The dimensionality of the nanostructures plays a pivotal role in determining the sensing performance of metal oxide semiconductors. In this paper, 2-D TiO ₂ nanosheets were assembled to form hierarchical 3-D nanoflowers by a low-temperature hydrothermal process and tested for volatile organic compound (VOC) sensing. Structural characterization, such as X-ray diffraction, revealed the anatase crystallinity of the TiO ₂ nanoflowers. The chemical composition of the nanoflowers was confirmed through energy dispersive spectroscopy and X-ray mapping techniques. Field emission scanning electron microscopy results demonstrated the 3-D nanoflower like structure, consisting of 2-D nanosheets of length 120 nm and a thickness of 12-23 nm. A suitable growth mechanism for hierarchical nanoflowers has been proposed. The nanoflowers were found to offer promising sensing performance toward VOCs, such as acetone, methanol, 2-butanone, toluene, and 2-propanol at relatively low optimum operating temperature of 60 °C, 90 °C, 60 °C, 120 °C, and 60 °C, respectively. The sensor appreciably showed fast response (~6-15 s) and recovery (~15-39 s) characteristics. Furthermore, the sensor offered high selectivity toward acetone. The sensing performance of the nanoflowers has been correlated with a space charge model at the grain boundary.

Discotic liquid crystals (DLCs) are considered as fascinating systems due to their unique property of self-assembly to yield different columnar structures. DLCs are organic semiconductors and create pathways for the development of numerous optical and electrical devices. The thin films of DLCs can be considered as low dimensional system which can exhibit remarkable optical and physical properties. In this article, we present a review on ultrathin films of some interesting DLC molecules at air–water and air–solid interfaces. The Langmuir monolayer and Langmuir–Blodgett films of DLC molecules are extensively studied. The ultrathin films of DLC molecules can yield highly anisotropic layer wherein the molecular orientation and aggregation can have large impact on the physicochemical properties of the film. Different surface phases with different molecular orientations as function of surface density and temperature can be obtained by forming the Langmuir monolayer of the DLC molecules at the air–water interface. The Langmuir monolayer in a particular phase can be deposited onto the active area of a device layer-by-layer by employing a highly controlled Langmuir–Blodgett technique. Here, we report some interesting results related on molecular orientation of the DLC molecules at different interfaces. Such aggregation of DLC molecules in ultrathin films may find applications in thin film-based electro-optical devices. GRAPHICAL ABSTRACT

In this paper, sol-gel derived undoped p-type nanotitania thin films particularly aimed to detect low ppm (5-100 ppm) methanol at low temperature (75-150°C) is reported. Anantase TiO ₂ thin film was deposited by sol-gel technique and p-type conductivity of the film was confirmed by Hall measurement. Nanocrystalline structure (12-15 nm) of the TiO ₂ film was confirmed by X-ray diffraction study and field emission scanning electron microscopy, respectively. Photoluminance spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the defect structure. Methanol sensor study was carried for detecting the concentration range of 5 to 100 ppm in the temperature range of 75 to 150°C. Highly promising sensing performance was observed at an optimum operating temperature of only 100°C with 102% response magnitude (in 100 ppm methanol) and appreciably fast response and recovery time (~18 and ~21 s, respectively). The possible mechanism behind the origin of p-type conductivity has been correlated with the defect distribution model. Detailed sensing mechanism of the p-nano-titania has been explained using Schottky barrier model.

The dipolar and surface plasmon properties of metallic nanoparticles, especially gold and silver NPs made them suitable candidates for doping with LC system, which provides faster switching time, low power consumption in the display devices. The doping of NPs in the LC system influences the physical properties such as dielectric anisotropy, optical anisotropy, elastic constants, viscosity, and conductivity. In this work, we report the effect of doping of hexane thiol functionalized silver nanoparticles (f-AgNps) of average diameter 3-5nm on the electro-optical switching properties of nematic LC 4-trans-pentyl-cyclohexyl cyanobenzene (5PCH) in the twisted nematic geometry. The threshold as well as switching voltages have also reducedin the nanocomposites of 5PCH compared to pure 5PCH. The steepness of the V-T graph necessary for better multiplexing performance and high contrast has increased by 230% in the 0.025 wt% of f-AgNPs doped 5PCH compared to pure 5PCH. The ion current for 0.025 wt% f-AgNPs doped nanocomposites of 5PCH has reduced by 60% compared to pure 5PCH. We have observed faster switching time in f-AgNPs nanocomposites compared to pure 5PCH due to the decrease of visco-elastic ratio. The total response time of 0.05 wt% f-AgNPs nanocomposites is reduced by 19% compared to pure 5PCH.