Nanoscale Thin Layers Research Articles

Elastic Mismatch Influence on Modes I and II Ratio during Buckling-induced Delamination

In the field of modern electronic, medical and aero-space industry there has been an increasing demand on the investigation and development of new materials and their usage as thin films and coatings. To ensure a proper and long-life reliability of the device composed of several micro- and nano-scale thin layers, not only the reliability of used materials has to be engineered, but also the interface stability between the layers must be ensured. Modern thin film applications use the combination of metallic conductive thin films on compliant substrates or hard coatings, connecting two, highly dissimilar materials. Therefore, in order to correctly assess the interface adhesion and fracture criteria, the elastic mismatch between the thin film and substrate must be properly accounted for. A widely used method to measure the adhesion between thin film and substrate is the buckling-induced delamination by Hutchinson and Suo (1992) where the adhesion energy of the thin film is evaluated as a function of the mode-mixity (for mixed-mode I+II) angle. However, a common practice in such measurements is to disregard the elastic mismatch of film and substrate. Recent research showed that the elastic mismatch has significant impact on the value of the mode-mixity angle. Since the dependence of the adhesion energy on the ratio between modes I and II is used for the interface fracture criteria, the errors introduced by disregarding the elastic mismatch influence may lead to errors in estimation of the critical crack driving force. In this study, we apply our model of the influence of the elastic mismatch on several fracture criteria in combination with experimental measurements of three film-substrate systems. Application of a more precise approach with use of the elastic mismatch influence show change in obtained mode I critical crack driving force. Therefore, the presented work highlights the need for precise assessment of the elastic mismatch influence on the mode-mixity when measuring the adhesion of thin films.

Nanoscale TiO2 Coatings Improve the Stability of an Earth-Abundant Cobalt Oxide Catalyst during Acidic Water Oxidation.

The large-scale deployment of proton-exchange membrane water electrolyzers for high-throughput sustainable hydrogen production requires transition from precious noble metal anode electrocatalysts to low-cost earth-abundant materials. However, such materials are commonly insufficiently stable and/or catalytically inactive at low pH, and positive potentials required to maintain high rates of the anodic oxygen evolution reaction (OER). To address this, we explore the effects of a dielectric nanoscale-thin layer, constituted of amorphous TiO2, on the stability and electrocatalytic activity of nanostructured OER anodes based on low-cost Co3O4. We demonstrate a direct correlation between the OER performance and the thickness of the atomic layer deposited TiO2 layers. An optimal TiO2 layer thickness of 4.4 nm enhances the anode lifetime by a factor of ca. 3, achieving 80 h of continuous electrolysis at pH near zero, while preserving high OER catalytic activity of the bare Co3O4 surface. Thinner and thicker TiO2 layers decrease the stability and activity, respectively. This is attributed to the pitting of the TiO2 layer at the optimal thickness, which allows for access to the catalytically active Co3O4 surface while stabilizing it against corrosion. These insights provide directions for the engineering of active and stable composite earth-abundant materials for acidic water splitting for high-throughput hydrogen production.

Designing a Nanoscale Three-phase Electrochemical Pathway to Promote Pt-catalyzed Formaldehyde Oxidation.

Gas-phase heterogeneous catalysis is a process spatially constrained on the two-dimensional surface of a solid catalyst. Here, we introduce a new toolkit to open up the third dimension. We discovered that the activity of a solid catalyst can be dramatically promoted by covering its surface with a nanoscale-thin layer of liquid electrolyte while maintaining efficient delivery of gas reactants, a strategy we call three-phase catalysis. Introducing the liquid electrolyte converts the original surface catalytic reaction into an electrochemical pathway with mass transfer facilitated by free ions in a three-dimensional space. We chose the oxidation of formaldehyde as a model reaction and observed a 25000-times enhancement in the turnover frequency of Pt in three-phase catalysis as compared to conventional heterogeneous catalysis. We envision three-phase catalysis as a new dimension for catalyst design and anticipate its applications in more chemical reactions from pollution control to the petrochemical industry.

Surface-enhanced raman scattering nanostructures potential for biomedical applications

Owing to the definitely excellent property of nanostructures such as controllable release of ions from the buried nanoscale thin layers, cell response to microscale morphological changes of substrates, distinctively enhancing sensitivity rendered by electrodes with sizes less than 10 micrometers, and dramatically increasing electromagnetic field from local surface plasmon resonance of nanostructures, nanostructures are playing more and more crucial role in the challenging fields. As one of the most sensitive spectroscopic tools, surface enhanced Raman scattering (SERS) shows highly sensitive biological and chemical detection, such as applications for a better biomedical applications and ecotoxicology. It is well known that surfaces with functioned nanostructures often possessthe formation of surface plasma resonance resulted in SERS distinctive enhancement attractively. Therefore, nanostructures(such as nanorods and nanobranches/wires, nanofractal, nanoprisms, and hybrid nanostructures) for SERS are marked aim to provide the related vital information. It should be pointed out that there are a lot of substantial improvements related to the technical innovation in SERS fabrication with anisotropic nanostructures. However, obstacles or challenges are still to prevent these techniques from extensively applying in the practical applications, especially for the SERS-based systems. The significantly crucial case is that it is hard to control anisotropic nanoobjects assembly into ordered structures because the degree of order among the individual building blocks, spatial arrangement and the assembly direction determine the new and/or improved properties.

Polymer Dielectrics: A Scalable, High‐Throughput, and Environmentally Benign Approach to Polymer Dielectrics Exhibiting Significantly Improved Capacitive Performance at High Temperatures (Adv. Mater. 49/2018)

High-throughput production of high-temperature capacitor films is realized by Qi Li, Jinliang He, Qing Wang, and co-workers in article number 1805672 through fast and continuous deposition of a nanoscale thin layer of an insulating barrier using atmospheric-pressure plasma-enhanced chemical vapor deposition. This approach should be adaptable to the industrial extrusion method for highly productive manufacturing of capacitor films.

Perpendicular magnetic tunnel junction (p-MTJ) spin-valves designed with a top Co2Fe6B2 free layer and a nanoscale-thick tungsten bridging and capping layer

Recently, p-MTJ spin-valves with top Co2Fe6B2 free layers have been widely studied. They potentially experience crystallinity degradation in the face-centered-cubic (fcc) structure of the MgO tunneling barrier as a result of the diffusion of Ta atoms and a significant amount of Fe atoms from the Co2Fe6B2 free and pinned layers. A new design of the p-MTJ spin-valve using a nanoscale-thick W bridging and capping layer demonstrated the absence of significant crystallinity degradation in the fcc structure and showed a limited diffusion of Fe atoms, thus achieving a TMR ratio of ~143% at an ex-situ annealing temperature of 400 °C. Coating quantum tunneling devices with thin metallic bridges may lead to magnetic memory cells smaller than 20 nanometres. Dynamic-random-access memory (DRAM) devices are popular because of their simple one-transistor, one-capacitor construction, but they are tricky to produce at nanoscale dimensions. A promising way to construct alternative DRAM devices based on perpendicular magnetic tunnel junctions (p-MTJ) has now been outlined by Jea-Gun Park and colleagues from Hanyang University in South Korea. Their device, which sandwiches a magnesium oxide tunnel barrier between layers of magnetic cobalt—iron—boron films, uses external magnetic fields to switch between on and off memory states. Normally, such p-MTJ devices suffer from degraded magnesium oxide crystallinity and deleterious diffusion of iron atoms. However, the team found that nanoscale-thin layers of tungsten placed under and above the magnetic films prevented premature device breakdown. New design of the p-MTJ spin-valve using W bridging and capping layer demonstrated no significant crystallinity degradation and no considerable Fe atoms diffusion, thus achieving the TMR ratio of ~143% at an ex-situ annealing temperature of 400 oC. A better crystallinity of the MgO layer for W case than Ta case would be related to less diffusion amount of metal atoms and lattice strain in MgO layer. In addition, higher Fe and Co atom concentrations of Co2Fe6B2 free and pinned layers for W case than Ta case would be associated with less solubilities in W layers than Ta layers.

Turning Redundant Ligands into Treasure: A New Strategy for Constructing MIL-53(Al)@Nanoscale TiO2 Layers.

A strategy for in situ fabrication of nanoscale-thin layers of anatase TiO2 coated on the metal-organic framework (MOF) material, MIL-53(Al), is developed. The preparation conditions for crystallized TiO2 are normally incompatible with the thermal and chemical stability of MOFs. Based on our strategy, we found that the redundant organic ligands (1,4-benzenedicarboxylic acid, H2 BDC) within the pores of the as-synthesized MOF play a key function in the protection and support of the framework during hydrothermal loading of the TiO2 precursor, as well as in preventing the infiltration of the precursor into the pores. After annealing, a nanoscale-thin layer of highly crystalline anatase TiO2 , with a thickness of 6-10 nm, was successfully attached to the external surface of the MIL-53(Al) crystals, while the porous framework remains intact. The core-shell structure of the MOF@TiO2 nanocomposite endows the resulting materials with additional optical response and enhanced moisture and chemical stability.

Enhanced Photoelectrical Performance of DSSC by Co-Doped SnO<sub>2</sub> Nanoparticles

Investigation of the I-V characteristics of the DSSC based on interconnected with cobalt-doped SnO2 nanoparticles covered with a nano-scale thin layer which was absorbed by natural dyes are described. The presence of co-doped SnO2 has been confirmed by its characteristic XRD pattern and the shape of the particle is confirmed by SEM. The thickness of the protective layer can be conveniently controlled by the mole value of co-doped SnO2 used in the preparation of the thin film and the optimum conditions for best performance of the DSSC are presented together with possible explanation for the variations observed. An optimum light-to-electricity conversion efficiency of 0.37 % in the presence of a layer of co-doped SnO2 has been obtained which enhancement over the cell prepared with other natural dyes. The characterization of the sample using different techniques was explained (change the sentence).

Enhanced Photoelectrical Performance of DSSC by Co-Doped SnO<sub>2</sub> Nanoparticles

Investigation of the I-V characteristics of the DSSC based on interconnected with cobalt-doped SnO2 nanoparticles covered with a nano-scale thin layer which was absorbed by natural dyes are described. The presence of co-doped SnO2 has been confirmed by its characteristic XRD pattern and the shape of the particle is confirmed by SEM. The thickness of the protective layer can be conveniently controlled by the mole value of co-doped SnO2 used in the preparation of the thin film and the optimum conditions for best performance of the DSSC are presented together with possible explanation for the variations observed. An optimum light-to-electricity conversion efficiency of 0.37 % in the presence of a layer of co-doped SnO2 has been obtained which enhancement over the cell prepared with other natural dyes. The characterization of the sample using different techniques was explained (change the sentence).

First-principles molecular dynamics investigation of the atomic-scale energy transport: From heat conduction to thermal radiation

First-principles molecular dynamics simulation based on a plane wave/pseudopotential implementation of density functional theory is adopted to investigate atomic scale energy transport for semiconductors (silicon and germanium). By imposing thermostats to keep constant temperatures of the nanoscale thin layers, the initial thermal non-equilibrium between the neighboring layers is established under the vacuum condition. Models with variable gap distances with an interval of lattice constant increment of the simulated materials are set up and statistical comparisons of temperature evolution curves are made. The equilibration time from non-equilibrium state to thermal equilibrium state of different silicon or/and germanium layers combinations are calculated. The results show significant distinctions of heat transfer under different materials and temperatures combinations. Further discussions on the equilibrium time are made to explain the simulation results. As the first work of the atomic scale energy transport spanning from heat conduction to thermal radiation, the simulation results highlight the promising application of the first-principles molecular dynamics in thermal engineering.

Investigation of additives for electroless plating of nanowires

Abstract The goal of this work is to deposit nanoscale metal features on a nonconductive substrate in a specific and controlled manner in order to make nanoscale devices. To this end we studied the effects of several plating additives on electroless plating of nanoscale-thin layers in a model system, namely palladium metal on plain and chemically modified silicon oxide substrates. We selected and tested a series of candidate additives including sulfur- and sulfonate-containing molecules such as 3-mercapto-1-propanesulfonate (MPS) and propane disulfonate (PDS). Comparative growth rates, surface composition, morphology, and surface electrical conductivity on homogeneous surfaces were used as a proxy for determining the specificity and quality of deposits on a heterogeneous substrate. MPS and PDS showed the greatest effect on the electroless seeding and plating of palladium on the surface. This work shows that the use of particular additives under electroless plating conditions can lead to nanoscale-thin, selective, and conductive deposits of palladium metal.

The interconnected CaCO 3 coated SnO 2 nanocrystalline dye-sensitized solar cell with superior performance

Design, Development, fabrication and investigation of the I– V characteristics of the DSSC based on interconnected 15 nm SnO 2 nanoparticles covered with a nano-scale thin layer of CaCO 3 are described. The presence of CaCO 3 has been confirmed by its characteristic XRD pattern and EDX plots. The thickness of the protective layer can be conveniently controlled by the molar ratio of SnO 2:CaCO 3 used in the preparation of the thin film and the optimum conditions for best performance of the DSSC are presented together with possible explanations for the variations observed when the molar ratio is changed. An optimum light-to-electricity conversion efficiency of 5.4% in the presence of a layer of CaCO 3 has been obtained which is 3.2 times enhancement over the cell prepared without CaCO 3. The characterization of the surface using different techniques is explained.

Fabrication of nanoscale photochromic materials by vapor deposition method

AbstractVapor deposition method was used to obtain nanocrystals of N‐(3,5‐di‐tert‐butylsalicylidene)‐4‐ aminopyridine (1) and N‐(3,5‐di‐tert‐butylsalicylidene)‐4‐iodoaniline (2), and nanoscale thin layers (65 nm thick) of cis‐1,2‐dicyano‐1,2‐bis(2,4,5‐trimethyl‐3‐thienyl)ethene (3). Compound 3 was also deposited on a substrate previously covered by gold nanoparticles (Ø = 100 nm). Nanoscale crystals of 1 and 2 showed similarities with bulk crystals: they exhibit photochromic properties and they have similar shapes according to Atomic force microscopy (AFM) investigations. The thin layers of 3, with and without gold nanoparticles, showed light‐induced absorption change in the visible. Copyright © 2007 John Wiley & Sons, Ltd.

Visualization of interactions between organic polymer surfaces and ion beams obtained from molecular dynamics Simulations

Molecular dynamics simulation combined with sophisticated visualization techniques may be one of the most powerful scientific tools for the study of atomic-level surface reactions during plasma-wall interactions. This paper shows visualization of an organic polymer model substrate before and during molecular beam injections. The classical interatomic potential model functions used in the present work are developed to describe chemical reactions, i.e., formation and breakup of chemical bonds under strongly nonthermal-equilibrium conditions. We have observed that, during beam injections, nonthermal-equilibrium chemical reactions take place in a nano-scale thin layer of the substrate top surface, which determines characteristics of the process, such as etching/deposition rates and selectivity.