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Hydrolytically polymerized poly(methyl-co-vinyl)siloxane is cross-linked by radically and dehydrolytically at elevated temperature. Peroxide-type thermal radical generator is found to cross-link the polymer at the vinyl and methyl pendant groups. In parallel, free silanol (Si-OH) end groups in the polymer also contribute to cross-linking by dehydrolytic polycondensation. By use of these two-fold cross-linking mechanisms, we were able to deposit highly cross-linked siloxane polymer film which provides excellent optical and electrical properties. Cured film of 500 nm thickness exhibited the pencil hardness of 9H on glass with > 95% visible light transmittance. These excellent features are applied to optical hard coating for flexible displays and touch panels. The cured film also exhibited excellent electric properties. The leakage current of the film is as low as that of CVD dielectric film, and the break down field is exceeded 3 MV/cm, which enabled the film to be applied to insulator in thin film transistor. We carried out analyses of the polymer in film and powder form with 13C- and 29Si-NMR MAS, FT-RAMAN and FTIR-ATR methods to investigate curing mechanism. The analysis results clearly indicated that the cured film contains unique Si-(CH)n-Si bonds generated by radical crosslinking, and all the Si-OH bonds are consumed by hydrolytic polycondensation as well. The Si-(CH)n-Si bonds are more rigid and less polar than Si-O-Si bond, which should be the major reasons that radical condensation remarkably reinforced the film. This radically and thermally cured poly(methyl-co-vinyl)siloxane film was applied to Mo-gate thin film transistor fabricated on glass as the gate insulator. The I-V characteristics from the transistor were equivalent to those made using CVD-SiN insulator.
All-printed electronics is the key technology to ultra-low-cost, large-area electronics. As a critical step in this direction, we demonstrate that femtosecond laser processing (sintering and ablation) of solution deposited metal nanoparticles enables direct metal patterning at low-temperature with ultra high resolution (∼300nm) to overcome the resolution limitation of the current inkjet direct writing processes.
This could be explained by the combined effects of novel properties of metal nanoparticles such as melting temperature drop, strong absorption of the incident laser beam at surface plasmon mode, lower conductive heat transfer loss, and the relatively weak bonding between nanoparticles. Local thermal control of the laser sintering process could minimize the heat-affected zone and the thermal damage to the substrate and further enhance the resolution of the process. This local nanoparticle deposition and energy coupling enable an environmentally friendly and cost-effective process as well as a low-temperature manufacturing sequence to realize large-area, flexible electronics on polymer substrates.
Intrinsic γ-Copper (I) Chloride is an ionic I-VII compound semiconductor material with relatively low conductivity. To fabricate an efficient electroluminescent device based on CuCl nanocrystals (NC) the conductivity of the CuCl NC film should be relatively high. In order to improve the conductivity of CuCl films, nanocrystals were embedded in a highly conductive polymer (Polyaniline) and deposited on glass substrates via the spin-coating method. The deposited films were heated at 140°C for durations between 1 and 12 hours in vacuo. The room temperature UV-Vis absorption spectra for all CuCl films showed both Z1,2 and Z3 excitonic absorption features and the absorption intensity increased as the anneal time increased. Room temperature photoluminescence (PL) measurements of the hybrid films reveal very intense Z3 excitonic emission. Room temperature X-ray diffraction (XRD) confirmed the preferential growth of CuCl nanocrystals whose average size is ≈40 nm in the <111> orientation. Resistivity measurements were carried out using a four-point probe system, which confirmed that the resistivity of the composite film was ≈500 Ω/cm. This is an improvement when compared to the vacuum evaporated CuCl thin films.
NaLu1-xYbx(WO4)2 films have been prepared by spin coating of sol-gel precursor solutions and thermal annealing between 400 and 800 °C. Films obtained on sapphire have a dense and transparent ceramic microstructure and photoluminescence properties similar to those of single crystals with same composition. The application of these films as laser media is envisaged.
Tin zinc oxide (SnZnO) thin film transistors (TFTs) with different component fraction fabricated by solution process were reported. Sn chloride and Zn acetate were used as precursor and the maximum annealing temperature was 500°C. The electrical characteristics of TFTs were acutely affected by the molar ratio between Sn and Zn in the lattice, and showed the highest mobility and on-to-off ratio of about 17 cm2/Vs and 2×106, respectively. The origins of the high performance were traced through both structural and electrical aspects. Sn was generally considered to offer carrier path by superposition of s orbital, but it was found that the increase of Sn fraction only below specific value in lattice contributed to increase mobility, which could be explained by the structural distortion and the defect generation. Zn atoms introduced in the lattice were necessary to control both mobility and carrier concentration. From these results, the solution-processed SnZnO TFT with high performance was suggested.
We have employed a simple and novel solution processing method to prepare V2O5-WO3 composite films which demonstrate enhanced Li-ion intercalation properties for applications in lithium-ion batteries. It should be noted that this solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods. The V2O5-WO3 composite films show enhanced Li-ion intercalation properties compared to pure V2O5 and WO3 films. For example, V2O5-WO3 film with a molar ratio V2O5/WO3 of 10/1 exhibits a discharge capacity of 254 mA•h/g, while the pure V2O5 film delivers a discharge capacity of 76 mA•h/g at a high current density of 1.33 A/g. Such enhanced Li-ion intercalation properties are attributed to the reduced crystallinity and increased porosity and surface area in the composite films. In addition, the chronopotentiometric curves of the V2O5-WO3 film with a mol ratio of 10:1 are distinctively different from those of pure oxide films and other composite films with different V2O5/WO3 mol ratios, suggesting a different Li-ion intercalation process in the V2O5-WO3 film with the mol ratio of 10/1.
We report on a novel light sensing scheme based on a silicon/fullerene-derivative hetero-junction that allows the realization of optoelectronic devices for the detection of near to mid infrared radiation. Despite the absent absorption of silicon and the fullerene-derivative for wavelengths beyond 1.1 µm and 0.72 µm, respectively, a hetero-junction of these materials absorbs and generates a photo-current due to absorption in the near to mid infrared. This photo-current is caused by an interfacial absorption mechanism .
Besides its scientific relevance, the simple fabrication process of the hetero-junction (e.g. the fullerene-derivative is deposited by spin-coating on Si) as well as its compatibility with the established and rather cheap CMOS technology makes the presented hybrid approach a promising candidate for widespread applications.
Zinc oxide (ZnO) is an emerging optoelectronic material in large area electronic applications due to its various functional behaviors. We report on the fabrication and the characterization of ZnO nanorods. The ZnO nanorods were synthesized using sol-gel hydrothermal technique on oxidized silicon substrates. Different annealing temperatures were explored in the sol-gel hydrothermal synthesis of the ZnO nanorods. In order to investigate the structural properties, the ZnO nanorods were measured using X-ray diffractometer (XRD). The optical properties were measured using ultraviolet-visible (UV-Vis) spectroscopy. The influence of the annealing treatment on the structural and optical properties of the ZnO nanorods will be revealed and discussed in this paper.
Controlled reaction conditions in simple, template-free hydrothermal processes yield Tm-Lu2O3 and Tm-GdVO4 nanocrystals with well-defined specific morphologies and sizes. In both oxide families, nanocrystals prepared at pH 7 reaction media exhibit photoluminescence in ∼1.95 μm similar to bulk single crystals. For the lowest Tm3+ concentration (0.2 % mol) in GdVO4 measured 3H4 and 3F4 fluorescence lifetimes τ are very near to τrad.
We achieved the preparation of nanostructures based on negative tone inorganic resists by DUV lithography (193 nm). This entails the preparation of a complex of a transition metal by reaction between the metal alkoxide and a suitable ligand. The reaction was carried out in a solvent. Then, a partial hydrolysis of the complex allowed forming metal-oxides inorganic chains by condensation with good film-forming and photopatterning properties. This step corresponds to the synthesis of multifunctional oligomers that can be crosslinked by DUV irradiation.
We obtained well-defined patterns exhibiting low rugosity with width down to 75 nm. An achromatic interferometer based on an ArF excimer laser was used to write the nanostructures. The sensitivity of the resin at 193 nm is in the order of magnitude of organic photoresists used in the microelectronics industry.
The photoinduced processes were studied with care in order to state the physico-chemical phenomena occurring upon DUV-irradiation. FTIR, XPS and XRD were used for characterizing the material structure after irradiation and thermal treatment. Nanostructures were studied by AFM.
The main interest of this resist is that after irradiation, the material is mainly inorganic. It can even be totally mineralized through a subsequent pyrolysis procedure. The process is compatible with a wide range of chemicals (ZrO2, TiO2…). Using lithographic route, it is possible to obtain such nanostructures on relatively wide surfaces. With this new process, we are targeting applications in microelectronics, optics, photonics, photocatalysis, photovoltaic…
A transparent colloidal solution of YVO4:Bi3+,Eu3+ nanophosphor is prepared by the wet chemical synthesis in the presence of sodium citrate. When an ethylene glycol solution of Bi(NO3)3, aqueous solutions of (Y,Eu)(NO3)3, sodium citrate, and Na3VO4 are mixed and aged at 85 °C, crystalline YVO4:Bi3+,Eu3+ spherical nanoparticles of ∼ 20 nm in size are formed via the amorphous precursor during aging, as confirmed by X-ray diffractometry and transmission electron microscopy. The crystallization completes at the aging time of ∼ 25 min. At the same time, a sudden reduction in the hydrodynamic size is observed by dynamic light scattering analysis, and the colloidal solution becomes transparent to naked eyes. The nominal molar percentage of sodium citrate relative to the sum of metallic ions, Y3+, Bi3+, and Eu3+, affects the particle size and the aggregation property of the nanoparticles. The sample prepared at 50 mol% citrate, followed by aging at 85 °C for 60 min have the minimum mean size of primary nanoparticles, 21 nm, the minimum mean hydrodynamic size, 36 nm, and hence the highest transparency.
We describe the production of photovoltaic modules with high-quality large-grain copper indium gallium selenide (CIGS) thin films obtained with the unique combination of low-cost ink-based precursors and a reactive transfer printing method. The proprietary metal-organic inks contain a variety of soluble Cu-, In- and Ga- multinary selenide materials; they are called metal-organic decomposition (MOD) precursors, as they are designed to decompose into the desired precursors. Reactive transfer is a two-stage process that produces CIGS through the chemical reaction between two separate precursor films, one deposited on the substrate and the other on a printing plate in the first stage. In the second stage, these precursors are rapidly reacted together under pressure in the presence of heat. The use of two independent thin films provides the benefits of independent composition and flexible deposition technique optimization, and eliminates pre-reaction prior to the synthesis of CIGS. In a few minutes, the process produces high quality CIGS films, with large grains on the order of several microns, and preferred crystallographic orientation, as confirmed by compositional and structural analysis by XRF, SIMS, SEM and XRD. Cell efficiencies of 14% and module efficiencies of 12% were achieved using this method. The atmospheric deposition processes include slot die extrusion coating, ultrasonic atomization spraying, pneumatic atomization spraying, inkjet printing, direct writing, and screen printing, and provide low capital equipment cost, low thermal budget, and high throughput.
We demonstrate high performance zinc-tin oxide (ZTO) thin-film transistors (TFTs) with low operation voltage, small channel length and low parasitic capacitance. Both the zinc tin oxide and the high-k dielectric, ZrO2, were solution processed by sol-gel methods. A self-aligned process was employed to minimize the parasitic capacitance. The transistors with a channel length of 8 μm operate at 5 V and have a saturation mobility of 2.5 cm2/V·s and an on/off ratio of 5.9×106. Gate-induced surface relief has been found to have strong effect on the performance of the active layer.
Recent years, although silica aerogel is expected to be the material for energy savings, the lack of the strength prevents from commercial usages such as heat-insulating windows. To improve mechanical properties, methyltrimethoxysilane is used as a precursor of aerogels because the network becomes flexible due to the relatively low cross-linking density and to the unreacted methyl groups. Because of the strong hydrophobicity of MTMS-derived condensates, uniform and homogeneous gel networks are hardly attained. In this study, we employed surfactant n-hexadecyltrimethylammonium chloride (CTAC) in starting compositions to control phase separation during a 2-step acid/base sol-gel reaction. By changing the starting composition, properties of aerogels such as bulk density and light transmittance are affected. With increasing amount of CTAC, the gel networks became denser and less transparent. Highly transparent aerogels were obtained when the amount of urea was increased.
There is an increasing need for integrating high dielectric constant ceramic thin film components in organic and 3D IC packages to lower the power-supply impedance at high frequencies and supply noise-free power to the ICs. Sol-gel approach is very attractive for high density capacitors because of its ability to precisely control the composition of the films and the ease of introducing dopants to engineer the dielectric properties such as breakdown voltages and DC leakage characteristics. Thin films on copper foils lend themselves to organic package integration with standard foil lamination techniques used in package build-up processes. However, fabrication of thin film barium titanate on copper foils is generally affected by process incompatibility during crystallization in reducing atmospheres, leading to poor crystallization, oxygen vacancies and copper diffusion through the film that degrades the electrical properties.
This paper focuses on the dielectric properties and electrical reliability of thin films on copper foils. Thin film (300-400 nm) embedded capacitors with capacitance density of 2 μF/cm2, low leakage current and high breakdown voltage were fabricated via sol-gel technology and foil lamination. To lower the leakage current, the chemical composition was altered by incorporating – 1.) Excess barium 2.) Acceptor dopants such as Mn. Both approaches lowered the leakage current compared to that of pure barium titanate. SEM analysis showed enhanced densification and refined grain structure with chemistry modification. The films showed good stability in leakage currents at 150 C with an applied field strength of 100 kV/cm, demonstrating the electrical reliability of these films.
Al-doped ZnO (AZO) nanoparticles (NPs) were synthesized by the solvothermal decomposition. The as-synthesized AZO NPs were characterized by X-ray diffraction and transmission electron microscopy. These NPs were well dispersible in non-polar solvents at high concentration to produce AZO nanoink. The AZO nanoparticulate films were prepared from AZO nanoink by spin coating technique. Thickness, surface morphology, optical transparency and conductivity of the films were characterized by surface profilometer, scanning electron microscopy, UV-Vis spectroscopy and Hall measurements. The AZO nanoparticlulate films had highly optical transmittance and well electrical conductivity, which are potential for optoelectronic applications.
Carbon foams with a reticulated macrostructure were prepared by a polymer sponge replication method. The electromagnetic parameters of carbon foams with variable electric conductivity were measured at a frequency of 2450MHz. Compared with the same composition pulverized powders, carbon foams have relatively lower dielectric constant but much larger dielectric loss, and more remarkably, carbon foams have magnetic loss. The microwave absorbing property measurement of carbon foams was also conducted. A relatively broad absorbing band performance has been got for carbon foams, and the absorbing values exceeds 7dB almost in the whole measured frequency range of 4-15GHz, while the frequencies range for absorbing values exceeding 8dB are about 7 GHz for the carbon foam with an electric conductivity of 0.46S/m. It is worthy that the broad absorbing band feature of the carbon foam is obtained without any impedance match design, which indicates carbon foams have a great possibility of being applied as RAMs. The special electromagnetic loss characteristics and prominent radar absorbing properties about carbon foams indicate macrostructure modification is possibly a new and effective way to modulate the electromagnetic properties of RAMs besides the traditional composition variation.
Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) consists of abundant and cheap elements and is therefore a very promising alternative to semiconductors based on Ga or In as solar absorber material. In addition it displays very beneficial properties like a high optical absorption coefficient and an ideal band gap for photovoltaic applications. In this contribution we present the preparation of CZTS thin films from metal salts (copper(I) iodide, zinc(II) acetate and tin(II) chloride) and thioacetamide as sulfur source by a solution based precursor method. CZTS solar cells based on these films as absorber layer with a simple ITO/CZTS/CdS/Al assembly are fabricated and characterized. Efficiencies up to 0.5% were achieved demonstrating the potential of this precursor method for the preparation of CZTS thin films for photovoltaic applications.