This study reports the fast response and recovery of hydrogen sensing in nanoparticle-graphene composite layers fabricated using chemical methods and comprising of isolated Pd alloy nanoparticles dispersed onto graphene layers. For 2% hydrogen at 40 °C and 1 atm pressure, a response time of <2 s and a recovery time of 18 s are observed. The fast response and recovery observed during sensing are due to hydrogen-induced changes in the work function of the Pd alloy and modification in the distribution of defect states in the graphene band gap due to gas adsorption. The results of hydrogen sensing in the new class of Pd-Pt nanoparticle-graphene composite material are important for understanding the effect of gas adsorption on electronic conduction in graphene layers and for developing a new type of gas sensor based on changes in the electronic properties of the interface.

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We report Raman spectroscopic studies of the nanosized rare earth sesquioxides, namely yttrium sesquioxide (Y(2)O(3)), gadolinium sesquioxide (Gd(2)O(3)) and samarium sesquioxide (Sm(2)O(3)), under high pressure. The samples were characterized using x-ray diffraction, Raman spectroscopy and atomic force microscopy at atmospheric pressures. Y(2)O(3) and Gd(2)O(3) were found to be cubic at ambient, while Sm(2)O(3) was found to be predominantly cubic with a small fraction of monoclinic phase. The strongest Raman peaks are observed at 379, 344 and 363 cm(-1), respectively, for Y(2)O(3), Sm(2)O(3) and Gd(2)O(3). All the samples were found to be nanosized with 50-90 nm particle sizes. The high pressures were generated using a Mao-Bell type diamond anvil cell and a conventional laser Raman spectrometer is used to monitor the pressure-induced changes. Y(2)O(3) seems to undergo a crystalline to partial amorphous transition when pressurized up to about 19 GPa, with traces of hexagonal phase. However, on release of pressure, the hexagonal phase develops into the dominant phase. Gd(2)O(3) is also seen to develop into a mixture of amorphous and hexagonal phases on pressurizing. However, on release of pressure Gd(2)O(3) does not show any change and the transformation is found to be irreversible. On the other hand, Sm(2)O(3) shows a weakening of cubic phase peaks while monoclinic phase peaks gain intensity up to about a pressure of 6.79 GPa. However, thereafter the monoclinic phase peaks also reduce in intensity and mostly disordering sets in which does not show significant reversal as the pressure is released. The results obtained are discussed in detail.

With the objective of understanding the role of size and current level of filamentary regions on the resistive switching parameters, detailed conductive atomic force microscope investigations of resistive memory cells having different dimensions have been carried out in this study. Cu-Cu(2)O-Ti memory cells having dimensions of 150, 50 and 25 μm have been fabricated on the same substrate using a stencil lithography technique. The dependence of resistive switching parameters on the device dimensions can be directly related to the average size, current level of the filaments and difference in these parameters between the low resistance state (LRS) and high resistance state (HRS). It is observed that the large increase in the ratio of current in the two states in cells having lower dimensions is mainly due to the smaller number of conducting regions in the HRS, indicating efficient switching from the LRS to the HRS at lower dimensions.

In the present study, nanoscale variations in the work function values and the resulting changes in junction properties of chemical vapour deposited two-dimensional (2D) MoS 2 domains has been investigated as a function of number of layers using Kelvin Probe Force Microscopy (KPFM) and Conductive Atomic Force Microscopy(CAFM) techniques. Raman spectroscopy has been employed to obtain the magnitude of difference between E 2g and A 1g peaks which has been used as a signature of the number of layers. Surface potential of MoS 2 monolayer sample exhibits a value of -427 mV (~7.2 mV for bulk) along with a large spread of about 29mV (~3mV for bulk). The present study shows that the optical and electronic properties of MoS 2 1-2 layer samples exhibit a large difference from its bulk counterpart. These characteristic features remain intact even in the presence of adsorbates and defects which result in spread in surface potential values and corresponding changes in junction characteristics. These results are important for the application of Chemical Vapor Deposition (CVD) grown MoS 2 monolayers for semiconductor devices.

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This study reports an enhanced and unusual pulse like hydrogen sensing response in Pd nanoparticle layers. The faster H adsorption due to increased surface area and closure of conducting paths as a result of lattice expansion on hydride formation are the primary reasons for this. In comparison, Pd thin films exhibit a slow and subdued sensing response because of the overlap of the above two opposing effects and hydrogen induced lattice strain. Temperature independent conductivity in the temperature range of 20–300K confirms the presence of interparticle gaps in the case of Pd nanoparticle layers.

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