This study reports on the mid-infrared (mid-IR) photothermal response of multilayer MoS₂ thin films grown on crystalline (p-type silicon and c-axis-oriented single crystal sapphire) and amorphous (Si/SiO₂ and Si/SiN) substrates by pulsed laser deposition (PLD). The photothermal response of the MoS₂ films is measured as the changes in the resistance of the MoS₂ films when irradiated with a mid-IR (7 to 8.2 μm) source. We show that enhancing the temperature coefficient of resistance (TCR) of the MoS₂ thin films is possible by controlling the film-substrate interface through a proper choice of substrate and growth conditions. The thin films grown by PLD are characterized using X-ray diffraction, Raman, atomic force microscopy, X-ray photoelectron microscopy, and transmission electron microscopy. The high-resolution transmission electron microscopy (HRTEM) images show that the MoS₂ films grow on sapphire substrates in a layer-by-layer manner with misfit dislocations. The layer growth morphology is disrupted when the films are grown on substrates with a diamond cubic structure (e.g., silicon) because of twin growth formation. The growth morphology on amorphous substrates, such as Si/SiO₂ or Si/SiN, is very different. The PLD-grown MoS₂ films on silicon show higher TCR (-2.9% K^-1 at 296 K), higher mid-IR sensitivity (ΔR/R = 5.2%), and higher responsivity (8.7 V·W^–1) compared to both the PLD-grown films on other substrates and the mechanically exfoliated MoS₂ flakes transferred to different substrates.

Nanocellulose is a sustainable and eco-friendly nanomaterial derived from renewable biomass. In this study, we utilized the structural advantages of two types of nanocellulose and fabricated freestanding carbonized hybrid nanocellulose films as electrode materials for supercapacitors. The long cellulose nanofibrils (CNFs) formed a macroporous framework, and the short cellulose nanocrystals were assembled around the CNF framework and generated micro/mesopores. This two-level hierarchical porous structure was successfully preserved during carbonization because of a thin atomic layer deposited (ALD) Al₂O₃ conformal coating, which effectively prevented the aggregation of nanocellulose. These carbonized, partially graphitized nanocellulose fibers were interconnected, forming an integrated and highly conductive network with a large specific surface area of 1,244 m²·g^–1. The two-level hierarchical porous structure facilitated fast ion transport in the film. When tested as an electrode material with a high mass loading of 4 mg·cm^–2 for supercapacitors, the hierarchical porous carbon film derived from hybrid nanocellulose exhibited a specific capacitance of 170 F·g^–1 and extraordinary performance at high current densities. Even at a very high current of 50 A·g^–1, it retained 65% of its original specific capacitance, which makes it a promising electrode material for high-power applications.

Nanowire sensors based on variations of their electrical properties show great potential for real-time, in situ monitoring of molecular adsorption and desorption. Although the molecular adsorption-induced change in the electronic work function is very sensitive, it does not have any specificity. However, the temperature dependency of the adsorption-induced work function variation can provide limited selectivity based on the desorption temperature. In this study, we report the in situ probing of molecular desorption by monitoring the work function variations of a single Pt nanowire as a function of temperature. The work function of a clean Pt nanowire shows a significant variation due to vapor adsorption at room temperature. Increasing the temperature of the nanowire results in a variation of the work function due to molecular desorption. Experimentally measured differential work function as a function of temperature shows desorption peaks at 36 and 44 ℃ for methanol and ethanol molecules respectively. Adsorption-induced variation of the Pt nanowire work function was further confirmed using ultraviolet photoelectron spectroscopy before and after exposure to methanol vapor. These results show that the molecular adsorption/desorption-induced variation of the work function and its temperature dependency can be used for developing nanoscale electro-calorimetric sensors.