This paper demonstrated a flexible humidity sensor based on tin dioxide/reduced graphene oxide (RGO) nanocomposite film. The humidity sensor was fabricated on a polyimide substrate with microelectrodes by using a facile one-step hydrothermal route. The hydrothermal synthesized SnO 2 nanoparticles and SnO 2 /RGO hybrid nanostructures were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The humidity sensing properties of the presented SnO 2 /RGO nano-hybrid sensor were investigated by exposing it to a broad humidity range of 11–97%RH at room temperature. Compared with traditional humidity sensors, the SnO 2 modified graphene sensor demonstrated an ultrahigh sensitivity and a rapid response/recovery characteristic over a full humidity range measurement, highlighting the unique advantages of hydrothermal synthesis for sensors fabrication. Finally, the possible humidity sensing mechanism of the proposed sensor was discussed by using complex impedance spectra and bode diagrams. These observed results demonstrate that RGO modified with metal oxide is promising nanomaterials for constructing high performance humidity sensors in widespread applications.

Fabrication and characterization of an ultrasensitive humidity sensor based on metal oxide/graphene hybrid nanocomposite

Introduction to electrodynamics, 3rd edition [Book Review]

Due to its excellent electrical and optical properties, tin selenide (SnSe), a typical candidate of two-dimensional (2D) semiconductors, has attracted great attention in the field of novel optoelectronics. However, the large-area growth of high-quality SnSe films still remains a great challenge, which limits their practical applications. Here, wafer-size SnSe ultrathin films with high uniformity and crystallization were deposited via a scalable magnetron sputtering method. The results showed that the SnSe photodetector was highly sensitive to a broad range of wavelengths in the UV-visible-NIR range, especially showing an extremely high responsivity of 277.3 A W-1 with the corresponding external quantum efficiency of 8.5 × 104% and detectivity of 7.6 × 1011 Jones. These figures of merits are among the best performances for the sputter-fabricated 2D photodetector devices. The photodetecting mechanisms based on a photogating effect induced by the trapping effect of localized defects are discussed in detail. The results indicate that the few-layered SnSe films obtained from sputtering growth have great potential in the design of high-performance photodetector arrays.

Wafer-size growth of 2D layered SnSe films for UV-Visible-NIR photodetector arrays with high responsitivity

The present study demonstrates a solution-processed humidity sensor based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]:polyvinylpyrrolidone (MEH-PPV:PVP) organic microstructured composite thin film. The capacitive type humidity sensor has been fabricated in the surface type geometry of Al/MEH-PPV:PVP/Al, wherein organic composite (MEH-PPV:PVP) has been deposited onto the aluminium electrodes by electrospinning technique. The structural and morphological properties of organic thin film have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The humidity sensing properties of the sensor have been investigated at ∼1 volt AC operational bias, by measuring the capacitance as a function of a broad range (20–90%) of relative humidity (RH). The temperature and operational frequency dependency of the capacitance of the sensor has also been analyzed in detail. The proposed sensor exhibits high sensitivity (114 fF/% RH @ 100 Hz), small hysteresis (∼2% RH) and fast response (18 s and 8 s for adsorption and desorption processes, respectively). Compared with traditional spin-coated and drop-casted organic humidity sensors, the microstructure composite based sensor has demonstrated significantly improved sensing parameters, highlighting the unique advantages of the electrospinning process for humidity sensor fabrication. The possible humidity sensing mechanism of the proposed capacitive sensor has also been elaborated.

Humidity sensor based on electrospun MEH-PPV:PVP microstructured composite

In this paper, we reported comparative study of the humidity characteristics of graphene/silver nanoparticles composite (Gr-AgNps) and graphene/silver nanoparticles/PMMA composite (Gr-AgNps-PMMA) based efficient humidity sensors. Aqueous solution of Gr-AgNps and Gr-AgNps-PMMA was drop casted over interdigitated copper electrodes with 50 μm gap embedded in the substrates in dust free environment. The band gap obtained from the UV–vis spectra for Gr-AgNps and Gr-AgNps-PMMA based humidity sensors was 4.7 and 4.1 eV respectively. The capacitive and resistive humidity response was studied using LCR meter (GW Instek817). Apparent increase in capacitance was observed (100–10,000 nF) with the increase in the humidity percentage (30–95%RH) at lower frequencies for both the sensors. Resistance of the sensors dropped to zero as the humidity level is increased from 30 to 95%RH in the chamber. The devices were tested for real time stability and for fast response/recovery time. Both the devices showed an excellent stability and response by recording their resistance and capacitance respectively. A lagging of RH decreasing response from RH increasing response was observed at 500 Hz frequency for both the sensors depicted from the hysteresis curve. The humidity response of Gr-AgNps was comparatively better than that of the Gr-AgNps-PMMA based humidity sensors.

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Capacitive and resistive response of humidity sensors based on graphene decorated by PMMA and silver nanoparticles

Cobalt phthalocyanine (CoPc), an organic semiconductor, has been introduced as an active sensing layer in a surface-type multipurpose sensor owing to its stability, low fabrication cost, and multifunctional sensitivity. The capacitance of the sensor was recorded to increase 26.7-fold for a change in relative humidity (RH) from 0% to 92.3%, 12.6-fold for a change in illumination from 11.5 lx to 23,000 lx, and 5.2-fold for a change in temperature from 27°C to 187°C. The morphology of the active thin film of the sensor was analyzed by atomic force microscopy, revealing a rough surface favorable for moisture absorption and light harvesting. The CoPc film was amorphous in nature according to x-ray diffraction analysis. By virtue of its response to humidity, light, and temperature, this represents an attractive approach for cost-effective environmental sensing applications.

Sensing Properties of Cobalt-Phthalocyanine-Based Multipurpose Sensor

Investigating sensing properties of poly-(dioctylfluorene) based planar sensor

This paper reports on the thin film characterization of a synthesized small molecular semiconductor N-butyl-N′-(6-hydroxyhexyl) perylene-3,4,9,10-tetracarboxylic acid diimide (N-BuHHPDI) and its potential use in Ag/N-BuHHPDI/PEDOT:PSS/p-Si heterojunction device. The device is fabricated using spin coating of a conducting polymer PEDOT:PSS on p-Si substrate followed by thermal deposition of a 100-nm-thin layer of N-BuHHPDI. To complete the fabrication of Ag/N-BuHHPDI/PEDOT:PSS/p-Si heterostructure, silver (Ag) is used as the top electrode. The device shows non-ohmic and asymmetrical current–voltage (I–V) characteristics in dark conditions at 25°C which confirm the successful formation of rectifying heterojunction. Various diode parameters such as ideality factor (n), barrier height (ϕb), series resistance (Rs) and charge carrier mobility across the interface of the heterojunction are measured from the I–V characteristics. The non-ideal behavior of the diode is correlated with the film morphology obtained by atomic force microscopy. Fourier transformed infrared spectroscopy is performed to confirm the successful preparation of N-BuHHPDI. The fluorescence lifetime (22 ns) of the N-BuHHPDI thin film is measured via fluorescence spectroscopy. Different charge conduction mechanisms including the dominant one are studied for the fabricated device.

Dil Nawaz Khan

Papers

Sensing Properties of Cobalt-Phthalocyanine-Based Multipurpose Sensor

Investigating sensing properties of poly-(dioctylfluorene) based planar sensor

Perylene Tetracarboxylic Diimide: Characterization and Its Role in the Electrical Properties of an Ag/N-BuHHPDI/PEDOT:PSS/p-Si Heterojunction Device