Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

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Principles Of Fluorescence Spectroscopy

Metal oxide-based resistive-type gas sensors are solid-state devices which are widely used in a number of applications from health and safety to energy efficiency and emission control. Nanomaterials such as nanowires, nanorods, and nanoparticles have dominated the research focus in this field due to their large number of surface sites facilitating surface reactions. Previous studies have shown that incorporating two or more metal oxides to form a heterojunction interface can have drastic effects on gas sensor performance, especially the selectivity. Recently, these effects have been amplified by designing heterojunctions on the nano-scale. These designs have evolved from mixed commercial powders and bi-layer films to finely-tuned core–shell and hierarchical brush-like nanocomposites. This review details the various morphological classes currently available for nanostructured metal-oxide based heterojunctions and then presents the dominant electronic and chemical mechanisms that influence the performance of these materials as resistive-type gas sensors. Mechanisms explored include p–n and n–n potential barrier manipulation, n–p–n response type inversions, spill-over effects, synergistic catalytic behavior, and microstructure enhancement. Tables are presented summarizing these works specifically for SnO2, ZnO, TiO2, In2O3, Fe2O3, MoO3, Co3O4, and CdO-based nanocomposites. Recent developments are highlighted and likely future trends are explored.

Nanoscale metal oxide-based heterojunctions for gas sensing: A review

It is clear that the above can lead to confusion when scientists of different countries are trying to communicate with each other. Another example is the burrowing rodent called a gopher found throughout the western United States. In the southeastern United States the term gopher refers to a burrowing turtle very similar to the desert tortoise found in the American southwest. One final example; two North American mammals known as the elk and the caribou are known in Europe as the reindeer and the elk. We never sing “Rudolph the Red-nosed elk”! Confused? This was the reason for creating an internationally recognized system of naming organisms. To avoid confusion, living organisms are assigned a scientific name based on Latin or Latinized words. The English sparrow is Passer domesticus or Passer domesticus (italics or underlining these two names is the official written representation of a scientific name). Using a uniform naming system allows scientists from all over the world to recognize exactly which life form a scientist is referring to. The naming process is called the binomial system of nomenclature. Passer is comparable to a surname and is called the genus, while domesticus is the specific or species name (like your given name) of the English sparrow. Now scientists can give all sparrow-like birds the genus Passer but the species name will vary. All similar genera (plural for genus) can be grouped into another, “higher” category (see below). Study the following for a more through understanding of taxonomy. Taxonomy Analogy Kingdom: Animalia Country

Diversity of life

Graphene-based materials are gaining heightened attention as novel materials for environmental applications The unique physicochemical properties of graphene, notably its exceptionally high surface area, electron mobility, thermal conductivity, and mechanical strength, can lead to novel or improved technologies to address the pressing global environmental challenges This critical review assesses the recent developments in the use of graphene-based materials as sorbent or photocatalytic materials for environmental decontamination, as building blocks for next generation water treatment and desalination membranes, and as electrode materials for contaminant monitoring or removal The most promising areas of research are highlighted, with a discussion of the main challenges that we need to overcome in order to fully realize the exceptional properties of graphene in environmental applications

Environmental applications of graphene-based nanomaterials.

Raman investigation of N-implanted ZnO: Defects, disorder and recovery

A single step process to grow Au capped oxygen deficient GeO2 crystalline nanowires via generation of growth species through the metal induced surface decomposition of Ge substrate is reported. Without the external source supply, the growth of the Au-GeO2 nanowires on the Ge substrate is addressed with possible mechanism. Despite high band gap, application of GeO2 as a possible new material for visible light photodetection is presented. The as-grown samples were found to have a photo-response of ≥102 with 17% external quantum efficiency at −2.0 V applied bias upon visible-light illumination (λ = 540 nm, 0.2 mW/cm2). This visible-light detection can be attributed to the oxygen vacancy related defect states as well as localized surface plasmon resonance induced absorption and subsequent hot electron injection from Au to conduction band of GeO2. The photodetection performance of the devices has been understood by the proposed energy band diagrams. In addition, ≈4 times enhancement in the efficiency has been ...

Growth of Au capped GeO2 nanowires for visible-light photodetection

Ternary cobalt-nickel silicide/n-Si Schottky diodes have been fabricated by sputtering using an equiatomic cobalt- nickel alloy target. A minimum sheet resistivity of the ternary silicide is found to be 5-7 Omega/sq. Grazing-incidence X-ray diffraction shows the formation of ternary silicide phases. Cross-sectional TEM micrograph shows a fairly uniform diffusion of metals into Si with the formation of fully silicided film. Selected-area electron diffraction pattern exhibits the crystalline nature of the silicide layer. Temperature-dependent electrical current-voltage measurements have been used to characterize an optimized Schottky diode formed by annealing at 450degC. The room-temperature barrier height and ideality factor are found to be 0.656 eV and 1.6, respectively, from the I-V characteristics. The series resistance of the diode has been calculated and is found to be 1-11.8 kOmega. The variation of barrier height has been attributed to the inhomogeneity in Schottky junction.

Schottky Barrier Characteristics of Cobalt–Nickel Silicide/n-Si Junctions for Scaled-Si CMOS Applications

Polycrystalline SrBi2Ta2O9 (SBT) thin films were grown on Pt/Ti/SiO2/Si substrates by pulsed laser ablation technique. Phase analyses of the deposited films were studied by grazing incidence x-ray diffraction. Microstructural and interfaces of the SBT film were investigated using a field emission scanning electron microscope. The dc leakage current behavior was studied at different temperatures, and the current transport mechanism was investigated. The calculated activation energies from the Arrhenius plot were attributed to the shallow traps existing near the conduction band of the SBT thin films. The current-voltage plot could be clearly separated into three regions, i.e., Ohm’s law, trap-filled limited, and Child’s law. At a low electric field, the current density–voltage characteristics showed the Ohmic behavior. Lampert’s theory of space charge limited conduction was found to be suitable to explain the current conduction through SBT films. The trap-filled limited voltage increases with increasing tem...

Temperature dependent leakage current behavior of pulsed laser ablated SrBi2Ta2O9 thin films

Ge nanowires were grown on Au-coated Si (100) substrates using vapor-liquid-solid technique. Temperature dependent photoluminescence spectra of Mn doped nanowires showed dominant impurity emissions due to transition from an intermediate T41 to A61 ground state of Mn2+ in Ge nanowire. Magnetic hysteresis loop showed paramagnetic to ferromagnetic transition with decreasing temperature. Temperature dependent electrical resistivity indicated the formation of Mn related acceptor level in Ge at 0.159 eV from the valence band.

Samit K. Ray

Papers

Raman investigation of N-implanted ZnO: Defects, disorder and recovery

Growth of Au capped GeO2 nanowires for visible-light photodetection

Schottky Barrier Characteristics of Cobalt–Nickel Silicide/n-Si Junctions for Scaled-Si CMOS Applications

Temperature dependent leakage current behavior of pulsed laser ablated SrBi2Ta2O9 thin films

Synthesis and temperature dependent photoluminescence properties of Mn doped Ge nanowires