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In this paper, we report on the gas sensing properties of mixed oxide Zn-Cu nanostructures obtained by self-organized chemical deposition are presented. The nanosensors are made from individual ZnO whiskers and are coated with CuO/Cu2O. They exhibit selectivity towards H2 and NH3 over other tested gases. Measurements were made in the temperature range between 20 - 175 oC. In order to determine the crystalline phases of the studied nanostructures, XRD diffractogram was measured, and SEM images were obtained for the morphological analysis.

In this work it was investigated the reliability to ionizing radiation of Eu-doped ZnO nanostructured films functionalized with Pd. Morphological, sensorial and electrical properties of sensors were studied initially, after irradiation and after 6 months to observe the influence of irradiation.

Dielectric materials are of great interest in a vast amount of applications ranging from cable insulation to advanced electronic devices. The emerging trend of device miniaturization is creating an increased demand for dielectric thin films that can be produced precisely on the nanometer scale. In addition, special mechanical properties are often required, for example in the field of flexible organic electronics. Polymers are first-choice materials for this purpose. However, it is extremely difficult to produce precise nanoscale thin films, which have a low defect density and are free of e.g. residual solvent, by wet chemistry approaches. Initiated chemical vapor deposition (iCVD) is a solvent-free polymer thin film deposition process which can be used to produce high quality dielectric thin films with nanoscale control and circumvents thus these problems. This work demonstrates the versatility of the iCVD process in the field of electrical applications by some new application examples of iCVD. By adding e.g. a hydrophobic organosiloxane thin film on columnar zinc oxide (ZnO:Fe) gas sensing structures there was a change in the selectivity from ethanol to hydrogen, as well as improved performance at high humidity level. The modified sensors can thus be used in humid ambient, especially for breathing tests, which can lead to the diagnosis of some diseases by cutting edge non-invasive approaches.

TiO2/Cu2O/CuO multi-nanolayers highly sensitive toward volatile organic compounds (VOCs) and H2 have been grown in various thicknesses by a cost-effective and reproducible combined spray-sputtering-annealing approach. The ultrathin TiO2 films were deposited by spray pyrolysis on top of sputtered-annealed Cu2O/CuO nanolayers to enhance their gas sensing performance and improve their protection against corrosion at high operating temperatures. The prepared heterostructures were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet visible (UV-vis) and micro-Raman spectroscopy. The gas sensing properties were measured at several operating temperatures, where the nanolayered sensors with oxide thicknesses between 20 and 30 nm (Cu2O/CuO nanolayers) exhibited a high response and an excellent selectivity to ethanol vapor after thermal annealing the samples at 420 °C. The results obtained at an operating temperature of 350 °C demonstrate that the CuO/Cu2O nanolayers with thicknesses between 20 and 30 nm are sensitive mainly to ethanol vapor, with a response of ∼150. The response changes from ethanol vapors to hydrogen gas as the thickness of the CuO/Cu2O nanolayers changes from 50 to 20 nm. Density functional theory-based calculations were carried out for the geometries of the CuO(1¯ 11)/Cu2O(111) and TiO2(111)/CuO(1¯ 11)/Cu2O(111) heterostructures and their sensing mechanism toward alcohols of different chain lengths and molecular hydrogen. The reconstructed hexagonal Cu2O(111) surface and the reconstructed monoclinic CuO(1¯ 11) and TiO2(111) facets, all of which terminate in an O layer, lead to the lowest surface energies for each isolated material. We studied the formation of the binary and ternary heteroepitaxial interfaces for the surface planes with the best-matching lattices. Despite the impact of the Cu2O(111) substrate in lowering the atomic charges of the CuO(1¯ 11) adlayer in the binary sensor, we found that it is the different surface structures of the CuO(1¯ 11)/Cu2O(111) and TiO2(111)/CuO(1¯ 11)/Cu2O(111) devices that are fundamental in driving the change in the sensitivity response observed experimentally. The experimental data, supported by the computational results, are important in understanding the use of the multi-nanolayered films tested in this work as reliable, accurate, and selective sensor structures for the tracking of gases at low concentrations.

A comparative investigation of the post-electroplating treatment influence on the gas detecting performances of single ZnO nanorod/nanowire (NR/NW), as grown by electrochemical deposition (ECD) and integrated into nanosensor devices, is presented. In this work, hydrothermal treatment (HT) in a H2O steam and conventional thermal annealing (CTA) in a furnace at 150 °C in ambient were used as post-growth treatments to improve the material properties. Herein, the morphological, optical, chemical, structural, vibrational, and gas sensing performances of the as-electrodeposited and treated specimens are investigated and presented in detail. By varying the growth temperature and type of post-growth treatment, the morphology is maintained, whereas the optical and structural properties show increased sample crystallization. It is shown that HT in H2O vapors affects the optical and vibrational properties of the material. After investigation of nanodevices based on single ZnO NR/NWs, it was observed that higher temperature during the synthesis results in a higher gas response to H2 gas within the investigated operating temperature range from 25 to 150 °C. CTA and HT or autoclave treatment showed the capability of a further increase in gas response of the prepared sensors by a factor of ∼8. Density functional theory calculations reveal structural and electronic band changes in ZnO surfaces as a result of strong interaction with H2 gas molecules. Our results demonstrate that high-performance devices can be obtained with high-crystallinity NWs/NRs after HT. The obtained devices could be the key element for flexible nanoelectronics and wearable electronics and have attracted great interest due to their unique specifications.

Monitoring volatile organic compounds (VOCs) in harsh environments, especially for safety applications, is a growing field that requires specialized sensor structures. In this work, we demonstrate the sensing properties toward the most common VOCs of columnar Al

In this study, a strategy to prepare CuO/Cu2O/Cu microwires that are fully covered by a nanowire (NW) network using a simple thermal-oxidation process is developed. The CuO/Cu2O/Cu microwires are fixed on Au/Cr pads with Cu microparticles. After thermal annealing at 425 °C, these CuO/Cu2O/Cu microwires are used as room-temperature 2-propanol sensors. These sensors show different dominating gas responses with operating temperatures, e.g., higher sensitivity to ethanol at 175 °C, higher sensitivity to 2-propanol at room temperature and 225 °C, and higher sensitivity to hydrogen gas at ∼300 °C. In this context, we propose the sensing mechanism of this three-in-one sensor based on CuO/Cu2O/Cu. X-ray diffraction (XRD) studies reveal that the annealing time during oxidation affects the chemical appearance of the sensor, while the intensity of reflections proves that for samples oxidized at 425 °C for 1 h the dominating phase is Cu2O, whereas upon further increasing the annealing duration up to 5 h, the CuO phase becomes dominant. The crystal structures of the Cu2O-shell/Cu-core and the CuO NW networks on the surface were confirmed with a transmission electron microscope (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED), where (HR)TEM micrographs reveal the monoclinic CuO phase. Density functional theory (DFT) calculations bring valuable inputs to the interactions of the different gas molecules with the most stable top surface of CuO, revealing strong binding, electronic band-gap changes, and charge transfer due to the gas molecule interactions with the top surface. This research shows the importance of the nonplanar CuO/Cu2O layered heterostructure as a bright nanomaterial for the detection of various gases, controlled by the working temperature, and the insight presented here will be of significant value in the fabrication of new p-type sensing devices through simple nanotechnology.

For a fast and reliable monitoring of hazardous environments, the discrimination and detection of volatile organic compounds (VOCs) in the low ppm range is critically important, which requires the development of new chemical sensors. We report herein, a novel approach to tailor the selectivity of nanocomposite thin film sensors by investigating systematically the effect of surface decoration of Ag-doped ZnO (ZnO:Ag) columnar thin films. We have used AgPt and AgAu noble bimetallic alloy nanoparticles (NPs) to decorate the surfaces of ZnO:Ag and we have measured their resulting gas sensing properties towards VOC vapors and hydrogen gas. The gas response of the nanocomposite containing AgAu NPs to 100 ppm of ethanol, acetone, n-butanol, 2-propanol and methanol vapors was increased on average by a factor of 4 compared to the pristine ZnO:Ag columnar films. However, decoration with AgPt NPs led to a considerable reduction of the gas response to all VOC vapors and an increase of the response to H2 gas by roughly one order of magnitude, indicating a possible route to tailor the selectivity by surface decoration. As such, the reported NP-decorated ZnO:Ag thin film sensors should be suitable for the detection of H2 in Li-ion batteries, which is an early indication of the thermal runaway that leads to complete battery failure and possible explosion. To understand the impact of NP surface decoration on the gas sensing properties of ZnO:Ag thin films, we have employed density functional theory calculations with on-site Coulomb corrections and long-range dispersion interactions (DFT+U–D3-(BJ)) to investigate the adsorption of various VOC molecules and hydrogen onto the Ag-doped and NP-decorated (10[1 with combining macron]0) surface of zinc oxide ZnO. The calculated surface free energies indicate that Ag5Au5/ZnO(10[1 with combining macron]0):Ag is the most favourable system for the detection of VOCs, which based on its work function is also the most reactive towards these species. Our calculated adsorption energies show that Ag9Pt/ZnO(10[1 with combining macron]0):Ag has the largest preference for H2 gas and the lowest preference for the organic adsorbates, which is in line with the high selectivity of AgPt/ZnO:Ag sensors towards the hydrogen molecule observed in our experiments.

Metal oxide gas sensors are of great interest for applications ranging from lambda sensors to early hazard detection in explosive media and leakage detection due to their superior properties with regard to sensitivity and lifetime, as well as their low cost and portability. However, the influence of ambient gases on the gas response, energy consumption and selectivity still needs to be improved and they are thus the subject of intensive research. In this work, a simple approach is presented to modify and increase the selectivity of gas sensing structures with an ultrathin polymer thin film. The different gas sensing surfaces, CuO, Al2O3/CuO and TiO2 are coated with a conformal < 30 nm Poly(1,3,5,7-tetramethyl-tetravinyl cyclotetrasiloxane) (PV4D4) thin film via solvent-free initiated chemical vapor deposition (iCVD). The obtained structures demonstrate a change in selectivity from ethanol vapor to 2-propanol vapor and an increase in selectivity compared to other vapors of volatile organic compounds. In the case of TiO2 structures coated with a PV4D4 thin film, the increase in selectivity to 2-propanol vapors is observed even at relatively low operating temperatures, starting from >200 °C. The present study demonstrates possibilities for improving the properties of metal oxide gas sensors, which is very important in applications in fields such as medicine, security and food safety.

Lithium-ion batteries (LIBs) still need continuous safety monitoring based on their intrinsic properties, as well as due to the increase in their sizes and device requirements. The main causes of fires and explosions in LIBs are heat leakage and the presence of highly inflammable components. Therefore, it is necessary to improve the safety of the batteries by preventing the generation of these gases and/or their early detection with sensors. The improvement of such safety sensors requires new approaches in their manufacturing. There is a growing role for research of nanostructured sensor’s durability in the field of ionizing radiation that also can induce structural changes in the LIB’s component materials, thus contributing to the elucidation of fundamental physicochemical processes, catalytic reactions or inhibitions of the chemical reactions on which the work of the sensors is based. A current method widely used in various fields, Direct Ink Writing (DIW), has been used to manufacture heterostructures of Al2O3/CuO and CuO:Fe2O3, followed by an additional ALD and thermal annealing step. The detection properties of these 3D-DIW printed heterostructures showed responses to 1,3-dioxolan (DOL), 1,2-dimethoxyethane (DME) vapors, as well as to typically used LIB electrolytes containing LiTFSI and LiNO3 salts in a mixture of DOL:DME, as well also to LiPF6 salts in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) at operating temperatures of 200 °C–350 °C with relatively high responses. The combination of the possibility to detect electrolyte vapors used in LIBs and size control by the 3D-DIW printing method makes these heterostructures extremely attractive in controlling the safety of batteries.

The gas sensing properties of heterojunctions based on binary and ternary metal oxides (CuAl 2 O 4 /Al 2 O 3 /CuO/Cu 2 O, ZnAl 2 O 4 /ZnO and Zn 2 SnO 4 ) were investigated in detail and demonstrated excellent sensitivity and selectivity to a series of gases and volatile organic compounds (VOCs), such as H 2 , CO and ethanol. The dynamic measurements showed excellent response stability at low and high relative humidity, which is very important for applications like diseases detection by breath analysis.

Nanosensors and microsensors are important for environmental and biomedical monitoring due to their extraordinary properties. In this work sensor devices are fabricated for the detection of H 2 gas and ethanol vapors. These devices are based on ZnO single nanowires, heterostructures composed of TiO 2 /ZnO columns doped with Cd, as well as TiO 2 /CuO:Ni, Ag and on a functionalization with Pd and other noble nanodots.

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Rapid detection and fast response of nanoelectronic devices based on semiconducting oxides is nowadays a modern and stringent subject of research. Device performances depend mainly on the morphologies of the metal oxide nanostructures. In the scope of this work, the influence of the structural morphology of three-dimensional (3-D) ZnO nano- and microstructured networks on the room temperature UV detection properties is studied in detail. We show that the formation of multiple potential barriers between the nanostructures, as well as the diameter of the nanostructures, which is in the same order of magnitude as the Debye length, strongly influence the UV sensing properties. Consequently, 3-D ZnO networks consisting of interconnected ultra-long wire-like tips (up to 10 μm) and with small wire diameters of 50–150 nm, demonstrated the highest UV sensing performances (UV response ratio of ∼3100 at 5 V applied bias voltage). Furthermore, we demonstrate the possibility of substantially increasing the UV sensing performances of individual ZnO nanowire (NW) (diameter of ∼50 nm) by surface functionalization with carbon nanotubes (CNTs), showing high response ratio (∼60–50 mW/cm2), as well as fast response (∼1 s) and recovery (∼1 s) times. The obtained results thus provide a platform with respect to the next generation of portable UV radiation detectors based on semiconducting oxide networks.

Nanomaterials for highly selective and sensitive sensors toward specific gas molecules of volatile organic compounds (VOCs) are most important in developing new-generation of detector devices, for example, for biomarkers of diseases as well as for continuous air quality monitoring. Here, we present an innovative preparation approach for engineering sensors, which allow for full control of the dopant concentrations and the nanoparticles functionalization of columnar material surfaces. The main outcome of this powerful design concept lies in fine-tuning the reactivity of the sensor surfaces toward the VOCs of interest. First, nanocolumnar and well-distributed Ag-doped zinc oxide (ZnO:Ag) thin films are synthesized from chemical solution, and, at a second stage, noble nanoparticles of the required size are deposited using a gas aggregation source, ensuring that no percolating paths are formed between them. Typical samples that were investigated are Ag-doped and Ag nanoparticle-functionalized ZnO:Ag nanocolumnar films. The highest responses to VOCs, in particular to (CH3)2CHOH, were obtained at a low operating temperature (250 °C) for the samples synergistically enhanced with dopants and nanoparticles simultaneously. In addition, the response times, particularly the recovery times, are greatly reduced for the fully modified nanocolumnar thin films for a wide range of operating temperatures. The adsorption of propanol, acetone, methane, and hydrogen at various surface sites of the Ag-doped Ag8/ZnO(0001) surface has been examined with the density functional theory (DFT) calculations to understand the preference for organic compounds and to confirm experimental results. The response of the synergistically enhanced sensors to gas molecules containing certain functional groups is in excellent agreement with density functional theory calculations performed in this work too. This new fabrication strategy can underpin the next generation of advanced materials for gas sensing applications and prevent VOC levels that are hazardous to human health and can cause environmental damages.

In this work, the one-step three-dimensional (3D) printing of 20 nm nanowire (NW)-covered CuO/Cu2O/Cu microparticles (MPs) with diameters of 15-25 μm on the surface of the glass substrate forming an ordered net is successfully reported for the first time. 3D-printed Cu MP-based stripes formed nonplanar CuO/Cu2O/Cu heterojunctions after thermal annealing at 425 °C for 2 h in air and were fully covered with a 20 nm NW net bridging MPs with external Au contacts. The morphological, vibrational, chemical, and structural investigations were performed in detail, showing the high crystallinity of the NWs and 3D-printed CuO/Cu2O/Cu heterojunction lines, as well as the growth of CuO NWs on the surface of MPs. The gas-sensing measurements showed excellent selectivity to acetone vapor at an operating temperature of 350 °C with a high gas response about 150% to 100 ppm. The combination of the possibility of fast acetone vapor detection, low power consumption, and controllable size and geometry makes these 3D-printed devices ideal candidates for fast detection, as well as for acetone vapor monitoring (down to 100 ppm). This 3D-printing approach will pave a new way for many different devices through the simplicity and versatility of the fabrication method for the exact detection of acetone vapors in various atmospheres.

A comparative investigation of the post-electroplating treatment influence on the gas detecting performances of single ZnO nanorod/nanowire (NR/NW), as grown by electrochemical deposition (ECD) and integrated into nanosensor devices, is presented. In this work, hydrothermal treatment (HT) in a H

In this work, the β-Ga2O3 nanostructures were obtained by thermal annealing in air of β-Ga2S3 single crystals at relatively high temperatures of 970 K, 1070 K and 1170 K for 6 h. The structural, morphological, chemical and optical properties of β-Ga2O3–β-Ga2S3 layered composites grown at different temperatures were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) as well as photoluminescence spectroscopy (PL) and Raman spectroscopy. The results show that the properties of obtained β-Ga2O3–β-Ga2S3 composites were strongly influenced by the thermal annealing temperature. The XRD and Raman analyses confirmed the high crystalline quality of the formed β-Ga2O3 nanostructures. The absorption edge of the oxide is due to direct optical transitions. The optical bandwidth was estimated to be approximately 4.34-4.41 eV, depending on the annealing temperature. Annealing of the β-Ga2S3 monocrystals at a higher temperature of 1170 K showed the complete conversion of the surface to β-Ga2O3. These results demonstrate the possibility to grow high quality β-Ga2O3–β-Ga2S3 layered composites and β-Ga2O3 nanostructures in large quantities for various applications such as gas sensing, non-toxic biomedical imaging, nonlinear optical, as well as power device applications. Micro and nanocrystallites present on the surface of the Ga2O3 layer contribute to a diffusion of the incident light which leads to an increase of the absorption rate allowing thus to reduce the thickness of the Ga2O3 layer, in which the generation of unbalanced charge carriers takes place. By decreasing the Ga2O3 layer thickness in such layered composites, the efficiency of photovoltaic cells based on such junctions can be increased.

International audience; Herein, the room temperature gas sensing properties of a device fabricatedbased on an individual gold nanoparticles (AuNPs)-functionalized zinc oxide nanowire (ZnO NW) is reported. The Au-NPs/ZnO nanowires were depositedusing theelectrochemical approachin a classical three-electrode electrochemical cell. The dual beam focused ion beam/scanning electron microscopy (FIB/SEM) was usedto integrate the singlenanostructuresinto gas sensing nanodevices.The results are promising for futureapplications in monitoring H2gas for health care applications and clinical breath analysis.

In this study, a strategy to prepare CuO/Cu

International audience; In this work, an individual nanowire of zinc oxide (ZnO-NW), decorated with gold nanoparticles (Au-NPs/ZnO-NW), was integrated in a nanophotodetector using a dual beam focused electron/ion beam (FIB/SEM) system. Au-NPs/ZnO-NW arrays were synthesized by one-step electrochemical deposition at relative low-temperatures (90 °C). The nanodevice fabricated with a single nanowire Au-NPs/ZnO-NW demonstrated fast detection of UV radiation up to the operating temperature of 120 ºC. The improved UV sensing properties of an individual Au-NPs/ZnO-NW compared to a single, undecorated, ZnO NW was explained based on the formation of Schottky barriers at the Au/ZnO NW interface, which resulted in a much more narrowed conduction channel and a lower dark current. These results prove that high-performance hybrid nanomaterials may possess superior electrical, optical and sensing properties and are of great interest for further fundamental studies.

Gas sensors are demanded in many different application fields. Especially the ever-growing field of batteries creates a great need for early hazard detection by gas sensors. Metal oxides are well known for gas sensing; however, moisture continues to be a major problem for the sensors, especially for the application in battery systems. This study reports on a new type of moisture protected gas sensor, which is capable to solve this problem. Sensitive nano-materials of CuO/Cu2O/ZnO:Fe heterostructures are grown and subsequently coated with an ultrathin hydrophobic cyclosiloxane-polymer film via initiated chemical vapor deposition to protect the sensor from moisture. The monomer 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane is combined with the initiator perfluorobutanesulfonyl fluoride to obtain hydrophobic properties. Surface chemistry, film formation and preservation of functional groups are confirmed by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. It turns out that the hydrophobicity is retained even after annealing at 400 °C, which is ideal for gas sensing. Molecular distances in the polymer nanolayer are estimated by geometry optimization via MMFF94 followed by density functional theory. Compared with unprotected CuO/Cu2O/ZnO:Fe, the coated CuO/Cu2O/ZnO:Fe exhibit a much better sensing performance at a higher relative humidity, as well as tunability of the gas selectivity. This is highly beneficial for hazard detection in case of thermal runaway in batteries because the sensors can be used under high concentrations of relative humidity, which is ideal for Li–S battery applications.

The massive application requests for high-performance sensors indicate on the importance of precise controlling of the semiconducting oxide characteristics. The sensor longevity needed for the remote areas in harsh environments is mandatory and can benefit greatly from self-cleaning abilities. To serve this demand, we present in our work ultra-thin TiO2 films deposited with different thicknesses down to 15 nm on glass substrates using atomic layer deposition (ALD). The morphological, chemical, topographic, electronic and chemical properties of the fabricated films were investigated in detail, showing the presence of the anatase phase. As it is known by the literature, the UV and gas sensing properties are highly dependent on the thickness of the films, however fully reversible and capable of long term detection. Thinner films (15 nm) showed higher UV and gas sensing performances than thicker films (45 nm), which was related to the film thickness comparable to the Debye length. Further improvement in the UV sensing properties was achieved by surface functionalization of TiO2 films with Au nanoparticles. The UV response increased by about one order of magnitude after the surface functionalization with Au nanoclusters/nanoparticles. All TiO2 ultra-thin films demonstrated good selectivity to hydrogen gas, independent of the thickness. The samples with 15 nm thickness showed a response of ~ 600% to 100 ppm of H2 at 250 °C operating temperature. The presented study demonstrates the importance of the film thickness and surface functionalization with noble metals nanoclusters for sensing applications of ultra-thin TiO2 layers. Such ultra-thin films could be used for the development of a series of integrated detectors and chemical field effect transistors (chemFETs) directly on highly complex chips.

The structural morphology of metal oxide nano- and microstructures plays a crucial role in the performances of sensors and especially of nanosensors. Here, a simple approach on the synthesis of three-dimensional (3D) highly porous ZnO nano- and microstructure networks with four different arm morphologies in the same process is reported. Systematic studies about the growth of micro- and nanotetrapods were performed and the corresponding mechanism has been discussed in detail. The difference in the morphologies of the obtained structures was understood on the basis of synthesis temperature variations, content of Zn vapor and oxygen in the furnace at different locations, which result in different growth rates along the ZnO c-axis. The approach developed in this work gives the possibility to simultaneously grow the interconnected networks of nano-ZnO-tetrapods (T), ZnO-T, with complex arm morphologies, ZnO-T-nanosheets, and ZnO nanowires (NW)-T. The obtained free-standing network material was integrated in an electronic device for gas/vapor sensing investigations. The individual structures with different morphologies (NW with a diameter down to 30 nm, two interconnected NWs, microsheets, and nanotetrapods with a diameter of the arms in the range of 40–80 nm) were integrated into nanosensor devices in order to investigate the influence of the morphology on the electrical and gas sensing properties. The results showed higher (S ≈ 510–2500 ppm) ammonia vapor sensing properties of ZnO-T compared to ZnO-T-nanosheets and ZnO-NW-T, revealing the importance of nano-junctions in nano-sensor devices. The presented approach offers the possibility to understand the importance of exposed facets and junctions on the sensing properties of such nanostructures. These results offer new opportunities for further experimental and fundamental studies of oxide morphologies in the context of nanosensor applications for environmental monitoring.

Detection and differentiation of volatile organic compounds (VOC) is highly important since these gaseous pollutants degrade the air quality and represent, even in small amounts, a threat to human health. In this work, a simple and cost-effective method to synthesize a multilayered (CuO-Cu2O)/ZnO:Al nanostructured film forming non-planar heterojunctions for efficient detection of volatile organic compound vapors is presented. While the ZnO:Al layer with different contents of Al (∼0.1 and 0.2 at%) was deposited on a glass substrate via a synthesis from chemical solutions (SCS, at a temperature

In this work the gas sensing properties of nanosensors fabricated by a “bottom-up” approach in a FIB/SEM system based on a single Pd modified ZnO nanowire is investigated in detail. Synthesis, surface doping and functionalization of ZnO nanowires (NWs) with Pd (Pd/ZnO) in a one − step process were performed during electrochemical deposition. The influence of the diameter of the NW, the operating temperature and the humidity are studied in detail and corresponding sensing mechanisms are proposed. An increase in the gas response by a decrease of the NW diameter was observed. Also, by increasing the operating temperature to 200 °C an enhancement in the hydrogen gas response of about 3.5 times (from ≈400 to 1440 to 100 ppm) was obtained and was attributed to the increased catalytic properties of the Pd nanoparticles (NPs). However, long-term investigations revealed a lowered signal stability of the nanosensor operated at higher temperatures. Thus, one can conclude that operation at room temperature is more efficient for real applications, due to the higher reliability of the nanodevices. The presented results demonstrate the importance of nanosensor applications and their high flexibility. The very low current values in the passive regime (in the range of pA − nA) and a very small dimension of the device results in an ultra-low power consumption, which is a key aspect for battery powered handheld instruments.

Hybridization of micro- and nanostructures of semiconducting oxides is known to be an efficient way to greatly improve their sensing properties and photocatalytic activity. In this work, zinc oxide (ZnO) tetrapod (T) three-dimensional (3-D) highly porous networks were hybridized with MexOy and ZnxMe1-xOy compounds (Me = Sn, Fe, Bi, Cu or Al), and their ultraviolet (UV) sensing properties were investigated. Additionally, individual Al-doped ZnO-T (ZnO-T:Al) with different diameters were integrated into devices using a FIB/SEM system to study the influence of diameter on the UV sensing properties. ZnO-T−CuO hybrid networks demonstrated the highest increase in UV response (with about 2.5 times) and decrease in response and recovery time (τr1 = τr2 ≈ 0.03 s and τd1 = τd2 ≈ 0.045 s) compared to pristine ZnO-T networks before hybridization, which is quite promising for applications in fast optical communication. The ZnO-T−Zn2SnO4 hybrid networks showed only a slight increase in UV response while other types of hybrid networks showed a considerable decrease in UV response, especially in the case of ZnO-T−Bi2O3 hybrid networks, which could be attributed to the fast recombination of photoexcited electrons and holes in Bi2O3 under the UV light illumination. The results demonstrate that hybridization with p-type materials is more efficient due to higher photogenerated charge separation properties. In the case of individual structures the device based on a microwire with lower diameter showed higher stability and good repeatability with a relatively high UV response of about 5.5. The excellent UV sensing properties combined with ultra-low power consumption make such devices very attractive for real applications like portable UV dosimeters. This work demonstrated the high efficiency of ZnO-T hybridization with p-type metal oxides for improvement of UV sensing properties.

The present work demonstrates a very simple and unique strategy for efficient photocatalysis using ZnO ceramic nano- and microtetrapods synthesized by a flame transport synthesis approach. Due to their three-dimensional (3D) morphology, highly porous interconnected networks as flexible ceramics with sufficient mechanical strength can be easily fabricated and efficiently utilized in applications like e.g., photocatalysis, liquid filtering, and membranes. The photocatalytic response can be further enhanced by hybridization of the ZnO tetrapods with different metal oxides which has been explored in detail here. The Cu- and Bi- hybridized ZnO tetrapodal ceramic networks showed the least and highest photocatalytic activities against methylene blue, respectively, whereas, the others exhibited intermediate responses. The observed photocatalytic behaviors of pure and hybrid ZnO tetrapods based flexible ceramic 3D networks are briefly presented and discussed.

In this work, the UV sensing properties of Sn-doped and/or alloyed zinc oxide (ZnO) microstructures with different morphologies were investigated in order to elaborate the high performance UV photodetectors. We have compared two types of morphologies, i.e. Sn-doped ZnO films (ZnO:Sn) and ZnO microtetrapod (T) networks alloyed- and doped-with Sn (ZnO-T:Sn). The UV response ( I UV /I dark ) of ZnO:Sn is about 10 3 and 10 2 for 0.1 and 0.4 at% Sn, respectively. The three-dimensional highly porous ZnO-T:Sn networks demonstrated higher UV response (by two orders of magnitude) and much faster recovery for detection of UV light, which were attributed to the domination of fast processes such as modulation of potential barriers formed at the interface of the tetrapod arms, which are less dependent on adsorbed species. Thus, the UV response for devices with a distance between the pads (interelectrode distance) of about 60, 400, 800 and 1500 μm is 1.7 × 10 5 , 2.4 × 10 4 , 6.7 × 10 3 and 925, respectively. All samples demonstrated a sharp increase in photocurrent under illumination with UV light, as well as a fast recovery to the initial electrical baseline. Also, the influence of relative humidity on the rapidity of photodetectors based on ZnO:Sn films and ZnO-T:Sn networks was investigated, confirming a low impact on the rapidity of ZnO-T:Sn networks, with good repeatability and stable electrical baseline, which is very important for effective applications.

Highly porous hybrid materials with unique high-performance properties have attracted great interest from the scientific community, especially in the field of gas-sensing applications. In this work, tetrapodal-ZnO (ZnO-T) networks were functionalized with carbon nanotubes (CNTs) to form a highly efficient hybrid sensing material (ZnO-T–CNT) for ultrasensitive, selective, and rapid detection of ammonia (NH3) vapor at room temperature. By functionalizing the ZnO-T networks with 2.0 wt % of CNTs by a simple dripping procedure, an increase of 1 order of magnitude in response (from about 37 to 330) was obtained. Additionally, the response and recovery times were improved (by decreasing them from 58 and 61 s to 18 and 35 s, respectively). The calculated lowest detection limit of 200 ppb shows the excellent potential of the ZnO-T–CNT networks as NH3 vapor sensors. Room temperature operation of such networked ZnO–CNT hybrid tetrapods shows an excellent long-time stability of the fabricated sensors. Additionally, ...

Fabrication of multifunctional devices based on nano- and microstructures of a single semiconducting oxide is an important step for a better understanding of their maximum sensing properties and the base for the development of bottom-up nanotechnologies. In this work we have fabricated, for the first time devices based on a single or two interconnected ZnO tetrapods (T), doped with Fe and alloyed with Fe2O3 nanoparticles (NPs) and microparticles (MPs) in order to improve their sensing properties towards ultraviolet (UV) sensing and ethanol vapour (EtOH). Compared to pristine ZnO-T improved UV and gas sensing properties of Fe-doped ZnO-T were observed. By Fe2O3-alloying of Fe-doped ZnO-T further improvement in sensing properties was obtained with a reduced influence of the relative humidity (RH) on the sensing response. A gas sensing mechanism was proposed and discussed in detail based on the alloyed Fe2O3 NPs and MPs. The results presented here demonstrate the efficiency of doping and alloying of single ZnO microstructures with other semiconducting oxides to improve their sensing properties, including the decrease in influence of RH on the gas response and the rapidity of the sensors.

In this work, the UV and gas sensing properties of single Fe-doped and Fe2O3-functionalized ZnO micro- and nanowires are reported. The influence of microwire diameter and concentration of Fe2O3 micro- and nanoparticles on the sensing properties of the fabricated devices was investigated. Results clearly reveal that sensors with a higher response can be obtained by a decrease in the diameter of micro- and nanowires and an increase of the Fe2O3 micro- and nanoparticle concentration on the surface of microwires. The enhanced sensing properties can be explained based on excellent charge separation properties of the formed Fe2O3/ZnO heterojunctions in the case of UV response which prolong the photocarrier lifetime and based on excellent catalytic properties of Fe2O3 in the case of gas sensing. The presented results demonstrate the importance of surface functionalization of single ZnO structures with other semiconducting oxide micro- and nanoparticles for the improvement of their sensing properties, i.e., UV and ethanol sensing, even for a single wire/rod with micro- and nanometric diameter.

Copper oxide nanostructured films were synthesized via a chemical synthesis (SCS) method and annealed in low vacuum. The morphological properties were investigated using scanning electron microscopy (SEM). The elaborated sensor structures based on CuO/Cu2O films were tested to 100 ppm of acetone vapor. It was observed that by applying different temperatures for rapid thermal annealing the surface morphology of the films can be modified, as well as the composition of the films, which leads to the changes in gas response value for the tested gases. The possibility of controlling the sensitivity of the sensors by changing the RTA treatment temperature and the operating temperature was demonstrated.

Sensors start to play an ever increasing role in human life and new technologies for their cost-effective mass production are required. In this work, the one-step 3D-printing of nanoflakes—nanowire covered Fe2O3/Fe–CuO/Cu2O/Cu microparticles (MPs) with diameters of ~10 µm on the surface of glass substrate successfully forming an ordered net is reported for the first time. 3D-printed Fe–Cu and only Cu MPs-based stripes formed non-planar CuO/Cu2O/Cu and Fe2O3/Fe–CuO/Cu2O/Cu heterojunctions after thermal annealing at 425 ℃ for 4 h in air and were fully covered with nanoflakes of Fe2O3 and CuO nanowire net bridging MPs with external Au-contacts. The morphological, chemical and structural investigations were performed in detail, showing the high crystallinity of the 3D printed material. This concept proves to be easily translatable to other semiconducting, metallic or functional microparticles for the rapid fabrication of sensor devices.

The impact of (bulk) material and rear surface (contact) quality to the efficiency is found to be quite hard to measure on a processed solar cell. We will show with this paper that CELLO (solar cell local characterization) photo-impedance-spectroscopy measurements are capable of separating bulk from rear side effects on locally resolved maps. This study focuses on multicrystalline Aluminium-BSF solar cells which have been produced according to a co-firing parameter optimization process with a wide parameter space. It is found that the rear side recombination velocity on some locations of the Al-BSF cell is much better than compared to PERC cells. Thus, the full potential of Al-BSF solar cells is much higher than usually expected and anticipated. In the future paste and co-firing optimizations are required to transfer the excellent local values of Al-BSF cells to the full cell area for excellent global values that result in cell efficiencies higher than today PERC solar cells. Thus, the time of Al-BSF solar cells is for our opinion not over yet.

International audience; In this work, ultraviolet (UV) nanophotodetectors based on individual gold-functionalized ZnO nanowires (Au/ZnO NWs) with different diameters and with different Au content were fabricated using a focused ion beam/scanning electron microscopy (FIB/SEM) system. The influence of the Au content, the diameter of the NWs, the applied bias voltage, the temperature and the relative humidity during operation on the UV sensing properties was investigated in detail. The necessity of a higher Au nanoparticles (NPs) coverage of individual Au/ZnO NWs in order to obtain higher UV response is demonstrated for the first time. A high UV response (IUV/Idark) of 21 for an individual Au/ZnO NW (with ~ 6.4% Au NPs coverage) was obtained, which is by a factor of 17 higher compared to unmodified ZnO NWs. The investigation regarding the NW diameter confirmed that thinner NWs are more suitable for UV sensing applications due to the greater influence of surface phenomena on electrical properties. Most importantly, the elaborated nanophotodetectors in this work, based on individual Au/ZnO NWs, show an extreme low influence caused by water vapors, i.e. relative humidity on UV response, which is critical for practical applications of high performance UV photodetectors in normal ambient conditions. Our experimental results demonstrate clearly that the n-type Au/ZnO NWs with enhanced optoelectronic properties are highly promising building nano-blocks for near future nano-optoelectronic devices and possible for biosensing applications.

In this research, the low-temperature single-step electrochemical deposition of arrayed ZnO nanowires (NWs) decorated by Au nanoparticles (NPs) with diameters ranging between 10 and 100 nm is successfully demonstrated for the first time. The AuNPs and ZnO NWs were grown simultaneously in the same growth solution in consideration of the HAuCl4 concentration. Optical, structural, and chemical characterizations were analyzed in detail, proving high crystallinity of the NWs as well as the distribution of Au NPs on the surface of zinc oxide NWs demonstrated by transmission electron microscopy. Individual Au NPs-functionalized ZnO NWs (Au-NP/ZnO-NWs) were incorporated into sensor nanodevices using an focused ion bean/scanning electron microscopy (FIB/SEM) scientific instrument. The gas-sensing investigations demonstrated excellent selectivity to hydrogen gas at room temperature (RT) with a gas response, Igas/Iair, as high as 7.5–100 ppm for Au-NP/ZnO-NWs, possessing a AuNP surface coverage of ∼6.4%. The concent...