Unique Interfacial Structure Research Articles

Investigation on the interfacial stability of multilayered Cu–W films at elevated deposition temperatures during co-sputtering

Cu–W nano-multilayered films show great potential applications in microelectronic, plasma and nuclear fields due to the unique interfacial structure. In this paper, Cu–W films with different microstructures were synthesized by co-sputtering at different deposition temperatures. At room temperature, a nano-multilayered structure with the modulation period (λ) of 5 nm appears with alternatively arrayed W-rich and Cu-rich regions. With the increase of the deposition temperature, the periods of the nano-layers become larger and fuzzy, and finally the totally separated phases of Cu and W grains can be identified at temperature higher than 300 °C. The dominant mechanism of such microstructural evolution can be ascribed by the surface diffusion ability of the deposited atoms as evidenced by temperature as well as deposition time. The hardness of the films declines with the elevated temperatures and by analyzing the hardening mechanisms, the interfacial strengthening effect was verified due to the high hardness in nano-multilayered Cu–W films.

Heavy Anionic Complex Creates a Unique Water Structure at a Soft Charged Interface

Ion hydration and interfacial water play crucial roles in numerous phenomena ranging from biological to industrial systems. Although biologically relevant (and mostly smaller) ions have been studied extensively in this context, very little experimental data exist about molecular scale behavior of heavy ions and their complexes at interfaces, especially under technologically significant conditions. It has recently been shown that PtCl62- complexes adsorb at positively charged interfaces in a two-step process that cannot fit into well-known empirical trends, such as Hofmeister series. Here, a combined vibrational sum frequency generation and molecular dynamics study reveals that a unique interfacial water structure is connected to this peculiar adsorption behavior. A novel sub-ensemble analysis of MD simulation results show that after adsorption, PtCl62- complexes partially retain their first and second hydration spheres, and it is possible to identify three different types of water molecules around them based on their orientational structures and hydrogen bonding strengths. These results have important implications for relating interfacial water structure and hydration enthalpy to the general understanding of specific ion effects. This in turn influences interpretation of heavy metal ion distribution across and reactivity within, liquid interfaces.

Facet-Dependent Cuprous Oxide Nanocrystals Decorated with Graphene as Durable Photocatalysts under Visible Light.

Three morphologies (octahedral, hierarchical and rhombic dodecahedral) of crystal Cu2O with different facets ({111}, {111}/{110}, and {110}) incorporating graphene sheets (denoted as o-Cu2O-G, h-Cu2O-G and r-Cu2O-G, respectively) have been fabricated by using simple solution-phase techniques. Among these photocatalysts, the r-Cu2O-G possesses the best photocatalytic performance of 98% removal efficiency of methyl orange (MO) with outstanding kinetics for 120 min of visible light irradiation. This enhancement is mainly due to the dangling “Cu” atoms in the highly active {110} facets, resulting in the increased adsorption of negatively charged MO. More importantly, the unique interfacial structures of Cu2O rhombic dodecahedra connected to graphene nanosheets can not only decrease the recombination of electron-hole pairs but also stabilize the crystal structure of Cu2O, as verified by a series of spectroscopic analyses (e.g., X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM)). The effective photocatalysts developed in this work could be applied to the efficient decolorization of negatively charged organic dyes by employing solar energy.

Unraveling the discrepancies in size dependence of hardness and thermal stability in crystalline/amorphous nanostructured multilayers: Cu/Cu-Ti vs. Cu/HfO2.

Crystalline/amorphous interfaces (CAIs) confer outstanding mechanical properties on crystalline/amorphous nanostructured multilayers (C/ANMs), which are widely used in micro/nanodevices, because their unique interfacial structure possesses high strain compatibility. In this study, Cu/X (X = Cu-Ti, HfO2) C/ANMs with equal layer thicknesses (h) were comparatively investigated in terms of size-dependent hardness (H) and thermal stability to uncover the fundamental difference(s) between Cu/Cu-Ti and Cu/HfO2. It was found that both as-deposited Cu/Cu-Ti and Cu/HfO2 C/ANMs exhibited a maximum hardness at a critical thickness of h ∼30 nm, which was caused by a transition from confined dislocation gliding to dislocation transmission across the interface. Specifically, the Cu/Cu-Ti C/ANMs exhibited annealing hardening, whereas the Cu/HfO2 C/ANMs exhibited annealing softening associated with a minimum softening at h ∼ 30 nm, which was closely correlated with their thermal stability. In comparison with monolithic amorphous X thin films, the glassy X nanolayers in the present Cu/X C/ANMs exhibited reduced thermal stability and a trend that smaller sizes led to higher stability. The underlying mechanism of the size-dependent crystallization behavior of X nanolayers is discussed in terms of the constraining effects of the interface. These findings provide deep insights into the design of Cu/metallic-glass and Cu/ceramic-glass C/ANMs with optimal performance.

Reagent-Free Synthesis and Plasmonic Antioxidation of Unique Nanostructured Metal-Metal Oxide Core-Shell Microfibers.

A photoresponsive inorganic microfiber with a plasmonic core-shell structure responds to visible light to achieve self-protection against oxidation in an open environment. The microfibers are synthesized via a newly developed reagent-free electrolytic method and have unique interfacial structures and high surface activity.

La2O2CO3 Encapsulated La2O3 Nanoparticles Supported on Carbon as Superior Electrocatalysts for Oxygen Reduction Reaction.

Constructing nanoscale hybrid materials with unique interfacial structures by using various metal oxides and carbon supports as building blocks are of great importance to develop highly active, economical hybrid catalysts for oxygen reduction reaction (ORR). In this work, La2O2CO3 encapsulated La2O3 nanoparticles on a carbon black (La2O2CO3@La2O3/C) were fabricated via chemical precipitation in an aqueous solution containing different concentrations of cetyltrimethyl ammonium bromide (CTAB), followed by calcination at 750 °C. At a given CTAB concentration 24.8 mmol/L, the obtained lanthanum compound nanoparticles reach the smallest particle size (7.1 nm) and are well-dispersed on the carbon surface. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrate the formation of La2O2CO3 located on the surface of La2O3 nanoparticles in the hybrid. The synthesized La2O2CO3@La2O3/C hybrid exhibits a significantly enhanced electrocatalytic activity in electrocatalysis experiments relative to pure La2O3, La2O2CO3, and carbon in an alkaline environment, by using the R(R)DE technique. Moreover, its long-term stability also outperforms that obtained by commercial Pt/C catalysts (E-TEK). The exact origin of the fast ORR kinetics is mainly ascribed to the La2O2CO3 layer sandwiched at the interface of carbon and La2O3, which contributes favorable surface-adsorbed hydroxide (-OH(-)(ad)) substitution and promotes active oxygen adsorption at the interfaces. The unique covalent -C-O-C(═O)-O-La-O- bonds, formed at the interfaces between La2O2CO3 and carbon, can act as active sites for the improved ORR kinetics over this hybrid catalyst. Therefore, the fabrication of lanthanum compound-based hybrid material with an unique interfacial structure maybe open a new way to develop carbon-supported metal oxides as next-generation of ORR catalysts.

Hybrid ZnO/Ag nanocomposites: Fabrication, characterization, and their visible-light photocatalytic activity

We reported a simple and practical method for the fabrication of ZnO/Ag nanocomposites by applying small-molecule mediated ligand exchange strategy. The products were characterized by XRD, EDS and TEM. The unique interfacial structures in the ZnO/Ag nanohybrids induced the strong electronic coupling, resulting in tailored optical absorption property and a distinct PL quenching. Moreover, these ZnO/Ag nanoassemblies displayed obviously improved visible-light-driven photocatalytic activity toward dye photo-removal reaction compared to bare ZnO sample. In addition, photoactive ZnO/Ag heterostructures revealed the outstanding recycled performance.

Numerical Modelling of Multilayered Coatings – Latest Developments and Applications

The remarkable mechanical properties of multilayered coatings, such as super-hardness, excellent resistance against cracking, low wear-rate and high thermal-stability, are due to their unique interfacial structures and deformation mechanisms at the nanometer scale. The multilayered coating process itself is a typical multi-scale phenomenon. The modelling of multilayered coatings has become an important topic in research recently, largely due to the recent progress that has been made in the numerical modelling of materials and structures at different length-scales as well as the improved effectiveness achieved in linking such progress in numerical modelling to enable multi-scale modelling. In this paper, numerical modelling for the analysis of multilayered coatings at individual length-scales: Continuum, Molecular and Nano-scale, is reviewed, along with that at multi-scale modelling. Examples are presented showing numerical models obtained using: the Finite Element Method (FEM), Molecular Dynamics (MD), First-principles calculations and Multi-scale modelling, are presented. Their relative limitations are discussed and challenges to their future work highlighted.

Synthesis of highly efficient and recyclable visible-light responsive mesoporous g-C3N4 photocatalyst via facile template-free sonochemical route

Herein we demonstrate a facile template-free sonochemical strategy to synthesize mesoporous g-C3N4 with a high surface area and enhanced photocatalytic activity. The TEM and nitrogen adsorption–desorption studies confirm mesoporous structure in g-C3N4 body. The photocatalytic activity of mesoporous g-C3N4 is almost 5.5 times higher than that of bulk g-C3N4 under visible-light irradiation. The high photocatalytic performance of the mesoporous g-C3N4 was attributed to the much higher specific surface area, efficient adsorption ability and the unique interfacial mesoporous structure which can favour the absorption of light and separation of photoinduced electron–hole pairs more effectively. A possible photocatalytic mechanism was discussed by the radicals and holes trapping experiments. Interestingly, the synthesized mesoporous g-C3N4 possesses high reusability. Hence the mesoporous g-C3N4 can be a promising photocatalytic material for practical applications in water splitting as well as environmental remediation.

Efficient adsorption and photocatalytic pceerformance of flower-like three-dimensional (3D) I-doped BiOClBr photocatalyst

Uniform well crystallized flower-like three-dimensional (3D) BiOClBr and I-doped BiOClBr microspheres with diameter of 1 μm were synthesized through a simple EG-assisted solvothermal method. The existence of I atoms in the BiOClBr compound could greatly enhance both adsorption and photocatalytic activity as compared with the BiOClBr and BiOX (Cl, Br, I) monomers. The highest catalytic performance of the flower-like 3D I-doped BiOClBr microspheres was preliminary deduced to be due to the much higher specific surface area, efficient sorption capacity as well as the unique interfacial structure. These factors may favor the absorption of light and separation of photogenerated charged carriers more effectively.

Rod like attapulgite/poly(ethylene terephthalate) nanocomposites with chemical bonding between the polymer chain and the filler

Poly(ethylene terephthalate) (PET) nanocomposites containing rod-like silicate attapulgite (AT) were prepared via in situ polymerization. It is presented that PET chains identical to the matrix have been successfully grafted onto simple organically pre-modified AT nanorods (MAT) surface during the in situ polymerization process. The covalent bonding at the interface was confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The content of grafted PET polymer on the surface of MAT was about 26 wt%. This high grafting density greatly improved the dispersion of fillers, interfacial adhesion as well as the significant confinement of the segmental motion of PET, as com- pared to the nanocomposites of PET/pristine AT (PET/AT). Owing to the unique interfacial structure in PET/MAT compos- ites, their thermal and mechanical properties have been greatly improved. Compared with neat PET, the elastic modulus and the yield strength of PET/MAT were significantly improved by about 39.5 and 36.8%, respectively, by incorporating only 2 wt % MAT. Our work provides a novel route to fabricate advanced PET nanocomposites using rod-like attapulgite as fillers, which has great potential for industrial applications.

Characterizing Flux through Micro- and Nanostructured Composites

Nano- and microstructured materials differ from bulk materials because they are heterogeneous matrixes with large internal surface area. Interfaces inside nano- and microstructured composites can impact flux of probes through the matrix through unique interfacial chemistry and structure, interfacial binding and repulsion, and interfacial gradients. Gradients in properties are established at the interface between immiscible components; gradients generate forces which can drive flux. In microstructured composites, where a large fraction of molecules moving through the composite are exposed to interfaces and their associated chemistry, structure, and gradients, effects unimportant in homogeneous materials should be considered. First, the relationship between structure and flux can be evaluated by varying the ratio of internal surface area to internal volume of the composite. Structure−flux relationships provide design constraints for forming composite materials. Second, the structure of the interface itself impacts flux. Third, structure−flux relationships will fail as characteristic dimensions of the nanostructure approach molecular dimensions. Examples from the literature are used to illustrate these points.

The effects of nucleation and growth on epitaxy in the CoSi 2/Si system

The epitaxial perfection and microstructure in thin CoSi 2(111)(and NiSi 2) films on silicon has been examined using transmission electron microscopy, including high resolution cross section techniques. We find that, under ultrahigh vacuum preparation conditions only, genuine single-crystal epitaxy can occur for both reacted and codeposited CoSi 2 films. A unique interfacial defect structure is associated with this epitaxy, in which the silicide films are rotated through 180° about (111) with respect to the silicon substrates. Under less than perfect clean conditions epitaxial perfection is never obtained for CoSi 2. Moreover such perfection has never been attained under any conditions for NiSi 2 on Si(111). By studying the evolution of epitaxy and defect structure in thin and thick films we have proposed a model to explain the unique quality of ultrahigh vacuum CoSi 2 films. The model invokes a defect pinning mechanism to explain the dominance of the 180°-rotated epitaxy during silicide growth.

The Effects of Nucleation and Growth on Epitaxy in the CoSi2/Si System

The epitaxial perfection and microstructure in thin CoSi2 (111) (and NiSi2) films on silicon has been examined using transmission electron microscopy, including high resolution cross section techniques. We find that, under ultrahigh vacuum preparation conditions only, genuine single-crystal epitaxy can occur for bothreacted and codeposited CoSi2 films. A unique interfacial defect structure is associated with this epitaxy, in which the silicide films are rotated through 180° about (111) with respect to the silicon substrates. Under less than perfectly clean conditions epitaxial perfection is never obtained for CoSi2. Moreover such perfection has never been attained under any conditions for NiSi2 on Si(111). By studying the evolution of epitaxy and defect structure in thin and thick films we have proposed a model to explain the unique quality of ultrahigh vacuum CoSi2 films. The model invokes a defect pinning mechanism to explain the dominance of the 180°-rotated epitaxy during silicide growth.