A study of specific features of the electronic spectrum of quantum dots in CdSe semiconductor

Monolayers of CdSe/CdS/ZnS quantum dots (QDs) formed on the aqueous subphase and transferred to solid substrates by the Langmuir–Blodgett method have been studied. The samples obtained were examined by transmission electron microscopy, atomic-force microscopy, and scanning tunnel microscopy. The structure of the QD monolayer obtained on the substrate was analyzed. Specific features of the electronic spectrum of the quantum objects formed in the samples under study were determined.     

Interfacially organized DNA/polycation complexes: a route to new planar polymeric and composite nanostructures

Effects of nano-scale supramolecular organization and patterning in amphiphilic polycation monolayer formed by poly-4-vinilpyridine with 16% cetylpyridinium groups and in novel planar DNA/amphiphilic polycation complexes formed at the air-aqueous DNA solution interface and deposited on the solid substrates have been studied using AFM. Stable ordered quasi-crystalline planar polymeric monolayer structures were formed by amphiphilic polycation molecules. Extended net-like and quasi-circular toroidal condensed conformations of deposited planar DNA/amphiphilic polycation complexes were obtained in dependence on the amphiphilic polycation Langmuir monolayer state during the DNA binding. Those monolayer and multilayer DNA/polycation complex Langmuir–Blodgett films were used as templates and nanoreactors for generation of inorganic nanostructures. As a result, ultrathin polymeric nanocomposite films with integrated DNA building blocks and inorganic semiconductor (CdS) and iron oxide nanoparticle quasi-linear arrays or aggregates (nanorods) were formed successfully and characterized by TEM. The data obtained give evidence for effectiveness of the monolayer techniques for study mechanisms of DNA structural transformations caused by complexation with cationic compounds and demonstrate its perspectives for creation of new planar DNA-based self-organized stable polymeric complex nanostructures and nanocomposites with nano-scale structural ordering.     

A New Support Film for Cryo Electron Microscopy Protein Structure Analysis Based on Covalently Functionalized Graphene

Protein adsorption at the air–water interface is a serious problem in cryogenic electron microscopy (cryoEM) as it restricts particle orientations in the vitrified ice-film and promotes protein denaturation. To address this issue, the preparation of a graphene-based modified support film for coverage of conventional holey carbon transmission electron microscopy (TEM) grids is presented. The chemical modification of graphene sheets enables the universal covalent anchoring of unmodified proteins via inherent surface-exposed lysine or cysteine residues in a one-step reaction. Langmuir–Blodgett (LB) trough approach is applied for deposition of functionalized graphene sheets onto commercially available holey carbon TEM grids. The application of the modified TEM grids in single particle analysis (SPA) shows high protein binding to the surface of the graphene-based support film. Suitability for high resolution structure determination is confirmed by SPA of apoferritin. Prevention of protein denaturation at the air–water interface and improvement of particle orientations is shown using human 20S proteasome, demonstrating the potential of the support film for structural biology.     

Single-walled carbon nanotubes nanocomposite microacoustic organic vapor sensors

We have developed highly sensitive microacoustic vapor sensors based on surface acoustic waves (SAWs) configured as oscillators using a two-port resonator 315, 433 and 915 MHz device. A nanocomposite film of single-walled carbon nanotubes (SWCNTs) embedded in a cadmium arachidate (CdA) amphiphilic organic matrix was prepared by Langmuir–Blodgett technique with a different SWCNTs weight filler content onto SAW transducers as nanosensing interface for vapor detection, at room temperature. The structural properties and surface morphology of the nanocomposite have been examined by X-ray diffraction, transmission and scanning electron microscopy, respectively. The sensing properties of SWCNTs nanocomposite LB films consisting of tangled nanotubules have been also investigated by using Quartz Crystal Microbalance 10 MHz AT-cut quartz resonators. The measured acoustic sensing characteristics indicate that the room-temperature SAW sensitivity to polar and nonpolar tested organic molecules (ethanol, ethylacetate, toluene) of the SWCNTs-in-CdA nanocomposite increases with the filler content of SWCNTs incorporated in the nanocomposite; also the SWCNTs-in-CdA nanocomposite vapor sensitivity results significantly enhanced with respect to traditional organic molecular cavities materials with a linearity in the frequency change response for a given nanocomposite weight composition and a very low sub-ppm limit of detection.     

Nonepitaxial Gold‐Tipped ZnSe Hybrid Nanorods for Efficient Photocatalytic Hydrogen Production

For the first time, colloidal gold (Au)–ZnSe hybrid nanorods (NRs) with controlled size and location of Au domains are synthesized and used for hydrogen production by photocatalytic water splitting. Au tips are found to grow on the apices of ZnSe NRs nonepitaxially to form an interface with no preference of orientation between Au(111) and ZnSe(001). Density functional theory calculations reveal that the Au tips on ZnSe hybrid NRs gain enhanced adsorption of H compared to pristine Au, which favors the hydrogen evolution reaction. Photocatalytic tests reveal that the Au tips on ZnSe NRs effectively enhance the photocatalytic performance in hydrogen generation, in which the single Au‐tipped ZnSe hybrid NRs show the highest photocatalytic hydrogen production rate of 437.8 µmol h^?1 g^?1 in comparison with a rate of 51.5 µmol h^?1 g^?1 for pristine ZnSe NRs. An apparent quantum efficiency of 1.3% for hydrogen evolution reaction for single Au‐tipped ZnSe hybrid NRs is obtained, showing the potential application of this type of cadmium (Cd)‐free metal–semiconductor hybrid nanoparticles (NPs) in solar hydrogen production. This work opens an avenue toward Cd‐free hybrid NP‐based photocatalysis for clean fuel production.     

Self-assembled silver nanoprisms monolayers at the liquid/liquid interface

A crown ether derivative (4′-aminobenzo-15-crown-5 hydrotetrafluoroborate) can mediate the self-assembly of silver nanoprisms at the liquid/liquid interface in the form of a stable hybrid nanocomposite film. The metallic luster of the interfacial film results from the electronic coupling of Ag nanoprisms, suggesting the formation of closely packed nanoprism thin films. The interfacial film of nanoprisms could be transferred to solid substrates as a Langmuir–Blodgett film. The properties of films were studied by UV–vis spectroscopy and transmission electron microscopy.     

Engineering Gold Nanorod–Copper Sulfide Heterostructures with Enhanced Photothermal Conversion Efficiency and Photostability

Plasmonic gold nanorods (Au NRs)–copper sulfide heterostructures have recently attracted much attention owing to the synergistically enhanced photothermal properties. However, the facile synthesis and interface tailoring of Au NRs–copper sulfide heterostructures remain a formidable challenge. In this study, the rational design and synthesis of Au NRs–Cu₇S₄ heterostructures via a one‐pot hydrothermal process is reported. Specifically, core–shell and dumbbell‐like Au NRs–Cu₇S₄ heterostructures are obtained with well‐controlled interfaces by employing the Au NRs with different aspect ratios. Both core–shell and dumbbell‐like Au NRs–Cu₇S₄ have proven effective as photothermal therapy agents, which offer both high photothermal stability and significant photothermal conversion efficiency up to 62%. The finite‐difference time domain simulation results confirm the coupling effect that leads to the enhanced local field as well as the optical absorption at the heterostructure interface. Importantly, these Au NRs–Cu₇S₄ heterostructures can be compatibly used as an 808 nm laser‐driven photothermal therapy agents for the efficient photothermal therapy of cancer cells in vitro. This study will provide new insight into the design of other noble metal–semiconductor heterostructures for a broad range of applications utilizing surface plasmon resonance enhancement phenomena.     

The catalyst-assisted synthesis of high quality CdS single-crystal nanowires through an epitaxy mechanism

High quality wurtzite CdS nanowires have been synthesized by thermal evaporation of CdS powder onto Si substrate in the presence of Au catalyst at 650 degrees C by using pure H2 as a carrier gas. The nanowires were 10 nm in diameter and a few tens of micrometers in length. XRD patterns demonstrated that as prepared CdS is a pure crystalline material. High-resolution transmission electron microscopy of the materials showed that all CdS nanowires grew along (0001). According to analysis of selective area electron diffraction patterns taken from the interface, we proposed that there is a kind of epitaxy relationship in the interface region between Au catalyst and CdS grown, i.e., (0001)CdS // (111)Au, and [1210]CdS // [011]Au.     

Templated biomineralization of Au nanoplates under bovine serum albumin Langmuir monolayers

Au nanoplates were generated by spontaneous reduction of chloroaurate ions (AuCl₄⁻) under bovine serum albumin (BSA) Langmuir monolayers at room temperature. The structure of the resulting Au particulates was analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), selected-area electron diffraction (SAED), and high resolution transmission electron microscopy (HRTEM). The results showed that BSA provided dual functions for both reducing Au³⁺ ions and directing anisotropic growth of Au particles into plate-like structure as well. Amorphous Au particulates were obtained firstly in a relatively short reaction time, and then anisotropic Au nanoparticles were generated at extended reaction durations. The triangular Au nanoplates oriented along (1 1 1) basal planes were obtained via the reduction of chloroaurate ions by BSA with a relatively longer reaction duration. The present research provides a biological route to produce single-crystalline gold nanoplates with a wide variety of applications, and it also verifies that the interaction between protein/peptide and gold ions/surface may be used advantageously for green chemical synthesis of nanogold. Hopefully, this would contribute to promote genuine green biomimetic synthesis of nanomaterials with prescribed geometrical features where rationally designed multifunctional peptides are preferred.     

Electrochemical Deposition of ZnO Nanorods on Transparent Reduced Graphene Oxide Electrodes for Hybrid Solar Cells

Monocrystalline ZnO nanorods (NRs) with high donor concentration are electrochemically deposited on highly conductive reduced graphene oxide (rGO) films on quartz. The film thickness, optical transmittance, sheet resistance, and roughness of rGO films are systematically studied. The obtained ZnO NRs on rGO films are characterized by X‐ray diffraction, transmission electron microscopy, photoluminescence, and Raman spectra. As a proof‐of‐concept application, the obtained ZnO NRs on rGO are used to fabricate inorganic–organic hybrid solar cells with layered structure of quartz/rGO/ZnO NR/poly(3‐hexylthiophene)/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (P3HT/PEDOT:PSS)/Au. The observed power conversion efficiency (PCE, η), ≈ 0.31%, is higher than that reported in previous solar cells by using graphene films as electrodes. These results clearly demonstrate that rGO films with a higher conductivity have a smaller work function and show a better performance in the fabricated solar cells.     

Langmuir–Blodgett Nanowire Devices for In Situ Probing of Zinc‐Ion Batteries

In situ monitoring the evolution of electrode materials in micro/nano scale is crucial to understand the intrinsic mechanism of rechargeable batteries. Here a novel on‐chip Langmuir–Blodgett nanowire (LBNW) microdevice is designed based on aligned and assembled MnO₂ nanowire quasimonolayer films for directly probing Zn‐ion batteries (ZIBs) in real‐time. With an interdigital device configuration, a splendid Ohmic contact between MnO₂ LBNWs and pyrolytic carbon current collector is demonstrated here, enabling a small polarization voltage. In addition, this work reveals, for the first time, that the conductance of MnO₂ LBNWs monotonically increases/decreases when the ZIBs are charged/discharged. Multistep phase transition is mainly responsible for the mechanism of the ZIBs, as evidenced by combined high‐resolution transmission electron microscopy and in situ Raman spectroscopy. This work provides a new and adaptable platform for microchip‐based in situ simultaneous electrochemical and physical detection of batteries, which would promote the fundamental and practical research of nanowire electrode materials in energy storage applications.     

Photoisomerization of amphiphilic azobenzene derivatives in Langmuir Blodgett films prepared as polyion complexes, using ionic polymers

Polyion complexation in mixed Langmuir and Langmuir Blodgett (LB) films of photochromic amphiphilic azobenzene carboxylic acids, 11-[4-(4-hexylphenyl)azo] phenoxyundecanoic acid, 11-(4-phenylazo)phenoxyundecanoic acid, and diamine grafted poly(methylmethaacrylate) polymers has been studied. Monolayer behaviour of the pure components and mixed films was studied through pressure–area isotherms and LB films were characterized by spectroscopic, X-ray diffraction and Atomic force microscopy techniques. Aggregation (H-type), often observed in LB films of pure amphiphilic azo acids, was partly avoided in the mixed LB films as indicated by absorption spectral studies. Photoisomerization of the polyion complexed LB films was also studied. The results altogether demonstrate that amine grafted polymer enter into a polyion complexation with azo acid carboxylate group. LB films could be obtained by transfer of the composite monolayers and these LB films exhibited different levels of aggregation of the azo acids. Reversible photoisomerization was observed in LB films with unaggregated azo acid.     

Soft-template synthesis of single-crystalline CdS dendrites

The single-crystalline CdS dendrites have been fabricated from the reaction of CdCl2 and thiourea at 180 degrees C, in which glycine was employed as a soft template. The obtained products were explored by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electronic diffraction. The optical properties of CdS dendrites have been investigated by ultraviolet and visible light (UV-vis) and photoluminescence techniques. The investigations indicated that the dendrites were grown due to the anisotropic properties enhanced by the use of Glycine in the route.     

Periodic FTO IOs/CdS NRs/CdSe Clusters with Superior Light Scattering Ability for Improved Photoelectrochemical Performance

Periodic fluorine‐doped tin oxide inverse opals (FTO IOs) grafted with CdS nanorods (NRs) and CdSe clusters are reported for improved photoelectrochemical (PEC) performance. This hierarchical photoanode is fabricated by a combination of dip‐coating, hydrothermal reaction, and chemical bath deposition. The growth of 1D CdS NRs on the periodic walls of 3D FTO IOs forms a unique 3D/1D hierarchical structure, providing a sizeable specific surface area for the loading of CdSe clusters. Significantly, the periodic FTO IOs enable uniform light scattering while the abundant surrounded CdS NRs induce additional random light scattering, combining to give multiple light scattering within the complete hierarchical structure, significantly improving light‐harvesting of CdS NRs and CdSe clusters. The high electron collection ability of FTO IOs and the CdS/CdSe heterojunction formation also contribute to the enhanced charge transport and separation. Due to the incorporation of these enhancement strategies in one hierarchical structure, FTO IOs/CdS NRs/CdSe clusters present an improved PEC performance. The photocurrent density of FTO IOs/CdS NRs/CdSe clusters at 1.23 V versus reversible hydrogen electrode reaches 9.2 mA cm^?2, which is 1.43 times greater than that of CdS NRs/CdSe clusters and 3.83 times of CdS NRs.     

Growth of CdS nanoparticles in Y- and Z-type Langmuir–Blodgett thin film using 1,3-bis-(p-iminobenzoic acid)indane

Cadmium sulphide (CdS) nanoparticles were formed in 1,3-bis-(p-iminobenzoic acid)indane by exposing Cd²⁺ doped Y- and Z-type multilayered Langmuir–Blodgett (LB) films to H₂S gas. The growth of CdS nanoparticles were monitored by UV–visible spectroscopy measurements. It was observed that CdS nanoparticles in both Y- and Z-type LB films cause a blue-shift in absorption spectra. The surface morphology of LB films were characterized with atomic force microscopy DC electrical measurements were carried out for these LB films grown in a metal/LB film/metal sandwich structures with and without CdS nanoparticles. By analyzing I–V curves and assuming Schottky conduction mechanism the barrier height was found to be as 1.25 and 1.17?eV for Y-type unexposed and exposed samples; 1.18 and 1.25?eV for Z-type unexposed and exposed samples, respectively.     

Preparation of novel CdS-graphene/TiO2 composites with high photocatalytic activity for methylene blue dye under visible light

In this study, CdS combined graphene/TiO₂ (CdS-graphene/TiO₂) composites were prepared by a sol–gel method to improve on the photocatalytic performance of TiO₂. These composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and transmission electron microscopy (TEM). The photocatalytic activities were examined by the degradation of methylene blue (MB) under visible light irradiation. The photodegradation rate of MB under visible light irradiation reached 90·1% during 150 min. The kinetics of MB degradation were plotted alongside the values calculated from the Langmuir–Hinshelwood equation. 0·1 CGT sample showed the best photocatalytic activity, which was attributed to a cooperative reaction between the increase of photo-absorption effect by graphene and photocatalytic effect by CdS.     

Growth and structure of polycrystalline Cr/Au multilayered thin films

Metallic multilayered thin films have recently been investigated due to their new magnetic and transport properties. The interest here is focussed on the characterization of the interfaces between the layers. The analysis of growth and structure of polycrystalline Cr/Au multilayers is accomplished by two complementary techniques: in situ ultrahigh vacuum scanning tunnelling microscopy and ex situ transmission electron microscopy. The combination of these powerful methods provides detailed information about structural characteristics such as crystallite size, surface roughness and crystallographic orientation. Moreover, conclusions can be drawn on the atomic arrangement and growth mechanism at the Cr-Au interface. The results are supported by semiempirical and theoretical expectations.     

Swift morphosynthesis of hierarchical nanostructures of CdS via microwave-induced semisolvothermal route

For the swift generation of hierarchical nanostructures of CdS, we propose herein a docile microwave-induced semi-solvothermal reaction (i.e., involving simultaneous usage of nonaqueous and aqueous solvents) between cadmium acetate and thiourea in binary solution of diethylenetriamine and deionized water. Typically, such microwave-assisted reaction was accomplished within 5 minutes as against 12 h required in conventional approach. The resultant products were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis by X-rays, laser Raman spectroscopy and photoluminescence spectroscopy. X-ray diffraction data indicates occurrence of hexagonal CdS with strong (002) preferred orientation. SEM images reveal formation of solvent-ratio dependent complex morphological (i.e., hierarchical) features both at the microscale and nanoscale. Fine-scale microstructure examination by TEM discloses formation of entangled nanorods, nano(potato)sticks, nanoflowers etc. Elemental analysis facility (equipped with TEM) suggests presence of Cd rich product. Raman spectroscopy shows the fundamental and overtone bands pertaining to hexagonal CdS with remarkable enhancement in relative intensities of such bands in case of sample corresponding to diethylenetriamine(DETA)/deionized water(DI) volume ratio of 6:1. Room temperature photoluminescence spectra mainly reveal broad asymmetric emission background composed of classical band edge and trap-induced emission in CdS.     

Self‐Assembly of Ferromagnetic Organic–Inorganic Perovskite‐Like Films

Perovskite‐based organic–inorganic hybrids hold great potential as active layers in electronics or optoelectronics or as components of biosensors. However, many of these applications require thin films grown with good control over structure and thickness—a major challenge that needs to be addressed. The work presented here is an effort towards this goal and concerns the layer‐by‐layer deposition at ambient conditions of ferromagnetic organic–inorganic hybrids consisting of alternating CuCl₄‐octahedra and organic layers. The Langmuir‐Blodgett technique used to assemble these structures provides intrinsic control over the molecular organization and film thickness down to the molecular level. Magnetic characterization reveals that the coercive field for these thin films is larger than that for solution‐grown layered bulk crystals. The strategy presented here suggests a promising cost effective route to facilitate the excellently controlled growth of sophisticated materials on a wide variety of substrates that have properties relevant for the high density storage media and spintronic devices.     

TEM and HAADF-STEM study of the structure of Au nano-particles on CeO<Subscript>2</Subscript>

The structure and growth process of Au particles on CeO₂ were observed by the transmission electron microscope (TEM) equipped with the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) system. The growth of Au particles on CeO₂ was shown to be mainly Ostwald ripening under heating at various temperatures, although it is suppressed in the hydrogen atmosphere. In the HAADF-STEM observation of Au/CeO₂ interfaces with the orientation relationship of (111)[1–10]Au//(111)[1–10]CeO₂, (111)[−110]Au//(111)[1–10]CeO₂ and atomic columns of Au and Ce were successfully resolved, and the interface structure was analyzed in details for the first time.