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A novel combined setup of a gas aggregation source and a secondary radio frequency discharge is used to generate, confine, and coat nanoparticles. The approach is demonstrated by generating Ag@SiO2 nanoparticles with a well-defined surface coating.

Colored imaging of magnetic nanoparticles (MNP) is a promising noninvasive method for medical applications such as therapy and diagnosis. This study investigates the capability of the magnetoelectric sensor and projected gradient descent (PGD) algorithm for colored particle detection. In the first step, the required circumstances for image reconstruction are studied via a simulation approach for different signal-to-noise ratios (SNR). The spatial accuracy of the reconstructed image is evaluated based on the correlation coefficient (CC) factor. The inverse problem is solved using the PGD method, which is adapted according to a nonnegativity constraint in the complex domain. The MNP characterizations are assessed through a magnetic particle spectrometer (MPS) for different types. In the experimental investigation, the real and imaginary parts of the MNP’s response are used to detect the spatial distribution and particle type, respectively. The experimental results indicate that the average phase difference for CT100 and ARA100 particles is 14 degrees, which is consistent with the MPS results and could satisfy the system requirements for colored imaging. The experimental evaluation showed that the magnetoelectric sensor and the proposed approach could be potential candidates for color bio-imaging applications.

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.

Here, a 4N-in-1 hybrid substrate concept (nanocolumnar structures, nanocrack network, nanoscale mixed oxide phases, and nanometallic structures) for ultra-sensitive and reliable photo-induced-enhanced Raman spectroscopy (PIERS), is proposed. The use of the 4N-in-1 hybrid substrate leads to an ≈50-fold enhancement over the normal surface-enhanced Raman spectroscopy, which is recorded as the highest PIERS enhancement to date. In addition to an improved Raman signal, the 4N-in-1 hybrid substrate provides a high detection sensitivity which may be attributed to the activation possibility at extremely low UV irradiation dosage and prolonged relaxation time (long measurement time). Moreover, the 4N-in-1 hybrid substrate exhibits a superior photocatalytic degradation performance of analytes, allowing its reuse at least 18 times without any loss of PIERS activity. The use of the 4N-in-1 concept can be adapted to biomedicine, forensic, and security fields easily.

Polymer–metal composite films with nanostructured metal and/or polymer interfaces show a significant perspective for optoelectronic applications, for example, as sensors or in organic photovoltaics...

Gold/titanium dioxide (Au/TiO2) nanohybrid materials have been widely applied in various fields because of their outstanding optical and photocatalytic performance. By state-of-the-art polymer templating, it is possible to make uniform nanostructured TiO2 layers with potentially large-scale processing methods. We use customized polymer templating to achieve TiO2 nanostructures with different morphologies. Au/TiO2 hybrid thin films are fabricated by sputter deposition. An in-depth understanding of the Au morphology on the TiO2 templates is achieved with in situ grazing-incidence small-angle X-ray scattering (GISAXS) during the sputter deposition. The resulting Au nanostructure is largely influenced by the TiO2 template morphology. Based on the detailed understanding of the Au growth process, characteristic distances can be selected to achieve tailored Au nanostructures at different Au loadings. For selected sputter-deposited Au/TiO2 hybrid thin films, the optical response with a tailored localized surface plasmon resonance is demonstrated.

The deposition of well-defined photochromic thin films is highly attractive but challenging when it comes to practical applications. In conventional wet chemistry methods, the choice of potential m...

Copper (Cu) as an excellent electrical conductor and the amphiphilic diblock copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as a polymer electrolyte and ionic conductor can be combined with an active material in composite electrodes for polymer lithium-ion batteries (LIBs). As interfaces are a key issue in LIBs, sputter deposition of Cu contacts on PS-b-PEO thin films with high PEO fraction is investigated with in situ grazing-incidence small-angle X-ray scattering (GISAXS) to follow the formation of the Cu layer in real-time. We observe a hierarchical morphology of Cu clusters building larger Cu agglomerates. Two characteristic distances corresponding to the PS-b-PEO microphase separation and the Cu clusters are determined. A selective agglomeration of Cu clusters on the PS domains explains the origin of the persisting hierarchical morphology of the Cu layer even after a complete surface coverage is reached. The spheroidal shape of the Cu clusters growing within the first few nanometers of sputter deposition causes a highly porous Cu-polymer interface. Four growth stages are distinguished corresponding to different kinetics of the cluster growth of Cu on PS-b-PEO thin films: (I) nucleation, (II) diffusion-driven growth, (III) adsorption-driven growth, and (IV) grain growth of Cu clusters. Percolation is reached at an effective Cu layer thickness of 5.75 nm.

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.

Organic gradient materials are an inherent part of many functional structures in the natural world. Synthetic organic materials, like polymers, are thus the perfect choice to artificially recreate these structures for functional purposes. This work reports on new high-quality gradient copolymer films via large-area deposition from the vapor phase and circumvents thus problems related to current wet chemistry approaches. It enables furthermore for the first time the transfer of this gradient approach to the nanoscale, introducing a new class of organic gradient nanomaterials. This facilitates completely new organic gradient functionality on the nanoscale, not achievable with materials currently in use. Fully functional gradient films of 21 nm have been synthesized, which open up new pathways for many application fields. Their versatility is demonstrated by some application examples ranging from every day life (adhesion of PTFE in frypans) to advanced subwavelength devices on large-area substrates as well as complex geometries.

In this work, we demonstrate the first synthesis of photochromic polymer thin films via initiated chemical vapor deposition (iCVD) using bifunctional, crystalline styrenediazocine as a photochromic unit. Since it represents a solid compound, an innovative custom-made sublimation unit is introduced, which allows the sublimation of the chromophore as well as its transport inside the reactor chamber, maintaining the functionality of the photoswitch. Styrenediazocine was co-polymerized with 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V₃D₃), a heterocycle with triple vinyl functionality, in a radical polymerization reaction from the gas phase. The structural as well as functional properties of the resulting films were characterized by various methods, including X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, and UV–vis spectroscopy. It could be confirmed that, via iCVD, photoswitchable polymer thin films have been obtained. The polymer is based on a copolymer structure where all photoswitchable molecules are covalently bonded in the main polymer chain. Our approach could pave the way for a completely new class of high-quality, photochromic thin films that are basically applicable on almost every kind of substrate for novel, interdisciplinary application fields, where particularly classical wet chemistry methods cannot be applied.

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.

Random networks of nanoparticle-based memristive switches enable pathways for emulating highly complex and self-organized synaptic connectivity together with their emergent functional behavior known from biological neuronal networks. They therefore embody a distinct class of neuromorphic hardware architectures and provide an alternative to highly regular arrays of memristors. Especially, networks of memristive nanoparticles (NPs) poised at the percolation threshold are promising due to their capabilities of showing brain-like activity such as critical dynamics or long-range temporal correlation (LRTC), which are closely connected to the computational capabilities in biological neuronal networks. Here, we adapt this concept to networks of Ag-NPs poised at the electrical percolation threshold, where the memristive properties are governed by electro-chemical metallization. We show that critical dynamics and LRTC are preserved although the nature of individual memristive gaps throughout the network is fundamentally changed by filling the gaps with an insulating matrix. The results in this work generate important contributions towards the practical applicability of critical dynamics and LRTC in percolating NP networks by elucidating the consequences of NP network encapsulation, which is considered as an important step towards device integration.

Imaging of magnetic nanoparticles (MNPs) is of great interest in the medical sciences. By using resonant magnetoelectric sensors, higher harmonic excitations of MNPs can be measured and mapped in space. The proper reconstruction of particle distribution via solving the inverse problem is paramount for any imaging technique. For this, the forward model needs to be modeled accurately. However, depending on the state of the magnetoelectric sensors, the projection axis for the magnetic field may vary and may not be known accurately beforehand. As a result, the projection axis used in the model may be inaccurate, which can result in inaccurate reconstructions and artifact formation. Here, we show an approach for mapping MNPs that includes sources of uncertainty to both select the correct particle distribution and the correct model simultaneously.

ACS applied nano materials 5(3), 3832 - 3842 (2022). doi:10.1021/acsanm.1c04473, Tailoring of plasmon resonances is essential for applications in anti-counterfeiting. This is readily achieved by tuning the composition of alloyed metal clusters; in the most simple case binary alloys. Yet, one challenge is the correlation of cluster morphology and composition with the changing optoelectronic properties. Hitherto, the early stages of metal alloy nanocluster formation in immiscible binary systems like silver and copper has been accessible by molecular dynamics simulations and transmission electron microscopy. Here, we investigate in real-time the formation of supported silver, copper and silver-copper-alloy nanoclusters during sputter deposition on poly(methyl methacrylate) by combining in situ surface sensitive X-ray scattering with optical spectroscopy. While following the transient growth morphologies, we quantify the early stages of phase separation at the nanoscale, follow the shifts of surface plasmon resonances and quantify the growth kinetics of the nanogranular layers at different thresholds. We are able to extract the influence of scaling effects on the nucleation and phase selection. The internal structure of the alloy cluster shows a copper-rich core/silver-rich shell structure, since the copper core yields a lower mobility and higher crystallization tendency than the silver fraction. We compare our results to molecular dynamics simulation and transmission electron microscopy data. This demonstrates a route to tailor accurately the plasmon resonances of nanosized, polymer supported clusters which is a crucial prerequisite for anti-counterfeiting., Published by ACS Publications, Washington, DC

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.

Recently, Delta-E effect magnetic field sensors based on exchange-biased magnetic multilayers have shown the potential of detecting low-frequency and small-amplitude magnetic fields. Their design is compatible with microelectromechanical system technology, potentially small, and therefore, suitable for arrays with a large number N of sensor elements. In this study, we explore the prospects and limitations for improving the detection limit by averaging the output of N sensor elements operated in parallel with a single oscillator and a single amplifier to avoid additional electronics and keep the setup compact. Measurements are performed on a two-element array of exchange-biased sensor elements to validate a signal and noise model. With the model, we estimate requirements and tolerances for sensor elements using larger N. It is found that the intrinsic noise of the sensor elements can be considered uncorrelated, and the signal amplitude is improved if the resonance frequencies differ by less than approximately half the bandwidth of the resonators. Under these conditions, the averaging results in a maximum improvement in the detection limit by a factor of N. A maximum N≈200 exists, which depends on the read-out electronics and the sensor intrinsic noise. Overall, the results indicate that significant improvement in the limit of detection is possible, and a model is presented for optimizing the design of delta-E effect sensor arrays in the future.

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Metal top electrodes such as gold are widely used in organic solar cells. The active layer can be optimized by modifications of the polymer band gap via side-chain engineering, and low band gap polymers based on benzodithiophene units such as PTB7 and PTB7-Th are successfully used. The growth of gold contacts on PTB7 and PTB7-Th films is investigated with in situ grazing incidence small-angle X-ray scattering (GISAXS) and grazing incidence wide-angle X-ray scattering (GIWAXS) during the sputter deposition of gold. From GIWAXS, the crystal structure of the gold film is determined. Independent of the type of side chain, gold crystals form in the very early stages and improve in quality during the sputter deposition until the late stages. From GISAXS, the nanoscale structure is determined. Differences in terms of gold cluster size and growth phase limits for the two polymers are caused by the side-chain modification and result in a different surface coverage in the early phases. The changes in the diffusion and coalescence behavior of the forming gold nanoparticles cause differences in the morphology of the gold contact in the fully percolated regime, which is attributed to the different amount of thiophene rings of the side chains acting as nucleation sites.

This study aims at deposition and characterization of antibacterial, hydrophobic and semitransparent metal/plasma polymer nanocomposite coating, containing Ag nanoparticles, onto cotton fabrics intended to be used in medical applications. The nano composite coatings were obtained via a simple, one step and ecofriendly plasma based co-deposition approach where silver was magnetron sputtered simultaneously with plasma polymerization of hexamethyldisiloxane (HMDSO) monomer. The nanocomposite thin films containing different concentration of silver were deposited either by varying silver sputter rate or thickness of the plasma polymer matrix to obtain a good balance between optical properties of the coated fabric and its long term antibacterial performance. The obtained coatings were investigated in detail with respect to their composition, morphology, optical properties, nanoparticle size distribution, silver ion release efficiency, antibacterial performance, water contact angle and washing stability of the coating. The thickness of the plasma matrix was found to be more important in controlling the release of silver ions as well as affecting the optical properties of the coating. The water contact angle on the coated fabric was up to 145°, close to super hydrophobicity. The coating showed effective antibacterial efficacy against Staphylococcus epidermidis (a Gram positive bacterium) which was present even when fabric was subjected to 10 repeated washing cycles indicating good washing stability of the coating.

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.

Recently, we reported on the preparation of Teflon AF 1600 based electret films with extremely high charge stability by thermal evaporation and corona discharge [Hirschberg et al. Organic Electronics 57 (2018) 146]. Here we present investigations on thermally evaporated electret films made of Teflon AF 2400 with even improved charge stability. Deposition of smooth films without micropores at rates exceeding 10 nm/s was achieved with a specially designed evaporator. The evaporated thin films exhibit an extraordinary dielectric breakdown strength, which is almost one order of magnitude above the bulk value for films thicknesses in the μm range. The resulting maximum charging potential is as high as 267 V for a 5.4 μm electret film. Films of 15 μm could be charged up to 600 V. The charge stability was investigated as function of charging potential, film thickness, and the polarity of the charges. Negative charging proved to provide a much higher charge stability. The charge stability decreases with increasing charging voltage, which is shown to be due to filling of more shallow traps upon at higher charging voltages. Thicker films exhibit higher charge stability. This observation is in line with the proposed internal charge decay mechanism and can be explained in terms of longer charge migration paths. The reproducibility of the fabrication process of the thin film was tested involving about 200 samples. An excellent standard deviation of 2.9% was found for a charging voltage of 250 V, which makes the preset fabrication method very attractive for industrial applications.

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.

Inspired by recent developments in the field of nanogenerators and piezotronics, two different approaches for the improvement of magnetic field sensing are discussed and their feasibility has been experimentally demonstrated. In the first concept, it could be shown that a piezotronic read-out eliminates the need for an external pre-amplifier in MEMS type cantilever sensors. This leads to reduced noise and lower power consumption, which makes the sensors interesting for self-powered applications. Furthermore, the lower noise is measured at short integration times, which reveals further application strategies for piezotronic sensor read-out. In the second concept, a new nanogenerator inspired utilization of electret film allows a reduction of the resonance frequency of cantilever sensors. This reduction is accompanied by higher amplitudes and lower Q-factors allowing energy efficient broadband measurements. A theoretical model has been developed based on an anharmonic oscillator, which is in good agreement with the observed experimental results. Both the demonstrated strategies can help to improve the energy efficiency of the presented magnetic field sensors, allowing lower power consumption and a decreased noise level.