota-Carrageenan (I-Carrageenan) is one of the biopolymer with good film-forming nature and with good mechanical stability. I-Carrageenan-based biopolymer membranes doped with ammonium bromide (NH₄Br) have been prepared using solution-casting technique, and distilled water is used as a solvent. The prepared I-Carrageenan-based biopolymer membranes have been characterized using FTIR, XRD, and AC impedance techniques. The complexation between the polymer and salt has been revealed by FTIR. The increase in the amorphous nature of the film due to the addition of salt has been confirmed by XRD. From AC impedance technique, the conductivity of pure I-Carrageenan has been found to be 1.46 × 10⁻⁵ S/cm. The addition of different wt% of NH₄Br increases the conductivity and reaches the highest value of 1.08 × 10⁻³ S/cm for 20% NH₄Br, and the conductivity decreases on further addition of NH₄Br due to the formation of ion aggregates.