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. ...

/pdf/a-comprehensive-review-of-zno-materials-and-devices-21a3zjadem.pdf

A comprehensive review of zno materials and devices

Oxygen vacancies in crystal have important impacts on the electronic properties of ZnO. With ZnO2 as precursors, we introduce a high concentration of oxygen vacancies into ZnO successfully. The obtained ZnO exhibits a yellow color, and the absorption edge shifts to longer wavelength. Raman and XPS spectra reveal that the concentration of oxygen vacancies in the ZnO decreased when the samples are annealed at higher temperature in air. It is consistent with the theory calculation. The increasing of oxygen vacancies results in a narrowing bandgap and increases the visible light absorption of the ZnO. The narrowing bandgap can be confirmed by the enhancement of the photocurrent response when the ZnO was irradiated with visible light. The ZnO with oxygen vacancies are found to be efficient for photodecomposition of 2,4-dichlorophenol under visible light irradiation.

Oxygen vacancy induced band-gap narrowing and enhanced visible light photocatalytic activity of ZnO.

Photoelectrochemical (PEC) water splitting for hydrogen production is a promising technology that uses sunlight and water to produce renewable hydrogen with oxygen as a by-product. In the expanding field of PEC hydrogen production, the use of standardized screening methods and reporting has emerged as a necessity. This article is intended to provide guidance on key practices in characterization of PEC materials and proper reporting of efficiencies. Presented here are the definitions of various efficiency values that pertain to PEC, with an emphasis on the importance of solar-to-hydrogen efficiency, as well as a flow chart with standard procedures for PEC characterization techniques for planar photoelectrode materials (i.e., not suspensions of particles) with a focus on single band gap absorbers. These guidelines serve as a foundation and prelude to a much more complete and in-depth discussion of PEC techniques and procedures presented elsewhere.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400005653

Accelerating materials development for photoelectrochemical hydrogen production: Standards for methods, definitions, and reporting protocols

Electrostatic correlations play an important role in physics, chemistry and biology. In plasmas they result in thermodynamic instability similar to the liquid–gas phase transition of simple molecular fluids. For charged colloidal suspensions the electrostatic correlations are responsible for screening and colloidal charge renormalization. In aqueous solutions containing multivalent counterions they can lead to charge inversion and flocculation. In biological systems the correlations account for the organization of cytoskeleton and the compaction of genetic material. In spite of their ubiquity, the true importance of electrostatic correlations has come to be fully appreciated only quite recently. In this paper, we will review the thermodynamic consequences of electrostatic correlations in a variety of systems ranging from classical plasmas to molecular biology.

/pdf/electrostatic-correlations-from-plasma-to-biology-40zvrs24qt.pdf

Electrostatic correlations: from plasma to biology

https://hal.archives-ouvertes.fr/hal-00120432/document

Raman Spectroscopy of Nanomaterials: How Spectra Relate to Disorder, Particle Size and Mechanical Properties

Effect of confinement is investigated on optical phonons of different symmetries in the nanoparticles of zinc oxide with wurtzite structure using Raman spectroscopy. An optical phonon confinement model is used for calculating the theoretical line shapes, which exhibit different asymmetric broadening and shifts, depending on the symmetries of phonon and their dispersion curves. The best fit to the data is found for particle diameters consistent with those estimated using x-ray diffraction.

Optical phonon confinement in zinc oxide nanoparticles

If the medium surrounding a nano-grain does not support the vibrational wavenumbers of a material, the optical and acoustic phonons get confined within the grain of the nanostructured material. This leads to interesting changes in the vibrational spectrum of the nanostructured material as compared to that of the bulk. Absence of periodicity beyond the particle dimension relaxes the zone-centre optical phonon selection rule, causing the Raman spectrum to have contributions also from phonons away from the Brillouin-zone centre. Theoretical models and calculations suggest that the confinement results in asymmetric broadening and shift of the optical phonon Raman line, the magnitude of which depends on the widths of the corresponding phonon dispersion curves. This has been confirmed for zinc oxide nanoparticles. Microscopic lattice dynamical calculations of the phonon amplitude and Raman spectra using the bond-polarizability model suggest a power-law dependence of the peak-shift on the particle size. This article reviews recent results on the Raman spectroscopic investigations of optical phonon confinement in several nanocrystalline semiconductor and ceramic/dielectric materials, including those in selenium, cadmium sulphide, zinc oxide, thorium oxide, and nano-diamond. Resonance Raman scattering from confined optical phonons is also discussed. Copyright © 2007 John Wiley & Sons, Ltd.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jrs.1684

Raman spectroscopy of optical phonon confinement in nanostructured materials

Optical and Raman scattering studies on SnS nanoparticles

In the present study, x-ray diffraction, Raman spectroscopy, spectroscopic ellipsometry, photoluminescence, and x-ray photoelectron spectroscopy techniques were used to study the effect of 120 MeV 107Ag9+ ion irradiation on nanocrystalline Cu2O thin films grown by the activated reactive evaporation technique. The influence of dense electronic excitations during ion irradiation on the structural and optical properties of the Cu2O thin films was studied. Experimental results demonstrate that the phase and the size of nanocrystallites in the Cu2O thin films as well as associated surface states can be tailored by controlling ion fluence. The Cu2O higher symmetry cubic phase is observed to be quite stable under a higher temperature and irradiation-induced thermal spikes, which accompanies ion irradiation.

Modifying the nanocrystalline characteristics: structure, size, and surface states of copper oxide thin films by high-energy heavy-ion irradiation

Dilute aqueous polystyrene suspensions are found to exhibit a novel vapor-liquid condensation. Upon deionization, weakly interacting homogeneous suspensions below a critical particle concentration condense into a concentrated phase with liquidlike order and a dilute vapor phase. This phenomenon strongly suggests net attraction between particles at interparticle separation several times the particle diameter. The present results are understood on the basis of an effective interparticle model potential.

M. Rajalakshmi

Papers

Optical phonon confinement in zinc oxide nanoparticles

Raman spectroscopy of optical phonon confinement in nanostructured materials

Optical and Raman scattering studies on SnS nanoparticles

Modifying the nanocrystalline characteristics: structure, size, and surface states of copper oxide thin films by high-energy heavy-ion irradiation

Vapor-liquid condensation in charged colloidal suspensions.