Nonthermal plasmas are currently being studied as a green alternative to the Haber-Bosch process, which is, today, the dominant industrial process allowing for the fixation of nitrogen and, as such, a fundamental component for the production of nitrogen-based industrial fertilizers. In this context, the gliding arc plasma (GAP) is considered a promising choice among nonthermal plasma options. However, its stability is still a key parameter to ensure industrial transfer of the technology. Nowadays, the conventional approach to stabilize this plasma process is to use external resistors. Although this indeed allows for an enhancement of the plasma stability, very little is reported about how it impacts the process efficiency, both in terms of NOx yield and energy cost. In this work, this question is specifically addressed by studying a DC-powered GAP utilized for nitrogen fixation into NOx at atmospheric pressure stabilized by variable external resistors. Both the performance and the stability of the plasma are reported as a function of the utilization of the resistors. The results confirm that while the use of a resistor indeed allows for a strong stabilization of the plasma without impacting the NOx yield, especially at high plasma current, it dramatically impacts the energy cost of the process, which increases from 2.82 to 7.9 MJ/mol. As an alternative approach, we demonstrate that the replacement of the resistor by an inductor is promising since it allows for decent stabilization of the plasma, while it does not affect either the energy cost of the process or the NOx yield.

Copper oxides CuO and Cu2O are promising p-type semiconductors for low cost and environmentally friendly solar energy conversion applications. To design optimized devices, a precise control of their optoelectonic properties is necessary. Direct current reactive magnetron sputtering was used to synthesize CuO and Cu2O thin films, and their optoelectronic properties were assessed and compared. It is shown how a heated or biased substrate can modify the electrical properties of sputtered copper oxides. Applying a negative bias mostly increases the hole density and conductivity of the material by one order of magnitude, with a moderate increase of mobility, while heating the substrate (523 K) leads to a clear increase of the hole mobility (up to 0.3 and 4.5 cm2/V s for CuO and Cu2O, respectively) and a decrease of the hole density. A hole density of 1015 cm−3 was reached for Cu2O, while for CuO, it remained as high as 1019 cm−3.

This letter investigates the large spread of values of capacitance measured in Si/TiO2 MIS structures for different properties of the TiO2 layer and proposes an approach to understand the behavior of the system. Experimental results show large variations of the maximum capacitance with TiO2 thickness for the as-deposited structures and further highlight the change of trend after annealing. Simulations qualitatively depict the theoretical trends explaining the C–V characteristics to the first order, by the different behaviors of the oxide layer in the structure and the distribution of the majority carriers showing depletion effects.

For many applications, as for example tandem dye-sensitized solar cells (DSSCs), the development of transparent p-type semiconductor with good charge transport properties is crucial. In this work, a nitrogen-doped TiO2 material is transformed by ion implantation into an efficient hole transport layer that could reduce the electron-hole recombination processes in the devices. Theoretical calculations allowed to demonstrate that the position of nitrogen species as well as their respective ratio impact the optical and electrical properties of N-doped TiO2 materials. The chemical composition was therefore tuned by the ion implantation parameters, achieving a high transparency in the UV-visible region while generating delocalized states near the top of the valence band that do not act as traps. In terms of electrical properties, beyond the possibility to tune the electrical behavior of TiO2 from n-type to p-type upon nitrogen doping, we succeed to increase the conductivity by a higher electron mobility without change in their density, which is of prime interest for charge transport application.

This chapter will present a brief overview of the current sensors for VOC detection, in particular formaldehyde which has become one of the most problematic gases in indoor air. Many sensing technologies were exploited for this purpose but, in this chapter, we will focus on the impedimetric sensors. These sensors consist in a sensitive layer deposited on an insulating substrate fitted with a pair of electrodes. The detection is based on the change of conductivity of the sensitive layer due to surface interactions with the target gas provoking an electron transfer. This kind of sensor acts as a simple variable resistance and is often called chemiresistor. By principle, these sensors are simple, easy to integrate in classical electronics and cheap. Considering the nature of the sensitive coating, we can distinguish several families: metal oxide sensors, semiconductor polymer sensors or based on graphene. All 3 types of sensors will be described in this chapter.

Today, significant attention has been brought to the development of sensitive, specific, cheap, and reliable sensors for real-time monitoring. Molecular imprinting technology is a versatile and promising technology for practical applications in many areas, particularly chemical sensors. Here, we present a chemical sensor for detecting formaldehyde, a toxic common indoor pollutant gas. Polypyrrole-based molecularly-imprinted polymer (PPy-based MIP) is employed as the sensing recognition layer and synthesized on a titanium dioxide nanotube array (TiO2-NTA) for increasing its surface-to-volume ratio, thereby improving the sensor performance. Our sensor selectively detects formaldehyde in the parts per million (ppm) range at room temperature. It also shows a long-term stability and small fluctuation to humidity variations. These are attributed to the thin fishnet-like structure of the PPy-based MIP on the highly-ordered and vertically-aligned TiO2-NTA.

TiO2 nanotube arrays (TNA) elaborated on transparent and conducting substrates are promising materials for photoanodes in dye-sensitized solar cells as the reduced dimensionality enhances their transport properties. TNA were obtained by anodization of Ti films deposited by magnetron sputtering on transparent conducting oxide-coated glass. This study presents the impact of introducing a compact TiO2 underlayer on the morphological, optical and electrochemical properties of the TNA photoanodes.

Titanium dioxide (TiO2) has been an important material for decades, combining numerous attractive properties in terms of economy (low price, large availability) or ecology (non-toxic), as well as broad physical and chemical possibilities. In the last few years, the development of nanotechnologies offered new opportunities, not only in an academic perspective but also with a view to many applications with particular reference to the environment. This chapter focuses on the many ways that allow to tailor and organize TiO2 crystallites at the nanometre scale to make the most of this amazing material in the field of photovoltaics and gas sensing.

Introduction TiO2 nanotube arrays obtained by anodization of Ti are promising materials for various applications such as sensors, photocatalysis or photovoltaics. The most commonly used substrate is an opaque Ti foil. However, it can be important to elaborate the nanotubes on a transparent substrate (especially for solar cells) on which metallic Ti has been sputtered. This work shows and discuss the differences of morphological and optical properties of TiO2 nanotube films anodized on isolating and conducting (FTO) glass. * arnaud.krumpmann@umons.ac.be