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A ZnO/Cu 2 O-based combinatorial heterojunction device library was successfully fabricated by a simple spray pyrolysis technique using ITO-coated glass as the substrate. The combinatorial approach was introduced to analyze the impact of the ZnO and Cu 2 O layer thicknesses on the performance of the solar cells. The thickness of the ZnO layer was varied from ∼50 to 320 nm, and the Cu 2 O layer was deposited orthogonal to the ZnO thickness gradient. In the case of Cu 2 O, the thickness varied from ∼200 to 800 nm. The photovoltaic performance of the cells is strongly dependent on the absorber layer thickness for a particular window layer thickness and reaches a maximum short-circuit current density of 3.9 mA/cm 2 when the absorber layer thickness just crosses ∼700 nm. Reducing the thicknesses of the active layers leads to a sharp decrease in the device performance. It is shown that the entire built-in bias of the heterojunction is created in the absorber layer due to low carrier density. The poor performance of the devices having lower thicknesses is attributed to different interfacial phenomena such as optical losses due to the thin Cu 2 O layer, back-contact recombination of the carriers due to the low layer thickness because a minimum heterojunction thickness is required for the formation of the full built-in bias that slows down the recombination of the carriers, and other factors.

In obtaining uniform array of ZnO 1D nanostructures, especially using solution based methods, the thickness and the morphology of the epitaxial seeds layer are very important. The paper presents the effect of the thickness and the morphology of the Al:ZnO seeds layer on the morphology and properties of ZnO nanowires array grown by hydrothermal method. Compact and vertically aligned ZnO 1D nanostructures were obtained. Concentration of 0.02 M of zinc nitrate was found to be optimal for growing nanowires with diameters up to 50 nm and lengths between 1.5 and 2.5 microns. Using 0.04 M solution, nanorods with diameter between 50 and 100 nm were obtained. The correlation between the crystal structure and optical properties of ZnO nanowires is discussed. From electrical measurements on single nanowire, resistivity value of 9 x 10(-2) omega cm was obtained. The I-V curves of single ZnO NWs show quasi diode characteristic when an e-beam is irradiating the NWs, and a typical semiconductive behaviour when the e-beam is turned off.

An increase in the demand for the next generation of "Internet‐of‐Things" (IoT) has motivated efforts to develop flexible and affordable smart electronic systems, in line with sustainable development and carbon neutrality. Cellulose holds the potential to fulfil such demands as a low‐cost green material due to its abundant and renewable nature and tunable properties. Here, a cellulose‐based ionic conductive substrate compatible with printing techniques that combines the mechanical robustness, thermal resistance and surface smoothness of cellulose nanofibrils nanopaper with the high capacitance of a regenerated cellulose hydrogel electrolyte, is reported. Fully screen‐printed electrolyte‐gated transistors and universal logic gates are demonstrated using the engineered ionic conductive nanopaper and zinc oxide nanoplates as the semiconductor layer. The devices exhibit low‐voltage operation (<3 V), and remarkable mechanical endurance under outward folding due to the combination of the robustness of the nanopaper and the compliance of the semiconductor layer provided by the ZnO nanoplates. The printed devices and the ion‐conductive nanopaper can be efficiently recycled to fabricate new devices, which is compatible with the circular economy concept. [ABSTRACT FROM AUTHOR]

Printed electronics answers to the emerging trend of using truly inexpensive and easily accessible techniques to design and fabricate low‐cost and recyclable flexible electronic components. Nevertheless, printing of inorganic semiconductor materials arises some barriers for flexible electronics, as they usually may require high annealing temperatures to enhance their electronic performances, which are not compatible with paper. Here, the formulation of a water‐based, screen‐printable ink loaded with zinc oxide nanoparticles that does not require any sintering process is reported. The ink is used to create the channel in fully printed electrolyte‐gated transistors on paper, gated by a cellulose‐based ionic conductive sticker. The high conformability of the electrolyte‐sticker mitigates the effect of the surface roughness of the channel, yielding transistors that operate under low voltage (<2.5 V) with a current modulation above 104 and μSat ≈ 22 cm2 V−1 s−1. These devices operate even under moderate outward bending conditions. The screen‐printed transistors are readily integrated in "universal" logic gates (NOR and NAND) by using ubiquitous calligraphy accessories for patterning of conductive paths and graphitic load resistances. This demonstrates the manufacturing of reliable and recyclable cellulose‐based iontronic circuits with low power consumption, paving the way to a new era of sustainable "green" electronics. [ABSTRACT FROM AUTHOR]

Zinc oxide nanoparticles (ZnONPs) have received considerable attention as an antibacterial agent particularly in the textile industry. In the present work a successful procedure for in situ growth of ZnONPs in textiles was developed. The results obtained showed that a combination of in situ synthesis and the sol–gel method promoted a uniform and dense adsorption of the nanoparticles both inside and on the surface of fabric fibres. The fabrics finished with ZnONPs have been investigated for antibacterial properties by the agar diffusion method and by the absorption method according to the ISO 20743:2013 standard and exhibited an antibacterial effect against methicillin resistant Staphylococcus aureus ATCC33591, Staphylococcus epidermidis ATCC1228, Staphylococcus aureus RN4220 and Propionibacterium acnes ATCC6919. Moreover, tests conducted with hydrogen peroxide suggested the involvement of reactive oxygen species, namely the involvement of hydrogen peroxide, in the antibacterial activity of the zinc oxide nanoparticles. Therefore, the synthesised nanoparticles showed great potential to be used as coatings for medical, cosmetic or sports fabrics. [ABSTRACT FROM AUTHOR]

In the present study, zinc oxide (ZnO) nanorods (NRs) with a hexagonal structure have been synthesized via a hydrothermal method assisted by microwave radiation, using specialized cardboard materials as substrates. Cardboard-type substrates are cost-efficient and robust paper-based platforms that can be integrated into several opto-electronic applications for medical diagnostics, analysis and/or quality control devices. This class of substrates also enables highly-sensitive Raman molecular detection, amiable to several different operational environments and target surfaces. The structural characterization of the ZnO NR arrays has been carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical measurements. The effects of the synthesis time (5-30 min) and temperature (70-130 °C) of the ZnO NR arrays decorated with silver nanoparticles (AgNPs) have been investigated in view of their application for surface-enhanced Raman scattering (SERS) molecular detection. The size and density of the ZnO NRs, as well as those of the AgNPs, are shown to play a central role in the final SERS response. A Raman enhancement factor of 7 x 105 was obtained using rhodamine 6 G (R6G) as the test analyte; a ZnO NR array was produced for only 5 min at 70 °C. This condition presents higher ZnO NR and AgNP densities, thereby increasing the total number of plasmonic "hot-spots", their volume coverage and the number of analyte molecules that are subject to enhanced sensing. [ABSTRACT FROM AUTHOR]

In the present work, tracing and Whatman papers were used as substrates to grow zinc oxide (ZnO) nanostructures. Cellulose-based substrates are cost-efficient, highly sensitive and environmentally friendly. ZnO nanostructures with hexagonal structure were synthesized by hydrothermal under microwave irradiation using an ultrafast approach, that is, a fixed synthesis time of 10 min. The effect of synthesis temperature on ZnO nanostructures was investigated from 70 to 130 °C. An Ultra Violet (UV)/Ozone treatment directly to the ZnO seed layer prior to microwave assisted synthesis revealed expressive differences regarding formation of the ZnO nanostructures. Structural characterization of the microwave synthesized materials was carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical characterization has also been performed. The time resolved photocurrent of the devices in response to the UV turn on/off was investigated and it has been observed that the ZnO nanorod arrays grown on Whatman paper substrate present a responsivity 3 times superior than the ones grown on tracing paper. By using ZnO nanorods, the surface area-to-volume ratio will increase and will improve the sensor sensibility, making these types of materials good candidates for low cost and disposable UV sensors. The sensors were exposed to bending tests, proving their high stability, flexibility and adaptability to different surfaces. [ABSTRACT FROM AUTHOR]

The present work reports on the handwriting of electronic circuits on paper based on the deposition of an inorganic oxide semiconductor, exploiting the pen‐on‐paper (PoP) approach. The method relies on the use of a parallel metal plate pen, well known from calligraphy applications, which permits controlled deposition of a continuous zinc oxide (ZnO) dual‐phase layer on conventional printing paper. The hand‐drawn ZnO film exhibits a continuous and uniform surface with a thickness of roughly 1.5 µm, allowing the application as active layer for UV sensors and field effect transistors on paper. Photocurrent generated from the UV radiation reaches values up to 3.4 mA cm−2 with switching times on the order of few seconds. The final written paper transistors, where paper plays simultaneously the role of substrate and dielectric, reaches On/Off current ratios (IOn/IOff) of about two orders of magnitude and field effect mobility close to 5 × 10−3 cm2 V−1 s−1. As a final proof‐of‐concept a common source amplifier showing clear inverting characteristics is fabricated using a PoP written driving ZnO‐based transistor and a pencil‐drawn track as the load resistance. [ABSTRACT FROM AUTHOR]

The present work reports the influence of zinc oxide (ZnO) seed layer annealing temperature on structural, optical and electrical properties of ZnO nanorod arrays, synthesized by hydrothermal method assisted by microwave radiation, to be used as UV sensors. The ZnO seed layer was produced using the spin-coating method and several annealing temperatures, ranging from 100 to 500 °C, have been tested. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectrophotometry measurements have been used to investigate the structure, morphology, and optical properties variations of the produced ZnO nanorod arrays regarding the seed layer annealing temperatures employed. After the growth of ZnO nanorod arrays, the whole structure was tested as UV sensors, showing an increase in the sensitivity with the increase of seed layer annealing temperature. The UV sensor response of ZnO nanorod arrays produced with the seed layer annealed temperature of 500 °C was 50 times superior to the ones produced with a seed layer annealed at 100 °C. [ABSTRACT FROM AUTHOR]

We report the effect of a disperse carbon interlayer between the n-a-Si:H layer and an aluminium zinc oxide (AZO) back contact on the performance of amorphous silicon solar cells. Carbon was incorporated to the AZO film as revealed by x-ray photoelectron spectroscopy and energy-dispersive x-ray analysis. Solar cells fabricated on glass substrates using AZO in the back contact performed better when a disperse carbon interlayer was present in their structure. They exhibited an initial efficiency of 11%, open-circuit voltage Voc = 1.6 V, short-circuit current JSC = 11 mA cm−2 and a filling factor of 63%, that is, a 10% increase in the JSC and 20% increase in the efficiency compared to a standard solar cell. [ABSTRACT FROM AUTHOR]

Abstract: ZnO is a natural n-type widespread semiconductor with wide direct bandgap of 3.37eV, large exciton bending energy (60meV) and high optical gain (300cm−1). One dimensional ZnO nanomaterials such as nanowires or nanorods have focused much attention due to their multifunctionality in optoelectronic devices, gas sensing, piezoelectricity and thin film transistors for transparent and flexible electronics. Solution-phase chemical synthesis of nanomaterials has several important advantages, as low temperatures, high versatility, low cost, simple equipments and handling. The paper presents the chemical bath deposition synthesis and characterization of ZnO 1D nanostructures grown on glass substrates seeded with gold layer, pre-prepared ZnO nanoparticles or sol–gel derived ZnO layer. The obtained ZnO nanowires/nanorods were structurally and morphologically characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and the growth mechanism is discussed. The seed layer significantly affects the surface distribution and orientation of the grown 1D nanostructures. The diameter of the nanowires is mainly controlled by the concentration and temperature of the growth solution. The effect of growth conditions on the surface chemical composition and surface states/defects of semiconducting 1D nanostructures was investigated using X-ray photoelectron spectroscopy. The optical and electrical properties are presented. [Copyright &y& Elsevier]

During the last years, oxide semiconductors have shown that they will have a key role in the future of electronics. In fact, several research groups have already presented working devices with remarkable electrical and optical properties based on these materials, mainly thin-film transistors (TFTs). Most of these TFTs use indium-tin oxide (ITO) as the material for source/drain electrodes. This paper focuses on the investigation of different materials to replace ITO in inverted-staggered TFTs based on gallium-indium-zinc oxide (GIZO) semiconductor. The analyzed electrode materials were indium-zinc oxide, Ti, Al, Mo, and Ti/Au, with each of these materials used in two different kinds of devices: one was annealed after GIZO channel deposition but prior to source/drain deposition, and the other was annealed at the end of device production. The results show an improvement on the electrical properties when the annealing is performed at the end (for instance, with Ti/Au electrodes, mobility rises from 19 to 25 cm²/V · s, and turn-on voltage drops from 4 to 2 V). Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we could confirm that some diffusion exists in the source/drain electrodes/semiconductor interface, which is in close agreement with the obtained electrical properties. In addition to TOF-SIMS results for relevant elements, electrical characterization is presented for each kind of device, including the extraction of source/ drain series resistances and TFT intrinsic parameters, such as μi (intrinsic mobility) and VTi (intrinsic threshold voltage). [ABSTRACT FROM AUTHOR]

In this paper, we present the preliminary results concerning the deposition of highly transparent and conductive gallium-doped zinc oxide (GZO) deposited on transparent flexible substrate based on cellulose derivatives. Prior to the deposition of the GZO film, the surface of the polymer have been coated with a thin silicon dioxide (SiO2) layer deposited by thermal evaporation assisted by an electron gun. By doing this surface treatment, we succeeded in depositing highly conductive and transparent GZO with an electrical resistivity of 2.0×10−3 Ω cm and an average optical transmittance in the visible part of the spectrum (400–700 nm) of 70% by r.f. magnetron sputtering at room temperature. Besides the optoelectronic properties, the films are mechanically stable with a polycrystalline structure with a strong preferred (002) orientation, parallel to the substrate. [Copyright &y& Elsevier]

In this paper, we present results concerning the thickness dependence (from 70 to 890 nm) of electrical, structural, morphological and optical properties presented by gallium-doped zinc oxide (GZO) deposited on polyethylene naphthalate (PEN) substrates by r.f. magnetron sputtering at room temperature. For thicknesses higher than 300 nm an independent correlation between the electrical, morphological, structural and optical properties are observed. The lowest resistivity obtained was 5×10−4 Ω cm with a sheet resistance of 15 Ω/□ and an average optical transmittance in the visible part of the spectra of 80%. It is also shown that by passivating the surface of the polymer by depositing a thin silicon dioxide layer the electrical and structural properties of the films are improved nearly by a factor of two. [Copyright &y& Elsevier]

Gallium-doped zinc oxide films were prepared by r.f. magnetron sputtering at room temperature as a function of the substrate–target distance. The best results were obtained for a distance of 10 cm, where a resistivity as low as 2.7×10−4 Ω cm, a Hall mobility of 18 cm2/Vs and a carrier concentration of 1.3×1021 cm−3 were achieved. The films are polycrystalline presenting a strong crystallographic c-axis orientation (002) perpendicular to the substrate. The films present an overall transmittance in the visible part of the spectra of approximately 85%, on average. [Copyright &y& Elsevier]

The fabrication of low-cost, flexible, and recyclable electronic devices has been the focus of many research groups, particularly for integration in wearable technology and the Internet of Things (IoT). In this work, porous zinc oxide (ZnO) nanostructures are incorporated as a UV sensing material into the composition of a sustainable water-based screen-printable ink composed of carboxymethyl cellulose (CMC). The formulated ink is used to fabricate flexible and foldable UV sensors on ubiquitous office paper. The screen-printed CMC/ZnO UV sensors operate under low voltage (≤2 V) and reveal a stable response over several on/off cycles of UV light exposure. The devices reach a response current of 1.34 ± 0.15 mA and a rise and fall time of 8.2 ± 1.0 and 22.0 ± 2.3 s, respectively. The responsivity of the sensor is 432 ± 48 mA W−1, which is the highest value reported in the literature for ZnO-based UV sensors on paper substrates. The UV-responsive devices display impressive mechanical endurance under folding, showing a decrease in responsivity of only 21% after being folded 1000 times. Their low-voltage operation and extreme folding stability indicate a bright future for low-cost and sustainable flexible electronics, showing potential for low-power wearable applications and smart packaging. [ABSTRACT FROM AUTHOR]

The degradation of organic pollutants in wastewaters assisted by oxide semiconductor nanostructures has been the focus of many research groups over the last decades, along with the synthesis of these nanomaterials by simple, eco-friendly, fast, and cost-effective processes. In this work, porous zinc oxide (ZnO) nanostructures were successfully synthesized via a microwave hydrothermal process. A layered zinc hydroxide carbonate (LZHC) precursor was obtained after 15 min of synthesis and submitted to different calcination temperatures to convert it into porous ZnO nanostructures. The influence of the calcination temperature (300, 500, and 700 °C) on the morphological, structural, and optical properties of the ZnO nanostructureswas investigated. All ZnO samples were tested as photocatalysts in the degradation of rhodamine B (RhB) under UV irradiation and natural sunlight. All samples showed enhanced photocatalytic activity under both light sources, with RhB being practically degraded within 60 min in both situations. The porous ZnO obtained at 700 °C showed the greatest photocatalytic activity due to its high crystallinity, with a degradation rate of 0.091 and 0.084 min−1 for UV light and sunlight, respectively. These results are a very important step towards the use of oxide semiconductors in the degradation of water pollutants mediated by natural sunlight. [ABSTRACT FROM AUTHOR]

The interest in advanced photocatalytic technologies with metal oxide-based nanomaterials has been growing exponentially over the years due to their green and sustainable characteristics. Photocatalysis has been employed in several applications ranging from the degradation of pollutants to water splitting, CO2 and N2 reductions, and microorganism inactivation. However, to maintain its eco-friendly aspect, new solutions must be identified to ensure sustainability. One alternative is creating an enhanced photocatalytic paper by introducing cellulose-based materials to the process. Paper can participate as a substrate for the metal oxides, but it can also form composites or membranes, and it adds a valuable contribution as it is environmentally friendly, low-cost, flexible, recyclable, lightweight, and earth abundant. In term of photocatalysts, the use of metal oxides is widely spread, mostly since these materials display enhanced photocatalytic activities, allied to their chemical stability, non-toxicity, and earth abundance, despite being inexpensive and compatible with low-cost wet-chemical synthesis routes. This manuscript extensively reviews the recent developments of using photocatalytic papers with nanostructured metal oxides for environmental remediation. It focuses on titanium dioxide (TiO2) and zinc oxide (ZnO) in the form of nanostructures or thin films. It discusses the main characteristics of metal oxides and correlates them to their photocatalytic activity. The role of cellulose-based materials on the systems' photocatalytic performance is extensively discussed, and the future perspective for photocatalytic papers is highlighted. [ABSTRACT FROM AUTHOR]

Low-cost and large-scale production techniques for flexible electronics have evolved greatly in recent years, having great impact in applications such as wearable technology and the internet of things. In this work, we demonstrate fully screen-printed UV photodetectors, successfully fabricated at a low temperature on a cork substrate, using as the active layer a mixture of zinc oxide nanoparticles and ethylcellulose. The photoresponse under irradiation with a UV lamp with peak emission at 302 nm exhibited a quasi-quadratic behavior directly proportional to the applied voltage, with a photocurrent of about 5.5 and 20 μA when applying 1.5 V and 5 V, respectively. The dark current stayed below 150 nA, while the rise and falling times were, respectively, below 5 and 2 s for both applied voltages. The performance was stable over continuous operation and showed a degradation of only 9% after 100 bending cycles in a 45 mm radius test cylinder. These are promising results regarding the use of this type of sensor in wearable applications such as cork hats, bracelets, or bags. [ABSTRACT FROM AUTHOR]

Fully printed and flexible inorganic electrolyte gated transistors (EGTs) on paper with a channel layer based on an interconnected zinc oxide (ZnO) nanoparticle matrix are reported in this work. The required rheological properties and good layer formation after printing are obtained using an eco-friendly binder such as ethyl cellulose (EC) to disperse the ZnO nanoparticles. Fully printed devices on glass substrates using a composite solid polymer electrolyte as gate dielectric exhibit saturation mobility above 5 cm2 V−1 s−1 after annealing at 350 °C. Proper optimization of the nanoparticle content in the ink allows for the formation of a ZnO channel layer at a maximum annealing temperature of 150 °C, compatible with paper substrates. These devices show low operation voltages, with a subthreshold slope of 0.21 V dec−1, a turn on voltage of 1.90 V, a saturation mobility of 0.07 cm2 V−1 s−1 and an Ion/Ioff ratio of more than three orders of magnitude. [ABSTRACT FROM AUTHOR]

Transport properties of photo-induced charge carriers through different grains in the polycrystalline photovoltaic devices strongly depend on the microstructural pattern of the active layers. Therefore, photocurrent mapping with nanoscale resolution is important to know about the electrical responses of the different grains in the polycrystalline photovoltaic devices. Here, we have used photoconductive atomic force microscopy for mapping the photocurrent with nanoscale resolution of two types of ZnO nanorods/Cu 2 O based solar cells. The morphology and current have been measured simultaneously with nanoscale resolution from the top surfaces of the devices at different applied voltages. It is demonstrated that the nanostructure of the active layers is one of the most important variables determining device performances. Different local photovoltaic performances have been observed from these two devices due to various microstructural and electrical phenomena of their seed layers. On the other hand, significant variations in short-circuit current have been observed from different grains of the devices which appeared more alike in the micrograph owing to various transport properties of photocarriers. It is observed that the grain boundaries are more preferable for charge collection over the grain interiors. It shows a higher short circuit current close to the boundary than the grain inside. This study illustrates an important area for future fundamental research to enhance the performances of the polycrystalline photovoltaic devices through better control of morphology and improving the inherent properties of the active layers. [ABSTRACT FROM AUTHOR]

Ultrasonic spray pyrolysis deposition of ZnO-based materials offers an attractive high-throughput low-cost route towards industrial production of high-quality transparent conductive oxide (TCO) thin-films. In this work, undoped and aluminium-doped ZnO films have been grown employing ultrasonic spray pyrolysis at relatively low-temperate (300 °C), followed by a post-annealing treatment. The role of Al concentration in the starting solution, as well as the rapid thermal annealing (RTA) atmosphere, were investigated and correlated to the morphological, structural, electrical and optical properties of the films. The remarkable enhancement of electrical conductivity attained here is mainly ascribed to the combined effects of: (1) homogenous incorporation of Al 3+ into the ZnO matrix, which enhances crystal quality providing higher electronic mobility; and (2) the RTA which releases the localized electrons caused by oxygen absorption and thereby increases the free carrier density. Under optimum deposition conditions, a low resistivity and a high optical transmittance around 4 × 10 −3 Ω cm and 87%, respectively, were obtained. The application of the RTA post-process after low temperature growth has several advantages relative to the direct growth at high temperature (usually 400–575 °C), such as shorter growth time and lower cost associated to the spray pyrolysis equipment requirements and usage. The results suggest that the electrical and optical properties of the ZnO:Al films can be further improved for solar cell applications by controlling the temperature of the post-deposition annealing in reducing atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: Emulsion detonation synthesis method was used to produce undoped and Al-doped ZnO nanostructured powders (0.5–2.0wt.% Al2O3). The synthesized powders present a controlled composition and a morphology which is independent on the doping level. The XRD results indicate wurtzite as the single phase for undoped ZnO and the presence of gahnite as secondary phase for Al-doped ZnO powders. The sintering behavior of each powder was studied based on their linear shrinkage and shrinkage rate curves, showing the high sinterability of the powders. Activation energies for densification in the earlier stage were calculated for all compositions and possible sintering mechanisms are suggested depending on the doping level. The high chemical homogeneity and sinterability and the lower electrical resistivity of the bulk Al-doped sintered samples demonstrates the feasibility of emulsion detonation synthesis for the production of high quality Al-doped ZnO powders to be used in ceramic sputtering targets manufacture. [Copyright &y& Elsevier]

Abstract: This work reports the production of ceramic targets based on nanostructured Al-doped ZnO (AZO) powders for sputtering applications. The nanostructured powder is obtained by a new patented process based on the detonation of an emulsion containing both Zn and Al metal precursors in the final proportion of 98:2wt% (ZnO:Al2O3), through which the Al contains is highly uniform distributed over ZnO. Due to the nanostructured powder characteristics, the targets can be sintered at substantially lower temperatures (1150–1250°C) by conventional sintering, contributing to production costs reduction of ceramic targets and consequently the costs of photovoltaic and displays industries. Electrical resistivity values around 3.0–7.0×10−3 Ωcm have been obtained depending on final microstructure of the targets. The electro-optical properties of the films produced at room temperature with thicknesses around 360nm, besides being highly uniform exhibit a resistivity of about 1×10−3 Ωcm and a transmittance in the visible range above 90%. [Copyright &y& Elsevier]

Abstract: The influence of doping on the morphology, physical and electrical properties of zinc oxide produced by the sol-gel method was examined. Undoped zinc oxide was observed to form relatively porous films. Addition of an Al dopant influenced the sheet resistance, but did not result in a change in morphology, examined by atomic force microscopy when compared to undoped films. In the case of electrical measurements, undoped ZnO films were extremely resistive. A minimum dopant concentration of 2at.%. Al was required to produce materials which were more conductive, as observed by sheet resistance measurements, which were shown to vary with annealing temperature. The versatile nature of sol-gel processing was demonstrated by selective ink-jet deposition of sol-gel droplets which were annealed to form oxide materials. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) has attracted recent interest for a range of applications, including use as a transparent conductive oxide (TCO) and in gas sensor devices. This paper compares ZnO films grown using two methods designed for the production of thin films, namely sol–gel and aerosol assisted chemical vapour deposition (AACVD) for potential use in sensor and TCO applications. Materials produced by the sol–gel route were observed to be amorphous when annealed at 350°C, but were crystalline when annealed at higher temperatures and had a relatively open grain structure when compared to the AACVD films. Electrical characterization showed that materials were highly resistive, but that their properties varied considerably when the measurements were performed in vacuum or in air. This behaviour was rapidly reversible and reproducible for room temperature measurement. In contrast materials grown by aerosol-assisted CVD were non-porous, polycrystalline and conductive. Measured electrical properties did not vary with changing measurement atmosphere. These differences are discussed in terms of the structural characterisation of the films and some comments are made regarding the suitability of both approaches for the growth of ZnO thin film sensor materials. [Copyright &y& Elsevier]