Investigating cooperative effects in small cobalt and cobalt-nickel alloy clusters with attached ethanol.

Small cationic cobalt, and cobalt-nickel alloy clusters with ethanol attached are generated in a pulsed molecular beam experiment using a laser ablation source. While the metal center is successively varied with respect to size and composition, a full-size study of these transition metal clusters is possible. The clusters are investigated via IR photodissociation spectroscopy in the region of OH- and CH-stretching vibrations. The results are compared with theoretical data obtained from DFT calculations. Both frequency shifts and structural changes according to cluster size and composition are identified and discussed in detail, also with respect to cooperative effects. Trimeric metal clusters with an uneven number of nickel atoms show evidence for C-O cleavage of the ethanol molecule. This result is elucidated by further calculations concerning the reactivity, charge and energetic distributions.

Structural Investigation of Small Nickel-Ethanol Clusters Using Vibrational Spectroscopy in a Molecular Beam.

The structural identification of small nickel clusters with ethanol can help to understand fundamental steps for heterogenous catalysis. We investigate the rows [Nix (EtOH)1 ]+ with x=1-4, and [Ni2 (EtOH)y ]+ with y=1-3 via IR photodissociation spectroscopy in a molecular beam experiment. Analyzing the CH- and OH-stretching frequencies and comparing these experimental results with density functional theory (DFT) calculations on the PW91/6-311+G(d,p) level leads to the identification of intact motifs for all clusters and hints for C-O cleavage of the ethanol in two particular cases. Furthermore, we analyze the effects of frequency shifts with the increasing clusters sizes using the results of natural bond orbitals (NBO) analyses and an energy decomposition method.

A re-useable microreactor for dynamic and sensitive photocatalytic measurements: Exemplified by the photoconversion of ethanol on Pt-loaded titania P25.

Despite numerous advancements in synthesizing photoactive materials, the evaluation of their catalytic performance remains challenging since their fabrication often involves tedious strategies, yielding only low quantities in the µ-gram scale. In addition, these model catalysts exhibit different forms, such as powders or film(-like) structures grown on various supporting materials. Herein, we present a versatile gas phase µ-photoreactor, compatible with different catalyst morphologies, which is, in contrast to existing systems, re-openable and -useable, allowing not only post-characterization of the photocatalytic material but also enabling catalyst screening studies in short experimental time intervals. Sensitive and time-resolved reaction monitoring at ambient pressure is realized by a lid-integrated capillary, transmitting the entire gas flow from the reactor chamber to a quadrupole mass spectrometer. Due to the microfabrication of the lid from borosilicate as base material, 88% of the geometrical area can be illuminated by a light source, further enhancing sensitivity. Gas dependent flow rates through the capillary were experimentally determined to be 1015-1016 molecules s-1, and in combination with a reactor volume of 10.5 µl, this results in residence times below 40 s. Furthermore, the reactor volume can easily be altered by adjusting the height of the polymeric sealing material. The successful operation of the reactor is demonstrated by selective ethanol oxidation over Pt-loaded TiO2 (P25), which serves to exemplify product analysis from dark-illumination difference spectra.

Spin-Wave Optics in YIG Realized by Ion-Beam Irradiation.

Direct focused-ion-beam writing is presented as an enabling technology for realizing functional spin-wave devices of high complexity, and demonstrate its potential by optically-inspired designs. It is shown that ion-beam irradiation changes the characteristics of yttrium iron garnet films on a submicron scale in a highly controlled way, allowing one to engineer the magnonic index of refraction adapted to desired applications. This technique does not physically remove material, and allows rapid fabrication of high-quality architectures of modified magnetization in magnonic media with minimal edge damage (compared to more common removal techniques such as etching or milling). By experimentally showing magnonic versions of a number of optical devices (lenses, gratings, Fourier-domain processors) this technology is envisioned as the gateway to building magnonic computing devices that rival their optical counterparts in their complexity and computational power.

Skyrmions Under Control-FIB Irradiation as a Versatile Tool for Skyrmion Circuits.

Magnetic data storage and processing offer certain advances over conventional technologies, amongst which nonvolatility and low power operation are the most outstanding ones. Skyrmions are a promising candidate as a magnetic data carrier. However, the sputtering of skyrmion films and the control of the skyrmion nucleation, motion, and annihilation remains challenging. This work demonstrates that using optimized focused ion beam irradiation and annealing protocols enables the skyrmion phase in W/CoFeB/MgO thin films to be accessed easily. By analyzing ion-beam-engineered skyrmion hosting wires, excited by sub-100 ns current pulses, possibilities to control skyrmion nucleation, guide their motion, and control their annihilation unfold. Overall, the key elements needed to develop extensive skyrmion networks are presented.

Filtration-processed biomass nanofiber electrodes for flexible bioelectronics.

An increasing demand for bioelectronics that interface with living systems has driven the development of materials to resolve mismatches between electronic devices and biological tissues. So far, a variety of different polymers have been used as substrates for bioelectronics. Especially, biopolymers have been investigated as next-generation materials for bioelectronics because they possess interesting characteristics such as high biocompatibility, biodegradability, and sustainability. However, their range of applications has been restricted due to the limited compatibility of classical fabrication methods with such biopolymers. Here, we introduce a fabrication process for thin and large-area films of chitosan nanofibers (CSNFs) integrated with conductive materials. To this end, we pattern carbon nanotubes (CNTs), silver nanowires, and poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) by a facile filtration process that uses polyimide masks fabricated via laser ablation. This method yields feedlines of conductive material on nanofiber paper and demonstrates compatibility with conjugated and high-aspect-ratio materials. Furthermore, we fabricate a CNT neural interface electrode by taking advantage of this fabrication process and demonstrate peripheral nerve stimulation to the rapid extensor nerve of a live locust. The presented method might pave the way for future bioelectronic devices based on biopolymer nanofibers.

Reconfigurable Electronic Platforms: A Top-Down Approach to Learn about Design and Integration of Electronic Systems.

This case report presents a real example of a study which introduces the use of reconfigurable platforms in the teaching of electronics engineering to establish a bridge between theory and practice. This gap is one of the major concerns of the electronics engineering students. Different strategies, such as simulation tools or breadboard implementations, have been followed so far to make it easier for students to practice what they study in lectures. However, many students still claim to have problems when they face real practical implementations. The use of reconfigurable platforms as a teaching tool is proposed to provide the students the possibility of fast experimentation, reducing both development time and the learning curve. In addition, reconfigurable platforms available on the market make this methodology suitable to be applied throughout the different courses of their curricula. The feasibility of this approach is demonstrated in a course at the M.Eng. level, where the objective is the study, design and development of electronic sensor nodes. We firmly consider, based on the students' results and reflections collected during the course, that this methodology helps students to address the theoretical framework from a practical viewpoint, as well as to acquire some of the fundamental skills for their professional careers, such as the usage of communication protocols and embedded systems programming, in a more intuitive way when compared to traditional teaching methodologies.

Experimental demonstration of a concave grating for spin waves in the Rowland arrangement.

We experimentally demonstrate the operation of a Rowland-type concave grating for spin waves, with potential application as a microwave spectrometer. In this device geometry, spin waves are coherently excited on a diffraction grating and form an interference pattern that focuses spin waves to a point corresponding to their frequency. The diffraction grating was created by focused-ion-beam irradiation, which was found to locally eliminate the ferrimagnetic properties of YIG, without removing the material. We found that in our experiments spin waves were created by an indirect excitation mechanism, by exploiting nonlinear resonance between the grating and the coplanar waveguide. Although our demonstration does not include separation of multiple frequency components, since this is not possible if the nonlinear excitation mechanism is used, we believe that using linear excitation the same device geometry could be used as a spectrometer. Our work paves the way for complex spin-wave optic devices-chips that replicate the functionality of integrated optical devices on a chip-scale.

Silicon Nanosheets versus Graphene Nanosheets: A Comparison of Their Nonlinear Optical Response.

Silicene, the silicon analogue of graphene, represents a new class of two-dimensional (2D) materials, which shares some of the outstanding physical properties of graphene. Furthermore, it has the advantage of being compatible with the current Si-based technology. However, this 2D material is not stable and is quite prone to oxidation. The hydride-terminated silicene, called silicane, is a more stable form of 2D silicon, if functionalized via, for example, the hydrosilylation reaction. In this work, the third-order nonlinear optical (NLO) properties of two functionalized silicanes, namely hydride-terminated silicon nanosheets (SiNS-H) and 1-dodecene-functionalized silicon nanosheets (SiNS-dodecene), are accessed and compared to those of single-layer graphene, under 35 ps, 532 and 1064 nm excitation. The present results show that the functionalized silicanes exhibit comparable and even higher NLO response than that of single-layer graphene, making them strong competitors of graphene and very interesting candidates for future photonic and optoelectronic applications.

Printed and Flexible Microheaters Based on Carbon Nanotubes.

This work demonstrates a cost-effective manufacturing method of flexible and fully printed microheaters, using carbon nanotubes (CNTs) as the heating element. Two different structures with different number of CNT layers have been characterized in detail. The benchmarking has been carried out in terms of maximum operating temperature, as well as nominal resistance and input power for different applied voltages. Their performances have been compared with previous reports for similar devices, fabricated with other technologies. The results have shown that the heaters presented can achieve high temperatures in a small area at lower voltages and lower input power. In particular, the fully printed heaters fabricated on a flexible substrate covering an area of 3.2 mm2 and operating at 9.5 V exhibit a maximum temperature point above 70 °C with a power consumption below 200 mW. Therefore, we have demonstrated that this technology paves the way for a cost-effective large-scale fabrication of flexible microheaters aimed to be integrated in flexible sensors.

Lateral silicon oxide/gold interfaces enhance the rate of electrochemical hydrogen evolution reaction in alkaline media.

The production of solar hydrogen with a silicon based water splitting device is a promising future technology, and silicon-based metal-insulator-semiconductor (MIS) electrodes have been proposed as suitable architectures for efficient photocathodes based on the electronic properties of the MIS structures and the catalytic properties of the metals. In this paper, we demonstrate that the interfaces between the metal and oxide of laterally patterned MIS electrodes may strongly enhance the catalytic activity of the electrode compared to bulk metal surfaces. The employed electrodes consist of well-defined, large-area arrays of gold structures of various mesoscopic sizes embedded in a silicon oxide support on silicon. We demonstrate that the activity of these electrodes for hydrogen evolution reaction (HER) increases with an increase in gold/silicon oxide boundary length in both acidic and alkaline media, although the enhancement of the HER rate in alkaline electrolytes is considerably larger than in acidic electrolytes. Electrodes with the largest interfacial length of gold/silicon oxide exhibited a 10-times larger HER rate in alkaline electrolytes than those with the smallest interfacial length. The data suggest that at the metal/silicon oxide boundaries, alkaline HER is enhanced through a bifunctional mechanism, which we tentatively relate to the laterally structured electrode geometry and to positive charges present in silicon oxide: Both properties change locally the interfacial electric field at the gold/silicon oxide boundary, which, in turn, facilitates a faster transport of hydroxide ions away from the electrode/electrolyte interface in alkaline solution. This mechanism boosts the alkaline HER activity of p-type silicon based photoelectrodes close to their HER activity in acidic electrolytes.

Fabrication and Characterization of Humidity Sensors Based on Graphene Oxide-PEDOT:PSS Composites on a Flexible Substrate.

In this paper, we present a simple, fast, and cost-effective method for the large-scale fabrication of high-sensitivity humidity sensors on flexible substrates. These sensors consist of a micro screen-printed capacitive structure upon which a sensitive layer is deposited. We studied two different structures and three different sensing materials by modifying the concentration of poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) in a graphene oxide (GO) solution. The results show that the aggregation of the PEDOT:PSS to the GO can modify its electrical properties, boosting the performance of the capacitive sensors in terms of both resistive losses and sensitivity to relative humidity (RH) changes. Thus, in an area less than 30 mm2, the GO/PEDOT:PSS-based sensors can achieve a sensitivity much higher (1.22 nF/%RH at 1 kHz) than other similar sensors presented in the literature which, together with their good thermal stability, time response, and performance over bending, demonstrates that the manufacturing approach described in this work paves the way for the mass production of flexible humidity sensors in an inexpensive way.

Low-Cost Gas Sensing: Dynamic Self-Compensation of Humidity in CNT-Based Devices.

Solid-state gas sensors are a cost-effective and well-spread alternative to conventional gas sensing, employable in most environments, ranging from homes and offices to harsh industrial scenarios. The emergence of carbon nanotubes (CNTs) as sensing material in solid-state gas sensors paved the way to a new class of devices, which are semitransparent, flexible, and with a remarkably low environmental impact. These devices, however, lack selectivity to other gases and concurring physical phenomena, such as temperature and pressure changes. In this contribution, we show how by measuring the impedance of CNT-based gas sensors at different frequencies, it is possible to evaluate sensitivity coefficient for the immediate compensation of moisture content in the air, while still preserving in the considered ranges of average sensitivities as high as 0.045, 0.112, 7.842 × 10-5, and 0.041 % Z/ppm for ammonia, carbon dioxide, carbon monoxide and ethanol gas, respectively. With this simple approach, it will be possible to develop simple sensor read-out systems, with reduced external electronic, simplifying the route to low-cost and low-power sensor nodes for the internet of things.

Cost-effective PEDOT:PSS Temperature Sensors Inkjetted on a Bendable Substrate by a Consumer Printer.

In this work, we report on a fabrication protocol to produce fully inkjet-printed temperature sensors on a bendable polyethylene terephthalate (PET) substrate. The sensing layer is made of polymer-based Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) ink that is electrically contacted by an underlying interdigitated electrode (IDE) structure based on a silver nanoparticle (AgNP) ink. Both inks are available commercially, and no further ink processing is needed to print them using a cost-effective consumer printer with standard cartridges. The fabricated sensor modules are tested for different IDE dimensions and post-deposition treatments of the AgNP film for their response to a temperature range of 20 to 70 °C and moisture range of 20 to 90% RH (relative humidity). Attributed to the higher initial resistance, sensor modules with a larger electrode spacing of 200 µm show a higher thermal sensitivity that is increased by a factor of 1.8 to 2.2 when compared to sensor modules with a 150 µm-spacing. In all cases, the sensors exhibit high linearity towards temperature and a response comparable to state of the art.

A Facile and Efficient Protocol for Preparing Residual-Free Single-Walled Carbon Nanotube Films for Stable Sensing Applications.

In this article, we report on an efficient post-treatment protocol for the manufacturing of pristine single-walled carbon nanotube (SWCNT) films. To produce an ink for the deposition, the SWCNTs are dispersed in an aqueous solution with the aid of a carboxymethyl cellulose (CMC) derivative as the dispersing agent. On the basis of this SWCNT-ink, ultra-thin and uniform films are then fabricated by spray-deposition using a commercial and fully automated robot. By means of X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), we show that the CMC matrix covering the CNTs can be fully removed by an immersion treatment in HNO3 followed by thermal annealing at a moderate temperature of 100 °C, in the ambient air. We propose that the presented protocols for the ink preparation and the post-deposition treatments can in future serve as a facile and efficient platform for the fabrication of high-quality and residual-free SWCNT films. The purity of SWCNT films is of particular importance for sensing applications, where residual-induced doping and dedoping processes distort the contributions from the sensing specimen. To study the usability of the presented films for practical applications, gas sensors are fabricated and characterized with the CNT-films as the sensing material, screen printed silver-based films for the interdigitated electrode (IDE) structure, and polyimide as a flexible and robust substrate. The sensors show a high and stable response of 11% to an ammonia (NH3) test gas, at a concentration of 10 ppm.

Aqueous Synthesis, Degradation, and Encapsulation of Copper Nanowires for Transparent Electrodes.

Copper nanowires (CuNWs) have increasingly become subjected to academic and industrial research, which is attributed to their good performance as a transparent electrode (TE) material that competes with the one of indium tin oxide (ITO). Recently, an environmentally friendly and aqueous synthesis of CuNWs was demonstrated, without the use of hydrazine that is known for its unfavorable properties. In this work, we extend the current knowledge for the aqueous synthesis of CuNWs by studying their up-scaling potential. This potential is an important aspect for the commercialization and further development of CuNW-based devices. Due to the scalability and homogeneity of the deposition process, spray coating was selected to produce films with a low sheet resistance of 7.6 Ω/sq. and an optical transmittance of 77%, at a wavelength of 550 nm. Further, we present a comprehensive investigation of the degradation of CuNWs when subjected to different environmental stresses such as the exposure to ambient air, elevated temperatures, high electrical currents, moisture or ultraviolet (UV) light. For the oxidation process, a model is derived to describe the dependence of the breakdown time with the temperature and the initial resistance. Finally, polymer coatings made of polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA), as well as oxide coatings composed of electron beam evaporated silicon dioxide (SiO2) and aluminum oxide (Al2O3) are tested to hinder the oxidation of the CuNW films under current flow.

On the Frequency Response of Nanostructured Thermoacoustic Loudspeakers.

In this work, we investigate the thermal and acoustic frequency responses of nanostructured thermoacoustic loudspeakers. An opposite frequency dependence of thermal and acoustic responses was found independently of the device substrate (Kapton and glass) and the nanometric active film (silver nanowires and nm-thick metal films). The experimental results are interpreted with the support of a comprehensive electro-thermo-acoustic model, allowing for the separation of the purely thermal effects from the proper thermoacoustic (TA) transduction. The thermal interactions causing the reported opposite trends are understood, providing useful insights for the further development of the TA loudspeaker technology.

On the sintering of solution-based silver nanoparticle thin-films for sprayed and flexible antennas.

In this work, we report on the fabrication and characterization of sub-300 nm electrode films based on solution-processed silver nanoparticles (AgNPs). Following the deposition of the electrode material using a scalable and homogenous spray process, the films are treated with thermal or photonic sintering to promote the coalescence of the nanoparticles and in turn decrease the resistivity of the films. After sintering, a resistivity of 63 ± 13 nΩ m is achieved for the AgNP films, which is only by a factor of four larger than the literature value for bulk silver. Both post-deposition treatments show a similar performance with regard to the achieved resistivity. However, photonic sintering avoids the need for thermal annealing at substrate temperatures of 150 °C and above. In addition, the photonic sintering process can easily be embedded in a roll-to-roll process and is extremely fast with light exposure times below 3 ms. Thus, this manufacturing technique paves the way for the use of flexible substrates in electronics. As a simple and practical application, we present the use of AgNP films for antennas operating in the 5 GHz band on flexible polyethylene terephthalate substrate. An original coplanar design is employed for the fabrication of antennas with a single conductive layer that exhibit a maximum return loss and radiation of -27 dB and 95%, respectively.

Ambient Processed, Water-Stable, Aqueous-Gated sub 1 V n-type Carbon Nanotube Field Effect Transistor.

In this paper we report for the first time an n-type carbon nanotube field effect transistor which is air- and water-stable, a necessary requirement for electrolyte gated CMOS circuit operation. The device is obtained through a simple process, where the native p-type transistor is converted to an n-type. This conversion is achieved by applying a tailor composed lipophilic membrane containing ion exchanger on the active channel area of the transistor. To demonstrate the use of this transistor in sensing applications, a pH sensor is fabricated. An electrolyte gated CMOS inverter using the herein proposed novel n-type transistor and a classical p-type transistor is demonstrated.

A Handwriting Method for Low-Cost Gas Sensors.

In this study, we report on an automated method based on a handwritten technique for the fabrication of low-cost gas sensors based on carbon nanotube (CNT) networks. Taking advantage of the inherent low-cost, flexible, and uncomplicated characteristics of pen-based techniques and combining them with an automated robotic system allows for high-resolution patterns, high reproducibility, and relatively high throughput considering the limitations of parallel processing. To showcase this, gas sensors capable of sensing NH3, CO2, CO, and ethanol, as well as temperature and relative humidity, are fabricated and characterized displaying competitive performance in relation to previously reported devices. The presented process is compatible with a variety of solutions and inks and, as such, allows for an easy integration into existing printing and coating frameworks with the greatest advantage being the ease of creating prototypes because of the nonstringent material requirements.