Metallic Nanofilm Research Articles

Plasmon Thermal Conductance and Thermal Conductivity of Metallic Nanofilms

The thermal conductance and thermal conductivity of surface plasmon polaritons propagating along a metallic nanofilm deposited on a substrate are quantified and analyzed, as functions of the film thickness, length, and temperature. This is done by analytically solving the dispersion relation of plasmons for their wave vectors and propagation length. It is shown that the plasmon energy transport along the film interfaces is driven by two modes characterized by symmetric and antisymmetric spatial distributions of the magnetic field. For a gold nanofilm deposited on a silicon substrate, both modes have comparable contributions of the plasmon thermal conductance, which takes higher values for hotter and/or longer nanofilms and saturates for films thicker than 50 nm. This saturation arises from the decoupling of the plasmon modes, the transition of which to a coupled state for thinner films maximizes the plasmon thermal conductivity. For a 1-cm-long gold nanofilm at 300 K, the maximum thermal conductivity appears for a thickness of 10 nm and takes the value of $15\phantom{\rule{0.2em}{0ex}}\mathrm{W}\phantom{\rule{0.1em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, which is about 25% of its electron counterpart. As a result of the huge propagation distance ($>1\phantom{\rule{0.2em}{0ex}}\mathrm{cm}$) of plasmons, this plasmon thermal conductivity increases significantly with the film length and temperature and it could therefore be useful to improve the heat dissipation along metallic nanofilms.

Влияние осцилляций Фриделя на работу выхода нанопленок иттербия

The effect of standing waves of charge density (Friedel oscillations) generated by an interface of the ‘metallic ytterbium nanofilm  single-crystal silicon substrate’ type on the work function of ytterbium nanolayers has been studied. It is shown that in the range of nanofilm thicknesses from 0 to 8 monatomic layers, the work function has an oscillating character. This feature of the dependence of the work function on the nanofilm thickness is a consequence of the fact that the standing waves change nonmonotonically the power (momentum) of the electric double layer, which exists on the metal surface and affects the work function of the metal. This ultimately determines the oscillating nature of the dependence of the work function on the thickness of the nanofilms.

Effect of Friedel Oscillations on the Work Function of Ytterbium Nanofilms

The effect of standing waves of charge density (Friedel oscillations) generated by an interface of the metallic ytterbium nanofilm single-crystal silicon substrate type on the work function of ytterbium nanolayers has been studied. It is shown that in the range of nanofilm thicknesses from 0 to 8 monatomic layers, the work function has an oscillating character. This feature of the dependence of the work function on the nanofilm thickness is a consequence of the fact that the standing waves change nonmonotonically the power (momentum) of the electric double layer, which exists on the metal surface and affects the work function of the metal. This ultimately determines the oscillating nature of the dependence of the work function on the thickness of the nanofilms. Keywords: surface, nanofilm, work function, Friedel oscillations, electric double layer, ytterbium.

Pressure dependent thermoreflectance spectroscopy induced by interband transitions in metallic nano-film

SummaryUtilizing high-pressure to modulate optical properties, such as thermoreflectance (dR/dT), over a wide range has received much attention. Nevertheless, how the pressure exerts on the complex dielectric constant and finally on dR/dT remains elusive. Here, we perform a thoroughly experimental and theoretical investigation on dR/dT of Al nano-film from 0 to 25 GPa. The dR/dT values exhibit a sine-like pressure-dependence, with the zero-crossing appearing at around 6 GPa. These special phenomena are well explained from electron transition viewpoints. The first-principles calculations show that the energy difference of parallel bands is enlarged from 1.45 to 2 eV, thereby increasing the threshold for electron transitions. The lifted threshold changes the optical absorption rates of Al and the density of states of the electrons involving interband transitions; finally, the resulting dR/dT exhibits such a pressure-dependent behavior. Our findings provide a deep insight on pressure-induced electronic transitions and photon-electron interactions in metals.

Pressure Dependent Thermoreflectance Spectroscopy Induced by Interband Transitions in Metallic Nano-Film

Utilizing high-pressure to modulate optical properties, such as thermoreflectance (dR/dT), over a wide range has received much attention. Nevertheless, how the pressure exerts on the complex dielectric constant and finally on dR/dT remains elusive. Here, we perform a thoroughly experimental and theoretical investigation on dR/dT of Al nano-film from 0 to 25 GPa. The dR/dT values exhibit a sine-like pressure-dependence, with the zero-crossing appearing at around 6 GPa. These special phenomena are well explained from electron transition viewpoints. The first-principles calculations show that the energy difference of parallel bands is enlarged from 1.45 to 2 eV, thereby increasing the threshold for electron transitions. The lifted threshold changes optical absorption rates of Al and the density of states of electrons involving interband transitions, finally resulting in that dR/dT exhibits such a pressure-dependent behavior. Our findings provide a deep insight on pressure-induced electronic transitions and photon-electron interactions in metals.

Metallic Nanofilm Enhanced Fluorescence Cell Imaging: A Study of Distance-Dependent Intensity and Lifetime by Optical Sectioning Microscopy.

Simple, stable, easily-fabricated smooth metallic nanofilm can improve the imaging intensity and imaging contrast. However, its application in micrometer-scale cells has not been popularized due to the lack of full understanding of their related fluorescence properties. In this study, fluorescence enhancement of cell imaging on smooth Au nanofilm was investigated over a micrometer-scale range via employment of the optical sectioning method available with a laser scanning confocal fluorescence microscope. The fluorescence enhancement reduced with the distance away from the surface of metallic nanofilm, and this distance dependence was determined by the factors of numerical aperture, dye-substrate distance, and emission wavelength. In addition, distance-dependent fluorescence lifetime images of cells were also measured to study the interaction between fluorophores and metallic film. The enhancement effect of Au nanofilm on fluorescence cell imaging can be induced not only by the standing wave formed by the reflected light and exciting light but also by the interaction between fluorophore and surface plasmons on the metallic nanofilm. Our study on smooth metallic nanofilm should pave the way for utilizing its uniform fluorescence enhancement characteristic for biological imaging.

Effective electrocatalytic methanol oxidation of Pd-based metallic glass nanofilms.

Compared to their conventional polycrystalline Pd counterparts, Pd79Au9Si12 (at%) - metallic glass (MG) nanofilm (NF) electrocatalysts offer better methanol oxidation reaction (MOR) in alkaline medium, CO poisoning tolerance and catalyst stability even at high scan rates or high methanol concentrations owing to their amorphous structure without grain boundaries. This study evaluates the influence of scan rate and methanol concentration by cyclic voltammetry, frequency-dependent electrochemical impedance spectroscopy and a related equivalent circuit model at different potentials in Pd-Au-Si amorphous NFs. Structural and compositional differences for the NFs are assessed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray (EDX) mapping and X-ray diffraction (XRD). The ratio of the forward to reverse peak current density ipf/ipb for the MG NFs is ∼2.2 times higher than for polycrystalline Pd NFs, evidencing better oxidation of methanol to carbon dioxide in the forward scan and less poisoning of the electrocatalysts by carbonaceous (e.g. CO, HCO) species. Moreover, the electrochemical circuit model obtained from EIS measurements reveals that the MOR occurring around -100 mV increases the capacitance without any significant change in oxidation resistance, whereas CO2 formation towards lower potentials results in a sharp increase in the capacitance of the Faradaic MOR at the catalyst interface and a slight decrease in the corresponding resistance. These results, together with the high ipf/ipb = 3.37 yielding the minimum amount of carbonaceous species deposited on the thin film during cyclic voltammetry and stability in the alkaline environment, can potentially make these amorphous thin films potential candidates for fuel-cell applications.

Intersubband pairing induced Fulde-Ferrell phase in metallic nanofilms

We consider a free-standing metallic nanofilm with a predominant intersubband paring which emerges as a result of the confinement in the growth direction. We show that the Fermi wave vector mismatch between the subbands, detrimental to the intersubband pairing, can be compensated by the non-zero center of mass momentum of the Cooper pairs. This leads to the spontaneous appearance of the intersubband Fulde-Ferrell (IFF) state, even in the absence of an external magnetic field. Our study of the intrasubband pairing channel on the stability of the IFF phase shows that the former strongly competes with the intersubband pairing, which prohibits the coexistence of the two superconducting phases. Interestingly, upon application of the magnetic field we find a transition to an exotic mixed spin-singlet subband-triplet and spin-triplet subband-singlet paired state. Finally, we discuss the possibility of existence of the IFF pairing in novel superconducting materials.

Ultrahigh hydrogen-sorbing palladium metallic-glass nanostructures

The hydrogenation mechanism in a Pd–Si–Cu metallic glass nanofilm, and its post-characterization by chronoamperometry/cyclic voltammetry and HR(S)TEM analyses.

Interaction of magnetic elements in metallic ferromagnetic nanofilms

In this paper, a comparative analysis of the distances between magnetic elements is made, under which a noticeable effect arises when they interact. The sides of the domain (domain walls), the terminal part of the domain (domain apex), we called magnetic elements. During magnetization, the domain structure is restructured. The distances between the domain walls, between the domain wall and domain apex, between the apexes of the domains change. A metallic ferromagnetic nanofilm can be a medium for recording information with the help of magnetic moments of electrons. Interaction of domain walls, the interaction of the domain wall and the domain apex, the interaction of the domain apexes in the design of storage devices must be taken into account.

Controllable Steering and Tuning of Surface Plasmons on the Metallic Nano-film with Nanoslits Array

A scheme of steering and tuning surface plasmon wakes (SWs) on the metallic nano-film (MNF) excited by a free-electron-beam is demonstrated. With a well-designed array of nanoslits etched in the MNF, the SWs can be steered to propagate along the MNF in definite directions via a unique Smith-Purcell effect. Both the frequency and direction of SWs can be well controlled by adjusting the beam velocity and MNF parameters: the SW frequency can be tuned from the infrared to the ultraviolet, and the SWs can propagate both forwardly and backwardly. These results may indicate promising applications for surface plasmon devices on chip. And also the proposed scheme may offer an effective way for nondestructive detections of the particle velocity and dielectric index.

A multi-layer microchip for high-throughput single-cell gene expression profiling

Microfluidics or Bio-MEMS technology offers significant advantages for performing high-throughput screens and sensitive assays. The ability to correlate single-cell genetic information with cellular phenotypes is of great importance to biology and medicine because it holds the potential to gain insight into disease pathways that is unavailable from ensemble measurements. Previously, we reported two kinds of prototypes for integrated on-chip gene expression profiling at the single-cell level, and the throughput was designed to be 6. In this work, we present a five-layer microfluidic system for parallelized, rapid, quantitative analysis of RNA templates with low abundance at the single-cell level. The microchip contains two multiplexors and one partitioning valve group, and it leverages a matrix (6 × 8) of quantitative reverse transcription polymerase chain reaction (RT–qPCR) units formed by a set of parallel microchannels concurrently controlled by elastomeric pneumatic valves, thereby enabling parallelized handling and processing of biomolecules in a simplified operation procedure. A comprehensive metallic nanofilm with passivation layer is used to run polymerase chain reaction (PCR) temperature cycles. To demonstrate the utility of the approach, artificial synthesized RNA templates (XenoRNA) and mRNA templates from single cells are employed to perform the 48-readout RT–qPCRs. The PCR products are imaged on a fluorescence microscope using a hydrolysis probe/primer set (TaqMan). Fluorescent intensities of passive reference dye and a fluorescein amidite reporter dye are acquired and measured at the end of PCR cycles.

Heterogeneous versus homogeneous electron transfer reactions at liquid–liquid interfaces: The wrong question?

The exact mechanism of the electron transfer reactions at liquid–liquid interfaces still remains a source of interrogation. The purpose of this paper is to revisit this topic using a finite element simulation approach to analyze cyclic voltammograms for some previously published systems. Also, we compare the voltammograms obtained in the absence or presence of an adsorbed gold nanoparticle film. The current results indicate that the electron transfer between ferrocene in the organic phase and hexacyanoferrate(III) in the aqueous phase takes place by a potential independent homogeneous reaction in the aqueous phase, while the observed potential dependence stems from that of the concomitant ion transfer reaction of ferrocenium. In the presence of the interfacial gold nanofilm the electron transfer takes place by a bipolar mechanism where the electrons are shuttled through the metallic nanofilm.

自立金属ナノ薄膜のその場電界放射走査型電子顕微鏡観察疲労/クリープ強度試験法の開発

Experimental technique of in situ FESEM fatigue/creep experiments has been developed to investigate the mechanisms of fatigue/creep crack propagation in freestanding metallic nano-films. We developed an in situ FESEM fatigue/creep dual-mode testing machine which was able to conduct the fatigue or creep experiments inside the FESEM chamber. The testing machine has the capability to apply high-frequency cyclic load or constant load under load-control conditions to the freestanding metallic nano-film specimens. In situ FESEM observations of the fatigue crack propagation in 523-nm-thick freestanding copper (Cu) films confirmed that intrusions/extrusions were formed ahead of the fatigue crack tip in the lower stress intensity factor range (ΔK), and the size of the intrusions/extrusions increased as the number of stress cycles increased. The fatigue crack then propagated preferentially through these intrusions/extrusions. In the higher ΔK, the fatigue crack propagated in tensile fracture mode. In addition, in situ FESEM observations of the creep crack propagation in 391-nm-thick freestanding gold (Au) films confirmed that voids were formed ahead of the creep crack tip, and the crack then propagated by coalescence of the voids and the crack. These results indicate that this experimental technique is effective to clarify the mechanisms and mechanics of fatigue/creep crack propagation in freestanding nano-films.

Curved Surface Plasmon Polariton Excitation With Shaped Beam by Fifth-Power Phase Mask

We experimentally demonstrate a novel and simple method for the excitation of a curved surface plasmon polariton on a silver nanofilm. We generated an Airy-like shaped beam in the Fourier plane by using a fifth-power phase mask imposed on a spatial light modulator to excite surface plasmon polariton on the silver nanofilm consisting of silver nanoparticles. The intensity distribution of the surface plasmon polariton trajectories was recorded by the leakage radiation microscope, which indicates that a plasmonic polynomial beam is produced on the silver nanofilm. This method provides relatively commercial and dynamic manipulation of a curved surface plasmon polariton on a noble metallic nanofilm.

Partial coherence and polarization of a two-mode surface-plasmon polariton field at a metallic nanoslab.

Rigorous electromagnetic theory is utilized to characterize the partial spatial coherence and partial polarization of a two-mode field consisting of the long-range and the short-range surface-plasmon polariton at a metallic nanofilm. By employing appropriate formulations for the spectral degrees of coherence and polarization, we examine the fundamental limits for these quantities associated with such a superposition field and explore how the degrees are influenced when the media, frequency, and slab thickness are varied. It is in particular shown that coherence lengths extending from subwavelength scales up to thousands of wavelengths are possible and their physical origins are elucidated. In addition, we demonstrate that for ultra-thin films the generally highly polarized two-mode field can be partially polarized in close vicinity of the polariton excitation region. The results could benefit cross-disciplinary electro-optical applications in which near-field interactions between plasmons and nanoparticles are exploited.

Efficient single photon emission and collection based on excitation of gap surface plasmons.

Combining the advantages of ultrahigh photon emission rates achievable in the gap surface plasmon polaritons with high extraction decay rates into low-loss nanofibers, we demonstrate theoretically the efficient photon emission of a single dipole emitter and one-dimensional nanoscale guiding in metallic nanorod-coupled nanofilm structures coupled to dielectric nanofibers. We find that total decay rates and surface plasmon polariton channel decay rates orders of magnitude larger than those characteristic of metallic nanofilms alone can be achieved in ultrastrong hot spots of gap plasmons. For the requirement of practical applications, propagating single photons with decay rates of 290γ_{0}-770γ_{0} are guided into the phase-matched low-loss nanofibers. The proposed mechanism promises to have an important impact on metal-based optical cavities, on-chip bright single photon sources and plasmon-based nanolasers.

Enhanced transmission of the femtosecond laser pulse through metallic nanofilm

Abstract We investigate the optical properties of metallic nanofilm heated by the femtosecond laser pulse. Equations for fields and temperatures were solved to calculate the transmission coefficient. It is found that fast electron heating upon absorption of the pulse leads to an increase in the intensity of radiation passing through the metallic nanofilm.

Metallic nanofilm half-wave plate based on magnetic plasmon resonance

We proposed and fabricated a nanofilm half-wave plate consisting of periodic arrays of orthogonally coupled slit-hole resonator structures in Au film. Experimental results reveal that 95.2% of energy of the incident linearly polarized light is converted to the perpendicular polarization direction after reflection from the nanostructure. The wave plate is single layer with only 180 nm thickness, which is much thinner than the operation wavelength. Our method can be expanded to other resonant structures or transmitted case.

Activation of Aluminum by Small Alloying Additions of Bismuth

This paper investigates the effect of small alloyed Bi content and heat-treatment on anodic activation of aluminum in chloride solution. AlBi model alloys containing 20, 100 and 2000 ppm were investigated by use of electrochemical polarization in chloride solution and subsequent characterization of corrosion morphology. Activation after 1 h heat treatment at 600°C in air was independent of Bi concentration in the alloy because it was caused by segregation of a nearly continuous metallic nanofilm at the oxide-metal interface. Enrichment of bismuth in the form of particles was not sufficient to cause activation. Hydrated aluminum oxide, about 1.5 μm in thickness, was formed during cooling in humid air or water after heat-treatment, demonstrating the activating effect of Bi at elevated temperature in the absence of chloride. The polarization curve of AlBi alloys showed two oxidation peaks. The first peak occurred by destabilizing the oxide layer by the Bi nanofilm, resulting in superficial etching and undermining of the thermally formed oxide film. The second peak was caused by crevice corrosion in the gap formed between the metal and undermined oxide film. Pitting of the bulk metal started after the oxide was removed at −0.88 VSCE.