One‐step Synthesis of AuAg Alloy Nanodots and its Electrochemical Studies towards Nitrobenzene Reduction and Sensing

Efficient, stable, and low‐cost electrocatalysts for the degradation and sensing of environment pollutants are essential components of clean environment monitoring. Here we report, one‐step synthesis and characterization of 1–3 nm diameter sized bi‐metallic AuAg nanodots (NDs) embedded in amine functionalized silicate sol‐gel matrix (SSG) and its electrochemical studies toward nitrobenzene. The SSG was used as a reducing agent as well as stabilizer for the prepared mono‐ and bi‐metallic nanoparticles (NPs). From the HRTEM, STEM‐EDS and XPS analyses, the bi‐metallic AuAg NDs were identified as an alloy and not the mixtures of Au and Ag NPs. Characteristic surface plasmon resonance (SPR) band between the Au and Ag NPs SPR absorption region was noticed for the prepared AuAg NDs. The AuAg alloy NDs with different concentrations of Au and Ag (Au₂₅Ag₇₅, Au₅₀Ag₅₀ and Au₇₅Ag₂₅ NDs) modified electrodes exhibited synergistic electrocatalytic effect than did the Au and Ag NPs towards nitrobenzene reduction and detection. Together with ultra‐small size and exceptional colloidal stability features within these SSG‐AuAg NDs pave convenient way for nanotechnology‐based catalysts development and sensor applications.     

Fabrication of 2D ordered arrays of cobalt silicide nanodots on (0 0 1)Si substrates

Two-dimensional (2D) periodic arrays of Co metal and Co silicide nanodots were successfully fabricated on (0 0 1)Si substrate by using the polystyrene (PS) nanosphere lithography (NSL) technique and thermal annealing. The epitaxial CoSi₂ was found to start growing in samples after annealing at 500 °C. The sizes of the Co silicide nanodots were observed to shrink with annealing temperature. From the analysis of the selected-area electron diffraction (SAED) patterns, the crystallographic relationship between the epitaxial CoSi₂ nanodots and (0 0 1)Si substrates was identified to be [0 0 1]CoSi₂//[0 0 1]Si and (2 0 0)CoSi₂//(4 0 0)Si. By combining the planview and cross-sectional TEM examination, the epitaxial CoSi₂ nanodots formed on (0 0 1)Si were found to be heavily faceted and the shape of the faceted epitaxial CoSi₂ nanodot was identified to be inverse pyramidal. The observed results present the exciting prospect that with appropriate controls, the PS NSL technique promises to offer an effective and economical patterning method for the growth of a variety of large-area periodic arrays of uniform metal and silicide nanostructures on different types of silicon substrates.     

Dependence of surface distribution of self-assembled InSb nanodots on surface morphology and spacer layer thickness

Self-assembled InSb nanodots (NDs) were grown on a GaSb (1 0 0) substrate using metal-organic vapour phase epitaxy (MOVPE). The effects of etching depth of the substrate and thickness of the GaSb buffer layer on the density and size distribution of single and double layer dots were studied for detector applications. The etch depth of the substrate was varied up to 30 μm. In this particular study, the dots were grown at 450 °C and the GaSb spacer thickness was varied between 50 nm and 200 nm. The optimum substrate etch depth was found to be 30 μm while the best spacer thickness was found to be 200 nm.     

Charging/discharging kinetics in LPCVD silicon nanocrystal MOS memory structures

The paper focuses on the peculiarities of charging/discharging kinetics and write/erase (W/E) window formation in nanocrystal metal-oxide semiconductor (MOS) non-volatile memory (NVM) structures prepared by low-pressure chemical vapor deposition (LPCVD) of amorphous silicon, followed by solid phase crystallization and thermal oxidation. It is generally known that the W/E window formation via pulse injection depends on the kinetics of carriers trapping (electrons and/or holes) in the nanocrystal NVM structure and consequently on the cumulative time of recharging bias application, i.e. pulse duration and number of applied pulses. In this work, we have shown that with the same cumulative time biasing but different charging pulse durations, the resulting W/E window width can be rather different, demonstrating a staircase window formation. This phenomenon is interpreted by a model of partial fast charge draining from the trapping sites in the vicinity of Si nanoclusters into the Si substrate. The detailed experimental investigation of charging/discharging kinetics of the considered structures in combination with computer simulations lead to the conclusion that there is a single process of negative charge trapping with a time constant of 235±35 ms and at least four processes of positive charge trapping with time constants distributed in the range from <10 ms to >10 s.     

The effect of size on the resistive switching characteristics of NiO nanodots

NiO nanodots were fabricated via a shattering process using an AFM tip, where an NiO nanodot with a diameter of approximately 90 nm was broken into very small pieces. The pieces showed diverse diameters, including three diameters of approximately 10, 20, and 30 nm. The NiO nanodots exhibited unipolar switching characteristics including bistable resistivity during 200 repeated switching cycles. Significantly, the magnitude of the “ON currents” was observed to depend on the formation of conducting filaments in the NiO nanodots. We suggest that the critical diameter of the RRAM NiO nanodots is approximately 30 nm.     

Synthetic Strategies for the Selective Functionalization of Carbon Nanodots Allow Optically Communicating Suprastructures

The surface of Carbon Nanodots (CNDs) stands as a rich chemical platform, able to regulate the interactions between particles and external species. Performing selective functionalization of these nanoscale entities is of practical importance, however, it still represents a considerable challenge. In this work, we exploited the organic chemistry toolbox to install target functionalities on the CND surface, while monitoring the chemical changes on the material's outer shell through nuclear magnetic resonance spectroscopy. Following this, we investigated the use of click chemistry to covalently connect CNDs of different nature en-route towards covalent suprastructures with unprecedent molecular control. The different photophysical properties of the connected particles allowed their optical communication in the excited state. This work paves the way for the development of selective and addressable CND building blocks which can act as modular nanoscale synthons that mirror the long-established reactivity of molecular organic synthesis.