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A high performance humidity sensor for environmental and health monitoring was fabricated with a polymer–polymer composite sensing layer. PEDOT:PSS/PVA composite was synthesized by physically mixing PEDOT:PSS aqueous solution with PVA aqueous solution and was then sonicated and stirred at elevated temperatures. Sensors were fabricated by depositing the sensing layer on an IDT printed on a piezoelectric substrate. The sensors’ electrical characterizations were performed to find out the response toward varying humidity levels. The results showed that the composite's response toward humidity change is very stable and can effectively measure low humidity levels with fast response time. The AC capacitance and impedance of the sensor were measured between 0%RH and 80%RH. The maximum change in impedance was from 137 kΩ to 110 kΩ and for capacitance from 96 pF to 124 pF. The sensors were deployed in a real time humidity measurement and the readings were converted into corresponding %RH. The results indicated that the sensors show promising response with ±1% reading error. The response and recovery times of the sensor were measured to be 0.625 s and 0.53 s respectively showing excellent performance of the sensor toward increasing and decreasing humidity levels. [ABSTRACT FROM AUTHOR]

The conventional atomic layer deposition (ALD) technologies are capable of fabricating supreme quality thin films of a wide variety of materials, but sequential introduction and purging of precursors and inert gases prevent its application in the mass production of thin films under atmospheric conditions. In this study, we introduce a novel technique of roll-to-roll atmospheric (R2R-A)ALD using a multiple-slit gas source head. Thin films of Al2O3 are developed on a movable web of polyethylene terephthalate (PET) substrate at 50 °C. The Al2O3 deposition is carried out under a working pressure of 740 Torr, which is very near to atmospheric pressure (760 Torr). An appreciable growth rate of 0.98 Å per cycle is observed at a carefully optimized web velocity of 7 mm s−1. Good morphological, chemical, electrical, and optical characteristics are shown by the Al2O3 films produced at a large scale. Low root mean square roughness ( Rq) values of 1.85 nm and 1.75 nm are recorded for the Al2O3 films deposited at 50 °C over 75 and 125 ALD cycles, respectively. The appearance of Al 2p, Al 2s, and O 1s peaks at the binding energies of 74 eV, 119 eV, and 531 eV, respectively, in the X-ray photoelectron spectroscopy (XPS) analysis confirms the fabrication of Al2O3 films, which is also supported by Fourier transform infrared spectroscopy (FTIR). The films show excellent insulating properties, and optical transmittance of more than 85% is recorded in the visible region. [ABSTRACT FROM AUTHOR]

Silver nanowires (AgNWs) films were coated conformally with aluminum oxide (Al2O3) through atomic layer deposition (ALD) at very low temperature. The AgNWs films were first fabricated through spin coating on polyamide substrates. Later on Al2O3coatings were deposited on the spin coated AgNWs films by ALD at a very low deposition temperature of 50 °C using trimethylaluminum and distilled water. The optimized ALD cycle involves a very short H2O purging step of only 10 s, which not only removes the residual H2O vapors effectively but also enhances the efficeny of the process by reducing the total time required for completion of Al2O3deposition. The surface morphology was observed through field-emission scanning electron microscopy and film crystallinity using X-ray diffractometer, respectively. The observed results revealed conformal and amorphous nature of Al2O3coatings on AgNWs films. The chemical composition and films purity were analyzed by X-ray photoelectron spectroscopy. It has been verified by the results that the ALD technique is well capable of depositing uniform Al2O3coatings on AgNWs films at very low temperature. The deposited coatings are expected to be of very much interest in flexible electronic applications in near future. [ABSTRACT FROM AUTHOR]

Highlights: [•] Good quality Al2O3 thin films are fabricated on PEN substrates through ALD. [•] Hydrophobicity of Al2O3 films has been enhanced greatly by C3F8 plasma treatment. [•] C3F8 plasma treated films have retained good surface morphology. [•] C3F8 plasma treated films have shown high optical transmittance of more than 90%. [Copyright &y& Elsevier]

This paper reports on the fabrication of good quality AlO thin films on flexible substrates including polyethylene naphthalate (PEN), polyethylene terephthalate (PET) and Polyamide at different temperatures down to 50 °C under very short water purging steps of 10 s. AlO films with appreciable growth rates having good morphological, chemical, electrical and optical characteristics have been produced. Growth rates of 1.16, 1.14 and 1.15 Å/cycle have been observed at 50 °C for PET, PEN and polyamide substrates respectively. The surface morphology has been improved with the increase in deposition temperature. Low average arithmetic roughness of 0.88 and 0.78 nm have been recorded for the AlO films deposited at 150 °C on PEN and polyamide respectively. The XPS analysis confirmed the fabrication of AlO films without any carbon contamination and Al 2p, Al 2s and O 1s peaks were appeared at binding energies of 74, 119 and 531 eV, respectively. Excellent insulating properties were observed for the AlO films and optical transmittance of more than 85 % was recorded in the visible region. The experimental results suggest that polymeric materials are excellent candidates to be used as substrates in the fabrication of AlO thin films through atomic layer deposition. [ABSTRACT FROM AUTHOR]

Abstract: In this article, we report the application of a non-vacuum based direct printing technique of electrohydrodynamic atomization (EHDA) for the deposition of single-walled carbon nanotube (SWCNT) thin films of 90nm thickness onto flexible polyethersulfone (PES) substrates. The optimization of EHDA process to achieve a stable cone jet for the uniform deposition of SWCNT thin films is discussed in detail. The physico-chemical characterization of SWCNT thin films has been carried out using X-ray diffraction, UV–vis spectroscopy and Fourier-transform infra red spectroscopy techniques. The field emission scanning electron microscope studies revealed the surface morphology of SWCNT thin films. Further, the electrical study of the SWCNT thin films exhibited a linear ohmic behavior at room temperature as well as at elevated temperatures. [Copyright &y& Elsevier]

A flexible humidity sensor has been fabricated by a transfer printing technique. The device is fabricated by spin coating a composite of an equal (1:1) wt% ink of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and zinc-stannate (ZnSnO 3 ) on a water soluble substrate (WSS), screen printing silver interdigitated (IDT) electrodes and spin coating low modulus Polydimethylsiloxane (PDMS) on top of the IDTs. The water soluble substrate is then dissolved and removed and the device is laminated onto an arbitrary substrate in an inverted configuration. The device performance has been tested by transferring onto curved plastic substrates with different radii of curvature R c . The devices show impedance change from ∼18 MΩ to ∼1.8 MΩ from 0% to 90% relative humidity (RH) with a negligible variation in results, over different bending radii. The transfer printing technique reported here would provide efficient and reliable route for the fabrication of flexible electronics on nonconventional substrates in environmental sensing, soft robotics, and artificial skin etc. [ABSTRACT FROM AUTHOR]

Abstract: This article presents an attractive printing technique for thin film deposition of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on flexible substrates known as electrohydrodynamic atomization (EHDA). Optimum flow rate and applied potential for stable cone jet mode has been confirmed through identification of process operating envelop. The uniformity and film thickness has been investigated by a field emission scanning electron microscope. The thin film shows nearly 75–82% transmittance in visible region. The electrical study shows good ohmic behavior of PEDOT:PSS thin film with the resistivity of approximately 49.6 mΩ cm. [Copyright &y& Elsevier]

Abstract: In this study, highly transparent, 250nm thick films of Aluminum doped Zinc-oxide (ZnO:Al) are achieved on glass substrates at ambient conditions through a solution processing technique called electrohydrodynamic atomization. A 10wt.% monodispersed solution containing 6% ZnO:Al nanoparticles (ZnO/Al2O3) in ethanol has been synthesized first and then used in the deposition process as the working solution. Pure and uniform transparent films with an average transmittance of 93% have been deposited with crystal structure exhibiting both zincite and gahnite phases. Surface composition purity has been confirmed using X-ray photoelectron spectroscopy technique and the clear indication of Zn-2p and Al-2p peaks confirms surface integrity. Fourier Transform Infrared analysis further confirms the presence of aluminum in the samples. The electrical properties are studied by recording and analyzing the current–voltage (I–V) measurements and the resistivity has been estimated from the slope of the IV-curve which is approximately 25mΩ.cm. The layer roughness has been characterized using atomic force microscopy. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) is a useful material in the fabrication of many electronic devices because of its wide band-gap, excellent transparency and high electron mobility. Thin films of ZnO have been fabricated where an alcosol solution containing 7wt.% ZnO nano-particles was synthesized and subjected to controlled flow through a metal capillary exposed to an electric field at the ambient temperature to generate an electrohydrodynamic jet, which subsequently disintegrated into droplets thereby depositing a uniform thin film of zinc oxide on the glass substrates with an average thickness of 115nm at a constant substrate speed of 0.25mm/s. Pure and perfectly uniform transparent films with an average transmittance of 88% have been deposited with wurtzite crystal structure and an electrical resistivity of approximately 64Ω.cm. [Copyright &y& Elsevier]

Abstract: A rather new technique for the deposition of CIS layer has been discussed in this paper namely Electrospray Deposition (ESD). Thin films composed of Copper–Indium–diSelenide, have been achieved using the ESD technique for the ultimate manufacture of CIS based solar cell. CIS nano-particle inks are used in the ESD process for the deposition of ∼2 μm CIS layers on ITO coated substrates whereby ITO coating can be used as the back contact of the solar cell. Different parameters affecting the ESD process and the deposited layer thickness and uniformity such as stand-off distance, flow rate and voltage have been examined as well to come up with an optimized parameter combination. Layers with fine uniformity are achieved at two different substrate speeds, 0.5 mm/s and 1.0 mm/s. The thickness of the deposited films varied from 400 nm to 2.7 μm with varying flow rate from 30 μl/h to 230 μl/h and 2.8 μm–1.3 μm with varying stand-off distance from 13 mm to 6 mm. The cost-effectiveness, room-temperature operation, environment friendliness and simplicity of ESD process with its possible integration with high throughput manufacturing processes like Roll-to-Roll process makes it an idyllic candidate for deployment in the solar cell fabrication process at a large scale. [Copyright &y& Elsevier]

Abstract: This paper presents fabrication of thin film transistors using direct write technology following electrohydrodynamic approach for patterning and spray deposition. In this research colloidal solution of Ag nanoparticles is used for patterning of gate, source and drain contacts, while SiO2 and ZnO colloidal solutions are used for dielectric and semiconductor layers of TFTs using EHD printing technology. For direct patterning, different electrode configurations for inkjet head are used and a new nozzle head is developed for getting stable meniscus and uniform patterning. To minimize the disturbances caused by vertically inserted thin electrode, a hollow conductor is used in new setup, which serves both for ink feed and as an actuation electrode. The new configuration helps in minimizing the extraction voltage for jetting and also repeatability of experiment by keeping fixed parameters of the nozzle head is possible. By using metallic enclosed glass capillary head, conductive pattern lines for gate, source and drain contacts with good uniformity and regular boundaries are printed on glass substrate. Conductive lines having width of around 70μm are achieved with appreciable aspect ratio. A channel length of 50μm and width of 1.5mm is obtained by using EHD direct printing of Ag colloidal solution. Layer thickness of SiO2 achieved is around 300nm while ZnO thickness achieved is around 100nm. A standard deviation in layer thickness of around 25nm for SiO2 and 10nm for ZnO electrosprayed layers is observed. A complete prototype of thin film transistor has been successfully fabricated by using EHD technology in this research. Contact angle analyzer is also used for finding various parameters like contact angle, wetting energy and spreading coefficient of the colloidal solutions which helps in determining the surface properties of the deposited layers. All experiments were performed in ambient conditions and environment. [Copyright &y& Elsevier]