Metallic Nanofilm Research Articles

Development of Fatigue Crack Propagation Technique for Freestanding Nano-Films

We developed an experimental technique for evaluating fatigue crack propagation properties of freestanding nano-films and conducted tensile and fatigue crack propagation experiments for about 500-nm-thick freestanding copper (Cu) films. We employed a sacrificial etching method for fabricating freestanding metallic nano-film specimens. A piezoelectric-actuator with long stroke and a load cell for small load were used for applying cyclic loading to nano-films. We developed original jigs for handling and aligning the nano-film specimens. Focused ion beam (FIB) was employed to introduce a single side-edge-notch in the nano-film specimens for fatigue crack propagation experiments. The results of tensile experiments revealed that the nano-films have resistance to plastic deformation comparable to cold-rolled Cu bulk, but have lower ductility. The results of fatigue crack propagation experiments revealed that a fatigue crack stably propagates in the nano-film by a uniaxial cyclic loading with constant maximum stress before unstable fracture. The fatigue crack propagation rate da/dN of the Cu nano-films is higher than that of Cu bulk counterpart in higher stress intensity factor range, ΔK. Fatigue crack started to propagate from the notch tip below the threshold value of Cu bulk with coarse grains, and the Cu nano-films show similar fatigue crack propagation properties to Cu bulk with ultrafine grains in lower ΔK. Morphology of the fracture surface transited from microstructure-sensitive rough surface to microstructure-insensitive ductile surface or chisel point fracture as fatigue crack propagated. This suggests that the dominant fracture mechanism changes from the accumulation of cyclic deformation to the monotonic tensile-dominant fracture.

Surface Segregation of Trace Element Bismuth during Heat Treatment of Aluminum

Surface segregation of bismuth and resulting oxidation of rolled aluminum bismuth model alloys during heat-treatment were investigated by electron-optical techniques, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Heat treatment at 600°C caused segregation of liquid Bi in the form of a metallic nanofilm at the oxide-metal interface. Breakdown of thermally-formed γ-Al2O3 crystalline oxide by the liquid Bi film during subsequent cooling in water produced a composite oxide layer, consisting of remnants of the γ-Al2O3 layer on top and an amorphous hydrated layer of about 1.5 μm thick between the γ-Al2O3 layer and the metal. Cooling in laboratory air after heat-treatment gave a slightly thinner (about 1 μm) amorphous layer than that compared to water cooling. Formation of the thick aluminum oxide layer during cooling was attributed to the maintenance of the depassivating BiAl interfacial nanofilm by dealloying of the Al component of the metal. Existence of the BiAl interfacial film in a fluidized state during cooling, which is a necessary condition for oxide growth, was further enhanced by significant depression of the solidification point of the film due to its nanometer order of thickness.

Atomistic simulations of the tensile strength of a disclinated bicrystalline nanofilm

The tensile strength of a metallic bicrystalline nanofilm containing a wedge disclination in the middle of a grain boundary (GB) terminating at the film surfaces was studied via atomistic simulations. The results show that an increase in the disclination power strengthens the film, which is contrary to intuition, if a crack initiates at one end of the terminated GB, whereas it weakens the film if a crack initiates at the disclination core. Both the strengthening and weakening demonstrate a size effect for film thickness in the range 10–20 nm, and are also significantly influenced by the GB misorientation. It is further shown that the strength can be increased to ∼80% of the theoretical strength of a defect-free film by introducing a disclination of moderate power in the GB.

Cavity Plasmon Resonance Biosensing

Surface plasmon resonance (SPR) spectroscopy has demonstrated unprecedented performance in label-free real-time probing of various biopolymer, ligand, protein, and DNA interactions. Since its inception in the late sixties, the basic physical phenomenon underlying the SPR biosensing remained unchanged, namely, resonant absorption of TM-polarized light incident upon a metallic nanofilm above the critical total internal reflection angle. Since the SPR field is strictly confined to the metal-analyte interface, the measurements are usually limited to molecular adsorbates located in an immediate vicinity of this surface. Herein, we propose a novel biosensing method utilizing cavity plasmon resonance (CPR) excitation in nanofilms. As opposed to the classical TM-polarized SPR, the CPR is applicable for both TE and TM polarizations and does not require complicated evanescent field excitation conditions. It holds a promise for highly sensitive real-time probing of scalable amounts of analytes in a variety of frequency bands.

ANALYSIS OF SURFACE PLASMONS EXCITATIONS FROM FABRICATION DEFECTS OF METALLIC NANOFILM WITH NONSYMMETRICAL AND FINITE GRATING-LIKE CORRUGATION

The influence of fabrication errors of metallic nanofilm with the grating-like and nonsymmetrical corrugation on one or two sides on surface plasmons resonance is analyzed by using boundary integral method. The scattering cross-section and the near-field intensity distribution of its corresponding resonant wavelengths for the finite grating-like nanostructure with or without fabrication defects are numerical investigated. The results show that the resonant wavelength is influenced by the fabrication flaws. More detailed directions of the electric flux lines around the metallic grating-like nanostructure and the near-field intensity distribution indicate that the excitation of surface electrons is influenced. This investigation will provide useful information for the fabrication of the metallic grating-like nanostructure and the experimental error analysis of the scientists.

Oscillations of the superconducting temperature induced by quantum well states in thin metallic films: Numerical solution of the Bogoliubov–de Gennes equations

Quantum confinement of electrons in a high-quality metallic nanofilm results in the formation of quantum-well states. The band of single-electron states is split into a series of subbands moving in energy with changing film thickness. When the bottom of such a subband passes through the Fermi surface, a shape resonance appears leading to oscillations of the critical temperature ${T}_{c}$ as a function of film thickness. We present a quantitative description of recent experimental data on the film-thickness dependence of ${T}_{c}$ in Pb nanofilms with atomic-scale uniformity in thickness [Science 306, 1915 (2004)] through a numerical solution of the Bogoliubov--de Gennes equations.

原子シミュレーションによる金属ナノ薄膜の理想構造強度評価(OS13a 電子・原子シミュレーションに基づく材料特性評価)

原子シミュレーションによる金属ナノ薄膜の理想構造強度評価(OS13a 電子・原子シミュレーションに基づく材料特性評価)