Stability,electronic, and optical properties of two-dimensional phosphoborane

The structure and properties of two-dimensional phosphoborane sheets were computationally investigated using Density Functional Theory calculations. The calculated phonon spectrum and band structure point to dynamic stability and allowed characterization of the predicted two-dimensional material as a direct-gap semiconductor with a band gap of ~1.5 eV. The calculation of the optical properties showed that the two-dimensional material has a relatively small absorptivity coefficient. The parameters of the mechanical properties characterize the two-dimensional phosphoborane as a relatively soft material, similar to the monolayer of MoS₂. Assessment of thermal stability by the method of molecular dynamics indicates sufficient stability of the predicted material, which makes it possible to observe it experimentally.     

烷基链工程对两亲有机半导体热力学性能影响的研究

Due to their special polar structure, amphiphilic molecules are simple to process, low in cost and excellent in material properties. Thus, they can be widely applied in the preparation of functional film materials and bionics related to cell membranes. Therefore, amphiphilic organic semiconductor materials are receiving increasing attention in research and industrial fields. The structure of organic amphiphilic semiconductor molecules usually consists of three functional parts: a hydrophilic group, a hydrophobic group, and a linking group between them. The adjustment of their correlation to achieve the target performance is particularly important and needs experimental discussion regarding synthetic methodologies. In this work, we focused on the engineering of a substituent alkyl-chain, and an amphiphilic functional molecule (benzo[b]benzo[4, 5] thieno[2, 3-d]thiophene, named C_nPA-BTBT, n = 3–11) was proposed and synthesized. This molecule links the hydrophobic semiconductor backbone and hydrophilic polar group through alkyl chains of different lengths. Fundamental properties were investigated by nuclear magnetic resonance (NMR) and ultraviolet-visible spectroscopy (UV-Vis) to conform the structure and the band gap properties of the designed organic semiconductor. Thermodynamic features were investigated by thermogravimetric analysis (TGA) and corresponding differential thermal gravity (DTG), which indicate that the functional molecule C_nPA-BTBT (n = 3–11) has a great stability in ambient conditions. Moreover, the results show that the binding ability of the amphiphilic molecule to water molecules was regulated by the odd-even alternating effect of the alkyl chain and the intramolecular coupling with BTBT. Furthermore, differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were used to study the material properties in detail. As the length of the alkyl chain increased, the functional molecule C_nPA-BTBT (n = 3–11) gradually changed from "hard" species with no thermodynamic changes to a transition one with a pair of thermodynamic peaks, and eventually to a "soft" one as a typical liquid crystal with clear observation of Maltese-cross spherulites. The cooling and freezing points were further studied, and the values and trends of their enthalpy and corresponding temperature fluctuated and alternated due to the volume effect, odd-even alternating effect, flexibility, and other functions of the alkyl chain. Three molecular models were proposed according to the thermodynamic study results, namely the brick-like model, transition model, and liquid crystal model. This work presents in-depth discussion on material structure and corresponding thermodynamic properties, and it is an experimental basis for the design, synthesis, optimization, and screening of target performance materials.     

Novel advances in metal-based solar absorber for photothermal vapor generation

Access to safe drinking water has become an extremely urgent research topic worldwide. In recent years, the technology of solar vapor generation has been extensively explored as a potential and effective strategy of transforming elements content in seawater. In this review, the basic concepts and theories of metal-based photothermal vapor generation device (PVGD) with excellent optical and thermal regulatory are introduced. In the view of optical regulation, how to achieve high-efficiency localized evaporation in different evaporation system (i.e., volumetric solar heating and interface solar heating) is discussed; from the aspect of thermal regulation, the importance of selective absorption surface for interfacial PVGD is analyzed. Based on the above discussion and analysis, we summarize the challenges of metal-based desalination device.     

Molecular engineering of CxNy: Topologies,electronic structures and multidisciplinary applications

As a class of metal-free two-dimensional (2D) semiconductor materials, polymeric carbon nitrides have attracted wide attention recently due to its facile regulation of the molecular and electronic structures, availability in abundance and high stability. According to the different ratios of C and N atoms in the framework, a series of C_xN_y materials have been successfully synthesized by virtue of various precursors, which further triggers extensive investigations of broad applications ranging from sustainable photocatalytic reactions and highly sensitive optoelectronic biosensing. In view of topological structures on their electronic structures and material properties, the as-reported C_xN_y could be generally classified into two main categories with three- or six-bond-extending frameworks. Owing to the effective n→π* transition in most C_xN_y materials, the relative energy level of the lone-pair electrons on N atoms is high, which thus endows the materials with the capability of visible light absorption. Meanwhile, the different repeating units, bridging groups and defect sites of these two kinds of C_xN_y allow them to effectively drive a diverse of promising applications that require specific electronic, interfacial and geometric properties. This review paper aims to summarize the recent progress in topological structure design and the relevant electronic band structures and striking properties of C_xN_y materials. In the final part, we also discuss the existing challenges of C_xN_y and outlook the prospect possibilities.     

Reconfigurable Plasmonic Nanostructures Controlled by DNA Origami

Precise surface functionalization and reconfigurable capability of nanomaterials are essential to construct complex nanostructures with specific functions.Here we show tire assembly of a reconfigurable plasmonic nanostructure,which executes both conformational and plasmonic changes in response to DNA strands.In this work,different sized gold nanoparticles(AuNPs)were arranged site-specifically on the surface of a DNA origami clamp nanostructure.The opening and closing of the DNA origami clamp could be precisely controlled by a series of strand emplacement reactions.Therefore,the patterns of these AuNPs could be switched between two different configura-tions.The observed plasmon band shift indicates the change of the plasmonic interactions among the assembled AuNPs.Our study achieves the construction of reconfigurable nanomaterials with tunable plasmonic interactions,and will enrich the toolbox of DNA-based functional nanomachinery.     

SERS Activity of Semiconductors: Crystalline and Amorphous Nanomaterials

Surface‐enhanced Raman scattering (SERS) spectroscopy on semiconductors has attracted increasing attention due to its high spectral reproducibility and unique selectively to target molecules. Recently, endeavors have been made in fabricating novel SERS‐active semiconductor substrates and exploring new enhancement mechanisms to improve the sensitivity of semiconductor substrates. This Minireview explains the enhancement mechanism of the semiconductor SERS effect in a brief tutorial and summarize recent developments of novel semiconductor substrates, in particular with regard to the remarkable SERS activity of amorphous semiconductor nanomaterials. Potential applications of semiconductor SERS are also a key issue of concern. We discuss a variety of promising applications of semiconductor SERS in the fields of in situ analytical chemistry, spectroelectrochemical analysis, biological sensing, and trace detection.     

Application of Autoradiography to the Investigation of New Doping Techniques of Semiconductor Materials

The development of technology of new semiconductor devices requires fundamental studies of a number of phenomena taking place in semiconductors during the doping process or accompanying the doping process.

These studies are concerned with the following problems:

1. Diffusion of gold in silicon and the effect of diffusion layers (particularly phosphorus layers) and epitaxial silicon layers on the distribution of gold in thin silicon plates.

2. Distribution of admixtures in silicon introduced with the aid of the ion implantation technique. Our studies concerned with the second of the above mentioned problems comprised an autoradiographic examination of the homogeneity of the beam of phosphorus ions implanted in silicon, and a study of some apparatus factors and of the purity of the basic material on the implantation.     

Pt coated Cr2O3 thin films for resistive gas sensors

The resistive response of atomic layer deposited thin epitaxial α-Cr₂O₃(0 0 1) films, to H₂ and CO in air, was studied. The films were covered with Pt nanoislands formed by electron-beam evaporation of a sub-monolayer amount of the material. The gas measurements were performed at 250°C and 450°C. These temperatures led to different proportion of chemical states, Pt²⁺ and Pt⁴⁺, to which the Pt oxidized. The modification was ascertained by the X-ray photoelectron spectroscopy method. As a result of the modification, the response was fast at 250°C, but slowed at 450°C. A disadvantageous abundance of Pt⁴⁺ arising at 450°C in air could be diminished by high-vacuum annealing thus restoring the response properties of the system at 250°C.      

Wire metamaterial based on semiconductor matrices

In this Letter, we have presented a new approach for the fabrication of nanowire media (wire metamaterials) by electrochemical methods. A^IIIB^V porous matrices (a host medium) were prepared by anodic electrochemical etching of industrial substrates. The host medium has been filled via electrochemical deposition with a metal and by means of annealing process. We have shown that this technique can be used to fabricate a nanowire medium with unique parameters (such as aspect ratio, high electric permittivity and strong χ⁽³⁾ nonlinearity near the fundamental absorption edge of the host media). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)