Nanoscale Multilayer Films Research Articles

Redox-switchable binding of ferrocyanide with tetra(viologen)calix [4] resorcine

A binding of ferrocyanide ([Fe(CN)6]4−) with octa-cationic tetra(viologen) calix [4] resorcine (MVCA8+) and its “model” compound––dimethyl viologen (MV2+) has been studied by cyclic voltammetry in DMSO-H2O media (60 vol.% aqueous DMSO, 0.1 M NaClO4). It was found that MV2+ does not interact with ferrocyanide. By contrast, a reversible redox-switchable interaction between [Fe(CN)6]4− and MVCA8+ has been observed. MVCA8+ forms a 1:1 supramolecular complex MVCA8+:[Fe(CN)6]4− with ferrocyanide while its reduced forms (MVCA4+· and MVCA0) do not interact with the tetraanion. The switching of the ferrocyanide binding is also observed in the one electron oxidation of [Fe(CN)6]4− to [Fe(CN)6]3−. It has been shown, that the calix [4]resorcine in its partial and fully reduced forms and its complex with ferrocyanide form well-defined nanoscale multi-layer films on the electrode surface.

Growth and structural characterization of epitaxial Cu/Nb multilayers

Electron beam evaporation with optimized deposition parameters has been used to grow good quality epitaxial Cu/Nb nanoscale multilayered films on sapphire substrates. The quality of the epitaxial films, as measured by the intensities and widths of the X-ray diffraction peaks, increases with increasing deposition temperature. However, high deposition temperatures also enhance the tendency for layer pinch-off which eventually leads to spheroidization and growth of multilayer films with polycrystalline islands. Deposition temperatures and rates were optimized to produce the highest quality epitaxial films with continuous nanolayers, suitable for in situ deformation experiments in a synchrotron-based Laue micro-diffraction set up.

Deformation and material removal in a nanoscale multi-layer thin film solar panel using nanoscratch

Amorphous Si thin film solar panels are multi-layer structures consisting of nanometric layers of hard and brittle materials. The deformation and material removal characteristics of the panel cross-section were investigated using nano-mechanical testing. Nanoindentation and nanoscratching were performed using indenters of various geometries at a range of loads. Atomic force microscopy and electron microscopy were used to study the resulting deformation structures and mechanisms. Plastic deformation of the brittle layers was observed below a critical scratch depth, where material removal occurred without fracture. The critical depth was found to be dependent on indenter geometry and material properties. The indenter tip with the smallest included angle resulted in the greatest scratch depths and material removal. The increased scratching speed also improved the removal efficiency. The results of this work can be applied to develop the ductile regime machining process for thin film solar panels.

Biosynthesis of Calcium Hydroxylapatite Coating on Sputtered Ti/TiN Nano Multilayers and their Corrosion Behavior in Simulated Body Solution

Titanium/titanium nitride (Ti/TiN) nanoscale multilayered films were deposited onto 316L stainless steel substrates by reactive magnetron sputtering using a Ti target. Coatings characterized by X-ray diffraction showed that the stack possesses centered cubic structure. The X-ray photoelectron spectroscopy survey spectra on the etched surfaces of the stack film on steel exhibited the characteristic Ti2p, N1s, and O1s peaks at the corresponding binding energies 454.5, 397.0, and 530.6 eV, respectively. Platelet adhesion experiments were carried out to examine the interaction between blood and the materials in vitro. The results indicated that the smoothness and lower isoelectric point contribute to better hemocompatibility of the Ti/TiN nanoscale multilayered coating. The biomediated synthesis of calcium hydroxylapatite (HA) was carried out on coated substrates using calcium-depositing bacteria. The observation of low corrosion current density (I(corr)) for the calcium HA-coated Ti/TiN specimens in simulated body fluid confirmed their highly resistive nature under the testing condition.

Quantitative TEM analysis of Al/Cu multilayer systems prepared by pulsed laser deposition

Thin films composed of alternating Al/Cu/Al layers were deposited on a (111) Si substrate using pulsed laser deposition (PLD). The thicknesses of the film and the individual layers, and the detailed internal structure within the layers were characterized by means of transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and energy-filtered TEM (EFTEM). Each Al or Cu layer consists of a single layer of nano-sized grains of different orientations. EFTEM results revealed a layer of oxide about 2 nm thick on the surface of the Si substrate, which is considered to be the reason for the formation of the first layer of nano-sized Al grains. The results demonstrate that the PLD technique is a powerful tool to produce nano-scale multilayered metal films with controllable thickness and grain sizes.

Mechanical properties and wear behaviours of CrN/TaN nanoscale multilayered thin films

CrN/TaN nanoscale multilayered thin films with a lamination of hard transition metal nitrides were deposited by closed field unbalanced magnetron sputtering (CFUBMS). The bilayer period (λ) of all of the laminated layers was controlled within the range from 4.3 to 43 nm. The CrN/TaN nanoscale multilayered thin films exhibited a (200) preferred orientation. The mechanical properties of the thin films, as determined by nano-indentation testing, showed a dependence on various bilayer periods (λ). The multilayer with a bilayer period of 5.4 nm exhibited high hardness, high resistance to plastic deformation, and high wear resistance.

In situ TEM studies of local transport and structure in nanoscale multilayer films

This paper describes a novel technique for studying structure–transport correlations in nanoscale multilayer thin films. Here, local current–voltage characteristics from simplified magnetic tunnel junctions are measured in situ on cross-sectional transmission electron microscopy (TEM) samples and correlated directly with TEM images of the microstructure at the tunneling site. It is found that local variations in barrier properties can be detected by a point probe method, and that the tunneling barrier height and width can be extracted.

Nano-structured CrN/CN x multilayer films deposited by magnetron sputtering

CrN/CN x nano-scale multilayered films have been grown on both Si(1 0 0) and high speed steel substrates (HSS) by closed-field unbalanced magnetron sputtering. Designed experimental parameters enabled an evaluation of the effects of negative substrate bias voltage ( V b), and bi-layer thickness λ (by changing substrate rotation rate) during deposition on the structural and mechanical properties of reactively sputtered CrN/CN x multilayer thin films. In all cases, the CN x layers prepared at OEM = 55% were amorphous independent of V b, while the microstructures of the CrN layers were dependent primarily on V b. The CrN layers showed a mixed structure phase consisting of CrN, Cr 2N, and Cr at V b = −(40–120) V. At higher V b values (−140 V or above), the Cr 2N phase was dominant along with low CrN phase content. AFM measurements revealed that the root-mean-square (rms) surface roughness of the CrN/CN x film was 2.5 nm at V b = −200 V whereas the rms values were about 9.5–3.3 2 nm for lower V b values of −(40–180 V). By nanoindentation measurements, a maximum hardness of ∼36 GPa was observed in a film prepared at V b = −140 V. The improved mechanical properties of the CrN/CN x multilayer films are correlated to the phase formation during deposition.

Thermal stability of sputtered Cu∕304 stainless steel multilayer films

We report on the thermal stability of sputter-deposited Cu∕304 stainless steel nanoscale multilayer films. For individual layer thickness of approximately 70nm, the layered morphology was stable up to 600°C with no significant change in the hardness. The stainless steel layer had a duplex bcc+fcc structure that was also preserved in annealed films. After annealing at temperatures of 650°C or higher, the hardness of these multilayer films decreased from 4.75to3.4GPa due to morphological evolution from layers to equiaxed grains and coarsening of the nanolayers.

Nano-Structured CrN/CN<sub>x</sub> Multilayer Films

CrN/CNx nano-scale multilayered films were deposited on Si (100) substrate by closed-field unbalanced magnetron sputtering. Designed experimental parameters enabled an evaluation of the effects of negative substrate bias voltage (Vb), and bi-layer thickness λ (by changing substrate rotation rate) during deposition on the structural and mechanical properties of multilayer films. These multilayers were characterized and analyzed by transmission electron microscope (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and nanoindentation measurements. In all cases, the CNx layers were amorphous and independent of Vb, while the microstructures of the CrN layers were dependent primarily on Vb. The CrN layers showed a mixed structure phase consisting of CrN, Cr2N, and Cr at Vb = -(40-120) V. At higher Vb values (-140 V or above), the Cr2N phase was dominant along with low CrN phase content. AFM measurements revealed that the root-mean-square (rms) surface roughness of the CrN/CNx film was 2 nm at Vb= -200 V whereas the rms values were about 9.5-3.3 nm for lower Vb values of -(40-180 V). By nanoindentation measurements, a maximum hardness of about 36 GPa was observed at Vb= -140 V. The improved mechanical properties of the films are correlated to the phase formation during deposition.

Effect of deposition pressure on microstructure and tribological behavior of MoS x /MoS x -Mo nanoscale multi-layer films

MoSx/MoSx-Mo multi-layer films consisted of several bilayers and a surface layer on steel substrate were deposited by d.c. magnetron sputtering at different deposition pressures. Each bilayer contained a MoSx layer with 80 nm in thickness and a MoSx-Mo composite layer with 20 nm in thickness. With the increase of deposition pressure, the perpendicular orientation of the basal plane prevailed while the parallel orientation decreased. The tribological properties of the multi-layer films were investigated by using a ball-on-disk tribometer both in vacuum and in humid air. The multi-layer film deposited at 0.24 Pa had a compact, consistent layered structure with high intensity of (002) plane and low S content compared to the others deposited at 0.32 and 0.40 Pa, and showed the lowest friction coefficient and wear rate in humid air.

Fabrication of a Molecular-Level Multilayer Film on Organic Polymer Surfaces via Chemical Bonding Assembly

A fresh multilayer film was fabricated on a molecular level and successfully tethered to the surface of a hydroxylated organic substrate via chemical bonding assembly (CBA). Sulfate anion groups (SO4-) were preintroduced onto the surface of biaxially oriented polypropylene (BOPP) films via a reference method. Upon hydrolysis of the SO4- groups, hydroxyl groups (--OH) were formed that subsequently acted as initial reagents for a series of alternate reactions with terephthalyl chloride (TPC) and bisphenol A (BPA). A stable and well-defined multilayer film was thus fabricated via the CBA method. As a result of the nanoscale multilayer fresh film being abundant with reactive groups, it is believed that the film and its fabrication method should provide a fundamental platform for further surface functionalization and direct the design of advanced materials with desired properties.

Mechanical property optimisation of materials by nanostructuring: reduction of residual compressive stress in ta-C film

Optimisation of the mechanical properties of a tetrahedral amorphous carbon (ta-C) thin film was attempted by nanostructuring. In this study, nanoscale multilayer films of ta-C and Si incorporated ta-C:Si layers were prepared. The residual compressive stress of the multilayer films decreased drastically without a decrease in the hardness and elastic modulus, compared with the monolithic films. No significant change in the atomic bond structure was observed in Raman spectral analysis. The present results thus provide a new possibility of application of the ta-C film in harsh environments.

Compliant, Robust, and Truly Nanoscale Free‐Standing Multilayer Films Fabricated Using Spin‐Assisted Layer‐by‐Layer Assembly

Free‐standing multilayer gold‐nanoparticle containing films with an overall thickness ranging from 20–70 nm have been fabricated. These films are compliant, robust, and long‐living, and can be manufactured very time‐efficiently with spin‐assisted layer‐by‐layer assembly with an exceptionally high level of uniformity and integrity, which facilitate their ability to sustain multiple elastic deformations (see Figure).

Rolling textures in nanoscale Cu/Nb multilayers

Rolling textures in nanoscale multilayered thin films are found to differ markedly from textures observed in bulk materials. Multilayered thin films consisting of alternating Cu and Nb layers with columnar grains were produced by magnetron sputtering, with individual layer thickness ranging from 4 μm to 75 nm and Cu/Nb interfaces locally satisfying the Kurdjumov–Sachs (K–S) orientation relations. After rolling to 80% effective strain, samples with a larger initial layer thickness develop a bulk rolling texture while those with a smaller initial layer thickness display co-rotation of Cu and Nb columnar grains about the interface normal, in order to preserve the K–S orientation relations. The resulting K–S texture has 〈0 0 1〉Nb parallel to and 〈1 1 0〉Cu approximately 5° from the rolling direction. A crystal plasticity model based on the Principle of Minimum Shear captures the K–S texture approximately and suggests that Nb drags Cu along in the rotation process.

The Effect of Layer Thickness on Polycrystalline Zirconia Growth in Zirconia-Alumina Multilayer Nanolaminates

ABSTRACTThe mechanical properties of zirconia are known to be a function of phase composition. We show here that a nanolaminate geometry can be used to control the phase composition of zirconia films. The experiment consisted of growth of nanoscale multilayer films (nanolaminates) of polycrystalline zirconia and amorphous alumina by reactive sputter deposition on Si (111) and fused silica substrates. The films were characterized using x-ray diffraction and high resolution electron microscopy. The results show that both monoclinic (m) and tetragonal (t) zirconia polymorphs were formed in the zirconia layers. Most crystallites are oriented with either close-packed {111}-t or {111}-m planes parallel to the substrate. The volume fraction of tetragonal zirconia, the desired phase for transformation-toughening behavior, increases with decreasing zirconia layer thickness. Nanolaminates with a volume fraction of tetragonal zirconia exceeding 0.8 were produced without the addition of a stabilizing dopant, and independent of the kinetic factors that limit tetragonal zirconia growth in pure zirconia films.

Jet Vapor Deposition of Nanostructure Composite Materials

ABSTRACTWe describe the use of Jet Vapor Deposition for efficient synthesis of nanoscale multilayer films, ceramic-organic films, cluster embedded films, and colloids.