Complex oxides and semiconductors exhibit distinct yet complementary properties owing to their respective ionic and covalent natures. By electrically coupling complex oxides to traditional semiconductors within epitaxial heterostructures, enhanced or novel functionalities beyond those of the constituent materials can potentially be realized. Essential to electrically coupling complex oxides to semiconductors is control of the physical structure of the epitaxially grown oxide, as well as the electronic structure of the interface. Here we discuss how composition of the perovskite A- and B-site cations can be manipulated to control the physical and electronic structure of semiconductor—complex oxide heterostructures. Two prototypical heterostructures, Ba1−x Srx TiO3/Ge and SrZrx Ti1−x O3/Ge, will be discussed. In the case of Ba1−x Srx TiO3/Ge, we discuss how strain can be engineered through A-site composition to enable the re-orientable ferroelectric polarization of the former to be coupled to carriers in the semiconductor. In the case of SrZrx Ti1−x O3/Ge we discuss how B-site composition can be exploited to control the band offset at the interface. Analogous to heterojunctions between compound semiconducting materials, control of band offsets, i.e., band-gap engineering, provides a pathway to electrically couple complex oxides to semiconductors to realize a host of functionalities.

Transition metal oxides (TMOs) have recently demonstrated to be a good alternative to boron/phosphorous doped layers in crystalline silicon heterojunction solar cells. In this work, the interface between n-type c-Si (n-Si) and three thermally evaporated TMOs (MoO3, WO3, and V2O5) was investigated by transmission electron microscopy, secondary ion-mass, and x-ray photoelectron spectroscopy. For the oxides studied, surface passivation of n-Si was attributed to an ultra-thin (1.9–2.8 nm) SiOx∼1.5 interlayer formed by chemical reaction, leaving oxygen-deficient species (MoO, WO2, and VO2) as by-products. Carrier selectivity was also inferred from the inversion layer induced on the n-Si surface, a result of Fermi level alignment between two materials with dissimilar electrochemical potentials (work function difference Δϕ ≥ 1 eV). Therefore, the hole-selective and passivating functionality of these TMOs, in addition to their ambient temperature processing, could prove an effective means to lower the cost and simplify solar cell processing.

Magnetic core–shell nanoparticles (CSNs) have potential applications in spintronic devices, drug delivery systems, and magnetic random access memory. By use of our hydrothermal nano-phase epitaxy method, we have accomplished synthesis of novel, well-ordered α-Cr2O3@α-Mn0.35Cr1.65O2.94 inverted CSNs. XRD and TEM analyses show a core–shell structure with corundum phase throughout the core and shell with a minimal amount of interface defects. TEM-EDX and XPS data show Mn having the +2 oxidation state in the shell of the CSNs. Magnetization measurements at 5 K show a weak coercivity (H C) value of 8 Oe and an exchange bias field (H E) of 293 Oe. Ab initio calculations show that Mn incorporation in α-Cr2O3 results in narrowing of the energy band gap, substantiated by UV–Vis measurements, and half metallic behavior in case of Mn(III) substitution. Our calculations substantiate that Mn substitution in α-Cr2O3 results in a combination of antiferromagnetic and weak ferrimagnetic character of our CSNs.

Diatoms microalgae can be regarded as living factories producing nanostructured and mesoporous biosilica shells (frustules) having a highly ordered hierarchical architecture. These unique, morphological, chemical and mechanical properties make diatoms’ biosilica a very attractive nanomaterial for a wide variety of applications. Methods of purification of frustules that preserve their nanostructured morphology have been set up as well as in vivo or in vitro chemical modification protocols of the biosilica with functional molecules to generate biohybrid active materials for photonics, sensing, drug delivery and electronics. Herein we describe, with some selected examples, the great variety of applications envisaged for native and modified frustules, highlighting the material scientists’ benefit to avail of nature in the construction of highly ordered biohybrid architectures for nanotechnology. New concepts for the biotechnological production of nanomaterials are opened by the use of diatoms as living factories.

Three dimensional (3D) porous graphene decorated with MoO2 nanoparticles were successfully synthesized by hydrothermal method and characterized by SEM and TEM, x-ray diffraction, Raman spectra, x-ray photoelectron spectroscopy, nitrogen adsorption–desorption analysis and electrochemical experiments. The results revealed that the in situ formed monoclinic MoO2 nanoparticles were randomly decorated on the surface of graphene sheets and the obtained graphene–MoO2 nanohybrids were 3D porous structures. The mass ratio of molybdenum precursor with GO has effects on the specific surface area and the electrochemical properties of the nanocomposite. The M30G1 (the mass ratio of molybdenum precursor with GO was 30:1) composite electrode exhibited a higher specific capacitance and better cycling stability. The specific capacitances were 356 F/g at the current density of 0.1 A/g in KOH electrolyte, which predicted their potential application in energy storage. The electrochemical performance of M30G1 composite was also investigated in Na2SO4 electrolyte, which was poorer than that in KOH electrolyte. Therefore, the chosen of electrolyte is important to materials performance.

We report the development of hybrids consisting of supercapacitive graphene oxide (GO), reduced GO (rGO), electrochemically reduced GO (ErGO), multilayer graphene (MLG) decorated with pseudocapacitive nanostructured cobalt oxides (CoO, Co3O4) and nanoparticles (CoNP) via electrodeposition and hydrothermal synthesis facilitating chemically bridged (covalently and electrostatically anchored) interfaces with tunable properties. These hybrid samples showed heterogeneous transport behavior determining diffusion coefficient (4 × 10−8–6 × 10−6 m2/s) following CoO/MLG < Co3O4/MLG < Co3O4/rGOHT < CoO/ErGO, CoNP/MLG and delivering the maximum specific capacitance >550 F/g for Co3O4/ErGO and Co3O4/MLG. We found an ultrahigh sensitivity of 4.57 mA/(mM cm2) and excellent limit of glucose detection <50 nM following Co3O4/rGOHT < CoO/ErGO < CoNP/MLG < Co3O4/MLG. These findings are due to open pore network and topologically multiplexed conductive pathways provided by graphene nanoscaffolds to ensure rapid charge transfer and ion conduction. Density functional theory determined density of states in the vicinity of Fermi level in-turn providing contribution toward electroactivity due to orbital re-hybridization.

In this study, three types of graphene films—hydrothermal reduced graphene oxide (GO) film, thermal reduced GO film, and GO film—on silicon substrate by using 3-aminopropyl triethoxysilane (APTES) as the interface adhesive layer were prepared for investigation. The chemical compositions of the samples were characterized by x-ray photoelectron spectroscopy (XPS). Surface morphologies, adhesive forces, and nano friction forces in air and aqueous solutions with different pH values were investigated by atomic force microscopy (AFM). Results showed that capillary force dominated the adhesive force in air condition, and adhesive force was much smaller in aqueous solution than in air due to the disappearance of the capillary force. Adhesive force and friction coefficient of the three samples slightly decreased with the increase of pH values. Hydrothermal reduced GO film exhibits the best lubricity both in air and in liquids among those three films.

A new lithium ion hybrid supercapacitor is reported, in which the negative electrode was made from ZnO nano-crystals coated with a nitrogen doped carbon, and a positive electrode composed of activated carbon. The ZnO nano-crystals were highly dispersed in a nitrogen doped carbon matrix through a bio-inspired route. Dopamine, used as the nitrogen and carbon source, self-polymerized and deposited onto the surface of ZnO nano-crystal. After pyrolysis, a nitrogen doped amorphous carbon coated ZnO nano-crystal materials were obtained. The characteristics of the synthesized carbon coated ZnO nano-crystal electrode as well as the electrochemical performance of the hybrid device were investigated. The ZnO nano-crystal structure was preserved in the course of the carbon coating. The lithium ion supercapacitor demonstrated a high capacity and good cycling stability. Such good performance can be attributed to improved conductivity, the prevention of ZnO nano particles from pulverization and the high degree of crystallinity of the ZnO material.

Wear resistance plays an important role to ensure the machining precision of machine tool using gray cast iron guide rail. Bio-inspired surfaces imitating the cuticle of desert scorpion and shell archetype with alternate units were prepared on gray cast iron using biomimetic coupling laser remelting in air and water. Samples consisting of striature bionic units with various distributions were examined under dry sliding condition using a home-made wear testing machine. It was found that samples with bionic units displayed better wear resistance than the untreated gray cast iron. While samples with bionic units processed in water by laser returned highest wear resistance in the short run, samples with alternatively distributed units (processed by laser) presented better wear resistance in the long run. However, to understand the stress distributions and the wear mechanism of the samples finite element method was used in this study. Based on the experimental evidences, a two-stage wear mechanism was proposed.

Cu–FeS composites without lead were prepared by power metallurgy process. The friction and wear properties were examined on a “block-on-ring” testing machine under dry sliding conditions with and without oil immersion. Results showed that both the frictional coefficient and the wear volumes decreased with increased FeS content in the composite under dry sliding conditions. In the condition of dry friction without oil immersion, the FeS solid lubricating film formed and played a role of antifriction and adhesion resistance. Under the dry friction condition with oil immersion, the lubricant oil stored in the porous FeS layer precipitated to the surface to form the oil film, which could work together to achieve a liquid–solid synergistic lubrication with the FeS transfer film. The lubrication performance of the collaborative lubrication reaction is better than that of the solid transfer film. With the increase of FeS, the collaborative lubrication became more obvious.

The absorber layers for chalcopyrite solar cells were fabricated by selenization of the stacked metal layers (SML). Co-sputtering and sequential sputtering methods were utilized to prepare the SML, and the variation of the stacking sequences and the effect of each stacked layer thickness were investigated. The stacking sequence of In/CuGa⋯In/CuGa was found having advantages in the SML growth and the average size of indium hillocks might be tailored by changing the thickness of each stacked layer. The SML in the stacking mode of In/CuGa⋯In/CuGa prepared while the thickness for each indium layer fixed at approximately 83 nm exhibited the desired morphology with evenly distributed indium hillocks in small diameters. The selenized ${\rm{CuI}}{{\rm{n}}_x}{\rm{G}}{{\rm{a}}_{1 - x}}{\rm{S}}{{\rm{e}}_2}$ (CIGS) layer showed a smooth surface and largest grain size with phase segregation being suppressed effectively. The hole mobility of the best CIGS layers reached 8.36 cm2/V s.

Two- and three-dimensional assemblies of carbon nanomaterials such as carbon nanotubes and graphene are necessary to harness their remarkable physicochemical properties in many clean energy, electronics, and biomedical applications. Herein we report a facile, economical, and versatile method for layer-by-layer fabrication of chemically-crosslinked carbon nanomaterial assemblies by ultrasonic spray coating combined with radical-initiated crosslinking reaction. The chemical, surface, and mechanical properties of the carbon nanomaterial coatings were characterized by Raman spectroscopy, atomic force microscopy, scanning- and transmission-electron microscopy, and nano-dynamic mechanical analysis. Our results indicate that the macroscopic 2D assemblies of crosslinked carbon nanotubes or graphene nanoparticles have surface uniformity, are chemically-crosslinked, and are mechanically robust. We further provide proof-of-concept demonstration of fabricating free-standing, porous, 3D single-walled carbon nanotube structures. Taken together, the results opens avenues toward adapting our method to enable 3D printing or additive manufacturing of all-carbon nanomaterial structures.

A cost-effective and highly efficient method was proposed for preparing reduced graphene (rEG) by modified Hummers approach. The influence of ratio of KMnO4 to graphite, oxidation time and oxidation temperature on oxidative degree of graphite oxide (GO) was investigated by x-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The thermal exfoliated graphene (EG) was characterized with transmission electron microscopy (TEM), FTIR, Raman spectrum and Brunauer–Emmett–Teller (BET) method. The EG was treated for 4 h at 800 °C with H2/Ar mixed atmosphere (15/85, v%) to remove the residual functional groups. The characterization of x-ray photoelectron spectroscopy (XPS) showed that rEG contains less functional groups than EG, which shows the C/O ratio increased from 10.6 (EG) to 34.71 (rEG). The results indicate that treating EG with a mixed H2/Ar atmosphere (15/85, v%) remarkably removes residual functional groups of EG, supplying a simple and feasible approach with large scale production of reduced graphene.

Bulk metallic glasses own unique mechanical properties such as high strength and excellent elastic behavior due to their amorphous atomic structure. Nonetheless, they usually fail catastrophically by shear localization without showing any macroscale plastic deformation under tension and therefore are notoriously brittle. In this study, graphene was proposed as an effective reinforcement to improve the ductility and toughness of metallic glass for possessing a unique combination of strong in-plane strength and weak interbonding with the metal matrix based on molecular dynamics simulations. Both continuous and discontinuous graphene sheets with various configurations and lengths were taken into account. It was found that with proper dispersion of the graphene reinforcements, more than 100% increase in the ductility and more than 150% increase in the toughness can be achieved in the nanocomposites as compared to the monolithic metallic glass of similar size, which was enabled by spreading and delocalizing the plastic shearing deformation in the nanocomposites because of the dual effects of the added graphene.

Ordered mesoporous carbons (OMCs) are appealing alternatives to conventional porous activated carbon applied to electronic energy storage and conversion devices. Nitrogen-doped OMC (NOMC) was prepared with a soft-template strategy directly using task-specific ionic liquid with dicyanamide anion as the nitrogen dopant, and utilized as supercapacitors for the first time. Compared with pristine OMC, NOMC showed excellent electrochemical capacitive behavior in 6 M KOH electrolyte. NOMC possessed a high specific capacitance of 427 F/g at a current density of 1 A/g and exhibited a stable cycle life (almost 98% retained at a current density of 5 A/g after 2000 cycles). The outstanding capacitive performance of NOMC was ascribed to the synergetic effects of its bimodal mesoporous structure, large specific surface area (1919 m2/g), and nitrogen doping (3.52 wt%), which help to accelerate the ion diffusion, increase the surface charge storage, and intensify pseudo-capacitive reactions.

We outline the scrutiny of the two probe devices formed by placing the nonclassical fullerene molecules CM (20 ≤ M ≤ 30) within semi-infinite gold electrodes using density functional theory. The electronic structure and molecular orbitals of isolated fullerene molecules are broadened to form junction devices with charge injection at zero as well as variegated bias respectively. The molecular junctions thus formed are contemplated for two important electrical constitutions, current, and conductance. These parameters are then elaborated and contemplated for their electronic parameters namely, the density of states, transmission coefficient, molecular orbitals, molecular projected self-consistent Hamiltonian states, electron density, and Mulliken population. We conclude that C20 and C24 fullerene molecule exhibits extremely metallic behavior while others fail to demonstrate such behavior. The molecular device, thus formed, strongly supports the superconductive behavior of the C24 molecule with an ability to easily adapt by modulating its active molecular orbitals under applied potential.

Polymer nanocomposites are being considered as future materials to effectively attenuate high energy radiations. The present work addresses effects of neutron radiation on the mechanical properties of lightweight multifunctional polymer composite which were fabricated by dispersing nanoparticles with radiation shielding properties in an epoxy polymer. Three different types of nanoparticles including boron nanopowder, gadolinium, and boron carbide, which are known for excellent radiation absorbing characteristics, were dispersed into epoxy resin to form core sheets for final hybrid sandwich structure. The neutron radiation shielding performance of nanocomposites and their mechanical and thermophysical properties were investigated. The study indicates that the neutron shielding efficiency increased significantly by introduction of nanoparticles. Moreover, the mechanical testing and thermophysical analysis showed that the core materials can retain the structural integrity after they are exposed to the highly thermalized neutron radiation in steady-state mode with a flux of 3 × 1013 n/cm2/s.

Nanoindentation testing of compliant materials has recently attracted substantial attention. However, nanoindentation is not readily applicable to softer materials, as numerous challenges remain to be overcome. One key concern is the significant effect of adhesion between the indenter tip and the sample, leading to larger contact areas and higher contact stiffness for a given applied force relative to the Hertz model. Although the nano-Johnson–Kendall–Roberts (JKR) force curve method has demonstrated its capabilities to correct for errors due to adhesion, it has not been widely adopted, mainly because it works only with perfectly spherical tips. In this paper, we successfully extend the nano-JKR force curve method to include Berkovich and flat indenter tips by conducting numerical simulations in which the adhesive interactions are represented by an interaction potential and the surface deformations are coupled by using half-space Green’s functions discretized on the surface.

The main aim of this research was investigation of the processing-structure-property relationship for polymer blends. The paper presents the results of tests on the structure, basic physical and porous properties of polymer films blend of low density polyethylene (LDPE) with poly(4-methyl-1-pentene) (PMP). Studies utilizing LDPE/PMP blends were undertaken to investigate a three-stage process: melt-extrusion/annealing/uniaxial-stretching (MEAUS), and a two-stage process: melt-extrusion/uniaxial and biaxial stretching (MEUS and MEUBS), used to produce porous films. The permeability and porosity results coupled with small-angle x-ray scattering data provide a direct connection between changes in microstructure to the observed changes in gas transport properties.

Protein cage based nanoarchitectures hold great potential in the fields of energy, catalysis, and bio-applications owing to their ability to tune material’s properties in a benign biomimetic approach. We demonstrate the self-assembly of bacteriophage P22 using inorganic nanoparticles and dendrimers for the first time. Inorganic nanoparticles (iron oxide, CoFe2O4, and Au) and polyamidoamine serve as model systems for rigid and soft linker materials, respectively, to induce P22 assembly via electrostatic interaction. We observed distinctly different packing of P22 using nanoparticles as compared to the polyamidoamine polymer. Notably, the ratio of nanoparticle: P22 and ligand packing on the nanoparticle surface are dominant controls for this assembly. The best results are obtained at 6.5:1 nanoparticle:P22 number ratio in the presence of 50 mM NaCl, pH = 6. In contrast, dense area assembly of P22 is observed at 8:1 polyamidoamine:P22 number ratio with 1 M NaCl (pH ∼ 7.5) for the dendrimer.