Electron beam lithography of hybrid sol–gel negative resist

The direct pattering process here described is proposed as an alternative to conventional multi step nanofabrication techniques, merging materials with novel functional properties and the simplification of the fabrication processes. We report the use of an innovative hybrid sol–gel material working as negative resists for EBL lithography and showing a resolution better than 100 nm. Tailoring the optical and mechanical properties, few examples of photonic nanostructure were fabricated with a simple e-beam exposure that greatly simplify the nanofabrication process.     

High-efficiency hybrid organic–inorganic light-emitting devices

We report efficient red, orange, green and blue organic–inorganic light emitting devices using light emitting polymers and polyethylenimine ethoxylated (PEIE) interlayer with the respective luminance efficiency of 1.3, 2.7, 10 and 4.1 cd A⁻¹, which is comparable to that of the analogous conventional devices using a low work-function metal cathode. This is enabled by the enhanced electron injection due to the effective reduction of the ZnO work-function by PEIE, as well as hole/exciton-blocking function of PEIE layer. Due to the benign compatibility between PEIE and the neighboring organic layer, the novel phosphorescent organic–inorganic devices using solution-processed small molecule emissive layer show the maximum luminance efficiency of 87.6 cd A⁻¹ and external quantum efficiency of 20.9% at 1000 cd m⁻².     

Nanoparticle-dispersed high-k organic–inorganic hybrid dielectrics for organic thin-film transistors

We fabricated solution-processable thin gate dielectrics for organic thin-film transistors (OTFTs) using an organosiloxane-based organic–inorganic hybrid material. The electrical characteristics of the hybrid dielectrics were controlled by adjusting the zirconium alkoxide concentration. Microstructural observation and chemical analysis allow us to determine the influence of microstructure and composition on the electrical properties of the hybrid dielectrics. Our hybrid material is composed of three phases: ZrO₂, ZrSiO₄, and organosiloxane. OTFTs based on the hybrid dielectrics exhibited better electrical performance compared to transistors based on poly(4-vinylphenol) (PVP). Using a dielectric with a higher dielectric constant and fewer hydroxyl groups enabled us to fabricate a transistor with a lower off-current, higher on/off current ratio, and lower threshold voltage.     

UV-curable organic–inorganic hybrid gate dielectrics for organic thin film transistors

UV-curable hybrid thin films were prepared from ZrO₂ hybrid sols containing the acrylic monomer, DPHA, on substrates. The prepared ZrO₂ hybrid sols showed long-term storage stability. Hybrid dielectrics were prepared by sol–gel process and UV cross-linking below 160 °C. Leakage currents of dielectric layers remained below 10⁻⁶ A in 2 MV/cm and dielectric constants were measured to be 3.85–4 at 1 kHz. In addition, organic–inorganic hybrid thin films have smooth and hydrophobic surface. Pentacene OTFTs with thin hybrid dielectrics exhibit of mobility as large as 2.5 cm²/V s, subthreshold swing as low as 0.2 V/decade, an on–off ratio of 10⁵. These results demonstrated that UV-curable sol–gel hybrid systems are suitable for gate dielectrics in OTFTs.     

UV-directly patternable organic–inorganic hybrid composite dielectrics for organic thin-film transistors

A research on the design, synthesis, and characterization of novel cross-linked polymer organic–inorganic hybrid materials as gate insulators for organic thin-film transistors (OTFTs) with vanadyl-phthalocyanine as the organic semiconductor is presented. The hybrid films (0.5–1.2 μm thick) can be easily prepared by sol–gel technology and fabricated by spin-coating a mixture of zirconium n-butoxide sol with a side-chain triethoxysilane-capped polyurethane solution in ambient conditions, followed by curing at low temperatures (∼120 °C) and cross-linking under UV light. OTFTs with this film as gate insulator were achieved with good processability, high charge-carrier mobility of 0.56 cm²/Vs, surface roughness of around 0.49–0.59 nm, ultralow threshold of −6 V, and ultralow leakage of 0.24 mA. Hybrid films with various compositions were investigated, and the results showed that the field-effect mobility of the OTFTs was dominated by the high dielectric constant component ZrO₂. The result indicated that these hybrid materials are promising candidates for the exploration of devices using OTFTs.     

Electrosynthesis of organic–inorganic compounds (p–n heterojunction)

An electrochemical deposition procedure by cyclic voltammetry, in an electrolyte solution was adopted for the preparation of thin films of polypyrrole–gallium arsenide composite materials. The properties of the composite layers were studied by cyclic voltammetry, electrochemical impedance spectroscopy and photoelectrochemical measurements. The p- and n-type semiconductor behaviour of the polypyrrole (PPy) and gallium arsenide (GaAs) were studied by photocurrent measurements. It was found that the composite material (PPy–GaAs) had a (p–n) heterojunction behaviour.     

High performance sol–gel spin-coated titanium dioxide dielectric based MOS structures

High-κ TiO₂ thin films have been fabricated using cost effective sol–gel and spin-coating technique on p-Si (100) wafer. Plasma activation process was used for better adhesion between TiO₂ films and Si. The influence of annealing temperature on the structure-electrical properties of titania films were investigated in detail. Both XRD and Raman studies indicate that the anatase phase crystallizes at 400 °C, retaining its structural integrity up to 1000 °C. The thickness of the deposited films did not vary significantly with the annealing temperature, although the refractive index and the RMS roughness enhanced considerably, accompanied by a decrease in porosity. For electrical measurements, the films were integrated in metal-oxide-semiconductor (MOS) structure. The electrical measurements evoke a temperature dependent dielectric constant with low leakage current density. The Capacitance–voltage (C–V) characteristics of the films annealed at 400 °C exhibited a high value of dielectric constant (~34). Further, frequency dependent C–V measurements showed a huge dispersion in accumulation capacitance due to the presence of TiO₂/Si interface states and dielectric polarization, was found to follow power law dependence on frequency (with exponent ‘s’=0.85). A low leakage current density of 3.6×10⁻⁷ A/cm² at 1 V was observed for the films annealed at 600 °C. The results of structure-electrical properties suggest that the deposition of titania by wet chemical method is more attractive and cost-effective for production of high-κ materials compared to other advanced deposition techniques such as sputtering, MBE, MOCVD and ALD. The results also suggest that the high value of dielectric constant ‘κ‘ obtained at low processing temperature expands its scope as a potential dielectric layer in MOS device technology.     

Thermal properties of channel optical waveguides based on sol–gel materials

Temperature characteristics of various channel waveguides fabricated using the sol–gel technology are analyzed. It is shown that the limitation of transverse sizes of waveguides leads to significant variations in the temperature characteristics due to field concentration in the sol–gel material of the waveguide, which depends on the type of the channel waveguide and its parameters (geometrical sizes and refractive index of the sol–gel material). Recommendations on the selection of the type of waveguide and its parameters for specific applications in multiplexers, switches, optical cavities, etc. are presented.     

Characterization of ZrTiO4 thin films prepared by sol–gel method

The electrical properties, memory switching behavior, and microstructures of ZrTiO₄ thin films prepared by sol–gel method at different annealing temperatures were investigated. All films exhibited ZrTiO₄ (111) and (101) orientations perpendicular to the substrate surface, and the grain size increased with increasing annealing temperature. A low leakage current density of 1.47×10^?6 A/cm² was obtained for the prepared films. The I–V characteristics of ZrTiO₄ capacitors can be explained in terms of ohmic conduction in the low electric field region and Schottky emission in the high electric field region. An on/off ratio of 10² was measured in our glass/ITO/ZrTiO₄/Pt structure with an annealing temperature of 600 °C. Considering the primary memory switching behavior of ZrTiO₄, ReRAM based on ZrTiO₄ shows promise for future nonvolatile memory applications.     

Electric conduction of PbBr-based layered perovskite organic–inorganic superlattice having carbazole chromophore-linked ammonium molecule as an organic layer

We have successfully prepared thin films of PbBr-based layered perovskite having hole-transporting carbazole chromophore-linked ammonium molecules as an organic layer by a simple spin-coating from the N,N-dimethylformamide solution in which the stoichiometric amount of lead bromide and carbazole-linked ammonium bromides was dissolved. Their X-ray diffraction profiles exhibited that their layer structure formed (0 0 n)-orientation, where c-axis is perpendicular to the substrate plane. Their layer structure depended on the alkyl chain length of ammonium molecules. When methylene length of C₅H₁₀ was employed in the carbazole-linked ammonium molecules, highest orderliness of the layer structure was attained; higher-order X-ray diffraction peaks were observed in the layered perovskite films. In the layered pervskite film, in-plane conduction, namely conduction in the direction of the stacking of carbazole chromophore, was measured. For comparison, conductivity of poly(N-vinylcarbazole) (PVCBz) thin film was also measured. The conductivity of the layered perovskite thin film (1.8 × 10^?10 Scm^?1 at 303 K) was about three order of magnitude larger than that of the PVCBz thin film (5.3 × 10^?14 Scm^?1 at 303 K). Despite the much higher conductivity of the layered peroskite thin film, the activation energy of the conductivity of the layered perovskite thin film (1.44 eV) was about 2.4 times larger than that of the PVCBz thin film (0.61 eV). This phenomenon is probably due to difference in film morphology through considering the results of AFM observation.     

Sol–gel deposited SiO2 and hybrid low dielectric constant thin films

The paper presents the comparative analysis of effect of hydrochloric (HCl), hydrofluoric (HF) acid catalyst and organic material methylmethacrylate (MMA) on dielectric constant of thin films. The dielectric constant of thin film obtained by using HCl catalyst is 3.63 which have been successfully reduced to 2.97 for hybrid thin films via incorporation of carbon. The deposited low k dielectric thin films observed to have good adhesion with p-silicon substrate and hence pertinent for interlayer dielectric (ILD) in ultra-large scale integrated (ULSI) circuits applications. The deposited films have been characterized by ellipsometer for refractive index, further material compositions have been studied by using Fourier transform infrared (FTIR) spectroscopy and energy dispersive spectroscopy (EDAX).     

A flexible moisture barrier comprised of a SiO2-embedded organic–inorganic hybrid nanocomposite and Al2O3 for thin-film encapsulation of OLEDs

We demonstrated a high performance flexible multi-barrier containing a silica nanoparticle-embedded organic–inorganic hybrid (S–H) nanocomposite and Al₂O₃. The multi-barrier was prepared by low-temperature Al₂O₃ atomic layer deposition and with a spin-coated S–H nanocomposite. The moisture barrier properties were investigated with a water vapor transmission rate (WVTR), estimated by a Ca test at 30 °C, 90% R.H.. Moisture diffusion was effectively suppressed by the sub-700 nm thick multi-barrier incorporating well-dispersed silica nanoparticles in the organic layer. A low WVTR of 1.14 × 10^?5 g/m² day and average transmittance of 85.8% in the visible region were obtained for the multi-barrier. After bending under tensile stress mode, the moisture barrier property of the multi-barriers was retained. The multi-barrier was successfully applied to thin-film encapsulation of OLEDs. The thin-film encapsulated OLEDs showed practicable current–voltage–luminance (I–V–L) characteristics and stable real operation over 700 h under ambient conditions.     

Properties of fluorine-doped SnO2 thin films by a green sol–gel method

Fluorine doped tin oxide (FTO) films were fabricated on a glass substrate by a green sol–gel dip-coating process. Non-toxic SnF₂ was used as fluorine source to replace toxic HF or NH₄F. Effect of SnF₂ content, 0–10 mol%, on structure, electrical resistivity, and optical transmittance of the films were investigated using X-ray diffraction, Hall effect measurements, and UV–vis spectra. Structural analysis revealed that the films are polycrystalline with a tetragonal crystal structure. Grain size varies from 43 to 21 nm with increasing fluorine concentration, which in fact critically impacts resultant electrical and optical properties. The 500 °C-annealed FTO film containing 6 mol% SnF₂ shows the lowest electrical resistivity 7.0×10⁻⁴ Ω cm, carrier concentration 1.1×10²¹ cm⁻³, Hall mobility 8.1 cm²V⁻¹ s⁻¹, optical transmittance 90.1% and optical band-gap 3.91 eV. The 6 mol% SnF₂ added film has the highest figure of merit 2.43×10⁻² Ω⁻¹ which is four times higher than that of un-doped FTO films. Because of the promising electrical and optical properties, F-doped thin films prepared by this green process are well-suited for use in all aspects of transparent conducting oxide.     

Spectroscopic studies of sol–gel grown CdS nanocrystalline thin films for optoelectronic devices

CdS is one of the highly photosensitive candidate of II–VI group semiconductor material. Therefore CdS has variety of applications in optoelectronic devices. In this paper, we have fabricated CdS nanocrystalline thin film on ultrasonically cleaned glass substrates using the sol–gel spin coating method. The structural and surface morphologies of the CdS thin film were investigated by X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) respectively. The surface morphology of thin films showed that the well covered substrate is without cracks, voids and hole. The round shape particle has been observed in SEM micrographs. The particles sizes of CdS nanocrystals from SEM were estimated to be～10–12 nm. Spectroscopic properties of thin films were investigated using the UV–vis spectroscopy, Photoluminescence and Raman spectroscopy. The optical band gap of the CdS thin film was estimated by UV–vis spectroscopy. The average transmittance of CdS thin film in the visible region of solar spectrum found to be～85%. Optical band gap of CdS thin film was calculated from transmittance spectrum ～2.71 eV which is higher than bulk CdS (2.40 eV) material. This confirms the blue shifting in band edge of CdS nanocrystalline thin films. PL spectrum of thin films showed that the fundamental band edge emission peak centred at 459 nm also recall as green band emission.     

Electrical and optical properties of polyethylene glycol-assisted sol–gel solid state reaction-synthesized nanostructured CdTiO3

Nanostructured ilmenite CdTiO₃ was synthesized by the sol–gel solid state reaction method using polyethylene glycol 4000 as templating agent and characterized by powder X-ray diffraction, energy dispersive X-ray analysis, high resolution scanning electron microscopy, and UV–vis diffuse reflectance, photoluminescence, and solid state impedance spectroscopies. Band gap of the prepared CdTiO₃ is much smaller than the widely reported one. The visible light emission of the synthesized CdTiO₃ is similar to that of anatase TiO₂.     

Preparation,characterization and photochemical degradation of dyes under UV light irradiation by inorganic–organic nanocomposite

An inorganic–organic nanocomposite consisting of 12-tungstophosphoric acid (H₃PW₁₂O₄₀) supported on Polyaniline (PANI) has been successfully synthesized by one-step and two-step methods. X-ray diffraction, Fourier-transformed infrared spectroscopy, scanning electron microscopy and electronic absorption spectroscopy indicated that the Polyphosphotungstate (PPT) was chemically attached to the PANI support; the primary Keggin structure remained intact. The photocatalytic and sonocatalytic activity of PPT/PANI was tested by degradation of organic dyes such as Methylene Blue, Rhodamin B, Bromothymol Blue, Methyl Orange and Nylosan Black 2-BC in aqueous solution; the nanocomposite showed higher photocatalytic and sonocatalytic activity than pure polyphosphotungstate or pure PANI.     

ZnO/p-Si heterojunction photodiode by sol–gel deposition of nanostructure n-ZnO film on p-Si substrate

The electrical and photovoltaic properties of the nanostructure ZnO/p-Si diode have been investigated. The nanostructure ZnO/p-Si diode was fabricated using sol–gel spin coating method. The ideality factor and barrier height of the diode were found to be 3.18 and 0.78 eV, respectively. The obtained n ideality factor is higher than 2, indicating that the diode exhibits a non-ideal behavior due to the oxide layer and the presence of surface states. The nanostructure of the ZnO improves the quality of ZnO/p-Si interface. The diode shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 0.26 V and short-circuits current I_sc of 1.87×10^?8 A under 100 mW/cm². It is evaluated that the nanostructure ZnO/p-Si diode is a photodiode with the obtained electronic parameters.     

Synthesis and characterization of nano Ag/Pt and methyl violet co-doped sol–gel porous material

Nano Ag/Pt and methyl violet (MV) co-doped sol–gel substrates have been prepared and characterized by spectral and microscopic techniques. MV was encapsulated in the sol–gel medium along with the bimetal nanoparticles and the resultant materials were compared. MV adsorbed on the surface of nanometal particles and encapsulated into the substrate of both is proposed as a scheme. Photodegradation of four different dyes (MV, methyl green, malachite green and Congo red) as probes, by prepared only bimetal doped substrate is examined and discussed to understand the mechanism.