The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13

In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28

Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37



Figure 1

Physical properties of AuNPs and schematic illustration of an AuNP-based detection system.



In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.

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Gold nanoparticles in chemical and biological sensing.

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

Optical properties of ZnO nanostructures.

There has been a renaissance of interest in exploring highly efficient thermoelectric materials as a possible route to address the worldwide energy generation, utilization, and management. This review describes the recent advances in designing high-performance bulk thermoelectric materials. We begin with the fundamental stratagem of achieving the greatest thermoelectric figure of merit ZT of a given material by carrier concentration engineering, including Fermi level regulation and optimum carrier density stabilization. We proceed to discuss ways of maximizing ZT at a constant doping level, such as increase of band degeneracy (crystal structure symmetry, band convergence), enhancement of band effective mass (resonant levels, band flattening), improvement of carrier mobility (modulation doping, texturing), and decrease of lattice thermal conductivity (synergistic alloying, second-phase nanostructuring, mesostructuring, and all-length-scale hierarchical architectures). We then highlight the decoupling of th...

Rationally Designing High-Performance Bulk Thermoelectric Materials

Gold nanoparticles (AuNPs) are important components for biomedical applications. AuNPs have been widely employed for diagnostics, and have seen increasing use in the area of therapeutics. In this mini-review, we present fabrication strategies for AuNPs and highlight a selection of recent applications of these materials in bionanotechnology.

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Gold nanoparticles: preparation, properties, and applications in bionanotechnology.

X-ray structural analysis and high-temperature thermoelectric properties measurements are performed on polycrystalline samples of artificial mineral Cu12−xNixSb4S13 tetrahedrite. Analysis of the atomic displacement parameter manifests low-energy vibration of Cu(2) out of CuS3 triangle plane. The vibration results in low lattice thermal conductivity of less than 0.5 W K−1 m−1. By tuning of the Ni composition x and decrease of electronic thermal conductivity, dimensionless thermoelectric figure of merit for x = 1.5 achieves 0.7 at 665 K, which is a considerably high value among p-type Pb-free sulfides. Because the tetrahedrite is an environmentally friendly material, it constitutes a good thermoelectric material for use in support of a sustainable society.

High-performance thermoelectric mineral Cu12−xNixSb4S13 tetrahedrite

The correlation between photoluminescence (PL) and structural properties of ZnO crystals has been investigated using fine particles prepared by a precipitation method and subsequent heat treatment. The ZnO particles heat-treated at temperatures less than 600°C exhibited red emission centered at 1.9 eV for a weak light excitation similar to that observed in ZnO thin films sputter-grown under thermally non-equilibrium conditions. Heat treatment at high temperatures reduced the red PL while it enhanced the green PL around 2.45 eV. Raman scattering and X-ray diffraction measurements showed that the ZnO particles obtained at lower temperatures have a greater lattice disorder accompanied by a specific lattice expansion along the c-axis of the ZnO crystal which would introduce defect states in the band gap. In addition, electrical conductivity measurements suggested that the lattice disorder is associated with interstitial Zn. These results indicate that the lattice disorder along the c-axis of the ZnO crystal, i.e., the interstitial Zn is most likely responsible for the red PL observed for both ZnO particles and thin films. On the other hand, recombination centers such as singly charged oxygen vacancies contributing to the green emission may be too low in concentration to affect the structural quality.

Photoluminescent and Structural Properties of Precipitated ZnO Fine Particles

We have investigated thermoelectric properties of synthesized mineral Cu10Tr2Sb4S13 (Tr = Mn, Fe, Co, Ni, Cu, and Zn) tetrahedrites, which have a cubic and complex crystal structure. The mother phase Tr = Cu shows metal–semiconductor transition and anomalous hysteresis. Through various Tr substitutions, the thermopower was increased and thermal conductivity was decreased. Results show that Tr = Ni had the largest dimensionless figure of merit Z T of 0.15 at 340 K. The main advantage for the large Z T is the quite low lattice thermal conductivity. Because of the large Z T and the environmentally friendly components, tetrahedrites are anticipated as a good thermoelectric material.

https://iopscience.iop.org/article/10.1143/APEX.5.051201/pdf

Thermoelectric Properties of Mineral Tetrahedrites Cu$_{10}$ Tr $_{2}$Sb$_{4}$S$_{13}$ with Low Thermal Conductivity

Zinc oxide (ZnO) thin films have been deposited on glass substrates from isopropyl solutions of zinc acetate by using the Charged Liquid Cluster Beam (CLCB) technique. The structure of the films is determined by the temperature of the substrate. Raman scattering spectra of the films obtained by non-resonant excitation are similar to those of bulk polycrystalline ZnO. The photoluminescence (PL) spectra of the films exhibit at 10 K four broad emission bands in the visible and near infrared spectral range. The effect of post-deposition annealing on the red emission band is also reported.

Photoluminescence and Raman spectra of ZnO thin films by Charged Liquid Cluster Beam Technique

Substitution effects of 3d transition metal (TM) impurities on electronic and magnetic properties for Cu12Sb4S13 tetrahedrite are investigated by the combination of low-temperature experiments and first-principles electronic-structure calculations. The electrical resistivity for the cubic phase of Cu12Sb4S13 exhibits metallic behavior due to an electron-deficient character of the compound. Whereas that for 0.5 ≤ x ≤ 2.0 of Cu12−xNixSb4S13 exhibits semiconducting behavior. The substituted Ni for Cu is in the divalent ionic state with a spin magnetic moment and creates impurity bands just above the Fermi level at the top of the valence band. Therefore, the semiconducting behavior of the electrical resistivity is attributed to the thermal excitation of electrons from the valence band to the impurity band. The substitution effect of TM on the electronic structure and the valency of TM for Cu11.0TM1.0Sb4S13 are systematically studied by the calculation. The substituted Mn, Fe, and Co for Cu are found to be in ...

Mikio Koyano

Papers

High-performance thermoelectric mineral Cu12−xNixSb4S13 tetrahedrite

Photoluminescent and Structural Properties of Precipitated ZnO Fine Particles

Thermoelectric Properties of Mineral Tetrahedrites Cu$_{10}$ Tr $_{2}$Sb$_{4}$S$_{13}$ with Low Thermal Conductivity

Photoluminescence and Raman spectra of ZnO thin films by Charged Liquid Cluster Beam Technique

Systematic study of electronic and magnetic properties for Cu12–xTMxSb4S13 (TM = Mn, Fe, Co, Ni, and Zn) tetrahedrite