Nanoscale Multilayer Thin Films Research Articles

Nanoscale Multi-Layer Thin Film Fabricated by Cathodic Arc Evaporation (CAE) Method

In the present study, TiN and CrN single-layer and TiN/CrN nanoscale multi-layer thin films have been deposited on 420C stainless steel (SS) substrate using a cathodic arc evaporation (CAE) method. The nanoindentation test showed that hardness of TiN/CrN nanoscale multi-layer thin film was 30 GPa that is harder than TiN (HTiN = 23 GPa) and CrN (HCrN = 19 GPa). Ball-on-disk tribometer and Rockwell-C indentation methods showed respectively better sliding wear performance for TiN/CrN nanoscale multi-layer coating and better adhesion strength for CrN single-layer coating in comparison to all samples. Finally it was found that the TiN/CrN nanoscale multi-layer thin film can be used for tribological applications on 420C SS where high hardness and wear resistance and low friction coefficients are essential.

Atomistically Informed and Dislocation-Based Viscoplasticity Model for Multilayer Composite Thin Films

Nano-scale multilayer composite thin films are potential candidates for coating applications at harsh environments due to their promising mechanical and thermal properties. In this study, a viscoplasticity continuum model based on the plastic flow potential of metal/ceramic nanolayer composites, obtained from molecular dynamics (MD) simulations, is developed to build up a multiscale model bridges atomistic simulation with continuum models for the thin film composites. The model adopts a power law hardening considering confined layer slip (CLS) mechanism and accounts for the evolution of dislocation density based on the statistically stored dislocations and geometrically necessary dislocations. It is then implemented into a finite element code (ls-dyna) to investigate the deformation behavior of nanolayer composites at the macroscale. The deformation behavior of a high strength steel coated with Nb/NbC multilayer is also examined.

Residual Stresses in Cu/Ni Multilayer Thin Films Measured Using the Sin2ψ Method

Residual stresses in multilayer thin films are of substantial importance to the service life of advanced engineering systems. In this investigation, the residual stresses in magnetron sputtered Cu/Ni multilayer thin films were characterized using x-ray diffraction (XRD) and the sin2ψ method. The influence of layer thickness on residual stress was explored for films with alternating Ni and Cu layers with equal layer thicknesses ranging from 10 nm to 100 nm. To address peak broadening and overlapping, the Gaussian Mixture Model (GMM) and Expectation Maximization (EM) algorithm were employed, and the peak position was determined using the Center of Gravity (CoG) method. Results showed tensile residual stress in both the Cu and Ni layers and a prominent layer thickness dependence. The stress in the Ni layers increased from roughly 880 MPa to 1550 MPa with decreasing layer thickness from 100 nm to 10 nm. In the Cu layers, the stress remained relatively constant at ~250 MPa and then substantially decreased for the 10 nm thickness. The findings confirm that the XRD-based approach can be applied for residual stress measurement in nanoscale multilayer thin films, provided that peak broadening and overlapping issues are addressed. Furthermore, the residual stress in metal multilayers is strongly dependent on layer thickness.

Confinement of phonon propagation in laser deposited tungsten/polycarbonate multilayers

Nanoscale multilayer thin films of W and PC (Polycarbonate) show, due to the great difference of the components’ characteristics, fascinating properties for a variety of possible applications and provide an interesting research field, but are hard to fabricate with low layer thicknesses. Because of the great acoustic mismatch between the two materials, such nanoscale structures are promising candidates for new phononic materials, where phonon propagation is strongly reduced. In this article we show for the first time that W/PC-multilayers can indeed be grown with high quality by pulsed laser deposition. We analyzed the polymer properties depending on the laser fluence used for deposition, which enabled us to find best experimental conditions for the fabrication of high-acoustic-mismatch W/PC multilayers. The multilayers were analyzed by fs pump-probe spectroscopy showing that phonon dynamics on the ps time-scale can strongly be tailored by structural design. While already periodic multilayers exhibit strong phonon localization, especially aperiodic structures present outstandingly low phonon propagation properties making such 1D-layered W/PC nano-structures interesting for new phononic applications.

Effect of bilayer period on structural and mechanical properties of nanocomposite TiAlN/MoN multilayer films synthesized by cathodic arc ion-plating

TiAlN/MoN multilayers were deposited on Si (100) and cemented carbide substrates using TiAl and Mo targets in a cathodic arc ion plating system with 1-fold rotation. The bilayer thickness (Λ) of all the layers was controlled via rotational speed of substrate holder within a rage of 21 to 124nm. The TiAlN/MoN has a multilayered structure in which nano-crystalline TiAlN layers alternate with the nano-crystalline MoN layers. The Ti:Al ratios measured by EDS over all samples were closed to the designed ratio and corresponded to Ti0.70Al0.30N composition. TiAlN/MoN nanoscale multilayer thin films exhibited a TiAlN (200), TiAlN (220), MoN (202) and MoN (200) crystalline orientation. The highest hardness and Young's modulus were obtained with a bilayer period of 25nm, while wear rate decreased with decreasing bilayer period. On average, nanoindentation measurements combined with atomic force microscopy (AFM) and cross-sectional scanning electron microscopy (SEM) revealed improved mechanical properties of TiAlN/MoN films with decreasing bilayer period were attributed to their densified microstructure with development of fine grains and reduced surface roughness.

Physical characteristics of localized surface plasmons resulting from nano-scale structured multi-layer thin films deposited on D-shaped optical fiber

Novel surface plasmonic optical fiber sensors have been fabricated using multiple coatings deposited on a lapped section of a single mode fiber. UV laser irradiation processing with a phase mask produces a nano-scaled surface relief grating structure resembling nano-wires. The resulting individual corrugations produced by material compaction are approximately 20 μm long with an average width at half maximum of 100 nm and generate localized surface plasmons. Experimental data are presented that show changes in the spectral characteristics after UV processing, coupled with an overall increase in the sensitivity of the devices to surrounding refractive index. Evidence is presented that there is an optimum UV dosage (48 joules) over which no significant additional optical change is observed. The devices are characterized with regards to change in refractive index, where significantly high spectral sensitivities in the aqueous index regime are found, ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity.

Self-Assembled Nano-heterostructural Thin Film for Optical Lens

The layer-by-layer (LBL) self-assembly method enables the deposition of functional nanoscale multilayer thin films on intricate-shape substrates. The present problem with optical devices is the formation of a uniform coating of a nanoscale heterostructural thin film on both faces of the lens. In this paper, we introduce self-assembled heterostructural optical films with higher- and lower-refractive index layers, which were fabricated using a stable water base titanium complex [titanium(IV) bis(ammonium lactato) dihydroxide (TALH)] and cationic and anionic polyelectrolytes [poly(diallyldimethylammonium chloride) (PDDA)] and [poly(acrylic acid) (PAA)] on a lens via the LBL method. The antireflectance characteristics of (PDDA/TALH)20/(PDDA/PAA)20 showed a maximum transmittance of 99.2% with (PDDA/TALH)20 (ca. 1.75, 80 nm) and (PDDA/PAA)20 (ca. 1.48, 87 nm) on both faces of the lens. These results demonstrate that we can control the refractive index and film thickness of self-assembled nano-heterostructural films on optical lenses.

The effect of Mg 0.1Zn 0.9O layer thickness on optical band gap of ZnO/Mg 0.1Zn 0.9O nano-scale multilayer thin films prepared by pulsed laser deposition method

Epitaxial ZnO/Mg 0.1Zn 0.9O (MZO) nano-scale multilayer thin films were prepared on Al 2O 3 (0001) substrates by pulsed laser deposition. The ZnO/MZO multilayer thin films were grown by stacking alternate layers of ZnO and Mg 0.1Zn 0.9O with a laser fluence, repetition rate, substrate temperature and oxygen partial pressure of 3 J/cm 2, 5 Hz, 600 °C and 3.8 × 10 − 7 Pa, respectively. The thickness of an individual ZnO layer was maintained at 3 nm, whereas that of the MZO layers was varied from 3 nm to 15 nm. Cross-sectional transmission electron microscopy revealed alternating layers of bright and dark contrast, indicating the formation of a ZnO/MZO multilayer. X-ray diffraction results showed that multilayer thin films were epitaxially grown as a hexagonal wurzite phase with orientation relationship of ( 0001 ) [ 10 1 ¯ 1 ] multilayer | | ( 0001 ) [ 10 1 ¯ 1 ] substrate . The 2θ value of the (0002) peak of the ZnO/MZO multilayer thin films increased from 34.30° to 34.71°, indicating that Mg is replaced with Zn in the hexagonal lattice in the MZO of ZnO/MZO multilayer. UV–visible spectroscopy showed a systematic increase in the band gap of the ZnO/MZO multilayer thin films from 3.34 eV to 3.70 eV with increasing MZO layer thickness, which suggests that the band gap energy of a ZnO/MZO multilayer thin film can be controlled by varying the thickness of each constituent layer.

Bilayer period dependence of CrN/CrAlN nanoscale multilayer thin films

CrN/CrAlN nanoscale multilayer thin films with a bilayer period ( λ ) ranging from 4.4 to 44.1 nm were deposited on Si wafers (100) by closed field unbalanced magnetron sputtering (CFUBMS). The λ of the layers was controlled by the rotation speed of the substrate holder. The coatings were characterized by high resolution X-ray diffraction and field emission transmission electron microscopy. The CrN/CrAlN nanoscale multilayer thin films exhibited a CrN (200) and AlN (200) crystalline orientation. Nano-indentation testing revealed a hardness ranging from 37 to 46 GPa according to the bilayer period. The highest hardness was obtained with a bilayer period of 5.5 nm due to the high resistance to plastic deformation.

Peak/Plateau Strength in Nanoscale Multilayer Thin Films: Constrained vs Unconstrained Dislocation Nucleation

AbstractThe peak/plateau strength of multilayer thin films is analyzed in terms of the stress to bow out a dislocation loop from an interface. Comparison of approximate analytic models to experimental data suggests that the bow out is “constrained” by nearby interfaces, at least for e-NbN/Mo and e-Ni/Cu films. Estimates of the interfacial pinning distance to form the bow out are ˜20b for e-NbN/Mo and ˜70b for e-Ni/Cu around peak/plateau strength (b is the magnitude of Burgers vector).

Effect of bilayer period on CrN/Cu nanoscale multilayer thin films

Thin films with a CrN/Cu multilayer structure comprising a superhard coating with a lamination of hard transition metal nitride and soft metal were synthesized by Closed Field Unbalanced Magnetron Sputtering (CFUBMS). The bilayer thickness (λ) of all of the laminated layers was controlled via the rotational speed of the substrate holder within the range from 4.7 to 47.1 nm. The structural characterization of the coatings was investigated using high resolution X-ray diffraction (HRXRD) and field emission transmission electron microscopy (FETEM). The preferred orientation of the CrN/Cu nanoscale multilayer thin films was CrN (200) and Cu (200). The surface morphology of the films was examined by atomic force microscopy (AFM). The mechanical properties of the coatings, as determined by nano-indentation testing and the ball-on-disc test varied with the bilayer thickness (λ). The multilayer with a bilayer thickness of 7.9 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.

Transmission of a screw dislocation across a coherent, non-slipping interface

Current research on nanocrystalline metals and nanoscale multilayer thin films suggests extraordinary plastic strength is due to confinement of slip to individual grains or layers. To assess the magnitude of confinement, a Peierls model of slip transmission of a screw dislocation across a coherent, non-slipping interface is presented. The results reflect that large interfacial barriers to transmission are generated by rapid fluctuations in dislocation line energy near the interface due to elastic modulus mismatch, stacking fault energy mismatch, and antiphase boundary energy for transmission into an ordered phase. Coherency stress is predicted to dramatically alter the dislocation core configuration and impart additional strength regardless of the sign. Contributions to strength are not additive due to nonlinear coupling via the dislocation core configuration. The predicted barrier strength for a coherent (0 0 1) Cu/Ni interface is comparable to atomistic (EAM) results but larger than estimates from hardness data.

Nanoscale multilayer PbS thin films fabricated by liquid–liquid interface reaction technique for solar photovoltaic applications

In the present communication, the self-assembly of nanocrystalline PbS at the liquid–liquid interface is reported. The PbS nanocrystals were, subsequently, transformed in the form of thin films by dip coating. The resultant films were characterized by SEM-EDAX, TEM-SAED, XPS and UV–visible spectroscopy. Pyramidal features at the nanometer scale and a sharp excitonic peak at 656 nm are the salient aspects of this work. The band gap of the order of 1.8 eV (associated with the excitonic feature) is ideally suited for solar photovoltaic applications.

Dislocation Confinement and Ultimate Strength in Nanoscale Polycrystals

ABSTRACTNanoscale polycrystalline metals typically exhibit increasing hardness with decreasing grain size down to a critical value on the order of 5 to 30 nm. Below this, a plateau or decrease is often observed. Similar observations are made for nanoscale multilayer thin films. There, TEM observations and modeling suggest that the hardness peak may be associated with the inability of interfaces to contain dislocations within individual nanoscale layers. This manuscript pursues the same concept for nanoscale polycrystalline metals via an analytic study of dislocation nucleation and motion within a regular 2D hexagonal array of grains. The model predicts a hardness peak and loss of dislocation confinement in the 5 to 30 nm grain size regime, but only if the nature of dislocation interaction with grain boundaries changes in the nanoscale regime.

Fracture mechanisms in nanoscale layered hard thin films

Depth sensing nanoindentation and nanoscratch testing were combined with atomic force microscopy and electron microscopy observations to study mechanical properties and fracture behavior of a number of TiAlN(Si, C,…) hard thin films. Various nanoscale multilayer thin films were deposited onto the cemented carbide substrates using cathodic arc PVD. Failure modes were activated either by a cycle of indentation or by microscratching of the samples to provide an estimation of the fracture toughness and interfacial fracture energies. Load–displacement curves were characterized by small discontinuities due to the formation of nano and microscale cracks through the film thickness. Under sufficiently high load the occurrence of large-scale cracks consists of the successive lateral cracks at the contact site, or corner Palmqvist type radial cracks around the contact area depending on the film structures. Such indentation behaviors can be attributed to small modulus mismatch between the film and the substrate, good adhesion of the film, and in particular high toughness of both substrate and films in spite of great differences in their respective hardness. Various modes of failure and the sequences of fracture events were determined using stepwise or continuously increasing load scratch tests. Some films were found to be more sensitive to tensile stress behind the indenter which generates through thickness vertical microcracks on the scratch track. Other films appeared to be more susceptible to compressive stress ahead of the indenter leading to local delamination at the interface between the layers and irregular microcracks under the contact area.