Biohybridization of Supported Gold Nanoassemblies on Silicon

Understanding the molecular interactions of bio-organic molecules with metal nanoassemblies on a semiconductor surface is important to developing potential applications involving hybrid bio-organic metal interfaces. Here, we provide the first study of room-temperature growth evolution of l-cysteine on three notable Au nanoassemblies supported on the Si(111)­7×7 surface. Our results indicate unidentate and/or bidentate arrangement of adsorbed cysteine on the Si substrate through Si–N and/or Si–S linkages, while in coexistence with the supported Au monomers and dimers. Similar to thiol-containing molecules adsorbed on other noble metals, cysteine chemisorbs via the S atom in neutral form on the supported Au nanocrystallite film. On the supported gold honeycomb nanonetwork, cysteine undergoes unidentate chemisorption through the thiol group with Au atoms and through the amino group with Si adatoms, which enables the remaining free functional groups to selectively bond with different incoming molecules. Instead of the “universal” three-stage growth found for cysteine adsorption on a pristine Si(111)­7×7 surface, we observe the two-stage growth of cysteine on the supported gold honeycomb nanonetwork (i.e., without a transitional layer), similar to that found on a gold single-crystal surface. The formation of the ultrathin gold-silicide layer (honeycomb) has effectively transformed the semiconductor surface to a metal-like surface

Bimetallic Nanoparticles for Arsenic Detection

Effective and sensitive monitoring of heavy metal ions, particularly arsenic, in drinking water is very important to risk management of public health. Arsenic is one of the most serious natural pollutants in soil and water in more than 70 countries in the world. The need for very sensitive sensors to detect ultralow amounts of arsenic has attracted great research interest. Here, bimetallic FePt, FeAu, FePd, and AuPt nanoparticles (NPs) are electrochemically deposited on the Si(100) substrate, and their electrochemical properties are studied for As­(III) detection. We show that trace amounts of As­(III) in neutral pH could be determined by using anodic stripping voltammetry. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, and Pd) than pristine noble metal NPs (without Fe alloying). Limit of detection and linear range are obtained for FePt, FeAu, and FePd NPs. The best performance is found for FePt NPs with a limit of detection of 0.8 ppb and a sensitivity of 0.42 μA ppb^–1. The selectivity of the sensor has also been tested in the presence of a large amount of Cu­(II), as the most detrimental interferer ion for As detection. The bimetallic NPs therefore promise to be an effective, high-performance electrochemical sensor for the detection of ultratrace quantities of arsenic

Nitrogen Doped Reduced Graphene Oxide Based Pt–TiO₂ Nanocomposites for Enhanced Hydrogen Evolution

Electrochemical hydrogen production from water is an attractive clean energy generation process that has enormous potential for sustainable development. However, noble metal catalysts are most commonly used for such electrochemical hydrogen evolution making the process cost ineffective. Thereby design of hybrid catalysts with minimal use of noble metals using a suitable support material is a prime requirement for the electrolysis of water. Herein, we demonstrate the superior hydrogen evolution reaction (HER) activity of the platinum nanoparticles (Pt NPs) supported on faceted titanium dioxide (TiO₂) nanocrystals (Pt–TiO₂) and nitrogen doped reduced graphene oxide (N-rGO) based TiO₂ nanocomposite (Pt–TiO₂–N-rGO). The ternary Pt–TiO₂–N-rGO nanocomposite exhibits a superior HER activity with a small Tafel slope (∼32 mV·dec^–1), exchange current density (∼0.22 mA·cm^–2), and excellent mass activity (∼3116 mA·mg_pt^–1) at 300 mV overpotential. These values are better/higher than that of several support materials investigated so far. The excellent HER activity of the ternary Pt–TiO₂–N-rGO nanocomposite is ascribed to the presence of Ti­(III) states and enhanced charge transportation properties of N-rGO. The present study is a step toward reliable electrochemical hydrogen production using faceted TiO₂ nanocrystals as support material

Engineered Electronic States of Transition Metal Doped TiO₂ Nanocrystals for Low Overpotential Oxygen Evolution Reaction

Electrochemical oxygen evolution reaction (OER) involves high overpotential at the oxygen evolving electrode and thereby suffers significant energy loss in the proton exchange membrane water electrolyzer. To reduce the OER overpotential, precious ruthenium and iridium oxides are most commonly used as anode electrocatalyst. Here we report marked reduction in overpotential for the OER using transition metal (TM) doped TiO₂ nanocrystals (NCs). This reduction in overpotential is attributed to d-orbitals splitting of the doped TMs in the TM-doped TiO₂ NCs and their interactions with the oxyradicals (intermediates of OER) facilitating the OER. The d-orbital spitting of TMs in TM-doped TiO₂ NCs is evident from the change in original pearl white color of undoped TiO₂ NCs and UV–vis absorption spectra

Induced Complementary Resistive Switching in Forming-Free TiO_<i>x</i>/TiO₂/TiO_<i>x</i> Memristors

The undesirable sneak current path is one of the key challenges in high-density memory integration for the emerging cross-bar memristor arrays. This work demonstrates a new heterojunction design of oxide multilayer stacking with different oxygen vacancy contents to manipulate the oxidation state. We show that the bipolar resistive switching (BRS) behavior of the Pt/TiOx/Pt cross-bar structure can be changed to complementary resistive switching (CRS) by introducing a thin TiO2 layer in the middle of the TiOx layer to obtain a Pt/TiOx/TiO2/TiOx/Pt device architecture with a double-junction active matrix. In contrast to the BRS in a single-layer TiOx matrix, the device with a double-junction matrix remains in a high-resistance state in the voltage range below the SET voltage, which makes it an efficient structure to overcome the sneak path constraints of undesired half-selected cells that lead to incorrect output reading. This architecture is capable of eliminating these half-selected cells between the nearby cross-bar cells in a smaller programming voltage range. A simplified model for the switching mechanism can be used to account for the observed high-quality switching performance with excellent endurance and current retention properties

Bimetallic Au@M (M = Ag, Pd, Fe, and Cu) Nanoarchitectures Mediated by 1,4-Phenylene Diisocyanide Functionalization

Hybridization with gold has attracted a lot of attention in many application areas such as energy, nanomedicine, and catalysts. Here, we demonstrate electrochemical hybridization of two different metals by using bare and 1,4-phenylene diisocyanide (PDI) functionalized gold nanoislands (GNIs) supported on a Si substrate. As pristine GNIs are not tightly locked on the Si surface, bimetallic Au@M (M = Ag, Pd, Fe, and Cu) core–shell type nanostructures are produced by an electric-field-induced clustering of GNIs and metal deposition. On the other hand, upon functionalization of GNIs by PDI, 3D island growth on the functionalized GNI template is observed as PDI acts as a protector against the electric-field-induced clustering. Depth-profiling X-ray photoelectron spectroscopy reveals no discernible difference in the interfacial electronic structures of hybrid metals prepared by using pristine and PDI-functionalized GNI templates. This work demonstrates a new approach to produce a secured template and to manipulate growth of hybrid nanoparticles on this template supported on a Si substrate by using electrodeposition and organic functionalization