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Two dimensional (2D) materials have offered unique electrical, chemical, mechanical and physical properties over the past decade owing to their ultrathin, flexible, and multilayer structure. These layered materials are being used in numerous electronic devices for various applications, and this review will specifically focus on the resistive random access memories (RRAMs) based on 2D materials and their nanocomposites. This study presents the device structures, conduction mechanisms, resistive switching properties, fabrication technologies, challenges and future aspects of 2D-materials-based RRAMs. Graphene, derivatives of graphene and MoS 2 have been the major contributors among 2D materials for the application of RRAMs; however, other members of this family such as hBN, MoSe 2 , WS 2 and WSe 2 have also been inspected more recently as the functional materials of nonvolatile RRAM devices. Conduction in these devices is usually dominated by either the penetration of metallic ions or migration of intrinsic species. Most prominent advantages offered by RRAM devices based on 2D materials include fast switching speed (<10 ns), less power losses (10 pJ), lower threshold voltage (<1 V) long retention time (>10 years), high electrical endurance (>10 8 voltage cycles) and extended mechanical robustness (500 bending cycles). Resistive switching properties of 2D materials have been further enhanced by blending them with metallic nanoparticles, organic polymers and inorganic semiconductors in various forms.

In this paper, we present the effect of varying humidity levels on the electrical parameters and the multi frequency response of the electrical parameters of an organic-inorganic composite (PEPC+NiPc+Cu2O)-based humidity sensor. Silver thin films (thickness ~200 nm) were primarily deposited on plasma cleaned glass substrates by the physical vapor deposition (PVD) technique. A pair of rectangular silver electrodes was formed by patterning silver film through standard optical lithography technique. An active layer of organic-inorganic composite for humidity sensing was later spun coated to cover the separation between the silver electrodes. The electrical characterization of the sensor was performed as a function of relative humidity levels and frequency of the AC input signal. The sensor showed reversible changes in its capacitance with variations in humidity level. The maximum sensitivity ~31.6 pF/%RH at 100 Hz in capacitive mode of operation has been attained. The aim of this study was to increase the sensitivity of the previously reported humidity sensors using PEPC and NiPc, which has been successfully achieved.

Glaucoma is a chronic ocular degenerative disease that can cause blindness if left untreated in its early stages. Deep Convolutional Neural Networks (Deep CNNs) and its variants have provided superior performance in glaucoma classification, segmentation, and detection. In this paper, we propose a two-staged glaucoma classification scheme based on Deep CNN architectures. In stage one, four different ImageNet pre-trained Deep CNN architectures, i.e., AlexNet, InceptionV3, InceptionResNetV2, and NasNet-Large are used and it is observed that NasNet-Large architecture provides superior performance in terms of sensitivity (99.1%), specificity (99.4%), accuracy (99.3%), and area under the receiver operating characteristic curve (97.8%) metrics. A detailed performance comparison is also presented among these on public datasets, i.e., ACRIMA, ORIGA-Light, and RIM-ONE as well as locally available datasets, i.e., AFIO, and HMC. In the second stage, we propose an ensemble classifier with two novel ensembling techniques, i.e., accuracy based weighted voting, and accuracy/score based weighted averaging to further improve the glaucoma classification results. It is shown that ensemble with accuracy/score based scheme improves the accuracy (99.5%) for diverse databases. As an outcome of this study, it is presented that the NasNet-Large architecture is a feasible option in terms of its performance as a single classifier while ensemble classifier further improves the generalized performance for automatic glaucoma classification.

Flexible rubber based CNT/CNT-OD/Al cells were designed, fabricated and tested for multi-sensing and filter applications. Rubbing-in technology was used to fabricate the cells containing 12–17 μm thick active layers of CNT-OD (50:50 wt%). I – V characteristics of the cells were measured and the nonlinearity coefficient ( β ) was found in the interval of 1.8 to 2.3. The cells were tested for pressure, displacement and temperature sensing in the range of 0–33 gf/cm 2 , 0–250 μm and 21–67 °C, respectively. Sensing mechanism was based on resistance/impedance change. The cells showed sensitivities up to −424.2 Ωcm 2 /gf, −40.0 Ω/μm and −402 Ω/°C for pressure, displacement and temperature, respectively. The cells’ cutoff frequency was equal to 20 kHz. The fabricated cells potentially can be used as displacement, pressure, temperature sensors and frequency low pass filter as well.

This work examines the physics of a non-invasive multi-functional elastic thin-film graphite flake–isoprene sulfone composite sensor. The strain design and electrical characterization of the stretching force, acceleration, and temperature were performed. The rub-in technique was used to fabricate graphite flakes and isoprene sulfone into sensors, which were then analyzed for their morphology using methods such as SEM, AFM, X-ray diffraction, and Fourier transform infrared spectroscopy to examine the device’s surface and structure. Sensor impedance was measured from DC to 200 kHz at up to 20 gf, 20 m/s2, and 26–60 °C. Sensor resistance and impedance to stretching force and acceleration at DC and 200 Hz rose 2.4- and 2.6-fold and 2.01- and 2.06-fold, respectively. Temperature-measuring devices demonstrated 2.65- and 2.8-fold decreases in resistance and impedance at DC and 200 kHz, respectively. First, altering the graphite flake composite particle spacing may modify electronic parameters in the suggested multi-functional sensors under stress and acceleration. Second, the temperature impacts particle and isoprene sulfone properties. Due to their fabrication using an inexpensive deposition technique, these devices are environmentally friendly, are simple to build, and may be used in university research in international poverty-line nations. In scientific laboratories, such devices can be used to teach students how various materials respond to varying environmental circumstances. They may also monitor individuals undergoing physiotherapy and vibrating surfaces in a controlled setting to prevent public health risks.

Here we described the effect of displacement, force and infrared irradiation on the resistance and impedance of tri-electrode multifunctional sensors. These sensors are based on the gel type composite of carbon nanotubes (CNT), nickel phthalocyanine (NiPc) and edible oil. The channel of this tri-electrodes (field effect transistors) structure is made of CNT-NiPc-oil gel composite using rubbing-in technology. The tri-electrode sensors’ response depends upon the direction of force/displacement and shows an anisotropy. Application of force or displacement from the top causes to decrease resistance and the impedance and vice versa in case of applying force or displacement from the side. The displacement and force sensitivities were up to −273.3 Ω μm −1 and −46.5 Ω gf −1 from the top and 480.0 Ω μm −1 and 3.1 × 10 2 Ω gf −1 from the side, respectively, for the sensing ranges 0–150 μm and 0–215 gf. Under the effect of the infrared irradiation from any direction the impedance and the resistance of the sensor reduces. On changing infrared irradiation intensity from 0 to 2500 W m −2 the sensitivities from top and side of the sensor were −37.4 Ωm 2 W −1 and −16.5 Ωm 2 W −1 , respectively. The investigated sensors may potentially be used as prototypes to develop gel-electronic-based shockproof sensors. The technological achievement in fabricating these devices is the consumption of environmentally friendly materials, particularly edible oil (organic). The edible oil allows to formulate uniform composite gel-films, that may not be comprehended only by ingredients mixing. The fabricated sensors are highly attractive for commercialization.

Carbon nanotube–glue composite gel-based surface-type elastic sensors with a cylindrical shape deformable (flexible) metallic body were fabricated for tactile pressure and compressive displacement sensing. The fabrication of the sensors was performed using the rubbing-in technique. The effect of the pressure and the compressive displacement on the capacitance and the impedance of the sensors were investigated at various frequencies (in the range of 1 kHz to 200 kHz). It was found that under the effect of pressure from 0 to 9 g/cm2, the capacitance increased by 1.86 and 1.78 times, while the impedance decreased by 1.84 and 1.71 times at the frequencies of 1 kHz to 200 kHz, respectively. The effect of displacement on the impedance and the capacitance of the device was also investigated at various frequencies from 1 kHz to 200 kHz. The results showed that under the effect of compressive displacement up to 25 µm, the impedance of the sensors decreased on average by 1.19 times, while the capacitance increased by 1.09 times, accordingly. The frequency response of the displacement sensor showed that it matched with the low-pass filter. The obtained results are explained based on changes in the shape and geometrical parameters of the cylindrical-shaped conductive body. These results have also been explained on the basis of the distance between the conductive plates of the capacitive sensors during compression, which takes place under the effect of applied pressure or displacement. Moreover, the design of the sensors is simple and easy to fabricate, and their use is also earthy. The fabricated sensors have great potential for commercialization.

Optimized surface-type impedimetric and capacitive proximity sensors have been fabricated on paper substrates by using rubbing-in technology. The orange dye (OD) and silicone glue (SG) composite-gel films were deposited on the zig-zag gap between two aluminum electrodes fixed on a paper (dielectric) substrate. The effect of proximity of various objects (receivers) on the impedance and the capacitance of the sensors was investigated. These objects were semi-cylindrical aluminum (metallic) foil, a cylindrical plastic tube filled with water, a kopeck-shaped plastic tube filled with carbon nanotubes and a human finger. The mechanism of sensing was based on the change in impedance and/or the capacitance of the sensors with variation of proximity between the surfaces of the sensor and the object. On decreasing proximity, the impedance of the sensors increased while the capacitance decreased. The impedimetric proximity sensitivities of CNT, water, metal-based receivers and the finger were up to 60 × 10[sup.3] Ω/mm, 35 × 10[sup.3] Ω/mm, 44 × 10[sup.3] Ω/mm and 6.2 × 10[sup.3] Ω/mm, respectively, while their capacitive sensitivities were −19.0 × 10[sup.−2] pF/mm, −16.0 × 10[sup.−2] pF/mm, −16.4 × 10[sup.−2] pF/mm and −1.8 × 10[sup.−2] pF/mm. If needed for practical application, the sensors can be built in to the Wheatstone bridge, which can also increase the sensitivity of the measurement. Moreover, the sensor’s materials are low cost, while the fabrication technique is easy and ecologically friendly. The sensor can also be used for demonstrative purposes in school and college laboratories.

Here, we present the design, fabrication and characterization of shockproof rubber–jelly (NiPc–CNT–oil) composite-based resistors. To fabricate the resistors, gels of CNT and NiPc with edible oil were prepared and deposited on a flexible rubber substrate using rubbing-in technique. The devices’ resistance and impedance were investigated under the effect of pressure, displacement, humidity, temperature and mechanical vibrations. The resistance and the impedance decreased, on average, by 1.08 times under the effect of pressure (up to 850 gf/cm2) and by 1.04 times under the effect of displacement (up to 50 µm). Accordingly, upon increasing the humidity from 60% to 90% RH, the resistance and impedance decreased by up to 1.04 times, while upon increasing the temperature from 25 °C to 43 °C, the resistance and impedances also decreased by up to 1.05 times. Moreover, under the effect of vibration, a decrease in resistance and impedance, by up to 1.03 times, was observed. The investigated samples can potentially be used as prototypes for the development of shockproof jelly electronic-based devices in particular resistors. The technological achievement in the fabrication of these devices is the use of edible organic oil, which allows for the fabrication of uniform jelly films of organic materials that cannot be realized simply by mixing “dry” ingredients. Especially, we highlight that edible organic oil is environmentally friendly, unlike some other inorganic oils that are used in practice.

The flexible and shockproof rubber-based Al/OD-Gel/Cu electrochemical cell was designed, fabricated, and investigated for the detection of IR and UV irradiations. For this purpose, the transparent gel–orange dye composite was deposited on the porous rubber substrate between aluminum and copper electrodes. It was observed that the gel–orange dye composite was mechanically like a gel: soft and flexible. Electrically, this composite (gel–orange dye) forms a flexible electrolyte. It was found that the impedance of the samples under the effect of infrared irradiation decreased by 2.02 to 2.19 times on changing frequency from 100 Hz to 200 kHz. Accordingly, under the effect of ultraviolet irradiation, the impedance of the samples decreased by 1.23 to 1.45 times on increasing frequency from 100 Hz to 200 kHz. Under the effect of infrared irradiation up to 4000 W/m2, the cell’s open-circuit voltage increased by 1.59 times. The cell’s open-circuit voltage also increased by 1.06 times under the effect of ultraviolet irradiation up to 200 uW/cm2. The mechanism of the absorption of the infrared and ultraviolet irradiations by the OD–Gel composite has been discussed in detail. The fabricated flexible rubber substrate-based Al/OD-Gel/Cu electrochemical cells can be used as a prototype for the development of gel electronics-based devices.