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.

Recent interest in biological imaging, remote sensing, and biochemical spectroscopy has made nanoscale Terahertz (THz) emitters based on semiconductors become extremely attractive. THz lasers with good performance (emitting over 1 milliWatt CW at 10 K) have been fabricated from the group III-V compounds by molecular beam epitaxy, but such devices are complex with over 500 quantum wells and barriers and are incompatible with low cost Si processing. Similar devices from the SiGe system have had difficulties because the strain limits the total number of active layers, and have produced relatively poor performance (peak powers near 5 nW), even using strain symmetric active regions on virtual substrates of relaxed SiGe buffers. We report here on the characteristics of a new type of THz emitting device with higher powers (above 0.1 milliWatt) based on radiative impurity transitions in doped silicon, which can be simply fabricated without Ge alloying. The THz emitters were fabricated from both p-type and n-type doped silicon wafers with typical resistivities of 5 Ω-cm, using conventional photolithography and metal contact lift off. Samples were electrically pulsed and the electroluminescence was measured by Fourier Transform Infrared spectrometry. At 4.2 K, the emission spectra showed several peaks centered around 8.1 THz for the boron doped device, 7 to 13 THz for the gallium doped device, and 6.6 THz for the phosphorus doped device. The electroluminescence was attributed to radiative transitions from excited p-like to s-like hydrogenic dopant states, with emission energies in remarkable agreement with the known dopant absorption levels. Current-voltage measurement suggested an excitation mechanism based on impact ionization of neutral dopants by hot carriers. The net quantum efficiency (emitted photons per injected electron) was estimated to be up to 2 × 10−3. The temperature dependence will be reported with operation above 30 K.

The Emission of Terahertz Radiation from Doped Silicon Devices

Characteristics of UHVCVD grown Si/Si1−x−yGexCy/Si quantum well heterostructure

Utilizing the remarkably high light absorption and long carrier diffusion length of inorganic perovskites, superior performance self-powered broadband photodetectors using the vertical heterojunction of cesium lead iodide (CsPbI3) nanocrystals (NCs) and zinc oxide (ZnO) films on a flexible platform are reported. Here, the pure cubic or α-phase of as-synthesized CsPbI3 NCs facilitate the novelty of the present work in terms of their enhanced structural stability suitable for optical applications. The α-CsPbI3/ZnO device exhibits superior performance with photoresponsivity of ≈8.2 AW−1, ON/OFF ratio of ≈2.4 × 104, and specific detectivity up to ≈1.4 × 1012 Jones. Furthermore, the piezo-phototronic effect of ZnO has been exploited to enhance the device performance by utilizing the compressive strain-induced piezoelectric charges for modulating the generation, separation, and transportation of charge carriers. By introducing an approximate −0.042% compressive strain in the hybrid heterostructure, the enhancement of photocurrent, spectral responsivity, and specific detectivity of the detector by ≈619%, ≈536%, and ≈506%, respectively, under visible light illumination has been successfully achieved. This work not only presents an inventive method for improving the performance of perovskite photodetectors through interface engineering, but it also provides a thorough understanding of the piezo-phototronic effect on optoelectronic devices. 

Piezo‐Phototronic Effect‐Induced Self‐Powered Broadband Photodetectors using Environmentally Stable
 α
 ‐CsPbI
 3
 Perovskite Nanocrystals

Transition-metal tellurides (TMTs) are promising materials for "post-graphene age" nanoelectronics and energy storage applications owing to their industry-standard compatibility, high electron mobility, large spin-orbit coupling (SOC), etc. However, tellurium (Te) having a larger ionic radius (Z = 52) and broader d-bands endows TMTs with semimetallic nature, restricting their application in photonic and optoelectronic domains. In this work, we report the optical properties of the quantum-confined semiconducting phase of cobalt ditelluride (CoTe2) for the first time, exhibiting excellent two-color band photoabsorption attributes covering the UV-visible and near-infrared regions. Furthermore, novel excitonic resonances (X) of size-varying CoTe2 nanocrystals and quantum dots (QDs) are indicated by their temperature-dependent emission characteristics, which are attributed to the splitting of band edge states via confinement. On the other hand, the sudden rupture of the large-area CoTe2 nanosheets via ultrasonication incorporates Co vacancy-mediated localized trap states within the band gap, which is attributed to the superior room-temperature photoluminescence (PL) quantum yield of QDs and further corroborated using Raman analysis and atomistic density functional theory (DFT) simulations. Most interestingly, the excitonic peak of CoTe2 QDs reveals a unique positive-to-negative thermal quenching transition phenomenon, owing to the thermal activation of nonradiative surface trap states. These results introduce an exciting approach for the defect-mediated color-saturated light emission that paves the way for solution-processed telluride-based QD light-emitting diodes.

Vacancy-Mediated Anomalous Emission Characteristics of Size-Confined Semiconducting CoTe2.

The Schottky barrier height of Ti on p-type Si1–xGex/Si and Si have been investigated-in the temperature range 110–250 K using the current voltage technique. Rutherford Backscattering Spectroscopy ...

Samit K. Ray

Papers

The Emission of Terahertz Radiation from Doped Silicon Devices

Characteristics of UHVCVD grown Si/Si1−x−yGexCy/Si quantum well heterostructure

Piezo‐Phototronic Effect‐Induced Self‐Powered Broadband Photodetectors using Environmentally Stable α ‐CsPbI 3 Perovskite Nanocrystals

Vacancy-Mediated Anomalous Emission Characteristics of Size-Confined Semiconducting CoTe2.

Schottky Barrier Height of Ti on Strained Layer Si/Si1–xGex Films