Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Green synthesis of metal nanoparticles using plants

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.

A method for growing vertical ZnO nanowire arrays on arbitrary substrates using either gas-phase or solution-phase approaches is presented. A ∼10 nm-thick layer of textured ZnO nanocrystals with their c axes normal to the substrate is formed by the decomposition of zinc acetate at 200−350 °C to provide nucleation sites for vertical nanowire growth. The nanorod arrays made in solution have a rod diameter, length, density, and orientation desirable for use in ordered nanorod−polymer solar cells.

/pdf/general-route-to-vertical-zno-nanowire-arrays-using-textured-37vpv215yi.pdf

General Route to Vertical ZnO Nanowire Arrays Using Textured ZnO Seeds

The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Metal oxides for solid-state gas sensors: What determines our choice?

Temperature-dependent resistive switching of amorphous carbon/silicon heterojunctions

Using atomistic simulation method, we developed a set of interatomic potential parameters which accurately reproduced the complex atomic structure of multiferroic hexagonal manganite YMnO3. We then demonstrated a systematic study of intrinsic defects, and the fine atomic configurations and local structural distortions of two types of transverse domain wall. Moreover, the energy and structure details of transverse domain walls in oxygen deficient YMnO3 were revealed. Insights into the conductance enhancement was obtained. The present study sheds light on the understanding of structure-property relation in YMnO3.

Atomistic simulation study of transverse domain wall in hexagonal YMnO3

CoxC1−x granular films and pure carbon films were deposited on n-type Si substrates using the pulsed laser deposition method. Three types of samples were obtained: pure C/Si, CoxC1−x granular film/Si with Co dispersed in the C film, and CoxC1−x/Si with Co segregated at the interface. After comparing the physical properties and structures of these three types of samples, we found that the segregation of Co at the interface not only increased the maximum value of magnetoresistance but also improved the magnetoresistance sensitivity in the CoxC1−x/Si system.

The effect of Co on room temperature positive magnetoresistance in the CoxC1−x/Si system

Si enhances the growth of B4C nanowires

In this article, we review our recent work on quantum phase transition in two-dimensional strongly correlated fermion systems. We discuss the metal–insulator transition properties of these systems by calculating the density of states, double occupancy, and Fermi surface evolution using a combination of the cellular dynamical mean-field theory (CDMFT) and the continuous-time quantum Monte Carlo algorithm. Furthermore, we explore the magnetic properties of each state by defining magnetic order parameters. Rich phase diagrams with many intriguing quantum states, including antiferromagnetic metal, paramagnetic metal, Kondo metal, and ferromagnetic insulator, were found for the two-dimensional lattices with strongly correlated fermions. We believe that our results would lead to a better understanding of the properties of real materials.

Xiaozhong Zhang

Papers

Temperature-dependent resistive switching of amorphous carbon/silicon heterojunctions

Atomistic simulation study of transverse domain wall in hexagonal YMnO3

The effect of Co on room temperature positive magnetoresistance in the CoxC1−x/Si system

Si enhances the growth of B4C nanowires

Quantum phase transitions in two-dimensional strongly correlated fermion systems