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Several different methods are established for the analysis of gases, including optical spectroscopy, photoacoustic spectroscopy as well as colorimetric and resistive sensing, the measurements systems are either too complex or have limited sensitivity. In particular, when the goal is to apply a large number of sensors in networks, it is highly desirable to have devices that are simple, have low cost and energy consumption, yet sensitive and selective to monitor analytes even in traces. Herein, we propose a new type of resistive sensor device based on a composite of single-wall carbon nanotubes and an ion-in-conjugation polymer, poly(1,5-diaminonaphthalene-squaraine), capable of detecting H2S and NH3 in air even at room temperature with a theoretical concentration limit of ∼1 ppb and ∼7 ppb, respectively. Density functional theory calculations revealed that H atoms of the analytes and O atoms of the polymer chain interact and form hydrogen bonds, and the electron withdrawal from the gas molecules by the polymer chain results in the change of its electrical conductivity. To demonstrate the feasibility of the new nanocomposites in sensing, we show the devices for monitoring food safety with good sensor stability of operation for at least 3 months of period of time.

H₂S is a toxic and corrosive gas, whose accurate detection at sub-ppm concentrations is of high practical importance in environmental, industrial, and health safety applications. Herein, we propose a chemiresistive sensor device that applies a composite of single-walled carbon nanotubes (SWCNTs) and brominated fullerene (C₆₀Br₂₄) as a sensing component, which is capable of detecting 50 ppb H₂S even at room temperature with an excellent response of 1.75% in a selective manner. In contrast, a poor gas response of pristine C₆₀-based composites was found in control measurements. The experimental results are complemented by density functional theory calculations showing that C₆₀Br₂₄ in contact with SWCNTs induces localized hole doping in the nanotubes, which is increased further when H₂S adsorbs on C₆₀Br₂₄ but decreases in the regions, where direct adsorption of H₂S on the nanotubes takes place due to electron doping from the analyte. Accordingly, the heterogeneous chemical environment in the composite results in spatial fluctuations of hole density upon gas adsorption, hence influencing carrier transport and thus giving rise to chemiresistive sensing.

Solar cells based on c-Si/porous-Si/CdS/ZnₓCd₁₋ₓO heterojunctions were synthesized by depositing CdS films on c-Si/porous-Si (PS) substrates by electrochemical deposition (ED). PS layers with systematically varied pore diameter (8÷45 nm) and were fabricated on p-type c-Si wafers using electrochemical etching. The window layers of ZnₓCd₁₋ₓO with several Zn concentrations(x=0.2; 0.4; 0.5 and 0.6) were also deposited on the CdS buffer layers by ED. The photoelectrical properties of heterojunctions were studied as functions of PS pore size and Zn content in ZnₓCd₁₋ₓO. The optimal pore size and Zn contents were found to be 10 nm and x=0.6, respectively. These yielded a solar cell sample exhibiting an efficiency of 9.9%, the maximum observed in this study.

The rapid oxide formation on pristine unprotected copper surfaces limits the direct application of Cu nanomaterials in electronics and sensor assemblies with physical contacts. However, it is not clear whether the growing cuprous (Cu₂O) and cupric oxides (CuO) and the formation of core-shell-like Cu-Cu₂O/CuO nanowires would cause any compromise for non-contact optical measurements, where light absorption and subsequent charge oscillation and separation take place such as those in surface plasmon-assisted and photocatalytic processes, respectively. Therefore, we analyze how the surface potential of hydrothermally synthetized copper nanowires changes as a function of time in ambient conditions using Kelvin probe force microscopy in dark and under light illumination to reveal charge accumulation on the nanowires and on the supporting gold substrate. Further, we perform finite element modeling of the optical absorption to predict plasmonic behavior of the nanostructures. The results suggest that the core-shell-like Cu-Cu₂O/CuO nanowires may be useful both in photocatalytic and in surface plasmon-enhanced processes. Here, by exploiting the latter, we show that regardless of the native surface oxide formation, random networks of the nanowires on gold substrates work as excellent amplification media for surface-enhanced Raman spectroscopy as demonstrated in sensing of Rhodamine 6G dye molecules.