Compositional effects of hybrid MoS2-GO active layer on the performance of unipolar, low-power and multistate RRAM device.

Currently, 2D nanomaterials-based resistive random access memory (RRAMs) are explored on account of their tunable material properties enabling fabrication of low power and flexible RRAM devices. In this work, hybrid MoS2-GO based active layer RRAM devices are investigated. A facile hydrothermal co-synthesis approach is used to obtain the hybrid materials and a cost-effective spin coating method adopted for the fabrication of Ag/MoS2-GO/ITO RRAM devices. The performance of the fabricated hybrid active layer RRAM device is analysed with respect to change in material properties of the synthesized hybrid material. The progressive addition of 0.5, 1.5, 2.5 and 4.5 weight % of GO to MoS2, results in a hybrid active layer with higher intermolecular interaction, in the case of Ag/MoS2-GO4.5/ITO RRAM device, resulting in a unipolar resistive switching RRAM behavior with low SET voltage of 1.37 V and highIon/Ioffof 200 with multilevel resistance states. A space charge limited conduction mechanism is obtained during switching, which may be attributed to the trap states present due to functional groups of GO. The increased number of conduction pathways on account of both Ag+ions and oxygen vacancies (Vo2+), participating in the formation of conducting filament, results in higherIon/Ioff. This is the first report of unipolar Ag/MoS2-GO/ITO RRAM devices, which are particularly important in realizing high density crossbar memories for neuromorphic and in-memory computing as well as enabling flexible 2D nanomaterials-based memristor applications.

The role of ambient ice-like water adlayers formed at the interfaces of graphene on hydrophobic and hydrophilic substrates probed using scanning probe microscopy.

In this work, we report the role of ice-like water adlayers (IWLs) formed under ambient conditions in between mechanically exfoliated as-prepared and patterned few layer graphene (FLG) and multi-layer graphene (MLG) on hydrophobic Si and hydrophilic SiO2/Si substrates. The growth of the IWL is probed by measuring the height changes in graphene using intermittent contact atomic force microscopy (IC-AFM) and their electrostatic effect is studied using electrostatic force microscopy (EFM) over time. It is found that more IWLs are formed within a shorter period of time, when both as-prepared graphene and underlying substrates are either hydrophobic or hydrophilic in nature. In contrast, AFM voltage nanolithographically patterned trenches on FLG and MLG on the Si substrate show quick formation of IWLs. The effect of IWL formed, on the dimensions of trenches, is correlated with the variation of the measured EFM phase shift over time. This study demonstrates the dependence of the formation of IWLs under ambient conditions on the affinity towards water, at the interface of graphene on hydrophobic and hydrophilic substrates, which has important implications for the performance of graphene-based nanoelectronic devices.

Interaction and dynamics of ambient water adlayers on graphite probed using AFM voltage nanolithography and electrostatic force microscopy.

In this work, we report the impact of the interaction and dynamics of increasing ambient water adlayers on etch patterns on a hydrophobic highly oriented pyrolytic graphite (HOPG) surface obtained using atomic force microscopy (AFM) voltage nanolithography in contact mode by applying a positive bias to the sample. The changes in the dimensions of the etch patterns were investigated as a function of the increasing number of water adlayers present on the HOPG, which is varied by changing the time interval since HOPG cleavage. Changes in the width of the etch patterns and the surrounding water droplets were monitored with time, using intermittent-contact-mode AFM. Electrostatic force microscopy (EFM) has been employed to study the charged nature of the etch patterns and the neighboring water film with time. The width of the etch patterns made on freshly cleaved HOPG shows an increase of ∼33% over 48 h, whereas nine-day-old cleaved HOPG shows a 79% increase over the same period. No changes in the dimensions are observed while imaging in a nitrogen atmosphere soon after lithography. In ambient conditions, the EFM phase shift of the patterns shows a large change of ∼84-88% over 30 h. This study demonstrates the effect of the stored electrostatic energy of a polarized ice-like water adlayer, resulting in changes in the dimensions of the etch patterns long after lithography, whereas liquid-like water droplets do not affect the etch patterns.

Cellular network formation of hydrophobic alkanethiol capped gold nanoparticles on mica surface mediated by water islands.

Dendritic and cellular networks of nanoparticles are known to form commonly either by random diffusion-limited aggregation or by solvent evaporation dynamics. Using alkanethiol capped gold nanoparticles deposited on mica imaged under ambient and controlled water vapor conditions by atomic force microscope and in situ scanning electron microscope, respectively, we show a third mechanism in action. The cellular network consisting of open and closed polygons is formed by the nucleation and lateral growth of adsorbed water islands, the contact lines of which push the randomly distributed hydrophobic nanoparticles along the growth directions, eventually leading to the polygonal structure formation as the boundaries of the growing islands meet. Such nanoparticle displacement has been possible due to the weakly adhering nature of the hydrophilic substrate, mica. These results demonstrate an important but hitherto neglected effect of adsorbed water in the structure formation on hydrophilic substrates and provide a facile tool for the fabrication of nanoparticle networks without specific particle or substrate modifications and without a tight control on particle deposition conditions during the solvent evaporation.

Preparation and evaluation of nimesulide-loaded ethylcellulose and methylcellulose nanoparticles and microparticles for oral delivery.

The present study was designed to assess and compare with a range of surfactant-coated, nimesulide-free, and nimesulide-loaded ethylcellulose/methylcellulose (EC/MC) nanoparticles that were prepared by varying drug concentration (ED/MD), polymer concentration (EP/MP), and surfactant concentration (ES/MS). EC/MC nanoparticles prepared by desolvation method produced discrete particles and they were characterized by SEM, AFM, and FTIR studies. The particles mean size diameter (nm) ranged from 244 to 1056 nm and 1065 to 1710 nm for EC and MC nanoparticles, respectively. Studies on drug: polymer ratio showed a linear relationship between drug concentration and percentage of loading in nanoparticles. The encapsulation efficiency decreased with the increase of nimesulide concentration with respect to polymer concentration. Encapsulation efficiency of drug-loaded nanoparticles was varied between 32.8% and 64.9%. The in vitro release of drug-loaded nanoparticles was found to be a first order. This was significantly increased in EC nanoparticles (95.50%) in comparison with MC nanoparticles (95.12%) after 12 h in 24 h long study. Nimesulide release from EC nanoparticles was much slower at slightly alkaline pH 7.4. The in vitro hemolysis tests of nanoparticles were carried out to ascertain the hemocompatibility and shown to be insignificant for EC nanoparticles. In comparison, ES4 from EC formulations with nimesulide was found to be promising with slow and sustained drug release.